Abstract
To produce energy from livestock excretion, since compost fermentation heat is expected, efficient recovery technology and a method to do so are required but have not been developed. As for subsidiary materials used for compost processing, such as straw, sawdust and bark, acquisition is difficult and prices are soaring due to the demand for biomass energy. Thus, we examined the use of compost fermentation heat through drying of the return compost mixed at the time of compost material adjustment. Aeration by negative pressure composting at a plant set up by a dairy farmer was used for this examination. Exhaust gas, which is discharged from the composting plant, and fresh air are heat-exchanged by using a single gas-gas heat exchanger or a combination of two such heat exchangers. The capability of each (single or double) was examined by measuring the temperature of the fresh air after the exchange and by adjusting the amount of inputted fresh air. As a result, when the amount of inputted fresh air was increased when using only one gas-gas heat exchanger, the recoverable quantity of heat increased (28.0MJ/h). By combining two gas-gas heat exchangers, the compost was dried using fresh air after the heat exchange (mean: 47.3°C; 34.1m3/min; total 72 h). It was shown that the moisture content of the compost can be reduced from 68.0% to 48.7%, and the amount of subsidiary materials consumed could be reduced by about 20% when using this type of compost as the return compost. It is thought that not only aeration by negative pressure composting at this plant but also in closed vertical composting facilities is applicable to institutions which collect and discharge exhaust gas.
