COMPARATIVE ASSESSMENT OF THE EFFECT OF EKIBASTUZ COAL AND BIOMASS MASS RATIO ON FIXED-BED COMBUSTION INTENSITY

Abstract

The combined combustion of coal and biomass is a promising direction for improving the efficiency of using low grade coal and incorporating renewable agricultural waste into the energy cycle. The aim of this work is to determine the effect of the mass fraction of corn biomass on the characteristics of bed combustion of high ash Ekibastuz coal and to identify the compositions of composite fuel that ensure the most intense and complete combustion. Crushed corn processing waste with a particle size of less than 1 mm was used as a biofuel component. Coal and biomass were mixed in the range from 10 to 90 wt. % and cylindrical fuel briquettes were formed using the cold pressing method with an aqueous molasses solution as a binder. The moisture content, ash content, volatile matter yield, elemental composition, and calorific value were determined for the initial components. The thermal behavior of coal, biomass, and their mixtures was studied using the thermogravimetric method. It has been established that an increase in the proportion of corn biomass contributes to an increase in the combustion efficiency of the composite fuel: from 61.4 % for pure Ekibastuz coal to 96.2 %, while for pure corn biomass the combustion efficiency reaches 98.3 %. The maximum combustion temperature changes non monotonically. For pure coal, it is about 550 °C, and with the addition of biomass it increases to 798 °C for the E60K40 composition. Elevated temperature values are also characteristic of the E50K50 and E30K70 compositions. The obtained results show that corn biomass acts as a highly reactive component, promoting accelerated fuel heating and the development of the active combustion stage, while coal ensures a more prolonged heat release due to the oxidation of the carbonaceous residue. The scientific novelty of the work lies in establishing the patterns of influence of the mass fraction of corn biomass on the degree of combustion and the temperature regime of layer combustion of high‑ash Ekibastuz coal, as well as in identifying the non‑monotonic nature of the change in the maximum combustion temperature when varying the composition of the composite fuel. The most pronounced combination of high reactivity and temperature effect within the studied range was found for an intermediate composition of 70–30 wt. %. The practical significance of the results lies in the possibility of using the obtained patterns in the development and selection of the composition of coal‑biomass fuel briquettes for more efficient use of low‑grade Ekibastuz coal and for incorporating corn processing waste into the energy cycle. The final selection of the composition of the composite fuel should be carried out taking into account a set of indicators, including the heat of combustion, the rate and degree of burnout, and the temperature regime.