Note: Descriptions are shown in the official language in which they were submitted.
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This invention pertains to processes for gasifying
hydrocarbon feedstocks to form -an effluent consisting essentially
of methane, and an aromatic fraction which is substantially
benzene and to the production of synthetic natural gas (methane)
by the gasification of hydrocarbon feedstock. Hydrocarbon
feedstocks are vaporized in the presence of hydrogen and then
with an excess of hydrogen are reacted at high temperature to
produce an effluent gas containing essentially methane, aromatics,
acid gases such as hydrogen sulfide and excess hydrogen. In
one aspect of the invention the effluent from the gasification
step is then further processed by condensing and~or absorbing
out the aromatic fraction, removing the acid gases and finally,
separating the hydrogen from the methane to produce a synthetic
natural gas (SNG) having a heating value of approximately 1,000
BTU/SCF. The resulting synthetic natural gas can be discharged
into a storage receptacle or put into a pipeline for use by
residential communities or industrial concerns.- The aromatics
removed from the gasifier effluent are revaporiæed and recycled
to the gasifier for reaction to extinction. The acid gases
containing mainly hydrogen sulfide are reacted to produce -
elemental sulfur.
The gasifier effluent, is suitable as a plant fuel or ~
feedstream for further processing into a hydrogen-carbon mono- ~ ;
xide synthesis gas or hydrogen gas.
Gasification of hydrocarbon feedstocks, mainly drude
oil and crude oil fractions, to produce a synthetic pipeline
gas either rich in hydrogen or rich in methane is shown by
many processes in the prior art.
U.S. Patent 3,870,481 discloses and claims a process
for producing synthetic natural gas from crude oil which encom-
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passes vaporizing a substantial portion of the crude oil at a
temperature of between 600 and 1,000F, thereafter introducing
the vaporized crude oil and hydrogen gas into a gasification
vessel maintained at a temperature in excess of l,000F wherein
the Eeedstream is gasified producing an effluent consisting
essentially of hydrogen, hydrogen sulfide, methane, ethane and
residual aromatic hydrocarbons; thereafter cooling the effluent
gas stream to ambient temperature and recovering the waste heat,
drying the effluent and removing the hydrogen sulfide and resi-
dual aromatics from the effluent, cryogenically separating themethane and the ethane from the hydrogen and thereafter reacting
the ethane with steam to produce additional methane and carbon
dioxide and removing the carbon dioxide from the steam. The
two methane streams are combined and discharged into a product
pipeline or storage vessel. -
After developing the process embodied in U.S. Patent
3,870,481, new discoveries were made and the process of the ` '
present invention devised wherein excess hydrogen is used and
the temperature of the gasifier is maintained at a temperature
level in excess of 1500F, to gasify the aromatics in the feed-
stocks and to suppress-the formation of ethane, thus increasing
the methane content of the gasifier effluent. Thus a process
had been developed wherein heavy crude oils and other hydro-
carbon feedstocks could be successfully gasified and the gasifier
effluent could be processed to produce a synthetic natural gas.
It was also discovered that if the aromatic removed from the ~`
gasifier effluent were revaporized and recycled to the gasifier,
these aromatics could be gasified to methane and the net pro- `
duction of aromatics could be reduced or eliminated.
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One typical hydrocarbon feedstock for::the process .
could have the following characteristics: .. .
1. A gravity of 10 API. .
2. A metal content of 350 ppm of vanadium. .
3. A sulfur content of 3~.
It is contemplated that hydrocarbon feedstock for the . .
process of the present invention will come from heavy:crude oils
which are now shut-in because of limited market demand due to ~.
their inherent characteristics, bitumen produced from tar sands, . .:.:
shale oil, liquids produced from coal using new lique~action ....
and hydrogenation technologies now under development, volatiles :-
from the coking of coal, aromatic hydrocarbons, naphtha, ~as :.
oils, crude oil distillates and crude oil residues. In view of ;~
the current world situation involving natural gas shortag.es and
the existence of large reserves of bitumen, the process of the
present invention will, in the future, be of increasing import- ~. .
ance.
While the process of the present invention is suitable
for gasifying conventional crude oils, it is primarily designed
for those types of heavy hydrocarbon feedstocks which must be
considered the source of future synthetic natural gas. Crude
oils with high metal contents, particular-ly; vanadium, are ex-
tremely detrimental to catalysts used in conventional oil refin- .
eries for manufaaturing gasoline. Heavy oils also generate
large volumes of residues tbottoms) that become difficult to -
utilize when a conventional process, depending upon catalytic : .
conversion, is used. Heavy hydrocarbon feedstocks processed by
thermal rather than catalytic techniques provide overall process
economies. ~:~
Crude oil is a heterogeneous mixture of hydrocarbon .
compounds... It was found that the ability to hydrogasify .`
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(gasify in the presence of hydrogen) a given oil fraction in a
gasifier is affected by the nature of the hydrocarbon compound
introduced into the gasifier. It has been discovered that when
operating the gasifier at a temperature below 1500F, with a
gasifier feedstream containing a fraction of heavy polycyclic
hydrocarbons (characterized as having a high boiling point and
as being highly aromatic), that these fractions tended to pass `
through the gasifier without substantial gasification (reaction).
Furthermore, it was found that the effluent from the gasifier
contained these unreacted polycyclic oil compounds and that the ~-
recovery of waste heat in a waste heat boiler from the effluent
stream of the gasifier was impossible because these polycyclic
compounds are tarry in nature and when condensed would foul the
surface of the heat exchanger. Thus, quenching of the effluent -
directly out of the gasifier was required resulting in a loss
of overall thermal efficiency.
In order to overcome these problems and provide an
improved process it was discovered that by increasing the temp-
erature of the gasifier to a temperature above 1500F and pre-
ferably about 1600F while maintaining a pressure of 600 psig,
that these heavy polycyclic oil compounds could be gasified in
the presence of hyrdrogen ~(hydrogasified). The gasifier - ~ -
effluent is substantially methane with very little ethane ;
(gasification reaction below 1500F produces substantial ethane~
Furthermore, it was found that the aromatics in the effluent ;
were free of the heavy tarry polycyclic compounds and consisted
of compounds which were mainly benzen~. The effluent from
the hydrogasification reactor (hydrogasifier) was thus suitable
for waste heat recovery since this could be accomplished without ~-
fouling of the waste heat boiler surfaces.
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With the process of the present invention aromatic
compounds in the gasifier effluent can be removed and recycled
back to the gasifier as a vapor for conversion to methane or
used in other process schemes as needed. By controlling the
recycle stream, the process can be run with no net production
of aromatic compounds.
The process of the invention yields an effluent with-
out formation of substantial amounts of carbon in the process
reactor by maintâining sufficiently high concentration of un~
reacted hydrogen in gasifier effluent. It was found necessary
to maintain a minimum unreacted hydrogen content in the effluent
gas at the desired operating conditions of about 65% by volume
in order to prevent substant~al carbon formation in the gasifier.
The principal advantage of our discovery and process
resides in the method of gasifying heavy hydrocarbon feedstocks
containing heavy polycyclic oil compounds to produce essentially
methane and light aromatics such as benzene and to recycle these
aromatiCS to extinction to produce only methane, if desired.
This makes possible the use of hydrocarbon feedstocks which
exist in large volumes in the world but which were not hereto-
fore considered suitable for use in this manner.
Furthermore, there is shown a one-step method for pro-
ducing substantially methane from a hydrocarbon feedstream
wherein waste heat boilers can be used for heat recovery when
heavy polycyclic compounds are contained in the feedstream.
Thus in accord with another aspect of the present
invention, a process for producing synthetic natural gas having
a heating value of approximately 1,000 BTU/SCF from hydrocarbon
feedstocks can be achieved by vaporizing the hydrocarbon feed-
stock in the presence of hydrogen and then injecting thevaporized hydrocarbon
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feedstock together with excess hydrogen into a gas recycle hydro-
generator (GRH) operated at a minimum pressure of 75 psig such
as disclosed by the British Gas Corporation (formerly British Gas
Council) in U.S. Patent 3,363,024. The GRH reactor is an adia-
batic open vessel reactor with a concentric draft tube into which
the hydrogen/oil vapor is injected. Gas recirculation within
the reactor is caused by jetting the reactants into the draft
tube, whereby the gases within the reactor are entrained with
the newly injected reactants. Operating the reactor at a minimum
pressure of 75 psig and at a temperature in excess of 1500 F.
in combination with the high recirculation rate ensures that the
injector vapor is brought to reaction tempearture in a matter of -
milliseconds. The hydrogen/oil vapor mixture reacts to produce a
gasifier effluent consisting essentially of methane, aromatics
and acid gases together with a large amount (approximately 65%)
of free hydrogen. After removal from the reactor, the hot effl-
uent can be cooled to ambient with heat recovery for use elsewhere
in the process. Cooling of the effluent can be accomplished by
any known methods 1ncluding a combination quench and cooling. ~;
During heat recovery the condensible aromatics are condensed
and removed from the effluent stream. Subsequently, the acid gases
and noncondensible aromatic fraction are removed from the effluent
thus producing a product stream consisting essentially of methane
and hydrogen. The methane is separated from the hydrogen by
cryogenic techniques and is ready for use as a synthetic natural
gas. The hydrogen is recycled to the gasified for use in gasify-
ing the hydrocarbon feedstocks.
Another suitable reactor is the Fluidized Bed Hydro-
generator (E'BH) developed by the British Gas Corporation and dis-
closed in U.S. Patent 3,124,436. This reactor operates on a simi- ~ ~ -
lar principle as the GRH except that hot carbon particles are
recirculated with the gas. The hot recirculating carbon parti-
cles would serve to supply heat to the feedstream which would -
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be introduced into the reac-tor, operated at a pressure in excess
of 300 psig as specified by patentees and at a temperature in ex-
cess of 15500F. in accord with our invention, as hydrocarbon-
hydrogen vapor.
The aromatic condensate is composed primarily of ben-
zene and naphthalene with small quantities of heavier compounds.
In one aspect of the invention the condensate is revaporized and
returned to the reactor.
BRIEE' DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram illustrating the process of
gasifying hydrocarbon feedstocks according to the present invention;
Fig. 2 is a block diagram illustrating an alternate pro-
cess according to the invention utilizing liquefied coal, prepared
as part of the process, as a feedstock;
Fig. 3 is a schematic flow diagram of a plant embodying
the process of the invention for producing synthetic natural gas;
Fig. 4 is a plot of GRH Reactor Temperature against
volume percent of ethane in the reactor effluent.
Referring to Figure 1, the overall process according to
the invention, is shown in block form. In Figure 1, arrow 10
includes the hydrocarbon feedstock which is selected from those
materials such as crude oil, bitumen produced from tar sands,
shale oil, liquid volaties resulting from coking of coal, lique- ~ -
fied coal resulting from solvating coal with a solvent and hyd-
rogen, aromatic hydrocarbons, naphtha, gas oils, crude oil dis-
tillates and crude oil residues. In the one stage gasification
step 12 the hydrocarbon feedstock is preheated to about 700F.
and vaporized in the presence of hydrogen which is initially
heated to a temperature in excess of 750F. in accord with the
vaporization technique disclosed in U.S. Patent 3,870,481. Other
vaporization methods can be used so long as such methods provide
a vaporized hydrocarbon feed. The vaporized hydrocarbon and
excess hydrogen feed are introduced into the single stage gasi-
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fier. As set out above, the preferred gasification vessel is that
disclosed in U.S. Patent 3,363,024 and commonly referred to as a -
gas recycle hydrogenerator (GRH). ;
However, any gasification vessel is suitable so long as :~
the feedstream is heated rapidly (less than one second) to temp-
erature and the feedstream is allowed to dwell at temperature
for a long enough time period (greater than one second) so that
the overall gasifier effluent consists essentially of methane,
aromatic compounds (mostly benzene), unreacted hydrogen in the
: : ......
amount of at least 40~ by volume of the effluent together with
minor amounts of ethane, ethane compounds, ethylene, propane,
propylene and hydrogen sulfide if sulphur is present in the
feedstock.
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The hydrocarbon feedstock and hydrogen are injected
into the gasifier, recirculated, and reacted to form an efflu-
ent stream shown by arrow 14 consisting essentially of methane,
aromatics, hydrogen sulfide and excess hydrogen. The effluent
is cooled to ambient temperature in the purification section
16 thus condensing out the condensible aromatics which are
primarily benzene and naphthalene. Removal of the residual
aromatics and hydrogen sulfide is accomplished by a purification
process such as disclosed in U.S. Patent 2,863,527. The process
disclosed in this patent is known commercially as the Rectisol
Process marketed by Lurgi Mineralol Technic GMbH, Frankfurt Am
Main, West Germany.
After the gasifier effluent 14 passes through the
purification section 16 a product stream designated by arrow
18 containing essentially hydrogen and methane, is subjected
to a cryogenic separation designated by block 20. In the
cryogenic separator the hydrogen is separated from the methane
yielding a synthetic natural gas stream consisting essentially
of methane (designated by arrow 22). While cryogenic separation
of the hydrogen is preferred, other techniques for hydrogen
removal can be used. Among these are pressure swing adsorption
and gas diffusion through a membrane. The synthetic natural
gas stream consists essentially of methane with minor amounts,
e.g., less than 2~ of hydrogen and ethane.
The condensible aromatics consisting essentially of
benzene and naphthalene (designated by arrow 24) are recycled
to the vaporizer for revaporization and gasification. The
condensible aromatics are continuously recycled in this manner
until extinguished thereby eliminating the production of by-
products which may be undesirable or uneconomical to produce. ;~
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The hydrogen sulfide separated out in the purification
section and designated by arrow 26 is conducted to a sulfur
plant which embodies the Claus Process as is well known in the
art. The Claus Process is discussed in detail in an article
by V. W. Gamson and R. H. Elkins entitled "Sulfur From Hydrogen
Sulfide" which appeared in Chemic~al Engin~ë~e~ring Pro~gre~ss,
Volume 49, Number 4, April, 1953 beginning at page 203. ,
Hydrogen represented by arrow 28 removed from the
cryogenic separation unit is recycled to the gasification step
10 for use in the vaporization of the hydrocarbon feedstock and ' ,
as excess hydrogen to be added to the gasifier.
Included in the overall process scheme is an oxygen '
plant 30 which produces oxygen designated by arrow 32 for use
in a hydrogen plant 34 to produce hydrogen 35 for use in the - ~ ,
vaporization and gasification of the hydrocarbon feedstock. ,
The hydrogen plant produces hydrogen by the well known partial
oxidation process. The balance of the hydrogen plant 34 includes ,'
waste heat recovery systems, water gas shift, acid gas removal ~ '
and methanation systems to produce high purity hydrogen by the ~'
20 reaction of CO and ste-am and subsequent removal of the hydrogen '
sulfide and Co2. CO2 from the hydrogen plant 34 is vented ,~
through a conduit 36 and the hydrogen 35 passed to the process '
stream. Hydrogen sulfide 38 produced in the hydrogen plant
34 is conducted to the sulfur plant where elemental sulfur ~ , -
40 is produced.
Figure 2 is a schematic of the process of Figure 1 -`
wherein the process includes the additional steps of prepar,ation
and grinding followed by solvating coal to produce a liquefied
coal for introduction into the gasifier for gasifidation to
produce a synthetic natural gas. In the process of Figure 2
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there is included a source of coal ~6 which is introduced to
a preparation and grinding facility designated by block 48
wherein the coal is finely ground and given an initial separ-
ation to remove unwanted gangue materials. The ground coal
50 is introduced to a coal soluation process 52 wherein the
coal is liquefied by reacting with a solvent and hydrogen.
The solvation process can be chosen from any of those available
or under development such as the P and M Process developed by
Pittsburgh and Midway Coal Mining Company and the Consol CSF
Process developed by the Consolidation Coal Company. The
liquefied coal 54 together with hydrogen and other gases 56
generated in the initial solvation step are introduced into
the vaporizer and the process continues such as described in
relation to Figure 1.
In the coal solvation process, nitrogen 58 from the -~ -
o~ygen plant 30' can be used as an inerting atmosphere in
preparing the coal for solvation.
In the process of Figure 2 it is contemplated that
substantially all of the ash from the coal will be removed in
the coal solvation step and will not affect the overall process.
Figure 3 is a schematic flow sheet of a plant which
would be suitable for producing 150,000,000 standard cubic feet
per day of synthetic natural gas from approximately 30,000
barrels per day of a heavy crude oil. The product of the plant
described in Figure 3 is a synthetic natural gas containing
essentially methane with minor amounts of hydrogen and ethane
having a heating value of about 1,000 btu per standard cubic
feet and is delivered at 1,000 psig pressure. The plant features ;
recovering sulfur as a by-product. Such a plant would have an
expected thermal efficiency of about 78~ and includes six major
processing section namely gasification, purification, (comprising
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aromatic separation, acid gas, removal, shift and carbon dioxide
removal? cryogenic separation, oxygen supply, hydrogen supply
and sulfur recovery. Such a plant is designated to be self- ,
sufficient by incorporating a combined cycle power generation
system and all required off-site areas.
When in operation, a hydrocarbon feedstock such as ,
heavy crude oil, hydrogen and recycled aromatic condensate are
fed to the gasification section to produce a 600 psig gasifier '
effluent (containing aromatic liquid condensate) and a residual ~,
oil fraction. ''''~
In the schematic diagram of Figure 3 the process
flows throughout the system are designated by the arrows shown. ,
. . ~ .
The hydrocarbon feed 60 is introduced to the vapor- ~ '
izer 62 through suitable intermediate conduits by means of '
pump 64 and oil preheater 66 wherein the oil is raised to a ,
temperature of about 700~F. Hydrogen and recycled aromatics
(arrow 73) are introduced to the vaporiæer 62 through hydrogen
preheater 68 and waste heat recovery boiler 70 wherein the
temperature of the hydrogen is raised to a level in excess of
750~F. In one type of vaporizer hot hydrogen is sparged into
the hydrocarbon feedstock beneath the liquid level in the
vaporizer. The vaporized hydrocarbon feedstock and excess
hydrogen then flows as indicated by arrow 70' to the gas
recycle hydrogenator (GRH~ 72 wherein the gasification of the
hydrocarbon feedstock takes place. Hydrogen and recycled
aromatics introduced through a conduit 74 are used to control
temperature in the GRH 72, ~s described previously, the GRH
reactor 72 is an adiabatic open vessel reacotr with a concent-
ric draft tube into which the hydrogen/hydrocarbon vapor is
injected. Gas recirculation within the reactor is caused by '
jetting the re,actants into the draft tube whereby the gases ''
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within the reactor are entrained in the reactant stream. Re-
circulation rates within the reactor of approximately 10 ~o
20 times the injected vapor volume may be obtained using this
device. The high recirculation rate of hot gases, combined with
the temperature of greater than 1500~F in the G~I assures that
the injected vapor is brought to reaction temperatures in a
matter of milli-seconds. The hydrogen-feedstock vapor mixture
reacts to produce primarily methane, aromatics and hydrogen ~ ;
sulfide. With the hydrogen/oil vapor inlet temperature fixed,
the temperature within the GRH is controlled by a gas recycle
stream consisting of hydrogen and/or recycle aromatics which
prevents overheating of the GRH reactor due to the exothermic
hydrogenation reactions. Approximately 65~ of the effluent
from the GRH reactor remains as free hydrogen and this hydrogen
is recovered subsequentlv and recirculated back to the vaporizer.
The average residence time for the feedstock in the GRH reactor
is 5 to 15 seconds. The hot effluent gases 76 from the GR~I
reactor are cooled to ambient by passing through a waste heat
recovery boiler 70 oil preheater 66 and conduit 78 to the pur-
ification unit where the condensed aromatic fraction is recover-
ed in the aromatic separator 80. The condensed aromatics are
removed from separator 80 by conduit 82 mixed with hydrogen
from preheater 68 further preheated by passing through waste
heat recovery boiler 70 and introduced to the GRH 72 and/or
vaporizer 62 by means of conduit 84 The gasifier effluent
after removal of the condensible aromatics is compressed to
about 750 psig in recycle compressor 86 to permit further
processing and recycling of the hydrogen. The effluent from
recycle compressor 86 consists primarily of hydrogen, methaner
ethane and hydrogen sulfide saturated with benzene. The
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effluent 88 is scrubbed with a non-volatile oil to remove
residual benzene in oil absorber ~9 and then scrubbed with a
22% diethanolamine solution in a packed tower 92. The die-
thanolamine (DEA) is regenerated in the acid gas removal system
of the hydrogen supply section. The gasifier effluent thus
treated leaves the DEA column at about 120F and is cooled to
approximately 40F in precooler 94 The oil used to remove
benzene is stripped of the benzene with a portion of recycled `
hydrogen, as will subsequently be discussed, at about 175 and
700 psig in oil stripper 96. The oil is then cooled to about
100F and recirculated by means of pump 98 to the oil scrub
column 90. The gasifier effluent precoo~led to about 40F in
precooler 94 and containing essentially hydrogen and methane
is passed through a dryer 100 to remove water and prevent
freeze-out in the cryogenic separation unit 102. In the cryo-
genic separation unit 102 the hydrogen is separated from the
synthetic natural gas by cooling the effluent to a temperature
of about -237F to condense the SNG. Refrigeration is supplied
by flashing the product to relatively low pressures and rewarm~
ing the recycle and product streams against the feed. The SNG
product is recompressed in product compressor 104 to the desired
product pressure and conducted to the point of use, e.g., ~ ~
pipéline or storage. ~ -
The separated hydrogen 106 is conducted through pre-
cooler 94 back to the gasification section of the process. ~-
The recycled hydrogen is conducted back to the gasif-
ication unit through conduits 106, 108, 110 to the hydrogen
preheater. Portions of the recycled hydrogen can be withdrawn
for e~ample by a conduit designate~d as arrow 112 and used to ~ -
remove the benzene from the oil in oil stripper 96. The re-
covered benæene and hydrogen from oil stripper 96 is returned
to the recycle ;
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stream by a conduit 114. ~ -
In addition to the gasification unit, the necessary sup- -
port systems are also shown in Figure 3. The first of such systems
is an air separation unit generally encompassing an air plant
116 wherein air is liquefied and separated into nitrogen and
oxygen. A portion of the oxygen product is liquefied and taken
by a suitable conduit to a storage vessel 120. Gaseous oxygen
is recovered from the air plant 116 and introduced through suit-
able conduits designated 122, 124 to the hydrogen plant. Gaseous
oxygen can be stored in a suitable vessel 126 and additional
oxygen added from the liquefied storage vessel 120 through
suitable heaters and pumps such as 128. Gaseous oxygen is then
fed through conduit 124 to a plurality of reactors 130 wherein
the oxygen and residual oil from vaporizer 62 are reacted with
steam at about 800 psig and 2,600F. to produce a crude synthe-
sis gas. Each reactor, commonly referred to as a partial oxi-
:. . .
dation or POX reactor produces a crude synthesis gas. The re- -
actor effluent is cooled in an adjacent waste heat boiler (not
shown) producing 1,300 psig. steam. Entrained soot produced in
reactors 130 which is about 3 weight percent of the feed oil is
removed by water scrubbing in scrubbers 132 and will be re- -
cycled to the process. Carbon recycle will take place in a re-
cycle reactor generally designated 134 which is offered commer-
cially by the Shell Oil Company. The water slurry is contacted
with vigorous agitation with naphtha in reactor 134 thus extract-
ing the soot from the water phase by retaining the soot in the
hydrocarbon phase. The naphtha is then mixed with the feed to ~-
the reactors 130 and after stripping the naphtha for recycling
the carbon remains as a slurry in the feed oil.
The product of the hydrogen plant 136 is a mixture of
carbon monoxide and hydrogen with about 6% CO2 and about 1% ~
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hydrogen sulfide. The effluent is conducted to a carbonate
absorber 138 at about 690 psia where nearly all of the CO
and H2S are scrubbed from the gas by a carbonate solution cir-
culating continuously between absorber and regenerator towers.
The solution at the bottom of the absorber 138 after reduction
of pressure from 690 psia to about 8 psig is conducted by a
conduit 140 to a carbonate stripper 142 where steam stripping
is carried out at about 240F thus liberating the acid gas
contained in the solution. The hot solution is conducted from
the carbonate stripper 142 via pump 144 back to the carbonate
absorber 138 to complete the circulating solution circuit. The
effluent from the carbonate absorber 138 containing about 0.5~
C2 and 0.2% H2S together with the carbon monoxide and hydrogen
is air cooled (not shown) and conducted by conduit 145 for
further scrubbing by a DEA solution circulating continuously
between a DEA absorber 147 and a DEA stripper 146. The bottoms
from the stripper 146 are pumped through a heat exchanger (not
shown) for cooling to 120~F and returned to absorber 147 to ~--
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complete the circuit. The DEA regeneratore acid off-gas passes ;
through the carbonate regenerator via conduit 150 and the com-
b~ned acid gas stream is cooled, compressed and transferred to
a reaction furnace 152 and converter 154 for conversion to
elemental sulfur which is withdrawn at 156. The reaction fur-
nace and converter 152~ 154 respectively are part of a con-
ventional Claus plant.
The purified hydrogen/CO gas from the acid gas removal
unit is conducted to a shift unit via suitable conduits 158. A .
portion of the hydrogen/CO synthesis gas mixture can be with-
drawn to use as fuel for running the plant as designated by
arrow 160. The hydrogen/CO mixture introduced to the shift
unit is conducted
16 -
through a conventional shift converter wherein the CO is con-
verted to hydrogen by the conventional shift reaction. Initially,
the H2/CO syn gas mixture is passed through a gas saturator wherein
the necessary water vapor is added to the gas. The pH of the
water is automatically controlled in the range of 7.5-8.5 to
neutralize the effect of corrosion from the carbon dioxide water
mixture. The saturator effluent 162 has steam added to it
through a conduit 164 as needed to adjust the N2O/CO ratio for
shift. The syn gas is conducted to a high temperature shift
converter 166 containing a conventional iron-chrome base material
which has been known for many years. From the high temperature
shift converter 166, the gases are conducted to a zinc oxide
desulfurizer 168 which is used to prevent any traces of sulfur
from penetrating to the low temperature shift converter 170 next
to the stream. The low temperature shift converter 170 con-
tains a copper based catalyst that will reduce the carbon mono-
xide level to about 1%. Such catalysts have been known in the
art for more than 10 years.
The effluent from the low temperature shift converter is
cooled through a suitable cooler 172 and then passes through a
carbon dioxide removal unit similar to those previously des- -
cribed in conjunction with the purification and acid gas removal
units. The final purification unit consists generally of the
same hot carbonate process used in the first acid gas removal
unit except there is included, in addition to the carbonate ~
absorber 174 carbonate stripper 176 and pump 178, a methanator ;~ -
180. The primary process differences are removal of CO2 only,
rather than the combination of CO2 and hydrogen sulfide, and
addition of a methanator for reduction of carbon oxides to the
desired levels in the hydrogen product from the total facility~
The CO2 removal unit receives crude hydrogen from the shift unit.
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In this unit the carbon dioxide will be removed and remaining
traces of CO2 and CO will be-methanated.
The effluent from methanator 180 is conducted into
the recycle conduit 110 as shown by arrow 182. The foregoing
describes a process that will produce a synthetic natural gas
having heating value of approximately 1,000 btu per standard
cubic foot in quantities of approximately 150,000,000 standard
cubic feed per day.
Several tests were run to verify the expected results
of a process built in accordance with the foregoing description.
One method of running tests was in accord with the
system described in Figure 3 of the U.S. Patent No. 3,870,481
An identical test set up was used and the results from running
Kuwait Topped crude oil and benzene in such a test setup are
set forth in Table 1. Kuwait Topped crude oil as received had
the minus 360F fraction removed prior to running the test.
.
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From the foregoi~g it is o~vious that the gasifier
operating at a temperature in excess of lSQ0 and with excess
hydrogen is effective to suppress~ethane formation and to provide
an effluent that is substantially-methane and hydrogen.
The benzene runs were accomplished with total vapor- -~
ization of the benzene hydrocarbon feedstock in the vaporizer
before it was injected into the gasifier. The extent of
vaporization of the hydrocarbon feedstock will depend upon its
composition, For example with the Topper Kuwait crude oil
used in the tests the operation was optimized when approximately
75% of the topped crude oil was vaporized, Lighter feedstocks
such as naphtha would completely vaporize while the heavy
crude oils and heavy crude-like materials such as bitumen
produced from tar sands, shale oils, and solvated coal would
only be partially vaporized at these process conditions. -
Parallel tests~:,were run in a pilot plant operated
by the British Gas Council at Solihull, England with the GRH
operating at elevated temperature and with excess hydrogen
using Topped Kuwait crude oil as set forth in Table II, and
a Monagas crude oil as set forth in Table III. Monagas crude
oil is a Venezuelan bitumen believed to be suitable as an ~-
alternative feedstock.
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From the foregoing Tables II and III, it is obvious
that the elevated temperature operation of the gas recycle
..... ..
hydrogenerator combined with the use of excess hydrogen produces
a gasifier effluent that is substantially methane. The forma-
tion of ethane is effectively suppressed and carbon formation
is also minimized.
Table IV sets forth the data from three experimental
runs conducted to show that when the gasifier temperature is ~ -
maintained above 1550F, the ethane content in the effluent is
less than 5 mole percent. The comparative runs set out in
Table IV show that for a given feedstock, e.g. No. 2 fuel oil,
when the GRH temperature dropped from 1555 F. (Run F2G-08) to
1400 F. (Runs F2G-09 and F2G-10) the ethane content of the effl-
uent went from 4.6? by volume (mole percent) to over 15% by
. . . . .
volume (mole percent). ~;
TABLE IV
-- . , .: .
VAPOR~ZER - GR~I Tests
G~H ~ erating Temperature i400-1555 F.
Test Data No. 2 Fuel Oil
Feedstock 350-600
Vaporizing
2 Pressure, PSIG Conden-
Productsate
Vap. GRH Composition TW % of
Run Run Time Temp. F. GRH Temp. Press. Volume % GRH
No. Hrs. (Mean Wall) F. (Effluent H2 O1l;Feed
F2G-08 11 730 1555 600 36.3 4.6 56.4 21.4
F2G-09 11 680 1400 350 25.1 15.6 54.8 27.0
F2G-10 11 695 1400 400 26.5 15.9 52.5 26.8
~ - - ' ~ '
The data from TabIes I-IV, along with data reported in
U.S. Patent 3,363,024, 3,591,356 and 3,870,481, together with test
.. : .
data reported by the British Gas Council (now British Gas Corp-
oration) in a document entitled "The Hydrogenation of Oils to -
.
Gaseous Hydrocarbons" identified as Research Communication GC122 ~-
of the Gas Council, November 1965 is shown in the graph of ~'ig-
ure 4 of the drawing wherein reactor temperature is plotted
against the volume percent of ethane in the reactor ef~luent.
Figure 4 also shows tne temperature limits of various prior art
, -23-
.
~ ~ 7 ~ !
, . ~
_
patents drawn to gasification of hydrocarbon feedstocks. Thus
it is readily apparent from the data of Table IV and the plot of
Figure 4 that when the gasifier (reactor) is operated at temp-
eratures in excess of 1550F., the ethane content of the efflu-
ent is below 5 volume percent (mole percent).
Several tests have been run using liquids derived from
coal with similar results.
Lighter oils have also been run successfully however
if lighter oils were available, the process could include a topp-
ing tower and a Catalytic Rich Gas unit to process the lighterfractions such as disclosed in U.S. Patent 3,870,481. This would
reduce the investment in the hydrogen producing area because of
the reduced size of the partial oxidation system and oxygen plants.
The process of this invention can be used for the pro-
duction of hydrogen, carbon monoxide, or hydrogen and carbon mon- ~
oxide rather than for the production of SNG. Currently the major ~ -
portion of the hydrogen, carbon monoxide, or hydrogen and carbon ~-
monoxide produced together is by the catalytic steam reforming of ;;-
natural gas. These products can also be produced by partial
oxidation of heavier hydrocarbon feedstocks with oxygen and steam
in a partial oxidation gasifier. Where natural gas is in short
supply, heavier hydrocarbon feedstocks will have to be utilized ~-
for producing hydrogen or hydrogen and carbon monoxide. Partial
oxidation of heavier feedstocks is substantially more expensive
than steam reforming natural gas. The present invention can be
adapted to produce hydrogen, carbon monoxide, or hydrogen and
carbon monoxide from heavier hydrocarbon feedstocks without the
use of a partial oxidation gasifier. The method of the present
invention for producing hydrogen from a heavy hydrocarbon feed -~
stock is utilized by gasifying the feedstock in the one stage
gasification reactor to produce an effluent which is purified
to give a product stream of gases that are essentially methane
and hydrogen. This product stream is then mixed with steam and
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catalytically reformed to carbon monoxide and hydrogen in a
steam reformer using this well known technology. A relatively
pure stream of hydrogen can be produced by further reacting the ,~
carbon monoxide with steam over a bed of shift catalysts while
maintaining different operating conditions and then purging this
stream of the carbon dioxide formed. Part of this hydrogen pro-
duce can be recycled back to the one stage gasification reactor,
thus avoiding the use of partial oxidation while gasifying a heavy
hydrocarbon feedstock.
If carbon monoxide is desired, the gas from the re-
former is not shifted but is separated by well known technology
into its components and a portion of the hydrogen is recycled.
It is within the scope of the invention to utilize -
mixed feedstocks such as mixtures of different crude oil fractions, ~-
.: .
crude oil and coal derived liquids and the like. ;
.,
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