Sulphuric acid from metallurgical industries' off-gases

The technology of sulphuric acid production from non-ferrous metallurgy off-gases with capacity range from 100 to 800 thousand MTPY (manufacture of product sulphuric acid per GOST 2184-2013 “Commercial grade sulphuric acid” with concentration not less than 92.5% w/w) developed at NIUIF is based on a “long” scheme with a wet cleaning unit.

The developed process includes the following technological and auxiliary units:

Technological units:

  • wet cleaning unit;
  • compressor unit;
  • conversion unit;
  • drying and absorption unit;
  • stack.

Auxiliary units:

  • acid storage;
  • cooling water unit;
  • start-up heater;
  • instrumental air unit.

Technology description

The process flowsheet is shown in Fig. 1.

Smelters or roasters off-gases, containing sulphur dioxide are sent to the wet cleaning unit, where gas is cooled and “wet” cleaned from dust and impurities, harmful to vanadium catalysts, in two scrubbers as well as the first and second stages of wet electrostatic precipitators.

Further, the gas, due to the vacuum created by the blower, is drawn into a drying tower, where it is dried to a moisture content of not more than 0.01% vol.

Gas, purified and dried in the drying tower, is sucked in by the blower and fed to the conversion unit. All equipment before the blower operates under vacuum, after under pressure.

In the conversion unit, the dried gas is heated in heat exchangers to a catalyst ignition temperature of 390-420°C and is fed to the converter catalyst layers for catalytic conversion.

After the converter, the process gas is cooled to the desired temperature in the heat exchanger and sent for the absorption of the SO3, obtained in the converter, to the absorber where sulphuric acid is formed.

After the absorber, the process gas is sent to the stack.

Excess sulphuric acid from the absorber cycle enters the drying tower cycle. From the drying tower cycle, an excess of 93.0% product sulphuric acid is sent to the storage.

The main advantages of the proposed technology:

1. Low emissions of harmful substances into the atmosphere.

2. Low energy costs due to the use of equipment with minimal energy consumption (sulphuric acid pumps, blowers, compressors).

3. Intensification of the system by increasing linear velocities in the converter and tower equipment and increasing the sulphur dioxide concentration in the process gas.

4. A simplified flowsheet with a minimum amount of equipment (pumps, coolers, fittings, etc.).

The technology and equipment used in the proposed process correspond to modern achievements in the field of science and technology for sulphuric acid production.

The technological and environmental indicators achieved in the proposed sulphuric acid production process correspond to the world level of similar sulphuric acid productions.

Sulphuric acid production flowsheet from metallurgical industries’ off-gases.

Fig. 1 - Sulphuric acid production flowsheet from non-ferrous metallurgy off-gases

1S – first scrubber; 2S – second scrubber; EP1, EP2 – “wet” electrostatic precipitators; DT – drying tower; B – blower; SE – spray eliminator; HE1, HE2, HE 3, HE 4 – heat exchangers; C – converter; PF – press-filter; 1ST – stripping tower; 2ST – stripping tower; А – absorber; S – stack.