Computer Simulation of Biomass Gasification Process for Oil Palm Fronds in a Downdraft Gasifier

Biomass Gasification is a process of converting carboneous material that result in the production of combustible gases called syngas consisting of Carbon Monoxide (CO), Hydrogen (H2), Carbon Dioxide (CO2) and Methane (CH4). A model was developed to simulate biomass gasification process in a downdraft gasifier using computer software. Design parameters and operating conditions of the gasifier highly influence the resulting syngas composition. It is difficult to manually determine the optimum parameters and operating conditions that result in higher performance and safe operation of the unit. Thus, there is a need to predict the output of the gasification system by means of computer software. The objective of this project is to simulate biomass gasification process in a downdraft gasifier using Oil Palm Fronds (OPF) as a feedstock by means of Aspen Plus software. The optimum operating conditions that would result in the best composition of syngas is determined at the end of this project. As a first step, duplication of past work paper is done and the result is compared to verify that the work done and future work by the author in modeling processes using Aspen Plus is reliable. Three simulation diagrams with variation in component used and arrangement are created. At the end of this project, the latest improvement of simulation model is chosen based on comparison with past work paper. Sensitivity analysis is carried out to investigate the effect of varying temperature at 300 – 1000oC, pressure at 0 – 7 bar and air fuel ratio (AFR) at 0.1 – 0.7 to composition of syngas. On the rate of production of CO, the mole composition increases when the temperature increases. The rate of production of H2 is nearly constant over the range of temperature while the production of CO2 decreases when temperature increases. A variation in pressure does not give significant impact to production of syngas. The rate of production of CO2 increases with AFR while that of H2 is independent of AFR. The rate of production of CH4 tends to be high at AFR less than 0.3 while CO give maximum output at AFR approximately 0.1 – 0.2. The simulation shows that the optimum operating condition would be at temperature range of 400–500 oC, air fuel ratio range of 0.1–0.2 and pressure range of 1.0–2.0 bar.