Experimental tests of co-combustion of pelletized leather tannery wastes and hardwood pellets

This study examines the possibility of using pelletized leather tannery wastes (LTW) in the co-combustion process with hardwood pellets (HP). The experiments were carried out in a small-scale combustion reactor and were followed by thermogravimetric analysis (TGA) of fuels in the nitrogen and air atmosphere. The experimental investigation has indicated that the leather tannery wastes can be an interesting fuel with a relatively high heating value (HHV), at the level of 16 MJ/kg, and the volatile content of about 68%. Thermal decomposition of the leather tannery sample occurs at temperatures ranging between 220 and 420 °C, with the maximum of intensity at 320 °C. The experimental results indicated that the averaged maximum temperatures obtained during the combustion reached similar values for all samples, which indicates that doping wood pellets with leather waste pellets does not have a significant impact on the temperature characteristics of the combustion process. However, decreasing the amount of hardwood pellets in the mixture reduces the bulk density of the fuel bed and the combustion front velocity. The emission of nitrogen oxides for combusting blends is twice as high as for combustion of pure HP, which is related to higher nitrogen content in leather waste as well as higher ash content.