Rice hulls pellets as alternate solid fuel for energy generation

Abstract

Rice is the staple diet of over half the population of the world at an estimated production volume of well over 800 million metric tonnes per month, the second largest produced cereal in the world. Rice grows from tropics to subtropical to warm temperature countries up to 400 S and 500 N of the equator. Four major environments are associated with rice growing as follows: irrigated, rain-fed lowlands, upland and flood prone. Fifty per cent of rice grown are consumed by China and India, and until a few years ago, the rice hulls (husks) resulting from hulling have been considered as agricultural waste and only used in a few small end applications. However, due to diligent research, the full potential of this valuable commodity is being realized and three significant products are being manufactured using this biomass – polymeric composite resins, polymeric lumber as an ideal substitute for natural wood, and more recently, rice hulls solid pellets as an alternative for diesel oil and coal as fuel for energy generation. While the first two are made from combinations of rice hulls flour and polymer resins, the last one is made by compression with suitable small quantities of additives primarily for adhesion. The dimensions and densities of these solid pellets can be varied to suit end applications and also to assist fuel feeding systems. When rice hulls solid pellets are used as fuel, they will generate ash in the combustion chamber and also flue ash which can be easily collected and both items can be successfully recycled. They can be used as filler for bricks, for roofing tiles, extraction of silica (>70%), fertilizer, chemical spill absorbents, filtration mediums and some others. The high content of silica in the ash will provide an enhanced moisture barrier for bricks and roofing tiles. A major end application is its usage as a component for the production of Portland cement. Rice hulls are also an ideal feedstock for producing bio-diesel, and for this purpose, thermochemical processes like pyrolysis and gasification can be used. This research study shows that rice hulls basically consisting of lignin polymer and 20% silica can be made into solid pellets and effectively used as an alternate fuel for petro-based diesel oil and coal for generation of energy. This emerging fuel from renewable sources can even replace the current usage of wooden pellets. Moreover, the resulting ash and flue ash from the combustion of rice hulls will have many viable end uses in industrial, commercial and chemical industries.