Claus sulfur recovery

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. 

This is a desirable side reaction in the first catalytic reactor of the Claus sulfur recovery process. 

A disadvantage of the hydrocarbon—sulfur process is the formation of one mole of hydrogen sulfide by-product for every two atoms of hydrogen in the hydrocarbon. Technology for efficient recovery of sulfur values in hydrogen sulfide became commercially available at about the same time that the methane—sulfur process was developed. With an efficient Claus sulfur recovery unit, the hydrocarbon—sulfur process is economically attractive. 

Raw material usages per ton of carbon disulfide are approximately 310 m of methane, or equivalent volume of other hydrocarbon gas, and 0.86—0.92 ton of sulfur (87,88), which includes typical Claus sulfur recovery efficiency. Fuel usage, as natural gas, is about 180 m /ton carbon disulfide excluding the fuel gas assist for the incinerator or flare. The process is a net generator of steam the amount depends on process design considerations. 

Fluid catalyst regenerator Fuel gas combustion Claus sulfur recovery TRS X Storage tanks... 

The Stretford Process sweetens and also produces sulfur. It is good for low feed gas concentrations of H2S. Economically, the Stretford Process is comparable to an amine plant plus a Claus sulfur recovery plant. Usually, the amine/Claus combination is favored over Stretford for large plants. Stretford can selectively remove H2S in the presence of high CO2 concentrations. This is the process used in the coal gasification example in the Introduction. 

Figure 7. Claus sulfur recovery flow diagram.

Claus sulfur recovery plant, 23 601 Clay, 5 640. See also Clays in FCC catalysis, 11 681 as filler, 11 312... 

Modified carbon fibers, 13 383-385 Modified cellulosic membranes, in hemodialysis, 26 825, 826-828t Modified chemical vapor deposition (MCVD), in fiber optic fabrication, 11 136-137, 138, 139 Modified-Claus sulfur recovery process, 23 601, 602... 

Process Alternatives. Process alternatives for sulfur recovery are shown schematically in Figure 2. The choice of either elemental sulfur or sulfuric acid will depend on economics and markets related to each plant location. Elemental sulfur may be produced by gas-phase oxidation (the Claus process) or liquid-phase oxidation (e.g., the Stretford process). Stretford units were described in Section 1 and are well discussed in the literature (1, 2> 5) Claus sulfur recovery efficiency is usually less than required by current air emission standards. Therefore, some form of tail-gas treating is required. Sulfuric acid may be produced by the well-known contact process (6). This process is licensed by a number of firms, each of which has its own... 

The generation of the required reducing gas is very expensive because natural gas or low sulfur oil are used. Both of these fuels are in short supply and do not offer long-term solutions to the problem. However, in certain industrial processes, like petroleum refineries, a reducing gas could be readily available. Also, if a Claus sulfur recovery plant existed on-site, the concentrated SO2 stream could be sent to the Claus plant where it would mix with the H2S containing gas streams. Final adjustment of the H2S S02 ratio would be necessary. If the overall sulfur balance were favorable, the need for a reducing gas could be avoided. Either of these options could make the use of a recovery process economically attractive for industrial applications. 

Claus Sulfur Recovery Process The Claus process is a controlled combustion process commonly used for the recovery of sulfur from H2S. Temperatures >2,000°F (1,093.3°C) are achieved during combustion and yields of about 95% are typical. The basic reaction involves the following ... 

Environmental regulations may force the "Claus" sulfur recovery to exceed 99%, requiring tail gas treatment. High CO2 in the original Claus feed, hence in the Claus tail gas, works strongly against the tail gas processes which use amine solution to extract H2S, and subsequently require incineration of residual H2S in a large volume of CO2. 

Claus sulfur recovery unit, 200 long tons per day (ltpd) 11... 

Processes of this type are most frequently used for pro-cessir tail gases from Claus sulfur recovery plants, wiiich are operated to contain the correct stoichiometric proportions of hydrogen sulfide and sulfur dioxide [791. The other type of direct converaon process uses an alkaline solution (often sodium carbonate) containing one or more mild oxidizing agents that oxidize hydrogen sulfide to sulfur and are then themselves regenerated by oxidation with air [80]. 

Claus Sulfur Recovery Process, At the sulfur plant, H2S is combined with sour-water stripper off-gas and sent to a Claus unit. Invented in 1881 by Carl Freidrich Claus/ almost every refinery in the world uses some version of this process to convert H2S into elemental sulfur. A simplified version of Claus-reaction chemistry is shown in Figure 26. 

Figure 14-22. Simplified flow diagram of Suiflnol unit integrated Into an overali process including a Claus sulfur recovery unit and a tall gas treatment system. (Taylor and Hugill, 1991)...

Fig. 14.4. Republic Refining Co. 440 metric ton/day Claus sulfur recovery unit (left) and SCOT tailgas cleanup unit (right). (Courtesy Ortloff Engineers, Ltd.)...

TABLE 2.9. Operation of Claus Sulfur Recovery Plant. 

Claus felt that the cyclic process could be simplified if the hydrogen sulfide were converted to sulfur by an iron catalyst in a kiln. It was later found that dried Weldon process mud or bauxite would operate as a catalyst at a lower temperature than ferric oxide. This not only extended the life of the kiln but also increased sulfur yield. Problems with blocked beds were overcome as technology evolved and proper reactors containing solid catalyst particles were developed. Thus, the modem Claus sulfur recovery process originated from the statutory obligation to remove sulfur from town gas in Victorian gas works. 

The formation of carbon oxysitlfide and carbon disitlfide in the furnace leads to problems when high overall conversion is reqitired. Alitmina catalysts are not sufficiently active to convert carbon disitlfide and oxysulfide in the first reactor unless a high temperature is reached at the bottom of the bed. When this is not possible, the bottom third of the bed can be loaded with either an iron-promoted alumina or a newer titania catalyst. Cobalt/molybdate/alumina catalysts were also tested in early attempts to hydrogenate the impurities, but it was found that conditions in the first reactor favored sulfur dioxide hydrogenation instead. All of the catalyst types used in Claus sulfur recovery plants are described in Tables 2.10 and 2.11. 

TABLE 2.10. Catalysts Used for Claus Sulfur Recovery. 

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