Published: November 10, 2011 r2011 American Chemical Society 5786 dx.doi.org/10.1021/ef201271b | Energy Fuels 2011, 25, 5786–5790 ARTICLE pubs.acs.org/EF Physicomechanical Properties of Rice Husk Pellets for Energy Generation Bruna Missagia,* Cinthya Guerrero, Satyanarayana Narra, Yiling Sun, Peter Ay, and Hans Joachim Krautz Chair of Power Plant Technology, Brandenburg University of Technology, Cottbus, Germany ABSTRACT: The use of biomass for energy generation is a promising alternative due to its potential to satisfy environmental compatibility. Rice is one of the world’s most important food crops. Processing of paddy leads to the generation of crop and agro- industrial wastes, which are voluminous and difficult to handle. By upgrading this biomass into a uniform compressed fuel, namely pellets or briquettes, its density increases, improving the storage, transportation, and combustion characteristics. In this study, densification characteristics of Brazilian rice husks were studied using a laboratory compactor, Hosokowa Bepex, Type L200/50GpK, for the production of pellets. Experiments showed that their bulk density in raw form increased 6.3 times. The effects of different particle sizes (rice husks milled with 2 mm, 4 mm, and 6 mm sieve meshes) and moisture contents (17%, 19%, and 20%) on the durability of the rice husk pellets were assessed. It was concluded that rice husk pellets with 17% water content and made of raw material ground with 2 mm, 4 mm, and 6 mm sieves are durable and stable and comply with the standard quality values of agricultural pellets as specified in Agro and Agro+. Biomass conversion technologies, using pellets, might facilitate the development of decentralized energy systems in rural areas. Nevertheless, in order to be deployed in an efficient and responsible way, economic, technical, environmental, and social aspects over the whole supply chain should also be taken into consideration. ’ INTRODUCTION Biomass is one of the most promising and heavily subsidized renewable energy sources. 1 Agricultural waste is becoming an increasingly important energy source due to its environmental benefits and because its use does not interfere with traditional agricultural practices or jeopardize food security. Countries carry- ing out intensive agricultural practices produce a vast amount of residues, which could have enormous energetic potential. The national rice production in Brazil for the 2009/2010 harvest was 12 million tons, the average national productivity being ca. 4 ton/ha. 2 Processing of paddy leads to the generation of crop and agro-industrial wastes. Approximately 22% of the rice grain is constituted of husks. Loose rice husks have a low bulk density of about 85À110 kg/m 3 . 6 The densification process of biomass into pellets or briquettes can increase bulk density up to 10 times. 5 The pellet density is measured as the ratio of the mass of pellets in a predefined volume. The density of Brazilian rice husks was reported to be 98.52 kg/m 3 , while the density of raw rice husk pellets was 621.469 kg/m 3 in previous experiments. The higher the pellet density, the higher is the energy density and the lower are the transportation and storage costs. Rice husk pellets are a solid fuel with uniform shape and size suitable for direct combustion or cofiring with coal, pyrolysis, or gasification. Moisture content affects the calorific value of the pellets. A low moisture content fosters more predictable combustion efficiency. Typically, pellet fuels have a moisture content of approximately 10%. 11 The lower heating value of Brazilian rice husk pellets was reported to be 13 MJ/kg (5588.7 BTU/lb) with a moisture content of 8.5% in previous experiments. 11 Rice husk pellets could meet the thermal and mechanical energy requirements of the rice mills themselves. 3,4 In Brazil, briquetting machines were introduced in the 1980s. They were sold initially to rice mills, but afterward the wood factories became the main users. The most common raw materials used are saw dust, rice husks, and sugar cane bagasse. 7 The quality parameters of biomass pellets like density, abra- sion, and durability are influenced by several factors, including process variables (die temperature, pressure, and geometry),; feedstock variables (moisture content, particle size, shape, and distribution), and feedstock composition (protein, fat, cellulose, hemicelluloses, and lignin). 8 Some other process variables in- clude feed rate, binder usage, and biomass preheating. 5 Different biomass materials require different optimum condi- tions of fabrication. Water content is a key parameter influencing the solid fuel quality since it affects the combustion behavior and the stability of biomass pellets. Too high of a water percentage leads to poor combustion and increases in the risk of dust buildup in the chimney. When water content is too low, pellets are less stable. The objective of this paper is to assess some selected physicomechanical properties of rice husk pellets, namely abra- sion and strenghth, and their variation due to different moisture contents and particle sizes. ’ MATERIALS AND METHODS The rice husks used for the experiments were collected, stored, and dried during the months of May and June, 2008 in the Federal State of Minas Gerais, Brazil before their transportation to the laboratory facilities in Cottbus, Germany. Particle Size Distribution and Moisture Content of Rice Husks. Prior to pelleting, biomass can be milled to a specific particle size. The milling partially breaks down the lignin, increases the specific surface area of the material, and improves binding. 5 The rice husks were Received: August 24, 2011 Revised: November 10, 2011