ABSTRACT

There are six main processes by which a gaseous pollutant may be removed from an air stream. Table 10.1, taken from the EPA handbook,1 lists those processes with the advantages and disadvantages of using each one. The table may be used as a guide to determine which process may provide the best means of cleaning the air stream. Separation processes are used as a means of air pollution control for both particulate matter and gas. These processes essentially remove the pollutant from the carrier gas resulting in a cleaned gas stream. If the pollutant content of the cleaned stream meets the effluent emission standards, the cleaned stream can be discharged to the atmosphere. Absorption and adsorption are both diffusional separation processes that can be used to collect hazardous air pollutants. In the case of absorption, the pollutant is transferred to the solvent, which then may need further treatment, referred to as regeneration. Recovery of the solvent might be undertaken by distillation or by stripping the absorbed material from the solvent. The problem of treating the waste material in the stream separated from the solvent remains. If the pollutant material has a value, adsorption may provide the means for the material to be more readily recovered. In the case of particulate matter, wet scrubbing collects the particles primarily through the mechanism of inertial impaction. Gaseous contaminants such as sulfur oxide, nitrogen oxide, and hydrochloric acid, if present along with the particulates, may be collected simultaneously by absorption.