CA1097078A

CA1097078A - Method of prducing a gas mixture containing carbon monoxide and hydrogen gas for further processing or combustion

Info

Publication number: CA1097078A
Application number: CA287,530A
Authority: CA
Inventors: Olle Wijk; Mihkel Mathiesen; Sven Eketorp
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-03-29
Filing date: 1977-09-26
Publication date: 1981-03-10
Also published as: DD132978A5; DE2713864A1; SE433500B; SE7706876L; BR7801954A

Abstract

ABSTRACT
A method for producing a mixture of carbon monoxide and hydrogen gas which mixture is substantially free of sulphur and dust. The gas mixture is produced from coal which is in-jected into a metal bath in a stoichiometric excess relative to the oxygen, in the form of oxidic compounds, contained in the metal bath. Oxygen and a coolant are also injected into the bath.

Description

~09~70~7l3 METHOD OF PRODUCING A GAS MIX~URE CONTAIMING CARBON
MONOX~DR AND HYDROGEN GAS FOR FURTHER PROCESSING OR
COMBUSTION
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This invention relates to a method of producing a gas mixture containing carbon monoxide (CO) and hydrogen gas tH2)J which gases are intended for combustion or further processing.

A number o~ methods are known to produce carbon monoxide (CO) and hydrogen gas (H2) on an industrial scale. It is known to gasi~y coal to carbon monoxide, rOr example, by the Lurgi process, the Hygas-process and Bigas-process. It also is known, to produce hydrogen gas, for example, by hydrolysis or cracking at high temperature.
Hydrocarbon compounds generally are produced by proceeding from a.o. carbon monoxide and hydrogen gas.

The coal used mostly is contaminated, ~or example by relatively high contents of sulphur. Said ooal gasification processes, at which large amounts of coal are combusted, therefore emit great amounts o~ sulphur dioxide (SO2), which constitute a great problem~, because the emission of sulphur dioxide has an unfavour-able e~eot on atmosphere, nature, environment~etQ.

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1(~97078 The waste gases from coal gasification plants, besides, often contain substantial amounts of dust, consisting a.o. of oxides of the contaminants.

The present invention solves the aPoresaid problems. At the method according to the invention hydrogen gas is pro~uced simultaneously with carbon monoxide and, therefore, the method is very attractive for the production of hydrocarbon compounds such as, for example, methanol.

The present invention, thus, relates to a method of producin~ a gas mixture substantially free of sulphur and dust for further processing or combustion, which ~ixture substantially consists of carbon monoxide (CO) and hydrogen gas (H2) from carbon (C) in the form of coal containing a certain amount of water, hydrocarbons and/or carbon compounds such as or~anic material. The invention characterized thereby that said carbon is injected into a metal bath in a stoichiometric excess relative to oxy~en in the form of oxidic oompounds contained in the metal bath, bogether with oxygen . , .
; 1 and together with a coolant.

The invention is described below in ~reater detail, partly with reference to the accompanying drawing, in which Fig. 1 shows an apparatus, in which the method according to the invention can be e~ applied.

In Fig. 1 a gasification reactor with the general designation I
~or producing gas according to the invention is shown in a sche-, .

~0971)7~3 ~atic manner. The gasification reactor,~which in principle is per se known, comprises a furnace body 2, preferably an electric heating unit 3, one or more tuyeres 4 and a collecting hood 6 for generated gases. The walls of the furnace body 2 are made Or a heat-resistant material, such as bricks, and an outer wall 10 of metal. The electric heating unit 3 preferably is an electric inductor. The numeral 11 designates electric wire connecting points. O.ne or more powder injectors 5 are connected via conduits 7 to the tuyere or tuyeres 4. A carrier gas, which prererably is oxygen, flows in the conduit 7 through a proportioning member 8 associated to each powder injector 5. The proportioning member 8 is capable to deliver the reactants to be injected into the apparatus from the container of the powder injector 5 to the conduit 7 in a certain proportion relative to each other and to the amount of passing carrier gas. Said carrier gas also may be, or example, a mixture of carbon monoxide and carbon dioxide. In that case, however, oxygen must be added in a different way.
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The metal 9 in the furnace body i8 intended be maintained fluid.

When reactants are not injeated into the ga~irication reaator, the - ~
~ metal bath 9 is maintained hot by said heating unit 3.
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~ The~powder injectors 5 can comprise several oontainers fGr differ-.
` ent reactants. Reactants in solid state are introduced into the ; powder~in~ectors in powdered state. The reacta~nts, thus, are injected as a mixture o~ gas, solid powder grains and possibly liquid.

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The method according to the invention is carried out as follows.
Carbon (C) in the form of commercial coal containing a certain amount of water, hydrocarbons and/or carbon compounds and oxygen are injected, together with a coolant, into the metal bath 9. The carrier gas, which preferably consists of said oxygen, drives remainders of said reactants from said powder injector 5 into the metal bath 9.

At the method according to the invention it is proceeded from a starting bath, which is molten and maintained hot either by a separate melting ~urnace or by the available heating unit 3.
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At the beginning of the injection the reactor is inclined, so that the tuyere or tuyeres 4 open above the bath surface. Arter the injection has been started, the reactor is erected so that the tuyere or tuyeres open beneath the bath surface.

The`reactants and the coolanb can also be injected by means of one ;- -or more lances immersed from above into the bath. In certflin cases, furthermore, the coolant can be added to the metal bath ~rom above.
When a lance is used, it is immersed into the metal bath first after the passage of the carrier gas and powder through the lance has been started.

At the temperature prevailing in a metal bath of the kind here referred to, carbon very rapidly and with great yield is oxidized to carbon monoxide.
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:- , - 109'7~)~8 Commercial coal, as mentioned, contains a certain amount of water and certain amounts of hydrocarbon compounds.

Injected hydrocarbons, other carbon compounds and water are cracked in the metal bath, so that carbon, oxygen and hydrogen are released. Injected carbon and oxygen, and carbon and oxygen formed at cracking react to carbon monoxide according to the exothermic reaction 2C + 2 ~~~ 2CO (~) .

The released hydrogen passes off in the form of hydrogen gas (H2).

The cracking of hydrocarbons and water are endothermic reactions.
The exothermic oxidation of carbon, however, results in the form-ation of a heat exceæs9 ~o that the metal bath must be cooled, which i8 ef~ected by introducing said coolant into the metal .
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. ~ , The coolant according to the invention may contain a hydrogen-containing compound~ preferably water. When using water as coolant, it i9 cracked 80 that great amounts of hydrogen gas are formed, , at the same time as the necessary amount of injected oxygen drops.

The gases carbon monoxide and hydrogen gas thu~ generated are collected in the collecting hood 6 and recovered in a desired manner.

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For different reasons, however, it is dçsirable that the coolant contains metal or metal oxides of the same metal, of which the bath substantially is composed. This is especially favourable in the case when said method is combined with the production of a metal. In such cases the coolant preferably contains ore concen-trate consistin~ substantially of metal oxide.

Metal oxides injected are reduced in the metal bath according to the ~ormula MeO ~ C --~ CO (g) + Me :
' where Me designates the respective metal. The aooling is effected thereby that the cracking of the oxides is an endothermic reaction.

, As an example oan be mentioned that, when the metal bath is an ron~bath, the ore concentrate substantially consists of Fe203, Pe304 and~FeO-Metal ~xides are 1nJected into the metal bath in the manner described abave.

Slag formers, for example calcium oxide (CaO), prererably are added in order to flush gangue, which is introduced into the bath with the metal oxides, and coal ash, which is introduced with injected carbon.

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When the metal bath consistR Or a metal with a hi~her arfinity to sulphur than to oxygen, preferably metal scrap of the respecti~e ~ ~ ' '' ' ~ ` . ' . . , ~ .

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metal is injected.

Examples of such metals are copper, lead and zinc.

Metal scrap is added to the bath either through said injection or by applying it from above down into the metal bath. In this latter case cooling substantially is effected by heating the metal scrap to a temperature above meltin~ temperature.

The reactions combustion of coal, cracking of oxides, hydrocarbons and water, and the melting of metal scrap take place in the metal bath, which constitutes a heat-absorbing and heat-emitting, respectively, medium for the reaptions. The metal bath, further-more, is a filter for dust particles, for example oxides, which are introduced with the reactants or formed during said reactions, and for developing rising gases such as carbon dioxide (C~2) and sulpbur dioxide (S02). The metal bath particularly is an absorption medium for by-products formed at the reactio~s where components have a hig?h affinity to the metal bath. Accordin~? to the present invention, thus, a substantially dust-rree waste gaa is obtaine~, owing to the dust absorption in the metal bath. ~dditionally, the waste gas has a very low content of sulphur dioxide, because sulphur released at the combustion Or coal and at the solution Or coal into the~metal bath is absorbed by the same. According to the invention, the metal in the metal bath can partly be selected with respect to the desired capacity of absorbing sulphur. The metal8 zinc, copper, lead, iron and nickel have a high affinity , ' ' ' '' ~ .

1097~'78 to sulphur, declining in said order, wi~hin the temperature range near the melting point of the metal in question.

It is, thus, especially advantageous to select the metals zinc or copper, when the sulphur content in the injected coal i~ high, in order to suppress the formation of sulphur dioxide.

A further advantage is obtained at the use of metals, such as zinc, copper, lead etc., which have a relatively lower melting point than iron. Said lower melting point has the effect that the lining of the furnace body 2 has a suhstantially longer li~e than it would have if iron was used. This implies a substantial economic and practical advantage, in view of the fact that the , exchange of furnace lining is expensive and tedious. A separation of sulphur, furthermore, from the metal bath i9 simple, and the sulphur can be recovered as a pure gas of sulphur dioxide for the production in known manner of, for example, sulphuric acid (H2S04).
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~epending on the metal in the metal bath, the reactions between carbon and oxygen contained in the injected reactants take place in one o~ the following four ways, or combinations thereof:

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aj Oxygen is solved in the bath. The oxygen originates from in-~
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jected oxygen, cracked water or other crac~ed oxides or hydro-carbon~. Carbon particles located within the bath or on the phase boundarg surface gasJmetal are oxidized by oxygen solved , - ' g ~ ~ ' . ~ , ' : .
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1097()7l3 in the ~etal, according to the formula~:

2 ~ 2 o ~ O ~ 2C(s) --~ CO(g) ~his takes place in the cases when the metal solves-in oxygen, but doe~ not solve-in carbon, such as for example copper.
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b) The reactants react directly with each other in the injection . jet, according to the formula:
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~ 2 + 2C(s) --~ 2(CO(g) . ' ~, . .
c) Carbon is solved into the bath. The carbon is oxidize~ by oxy-gen at the phase boundary gas/metal or at oxide particles in the bath, acoording to the formulae:

. C ( S )--~ C
C ~ 1l202 --~ CO(g) This takes place in the cases when the metal solves-in carbon, : but doe8:not or only partially solve-in oxygen, such as rOr ex~rpl~iron. ~.

d) Carbon:and oxygen are.sol~ed into thè bath~where they react ; and thereby-form carbon monoxide,.according to the formulae:
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C(s) ~ C
2 ~ 2 0 C + O ~ CO(g) This applies, for example, to an iron bath.

Oxygen in injected water and in possibly injected hydrocarbons is cracked off and reacts like injected oxygen with carbon in some of the ways a)-d) stated above, or combinations thereo~. A~ said - cracking hydrogen is released.

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At the temperature prevailing in an iron bath (for example 1400C -1600Cj the equilibrium for the reaction 2CO~_ C02 + C is substantially offset to the left. In a metal bath with a consider--ably lower temperature, such as lead, a high CO-content is main-tain~ed by the oxygen deficit, beoause then the equilibrium is less substantially offset to the left.

When applying the method accordin~ to the invention, carbon, oxygen, water and possibly nydrocarbons are added in suah proportions, that the waste gas shows the most suitable composition of carhon monoxide and hydrogen gas with respect to its intended use. The waste gas, ~or example, can be used as combustion gas ~CO),hydrogen , : ~
: gas ~(H2)~ f~r the manufacture of hydrocarbons, suoh as methanol ;(C~I30H) or for the~manufacture of hydrogen- nitrogen compounds, : ~ . . ~ : .
- such as ammonia (NH ).

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1097~7B

Said method is extremely favourable for~the manufacture Or methanol, because both carbon monoxide and hydrogen gas are generated. At the synthesizing of hydrogen gas and carbon monoxide to methanol a hydrogen gas/carbon monoxide ratio of 2,1:1 is required. At the combustion of coal with injection Or only carbon and oxygen a ratio 1:4 i8 obtained.

By the addition of water as coolant, however, the hydrogen content in the waste gas can be increased to a ratio of 1:1 theoretically.
This ratio is te ~ regarded as a stoichiometric maximum. Injected water, however, cools the-metal bath substantially, so there is, without supply of external heating energy by, for example, said heating unit 3, a thermal maximUm, which is 1:4,2 when only carbon~
water and oxygen are injected. In order to obtain said lastmen-tioned ratio, it may be mentioned as an example that for develop-ing IONm3 waste gas per minute and ton of bath 2,6 kmol H 0 and 4,0 kmol oxygen together with 10,8 kmol carbon per minute are injeoted into a bath of the wei~ht of ~0 tons. By injecting h~dro-carbons with an average aomposit,ion between CH2 and CM4 the ratio ; ~can be increased, becausb their cracking to~ether with the 9ub- i sequent oxidizing of carbon is an exothermic reaotion series.
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At the method according to~the invention carbon is inJected, as t mentioned a~ove~ in a stoichiometric excess relative to oxygen contained in form of ~xidic compound~ in the metal bath. ~he excess amount o~ carbon is oxidized by oxygen injected with the reactants~
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Said carbon and oxygen, further, are lniected in such a stoichio-metric rationrelative to each other, that the formation of carbon dioxide (C02) and water (H20) is suppressed.

The proportion between carbon (C) and hydrogen (H), which are in-jected, preferably is such that the mole ratio between injected carbon and injected hydrogen is 0,25:1 to 4:1.

Furthermore, the proportion between carbon (C) and oxygen (0), which are injected, is such that the mole ratio between injected carbon and injectéd oxygen i8 1,2:1 to 4,6:1.
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For the proquction of methanol from the gas mixture, preferably part of the~generated carbon monoxide is used for the formation Or .
hydrogen gas in known manner according to the exothermic reaction ~ i .: ;
CO(g) ~ H20~g) - ~ H2(g) + C02(g) whereafter the carbon monoxide is washed out of the ~as mixture.
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The gas mixture and the amount of carbon monoxlde are thereat adjusted to the production Or hydrogen gas, so that the remaining gas has a hydrogen gas/carbon monoxide ratio of 2,1:1, i.e. the stoichiometrio ratio o~ these gases in methanol. The waste gas is passed further to a know~ synthesizing process ~or methanol. In the rollowing, an example o~ a synthesizing process briefly is sta~ed.
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109'~
The syn~hesizing proceeds in the steps as rOllOws:

a) The gas mixture of carbon monoxide and hydrogen gas is passed through a cooling and dust cleaning unit. Although the gas mix-ture substantially is free of dust, it must be dust cleaned because the gas mixture used for the production of methanol i9 required to be absolutely free of dust.

b) The gas ~ixture is passed to and collected in a gas-holder in order to balance intermittent steps in the process.

c) The cooled cleaned gas is compressed to 30 bar and reacted with water vapour in a so-called shift-reactor where ingoing gas is heat exchanged with out¢oing gas, whereat the exothermic reaction CO + H20 --~ H2 + C2 takes place, as described above, in order to adjust the hydrogen gas/carbon monoxide ratio to 2,1:1.

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d) Carbon dioxide and possibly remaining sulphur compounds are re-moved in an absorption system.

e) The gas is compressed to 100 bar whereafter the synthesis to methanol takes place in a reactor w~lere ingoing gas is heat ex-changed against outgoing gas.
f) The outgoing gas i8 condensed to liquid methanol.

An alternative to utiliæing part o~ the generated carbon monoxide for reaction With water to hydrogen gas and carbon dioxide i9 to separate part o~ thé generated carbon dioxide in known manner, so~that the gas mixture is caused to directly assume the stoichio-metric ratio of carbon monoxide and hydrogen g~8 in methanol.

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1097(178 The generated gas mlxture of carbon mon~xide and hydrogen gas can also be caused to assume the stoichiometric ratio in hydrocarbon compounds other than methanol, such as ror example ethanol, butanol etc. This can take place either by reactin~ part of the generated carbon monoxide with water to hydro~en ~as and carbon dioxide or by separating part o~ the generated gas mixture.

A very ~reat advantage o~ the method according to the invention is, that the carbon inj ected can be of a widely varying quality.
Lignite, for example, or anthracite can be used as well as coal types with high or low sulphur content. Furthermore, as mentioned, hydrocarbons of various kinds and other carbon compounds can be injected. Coal in the form o~ ve~etable material, such as peat ~and wood pro,ducts in atomized state may al80 be injected.

The metal in the metal bath has a high affinity to sulphur which, therefore, is solved into the metal bath. Preferably such amounts of reactants are injected, that the sulphur content in the metal bath is caused to increase at maximum to suoh a value, that the sulphur dioxide content in the ~as mixture is 1000 ppm, whereafter the metal bath i9 subjected to desulphurization. Depending on the ~ selected metal, the desulphurization thereo~ i9 carried out in h ~ difrerent ways. When the affinity of the metal to oxygen is much lower than~that~of the sulphur, as is the case for example with oopper, the dssu1phurization is ~arried out by~oxidizing the sulphur in known manner according to the formula Cu2S ~ 2 ~~~
2Cu ~ S02. When,~however, the a~finity of the metal to oxygen i9 ~: ' : .': ` `

1097t~78 not sufficiently much lower than that o~ the sulphur, as is the case for example with iron, the desulphurization is carried out with a desulphurizing agent, for example calcium oxide, CaO, according to the formula CaO ~ s2 __~ CaS + o2 The desulphuriza~io~ preferably is carried out at an occasion when no injection takes place, so that an efficient collection of sulphur dioxide and CaS, respectively, can take place.

When a coolant containing metal or metal oxide3 is aAded, the volume of the metal bath increases. As by-products, thus, molten or reduced-out metal and slag originating from coal ash and gangue, as mentioned, are obtained. After said desulphurization and removal Or slag, part of the metal is poured on in known manner, so that the metal bath reassumes a suitable volume.

The present invention, as desoribed, offers great advantages over known processes of coal gasification. The most important advant-ages are that a ~a~ substantialiy free Or sulphur and dust can be generated from ¢oal with high sulphur and dust contents, and that sulphur, which has been injected with the reactants into the metal bath, is removed ~rom the bath in a relatively concentrated state :
and is collected. Collected sulphur in the form of sulphur dioxide : can bé used as raw material, for example, for the manufacture of sulphuric acid.
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1097-~78 A further great advantage is, that subs~antially all carbon con-tained in the reactants is oxidized to carbon monoxide. According to the invention, furthermore, great amounts of hy~rogen gas are produced ~ubstantially by injection of water, which also con-stitutes a coolant for the exothermic oxidizing of carbon, or by injection of hydrocarbons.

The by-product from a process according to the present method is metallic material, which renders it possible to combine the gasi-.

fication of coal with metal production, whereat also the by-product represents a great value.

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A great advantage is also the easy control of the process, becau~e the reactants to be injected can be selected within wide limits for bringin~ about dirferent desired gas compositions.

he inventi~on is not to be regarded restricted to the examples of embodiments statéd above. The amounts of injected material of dif~erent kind, ~or example, oan be varied widely within the valuec stated in the examples. A great proportion o~ injeoted ,. ~:, ~ , ~ , material, rOr example, may consist of hydrooarbons, Furthermore, metal baths other than those ment1oned above can be ; used~. A great number o~ gas compositions in addition to the ones stated above~ oan be produced aocording to the~invention.

The invention~ thus5 can be varied within it,s scope defined by the atta¢hed claims.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of producing a gas mixture substantially free of sulphur and dust for further processing or combustion, consisting substantially of carbon monoxide (CO) and hydrogen gas (H2) from carbon (C) in the form of coal containing a certain amount of water, hydrocarbons and carbon compounds, characterized in that said carbon is injected into a metal bath in a stoichiometric excess relative to the oxygen in the form of oxidic compounds con-tained in the metal bath, together with oxygen and together with a coolant.

2. A method according to claim 1, characterized in that said carbon and oxygen are injected in such a stoichiometric ratio relative to each other, that the formation of carbon dioxide (CO2) and water (H2O) is suppressed.

3. A method according to the claim 1, characterized in that said coolant comprises metal oxides of substantially the same metal constituting the main constituent in said metal bath.

4. A method according to claim 1, 2 or 3, characterized in that said organic material comprises peat or wood products.

5. A method according to claim 1, 2 or 3, characterized in that carbon or carbon compounds containing sulphur are injected into the metal bath in such an amount, that the sulphur content in the metal bath is caused to be at maximum of such a value, that the sulphur dioxide content in the gas mixture is 1000 ppm, whereafter the metal bath is desulphurized in a known manner.

6. A method according to any one of the claims 1, 2 or 3, characterized in that the mole ratio carbon (C) to hydrogen (H) injected into the metal bath is 0,25:1 to 4:1.

7. A method according to any one of the claims 1, 2 or 3, characterized in that the mole ratio carbon (C) to oxygen (O) in-jected into the metal bath is 1,2:1 to 4,6:1.

8. A method according to the claims 1 or 3, character-ized in that said coolant contains water.

9. A method according to claim 1, characterized in that the main constituent metal in the metal bath is iron.

10. A method according to claim 1, characterized in that the main constituent metal in the metal bath is copper.

11. A method according to claim 1, characterized in that said carbon, oxygen and water are injected in such proportions relative to each other, that said gas mixture is caused to assume such contents of carbon monoxide and hydrogen gas, that by reaction of a certain amount of water and generated carbon monoxide to hydrogen gas and carbon dioxide the gas mixture is caused to assume the stoichiometric ratio of carbon monoxide and hydrogen gas in a hydrocarbon compound selected from the group consisting of methanol, ethanol and butanol, and that said gas mixture is converted to said hydrocarbon compound in a suitable way known per se.

12. A method according to claim 1, characterized in that carbon, oxygen and said water are injected in such proportions relative to each other, that said gas mixture is caused to assume such contents of carbon monoxide and hydrogen gas, that by removal of a certain amount of carbon monoxide from the gas mixture the gas mixture is caused to assume the stoichiometric ratio for a hydrocarbon compound selected from the group consisting of methanol, ethanol and butanol, and that said gas mixture is converted to said hydrocarbon compound in a suitable way known per se.

13. A method according to claim 11 or 12, characterized in that said hydrocarbon compound consists of methanol.