Thermodynamics Simulation Performance of Rice Husk Combustion with a Realistic Decomposition Approach on the Devolatilization Stage

Soen Steven,Abrar Riza,Carolus Borromeus Rasrendra,Pandit Hernowo,Yazid Bindar,Anton Irawan,Elvi Restiawaty

doi:10.1007/s12649-021-01657-x

Abstract

The high calorific value of rice husk and rich silica content in rice husk ash make its valorization becomes attractive. 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. In this study, devolatilization of rice husk is simulated to form gas (64.78%), liquid/tar (7.28%), solid/char (27.94%), and all of these are then oxidized with 100% excess air to form flue gas. From the calculation, about 2.6 MJ/kg of specific combustion energy is produced. The maximum combustion temperature in the furnace is up to 1457 °C for perfect insulation and up to 1400 °C if there is a 5% heat loss due to radiation. Furthermore, the thermodynamics simulation expressed that NOX emission amount from rice husk combustion is negligible and there is still a probability for CO and H2 to be produced at above 500 °C due to Boudouard reaction and homogeneous water gas shift reaction (WGSR). 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 700 °C. Supplying excess air of about 180–200% is advantageous to keep the combustion temperature at 700 °C to avoid silica crystalline formation which harms human health, as well as suppressing NOX emission and reducing CO emission from the simultaneous reaction of Boudouard-WGSR. Finally, the study concluded that a realistic decomposition approach could predict the rice husk combustion performance with reasonable and logical results.Graphical Abstract

Highlights

Biomass utilization as an alternative fossil fuel and chemicals surrogates has become a major concern
The discussion comprises of problem preliminary analysis, devolatilized products result, specific energy produced from rice husk combustion, adiabatic flame temperature, air supply strategy for maintaining rice husk combustion temperature, and the flue gas composition analysis due to the attendance of Boudouard reaction and homogeneous water gas shift reaction (WGSR)
Under a realistic decomposition approach, rice husk devolatization produce 63.37% gases, 8.69% tar, and 27.94% char which are oxidized by 100% excess air to produce flue gas with the composition of 13.69% CO2, 4.79% H2O, 0.20% NO, 70.60% N2, and 10.72% remaining O2

Summary

Introduction

Biomass utilization as an alternative fossil fuel and chemicals surrogates has become a major concern. Energy production through rice husk combustion mostly relied on direct experiments and validate the results with thermodynamics simulation They have focused on specific combustion energy calculation, rice husk combustion temperature monitoring, and flue gas composition prediction and analysis. The thermodynamics study from the research papers and well-established textbooks mostly proposed that at the devolatilization stage, biomass will decompose to C, H, O, N elements prior to being oxidized to form flue gas [10,11,12]. This approach is simple but quite unrealistic so that it should be developed with a more realistic one. The discussion comprises of problem preliminary analysis, devolatilized products result, specific energy produced from rice husk combustion, adiabatic flame temperature, air supply strategy for maintaining rice husk combustion temperature, and the flue gas composition analysis due to the attendance of Boudouard reaction and homogeneous water gas shift reaction (WGSR)

Devolatilized products prediction calculation

Combustion efficiency calculation

Findings

Thermodynamics calculation procedure

Conclusion and suggestion