L. Virbickas, I. Kliopova
Kaunas University of Technology,
Keywords: logging waste, GHG, renewable energy, emissions
Summary:European countries set more and more goals in the field of renewable energy sources. In northern countries, where there is not so much sun but sufficient forests, biofuels are the main renewable energy source. In Lithuania, more than 60% of thermal energy is produced from biofuels, and by 2050 the goal is to reach 100%. Many claims that the use of biofuels for energy production is environmentally neutral due to the carbon accumulated during plant growth. However, it has not been estimated how much additional energy is needed to produce a certain amount of energy from forest resources. Considerable amounts of fossil fuel are used in the harvesting process for mechanized harvesting, loading, shredding of biomass and biofuel transportation to combustion plants. Logging waste potential in Lithuania is over 1 mil. m3 per year. The most common tree species in the country is Scots Pine (Pinus Sylvestris) – 34.6%. Research object: Biofuel production chain and combustion for thermal energy production. System boundary: land preparation, harvesting of wood biomass (timber wood, firewood, forest residues), logging of biomass to chipping and then – to combustion and large combustion plants (LCP) for thermal energy production. The aim of the research - to evaluate the impact on air quality and climate change of biofuel production from forest biomass in Scots Pine forests stands and to estimate the efficiency of energy recovery. An experiment was carried out in the final felling forest areas with a purpose to determine the energy consumption for the preparation and transportation of woody biomass and to determine the main output of the processes (timber, firewood, and logging waste). These data were used for the created database with various material, energy and fuel flow charts for further estimation. The results of analysis show that over 160 t of different biofuel (bark, cuttings, sawdust, and logging waste) can be produced from pine biomass, selected from 1 ha of fertile area during forest main felling (after 100 years), and over 500 MWh of thermal energy can be supplied to heat supply system, incl. 140 MWh due to burning logging waste. The efficiency of energy recovery in the case of biofuel production from Pine stands forest is up to 96% (without logging waste) and up to 95.7% - with logging waste. The energy consumption of this system is about 43 kWh per MWh of produced heat energy per 1 ha. The direct impact on air quality due to air emissions is 1.36 kg MWh-1 per 1 ha. The direct impact to clime change due to GWP is 5.61 kg CO2e MWh-1 per ha (without assessing biogenic origin GHGs) and over 410 kg CO2e MWh-1 per ha, incl. biogenic CO2. This paper will present the results of a comparative analysis of the system outputs due to different growing conditions and/or woody biomass management solutions. Besides, recommendations regarding increasing efficiency of energy recovery and minimization of environmental impact will be presented.