Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~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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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
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; 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-
,
1 3
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~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
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~ 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
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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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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
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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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1097U ~
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
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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:
:
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
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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:
. .
~ 2 + 2C(s) --~ 2(CO(g)
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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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1 n
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109~707~
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
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: gas ~(H2)~ f~r the manufacture of hydrocarbons, suoh as methanol
;(C~I30H) or for the~manufacture of hydrogen- nitrogen compounds,
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- such as ammonia (NH ).
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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
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CO(g) ~ H20~g) - ~ H2(g) + C02(g)
whereafter the carbon monoxide is washed out of the ~as mixture.
:
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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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.
.
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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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
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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.
.
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
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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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