Chloride Deposit Formation in a 24 MW Waste to Energy Plant

Abstract

Waste-to-energy (WTE) plants are utilized for the production of heat and electricity from municipal solid waste (MSW) and refused derived fuel (RDF). However, a desire to raise the steam temperature in order to improve the electrical efficiency of WTE plants has introduced potential high temperature corrosion problems to the heat transfer surface, due to high chlorine content (0.5wt.%∼1.0wt.%) in MSW. To study the corrosion mechanism and deposits chemistry, full scale investigations were therefore conducted in a WTE plant in Tianjin, China. Deposit and corrosion probes were inserted and exposed to the flue gas at five different locations. After nine months exposure, two different alloy probes were taken out and analyzed. Meanwhile, the chlorine flow in the waste incinerator was also investigated via stack sampling and analysis of the residue's composition. The results showed: the most significant outlet for chlorine flow is via fly ash, accounting for 40.3% of total chlorine. Other main distributions are approximate 6.7% in bottom ash, 31.4% in semi-dry scrubber and bag filter ash, 2.75% discharged from stacks and rest in the leachate. The chlorine content was 0.92% via back-calculation method, which kept consistence with the elemental analysis. The deposits on the probes showed similar but distinct characteristics: all deposits were rich in sulfur and calcium content, potassium decreasing with flue gas flow suddenly showed highest value at Evaporator. With the deposits growth, the deposits can be classified into outer, inner and interface. The sodium and sulfur contents were rich in interface; silicon and magnesium were rich in inner; and calcium and chlorine were very high in the outer.