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The plant design must be adapted to the physical conditions that change for high concentration processes of sulfuric acid to 92-96 wt%, especially as follows:
- Reduction of operation pressure and increase of operation temperature contingent to the sulfuric acid vapor pressure diagram
- Installation of a washing column to reduce the acid content of the evaporated water
The available material combinations have special importance for the choice of facility. Only few materials remain resistant for steam temperatures of maximum 219°C, or oil temperatures of 290°C at a sulfuric acid concentration of 96 wt%. QVF facilities use the ideal combination of borosilicate glass, glass lining, tantalum, and SiC.
Usually, forced circulation evaporators or horizontal-boilers are used, contingent to operational parameters and the composition of waste acid.
QVF plants for Acid Concentration
QVF designs concentration and cleaning plants for sulfuric acid often based on tests that have been operated using original acid at our test facility. We ensure to you that QVF’s know-how about corrosion-free materials delivers the highest level of reliability and security, next to the confidence gained by testing and the experience built from over 100 plants for our satisfied customers.
Option 1: Forced Circulation Evaporator
Advantages:
- No evaporation at the heating surface, thus no or significantly reduced contamination/incrustation of the heating surfaces.
- High heat transfer due to high fluid speed within the heater, thus small heating surfaces deployed, even for a relatively low temperature difference betweensteam and boiling temperature of the acid
- Steady and high evaporation due to the relaxed evaporation
- The relatively small operating content ensures a very secure operation and quick adaptation to changing performance demands to the plant ranging from 0 to 100%; the facility may quickly be started-up or shut-down.
The natural-design circulation evaporator that includes gas support represents a modification of the forced circulation evaporator, whereby the inert gas proportion burdens the condensation, thus the necessary performance of the vacuum pump must be increased.
Option 2: Horizontal boiler
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For the QVF horizontal boiler, the acid to be concentrated flows through the baffles that separate the horizontal boiler body, and unfolds a temperature profile due to the concentration in the evaporator, which increases the existing temperature differencebetween staem and acid (see illustration of temperature profile). |
Temperature profile of horizontal boiler
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Advantages:
- Best use of the tantalum heating surfaces due to the concentration profile throughout the length of the evaporator. Due to this, the mean temperature gradient that is displayed increases and the necessary heating surface is reduced.
- High mean coefficient for heat transfer up to 4,000 W/m2K
- Low fluid pressure on the heating surfaces, thus low-pressure differentials in the evaporator.
- A sufficiently dimensioned evaporator body minimizes entrainment.
- Acid losses in the exhaust steams due to partial pressure reasons are held very low by implementing the concentrationing profile along the horizontal evaporator.
- Low acid volume in the evaporator for secure and flexible operation, well adapted for changing capacities ranging from 25% to 100% without loss of performance.
- No mechanically moving parts within the acid circulation, no circulation pump.
- Low design height of evaporator.
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