Co-processing of coal and hydrochar produced from hydrothermal carbonization (HTC) waste biomass

Abstract

Partial substitution of coal by renewable biomass in existing coal-fired boilers for power generation is increasingly attractive in response to the depletion of fossil fuels together with the current concerns over environmental pollution and climate change. However, previous studies related to biomass-coal co-processing have identified several technical constraints caused by the inherent properties of biomass materials, and the relatively poor fuel quality of biomass feedstocks compared to coal. Hydrothermal carbonization (HTC) offers a promising conversion process to upgrade raw biomass feedstocks. The resultant hydrochar has homogenized properties such as density and size, and also possesses increased fuel quality in comparison to raw biomass. In this study, co-processing of coal and hydrochar was investigated with regard to fuel-to-energy efficiency and pollutant emissions. The results indicated that due to similarity of fuel quality, synergistic interactions between hydrochar and coal were observed during the co-combustion process, resulting in high combustion efficiency of the hydrochar-coal blends. Moreover, the addition of hydrochar to coal significantly decreased the total nitrogen percentage in the char, promoted the conversion of gaseous nitrogen compounds into N2 and suppressed the formation of high-ring polycyclic aromatic hydrocarbons (PAHs) in tars than those in tars from coal alone during co-pyrolysis. These findings suggested that the co-processing of hydrochar-coal blends for energy production had multiple benefits such as increased combustion efficiency and decreased pollutant emissions. © 2013 by Nova Science Publishers, Inc. All rights reserved.