A method of concentrating dilute sulfuric acid in a three-stage forced-circulation vacuum evaporation plant plant using forced circulation.

摘要

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 DEG to 120 DEG 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 DEG to 90 DEG 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 DEG to 120 DEG 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).