Abstract
Rice husk and straw are by-products of rice cultivation and processing industry and can be used as an energy source. Proper understanding of the physical properties of rice residues is necessary for utilizing them in thermochemical conversion processes such as gasification and combustion. The physical properties (moisture content, particle size, bulk density and porosity) of rice husks and straws obtained from three countries (Egypt, Cuba and China) were evaluated in this study. The moisture contents of rice husks and straws were in the ranges of 4.60-6.07% and 6.58-6.92%, respectively. For all rice varieties tested, the moisture content of the straws was higher than these of the husks. The particle sizes of rice husks and straws were in the ranges of 0.212-0.850 mm and 0-0.710 mm, respectively. All the rice husk varieties had a normal distribution of particle size around the main value of 0.6 mm while the particle size distribution for the rice straws showed a decreasing trend, the larger the particle size the higher was the weight percentage. The bulk density of rice husks and straws were in the ranges of 331.59-380.54 kg m-3 and 162.03-194.48 kg m-3, respectively. The bulk density values of rice straws were lower than those of rice husks. A negative linear relationship between the bulk density and the average particle size was observed for rice husks and straws. The porosity of rice husks and straws were in the ranges of 63.64-68.94% and 71.21-85.28%, respectively. A positive linear relationship between the porosity and the average particle size was observed for rice husks and straws. Also, a negative linear relationship between the porosity and the bulk density was observed. The results obtained from this study showed significant differences in the physical properties of the rice husks and straws collected from different countries (located in three different continents). These differences may be due to variations in climatic conditions, soil type, methods of cultivation and type of fertilizer used. The results also indicated that different parts of rice plant (straw and husk) had different physical properties. Also, significant differences were observed among rice varieties even though they were grown under the same climatic conditions using same soil type and cultivation method as in the case of the long and short grain rice variety of Egypt.
Highlights
Rice is a staple food of over half the world's population and about one-fifth of the world’s population is engaged in rice cultivation (Reidy, 2011)
A negative linear relationship between the bulk density and the average particle size was observed for rice husks and straws
A positive linear relationship between the porosity and the average particle size was observed for rice husks and straws
Summary
Rice is a staple food of over half the world's population and about one-fifth of the world’s population is engaged in rice cultivation (Reidy, 2011). The global paddy rice production continued to increase at an average rate of 16.48 million tonnes per year during the last ten years (Fig. 1), reaching about 718.3 million tonnes in 2011 (FAO, 2011), with an estimated value of US$ 240 billion. Egypt and Cuba (countries used in this study) contribute 27.51, 0.63 and 0.07% to the global rice production and are ranked 1th, 16th and 39th, respectively. The per capita rice production, rice consumption and rice exports of the top 10 counties are presented, respectively. Rice husk and rice straw are the main products of rice cultivation and processing (Binod et al, 2010). The average ratio of rice grain: rice husk: rice straw is 1:0.25:1.25 (Haefele et al, 2011)
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