## 1 Introduction  
Thermal energy generation at coal-fired thermal power plants and boiler houses is accompanied by the release of a large amount of carbon dioxide into the atmosphere, which has a greenhouse effect. This has become a worldwide problem as coal is widely used as the main energy fuel in different regions. A partial reduction in carbon dioxide emissions can be achieved by switching to the combustion of fuel mixtures based on coal and biomass for a short period of time during the development and implementation of new low-carbon technologies for heat production [1, 2]. Some scientific developments have already passed practical testing. It was found that not only greenhouse gas emissions into the atmosphere but also fine ash particles are reduced [3]. The use of biomass as an additive to coal contributes to the improvement of energy, environmental, and economic performance [4, 5, 6]. One of the solutions to the problem of reducing the carbon footprint is associated with the development and implementation of new low-carbon technologies for thermal energy production by burning mixtures based on coal with renewable biomass. The use of biomass as an additive to coal improves not only the energy and economic indicators of heat generation but also helps to solve the problem of reducing greenhouse emissions since biomass is classified as a carbon-neutral fuel. It is believed that when biomass is burned, as much CO\({}_{2}\) is released as it is absorbed from the atmosphere during its formation [7; 8; 9]. Back in the early 2000s, [PERSON]. [10] found that co-combustion of coal and biomass (grass and wood waste) is a promising way to reduce greenhouse gas emissions, including carbon dioxide. The main advantages of biomass as an energy fuel compared to solid fossil fuels are as follows: Biomass is a waste from various industries; the biomass cost depends only on the distance of transportation to the thermal power facility; less harmful gaseous substances are formed when biomass is burned; biomass is a renewable energy source. The disadvantages of biomass as an energy fuel include the following: high hydrophilic ability, leading to rapid saturation of biomass fuel particles with moisture (for example, during storage or transportation) and directly affecting particle adhesion; reduction in calorific value and deterioration of combustion characteristics; variability of the geometric shape of fine particles; high tendency to smolder and spontaneous combustion, affecting the deterioration of combustion characteristics; relatively low reserves compared to solid fossil fuels. An important disadvantage of using biomass as an energy supplement to solid natural fuel is the need for its grinding. Nevertheless, considering all the above disadvantages, biomass is one of the most promising energy resources for the production of thermal energy [11; 12]. The shift to burning solid fuel mixtures is hampered primarily by the lack of experimental data and the large variability of power plants, which are radically different from each other in combustion technology and the solid power fuels used. To obtain the necessary data, the method of balance testing of existing boilers is used, but it is expensive and time-consuming. A less expensive method is to use an experimental method on an installation that simulates the operation of a boiler furnace. But in this case, the experiment will be local in nature. The CFD modeling method (Computational Fluid Dynamics Modeling) is also widely used when analyzing the upcoming reconstruction of a power plant or shifting it to non-standard fuel [13; 14]. This method has relatively high reliability and has proven itself in terms of practical application. But to use it, a large amount of initial data is required, obtained either during balance tests of the boiler or when using experimental stands that simulate the operation of the boiler furnace [15; 16].