Sulfite pulping corrosion

Liquid sulfur dioxide discolors iron, copper, and brass at ca 300 ppm moisture and produces light scale at ca 0.1 wt % moisture and serious corrosion at ca 0.2 wt % or higher moisture content. Copper and brass can be used to handle wet sulfur dioxide where some corrosion can be tolerated, or where the moisture level is low. Wooden tanks are widely used for sulfurous acid preparation, handling, and storage. Sulfite pulp digestors are made of steel lined with acid-resistant brick. 

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 pulping is a process that uses mildly acidic sulfite solutions instead of the very alkaline solutions used in kraft pulping. Murarka et al. [201] published results of corrosion tests in acidic condensates in vapor phase sulfite pulping using a batch type laboratory reactor in which acid was condensed and collected. He devised a means to prevent corrosion due to the acid condensation. 

Sulfur dioxide Fuel combustion (coal, oil), smelting and casting, manufacture of paper by sulfite process Primary metals (ferrous and nonferrous) pulp and paper Sensory and respiratory irritation, vegetation damage, corrosion, possible adverse effect on health... 

Fourdrinier machine—The machine that forms paper from pulp, named after the English family that financed its development in the early 1 800s. Furnish—Specific combination of pulp and other ingredients used to make a particular kind of paper. Kraft process—process in which sodium sulfate is reduced by heating with carbonaceous matter in a furnace to form sodium sulfide, which is then used in a water solution with sodium hydroxide as a cooking liquor. The wood pulp is then cooked under pressure and at high temperatures. The kraft process, also known as the sulfate process, has a less corrosive influence on iron and steel than the sulfite process. 

Ugnin Lignin is a colorless to brown crystalline product recovered from the paper-pulp sulfite liquor. It is generally available in powder form and used as an extender in furfural and phenolic molding compounds. Lignin is also used as a low-cost extender in adhesives and coatings, especially those used in the construction industry. It is also used as a corrosion inhibitor and as a natural binder to make low-pressure laminates from compressed wood products. 

Spent or black pulping liquors contain 10<7o to 20 o solids and must be concentrated to a solids content exceeding 50% in order to maintain burning in recovery furnaces. The liquor from the acid sulfite process requires equipment that will resist corrosion and be unaffected by scaling, but extractives in the liquor do not affect concentration or burning. 

---