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Standard Process Modules

- Sulfuric acid concentration -
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Module for high concentrated sulfuric acid
Concentrated sulfuric acid is used within many chemical processes where the consequent dilution of acid occurs. For example concentrated sulfuric acid is used for drying of gases like chlorine, bromine, hydrogen chloride or methyl chloride. If the dilute sulfuric acid is concentrated back to its initial composition, it will be possible to recycle the sulfuric acid to the process and to generate savings in raw material costs and in effluent disposal costs.


In the following, standard process plants developed by QVF® for concentration of low and medium loads of sulfuric acid are described. Materials of construction for parts wetted with acid are exclusively borosilicate glass, quartz, tantalum, silicon carbide, PVDF and PTFE. Therefore the excellent corrosion resistance across the complete range of concentration ensures reliable operation. The concentration of sulfuric acid is essentially the evaporation of water. This concentration process is carried out under vacuum in order to decrease the boiling temperature, which is particularly necessary for higher sulfuric acid concentrations. The working pressure is chosen carefully with reference to the temperature P117e.3 difference between the heating agent and the process as well as the temperature of the cooling agent. In addition to heating by means of saturated steam, electrically heating by immersion heating units made of quartz can be useful. Thus the energy for vacuum generation is reduced considerably and it is still possible to condense the vapor by means of ordinary cooling water even for a final sulfuric acid concentration of 96 wt.-% H2SO4. In case of a liquid concentration above 75wt.-% H2SO4 it has to be taken into account that the H2SO4 content of the vapor increases very steeply. For this reason vapor scrubbing columns are placed upstream to the evaporators in order to minimize the sulfuric acid content of the condensed waste water. The scrubbing columns are equipped with the structured packing DURAPACK® made of borosilicate glass, which enables high capacity, low pressure drop and simultaneously high efficiency mass transfer even for treatment of boiling concentrated sulfuric acid.


The QVF® standard plant for concentration of sulfuric acid is depicted in the flow sheet shown overleaf. Weak sulfuric acid, e.g. sulfuric acid of 80 wt.-% H2SO4, is fed by dosing pump P1 via recuperator H1, into scrubbing column C1. In H1 the acid is preheated by means of the of concentrated product acid, e.g. sulfuric acid of 96 wt.-% H2SO4. In scrubbing column C1 the acidic content of the vapor, produced in evaporator H2 and scrubbing column C2, is washed out. Next the acid enters the horizontal evaporator H2 at one end and leaves it with higher concentration at the other. Evaporator H2 is designed as a horizontal vessel made of borosilicate glass. The lower part of the evaporator is equipped with baffles in transverse direction. In flow direction the baffles approximate to a chamber cascade, and the acid is concentrated step by step within the chambers. Discharge of higher concentrated acid out of horizontal evaporator H2 is done via free overflow and the acid is fed to the top of scrubbing column C2. The aim of column C2 is the first step purification of the vapor rising from evaporator H3. The further scrubbing of acidic content from the vapor out of evaporator H3 is carried out together with the vapor out of evaporator H2 in scrubbing column C1. Intermediate strength acid from column C2 enters evaporator H3 and leaves this vessel with the desired concentration. The heating of evaporator H3 is maintained electrically by immersion heating units made of quartz, enabling operation at temperatures of 180-220°C. Discharge of high concentrated product acid from evaporator H3 to recuperator H1 is done via free overflow. The horizontal concept of both evaporators and of the free flow acid discharge eliminates the need for any pump in the hot process section. Vapor from scrubbing column C1 is condensed in condenser H6. Arising condensate leaves the plant via free overflow out of separator T2. Vacuum generation is achieved by liquid jet pump where the arising condensate is used as working fluid. Due to the use of condensate as working fluid, additional waste streams are avoided. QVF® standard plants for sulfuric acid concentration are equipped with automated process control systems, the operation is through "on screen" control.

Horizontal boiler, figure shows the former program


QVF® standard plants for sulfuric acid concentration combine the following substantial advantages:

  • A plant which is, insulated, pre-assembled to a great extent and requiring only short time for erection on site.
  • Small space requirement.
  • A low overall height due to the use of the horizontal evaporator.
  • No additional waste water streams besides vapor condensate.
  • Exclusive application of reliable materials of construction with excellent corrosion resistance.
  • No pumps in the "hot" acid section.

Plants of further sizes are available as standard. On request it is possible to provide all standard plants with modifications, e.g. application of glass lined steel instead of glass in the hot acid section. The following table gives performance figures for standard plants of size 2. Our complete service capability for sulfuric acid concentration is of course far wider than the standard plants presented above. Thus we can offer many different solutions for concentration and purification. Our highly experienced engineers will be pleased to offer an individual proposal tailored to your needs. Please contact us!

  standard plan, size2   case 1   case 2
  inlet (feed acid) H2SO4   60 wt.-%   80 wt.-%
  outlet (product acid) H2SO4   70 wt.-%   96 wt.-%
  maximum capacity feed acid   750 kg/h   750 kg/h
  saturated steam 17 bara   ca. 250 kg/h   ca. 80 kg/h
  cooling water requirement (20°C - 25°C)   ca. 15m3/h    ca. 5m3/h
  electrical power   ca. 18 kW   ca. 18 kW
  operating pressure (vacuum)   ca. 200 mbara   ca. 60 mbara
  space requirement (LxWxH)   4x2x4 m   4x2x4 m


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