Sulfur Recovery Processes

In two processes under development as of 1997, the sulfur dioxide stream reacts with reduciag gas over a proprietary catalyst to form elemental sulfur. Both processes have achieved a sulfur recovery of 96% ia a single reactor. Multiple reactor systems are expected to achieve 99+% recovery of the feed sulfur. The direct sulfur recovery process (DSRP), under development at Research Triangle Institute, operates at high temperature and pressure. A similar process being developed at Lawrence Berkeley Laboratory is expected to operate near atmospheric pressure. 

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

Fig. 3. Lime-sulfuric recovery process for citric acid.

Rather than oxidize the SO2, it can be reduced in a process similar to the one illustrated in Figure 25.23. The S02 is reduced to H2S. The resulting H2S can then be separated and fed to a sulfur recovery process. 

MCRC A variation on the CBA sulfur recovery process using multiple Claus converters. Developed by the Delta Engineering Corporation in 1983 and used in Canada, China, and Mexico. 

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... 

Noranda submerged tuyere process, 16 146 Noranda sulfur recovery process, 23 575 NOR arrays, 22 258 Norbornene, copolymerization with benzvalene, 7 515... 

Orkla sulfur recovery process, 23 575 Orlistat, 3 95-96 Orion, 11 188 Ormetoprim... 

Sulfur recovery processes convert acid gases containing H2S and other sulfur compounds to elemental sulfur and sulfuric acid. Table II is a summary of many of the available sulfur recovery processes. 

Figure 2. Schematic of sulfur recovery process alternatives...

Table III. Guidelines for Selection—Sulfur Recovery Processes...

The selection of a sulfur recovery process should mainly be guided by economics and commercial status. Here are some other possible guidelines ... 

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 ... 

UCBSRP [University of California Berkeley Sulfur Recovery Process] A process for removing hydrogen sulfide and sulfur dioxide from natural gas. These gases react together in a polyglycol solvent with a catalyst, yielding elemental sulfur. Not piloted as of 1997. 

The sodium-base sulfite systems present experience with sulfur recovery processes that may have wide application outside the paper pulp industry. The basic chemistry involved is historically very old (122). Essentially, four steps underlie the various processes ... 

Typical Claus Plant Sulfur Recovery Process. 2-33... 

The need to remove CO2 and COS varies with the application and sulfur removal requirements. CO shifting increases the COj content in the coal gas and converts most COS to H2S. Synthesis gas for chemicals usually requires the removal of CO2, whereas IGCC applications are enhanced by leaving the CO2 in the coal gas for better NO, control, higher power output, and lower-cost acid gas removal/sulfur recovery. COS is produced in much smaller amounts than is HjS. Some acid gas removal processes can effectively remove COS with the H2S, or convert it to additional H2S. Most sulfur recovery processes effectively convert COS to additional elemental sulfur. 

Conventional acid gas removal processes produce purified coal gas and a concentrated acid gas. The H2S and COS in this low-pressure acid gas stream convert easily and efficiently to high-value liquid elemental sulfur. Sulfur recovery processes are commercially well-proven technologies that the oil, chemical, and natural gas industries have used extensively for over 50 years. In fact, U.S. oil refineries have been required to operate their sulfur plants with over 99.8% sulfur recovery for many years. The conversion of H2S to sulfur in coal gasification processes has a number of technical and economic advantages over sulfur recovery from SOj in direct coal combustion processes. 

Coal gasification also produces extremely low amounts of NO,. Coal gasification converts most of the feed coal (chemically bound) nitrogen to N2. A portion of the coal nitrogen is converted to NH3 and HCN in coal gasification. However, this is removed during gas purification and usually converted to N2 in the sulfur recovery process. The combustion of coal-derived coal gas produces low levels of thermal NO because of the low adiabatic flame temperature of coal-derived gas, when it contains large amounts of N2, CO2 and water (H2O) (8,9). 

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. 

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