Effective use of dairy manure mixed with sand bedding for gasification

Sand is the most commonly used bedding material in commercial dairies. The advantage of using sand in dairies is the health and well-being of the animals. When manure is harvested, sand is mixed with the manure, which decreases the energy content of the mixed material. Hence, when used for thermal energy conversion processes, the mixture will be difficult to convert into energy or power. The sand should be removed from the mixture for sustainable energy conversion. A method to remove the sand from sand-manure mixtures was designed and investigated in the current study. The "as-received" manure had more than 70% ash, and this was reduced to less than 40% to 50% after sieving with a 40 mesh screen. The ideal moisture content during the separation process was less than 10% (wet basis). The manure-sand mixture was ground prior to separation. The higher heating value of the sand-separated manure increased to almost twice the original value. From the pilot-scale manure handling system that was developed, a maximum of 25% of the initial dried sand-manure mixture was recovered after employing simple box-type drying and continuous sand separation, while the separated sand showed a reusable quality for bedding. Six indices of ash fusion prediction equations were applied and indicated a low potential for ash agglomeration and slagging due to high silica concentrations in the processed manure. Finally, the processed manure was successfully gasified and flared with a lower heating value of 3.3 MJ Nm^-3.