Inhibiting fly ash reactivity by adding N- and S- containing compounds

Abstract

The inhibitory effect of thiourea (TUA), ammonium thiosulfate (TSA) and amidosulfonic acid (ASA) on the reactivity of fly ash air was investigated using a thermobalance at different heating rates (5, 10 and 20 K min^-1). A model fly ash (activated carbon + 50 wt% CuCl₂·2H₂O, pyrolyzed at 700 °C and washed) was used as carbonaceous material. Adding CuCl₂·2H₂O to the activated carbon led to an increased rate of decomposition with the air's oxygen. TUA and TSA behaved in a similar way, accelerating the decomposition of the model fly ash. ASA also accelerated the decomposition but to a lower extent. We postulate that the increase in decomposition rate is caused by a reaction between carbonaceous material and N and S-containing compounds. The formation of nitrogenated and sulphured compounds was confirmed by TG-MS. A kinetic model based on a single reaction of order 0.6 showed very good correlations with all the heating rates tested in oxidant atmosphere.

Keywords: Amidosulfonic acid; Ammonium thiosulfate; Inhibition; Model ash; Thermogravimetry; Thiourea.