Project Reports

India has a major agribusiness sector which has achieved remarkable successes over the last three and a half decades. Agricultural waste or residue is made up of organic compounds from organic sources such as rice straw, oil palm empty fruit bunch, sugar cane bagasse, coconut shell, and others. Rice husk from paddy (Oryza sativa) is one example of alternative material that has a great potential. Rice husk a major by-product of the rice milling industry, is one of the most commonly available lignocellulosic materials that can be converted to different types of fuels and chemical feedstocks through a variety of thermochemical conversion processes. Rice husk is an agricultural residue abundantly available in rice producing countries.The husk surrounds the paddy grain. During milling of paddy about 78 % of weight is received as rice, broken rice and bran. Rest 22 % of the weight of paddy is received as husk. This husk is used as fuel in the rice mills to generate steam for the parboiling process. This husk contains about 75 % organic volatile matter and the balance 25 % of the weight of this husk is converted into ash during the firing process, is known as rice husk ash.  This RHA in turn contains around 85 % - 90 % amorphous silica.The moisture content ranged from 8·68 to 10·44%, and the bulk density ranged from 86 to 114 kg/ m³.  

Rice husk is unusually high in ash, which is 92 to 95% silica, highly porous and lightweight, with a very high external surface area. Its absorbent and insulating properties are useful to many industrial applications, such as acting as a strengthening agent in building materials. Rice husks are processed into rectangular shaped particle boards.

Construction industry is one of the fastest growing sectors in India. Rapid construction activity and growing demand of houses has lead to the short fall of traditional building materials. Bricks, Cement, sand, and wood are now becoming scares materials. Demand of good quality of building materials to replace the traditional materials and the need for cost effective and durable materials for the low cost housing has necessitated the researchers to develop variety of new and innovative building materials. Construction materials of special requirements for the houses in different geographical region to overcome the risk of natural hazard and for protection from sever climatic conditions has also emphasised the need for development of lightweight, insulating, cost effective, durable and environment friendly building materials. Rice hulls can be put to use as building material, fertilizer, insulation material or fuel. Rice hulls uses include aggregates and fillers for concrete and board production, economical substitute for microsilica, absorbents for oils and chemicals, soil ameliorants, as a source of silicon, as insulation powder in steel mills so as to name a few.

India is a major rice producing country, and the husk generated during milling is mostly used as a fuel in the boilers for processing paddy, producing energy through direct combustion and / or by gasification. About 20 million tones of RHA are produced annually. This RHA is a great environment threat causing damage to the land and the surrounding area in which it is dumped. Lots of ways are being thought of for disposing them by making commercial use of this RHA.

The annual rice husk produce in India amounts is generally approximately 120 million tons. Rice husk is generally not recommended as cattle feed since its cellulose and other sugar contents are low. Furfural and rice bran oil are extracted from rice husk. Industries use rice husk as fuel in boilers and for power generation. Among the different types of biomass used for gasification, rice husk has a high ash content varying from 18 – 20 %. Silica is the major constituent of rice husk ash and the following tables gives typical composition of rice husk and rice husk ash. With such a large ash content and silica content in the ash it becomes economical to extract silica from the ash, which has wide market and also takes care of ash disposal.

A number of rice-producing countries, (e.g. Thailand), are currently conducting research on industrial uses of rice hulls.