Metallgesellschaft Aktiengesellschaft

Volker Wichert

Hartmut Wagner

Roland Fach

Klaus Begerow

Gunter Okon

Manfred Henn

Klaus Engels

The process of concentrating a dilute sulfuric acid in a three-stage vacuum evaporation plant includes feeding an entry dilute sulfuric acid to a first evaporation stage of a vacuum evaporation plant to form an overhead vapor (6), withdrawing a finally concentrated sulfuric acid from the third evaporation stage (3), using steam or the overhead vapor (6) of the first evaporation stage as a heating fluid in the three-stage vacuum evaporation plant, maintaining the entry dilute sulfuric acid under a pressure of 0.4 to 0.7 bar and at a temperature of 80.degree. to 120.degree. C. in the first evaporation stage (1), maintaining the partially concentrated sulfuric acid under a pressure of 0.02 to 0.06 bar and at a temperature of 50.degree. to 90.degree. C. in the second evaporation stage (2), maintaining the further concentrated sulfuric acid under a pressure of 0.02 to 0.06 bar and at a temperature of 80.degree. to 120.degree. C. in the third evaporation stage (3), and condensing overhead vapors (8,8a) formed in the second and third evaporation stages. Each evaporation stage (1,2,3) includes an evaporation vessel (1b,2b,3b) and a connected recycle line including a shell-tube heat exchanger (1a,2a,3a) and pump. The process also includes continuously feeding about 30 to 95% of the entry dilute sulfuric acid (4) to the first evaporation vessel in the first evaporation stage (1) and continuously feeding the balance of the entry dilute sulfuric acid to the second evaporation vessel in the second evaporation stage (2).

Process of concentrating a dilute sulfuric acid in a three-stage

A process for decreasing the tendency to form deposits in plants for evaporating spent sulfite liquors used to produce woodpulp. In the process, the liquors are treated with polyacrylic acids having a low molecular weight. In order to prevent virtually any deposition and to increase the evaporation rate, an aqueous solution of polyacrylic acid having a low molecular weight is added to the spent sulfite liquor in an entrance stage of the multiple-effect sulfite liquor in an entrance stage of the multiple-effect evaporating system and an aqueous solution of a copolymer of sulfonated styrene and maleic anhydride or an aqueous solution of a polyacrylic acid having a low molecular weight is added to the spent sulfite liquor in at least one succeeding stage of the multiple-effect evaporating system.

Process for decreasing the tendency to form deposits in plants for

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Voerde, Germany

Volker Wichert