Each fuel has a specific energy quantity; after combustion, energy becomes an useful resource for specific purposes (electric energy & heat production).
The main available energy quantity is strictly related to heating value of used fuel.
This heating value indicates energy quantity which can be obtained by full combustion of mass unit.
Literature demonstrates that lower heating value of wood (PCL), coming from different wood qualities, varies in a quite limited range [between 2,5 and 5,5 kWh/kg].
In conifers it is about 2% higher than broad leaf ones. This difference is especially due to the higher lignin quantity of conifers and also to the higher resin, wax and oil quantities.
Heating value of textile waste, containing cellulosic fibers, is higher than wooden waste.
Heating value of sewage sludge, containing high quantity of carbon, if dried at 20% of moisture, is an optimal value.
Wood moisture can modify its heating value reducing it while moisture increases. It happens because a part of released energy during combustion process is used for water evaporation and it is not available for thermal use. Water evaporation needs about 667 Wh of energy far each kg of water.
The formula for wood heating value calculation (kWh/kg) with a specific water quantity [M%] is the following:
Heating value variation (with PCM = 5,14 kWh/kg = 18,5 MJ/kg controllare anche questa) according to M is shown in the following diagram.
An evaluation of wood heating value allows to make energetic comparisons with fossiI fuels most used.
