Abstract

The prevalent challenges of global warming, food security, food production, crop production systems, environment control called for consideration and better utilization of green energy system such as biomass. The advanced thermo-chemical conversion of the renewable energy source which is aimed at production of optimal yield of energy has not been well understood. In order to have better physical insights into the detailed structure of the biomass burning process inside a solid bed, the kinetics of the biomass combustion and gasification must be properly analyzed. Consequently, improved kinetic models of the combustion and gasification zones in the thermochemical conversion system are very required. Therefore, the present study focuses on the development of improved kinetic modeling of the combustion and gasification zones in the biomass gasification system. The performance of the biomass gasifier system is evaluated through the equivalence ratio, the syngas composition, cold gas efficiency and lower heating value. Also, the effects of the equivalent ratio on gas compositions, the gasifier performance and the low heating value of the biomass are analyzed. From the analysis, it is established that the concentration of CO, H2 and CH4 in the gasifier decrease as the equivalence ratio increases. However, CO2 concentration increases with an increase in the equivalence ratio. The cold efficiency and LHV decreases as the equivalence ratio increases while the gas yield increases with an increase in the equivalence ratio. The quantity of gas produced increases as the amount of oxygen consumed increases. Also, the ratio of CO/CO2 decreases as the temperature of the reduction zone increases. Such analysis as presented in this work, is very useful as a time-saving and cost-effective tool for designing and optimizing the biomass gasifier. Therefore, it is evident that this work will play a significant role in the system design including analysis of the distribution of products and ash deposit in the downdraft gasifiers.

Highlights

  • In the past few decades, the increasing concerns of global warming and fuel prices have aroused the development of new technologies in alternative energy

  • The decrease in carbon monoxide (CO) concentration as the equivalent ratio increases is due to oxidation of CO at higher equivalence ratio, which is further validated by the increasing trend of CO2 concentration with equivalence ratio

  • The performance of the biomass gasifier system was evaluated through the equivalence ratio, the syngas composition, cold gas efficiency and lower heating value

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Summary

Introduction

In the past few decades, the increasing concerns of global warming and fuel prices have aroused the development of new technologies in alternative energy. Fixed bed gasifiers include updraft and downdraft gasifiers The updraft gasifier comes with simple design,, high charcoal burn-out and internal heat exchange Such reactor has low gas exit temperatures and. Zhou et al [9] adopted a CFD model to simulate the optimal conditions for the production of hydrogen-rich gas in a fluidized bed biomass gasifier. Wang and Yan [11] carried out an overview of different CFD studies on thermo-chemical biomass conversions such as gasification and combustion processes in fixed beds, furnaces, and fluidized beds. The predictions of the temperature and pressure distributions and histories of a biomass particle in a downdraft gasifier are major determinants of a detailed characterization study of thermochemical conversions of biomass Such predictions are heavily dependent on the kinetic modeling of the reaction process in the biomass gasification system [29, 30]. The effects of the equivalent ratio on gas compositions, the gasifier performance and the low heating value of the biomass are analyzed and presented

The description of downdraft biomass gasifier
Kinetic reactions models for the combustion and the gasification processes
Results and discussion
Conclusion
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