Grass pellet Quality Index: A tool to evaluate suitability of grass pellets for small scale combustion systems

US renewable fuels policy strongly encourages biomass crop production, which should lead to expansion of biomass heating scenarios. Chemical composition of grass biomass can be extremely variable, depending on species, soil fertility, and harvest management. Biomass quality concerns have hindered the development of grass biomass for residential combustion, with no comprehensive evaluation system for grass pellet quality. Quality labeling will strengthen the fledgling grass biomass heating market, gain consumer confidence, and help to control combustion related emissions. The proposed system sums qualitatively different parameters into one Quality Index for relative evaluation and ranking of grass pellets for residential combustion potential. Parameters were selected and weighted for their relative importance based on available literature. Weighting was accomplished by adjusting the compositional working range for each parameter. A limit also was established for each parameter, beyond which the pellet lot was considered as unacceptable for residential combustion, regardless of the total Quality Index score. The model structure allows for effective evaluation and ranking of grass pellet lots regardless of the specific values ultimately chosen for acceptable limits and working ranges by the industry. Applying the Quality Index to a range of grass pellet types resulted in a reasonable ranking of pellets based on physical characteristics and composition.

► A Quality Index ranking grass pellets for combustion potential does not exist.
► Grass pellet biomass is extremely variable and therefore quality control is essential.
► Proposed system sums qualitatively different parameters into one index value.
► Model structure allows for effective evaluation and ranking.