Production of carbon monoxide by the gasification of carbonaceous materials

An increased amount of carbon monoxide is produced in a process for the gasification of carbonaceous materials by employing a reverse water gas shift reaction in the process. Raw gas produced by the gasification of carbonaceous materials contains predominantly carbon monoxide and hydrogen along with hydrogen sulfide, carbon dioxide, water and methane. Carbon dioxide is separated from the raw gas as is the hydrogen sulfide. Thereafter, the carbon monoxide is separated from the raw gas to yield one portion of the carbon monoxide product gas. After the removal of carbon monoxide the raw gas consists of a hydrogen-rich gas. The hydrogen-rich gas which may be purified is mixed with the previously separated carbon dioxide along with any imported carbon dioxide and along with a recycle gas from a catalytic reaction loop. This mixed gas is conveyed to a heat exchanger in the catalytic reaction loop and passed through a heat exchanger located immediately after the gasifier through which the raw product gas passes. In the heat exchanger the hot raw product gas indirectly contacts the mixed gas and transfers some of its sensible heat to the mixed gas to effect the catalytically promoted, endothermic reaction of carbon dioxide and hydrogen to produce a carbon monoxide-containing gas. The indirect contacting for heat exchange is conducted in a manner that limits the accumulation of elemental carbon from any of the carbon-containing components of the mixed gas. The carbon monoxide is separated from the other components of the carbon monoxide-containing gas to yield a second portion of carbon monoxide gas which is then combined with the first portion of carbon monoxide product gas to give the increased amount of carbon monoxide product gas.

BACKGROUND OF THE INVENTION 
This invention relates to a process for gasification of carbonaceous 
materials to produce a carbon monoxide-rich gas. More specifically, this 
invention relates to increasing the amount of carbon monoxide produced in 
a process of gasifying carbonaceous materials at elevated temperatures to 
maximize the yield of carbon monoxide from such a process. 
Oil and natural gas are used as feedstocks or fuels for many chemical and 
mechanical processes. These raw materials are rapidly becoming depleted 
and alternative sources are being developed. One alternative source 
present in the United States is the vast deposits of coal. Coal, coal 
gasification, and coal liquefaction products are seriously being promoted 
as substitute feedstocks and fuels for chemical and mechanical processes. 
Reducing and synthesis gases that are useful as fuels and as reactants in 
ore reduction processes have been produced by catalytic reforming of 
natural gas via the methane-steam reaction, partial oxidation of 
hydrocarbon fuels, and by gasification of coal and coke. Because of the 
depletion of oil and natural gas, more emphasis is being placed on the 
production of reducing and synthesis gases from coal and coke 
gasification. The production of a carbon monoxide-rich reducing gas by 
gasification of coal or coke has become of increasing interest. This 
carbon monoxide-rich reducing gas is useful since the carbon monoxide 
reacts with many metal oxides or other metallic compounds, such as 
metallic halides, to produce carbon dioxide and the corresponding metals 
or lower metal oxides. A few of the metals whose oxides are reduced by 
carbon monoxide include iron, aluminum, cobalt, copper, lead, manganese, 
molybdenum, nickel, silver and tin. In addition, a carbon monoxide-rich 
gas has many other chemical applications, such as the production of metal 
carbonyls, phosgene, toluene diisocyanate, and synthetic acids, including 
acetic acid. The carbon monoxide is also employed in oxo synthesis 
processes, and developments are reported to be underway to employ carbon 
monoxide for production of terephthalic acid and p-cresol, and to use it 
as a co-monomer in thermoplastics. 
The production of carbon monoxide-containing reducing gas by coal or coke 
gasification has been performed for many years by blue gas generators and 
producers, water gas generators, blast furnaces and coke ovens. The gas 
produced by these methods contains carbon monoxide along with quantities 
of hydrogen, water, carbon dioxide, methane and hydrogen sulfide. A recent 
development has occurred in the art to increase the yield of carbon 
monoxide obtained from coal and coke gasification. This development 
involves pre-drying the coal to be gasified with air, oxygen, and/or steam 
while supplying carbon dioxide to the gasification reaction. Several 
examples where carbon dioxide addition to the gasifier is disclosed are in 
U.S. Pat. Nos. 3,801,288 (Leas et al.); 3,840,353 (Squires); and 3,976,442 
(Paull et al.). According to these teachings, the carbon dioxide added to 
the gasifier can be produced internally in the gasification process or can 
be introduced from an external source. This method does increase the 
amount of carbon monoxide in the raw gas emitted from the gasifier but the 
presence of other gases, most notably hydrogen, cannot be avoided due to 
the natural consistency of coal as well as due to the thermo-dynamic 
constraints which govern gasifier performance. 
It is an object of the present invention to provide a process for 
maximizing the production of a carbon monoxide-rich gas from a process for 
the gasification of carbonaceous materials. 
It is a further object of the present invention to provide a gasification 
process to produce a carbon monoxide-rich gas in an efficient, safe, and 
economic manner utilizing available heat sources present in the process. 
It is an additional object of the present invention to provide an 
integrated process gasification of carbonaceous material to supply a 
sufficient amount of carbon monoxide for an ore reduction process, and for 
utilizing carbon dioxide produced in the ore reduction process to produce 
more carbon monoxide in the process for gasification of carbonaceous 
materials. 
It is another additional object of the present invention to provide a 
process whereby hydrogen present in gases produced by gasification 
processes for carbonaceous materials is utilized in the production of the 
increased amount of carbon monoxide from the gasification process. 
SUMMARY OF THE INVENTION 
According to the process of this invention, the amount of carbon monoxide 
produced in the gasification of carbonaceous materials is maximized in an 
efficient, safe, and economic manner. This is accomplished by recovering 
the carbon monoxide in the raw gas from the gasification of carbonaceous 
materials and by converting the carbon dioxide and hydrogen in the raw gas 
from the gasification, along with any additional carbon dioxide, into a 
carbon monoxide-containing gas wherein the sensible heat of the raw gas 
produced by the gasification of the carbonaceous material is utilized to 
effect the conversion. 
The process of the present invention comprises: indirectly contacting the 
hot raw gas obtained from the gasification of carbonaceous materials with 
a mixed gas containing carbon dioxide and hydrogen while the mixed gas is 
in the presence of a catalyst that suitably promotes the reverse water gas 
shift reaction. The indirect contact provides the heat necessary to 
perform the endothermic reaction of carbon dioxide and hydrogen to produce 
carbon monoxide. The carbon dioxide and hydrogen in the mixed gas are 
obtained from the raw gas previously produced by the gasification of 
carbonaceous materials. Also, additional carbon dioxide can be added to 
the mixed gas from a source external to the gasification process. 
The process of the present invention proceeds in the following manner. Raw 
gas is produced by the gasification of carbonaceous materials and the raw 
gas contains predominantly carbon monoxide and hydrogen, with some carbon 
dioxide and hydrogen sulfide and a minor amount of methane. Hydrogen 
sulfide is removed from the raw gas by an acid gas removal step. Also, 
carbon dioxide is removed and recovered while residual water is usually 
removed in the same operation. Then the carbon monoxide is separated from 
the hydrogen to produce a first portion of the carbon monoxide-rich gas of 
the present invention. The hydrogen is combined with the carbon dioxide 
which was removed previously from the raw gas along with any added carbon 
dioxide from an external source to form a mixed gas. This mixed gas is 
conveyed to an heat exchanger for the indirect contact with the raw gas 
produced by the gasification of the carbonaceous material. The heat 
exchanger is located immediately after the gasifier, and in the heat 
exchanger the mixed gas is in the presence of a conventional water gas 
shift reaction catalyst while indirectly contacted with the hot raw gas. 
The indirect contacting is conducted in such a manner as to limit the 
accumulation of elemental carbon from any of the carbon-containing 
components in the raw gas. The sensible heat of the hot raw gas enables 
the water gas shift reaction to proceed whereby a carbon 
monoxide-containing gas is produced. The carbon monoxide in this gas is 
separated and combined with the first portion of carbon monoxide to yield 
the carbon monoxide-rich product gas of the present invention. 
To promote activity and to prevent deactivation of water gas shift reaction 
catalyst, the mixed gas can be preheated before it is placed in the 
presence of the catalyst by indirect heat exchange contact with the raw 
gas from the gasification of carbonaceous materials. The preheating avoids 
catalyst deactivation by limiting the deposition of carbon upon the 
catalyst. 
To take full advantage of maximizing the amount of carbon monoxide produced 
in the gasification of carbonaceous materials, the process of the present 
invention may include introducing carbon dioxide to the gasification 
reaction to increase the amount of carbon monoxide in the raw gas from 
gasification. 
The process of the present invention can be integrated with an ore 
reduction process. The integrated process would involve using the carbon 
monoxide-rich gas produced in the process of the present invention to 
reduce ores and using a portion of about 30 volume percent to about 80 
volume percent of the carbon dioxide given off in the ore reduction 
process to be added to the mixed gas of carbon dioxide and hydrogen and/or 
be introduced into the gasification reaction in the process of the present 
invention.

GENERAL DESCRIPTION OF THE INVENTION 
Before describing the preferred embodiment of the present invention, a 
general description of the process of the invention in its broadest 
aspects is given with reference to FIG. 1. 
Referring to FIG. 1, carbonaceous materials is conveyed to the gasifier by 
conduit 10. This carbonaceous material includes any type of coal of which 
nonlimiting examples are anthracite, subanthracite, lignite, bituminous 
coal and subbituminous coal, and also includes cokes either coal or 
petroleum derived, char, and liquid hydrocarbons. The carbonaceous 
material may be slurried with water or other liquids to expedite its 
introduction into the gasifier. If the carbonaceous material is coal, it 
is usually dried and ground to fine sizes. Also conveyed to the gasifier 
14 is the entraining medium that reacts with the carbonaceous material to 
produce the raw gases emitted from the gasifier. The entraining medium can 
be oxygen, air, steam, or carbon dioxide, with or without water, or any 
mixture thereof. However, air is not used alone as the entraining medium 
but in combination with any other aforementioned entraining mediums. Nor 
is it used excessively, since undesirable inert gases such as nitrogen and 
argon will be present and will be carried along in the processing. Also, 
the use of steam is undesirable with carbonaceous materials that contain a 
large amount of moisture or are slurried with water into the gasifier. 
The carbonaceous material and entraining medium conveyed to gasifer 14 are 
reacted therein to produce hot raw gas. This gas contains predominantly 
carbon monoxide and hydrogen with smaller amounts of water vapor, carbon 
dioxide, hydrogen sulfide, carbon disulfide and methane. The amount of 
methane in the raw gas is usually less than 1.0 volume percent, whenever 
the gasifier operates at temperatures in excess of about 2000.degree. F. 
The gasification reaction is conducted by any method known to those 
skilled in the art that will produce a raw gas with the aforementioned 
constituents at a temperature leaving the gasifer greater than 
1300.degree. F. (704.degree. C.). The pressure of the gasifier can range 
from 1 atmosphere to 175 atmospheres, absolute. Examples of such 
gasification reactions include those reactions conducted in gasification 
vessels by entrained flow, or in a fixed bed reactor or fluidized bed 
reactor in any flow arrangement. The raw gas leaving the gasifier by 
conduit 16 may possibly contain, in addition to the aforementioned 
constituents, some ungasified carbonaceous material, slag, ash and tar. If 
any molten slag is entrained with the gas, the gas would be sprayed with 
water or cooled with a recycle gas to prevent any subsequent adhesion of 
the slag to any heat transfer surfaces located after the gasifier. 
Remaining ash or slag that does not leave the gasifier entrained in the 
raw gas is removed from the gasifier by conduit 18. 
The raw gas in conduit 16 is conveyed to Heat Exchanger 20 at a temperature 
usually in the range of around 2000.degree. F. (1093.degree. C.). The heat 
exchanger may be any conventional heat exchanger for indirectly contacting 
a hot gaseous fluid with a cool fluid that is in the presence of a 
catalyst. Examples of such heat exchangers include those wherein the hot 
gaseous fluid passes over tubes packed with catalyst and containing the 
cooler fluid, or wherein the hot gaseous fluid may pass through tubes that 
are enveloped in a catalyst bed or fluidized bed of catalyst in direct 
contact with the cooler fluid. The raw gas leaving heat exchanger 20 is 
cooled to a temperature in the range of about 600.degree. F. (316.degree. 
C.) to about 1000.degree. F. (538.degree. C.). 
These cooled raw gases are conveyed to other process steps by conduit 22. 
These subsequent process steps may vary to some degree regarding the 
location of particulate removal or additional heat exchange equipment. 
Usually, as in FIG. 1, the cooler raw gas in conduit 22 is conveyed to 
Particle Removal Zone 24, although further heat may be removed from the 
cooler raw gas by additional heat exchangers or waste heat or steam 
boilers before particles are removed from the gas and the gas is 
compressed. Alternatively, the raw gas conveyed by conduit 22 may be used 
to indirectly preheat the entraining medium which enters the gasifier by 
conduit 12 before particulates are removed from the raw gas. In zone 24, 
any remaining ash or slag particles are removed from the raw gas by 
mechanical centrifugal separators, cyclone separators, venturi scrubbers, 
gravity separators or electrostatic precipitators. 
The gas leaves zone 24 via conduit 26 and is conveyed to an Acid Gas 
Removal Zone 28. In this zone, hydrogen sulfide, carbonyl sulfide and, 
unavoidably, some carbon dioxide are removed from the gas. This removal is 
accomplished by any one of several of the well-known acid gas removal 
processes. The chemical reaction processes such as amine and carbonate 
systems may be used or physical absorption processes known by trade 
designations of Rectisol, Purisol and Selexol may be used. The recovered 
sulfur-containing gases are conveyed via conduit 30 to a sulfur removal 
zone 32, which may be the well-known Claus process or Stretford process, 
for recovery of elemental sulfur. The carbon dioxide that is unavoidably 
removed from the raw gas with the hydrogen sulfide may be recovered if 
sulfur-containing gases are recovered by the Stretford process. This 
recovered carbon dioxide may be combined with the carbon dioxide 
subsequently recovered from the raw gas and from any external sources to 
be reacted with hydrogen in the reverse water-gas shift reaction. 
The desulfurized gas is conveyed from the Acid Gas Removal Zone 28 by 
conduit 34 to a Carbon Dioxide and Water Removal Zone 36. Here carbon 
dioxide is removed from the gas by any known method, such as scrubbing and 
absorption with cold methanol. In addition, residual water vapor that was 
not removed in zone 28 ordinarily will be removed simultaneously with the 
carbon dioxide. The water is conveyed from the CO.sub.2 Removal Zone 36 by 
conduit 38 and combined with water in conduit 40 from the Acid Gas Removal 
Zone 28 and all this water is removed from the process. Also, the gas may 
be dried in zone 36 by using a chemical absorbent, such as triethylene 
glycol. 
The raw gas that has now been cooled and cleaned is conveyed by conduit 42 
to a Carbon Monoxide Recovery Zone 44 for a recovery of a portion of the 
product of this invention. The CO recovery step may be performed by any 
method known to those skilled in the art, such as cryogenic separation 
methods such as those taught in German Offenlegungschrift No. 2,323,410, 
hereby incorporated by reference, or by selective chemical methods as 
taught in German Offenlegungschrift No. 2,057,162, also hereby 
incorporated by reference. Alternatively the carbon monoxide may be 
recovered by the "Cosorb" process available from Tenneco Chemicals, Inc. 
The carbon monoxide product is removed from the CO Recovery Zone by 
conduit 46 as the first portion of the carbon monoxide-rich gas of the 
process of the present invention. 
The remaining gas of what was originally the raw gas contains mostly 
hydrogen. If this hydrogen-rich gas contains more than about two percent 
by volume of nitrogen and argon, then the hydrogen-rich gas should be 
subjected to a hydrogen purification step (not shown in FIG. 1). The 
hydrogen purification step would be added to remove inerts from the 
hydrogen-rich gas by any known process, such as the use of molecular 
sieves, or an alternative means such as is disclosed in U.S. Pat. No. 
3,113,889, hereby incorporated by reference. The hydrogen-rich gas is 
conveyed from the CO Recovery Zone by conduit 48 to Mixing Zone 50. In 
this zone the hydrogen-rich gas is mixed with the carbon dioxide conveyed 
from the Carbon Dioxide Removal Zone 36 by conduit 52 to the Mixing Zone 
and with recycle gas conveyed by conduit 72 from the reverse water gas 
shift reaction, which is described in greater detail infra. Also, 
additional carbon dioxide can be supplied from a source external to the 
process and combined with the carbon dioxide in conduit 52 or supplied 
directly to Mixing Zone 50. In FIG. 1 this additional carbon dioxide is 
supplied to conduit 52 by conduit 54. This mixing zone can be any vessel 
known to those skilled in the art for mixing gases and can even consist of 
merely a wider diameter conduit than the conduits conveying the gases to 
the mixing zone. 
The mixed gas containing predominantly carbon dioxide and hydrogen is 
conveyed from the Mixing Zone by conduit 56 to Heat Exchanger 20. Here the 
raw gas from conduit 16 indirectly contacts the mixed gas while the mixed 
gas is in the presence of a water gas shift reaction catalyst. The 
sensible heat of the raw gas provides the heat needed to conduct the 
catalytically promoted, endothermic, reverse, water gas shift reaction: 
EQU CO.sub.2 +H.sub.2 .revreaction.CO+H.sub.2 O Eq. 1 
By using this reaction, the hydrogen contained in the raw gas from the 
gasifier may ultimately react with carbon dioxide externally to the 
gasifier, to generate additional carbon monoxide, and thereby overcome the 
constraints of increasing the carbon monoxide content of the raw gas in 
the gasifier. 
The reaction represented by Equation 1 is endothermic and therefore 
requires high temperatures, for example, around 1000.degree. F. 
(538.degree. C.) to about 1500.degree. F. (816.degree. C.) to promote the 
equilibrium formation of carbon monoxide. In addition, the use of high 
temperatures discourages various exothermic reactions such as 
EQU 4H.sub.2 +CO.sub.2 .fwdarw.CH.sub.4 +2H.sub.2 O Eq. 2 
which compete for the available hydrogen. From a kinetic standpoint, the 
reaction represented by Equation 1 is slow unless promoted by the use of 
elevated pressures or by the use of well-know catalysts. Examples of these 
catalysts include: one or more metals of the Groups VIb, VIIb and/or VIII 
of the Periodic Table, as an active agent which metals or their mixtures 
are used as such or as their oxides and/or sulfides, the sulfides being 
used when a sulfur resistant catalyst is required. The sulfur resistant 
catalyst is needed if acid gases are not removed from the raw gases and 
they are allowed to travel through the process. In addition, commercially 
available catalysts commonly used in the steam reforming of natural gas 
may be used. An example of such a catalyst would be that which is 
available from Catalysts and Chemicals, Inc. under the trade description 
"C11-9". If the catalyst becomes deactivated due to carbon deposits, the 
catalyst may be subjected to oxidation to burn off the carbon, thereby 
regenerating the catalyst. Alternatively, the deposition of carbon on the 
catalyst can be avoided by preheating the cool gas before it contacts the 
catalyst. 
The carbon monoxide-containing gas leaving the heat exchanger is conveyed 
by conduit 58 to a Water Condensation and Gas Dehydration Zone 60 to 
remove water present as a product from the reverse water gas shift 
reaction. The water can be removed by any process known to those skilled 
in the art, for example, by cooling the gas and, if desired, extensive 
drying of the gas by a well-known chemical method such as absorption with 
ethylene glycol or triethylene glycol. Also, since the carbon 
monoxide-containing gas in conduit 58 is at an elevated temperature after 
the reverse water gas shift reaction, heat exchangers or waste heat 
boilers may be used to recover some heat before the gas is treated for 
removal of water. The water removed is combined by conduit 62 with other 
water recovered in the process. The heat contained in gas conveyed by 
conduit 58 may, if so desired, be used for indirectly heating all or a 
portion of the entraining medium (up to 1000.degree. F.) which is conveyed 
into the gasifier by conduit 12. Likewise, this heat may be used for 
indirectly heating all or a portion of the carbon monoxide product of this 
invention to thereby provide the carbon monoxide product at temperatures 
in excess of 1000.degree. F. (538.degree. C.), which is especially 
desirable in some direct ore reduction processes. If the carbon monoxide 
product is heated in such a manner there is a possibility that a small 
amount of elemental carbon can form from the carbon monoxide. If this 
happens, the elemental carbon may be separated from the heated carbon 
monoxide product whereupon such elemental carbon would be combined with 
the carbonaceous feed introduced to the gasifier by conduit 10 so that 
such elemental carbon may be re-gasified. 
The dehydrated carbon monoxide-rich gas is conveyed by conduit 64 to 
another Carbon Monoxide Recovery Zone, Zone 68. This zone may employ any 
process known to those skilled in the art to remove carbon monoxide to 
constitute the second portion of carbon monoxide produced by the process 
of the present invention. This portion of carbon monoxide is conveyed by 
conduit 70 to be combined with the carbon monoxide in conduit 46 to form 
the carbon monoxide-rich gas produced by the process of the present 
invention for use in ore reduction or chemical processing. The other gases 
in the gas of conduit 64, e.g., unreacted carbon dioxide and unreacted 
hydrogen along with a small amount of methane, are recycled by conduit 72 
to the reverse water gas shift loop directly by the Mixing Zone 50. The 
methane present in the gas recycled by conduit 72 equates to the 
steady-state concentration (which approximates equilibrium conditions) of 
methane present in the gas leaving the heat exchanger via conduit 58. 
Thus, there is no net formation of methane, ordinarily. An exception 
occurs whenever the raw gas produced in the gasifier contains significant 
amounts of methane, which ordinarily would not be the case since, as 
previously mentioned, the raw gas leaving the gasifier is at a temperature 
in excess of 2000.degree. F. when the invention is practiced typically. 
Methane present in the raw gas would be recovered along with the hydrogen 
which is conveyed by conduit 48 from the CO recovery zone 44. This methane 
would clearly then ultimately contact the catalyst contained within the 
heat exchange zone 20, whereupon there would be a net destruction of 
methane to additional carbon monoxide by endothermic means such as, 
EQU CH.sub.4 +H.sub.2 O.revreaction.CO+3H.sub.2 Eq. 3 
Since the aforedescribed process required conveying gases and some liquids 
to and from various zones, those skilled in the art will realize that 
motive forces must be installed at various locations in the process. These 
motive forces include difference in pressures between zones, compressors 
and pumps. The locations of these motive forces will be those necessary to 
move the materials throughout the entire process. 
Although the invention in its broadest scope features use of two separate 
CO recovery zones, i.e., 44 and 68, it is possible under certain 
circumstance to use just one CO recovery zone. This circumstance arises 
when the inert compounds, i.e., nitrogen or argon, present in the raw gas 
are sufficiently low in a concentration to avoid the use of the 
aforementioned hydrogen purification step which may be rendered to gas 
conveyed by conduit 48 from the CO recovery zone 44. In such a 
circumstance, gas conveyed by conduit 64 from Water Condensation Zone 60 
would be directly conveyed to the CO Recovery Zone 44 and the CO Recovery 
Zone 68 would be eliminated. In such a case, the gas conveyed by conduit 
48 from CO Recovery Zone 44 would contain principally the hydrogen 
initially present in the raw gas along with the recycled gas ordinarily 
characterized as that conveyed by conduit 72. The gas conveyed by conduit 
48 would then be conveyed to Mixing Zone 50. Also, under this circumstance 
the CO removed by conduit 46 would contain the aforementioned first 
portion of CO product along with the increased portion of CO product 
afforded by the invention. Furthermore, it should be noted that an 
additional means of eliminating a hydrogen purification step would involve 
taking a "bleed stream" from the system (not shown on FIG. 1), for 
example, from the gas conveyed by conduit 64, as a means of removing 
continuously or periodically the inert compounds from the system. 
The total yield from both portions of carbon monoxide in accordance with 
this invention gives 30-80% more carbon monoxide than in the prior 
disclosed methods for gasification of carbonaceous materials. 
An additional advantage of the invention is that the raw gas which 
indirectly contacts the carbon dioxide and hydrogen-rich mixed gas 
contains essentially no free oxygen, i.e., less than 0.1 volume percent. 
This minimizes the possibility of explosion in the event of a failure of 
the heat exchanger materials of construction. Whereas, if a hot combustion 
gas were used alternatively to the hot raw gas from the gasifier, then the 
free oxygen always present in the combustion gas poses an imminent safety 
hazard. Such explosions have been known to occur in heretofore known 
furnaces, such as those used in the steam reforming of natural gas. 
PREFERRED EMBODIMENT 
For a better understanding of the present invention, its objects and 
advantages, reference should be had to the following decription of the 
preferred embodiment of the present invention and to FIG. 2 which 
illustrates schematically the preferred embodiment of the present 
invention. 
The preferred gasification process used with the process of the present 
invention is the Koppers-Totzek gasification process, better known as the 
K-T gasification process. This process employs the partial oxidation of a 
carbonaceous feed in suspension with oxygen and steam to produce a product 
gas high in carbon monoxide and hydrogen with negligible amounts of 
methane. The process does not produce tars, oils or phenols and the 
by-products are elemental sulfur and a granulated slag. 
As shown in FIG. 2, coal, which is dried to a degree depending upon its 
rank and pulverized, is conveyed by conduit 80 into gasifier 82 wherein it 
is entrained with oxygen and carbon dioxide. Alternatively, steam may be 
used instead of carbon dioxide, but carbon dioxide is preferred for 
practice of the invention. The oxygen is added to the gasifier by conduit 
84 and the carbon dioxide is added to the gasifier by conduit 86. The 
gasifier 82 operates with entrained flow of these reactants, coal, oxygen, 
and carbon dioxide, and exothermic reactions produce a flame temperature 
of around 3500.degree. F. (1927.degree. C.). The gasification of the coal 
is almost complete and instantaneous. A gas containing predominantly 
carbon monoxide and hydrogen with smaller amounts of carbon dioxide, 
hydrogen sulfide, carbonyl sulfide, methane, nitrogen, and argon and water 
leave the gasifier at a temperature characteristically ranging from about 
2500.degree. F. (1371.degree. C.) to about 3000.degree. F. (1649.degree. 
C.). This exit temperature is somewhat lower than the flame temperature 
due to heat losses and endothermic reactions which occur beyond the flame 
zone. The oxygen conveyed to the gasifier will normally have a purity of 
at least 98 volume percent in order to minimize the inert content of the 
ultimate carbon monoxide product or to minimize the subsequent 
accumulation of inerts within the various gas processing steps that are 
employed. Ash in the coal feed is liquified at the high reaction 
temperature and approximately 20 to 70 percent of the molten ash drops out 
of the gasifier into a slag quench tank (not shown in FIG. 2) via conduit 
88. 
The raw gas exits gasifier by conduit 90 and is sprayed with water 
introduced by conduit 92 in order to lower the gas temperature to slightly 
below the fusion temperature (1900.degree. F. to about 2400.degree. F.) 
(1038.degree. C. to 1316.degree. C.) of the molten ash particles carried 
by the gas so that there is no subsequent adhesion of slag to heat 
transfer surfaces. Alternatively, cool recycled gas instead of water spray 
may be used for cooling the gas by the methods taught in U.S. Pat. No. 
3,963,457. The raw gas, having been sprayed with water, enters heat 
exchanber 94 where a portion of the available sensible heat of the gas is 
indirectly transferred to effect the catalytically promoted endothermic 
reaction of carbon dioxide and hydrogen. The carbon dioxide and hydrogen 
are provided by mixed gas containing predominantly carbon dioxide and 
hydrogen which is produced in a subsequent step of the process and 
conveyed to heat exchanger 94 by conduit 154. Normally the mixed carbon 
dioxide-hydrogen rich gas to be reacted will flow preferably in a 
counter-current fashion to the raw gas from the gasifier. However, any 
flow arrangement may be used as long as the temperature of the gas leaving 
the gasifier is, at a given point along the axis of flow, higher than the 
temperature of the carbon dioxide-hydrogen rich gas. 
As carbon dioxide reacts with hydrogen to form carbon monoxide and water 
via the reverse gas shift reaction, it is important to give due 
consideration to means of preventing the formation of carbon (soot) which 
can occur as the gas is heated. A common well-known mechanism by which 
carbon can form is described by the reaction 
EQU 2CO.fwdarw.CO.sub.2 +C Eq. 4 
This reaction is discouraged by employing high temperatures and, for the 
typical carbon monoxide and carbon dioxide partial pressures which are 
encountered in the practice of the invention, carbon will not form above 
temperatures ranging from 850.degree. to 950.degree. F. (454.degree. C. to 
510.degree. C.). Therefore, to prevent the possibility of carbon formation 
upon the catalyst surfaces, the invention features the use of two 
treatment stages within heat exchanger 94. The first stage 96 is a heating 
stage wherein the mixed gas, which has a negligible carbon monoxide 
content, is first heated without the use of a catalyst to a temperature 
greater than the temperature at which carbon can theoretically form within 
the second stage 98, which is a catalyst-containing reaction stage. The 
catalyst in the second reaction stage is preferably a catalyst packed tube 
through which the mixed gas flows while in indirect contact with the hot 
reducing gas. The catalyst is any conventional water gas shift reaction 
catalyst, for example, 85 weight percent of Fe.sub.2 O.sub.3 and 15 weight 
percent of Cr.sub.2 O.sub.3, to convert the carbon dioxide and hydrogen 
into carbon monoxide and water. Alternatively, a cobalt-molybdenum shift 
catalyst may be used. Alternatively, ceramic type catalyst commony used in 
the steam reforming of natural gas may be used, for example, the catalyst 
available from Catalysts and Chemicals, Inc. under the trade designation 
"C11-9" could be used. The mixed gas flows into the first stage 96 and is 
in indirect contact with the raw gases from the gasifier and is heated to 
a temperature in the range of about 850.degree. F. (454.degree. C.) to 
950.degree. F. (510.degree. C.) and then flows into the second stage of 
the heat exchanger and through the packed catalyst tube. Here the carbon 
dioxide and hydrogen in the mixed gas react to produce carbon monoxide and 
water to yield a carbon monoxide-containing gas by Equation 1. The heat 
for this endothermic reaction is provided by the sensible heat of the raw 
gas that indirectly contacts the mixed gas in the presence of the 
catalyst. 
The cooled raw gas leaves the heat exchanger via conduit 100 at a 
temperature in the range from about 600.degree. F. to about 1000.degree. 
F. (316.degree. C. to 538.degree. C.) and passes to steam generator 102 
wherein most of the remaining sensible heat of the gas is regained in the 
form of steam. The cooled raw gas leaves the steam generator at 
temperatures ranging from about 250.degree. F. to about 450.degree. F. 
(121.degree. C. to 232.degree. C.) and then is scrubbed of particles and 
compressed, if necessary, in Particle Removal and Compression Zone 106. 
The particles are removed from zone 106, as is the water, via conduits 108 
and 110, respectively. 
The cooled scrubbed and compressed gas leaves zone 106 via conduit 112 to 
Acid Gas Removal Zone 114 wherein sulfurous compounds, hydrogen sulfide 
and carbon oxysulfide and unavoidably a portion of carbon dioxide (usually 
around 10%), are removed by either the Rectisol, Purisol or Selexol 
physical absorption process. The recovered gases from the acid gas removal 
zone are sent to a sulfur recovery unit 118 via conduit 116. In the sulfur 
recovery unit, which is preferably a Claus process, elemental sulfur is 
recovered in conduit 120. Any water removed in the acid gas removal zone 
is removed from the process by conduit 122. 
Desulfurized gas leaving the acid gas removal zone via conduit 124 is 
treated in Carbon Dioxide and Water Removal Zone 126 for removal of carbon 
dioxide, preferably by the absorption with chilled methanol. Residual 
water vapor will also be removed simultaneously with the carbon dioxide 
and this water is conveyed to conduit 122 for removal from the process. 
The gas removed from the carbon dioxide and water removal zone contains 
chiefly carbon monoxide and hydrogen. This gas is conveyed by conduit 128 
to a Carbon Monoxide Recovery Zone 130. Herein the first portion of the 
carbon monoxide product from the applicant's improved process is 
recovered, preferably by the "Cosorb" process available from Tenneco 
Chemicals, Inc. The carbon monoxide product gas is removed from the carbon 
monoxide recovery zone via 132. The remaining gas removed from the carbon 
monoxide recovery zone is rich in hydrogen and is preferably conveyed via 
conduit 134 to Hydrogen Purification Zone 136 wherein any nitrogen and 
argon is removed and conveyed from the process via conduit 138. Employing 
this hydrogen purification step minimizes the impurity content of gas 
stream circulated through the process and further minimizes the amount of 
purge stream which must be taken for deaccumulation of inerts. 
The hydrogen-rich gas from the hydrogen purification zone is conveyed via 
conduit 140 to a high pressure compressor assembly 142 wherein it is mixed 
with carbon dioxide from the carbon dioxide and water removal zone which 
is conveyed to zone 142 by conduit 144. Additional carbon dioxide can be 
introduced into the process from an external source by conduit 146 which 
introduces the carbon dioxide into conduit 144. The imported carbon 
dioxide equates to the carbon dioxide fed into the gasifier plus the 
carbon dioxide removed in the acid gas removal zone plus carbon dioxide to 
be ultimately reacted catalytically with available hydrogen plus any minor 
carbon dioxide losses, e.g., leaks, less the carbon dioxide contained in 
the gas leaving the gasifier. This imported carbon dioxide may come from 
any available source and preferably should contain 2% or less of gases 
which are inert to the process. This carbon dioxide could be recovered 
from any remotely available combustion gas or could be produced 
synthetically, as by the reaction of a mineral acid with limestone. For 
direct ore reduction application there would rarely be an instance when 
carbon dioxide would not be available for import to the process. This 
occurs because carbon dioxide is generated in the reduction process, e.g., 
EQU Fe.sub.2 O.sub.3 +3CO.fwdarw.2Fe+3CO.sub.2 Eq. 5 
on an equimolar basis to the amount of carbon monoxide reacted. For 
bituminous coal, typically only 30% or less of the carbon monoxide 
generated in the reduction process need be recovered for return to the 
carbon monoxide production process. Before the internal and external 
sources of CO.sub.2 that are conveyed in conduit 144 are delivered to the 
high pressure compressor assembly 142, a portion of the carbon dioxide is 
diverted via conduit 148 to compressor 150 and then on to the gasifier via 
conduit 86. The portion of carbon dioxide diverted to be introduced into 
the gasifier is generally in the range of an amount greater than 0 to 
about 50% and typically around 30% of the total carbon dioxide contained 
in conduit 144 before conduit 148 begins. In addition to carbon dioxide 
and hydrogen being introduced into zone 142, recycled gas from the carbon 
monoxide catalytic reaction loop is also introduced into zone 142 by 
conduit 152. The carbon monoxide catalytic reaction loop includes both 
zones 96 and 98 of heat exchanger 94, conduit 156, steam generator 158, 
conduit 160, Water Condensation and Gas Dehydration Zone 162, conduit 164, 
Carbon Monoxide Recovery Zone 166, conduit 152, High Pressure Compressor 
Assembly 142, and conduit 154. 
Carbon dioxide, hydrogen and recycled gas from the catalytic reaction loop 
are introduced to appropriate stages of a high pressure compressor 
assembly for delivery of the resulting mixture via conduit 154 to the 
first stage 96 of the heat exchanger 94. Typically, the gas in conduit 154 
of the carbon monoxide catalytic reaction loop is delivered at a pressure 
ranging from about 20 to about 175 atmospheres absolute, thereby to 
enhance the heat transfer rates and/or reaction rates of the first stage 
96 (heating zone) of the heat exchanger and second stage 98 (catalytic 
reaction zone) of the heat exchanger. The compressor assembly 142 would 
not be equipped with an after-cooler to thereby retain a portion of the 
heat of compression and hence reduce the heat load required in zone 96. 
Present technology permits the gas in conduit 154 to leave the compressor 
at temperatures from up to 450.degree. F. (232.degree. C.) to about 
500.degree. F. (260.degree. C.) 
The gas delivered to the first stage 96 is heated within this stage to a 
temperature ranging from about 850.degree. F. to about 950.degree. F. 
(454.degree. C. to 510.degree. C.) and then passes to the catalyzed 
reaction stage 98 wherein the gas is further heated to temperatures in the 
range from about 1300.degree. F. to about 1600.degree. F. (704.degree. C. 
to 871.degree. C.) where the catalyst is typically composed of 85 weight 
percent of Fe.sub.2 O.sub.3 and 15 weight percent of Cr.sub.2 O.sub.3 
which is packed in the tube through which the gas flows in the second 
stage. In the second stage the carbon monoxide is chemically formed at the 
same rate at which available hydrogen is generated from the gasifier. 
The carbon monoxide-containing gas leaving the catalyzed reaction stage 98 
flows via conduit 156 to steam generator 158. The flow of boiler feed 
water into steam generator 158 and steam generator 102 via conduit 159 and 
103, respectively, as well as the flow of steam or hot water through steam 
generators 102 and 158 is preferably integrated so that superheater coils 
are located within the steam generator 158 since the sulfur-free gas in 
conduit 156 would be less damaging to the tubes of the superheater, 
thereby requiring less periodic maintenance. The carbon 
monoxide-containing gas leaves the steam generator 158 at temperatures 
ranging from about 300.degree. F. (149.degree. C.) to about 500.degree. F. 
(260.degree. C.) by conduit 160. This gas is introduced to a water 
condensation and gas dehydration zone 162. Water is then removed by 
cooling the gas, and extensive drying of the gas is performed by 
absorption with triethylene glycol, where a suitable azeotropic 
distillation agent like iso-octane can be used. 
Dehydrated carbon monoxide-rich gas is removed from zone 162 in conduit 164 
and sent to Carbon Monoxide Recovery Zone 166 to produce the second 
portion of the carbon monoxide-rich gas product of applicant's invention. 
This second portion of carbon monoxide product is removed from the carbon 
monoxide recovery zone by conduit 168 and is combined with the first 
carbon monoxide product in conduit 132. Preferably the combined carbon 
monoxide product is conveyed via conduit 132 to an ore reduction process. 
The gas leaving the carbon monoxide recovery zone 166 via conduit 152 is 
recycled to the catalytic reaction loop. From conduit 152 there is an 
inert purge 170 to remove any inert gases from the recycle gas to avoid 
the buildup of these inert gases. The gas in conduit 152 contains 
unreacted hydrogen, unreacted carbon dioxide and a small amount of 
methane. 
The gas in conduit 154 fed to the first stage 96 of the heat exchanger 94 
will be composed principally of carbon dioxide and hydrogen, normally in 
approximately an equimolar ratio, along with typically 5% methane and less 
than 3% total carbon monoxide, water vapor and inerts. The gas in conduit 
156 leaving the reverse water gas shift catalytic reaction zone will 
contain the same components as the gas in conduit 154, except additional 
carbon monoxide and water vapor with a corresponding equimolar reduction 
in carbon dioxide and hydrogen will be present. The concentrations of the 
components in the gas in conduit 156 will approximately correspond to 
those attainable upon equilibrium of the gas at the temperature and 
pressure of this gas. The methane present in the gas is formed by the 
reactions: 
EQU CO.sub.2 +4H.sub.2 .revreaction.CH.sub.4 +2H.sub.2 O Eq. 6 
EQU CO+3H.sub.2 .revreaction.CH.sub.4 +H.sub.2 O Eq. 7 
The content of methane reaches a steady-state level where the methane 
contained in feed gas in conduit 154 equates to the equilibrium amount of 
methane in the exit gas in conduit 156. Thus, there is ordinarily no net 
formation of methane. An exception occurs whenever the raw gas exiting the 
gasifier by conduit 90 contains significant amounts of methane, which 
ordinarily is not the case since the gasifier 82 is preferably operated at 
a flame temperature of about 3500.degree. F. Methane present in the raw 
gas would appear in the hydrogen-rich gas conveyed by conduit 140 into the 
CO catalytic reaction loop. Upon entering the CO reaction loop, this 
methane is reacted, endothermically, via the reverse reactions of 
reactions 6 and 7 to thereby form additional carbon monoxide or hydrogen 
which can in turn react with carbon dioxide via reaction 1. 
A feature of the preferred embodiment of the process of applicant's 
invention involves making sure that the gas in conduit 154, which is fed 
into the heating stage 96 of heat exchanger 94, is not of such a rate that 
insufficient sensible heat is available in the gas from conduit 90 
containing the raw gas from the gasifier, so that the desired heating of 
the gas and endothermic formation of carbon monoxide by the reverse water 
gas shift catalyst reaction would not be achieved. This situation is 
prevented by insuring that the steady-state concentration of methane in 
the reaction loop does not exceed approximately 40% by volume. This high 
level methane can be avoided by designing the process to insure that the 
gas in conduit 156 is kept at a temperature of at least 1300.degree. F. 
(704.degree. C.) for the range of pressures of about 20 to about 175 
atmospheres that are encountered. 
The procedure for determining the components and their amounts in the gas 
in conduit 154 which is fed to the first heating stage 96 of heat 
exchanger 94 of the process involves first establishing the amount of 
carbon dioxide which is to be chemically formed in the reaction zone 98 
and then to compute in a straightforward manner the feed gas in conduit 
154 subject to the constraints of a mass balance and equilibrium 
conditions for the gas in conduit 156. 
In order to further illustrate the invention, attention is directed to the 
following comparative examples. 
The following comparative examples are based on the gasification of a 
bituminous coal of Kentucky origin. After drying and pulverization, the 
coal fed to the gasifier has the following ultimate analysis: 
______________________________________ 
Weight Percent 
______________________________________ 
Carbon 73.8 
Hydrogen 5.0 
Nitrogen 1.4 
Sulfur 3.2 
Oxygen 5.3 
Ash 9.3 
Moisture 2.0 
100.0 Total. 
______________________________________ 
A high temperature entrained-flow type gasifier is to be employed and is 
designed with a gas production capability of 5,415.0 lb. moles/hr., or 
34,250 standard cubic feet per minute. 
EXAMPLE 1 
The reactants introduced into the gasification process of the prior art 
include coal, oxygen, and steam. Table I shows the amounts of reactants, 
the components and amounts of the raw gas produced in the gasifier and 
total amounts of carbon monoxide, carbon dioxide and hydrogen produced. 
TABLE I 
______________________________________ 
Gasifier Feeds, lbs/hr 
Coal 50,381 
Oxygen (98% purity) 
46,385 
Steam 19,912 
Carbon Dioxide 0 
Total 116,678 
______________________________________ 
Raw Gas Produced: 
lb/hr lb-moles/hr vol. % 
______________________________________ 
Carbon Monoxide 69,471 2481.1 45.82 
Carbon Dioxide 20,240 460.0 8.49 
Hydrogen 3,194 1597.2 29.50 
Water 13,885 771.4 14.25 
Nitrogen and Argon 
1,537 54.9 1.01 
Hydrogen Sulfide 1,629 47.9 0.88 
Carbonyl Sulfide 150 2.5 0.05 
Total 110,106 5415.0 100.00 
Ungasified Coal and Ash, lb/hr 
6,572 
Total CO Produced 
lb/hr 69,471 
lb/lb coal 1.379 
lb-moles/hr 3,481 
Total CO + H.sub.2 Produced 
lb-moles/hr 4078.3 
lb-moles/lb coal 0.0809 
______________________________________ 
EXAMPLE 2 
The reactants introduced into the gasification process of the prior art, 
known as the KT Gasification Process, include coal, oxygen, and carbon 
dioxide. Table II shows the amounts of reactants; the components and 
amounts of the raw gas produced in the gasifier; and total amounts of 
carbon monoxide, carbon dioxide, and hydrogen produced that are used or 
produced in the prior art gasification process. 
TABLE II 
______________________________________ 
Gasifier Feeds, lbs/hr 
Coal 55,187 
Oxygen (98% purity) 
50,685 
Steam 0 
Carbon Dioxide 30,360 
Total 136,232 
______________________________________ 
Raw Gas Produced: lb/hr lb-moles/hr 
vol. % 
______________________________________ 
Carbon Monoxide 96,631 3451.1 63.73 
Carbon Dioxide 20,240 460.0 8.49 
Hydrogen 2,057 1028.4 18.99 
Water 6,485 360.3 6.66 
Nitrogen and Argon 
1,680 60.0 1.11 
Hydrogen Sulfide 1,782 52.4 0.97 
Carbonyl Sulfide 168 2.8 0.05 
Total 129,043 5415.0 100.00 
Ungasified Coal and Ash, lb/hr. 
7,189 
Total CO Produced 
lb/hr 96,631 
lb/lb coal 1.751 
lb-moles/hr 3,451 
Total CO + H.sub.2 Produced 
lb-moles/hr 4479.5 
lb-moles/lb coal 0.0812 
______________________________________ 
EXAMPLE 3 
This example illustrates and compares the gasification process of the 
present invention to those of Examples 1 and 2. The reactant feeds for the 
gasifier are the same as those in Example 2. Table III shows the 
components and amounts of the mixed gas conveyed to the indirect heat 
exchanger, the components and amounts of gas contained in the carbon 
monoxide-rich gas coming from the heat exchanger after the reverse water 
gas shift reaction, the total amount of carbon monoxide produced, and the 
overall amount of carbon dioxide imported to the process. 
TABLE III 
______________________________________ 
Mixed Gas lb/hr lb-moles/hr 
vol. % 
______________________________________ 
Carbon Dioxide 89,593 2036.2 47.24 
Hydrogen 4,114 2056.8 47.71 
Methane 3,482 217.6 5.05 
Total 97,189 4310.6 100.00 
______________________________________ 
Carbon Monoxide-Rich Gas 
lb/hr lb-moles/hr 
vol. % 
______________________________________ 
Carbon Monoxide 28,795 1028.4 23.86 
Hydrogen 2,057 1028.4 23.86 
Carbon Dioxide 44,343 1007.8 23.38 
Water Vapor 18,512 1028.4 23.86 
Methane 3,482 217.6 5.04 
Total 97,189 4310.6 100.00 
Carbon Monoxide Recovered, 
lb-moles/hr 1028.4 
Overall Carbon Dioxide Imported, 
lb-moles/hr 1304.4 
______________________________________ 
The amount of carbon monoxide recovered in Table III (1028.4 lb-moles/hr) 
is added to the amount produced in Table II (3451.1 lb-moles/hr), yielding 
a total amount of carbon monoxide produced (4479.5 lb-moles/hr) by the 
process of the present invention. The total amount of carbon monoxide 
produced in accordance with the invention, when the combination of CO from 
Examples 2 and 3 is taken, is approximately 30 percent higher than the 
carbon monoxide produced in situ within the gasifier as in Example 2. The 
total carbon monoxide produced in accordance with the invention is about 
80 percent higher than produced in situ within the gasifier as in Example 
1. 
Table IV shows a heat balance across the heat exchanger 94 of FIG. 2. 
TABLE IV 
______________________________________ 
Million of Btu's/hr 
______________________________________ 
Heat In 
Enthalpy of raw gas @ 2000.degree. F. 
101.9 
Enthalpy of mixed gas @ 450.degree. F. 
13.6 
Total Input 115.5 
Heat Out 
Enthalpy of carbon monoxide-rich 
gas @ 1500.degree. F. 55.1 
Enthalpy of cooled raw gas @ 910.degree. F. 
41.0 
Standard endothermic heat of reaction 
for 1028.4 lb. moles of CO.sub.2 reacting 
(CO.sub.2 + H.sub.2 .fwdarw. CO + H.sub.2 O) 
18.2 
Heat Losses 1.2 
Total Output 115.5 
______________________________________ 
In the prior art method, the raw gas would be sent directly to a waste heat 
recovery unit thereby affording 101.9 million Btus per hour of enthalpy 
valve for generation of steam. Instead, with this invention, the cooled 
raw gas would be sent to a steam generator (41.0 million Btu per hour) as 
would the carbon monoxide-rich gas (55.1 million Btu per hour). The total 
heat available for steam generation in accordance with the invention 
(41.0+55.1=96.1 million Btus per hour) is still about 94% of the heat 
available in practice with the prior art (101.9 million Btus per hour). 
Thus the invention represents a very efficient means of supplying the 
necessary endothermic heat for the reverse water gas shift reaction. 
The foregoing has described a process for the gasification of carbonaceous 
materials where the yield of carbon monoxide is increased. In a typical 
entrained gasification process the gas produced is composed of carbon 
monoxide and hydrogen in major quantities, and carbon dioxide, hydrogen 
sulfide, water and methane in minor quantities. By the process of the 
present invention the carbon monoxide produced by gasification of 
carbonaceous materials equals the amount of carbon monoxide normally 
produced plus an amount of carbon monoxide that is equal to the amount of 
available hydrogen in the gas from the gasifier. This increased yield is 
accomplished in an efficient, safe, and economical manner and provides a 
carbon monoxide-rich gas for ore reduction processes or chemical feedstock 
applications.