Improving thermal conversion properties of rice straw by briquetting

Publication Type

Contribution to conference

Authors

Munder, S; Karaj, S; Gummert, M; Haefele, SM; Müller, J

Year of publication

2012

Conference name

International Workshop on the innovative uses of rice straw and rice husk

Conference location

International Rice Research Institute, Los Baños, Philippinen

Conference date

December 11 - 13, 2012

Keywords

rice, thermal processing

Rice is the staple food for more than half of the human population. As an agricultural residue, more than 600 million tons rice straw are produced yearly in Asia. In many countries of the world this straw is field burned after harvest. Not only is this practice polluting the environment but it is also a waste of potential revenues and energy. Alone for Southeast Asia, there is a potential quantity of 200 million tons of rice straw available. On a conservative attempt the average lower heating value is 14 MJ/kg. The amount of energy available from this rice straw is equivalent to 2800 PJ or 14% of the total primary energy supply in Southeast Asia. If the straw would be used for energy production, there would be some benefits. One is the reduction of greenhouse gas emissions and air pollution caused by field burning and anaerobic mineralization. Another is the reduction of traditional biomass use and therefore a decrease of deforestation. Additionally, the straw would gain a certain value which can increase the income on farm level. Solid biofuels made of rice straw would also increases the fuel availability on farm level which could have a significant impact on active food drying and though on the reduction of postharvest losses. Through the low density of rice straw, it is very unsuitable for transportation and storage. Furthermore, the low heating value per unit volume is making it technically unfeasible for direct use due to combustion and handling problems. A densification through briquetting or pelleting can solve these problems. The combination of bale opener, straw chopper, and a hydraulic piston briquetting press produced high quality briquettes from straw of up to 10% moisture content (13.4 to 15.6 MJ∙kg-1). The produced briquettes were cylindrically shaped, 66 mm in diameter and around 50 mm in length. This form enables them to be used as feedstock in automatic systems. Initial measurements of the consumption to output ratio show that the briquetting process only consumes 1.4% of the energy, the briquettes provide. With variation in pressure, solid densities of 0.74 to 0.97 g∙cm-3 and bulk densities of 377 to 477 kg∙m-3 could be achieved. This is a densification of up to more than ten times the straws initial bulk density. The briquettes durability, a measure for their ability to withstand impacts and abrasion occurring due to handling and transportation was found to be between 87.3 % and 95.3 %. Biomass materials, especially straw often, show a strong heterogeneity in their physical properties and chemical composition. Therefore a characterization of these properties as well as the determination of variance and a minimum number of required samples is important. Table 1 shows these data, analyzed according to DIN EN 14778.