Wellman Lord process

Regenerable absorption processes have also been developed. In these processes, the solvent releases the sulfur dioxide in a regenerator and then is reused in the absorber. The WelLman-Lord process is typical of a regenerable process. Figure 11 illustrates the process flow scheme. Sulfur dioxide removal efficiency is from 95—98%. The gas is prescmbbed with water, then contacts a sodium sulfite solution in an absorber. The sulfur dioxide is absorbed into solution by the following reaction ... 

Since the Claus process by itself removes only about 90% of the hydrogen sulfide in the gas stream, the Beaven, SCOT, or Wellman-Lord processes are often used to further recover sulfur. In the Beaven process, the hydrogen sulfide in the relatively low concentration gas stream from the Claus process can be almost completely removed by absorption in a quinone solution. 

Figure 25.26 Removal of SO2 using the Wellman-Lord process.

Another process for removal of S02 is the Wellman-Lord process11. The reactions are ... 

A flowsheet for the Wellman-Lord process is shown in Figure 25.26. Again the gas stream with S02 enters a scrubber into which is sprayed a sodium sulfite solution. This then goes to an evaporator/crystallizer to crystallize out the resulting sodium bisulfite, which converts the sodium bisulfite back to sodium sulfate, releasing the S02. The crystals are dissolved in water and recycled to the scrubber. The effect of the Wellman-Lord process is to produce a concentrated S02 stream from a dilute S02 stream. The resulting concentrated S02 still needs to be treated. 

The S02 from the Wellman-Lord process or any other concentrated S02 stream (e.g. gases from copper smelting) can be oxidized to S03 to produce sulfuric acid as discussed in Chapter 6. 

Several regenerable reagent processes for gas streams desulfurization include caustic-based systems and processes such as the Wellman-Lord process, the Citrate process,... 

SOXAL A flue-gas desulfurization process, basically similar to the Wellman-Lord process but regenerating the bisulfite solution in a membrane electrochemical cell. Developed by Allied Signal Group and piloted at the Florida Power Light Company, Miami, FL, in 1991. A larger demonstration plant was planned for Dunkirk, New York. 

Wellman-Lord The most widely used regenerable flue-gas desulfurization process. The sulfur dioxide is absorbed in sodium sulfite solution in a wet spray scrubber, forming sodium bisulfite ... 

Recycle processes convert the sulfur species in the tail gas to a single compound which is captured, concentrated, and returned to the Claus plant. Examples are the SCOT (10), Trencor (11), and Wellman-Lord (8,12) processes. The first two recover and recycle H2S while the Wellman-Lord process recovers and recycles SO2. 

Tail Gas Cleanup Process Efficiency - Required process efficiency depends on applicable emission regulations. Low-efficiency processes result in up to 99.0-99.5% overall sulfur recovery when combined with the Claus plant and include the Sulfreen, SNPA/Haldor-Topsoe, CBA, IFP, and Beavon Mark II processes. High-efficiency tail-gas treating processes can achieve overall sulfur recoveries of 99.8% and above under ideal conditions. These include the Beavon Mark I, SCOT, Trencor, and Wellman-Lord processes. 

In the Wellman-Lord process, sodium sulfite is used to capture the sulfur dioxide. The sodium bisulfite thus formed is later heated to evolve sulfur dioxide and regenerate the sulfite scrubbing material. The sulfur dioxide-rich product stream can be compressed or liquefied and oxidized to sulfuric acid, or reduced to sulfur. 

The catalyst is necessary to ensure that the components react with reasonable speed, bnt unfortnnately, the reaction does not always proceed to completion. For this reason, two or three stages are nsed, with sulfur being removed between the stages. For analysts it is valuable to know that carbon disulfide (CS2) is a by-product from the reaction in the high-temperature furnace. The carbon disulfide can be destroyed catalytically before it enters the catalytic section proper. Generally, the Clans process may remove only about 90% of the hydrogen sulfide in the gas stream, and as already noted, other processes, such as the Beaven process, SCOT process, or Wellman-Lord process are often used to recover additional sulfur. 

The Active Magnesia Process (24) can be viewed as the gas phase equivalent of the Wellman-Lord (to be discussed below) in that it serves primarily to concentrate the SO2 values in the combustion effluent to a suitable concentration for feed to an oxidative process yielding sulphuric acid. The absorption temperature, however, is quite low compared with typical combustion effluent temperatures. 

The Wellman-Lord Process is not, in itself, a conversion method, but rather a solution phase technique for concentrating a dilute SO2 effluent stream to provide a suitably rich feed for Claus redox conversion. When coupled with the Claus Process, it constitutes an overall desulphurisation system which involves all three phases gas, liquid solution, and solid crystalline. 

Elkem Technology s Elsorb process is similar to the Wellman-Lord process however, it employs a different solvent. An aqueous solution of sodium... 

Figure 25.4 shows a typical sulfur recovery plant based on the Claus process. The tail gas from the Claus reactors may be further processed to remove any remaining sulfur compounds. Combined H2S removal efficiencies of 99.5-99.99 percent are achievable.20 This may be done by low-temperature Claus-type solid-bed processes (e.g., the Sulfreen process), wet-Claus absorption/oxidation processes (e.g., the Clauspol 1500 process), or hydrogenation of the off-gas to form H2S for recycle (e.g., the SCOT process). Residual sulfur compounds in the tail gas are then incinerated to S02. The residual S02 in the oxidized tail gas may be scrubbed by any of several processes (e.g., the Wellman-Lord process) before being vented to the environment. It is feasible to bring the H2S content of... 

With the double contact process it is unnecessary to purify the tail gases to reduce their sulfur dioxide content still further, whereas tail gases from single contact plants have to be purified. This can be realized either by scrubbing with ammonia or with an aqueous solution of sodium sulfite and sodium hydrogen sulfite (Wellman-Lord process), absorption on activated charcoal (sulfacid process from Lurgi) or by oxidative gas purification such as in the peracidox process (oxidation of sulfur dioxide with hydrogen peroxide or peroxomonosulfuric acid). 

The Wellman-Lord process uses the effective sodium sulfite-sodium bisulfite equilibrium to capture sulfur dioxide from flue gases [40] (Eqs. 3.26 and 3.27). 

Wellman—Lord process. This is a regenerable-sorbent process, producing SO2 gas, which can be sold for industrial uses. It uses a solution of sodium sulfite (Na2S03), which absorbs SO2 and becomes a sodium bisulfite solution (NaHSOs). The sodium bisulfite is then decomposed in a forced circulation evaporator, releasing the SO2 at sufficiently high concentration to be compressed and sold as SO2 gas, or used for producing elemental sulfur or sulfuric acid. ... 

Magnesium oxide process. The magnesium oxide slurry is used to collect SO2, and the resulting magnesium sulfite is thermally treated to release the SO2 and regenerate the absorbent, as shown in Fig. 6. Like the Wellman-Lord process, this process... 

Existing single-contact acid plants can also be converted to doublecontact plants (63). In such cases, however, using add-on scrubber systems is an alternative, and several such systems have been used commercially. The Cominco ammonia absorption process has been used for many years (22, 64). The Lurgi Sulfacid process (65) and Wellman-Lord process (66) have had more recent and limited use. The Mitsu-bishi-JECCO process has also been applied to acid plant tail gases (27, 67, 68), but the gypsum by-product would be essentially a waste in the United States. 

The third class of control systems may use any of the sulfur dioxide control systems among those used commercially are the Haldor Topsoe (5, 80), Wellman-Lord (27, 07), and Chiyoda (27, 07, 87) systems. The circumstances are generally highly favorable for recovery processes that produce a stream of concentrated sulfur dioxide, since this can be recycled to the Claus plant. The application of processes that produce sulfuric acid or solid wastes will be dictated only by peculiar local circumstances. 

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