Claus catalytic converters

The Claus Catalytic Cbnverters. These units represent the heart of any sulfur recovery plant. While the bulk of the sulfur yield may be obtained in the front end reaction furnace the high overall recovery levels demanded by environmental regulations are largely dependent on the efficiency of the Claus catalytic converters. 

Catalysts help customers comply cost-effectively with clean-air regulations. Hydrocarbons, carbon monoxide, and nitrogen oxides can be removed using supported precious metal catalysts. Organic sulfur compounds are converted to H2S using nickel/molybdenum or cobalt/molyb-denum on alumina catalysts. Sulfur can be recovered in a Claus process unit. The Claus catalytic converter is the heart of a sulfur recovery plant. 

Bauxite catalysts (or alumina) are generally used in the Claus catalytic converters because of their high activity, durability, and low cost. Maximum equilibrium conversions are obtained at the lowest operating temperatures in the Claus catalytic converters. Theoretically, at this reactor temperature ( 230°C), 99% equilibrium conversion is possible. However, because the Claus reaction is a complex equilibrium reaction, the temperature cannot be lowered too much as sulfur will condense on the... 

Although the Claus catalytic conversion is a highly efficient process as presently employed in sulfur recovery plants the continuing efforts to reduce sulfur emissions to atmosphere demand that the last possible ounce of efficiency be squeezed from the process. Whether further small but critical improvements in the already high sulfur recovery efficiency can be achieved by more fine tuning of the converters and their catalyst charge remains to be seen. What cannot be accomplished in the catalytic converters will be achieved in the tail gas desulfurization processes. 

In the so-called Superclaus process, the last catalytic converter of the conventional Claus process is replaced by a catalytic converter containing the Superclaus catalyst . This catalyst consists of an a-alumina support with iron and chromium oxides as catalytic material. The Superclaus catalyst is highly selective for the direct oxidation of hydrogen sulphide ... 

H2S released from the stripper is treated in an O2- or air-blown Claus plant that oxidizes H2S to elemental sulfur. The tail gas from the Claus plant, still rich in sulfur compounds, is then treated in a Shell Claus off-gas treatment plant where those elements are catalytically converted to H2S and then recycled back to the absorption column of the AGR unit. 

The most important treatment process to prepare finished products is hydrodesulfurization (Section 6.8). The organic S- and Ncatalytically converted with H2 into the corresponding hydrocarbons, H2S and NH3, respectively. After separation, H2S is converted into elementary sulfur by the Claus process. 

As stated earlier, carbonyl sulfide and carbon disulfide hydrolyze fairly readily at temperatures in the range of 600° to 7(X)°F in the presence of water vapor and an active Claus catalyst. It is therefore advantageous to design the first catalytic converter for operation at this temperature level if high conversion efficiency is required and if substantial quantities of caibonyl sulfide and carbon disulfide are present. However, this results in inefficient operation of the first converter with respect to the Claus reaction, and installation of a third converter may be desirable to compensate for this loss in efficiency. If air pollution conirol regulations require high conversion efficiency, it is usually economical to use only two catalytic converters, and then remove residual sulfur compounds in a tail gas treating unit. 

The major problem with the split-flow configuration is that feed gas contaminants, which can deactivate the catalyst, have a direct path to the frrst catalytic converter. COS and CS2 formation would not be an issue in split-flow plants if equilibrium were attained in the reaction furnace. However, many Claus plant reaction furnaces are kinetically limited and do not achieve equilibrium. Therefore, both COS and CS2 can be formed in the reaction furnace and it is usually necessary to operate the first converter of a split-flow Claus plant at 620° to 660°F (325° to 350°C) to hydrolyze these compounds (Sames and Paskall, 1985). Increasing... 

Another Claus plant operating problem is condensation of sulfur on the catalyst resulting in rapid deactivation. This can be avoided by maintaining the temperature in the catalytic converters above the sulfur dew point of the gas mixture. Should sulfur condense on the catalyst, raising the gas temperature 50°F is usually sufficient to vaporize the condensed sulfur and reestablish catalyst activity (Norman, 1976). 

Process Description. Amoco has numerous configurations for the CBA process (Berman. 1992). involving from two to four total catalytic converters. The total number of converters utilized and their split between conventional Claus operation and sub-dewpoint operation is... 

Application of the process to the treatment of acid-gas streams is shown schematically in Figure 9-48. In this version, the sulfur dioxide is supplied by burning one-third of the acid gas in the same manner as in the split-flow Claus process (see Chapter 8). The glycol reactor is the equivalent of the catalytic converters of the Claus plant. 

The Claus process is the most widely used to convert hydrogen sulfide to sulfur. The process, developed by C. F. Claus in 1883, was significantly modified in the late 1930s by I. G. Farbenindustrie AG, but did not become widely used until the 1950s. Figure 5 illustrates the basic process scheme. A Claus sulfur recovery unit consists of a combustion furnace, waste heat boiler, sulfur condenser, and a series of catalytic stages each of which employs reheat, catalyst bed, and sulfur condenser. Typically, two or three catalytic stages are employed. 

Beavon [Beavon Sulfur Removal] Also called BSR. A process for removing residual sulfur compounds from the effluent gases from the Claus process. Catalytic hydrogenation over a cobalt/molybdena catalyst converts carbonyl sulfide, carbon disulfide, and other... 

Claus Process Parsons, Shell, Amoco Normally 15-20% HjS Production Co., through or more, with product Its licensees such as sulfur-burning, can Ford, Bacon Davis, handle H2S contents Ortloff, Olsen, and down to 5% many others 92 97% removal with 3 catalytic stages. COS CS2 not converted without provisions in design... 

Among the most effective of the modifications to Claus operating procedure is accurate temperature control of the catalyst beds. Gamson and Elkins (27) in the early 1950 s showed that equilibrium sulfur conversion efficiencies in the catalytic redox reaction rise dramatically as operating temperatures are lowered toward the dewpoint of sulfur. While some highly efficient subdewpoint Claus type processes are now in use the bulk of sulfur production from H2S still requires that the converters be operated above the dewpoint. Careful control of converter bed temperature has, however, contributed to improved efficiencies. This has in large part resulted from better instrumentation of the Claus train and effective information feed back systems. 

Elsewhere in this review we have commented on the problem of COS production as a result of high temperature reactions occurring in the front end furnace. Sulfur in this form is not subject to conversion to elemental sulfur in the catalytic redox Claus reaction and thus appears as COS in the tail gas where it is incinerated to SO2 thus adding to losses to the environment. The COS and any CS2 can be hydrolyzed to H2S which can then be converted by the redox Claus reaction. 

Beavon Also called BSR [Beavon Sulfur Removal], A process for removing residual sulfur compounds from the effluent gases from the Claus process. Usually used in conjunction with other processes. Catalytic hydrogenation over a cobalt-molybdena catalyst converts carbonyl sulfide, carbon disulfide, and other organic sulfur compounds to hydrogen sulfide, which is then removed by the Stretford process. A variation (BSR/MDEA), intended for small plants, uses preliminary scrubbing with methyl diethanolamine. Developed by the Ralph M. Parsons Company and Union Oil Company of California in 1971. More than 100 plants were operating in 2000. See also SCOT. 

SEPACLAUS [SEPAration CLAUS] An integrated process for removing hydrogen sulfide from coke-oven gases and converting it to elemental sulfur by the Claus process. It also catalytically decomposes the ammonia present. Offered by Krupp Koppers. 

Westvaco (1) A variation of the Claus process for removing hydrogen sulfide from gas streams, in which the sulfur dioxide is catalytically oxidized to sulfur trioxide over activated carbon at 75 to 150°C. The adsorbed sulfur trioxide is hydrated to sulfuric acid and then converted back to sulfur dioxide by reaction with the hydrogen sulfide at a higher temperature. 

Oil refineries and natural gas plants often produce large amounts of hydrogen sulfide, The most applied process for converting this hydrogen sulfide imo elemental sulfur is the modified Claus process. However, 3 to 5% of the H2S feed is not converted into sulfur and has to be treated alternatively. At the University of Utrecht a new catalytic process has been developed to oxidire hydrogen sulfide in Claus tail gas selectively to sulfur [ I,2 ... 

The hydrodesulfurization process involves catalytic treatment with hydrogen to convert the various sulfur compounds present to hydrogen sulfide. The hydrogen sulfide is then separated and converted to elemental sulfur by the Claus process. From this point some of the hydrogen sulfide is oxidized to sulfur dioxide by air and sulfur is formed by the overall reaction. 

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