Effect of Additives and Fuel Blending on Emissions and Ash-Related Problems from Small-Scale Combustion of Reed Canary Grass

Abstract

Agricultural producers are interested in using biomass available on farms to substitute fossil fuels for heat production. However, energy crops like reed canary grass contain high nitrogen (N), sulfur (S), potassium (K) and other ash-forming elements which lead to increased emissions of gases and particulate matter (PM) and ash-related operational problems (e.g., melting) during combustion. To address these problematic behaviors, reed canary grass was blended with wood (50 wt%) and fuel additives (3 wt%) such as aluminum silicates (sewage sludge), calcium (limestone) and sulfur (lignosulfonate) based additives. When burned in a top-feed pellet boiler (29 kW), the four blends resulted in a 17%–29% decrease of PM concentrations compared to pure reed canary grass probably because of a reduction of K release to flue gas. Nitrogen oxides (NOx) and sulfur dioxide (SO2) emissions varied according to fuel N and S contents. This explains the lower NOx and SO2 levels obtained with wood based products and the higher SO2 generation with the grass/lignosulfonate blend. The proportion of clinkers found in combustion ash was greatly lessened (27%–98%) with the use of additives, except for lignosulfonate. The positive effects of some additives may allow agricultural fuels to become viable alternatives.

Keywords

• agricultural biomass combustion
• energy crops
• additives
• fuel blending
• pellets
• gas emissions
• particulate matter
• ash-related problems
• melting