Question

Consider a pile of green wood chips at 60% moisture content (wet basis) and weighing 1 t. What is the oven-dry mass of biomass in the pile? The biomass has a heat of combustion of 16 MJ per oven-dry kg. This is the 'gross calorific value' corresponding to the heat output in a reaction of the type [CH,O]+O2 CO2(gas) +H2O(liq) The net calorific value (or 'lower heating value') is the heat evolved when the final water is gaseous; in practice this is the maximum thermal energy available for use when biomass is burnt. i The pile is left to dry to 50% moisture content (wet basis), when it looks much the same but has less water in it. ii The pile is left to dry for a few more weeks, and reaches 20% m.c. (w.b.), at which stage it has shrunk a little in volume and much in mass. For each situation calculate the total mass of the pile, the net heat energy available from burning the pile, and its net calorific value per wet kg.