Solid fuel production from cattle manure by dewatering using liquefied dimethyl ether

Abstract

Livestock manure is an animal waste that is generated worldwide, and is one of the most abundant waste materials generated in Japan. Its excess application as a fertilizer can cause negative environmental problems; i.e., groundwater pollution and greenhouse gas emissions. When livestock manure is used as a solid fuel, a significant amount of energy is required to remove the high water content by conventional heating, and the resulting dry material has a self-ignition risk that makes it difficult to treat and store. This study focused on an energy-saving dewatering technology using liquefied dimethyl ether (DME) at room temperature, and investigated the dewatering properties of DME and the resulting mass balance of water in cattle manure. The fuel characteristics and the self-ignition risk of the dewatered cattle manure were also investigated.Under optimum conditions, over 98% of the water and some of the crude fat content in cattle manure could be removed after 70min (seven batches) at a total DME/initial water ratio of 28.6. The manure was more efficiently dewatered than some other wet biomass such as sewage sludge and vegetable biomass. Moreover, a similarity in the kinetics between thermal drying and DME dewatering also emerged.The lower heating value (LHV) of DME dewatered manure under these conditions increased to 13.8MJ/kg, which was 18.1 times that of original cattle manure. The cattle manure dewatered by DME had a lower self-ignition risk than thermally dried cattle manure because of the extraction of crude fat by DME. Therefore, it could be more efficiently produced and safely used as a biomass fuel following DME dewatering.