Hydrothermal Conversion of Cattle Manure to Biooil: Effects of Conversion Parameters on Biooil

Abstract

Due to intensive feedlots operations, the role of cattle manure has changed from a cheap fertilizer to an agricultural waste. Hydrothermal conversion (HTC) is a potential technology of converting cattle manure waste to biooil. In this paper, HTC of cattle manure was studied with regards to the effects of conversion temperature, pressure, residence time, process gas and mass ratios of cattle manure to water on yields and properties of biooil. Results showed that within the temperature range of 260 ∼ 360 °C, biooil yield first increased and then decreased. The maximum biooil yield was obtained at 310 °C. The biooil yield was not further improved by higher initial operating pressure. In contrast, it decreased biooil yields from 38.49% under 0 psig to 6.51% under 150 psig. Longer residence times also reduced biooil yield. Compared with 38.49% of biooil produced with 15-minute residence time, only 12.95% of biooil remained after 40-minute residence time. Process gases also had important impacts on biooil yield. When N2 was replaced with CO, the maximum biooil yield increased to 48.76%. But, when air was used as process gas, the biooil yield decreased to 27.97%. Also, biooil yield decreased with larger mass ratios of cattle manure to water. When the ratio was 2, biooil yield was only 1.46% much less than 48.76% with ratio of 0.25. Therefore, biooil yield from HTC of cattle manure largely depended on the conversion temperatures and process gases. Higher conversion pressures, longer residence time and larger mass ratios of cattle manure to water had negative impacts on biooil yield. The mean high heating value of biooil from HTC of cattle manure was 37.0 MJ/kg.