Chlorine in Solid Fuels Fired in Pulverized Fuel Boilers — Sources, Forms, Reactions, and Consequences: a Literature Review^†

Abstract

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 (2/3), 89−165; Senior et al., Fuel Process. Technol. 63 (2/3), 187−213; and Senior, Sadler, and Sarofim, Preprints: Division of Fuel Chemistry, American Chemical Society 50 (1), 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 O2 and combustion temperatures. It also considers analyses conducted at 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 considerat...

An overview of problems and solutions for components subjected to fireside of boilers

“…About 90% of the coal power plants use these types of boilers for power generation [4,23]. Small proportion of wood, biomass and agricultural materials can also be used as fuel in pulverized fuel boilers [24].…”

“…Steam is generated when the hot flue gases flow outside the pipe due to convection. These hot gases transfer their heat to the water present in the tubes and come out with a lower temperature [24][25][26].…”

Improving Heat Recovery In Biomass-Fired Boilers

“…Tillman and others [65] note that the corrosion problems caused by biomass fuels generally arise from the chlorine and alkali metals (specifically K and Na) they contain. With the exception of wood and a handful of other fuel crops, biomass fuels contain significantly higher concentrations of chlorine than coal.…”

“…With the exception of wood and a handful of other fuel crops, biomass fuels contain significantly higher concentrations of chlorine than coal. [65] Field crops, with the exception of nut shells, pits and switchgrass, contain more chlorine than woody materials. Tables of typical chlorine and moisture concentrations in 20 biomass fuels [66] showed that chlorine concentrations, expressed as lb/10 6 Btu, ranged from 0.012 for willow, poplar and almond shells to 0.894 for rice straw and 0.923 for corn stover.…”

“…Frandsen has made detailed studies of the combustion chemistry of straw co-fired with coal. [102,103] Although straw fuels contain high concentrations of chlorine, Tillman and his co-authors reported [65] that co-firing 10% of straw in a Danish power station produced little, if any, corrosion attributable to chlorine. At 20% cofiring, the corrosion rate increased by a factor of 2 or 3, but was still considered manageable.…”