Valorization of coconut and banana wastes with petcoke and coal via steam gasification in a fluidized bed reactor

Abstract

Steam gasification experiments were conducted with coal and petcoke in conjunction with potentially renewable biomass substances, namely coconut shell, coconut husk, and banana peduncle, which are usually considered waste materials. The gasification performance in a bench-scale externally heated fluidized bed gasifier was evaluated based on the product syngas quality and the detailed characterization of feed and product samples using X-ray fluorescence (XRF), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy analysis. This work performed experiments at relatively constant operating parameters: solid feed rate, steam/O2 ratio, feed particle size, and gasification reactor temperature. Biomass waste resources showed an augmentation in the syngas product quality for both the coal and petcoke samples, especially in cold gas efficiency (CGE) and carbon conversion efficiency (CCE). A maximum increase in CCE from 44.3 % to 72 % for the coal sample and from 19.3 % to 36.0 % for the petcoke sample was witnessed, whereas for the CGE, a rise of 35.8 %–91.7 % for the coal and 44.3 %–59.8 % for the petcoke with 80/20 blended biomass waste samples, was observed compared to the coal and petcoke only samples. The maximum hydrogen product gas yield between 53 and 73.7 vol % and combustible gas yields between 62.2 and 86.7 vol % were obtained on a nitrogen gas-free basis during the experiments. The solid residues of different gasification experiments were characterized and analyzed by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) and field emission-scanning electron microscopy (FE-SEM) analytical techniques to elucidate the high yield of energy-intensive gases. FTIR analysis was performed on all the liquid product samples obtained during the gasification experiments. The presence of alkali and alkaline earth metals (AAEMs) in biomass wastes highlighted the catalytic effect of these elements during the gasification experiments. The current work provides an opportunity to reduce carbon footprints with effective and efficient utilization of conventional energy feedstocks in conjunction with other waste substrates.