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Coal Liquefaction
There are several avenues which can be employed to produce liquids from
coal. Figure 8-1 summarizes the various paths of converting coal to liquid fuels,
which generally are classified as either indirect or direct liquefaction. Indirect
liquefaction, which is already commercialized, involves gasification of the coal
followed by chemical processing at high pressure to yield a variety of liquid hy
drocarbons. One advantage of indirect liquefaction is that it yields a product mix
with a high percentage of liquid transportation fuel (e.g., gasoline), thus satisfy
ing one of America s primary energy needs.
The second approach is direct liquefaction, where the coal is hydrogenated un
der high pressures to form a liquid plus a solid residue. While this latter approach
has the attractive features of higher thermal efficiency and potentially lower pro
cessing costs than for indirect liquefaction, significant research and development
problems remain to be solved. Commercialization of these processes will proba
bly not occur until after 1990. Direct liquefaction also does not yield a high
percentage of gasoline but rather produces heavier components which do not
match up well with current fuel demands.
Given the choice between liquid and gaseous synfuel products from coal, coal
liquids have several distinct advantages over synthetic natural gas:
I. Liquefaction requires less chemical transformation and hydrogenation than
high Btu gasification. Since the HIC ratio of coal is 0.8, less hydrogen is
required to form a liquid
H C
2) than methane
H C
4). This should
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oal Liquefaction 95
Indirect liquefaction of coal generally follows one of three process schemes:
1. Fischer- Tropsch
2. Methanol synthesis
3. Catalytic conversion of methanol to gasoline
Normally Schemes 2 and 3 are integrated in the same plant in order to maximize
production of gasoline. Using Fischer- Tropsch synthesis, it is possible to obtain
high yields of both low and high molecular weight products, but the selectivity
towards intermediate weight products such as gasoline or diesel fuel is not good.
In order to maximize gasoline product and minimize heavy ends production,
methanol is first produced, followed by Scheme 3 using the Mobil M process.
Fischer Tropsch Processing
In 1925, the German chemist team of Franz Fischer and Hans Tropsch devel
oped a catalytic process to produce a variety of fuels from reacting carbon mon
oxide with hydrogen. This technology was used in several German plants during
World War II for the manufacture of gasoline and other products. After World
War II, a pilot plant was operated by the U.S. Bureau of Mines in Missouri, and
a commercial plant (7,000 bbllday) was operated during the 1950s in Browns
ville, Texas. This latter plant suffered a number of operational difficulties and
was shut down when cheap sources of natural gas and oil became available.
In 1980 the only major coal liquefaction plant operating on a commercial scale
in the world was the Sasol (Afrikaans acronym for South African Coal, Oil, and
Gas Corporation) I plant in Sasolburg, South Africa, which uses Fischer-Tropsch
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9
Coal Processing and Pollution Control
8-2
8-3)
can occur. 3,4
addition the above products can undergo secondary isomerization
and/or cyclization to form branched-chain and aromatic compounds. The selec
tivity and product mix of a given process is determined by the reactor configura
tion, catalyst composition, H2/CO feed ratio, and operating conditions tempera
ture and pressure). The types of catalysts employed commercially include iron,
cobalt, nickel, ruthenium, and zinc, and often contain promoters such as potas- ~-/
sium oxide) in small percentages.
For instance, if the fixed-bed Arge) process is operated with an alkali-rich
iron-based catalyst, a low H2/CO feed gas, and a low temperature, the wax selec
tivity can be increased from the normal 50 to above 75 . On the other hand,
operating the fluidized bed Kellogg Synthol) with an iron catalyst of low alkali
content and hydrogen-rich feed gas increases the methane selectivity from 10
to about 80 . Table 8-1 gives the typical product distribution for fixed- and
fluid-bed reactors. A wide product distribution is an inherent feature of the Fis
cher-Tropsch process. The maximum yields of gasoline and diesel fuel which
can be obtained in normal Fischer-Tropsch operation are about 40 and 18 ,
respectively. The normal H2/CO ratio is about 2: 1, with a temperature range of
450°F to 700°F and pressures from 5 to 40 atm.
South Africa the liquefaction process is usually operated to give maximum
gasoline selectivity. To meet octane specifications the required amount of gaso
line is hydrorefined to saturate olefins and remove all traces of oxygen-contain
ing compounds, followed by catalytic reforming. Hydrogenation is carried out
because straight-chain hydrocarbons produced by primary synthesis make a poor
quality gasoline. contrast, a good quality diesel fuel requires mainly straight
chain paraffins. Sasol II is designed to produce a mix of products: methane, light
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Coal Liquefaction 97
Table 8
Product Distribution in Sasol 13,4
Product
Methane
CI
Light gas C,-C.
Gasoline
Cs-C12
Light distillate
CIJ-CI9
Soft wax
C,o-C30
Hard wax
C30
Oxygenates
Methanol Synthesis
Fixed Bed
RG
5
13
15
23
18
4
Fluid Bed
SYNTHOL
10
33
39
5
4
2
7
Methanol has the potential to be used directly as a transportation fuel, I but it
can also be converted to gasoline. The selective synthesis of methanol from CO
and H2 involves the following reaction:
8-4
Carbon monoxide and hydrogen may react in many other ways, but elimination
of the side reactions is accomplished by using very selective catalysts and appro
priate operating conditions. By minimizing the undesirable reactions, the synthe
sis reaction will proceed until equilibrium is reached. The equilibrium methanol
content in the effluent mixture decreases with increasing temperature and in
creases with the square of the pressure. Two generic methanol synthesis pro
cesses, called low and high pressure, are used commercially. 5.6 The low pressure
process operates at a lower temperature than the high pressure process, using a
different catalyst. Its advantage is that lower compressor costs are achieved.
The synthesis gas prepared for methanol production from coal gasification can
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9 Coal Processing and Pollution Control
The use of carbon dioxide in the synthesis requires 50 more hydrogen than car
bon monoxide, thereby increasing the cost of gas compression. This disadvan
tage is compensated somewhat by elimination of the need to remove carbon diox
ide from the synthesis gas.
Preparation of the makeup gas synthesis gas) is the same for both the high and
low pressure processes, except sulfur removal is more rigorous in the low pres
sure case.7 The synthesis makeup gas might have the following composition:
Component
Hydrogen
Carbon Monoxide
Carbon Dioxide
Methane
Argon
Volume dry)
63.0
26.0
7.0
3.8
0.2
The hydrogen to carbon monoxide ratio from the gasifier is adjusted in a shift
reactor to achieve the above composition. Note that the ratio of 2: I for H2/CO is
not strictly required; generally a ratio between 2.3 to 2.5 is employed.
The high pressure process operates at about 5,000 psig. In large plants it is
economical to do all compression with centrifugal compressors. The minimum
capacity for such a plant is about 700 tons per day.6.7 The makeup gas is mixed
with the recycle stream in the last stage of the compressor and then proceeds to
the converter. Large plants typically use gas-quenched catalyst beds in the con
verter for temperature control. The converter outlet stream contains about 5
methanol by volume; the yield, based on CO
CO2 conversion, is approximately
95 -96 .
In the low pressure process developed by ICI see Figure 8-2), the makeup gas
is compressed to about 765 psig. It is then mixed with the recycle gas from the
synthesis loop and fed to the converter. The converter is similar to that used in
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Coal Liquefaction 199
NAPHTHA, SYNTHESIS GAS, ETC.
F EEOSTOCIC
(NAPHTHA OR
HYQROCARBON
GAS-C02)
CRUOE
ETHANOL
TAN
IMP\mITJ[S
HIGH-SOIL ING IMPURIT IES
Figure 8-2. The ICI low pressure methanol synthesis process.
extraction column. Thermal efficiencies for either methanol process are in the
50 to 55 range.
Gasoline Synthesis
Currently, there is only one commercially available process for the synthesis
of gasoline from methano1.4,s This is Mobil s MTG process. Methanol is con
verted via a reversible dehydration to form dimethyl ether and then olefins:
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oal rocessing and ollution ontrol
the temperature rise in the converter to a manageable level. About 80 of the
total heat of reaction is released in the conversion reactor. The reactor effluent is
condensed and the aqueous, liquid hydrocarbon, and gaseous phases are sepa
rated. Most of the gas is recycled. The converter may typically operate for 20
days before coking of the catalyst necessitates regeneration.
Table 8-2 gives material balance data for the Mobil M fixed-bed) process.
Pilot plant tests at the 4 barrel per day level have shown methanol conversion to
be very nearly stoichiometric, with 56 water and 43.5 hydrocarbons being
formed. About 75 of the hydrocarbons are in the gasoline fraction. In formulat
ing a gasoline of proper volatility, some of the n-butane formed is made part of ::-~
the gasoline. In addition, the remaining
C3
and
C4
gases, olefins, and isobutane
are alkylated to high-octane gasoline.8 Including the alkylation step raises the
yield of gasoline to nearly 90 . The following are typical properties of the syn
thetic gasoline:
Molecular Weight
Specific Gravity
Research Octane Number
irect iquefaction
93
0.720
96.8
Direct liquefaction requires addition of hydrogen to coal so that the
H
ratio
is increased to the range where the product is a liquid. Liquids produced are of
two principal types:
I. A synthetic, largely aromatic, crude suitable for further processing to gaso
line and other products.
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Coal Liquefaction 2 1
Table 8 2
Product Distribution for Mobil MTG Process
Operating Conditions:
Converter Outlet Temp.
Pressure
Recycle Ratio
Space Velocity
Product Distribution:
Yields: wt of Methanol Charged
Methanol Ether
Hydrocarbons
Water
CO,
CO2
Coke Others
Total
Hydrocarbon Distribution
Light Gas
Propane
Propylene
I-Butane
N-Butane
Butenes
Cs Gasoline
Total
Gasoline
ncluding Alkylate)
LPG
Fuel Gas
Total
Source: Mobil Oil Corporation
780°F
315 psig
9:1
2.0
0.0
43.4
56.0
0.4
0.2
100.0
1.4
5.5
0.2
8.6
3.3
l.l
79.9
100.0
85.0
13.6
1.4
100.0
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Coal Processing and Pollution Control
Figure 8 3 Methanol-to-gasoline route.
The design of a coal liquefaction process has the objective of generating a
product which has a composition as close as possible to existing liquid fuels.
This implies that the hydrogen to carbon ratio must be increased by adding hy
drogen ; other design objectives include removal of sulfur and nitrogen com
pounds and mineral matter. Liquefaction is accompanied by evolution of gaseous
hydrocarbons, water vapor, ammonia, and hydrogen sulfide not all nitrogen and
sulfur is released from the coal, however .
The liquefaction process is intimately related to low temperature pyrolysis4 in
the range between 350°C and 550°C.
In
fact, for most liquefaction processes,
pyrolysis is the rate-determining step. Pyrolysis reactions include loss of hy
droxyl groups, dehydrogenation of some aromatics, cleavage of methylene
bridges, and rupture of alicyclic rings, all leading to generation of free radical
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Coal Liquefaction 203
ture carbonization, pyrolysis, solvent extraction, hydrogenation) affects the
product yields for the same coal.
15
The large variation in light and residual oil
yields is noteworthy.
Most coals when contacted with organic solvents imbibe fluid, swell, and dis
solve to some extent in the solvent. A solvent such as pyridine can dissolve a
large percentage of coal at low temperature, and its behavior is non-selective,
i.e., the residue resembles the dissolved material. The dissolved coal may be a
true solution or a colloidal suspension.
At temperatures above 350°C, a solvent such as anthracene oil can be em
ployed to dissolve the coal. This solvent promotes thermal depolymerization re
actions and increases liquid yields. A hydrogen atmosphere high pressure) can
further increase th~ yields and quality of the extract by stabilizing the free radi
cal reactions, thus reducing the molecular weight of the product. These hydro
genation reactions are catalyzed by the mineral matter of the coal as well as by
Table 8-3
Composition of Coal Liquids
Hydrocarbons
N-paraffins
Isoparaffins
Cycloparaffins
Benzene
Naphthalene
Tetralin
Anthracene
Phenanthrene
Acenaphthylene
Pyrene
Chrysene
Fluorene
Oxygen Compounds
Phenol
Indanol
Dibenzofuran
Benzonaphthofuran
Sulfur Compounds
Thiophene
Benzothiophene
Dibenzothiophene
Nitrogen Compounds
Indole
Quinoline
Carbazole
Acridine
Benzacridine
Dibenzacridine
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4 oal rocessing and ollution ontrol
added external catalysts. Hydrogenation of the free radicals can also be enhanced
by using a hydrogen donor solvent such as tetralin. A hydrogen donor solvent
reacts with molecular gas-phase hydrogen and then transfers the hydrogen to
coal. The lower molecular weight liquefaction products then are more easily dis
solved in the solvent. Tetralin as well as some other solvents provide hydrogen
molecules which are more mobile than hydrogen gas alone, thus allowing lower
operating pressures. In these solvents the extraction efficiency can approach
100 under laboratory conditions.
The products from liquefaction are difficult to characterize chemically. Other
means of characterizing these liquids must therefore be employed, inCiudingl3.14
_J
1. Elemental analysis
2. Density, API gravity, viscosity
3. Distillation properties
4. Distribution of acidic, basic, and neutral compounds
5. Aromatic, paraffinic, olefinic carbons
6. Solubility in various solvents pentane, benzene, pyridine)
irect iquefaction Processes
Liquefaction process research and development has been particularly active in
the United States during the past decade; 17-19here are presently no commercial
processes of this type. Table 8-5 lists the current development programs which
are being tested on a pilot scale 5 to 1,000 tons per day).IO These processes have
all shown enough promise to pass beyond the small bench scale to the pilot stage.
They may be grouped under the following headings:
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Coal Liquefaction
5
f Direct Coal Liquefaction Projects
Type
Process
eveloper
ocation
izeRC-I
Southern Company
ilsonville,
tons/day
ServicesL
ittsburg
Ft. Lewis
0 tons/day
Tacoma), WA
Oil)
H-Coal
ydrocarbon Catlettsburg,
50-600
Research, Inc.
tons/day
.S. Bureau of
ruceton, PA
.25 to 10
O
tons/day
SFonsolidation
Cresap, W VA
0 tons/day Coal Company now moth-
balled)
aytown, TX
50 tons/day
mothballed)
Note: See Chapter 6 for a discussion of pilot plants based on hydropyrolysis processes Toscoal,
Coalcon, CS/R).
Table 8 6
Comparison of Major Coal Liquefaction Processes1
SRC I
RC IIDS Coal
Pressure, psia
1,500,950,000,200
850
505050 40
0
400-70
76
00*4 95
5
704
2.4
.74.3.8-5.3
Recycle ofecycle ofecycle of
ecycle of
eactor
hydrogen-
eavylurry
ted solventistillate
Upflowpflowpflow, plug-
bullated-olumnlow tubular
ed cataly-
eactoreactor
ic reactor
Mineral
i-Mo for
o-Mo or
olvent
i-Mo
a-
tion
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Coal Liquefaction 7
organic sulfur. In most cases the residue will not satisfy a 70 sulfur removal
requirement. The overhead from the vacuum flash, the wash solvent, and light
liquids removed in other parts of the process are separated into I) a light C5 to
400°F liquid by-product, 2) a 400°F to 500°F boiling liquid, used as filter wash
solvent, and 3) a 500°F to 800°F boiling process solvent, which is recycled. Ta
ble 8-7 presents the typical product distribution for the SRC-I process. SRC-I
tests at Ft. Lewis and Wilsonville have indicated that the process is operationally
reliable except for mechanical problems with valves and solid/liquid filtration.
Some valves do not survive beyond one month of operation. Promising ap-
Table 8·7
Product Distribution for Solvent Refined Coal SRC-1 10
Typical SRC Composition:
C
H
N
o
S
Ash
HHV
Operating Conditions:
Temperature
Pressure
Coal Feed Rate
Solvent/Coal Ratio
Gas Feed Rate
Hz Cone. in Feed Gas
Typical Yields:
CI
87.7
5.3
1.2
5.0
<0.5
0.2
16,000 Btullb
800-900°F
1,000-2,500 psig
25-100 Ibthrtft3
1.5-3.0 weight basis)
15,000-30,000 scf/ton-coal
60-95 mol
Yield wt dry coal)
2.2
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8 Coal Processing and Pollution Control
proaches to replace leaf filters include continuous centrifugation and the Kerr
McGee critical solvent deashing process.
20
Another version of this process, called SRC-II, produces an all-distillate liquid
product at the expense of higher hydrogen consumption. This is done by increas-
ing the residence time and using a recycle slurry of catalytically active minerals,
such as iron sulfide pyrite), yielding 15 -20 gas CI-C4), 45 -50 distil-
late syncrude including 15 naphtha), and 35 -40 residue 5 -10 undis
solved coal, the rest SRC). The distillate yield is about 2.5 bbllton coal with a
hydrogen requirement of 5 of the coal weight.
20.21
The sulfur level of the SRC
usually satisfies the 70 removal standard. The SRC-II process eliminates the ,
solid/liquid separation step. Not all coals are suitable for SRC production, with
coal mineral matter believed to be one reason for high variability in process per
formance.
Consol Synthetic Fuels CSF . This process is an early example of the first
class of liquefaction processes, involving a combination of pyrolysis and hydro
genation. Hydrogen is usually supplied through a hydrogen donor solvent such as
tetralin, although sometimes a small amount of molecular hydrogen is added.
Ash is filtered or otherwise separated and the partially hydrogenated coal further
hydrogenated. The CSF process, shown in Figure 8-5, used a ZnCh catalyst at
4,200 psi and 465°C for this stage. The hydrogenated solvent was recovered for
recycle. The CSF process was operated previously at the 20-ton-per-day level,
HYDROCARBONS
HYDROCARBON
GASES TO REFINERY
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Coal Liquefaction 9
HYDROGEN GAS
COAL
HEAVY SYN.CRUDE
SYN. CRUDE
SLURRYING
95 C
EXTRACTION
380 C
SLURRY
SOLVENT
RECOVERY
LI G HT
Oil
Ii
SOLVENT
EXTRACT
HYDROGENATION
4200
psj
65 C
HYDROGEN
DISTillATION
GAS
RECYCLE SOLVENT
lOW
TEMPERATURE
CARBONIZATION
CHAR
HYDROGEN - DONOR SOLVENT
Figure 8-6. CSF process-synthetic crude from coal.
but has now been abandoned as a commercial candidate due to operational prob
lems, mainly in solid-liquid separation at high temperature and pressure.
I?
Exxon Donor Solvent EDS . This process is similar to the CSF process and
is now the leading commercial donor solvent candidate. The EDS process is de
signed to maximize liquid products. It has been operated at a pilot scale 1.0 ton
per day), and demonstration scale 250 tons per day) in Baytown, Texas. The
feed coal is crushed, dried, and slurried with hydrogenated recycle solvent see
Figure 8-6, References 10 and 22). This slurry is fed to the non-catalytic lique
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210 Coal Processing and Pollution Control
Table 8 8
Product Yields of EDS Process for Different Coals 10
Residence time, min
Yields, wt maf coal:
H2
H20
CO,
H2S NH3
C,-C3
gas
C.-IOOO°F liquid
IOOO°F bottoms
Illinois
bituminous
40
-4.3*
12.2
4.2
7.3
38.8
41.8
Wyoming
subbituminous
6
-4.6
22.3
0.9
9.3
33.3
38.8
Texas
lignite
25 4
-3.9
21.7
1.7
9.1
33.3
38.1
Negative values denote consumption
essentially all of the organic matter in the bottoms to liquid products and fuel
gas. Hydrogen for the process is produced by steam reforming of the light hydro
carbon gases. Alternatively, partial oxidation gasification or direct combustion
of the vacuum bottoms may be employed. In the current version of EDS, the
latter approaches are preferred over Flexicoking.
The total liquid product is a mixture of the liquefaction and Flexicoking prod
uct streams. That portion of the liquids which boils below 350°F is suitable for
gasoline and petrochemical manufacturing, while the higher boiling components
may be used in fuel oil applications. The higher boiling fraction contains about
0.6 wt) sulfur and 0.8 wt) nitrogen. These levels maybe reduced by further
hydrotreating.
The testing of the EDS process has been sponsored by Exxon plus other pri
vate and public organizations. The coals tested up to 1982 included Illinois No.6
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Coal Liquefaction
211
HYDROGEN RECYCLE
H20
FUEL GAS
Figure 8 7
Exxon donor solvent EDS process.
bed of ebullated catalyst. The cobalt-molybdate catalyst is fluidized by the liquid
feed. Depending on the operating conditions, the product yield can be all distil
late material or distillate plus a liquefied residual.
The gaseous output from the reactor is scrubbed with a medium volatility oil to
remove light hydrocarbons, and the resulting stream of hydrogen is recycled.
The liquid slurry leaves the top of the reactor and is flashed to atmospheric pres
sure. The vapor phase from the flash is a high-Btu gas after purification to re
move
H2S
and CO2• The liquid phase consists of syncrude, ash, and unreacted
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212 Coal Processing and Pollution Control
Table 8 9
Product Yields of H Coal Process10
Recycle oil/coal ratio
Reactor temperature, of
Hydrogen partial pressure, psia
Yields, wt of dry coal:
C,-C3
C4-400°F
400-975°F
975°F
Unconverted coal
Ash
H
NH
H2S
CO
COz
Total
Hz consumption, wt of dry coal
Sulfur in 400°F
oil, wt
Fuel oil mode
2.1
850
1,760
7.71
16.90
18.28
32.45
6.75
10.95
6.67
0.53
2.55
l.01
103.80
3.80
0.49
Syncrude mode
2.1
850
1,830
9.97
23.66
23.21
19.25
5.68
11.67
7.37
0.84
2.65
0.95
105.25
5.25
0.26
boiler fuel. The major problems experienced in these tests were largely mechani
cal e.g., valve and pump failures);25,26 in addition, various components in coal
can contribute to catalyst poisoning.
A similar process Synthoil) was tested by the Bureau of Mines in the
1970s.4,I0,17Coal high sulfur bituminous) forms a 30 slurry in coal-derived oil
and passes through a fixed bed of pelletized cobalt-molybdate catalysts under
conditions of turbulent flow. Pressures and temperatures are the same as for H
Coal. Turbulence promotes contacting and prevents obstruction, resulting in a
low sulfur and ash product. This process is no longer a candidate for commercial
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Coal Liquefaction 213
300 to 500. The solid residue is similar to char, although with a higher volatile
content than with most chars obtained from pyrolysis.4
roperties of
coal
liquids. Coal liquids produced from direct liquefaction are
not suitable for use as a high grade fuel without further processing. Coal liquids
generally resemble petroleum residual oils black oils more than other petroleum
products, although their physical and chemical characteristics are sufficiently
different to place them in a separate classification.28 The distillation curves of
several coal liquids and of a typical domestic crude oil are compared in Figure 8
8. In general terms coal liquids contain more nitrogen and oxygen than petro
leum crudes. 29 Coal liquids are more aromatic and correspondingly more hydro:
gen-deficient than equivalent cuts from crude oils, thus the carbonlhydrogen
ratios of most coal liquids are considerably higher than those for petroleum
100
COED SYNCRUDE
~
60
°
~
w
:1:
:
..J
0
40
I
I~;
I
UPGRADED
SRC
0
80
TEXAS CRUDE
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214
Coal Processing and Pollution Control
crudes (see Table 8-10). Some coal liquids contain substantial quantities of as
phaltenes, a potential problem for subsequent upgrading. Coal liquids contain a
far higher proportion of higher boiling materials.
The upgrading of coal-derived liquids should achieve the following goals:
1. Reduction or removal of sulfur, nitrogen, oxygen, trace metals, ash.
2. Hydrogenation and increase of the hydrogen/carbon ratio.
3. Reduction in viscosity and boiling range.
4. Improvement of storage stability.
5. Reduction in toxicity and carcinogenicity.
(For data on upgrading of synthetic crudes, see References 28, 30, and 31.)
Commercialization and Economics of Synfuel Production
During the 1970s a great deal of interest in synthetic fuels arose in the United
States as well as the world because of the rapidly escalating price of oil and
shortfalls in oil supply. However, it appears that responses to the supply-demand
situation, such as increased conservation, production of more fuel-efficient auto
mobiles, additional oil production, and a flattening of oil prices, have considera
bly eased market pressures. It is doubtful that there will be much incentive (other
than for strategic purposes) during the 1980s to develop synthetic fuels, simply
because the cost of coal liquids is higher than that for crude oil. If oil prices
remain stable during this decade, the economic justification of a liquid synfuels
venture is very unlikely and may actually grow less attractive.
Even when the projected costs of synfuels appeared to be comparable to those
of conventional fuels in the late 1970s, there was still too much uncertainty in
market conditions to undertake a large-scale commercial venture with capital
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Coal Liquefaction 215
1. The difficulty in raising large amounts of risk capital by developers.
2. The lack of financial incentives, including faster depreciation, higher debt
financing, and tax credits. 32
3. The uncertainty about future world oil prices as well as future monetary
inflation.
In the absence of a concerted government program to stimulate synfuels, the pri
vate sector is and will be very reluctant to undertake a major program in coal
liquefaction. _
Based on a variety of studies on costs of synthetic fuels from coal and oil
shale,33,34 it appears that oil from oil shale and medium Btu gas are the most
economically attractive options for the near future. Table 8-11 summarizes the
approximate capital and operating costs (1980 dollars) for a variety of synfuel
options for equivalent 50,000-barrel-per-day plants, while Table 8-12 gives the
cost of fuels using 100% equity financing and a 10% rate of return (no inflation
effects). ,33 The strategy which is most attractive appears to be combined produc
tion of liquid fuels with SNG, rather than production of methanol or gasoline
only. The costs stated here probably have
±
30% reliability, which makes syn
fuel production potentially much more expensive than gasoline from crude oil.
Table 8-13 gives the distribution of various products and energy efficiencies ex
pected from various synthetic fuel options. The fraction of transportation fuel
includes methanol, gasoline, and LPG. In general fuels produced from indirect
Table 8-11
Best Available Capital and Operating Cost Estimates for Synfuel Plants
Producing 50,000 I Oil Equivalent of Fuel to End Users1
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216 Coal Processing and Pollution Control
Table 8-12
Consumer Cost of Various Synthetic Transportation Fuels
With 100 Equity Financing and 10 Real Return on
Investment Plant or Refining Gate
Plant or Refinery Gate
elivered Consumer Cost of Fuel
/Gallon Gasoline
/bbl 011 Equivalentquivalent
/106 Btu
Gasoline from32/bbl Crude Oil
47
.20.50 52.30
0.40
43.300.60 58.603.00
Gasoline/SNG
49
.250.00
Gasoline
67.602.90 52.300.40
77
.85
4.60
45.15.10
68
.854.70
71
.804.50
liquefaction tend to match up better with U.S. transportation fuel requirements
than those from direct liquefaction. While there are some practical problems in
using methanol or methanol gasoline in current automobiles, 35 there is long
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Coal Liquefaction 217
It is clear that research and development funding required to bring a single
direct liquefaction process to commercialization is significant, on the order of
several billion dollars. Hence when only a few plants are to be constructed, it
will be difficult for the private sector to absorb this front-end capital require
ment. Another impediment facing direct liquefaction plants is the wide variety of
compounds, some of which are carcinogenic, that are produced during process
ing.48 On the other hand, indirect liquefaction plants also pose a range of occupa
tional hazards;1 processes based on the Lurgi gasifier will generate a large quan
tity of pyrolysis products. For this reason entrained-bed gasification such as
Texaco) may be preferred over the fixed-bed systems.
Table 8-13
Selected Synfuel Processes and Products and their Efficiencies
Energy Efficiency
)
Fuel Transportation Fuel
Product Product
(Coal Input) (Coal Input)
NA NA
Process
Oil Shale
MethanoliSynthetic
Natural Gas SNG)
Methanol
Mobil Methanol to
Gasoline/SNG
Fuel
Product
( of output)
Gasoline 19)
Jet Fuel 22)
Diesel Fuel 59)
Methanol 48)
SNG 49)
Other 3)
Methanol 100)
Gasoline 40)
SNG 52)
65
55
63
33
27
8 oal rocessing and ollution ontrol
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