Abstract
In this study, palm kernel shells (PKS) were utilized in an air gasification process to produce syngas. Also, biochar prepared from pyrolysis of the mangosteen and durian peels in was used in the gasification process to enhance the tar removal efficiency. The expected outcomes of this study could result in not only the generation of renewable energy but also the waste utilization of agricultural residues. The effect of catalysts and biochar on tar reduction to improve the syngas quality were extensively studied. A downdraft gasifier equipped with catalytic and adsorption units was utilized to produce syngas. The process was operated with 1 kg of palm shell per batch at a fixed airflow rate of 25 L/min. The NiO/CaO catalysts with a fixed CaO amount of 10 wt% and various NiO contents of 2 wt%, 4 wt%, and 8 wt% were synthesized by co-impregnation on the ceramic supporter. The results of SEM analysis showed that the NiO and CaO were deposited and well dispersed on the porous ceramic ring supporters. The presence of an associated active NiO peak at a wavelength of 692 cm-1 was observed in the FTIR result. The durian and mangosteen peels residues were pyrolyzed at 400 – 700 oC for 2 hrs to prepare biochar to be used as tar adsorbent. The BET surface area of obtained biochar was 0.9219 - 0.9989 m2/g with a range of adsorption pore size of 11.193 - 11.912 nm. The syngas samples were collected from the gasification unit every 15 min during a 1-hr period of processing time. The syngas compositions were analyzed by gas chromatography. The GC results indicated that increasing NiO contents in the catalysts tended to result in increasing methane and carbon dioxide concentration of the syngas, possibly contributed from the further involving tar cracking reactions. With the presence of biochar, the amount of tar captured in the filter unit was significantly increased up to 9 times compared to the system without biochar.
Highlights
Thailand is an important food-production country with abundant plantation areas to produce agricultural products
Since the kernels contained a high amount of volatile matter, the material can be potentially combusted in the gasification process to generate energy
The results showed that the pore size distribution of the biochar made from durian peels appeared to be more uniform than those obtained from mangosteen
Summary
Thailand is an important food-production country with abundant plantation areas to produce agricultural products. Biomass residues from palm oil refinery process are approximately 78 to 82 percent, mainly composed of empty fruit bunch, fibers, and kernel shells. These biomass residues can be potentially used as feedstocks in thermochemical processes to produce biofuels or syngas (Lam et al, 2019). The decomposition of tar involves complex reaction pathways associated with the presence of hydrocarbon compounds Those reactions include partial oxidation, dry reforming, steam reforming, hydrogenation, thermal cracking, and carbon formation, which generally result in the formation of hydrogen, methane, carbon monoxide, and carbon dioxide as the end product species
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