The effect of drying on the heating value of biomass fuels

Abstract

There has been some speculation as to whether or not biomass fuels (such as feedlot manure) may lose volatile matter during the drying process. Since current standards state that heating value analysis may be performed before or after drying, and volatile matter analysis can only be performed after drying, and since many fuel suppliers are paid on a heating value basis of the fuel, there has been some controversy in this matter. Furthermore, it is known that if manure is left out at ambient temperatures over long periods of time, the heating value decreases as well. It is therefore the objective of this work to ascertain if in fact volatile matter is lost during the drying or aging process and, if so, to find an optimum aging and /or drying time and to model the loss of volatile matter. It has been found that, if indeed there is volatile matter loss over the drying process, then it is so small as to be negligible. Furthermore, no appreciable amount of volatile loss occurs even if the fuel is dried for extensive amounts of time as are generally needed to obtain constant weight in the fuel sample. It has also been found that heating value decreases with aging time (falling even after only one to two days at atmospheric conditions), yet the heating value of an initial (undried) fuel sample increases with aging time. This is because moisture is lost as well as combustibles so the heat produced by the fuel will increase with a decrease in moisture even though volatiles are lost.