Catalytic co-gasification is an important tar reforming technique, which may appreciably improve the quality of syngas through tar reforming reaction. In this study, wood chips (WC) were co-gasified with two coconut wastes, namely coconut shells (CS) and coconut fronds (CF), in a downdraft gasifier. The dolomite and limestone were used as tar reforming mediums. The effect of the blending ratio, catalyst type, biomass type and catalyst to biomass loading on gas composition and heating value of the syngas was investigated for different WC/CS and WC/CF blends. The results revealed that the WC/CS blending ratio of 70:30 produces the highest H₂ amount (11.70 vol.%), which was 31% higher than the H₂ amount of the other blends. The HHVsyngas of 70:30 blend was measured about 4.96 MJ/Nm3, which was also higher among all the tested blends. The co-gasification of 70:30 blend of WC/CS, when compared with same blending ratio WC/CF, produced two times higher CO, 60% higher H₂ and 75% higher HHVsyngas. During catalytic co-gasification of WC/CS blends with dolomite and limestone, the dolomite yielded 24%, 13.8% and 25.6% increment in CO, H₂, and CH₄, respectively. It is concluded that the coconut wastes can be substituted or co-gasified with wood after carrying out some major changes in a gasifier geometry.

Effect of blending ratio of WC/CS on (a) syngas composition and (b) higher heating value of syngas.

The experimental setup, used in the presented work, was a batch-type downdraft gasifier. In Figure 1, the design capacity of the gasifier was 33.6 kW (thermal). The gasifier was formed of a vertical cylindrical reactor body with 300 mm internal diameter, 1290 mm height and a throat diameter of 150 mm. The temperature in different zones of gasification was monitored using six Type-K thermocouples, which were fixed at different locations on the gasifier. All thermocouples were plugged into a USB 8-channel data logger (PICO TC-08) and connected to a computer for data recording. Air was supplied to the gasifier using a blower at a flow rate of 400 L/min. This flow rate was kept constant throughout the conducted research work. The air flow rate was controlled using a VFC (Variable flow controller) Series Dwyer rotameter. During gasification, the syngas in gasifier firstly entered to a cyclone separator where particulates and condensates were removed from the gas. In 2nd step, tar and moisture were removed from the gas after passing it through filters. The sample syngas was cooled and cleaned by a gas cooling and cleaning system. Clean and cooled syngas was analysed for volumetric gas composition by using an online gas analyser (Emerson X-stream X2GP). The gas composition measurements were performed after every second and recorded on a computer. The rest of the syngas was flared and vented out.

Schematic diagram of experimental setup

Syngas Composition: Blending ratios determine the proportions of wood chips and coconut waste in the feedstock. Adjusting this ratio can influence the composition of the produced syngas, affecting its calorific value, hydrogen content, and impurity levels. Optimizing the ratio can lead to a syngas with desired properties for various applications, such as fuel synthesis or power generation.

Thermal Efficiency: The right blending ratio can enhance the overall thermal efficiency of the gasification process. Each feedstock has its own thermal characteristics and reactivity. Combining them optimally can maximize the utilization of available energy and minimize energy losses during gasification.

Economic Viability: Balancing the cost-effectiveness of feedstocks is crucial for commercial viability. Choosing the appropriate blending ratio can optimize the cost of raw materials while maintaining desired syngas quality. This can have a significant impact on the economic feasibility of co-gasification projects.

Catalyst Effectiveness: Catalysts are often used in gasification processes to improve reaction kinetics, enhance tar cracking, and promote syngas cleanup. The loading amount and type of catalyst used can influence gasification kinetics, tar reduction efficiency, and overall process performance. Proper catalyst loading optimization can lead to higher conversion efficiencies and lower tar content in the syngas.

Comparison of syngas composition and HHV at 70:30 fuel blending ratio of WC, CF, and CS biomass

Current Market Demand: Analyzing the demand for alternative energy sources, particularly those derived from biomass, can provide insights into potential market interest. This includes understanding the demand for renewable energy sources and the willingness of industries to invest in research and development for such technologies.

Competitive Landscape: Assessing the existing technologies and solutions in the biomass gasification market helps in understanding potential competition. Identifying gaps in the market that the research could address or improve upon can indicate market potential.

Regulatory Environment: Regulations and policies related to renewable energy, waste management, and emissions reduction play a significant role in shaping market dynamics. Understanding how these regulations affect the adoption of biomass gasification technologies is crucial for assessing market potential.

Cost Considerations: Evaluating the cost-effectiveness of the proposed gasification process compared to existing methods or competing technologies is essential. Factors such as capital investment, operating costs, and potential cost savings or revenue generation from the process can influence market adoption.

Effect of catalyst loading on (a) syngas composition and (b) higher heating value of syngas produced from 70:30 blending ratio of WC/CS using dolomite as catalyst.