Abstract
Gasification of coal and biomass using CO2 and air mixture as a carrier gas offers an encouraging way to eliminate the shortage of energy and reduce carbon dioxide emissions. In the present study, the EulerianLagrangian approach was applied to understand the thermochemical conversion behavior of feedstock in entrained flow gasifier. Commercial CFD (Computational Fluid Dynamics) code ANSYS FLUENT®14 was used for the simulation purpose. It was observed that with variation in the CO2 in the air and the CO2 to cotton stalk ratio had a meaningful effect on gasification performance. The different ratios of air and CO2 in varying percentages such as 20% CO2, 30% CO2, 40% CO2, 50% CO2, 60% CO2, 70% CO2 and remaining percentages of air were introduced in entrained flow gasifier. With the increase in CO2 to cotton stalk ratio, the concentration of H2 and CO2 decreased whereas as the concentration of CO improved. It is revealed that mole fraction of CO and CH4 attained maximum when CO2% in the air was 50% and H2 mole fraction was observed maximum at a CO2% in the air was 30%. At 50% CO2 mixture in air, the maximum lower heating value and cold gas efficiency were observed. Therefore, the optimum situation might be 50% percentage CO2 in the gasifying agent for this entrained flow gasifier. Hence an increase in CO and H2, the cold gas efficiency and lower heating value reached the maximum. However, this study provides an appropriate route for energy production using cotton stalks as raw material and will help in designing and operation of the entrained flow reactor. The simulations indicate the thermodynamic limits of gasification and allow for the formulation of the general principles ruling this process. Moreover, no literature is available for the parametric investigations of Pakistani biomass gasification using entrained-flow gasifier. So this is a novel work for Pakistan and will be treated as foundation work for biomass gasification in the country.
Highlights
The conversion of biomass into biofuel is considered as a sustainable way to manage with the fossil fuels exhaustion and to meet environmental wellbeing [1]
This study is different from other studies as it focuses on the simulation of cotton stalks under varying CO2 concentrations as a carrier gas with air and their impact on the production quality of syngas
At fixed CO2 percentage, it was noticed that with increasing CO2/cotton stalks ratio intended that additional CO2 was introduced to the entrained flow reactor, and the air introduced to the entrained flow reactor was enhanced, at the same time supply of oxygen increased because of its fixed % in air
Summary
The conversion of biomass into biofuel is considered as a sustainable way to manage with the fossil fuels exhaustion and to meet environmental wellbeing [1]. Biomass gasification with CO2 as a gasifying medium influenced the syngas composition and production besides that it influenced the char properties and yield [14]. The modeling studies mostly present in previous work done by different authors on biomass thermochemical conversion focus only on pyrolysis steps or with sole char gasification steps [15]. This study is different from other studies as it focuses on the simulation of cotton stalks under varying CO2 concentrations as a carrier gas with air and their impact on the production quality of syngas. Cotton stalks gasification was performed through entrained flow gasifier using CO2 and air in varying percentages as a gasifying agent. Feeding rate of cotton stalks in gasifier was maintained at 61kg/hr throughout the CFD simulation study, while the CO2 % in the air was varied from 20-70%
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