Walnut Shell Pretreatment in Regard to Its Combustion Properties

Shortages in the energy market for traditional fuels, rising prices, and the requirements placed on member states by the European Union to reduce greenhouse gas (GHG) emissions are resulting in an increased interest in alternative energy sources. One such source is waste biomass. This biomass is not only ecological and publicly available, but, unlike other sources of renewable energy, it is independent of weather conditions or terrain. Unfortunately, despite the enormous potential, only a few types of biomass are currently used in the energy and heating industries. To change this, a material in the form of a walnut shell that has not been used in this field before is examined. In this work, pellets made from walnut shells were analyzed for combustion in heating boilers intended for this kind of fuel, commonly used in many households. The produced pellet was subjected to a combustion process, and the emitted flue gases were analyzed to check the suitability of the fuel for the heat-generating purpose. The exhaust gas was analyzed for the presence of compounds such as CO, NO_x, CH₄, and H₂S. In addition, a series of tests were conducted to determine how the drying process time and temperature of the biomass affect its subsequent heating value. As a result of this research, it was proven that the walnut shell is suitable for the production of pellets, thus obtaining high results for a calorific value of 16.90 MJ/kg, an ash content of 1.31%, and a moisture content of 8.25%. Thanks to the obtained results, it was concluded that the produced fuel can be compared with commercial pellets, as it does not differ from and even exceeds some of the values of fuels currently available on the market. The temperature and time during the drying of the biomass also showed correlations with the subsequent calorific value of the material, with a temperature of 110 °C and a time period of 90 min providing the best results.