United States Patent [19]
Stephens, Jr.
[11]
[45]
4,134,907
Jan. 16, 1979
2,409,235
2,537,496
2,562,802
2,589,925
2,601,121
2,686,819
2,694,624 7 Claims, 3 Drawing Figures
2,819,283 1/1958 Montgomery et aI...•........ 260/449.6
4,005,996 2/1977 Hansberger 260/449 M
Primary Examiner-Howard T. Mars
Attorney, Agent, or Firm-Sheridan, Ross, Fields &
McIntosh
A process for increasing the fuel value of a gas mixture
of carbon monoxide and hydrogen by converting part
of the hydrogen and part of the carbon in the carbon
monoxide of the gas mixture to methane, which comprises
continuously introducing the gas mixture into a .
fluid bed in the presence of iron under conditions of
pressure and temperature which promote the reduction
of carbon monoxide to carbon, the formation of iron
carbide from the iron and carbon, and the formation of
methane and iron from iron carbide and hydrogen, and
continuously removing from the fluid bed a methane
enriched gas mixture including carbon monoxide and
hydrogen having a substantially increased fuel value
over the gas mixture introduced into the fluid bed.
[57] ABSTRACf
[54] PROCESS FOR ENHANCING THE FUEL
VALUE OF LOW BTU GAS
[75] Inventor: Frank M. Stephens, Jr., Lakewood,
Colo.
[73] Assignee: Hazen Research, Inc., Golden, Colo.
[21] Appl. No.: 817,576
[22] Filed: Jul. 21, 1977
[51] Int. Cl.2 C07C 1/04
[52] U.S. Cl 260/449.6 M; 48/197 R;
260/676 R
[58] Field of Search 260/449 M, 449.6 M,
260/449.6 R, 676; 48/197
[56] References Cited
U.S. PATENT DOCUMENTS
10/1946 Atwell 260/449.6
1/1951 Watson 260/449.6
7/1951 Mayer 260/449.6
3/1952 Cain et aI....•....•...........•.... 260/449.6
6/1952 Mattox 260/449.6
8/1954 Johnson 260/449 M
11/1954 Sweetser 260/449 M
u.s. Patent Jan. 16, 1979 Sheet 1 of 3 4,134,907
t\.I
I~o C\l
rl
<.9 o
...J
--- -I
--- -2
a FeO
-2 -I 0 I
I I I
I I I 8 I I· a
OCc m~lfl
6 C\•J<•s>Co\J. ad
-2
Fe-O-H--C STABILITY DIAGRAM AT 1160° F(9000K)
FIG
u.s. Patent Jan. 16, 1979 Sheet 2 of 3 4,134,907
-2 -I a
LOG pcoYPCOz
234
C\J
::J:
~
0C\!
--- 2 ~
--- I 0a
-_...: a .-J
--- -I
2
FeO
Fe
I I I
I I I
.¢I q't0o '
rl-c IIII1III
~~~8
o
8
-2
6 8 1--------------------:;7.......-1
~(\14
ou~
02 g
Fe-Q-H-C STABILITY DIAGRAM AT I070°F (8500 K)
FIG 2
u.s. Patent Jan. 16, 1979 Sheet 3 of 3 4,134,907
LOG pcoYpco2
-2 -I 0 I 2 3 4
Fe203
N :r
~
Fe304
q.
:r:
0....
2 --- 2 C)
0 --- I ...J
0
FeO --- 0
FezC -I
-2 Fe Fe3C -2
Fe-Q-H-C STABILITY DIAGRAM AT 1250°F (9500 K)
FI G 3
1
4,134,907
2
BRIEF DESCRIPTION OF THE ORAWINGS
FIGS. 1-3 are stability diagrams indicating the gas
phase relationships between iron carbide and the hydro-
5 gen-carbon-oxygen system. The symbol aC refers to
the activity of carbon in the system. The symbol "P"
represents partial pressure. The amounts of gases are
essentially directly related to the partial pressures.
DESCRIPTION OF PREFERRED
EMBODIMENTS
The invention is based on establishing and maintaining
conditions in a fluid bed which promote the following
three reactions:
(1) CO + H2 -+ C + H20
(2) C + 3Fe -+ Fe3 C
(3) Fe3 C + 2H2 -+ 3Fe + C~
These reactions will proceed under atmospheric pressures,
although slightly elevated pressures may be preferred.
In the fluid bed reaction, the iron acts as an acceptor
of carbon in reaction (2) and as a donor of carbon in
reaction (3). It will be noted that iron is reformed or
regenerated in reaction (3) and that the iron carbide is
reformed or regenerated in reaction (2) so that after the
first addition of iron and iron carbide they are always
present in the reaction zone without further additions.
Reaction (3) can be made to proceed to the right
either by the addition of hydrogen or the removal of
methane. Hydrogen and carbon monoxide are being
c~ntinuously added in reaction (1) and methane, along
WIth the carbon monoxide and hydrogen not converted
is being continuously removed as part of the enriched
fuel gas.
The reactions can be made to proceed and controlled
by controlling the ratio of the various gases present,
that is, the ratio of methane to hydrogen, water to hydrogen,
carbon dioxide to carbon monoxide, etc. Charts
will be described hereinafter illustrating how control of
these ratios results in the reactions proceeding in the
required manner.
The fluidized bed reactor referred to herein is of the
conventional type in which fmely divided feed material
on a grate or perforate support is fluidized by upwardly
flowing gasses which may include or entirely comprise
the reactant gasses. Auxiliary equipment includes heating
and temperature control and monitoring equipment,
heat exchangers, scrubbers, cyclones, gas cycling equipment
and other.conventional equipment.
The reactants introduced into the reactor after the.
initial charge of iron carbide and iron are the low Btu
coal gasification gasses containing carbon monoxide
and hydrogen.
By proper balancing ofthe ratios ofthe hydrogen and
carbon bearing materials in accordance with tIle stability
diagrams, it is possible to make tIle hydrogen serve a
reducing function to reduce the carbon monoxide to
carbon, and the carbon serve a carburizing function as
iron carbide is formed. As stated previously, conditions
are .established and maintained so that iron serves both
a carbon acceptor. function and a carbon donor functions.
Additionally, reaction conditions are adjusted so
that hydrogen performs an additional reducing function
in reducing iron carbide to iron and forming methane
with the released carbon.
Because of the equilibrium conditions involved in
hydrogen-carbon-oxygen gas systems, the required hy-
SUMMARY OF THE INVENTION
A process for increasing the fuel value of a gas mixture
of carbon monoxide and hydrogen by converting 50
part of the hydrogen, and part of the carbon in the
carbon monoxide of the gas mixture to methane, which
comprises continuously introducing the gas mixture
into a fluid bed in a single reaction zone in the presence
of a mixture ofiron and iron carbide under conditions of 55
pressure and temperature which promote the reduction
of carbon monoxide to carbon along with the formation
of iron carbide by the reaction of iron and carbon followed
by the formation of methane and iron by the
reaction of iron carbide with hydrogen, while continu- 60
ously removing from the fluid bed a gas mixture including
methane, carbon monoxide and hydrogen having a
substantially increased fuel value over the gas mixture
introduced into the fluid bed. The gas mixture removed
has a Btu value of about 600 on the average and is a 65
suitable industrial or utility fuel. If methane alone is
required it can be recovered from the gas mixture removed
from the fluid bed by conventional procedures.
PROCESS FOR ENHANCING THE FUEL VALUE
OF LOW BTU GAS
BACKGROUND OF THE INVENTION
The need to use the extensive coal resources in this
country as a source of fuel gas is now quite evident in
view of the. rapid depletion of other sources.·Accordingly,
it has become essential to develop processes for
the economic production of fuel gas for industrial uses 10
from coal.
Atmospheric coal gasification processes are well
known and well developed. Typical of these proven
processes are the Koppers-Totzek, Winkler, WellmanGalusha,
Woodall-Duckman,and others. The gas pro- 15
duced from these gasification processes is a low Btu gas
comprising a mixture of carbon monoxide and hydrogen.
This gas mixture has a low fuel value of about 300 .
Btu/ft3 or less, on the average, which is too low for
most industrial uses. 20
The fuel value of the gas produced by the atmospheric
coal gasification processes can be enhanced
with the use of high temperatures and pressures, sometimes
accompanied by the use of oxygen and/or catalysts,
to make the hydrogen and carbon monoxide pres- 25
ent react to produce methane. Methane has a heat of
combustion of 1013 Btu/ft3, whereas carbon monoxide
and hydrogen have Btu's of about 322 and 325, respectively.
The chief disadvantage, of course, of these procedures
for enhancing the fuel value of the low Btu gas 30
is the expense involved. The expense is so great that low
Btu gas enhanced in this manner is not compeutivewith
other fuels available for industrial uses.
So-called intermediate Btu gas is suitable for industrial
uses, this gas having a Btu value of 450 Btu/ft3or 35
more. It will burn well in existing gas burner equipment
in power plants and other industrial applications with
only minor modification in the burner head. The Btu
value is high enough so that its use does not result in loss
of boiler efficiency and, further, this gas can beeconom- 40
ically piped moderate distances, which is not true for
low Btu gas.
Accordingly, it is an object of this invention to provide
a relatively inexpensive process for enhancing the
fuel value of the low Btu gas produced by coal gasifica- 45
tion processes.
4,134,907
3
drogen-carbon ratios will automatically require that
methane be present in the gas system. The quantity of
methane present or produced will be a function of carbon
to hydrogen ratios, as well as temperature and
pressure conditions, and all of these can be controlled. 5
FIGS. I, 2 and 3 are stability diagrams indicating the
gas phase relationships between iron carbide and the
hydrogen carbon-oxygen system at temperatures of
1160·, 1070· and 1250· F, respectively. The stability
diagrams indicate the relationship between log plots of 10
partial pressure ratios of the various gas components
which are in equilibrium with iron carbide in the pres-
4
EXAMPLE I
Using the stability diagrams, a computer program
was constructed which gives the equilibrium gas composition
expected for the process when various hydrogen
and carbon bearing gases are contacted with ironiron
carbide mixtures at various temperatures. Table 1
below shows examples of results oj)tained from this
computer program under varying conditions ofinlet gas
composition, temperature and pressure under which the
process is performed within the favorable methane production
gas ratios illustrated in FIGS. 1 - 3.
TABLE 7
Equilibrium Shift Calculations for Fe3C System
Temp Pressure
• F Atm H2
Section 2
53.0 1.0 31.0 1.0 13.0 1.0 7.7 16.4 0.9 19.4 54.0 1.7 400 674
53.0 1.0 31.0 1.0 13.0 1.0 12.7 14.0 2.5 18.9 50.0 1.6 400 638
53.0 1.0 31.0 1.0 13.0 1.0 19.3 11.4 5.9 17.0 44.9 1.5 400 595
Section 3
48.0 2.0 39.0 5.0 1.0 5.0 13.0 8.5 9.7 30.9 30.0 7.8 292 405
48.0 2.0 39.0 5.0 1.0 5.0 6.3 10.0 4.6 35.4 35.3 8.4 292 429
48.0 2.0 39.0 5.0 1.0 5.0 4.6 10.4 3.3 36.5 36.7 8.5 292 435
750
840
930
1020
1110
1200
1290
750
840
930
930 1
930 5
930 10
48.0
48.0
48.0
48.0
48.0
48.0
48.0
Btu/sef
Inlet Gas, Volume Percent Off-gas, Volume Percent Inlet Off
H2O CO CO2 CH4 N2 H2 H2O CO CO2 CH4 N2 Gas Gas
Section 1
2.0 39.0 5.0 1.0 5.0 4.6 9.7 1.7 38.0 37.5 8.6 292 434
2.0 39.0 5.0 1.0 5.0 8.0 9.0 4.5 35.6 34.7 8.3 292 422
2.0 39.0 5.0 1.0 5.0 13.0 8.5 9.7 30.9 30.0 7.8 292 405
2.0 39.0 5.0 1.0 5.0 19.8 8.0 17.1 24.2 23.6 7.2 292 382
2.0 39.0 5.0 1.0 5.0 27.9 7.1 25.2 17.0 16.3 6.5 292 356
2.0 39.0 5.0 1.0 5.0 35.6 5.9 32.1 10.8 9.7 5.8 292 331
2.0 39.0 5.0 1.0 5.0 41.6 4.6 36.8 6.7 4.9 5.4 292 312
EXAMPLE 2
In order to further illustrate the operativeness of the
invention and to illustrate the correlation between the
results obtained by the computer application of the
process and actual operation of the process, bench scale
tests. were made of the. process. The tests were run in
accordance with previously described procedure. Adequate
iron and iron carbide were present in the fluid bed
to start the reaction. No further addition of these components
was necessary. Results from actual tests are
recorded in each section with results from the computerized
test under identical conditions. The results are
recorded in Table 2.
The results recorded in section I of Table I show the
35 theoretical change in composition resulting when a gas
having a composition similar to commercially produced
"blue water gas" is subjected to the computerized program.
The results in section 2 ofthe Table show the theoretical
change in composition obtained when a gas having
a composition similar to gas produced by the Lurgi
oxygen-pressure gasification is subjected to the computerized
process. The large increase in yields of methane
within a well defmed temperature range graphically
illustrates the critical effect of temperature on the yield
of methane.
The results in section 3 ofthe Table show the theoretical
effect of pressure on the yield of methane when the
computerized process is applied to the same gas used for
the section I tests. Methane yield is increased from 30
volume percent to 36.7 volume percent by increasing
the pressure from one to ten atmospheres. Increased
pressures would probably show slight increase in methane
production but such pressures become uneconomic.
·ent process. These illustrate that definite amounts of
methane will exist in the system in the presence of the
iron carbide, and that the amount of methane preSent or
produced can be controlled by controlling the other 40
variables in the system. For example, the charts indicate
·the operative range of variables at specified temperatures
for insuring that Fe3C is present in the fluid bed.
They also show the effect of temperature on the pro-
·duction of methane and Fe3C when the other variables 45
foririsuring the presence of Fe3C in the fluid bed are
maintained substantially constant.
A feasible temperature range for the process is about
600· F to about 1200· F, preferably about 600· F to
about 950· F. Temperatures outside these ranges are not 50
economically feasible. Atmospheric pressures can be
used and are preferred, although slightly elevated pressures
of up to about 10 atmospheres are also suitable.
Higher pressures are uneconomical.
The iron to iron carbide ratio in the reaction area can 55
vary between about 10 percent iron carbide to 96 percentor
more iron carbide. Iron may be added in metallic
form or supplied from various sources, including
iron oxide. Some carbon dioxide can be used in the feed
gas as a source of carbon. It is an advantage of the 60
process that oxygen is removed from the process in the
form of water which is easily recovered. Ifany methane
is fed into the reactor, it is unreacted and recovered
with the product gas.
A 50 percent mixture of methane with carbon monox- 65
ide and hydrogen gives a gas mixture of 600 Btu. As can
be seen from the examples below, this intermediate fuel
gas is easily produced by the process of the invention.
5
4,'134~907
6
TABLE 2
Experimental Shift Da~ for Fe3G System
"
Temp Pressure
• F Atnl H2
Actual 1020
Computer' 1020
I, 65.0
1 65.0
"
Inlet Gas; Volume Percent Off-gas. Volume Percent
H2O Co. C()i:,'·CF4 Ni H2 H2O CO 'CO2' CF4 N2
','- Section I
2.0 'j3:0 0 0 0 60.7 2.5 12.6 2.4 21.8 0
2:0 33.0 '0 0 0 38.8 1.7 10.5 17.2 31.8 0
317 461
317 481
Actual
Computer
1020
1020
II
" " Section 2
~tg ,g :um ;:~ ~U f~:;::~ 13.0 4.8 :12.5 38.4 207
16.2 5.7 13.3 47.0 207
264 '
239
TABLE 3-continued
Pilot Plant Gas Composition Data
Reactor Products-Solid. Gas
Ratio
Off Gas COl H21 H21
Time H2O CO2 CO N2 H2 CH4 CO2 H2O CH3
0630 1.0 6.2 4.8 8 35 41 0.8 35.0 0.9
0700 1.0 6.2 5.0 8 35 40 0.8 35.0 0.9
0730 1.0 6.7 5.1 8 35 40 0.8 35.0 0.9
0800 2.4 7.5 7.9 7 35 40 l.l 14.6 0.9
0830 2.4 7.75 8.25 6.5 35 39 l.l 14.6 0.9
0900 2.4 8.6 8.9 7 34 38.3 1.0 14.2 0.9
0930 2.4 5.3 6.6 7 38 40 1.3 15.8 1.0
1000 2.3 4.4 4.5 5.5 41 33.5 1.0 17.8 1.2
1030 2.3 3.6 4.5 5.5 40 40 1.3 17.4 1.0
lIOO 2.4 4.5 5.2 7 39 41.5 1.2 16.3 0.9
1130 2.3 4.8 6.5 7 37 41.5 1.4 16.1 0.9
0.8 60
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.9
0.9
Ratio
29.2
27.5
35.0
35.0
35.0
35.0
34.0
34.0
34.0
35.0
35.0
35.0
35.0
H21
H20
EXAMPLE 3
Pilot Plant Gas Composition Data
Reactor Products-Solid. Gas
1.2 4.5 3.9 8 35 44 0.9
1.2 4.5 3.9 8 33 44 0.9
1.0 4.5 3.9 8 35 44 0.9
1.0 4.8 4.2 8 35 43 0.9
1.0 4.8 4.2 8 35 44 0.9
1.0 4.8 4.2 8 35 44 0.9
1.0 4.8 4.0 8 34 42 0.8
1.0 4.8 4.2 8 34 43 0.9
1.0 4.8 4.2 8 34 43 0.9
1.0 5.5 4.2 8 35 43 0.8
1.0 5.5 4.0 8 35 43 0.7
1.0 6.7 4.8 8 35 40 0.7
1.0 6.2 4.8 8 35 40 0.8
2400
0030
0100
0130
0200
0230
0300
0330
0400
0430
0500
0530
0600
____~O~ff~G~as~_=,__=-COI
Time H20 CO2 CO N2 H2 CF4 C02
The average methane content of the off-gas during
the 12-hour period exceeded 40 percent and the off-gas
had a Btu average value ofabout 560 as compared to the
Btu value of only 370 for the inlet gas.
35 Again, the results of the table show the feasibility of
the process for strongly enhancing the Btu value of a
Various gases were fed at a rate of 200 cubic feet per gas, including one containing methane. The results illusminute
to a two foot diameter fluidiz~d-bed reactor trate the feasible time period for the enhancement. Furcontaining
sufficient iron and iron carbide to ~tart the ther, the results show that large amounts ofmethane are
reaction. No f~her addition ?f these materials was 40 produced with large percentages of iron carbide to iron
necessary. The Inlet gases consl~te~ of ~ydrogen, c~- present in the fluid bed. For example, at 1000 the perbon
monoxide and carbon diOXide Introduced. In centage of iron carbide to iron in the bed was about 96
amounts conforming to favorable methane production percent. The results further establish the validity of the
ratios illustrated in FIGS. 1-3. A temperature of 930· F stability diagrams of FIGS. 1-3 for use in selecting
and atmospheric pressure w~~e used for al~ the tests. 45 favorable operating conditions for the process.
The inlet gas had a composition of approximately 82 What is claimed is:
percent hydrogen, 8 percent carbon dioxide and 10 1. A process for converting a first gas mixture conpercent
methane with a Btu value of abou! 370. The taining carbon monoxide and hydrogen into a second
ratio of iron carbide to iron varied from a ratio of about gas mixture having a substantially increased fuel value,
73/27 percent to 96/4 percent. 50 comprising methane, in a single reaction zone which
Analyses were made of t~e off-gas taken at h~f-hour comprises:
intervals for a 12 hour penod, the results of which are (a) maintaining iron and Fe3C in a fluid bed;
presented in Table 3. (b) continuously introducing said first gas mixture
TABLE 3 into said fluid bed;
55 (c) maintaining a temperature of about 600· F - 1200·
F and a pressure of about 1-10 atmospheres in said
fluid bed so that some of the carbon monoxide is
reduced to carbon, the iron is reacted with carbon
to form Fe3C, and the Fe3C is reacted with hydrogen
to form methane and reform iron, and
(d) continuously removing from said fluid bed as a
product said second gas mixture of methane, carbon
monoxide and hydrogen having an increased
fuel value.
65 2. The process of claim 1 in which carbon dioxide is
added to the first gas mixture as a source of carbon.
3. The process of claim 1 performed at a temperature
between about 600· F and 950· F.
The results recorded in section 1 of Table 2 are from
a test program using a 3:1 mixture of hydrogen to car- 15
bon monoxide as the inlet gas, this gas representing a
gasification process working with oxygen. At 1020· F
the actual test produced a gas with 21.8 percent methane
and a Btu value of461 as compared to the predicted
values of 31.8 percent methane and 481 Btu's. 20
The results recorded in section 2 of Table 2 show the
change in composition obtained by the process in a
representative gas containing relativ~ly large ~o~ts
of inert nitrogen, this gas representmg a gasification
process working with air. The actual test produced a 25
gas with 12.5 percent methane and a Btu value of 264 as
compared to a predicted methane content of 13.3 percent
and a Btu value of 239. An increase in Btu value of
over 30 percent was obtained in both instances.
The test results established the operativeness o~ f:he 30
process for producing methane, and prove th~ validity
of the stability diagrams of FIGS. 1-3 for use m selecting
conditions for operative and feasible production of
methane.
4,134,907
7
4. The process of claim 1 in which methane is separated
from said second gas mixture and recovered as a
product.
5. The process. of claim 4 in which methane is sepa- 5
rated from said second gas mixture and recovered as a
product.
6. A process for making methane from a gas mixture
of carbon monoxide and hydrogen in a single reaction 10
zone which comprises:
(a) maintaining iron and Fe3C in a fluid bed;
8
(b) continuously introducing said gas mixture into
. said fluid bed;
(c) maintaining a temperature of about 6000 F - 12000
F and a pressure of about 1-10 atmospheres in said
fluid bed so that some of the carbon monoxide is
reduced to carbon, the iron is reacted with carbon
to form Fe3C, and the Fe3C is reacted with hydrogen
to form methane and reform iron, and
(d) continuously recovering methane from the resulting
gas mixture.
7. The process of claim 6 performed at a temperature
beween about 6000 F - 9500 F. • • • • •
15
20
25
30
35
40
45
50
55
60
65