Energy & Fuels, Vol.23, No.7, 3379-3391, 2009
Chlorine in Solid Fuels Fired in Pulverized Fuel Boilers - Sources, Forms, Reactions, and Consequences: a Literature Review
Because Foster Wheeler North America Corp. (hereinafter "Foster Wheeler") is supplying and supporting Pulverized fuel (PF) boilers producing steam with higher temperatures and pressures, increasing emphasis must be given to potential sources of corrosion and deposition. Further. because Foster Wheeler is developing projects involving cofiring of biomass fuels (e.g., wood waste, agricultural materials) with coals from a variety of sources, again corrosion and deposition must be thoroughly investigated. Chlorine frequently is identified as a significant source of corrosion and deposition, both from coal and from biomass, and in PF boilers. Given the pressures to advance to higher steam pressures and temperatures, an investigation of the consequences of chlorine was undertaken. This investigation was designed to highlight the potential for Corrosion risks associated with once-through units and advanced cycles. This research took the form of a detailed literature investigation to evaluate chlorine in solid fuels: coals of various ranks and origins, biomass fuels of a variety of types, petroleum cokes, and blends of the above. The investigation focused upon an extensive literature review for papers, book chapters, and other documents dating back largely to 1991. The issues addressed focused upon deposition-slagging and fouling-and corrosion. Issues Such as mercury control facilitation, or HCl emissions, are not considered in this review. It is recognized that chlorine can facilitate mercury capture by influencing the oxidation state of mercury (see, e.g., Pavlish et al., Fuel Process. Technol. 82 (213). 89-165 Senior cl al., Fuel Process. Technol. 63 (213), 187-213; and Senior, Sadler, and Sarofim, Preprints: Division of Fuel Chemistry, American Chemical Society 50 (F). 295-298). This, however, is Outside the focus of this analysis. Municipal solid waste, and its derivatives, are also not included in this review. Issues With municipal waste tend to focus on formation of polychlorinated dioxins and furans (see, e.g., Everaert, Chemosphere 46, 439-448). again outside the considerations of this review. The focus is strictly corrosion and deposition. To address the deposition and corrosion issues, this review evaluates the following considerations: concentrations of chlorine in available solid fuels including various coals and biomass fuels, forms of chlorine in those fuels, and reactions-including reactivities-of chlorine in such fuels. The assessment includes consideration of alkali metals and alkali earth elements as they react with, and to, the chlorine and other elements (e.g., sulfur) in the fuel and in the gaseous products of combustion. The assessment also includes other factors of combustion: for example, combustion conditions including excess O-2 and combustion temperatures. It also considers analyses conducted as all levels: theoretical calculations, bench scale laboratory data and experiments, pilot plant experiments, and full Scale plant experience. Case studies and plant surveys form a significant consideration in this review. The result of this investigation focuses upon the concentrations of chlorine acceptable in coals burned exclusively, in coals burned with biomass, and in biomass cofired with coal. Values are posited bused upon type of fuel and combustion technology. Values are also posited based upon both first principles and field experience.