Empty fruit bunches-derived biochar from microwave-assisted pyrolysis as potential renewable solid fuel for power generation

The concerns on global climate change highlighted the need for renewable energy (RE) sources. Limited studies have been reporting on the utilization of Empty Fruit Bunch (EFB)-derived biochar (EFBC) as potential solid fuel for power generation. Microwave-assisted pyrolysis with susceptor has proven to be more efficient and economical for biomass conversion method. However, the technical risks and process efficiency on scale up microwave pyrolysis have not yet been fully assessed on demonstration plants. Therefore, this research aims to select the best conditions of bench scale microwave pyrolysis of EFB in the presence of alumina susceptor and further assess the process performance of the best conditions from the bench scale in upscaled conditions. Besides, this research intends to evaluate the feasibility of EFBC as solid fuel for power generation. Different pyrolysis temperatures between 200-400 ℃ as well as different feedstocks namely EFB pellet (PEFB) and EFB short fiber (FEFB) were used in a laboratory scale microwave pyrolyser (14 L), while the best conditions from the laboratory scale was applied in a 26x ratio upscaled microwave pilot pyrolyser (369 L). Further, FEFBderived biochar (FEFBC) produced from the upscaled study and Blended (90% coal: 10% FEFBC) were compared against Sub-bituminous coal (SBC) via combustion tests using a 150 kW pilot combustor. Accordingly, analyses were done for both scale studies on pyrolysis performance, product yield and properties, as well as energy efficiency. Moreover, fuel characterization and combustion characteristics analyses were assessed for FEFBC, Blended and SBC according to the coal standard. The results showed that temperature of 300 ℃ demonstrated the most ideal impact on the manufacture of biochar as well as residence time. EFB fiber achieved 62.5% faster process, 5.2% higher biochar yield and exhibited better biochar properties as compared to EFB pellet. Nevertheless, the process performance and biochar yield in the upscaled microwave pyrolysis have deteriorated, but apparently improved 58.3% of the energy output-input (EOI) ratio. Meanwhile, Blended sample has satisfied all standard coal parameters compared to FEFBC. Seemingly, Blended combustion generated 84% avoidance emission of nitric oxide (NO) gas than the SBC, though it increased the undesired ash slagging and fouling depositions. In conclusion, the 26x ratio upscaled condition has given better EOI, and thus it is feasible to produce FEFBC at large scale via microwave pyrolysis. This study also suggests that addition of FEFBC in coal has the potential to be renewable solid fuel in power generation and reduce greenhouse gas (GHG) emissions.

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