4,134,907 Process for enhancing the fuel value of low BTU gas

Patent Number/Link:

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

<.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

FeO

I I I

.¢I q't0o '

rl-c IIII1III

~~~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

:r:

0....

2 --- 2 C)

0 --- I ...J

FeO --- 0

FezC -I

-2 Fe Fe3C -2

Fe-Q-H-C STABILITY DIAGRAM AT 1250°F (9500 K)

FI G 3

4,134,907

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

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-

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

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.

4,'134~907

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

" " 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

0.9

Ratio

29.2

27.5

35.0

34.0

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 4.0 8 34 42 0.8

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

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;

(b) continuously introducing said gas mixture into

. said fluid bed;

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. • • • • •