Thermodynamics simulation performance of rice husk combustion with a realistic decomposition approach on the devolatilization stage

Abstract

\n Rice husk has a great potential in its calorific value and silica content in ash which makes its valorization through combustion becomes important and interesting. This study presents the thermodynamics simulation performance of rice husk combustion using a realistic decomposition approach. A non-ideal gas approach and fugacity coefficient were also considered in the calculation. From this study, rice husk is devolatilized to form gases (63.37%), tar (8.69%), char (27.94%), and all of these are then oxidized to form flue gas. The realistic decomposition approach calculated that about 2.6 MJ/kg of specific combustion energy is produced, the maximum combustion temperature is up to 1457oC for perfect insulation condition, and up to 1400oC if there is a heat loss. It is found that combustion equipped with larger excess air could quench the heat produced and reduce the combustion efficiency but could maintain the temperature at 700oC. Furthermore, the thermodynamics simulation expressed that NO emission amount from rice husk combustion is negligible and there is still a probability for CO and H2 to be produced at above 500oC due to Boudouard reaction and homogeneous water gas shift reaction (WGSR). The study showed that a realistic decomposition approach could predict the rice husk combustion performance with a reasonable and logical result. Supplying excess air of about 180–200% is advantageous to keep the combustion temperature at 700oC in order to prevent silica crystalline formation which harms human health, as well as suppressing NO emission and reducing CO emission from the simultaneous Boudouard and WGSR.