Comparison of Fine Ash Emissions Generated from Biomass and Coal Combustion and Valuation of Predictive Furnace Deposition Indices: A Review

To address important ash-related issues associated with burning solid biomass fuels for power generation, this paper reviews results of studies performed at the Northeastern University (NU) Combustion and Air Pollution laboratory and elsewhere under well-characterized conditions. It compares the physical and chemical characteristics of fine ash emissions generated from the combustion of pulverized biomasses to those from pulverized coals, since biomass is considered as a substitute fuel for coal in power generation, and assesses their furnace surface deposition propensities. Comparisons show that combustion of some biomasses may generate disproportionally higher emissions of submicron ash particles than combustion of coals (0.03-1.1 versus 0.04-0.06 kg/GJ, respectively). The high submicron emissions of biomass are problematic, as conventional particulate control devices have low collection efficiencies for such small particles. Moreover, the chemical composition of submicron particles of biomass typically contain large amounts of alkalis (potassium and sodium), chlorine, sulfur and, often, phosphorous, whereas those collected from combustion of coal contain large amounts of silicon, aluminum, iron, and sulfur. The composition of biomass ashes renders them more amenable to deposition on furnace surfaces, as calculations based on published empirical surface deposition indices show. These calculations, as well as experiences elsewhere, indicate that the slagging and, particularly, the fouling deposition prospects of most biomasses are significantly higher than those of coals. (C) 2015 American Society of Civil Engineers

Characterization of Particulate Matter Emitted from Combustion of Various Biomasses in O-2/N-2 and O-2/CO2 Environments

This work reports on the physical and chemical characteristics of the ashes of biomass residues burned in air as well as in simulated dry oxy-combustion conditions. Three pulverized biomass residues (olive residue, corn residue, and torrefied pine sawdust) were burned in a laboratory-scale laminar-flow drop tube furnace heated to 1400 K. Olive residue resulted in by far the largest particulate yields both submicrometer (PM1) and supermicrometer (PM1-18)-whereas torrefied pine sawdust resulted in the lowest. The collected particulate yields of these two biomasses were analogous to their ash contents. The collected particulate yields of corn residue, however, were lower than expected in view of its ash content. To investigate the effects of the oxygen mole fraction and of the background gas, the O-2 mole fraction was varied from 20% to 60% in either N-2 or CO2. Submicrometer particulate matter (PM1) emission yields of all three fuels were lower in O-2/CO2 than in O-2/N-2 environments; they typically, but not always, increased with increasing O-2 mole fraction in either background gas. The background gas had little effect on the chemical composition of the PM1 particles. High amounts of alkalis (potassium, calcium, and sodium) as well as of. chlorine were observed in PM1. In addition, phosphorus and sulfur also existed in high amounts in PM1 from combustion of corn residue. Supermicrometer particles (PM1-18) yields exhibited no clear trend when the background gas was changed or when the oxygen mole fraction was increased. The composition of these particles reflected the bulk ash composition of the parent fuels

Characterization of Particulate Matter Emitted from Combustion of Various Biomasses in O₂/N₂ and O₂/CO₂ Environments

This work reports on the physical and chemical characteristics of the ashes of biomass residues burned in air as well as in simulated dry oxy-combustion conditions. Three pulverized biomass residues (olive residue, corn residue, and torrefied pine sawdust) were burned in a laboratory-scale laminar-flow drop tube furnace heated to 1400 K. Olive residue resulted in by far the largest particulate yieldsboth submicrometer (PM₁) and supermicrometer (PM_1–18)whereas torrefied pine sawdust resulted in the lowest. The collected particulate yields of these two biomasses were analogous to their ash contents. The collected particulate yields of corn residue, however, were lower than expected in view of its ash content. To investigate the effects of the oxygen mole fraction and of the background gas, the O₂ mole fraction was varied from 20% to 60% in either N₂ or CO₂. Submicrometer particulate matter (PM₁) emission yields of all three fuels were lower in O₂/CO₂ than in O₂/N₂ environments; they typically, but not always, increased with increasing O₂ mole fraction in either background gas. The background gas had little effect on the chemical composition of the PM₁ particles. High amounts of alkalis (potassium, calcium, and sodium) as well as of chlorine were observed in PM₁. In addition, phosphorus and sulfur also existed in high amounts in PM₁ from combustion of corn residue. Supermicrometer particles (PM_1–18) yields exhibited no clear trend when the background gas was changed or when the oxygen mole fraction was increased. The composition of these particles reflected the bulk ash composition of the parent fuels