| Hydrothermal processing of swine manure is a novel technology that has shown very promising results in treating waste and producing oil. Oil yields of up to 70% were achieved in batch experiments. Since a continuous-mode process is more applicable for scale-up operations, a continuous hydrothermal process (CHTP) reactor system was developed. The effects of temperature, pressure, hydraulic residence time, and use of process gas, were evaluated to determine the optimal process condition. Products' (i.e., oil, aqueous and gas) composition were determined to better understand the mechanics of the reaction process and to provide information for further developments. The CHTP, composed of a high-pressure slurry feeder, a process gas feeder, a continuous-stirred tank reactor, a products separation vessel, and process controllers, had a capacity of processing up to 48 kg of manure slurry per day. Results showed an interaction between operating temperature and pressure. The highest oil yield of 70% of volatile solids was achieved at 305°C, 10.1 MPa, and 80 min hydraulic residence time without process gas. The addition of carbon monoxide in the process did not improve the oil yield but produced a more fluid oil product. The heating value of the oil product ranged from 25,176 kJ/kg to 33,065 kJ/kg. An energy balance showed that the process was a net energy producer. The carbon and hydrogen content of the oil were 62.7+/-6.4% and 9.6+/-0.4%, respectively. The nitrogen and sulfur content of the oil were 3.9+/-0.3% and 0.3+/-0.1%, respectively. The oil was primarily resins (∼45%) and asphaltenes (∼44%) with small amounts of saturates (∼3%) and aromatics (∼2%). Majority of the hydrocarbon compounds in the oil has boiling points within 316°C to 482°C. The aqueous product was found to contain volatile organic compounds primarily ketones and benzenyl compounds. Most of the N, P, and K content of the manure went to the aqueous product. The main gas product was CO2 accounting for ∼98% of the total. Carbon monoxide accounted for most of the rest. Methane, ethane, and ethene were also produced in negligible amounts. Trace amounts of aromatic compounds including benzene, ethylbenzene, toluene, and styrene were also detected in the gas product stream. |
