U.S. patent application number 12/869139 was filed with the patent office on 2011-03-24 for hydrocarbon gas processing.
This patent application is currently assigned to Ortloff Engineers, Ltd.. Invention is credited to Kyle T. Cuellar, Hank M. Hudson, Joe T. Lynch, Tony L. Martinez, John D. Wilkinson.
Application Number | 20110067443 12/869139 |
Document ID | / |
Family ID | 43755438 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110067443 |
Kind Code |
A1 |
Martinez; Tony L. ; et
al. |
March 24, 2011 |
Hydrocarbon Gas Processing
Abstract
A process and an apparatus are disclosed for the recovery of
ethane, ethylene, propane, propylene, and heavier hydrocarbon
components from a hydrocarbon gas stream. The stream is cooled and
divided into first and second streams. The first stream is further
cooled to condense substantially all of it and is thereafter
expanded to the fractionation tower pressure and supplied to the
fractionation tower at an upper mid-column feed position. The
second stream is expanded to the tower pressure and supplied to the
column at a mid-column feed position. A distillation vapor stream
is withdrawn from the column above the feed point of the first
stream, combined with a portion of the tower overhead vapor stream,
compressed to higher pressure, and directed into heat exchange
relation with the remaining tower overhead vapor stream to cool the
compressed combined vapor stream and condense at least a part of
it, forming a condensed stream. At least a portion of the condensed
stream is expanded to the tower pressure and directed to the
fractionation tower as its top feed. The quantities and
temperatures of the feeds to the fractionation tower are effective
to maintain the overhead temperature of the fractionation tower at
a temperature whereby the major portion of the desired components
is recovered.
Inventors: |
Martinez; Tony L.; (Midland,
TX) ; Wilkinson; John D.; (Midland, TX) ;
Lynch; Joe T.; (Midland, TX) ; Hudson; Hank M.;
(Midland, TX) ; Cuellar; Kyle T.; (Katy,
TX) |
Assignee: |
Ortloff Engineers, Ltd.
Midland
TX
|
Family ID: |
43755438 |
Appl. No.: |
12/869139 |
Filed: |
August 26, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61244181 |
Sep 21, 2009 |
|
|
|
61346150 |
May 19, 2010 |
|
|
|
61351045 |
Jun 3, 2010 |
|
|
|
Current U.S.
Class: |
62/620 |
Current CPC
Class: |
F25J 2240/02 20130101;
F25J 3/0233 20130101; F25J 2240/40 20130101; F25J 2200/76 20130101;
F25J 2235/60 20130101; F25J 3/0238 20130101; F25J 2200/92 20130101;
F25J 2200/30 20130101; F25J 2290/40 20130101; F25J 2200/94
20130101; F25J 2200/78 20130101; F25J 2270/12 20130101; F25J
2210/60 20130101; F25J 2200/74 20130101; F25J 2215/60 20130101;
F25J 2210/06 20130101; F25J 2290/12 20130101; F25J 2205/04
20130101; F25J 2200/02 20130101; F25J 2200/90 20130101; F25J
2230/08 20130101; F25J 3/0209 20130101; F25J 2270/02 20130101 |
Class at
Publication: |
62/620 |
International
Class: |
F25J 3/00 20060101
F25J003/00 |
Claims
1. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein following cooling, said cooled
stream is divided into first and second streams; and (1) said first
stream is cooled to condense substantially all of it and is
thereafter expanded to said lower pressure whereby it is further
cooled; (2) said expanded cooled first stream is thereafter
supplied to said distillation column at an upper mid-column feed
position; (3) said second stream is expanded to said lower pressure
and is supplied to said distillation column at a mid-column feed
position below said upper mid-column feed position; (4) an overhead
vapor stream is withdrawn from an upper region of said distillation
column and divided into at least a first portion and a second
portion; (5) a distillation vapor stream is withdrawn from a region
of said distillation column above said upper mid-column feed
position and is combined with said first portion to form a combined
vapor stream; (6) said combined vapor stream is compressed to
higher pressure; (7) said compressed combined vapor stream is
directed into heat exchange relation with said second portion,
whereby said second portion is heated and said compressed combined
vapor stream is cooled sufficiently to condense at least a part of
it and thereby form a condensed stream, and thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (8) at least a portion of said condensed
stream is expanded to said lower pressure and is thereafter
supplied to said distillation column at a top feed position; and
(9) the quantities and temperatures of said feed streams to said
distillation column are effective to maintain the overhead
temperature of said distillation column at a temperature whereby
the major portions of the components in said relatively less
volatile fraction are recovered.
2. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein prior to cooling, said gas
stream is divided into first and second streams; and (1) said first
stream is cooled to condense substantially all of it and is
thereafter expanded to said lower pressure whereby it is further
cooled; (2) said expanded cooled first stream is thereafter
supplied to said distillation column at an upper mid-column feed
position; (3) said second stream is cooled and thereafter expanded
to said lower pressure and supplied to said distillation column at
a mid-column feed position below said upper mid-column feed
position; (4) an overhead vapor stream is withdrawn from an upper
region of said distillation column and divided into at least a
first portion and a second portion; (5) a distillation vapor stream
is withdrawn from a region of said distillation column above said
upper mid-column feed position and is combined with said first
portion to form a combined vapor stream; (6) said combined vapor
stream is compressed to higher pressure; (7) said compressed
combined vapor stream is directed into heat exchange relation with
said second portion, whereby said second portion is heated and said
compressed combined vapor stream is cooled sufficiently to condense
at least a part of it and thereby form a condensed stream, and
thereafter discharging at least a portion of said heated second
portion as said volatile residue gas fraction; (8) at least a
portion of said condensed stream is expanded to said lower pressure
and is thereafter supplied to said distillation column at a top
feed position; and (9) the quantities and temperatures of said feed
streams to said distillation column are effective to maintain the
overhead temperature of said distillation column at a temperature
whereby the major portions of the components in said relatively
less volatile fraction are recovered.
3. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein said gas stream is cooled
sufficiently to partially condense it; and (1) said partially
condensed gas stream is separated thereby to provide a vapor stream
and at least one liquid stream; (2) said vapor stream is thereafter
divided into first and second streams; (3) said first stream is
cooled to condense substantially all of it and is thereafter
expanded to said lower pressure whereby it is further cooled; (4)
said expanded cooled first stream is thereafter supplied to said
distillation column at an upper mid-column feed position; (5) said
second stream is expanded to said lower pressure and is supplied to
said distillation column at a mid-column feed position below said
upper mid-column feed position; (6) at least a portion of said at
least one liquid stream is expanded to said lower pressure and is
supplied to said distillation column at a lower mid-column feed
position below said mid-column feed position; (7) an overhead vapor
stream is withdrawn from an upper region of said distillation
column and divided into at least a first portion and a second
portion; (8) a distillation vapor stream is withdrawn from a region
of said distillation column above said upper mid-column feed
position and is combined with said first portion to form a combined
vapor stream; (9) said combined vapor stream is compressed to
higher pressure; (10) said compressed combined vapor stream is
directed into heat exchange relation with said second portion,
whereby said second portion is heated and said compressed combined
vapor stream is cooled sufficiently to condense at least a part of
it and thereby form a condensed stream, and thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (11) at least a portion of said condensed
stream is expanded to said lower pressure and is thereafter
supplied to said distillation column at a top feed position; and
(12) the quantities and temperatures of said feed streams to said
distillation column are effective to maintain the overhead
temperature of said distillation column at a temperature whereby
the major portions of the components in said relatively less
volatile fraction are recovered.
4. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein prior to cooling, said gas
stream is divided into first and second streams; and (1) said first
stream is cooled to condense substantially all of it and is
thereafter expanded to said lower pressure whereby it is further
cooled; (2) said expanded cooled first stream is thereafter
supplied to said distillation column at an upper mid-column feed
position; (3) said second stream is cooled under pressure
sufficiently to partially condense it; (4) said partially condensed
second stream is separated thereby to provide a vapor stream and at
least one liquid stream; (5) said vapor stream is expanded to said
lower pressure and is supplied to said distillation column at a
mid-column feed position below said upper mid-column feed position;
(6) at least a portion of said at least one liquid stream is
expanded to said lower pressure and is supplied to said
distillation column at a lower mid-column feed position below said
mid-column feed position; (7) an overhead vapor stream is withdrawn
from an upper region of said distillation column and divided into
at least a first portion and a second portion; (8) a distillation
vapor stream is withdrawn from a region of said distillation column
above said upper mid-column feed position and is combined with said
first portion to form a combined vapor stream; (9) said combined
vapor stream is compressed to higher pressure; (10) said compressed
combined vapor stream is directed into heat exchange relation with
said second portion, whereby said second portion is heated and said
compressed combined vapor stream is cooled sufficiently to condense
at least a part of it and thereby form a condensed stream, and
thereafter discharging at least a portion of said heated second
portion as said volatile residue gas fraction; (11) at least a
portion of said condensed stream is expanded to said lower pressure
and is thereafter supplied to said distillation column at a top
feed position; and (12) the quantities and temperatures of said
feed streams to said distillation column are effective to maintain
the overhead temperature of said distillation column at a
temperature whereby the major portions of the components in said
relatively less volatile fraction are recovered.
5. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein said gas stream is cooled
sufficiently to partially condense it; and (1) said partially
condensed gas stream is separated thereby to provide a vapor stream
and at least one liquid stream; (2) said vapor stream is thereafter
divided into first and second streams; (3) said first stream is
combined with at least a portion of said at least one liquid stream
to form a combined stream, whereupon said combined stream is cooled
to condense substantially all of it and is thereafter expanded to
said lower pressure whereby it is further cooled; (4) said expanded
cooled combined stream is thereafter supplied to said distillation
column at an upper mid-column feed position; (5) said second stream
is expanded to said lower pressure and is supplied to said
distillation column at a mid-column feed position below said upper
mid-column feed position; (6) any remaining portion of said at
least one liquid stream is expanded to said lower pressure and is
supplied to said distillation column at a lower mid-column feed
position below said mid-column feed position; (7) an overhead vapor
stream is withdrawn from an upper region of said distillation
column and divided into at least a first portion and a second
portion; (8) a distillation vapor stream is withdrawn from a region
of said distillation column above said upper mid-column feed
position and is combined with said first portion to form a combined
vapor stream; (9) said combined vapor stream is compressed to
higher pressure; (10) said compressed combined vapor stream is
directed into heat exchange relation with said second portion,
whereby said second portion is heated and said compressed combined
vapor stream is cooled sufficiently to condense at least a part of
it and thereby form a condensed stream, and thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (11) at least a portion of said condensed
stream is expanded to said lower pressure and is thereafter
supplied to said distillation column at a top feed position; and
(12) the quantities and temperatures of said feed streams to said
distillation column are effective to maintain the overhead
temperature of said distillation column at a temperature whereby
the major portions of the components in said relatively less
volatile fraction are recovered.
6. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein following cooling, said cooled
stream is divided into first and second streams; and (1) said first
stream is cooled to condense substantially all of it and is
thereafter expanded to said lower pressure whereby it is further
cooled; (2) said expanded cooled first stream is thereafter
supplied at a mid-column feed position to a contacting and
separating device that produces a first overhead vapor stream and a
bottom liquid stream, whereupon said bottom liquid stream is
supplied to said distillation column; (3) said second stream is
expanded to said lower pressure and is supplied to said contacting
and separating device at a first lower column feed position below
said mid-column feed position; (4) a second overhead vapor stream
is withdrawn from an upper region of said distillation column and
is supplied to said contacting and separating device at a second
lower column feed position below said mid-column feed position; (5)
said first overhead vapor stream is divided into at least a first
portion and a second portion; (6) a distillation vapor stream is
withdrawn from a region of said contacting and separating device
above said mid-column feed position and is combined with said first
portion to form a combined vapor stream; (7) said combined vapor
stream is compressed to higher pressure; (8) said compressed
combined vapor stream is directed into heat exchange relation with
said second portion, whereby said second portion is heated and said
compressed combined vapor stream is cooled sufficiently to condense
at least a part of it and thereby form a condensed stream, and
thereafter discharging at least a portion of said heated second
portion as said volatile residue gas fraction; (9) at least a
portion of said condensed stream is expanded to said lower pressure
and is thereafter supplied to said contacting and separating device
at a top feed position; and (10) the quantities and temperatures of
said feed streams to said contacting and separating device are
effective to maintain the overhead temperature of said contacting
and separating device at a temperature whereby the major portions
of the components in said relatively less volatile fraction are
recovered.
7. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein prior to cooling, said gas
stream is divided into first and second streams; and (1) said first
stream is cooled to condense substantially all of it and is
thereafter expanded to said lower pressure whereby it is further
cooled; (2) said expanded cooled first stream is thereafter
supplied at a mid-column feed position to a contacting and
separating device that produces a first overhead vapor stream and a
bottom liquid stream, whereupon said bottom liquid stream is
supplied to said distillation column; (3) said second stream is
cooled and thereafter expanded to said lower pressure and supplied
to said contacting and separating device at a first lower column
feed position below said mid-column feed position; (4) a second
overhead vapor stream is withdrawn from an upper region of said
distillation column and is supplied to said contacting and
separating device at a second lower column feed position below said
mid-column feed position; (5) said first overhead vapor stream is
divided into at least a first portion and a second portion; (6) a
distillation vapor stream is withdrawn from a region of said
contacting and separating device above said mid-column feed
position and is combined with said first portion to form a combined
vapor stream; (7) said combined vapor stream is compressed to
higher pressure; (8) said compressed combined vapor stream is
directed into heat exchange relation with said second portion,
whereby said second portion is heated and said compressed combined
vapor stream is cooled sufficiently to condense at least a part of
it and thereby form a condensed stream, and thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (9) at least a portion of said condensed
stream is expanded to said lower pressure and is thereafter
supplied to said contacting and separating device at a top feed
position; and (10) the quantities and temperatures of said feed
streams to said contacting and separating device are effective to
maintain the overhead temperature of said contacting and separating
device at a temperature whereby the major portions of the
components in said relatively less volatile fraction are
recovered.
8. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein said gas stream is cooled
sufficiently to partially condense it; and (1) said partially
condensed gas stream is separated thereby to provide a vapor stream
and at least one liquid stream; (2) said vapor stream is thereafter
divided into first and second streams; (3) said first stream is
cooled to condense substantially all of it and is thereafter
expanded to said lower pressure whereby it is further cooled; (4)
said expanded cooled first stream is thereafter supplied at a
mid-column feed position to a contacting and separating device that
produces a first overhead vapor stream and a bottom liquid stream,
whereupon said bottom liquid stream is supplied to said
distillation column; (5) said second stream is expanded to said
lower pressure and is supplied to said contacting and separating
device at a first lower column feed position below said mid-column
feed position; (6) at least a portion of said at least one liquid
stream is expanded to said lower pressure and is supplied to said
distillation column at a mid-column feed position; (7) a second
overhead vapor stream is withdrawn from an upper region of said
distillation column and is supplied to said contacting and
separating device at a second lower column feed position below said
mid-column feed position; (8) said first overhead vapor stream is
divided into at least a first portion and a second portion; (9) a
distillation vapor stream is withdrawn from a region of said
contacting and separating device above said mid-column feed
position and is combined with said first portion to form a combined
vapor stream; (10) said combined vapor stream is compressed to
higher pressure; (11) said compressed combined vapor stream is
directed into heat exchange relation with said second portion,
whereby said second portion is heated and said compressed combined
vapor stream is cooled sufficiently to condense at least a part of
it and thereby form a condensed stream, and thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (12) at least a portion of said condensed
stream is expanded to said lower pressure and is thereafter
supplied to said contacting and separating device at a top feed
position; and (13) the quantities and temperatures of said feed
streams to said contacting and separating device are effective to
maintain the overhead temperature of said contacting and separating
device at a temperature whereby the major portions of the
components in said relatively less volatile fraction are
recovered.
9. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein prior to cooling, said gas
stream is divided into first and second streams; and (1) said first
stream is cooled to condense substantially all of it and is
thereafter expanded to said lower pressure whereby it is further
cooled; (2) said expanded cooled first stream is thereafter
supplied at a mid-column feed position to a contacting and
separating device that produces an overhead vapor stream and a
bottom liquid stream, whereupon said bottom liquid stream is
supplied to said distillation column; (3) said second stream is
cooled under pressure sufficiently to partially condense it; (4)
said partially condensed second stream is separated thereby to
provide a vapor stream and at least one liquid stream; (5) said
vapor stream is expanded to said lower pressure and is supplied to
said contacting and separating device at a first lower column feed
position below said mid-column feed position; (6) at least a
portion of said at least one liquid stream is expanded to said
lower pressure and is supplied to said distillation column at a
mid-column feed position; (7) a second overhead vapor stream is
withdrawn from an upper region of said distillation column and is
supplied to said contacting and separating device at a second lower
column feed position below said mid-column feed position; (8) said
first overhead vapor stream is divided into at least a first
portion and a second portion; (9) a distillation vapor stream is
withdrawn from a region of said contacting and separating device
above said mid-column feed position and is combined with said first
portion to form a combined vapor stream; (10) said combined vapor
stream is compressed to higher pressure; (11) said compressed
combined vapor stream is directed into heat exchange relation with
said second portion, whereby said second portion is heated and said
compressed combined vapor stream is cooled sufficiently to condense
at least a part of it and thereby form a condensed stream, and
thereafter discharging at least a portion of said heated second
portion as said volatile residue gas fraction; (12) at least a
portion of said condensed stream is expanded to said lower pressure
and is thereafter supplied to said contacting and separating device
at a top feed position; and (13) the quantities and temperatures of
said feed streams to said contacting and separating device are
effective to maintain the overhead temperature of said contacting
and separating device at a temperature whereby the major portions
of the components in said relatively less volatile fraction are
recovered.
10. In a process for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in which process (a) said gas stream is
cooled under pressure to provide a cooled stream; (b) said cooled
stream is expanded to a lower pressure whereby it is further
cooled; and (c) said further cooled stream is directed into a
distillation column and fractionated at said lower pressure whereby
the components of said relatively less volatile fraction are
recovered; the improvement wherein said gas stream is cooled
sufficiently to partially condense it; and (1) said partially
condensed gas stream is separated thereby to provide a vapor stream
and at least one liquid stream; (2) said vapor stream is thereafter
divided into first and second streams; (3) said first stream is
combined with at least a portion of said at least one liquid stream
to form a combined stream, whereupon said combined stream is cooled
to condense substantially all of it and is thereafter expanded to
said lower pressure whereby it is further cooled; (4) said expanded
cooled combined stream is thereafter supplied at a mid-column feed
position to a contacting and separating device that produces a
first overhead vapor stream and a bottom liquid stream, whereupon
said bottom liquid stream is supplied to said distillation column;
(5) said second stream is expanded to said lower pressure and is
supplied to said contacting and separating device at a first lower
column feed position below said mid-column feed position; (6) any
remaining portion of said at least one liquid stream is expanded to
said lower pressure and is supplied to said distillation column at
a mid-column feed position; (7) a second overhead vapor stream is
withdrawn from an upper region of said distillation column and is
supplied to said contacting and separating device at a second lower
column feed position below said mid-column feed position; (8) said
first overhead vapor stream is divided into at least a first
portion and a second portion; (9) a distillation vapor stream is
withdrawn from a region of said contacting and separating device
above said mid-column feed position and is combined with said first
portion to form a combined vapor stream; (10) said combined vapor
stream is compressed to higher pressure; (11) said compressed
combined vapor stream is directed into heat exchange relation with
said second portion, whereby said second portion is heated and said
compressed combined vapor stream is cooled sufficiently to condense
at least a part of it and thereby form a condensed stream, and
thereafter discharging at least a portion of said heated second
portion as said volatile residue gas fraction; (12) at least a
portion of said condensed stream is expanded to said lower pressure
and is thereafter supplied to said contacting and separating device
at a top feed position; and (13) the quantities and temperatures of
said feed streams to said contacting and separating device are
effective to maintain the overhead temperature of said contacting
and separating device at a temperature whereby the major portions
of the components in said relatively less volatile fraction are
recovered.
11. The improvement according to claim 1, 2, 3, 4, or 5 wherein
said distillation vapor stream is withdrawn from a region of said
distillation column below said upper mid-column feed position and
above said mid-column feed position.
12. The improvement according to claim 1, 2, 3, 4, or 5 wherein
said distillation vapor stream is withdrawn from a region of said
distillation column below said mid-column feed position.
13. The improvement according to claim 6, 7, 8, 9, or 10 wherein
said distillation vapor stream is withdrawn from a region of said
contacting and separating device below said mid-column feed
position and above said first and second lower column feed
positions.
14. The improvement according to claim 6, 7, 8, 9, or 10 wherein
said second overhead vapor stream is divided into said distillation
vapor stream and a second distillation vapor stream, whereupon said
second distillation vapor stream is supplied to said contacting and
separating device at said second lower column feed position.
15. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into an overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) first dividing means connected
to said first cooling means to receive said cooled stream and
divide it into first and second streams; (2) second cooling means
connected to said first dividing means to receive said first stream
and cool it sufficiently to substantially condense it; (3) second
expansion means connected to said second cooling means to receive
said substantially condensed first stream and expand it to said
lower pressure, said second expansion means being further connected
to said distillation column to supply said expanded cooled first
stream to said distillation column at an upper mid-column feed
position; (4) said first expansion means being connected to said
first dividing means to receive said second stream and expand it to
said lower pressure, said first expansion means being further
connected to said distillation column to supply said expanded
second stream to said distillation column at a mid-column feed
position below said upper mid-column feed position; (5) second
dividing means connected to said distillation column to receive
said overhead vapor stream separated therein and divide it into at
least a first portion and a second portion; (6) heat exchange means
connected to said second dividing means to receive at least a
portion of said second portion and heat it, thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (7) vapor withdrawing means connected to said
distillation column to receive a distillation vapor stream from a
region of said distillation column above said upper mid-column feed
position; (8) combining means connected to said second dividing
means and said vapor withdrawing means to receive said first
portion and said distillation vapor stream and form a combined
vapor stream; (9) compressing means connected to said combining
means to receive said combined vapor stream and compress it to
higher pressure; (10) said heat exchange means being further
connected to said compressing means to receive said compressed
combined vapor stream and cool it sufficiently to condense at least
a part of it, thereby forming a condensed stream while supplying at
least a portion of the heating of step (6); (11) third expansion
means connected to said heat exchange means to receive said
condensed stream and expand it to said lower pressure, said third
expansion means being further connected to said distillation column
to supply at least a portion of said expanded condensed stream to
said distillation column at a top feed position; and (12) control
means adapted to regulate the quantities and temperatures of said
feed streams to said distillation column to maintain the overhead
temperature of said distillation column at a temperature whereby
the major portions of the components in said relatively less
volatile fraction are recovered.
16. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into an overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) first dividing means prior to
said first cooling means to divide said gas stream into first and
second streams; (2) second cooling means connected to said first
dividing means to receive said first stream and cool it
sufficiently to substantially condense it; (3) second expansion
means connected to said second cooling means to receive said
substantially condensed first stream and expand it to said lower
pressure, said second expansion means being further connected to
said distillation column to supply said expanded cooled first
stream to said distillation column at an upper mid-column feed
position; (4) said first cooling means being connected to said
first dividing means to receive said second stream and cool it; (5)
said first expansion means being connected to said first cooling
means to receive said cooled second stream and expand it to said
lower pressure, said first expansion means being further connected
to said distillation column to supply said expanded cooled second
stream to said distillation column at a mid-column feed position
below said upper mid-column feed position; (6) second dividing
means connected to said distillation column to receive said
overhead vapor stream separated therein and divide it into at least
a first portion and a second portion; (7) heat exchange means
connected to said second dividing means to receive at least a
portion of said second portion and heat it, thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (8) vapor withdrawing means connected to said
distillation column to receive a distillation vapor stream from a
region of said distillation column above said upper mid-column feed
position; (9) combining means connected to said second dividing
means and said vapor withdrawing means to receive said first
portion and said distillation vapor stream and form a combined
vapor stream; (10) compressing means connected to said combining
means to receive said combined vapor stream and compress it to
higher pressure; (11) said heat exchange means being further
connected to said compressing means to receive said compressed
combined vapor stream and cool it sufficiently to condense at least
a part of it, thereby forming a condensed stream while supplying at
least a portion of the heating of step (7); (12) third expansion
means connected to said heat exchange means to receive said
condensed stream and expand it to said lower pressure, said third
expansion means being further connected to said distillation column
to supply at least a portion of said expanded condensed stream to
said distillation column at a top feed position; and (13) control
means adapted to regulate the quantities and temperatures of said
feed streams to said distillation column to maintain the overhead
temperature of said distillation column at a temperature whereby
the major portions of the components in said relatively less
volatile fraction are recovered.
17. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into an overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) said first cooling means being
adapted to cool said gas stream under pressure sufficiently to
partially condense it; (2) separating means connected to said first
cooling means to receive said partially condensed gas stream and
separate it into a vapor stream and at least one liquid stream; (3)
first dividing means connected to said separating means to receive
said vapor stream and divide it into first and second streams; (4)
second cooling means connected to said first dividing means to
receive said first stream and cool it sufficiently to substantially
condense it; (5) second expansion means connected to said second
cooling means to receive said substantially condensed first stream
and expand it to said lower pressure, said second expansion means
being further connected to said distillation column to supply said
expanded cooled first stream to said distillation column at an
upper mid-column feed position; (6) said first expansion means
being connected to said first dividing means to receive said second
stream and expand it to said lower pressure, said first expansion
means being further connected to said distillation column to supply
said expanded second stream to said distillation column at a
mid-column feed position below said upper mid-column feed position;
(7) third expansion means connected to said separating means to
receive at least a portion of said at least one liquid stream and
expand it to said lower pressure, said third expansion means being
further connected to said distillation column to supply said
expanded liquid stream to said distillation column at a lower
mid-column feed position below said mid-column feed position; (8)
second dividing means connected to said distillation column to
receive said overhead vapor stream separated therein and divide it
into at least a first portion and a second portion; (9) heat
exchange means connected to said second dividing means to receive
at least a portion of said second portion and heat it, thereafter
discharging at least a portion of said heated second portion as
said volatile residue gas fraction; (10) vapor withdrawing means
connected to said distillation column to receive a distillation
vapor stream from a region of said distillation column above said
upper mid-column feed position; (11) combining means connected to
said second dividing means and said vapor withdrawing means to
receive said first portion and said distillation vapor stream and
form a combined vapor stream; (12) compressing means connected to
said combining means to receive said combined vapor stream and
compress it to higher pressure; (13) said heat exchange means being
further connected to said compressing means to receive said
compressed combined vapor stream and cool it sufficiently to
condense at least a part of it, thereby forming a condensed stream
while supplying at least a portion of the heating of step (9); (14)
fourth expansion means connected to said heat exchange means to
receive said condensed stream and expand it to said lower pressure,
said fourth expansion means being further connected to said
distillation column to supply at least a portion of said expanded
condensed stream to said distillation column at a top feed
position; and (15) control means adapted to regulate the quantities
and temperatures of said feed streams to said distillation column
to maintain the overhead temperature of said distillation column at
a temperature whereby the major portions of the components in said
relatively less volatile fraction are recovered.
18. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into an overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) first dividing means prior to
said first cooling means to divide said gas stream into first and
second streams; (2) second cooling means connected to said first
dividing means to receive said first stream and cool it
sufficiently to substantially condense it; (3) second expansion
means connected to said second cooling means to receive said
substantially condensed first stream and expand it to said lower
pressure, said second expansion means being further connected to
said distillation column to supply said expanded cooled first
stream to said distillation column at an upper mid-column feed
position; (4) said first cooling means being connected to said
first dividing means to receive said second stream, said first
cooling means being adapted to cool said second stream under
pressure sufficiently to partially condense it; (5) separating
means connected to said first cooling means to receive said
partially condensed second stream and separate it into a vapor
stream and at least one liquid stream; (6) said first expansion
means being connected to said separating means to receive said
vapor stream and expand it to said lower pressure, said first
expansion means being further connected to said distillation column
to supply said expanded vapor stream to said distillation column at
a mid-column feed position below said upper mid-column feed
position; (7) third expansion means connected to said separating
means to receive at least a portion of said at least one liquid
stream and expand it to said lower pressure, said third expansion
means being further connected to said distillation column to supply
said expanded liquid stream to said distillation column at a lower
mid-column feed position below said mid-column feed position; (8)
second dividing means connected to said distillation column to
receive said overhead vapor stream separated therein and divide it
into at least a first portion and a second portion; (9) heat
exchange means connected to said second dividing means to receive
at least a portion of said second portion and heat it, thereafter
discharging at least a portion of said heated second portion as
said volatile residue gas fraction; (10) vapor withdrawing means
connected to said distillation column to receive a distillation
vapor stream from a region of said distillation column above said
upper mid-column feed position; (11) combining means connected to
said second dividing means and said vapor withdrawing means to
receive said first portion and said distillation vapor stream and
form a combined vapor stream; (12) compressing means connected to
said combining means to receive said combined vapor stream and
compress it to higher pressure; (13) said heat exchange means being
further connected to said compressing means to receive said
compressed combined vapor stream and cool it sufficiently to
condense at least a part of it, thereby forming a condensed stream
while supplying at least a portion of the heating of step (9); (14)
fourth expansion means connected to said heat exchange means to
receive said condensed stream and expand it to said lower pressure,
said fourth expansion means being further connected to said
distillation column to supply at least a portion of said expanded
condensed stream to said distillation column at a top feed
position; and (15) control means adapted to regulate the quantities
and temperatures of said feed streams to said distillation column
to maintain the overhead temperature of said distillation column at
a temperature whereby the major portions of the components in said
relatively less volatile fraction are recovered.
19. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into an overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) said first cooling means being
adapted to cool said gas stream under pressure sufficiently to
partially condense it; (2) separating means connected to said first
cooling means to receive said partially condensed gas stream and
separate it into a vapor stream and at least one liquid stream; (3)
first dividing means connected to said separating means to receive
said vapor stream and divide it into first and second streams; (4)
first combining means connected to said first dividing means and
said separating means to receive said first stream and at least a
portion of said at least one liquid stream and form a combined
stream; (5) second cooling means connected to said first combining
means to receive said combined stream and cool it sufficiently to
substantially condense it; (6) second expansion means connected to
said second cooling means to receive said substantially condensed
combined stream and expand it to said lower pressure, said second
expansion means being further connected to said distillation column
to supply said expanded cooled combined stream to said distillation
column at an upper mid-column feed position; (7) said first
expansion means being connected to said first dividing means to
receive said second stream and expand it to said lower pressure,
said first expansion means being further connected to said
distillation column to supply said expanded second stream to said
distillation column at a mid-column feed position below said upper
mid-column feed position; (8) third expansion means being connected
to said separating means to receive any remaining portion of said
at least one liquid stream and expand it to said lower pressure,
said third expansion means being further connected to said
distillation column to supply said expanded liquid stream to said
distillation column at a lower mid-column feed position below said
mid-column feed position; (9) second dividing means connected to
said distillation column to receive said overhead vapor stream
separated therein and divide it into at least a first portion and a
second portion; (10) heat exchange means connected to said second
dividing means to receive at least a portion of said second portion
and heat it, thereafter discharging at least a portion of said
heated second portion as said volatile residue gas fraction; (11)
vapor withdrawing means connected to said distillation column to
receive a distillation vapor stream from a region of said
distillation column above said upper mid-column feed position; (12)
second combining means connected to said second dividing means and
said vapor withdrawing means to receive said first portion and said
distillation vapor stream and form a combined vapor stream; (13)
compressing means connected to said second combining means to
receive said combined vapor stream and compress it to higher
pressure; (14) said heat exchange means being further connected to
said compressing means to receive said compressed combined vapor
stream and cool it sufficiently to condense at least a part of it,
thereby forming a condensed stream while supplying at least a
portion of the heating of step (10); (15) fourth expansion means
connected to said heat exchange means to receive said condensed
stream and expand it to said lower pressure, said fourth expansion
means being further connected to said distillation column to supply
at least a portion of said expanded condensed stream to said
distillation column at a top feed position; and (16) control means
adapted to regulate the quantities and temperatures of said feed
streams to said distillation column to maintain the overhead
temperature of said distillation column at a temperature whereby
the major portions of the components in said relatively less
volatile fraction are recovered.
20. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into a first overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) first dividing means connected
to said first cooling means to receive said cooled stream and
divide it into first and second streams; (2) second cooling means
connected to said first dividing means to receive said first stream
and cool it sufficiently to substantially condense it; (3) second
expansion means connected to said second cooling means to receive
said substantially condensed first stream and expand it to said
lower pressure, said second expansion means being further connected
to a contacting and separating means to supply said expanded cooled
first stream to said contacting and separating means at a
mid-column feed position, said contacting and separating means
being adapted to produce a second overhead vapor stream and a
bottom liquid stream; (4) said first expansion means being
connected to said first dividing means to receive said second
stream and expand it to said lower pressure, said first expansion
means being further connected to said contacting and separating
means to supply said expanded second stream to said contacting and
separating means at a first lower column feed position below said
mid-column feed position; (5) said distillation column being
connected to said contacting and separating means to receive at
least a portion of said bottom liquid stream; (6) said contacting
and separating means being further connected to said distillation
column to receive at least a portion of said first overhead vapor
stream at a second lower column feed position below said mid-column
feed position; (7) second dividing means connected to said
contacting and separating means to receive said second overhead
vapor stream separated therein and divide it into at least a first
portion and a second portion; (8) heat exchange means connected to
said second dividing means to receive at least a portion of said
second portion and heat it, thereafter discharging at least a
portion of said heated second portion as said volatile residue gas
fraction; (9) vapor withdrawing means connected to said contacting
and separating means to receive a distillation vapor stream from a
region of said contacting and separating device above said
mid-column feed position; (10) combining means connected to said
second dividing means and said vapor withdrawing means to receive
said first portion and said distillation vapor stream and form a
combined vapor stream; (11) compressing means connected to said
combining means to receive said combined vapor stream and compress
it to higher pressure; (12) said heat exchange means being further
connected to said compressing means to receive said compressed
combined vapor stream and cool it sufficiently to condense at least
a part of it, thereby forming a condensed stream while supplying at
least a portion of the heating of step (8); (13) third expansion
means connected to said heat exchange means to receive said
condensed stream and expand it to said lower pressure, said third
expansion means being further connected to said contacting and
separating means to supply at least a portion of said expanded
condensed stream to said contacting and separating means at a top
feed position; and (14) control means adapted to regulate the
quantities and temperatures of said feed streams to said contacting
and separating means to maintain the overhead temperature of said
contacting and separating means at a temperature whereby the major
portions of the components in said relatively less volatile
fraction are recovered.
21. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into a first overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) first dividing means prior to
said first cooling means to divide said gas stream into first and
second streams; (2) second cooling means connected to said first
dividing means to receive said first stream and cool it
sufficiently to substantially condense it; (3) second expansion
means connected to said second cooling means to receive said
substantially condensed first stream and expand it to said lower
pressure, said second expansion means being further connected to a
contacting and separating means to supply said expanded cooled
first stream to said contacting and separating means at a
mid-column feed position, said contacting and separating means
being adapted to produce a second overhead vapor stream and a
bottom liquid stream; (4) said first cooling means being connected
to said first dividing means to receive said second stream and cool
it; (5) said first expansion means being connected to said first
cooling means to receive said cooled second stream and expand it to
said lower pressure, said first expansion means being further
connected to said contacting and separating means to supply said
expanded cooled second stream to said contacting and separating
means at a first lower column feed position below said mid-column
feed position; (6) said distillation column being connected to said
contacting and separating means to receive at least a portion of
said bottom liquid stream; (7) said contacting and separating means
being further connected to said distillation column to receive at
least a portion of said first overhead vapor stream at a second
lower column feed position below said mid-column feed position; (8)
second dividing means connected to said contacting and separating
means to receive said second overhead vapor stream separated
therein and divide it into at least a first portion and a second
portion; (9) heat exchange means connected to said second dividing
means to receive at least a portion of said second portion and heat
it, thereafter discharging at least a portion of said heated second
portion as said volatile residue gas fraction; (10) vapor
withdrawing means connected to said contacting and separating means
to receive a distillation vapor stream from a region of said
contacting and separating device above said mid-column feed
position; (11) combining means connected to said second dividing
means and said vapor withdrawing means to receive said first
portion and said distillation vapor stream and form a combined
vapor stream; (12) compressing means connected to said combining
means to receive said combined vapor stream and compress it to
higher pressure; (13) said heat exchange means being further
connected to said compressing means to receive said compressed
combined vapor stream and cool it sufficiently to condense at least
a part of it, thereby forming a condensed stream while supplying at
least a portion of the heating of step (9); (14) third expansion
means connected to said heat exchange means to receive said
condensed stream and expand it to said lower pressure, said third
expansion means being further connected to said contacting and
separating means to supply at least a portion of said expanded
condensed stream to said contacting and separating means at a top
feed position; and (15) control means adapted to regulate the
quantities and temperatures of said feed streams to said contacting
and separating means to maintain the overhead temperature of said
contacting and separating means at a temperature whereby the major
portions of the components in said relatively less volatile
fraction are recovered.
22. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into a first overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) said first cooling means being
adapted to cool said gas stream under pressure sufficiently to
partially condense it; (2) separating means connected to said first
cooling means to receive said partially condensed gas stream and
separate it into a vapor stream and at least one liquid stream; (3)
first dividing means connected to said separating means to receive
said vapor stream and divide it into first and second streams; (4)
second cooling means connected to said first dividing means to
receive said first stream and cool it sufficiently to substantially
condense it; (5) second expansion means connected to said second
cooling means to receive said substantially condensed first stream
and expand it to said lower pressure, said second expansion means
being further connected to a contacting and separating means to
supply said expanded cooled first stream to said contacting and
separating means at a mid-column feed position, said contacting and
separating means being adapted to produce a second overhead vapor
stream and a bottom liquid stream; (6) said first expansion means
being connected to said first dividing means to receive said second
stream and expand it to said lower pressure, said first expansion
means being further connected to said contacting and separating
means to supply said expanded second stream to said contacting and
separating means at a first lower column feed position below said
mid-column feed position; (7) third expansion means connected to
said separating means to receive at least a portion of said at
least one liquid stream and expand it to said lower pressure, said
third expansion means being further connected to said distillation
column to supply said expanded liquid stream to said distillation
column at a mid-column feed position; (8) said distillation column
being connected to said contacting and separating means to receive
at least a portion of said bottom liquid stream; (9) said
contacting and separating means being further connected to said
distillation column to receive at least a portion of said first
overhead vapor stream at a second lower column feed position below
said mid-column feed position; (10) second dividing means connected
to said contacting and separating means to receive said second
overhead vapor stream separated therein and divide it into at least
a first portion and a second portion; (11) heat exchange means
connected to said second dividing means to receive at least a
portion of said second portion and heat it, thereafter discharging
at least a portion of said heated second portion as said volatile
residue gas fraction; (12) vapor withdrawing means connected to
said contacting and separating means to receive a distillation
vapor stream from a region of said contacting and separating device
above said mid-column feed position; (13) combining means connected
to said second dividing means and said vapor withdrawing means to
receive said first portion and said distillation vapor stream and
form a combined vapor stream; (14) compressing means connected to
said combining means to receive said combined vapor stream and
compress it to higher pressure; (15) said heat exchange means being
further connected to said compressing means to receive said
compressed combined vapor stream and cool it sufficiently to
condense at least a part of it, thereby forming a condensed stream
while supplying at least a portion of the heating of step (11);
(16) fourth expansion means connected to said heat exchange means
to receive said condensed stream and expand it to said lower
pressure, said fourth expansion means being further connected to
said contacting and separating means to supply at least a portion
of said expanded condensed stream to said contacting and separating
means at a top feed position; and (17) control means adapted to
regulate the quantities and temperatures of said feed streams to
said contacting and separating means to maintain the overhead
temperature of said contacting and separating means at a
temperature whereby the major portions of the components in said
relatively less volatile fraction are recovered.
23. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into a first overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) first dividing means prior to
said first cooling means to divide said gas stream into first and
second streams; (2) second cooling means connected to said first
dividing means to receive said first stream and cool it
sufficiently to substantially condense it; (3) second expansion
means connected to said second cooling means to receive said
substantially condensed first stream and expand it to said lower
pressure, said second expansion means being further connected to a
contacting and separating means to supply said expanded cooled
first stream to said contacting and separating means at a
mid-column feed position, said contacting and separating means
being adapted to produce a second overhead vapor stream and a
bottom liquid stream; (4) said first cooling means being connected
to said first dividing means to receive said second stream, said
first cooling means being adapted to cool said second stream under
pressure sufficiently to partially condense it; (5) separating
means connected to said first cooling means to receive said
partially condensed second stream and separate it into a vapor
stream and at least one liquid stream; (6) said first expansion
means being connected to said separating means to receive said
vapor stream and expand it to said lower pressure, said first
expansion means being further connected to said contacting and
separating means to supply said expanded vapor stream to said
contacting and separating means at a first lower column feed
position below said mid-column feed position; (7) third expansion
means connected to said separating means to receive at least a
portion of said at least one liquid stream and expand it to said
lower pressure, said third expansion means being further connected
to said distillation column to supply said expanded liquid stream
to said distillation column at a mid-column feed position; (8) said
distillation column being connected to said contacting and
separating means to receive at least a portion of said bottom
liquid stream; (9) said contacting and separating means being
further connected to said distillation column to receive at least a
portion of said first overhead vapor stream at a second lower
column feed position below said mid-column feed position; (10)
second dividing means connected to said contacting and separating
means to receive said second overhead vapor stream separated
therein and divide it into at least a first portion and a second
portion; (11) heat exchange means connected to said second dividing
means to receive at least a portion of said second portion and heat
it, thereafter discharging at least a portion of said heated second
portion as said volatile residue gas fraction; (12) vapor
withdrawing means connected to said contacting and separating means
to receive a distillation vapor stream from a region of said
contacting and separating device above said mid-column feed
position; (13) combining means connected to said second dividing
means and said vapor withdrawing means to receive said first
portion and said distillation vapor stream and form a combined
vapor stream; (14) compressing means connected to said combining
means to receive said combined vapor stream and compress it to
higher pressure; (15) said heat exchange means being further
connected to said compressing means to receive said compressed
combined vapor stream and cool it sufficiently to condense at least
a part of it, thereby forming a condensed stream while supplying at
least a portion of the heating of step (11); (16) fourth expansion
means connected to said heat exchange means to receive said
condensed stream and expand it to said lower pressure, said fourth
expansion means being further connected to said contacting and
separating means to supply at least a portion of said expanded
condensed stream to said contacting and separating means at a top
feed position; and (17) control means adapted to regulate the
quantities and temperatures of said feed streams to said contacting
and separating means to maintain the overhead temperature of said
contacting and separating means at a temperature whereby the major
portions of the components in said relatively less volatile
fraction are recovered.
24. In an apparatus for the separation of a gas stream containing
methane, C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components into a volatile residue gas fraction and a
relatively less volatile fraction containing a major portion of
said C.sub.2 components, C.sub.3 components, and heavier
hydrocarbon components or said C.sub.3 components and heavier
hydrocarbon components, in said apparatus there being (a) a first
cooling means to cool said gas stream under pressure connected to
provide a cooled stream under pressure; (b) a first expansion means
connected to receive at least a portion of said cooled stream under
pressure and expand it to a lower pressure, whereby said stream is
further cooled; and (c) a distillation column connected to receive
said further cooled stream, said distillation column being adapted
to separate said further cooled stream into a first overhead vapor
stream and said relatively less volatile fraction; the improvement
wherein said apparatus includes (1) said first cooling means being
adapted to cool said gas stream under pressure sufficiently to
partially condense it; (2) separating means connected to said first
cooling means to receive said partially condensed gas stream and
separate it into a vapor stream and at least one liquid stream; (3)
first dividing means connected to said separating means to receive
said vapor stream and divide it into first and second streams; (4)
first combining means connected to said first dividing means and
said separating means to receive said first stream and at least a
portion of said at least one liquid stream and form a combined
stream; (5) second cooling means connected to said first combining
means to receive said combined stream and cool it sufficiently to
substantially condense it; (6) second expansion means connected to
said second cooling means to receive said substantially condensed
combined stream and expand it to said lower pressure, said second
expansion means being further connected to a contacting and
separating means to supply said expanded cooled combined stream to
said contacting and separating means at a mid-column feed position,
said contacting and separating means being adapted to produce a
second overhead vapor stream and a bottom liquid stream; (7) said
first expansion means being connected to said first dividing means
to receive said second stream and expand it to said lower pressure,
said first expansion means being further connected to said
contacting and separating means to supply said expanded second
stream to said contacting and separating means at a first lower
column feed position below said mid-column feed position; (8) third
expansion means connected to said separating means to receive any
remaining portion of said at least one liquid stream and expand it
to said lower pressure, said third expansion means being further
connected to said distillation column to supply said expanded
liquid stream to said distillation column at a mid-column feed
position; (9) said distillation column being connected to said
contacting and separating means to receive at least a portion of
said bottom liquid stream; (10) said contacting and separating
means being further connected to said distillation column to
receive at least a portion of said first overhead vapor stream at a
second lower column feed position below said mid-column feed
position; (11) second dividing means connected to said contacting
and separating means to receive said second overhead vapor stream
separated therein and divide it into at least a first portion and a
second portion; (12) heat exchange means connected to said second
dividing means to receive at least a portion of said second portion
and heat it, thereafter discharging at least a portion of said
heated second portion as said volatile residue gas fraction; (13)
vapor withdrawing means connected to said contacting and separating
means to receive a distillation vapor stream from a region of said
contacting and separating device above said mid-column feed
position; (14) second combining means connected to said second
dividing means and said vapor withdrawing means to receive said
first portion and said distillation vapor stream and form a
combined vapor stream; (15) compressing means connected to said
second combining means to receive said combined vapor stream and
compress it to higher pressure; (16) said heat exchange means being
further connected to said compressing means to receive said
compressed combined vapor stream and cool it sufficiently to
condense at least a part of it, thereby forming a condensed stream
while supplying at least a portion of the heating of step (12);
(17) fourth expansion means connected to said heat exchange means
to receive said condensed stream and expand it to said lower
pressure, said fourth expansion means being further connected to
said contacting and separating means to supply at least a portion
of said expanded condensed stream to said contacting and separating
means at a top feed position; and (18) control means adapted to
regulate the quantities and temperatures of said feed streams to
said contacting and separating means to maintain the overhead
temperature of said contacting and separating means at a
temperature whereby the major portions of the components in said
relatively less volatile fraction are recovered.
25. The improvement according to claim 15, 16, 17, 18, or 19
wherein said vapor withdrawing means is connected to said
distillation column to receive said distillation vapor stream from
a region of said distillation column below said upper mid-column
feed position and above said mid-column feed position.
26. The improvement according to claim 15, 16, 17, 18, or 19
wherein said vapor withdrawing means is connected to said
distillation column to receive said distillation vapor stream from
a region of said distillation column below said mid-column feed
position.
27. The improvement according to claim 20, 21, 22, 23, or 24
wherein said vapor withdrawing means is connected to said
contacting and separating means to receive said distillation vapor
stream from a region of said contacting and separating means below
said mid-column feed position and above said first and second lower
column feed positions.
28. The improvement according to claim 20, 21, 22, or 23 wherein
(1) a third dividing means is connected to said distillation column
to receive said first overhead vapor stream and divide it into said
distillation vapor stream and a second distillation vapor stream;
(2) said contacting and separating device is adapted to be
connected to said third dividing means to receive said second
distillation vapor stream at said second lower column feed
position; and (3) said combining means is adapted to be connected
to said third dividing means to receive said distillation vapor
stream.
29. The improvement according to claim 24 wherein (1) a third
dividing means is connected to said distillation column to receive
said first overhead vapor stream and divide it into said
distillation vapor stream and a second distillation vapor stream;
(2) said contacting and separating device is adapted to be
connected to said third dividing means to receive said second
distillation vapor stream at said second lower column feed
position; and (3) said second combining means is adapted to be
connected to said third dividing means to receive said distillation
vapor stream.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a process and an apparatus for the
separation of a gas containing hydrocarbons. The applicants claim
the benefits under Title 35, United States Code, Section 119(e) of
prior U.S. Provisional Applications No. 61/244,181 which was filed
on Sep. 21, 2009, No. 61/346,150 which was filed on May 19, 2010,
and No. 61/351,045 which was filed on Jun. 3, 2010.
[0002] Ethylene, ethane, propylene, propane, and/or heavier
hydrocarbons can be recovered from a variety of gases, such as
natural gas, refinery gas, and synthetic gas streams obtained from
other hydrocarbon materials such as coal, crude oil, naphtha, oil
shale, tar sands, and lignite. Natural gas usually has a major
proportion of methane and ethane, i.e., methane and ethane together
comprise at least 50 mole percent of the gas. The gas also contains
relatively lesser amounts of heavier hydrocarbons such as propane,
butanes, pentanes, and the like, as well as hydrogen, nitrogen,
carbon dioxide, and other gases.
[0003] The present invention is generally concerned with the
recovery of ethylene, ethane, propylene, propane, and heavier
hydrocarbons from such gas streams. A typical analysis of a gas
stream to be processed in accordance with this invention would be,
in approximate mole percent, 88.1% methane, 6.0% ethane and other
C.sub.2 components, 2.5% propane and other C.sub.3 components, 0.2%
iso-butane, 0.2% normal butane, and 0.5% pentanes plus, with the
balance made up of nitrogen and carbon dioxide. Sulfur containing
gases are also sometimes present.
[0004] The historically cyclic fluctuations in the prices of both
natural gas and its natural gas liquid (NGL) constituents have at
times reduced the incremental value of ethane, ethylene, propane,
propylene, and heavier components as liquid products. This has
resulted in a demand for processes that can provide more efficient
recoveries of these products, for processes that can provide
efficient recoveries with lower capital investment, and for
processes that can be easily adapted or adjusted to vary the
recovery of a specific component over a broad range. Available
processes for separating these materials include those based upon
cooling and refrigeration of gas, oil absorption, and refrigerated
oil absorption. Additionally, cryogenic processes have become
popular because of the availability of economical equipment that
produces power while simultaneously expanding and extracting heat
from the gas being processed. Depending upon the pressure of the
gas source, the richness (ethane, ethylene, and heavier
hydrocarbons content) of the gas, and the desired end products,
each of these processes or a combination thereof may be
employed.
[0005] The cryogenic expansion process is now generally preferred
for natural gas liquids recovery because it provides maximum
simplicity with ease of startup, operating flexibility, good
efficiency, safety, and good reliability. U.S. Pat. Nos. 3,292,380;
4,061,481; 4,140,504; 4,157,904; 4,171,964; 4,185,978; 4,251,249;
4,278,457; 4,519,824; 4,617,039; 4,687,499; 4,689,063; 4,690,702;
4,854,955; 4,869,740; 4,889,545; 5,275,005; 5,555,748; 5,566,554;
5,568,737; 5,771,712; 5,799,507; 5,881,569; 5,890,378; 5,983,664;
6,182,469; 6,578,379; 6,712,880; 6,915,662; 7,191,617; 7,219,513;
reissue U.S. Pat. No. 33,408; and co-pending application Ser. Nos.
11/430,412; 11/839,693; 11/971,491; 12/206,230; 12/689,616;
12/717,394; 12/750,862; 12/772,472; and 12/781,259 describe
relevant processes (although the description of the present
invention in some cases is based on different processing conditions
than those described in the cited U.S. patents).
[0006] In a typical cryogenic expansion recovery process, a feed
gas stream under pressure is cooled by heat exchange with other
streams of the process and/or external sources of refrigeration
such as a propane compression-refrigeration system. As the gas is
cooled, liquids may be condensed and collected in one or more
separators as high-pressure liquids containing some of the desired
C.sub.2+ components. Depending on the richness of the gas and the
amount of liquids formed, the high-pressure liquids may be expanded
to a lower pressure and fractionated. The vaporization occurring
during expansion of the liquids results in further cooling of the
stream. Under some conditions, pre-cooling the high pressure
liquids prior to the expansion may be desirable in order to further
lower the temperature resulting from the expansion. The expanded
stream, comprising a mixture of liquid and vapor, is fractionated
in a distillation (demethanizer or deethanizer) column. In the
column, the expansion cooled stream(s) is (are) distilled to
separate residual methane, nitrogen, and other volatile gases as
overhead vapor from the desired C.sub.2 components, C.sub.3
components, and heavier hydrocarbon components as bottom liquid
product, or to separate residual methane, C.sub.2 components,
nitrogen, and other volatile gases as overhead vapor from the
desired C.sub.3 components and heavier hydrocarbon components as
bottom liquid product.
[0007] If the feed gas is not totally condensed (typically it is
not), the vapor remaining from the partial condensation can be
split into two streams. One portion of the vapor is passed through
a work expansion machine or engine, or an expansion valve, to a
lower pressure at which additional liquids are condensed as a
result of further cooling of the stream. The pressure after
expansion is essentially the same as the pressure at which the
distillation column is operated. The combined vapor-liquid phases
resulting from the expansion are supplied as feed to the
column.
[0008] The remaining portion of the vapor is cooled to substantial
condensation by heat exchange with other process streams, e.g., the
cold fractionation tower overhead. Some or all of the high-pressure
liquid may be combined with this vapor portion prior to cooling.
The resulting cooled stream is then expanded through an appropriate
expansion device, such as an expansion valve, to the pressure at
which the demethanizer is operated. During expansion, a portion of
the liquid will vaporize, resulting in cooling of the total stream.
The flash expanded stream is then supplied as top feed to the
demethanizer. Typically, the vapor portion of the flash expanded
stream and the demethanizer overhead vapor combine in an upper
separator section in the fractionation tower as residual methane
product gas. Alternatively, the cooled and expanded stream may be
supplied to a separator to provide vapor and liquid streams. The
vapor is combined with the tower overhead and the liquid is
supplied to the column as a top column feed.
[0009] In the ideal operation of such a separation process, the
residue gas leaving the process will contain substantially all of
the methane in the feed gas with essentially none of the heavier
hydrocarbon components, and the bottoms fraction leaving the
demethanizer will contain substantially all of the heavier
hydrocarbon components with essentially no methane or more volatile
components. In practice, however, this ideal situation is not
obtained because the conventional demethanizer is operated largely
as a stripping column. The methane product of the process,
therefore, typically comprises vapors leaving the top fractionation
stage of the column, together with vapors not subjected to any
rectification step. Considerable losses of C.sub.2, C.sub.3, and
C.sub.4+ components occur because the top liquid feed contains
substantial quantities of these components and heavier hydrocarbon
components, resulting in corresponding equilibrium quantities of
C.sub.2 components, C.sub.3 components, C.sub.4 components, and
heavier hydrocarbon components in the vapors leaving the top
fractionation stage of the demethanizer. The loss of these
desirable components could be significantly reduced if the rising
vapors could be brought into contact with a significant quantity of
liquid (reflux) capable of absorbing the C.sub.2 components,
C.sub.3 components, C.sub.4 components, and heavier hydrocarbon
components from the vapors.
[0010] In recent years, the preferred processes for hydrocarbon
separation use an upper absorber section to provide additional
rectification of the rising vapors. The source of the reflux stream
for the upper rectification section is typically a recycled stream
of residue gas supplied under pressure. The recycled residue gas
stream is usually cooled to substantial condensation by heat
exchange with other process streams, e.g., the cold fractionation
tower overhead. The resulting substantially condensed stream is
then expanded through an appropriate expansion device, such as an
expansion valve, to the pressure at which the demethanizer is
operated. During expansion, a portion of the liquid will usually
vaporize, resulting in cooling of the total stream. The flash
expanded stream is then supplied as top feed to the demethanizer.
Typically, the vapor portion of the expanded stream and the
demethanizer overhead vapor combine in an upper separator section
in the fractionation tower as residual methane product gas.
Alternatively, the cooled and expanded stream may be supplied to a
separator to provide vapor and liquid streams, so that thereafter
the vapor is combined with the tower overhead and the liquid is
supplied to the column as a top column feed. Typical process
schemes of this type are disclosed in U.S. Pat. Nos. 4,889,545;
5,568,737; and 5,881,569; assignee's co-pending application Ser.
No. 12/717,394; and in Mowrey, E. Ross, "Efficient, High Recovery
of Liquids from Natural Gas Utilizing a High Pressure Absorber",
Proceedings of the Eighty-First Annual Convention of the Gas
Processors Association, Dallas, Tex., Mar. 11-13, 2002. These
processes use a compressor to provide the motive force for
recycling the reflux stream to the demethanizer, adding to both the
capital cost and the operating cost of facilities using these
processes.
[0011] The present invention also employs an upper rectification
section (or a separate rectification column if plant size or other
factors favor using separate rectification and stripping columns).
However, the reflux stream for this rectification section is
provided by using a side draw of the vapors rising in a lower
portion of the tower combined with a portion of the column overhead
vapor. Because of the relatively high concentration of C.sub.2
components in the vapors lower in the tower, a significant quantity
of liquid can be condensed from this combined vapor stream with
only a modest elevation in pressure, often using only the
refrigeration available in the remaining portion of the cold
overhead vapor leaving the upper rectification section of the
column. This condensed liquid, which is predominantly liquid
methane, can then be used to absorb C.sub.2 components, C.sub.3
components, C.sub.4 components, and heavier hydrocarbon components
from the vapors rising through the upper rectification section and
thereby capture these valuable components in the bottom liquid
product from the demethanizer.
[0012] Heretofore, compressing either a portion of the cold
overhead vapor stream or compressing a side draw vapor stream to
provide reflux for the upper rectification section of the column
has been employed in C.sub.2+ recovery systems, as illustrated in
assignee's U.S. Pat. No. 4,889,545 and assignee's co-pending
application Ser. No. 11/839,693, respectively. Surprisingly,
applicants have found that combining a portion of the cold overhead
vapor with the side draw vapor stream and then compressing the
combined stream improves the system efficiency while reducing
operating cost.
[0013] In accordance with the present invention, it has been found
that C.sub.2 recovery in excess of 95% and C.sub.3 and C.sub.4+
recoveries in excess of 99% can be obtained. In addition, the
present invention makes possible essentially 100% separation of
methane and lighter components from the C.sub.2 components and
heavier components at lower energy requirements compared to the
prior art while maintaining the recovery levels. The present
invention, although applicable at lower pressures and warmer
temperatures, is particularly advantageous when processing feed
gases in the range of 400 to 1500 psia [2,758 to 10,342 kPa(a)] or
higher under conditions requiring NGL recovery column overhead
temperatures of -50.degree. F. [-46.degree. C.] or colder.
[0014] For a better understanding of the present invention,
reference is made to the following examples and drawings. Referring
to the drawings:
[0015] FIG. 1 is a flow diagram of a prior art natural gas
processing plant in accordance with U.S. Pat. No. 4,889,545;
[0016] FIG. 2 is a flow diagram of a natural gas processing plant
in accordance with the present invention; and
[0017] FIGS. 3 through 6 are flow diagrams illustrating alternative
means of application of the present invention to a natural gas
stream.
[0018] In the following explanation of the above figures, tables
are provided summarizing flow rates calculated for representative
process conditions. In the tables appearing herein, the values for
flow rates (in moles per hour) have been rounded to the nearest
whole number for convenience. The total stream rates shown in the
tables include all non-hydrocarbon components and hence are
generally larger than the sum of the stream flow rates for the
hydrocarbon components. Temperatures indicated are approximate
values rounded to the nearest degree. It should also be noted that
the process design calculations performed for the purpose of
comparing the processes depicted in the figures are based on the
assumption of no heat leak from (or to) the surroundings to (or
from) the process. The quality of commercially available insulating
materials makes this a very reasonable assumption and one that is
typically made by those skilled in the art.
[0019] For convenience, process parameters are reported in both the
traditional British units and in the units of the Systeme
International d'Unites (SI). The molar flow rates given in the
tables may be interpreted as either pound moles per hour or
kilogram moles per hour. The energy consumptions reported as
horsepower (HP) and/or thousand British Thermal Units per hour
(MBTU/Hr) correspond to the stated molar flow rates in pound moles
per hour. The energy consumptions reported as kilowatts (kW)
correspond to the stated molar flow rates in kilogram moles per
hour.
DESCRIPTION OF THE PRIOR ART
[0020] FIG. 1 is a process flow diagram showing the design of a
processing plant to recover C.sub.2+ components from natural gas
using prior art according to U.S. Pat. No. 4,889,545. In this
simulation of the process, inlet gas enters the plant at
120.degree. F. [49.degree. C.] and 1040 psia [7,171 kPa(a)] as
stream 31. If the inlet gas contains a concentration of sulfur
compounds which would prevent the product streams from meeting
specifications, the sulfur compounds are removed by appropriate
pretreatment of the feed gas (not illustrated). In addition, the
feed stream is usually dehydrated to prevent hydrate (ice)
formation under cryogenic conditions. Solid desiccant has typically
been used for this purpose.
[0021] The feed stream 31 is cooled in heat exchanger 10 by heat
exchange with cool residue gas (stream 43a), liquid product at
72.degree. F. [22.degree. C.] (stream 42a), demethanizer reboiler
liquids at 52.degree. F. [11.degree. C.] (stream 41), and
demethanizer side reboiler liquids at -20.degree. F. [-29.degree.
C.] (stream 40). Note that in all cases exchanger 10 is
representative of either a multitude of individual heat exchangers
or a single multi-pass heat exchanger, or any combination thereof.
(The decision as to whether to use more than one heat exchanger for
the indicated cooling services will depend on a number of factors
including, but not limited to, inlet gas flow rate, heat exchanger
size, stream temperatures, etc.) The cooled stream 31a enters
separator 11 at -18.degree. F. [-28.degree. C.] and 1025 psia
[7,067 kPa(a)] where the vapor (stream 32) is separated from the
condensed liquid (stream 33). The separator liquid (stream 33) is
expanded to the operating pressure (approximately 392 psia [2,701
kPa(a)]) of fractionation tower 17 by expansion valve 16, cooling
stream 33a to -53.degree. F. [-47.degree. C.] before it is supplied
to fractionation tower 17 at a lower mid-column feed point.
[0022] The vapor (stream 32) from separator 11 is divided into two
streams, 36 and 37. Stream 36, containing about 38% of the total
vapor, passes through heat exchanger 12 in heat exchange relation
with the cold residue gas (stream 43) where it is cooled to
substantial condensation. The resulting substantially condensed
stream 36a at -142.degree. F. [-96.degree. C.] is then flash
expanded through expansion valve 13 to slightly above the operating
pressure of fractionation tower 17. During expansion a portion of
the stream is vaporized, resulting in cooling of the total stream.
In the process illustrated in FIG. 1, the expanded stream 36b
leaving expansion valve 13 reaches a temperature of -144.degree. F.
[-98.degree. C.]. The expanded stream 36b is warmed to -139.degree.
F. [-95.degree. C.] and further vaporized in heat exchanger 22 as
it provides cooling and condensation of compressed recycle stream
44a (described later in paragraph [0026]). The warmed stream 36c is
then supplied at an upper mid-column feed point, in absorbing
section 17a of fractionation tower 17.
[0023] The remaining 62% of the vapor from separator 11 (stream 37)
enters a work expansion machine 14 in which mechanical energy is
extracted from this portion of the high pressure feed. The machine
14 expands the vapor substantially isentropically to the tower
operating pressure, with the work expansion cooling the expanded
stream 37a to a temperature of approximately -94.degree. F.
[-70.degree. C.]. The typical commercially available expanders are
capable of recovering on the order of 80-85% of the work
theoretically available in an ideal isentropic expansion. The work
recovered is often used to drive a centrifugal compressor (such as
item 15) that can be used to re-compress the residue gas (stream
43b), for example. The partially condensed expanded stream 37a is
thereafter supplied as feed to fractionation tower 17 at a
mid-column feed point.
[0024] The demethanizer in tower 17 is a conventional distillation
column containing a plurality of vertically spaced trays, one or
more packed beds, or some combination of trays and packing. The
demethanizer tower consists of two sections: an upper absorbing
(rectification) section 17a that contains the trays and/or packing
to provide the necessary contact between the vapor portions of the
expanded streams 36c and 37a rising upward and cold liquid falling
downward to condense and absorb the C.sub.2 components, C.sub.3
components, and heavier components; and a lower, stripping section
17b that contains the trays and/or packing to provide the necessary
contact between the liquids falling downward and the vapors rising
upward. The demethanizing section 17b also includes one or more
reboilers (such as the reboiler and side reboiler described
previously) which heat and vaporize a portion of the liquids
flowing down the column to provide the stripping vapors which flow
up the column to strip the liquid product, stream 42, of methane
and lighter components. Stream 37a enters demethanizer 17 at an
intermediate feed position located in the lower region of absorbing
section 17a of demethanizer 17. The liquid portion of the expanded
stream 37a commingles with liquids falling downward from absorbing
section 17a and the combined liquid continues downward into
stripping section 17b of demethanizer 17. The vapor portion of the
expanded stream 37a rises upward through absorbing section 17a and
is contacted with cold liquid falling downward to condense and
absorb the C.sub.2 components, C.sub.3 components, and heavier
components.
[0025] In stripping section 17b of demethanizer 17, the feed
streams are stripped of their methane and lighter components. The
resulting liquid product (stream 42) exits the bottom of tower 17
at 67.degree. F. [19.degree. C.] (based on a typical specification
of a methane to ethane ratio of 0.015:1 on a volume basis in the
bottom product) and is pumped to heat exchanger 10 by pump 20 to be
heated to 116.degree. F. [47.degree. C.] as it provides cooling to
the feed gas as described earlier.
[0026] Cold demethanizer overhead stream 39 exits the top of
demethanizer 17 at -146.degree. F. [-99.degree. C.] and is divided
into cold residue gas stream 43 and recycle stream 44. Recycle
stream 44 is compressed to 492 psia [3,390 kPa(a)] by compressor 21
before entering heat exchanger 22. The compressed recycle stream
44a is cooled from -121.degree. F. [-85.degree. C.] to -140.degree.
F. [-96.degree. C.] and substantially condensed by heat exchange
with expanded substantially condensed stream 36b as described
previously. The substantially condensed stream 44b is then expanded
through an appropriate expansion device, such as expansion valve
23, to the demethanizer operating pressure, resulting in cooling of
the total stream to -150.degree. F. [-101.degree. C.]. The expanded
stream 44c is then supplied to fractionation tower 17 as the top
column feed. The vapor portion of stream 44c combines with the
vapors rising from the top fractionation stage of the column to
form demethanizer overhead stream 39.
[0027] The cold residue gas stream 43 passes countercurrently to
the incoming feed gas in heat exchanger 12 where it is heated to
-26.degree. F. [-32.degree. C.] (stream 43a) and in heat exchanger
10 where it is heated to 98.degree. F. [37.degree. C.] (stream
43b). The residue gas is then re-compressed in two stages. The
first stage is compressor 15 driven by expansion machine 14. The
second stage is compressor 24 driven by a supplemental power source
which compresses the residue gas (stream 43d) to sales line
pressure. After cooling to 120.degree. F. [49.degree. C.] in
discharge cooler 25, the residue gas product (stream 43e) flows to
the sales gas pipeline at 1040 psia [7,171 kPa(a)], sufficient to
meet line requirements (usually on the order of the inlet
pressure).
[0028] A summary of stream flow rates and energy consumption for
the process illustrated in FIG. 1 is set forth in the following
table:
TABLE-US-00001 TABLE I (FIG. 1) Stream Flow Summary - Lb. Moles/Hr
[kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31
24,193 1,650 687 234 27,451 32 24,042 1,608 641 168 27,142 33 151
42 46 66 309 36 9,184 614 245 64 10,368 37 14,858 994 396 104
16,774 39 28,419 82 0 0 29,216 44 4,263 12 0 0 4,382 43 24,156 70 0
0 24,834 42 37 1,580 687 234 2,617 Recoveries* Ethane 95.79%
Propane 100.00% Butanes+ 100.00% Power Residue Gas Compression
13,294 HP [21,855 kW] Recycle Compression 224 HP [368 kW] Total
Compression 13,518 HP [22,223 kW] *(Based on un-rounded flow
rates)
DESCRIPTION OF THE INVENTION
[0029] FIG. 2 illustrates a flow diagram of a process in accordance
with the present invention. The feed gas composition and conditions
considered in the process presented in FIG. 2 are the same as those
in FIG. 1. Accordingly, the FIG. 2 process can be compared with
that of the FIG. 1 process to illustrate the advantages of the
present invention.
[0030] In the simulation of the FIG. 2 process, inlet gas enters
the plant at 120.degree. F. [49.degree. C.] and 1040 psia [7,171
kPa(a)] as stream 31 and is cooled in heat exchanger 10 by heat
exchange with cool residue gas (stream 43a), liquid product at
74.degree. F. [24.degree. C.] (stream 42a), demethanizer reboiler
liquids at 54.degree. F. [12.degree. C.] (stream 41), and
demethanizer side reboiler liquids at -19.degree. F. [-28.degree.
C.] (stream 40). The cooled stream 31a enters separator 11 at
-24.degree. F. [-31.degree. C.] and 1025 psia [7,067 kPa(a)] where
the vapor (stream 32) is separated from the condensed liquid
(stream 33). The separator liquid (stream 33/38) is expanded to the
operating pressure (approximately 401 psia [2,766 kPa(a)]) of
fractionation tower 17 by expansion valve 16, cooling stream 38a to
-59.degree. F. [-51.degree. C.] before it is supplied to
fractionation tower 17 at a lower mid-column feed point (located
below the feed point of stream 37a described later in paragraph
[0032]).
[0031] The vapor (stream 32) from separator 11 is divided into two
streams, 34 and 37. Stream 34, containing about 28% of the total
vapor, passes through heat exchanger 12 in heat exchange relation
with the cold residue gas (stream 43) where it is cooled to
substantial condensation. The resulting substantially condensed
stream 36a at -140.degree. F. [-96.degree. C.] is then flash
expanded through expansion valve 13 to the operating pressure of
fractionation tower 17. During expansion a portion of the stream is
vaporized, resulting in cooling of the total stream. In the process
illustrated in FIG. 2, the expanded stream 36b leaving expansion
valve 13 reaches a temperature of -144.degree. F. [-98.degree. C.]
before it is supplied at an upper mid-column feed point, in
absorbing section 17a of fractionation tower 17.
[0032] The remaining 72% of the vapor from separator 11 (stream 37)
enters a work expansion machine 14 in which mechanical energy is
extracted from this portion of the high pressure feed. The machine
14 expands the vapor substantially isentropically to the tower
operating pressure, with the work expansion cooling the expanded
stream 37a to a temperature of approximately -97.degree. F.
[-72.degree. C.]. The partially condensed expanded stream 37a is
thereafter supplied as feed to fractionation tower 17 at a
mid-column feed point (located below the feed point of stream
36b).
[0033] The demethanizer in tower 17 is a conventional distillation
column containing a plurality of vertically spaced trays, one or
more packed beds, or some combination of trays and packing. The
demethanizer tower consists of two sections: an upper absorbing
(rectification) section 17a that contains the trays and/or packing
to provide the necessary contact between the vapor portion of the
expanded streams 36b and 37a rising upward and cold liquid falling
downward to condense and absorb the C.sub.2 components, C.sub.3
components, and heavier components from the vapors rising upward;
and a lower, stripping section 17b that contains the trays and/or
packing to provide the necessary contact between the liquids
falling downward and the vapors rising upward. The demethanizing
section 17b also includes one or more reboilers (such as the
reboiler and side reboiler described previously) which heat and
vaporize a portion of the liquids flowing down the column to
provide the stripping vapors which flow up the column to strip the
liquid product, stream 42, of methane and lighter components.
Stream 37a enters demethanizer 17 at an intermediate feed position
located in the lower region of absorbing section 17a of
demethanizer 17. The liquid portion of the expanded stream 37a
commingles with liquids falling downward from absorbing section 17a
and the combined liquid continues downward into stripping section
17b of demethanizer 17. The vapor portion of the expanded stream
37a rises upward through absorbing section 17a and is contacted
with cold liquid falling downward to condense and absorb the
C.sub.2 components, C.sub.3 components, and heavier components.
[0034] A portion of the distillation vapor (stream 45) is withdrawn
from the upper region of absorbing section 17a in fractionation
column 17, above the feed position of expanded stream 36b in the
middle region of absorbing section 17a. The distillation vapor
stream 45 at -142.degree. F. [-96.degree. C.] is combined with a
first portion (stream 44) of overhead vapor stream 39 at
-144.degree. F. [-98.degree. C.] to form combined vapor stream 46
at -144.degree. F. [-98.degree. C.]. The combined vapor stream 46
is compressed to 686 psia [4,728 kPa(a)] by reflux compressor 21,
then cooled from -84.degree. F. [-65.degree. C.] to -140.degree. F.
[-96.degree. C.] and substantially condensed (stream 46b) in heat
exchanger 12 by heat exchange with cold residue gas stream 43, the
remaining second portion of demethanizer overhead stream 39 exiting
the top of demethanizer 17.
[0035] The substantially condensed stream 46b is flash expanded to
the operating pressure of demethanizer 17 by expansion valve 23. A
portion of the stream is vaporized, further cooling stream 46c to
-149.degree. F. [-101.degree. C.] before it is supplied as cold top
column feed (reflux) to demethanizer 17. This cold liquid reflux
absorbs and condenses the C.sub.2 components, C.sub.3 components,
and heavier components rising in the upper rectification region of
absorbing section 17a of demethanizer 17.
[0036] In stripping section 17b of demethanizer 17, the feed
streams are stripped of their methane and lighter components. The
resulting liquid product (stream 42) exits the bottom of tower 17
at 69.degree. F. [21.degree. C.] (based on a typical specification
of a methane to ethane ratio of 0.015:1 on a volume basis in the
bottom product) and is pumped to heat exchanger 10 by pump 20 to be
heated to 116.degree. F. [47.degree. C.] as it provides cooling to
the feed gas as described earlier. The cold residue gas stream 43
passes countercurrently to the incoming feed gas and compressed
combined vapor stream in heat exchanger 12 where it is heated to
-37.degree. F. [-39.degree. C.] (stream 43a), and countercurrently
to the incoming feed gas in heat exchanger 10 where it is heated to
97.degree. F. [36.degree. C.] (stream 43b) as it provides cooling
as previously described. The residue gas is then re-compressed in
two stages, compressor 15 driven by expansion machine 14 and
compressor 24 driven by a supplemental power source. After stream
43d is cooled to 120.degree. F. [49.degree. C.] in discharge cooler
25, the residue gas product (stream 43e) flows to the sales gas
pipeline at 1040 psia [7,171 kPa(a)], sufficient to meet line
requirements (usually on the order of the inlet pressure).
[0037] A summary of stream flow rates and energy consumption for
the process illustrated in FIG. 2 is set forth in the following
table:
TABLE-US-00002 TABLE II (FIG. 2) Stream Flow Summary - Lb. Moles/Hr
[kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31
24,193 1,650 687 234 27,451 32 23,983 1,593 626 157 27,042 33 210
57 61 77 409 34 6,607 439 172 43 7,450 35 0 0 0 0 0 36 6,607 439
172 43 7,450 37 17,376 1,154 454 114 19,592 38 210 57 61 77 409 39
27,081 78 0 0 27,845 44 2,925 8 0 0 3,007 45 194 1 0 0 200 46 3,119
9 0 0 3,207 43 24,156 70 0 0 24,838 42 37 1,580 687 234 2,613
Recoveries* Ethane 95.77% Propane 99.99% Butanes+ 100.00% Power
Residue Gas Compression 12,573 HP [20,670 kW] Reflux Compression
401 HP [659 kW] Total Compression 12,974 HP [21,329 kW] *(Based on
un-rounded flow rates)
[0038] A comparison of Tables I and II shows that the present
invention maintains essentially the same recoveries as the prior
art. However, further comparison of Tables I and II shows that the
product yields were achieved using significantly less power than
the prior art. In terms of the recovery efficiency (defined by the
quantity of ethane recovered per unit of power), the present
invention represents more than a 4% improvement over the prior art
of the FIG. 1 process.
[0039] Like the prior art of the FIG. 1 process, the present
invention uses the expanded substantially condensed feed stream 36b
supplied to absorbing section 17a of demethanizer 17 to provide
bulk recovery of the C.sub.2 components, C.sub.3 components, and
heavier hydrocarbon components contained in expanded feed 37a and
the vapors rising from stripping section 17b, and the supplemental
rectification provided by reflux stream 46c to reduce the amount of
C.sub.2 components, C.sub.3 components, and C.sub.4+ components
contained in the inlet feed gas that is lost to the residue gas.
However, the present invention reduces the rectification required
in absorbing section 17a over that of the prior art FIG. 1 process
by condensing reflux stream 46c without warming any of the feeds
(stream 36b and 37a) to absorbing section 17a. If the substantially
condensed stream 36b is warmed to provide condensing as is taught
in the prior art FIG. 1 process, not only is there less cold liquid
from stream 36b available for rectification of the vapors rising in
absorbing section 17a, there is much more vapor in the upper region
of absorbing section 17a that must be rectified by the reflux
stream. As can be seen by comparing reflux stream 44 in Table I
with reflux stream 46 in Table II, the net result is that more
reflux is required by the prior art FIG. 1 process to prevent the
C.sub.2 components from escaping to the residue gas stream than the
present invention requires, reducing its recovery efficiency
compared to the present invention. The key improvement of the
present invention over the prior art process is that only the cold
residue gas stream 43 is needed to provide the cooling in heat
exchanger 12, thereby condensing sufficient methane from compressed
combined vapor stream 46a for use as reflux while avoiding adding
significant rectification load in absorbing section 17a due to the
excessive vaporization of stream 36b that is inherent in the prior
art FIG. 1 process.
Other Embodiments
[0040] In accordance with this invention, it is generally
advantageous to design the absorbing (rectification) section of the
demethanizer to contain multiple theoretical separation stages.
However, the benefits of the present invention can be achieved with
as few as two theoretical stages. For instance, all or a part of
the expanded reflux stream (stream 46c) leaving expansion valve 23
and all or a part of the expanded substantially condensed stream
36b from expansion valve 13 can be combined (such as in the piping
joining the expansion valves to the demethanizer) and if thoroughly
intermingled, the vapors and liquids will mix together and separate
in accordance with the relative volatilities of the various
components of the total combined streams. Such commingling of the
two streams, combined with contacting at least a portion of
expanded stream 37a, shall be considered for the purposes of this
invention as constituting an absorbing section.
[0041] FIGS. 3 through 6 display other embodiments of the present
invention. FIGS. 2 through 4 depict fractionation towers
constructed in a single vessel. FIGS. 5 and 6 depict fractionation
towers constructed in two vessels, absorber (rectifier) column 17
(a contacting and separating device) and stripper (distillation)
column 19. In such cases, the overhead vapor stream 48 from
stripper column 19 flows to the lower section of absorber column 17
(via stream 49) to be contacted by reflux stream 46c and expanded
substantially condensed stream 36b. Pump 18 is used to route the
liquids (stream 47) from the bottom of absorber column 17 to the
top of stripper column 19 so that the two towers effectively
function as one distillation system. The decision whether to
construct the fractionation tower as a single vessel (such as
demethanizer 17 in FIGS. 2 through 4) or multiple vessels will
depend on a number of factors such as plant size, the distance to
fabrication facilities, etc.
[0042] Some circumstances may favor withdrawing the distillation
vapor stream 45 in FIGS. 3 and 4 from the lower region of absorbing
section 17a above the feed point of expanded stream 37a (stream
51), rather than from the upper region of absorbing section 17a
above the feed point of expanded substantially condensed stream 36b
(stream 50). Likewise in FIGS. 5 and 6, the vapor distillation
stream 45 may be withdrawn from absorber column 17 above the feed
point of expanded substantially condensed stream 36b (stream 50) or
above the feed point of expanded stream 37a (stream 51). In other
cases, it may be advantageous to withdraw the distillation vapor
stream 45 from the upper region of stripping section 17b in
demethanizer 17 (stream 52) in FIGS. 3 and 4. Similarly in FIGS. 5
and 6, a portion (stream 52) of overhead vapor stream 48 from
stripper column 19 may be combined with stream 44, with any
remaining portion (stream 49) flowing to the lower section of
absorber column 17.
[0043] As described earlier, the compressed combined vapor stream
46a is substantially condensed and the resulting condensate used to
absorb valuable C.sub.2 components, C.sub.3 components, and heavier
components from the vapors rising through absorbing section 17a of
demethanizer 17 or through absorber column 17. However, the present
invention is not limited to this embodiment. It may be
advantageous, for instance, to treat only a portion of these vapors
in this manner, or to use only a portion of the condensate as an
absorbent, in cases where other design considerations indicate
portions of the vapors or the condensate should bypass absorbing
section 17a of demethanizer 17 or absorber column 17. Some
circumstances may favor partial condensation, rather than
substantial condensation, of compressed combined vapor stream 46a
in heat exchanger 12. Other circumstances may favor that
distillation vapor stream 45 be a total vapor side draw from
fractionation column 17 or absorber column 17 rather than a partial
vapor side draw. It should also be noted that, depending on the
composition of the feed gas stream, it may be advantageous to use
external refrigeration to provide partial cooling of compressed
combined vapor stream 46a in heat exchanger 12.
[0044] Feed gas conditions, plant size, available equipment, or
other factors may indicate that elimination of work expansion
machine 14, or replacement with an alternate expansion device (such
as an expansion valve), is feasible. Although individual stream
expansion is depicted in particular expansion devices, alternative
expansion means may be employed where appropriate. For example,
conditions may warrant work expansion of the substantially
condensed portion of the feed stream (stream 36a) or the
substantially condensed reflux stream (stream 46b) leaving heat
exchanger 12.
[0045] Depending on the quantity of heavier hydrocarbons in the
feed gas and the feed gas pressure, the cooled feed stream 31a
leaving heat exchanger 10 in FIGS. 2 through 6 may not contain any
liquid (because it is above its dewpoint, or because it is above
its cricondenbar). In such cases, separator 11 shown in FIGS. 2
through 6 is not required.
[0046] The high pressure liquid (stream 33 in FIGS. 2 through 6)
need not be expanded and fed to a mid-column feed point on the
distillation column. Instead, all or a portion of it may be
combined with the portion of the separator vapor (stream 34)
flowing to heat exchanger 12. (This is shown by the dashed stream
35 in FIGS. 2 through 6.) Any remaining portion of the liquid may
be expanded through an appropriate expansion device, such as an
expansion valve or expansion machine, and fed to a mid-column feed
point on the distillation column (stream 38a in FIGS. 2 through 6).
Stream 38 may also be used for inlet gas cooling or other heat
exchange service before or after the expansion step prior to
flowing to the demethanizer.
[0047] In accordance with the present invention, the use of
external refrigeration to supplement the cooling available to the
inlet gas from other process streams may be employed, particularly
in the case of a rich inlet gas. The use and distribution of
separator liquids and demethanizer side draw liquids for process
heat exchange, and the particular arrangement of heat exchangers
for inlet gas cooling must be evaluated for each particular
application, as well as the choice of process streams for specific
heat exchange services.
[0048] In accordance with the present invention, the splitting of
the vapor feed may be accomplished in several ways. In the
processes of FIGS. 2, 3, and 5, the splitting of vapor occurs
following cooling and separation of any liquids which may have been
formed. The high pressure gas may be split, however, prior to any
cooling of the inlet gas as shown in FIGS. 4 and 6. In some
embodiments, vapor splitting may be effected in a separator.
[0049] It will also be recognized that the relative amount of feed
found in each branch of the split vapor feed will depend on several
factors, including gas pressure, feed gas composition, the amount
of heat which can economically be extracted from the feed, and the
quantity of horsepower available. More feed to the top of the
column may increase recovery while decreasing power recovered from
the expander thereby increasing the recompression horsepower
requirements. Increasing feed lower in the column reduces the
horsepower consumption but may also reduce product recovery. The
relative locations of the mid-column feeds may vary depending on
inlet composition or other factors such as desired recovery levels
and amount of liquid formed during inlet gas cooling. Moreover, two
or more of the feed streams, or portions thereof, may be combined
depending on the relative temperatures and quantities of individual
streams, and the combined stream then fed to a mid-column feed
position.
[0050] The present invention provides improved recovery of C.sub.2
components, C.sub.3 components, and heavier hydrocarbon components
or of C.sub.3 components and heavier hydrocarbon components per
amount of utility consumption required to operate the process. An
improvement in utility consumption required for operating the
demethanizer or deethanizer process may appear in the form of
reduced power requirements for compression or re-compression,
reduced power requirements for external refrigeration, reduced
energy requirements for tower reboilers, or a combination
thereof.
[0051] While there have been described what are believed to be
preferred embodiments of the invention, those skilled in the art
will recognize that other and further modifications may be made
thereto, e.g. to adapt the invention to various conditions, types
of feed, or other requirements without departing from the spirit of
the present invention as defined by the following claims.
* * * * *