Experimental study on optimisation of the burning process in a small scale pellet boiler due to air supply improvement
Riga Technical University, Institute of Energy Systems and Environment, Kronvalda blvd. ¹, Riga, LV-¹0¹0 Latvia;
The specific weight of biomass and pellets in thermal energy production has recently started to increase rapidly. The continually growing price of fossil fuels and European Union requirements to increase the share of renewable energy in thermal energy production are the main reasons of the biomass specific weight increase. Unfortunately, Latvia uses only a small part of the country’s existing biomass potential for the time being. A growth of the amount of biomass utilisation for energy production can be foreseen in the future, because such type of energy production has a number of advantages, one of which is the lesser amount of emissions that arise during the combustion process. However, the amount of emissions that arise during the combustion of wood pellets can get lower due to optimisation of the combustion process. Air supply is one of the main factors which have effect on the heat loss, boiler efficiency, and emissions levels. The main goal of this study is to optimise the pellet combustion process in a small scale pellet boiler due to the air supply improvement. Experimental research of the combustion process of a pellet boiler with nominal capacity ²⁵ kW was carried out during the work. First at all, the effect of changes in the amount of air supplied to the boiler combustion process was determined. Then, approbation of two methods for combustion process improvement was made. The first method was based on flame dissipation, but the second method included the opposite method – flame concentrating. However, the main task of both methods applied was to improve the process of mixing air and fuel. It was important to reduce the rate of air supplied, too. Four different gratings were used for dissipation of the flame. Cylinders without and with a spiral for flow swirl were used for flame concentration. The results of the study show that both methods, in general, have a positive impact on the combustion process.
% of massCOCarbon monoxide content in dry flue gases, % of massNOxNitric oxides content in dry flue gases, % of volumeHHydrogen content of test fuel (as fired basis), % of volumeO²Oxygen content of dry flue gases, % of volumePMDust content of dry flue gases, % of volumeTfgTemperature of flue gas, °C, air supply, flame concentrating. Nomenclature CCarbon content of test fuel (as fired basis), flame dissipation, pellet boiler