Screening and characterization of comminuted woody biomass feedstocks

Increasing fuel costs and environmental concerns have resulted in biomass energy becoming a feasible option for renewable energy compared to fossil fuels. The most commonly traded form of biomass energy feedstocks are chipped (wood chips) and ground (hog fuel) materials. Of these two feedstocks, particle size distribution is one of the biggest problems for fuel handling efficiency. Also, matching the specific feedstocks size to current conversion technology requirements is necessary to improve consumer confidence in feedstocks quality assurance. To meet the specifications for mobile biomass conversion technologies, biomass feedstocks can be accomplished with screening technology such as a star or deck screener. In chapter 2, analyzes the productivity and size distribution of the star and deck screen machines, with regard to two different material types (hog fuel and wood chips). Screen machines were set up with three different size categories; under, accept and over. Under size materials were set under 10 mm in size, accept size was between 10 mm to 50 mm, and over size materials were all over 50 mm. The results of the productivity study indicated that the star screen was more productive than the deck screen machine. Also, using wood chips material in both screen machines was more productive than using hog fuel. The results of the size distribution of screened materials were first that 13 mm had the highest portion of accepted sizes, and secondly that 25 mm size materials are dominantly found in the over size class, and pan size materials(saw dust) are the highest portion of the under size materials. In chapter 3, analyzing the character of the biomass feedstocks, wood chips and hog fuel shapes are defined based on ASABE definitions as chips, chunks, cubes, shavings, sticks, and strings. To classify the shapes of the biomass materials, length, width, and thickness of the particles were measured using a digital caliper. As a result of shape classification, hog fuel materials were shown to have more shape variation compared to wood chips feedstocks. Controlling the length of the hog fuel materials is the most important factor in determining the size and shape of the ground materials. It has been found that by reducing the length dimension of hog fuel, operators can reduce the occurrences of spear shapes (shavings, sticks, and strings) to chip shapes (chips and chunks). Also, increasing the width of stick shapes of wood chips feedstocks can change the shape to chips or cubes shapes which can convert spear shape (heterogeneous shape) to square shape (homogeneous shape). In the last chapter, to reduce diving problems, this study tested two different screen combinations using the DS6162 deck screen machine. The first screen setting consisted of four sets of 51 mm deck screens on the top screen and second screen setting with four sets of 19 mm and 51 mm deck screens on the top. As a result of this study, there was a significant reduction in the presence of oversized material in the accept size class. Also, the small size of the top screen combination resulted in higher accuracy than 51 mm tops. However, there was not a significant difference in mean productivity among the material types using the deck screen machine.