Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Reexamination Certificate
2000-01-24
2004-08-24
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
C422S169000, C422S172000, C423S574100
Reexamination Certificate
active
06780392
ABSTRACT:
The invention relates to a process and an apparatus for the conversion of hydrogen sulfide (H
2
S) into elemental sulfur (S).
Sulfur is required in many chemical processes either in elemental form or in the form of sulfuric acid. However, sulfur is highly toxic in the form of sulfur dioxide (SO
2
) or as hydrogen sulfide. Therefore, there are maximum permissible emission limit values for the sulfur compounds, which are becoming increasingly more stringent worldwide.
Fossil fuels, such as natural gas, coal, oil sand, oil shale and petroleum, comprise organic and inorganic sulfur compounds. It is necessary to remove these sulfur compounds or to convert them into harmless sulfur compounds. To remove the sulfur compounds from fuels and combustion products there exists a multiplicity of physical and chemical conversion processes.
In the case of solid fuels, the sulfur compounds are absorbed after the combustion in the power station as sulfur dioxide by a flue gas desulfurization system using milk of lime and converted into calcium sulfite. By oxidation with the residual oxygen present in the exhaust gas, gypsum is formed as end product.
In the case of liquid fuels, such as diesel fuel or light fuel oil, maximum permissible sulfur contents are prescribed. This is because flue gas desulfurization after possible consumption in engines, for example, can no longer be implemented. The desulfurization of these fuels is carried out in the refineries. The sulfur compounds present in the crude oil are recovered in the distillate, the heavy oil fraction having the highest sulfur concentrations.
The desulfurization is performed using gaseous hydrogen (H
2
). The organic sulfur compounds are converted in this case into hydrogen sulfide. The hydrogen sulfide, which is present in the gas mixture with hydrogen and other hydrocarbons, is scrubbed out in amine scrubbers as Claus gas or hydrogen sulfide gas at concentrations of up to 90% by volume of hydrogen sulfide. Hydrogen sulfide is also formed in the sour water stripping columns. In this case, hydrogen sulfide is present as aqueous condensate and is stripped out as sour water stripper gas (SWS gas) containing up to 50% by volume of hydrogen sulfide. In addition, up to 50% by volume of ammonia (NH
3
) can be present, which is formed by decomposition of organic nitrogen compounds.
The combustion of coal or heavy oil in power stations in which the fuel is gasified in advance under an oxygen deficit also produces a hydrogen-sulfide-containing synthesis gas, which is purified prior to the combustion.
Hydrogen sulfide, moreover, occurs at varying concentrations in associated oil field gas and in natural gas at a content of up to 30% by volume and in the off-gas from sewage treatment plants at a content of up to 5% by volume of hydrogen sulfide.
The industrial utilization of hydrogen sulfide is limited. Therefore, it is first converted into elemental sulfur and then in special plants into sulfuric acid. Elemental sulfur is required in the rubber industry. Sulfuric acid is used in the chemical industry.
Direct conversion of sulfuric acid into elemental sulfur is possible by thermal cleavage of hydrogen sulfide, wet oxidation of hydrogen sulfide in a liquid (aqueous) phase and dry oxidation of hydrogen sulfide in the vapor phase.
The direct conversion process most frequently utilized with over 2000 plants worldwide is the Claus process, which was developed as early as 1883. This process is based on a dry oxidation process. A multiplicity of process variants have arisen. All process variants are based on the same fundamental chemical reactions and on the use of a thermal reactor and a catalytic reactor.
The thermal reactor consists of a combustion chamber having a burner, a waste-heat boiler and a first sulfur condenser. The catalytic reactor is constructed to have two or three stages. The stages each have a heater, a catalyst bed and a sulfur condenser.
In the combustion chamber and the catalytic reactors, the fundamental chemical reactions below proceed:
1.
H
2
S
+
1
/
2
O
2
+
1.88
N
2
→
1
/
3
SO
2
+
2
/
3
H
2
S
+
1
/
3
H
2
O
+
1.88
N
2
2.
1
/
3
SO
2
+
2
/
3
H
2
S
+
1
/
3
H
2
+
1.88
N
2
→
S
+
H
2
O
+
1.88
N
2
Overall:
H
2
S
+
1.2
O
2
+
1.88
N
2
→
S
+
H
2
O
+
1.88
N
2
The remaining associated gases present due to the process, such as hydrogen, methane, higher hydrocarbons, ammonia, steam, carbon dioxide, react in accordance with their concentrations in a multiplicity of side reactions.
The actual Claus reaction between sulfur dioxide and hydrogen sulfide in which elemental sulfur and steam are formed is reaction 2. This proceeds in the catalyst bed.
Elemental sulfur is additionally directly produced by the thermal cleavage of hydrogen sulfide into sulfur and water in the combustion chamber:
H
2
S→H
2
+½S
2
This reaction is highly endothermic.
In terms of the process, one third of the amount of hydrogen sulfide, usually a mixture of Claus gas and sour water stripper gas, is burnt by the burner substoichiometrically by the combustion air to give one third of sulfur dioxide. The remaining hydrogen sulfide is thermally cleaved in the combustion chamber into sulfur and hydrogen in the temperature range between 900° C. and 1300° C. and is catalytically converted at temperatures between 180° C. and 400° C. in the catalytic reactors together with the unburnt hydrogen sulfide to give elemental sulfur and water. The reaction to give sulfur is optimum when the hydrogen sulfide/sulfur dioxide ratio is two to one. However, the optimum ratio is only reached to an approximation in practice.
The elemental sulfur formed in the combustion chamber is already separated off in the liquid state after cooling the process gas downstream of the waste-heat boiler and in the first sulfur condenser. In the downstream catalytic reactors, the cooled process gas is heated to the necessary reaction temperature prior to entry into the catalysts by the upstream heaters using high-pressure steam or a thermal oil. The sulfur formed by the Claus reaction is likewise separated off in the liquid state in the sulfur condensers.
On account of the varying hydrogen sulfide concentration in the feedgas, in the conventional Claus processes, there are two main variants: the main stream operation for hydrogen sulfide concentrations above 50% by volume and the side stream operation for hydrogen sulfide concentrations between 30% by volume and 50% by volume.
In the main stream operation, the entire quantity of hydrogen sulfide is partially combusted with the combustion air in the combustion chamber. Owing to the thermal cleavage of the hydrogen sulfide in the combustion chamber, a high proportion of sulfur is already separated off in the first sulfur condenser downstream of the waste-heat boiler. For hydrogen-sulfide-rich gas, the degree of sulfur conversion in a three-stage Claus process is 96 to 97%.
Downstream tail gas treatment plants, generally Claus processes having a thermal afterburning, then make it possible to comply with the regulatory limit values dependent on the plant capacity.
In the side stream operation, on account of the low heating value of the hydrogen sulfide gas, the gas stream is divided. At least one third of the hydrogen sulfide gas is burnt with the necessary combustion air in the combustion chamber and the resulting sulfur-dioxide-rich reaction gas is mixed with the remaining hydrogen sulfide gas upstream of the first reactor. In this process, no elemental sulfur is formed in the combustion chamber, since the hydrogen sulfide gas is completely combusted.
At hydrogen sulfide concentrations below 30% by volume, even the sidestream operation is no longer usable, on account of the low heating value. The combustion then becomes unstable. Furthermore, the sidestream operation generally requires an ammonia-free feedgas. Otherwise, the catalysts are contaminated by ammonia via the bypass.
Gross Gerhard
Spitaleri Vincenzo
Air Liquide Deutschland GmbH
Langel Wayne A.
LandOfFree
Method and device for converting hydrogen sulfide into... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for converting hydrogen sulfide into..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for converting hydrogen sulfide into... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3306684