Assessment of thermal energy use in technique of producing solid composite fuels from low-grade raw materials

The relevance of the work is conditioned by the tendency of power engineering focus on renewable energy sources owing to the need to use efficiently the traditional organic resources. The paper considers low-grade fuel (peat, sawdust and sapropel) and brown coal as one of the most requested renewable energy resources in Russia. The heat-technology processing into solid composite fuel is selected as the method to enrich this resource. The main aim of the research is to assess energy use for producing solid composite fuel from low-grade raw material by the example of heat-technology developed by the authors. The methods used in the research. Thermotechnical characteristics of low-grade fuels were determined by the standard methods GOST R 52911-2013, 55661-2013 and 55660-2013. Calorific value was studied using a bomb calorimeter ABK-1 according to GOST 147-2013. The methods of material and heat balances were used in assessing thermal costs. The reliability of the results was confirmed by comparing them with the results of other investigations. Results. Using heat of fuel organic mass decomposition and heat of combustion of thermal-processing by-products allowed covering completely heating needs for producing solid composite fuel from peat, brown coal and sawdust. When treating sapropel a part of heat input should be covered by external sources. Low-temperature pyrolysis of low-grade raw material may take place autothermally owing to heat of organic mass decomposition. In this case it is necessary that the moisture of raw materials at the reactor input was lower than the following values: for peat - 35 %, for the investigated brown coal - 54 %, for sawdust - 37 %. Low value of heat of lake sapropel organic decomposition does not allow organizing autothermal heat-processing.