4,257,781 Process for enhancing the fuel value of low BTU gas

Patent Number/Link:

United States Patent [19]

Stephens, Jr.

[11]

[45]

4,257,781

* Mar. 24, 1981

[73] Assignee:

[.] Notice:

[54] PROCESS FOR ENHANCING THE FUEL

VALUE OF LOW BTU GAS

[75] Inventor: Frank M. Stephens, Jr., Lakewood,

Colo.

U.S. PATENT DOCUMENTS

2,409,235 10/1946 Atwell 260/449.6

2,537,496 1/1951 Watson 260/449.6

2,562,806 7/1951 Mayer 260/449.6

2,589,925 3/1952 Cain et al. ~ 260/449.6

2,601,121 7/1902 Mattox 260/449.6

[57] ABSTRACT

2,686,819 8/1954 Johnson 260/449 M

2,694,624 11/1954 Sweetsen 260/449 M

2,819,283 1/1958 Montgomery 260/449.6

3,031,287 4/1962 Benson et al. 48/197 R

4,005,996 2/1977 Hausberger 260/449 M

4,134,907 1/1976 Stephens 48/197 R

Primary Examiner-Peter F. Kratz

Attorney, Agent, or Firm-Sheridan, Ross, Fields &

McIntosh

34 Claims, 3 Drawing Figures

In the field of chemical fuels, prior art coal gasification

.produces a fuel value of a mixture of carbon monoxide

and hydrogen which has a lower BTU than methane.

The present process uses coal resources more economically

for industry by converting part of the hydrogen

and part of the carbon in the carbon monoxide of the

gas mixture to methane, by 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.

Related U.S. Application Data

Continuation-in-part of Ser. No. 817,576, Jul. 21, 1977,

Pat. No. 4,134,907.

Int. C1.3 CI0K 3/04

U.S. C1 48/197 R; 260/449.6 M;

585/733

Field of Search 48/197 R; 260/449 M,

260/449.6 M, 676 R, 449.6 R; 585/733

References Cited

Hazen Research, Inc., Golden, Colo.

The portion of the term of this patent

subsequent to Jan. 16, 1996, has been

disclaimed.

[21] Appl. No.: 2,956

[22] Filed: Jan. 12, 1979

[63]

[56]

[51]

[52]

[58]

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4,257,781

DISCLOSURE OF THE INVENTION

A process for increasing the fuel value of a gas mixture

of carbon monoxide and hydrogen by converting 55

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 a mixture of iron and

iron carbide under conditions of pressure and tempera- 60

ture 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 continuously removing from the 65

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

BEST MODE FOR CARRYING OUT THE

INVENTION

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_Fe3C

(3) Fe3C+2H2-3Fe+CH4

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

continuously 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 finely divided feed material

on a grate or perforate support is fluidized by upwardly

flowing gases which may include or entirely comprise

the reactant gases. Auxiliary equipment includes heating

and temperature control and monitoring equipment,

heat exchangers, scrubbers, cyclones, gas cycling equipment

and other conventional equipment which is used

to remove solids from the off-gas stream and to remove

water and C02 from a recycle gas loop to shift the gas

system equilibrium.

The reactants introduced into the reactor after the

initial charge of iron carbide and iron are the low Btu

coal gasification gases containing carbon monoxide and

hydrogen.

By proper balancing of the ratios of the hydrogen and

carbon bearing materials in accordance with the stability

diagrams, it is possible to make the 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

bed. The gas mixture removed has a Btu value of about

600 on the average and is a suitable industrial or utility

fuel. If methane alone is required it can be recovered

from the gas mixture removed from the fluid bed by

5 conventional procedures.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-3 are stability diagrams indicating the gas

phase relationships between iron carbide and the hydro-

10 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.

PROCESS FOR ENHANCING THE FUEL VALUE

OF LOW BTU GAS

DESCRIPTION

This application is a continuation-in-part of my copending

application, U.S. Ser. No. 817,576, filed July

21, 1977 now U.S. Pat. No. 4,134,907.

TECHNICAL FIELD

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 15

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- 20

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/ft3or less, on the average, which is too low for

most industrial uses. 25

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- 30

ent react to produce methane. Methane has a heat of

combustion of 1013 Btu/ft3, whereas carbon monoxide

and hydrogen has 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 35

is the expense involved. The expense is so great that low

Btu gas enhanced in this manner is not competitive with

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 40

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

ofboiler efficiency and, further, this gas can be econom- 45

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- 50

tion processes.

4,257,781

are established and maintained so that iron serves both

a carbon acceptor function and a carbon donor function.

Additionally, reaction conditions are adjusted so

that hydrogen performs an additional reducing function

in reducing iron carbide to iron and forming methane 5

with the released carbon.

Because of the equilibrium conditions involved in

hydrogen-carbon-oxygen gas systems, the required hydrogen-

carbon ratios will automatically require that

methane be present in the gas system. The quantity of 10

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.

FIGS. 1, 2 and 3 are stability diagrams indicating the

gas phase relationships between iron carbide and the 15

hydrogen-carbon-oxygen system at temperatures of

1160·, 1070· and 1250· F., respectively. The stability

diagrams indicate the relationship between log plots of

partial pressure ratios of the various gas components

which are in equilibrium with iron carbide in the pres- 20

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

variables in the system. These stability diagrams show 25

that for any given temperature and pressure there is a

fixed relationship between the gas components and the

solid reactants iron and iron carbide thus indicating that

sures of up to about 10 atmospheres are also suitable.

Higher pressures are uneconomical.

The iron to iron carbide ratio in the reaction area can

vary between about 10 percent iron carbide to 96 percent

or 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

process that oxygen is removed from the process in the

form of water which is easily recovered. Hany methane

is fed into the reactor, it is unreacted and recovered

with the product gas.

A 50 percent mixture of methane with carbon monoxide

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.

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 I

below shows examples of results obtained from this

computer program under varying conditions of inlet gas

composition, temperature and pressure under which the

process is performed within the favorable methane production

gas ratios illustrated in FIGS. 1-3.

TABLE 1

Equilibrium Shift Calculations for Fe3C System

Pres- Btu/scf

Temp sure _--:;I:.:.:nlc:.et:....G=as:.:.:,-,V-"o",lu:.:.:m",e:...;P:...;e:.:.:rc::.:e:.:.:n:.:.:t_ __.:::O"'ff.-.g.."'a::.:s,_V:...;o::.:.lu::.:m;.:.e;:...::..P::.:er.:::c::.:en;.:.t Inlet Ofr

OF. Atm HZ HZO CO COZ CH4 NZ HZ HZO CO COZ CH4 NZ Gas Gas

9.7 1.7 38.0 37.5 8.6 292

9.0 4.5 35.6 34.7 8.3 292

8.5 9.7 30.9 30.0 7.8 292

8.0 17.1 24.2 23.6 7.2 292

7.1 25.2 17.0 16.3 6.5 292

5.9 32.1 10.8 9.7 5.8 292

4.6 36.8 6.7 4.9 5,4 292

750 48.0 2.0 39.0 5.0

840 48.0 2.0 39.0 5.0

930 48.0 2.0 39.0 5.0

1020 48.0 2.0 39.0 5.0

1110 48.0 2.0 39.0 5.0

1200 48.0 2.0 39.0 5.0

1290 48.0 2.0 39.0 5.0

750 53.0 1.0 31.0 1.0

840 53.0 1.0 31.0 1.0

930 53.0 1.0 31.0 1.0

930 I 48.0 2.0 39.0 5.0

930 5 48.0 2.0 39.0 5.0

930 10 48.0 2.0 39.0 5.0

Section I

1.0 5.0 4.6

1.0 5.0 8.0

1.0 5.0 13.0

1.0 5.0 19.8

1.0 5.0 27.9

1.0 5.0 35.6

1.0 5.0 41.6

Section 2

13.0 1.0 7.7 16.4

13.0 1.0 12.7 14.0

13.0 1.0 19.3 11.4

Section 3

1.0 5.0 13.0 8.5

1.0 5.0 6.3 10.0

1.0 5.0 4.6 10,4

0.9 19,4 54.0 1.7 400

2.5 18.9 50.0 1.6 400

5.9 17.0 44.9 1.5 400

9.7 30.9 30.0 7.8 292

4.6 35.4 35.3 8,4 292

3.3 36.5 36.7 8.5 292

434

422

405

382

356

331

312

674

638

595

405

-129

435

fixed gas compositions will be obtained if mixed gases

are contacted with iron carbide. Furthermore, the equi- 50

librium gas composition can be altered at any given

temperature and pressure by removal of one or more

reaction products from the system. For example, if

water vapor and/or carbon dioxide are continuously

removed by scrubbing in the recycle gas loop, then the 55

quantity of methane will continue to increase in the

reaction zone. 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 production of methane and 60

Fe3C when the other variables for insuring 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 65

about 950· F. Temperatures outside these ranges are not

economically feasible. Atmospheric pressures can be

used and are preferred, although slightly elevated pres-

The results recorded in section 1 of Table I show the

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 is section 2 of the 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 defined temperature range graphically

illustrates the critical effect of temperature on the yield

of methane.

The results in section 3 of the 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 1 tests. Methane yield is increased from 30

volume percent to 36.7 volume percent by increasing

4,257,781

the pressure from one to ten atmospheres. Increased

pressures would probably show slight increase in methane

production but such pressures become uneconomic.

Analyses were made of the off-gas taken at half-hour

intervals for a 12 hour period, the results of which are

presented in Table 3.

EXAMPLE 2 TABLe 3

In order to further illustrate the operativeness of the Pilot Plant Gas Composition Data Reactor Products-Solid, Gas

invention and to illustrate the correlation between the Ratio

results obtained by the computer application of the Off Gas COl H21 H21 process and actual operation of the process, bench scale Time H2O CO2 CO N2 H2 CH4 CO2 H2O CH3 tests were made of the process. The tests were run in 10

accordance with previously described procedure. Ade- 2400 1.2 4.5 3.9 8 35 44 0.9 29.2 0.8

0030 1.2 4.5 3.9 8 33 44 0.9 27.5 0.8

quate iron and iron carbide were present in the fluid bed 0100 1.0 4.5 3.9 8 35 44 0.9 35.0 0.8

to start the reaction. No further addition of these com- 0130 1.0 4.8 4.2 8 35 43 0.9 35.0 0.8

ponents was necessary. Results from actual tests are 0200 1.0 4.8 4.2 8 35 44 0.9 35.0 0.8

recorded in each section with results from the comput- 15 0230 1.0 4.8 4.2 8 35 44 0.9 35.0 0.8

0300 1.0 4.8 4.0 8 34 42 0.8 34.0 0.8

erized test under identical conditions. The results are 0330 1.0 4.8 4.2 8 34 43 0.9 34.0 0.8

recorded in Table 2. 0400 1.0 4.8 4.2 8 34 43 0.9 34.0 0.8

TABLE 2

Experimental Shift Data for Pe3C System

Btu/scf

Temp Pressure Inlet Gas, Volume Percent Off-gas, Volume Percent Inlet Off-

'P. Atm H2 H2O CO CO2 CH4 N2 H2 H2O Cll CO2 CH4 N2 Gas Gas

Section I

Actual 1020 65.0 2.0 33.0 0 0 0 60.7 2.5 12.6 2.4 21.8 0 317 461

Computer 1020 65.0 2.0 33.0 0 0 0 38.8 1.7 10.5 17.2 31.8 0 317 481

Section 2

Actual 1020 22.0 1.7 17.7 13.3 7.8 37.5 30.2 1.1 13.0 4.8 12.5 38.4 207 264

Computer 1020 22.0 1.7 17.7 13.3 7.8 37.5 15.9 1.9 16.2 5.7 13.3 47.0 207 239

The results recorded in section 1 of Table 2 are from

a test program using a 3:1 mixture of hydrogen to carbon

monoxide as the inlet gas, this gas representing a

gasification process working with oxygen. At 1020· F. 35

the actual test produced a gas with a 21.8 percent methane

and a Btu value of 461 as compared to the predicted

values of31.8 percent methane and 481 Btu's.

The results recorded in section 2 of Table 2 show the

change in composition obtained by the process in a 40

representative gas containing relatively large amounts

of inert nitrogen, this gas representing a gasification

process working with air. The actual test produced a

gas with 12.5 percent methane and a Btu value of 264 as

compared to a predicted methane content of 13.3 per- 45

cent 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 of the

process for producing methane, and prove the validity

of the stability diagrams of FIGS. 1-3 for use in select- 50

ing conditions for operative and feasible production of

methane.

EXAMPLE 3

Various gases were fed at a rate of 200 cubic feet per 55

minute to a two foot diameter fluidized-bed reactor

containing sufficient iron and iron carbide to start the

reaction. No further addition of these materials was

necessary. The inlet gases consisted of hydrogen, carbon

monoxide and carbon dioxide introduced in 60

amounts conforming to favorable methane production

ratios illustrated in FIGS. 1-3. A temperature of930· F.

and atmospheric pressure were used for all the tests.

The inlet gas had it composition of approximately 82

percent hydrogen, 8 percent carbon dioxide and 10 65

percent methane with a Btu value of about 370. The

ratio of iron carbide to iron varied from a ratio of about

73/27 percent to 96/4 percent.

0430 1.0 5.5 4.2 8 35 43 0.8 35.0 0.8

0500 1.0 5.5 4.0 8 35 43 0.7 .35.0 0.8

0530 1.0 6.7 4.8 8 35 40 0.7 35.0 0.9

0600 1.0 6.2 4.8 8 35 40 0.8 35.0 0.9

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 1.1 14.6 0.9

0830 2.4 7.75 8.25 6.5 35 39 1.1 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

1100 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

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.

Again, the results of the table show the feasibility of

the process for strongly enhancing the Btu value of a

gas, including one containing methane. The results illustrate

the feasible time period for the enhancement. Further,

the results show that large amounts of methane are

produced with large percentages of iron carbide to iron

present in the fluid bed. For example, at 1000 the percentage

of iron carbide to iron in the bed was about 96

percent. The results further establish the validity of the

stability diagrams of FIGS. 1-3 for use in selecting

favorable operating conditions for the process.

EXAMPLE 4

Gases containing hydrogen and carbon monoxide in a

ratio of three parts of hydrogen to one part of carbon

monoxide were fed at a rate of 200 cubic feet to a twofoot

diameter fluidized-bed reactor containing sufficient

iron and iron carbide to start the reaction. No further

addition of these materials was necessary. A temperature

of 840· F. and atmospheric pressure were used for

all tests. After the system reached equilibrium with

4,257,781

respect to off-gas composition, a portion of the off-gas

was taken through a water scrubbing step to remove the

water formed in the reaction and this scrubbed gas was

substituted for part of the incoming hydrogen and carbon

monoxide feed gas. As predicted from the stability 5

diagrams, this removal of water shifted the equilibrium

and permitted additional quantities of hydrogen and

carbon monoxide to react and form methane. Analysis

of the off-gas taken at half-hour intervals for a period of

twelve hours are presented in Table 4. 10

TABLE 4

4. The process of claim 1 wherein the reaction is

conducted at a pressure 'of from about I to about 10

atmospheres.

5. The process of claim 1 wherein methane is recovered

in continuous fashion from the reactor.

6. The process of claim 1 wherein carbon dioxide is

added to the reactor as a source of carbon.

7. The process of claim 1 wherein water is removed

from the reactor via a recycle gas stream.

8. The process of claim 7 wherein the water is contin-

Pilot Plant Gas Composition Data

for Reactor Products with Water Scrub Circuit

Off·gas Recycle Gas Ratio

Time H2O CO2 CO N2 H2 CH4 H2O CO/CO2 H2/H20 Hz/CH4

1800 8 6 4 10 32 40 3 0.7 4.0 0.8

1900 8 6 4 8 31 42 3 0.7 3.9 0.7

2000 8 6 5 7 29 44 3 0.9 3.6 0.7

2100 8 6 5 5 26 48 3 0.9 3.3 0.5

2200 8 6 5 3 24 52 3 0.9 3.0 0.5

2300 8 6 5 4 24 52 3 0.9 3.0 0.5

2400 7 4 5 4 22 56 2 1.3 3.1 0.4

0100 7 4 4 4 20 60 2 1.0 2.9 0.3

0200 6 5 5 4 22 58 2 1.0 3.7 0.4

0300 7 4 4 4 20 60 2 1.0 2.9 0.3

0400 6 4 3 4 20 62 2 0.8 3.3 0.3

0500 6 5 3 3 20 62 2 0.6 3.3 0.3

0600 6 5 3 3 20 62 2 0.6 3.3 0.3

30 uously removed.

9. The process of claim 1 wherein carbon dioxide is

removed via a recycle gas stream.

10. The process of claim 9 wherein the carbon dioxide

is continuously removed.

11. The process of claim 2 wherein the reaction is

conducted at a pressure of from about I to about 10

atmospheres.

12. The process of claim 2 wherein methane is recovered

in continuous fashion from the reactor.

13. The process of claim 2 wherein carbon dioxide is

added to the reactor as a source of carbon.

14. The process of claim 2 wherein water is removed

from the reactor via a recycle gas stream.

15. The process of claim 2 wherein the water is continuously

removed.

16. The process of claim 2 wherein carbon dioxide is

removed via a recycle gas stream.

17. The process of claim 16 wherein the carbon dioxide

is continuously removed.

18. The process of claim 4 wherein methane is recovered

in continuous fashion from the reactor.

19. The process of claim 4 wherein the water and/or

carbon dioxide is removed during the reaction by means

of a recycle gas stream.

20. The process of claim 4 wherein carbon dioxide is

added to the reactor as a source of carbon.

21. The process of claim 4 wherein water is removed

from the reactor via a recycle gas stream.

22. The process of claim 21 wherein the water is

60 continuously removed.

23. The process of claim 4 wherein carbon dioxide is

removed via a recycle gas stream.

24. The process of claim 23 wherein the carbon dioxide

is continuously removed.

25. A process for converting a first gas mixture containing

carbon monoxide and hydrogen into a second

gas mixture of methane, carbon monoxide and hydrogen

having a substantially increased fuel value over said

The average methane content of the gas increased

from 42 percent at the beginning of the run to a value of

62 percent at the end of the run to give an increased Btu

value of 690 as compared to the 300 Btu value of the

inlet gas. By shifting the equilibrium through the re- 35

moval of water vapor, the methane content was increased

as indicated by the stability diagrams.

Similar results were obtained when the equilibrium

was shifted by removing C02 from the recycle gas

through the addition of caustic to the water scrub recy- 40

cle loop. These results further establish the validity of

the stability diagrams of FIGS. 1-3 for use in selecting

favorable operating conditions for the process.

I claim:

1. A process for producing methane in a single reac- 45

tion zone in the presence of iron, Fe3C, carbon monoxide,

carbon dioxide, hydrogen and water comprising:

(a) maintaining in a fluidized bed, iron and Fe3C in a

single reactor without substantial further additions

of iron and/or Fe3C to the reactor;

(b) introducing a gas mixture containing carbon monoxide

and hydrogen into the reactor;

and hydrogen and balancing the ratio of

carbon monoxide, hydrogen, carbon dioxide, water 55

and methane under conditions such that a portion

of the carbon monoxide is reduced to carbon, iron

is reacted with the carbon to produce Fe3C, and

the Fe3C is reacted with hydrogen to form methane

and reform iron;

(d) removing water and/or carbon dioxide; via a

recycle gas stream; and

(e) recovering methane from the reactor.

2. The process of claim 1 wherein the reaction is

conducted at a temperature of from about 600· F. to 65

about 1200· F.

3. The process of claim 1 wherein the reaction is

conducted from about 600· F. to about 950· F.

4,257,781

first gas mixture in a single reaction zone which comprises,

(a) maintaining iron and Fe3C in a fluidized bed in the

reaction zone without substantial further additions 5

of iron and/or Fe3C to the reaction zone;

(b) continuously introducing said first gas mixture

into said fluidized bed in the reaction zone;

a circulating gas stream which removes water and/

or carbon dioxide so as to maintain mixtures of

carbon monoxide, carbon dioxide, hydrogen, water

and methane which are thermodynamically favor- 15

able for maintaining the presence of Fe3C and the

formation of methane;

(d) continuously removing from said reaction zone as

a product said second gas mixture of methane, 20

carbon monoxide and hydrogen having an increased

fuel value.

26. The process of claim 25 wherein the reaction is

conducted at a temperature of from about 6000 F. to

about 12000 F.

27. The process of claim 25 wherein the reaction is

conducted at a temperature of from about 6000 F. to

about 9500 F.

28. The process of claim 25 wherein the reaction is

conducted at a pressure of from about 1 to about 10

atmospheres.

29. The process of claim 25 wherein methane is recovered

in continuous fashion from the reactor.

30. The process of claim 25 wherein carbon dioxide is

added to the reactor as a source of carbon.

31. The process ofclaim 25 wherein water is removed

from the reactor via a recycle gas stream.

32. The process of claim 25 wherein the water is

continuously removed.

33. The process ofclaim 25 wherein carbon dioxide is

removed via a recycle gas stream.

34. The process of claim 25 wherein the carbon dioxide

is continuously removed.

* * * * *

ly:"4̘sNPA@s,"serif";mso-fareast-font-family: HiddenHorzOCR'>introducing the iron carbonyl enriched recycle gas

50 stream into the iron carbonyl decomposition process.

11. The process of claim 9 wherein sufficient vaporized

iron carbonyl is combined with the second portion

of the recycle gas stream to produce an iron carbonyl

enriched gas stream comprising about 5 to about 20%

by volume of iron carbonyl.

12. The process of claim 3 wherein the reducing gas

is hydrogen.

13. The process of claim 3 wherein the reducing gas

is carbon monoxide.

14. The process of claim 4 which further comprises

reducing iron containing material in a third reaction

vessel simultaneously with contacting the compressed

gas stream with reduced iron containing material in the

first and second reaction vessels.

15. The process of claim 14 wherein the carbon monoxide

enriched gas stream is compressed in four separate

stages and is cooled to about 500 C. between the

separate stages.

4,250,157

combining the vaporized iron carbonyl with the second

portion of the recycle gas stream to produce an iron

carbonyl enriched gas stream for use in the iron carbonyl

decomposition or reaction process. As shown in

FIG. 1, condensed iron carbonyl recovered from reac- 5

tion vessels 50, 52 and collected in receiver means 74 is

transferred from the receiver means to the vaporization

means 16 through conduit means 106, 108. Vaporization

means 16 comprises heater means, such as heater 110, in

the conduit means 108 for preheating the condensed 10

iron carbonyl to a temperature of about 1050 to about

1400 C., at a pressure of about 20 to about 38 atmospheres,

and vaporization column means 111 for receiving

iron carbonyl from heater 110, reducing the pressure

of the iron carbonyl to about 1 atmosphere to va- 15

porize the iron carbonyl and combining the vaporized

iron carbonyl with the second portion of the recycle gas

stream. Preheated iron carbonyl from heater 110 is

introduced into the vaporization column means and is

vaporized therein. The second portion of recycle gas is

simultaneously introduced into the vaporization column 20

means through conduit means 18 and is combined with

the vaporized iron carbonyl in any desired proportions

to produce an iron carbonyl enriched gas stream. The

enriched gas stream, comprising, for example, 10% iron

carbonyl, is transferred out of vaporization means 16 25

through conduit means 113 and is recycled to the iron

carbonyl decomposition or reaction process. Any iron

carbonyl which condenses in vaporization column

means 111 is collected in a bottom portion thereof and

is transferred to iron carbonyl collection means 30 such 30

as through conduit means 115.

During periods of excess iron carbonyl production or

vaporization means shut-down, condensed iron carbonyl

is transferred from receiver means 74 through

conduit means 106, 112 to iron carbonyl storage means 35

34. Cooling means, such as cooler 114, are preferably

provided in the conduit means 112 for cooling the iron

carbonyl to a temperature less than about 900 C. prior to

transferring the iron carbonyl to the storage means.

During periods of iron carbonyl production storage, 40

make-up iron carbonyl is transferred from storage

means 32 to vaporization means 16 through conduit

means 106, 108 is required.

While the foregoing process and apparatus have been

described in connection with various presently pre- 45

ferred and illustrative embodiments, various modifications

may be made without departing from the inventive

concepts. All such modifications are intended to be

within the scope of the appended claims, except insofar

as limited by the prior art.

What is claimed is:

1. A process for enriching the iron carbonyl content

of a recycle gas stream comprising carbon monoxide

and produced in an iron carbonyl decomposition or

reaction process to enable reuse of the recycle gas

stream in the iron carbonyl decomposition or reaction 55

process, comprising:

cooling an iron carbonyl lean recycle gas stream

produced in an iron carbonyl decomposition process

to a temperature of about 50 to about 150 C.;

adding carbon monoxide to the cooled recycle gas 60

streilm to produce a carbon monoxide enriched gas

stream;

compressing the carbon monoxide enriched gas

stream to a pressure of about 20 to about 38 atmospheres

under conditions suitable to prevent the 65

decomposition of substantial amounts of the iron

carbonyl in the carbon monoxide enriched recycle

gas stream; and

PATENT NO. :

DATED

INVENTOR(S) :

UNITED STATES PATENT AND TRADEMARK OFFICE

CERTIFICATE OF CORRECTION

4,250,157

February 10, 1981

Richard P. Ruskan, Humayon Z. Zafar, Duane N.

Goens, David E. Hyatt, Charlie W. Denney

It is certified that error appears in the above-identified patent and that said Letters Patent

are hereby corrected as shown below:

On the Abstract page, in the listing of the inventors,

"Ruskin" should read --Ruskan--.

~igncd and ~calcd this

El611111 Da'I of /J«-.1Hr I'll

ISEALI

GERALD J. MOSSINGHOFF

A"atllwO/fItw Commissioner ofPtJfents tJnd T1tJdemiJ1ks