Investigation of chloride deposit formation in a 24Â MWe waste to energy plant

Waste-to-energy (WTE) plants are widely utilized for the production of heat and electricity from municipal solid waste (MSW) and refuse-derived fuel (RDF). However, there is the potential for high temperature corrosion to occur on the heat transfer surface due to a high chlorine content (0.5-1.0 wt.%) in MSW. Therefore, a full scale investigation was conducted in a WTE plant located in Tianjin, China, to study the corrosion mechanism and deposit chemistry that occurs during engineering projects. Deposit and corrosion probes were inserted and exposed to flue gas at five different locations for nine months then two different alloy probes were removed and analyzed. The chlorine flow in the incinerator was also investigated via stack sampling and the analysis of the composition of the residual. The results demonstrate that fly ash dominates the output for chlorine mass flow, accounting for 40.3% of total chlorine. Bottom ash accounts for approximately 6.7%, semi-dry scrubber and bag filter ash 31.4%, stacks 2.75% and leachate 18.6%. Using the back-calculation method, the chlorine content is 0.92 wt.% which is consistent with the elemental analysis that considers alkali salts soluble in the leachate resulting from MSW storage prior to boiler combustion. All deposits have a high concentration of sulfur and calcium but the potassium and chlorine concentrations suddenly decrease with flue gas flow. The deposit growth can be classified into three layers: the outer layer, the inner layer and the interface. The sodium and sulfur contents are high in the interface while the silicon and magnesium are high in the inner layer and calcium and chlorine are considerably high in the outer layer. The results are valuable for a better understanding of chlorine characteristics in large-scale WTE plants thereby assisting in reducing chlorine corrosion.