Process Evaluation and Analysis of Variance of Rice Husk Gasification Using Aspen Plus and Design Expert Software

The global shift towards achieving carbon neutrality in energy production has sparked significant and growing interest across various sectors. As the world grapples with the urgent need to reduce greenhouse gas emissions and mitigate the impacts of climate change, there is an increasing focus on transforming lignocellulosic materials into alternatives that are more sustainable and environmentally friendly. This study presents a process evaluation of rice husk gasification using an Aspen Plus simulation environment coupled with an analysis of variance with the aid of Design expert software. The biomass sample was assessed as received for proximate and ultimate analyses and utilised as key input data into the Aspen plus environment. The process flow sheet was implemented using a combination of unit operation and unit process equipment with non-random two-liquid (NRTL) as thermodynamic and property data. Effect of gasification temperature (600-1100 oC), air-fuel ratio (0.05-1.00), feedstock moisture content (5-50wt%), oxygen/nitrogen ratio (0.25-1.00) on the syngas yield and composition, and tar production were investigated independently and collectively. Experimental design with AFR and O2/N2 ratio as variables at 3 levels (-1, 0, + 1) using central composite design (randomized) was conducted and analysis was carried out. The result of proximate and ultimate analyses indicated that rice husk has ash content, volatile matter and fixed-carbon content of 13.56, 16.37 and 70.07 wt% respectively with carbon, hydrogen, nitrogen, sulphur and oxygen of 40.15 wt%, 5.98 wt%, 0.41 wt%, 0.78 wt% and 52.68 wt% correspondingly. The simulation result showed that increasing feedstock moisture content, AFR and O2N2 promoted syngas production and tar formation rate except for feedstock moisture content, which displayed the opposite trend. Gasification temperature showed less impact on the syngas production rate but significantly reduced tar production rate. Feedstock moisture content increased methane (CH4), and carbon monoxide (CO) while significantly and marginally decreased carbon dioxide (CO2) and hydrogen content of syngas respectively. The effect of gasification temperature on the syngas composition was significant within 600-750oC with improved hydrogen and CO content of 7-14% and 50-53% while CH4 and CO2 depleted from 26 - 21% and 3.0-0.07% in that order. The result of ANOVA revealed that the quadratic model best described the syngas and tar production rate in rice husk gasification with AFR in degree one and degree two and O2/N2 as the significant factors for syngas production rate while AFR, O2/N2 and - AFR-O2/N2 interaction represent significant factors for tar production rate. The study presents a systematic approach for analysing the combined effects of AFR, O2/N2 and their interaction on the syngas production rate and quality from rice husks.