Evaluation of pellets produced with undergrowth to be used as biofuel

Abstract

Many European countries are developing the use of pellets or wood briquettes for the supplying of local energy. Many industries are being forced to replace fossil fuels by biomass because of its neutrality in relation to CO2 emissions, thus creating an interesting market for pellets. In Portugal, the most common undergrowth includes: esteva (Cistus Ladanifer), tojo (Ulex Europaeus), giesta (Sarothamus Scoparius), feto (Pteridium aquilium) and silva (Rubus ulmifolius). These undergrowth specimen are attractive due to the large volume available, but are not usually used for making pellets. It is possible to prevent large fires cleaning the forests, but this is an expensive task that could be compensated if the undergrowth can have some commercial value. The aim of this work is to obtain pellets with standard properties and evaluate the parameters that can qualify the performance of these pellets: moisture content, particle size distribution, high heating value, height of flame and burning time, pressure and temperature of the pelletizing process and mechanical durability. The results showed that the apparent density varies around 1260 kg/m3. The moisture content of different pellet varied between 2.79 and 7.46%, ash content was less than 3%, the calorific value is between 16-18kJ/kg, the durability results respect the values recommended by standards. After ignition the flame increases to an average height of 25 mm. The total burning time was in all cases dominated by the cinder combustion without visible flame and the total complete burning time varied between 400 and 600 s.