a gas stream containing at least 50 % by volume of ammonia but eventually no hydrogen sulphide is burned in a reaction region which is supplied with oxygen and oxygen - enriched air . both combustion and thermal cracking of ammonia takes place in the reaction region . the rate of supplying oxygen moleculars to the reaction region is from 75 to 98 % of the stoichiometric rate required for full combustion of all combustible fluids supplied to the reaction region . under these conditions essentially no ammonia remains in the effluent gas but formation of oxides of nitrogen can be minimised .