Technical and economic feasibility of combusting biocarbon in small scale pellet boilers

Biocarbon is a promising fuel which can have several applications: as peak load fuel in existing bioenergy plants, as substitute fuel for oil boilers, as quality fuel for high efficiency and low emission small-scale heating appliances, as fuel optimization by blending (“BIO CO-firing”) etc. The Integrated Pyrolysis Regenerated Plant (IPRP) designed and realized at the University of Perugia (Italy) produces a charcoal or biocarbon with an average calorific value of 29 MJ/kg, using chestnut wood as a raw material. The purpose of this work is to produce pellets with this biocarbon, test it in a 20 kWt boiler (changing air and fuel mass flow) and calculate mass and energy balances. This biocarbon was grinded and mixed with 10%w water and 25%w sawdust to obtain pellets with satisfactory durability (about 98%). The energetic characteristics of the pellet obtained by blending biocarbon and sawdust (having a heating value of 26.1 MJ/kg) are similar to those of torrefied pellets. This innovative fuel was tested in the 20 kWt pellet boiler to measure efficiency and emissions. The thermal efficiency reached with biocarbon pellets was around 87%, while emissions of particulate matter proved to be in the range of those of commercial wood pellets. Thermal performance and emissions data generated from the experimental campaign are used by SINTEF in Norway to assess the overall feasibility of the value chain and the performance of biocarbon pellets combustion in small scale boilers, by the point of view of cost-efficiency, thermal efficiency and environmental performance. In this way the results obtained for emissions and efficiency can be improved. The novelty of the work is represented by the use of a commercial boiler fed with biocarbon pellet and the calculation of mass and energy balances to optimize this new process. © 2017, ETA-Florence Renewable Energies. All right reserved.