U.S. patent application number 11/269662 was filed with the patent office on 2007-05-10 for method for designing a cryogenic air separation plant.
Invention is credited to John Harry Fassbaugh, Douglas Henry May, Herbert Raymond Schaub, Todd Alan Skare, Scott Alan Spriggs.
Application Number | 20070101762 11/269662 |
Document ID | / |
Family ID | 38002397 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070101762 |
Kind Code |
A1 |
Schaub; Herbert Raymond ; et
al. |
May 10, 2007 |
Method for designing a cryogenic air separation plant
Abstract
A method for designing a cryogenic air separation plant wherein
a particular plant which fits into a certain classification is
designed by first employing at least one predesigned subsystem for
that classification to form a base system and then completing the
design by adding to the base system at least one auxiliary
subsystem designed specifically for that particular plant.
Inventors: |
Schaub; Herbert Raymond;
(East Amherst, NY) ; Skare; Todd Alan; (The
Woodlands, TX) ; Fassbaugh; John Harry; (Elma,
NY) ; May; Douglas Henry; (Sanborn, NY) ;
Spriggs; Scott Alan; (East Amherst, NY) |
Correspondence
Address: |
PRAXAIR, INC.;LAW DEPARTMENT - M1 557
39 OLD RIDGEBURY ROAD
DANBURY
CT
06810-5113
US
|
Family ID: |
38002397 |
Appl. No.: |
11/269662 |
Filed: |
November 9, 2005 |
Current U.S.
Class: |
62/617 ; 62/620;
62/643; 62/902 |
Current CPC
Class: |
F25J 3/04412 20130101;
F25J 3/04296 20130101; F25J 2230/22 20130101; F25J 3/04381
20130101; F25J 3/04678 20130101; F25J 3/0489 20130101; F25J 2290/10
20130101; F25J 3/0409 20130101 |
Class at
Publication: |
062/617 ;
062/643; 062/620; 062/902 |
International
Class: |
F25J 3/00 20060101
F25J003/00 |
Claims
1. A method for designing a cryogenic air separation plant
comprising: (A) electing a plant classification from a set of plant
classifications; (B) defining a group of predesigned subsystems for
the elected plant classification; (C) initiating the design of a
specific cryogenic air separation plant within the elected plant
classification by choosing at least one predesigned subsystem to
form the base system of the cryogenic air separation plant; and (D)
completing the design of the cryogenic air separation plant by
adding to the base system an auxiliary system comprising at least
one subsystem designed specifically for the cryogenic air
separation plant.
2. The method of claim 1 wherein the base system comprises an air
prepurification system.
3. The method of claim 1 wherein the base system comprises a
primary heat exchanger.
4. The method of claim 1 wherein the base system comprises a
cryogenic distillation column.
Description
TECHNICAL FIELD
[0001] This invention relates generally to cryogenic air separation
and, more particularly,. to designing a cryogenic air separation
plant.
BACKGROUND ART
[0002] A cryogenic air separation plant is a very complicated
process plant which includes many different units and subsystems
such as distillation columns, condensers, reboilers,
prepurification systems, air compression systems, liquid pumps,
heat exchangers, storage tanks, process control systems, buildings
and other infrastructure. Accordingly, the designing of a cryogenic
air separation plant is a complicated and thus costly endeavor
which adds significantly to the overall costs of the plant beyond
the equipment and construction costs. This is because in most cases
each particular cryogenic air separation plant must be specifically
designed. Rarely will an existing design for a previously
constructed cryogenic air separation plant be exactly suited for
use in the construction of a new cryogenic air separation plant.
Any method which can reduce the complexity, time and cost for
designing a new cryogenic air separation plant would be very
useful.
SUMMARY OF THE INVENTION
[0003] A method for designing a cryogenic air separation plant
comprising:
[0004] (A) electing a plant classification from a set of plant
classifications;
[0005] (B) defining a group of predesigned subsystems for the
elected plant classification;
[0006] (C) initiating the design of a specific cryogenic air
separation plant within the elected plant classification by
choosing at least one predesigned subsystem to form the base system
of the cryogenic air separation plant; and
[0007] (D) completing the design of the cryogenic air separation
plant by adding to the base system an auxiliary system comprising
at least one subsystem designed specifically for the cryogenic air
separation plant.
[0008] As used herein the term "predesigned subsystem" means an
arrangement comprising a plurality of engineered components and
wherein each engineered component is connected to at least one
other engineered component of the subsystem.
[0009] As used herein the term "engineered component" means a fully
designed unit that performs at least one process step that is part
of an overall process comprising heat exchange, distillation,
compression and/or purification. Examples of engineered components
include feed pretreatment units (for example prepurifiers),
distillation columns, reboiler/condensers, heat exchangers, direct
contact coolers, chillers, liquid pumps, gas compressors, cooling
water towers, fluid expanders, process control units, liquid
storage vessels, motors and electrical switch gears.
[0010] As used herein the term "fully designed" means design work,
such as materials of construction specification, process equipment
sizing and selection, major valves sizing and selection, equipment
arrangement and location of all permanent support and loads,
process piping sizing and routing, process instrumentation and
controls specification, process analyzers selection and
specification, vent and pressure relief devices sizing and
specification, drain valves and headers sizing and specification,
casing sizing and specifications, static and operating weights
estimations, and shipping outline, has been completed.
[0011] As used herein the term "connected" means related by way of
material transfer, energy transfer, and/or data transfer.
BRIEF DEXRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a simplified schematic representation of one
embodiment of a cryogenic air separation plant which may benefit
from the application of the method of this invention.
[0013] FIG. 2 is a schematic representation of a predesigned
subsystem which may be used with the plant illustrated in FIG.
1.
[0014] FIG. 3 is a schematic representation of another predesigned
subsystem which may be used with the plant illustrated in FIG.
1.
[0015] The numerals in the Drawings are the same for the common
elements.
DETAILED DESCRIPTION
[0016] In the method of this invention cryogenic air separation
plant classifications based on specific requirements such as plant
size, i.e. capacity, product slate (oxygen, nitrogen, argon and/or
clean dry air, etc.), product type (gas and/or liquid), product
specification (purity and/or pressure) and location (back-up needs,
ambient conditions, local factors etc.), are defined. The desired
cryogenic air separation plant fits into one of the classifications
and is designed by fitting together at least one predesigned
subsystem for that classification with one or more subsystems
specifically designed for that particular cryogenic air separation
plant.
[0017] In the practice of this invention a base system is defined
to comprise at least one, preferably two or more, predesigned
subsystems that are common to meet different requirements
regarding, for example, product type and purity. An auxiliary
system is defined to comprise one or more subsystems that are
designed specifically to provide the complete plant. For example
the base system may provide for air compression, prepurification,
heat exchange, refrigeration supply, cryogenic distillation,
condensation/reboil, liquid pumping, liquefaction, process control;
and the auxiliary system may provide for product compression,
liquids storage, switchgear and transformers, cooling water, motor
control, buildings and other infrastructure. Any base system can
operate over a range of pre-determined conditions, and the specific
application requirements will fall within the allowable limits.
Generally the auxiliary system will address the specific
application requirements associated with product specifications or
location factors. These could include factors such as product
purity, pressure, backup needs, or cooling water needs. Once the
engineering work for the base system is completed, it can be reused
for all of the specific applications that have similar
requirements.
[0018] The invention will be more particularly described and
exemplified with reference to the Drawings. Referring now to FIGS.
1-3, ambient air 61 from air suction filter 101 is compressed in
main air compressor 102 which is driven.by motor 103. Resulting air
stream 63 is cooled in cooler 104, and cooled stream 64 is
subjected to free water removal in moisture removal system 105.
Resulting elevated pressure air stream 5 is then fed to
prepurification system 107, which is a continuously operating two
bed pressure swing adsorption (PSA) process. One bed purifies the
air of water, carbon dioxide, and most of the hydrocarbons in
stream 5 while the other bed is being regenerated by waste nitrogen
stream 47. The exiting contents of the regenerating bed leaves
prepurification system 107 as waste stream 50. Prepurified air
stream 6 then enters a dust filter (not shown) for the removal of
any remaining solid particles. Dust free prepurified air stream is
split into streams 8 and 11 and further compressed in compressors
109 and 113 respectively. Aftercoolers 110 and 114 remove the heat
of compression in the resulting air streams. The compressors 109
and 113, turbine 117, and motor 116 can be configured as a single
component or as combinations of one or more of them. Motor 116 can
supply additional power if the work generated by turbine 117 is not
sufficient to drive compressors 109 and 113. Likewise, if turbine
117 generates more work than is required by compressors 109 and
113, motor 116 removes the excess power from the system.
[0019] In primary heat exchanger 115, stream 15 is condensed
against boiling oxygen product and warming nitrogen gas, whereupon
it exits the cold end of primary heat exchanger 115 as subcooled
liquid air stream 17. Stream 17 is split into streams 19 and 20.
Stream 19 is fed to medium pressure column 118 several stages from
the bottom and stream 20 is fed to the middle of low pressure
column 121. Stream 10 is cooled in primary heat exchanger b 115 and
removed from primary heat exchanger 115 at an intermediate point.
Cooled air stream 16 is then fed to expansion turbine 117, which
supplies the refrigeration needs of the plant. Turbine discharge
air stream 18 is then fed to the bottom of medium pressure column
118. In column 118 the air is separated by cryogenic rectification
into oxygen-enriched and nitrogen-enriched portions.
Oxygen-enriched liquid 21 is removed from the bottom of the column
and passed into heat exchanger 120 where it is cooled against
warming nitrogen gas and from which it exits as a sub-cooled liquid
26. Subcooled oxygen-enriched liquid stream 26 is split into
streams 27 and 33. Stream 27 is fed directly to low pressure column
121 l below the feed point for stream 20 but above the bottom of
the column. Stream 33 is fed to the boiling side of
condenser/reboiler 122 where it is partially vaporized.
Oxygen-enriched vapor and liquid streams 29 and 30 exit
condenser/reboiler 122 and are fed to an intermediate point of low
pressure column 121, below that point where stream 27 enters the
column.
[0020] Nitrogen-enriched vapor 22 exits the top of the medium
pressure column 118 and enters the condensing side of
condenser/reboiler 119. Stream 22 is liquefied against vaporizing
bottoms liquid in column 121. Liquid nitrogen 23 leaving
condenser/reboiler 119 is split into two streams; stream 24 is
returned to column 118 as reflux and stream 25 is sent to heat
exchanger 120. Stream 25 is subcooled against warming nitrogen
vapor. Subcooled liquid nitrogen stream 31 is split into two
streams; stream 32 enters low pressure column 121 at or near the
top and stream 28 is sent liquid nitrogen storage vessel 127.
[0021] Low pressure distillation column 121 further separates its
feed streams into oxygen-rich and nitrogen-rich portions. An
oxygen-rich liquid stream 34 is removed from the bottom of column
121, where it is split into two streams; stream 35 is fed to liquid
oxygen storage vessel 125 and stream 36 is fed to cryogenic oxygen
pump 124 and raised to the pressure at which it will boil in
primary heat exchanger 115. High pressure liquid stream 37 is fed
to the cold end of primary heat exchanger 115 where it is warmed
and boiled against the condensing high pressure air stream 15.
Warmed, high pressure oxygen vapor product 48 exits the warm end of
primary heat exchanger 115.
[0022] Vapor stream 38 is removed from an intermediate point of low
pressure column 121 and fed to the bottom of argon column 123.
Liquid stream 39 exits the bottom of argon column 123 and is
returned to low pressure column 121 at the same point at which
stream 38 was withdrawn. Argon-enriched liquid stream 40 is removed
from the top of argon column 123 and fed to liquid argon storage
vessel 126. Also, argon-enriched vapor stream 41 exits the top of
argon column 123 and is fed to the condensing side of
condenser/reboiler 122. Argon-enriched liquid stream 42 exits
condenser/reboiler 122 and is returned to the top of argon column
123 as reflux.
[0023] Two nitrogen-rich streams are withdrawn from the top portion
of low pressure column 121. Product nitrogen-rich vapor 44 exits
the top of the low pressure column 121, is fed to heat exchanger
120, is warmed against cooling streams, and leaves as superheated
nitrogen vapor product stream 46. Waste nitrogen-enriched vapor 43
is removed from low pressure column 121 a few stages from the top,
is fed to heat exchanger 120, is warmed against cooling streams,
and leaves as superheated nitrogen vapor waste stream 45. Both
superheated nitrogen streams 45 and 46 are fed to the cold end of
primary heat exchanger 115 where they are warmed against cooling
air streams and exit primary heat exchanger 115 to form waste and
product streams 47 and 49, respectively.
[0024] As mentioned earlier, warm nitrogen-enriched waste stream 47
is fed to prepurifier vessel 107 in order to regenerate one of the
PSA beds. If nitrogen product is desired at elevated pressure, it
is compressed in compressor 134 (driven by motor 135) to form
nitrogen product 53. If the oxygen is boiled below its final
delivery pressure, it is compressed in oxygen compressor 129
(driven by motor 130) to form oxygen product 51.
[0025] In one embodiment of this invention the base system
comprises two sets of pre-engineered and fully designed components
(subsystems) 107 and 108. The first subsystem 107 (FIG. 2)
comprises all of the pieces of equipment needed to treat stream 5
and produce stream 6. The design of this portion of the plant is
common to every particular application that has similar air
throughput requirements regardless of any product slate variations
or further air compression requirements. This subsystem includes
process equipment, associated valves, piping, analyzers, electrical
connections, and other infrastructure needed to remove contaminants
of air.
[0026] The second subsystem 108 (FIG. 3), a cryogenic processing
unit, comprises contents of the air separation plant cold section
such as in the cold box. Again, the design of this portion of the
plant is common to applications that have similar product
requirements. The equipment in this pre-engineered and fully
designed subsystem includes distillation columns 118, 121, and 123,
condenser/reboilers 119 and 122, heat exchangers 115 and 120, all
of the associated valves and piping that are used to connect these
pieces together, analyzers, and all the necessary electrical
connections.
[0027] In any plant classification those subsystems required to
complete the plant and are not included in the base system are part
of an auxiliary system. Because of the differences in product
slate, purities, delivery pressures and location issues, each
auxiliary system is custom designed rather than operating the plant
in an inefficient manner. For example, one plant may require more
liquid back-up on account of its remote location, hence custom
designing storage vessels 125, 126, and 127 is preferred to
over-designing the vessels to fit all liquid makes and including it
in a base system. Likewise, main expansion turbine 117 will be
custom designed for each application to account for the differences
in liquid making requirements of each particular application. As
another example, if one application requires the delivery of oxygen
product at twice the pressure of another application, then
compressors 113 and 130 and pump 124 will be custom designed for
each plant. In another variation, if liquid air stream 17 is at a
sufficiently high pressure for a particular application, then it
would be advantageous to use a liquid turbine (not shown) to
generate additional refrigeration from that liquid prior to feeding
it to the two columns. Hence, the liquid turbine would be part of
an auxiliary system of this different application.
[0028] Table 1 examples of four different plants belonging to the
air separation process plant classification illustrated in FIG. 1.
This table lists only some of the subsystems required to form a
complete plant by the practice of this invention. The numerals in
parentheses listed in first column correspond to the labels in FIG.
1. This table is not exhaustive with respect to plant subsystems
and/or process variations, as there are many ways in which the
invention could be applied. The plant subsystems are categorized as
belonging to the base system (B) or belonging to an auxiliary
system (A). By definition, any subsystem that is part of the base
system (B) is necessarily the same for every plant belonging to a
given classification. Additionally, by definition, every plant
designed according to a given classification has to include each
and every subsystem that is part of the base system (B). Therefore,
Table 1 illustrates that the prepurification subsystem (107) and
cryogenic processing subsystem (108) in all four plants are part of
the base system. An auxiliary system in any plant will be different
from that in any other plant belonging to the same classification.
However, any subsystem that is part of an auxiliary system (A) by
definition can have either the same design or a different design
than that used in one or more of the other plants belonging to a
given classification. Furthermore, any subsystem that is part of an
auxiliary system (A) by definition does not have to be included in
the design of every plant belonging to a given classification. For
example, considering plant 1 as a base or a reference plant in a
given classification, if the delivery pressure of product nitrogen
from plant 2 is same or lower than that of product nitrogen leaving
cryogenic processing subsystem (108), then the auxiliary system of
plant 2 need not contain product nitrogen compression subsystem,
hence this is left blank. Similarly, in plant 3 the product oxygen
compression subsystem is not required, hence this is left blank. In
plant 4 more liquid nitrogen production is required, hence the
auxiliary system contains the nitrogen liquefier subsystem which
was not required in plant 1. Thus, in accordance with this
invention, plant subsystems are categorized as belonging to a base
system or an auxiliary system, and engineering costs are reduced by
custom designing only the auxiliary system. TABLE-US-00001 TABLE 1
Plant Number 1 2 3 4 Product Nitrogen (49) Delivery Pressure Base
Lower Lower Base Product Oxygen (48) Delivery Pressure Base Base
Lower Base Liquid Nitrogen Make Base Base Base Higher Plant
Subsystem/ Infrastructure Categorization Ambient Air Filtration
(101) A A A A Feed Air Compression (102, 103, 104, 105) A A A A
Prepurification (107) B B B B Air Compression for Oxygen Boiling
(113, 114) A A A A Air Compression for Refrigeration Supply (109,
110) A A A A Air Expansion for Refrigeration Supply (117) A A A A
Cryogenic Processing (17, 120, 118, 119, 121, 122, 123) B B B B
Liquid Oxygen Pumping (124) A A A A Oxygen Compression (129, 130) A
A A Nitrogen Compression (134, 135) A A Liquid Oxygen Storage (125)
A A A A Liquid Nitrogen Storage (127) A A A A Liquid Argon Storage
(126) A A A A Cooling Tower (not shown) A A A A Cooling Water
Treatment/Supply (not shown) A A A A Switchgear/Transformer (not
shown) A A A A Motor Control Center (not shown) A A A A Compressor
Building (not shown) A A A A Controls Infrastructure (not shown) A
A A A Nitrogen Liquefier (not shown) A
[0029] Additionally, this invention can be applied to cryogenic air
separation plants employing processes or classifications that are
substantially different than the one illustrated in FIGS. 1-3.
* * * * *