High-Temperature Characterization of Inorganic Particles and Vapors in a Circulating Fluidized Bed Boiler Cofiring Wood and Rubber Waste

Abstract

The effects of varying fuel mixtures and using a lime additive were studied in a 125-MW th circulating fluidized bed boiler. A high-temperature aerosol measurement method using a hot-dilution probe was used to characterize the particles and condensing inorganic vapors upstream from the superheater. The particle size distributions of the extracted samples indicate that when high-sulfur rubber waste, waste wood, and forest fuel were cocombusted, the hot flue gas contained no substantial amount of particulate matter in the fine (<0.3 μm) particle size range, although the SO 2 concentration exceeded 70 ppm. Only a nucleation mode was observed, which was presumably formed from inorganic vapors that condensed in the sampling probe. The size-segregated elemental analysis of the extracted samples indicated that when lime was added, the nucleation mode mainly comprised condensed alkali chlorides, while the sulfates dominated the mode when no lime was added. The presumed explanation for the sulfates in the nucleation mode was the sulfation of the alkali chlorides inside the sampling system. When only the wood fuels and no rubber fuel were cocombusted, the SO 2 concentration in the gas was approximately 5 ppm. In this case, an alkali sulfate particle mode formed at approximately 70 nm in the hot flue gas. In addition, vapors of alkali chlorides and lead formed particulate matter inside the sampling probe when using low dilution ratios.

An artifact-minimizing method for total dust sampling and chemical characterization of industrial high-temperature aerosols

“…There are basically two approaches to achieve a suppression of condensation: Either the aerosol is extracted from the boiler and instantaneously quenched (out-stack method) or the sampling substrate is located directly in the boiler (in-stack method). At high temperatures above approximately 600 C, all out-stack methods reported in the literature are known to introduce tremendous condensation artifacts Maguhn et al 2003;Strand et al 2004;Deuerling et al 2010;Sippula et al 2012;Yang et al 2013Yang et al , 2015. The reason is that the saturation vapor pressure of, e.g., NaCl and KCl drops by a factor of more than 10 6 when cooling from 1000 to 500 C (Ewing and Stern 1974).…”