2 replies to this topic

Does anyone know how to calculate an absorption tower height for SO3-H2SO4 system? I've already calculated for its diameter however when I'm about calculate for its required height there's no available data around (ie equilibrium data/curve). My packing is made out of 2" ceramic intalox saddles.

Thanks.

[marecki]

Does anyone know how to calculate an absorption tower height for SO3-H2SO4 system? I've already calculated for its diameter however when I'm about calculate for its required height there's no available data around (ie equilibrium data/curve). My packing is made out of 2" ceramic intalox saddles.

Thanks.

If you assume that reaction is instantaneously, for dilute system the SO3 gas phase surface mole fraction is kept to zero by chemical reaction, and you do not need the equilibrium data to calculate tower height. You can find the solution of similar issue (absorption with reaction) in "Handbook of Chemical Engineering Calculations" 3th edition N.P.Chopey.

Edited by marecki, 21 January 2010 - 07:59 AM.

[kkala]

Though the answer is apparently late, I think edmar speaks of the absorption tower* in the sulfuric acid plants, where produced SO3 (from catalytic conversion of SO2) is absorbed by H2SO4 94%** to give H2SO4 98% (those 94% and 98% may differ somehow from plant to plant). Absorption is exothermic (probably 90 deg C average temperature) and resulting acid is cooled before sending it to storage. There is also recirculating pump for the acid.
Equilibrium data can be found in Perry, Physical and Chemical data, Vapor pressures. In Perry's 7th edition, one can find water partial pressure (2-12), SO3 partial pressure (2-13), H2SO4 partial pressure (2-14), H2SO4 total pressure (2-15), over aqueous H2SO4 solutions, for several H2SO4 contents (up to 100% wt) and temperatures. Figures in parenthesis are the numbers of Perry's relevant tables.
E.g. for 94% H2SO4, vapor pressures in mbar abs are read as follows:
Temperature, 0C 90 200 300
partial H2O 0.315 63.1 1112
partial SO3 0.0000426 0.108 10.2
partial H2SO4 0.00835 3.29 88.2
total reported 0.324 66.5 1211
(the difference: total vapor pressure - sum of all three partial pressures is 0.00062, 0.002, 0.6 respectively, indicating data precise enough).
Over here (for refinery projects) we let tower suppliers advise the required height.

* In case there is an oleum tower, this is the secondary absorber, as literature says. But an oleum tower is probably a rear case, I have not seen any in local sulphuric acid plants.
** H2SO4 in the tower is close to 98% due to continuous recirculation. H2SO4 94% feeds the suction (buffer) tank of the recirculating pump. I had worked in a fertilizer industry producing H2SO4, but not dealt with the H2SO4 units, so my knowledge is only general.

Edited by kkala, 31 January 2010 - 04:02 AM.