Kinetic Simulation of Fine Particulate Matter Evolution and Deposition in a 25 kW Pulverized Coal Combustor

Abstract

In this paper, fine particulate matter (PM) evolution and deposition in pulverized coal combustion are simulated by solving the population balance equation using a quadrature-based method of moment. We first verify the stability of moment closure systems for the univariate nucleation−condensation/vaporization problem and some specific coagulation/breakage problems. A series of mechanistic experiments in a 25 kW pulverized coal combustor are used for comparison and validation. The simulated particle size distributions at different combustion stages agree reasonably well with the measurements. For sub-micrometer particle evolution at the early stage of bituminous coal combustion, soot oxidation is a main driving force. While in the post-flame region when burning sodium-rich Zhundong coal, the competing processes of condensation and homogeneous nucleation of Na 2 SO 4 vapor yield ultrafine PM 0.2 with a uniform content of Na. At the burnout region (∼1100 K), the sodium residual in the gas is in the form of NaCl. Ash deposition experiments in this region cause mineral to transport toward the probe. We reveal that, for burning Zhundong coal, homogeneous nucleation of NaCl vapor can hardly take place in the boundary layer. The vapor condensation flux onto the probe surface takes only 4% of the flux onto pre-existing fly ash particles, whose surface stickiness may be significantly enhanced.

Numerical Analysis on Reduction of Ultrafine Particulate Matter by a Kaolin Additive during Pulverized Coal Combustion

“…It is of practical significance to know at what condition the coagulation mechanism becomes non-negligible without running the simulation. One of the most convenient ways to achieve this is to measure the time scales for coal combustion τ com , chemical adsorption τ ads , and coagulation τ coag . Here, the combustion time scale is simply set according to the residence time; i.e., τ com = τ res = 1.4 s. The alkali vapor–kaolin reaction is assumed to be first-order and is described with global kinetics; therefore, the chemical adsorption time scale can be expressed as where k app is the apparent reaction rate constant.…”

“…One of the most convenient ways to achieve this is to measure the time scales for coal combustion τ com , chemical adsorption τ ads , and coagulation τ coag . 54 Here, the combustion time scale is simply set according to the residence time; i.e., τ com = τ res = 1.4 s. The alkali vapor−kaolin reaction is assumed to be first-order and is described with global kinetics; therefore, the chemical adsorption time scale can be expressed as 55 53 Shanxi anthracite 5 g of kaolin/100 g of coal (5%) 16.83% (PM 0. where k app is the apparent reaction rate constant. Plugging the parameters adopted in eq 23 into eq 31, we have τ ads ≈ 0.011 s, which is much smaller than the coal combustion time scale τ res .…”

Promoting Silicate Formation by Alkali Chloride Solid Solution during Thermal Conversion of Silicon-Containing Solid Fuels

“…A thorough understanding of the thermochemical behavior of alkali metals is essential to accurately quantifying their release extents. This knowledge is indispensable for the precise prediction of the formation and evolution of particulate matter (PM), considering that alkali metals serve as the primary mineral precursors to PM. , Moreover, a comprehensive analysis of the ASR under this interaction enhances the understanding of the mechanism for ash formation.…”

Special Issue of Energy & Fuels Honoring Michael T. Klein

“…Studies of emissions of particulate matter from coal combustion, presented by Huang et al, and particle emissions from combustion of municipal solid waste, presented by Yang et al, both find that alkali metals play an important role in the aggregation of the particles. Both Senior et al and Seshadri et al present studies of trace elements in air and water discharges from coal-fueled combustion.…”