Calorific Value
Calorific value is the amount of heat generated from combustion of a unit weight of a substance, expressed as kcal/kg. The calorific value is determined experimentally using Bomb calorimeter in which the heat generated at a constant temperature of 25Oc from the combustion of a dry sample is measured. Since the test temperature is below the boiling point of water, the combustion water remains in the liquid state. However, during combustion the temperature of the combustion gases remains above 100Oc so that the water resulting from combustion is in the vapour state. Table 3.5 shows typical values of the residue and calorific value for the components of municipal solid waste.
While evaluating incineration as a means of disposal or energy recovery, the following points should be kept in view:
· Organic material yields energy only when dry;
· The moisture contained as free water in the waste reduces the dry organic material per kilogram of waste and requires a significant amount of energy for evaporation; and
· The ash content of the waste reduces the proportion of dry organic material per kilogram of waste. It also retains some heat when removed from the furnace.
