GB360574A - Improvements in and relating to the washing of flue gases from combustion furnaces and the like - Google Patents

Abstract

Flue gases containing sulphur dioxide and oxygen are freed from sulphur dioxide by passing them through a chamber in co-current with an aqueous solution containing free ammonia. Crude ammonia liquor from coal distillation may be employed in the process. The ammonium sulphite initially formed is wholly or partially oxidized to ammonium sulphate by the oxygen also present. Preferably, the process is so controlled that the solution leaving the chamber is slightly acid. The duration of the contact between the flue gases and solution may be about one second the solution having a temperature up to 50 DEG C. The oxidation may if necessary be completed electrolytically, preferably in the presence of a chloride such as ammonium chloride or by treatment with an oxygen containing gas preferably in the presence of catalysts such as manganous salts, cuprous chloride, cobalt salts, iron salts preferably in the ferrous state or other heavy metal salts. If cobalt salts are employed the solution should have a pH of about 8, but ferrous salts are preferably employed at a pH not exceeding 6. Ferrous salts may also be present in the ammoniacal solution flowing in co-current with the flue gases and may be introduced by bringing the solution in contact with metallic iron, for example the internal surface of the apparatus. The process may be carried out in a vertical tower both the flue gases and ammoniacal liquor entering near the top and leaving near the bottom, a fan being provided on the outlet side to draw the flue gases through the tower. The tower may be provided with baffles for example wooden slats and may be formed or coated with acid-resisting alloy steels. The solution leaving the bottom after replenishment of the ammonia may be recirculated. The ammonium sulphate is recovered by crystallization either intermittently from the whole body of the liquor or continuously by withdrawing a small proportion of the liquor from the circuit, the liquor removed being replaced by water. Specifications 9432/99, [Class 1, Acids, alkalies, &c.], 356,283, and 356,757, [Group XXXVI], are referred to.