Pelletisation of biomass oil palm kernel shells for gasification

Abstract

Palm kernel shells are one of the waste products in the palm oil industry. This work was focused on investigating the properties of pellets made from the palm kernel shells for use in syngas generation through gasification. The strength of the pellets increased with compaction pressure but the strength reached a plateau when the pellets achieved no or near-zero porosities, indicating that the maximum strength was achieved. High compaction speeds and short hold time during the compaction process; high humidity conditions and long storage time during post-production were found to result in lower pellet strengths. These effects were mainly related to the porosities of the pellets, and new modifications of the Ryshkewitch-Duckworth model have been proposed to describe the relationships between the strength and the porosity. The strength of binary pellets made of palm kernel shell and HZSM-5 zeolite decreased with increasing zeolite composition. This decrease was associated with higher porosities and elastic rebound of the pellets in the presence of the zeolite particles. Modifications of the Ryshkewitch-Duckworth model have been proposed to predict the strength of the binary mixture pellet, based on strength at zero porosity and the bonding capacity of zeolite and palm kernel shell.In the gasification studies, the pellets achieved a higher conversion rate from biomass to gaseous products compared to raw palm kernel shells and ground shell powder. The gasification of binary palm kernel shell and HZSM-5 zeolite pellets was proven to be feasible but not as effective in reducing tar from the gaseous products as zeolite added in-situ with raw palm kernel shells. For the same amount of catalyst used, the amount of tar reduced was less when the pelletised form was gasified, compared to that when the raw, ungrounded form was gasified in situ with zeolite. This was probably due to zeolite being trapped within the binary pellet and hence not all the zeolite was available to crack the tar.