The Claus process is the most significant gas desulfurization process, recovering the sulfur element from hydrogen sulfide gas. First patented in 1883 by chemist Carl Friedrich Claus, Claus's process has become an industry standard. C. F. Claus was born in Kassel in the State of Hesse Germany in 1827, and studied chemistry in Marburg before he emigrated to England in 1852. Claus died in London in 1900.
The multi-step Claus process recovers sulfur from the hydrogen sulfide gas found in crude natural gas and from sludge-containing sulfide-containing gases derived from crude oil refining and other industrial processes. The by-products of gas are mostly from physical and chemical gas processing units (Selexol, Rectisol, Purisol and amine scrubbers) at refineries, natural gas processing plants and gasification or synthesis gas plants. These byproduct gases may also contain hydrogen cyanide, hydrocarbons, sulfur dioxide or ammonia.
More than 25% of H 2 S gas is suitable for sulfur recovery at the Claus plant directly, while alternative configurations such as separate flow regulation or feeding and air heating can be used to process leaner feeds.
The resulting hydrogen sulphide, for example, in the hydro-desulfurization of the naphtha refinery and other petroleum oils, is converted to sulfur in the Claus plant. The reaction takes two steps:
- 2Ã, H 2 S 3 O 2 -> 2 SO 2 2Ã, H 2 O
- 4a, H 2 S 2 SO 2 -> 3 S 2 4 H 2 O
Most of the 64 million tonnes of sulfur produced worldwide in 2005 are sulfur byproducts from refineries and other hydrocarbon processing plants. Sulfur is used for the manufacture of sulfuric acid, pharmaceuticals, cosmetics, fertilizers and rubber products. The element of sulfur is used as fertilizer and pesticide.
Video Claus process
History
This process was discovered by Carl Friedrich Claus, a German chemist who worked in England. British patents were issued to him in 1883. This process was later significantly modified by IG Farben.
Maps Claus process
Description of process
The schematic process flowchart of the basic 1st SuperClaus 2 1-reactor (converter) unit is shown below:
Claus technology can be divided into two process steps, thermal and catalytic.
Thermal steps
In a thermal step, the saturated hydrogen sulphide gas reacts in a substoichiometric combustion at temperatures above 850 ° C as elemental sulfur deposits in the downstream gas cooling process.
The content H 2 S and the concentration of other flammable components (hydrocarbons or ammonia) determine the location at which the feed gas is burned. Gas Claus (acid gas) with no flammable content other than H 2 S burned with spears around the center dampened by the following chemical reactions:
- 2 H 2 S 3 O 2 -> 2 SO 2 2 H 2 O ? (? H = -518 kJ mol -1 )
This is the total free-total oxidation of hydrogen sulfide exothermic which produces sulfur dioxide which reacts in subsequent reactions. Most important is Claus's reaction:
- 2 H 2 S SO 2 -> 3 S 2 H 2 O
The overall equation is:
- 2 H 2 S O 2 -> 2 S 2 H 2 O
The temperature inside the Claus furnace is often maintained above 1050 ° C. This ensures the BTEX (Benzene, Toluene, Ethyl benzene and Xylene) destruction that otherwise would clog the downstream Claus catalyst.
Gases containing ammonia, such as gases from acid reflux water stripper (SWS), or hydrocarbons are converted in reducing the burner. Adequate air is injected into the muffle for complete combustion of all hydrocarbons and ammonia. The air to the acid gas ratio is controlled such that a total of 1/3 of all hydrogen sulfide (H 2 S) is converted to SO 2 . This ensures a stoichiometric reaction to Claus's reaction in the second catalytic step (see following section below).
The separation of the combustion process ensures an accurate dose of required air volume required as a function of feed gas composition. To reduce the volume of process gas or obtain higher combustion temperatures, air requirements can also be covered by injecting pure oxygen. Some technologies that utilize high-level and low-level oxygen enrichment are available in industry, requiring the use of special burners in reaction furnaces for this process option.
Typically, 60 to 70% of the total sulfur quantities produced in the process are obtained in the thermal process step.
The main part of the hot gas from the combustion chamber flows through the process gas cooling tube and is cooled so that the sulfur formed in the reaction step condenses. The heat released by the process gas and the evolved heat of condensation is used to produce steam or low pressure. The viscous sulfur is removed at the outlet portion of the liquid from the process gas coolant.
Sulfur is formed in a thermal phase as highly reactive S 2 which combines exclusively into S 8 allotropes:
- 4 S 2 -> S 8
Side reactions
Other chemical processes occurring in the thermal stages of Claus's reaction are:
- The formation of hydrogen gas:
- 2 H 2 S -> S 2 2 H 2 ((i> H & gt; 0)
- CH 4 2 H 2 O -> CO 2 4 H 2
- The formation of carbonyl sulfide:
- H 2 S CO 2 -> S = C = O H 2 O
- The formation of carbon disulphide:
- CH 4 2 S 2 -> S = C = S 2 H 2 S
Catalytic step
The Claus reaction continues in the catalytic step with active aluminum (III) or titanium (IV) oxide, and serves to improve the sulfur yield. More hydrogen sulfide (H 2 S) reacts with SO 2 formed during combustion in the reaction furnace in Claus reaction, and produces sulfur gas element.
- 2 H 2 S SO 2 -> 3 S 2 H 2 O (? H = -1165.6 kJ mol -1 )
One suggested mechanism is that S 6 and S 8 desorb from the active site of the catalyst with the simultaneous formation of the cyclic sulfur element stabilized.
Recovery of catalytic sulfur consists of three steps: heating, catalytic reaction and cooling plus condensation. These three steps are usually repeated a maximum of three times. If the exhaust gas processing unit (TGTU) is added to the downstream of the Claus plant, only two catalytic stages are normally installed.
The first process step in the catalytic stage is the process of heating the gas. It is necessary to prevent sulfur condensation in the catalyst bed, which may cause catalyst fouling. The bed operating temperature required in the individual catalytic stage is achieved by heating the process gas in the reheater until the desired operating bed temperature is reached.
Several methods of reheating are used in industry:
- The hot-gas passer: which involves mixing the two process gas streams from the process gas coolant (cold gas) and bypass (hot gas) from the first run of the waste heat-boiler.
- Indirect steamers: gases can also be heated with high-pressure steam in heat exchangers.
- Gas/gas exchangers: where the gas cooled from the process gas cooling is indirectly heated from the hot gas exiting from the upstream catalytic reactor in a gas-to-gas exchanger.
- Directly fired heater: reheater fired using acid or fuel gas, which is burned sub-geometrically to avoid breakthroughs of oxygen that can damage the Claus catalyst.
The operating temperature typically recommended at the first catalyst stage is 315 ° C to 330 ° C (bottom base temperature). High temperatures in the first stage also help to hydrolyze the COS and CS 2 , which are formed in the furnace and will not be altered in the modified Claus process.
The catalytic conversion is maximized at lower temperatures, but care must be taken to ensure that each bed is operated above the sulfur dew point. The operating temperature of the next catalytic stage is usually 240 Â ° C for the second stage and 200 Â ° C for the third stage (bottom base temperature).
In the sulfur condenser, the process gas originating from the catalytic reactor is cooled to between 150 and 130 ° C. The condensation heat is used to produce steam on the condenser shell side.
Prior to storage, the liquid sulfur stream from the process gas coolant, sulfur condenser and from the final sulfur separator is passed to the degassing unit, where the gas (especially H 2 S) dissolved in sulfur is removed..
The exhaust gas from the Claus process still contains flammable components and sulfur compounds (H 2 S, H 2 and CO) burned in the incineration unit or further desulfurization in the gas treatment unit throw downstream.
Sub droplet Claus Process
The conventional Claus process described above is limited in its conversion because the reaction equilibrium is achieved. As with all exothermic reactions, larger conversions can be achieved at lower temperatures, but as mentioned, the Claus reactor must be operated above the sulfur dew (120-150 ° C) to avoid the liquid sulfur that physically disables the catalyst. To solve this problem, the Clauss sub-dew point is parallel oriented, with one operation and one reserve. When a reactor becomes saturated with adsorbed sulfur, the process flow is diverted to the standby reactor. The reactor is then regenerated by sending process gas which has been heated to 300-350 ° C to evaporate sulfur. This stream is sent to the condenser to recover sulfur.
Process performance
More than 2.6 tons of steam will be produced for each ton of sulfur.
The physical properties of the sulfur elements obtained in the Claus process can differ from those obtained by other processes. Sulfur is usually transported as a liquid (melting point 115 Â ° C). In the base sulfur viscosity increases rapidly at temperatures over 160 Â ° C due to the formation of polymer sulfur chains. Another anomaly is found in the residual solubility of H 2 S in liquid sulfur as a function of temperature. Usually the solubility of a gas decreases with increasing temperature but with H 2 S it is the opposite. This means that a toxic and explosive H 2 S gas may form in the upper chamber of each cooling sulfur liquid reservoir. The explanation for this anomaly is the sulfur endothermic reaction with H 2 S for the polysulfanes H 2 S x .
See also
- Amine treats
- Hydro-desulfurization
- Crystasulf
- Hydrogenation
- Acid gas
- Acid gas
References
Source of the article : Wikipedia
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