THERMOCHEMICAL PROCESSING OF AGRICULTURAL WASTES TO VALUE-ADDED PRODUCTS AND BIOENERGY
Location: Commodity Utilization Research
Title: Calorific values and combustion chemistry of animal manure
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: November 18, 2011
Publication Date: November 13, 2012
Citation: Uchimiya, S.M., He, Z. 2012. Calorific values and combustion chemistry of animal manure. In: He, Z., editor. Applied Research of Animal Manure: Challenges and Opportunities beyond the Adverse Environmental Concerns. New York, NY:Nova Science. p. 45-62.
Interpretive Summary: Combustion chemistry and calorific value studies are important for effectively converting agricultural wastes (biomass) to bioenergy. Compared to plant biomass, animal waste is a complex mixture of feces, urine, bedding materials, waste feed, and in some cases soil. In addition, animal waste contains a large amount of ash (mineral), and can contain more water than solid materials. These components cause handling problems as well as corrosion of biofuel production facilities. Manure in general contains lower energy than plant biomass. In addition to the use of manure as the direct source for bioenergy production, alternative and promising approaches are available. Examples include mixing manure with plant biomass before bioenergy production, utilization of composting and other manure processing options (that do not require heating), and the use of manure-derived charcoal as sterile and inexpensive fertilizer. These combined approaches will uniquely address waste management, bioenergy production, as well as agronomic/environmental utilization of processed animal wastes.
Combustion chemistry and calorific value analyses are the fundamental information for evaluating different biomass waste-to-energy conversion operations. Specific chemical exergy of manure and other biomass feedstock will provide a measure for the theoretically maximum attainable energy. The specific chemical exergy of 86 biomass ranged between 11.5 and 24.2 MJ kg-1 and increased in the following order of biomass grouping: manure < sludge < straws < grasses < hulls and shells < wood. In addition to the lower calorific value compared to lignocellulosic feedstock such as wood, manure contains a large amount of alkali metals and moisture that cause corrosion of biofuel production facilities. Partly due to the highly heterogeneous nature of manure consisting of feces, urine, bedding materials, waste feed (and their degradation products formed during storage) and in some cases soils, limited information is available in the literature on combustion kinetics of manure and its thermochemical conversion products. Further research is needed to understand the combustion chemistry of manures by utilizing (differential) thermogravimetric and calorimetric analyses. Calorific values and combustion kinetics of thermochemically converted manures, e.g., biochar, should also be fully investigated. In addition to the use of manure as a sole feedstock for combustion and thermochemical conversion, alternative approaches should be considered, particularly blending with plant biomass, combined thermochemical and biological (including composting) processing, and utilization of processed manures as a soil amendment on-farm to enhance the growth of lignocellulosic biomass feedstock. These combined approaches will uniquely address waste management, bioenergy production, as well as agronomic/environmental utilization of processed manure feedstock.