Characterization of Rice Straw for Energy use in Grain Drying: A Comparative Study

The utilization of rice straw for energy in grain drying has garnered significant attention in rice-producing countries. However, its effectiveness as a fuel in grain drying is uncertain due to a lack of information on its fundamental properties. Rice straw is considered a low-quality feedstock due to its high ash content 10-17%, which is higher than that of wheat straw a ~3%, and its high silica content in the ash 75% for rice straw and 55% for wheat straw. Conversely, rice straw has relatively low total alkali content less than 15% Na2O and K2O in total ash, while wheat straw has less than 25% alkali content in ash. Based on its slagging index (Rs 0.04) and fouling index (RF 0.24), it is expected that rice straw will not pose significant operational issues or result in different emissions compared to wheat straw and rice husk under similar conditions. This paper aims to explore these properties and how they can be enhanced through pretreatment technologies. The focus is on two fundamental properties: calorific (heating) value and density, and the pretreatment technologies employed are sizing and compression. Existing literature indicates that both the physical and chemical properties of rice straw can be significantly improved through these pretreatment methods. The compressive strength and heating value of the biomass briquette are influenced by the hot-pressing temperature. Increasing the percentage of rice bran in the briquette enhances its compressive strength and heating value. Interestingly, the energy required for compressing the rice straw briquette can be minimized by adding a certain percentage of binder (such as rice bran, sawdust, or other biomass waste) to the crushed rice straw.