Scrubbers Wellman-Lord

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. 

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 ... 

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. 

At Chiba, Japan, the Japan Synthetic Rubber Co. has two steam boilers with evaporation rates of 130 metric tons/hr, each equipped with Wellman-Lord sulfur dioxide recovery units. The load to each scrubber is essentially constant, but sulfur dioxide concentration varies from 400 to 2,000 ppm because of the varying quantities of waste process gas from the plant. 

Although it is possible to convert the SO2 removed from the flue gas to ammonium sulfate, sodium sulfate, or gypsum, the market for such by-products is quite restricted. More recently, interest has centered on processes that recover the SO2 in concentrated form. One such system, the Wellman Lord Process (licensed by Davy-McKee/Davy Corp. Pic.) uses a solution of sodium or potassium sulfite to absorb SO2. The liquid effluent contains a mixture of sulfites and bisulfites from which the less soluble bisulfites are crystallized. The recovered solids are heated to decompose the bisulfites to sulfites with the release of SO2. These sulfites then are redissolved in the liquid recycled to the scrubber. Only a... 

Although some minor mechanical problems were encountered, general operation of the plant was considosd to be mdimnely sahsfactory. It was accepted by the utility on September 16, 1977. Nonetheless, at the completion of the U.S. EPA-fiinded demonstration, the utility found it more economical to switch to low-sulfiir coal and decommissioned the FGD plant At Public Service Company of New Mexico s, San Juan Station, there are four Wellman-Lord systems, one each on the two 350 MW and the two 550 MW units. AU have venturi scrubbers. Initially, they produced elemental sulfur, but around 1980, they woe converted to sulfinic acid productioit Sodium sulfate from the plant was sold to a pulp and paper plant, but is presently bemg stoclqnled. Sodium thiosulfate is being sold and subsequently us for water treatment (Burnham, 1993). 

Wellman-Lord process A process used for flue gas desulphurization. Sulphur dioxide in the flue gas is absorbed in sodium sulphite in a wet spray scrubber column forming sodium bisulphite ... 

Tail gas emissions are controlled by improving the SO2 conversion efficiency and by scrubbing the tail gas. In a double-absorption process plant, a five-bed converter has 0.3 percent unconverted SO2, as compared to 0.5 percent for a four-bed converter. A Lurgi Peracidox scrubber may be used to remove up to 90 percent of the residual SO2 in the tail gas from a double-absorption plant. Hydrogen peroxide or electrolytically produced peroxymonosulfuric acid is used to convert the SO2 to H2SO4 in the Lurgi scrubber. Tail gas from single-absorption plants may be absorbed on activated carbon (Sulfacid) or scrubbed with ammonia or sodium sulfite (Wellman-Lord). 

---

See also in sourсe #XX -- [ ]

---