R E N E W a B L E Energy from Swine Waste

A thermochemical conversion (TCC) process was developed and researched to reduce waste and to produce renewable energy from swine manure. Experimental results showed that operating temperature and retention time were the key parameters. It is critical that a process gas, reducing or non-reducing gases but not water vapor, be added to the process in order to yield an oil product. The operating temperature ranged from 275°C to 350°C, corresponding operating pressures ranged from 5.5 to18 MPa. The initial pressures of process gases were 0.34-2.76 MPa (50 to 400 psi). Oil product was evaluated by elemental analysis, heating value, and benzene solubility. Oil viscosity and its change vs. storage time were also studied. Typical oil yield of the TCC process ranged from 60% to 65% on the input volatile solids. The average elemental composition of the raw oil products was 71.1% carbon, 8.97% hydrogen, 4.12% nitrogen, 0.2% sulfur, and 3.44% ash. The water content of raw oil varied from 11.3% to 15.8%, which was less dependent on the operating parameters. The average heating value of the oil products was 32,500 kJ/kg. These properties are comparable to those of liquefaction oils from wood sludge and other biomass. When CO was as the process gas, the oil viscosity was at the level of 0.5 Pa.s at operating temperatures of 315°C-350°C. The viscosity increased in the first 15d of storage, and did not substantially change over the rest of the 60d storage time. The TCC oil contains high sulfur and nitrogen content. Further investigation is necessary to reduce the high nitrogen and sulfur content before the full utilization of the oil product can be achieved.