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An extruder was developed and tested for forming biomass from agroprocessing wastes. The experimental treatments included four screw speeds (0.789, 1.05, 1.41and 1.57m/s.), four die hole diameters of extruder (6, 8, 10 and 12mm) and three moisture levels (7.5, 10.5 and 13.6%) of two agro-processing wastes at different particle size (sawmill dust (≤ 3mm) and coarser corncob grinds (≤6.5mm). The results of the experiments showed that the particle size had a significant effect on machine productivity, pellets density, durability and specific energy requirement. The finer sawdust resulted in higher productivity, pellets density, durability and lower specific energy than the coarser corncob grinds. The machine productivity of sawdust was higher value by about 7% than the productivity of corncobs. The pellets density ranged from 0.81 to 1.24g/cm 3 for sawdust and form 0.76 to 0.94g/cm 3 for corncobs. The durability of sawdust pellets was higher by about 15.6% for corncobs pellets. While, the energy requirement of sawdust pellets was lower value by about 41.7% than for corncobs pellets. The pellets produced on the smallest die and lower moisture content had the best quality values. The combustion test indicated that the combustion of the pellets is more regular than the combustion of loose materials and provided the highest flue gas temperature and low carbon monoxide contents emitted. INTRODUCTION he interest in producing energy from biomass has increased in recent years, owing to depleting fossil energy supplies and climate change caused by carbon emissions. Low densities of 40– 60 kg/m 3 for lignocellulosic and 200– 400 kg/m 3 for woody biomass limit their application for energy purposes. *Agric. Eng. Res. Ins. (AEnRI), Dokki, Giza, Egypt. E-Mail: Shoughy_AERI@Yahoo.com T Misr J. Ag. Eng., 30 (2): 537 558 BIOLOGICAL ENGINEERING Misr J. Ag. Eng., April 2013 538 Prior to use in energy applications these materials need to be densified (Sokhansanj et al., 2006 and Hess et al., 2009). The densified biomass can have bulk densities over 10 times the raw material, improves its handling characteristics, reduces transportation cost, enhances its volumetric calorific value, and produces a uniform, clean, stable fuel, or an input for further refining processes Granada et al., (2002). Due to the advantages of densification, several biomass materials have been experimentally studied to convert to densified fuels for example: rice husk, peanut shell, coconut fiber and palm fruit fiber, Chin and Siddiqui (2000). On average 2.5 tons of biomass on a dry basis have an energy potential equivalent to one ton of oil, El-Saeidy (2004). The most common residential fuel pellets in developed nations are made from sawdust and ground wood chips, which are by-products generated from furniture, lumber, and other industries. Corncobs also are one of the potential agriculture biomass feedstock for renewable energy industries to abate the current energy and the greenhouse gas problems. Corncobs can be used for producing heat, power, gas/fuels liquid and a wide variety of chemical productions such as furfural, xylitol and activated carbon. It can be used without pelleting for majority of applications such as industrial scale heating, Jin and Wang (2011). However, for applications required high quality feedstock such as home heating, corncobs may need to be pelleted. Furthermore, although corn cubs are almost cylindrical in shape, a mixture of whole and broken pieces of cobs may result due to breakage of cubs during corn combine harvesting and mechanical shelling, may lack free-flowing properties. Fuel pellets can be used in pellet burning fireplaces or stoves for residential use or burned in solid fuel boilers for industrial use. Most developed and industrialized nations are looking into developing technologies to use biomass more efficiently. Sweden has decided to phase out nuclear plants, reduce fossil fuel energy usage, and increase the use of biomass for energy (Bjorheden, 2006). Literature review showed that different biomass materials required different optimum conditions for pelleting process. Sokhansanj et al., (2005) concluded that the optimum moisture content for pelleting cellulosic materials is 8–12%, whereas for starch and protein materials, the optimum moisture content can range up to 20%. Mani et BIOLOGICAL ENGINEERING Misr J. Ag. Eng., April 2013 539 al., (2006) reported that the particle size has significant effect on the mechanical properties of pellets. Saptoadi (2006) found that the best results of combustion, the pellets dimensions should be as small as possible with coarse particle size. Kaliyan and Morey (2007) indicated that temperatures of around 85°C can occur in conventional ring-die pelleting machines due to frictional heating. Chevanan et al., (2010) revealed that the specific mechanical energy was found to be lowest for the 15% moisture content and highest at 20% moisture content. Tumuluru et al., (2010b) found that a larger die diameters of 7.2mm produced less-durable pellets compared to a smaller die diameter of 6.4mm. However, very small particle sizes can lead to jamming of the pellet mills and affect production capacity. The failure of several pelleting or briquetting projects (either technically or financially) in developing countries was mainly due to mismatching equipment to suit the specific characteristics of raw materials. Before selecting or designing any commercial machine, it is necessary to know the mechanical behavior of the material and the processing conditions. To increase production and a size reduction process, there is a need to develop more efficient mechanical screw pelletizer. We successfully developed and tested a machine for forming rice bran pellets, Shoughy et al., (2011). The objectives of the present work were to: Testing and evaluating an expeller machine used for rice bran pellets as a dual purpose for forming biomass pellets from agro-processing wastes. Study the effect of some operating parameters such as screw speed, die hole diameter of extruder and particle size of two agro-processing wastes (sawmill dust and corncobs) at various moisture levels on machine productivity, specific energy requirement and pellets quality (pellets density and durability) as well as flue gas temperature and gas emission during combustion test. MATERIALS AND METHODS Materials: Two types of agro-processing wastes (corncobs and sawmill dust) were used for the experiments. The ground corncobs sample were obtained after mechanical shelling at Sakha Research Station, Corn Section, Kafrelsheikh Governorate after 2012 summer harvesting season. While, BIOLOGICAL ENGINEERING Misr J. Ag. Eng., April 2013 540 grounds sawmill dust was fine particles size of wood obtained from local medium scale workshops in Kafrelsheikh, as a by-product generated from furniture and other wood industries. In the production of woody pellets from sawdust; a particle size of approximately ≤3.0mm is used. While, a particle size of coarser corncobs grinds of approximately ≤6.4mm is used. All of the samples were subsequently ground using a forage grinder with a screen opening sizes of 3-7mm. The authors decided to use these screen size based on the studies conducted by Adapa et al., (2009).The initial moisture contents of the ground corncubs and sawdust was 7.5 and 6.8% (w.b.), respectively. The moisture content (MC, %) of the samples were raised to 7.5, 10.5 and 13.6% (w.b.) by adding and sprinkling calculated amount of water and subsequently stored the samples in plastic bags in a cold room kept at 4°C for a minimum of 72h. Equipment: An expeller machine which successfully developed, modified and tested in Agriculture Engineering Research Institute for forming rice bran pellets are used to form biomass from agro-processing wastes. The extrusion process can be made continuous by a helical screw. Material is fed into an inlet hopper and moved forward by rotation of the screw. As it reaches the die, the pressure increases to the level required to force the material through the die holes. The rotating screw transports material from inlet to discharge as a result of the slipping of material on the screw surface. The friction between material and screw surface results in shearing and heating of the material. The original die outlet head has a chuck like outlet that changed and replaced by an outlet ring die have 20, 16, 14 and 12 round holes for forming biomass pellets at different diameters (6, 8, 10 and 12mm, respectively) by extrusion process, where the function of the chuck of the original outlet die to permit a final adjustment of pressure and capacity. Also, the barrel was modified to fit with biomass pelleting. The clearance between the flat steel bars inside the barrel (cage) was eliminated and the bars also sloped towards the die hole of the extruder by reducing the bars cross section in order to rise up the compression action of the screw towards the die holes of extruder to BIOLOGICAL ENGINEERING Misr J. Ag. Eng., April 2013 541 increase the extruder die work area. More details of this machine and their modification are found in Shoughy et al., (2011). Experimental treatments The performance of the extruder machine such as productivity and the required energy was evaluated. Pellets quality was also evaluated through the pellets density and durability as well as the combustion characteristics. The experimental treatments, included four levels of screw speed (0.79, 1.05, 1.4 and1.57 m/s), four levels of die hole diameter (6, 8, and 10, 12mm) and two different types of agro-processing wastes (corncobs (≤6.5mm) and sawmill dust (≤ 3mm)) at three moisture levels (7.5, 10.5 and 13.6%). Test procedure and measurements: Before each experiment, the samples were prepared at desired moisture content and the experimental run as follow: 1. Before pelleting operation the hopper was filled with the sample (2kg). 2. The pelleting machine was run.

BIOMASS TECHNOLOGY PRODUCTION FROM AGRO-PROCESSING WASTES BY AN EXPELLER MACHINE