Improving the Efficiency of Energy Use of Biofuels

The share of thermal power plants that consume renewable energy resources is growing worldwide. Wood and bio-coal pellets become more and more common as fuels. The technological cycle of pulp and paper production produces a large amount of wood waste, which must be used efficiently. However, bark-wood waste is hard-burning fuel, which causes the need to "light" the flare with high-calorie non-renewable fuel, is followed by the formation of carbon dioxide emitted into the atmosphere. Boilers KM-75-40, taken out of production in 1985, are still used at Russian enterprises for the use of bark-wood fuel as an energy source. Energy examination of the boiler KM-75-40 during its operation with bark-wood fuel (coniferous and deciduous wood bark, substandard chips and sawdust) showed that the design and technical condition of the boiler does not provide the required combustion rate of fuel components and environmental parameters that meet the requirements of the state standard, GOST. The present work aims at analyzing the possibilities of comprehensive improvement of efficiency of bark-wood fuel combustion in boilers KM-75-40. High-priority measures to improve the efficiency of these boilers were developed based on the research results. Boilers KM-75-40 have been in operation for more than 50 years and require replacement with modern low-emission heat generating systems. Prior to replacement, however, upgrading the boilers is recommended: their transition to the layer-vortex combustion technology and the use of bio-coal pellets, as an additive to the bark-wood fuel, in order to adjust the thermal characteristics of the combusted biofuel and steam capacity of the boilers. Bio-coal pellets produced from hydrolysis lignin, which has undergone soft pyrolysis, are promising for this purpose. Thermal and aerodynamic calculations of the boiler KM-75-40 with different proportion of pellets by heat release, as well as thermogravimetric studies were carried out to assess the effectiveness of co-combustion of bark-wood fuel and bio-coal pellets. The thermal calculation included: the circulation rate of fuel particles in the vortex zone, the granulometric composition of the combusted fuel mixture, the location features of combustion equipment, reducing the contamination of the heating surface. The transition to the combustion of this fuel mixture using the layer-vortex technology will allow to refuse from using non-renewable fuels in the boiler KM-75-40 when combusting high-moisture bark-wood fuel, will significantly increase the boiler efficiency and reduce the negative impact on the environment.