Syngas production from biomass gasification is a potentially sustainable and alternative means of conventional fuels. The current challenges for biomass gasification process are biomass storage and tar contamination in syngas. Co-gasification of two biomass and use of mineral catalysts as tar reformer in downdraft gasifier is addressed the issues. The optimized and parametric study of key parameters such as temperature, biomass blending ratio, and catalyst loading were made using Response Surface Methodology (RSM) and Artificial Neural Network (ANN) on tar reduction and syngas. The maximum H₂ was produced when Portland cement used as catalyst at optimum conditions, temperature of 900°C, catalyst-loading of 30%, and biomass blending-ratio of W52:OPF48. Higher CO was yielded from dolomite catalyst and lowest tar content obtained from limestone catalyst. Both RSM and ANN are satisfactory to validate and predict the response for each type of catalytic co-gasification of two biomass for clean syngas production.

Experimental set-up for co-gasification

The experiments were carried out on a bench-scale downdraft gasifier. Experimental setup was consist of an electric ceramic heater surrounded by the gasifier body. The process temperature of the heater was monitored and controlled with PID attached with a K-type thermocouple. The electric ceramic heater and gas cooling & clean system were switched on 30 min before starting the experiment. Air was used as gasification medium that was supplied at a rate of 3.0 L/min to the gasifier. The quantity of air was controlled and measured with a volume flow meter. Once the desired temperature achieved the mixture of biomass blend and catalyst was feed at the top of the gasifier. The product gas composition was analyzed by Emerson made X-stream X2GP online gas analyzer. The online gas analyzer was configured with a computer by an Ethernet connection. The raw syngas was sampled from the gasifier exit point right at the bottom of the gasifier. Tar in present in syngas was trapped by the applied standard procedure as described somewhere. Once syngas was passing from impinger bottles which placed in the mixture of ice and salt at temperature 20°C and -20°C, syngas was got cooled and became free of tar. The gas composition readings were recorded automatically with the interval of each second in a computer device. The air supply was stopped and heater was switched off after the consumptions of all fed materials. The ash and char were collected from the bottom of the gasifier and weighted after the cool down of the apparatus. The experimental and instrumentation set-up used in this investigation is shown in Fig. 1.

Process flow of experimental and ANN modeling methodology

Clean Syngas Production: Syngas (a mixture of hydrogen and carbon monoxide) is a valuable energy resource used in various industries, including power generation and chemical production. Optimizing the co-gasification process can lead to the production of cleaner syngas with reduced impurities, which enhances its usability and reduces environmental impact.

Resource Utilization: By blending wood and oil palm fronds, which are both biomass resources, you're effectively utilizing agricultural and forestry waste materials. This can help in waste management and reduce the environmental burden of disposing of these materials through conventional means.

Energy Efficiency: Parametric optimization ensures that the co-gasification process operates at its highest efficiency, maximizing the energy output from the biomass feedstock. This can lead to higher energy yields per unit of biomass input, making the process more economically viable and sustainable.

Emission Reduction: Co-gasification processes can be designed to minimize emissions of harmful pollutants such as particulate matter, sulfur compounds, and nitrogen oxides. This contributes to improved air quality and reduces the environmental footprint of energy production.

R squared plot during BRANN model training

Growing Demand for Clean Energy: With increasing concerns about climate change and air pollution, there is a growing global demand for clean energy sources. Syngas produced from biomass via co-gasification represents a renewable and low-carbon alternative to fossil fuels, making it attractive for various applications such as power generation, heat production, and industrial processes.

Policy Support and Renewable Mandates: Many countries have implemented policies and regulations aimed at promoting renewable energy sources and reducing greenhouse gas emissions. This includes incentives such as feed-in tariffs, renewable energy credits, and carbon pricing mechanisms, which can create a favorable market environment for clean syngas production technologies.

Waste Management and Sustainability: Co-gasification of wood and oil palm fronds offers a sustainable solution for managing agricultural and forestry waste materials. By converting these biomass resources into valuable syngas, the technology addresses both waste management challenges and the need for renewable energy sources, appealing to environmentally conscious consumers and industries.

Diversification of Energy Supply: Co-gasification technologies provide an opportunity to diversify the energy supply mix, reducing dependence on conventional fossil fuels such as coal, oil, and natural gas. This diversification enhances energy security and resilience, particularly in regions vulnerable to disruptions in fossil fuel supply chains.

Validation plots of ANN for (a-c) Portland cement, (d-f) dolomite, and (g-i) limestone during the air catalytic co-gasification of W/OPF blend