Sulphuric Acid

Filter › IAT & AT

SULPHURIC ACID / INTERMEDIATE ABSORPTION TOWER

PROCESS INFORMATION

Case A Conventional H2SO4 Process

In a sulphur burning or metallurgical double absorption H2SO4 plant where no Oleum is produced upstream, SO3 gas exits the third catalyst pass, is cooled down and enters the first ( = intermediate ) absorption tower, where H2SO4 is distributed over ceramic packing to absorb the SO3. When the gas exits the I.A.T. it returns to the converter to go into the fourth catalyst pass after being reheated in a gas/gas heat exchanger. Due to the high inlet gas temperature and the relatively low inlet acid temperature, mist is formed thermodynamically and acid droplets are mechanically entrained from the acid distribution system or packing.

In such processes the mist and droplets combine typically as a load of 2,000 – 2,500 mg/m3. The particle size spectrum will be sub-micron to medium sized ( 0.3 to 8 micron )

Case B Oleum By-Production

In a sulphur burning or metallurgical double absorption H2SO4 plant where Oleum is produced with a partial by-pass flow upstream, the by-pass flow will be returned at appx. 40 °C to join the main gas flow. Due to the high gas temperature of the main gas flow being ‘shock cooled’ by the Oleum Tower return gas flow, large amounts of sub-micron mist particles are formed. Then the total gas still enters the I.A.T. and when it is contacted by the relatively low inlet acid temperature, mist is again formed thermodynamically and acid droplets are mechanically entrained from the acid distribution system or packing.

Here this typically generates a load of 3,000 – 4,000 mg/m3. The particle size spectrum will be sub-micron to small sized (0.3 to 3 micron), average & majority 1 micron.

Case C Heat Recovery Process

In a heat recovery design H2SO4 plant, SO3 gas exits the third catalyst pass and enters the heat recovery tower or the ‘hot’ part of the first (= intermediate) absorbtion tower. Hot H2SO4 from the tower is fed to a boiler for generation of high and/or medium pressure steam. When the gas exits the (I.A.T.) tower it returns to the converter to go into the fourth catalyst pass after being reheated in a gas/gas heat exchanger.

Working in such a temperature regime, the degree of shock cooling far exceeds normal I.A.T. operations. Very large volumes of mist are formed thermodynamically and typically loads of 10,000 – 30,000 mg/m3 can be generated. The particle size spectrum will be sub-micron to small sized ( 0.3 to 3 micron ), majority < 1 micron. (The mist condition here is similar to that in a ‘Wet Catalysis’ plant absorber )

Case D Fluorine in Off-Gas

In some metallurgical double absorbtion H2SO4 plants there can be problems created by the presence of HF, which is highly corrosive to glass, and in particular to the small diameter glass fibres used in mist elimination. The ores being processed / smelted upstream to produce the SO2 feed gas contain Fluorine.

This can happen in any of the Cases A-C above.

HQ H2SO4

PROBLEMS TO SOLVE

Protect expensive and critical heat exchanger downstream from corrosion, so ideally the exit mist load should not exceed 20mg/m3, even with such very high inlet loads, E.G. Case C.

DESIGN SOLUTIONS

Option to include our STAR intermediate drainage rings to minimise flooding and pressure loss impacts

CANDLE FILTER ARRANGEMENT OPTIONS