Toxic Acid Gas Absorber Design Considerations for Air Pollution Control in Process Industries

This paper analyses the design parameters for an absorber used for removal of toxic acid gas (in particular sulfur dioxide) from a process gas stream for environmental health protection purposes. Starting from the equilibrium data, Henry's law constant was determined from the slope of the y-x diagram. Based on mass balances across the absorber, the minimum liquid-to-gas ratio was determined from which the minimum liquid flow rate and the actual operating conditions were established. Using a generalized flooding and pressure drop correlation, and the mass flow rates of liquid and gas, the mass flow rate of the gas per unit cross sectional area of the tower was determined. The operating point (ranging from 50 to 75% of flooding velocity) was used to determine the required cross-sectional area and diameter of the absorption tower. The operating liquid flow rate was observed to depend strongly on the inlet gas flow rate, solute concentration in the inlet liquid, and solute removal efficiency. The solute removal efficiency was varied from 80 to 99% at a fixed inlet toxic gas concentration of 3%. The tower diameter was observed to depend strongly on: the inlet total gas flow rate, percent of the flooding velocity selected, packing factor, size of packing, and on the type of material used (at fixed size of packing). The tower height, which was observed to depend strongly on toxic gas concentration in the inlet gas, and on the required toxic pollutant removal efficiency, was, however, independent of gas and liquid flow rates. (Contains 15 figures.)