Fuel consumption in the thermal treatment of low-calorific industrial food processing waste

Highlights: • Effect of an oxygen concentration in flue gases on the consumption of additional fuel was analysed. • Increasing oxygen concentration caused non-linear increasing consumption of extra fuel. • Above the 13.4% O2 concentration, the extra fuel consumption increases to infinity. Animal waste resulting from food production represents a potential sanitary risk. For this reason, it is necessary to apply an effective and ecologically safe procedure for eliminating this danger. In this process, one of the numerous legal obligations is maintaining a flue gas temperature of 850 °C. Animal waste has a relatively low calorific value and a high moisture content, so it requires a certain amount of auxiliary fuel to incinerate. The purpose of this paper is the minimization or elimination of auxiliary fuel consumption during the incineration of low-calorific waste. This article presents an analysis of two factors that determine the consumption of additional fuel, the waste mass flow and the oxygen concentration in the flue gas. The analysis was based on a comparison of the energy supplied and demanded for the incineration of pork bones under various operating conditions. The analysis and tests show three working categories of the system: additional fuel is not needed, additional fuel is needed, and a flue gas temperature of 850 °C is not achievable regardless of the quantity of additional fuel used. The research shows that thermal treatment of low-calorific waste units can work without or with a minimal amount of additional fuel. However, there is an area where the required temperature of 850 °C is not reached despite increasing the amount of burned auxiliary fuel.