O2- and NOsub(x)-removal from the dissolver off-gas by thermal reduction with H2 or NH3

The reference process for the removal of O2 and NOsub(x) from the dissolver off-gas is the catalytic reduction with H2. Because of the known disadvantages of catalysts, like reduction in efficiency by poisoning or thermal influence, the alternative method of thermal, flameless reduction with H2 and NH3 was tested. The reactions were carried out in a stainless steel and a quartz reactor. Both had a length of 850 mm, an inner diameter of 53 mm, and were heated by resistance heaters on the outside. The main component of the test gases was N2. Tested throughputs were 600, 800, and 1000 l/h (STP). Different amounts of O2 (0.5 and 1%), NO (750 and 1500 ppm) and H2 or NH3 (-40 to +100% of stoichiometric supply) were added. The reaction temperatures were varied between 450 and 750 deg. C. The goal of these tests was to remove O2 and NOsub(x) to below 1 ppm behind the reactor and NH3 (which is formed in the NOsub(x)-H2-reaction) to below the detection limit of 50 ppm