Analysis of Combined Biochar and Torrefied Biomass Fuel Production as Alternative for Residual Biomass Valorization Generated in Small-Scale Palm Oil Mills

Abstract

From the residual biomass generated by the palm oil sector in Ecuador, kernel shell (KS) is of major importance because it has been demonstrated that its use as solid fuel could replace diesel and LPG currently subsidized by the government to be used in the industrial and commercial sectors to produce thermal energy. The implementation of a torrefaction process could improve the KS handling and transportation operations, thus promoting its domestic use. However, the mesocarp fiber (MF) generated in the mills is 2.5 times the amount of KS generated. Therefore, this work analyzes an energy system that could valorize simultaneously MF and KS by the integration of pyrolysis and torrefaction processes, to produce biochar and torrefied fuel. A numerical model is used to analyze the integration of the pyrolysis and torrefaction processes considering a temperature range between 250 and 550 °C. It is observed that biochar and torrefied fuel could be produced simultaneously from pyrolysis process temperatures of 460 °C. The maximum load capacity of the integrated pyrolysis and torrefaction system corresponds to the highest temperature considered 550 °C (1 kg of KS per each kg of MF). However, the highest energy efficiency is found at lower pyrolysis process temperatures, near the auto-thermal operation temperature. The average efficiency of the analyzed energy system is 59.7%. Thus, the use of an integrated pyrolysis and torrefaction system could be an efficient alterative to be applied in small scale mills, to improve the KS energy density and valorize MF into biochar.