STUDY ON OXIDATION AND IGNITION OF MIXTURES OF PYROLYSIS LIQUIDS WITH LOW-REACTIVITY COAL

Abstract

The relevance of the work is determined by a wide interest in the technologies of pyrolysis of waste of various origin and the need to increase their effectiveness. Since pyrolysis liquid is an obligatory product of pyrolysis with yield up to 70 % of the mass of the raw material, its combustion is one of the essential conditions for maintaining the energy sufficiency of almost any technology. Problems with direct burning of such liquid are associated, majorly, with the instability of its properties and low calorific value. Its combustion in the mixture with traditional solid fuel allows leveling these shortcomings, which determines interest in the study on abovementioned processes. Purpose: determining the parameters of ignition and combustion of low reactivity coal mixtures with two different samples of pyrolysis liquids obtained at industrial pyrolysis enterprises, which use oil sludge and wood sawdust, as well as the identification of the relationships between the ignition parameters and the characteristics of fuel mixtures. Methods. Study on the properties of the component of used fuels was carried out using standard techniques. The oxidation parameters were determined by thermogravimetric analysis, and the data obtained were processed by the Coats–Redfern method. The characteristics of the ignition and combustion of fuel mixtures were determined using the experimental setup of fuel ignition in conditions similar to industrial equipment. Results. The properties of the studied low reactivity coal and two samples of pyrolysis liquid were determined, in particular, the values of the lower calorific value, ash content, as well as their elemental composition were determined. In the conditions of thermal analysis, the characteristics of the oxidation of the mixtures of low reactivity coal with pyrolysis liquids with a concentration of the latter equal to 5, 10 and 25 wt. % were investigated. It was established that the additive of pyrolysis oil did not lead to a significant change in the temperature ranges of the individual stages of the low reactivity coal oxidation, while the promotional effect of the additive was found, which consisted in a disproportionate reduction in the reaction rate compared to the composition of the fuel mixture. This conclusion was confirmed by a decrease in the value of activation energy for low reactivity coal as part of a mixture with pyrolysis oil. The addition of pyrolysis liquid also led to a decrease in the ignition delay time up to 65 %, while the maximum effect was achieved at 10 wt. % of the additive at 500 and 600 °C, and at 25 wt. % at 700 °C. A linear dependence of the ignition delay time on the lower calorific value was observed at 700 °C for mixtures of low reactivity coal with pyrolysis liquid from oil sludge and rubber waste. A similar relationship was observed between the activation energy for the mixture and the ignition delay time at 600 and 700 ° C for all considered pyrolysis liquids.

Keywords

• pyrolysis
• pyrolysis liquid
• ignition
• combustion
• activation energy
• lower calorific value