Pelleting and characterization of dry distillers' grain with solubles pellets as bio-fuel
Bio fuels are made from an extensive selection of fuels derived from biomass, including wood waste, agricultural wastes, and alcohol fuels. As a result of increased energy requirements, raised oil prices, and concern over greenhouse gas emissions from fossil fuels, bio fuels are acquiring increased public and scientific attention. The ethanol industry is booming and during the past several years, there has been an increase in demand for fuel ethanol and use of its co-products. To increase potential revenues from ethanol processing and its utilization, extensive research is proceeding in this field. In Western Canada, wheat is the primary raw material used in the production of ethanol by fermentation and distillers’ dried grains with solubles (DDGS) are one of the major co-products produced during this process. At present, the DDGS are generally sold as animal feed stock but with some alteration they could be used in other useful areas. Densification of biomass and use of it for fuel like wood pellets, hay briquettes, etc. have been studied for many years and have also been commercialized. In this thesis, pellets made from distillers’ dried grains have been investigated. DDGS were obtained from Noramera Bioenergy Corp. and Terra Grain Fuels Ltd. Before transforming them into pellets, they were characterized on the basis of physical and chemical properties. A California pilot-scale mill (with and without steam conditioning) was used for pelleting the distillers’ grains with solubles. A full factorial design with two levels of moisture content (i.e., 14 and 15.5% (w.b.)), hammer mill screen size (i.e., 3.2 and 4.8 mm) and temperature (i.e., 90 and 100°C) was used to determine the effects of these three factors on the pellet properties made from Noramera Bioenergy Corp., without steam conditioning. Different levels of moisture content were used for the pellets made from Terra Grain Fuels Ltd. (i.e., 11.5 and 13.09% (w.b.)), with steam conditioning. The initial moisture contents of the DDGS were 12.5 and 13.75% (w.b.) from Noramera and Terra Grain, respectively. The moisture content of DDGS grinds ranged from 11.6 to 12.03% (w.b.) for the Noramera samples, and from 11.5 to 13.09% (w.b.) for Terra Grain DDGS. The moisture content decreased with a decrease in the hammer mill screen size. The use of a smaller screen size achieved an increase in both the bulk and particle densities of the DDGS. The coefficient of internal friction was almost the same for both samples but cohesion was higher in Noramera samples (8.534 kPa). The DDGS obtained from Noramera Bioenergy Corp. contained dry matter (91.40%), crude fibre (4.98%), crude protein (37.41%), cellulose (10.75%), hemi-cellulose (21.04%), lignin (10.50%), starch (3.84%), fat (4.52%) and ash (5.16%); whereas the samples obtained from Terra Grain Fuels contained dry matter (87.69%), crude fibre (7.33%), crude protein (32.43%), cellulose (10.81%), hemi-cellulose (27.45%), lignin (4.37%), starch (4.18%), fat (6.37%) and ash (4.50%). The combustion energy of the Noramera samples was 19.45 MJ/kg at a moisture content of 8.6% (w.b.) whereas the combustion energy of Terra Grain samples was 18.54 MJ/kg at 12.31% (w.b.) moisture content. The durability of the pellets increased as the screen size decreased which is likely due to the fact that a smaller screen size produces more fine particles. This fill voids in the pellets and, hence, makes them more durable. The length of the pellets produced from Noramera DDGS increased with a decrease in moisture content possibly because pellets formed at higher moisture content absorb less moisture. Therefore, the length does not increase as much. Lateral expansion occurred most with higher temperature and lower moisture content and with lower temperature and higher moisture content. The length to diameter ratio of the pellets followed the same trend as the change in pellet length. The length of the pellets produced from Terra Grain also increased with a decrease in moisture content. The lateral expansion increased with increase in screen size and moisture content and also, with decrease in moisture content and increase in temperature. The length to diameter ratio increased with decrease in screen size and moisture content, similar to the change in pellet length. The highest bulk density of Noramera pellets resulted from smaller screen size and lower moisture. The particle density increased with a decrease in screen size and an increase in moisture content. The highest bulk density of Terra Grain pellets occurred with an increase in temperature and decrease in moisture content. The highest particle density occurred with an increase in temperature and decrease in screen size. The pellet hardness increased with a decrease in moisture content and screen size did not have any significant effect. The Terra Grain pellets were harder because they were subjected to steam conditioning. Steam conditioning helps to increase the hardness. The pellet durability increased with a decrease in screen size and increase in moisture content. The steam conditioning also caused the higher durability in the Terra Grain pellets. In terms of moisture absorption, the only significant factor was moisture content. Pellets with lower moisture content absorbed more moisture. The ash content values of pellets were higher in Noramera samples than in Terra Grain samples because of high moisture content in Noramera samples. The combustion energy of the Noramera pellets was higher than the Terra Grain pellets because of the high percentage of dry matter and lignin present in Noramera samples. The emission results for both the sample pellets were similar. When the DDGS pellets were compared to wood pellets, emission of nitrous oxide was lower for wood whereas, carbon dioxide was higher.
DegreeMaster of Science (M.Sc.)
CommitteeKushwaha, Lal; Christensen, Colleen; Zhang, Chris
Copyright DateNovember 2010
dried distillers' grains with solubles