Pre-concentration of Sulfuric Acid

Preconcentrating Sulfuric Acid

Concentrating sulfuric acid from 20 to 70wt% means to evaporate an enormous amount of water out of the sulfuric acid. Single- or multi stage natural circulation evaporators are used to minimize the required amount of heating steam. The below diagram shows a 3-stage plant where the 1st stage is heated by the vapor from the 2nd stage, the second stage is heated by the vapor from the 3rd stage and only the 3rd stage is heated with fresh steam. The 1st and 2nd stage are operated under vacuum in this example. The number of stages and the type of heating system for each stage are governed by the concentration of the waste acid and the available heating media. Account must also be taken to the behavior of the acid during the concentration process such as the generation of gases possibly leading to foams and the precipitation or evaporation of products present in the waste sulfuric acid.

Under certain conditions it can also be technically or economically advantageous to use forced-circulation evaporators or single-pass horizontal evaporators. Electrically heated quartz immersion heating sticks can also be an option for small evaporators.