Energy efficiency of bio-coal derived from hydrothermal carbonized biomass: Assessment as sustainable solid fuel for municipal biopower plant

The utilization of conventional biomass to generate electricity in the biomass thermal power plant is still inefficient due to high content of moisture, high impurity, and low heating value. To explore this limitation, in this research, hydrothermal carbonization (HTC) was selected as a sustainable process for producing green solid fuel or bio-coal with a rich of carbon content from palm shell and bamboo, remarkably as model biomass raw materials. The effect of biomass to water weight ratio (1:1 to 1:10), reaction temperatures (160 – 250 °C), and reaction times (1 – 6 h) were performed under autogenous pressure of promising aqueous media. The effect of organic and inorganic acid adding in the HTC of palm shell and bamboo was discussed. The obtained bio-coal was further well characterized with proximate and ultimate analysis and fuel properties. From the results, increasing reaction temperature and adding of acids led to increase carbon content, resulting to increase HHV of bio-coal. Effects of feedstocks (palm shell and bamboo), temperature, and types of acids revealed significantly results on the bio-coal yield accompanied with carbon content, the higher heating value (HHV), energy densification, and energy yield. The addition of inorganic acid in the HTC of biomass with high cellulose content provided higher HHV improvement than that of stony biomass. The highest HHV of 27.9 MJ/kg was obtained in bio-coal derived from palm shell feedstock with 1:1 water ratio and hydrothermally at 250 °C for 6 h. Surprisingly, this HHV is comparable to high-volatile bituminous coal. Moreover, an evaluating assessment for the utilization of this bio-coal instead of biomass feedstock to generate electricity in the thermal power plant with size of 9.9 MW capacity could reduce 34.4 % of fuel storage size, save nearly 29,709.36 USD/year in transportation costs and diminish CO2 emission during burning by approximately 56,732 tons/25 years.