STUDYING THE REGULARITIES OF THERMAL DECOMPOSITION OF SUNFLOWER HUSK UNDER CONDITIONS OF HIGH-SPEED HEATING

Fuel waste from oil extraction plants – sunflower husk – is used to replace organic fuel. The study of the regularities of thermal decomposition of the husk under conditions of high-speed heating in boilers is the aim of this work. The cellular model of sunflower husk (SH) includes three main components – 30–48% cellulose, 34–38% hemicellulose and 17–26% lignin. Depending on the structure, the elemental composition of the fuel, the quantitative and qualitative composition of volatiles, and, as a result, the calorific value differ. In addition, different molecular structures of individual components lead to different decomposition mechanisms during pyrolysis. Sunflower husk contains 14–18% (by weight) of bound carbon, 70–76% of volatiles, and 5–10% of moisture. The calorific value Qnr of the husk ranges from 15–21 MJ/kg. The thermal decomposition of SH in a fluidised bed at temperatures of 500–1000 °C produces volatiles and solid coke residue (up to 20–30% of the initial mass), which has low reactivity and high strength. To record waste gas yields, an experimental method was used to study the thermal processing of fuel in a laboratory reactor under conditions of high-speed heating in a fluidised bed using a mass spectrometer. Dynamic curves of waste gas yields have two distinctive sections: the first one corresponds to the release and burnout of volatiles, and the second, longer one – to the burnout of coke residue. The second stage determines the completeness of the utilisation of sunflower husk fuel, the design features of the combustion chamber, efficiency and operating parameters of the process. To reduce heat losses due to mechanical underburning, it is recommended to carry out this stage at temperatures above 850–900 oC. With an increase in temperature, a decrease in the total duration of husk burnout is observed. An empirical dependence of the burnout time of the husk in the fluidised bed on the temperature T was obtained: t = 3,55·105/Т1,53±2, s.