Mechanism Research Of Incineration Flue Gas Dry Scrubbing At High Temperature

Presently most of incineration flue gas scrubbers are running at moderate to low temperature. This kind of scrubbing mode separates flue gas purification from fly ashes disposal. Thus superheater corrosion cannot be avoided. Meanwhile, the fly ashes and flue gas purification products collected in those scrubbers are toxic because of their dioxin and heavy metal contents. In this work a new scrubbing mode, namely, flue gas dry scrubbing at high temperature was put forward. According to this mode, most of the acidic gas and fly ashes are removed at high temperature before superheater, so that superheater corrosion can be avoided and fly ashes collected under high temperature are less toxic and easy to dispose of. Based on the above idea, this work mainly focused on high temperature scrubbing of gas pollutants (including HCl and NO_x) from incinerators. Firstly, HCl scrubbing with Ca-based absorbents was investigated and measures to improve HCl dry interception efficiency were explored. On the basis of experimental research, numerical simulation on diffusion of absorbent particles sprayed into flue gas scrubber was carried out. The simulation results provided a guide for improving performance of the dry scrubber. Secondly, De-NO_x effect with hydrazine-based compounds as reductants at moderate to high temperatures was examined and the results were compared with having ammonia as reductant. Finally, the possibility of simultaneous HCl and NO scrubbing with Ca-based absorbents treated by hydrazine-based compounds was explored.In order to improve HCl dry interception efficiency, HCl dry scrubbing with modified lime treated by NaOH was studied which proved that at high temperature modified lime's reactivity is better than normal lime, because of modified lime's crystal structure being irregular, its product layer being porous and its calcination rate being low to fit reaction process. Modified lime forms different product components at different temperature, which is not the same as normal lime.In order to obtain the optimum temperature for HCl high temperature scrubbing, temperature influence on HCl equilibrium concentration, lime decomposition and lime conversion rates was investigated. The results showed that HCl equilibrium concentration rises when temperature rises or CO₂ partial pressure increases, but modified lime can partially eliminate CO₂'s negative impact on HCl absorption. Lime has higher conversion rate at high temperature than low temperature. Completely reacted lime at 200℃ regains its reactivity when the temperature is raised to 600 ℃.Experiments on a continuous absorbent-feeding scrubbing system which is composed of a horizontal reaction pipe and a Stairmand cyclone indicated that HCl removal efficiency of slaked lime increases with rising temperature until 650°C of its peak temperature. In the range of 400-1400mg/m³, removal efficiency increases with...