Development of the unified model for identification of composition of products from incineration, gasification, and slow pyrolysis

Abstract

This paper considers the processes of incineration, gasification, and slow pyrolysis. The common approach implies the use of individual models for the description of separate processes. When parameters acquire the values close to the boundary processes, the accuracy of description of the studied phenomena decreases. The specified processes do not have distinct boundaries between themselves and can smoothly transfer from one to another at changing external influences. While the physical and chemical processes are similar, the composition of the products of reactions, which are determined on the boundaries with the use of adjacent models, is different. In the most general form, the problems associated with incineration, gasification and slow pyrolysis are solved based on a unified model. The solution is complicated by the possibility of an unpredictable change in the composition of original substances. In addition, they can be located in various phase states: gaseous, liquid and solid. The previously developed system of equations that describes the process of combustion of organic fuel of unknown composition was taken as a basis for the unified model. The partial pressures of the products of reaction are the parameters of the model. In this approach, their condition is considered to be gaseous. The feature of the proposed unified model is the possibility of taking into account the condensed phase (coaly residue) of reaction products that is characteristic of slow pyrolysis. For a unified model, which describes the processes of incineration, gasification and pyrolysis, the calculation processes have differences. When studying the gasification and incineration processes, the temperature of the products of reaction is determined based on the equality of their enthalpy and the enthalpy of resulting substances. When studying the process of pyrolysis, the temperature of reactions and, respectively, of its products, is assigned. The found composition of the products and the assigned temperature allows calculating their enthalpy. The necessary amount of energy in the form of warmth to ensure the reaction of pyrolysis can be calculated based on the difference between the found enthalpy and the enthalpy of resulting substances. To prove the adequacy of the model, the calculations of cases of incineration and gasification of gaseous (methane), liquid (ethyl alcohol) and solid (pine wood) substances were conducted. The calculation of slow pyrolysis was performed for pine wood. Coincidence of the results with the data available in literature proved the relative errors admissible for engineering calculations. Based on the joint use of the model and previously developed method for determining the composition of gases mixture in the process of its incineration, the method of identification of the composition of hydrocarbon compounds of combustible substances in different aggregate states in real time mode was proposed.