Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2012
Publication Date: 7/25/2012
Citation: Novak, J.M., Cantrell, K.B., Watts, D.W. 2012. Compositional and thermal evaluation of lignocellulosic and poultry litter chars via high and low temperature pyrolysis. BioEnergy Research.(6) 114-130. Interpretive Summary: Plant and animal litter feedstocks can undergo thermochemical conversion via pyrolysis to generate an energy dense char byproduct. Effectively converting raw plant and litter feedstocks into char is dependent on their ash composition with elements such as chlorine, sulfur, and potassium. These elements can reduce biomass conversion efficiency into char and also cause corrosion of processing equipment. In this work, we characterized the elemental composition in several raw plant and poultry litter feedstocks and their counterparts to understand how individual elements may influence pyrolysis conversion. This will aid in selection of an appropriate feedstock for efficient char production. Relationships were examined among the char’s ash content and elemental compositions with mass yields and heating values. The examined raw feedstocks and chars contained mixed amounts of ash that consisted of chlorine, sodium, and sulfur. The plant-based chars had better thermal energy contents and lower ash quality implying suitable service in thermal energy production. A poultry litter char had greater ash contents, medium heating values, and contained chlorine and sulfur, which could promote corrosion issues during thermal energy processing. Among the examined feedstocks, plant-based materials can be more suitable for efficient thermal conversion into char largely due to lower ash and chlorine contents.
Technical Abstract: Inorganic elements in biomass feedstocks can influence thermochemical reactions as well as the resultant chars elemental, compositional, and thermal characteristics. Chars were produced using slow pyrolysis at less than 400 and at higher than 500 degree Celsius from sugarcane bagasse, peanut hulls, pecan shell, pine chips, poultry litter and switchgrass. The chars and raw feedstocks were characterized for their elemental, structural, and thermal properties to ascertain the implications of feedstock selection and pyrolysis temperatures on these properties. Char mass yields from the six feedstocks ranged between 28 to 78% by weight while yields calculated on a carbon basis ranged between 44 to 89%. In both instances, lower yields were obtained with increasing pyrolysis temperature. Pyrolysis temperatures greater than 500 degrees Celsius resulted in more neutral to alkaline pH chars possessing greater ash contents and increased aromatic character. A significant exponential curve response was revealed between char mass yields versus pyrolysis temperature. All raw feedstocks and chars contained mixed amounts of macro, micro, and trace element concentrations. Higher heating values increased with heightened pyrolysis temperature. The char’s heating values inversely correlated to their total ash and chloride content. Lignocelluloses chars had better thermal characteristics and lower ash quality concerns implying suitable service in thermal energy production. In contrast, poultry litter char had greater ash contents, medium heating values, and contained corrosive inorganic elements, which rendered it problematic as a feedstock for thermal energy generation.