Note: Descriptions are shown in the official language in which they were submitted.
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The lnvention relates to a process for the preparation
of synthesis gas by partial combustion of coal during which
process tar is formed. This tar is separated from the
resultant synthesis gas. At least part of the tar is
gasified by partial combustion, with formation of soot. The
soot is separated from the resultant gas. At least part of
the soot is partially combusted together with the coal.
As feed for the process accorcling to the invention any
solid carbonaceous material may be used. By solid carbonaceous
material is meant any solid fuel which consists substantially
of chemically bound or unbound carbon. In addition, this
material may contain hydrogen, oxygen, sulphur, nitrogen,
metals and/or ash. A starting material o~ this tyoe comprises,
fcr example, lignite, bituminous coal, sub-bituminous coal,
arthracite and coke.
Depending on the method followed to gasify the coal it
is first rendered into small pieces or oowder form before
being converted by partial combustion. The partial combuskion
of the coal with formation of tar can be carried out in any
desired manner, such as, for example, by means of the Lurgi
process or the Synthane process. These processes have been
described in "The Oil and Gas Journall' o~ 26th August, 1974,
pp. 80 and 84. Preferably the Lurgi process is u~sed for the
~;; first stage of the process according to the invention.~ This
process is extensivçly elucidated in "Ullmanns Enzyklopadie der
technischen Chemie", Vol~. 10, pp. 418~ll24. During the partial
combustion of the coal it is converted with oxygen, air or
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oxygen enriched air into a gas mixture which mainly
consists of hydrogen and carbon monoxide. In addition,
larger or smaller amounts of nitrogen, C02, H20, CH4, H2S
and COS may occur in the gas mixture, depending on the
nature of the coal, the composition of the oxidizirlg gas
and the gasification process used. As oxidizing gas use
is preferably made of oxygen since this produces a gas of
high calorific value.
An amount of 0.2'0.4 Nm3 of oxygen is suitably used
per kg of coal. As temperature moderator steam is prefer-
ably introduced during the partial combustion of the coal.
An amount of 2-9 kg of steam per Nm3 of oxygen is suitably
added to the reaction mixture.
After the coal has been gasified, pre~erably at a
temperature in the range from 700 to 1100C, the resultant
gas is withdrawn from the gasification reactor. This gas
generally has a temperature in the range ~rom 370 to 600C
and in additlon to the desired H2,` C0 and CH4, it contains
undesirable impurities such as tar, oil, naphtha~ phenols,
water, ammonia, hydrogen sulphide, carbon dioxide and dust
of coal and ash. In order to separate the impurities from
the desired gas the crude gas is cooled to a temperature
between 40 and 200C, preferably by indirect heat exchange
~ with water during which steam is generated. During this
process the tar~ the oil, the naphtha~ the phenols and the
water condense, while the coal and the ash are taken up in
.
the condensing liquid. The condensed liquid is separated
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from the remaining gas. Oil, naphtha, phenols and ash
and coal containing tar are recovered from the separated
liquid by means of fractional distillation. The gas may
be purified in a known manner of hydrogen sulphide, carbon
dioxide and any other impurities such as COS, CS2 and HCN.
At least part of the tar is gasified by partial
combustion with formation of soot. For this partial com-
bustion use may be made of oxygen or air, enriched or not
- enriched with oxygen. The tar is preferably gasified with
oxygen. This gasification may be carried out in any
desired manner. A review of the known processes for the
preparation of hydrogen and carbon monoxide containing gas
by partial combustion of liquid fuels is given in 'IChemiker
Zeitung" o~ 3rd March, 1972, pp. 123-134. The Shell
Gasification Process is preferably used for the gasification --
of the tar. This process is described in "Chemical Economy
and EngineeFing Review", December 1973j Vol. 5~ No. 129
pp. 22-28.
. . .
During the partia,l combustion of the tar steam is
~ preferably supplied as temperature moderator. Suitably
0.5-3 kg of steam~is~ added per kg of tar.
The bxygen or the oxygen-containlng gas is preferably
preheated to a temperature between 200 and 500C before it
is supplied to the reaction zone in which the partial com-
`~25 ~ bustlon of the tar takes place. After~preheating,-the hot
oxidizing gas is advantageously mixed with the tar and the
gas~tar mixture is preferably atomized under high pressure
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in a reactor. The excess pressure is advantageously
1-50 atm. higher than that in the reactor. This reactor
suitably comprises an empty steel vessel, the interior of
which is lined with heat-resistant material. A preferred
reactor is described in the U.K. patent specifications
780,120; 832,385; 850,409 and 967,885.
The partial combustion of the tar is preferably
carried out at a temperature in the range ~rom 1000 to
1500C, which temperature is the resu]t of the reaction
between the tar and oxygen and optionally steam.
The pressure maintained in the reactor may vary within
wide limits and is advantageously kept in the range ~rom
1 to 100 atm. abs. In order to convert into gas as much as
possible o~ the tar introduced into the reactor, the tar
droplets must be present in the reactor for a certain
residence time. It has been found that a residence time
between 1 and 15 seconds is sufficient to achieve this
object.
After the tar has, been converted into gas~ this
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reaction product~ which consists substantially o~ H2, C0,
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C02, N2 and H20, is discharged from the reactor.
This gas has a high temperature, generally a tempera-
ture-above 1100C~, and contains;ash, soot and hydrogen
sùlphide. Ruring the gasi~ication 0.05-0.20 kg o~ soot is ~ ;
generally formed per kg of tar. To permit the removal of
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the impurities, the gas is ~irst cooled. This cooling is
pre~erably effected by injection of water, steam and/or
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part of the cooled and puri~ied product gas. According to
another preferred embodiment of the process according to
the invention, the cooling is entirely or partly carried
out in a boiler in which steam is generated by means o~ the
waste heat.
The gas is preferably cooled to a temperature in the
range from 120 to 250C.
The solid matter content of the cooled gas is kept low
by choosing the conditions in the reactor appropriately.
Nevertheless, a reduction in the solid matter content is
desirable, for example if the gas has to be desulphurized,
and also if in the gas carbon monoxide has to be converted
with water into carbon dioxide and hydrogen. To this end
the gas is preferably passed through a scrubber in which it
is washed with a liquida preferably with water. An instal-
lation of this type is described in the U.K. patent
specification 826,209.
A washing treatment of this t~pe produces a gas which
contains substantially no solid matter and which has a
temperature between 20 and 80C. The dry gas freed of solid
matter~has a composition which is usually between the
following 1imits.
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TABLE I
% by volO
H2 15 - 5
CO 15 - 3
C2 7 - 30
CH4 ~ 5
H2S 0.05 - 0~50
N2 ~ ~ 1 - 55
It is preferably further purified by removing H2S and
posslbly at least part of the CO2. This purification may
be carried out in a known manner.
H2S and CO2 are preferably~removed from the gas by
,
: means of the ADIP process or the SULFINOL process, which
: ~ are described in the U.-K. patent specifications 1,444,963;
:15 ljl31,989; 965,358; 9579260 and 972,140.
: The dry gas~freed of solid matter and H2,S has a
: composition between the ~ollowing~limits~
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TAB`~E II
- % by vo
: ; ~ 15 - 50
CO :~ ~ ~ 15~ 30;
CH4 ~ ~ 5
H2S~ D.001 -~O.010
25~ N:2 ~ A ~ 55 :
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As has been described above, -tar is formed as a by-
product in the gasification of the coal. This tar generally
contains 1-25% of solid matter, viz. ash and unconverted or
partially converted coal particles.
Since a high solid-matter content impedes the subsequent
gasification of the tar, at least part of the solid matter
is preferably removed from at least part of the tar.
This may be effected in any suitable manner by allowing the
solid matter to settle from one part of the tar into another
part of the tar. Preferably, the solid matter is removed
from 25-75% of the tar by allowing the solid matter to settle
into 75-25% of the tar. Another advantageously used process
for the removal of the solid matter from the tar comprises
washing of the tar with hot water, preferably water at 125C.
The part of the tar from which the solid matter has
been removed is particularly suitable for gasification by
partial combustion. Conse~uently at least part of the said
tar is preferably used for this purpose.
The part of the tar from which no solid matter has been
removed or which as a result of the above settling process
now contains even more solid matter than it originally con- --
tained, is preferably recycled to the partial combustion of
the coal with or without having been mixed with the coal
intended as feed.
.
According to a preferred embodlment of the process
according to the invention,~25-75% of the tar is directly
gasified and 75-25% of the tar is recycled to the pa~tial
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combustion of the coal.
As has been mentioned above, soot is ~ormed during
the gasification of tar by partial combustion. This soot
is separated from the resultant synthesis gas and at least
part of this soot is partially combusted together with the
coal to obtain H2- and C0-containing gas. For the sepa-
ration of the soot from the gas use is advantageously made
of methods which have been described in the U.K. patent
specifications 826,209 and 1,267,896.
If part of the tar formed during the partial com-
bustion of the coal ls now also recycled to the partial
combustion of the coal, it is preferred to admix at least
part of the soot with at least part of the tar and the
~esultant tar/soot mixture is partially combusted together
with the coal. To incorporate the soot it is advantageous
to use that part of the tar which contains solid matter,
namely ash and unconverted or at least partially converted
coal. It is suitable to use 3-10 parts by weight of tar
per part by weight of'soot. ~ ~
The soot may be directly incorporated lnto the tar or
the soot may first be taken up in water and subsequently
~ in the tar. In the former case~the crude gas resulting
; from the partial combustion of part of the tar is contacted
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with another part of the tar? so that the soot is incorpo-
~25 rated into this latter part of the tar. In this process
the crude gas is preferably f1rst cooled to a temperature
in the range from 50 to 200C, while the tar which is
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intended for taking up the soot preferably has a temper-
ature in the range from 50 to 200C. In the latter case
soot-containing water which preferably has a soot content
of 0.5-10% by weight and a temperature in the range from
100 to 150C is contacted with stirring with tar which
preferably has a temperature in the range from 100 to
150C.
In the former case 0.001 m3 of tar is advantageously
used per Nm3 of soot-containing gas.
In the latter case 1 m3 of soot-containing water is
suitably contacted with 1 m3 of tar.
Starting from 1000 kg of coal lt is possible by means
of the process of the invention and after drying and
removal of H2S and CO2 to obtain 1500-3300 Nm3 of a
synthesis gas having the following composition:
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% by vol.
H2 ~3 ~ 45
- CO 19 - 24
CH4 8 - 30
N ~ A ~ ~ 1 45
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~ The invention will now be further elucidated with ~ ~
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~: reference to the~fo11Owine Example. ~ ~
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EXAMPLE
The starting material used was coal having the
~ollowing composition:
C 72.95 % by weight
H 4.88 % " "
0 10.78 % " ~'
S 1.36 % " "
N 1.56 % " "
ash 8.47 % " "
This coal contained 34.7% by weight Or volatile
components and also 2% by weight of water. The coal was
gasified by partial combustion together with a quantity o~
solid matter-containing tar from a subsequent stage of the
- process. Per kg of water and ash-free coal o.o6 kg of tar
was added and 0.356 kg of oxygen and 1.524 kg of steam
were used. The oxygen supplied had a temperature of 250C.
The steam temperature was 263C.
The gasification was carried out at a temperature
between 700 and 1100C and a pressure of 40 atm.abs.
After cooling of the resultant gas to 125C, tar was
removed from the gas.
O.lO kg of tar was recovered per kg of coal.
The tar contained 15% by welght of solld matter.
After drying, the resultant gas had the following
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composition:
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% by vol.
H2 29.3
CO ~5.5
C2 31.7
CH4 22.1
H2S 0.5
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A quantity of 2.08 Nm3 of this gas wae formed per kg
of water- and ash-free coal.
1~0 The solid matter was allowed to settle from 50% of
the tar into the rest of the tar. The two portions of tar
were subsequently separated. The pure tar was converted
in a separate reactor by partial combustion with I.057 kg
of oxy~en and 2.5 kg of steam per kg of tar into a soot-
containing synthesis gas. The temperature was 1100C and
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the pressure 40 atm.abs.
The crude synthesis gas was cooled to 180C by
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indirect heat exchange with waterO The gas was subsequently~
washed with water as a result of whlch the soot was absorbed
by the water. 0.15 kg of soot was ~ormed per kg of tar.
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~ The dry synthesis gas which was ~reed o~ soot had the
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rollowing composition~
% by vol.
H2 ~8.0
CO ~ 25.2
2 ~ 25.6
1.0
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A quantity of 2.57 Nm3 of this gas was formed per
kg of tar.
The part of the tar in which the solid matter from
the other part had settled was intimately mixed by stirring
with the soot-containing water at a temperature of 125C,
the soot being incorporated into the tar. The soot- -
containing tar and purified water were subse~uently sepa-
rated from each other. The soot- and solid-matter-
containing tar was recycled to the partial combustion of
the coal.
The synthesis gas recovered directly from the coal
was mixed with the synthesis gas recovered from the
purified tar. Ultimately~ 2.228 Nm3 of dry synthesis gas
was thus obtained per kg of coal, having the following
:
composition:
% by vol.
-H2 3 4
C0 ~ - 16.1
C2 ~ ~ 31-3
~20 ~ CH4 20.8
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H2S 0 5
; N2 ~ A 0.9 ~ ~
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