Process for removing ammonia, hydrogen sulfide and hydrocyanic acid from gases

Claim 1

A process for removing ammonia, hydrogen sulfide and hydrocyanic acid from gases in which ammonia-containing condensates are also initially present, said process comprising subjecting the gas to be cleaned to a first washing step with an alkaline solution adapted to absorb hydrogen sulfide and hydrocyanic acid, said solution being selected from the group consisting of sodium and potassium salts and alkaline ammonia solutions, treating said solution with air following said first washing step to oxidize the hydrogen sulfide absorbed by the solution to form elemental sulfur and removing said sulfur, said air and ammonia absorbed thereby being continuously discharged from said oxidation step, diverting a portion of said treated solution following the oxidation step and recycling the remaining solution for reuse in said first washing step, the treated solution containing cyanide and sulfur compounds, subjecting the gas to be cleaned to a second washing step with an inorganic acid solution selected from the group consisting of sulfuric acid, hydrochloric acid and ammonium bisulfite to remove ammonia from the gas by formation of an ammonia salt solution, mixing at least a part of said ammonia salt solution with said diverted portion of the solution from the first washing step, supplying to said mixture the air and absorbed ammonia discharged from the oxidation step, burning said mixture with a fuel gas and said air at a temperature to decompose the ammonia and the cyanide containing constituents of the mixture to nitrogen, carbon dioxide and water vapor, and to convert said sulfur compounds to sulfur dioxide, recovering from the products of combustion any other components present therein including sulfur dioxide and said inorganic acid, separating said sulfur dioxide, recirculating said recovered acid for reuse in said second washing step, adding sulfur dioxide recovered from said products of combustion to the inorganic acid recovered from the products of combustion to be carried by said inorganic acid through the second washing step, diverting a portion of the resulting salt solution carrying a predetermined amount of sulfur dioxide, adding said diverted salt solution to said condensates with an alkali solution, distilling the mixture thus formed to separate ammonia therefrom, and burning said distilled ammonia with said mixture of solutions from the first and second washing steps to decompose the ammonia.