U.S. patent number 3,607,157 [Application Number 04/844,112] was granted by the patent office on 1971-09-21 for synthesis gas from petroleum coke.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to Roger M. Dille, Warren G. Schlinger, William L. Slater, Joseph P. Tassoney.
United States Patent |
3,607,157 |
Schlinger , et al. |
September 21, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
SYNTHESIS GAS FROM PETROLEUM COKE
Abstract
Production of synthesis gas (mixtures of hydrogen and carbon
monoxide) in a refractory lined reaction zone of a partial
oxidation free-flow synthesis gas generator by feeding to said
reaction zone a stream of particulate petroleum coke containing
heavy metal constituents dispersed in H.sub.2 O. Attack of said
refractory lining by the metals and metal compounds present in said
petroleum coke, or their reaction products, is substantially
prevented by controlling the feedstreams to the reaction so that
entrained in the product gas leaving the reaction zone is an amount
of unconverted petroleum coke containing unreacted about 8 weight
percent or more of the quantity of carbon originally present in the
petroleum coke feedstream.
Inventors: |
Schlinger; Warren G. (Pasadena,
CA), Slater; William L. (La Habra, CA), Dille; Roger
M. (La Habra, CA), Tassoney; Joseph P. (Whittier,
CA) |
Assignee: |
Texaco Inc. (New York,
NY)
|
Family
ID: |
25291845 |
Appl.
No.: |
04/844,112 |
Filed: |
July 23, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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787191 |
Dec 26, 1968 |
|
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|
Current U.S.
Class: |
48/206; 48/197R;
252/373; 423/607; 48/63; 48/202; 423/562; 423/632 |
Current CPC
Class: |
C10J
3/78 (20130101); C10J 3/485 (20130101); C10J
3/506 (20130101); C10J 3/74 (20130101); C10J
2300/1823 (20130101); C10J 2300/1884 (20130101); C10J
2300/0956 (20130101); C10J 2300/0976 (20130101); C10J
2300/1846 (20130101); C10J 2300/0973 (20130101); C10J
2300/0959 (20130101); C10J 2300/0943 (20130101); C10J
2300/0906 (20130101); C10J 2300/1807 (20130101); C10J
2300/1892 (20130101) |
Current International
Class: |
C10J
3/46 (20060101); C01b 002/14 (); C10j 003/16 ();
C22b 059/00 () |
Field of
Search: |
;48/202,206,197,215
;252/373,376 ;23/19.1,134,140,183 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Scovronek; Joseph
Parent Case Text
This application is a continuation-in-part of our application Ser.
No. 787,191, filed on Dec. 26, 1968.
Claims
We claim:
1. A partial oxidation process for producing synthesis gas from
particulate petroleum coke containing heavy metal constituents
comprising mixing together to form a pumpable feed slurry
containing about 25 to 75 weight percent of solids said particulate
petroleum coke having a particle size of about 12 to 325 mesh and
H.sub.2 O, introducing a stream of said feed slurry into a
refractory lined reaction zone of a free-flow noncatalytic unpacked
partial oxidation synthesis gas generator, introducing a stream of
oxygen-rich gas into said reaction zone, bringing said streams into
contact with one another in said reaction zone to produce a
dispersion of said feed slurry and said oxygen-rich gas, and
reacting said dispersion in said reaction zone at an autogenous
temperature in the range of about 1,800.degree. to 3,500.degree. F.
and at a pressure in the range of about 100 to 3,000 p.s.i.g., and
controlling the amounts of said feedstreams to said reaction zone
so as to produce a hot product gas stream comprising principally
hydrogen and carbon monoxide and containing a controlled amount of
entrained unconverted particulate petroleum coke containing at
least 8 weight percent of the quantity of carbon originally present
in said petroleum coke feedstream, so that said entrained
unconverted petroleum coke retains a sufficient amount of said
heavy metal constituents or the oxidation products of said heavy
metal constituents from said reaction zone to prevent damage to
said refractory lining.
2. The process of claim 1 with the added steps of preheating said
stream of feed slurry to a temperature in the range of 100.degree.
to 400.degree. F. and preheating said stream of oxygen rich gas to
a temperature in the range of 100.degree. to 800.degree. F. and
wherein the entrained unconverted particulate petroleum coke in the
product gas stream leaving the reaction zone is in an amount so
that about 8 to 20 weight percent of the carbon originally present
in the petroleum coke feedstream is retained unreacted by said
entrained unconverted petroleum coke in the product gas stream, and
wherein about 17 to 60 weight percent of the heavy metal
constituents in the petroleum coke feedstream or their oxidation
products are retained by the unconverted particulate petroleum coke
entrained in said product gas stream, and wherein said heavy metal
constituents comprise heavy metals and their oxides, sulfides and
salts, and said heavy metals are selected from the group consisting
of vanadium, nickel, iron, chromium and molybdenum.
3. The process of claim 1 wherein said petroleum coke-water slurry
is atomized and mixed with said oxygen-rich gas by passing said
stream of slurry at a discharge velocity of about 5 to 50 feet per
second through the inner conduit of an annulus-type burner, passing
said stream of oxygen-rich gas at a discharge velocity in the range
of about 200 feet per second to sonic velocity through the annular
passage of said burner, and contacting said slurry stream with said
oxygen-rich gas stream in said reaction zone where combustion of
said atomized mixture takes place.
4. The process of claim 1 wherein said petroleum coke-H.sub.2 O
stream is atomized by passing said stream of oxygen-rich gas at a
discharge velocity in the range of about 200 feet per second to
sonic velocity through the inner conduit of an annulus-type burner
in said reaction zone and contacting said oxygen-rich gas stream
with a stream of said petroleum coke-H.sub.2 O stream passing at a
discharge velocity of about 5 to 50 feet per second through the
annular passage of said burner.
5. The process of claim 1 wherein said particulate petroleum coke
is dispersed in water to form the pumpable slurry less than 10
weight percent of a gelling agent.
6. The process of claim 1 with the added steps of quenching the hot
product gas stream from the reaction zone by discharging it
directly into a quench zone, thereby simultaneously cooling it with
quench water to a temperature in the range of about 300.degree. to
700.degree. F. and recovering most of said unconverted particulate
petroleum coke as an unconverted particulate petroleum coke-water
slurry, and scrubbing the cooled product gas stream from the quench
zone with water in a scrubbing zone to recover any remaining
unconverted particulate petroleum coke as an unconverted petroleum
coke-water slurry.
7. The process of claim 6 with the added step of dewatering at
least a portion of said unconverted particulate petroleum
coke-water slurry in a dewatering zone by sedimentation or
filtration, recovering vanadium and nickel from said dewatered
petroleum coke in a metals recovery zone, slurrying the metals-free
unconverted petroleum coke from the metals recovery zone with water
from the dewatering zone, and recycling said slurry as a portion of
the feed to the reaction zone of said synthesis gas generator.
8. In a partial oxidation process for producing synthesis gas in a
high temperature refractory lined reaction zone of a catalytic,
free-flow, unpacked synthesis gas generator, the improvement for
extending the life of said high temperature refractory lining while
reacting in said reaction zone as fuel a H.sub.2 O dispersion of
petroleum coke containing heavy metal constituents which
comprises:
1. feeding to said reaction zone in admixture are atomized
dispersion of said petroleum coke having a particle size in the
range of about 12 to 325 mesh and a stream of oxygen-rich gas
selected from the group consisting of air, substantially pure
oxygen, and oxygen-enriched air;
2. reacting the feed mixture of (1) in said reaction zone at an
autogenous temperature in the range of from about 1,800.degree. to
3,500.degree. F. and a pressure in the range of about atmospheric
to 3,000 p.s.i.g. to produce a hot effluent gas stream comprising
principally hydrogen and carbon monoxide and containing entrained a
controlled amount of unconverted particulate petroleum coke;
3. cooling the hot effluent gas stream from (2) and recovering the
unconverted particulate petroleum coke in water as a slurry;
4. determining the quantity of unconverted petroleum coke in the
effluent gas stream of (2) for a given period of time; 5.
responsive to the determination in (4), controlling the amount of
said unconverted particulate petroleum coke in the hot effluent gas
stream leaving (2) by regulating the ratio of free oxygen to carbon
in the feed mixture of (1) in the range of 0.7-1.5 atoms of oxygen
per atom of carbon and the ratio of H.sub.2 O to carbon in the feed
mixture of (1) in the range of 0.2-3.0 parts by weight of H.sub.2 O
per part by weigh of carbon so as to produce said hot effluent gas
stream leaving (2) comprising in mole percent dry basis: H.sub.2 25
to 45, CO 20 to 50, CO.sub.2 5 to 35, CH.sub.4 0.06 to 8.0,
(COS+H.sub.2 S) 0.1 to 2.0, and said entrained unconverted
petroleum coke containing about 8 to 20 weight percent of the
quantity of carbon originally present in the petroleum coke feed in
(1), so that said entrained unconverted particulate petroleum coke
in the product gas retains from about 17-60 weight percent of the
heavy metal constituents as contained in the petroleum coke feed of
(1) or the oxidation products of said heavy metal constituents as
produced in said reaction zone so that damage to said refractory
lining is prevented.
9. The process of claim 8 with the additional steps of cooling the
hot effluent gas steam from (2) in a cooling zone and recovering
said unconverted particulate petroleum coke from said effluent gas
by contacting it with water forming an unconverted particulate
petroleum coke-water slurry; dewatering said unconverted
particulate petroleum coke-water slurry in a dewatering zone
producing clear water and unconverted particulate petroleum coke;
recovering heavy metals from said dewatered unconverted particulate
petroleum coke in a metals recovery zone, leaving metals-free
unconverted particulate petroleum coke; forming a slurry of
metals-free unconverted particulate petroleum coke with the water
from said dewatering zone and recycling said slurry as a portion of
the feed to the reaction zone of said synthesis gas generator.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the production of synthesis gas from
petroleum coke. More particularly, it relates to improvements in
the partial oxidation process for generating hydrogen and carbon
monoxide from aqueous dispersions of particulate petroleum coke
containing heavy metal constituents which ordinarily attack the
refractory lining of the reaction zone.
The parent case, Ser. No. 787,191 pertains to the production of
synthesis gas from a slurry of particulate solid carboniferous
fuel, e.g., petroleum coke, coke from bituminous coal, coal, oil
shale, tar sands, pitch, or mixtures of said solid fuels in water
or in a hydrocarbon liquid fuel. A pumpable slurry containing 1 to
60 weight of ground solid carboniferous fuel in petroleum oil or 25
to 55 weight percent of ground solid carboniferous fuel in water at
a relatively low discharge velocity in the range of 5 to 50 feet
per second is mixed with a stream of oxidizing gas at a relatively
high discharge velocity in the range of 200 feet per second to
sonic velocity at the burner tip to form an atomized dispersion of
water, hydrocarbon liquid fuel, oxidizing gas and particulate solid
carboniferous fuel. Under synthesis gas generating conditions the
atomized dispersion is reacted to produce a gaseous mixture of
hydrogen and carbon monoxide. By said process, slurry feeds of
low-cost solid carboniferous fuels may be gasified without being
preheated.
2. Description of the Prior Art
The gasification of solid carboniferous fuels is well known in the
prior art. However, the gasification of certain petroleum cokes
containing heavy metal constituents was found to damage the
refractory lining in synthesis gas generation. This occurred when
the heavy metal constituents were present in the petroleum coke in
concentrations of about 100 to 5,000 parts per million or more.
These metal constituents or their reaction products were found to
attack the refractory lining, causing equipment failure and
shutdown. Now, hover, by the process of our invention this
difficulty has been substantially overcome.
SUMMARY
By the process of our invention a feedstream of petroleum coke
containing about 100 to 5,000 parts per million or more of heavy
metal constituents dispersed in H.sub.2 O may be reacted with an
oxygen-rich gas in a closed, compact, refractory lined reaction
zone of a free-flow, noncatalytic synthesis gas generator in such a
manner that damage to the refractory lining by said metal
constituents in the coke or their reaction products is
substantially prevented.
First, particles of the petroleum coke from about 12 to 325 mesh
and finer are dispersed in steam or liquid water. The dispersion is
atomized and reacted with an oxygen-rich gas in the refractory
lined zone of a synthesis gas generator. At an autogenous
temperature in the range of about 1,800 to 3,500 F. and a pressure
in the range of atmospheric to 3,000 p.s.i.g., and preferably 100
to 3,500 p.s.i.g., a hot product gas stream is produced comprising
principally hydrogen and carbon monoxide and containing minor
amounts of CH.sub.4, H.sub.2 S, N.sub.2, and A.
It was unexpectedly found that by permitting a small amount of the
petroleum coke feed to pass through the reaction zone unconverted
and entrained in the product gases leaving the reaction zone,
damage to the refractory lining is prevented. Thus, by controlling
the amount of unconverted petroleum coke in the product gases so
that about 8 weight percent and higher of the carbon originally
present in the petroleum coke feed is retained by said quantity of
unconverted petroleum coke in the product gas as unreacted carbon,
then from about 17 to 60 weight percent of any harmful heavy metal
constituent in the petroleum coke or its oxidation product is
retained by the unconverted petroleum coke entrained in the product
gases leaving the reaction zone and damage to the refractory lining
is prevented.
The quantity of unconverted particulate petroleum coke entrained in
the product gas for a given period of time and the amount of
unreacted carbon contained therein, as compared with the quantity
of carbon originally present in the petroleum coke feedstream, are
determined by standard sampling procedures and methods of chemical
analysis. Responsive to said determination the amount of
unconverted petroleum coke in the product stream leaving the
reaction zone unreacted is regulated by controlling the feedstreams
to the reaction zone, preferably by regulating the oxygen-to-carbon
atomic ratio in the feed or to some degree by regulating the
H.sub.2 O-to-fuel weight ratio in the feed to the reaction zone, or
by both methods.
The hot gaseous effluent from the reaction zone is contacted with
water in a gas cooling and scrubbing zone where substantially all
of the unconverted particulate petroleum coke is extracted from the
product gas. Subsequently, in a sedimentation tank, the unconverted
petroleum coke forms a petroleum coke-water slurry. The slurry is
drawn off at the bottom of the tank and is introduced into a metals
recovery zone where it is processed to recover vanadium and nickel.
Metal-free particulate petroleum coke may be slurried with water
and recycled to the generator as a portion of the feed; thus, no
net carbon is produced by the process. Also, clarified water from
the sedimentation tank and the metals recovery zone may be recycled
back to the quench and scrubbing zone.
It is therefore a principal object of the present invention to
produce synthesis gas from petroleum coke containing metal
constituents in a refractory lined gas generator without damaging
the refractory lining.
Another object of the present invention is to improve the economy
and efficiency of the continuous partial oxidation process for
producing large volumes of synthesis gas by burning as feed
pumpable water slurries containing high concentrations of low-cost
particulate petroleum coke.
A further object of the invention is to react water slurries of
particulate petroleum coke with an oxidizing gas in a novel manner
which avoids preheating the slurry and which produces superior
results upon gasification.
A still further object of the process of the invention is to
recover as valuable byproducts the vanadium and nickel found in
petroleum coke while protecting the refractory walls of the
reaction vessel from attack by said metals.
These and other objects and advantages of the invention will be
apparent from the following drawings wherein:
FIG. 1 is a general flow diagram of a preferred embodiment of the
process; and
FIG. 2 is an enlarged diagrammatic longitudinal cross section of
the front end of the annulus-type burner inserted into the top of
the synthesis gas generator shown in FIG. 1.
DESCRIPTION OF THE INVENTION
Petroleum coke containing minor amounts of heavy metal constituents
is ground to a particle size of about 12 to 325 mesh (U.S. Standard
Sieve Size) and then dispersed in either stream or liquid water in
preparation for gasification with an oxygen-rich gas in a compact,
unpacked, noncatalytic, refractory lined steel gas generator.
The gasification reaction may be carried out at a pressure in the
range of atmospheric to 3,000 p.s.i.g., and preferably in the range
of 100 to 3,000 p.s.i.g. Gasification is usually effected at a
temperature within the range of about 1,800 to 3,500.degree. F.,
and preferably in the range of about 2,200 to 2,800.degree. F.
The time in the reaction zone is a value in the range of 1 to about
8 seconds. The generator is insulated, and it is optional but
usually desirable to preheat the feedstreams.
The hot product gas from the reaction zone comprises principally
hydrogen and carbon monoxide and contains small amounts of
unconverted petroleum coke. There may also be included minor
quantities of carbon dixode, water vapor, hydrogen sulfide,
nitrogen and methane.
The hot gaseous product stream from the reaction zone of the
synthesis gas generator is quickly cooled below the reaction
temperature to a temperature in the range of 300 to 700.degree.F.
by being immediately discharged into a quench tank of the type
shown in the drawing and further described in U.S. Pat. No.
2,896,927, issued to R. E. Nagle et al. (which patent is
incorporated herein by reference). Further, during cooling most of
the unconverted particulate petroleum coke in the hot effluent
gaseous stream is simultaneously recovered as an unconverted
petroleum coke-water slurry in said quench water. Then, in a
scrubbing zone, the cooled effluent product gas stream may be given
an additional washing with water to remove any remaining
particulate petroleum coke. A gas-liquid contact apparatus such as
a venturi scrubber may be used for this operation.
Alternately, the hot product gas stream from the reaction zone may
be cooled to a temperature in the range of 300 to 700.degree. F. by
indirect heat exchange in a waste heat boiler. The entrained
unconverted particulate petroleum coke may be then scrubbed from
the carrier gas by contacting the effluent stream of colled product
gas with water in a gas-liquid contact apparatus, for example in a
spray tower, venturi scrubber, bubble plate contactor, packed
column, or in a combination of said equipment.
Particulate unconverted petroleum coke settles by gravity to the
bottom of the quench tank and scrubbing zone, forming an
unconverted petroleum coke-water slurry which is then concentrated
in a sedimentation vessel. Dissolved gases may be released from the
sedimentation vessel by reducing the tank pressure. The gases may
be then recovered as potential fuel gas. Clarified water overflow
from the sedimentation vessel may be treated to remove soluble
solids, mixed with makeup water, deaerated by conventional methods
to remove oxygen and prevent corrosion, and recycled to the quench
and scrubbing zone. Conventional deaeration procedures are
described in "Water Treatment For Industrial and Other Uses" by
Eskel Nordell, chapter 9, Reinhold Publishing Co., 1951.
Concentrated unconverted petroleum coke-water slurry from the
bottom of the sedimentation vessel may be recycled to the front end
of the process and mixed with raw ground petroleum coke to prepare
fresh slurry feed to the synthesis gas generator.
Although the stream of hot synthesis gas may be analyzed for
suspended unconverted petroleum coke, it is easier to determine the
quantity of unconverted particulate petroleum coke entrained in the
product gas stream from samples of the unconnverted petroleum
coke-water slurry over a given period of time, i.e., pounds per
hour.
Petroleum coke may be analyzed for carbon and metals by standard
methods of chemical analysis. For example, the carbon in the
petroleum coke may be burned to carbon dioxide, which is collected
and weighed; and metals may be determined from the ash by
spectrographic analysis.
Based on said determinations, conditions in the reaction zone are
regulated so that entrained in the product gas leaving the reaction
zone is an amount of unconverted petroleum coke containing 8 weight
percent or more of the quantity of carbon originally present in the
petroleum coke feedstream, and preferably in the range of 8 to 20
weight percent. Generally, no economic benefit is gained by
operating with a quantity of unconverted petroleum coke in the
product gas containing more than 20 weight percent of the amount of
carbon originally present in the petroleum coke feedstream.
Further, it was unexpectedly found that in this range of 8 to 20,
about 17 to 60 weight percent of a metal constituent or its
reaction product passes out of the reaction zone combined with the
unconverted petroleum coke. Nickel and vanadium and their reaction
compounds are primarily responsible for the deterioration of the
refractory lining; and, their elimination from the generator, along
with the unconverted petroleum coke, increases the life of the
refractory thousands of hours.
Control of the amount of unconverted petroleum coke in the product
gas may be accomplished preferably by regulating the
oxygen-to-carbon ratio at a level in the range of 0.7 to 1.5 atoms
of oxygen per atom of carbon in the fuel. Some control may also be
effected by regulating the weight ratio of H.sub.2 0 to fuel at a
level in the range of about 0.3 to 3.0 pounds of H.sub.2 0 per
pound of particulate petroleum coke fuel supplied to the reaction
zone. Control may also be effected by regulating at the same time
both the oxygen-to-carbon ratio and the H.sub.2 0-to-fuel
ratio.
The particulate petroleum coke may be introduced into the reaction
zone by any suitable method by which the petroleum coke particles
are atomized and highly dispersed in a carrier. Although steam and
liquid water are the preferred carriers for the particles of
petroleum coke, other suitable substances or combinations of
materials may be used, i.e., recycle product gas.
For example, the petroleum coke may be admixed with sufficient
water to form a pumpable slurry or dispersion containing from 25 to
55 weight percent of solids, or higher. The slurry may be then
passed through a tubular heating zone as a confined stream at
relatively high velocity. As the dispersion flows through the
heating zone in highly turbulent flow, water vaporizes and the
petroleum coke is pulverized and is finally discharged into the
reaction zone as a stream of fine solids entrained in stream at a
temperature in the range of about 100.degree. to 400.degree. F.
Oxygen-rich gas, which may be preheated to a temperature in the
range of about 100 to 800.degree. F., is introduced into said
reaction zone in admixture with the dispersion of steam and
petroleum coke. Further information about dispersing petroleum coke
in steam is disclosed in U.S. Pat. No. 2,987,387, issued to C. R.
Carkeek et al. which is herewith incorporated by reference.
In a preferred embodiment of this invention, the gasification of
liquid-solid phase slurries of water and particulate petroleum coke
(containing preferably about 25 to 55 weight percent of solids and
higher) may be accomplished without being preheated, in accordance
with the process of our invention, by using an annulus-type
burner.
An annulus-type burner by which a slurry feed of particulate
petroleum coke and water may be atomized, mixed together with a
stream of oxygen-rich gas, and discharged into the reaction zone is
shown in the drawing and will be described later in greater detail.
Other suitable burners are described in coassigned U.S. Pat. No.
2,928,460, issued to DuBois Eastman Charles P. Marion and William
L. Slater, which patent is incorporated herewith by reference. Such
annulus-type burners were previously used only for heavy liquid
hydrocarbon fuels.
A suitable annulus-type burner is shown in FIGS. 1 and 2 of the
drawing. The discharge end of the annulus burner assembly is
inserted into the reaction zone of a compact, unpacked, free-flow,
noncatalytic synthesis gas generator of the type described in
coassigned U.S. Pat. No. 2,980,523, issued to R. M. Dille et al.,
which patent is incorporated herewith by reference. The discharge
end of the annulus burner, for example as shown enlarged in FIG. 2
of the drawing herein, comprises an inner conduit through which the
petroleum coke-water slurry may be passed, surrounded by an annular
passage through which an oxygen-rich gas may be passed.
The oxygen-rich gas may be either air, oxygen-enriched air (40 mole
percent 0.sub.2 and more), substantially pure oxygen (95 mole
percent 0.sub.2 and more), or mixtures of gases such as steam and
one of said oxygen-rich gases.
Near the tip of the burner the annular passage converges inwardly
in the shape of a cone. The oxygen-rich gas is thereby accelerated
and discharged from the burner as a high velocity conical stream
having an apex angle in the range of about 30 .degree. to
45.degree. and an apex located from about 0 to 6 inches beyond the
burner face. When the high velocity stream of oxidizing gas hits
the relatively low velocity stream of petroleum coke slurry,
atomization of the slurry stream takes place and a fine mist
comprising minute particles of water and particulate coke highly
dispersed in said oxygen-rich gas is formed in the reaction zone.
The particles of petroleum coke impinge against one another and are
fragmented further. The discharge velocity of the slurry from the
burner is in the range of 5 to 50 feet per second and the discharge
velocity of the oxygen-rich gas is greater than 100 feet per second
and preferably in the range of 200 feet per second to sonic
velocity at the burner tip. In another embodiment of our invention,
the feed to the burner is reversed and the petroleum coke-water
slurry is passed through the annular passage while the oxygen-rich
gas is passed through the inner conduit. The relative velocities of
the streams remain the same.
In the atomized dispersion, relative proportions of petroleum coke,
water and oxygen-rich gas are regulated within the previously
stated ranges to ensure an autogenous temperature in the gas
generation zone within the range of 1,800 to 3,500.degree. F. In
addition to unconverted petroleum coke in the amount as previously
specified, the product gas includes in mole percent dry basis:
H.sub.2 25 to 45, CO 20 to 50, CO.sub.2 5 to 35, CH.sub.4 0.06 to
8, and COS+H.sub.2 S 0.1 to 2.0. Substantially no free carbon soot
is produced.
The process of the invention as just described requires no preheat
for the reactants. However, if desired, the oxygen-rich gas or an
oxygen-rich gas-stream mixture may be preheated to a temperature in
the range of about 100 .degree. to 800.degree. F.; and to improve
pumpability the feed slurry may be heated to a temperature in the
range of 100 to 400 .degree. F. but below the vaporization
temperature of the water in the slurry. Supplying steam to the
reaction zone is optional since the slurry feed usually contains
sufficient water to satisfy the process requirements.
The heavy metals and their compounds found in petroleum coke are
derived from naturally occurring metallic compounds present in the
petroleum from which the coke was made. The naturally occurring
metallic compounds in petroleum have a variety of forms including
oil-soluble materials, colloidally dispersed metallic compounds,
and complex organometallic compounds. The most common heavy metals
contained in petroleum coke, generally in the form of oxides,
sulfides and other salts, include vanadium, nickel, iron and
smaller amounts of chromium, and molybdenum. These metals and
compounds are referred to herein as heavy metal constituents and
are present in petroleum coke in varying amounts ranging from a
trace to over 5,000 parts per million by weight.
The reaction zone in which the partial oxidation of the petroleum
coke takes place is free from packing and catalyst and has nearly
minimum internal surface. It generally comprises a steel pressure
vessel provided with a high temperature refractory lining, for
example aluminum oxide. It is postulated that during gasification
of the petroleum coke, oxides of the aforesaid metal compounds and
metals combine with the refractory to form a composite having a
lower melting point that that of the original refractory. Nickel
and vanadium in concentrations above about 100 p.p.m. are
particularly destructive by combining with the alumina refractory
to form Ni0.sup.. A1.sub.2 0.sub.3 and V.sub.2 0.sub.3 .sup..
A1.sub.2 0.sub.3, whose crystalline structures weaken the alumina
refractory. As a result, at a temperature in the range of 1,800 to
3,500.degree. F. and at the preferred operating temperature in the
reaction zone of about 2,200 to 2,800.degree. F., the refractory
may spall and deteriorate in a relatively short time; for example,
in some cases within a few hours. However, by the process of our
invention the life of the refractory lining may be extended many
thousands of hours.
While the exact mechanism by which the heavy metal constituents or
their oxidation products produced in the reaction zone are
prevented from attacking the refractory lining is unknown, it may
be postulated that as the raw petroleum coke particles pass through
the reaction zone carbon is consumed by oxidation leaving behind
the heavy metal constituents or their oxidation products attached
to the unconverted petroleum coke. The metal constituents or their
oxidation products then leave the reaction zone in the product gas
along with the entrained unconverted portion of the petroleum coke
feed.
It has been found profitable to process the unconverted petroleum
coke-water slurry in order to remove the metal values. For example,
after dewatering the slurry by filtration, vanadium, nickel and
other metals may be recovered by the process comprising the steps
of roasting the unconverted petroleum coke in an oxidizing
atmosphere at a temperature of about 220.degree. F. but below the
ignition temperature, extracting the resulting water-soluble metal
salts with a dilute aqueous solution of a strong mineral acid,
e.g., 0.1 to 0.5 N HC1, washing the residue with water, and adding
phosphoric acid to the solution to precipitate the metals as the
phosphates, which are industrially useful as additives in the
manufacture of steel. The metals-free particulate petroleum coke is
then recycled as a portion of the feed to the synthesis gas
generator.
In the preparation of raw petroleum coke-water slurry feedstock to
the generator, in order to keep the solid particles of petroleum
coke in suspension thereby preventing the settling and plugging of
pipes, lines, pumps and valves, it was desirable to grind the raw
petroleum coke quite fine. Petroleum coke may be pulverized to a
particle or agglomerate size of from about 44 to 420 microns
diameter by any suitable standard procedure, e.g., U.S. Pat.
2,846,150, issued to Lincoln T. Work. The small size of the solid
fuel particle is important to assure a uniform suspension in the
liquid vehicle which will not settle out, to allow sufficient
motion relative to the gaseous reactions, and to assure
substantially complete gasification.
However, fine grinding will increase the surface area of the
petroleum coke and decrease the amount that can be mixed with water
to form a pumpable slurry. A water slurry of petroleum coke ground
to -325 mesh may be no longer pumpable when the solids content
exceeds about 40 to 50 weight percent. Thus, although fine grinding
may be desirable to prevent plugging, it is expensive and may
result in dilute slurries with excess water being added to the
synthesis gas generator. By increasing the particle size of the
petroleum coke to as large as -12 mesh (U.S. Standard Sieve Size),
the amount of particulate petroleum coke in the slurry may be
increased to about 75 weight percent. By adding about 2 to 10
weight percent of a gelling agent, the slurry becomes thixotropic
and settling is greatly diminished. Although the slurry may then
appear thickened or gelled, the slurry will easily work into a
fluid which can be readily pumped. Pectins may be used as gelling
agents in the preparation of petroleum coke-water slurries. A
pumpable petroleum coke-water slurry is one having a viscosity less
than 700 centipoise.
Petroleum coke consists of dehydrogenated and condensed
hydrocarbons of high molecular weight in the form of a matrix of
considerable physical extent comprising principally carbon and
containing dispersed throughout a very minor amount of
petroleum-based asphalticlike like compounds. Raw petroleum coke
suitable for use as a starting material in the process of this
invention may be produced by the "delayed coling" process for
converting heavy residual fuel oil into gasoline, gas oil, and
coke. Other suitable petroleum coking processes are available that
produce a petroleum coke having a similar structure and chemical
analysis. A typical delayed coking process is described in
Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, Vol.
15, Inter-Science Publishers 1968, pages 20-23. Typical analysis of
petroleum coke in weight percent follows:
Petroleum Coke
__________________________________________________________________________
Volatiles 3-7 Fixed Carbon 89-96 Ash* 0.1-1.3 Sulfur 1.0-5 H.sub.2
0 0 Density, g./m1. 1.28-1.6 Oil Absorption No., cc./g.r less than
1.0 Size, microns 44- 1,680
__________________________________________________________________________
DESCRIPTION OF THE DRAWING
A more complete understanding of the invention may be had to by
reference to the accompanying schematic drawing which shows the
previously described process in detail. Although the drawing
illustrates a preferred embodiment of the process of this
invention, it is not intended to limit the invention to the
particular apparatus or materials described.
With reference to the drawing, raw petroleum coke is passed through
line 1 into grinder 2 where it is mixed with a recycle stream of
water-petroleum coke slurry from line 3 and ground until about 88
weight percent of the petroleum coke passes through a U.S. Standard
Sieve of about 200 meshes per square inch. The water slurry of
ground petroleum coke is discharged through line 4 into mix-charge
tank 5 where a stream of water-petroleum coke slurry from line 6
may be added and the concentration of petroleum coke in the slurry
feed may be adjusted to 50 weight percent. With no preheat, the
water-petroleum coke slurry feedstream is pumped through lines 7
and 8 and is discharged at a relatively low velocity in the range
of 5 to 50 feet per second from the central conduit 9 of an
annulus-type burner 10, which is mounted in the top flanged head 11
of vertical, unpacked, free-flow, noncatalytic synthesis gas
generator 12. FIG. 2 depicts an enlarged view of the discharge end
13 of burner 10 which extends into the refractory lined reaction
zone 14 of the gas generator 12.
A stream of oxygen-rich gas, such as substantially pure oxygen (95
mole percent 0.sub.2 or more) or oxygen-enriched air (40 mole
percent 0.sub.2 or more) is introduced into the burner 10 through
line 15. The oxygen-rich gas is discharged through annular passage
15 of burner 10 at a relatively high velocity in the range of about
200 feet per second to sonic velocity. Reactant streams from 9 and
16 make contact at point 17 located about 0 to 6 inches beyond the
tip of burner 10. There the streams mix and form an atomized
dispersion. Reaction then takes place immediately at an autogenous
temperature in the range of 1,800.degree. to 3,000.degree. F., and
preferably at a temperature in the range of 2,200 to 2800.degree.
F., and at an elevated pressure in the range of about atmospheric
to 3,000 p.s.i.g., and preferably in the range of 100 to 3,000
p.s.i.g., to produce synthesis gas comprising principally carbon
monoxide and hydrogen and a quantity of entrained unconverted
petroleum coke containing unreacted carbon in the amount of 8
weight percent or more of the quantity of carbon originally present
in the petroleum coke feedstream to the reaction zone. Cooling
water is supplied to the burner through line 18 and is discharged
through line 19 to prevent the burner from overheating.
The hot effluent gas from reaction zone 14 is discharged directly
into quench water contained in quench chamber 20. Water in the
quench zone effects quick cooling of the hot effluent gas to below
the reaction temperature, provides a means for removing most of the
entrained unconverted particulate petroleum coke from the product
gas, and produces steam which is useful in subsequent operations.
For example, in the water-gas shift reaction for increasing the
hydrogen yield, H.sub.2 O and CO in the product gas are reacted
over an iron oxide-chromic oxide catalyst to product additional
H.sub.2 and CO.sub.2.
Most of the remaining entrained particulate petroleum coke is
removed from the cooled synthesis gas by passing the cooled
effluent gas stream from quench zone 20 through line 21 and into
venturi scrubber 22 where it is further contacted and scrubbed with
water from line 23. The scrubbed synthesis gas is then passed
through line 24 into gas-liquid separator 25 where condensed water
vapor in the gas stream drops to the bottom carrying with it any
remaining petroleum coke particles in the synthesis gas stream. A
product stream of solids-free synthesis gas is removed by way of
line 26 at the top of gas-liquid separator 25 for further use in
processes which are not shown in the drawing.
The carbon-water mixture from the bottom of gas-liquid separator 25
is passed through line 27 and mixed in line 28 with the particulate
unconverted petroleum coke-water slurry which is pumped from the
bottom of quench tank 20 by way of lines 29 and 30. The sensible
heat in the slurry in line 29 is used to heat the scrub water in
line 31 by means of heat exchanger 32. The unconverted particulate
petroleum coke-water slurry in line 28 is passed through pressure
reducing valve 33 and line 34 in sedimentation vessel 35.
Unconverted particulate petroleum coke settles by gravity to the
bottom of sedimentation vessel 35 where it is drawn off through
line 36 as a concentrated slurry of unconverted particulate
petroleum coke and water. With valves 37 and 38 closed and valves
39 and 40 open, this slurry may be recycled to grinder 2 for use as
a vehicle for the raw petroleum coke feed in line 1. By means of
pump 41, the slurry is passed through lines 42 to 46, and 3. If
desired, a portion of this slurry may be diverted through lines 47
and 6 into mix tank 5 in order to adjust the slurry concentration
from line 4. Dissolved gases are discharged through line 48 at the
top of sedimentation vessel 35 and recovered as potential fuel gas.
Clear water overflow is withdrawn from vessel 35 through line 49
and introduced into a conventional water treatment facility 50,
such as ion exchange resins, for removing soluble solids. Dissolved
gases may be released and removed through line 51.
Clear water is withdrawn through line 52 at the bottom of water
treatment facility 50, and mixed in line 53 with fresh makeup water
from lines 54 and 55 and water from line 56. By means of pump 57, a
first portion of water from line 53 is recycled to quench vessel 20
by way of line 31, heat exchanger 32, and lines 58 and 59. A second
portion of the water from line 53 is pumped through line 31, heat
exchanger 32, and lines 58 and 23 to provide sufficient hot water
to operate venturi scrubber 22 as previously described.
Periodically, heavy uncombustible solids that settle to the bottom
of quench vessel 20 are withdrawn as a water-solids slurry through
line 60, valve 51, line 62 and are passed into lock hopper 63. The
slurry is then passed through line 64, valve 65, line 66 into the
dewatering zone 67. Dewatering may be accomplished by standard
methods such as by filtration and centrifuge. By closing valve 39
and opening valve 37, unconverted petroleum coke-water slurry
bottoms from sedimentation tank 35 may be passed into dewatering
zone 67, by way of lines 36, 68 and 69. A portion of clarified
water from the bottom of dewatering zone 67 may be recycled to the
quench and scrubbing zones by way of lines 70, 56 and 53 in the
manner previously described. Another portion of the clear water may
be recycled to grinder 2 or mix-charge tank 5 by way of lines 70,
71, 72, 44, pump 41, and line 45 in the manner previously
described.
Substantially water-free unconverted petroleum coke is conveyed
from dewatering zone 67 over line 73 and into a metals recovery
zone 74. Any suitable process for recovering vanadium and nickel
from the unconverted petroleum coke may be used. Vanadium and
nickel are discharged from the metals recovery zone 74 through line
75. Vanadium and nickel-free petroleum coke from the bottom of
metals recovery zone 74 is passed through line 76 and slurried in
line 72 with water from line 71. Then, by means of pump 41, the
slurry is distributed to grinder 2 or to mix-charge tank 5 in the
manner previously described. Uncombustible solids are discharged
from metals recovery zone 74 through line 77 as waste.
EXAMPLE OF THE PREFERRED EMBODIMENT
The following example is offered as a better understanding of the
present invention, but the invention is not to be construed as
limited thereto.
EXAMPLE I
With reference to FIG. 1 of the drawing, 525 pounds of raw
petroleum coke prepared from reduced crude oil by the "delayed
coking" process are ground to -200 mesh (U.S. Standard Sieve Size)
and mixed with a recycle slurry comprising 27 pounds of unconverted
petroleum coke and 523 pounds of water. Analysis of the raw
petroleum coke as received and the recycled unconverted petroleum
coke are shown below in table I.
1,075 pounds per hour of the resulting slurry containing 51.4
weight percent of petroleum coke are discharged at a rate of 25
feet per second and at a temperature of 124.degree. F. from the
central passage of an annulus-type burner as shown in FIG. 2. The
burner is mounted through the top heat of a compact, unpacked,
free-flow, noncatalytic 11.8 cubic feet synthesis gas generator in
the manner shown in FIG. 1. 9024 standard cubic feet per hour
(SCFH) of oxygen (100 mole percent O.sub.2) at a rate of 350 feet
per second and at a temperature of 264.degree. F. are discharged
from the annular passage of said burner.
22,631 SCFH of dry synthesis gas are produced in the gas generator
from the ensuing partial oxidation reaction of the atomized streams
at a temperature of 2,550.degree. F. and at a pressure of 346
p.s.i.g.
An analysis of product gas follows: In mole percent dry basic:
H.sub.2 32.77, CO 45.46, CO.sub.2 20.58, H.sub.2 S 0.24, CH.sub.4
0.06, N.sub.2 0.79, and A 0.10. Also entrained in the product gas
stream are 27 pounds per hour of unconverted petroleum coke
containing 1,995 parts per million of nickel and 1,082 p.p.m. of
vanadium. This represents a recovery of 13 weight percent of the
nickel present in the feed and 10 weight percent of the vanadium
present in the feed.
The hot product gas stream issuing from the reaction zone of the
generator is immediately cooled in the quench chamber with water.
Substantially all of the unconverted petroleum coke is recovered
from the product gas stream by forming a petroleum coke-water
slurry comprising 6,030 pounds per hour of water and about 27
pounds per hour of unconverted petroleum coke containing about 5
weight percent of the amount of carbon originally present in the
petroleum coke feed. The slurry is cooled, combined with the
bottoms from the gas-liquid separator comprising 3,328 pounds per
hour of water and a trace of petroleum coke, and introduced into a
sedimentation vessel where the particulate unconverted petroleum
coke settles to the bottom by gravity.
8,900 pounds per hour of clarified water is removed as overflow
from the sedimentation vessel and introduced into a conventional
water treatment purification system. About 8,900 pounds per hour of
clarified water from the water treatment purification system and
400 pounds per hour of makeup water are recycled to the quench zone
and carbon scrubbing operation. The slurry underflow from the
sedimentation water comprising 470 pounds per hour of water and 27
pounds per hour of unconverted petroleum coke may be recycled to
the grinding operation (ball mill) or to the mix tank as the source
of water to produce the feed slurry, and also as a means for
disposing of the unconverted carbon.
About 2.9 pounds per hour of uncombustible ash are removed from the
bottom of the quench vessel by way of the lock hopper system and
are introduced into a conventional dewatering zone, for example, a
vacuum filter. 94 pounds per hour of water are removed from the ash
and recycled to the grinder or to the mix tank and the
uncombustible ash is discarded as waste. Thus, by operating in this
manner, there is no net carbon produced by the process. A summary
of the performance data for run 1 follows in table II.
Operating the synthesis gas generator in the manner described above
for run 1, within a relatively short time (less than 25 hours) the
refractory lining in the reaction zone begins to spall and
deteriorate.
To prevent this damage to the refractor, samples of the slurry
water and unconverted particulate petroleum coke from the quench
chamber are dried, analyzed, the amount of unconverted particulate
petroleum coke and the carbon therein that pass unreacted through
the reaction zone for a given period of time are determined.
Responsive to said determinations, the feedstreams to the reaction
zone are regulated in steps by decreasing the oxygen-to-fuel ratio,
by increasing the stream-to-fuel ratio, or by both of these
techniques, while maintaining all other conditions in the generator
substantially the same. This causes the unconverted petroleum coke
in the product gas to increase. When the amount of unconverted
petroleum coke in the product gas contains 8 weight percent or more
of the quantity of carbon originally present in the petroleum coke
feedstream, damage to the refractory lining in the generator is
substantially stopped.
For example, as a comparison with run 1, run 2 shows that by
decreasing the oxygen-to-fuel ratio in run 1 from 16.36 standard
cubic feet per hour per pound of particulate petroleum coke feed to
a value of 15.83 in run 2, and by increasing the H.sub.2 O-to-fuel
ratio in run 1 from 0.95 pounds of H.sub.2 O per pound of petroleum
coke feed to a value of 1.03, while maintaining other conditions
substantially the same, the temperature in the reaction zone
decreases from 2,550.degree. F. to 2,450.degree. F., and the
quantity of unconverted petroleum coke entrained in the product gas
increases from an amount containing about 5 weight percent of the
quantity of carbon originally present in the petroleum coke
feedstream to a quantity of entrained unconverted petroleum coke
containing 13 weight percent of the amount of carbon originally
present in the petroleum coke feedstream. Further, at this level
substantially all attack of the generator lining has stopped.
In run 2, 473 pounds of raw petroleum coke prepared from reduced
crude oil by the "delayed coking" process are ground to -200 mesh
(U.S. Standard Sieve Size) and mixed with a recycle slurry
comprising 71 pounds of unconverted petroleum coke and 563 pounds
of water. Analysis of the raw petroleum coke as received and the
recycled unconverted petroleum coke are shown below in table I.
1,107 pounds per hour of the resulting slurry containing 49.2
weight percent of petroleum coke are discharged at rate of 25 feet
per second and at a temperature of 132.degree. F. from the central
passage of an annulus-type burner as shown in FIG. 2. The burner is
mounted through the top head of a compact, unpacked, free-flow,
noncatalytic 11,8 cubic foot synthesis gas generator in the manner
shown in FIG. 1. 8,615 SCFH of oxygen (100 mole percent O.sub.2) at
a rate of 350 feet per second and at a temperature of 265.degree.
F. are discharged from the annular passage of said burner. 20,298
SCFH of dry synthesis gas are produced in the gas generator from
the ensuing partial oxidation reaction of the atomized stream at a
temperature of 2,450.degree. F. and at a pressure of 350
p.s.i.g.
An analysis of the product gas follows: In mole percent dry basis:
H.sub.2 33.02, CO 47.22, CO.sub.2 18.94, H.sub.2 S 0.06, CH.sub.4
0.20, N.sub.2 0.47, and A 0.09. Substantially no free carbon soot
is produced. Also entrained in the product gas stream are 71 pounds
per hour of unconverted petroleum coke containing 2,440 p.p.m. of
nickel and 2,380 p.p.m. of vanadium. This represents a recovery of
35.1 weight percent for nickel and 40.1 weight percent for
vanadium. The remaining nickel and vanadium is intermittently
removed along with heavy ash or slag in the lock hopper system at
the bottom of the quench vessel and eventually recovered in the
vanadium and nickel recovery section. A summary of the performance
data for run 2 follows in table II.
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TABLE I--ANALYSIS OF PETROLEUM COKE
Raw--line 1 Unconverted--line 36
__________________________________________________________________________
Element Units Run 1 Run 2
__________________________________________________________________________
C wt./% 89.28 89.28 83.60 91.34 H wt.% 2.58 2.58 4.55 0.57 N wt.%
2.35 2.35 0 0 Ash wt.% 2.41 2.41 9.95 6.2 S wt.% 1.6 1.16 1.90 1.89
Ni p.p.m. 750 710 1,995 2,440 V p.p.m. 500 590 1,082 2,380
__________________________________________________________________________
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TABLE II--PERFORMANCE DATA
Run 1 Run 2 Oxygen/Fuel Ratio, SCFH/lb. 16.36 15.83 H.sub.2 O/Fuel
Ratio, 1b./1b. 0.95 1.03 Oxygen/Carbon Ratio, atom/atom 1.16 1.12
Residence Time, sec. 5.54 5.79 O.sub.2 /Fuel, moles per MM B.t.u.
2.85 2.76 Heat of Combustion, B.t.u./lb. 15,122 15,122 Generator
Temperature, .degree. F. 2,550 2,450
__________________________________________________________________________
The process of the invention has been described generally and by
examples with reference to petroleum coke-water slurries and
synthesis gas of particular compositions for purposes of clarity
and illustration only. It will be apparent to those skilled in the
art from the foregoing that various modifications of the process
and materials disclosed herein can be made without departure from
the spirit of the invention.
* * * * *