Chlorine Sources, Sinks, and Impacts in WTE Power Plants

The principal sources of chlorine in the MSW feed to WTE power plants are food wastes (e.g., wheat, green vegetables, melon, pineapple), yard wastes (leaves, grass, etc.), salt (NaCl), and chlorinated plastics (mostly polyvinyl chloride). Chlorine has important impacts on the WTE operation in terms of higher corrosion rate than in coal-fired power plants, formation of hydrochloric gas that must be controlled in the stack gas to less than the U.S. EPA standard (29 ppm by volume), and potential for formation of dioxins and furans. Past Columbia studies have shown that the chlorine content in MSW is in the order of 0.5%. In comparison, chlorine concentration in coal is about 0.1%; this results in much lower HCl concentration in the combustion gases and allows coal-fired power plants to be operated at higher superheater tube temperatures and thus higher thermal efficiencies. Most of the chlorine output from a WTE is in the fly ash collected in the fabric filter baghouse of the Air Pollution Control system. This study examined in detail the sources and sinks of chlorine in a WTE unit. It is concluded that on the average MSW contains about 0.5% chlorine, which results in hydrogen chloride concentration in the WTE combustion gases of up to 600 parts per million by volume. About 45% of the chlorine content in MSW derives from chlorinated plastics, mainly polyvinyl chloride (PVC), and 55% from salt (NaCl) and chlorine-containing food and yard wastes. An estimated 97–98% of the chlorine input is converted to calcium chloride in the dry scrubber of the Air Pollution Control (APC) system and captured in the fly ash collected in the baghouse; the remainder is in the stack gas at a concentration that is one half of the U.S. EPA standard. Reducing the input of PVC in the MSW stream would have no effect on dioxin formation but would reduce the corrosion rate in the WTE boiler.