9 Coal Gasification for Hydrogen Manufacturing W. G. SCHLINGER—Texaco Research Center, P.O. Box 400, Montebello, CA 90640
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J. FALBE—Ruhrchemie AG Oberhausen, West Germany R. SPECKS—Ruhrkohle AG Essen, West Germany
The demand for non-polluting or clean fuels to meet our ever-increasing requirements for energy is continuing to expand. This demand is superimposed on a world which over the years has preferentially exploited its clean energy reserves -- natural gas and high gravity low sulfur crude oils. As a result, there is continuing pressure on development of technologies to convert the remaining less desirable fuels -- coal, high sulfur crude, tar sand oil, etc., into clean non-polluting energy sources. This pressure is particularly strong in the United States and Japan.
In the United States and Japan, as well as other industrialized countries, the regulating agencies have established stringent air and water pollution standards. Perfecting new technologies that will meet these pollution requirements is a real challenge to the process developer. Background. At the Texaco Montebello Research Laboratory in California, these challenges were recognized many years ago. Since the late 1940's this Laboratory has been carrying out research and development work on environmentally acceptable processes for converting heavy residual oils, tars, pitches, coal and coal liquifaction residues into synthesis gas. Synthesis gas, an approximately 50-50 mixture of hydrogen and carbon monoxide, can be efficiently converted to hydrogen, a much needed reactant in nearly all heavy fuel conversion technologies, using the long time commercially proven water gas shift reaction. Texaco's research efforts over the years have led to the development of two commercially viable processes The Texaco Synthesis Gas Generation Process for gasification of fluids which are pumpable at temperatures
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178
HYDROGEN: PRODUCTION AND MARKETING
as high as 600°F and The Texaco Coal Gasification
Process for gasification of solid carbonaceous mate-
rials which are fed to the gasifier as a slurry in water
or
other
carrier
fluid.
Texaco Synthesis Gas Generation Process. For many years. The Texaco Synthesis Gas Generation ProDownloaded by UNIV OF CALIFORNIA SANTA CRUZ on December 16, 2015 | http://pubs.acs.org Publication Date: March 26, 1980 | doi: 10.1021/bk-1980-0116.ch009
cess (3^, 2_, 3^) has been available for licensing throughout the world as an efficient technology for converting high-sulfur residual petroleum fuels and tars into synthesis gas. More than seventy-five plants have been built in twenty-two countries since
the first units came on stream in 1955. Most of these facilities have been associated with manufacture of
ammonia, methanol, and oxo-chemicals . The synthesis gas generation process involves reacting the residual fuel with a controlled amount
of high-purity oxygen and steam at pressures ranging from 300-1200 psi with the net production of hydrogen and carbon monoxide along with lesser amounts of carbon dioxide and methane.
The reactants are intro-
duced through a special burner at the top of a refractory lined pressure vessel or generator, and the desired autho-thermal non-catalytic reactions occur
rapidly at temperatures ranging from 2000-3000°F.
Small amounts of unconverted fuel or soot are recycled to extinction. The approximate enthalpy changes at 60°F of the basic exothermic and endothermic chemical
reactions are shown in Figure 1.
Sulfur present in
the fuel is converted to H2S and small amounts of COS, and organic nitrogen is reduced to elemental nitrogen
and ammonia.
The hot exiting gases are cooled through
appropriate heat recovery equipment and treated as
necessary to produce the desired product, or the hot gases are quenched in water in order to increase the steam content of the gas so that it can be fed directly to a shift conversion reactor to convert the carbon monoxide to hydrogen, if hydrogen is the desired end product. During shift conversion, the small
amount of COS in the gas is hydrolyzed to H2S .
Sub-
sequently, the gas is treated for removal of C02, H2S
and other undesirable impurities to produce a hydrogen purity as dictated by the downstream hydrogen con-
suming process. A wide variety of commercially proven gas treating technologies are available for the downstream gas purification.
Nearly thirty years ago it was recognized that fuel for the process could just as well be coal, and work on process development for production of synthesis gas from coal was initiated. At that time.
In Hydrogen: Production and Marketing; Smith, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9. schlinger et al.
Coal Gasification
179
economic incentives for using coal in place of petro-
leum were not very strong, and the process development proceeded on a low priority basis.
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Texaco Coal Gasification Process.
In the late
sixties, the solids gasification process finally evolved to its present form and the energy crisis brought on by the 1973 Arab oil embargo greatly accelerated the development of the Texaco Coal Gasification Process .
The coal gasification process for hydrogen manufacture involves a slagging entrained down flow gasifier fed with oxygen and a concentrated slurry of ground coal in water. The same type of refractory lined gasifier is employed as in the earlier oil gasification process, except provision is made to remove solidified slag through a water sealed lockhopper system.
Optionally, the gasifier may be fed with a slurry of coal in oil and a controlled amount of reaction
temperature moderator, such as steam. Facilities for recycling unconverted coal are also provided. A schematic flow diagram of the process is shown in Figure 2.
The process is capable of efficiently gasifying a wide variety of caking and non-caking bituminous and sub-bituminous coals, as well as petroleum coke.
Referring to Figure 2, raw coal is first fed to a grinding section where the coal is ground either wet or dry to a carefully controlled size distribution.
Control of the size distribution is important in order to maximize the coal concentration in the resultant
slurry. From the slurry preparation tank the coal is then fed through a specially designed burner where it is mixed with oxygen and additional moderator if
required. Upon leaving the refractory lined gasifier the gases are quenched in hot water and then the crude
raw synthesis gas is contacted with additional water in a venturi or orifice type scrubber at gasifier pressure to remove entrained particulates. Water removed from the scrubbing system and the quench chamber is recovered through a settler where the particulate matter is extracted and recycled to the gasifier. After water contacting, the particulate
loading in the raw gas is less than 1 mg/Nm3 .
The
water scrubbed gas is now ready for direct injection into the shift conversion section.
Although a variety
of older catalysts are available for shifting sulfur containing synthesis gas, the last ten years has seen
the development of high activity rugged cobalt moly
In Hydrogen: Production and Marketing; Smith, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
180
HYDROGEN: PRODUCTION AND MARKETING
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~Ù.HAT60°F BTU/LB-MOL
CH + H20
>¦ CO
+ 3/2H2
+49,000
CH +1/20 2
> CO
+ 1/2 H 2
-55,000
CH + 5/402
>- C02 + l/2H20
H20+ CO
*- CO 2 f
-229,000
Hg
-18,000
Figure 1. Gasification reactions
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