Production of a solid bio-fuel from waste bamboo chopsticks by torrefaction for cofiring with coal

- Waste bamboo chopsticks (WBC) were upgraded as a good-quality bio-fuel by torrefaction.
- Temperature and time both significantly affect the production of torrefied WBC (WBCT).
- The metals contents of WBCT satisfy with the regulations of Initiative Wood Pellets Buyers (IWPB).
- Wet-basis high heating value of WBCT of 21.72 MJ kg−1 meets coal standard of Taiwan Power Co. (TPC) and IWPB.
- Sulfur content of WBCT is lower than the ceiling set by TPC and IWPB.

In this study, waste bamboo chopsticks (WBC) were upgraded as solid bio-fuel by torrefaction using a tubular furnace with nitrogen as carrier gas. In order to fulfill the quality specifications of coal and industrial wood pellets, the effects of temperature and time of torrefaction on proximate and ultimate compositions and its dry-basis heating value (HHD) were studied and elucidated. The results showed that the mass yield of WBC is 69% at 563 K and 40 min, while HHD of WBC is increased from 19.31 to 23.04 MJ kg−1 with an energy densification factor of 1.19, which satisfy the specification of quality D of Taiwan Power Co. and I3 industrial quality of Initiative Wood Pellets Buyers. Further, the torrefied WBC (WBCT) pellets become convenient to store, transport and processing and hard to be rotten because of the modification of surface hydrophobicity. The ash content of WBCT is only 2.19 wt.% in wet basis, which is beneficial in practical boiler. Further, the energies needed for drying, heating and torrefaction is 2.31 MJ for processing 1 kg WBC with CO2 emission of 0.339 kg. Therefore, WBCT would be practical alternative as solid bio-fuel for cofiring with coal.