WASTE GAS TREATMENT AND APPARATUS THEREFOR

摘要

A method of removing nitrogen oxides from a gas stream, for example the waste gases of a plant in which nitrogen oxides is processed, includes reducing the nitrogen oxides by means of ammonia in the presence of a catalyst. During the reduction step, the waste gas is under superatmospheric pressure of up to 12 atm. abs. Preferably the pressure is between 2 and 5 atm. abs. The temperature of the waste gas is raised to between 260.degree.C and 340.degree.C prior to reduction. The ammonia can be introduced in the form of ammoniacal waste gases derived from the synthesis of ammonia. The apparatus for performing this method includes a reactor having one or more catalyst beds. A heat exchanger is interposed between the exit of the reactor and a gas turbine. The exchanger heats the waste gas entering the reactor by utilising the heat contained in the waste gas leaving the reactor. The gas turbine expands the waste gas from the reactor prior to its discharge through a stack.