Sains Malaysiana 49(7)(2020): 1729-1743

http://dx.doi.org/10.17576/jsm-2020-4907-23

Syngas Production from Rubberwood Biomass in Downdraft Gasifier Combined with Wet Scrubbing: Investigation of Tar and Solid Residue

(Pengeluaran Singas daripada Biojisim Kayu Getah dalam Sistem Pengegas Alir Turun Digabungkan dengan Penggahar Basah: Kajian Tar dan Sisa Pepejal)

SYED HASEEB SULTAN¹, ARKOM PALAMANIT²*, KUA-ANAN TECHATO³, MUHAMMAD AMIN⁴, KHURSHID AHMED⁵& ASADULLAH⁴

¹Sustainable Energy Management Program, Faculty of Environmental Management, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand

²Interdisciplinary Graduate School of Energy Systems, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand

³Environmental Assessment and Technology for Hazardous Waste Management Research Center, Faculty of Environmental Management, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand

⁴Department of Chemical Engineering, Faculty of Engineering, BUITEMS, Quetta, Pakistan

⁵Molecular Biotechnology Laboratory, Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Songkhla Province, Thailand

Received: 6 October 2019/Accepted: 12 March 2020

Abstract

Production of synthesis gas by gasification is still a challenge due to the tar in the synthesis gas (syngas). This tar needs to be eliminated by appropriate methods before using the syngas as a fuel. Moreover, the solid residue after gasification also needs to be properly managed or destroyed. Therefore, the aim of this study was to investigate tar and solid residue generated by gasification of rubberwood biomass, including rubberwood chips (RWC), rubberwood pellets (RWP), rubberwood unburned char (UBC), and their blends, in a downdraft gasifier. Waste vegetable oil (WVO) and water were used as scrubbing media. Properties of the biomass samples were characterized by proximate and ultimate analysis, as well as for the higher heating value. The downdraft gasifier was operated at 850 °C and equivalence ratio (ER) of 0.25. The concentrations of tar in syngas both before and after passing through the wet scrubber were determined. Chemical compounds in the tar were analysed by GC-MS. The solid residue remaining after gasification was separated into biochar and ash. The biochar was characterized by CHNS/O analyser, FTIR, SEM, and for the iodine number. The compounds in ash were determined by XRF. The results show that biomass type and scrubbing media affected the tar removal efficiency. Scrubbing syngas with WVO had better tar removal efficiency than scrubbing with water. The highest tar removal efficiency with WVO was 82.16%. The tar sample consisted of complex compounds as indicated by GC-MS, and these compounds depended on type of biomass feedstock. The solid residue obtained after gasification process contained biochar (unburned carbon) and ash. Some biochars can be used as solid fuels, depending on carbon content and energy content. The biochar also had a highly porous structure based on SEM imaging, and a high iodine number (930-1134 mg/g). The biochar contained the functional groups OH, C-O, and C-H, as indicated by FTIR. CaO, K₂O, SiO₂, and MgO were the major components in ash. The spent WVO, biochar, and ash need to be properly managed or utilized for sustainable gasification operations, and these results support that pursuit.

Keywords: Biomass; gasification; rubberwood biomass; syngas cleaning; tar removal

ABSTRAK

Penghasilan gas sintesis melalui proses pengegasan masih mencabar kerana kehadiran tar dalam gas sintesis (singas). Tar ini perlu disingkirkan melalui kaedah yang bersesuaian sebelum singas digunakan sebagai bahan api. Selain itu, sisa pepejal yang terhasil selepas proses pengegasan juga perlu diuruskan atau dimusnahkan dengan betul. Oleh demikian, tujuan kajian ini adalah untuk mengkaji tar dan sisa pepejal yang terhasil daripada proses pengegasan biojisim kayu getah, termasuk serpihan kayu getah, pelet kayu getah, arang kayu getah dan campuran kesemua bahan dalam pengegas alir turun. Minyak sayur terpakai dan air telah digunakan sebagai media penggahar. Ciri-ciri sampel biojisim telah dikaji melalui analisis proksimat dan muktamad, dan juga nilai pemanasan tinggi. Sistem pengegas alir turun telah beroperasi pada suhu 850 °C and nisbah kesetaraan 0.25. Kandungan tar dalam singas sebelum dan selepas melalui media penggahar telah diukur. Sebatian kimia dalam sampel tar telah dianalisis menggunakan GC-MS. Sisa baki pepejal selepas proses pengegasan telah dipisah daripada arang bio dan abu. Arang bio telah dicirikan melalui alat CHNS/O, FTIR, SEM, dan nombor iodin. Sebatian dalam abu dianalisis melalui XRF. Keputusan yang diperoleh menunjukkan bahawa jenis biojisim dan media penggahar telah mempengaruhi keberkesanan penyingkiran tar. Penggaharan singas menggunakan minyak sayur terpakai menunjukkan keberkesanan yang lebih baik berbanding dengan air daripada segi penyingkiran tar. Setinggi 82.16% penyingkiran tar telah tercapai menggunakan minyak sayur terpakai. Sampel tar mengandungi sebatian yang kompleks seperti yang ditunjukkan oleh GC-MS dan komposisi sebatian ini bergantung kepada jenis biojisim. Sisa pepejal terhasil selepas proses pengegasan mengandungi arang bio (karbon tak terbakar) dan abu. Sesetengah arang bio boleh digunakan sebagai bahan api pepejal yang bergantung kepada kandungan karbon dan tenaga. Arang bio yang terhasil juga mempunyai struktur berongga berdasarkan imej SEM dan nilai iodin yang tinggi (930-1134 mg/g). Arang bio yang terhasil mengandungi kumpulan berfungsi OH, C-O dan C-H seperti yang ditunjukkan oleh FTIR. CaO, K₂O, SiO₂ dan MgO adalah kandungan utama dalam abu. Minyak sayur terpakai, arang bio dan abu yang telah digunakan perlu diuruskan dengan betul untuk operasi pengegasan yang mampan dan hasil ini menyokong usaha tersebut.

Kata kunci: Biojisim; biojisim kayu getah; pembersihan singas; pembuangan tar; pengegasan

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*Corresponding author; email: arkom.p@psu.ac.th