A study of chlorine behavior in a simulated fluidized bed combustion system

Fluidized bed combustion techniques have been widely used throughout the wo rld in an effort to reduce sulfur oxide emissions, especially from burning high-sulfur coal. However, in the utilization of FBC systems for co-firing high chlorine coals with municipal solid waste (MSW) there are some concern s about the possible emission of polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). PCDD/Fs may be produced from the re action of volatile organic compounds (VOCs) and molecular chlorine under re latively low combustion temperature conditions. In oxygen-rich conditions d uring combustion molecular chlorine can be formed through the Deacon Reacti on when the temperature is around 600 degrees C. It is also likely that chl oride might affect the detailed chemistry of desulfurization in FBC process es. In order to better understand the behavior of chlorine in an FBC system during combustion processes, a comprehensive study was carried out in a si mulated FBC system with an on-line feeder at Western Kentucky University. C onditions used simulated the flue gas and operating conditions of an FBC sy stem. Optimum operating conditions to suppress HCl, Cl-2 and SOx emissions from FBC systems were determined. A better understanding of the chlorine be havior during combustion will help in controlling possible PCDD and PCDF fo rmation and reducing corrosion in FBC systems. The test results indicated t hat the formation of molecular chlorine is favored at temperatures above 60 0 degrees C, in oxygen-rich atmospheres, and in relatively high HCl concent rations. The reaction temperature plays a key role in the capture of HCl. T he optimum combustion conditions for controlling PCDD/Fs formation in FBC s ystems is to maintain combustion temperature around 850 degrees C in the be d area, 600 degrees C in the freeboard area, low oxygen concentrations in t he hue gas and enough residence time for tine particles in the freeboard. ( C) 2000 Elsevier Science Ltd. All rights reserved.