Combustion and pollutant emissions characteristics of Camellia oleifera shells in a vortexing fluidized-bed combustor

Abstract

Because of their saponin content, Camellia oleifera shells cannot be directly discarded. However, this eco-unfriendly agricultural waste is suitable for use as a fuel. A comparison between the combustion of crushed C. oleifera shell (CCS) and pelletized C. oleifera shells (PCS) was carried out in a pilot-scale fluidized-bed. Both directly combustion and flue gas recirculation (FGR) combustion modes were employed. The effects of particle size and the FGR ratio on the combustion behavior and pollutant emissions characteristics were also investigated. Results show that the combustion efficiencies for both CCS and PCS are higher than 99%. The combustion fraction in the bed region of CCS and PCS-6 are 55% and 85%, respectively, resulting in different combustion and pollutant emission characteristics. CCS has smaller CO and NO emissions and higher PCDD/Fs concentration of the fly ash compared with those of pelletized fuels. However, considering the material bridging in the feeding process of CCS, using pellets as the fuel is a better choice. The CO emissions increase while dioxin and furan emissions decrease with an increase in FGR ratio. The lowest NO emissions (about 150 ppm) of the three pelletized fuels combustion were achieved at an FGR ratio of 42%. In addition, all the pollutant emissions are lower than the minimum standards required for municipal solid waste (MSW) incinerators in Taiwan.