Process of removing hydrogen sulfide from exhaust gas

A feed gas which contains H.sub.2 S is combusted with oxygen and air in at least one burner, which opens into a combustion chamber. The resulting gas mixture contains H.sub.2 S and SO.sub.2 and is intended to be converted to elementary sulfur by the Claus process. The combustion chamber is supplied with oxygen through a central tube of the burner, with the H.sub.2 S-containing feed gas through a second tube, which coaxially surrounds the central tube, and with air through a coaxial outer tube. The feed gas supplied to the burner contains H.sub.2 S and at least 5% by volume hydrocarbons or CO.sub.2. Velocities of flow of oxygen of 50 to 250 m/sec. and of the H.sub.2 S-containing feed gas of 10 to 30 m/sec. are adjusted at the outlet of the burner. Temperatures in the range from 2000.degree. to 3000.degree. C. are generated in the core zone of the burner flame. A gas mixture which contains at least 2% by volume CO and at least 8% by volume H.sub.2 and is at temperatures from 1350.degree. to 1650.degree. C. is withdrawn from the combustion chamber.

BACKGROUND OF THE INVENTION 
This invention relates to a process of combusting an H.sub.2 S-containing 
feed gas with oxygen and air in at least one burner, which opens into a 
combustion chamber, to produce a gas mixture which contains H.sub.2 S and 
SO.sub.2 and is intended to be converted to sulfur by the Claus process, 
wherein the combustion chamber is supplied with oxygen through the central 
tube of the burner, with the H.sub.2 S-containing feed gas through at 
least one second tube, which coaxially surrounds the central tube, and 
with air through a coaxial outer tube. 
Such a process and related equipment have been described in German Patent 
34 30 015. In that known process, relatively low temperatures and low 
velocities of flow of the gases are maintained adjacent to the outlet of 
the burner. 
SUMMARY OF THE INVENTION 
It is an object of the invention to permit the processing of an H.sub.2 
S-containing feed gas which contains also hydrocarbons or CO.sub.2. In the 
process described first hereinbefore this is accomplished in accordance 
with the invention in that the burner is supplied with an H.sub.2 
S-containing feed gas which contains at least 5% by volume hydrocarbons or 
CO.sub.2, velocities of flow of oxygen of 50 to 250 m/sec and of the 
H.sub.2 S-containing feed gas of 10 to 30 m/sec are adjusted at the outlet 
of the burner, temperatures in the range from 2000.degree. to 3000.degree. 
C. are generated in the core zone of the burner flame, and a gas mixture 
which contains at least 2% by volume CO and at least 8% by volume H.sub.2 
and is at temperatures from 1350.degree. to 1650.degree. C. is withdrawn 
from the combustion chamber. 
Owing to the high temperatures, a substantial quantity of carbon dioxide is 
broken down to carbon monoxide and oxygen and part of the water is also 
broken down to hydrogen and oxygen. As a result, part of the oxygen is 
made available which is required to maintain the high temperatures that 
are required adjacent to the burner flame and in the combustion chamber so 
that the total oxygen demand will be low. The hydrogen contained in the 
product gas mixture from the combustion chamber is valuable in the further 
processing of the gas mixture because hydrogenating reactions can be 
performed without an addition of extraneous hydrogen. Besides, the gaseous 
components H.sub.2 and CO constitute a valuable product as a synthesis 
gas. 
In accordance with a desirable further feature of the invention, the gas 
mixture from the combustion chamber is conducted through a Claus zone, in 
which H.sub.2 S, H.sub.2 and CO are withdrawn from the hydrolysis zone, 
and H.sub.2 S is separated from the last-mentioned gas mixture. Said 
further processing stages may be operated in known manner. Details of said 
processing stages have been described in Published German Application 34 
15 722 and the corresponding U.S. Pat. No. 4,632,819 and in Ullmanns 
Encyklopadie der technischen Chemie, 4th edition (1982), Volume 21, pages 
8 to 26 and are incorporated herein by reference. 
Possible embodiments of the process will be explained with reference to the 
drawing, in which:

DETAILED DESCRIPTION OF THE INVENTION 
The combustion chamber 1 comprises a plurality of burners 2, 3 and known 
pilot burner 4. The burner 2 is suppied with oxygen through line 6, with 
the feed gas through line 7 and with air through line 8. For the sake of 
clearness, the identical supply lines connected to the burner 3 have been 
omitted. The pilot burner 4 is supplied with fuel through line 10 and with 
air through line 11. 
The outlet portion of a burner consists of concentric tubes, which are 
shown in FIG. 2. Oxygen flows through the central tube 13, which is 
constricted at its outlet, and leaves the tube at velocities of flow 
mounting to 50 to 250 m/sec. The central tube 13 is surrounded by a second 
tube 14, through which the feed gas is supplied to the combustion. The 
feed gas contains H.sub.2 S as well as at least 5% by volume hydrocarbons 
or CO.sub.2. The feed gas leaves the second tube 10 at a velocity of 10 to 
30 m/sec. Air is supplied through the outer tube 15. 
The desired reactions are promoted by the flame structure which results 
from the burner design, the nature of the gases and their velocities of 
flow. Temperatures in the range from 2000.degree. to 3000.degree. C., 
preferably of at least 2300.degree. C., are obtained in the core zone 18 
of the burner flame so that the conversion of CO.sub.2 to CO and oxygen 
and the thermal decomposition of water will be promoted. Being at 
relatively low temperatures, the air envelope 19 which surrounds the hot 
portion of the flame protects the refractory lining of the combustion 
chamber and restrains the cooling of the core portion 18 of the flame. The 
temperatures in the air envelope 19 of the flame are approximately in the 
range from 800 to 1300.degree. C.. Temperatures from about 1350.degree. to 
1650.degree. C. will be obtained adjacent to the outlet 20 of the 
combustion chamber. The gas mixture which is at said temperatures contains 
at least 2% by volume carbon monoxide and at least 8% by volume hydrogen. 
Said gas mixture also contains SO.sub. 2, which has been produced by the 
combustion of part of the H.sub.2 S. 
In accordance with FIG. 3 the gas mixture from the combustion chamber 1 is 
fed through line 21 to a Claus plant 22, in which H.sub.2 S and SO.sub.2 
are reacted on catalysts to form elementary sulfur in known manner at 
temperatures decreasing from an initial value of about 320.degree. C. to a 
final value of about 200.degree. C. The known catalysts consist, e.g., 
substantially of TiO.sub.2 and Al.sub.2 0.sub.3, which constitute 
different fixed beds. The exhaust gas from the Claus plant is conducted in 
line 23 to a hydrolysis zone 24, in which the components of the gas 
mixture are subjected to hydrolyzing and hydrogenating treatments. As the 
exhaust gas contains enough hydrogen, extraneous hydrogen need not be 
supplied for that hydrogenation. 
The following remarks are made on the hydrolysis zone and the hydrogenation 
which is effected in that zone at the same time: Residual COS and CS.sub.2 
are hydrolyzed with steam to H.sub.2 S on a catalyst which consists, e.g,, 
of an Al.sub.2 0.sub.3 support impregnated with Co and Mo. Residual 
elementary sulfur and SO.sub.2 are reacted with hydrogen to form H.sub.2 S 
at the same time. The hydrolysis and the hydrogenation are effected on the 
same catalyst, which constitutes a fixed bed, at temperatures from about 
300.degree. to 350.degree. C. The treated gas now consists substantially 
of H.sub.2 S, N.sub.2, CO and H.sub.2. That gas mixture is supplied 
through line 25 to a separating plant 26, in which H.sub.2 S is separated, 
e.g., by chemical adsorption, e.g., by means of methyl diethylenamines 
(MDEA). Separated H.sub.2 S is recycled in line 27 to the combustion 
chamber 1. CO, H.sub.2 and N.sub.2 are available as mixed gases in line 28 
for further use. 
EXAMPLES 
A combustion chamber provided with four burners is supplied with a feed gas 
having the following composition on a dry basis: 
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H.sub.2 S 86.0% by volume 
CO 0.2% by volume 
CH.sub.4 1.0% by volume 
CO.sub.2 10.7% by volume 
N.sub.2 2.0% by volume 
H.sub.2 0.1% by volume 
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In cases A, B and C, said feed gas is combusted in part at different 
air-oxygen ratios. The oxygen which is employed is technically pure and 
leaves the respective burner at a velocity of flow from 150 to 200 m/sec. 
The velocity of flow of the feed gas at the outlet of the burner is about 
20 to 25 m/sec. The rates stated in the following Tables are related to 
1000 sm.sup.3 of dry feed gas. 
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A B C 
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Air rate (sm.sup.3) 
438 182 105 
Oxygen rate (sm.sup.3) 
254 296 309 
Nitrogen-oxygen volume ratio 
1:1 0.4:1 0.25:1 
Temperature at outlet of 
1427 1480 1497 
combustion chamber (.degree.C.) 
Maximum flame 2500 2600 2800 
temperature (.degree.C.) 
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The gas mixture leaving the combustion chamber 1 is composed as follows (% 
by volume): 
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A B C 
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H.sub.2 S 8.3 9.5 9.9 
SO.sub.2 4.8 5.5 5.7 
H.sub.2 O 41.0 46.6 48.6 
COS 0.8 0.9 1.0 
CS.sub.2 0.2 0.3 0.3 
CO 3.5 4.5 4.8 
CO.sub.2 3.6 3.8 3.9 
H.sub.2 10.9 14.2 15.4 
N.sub.2 25.0 13.0 8.6 
Other Sulfur compounds 
1.9 1.7 1.8 
100.0 100.0 100.0 
Gas rate: 
without elementary sulfur 
1436 1232 1172 
(sm.sup.3) 
with elementary sulfur 
1761 1558 1498 
(sm.sup.3) 
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That gas mixture is subjected to a two-stage Claus gas catalysis, in which 
Ti0.sub.2 in the first stage and Al.sub.2 0.sub.3 in the second stage are 
used as catalysts. 97% of the sulfur are recovered by that catalysis. 
The exhaust gas from the Claus gas catalysis is hydrogenated and hydrolyzed 
in the following procedure: 
The gas mixture is reheated to 320.degree. C. and is fed to a reactor in 
which hydrogenation and hydrolysis are effected on one and the same 
catalyst (A.sub.2 0.sub.3 impregnated with Co and Mo). After that 
treatment the gas mixture contains sulfur compounds only in the form of 
H.sub.2 S and the water that has been formed in the reactions has been 
removed to a residual content of 4% by volume. The gas mixture is 
subsequently fed to a separating plant, in which the H.sub.2 S is removed 
to a residual content of about 10 ppm by volume by means of MDEA in the 
Sulften process of Ford, Bacon and Davis Inc. in Dallas, U.S.A. The 
remaining gas obtained in line 28 is composed as follows: 
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A B C 
______________________________________ 
H.sub.2 19.1 29.7 14.8 
CO 6.9 10.5 12.2 
CO.sub.2 8.9 11.1 12.2 
N.sub.2 61.1 44.7 36.8 
H.sub.2 O 
4.0 4.0 4.0 
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That gas mixture, particularly the mixtures obtained in Examples B and C, 
can be used, e.g., in the hydrogenating desulfurization of petroleum 
products or as a fuel gas.