Sulfite pulping recovery

ChemicalRecope . There are advantages and disadvantages to each of the base systems employed in sulfite pulping (see Table 4). Each has its own potential recovery systems except the calcium system, which is obsolete. Calcium-based Hquors can be burned, but scaling problems are severe, and conversion of the calcium sulfate to CaO is not economical. 

Various permutations of the black liquor recovery boiler design are used to combust soda liquors in the soda pulping process and alkaline earth liquors and ammonium liquor (red liquor) in the sulfite pulping process. 

Numerous sulfite chemical pulping recovery systems are in use today. Heat and sulfur can be recovered from all liquors generated however, the base chemical can only be recovered from magnesium and sodium base processes. See Smook s Handbook12 for more information. 

While sulfite pulping is less popular than Kraft pulping, it is more prevalent in the production of dissolving pulps. Further, sulfite pulping permits recovery of ethanol from the spent pulping liquor before incineration, as is... 

Since the prices of petroleum products have soared, valorization of natural resources has intensively attracted the attention of researchers in different fields. To fully utilize wood, which is a renewable raw material, one must make better use of its 25-30% lignin content which forms the principal dissolved material in the spent liquor of chemical pulping processes. The annual production of sulfite pulp in Canada is approximately 2.6 million tons (data based on 1979), thus, at least one million tons of lignosulfonate is produced, representing a potential resource of raw material for other uses. However, among 35 sulfite mills in Canada, only two or three of them possess a recovery system for spent liquor, that means a very small portion of lignosulfonate has been recovered. The recovered lignin has been... 

The requirements for water pollution control have been forcing a shift to concentrating spent sulfite pulping liquor by evaporation, followed by incineration with heat recovery (102). When calcium-base liquor is burned, the sulfur emerges as calcium sulfate and is not available for recycle to the pulping process. The flue gas from such furnaces in Sweden is reported to contain 0.2—0.3% sulfur dioxide, and in one Swedish mill a Bahco wet limestone scrubber is used to treat the gases (115). 

Sulfite pulping chemical recovery consists of greater amounts of sulfite, hydrogen sulfide, and hydrochloric acid than those used in the Kraft process. Because of these corrosive species, the internal portions of the recovery boilers and the evaporators are generally constructed of reinforced plastics, type 316L stainless steel, type 317L stainless steel, or nickel-based alloys. To prevent pitting and crevice corrosion, scale build-up should be prevented, wet-dry zones should be avoided, and chloride concentration should be kept to a minimum. 

Sulfite Process. The sulfite process uses a cooking liquor of sulfurous acid and a salt of the acid. Although calcium was the most widely used base at one time, it has been supplanted by sodium, magnesium, and ammonia. Lignin will react with the bisulfite ion (HSO3") under acidic conditions to form lignosulfonates that are soluble in water. For many years this was the preferred process because it produced pulps of light color that could easily be bleached, it used cheap chemicals in fairly limited amounts so that no recovery was necessary, and it was a relatively simple process to operate. 

National Emission Standards for Hazardous Air Pollutants for Primary Aluminum Reduction Plants National Emission Standards for Hazardous Air Pollutants for Chemical Recovery Combustion Source at Kraft, Soda, Sulfite, and Stand-Alone Semichemcial Pulp Mills National Emission Standards for Tanks—Level 1 National Emission Standards for Containers National Emission Standards for Surface Impoundments... 

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