Optimizing the Production of Fuel Briquettes from Pruning Wastes of Urban Trees and Grass

Conversion of tree and grass pruning wastes, as abundant and available lignocellulosic sources, into biofuels can be a viable alternative to fossil fuels that pollute the environment. In the present study, flammable briquettes were produced from the pruning remnants of urban trees including mulberry, elm, acacia and ash, as well as grass using a natural binder i.e. frankincense. Then, the optimal density and friction of the produced briquettes under the influence of pressure, moisture, temperature, mixing percentage and additive parameters were investigated using regression methods, support vector machine (SVM) and genetic algorithm. The results showed that with increasing moisture between 9 to 17%, the density of briquettes decreases. Also, the examination of mixing percentage showed that by decreasing the percentage of sawdust and increasing the percentage of grass, density and friction force decrease. The most optimal sample of this experiment was determined with a mixing percentage of 87.5% sawdust and frankincense 10% at a temperature of 100 °C, a pressure of 10 bar and a moisture content of 13%. In this case, the average density and friction force of the briquettes were 1020 kg/m3 and 44 N/mm respectively. The results showed that regression model of the density and friction test related variables are significant at 5% level. Hence, the variables are involved in the explanation of friction and density. According to the results, the high calorific value and low calorific value of briquettes produced from grass and sawdust are more, and the calorific value of additives has a significant impact on the process of briquette production due to the high sticking effect.