A process used to remove acid gases from flue gases that use sorbent materials such as hydrated lime or soda ash to remove sulphur dioxide and hydrochloric acid gas. They are also used to remove undesirable odours and corrosive gases from wastewater treatment plants, and use activated alumina as the sorbent material to remove hydrogen sulphide as well as mercaptans amongst others. In spray dryer absorbers, the flue gases are contacted with a finely atomized alkaline slurry where the acid gases are absorbed and react to form solid salts and are removed.