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The authors conducted pressure drop numerical simulations of multiphase gassolid flow characteristics, within a fly ash pneumatic conveying system, in 620 MW thermal power plant. The objective of this study is to verify the OpenFoam model by comparing the numerical results with pressure measurements taken along the considered pipeline. The numerical model is developed on the base of extensive experimental research of high-capacity long-distance pneumatic conveying system for Kolubara lignite fly ash. The numerical simulations of pneumatic conveying were performed using the Euler-Euler approach in OpenFoam, that is twoPhaseEulerFoam solver, for the air mass-flow rate of 5500 Nm³ per hour, the fly ash mass-flow rate 77 tonne per hour. The calculation input air pressure at the pipeline outlet was assumed to be as measured approximately 234 kPa, the air-ash mixture temperature was 373.15 K, the mean ash particle diameter of 0.128 µm, and physical density of ash 2100 kg/m³. Numerical mesh is generated as an O-grid for the first two pipeline sections, first with a length of 90 m, a diameter of 0.2604 m, and an inclination of 1.885°, and the second with a length of 102 m, a diameter of 0.3097 m, and an inclination of 2.163°, while every mesh cell is substantially larger than the diameter of the ash particle. The applied Euler-Euler approach enables a comprehensive investigation of the complex dynamics involved in pneumatic conveying, considering the two-phase nature of the system and providing valuable insights into the particle behavior, pressure drop, and other key parameters. The comparison of the experimental and numerical model simulations data show good agreement regarding pressure drop. Although Euler-Euler model is complex in terms of necessary closure models, it might prove itself as reliable for simulated conditions in future studies. [ABSTRACT FROM AUTHOR]

In order to obtain data on the effect of moisture content on the grindability of coals, experimental research was conducted. The experiment included six samples of coal from the Kolubara basin. The samples were selected based on experimentally obtained values of their Hardgrove grindability index (HGI), in order to cover the entire range of experimental HGI values. In addition to determining the HGI, proximate, and petrographic analyses were performed on all samples. Lignites are naturally tough, soft, and greasy when in a moist state. By reducing the moisture content, lignites become more brittle. For this reason, Hardgrove grindability index values have different values depending on the moisture content at which they are determined. The HGI has a non-linear dependence on the moisture content of the coal. All curves have two inflection points, one minimum and one maximum value of Hardgrove grindability index in the tested range. The minimum values of HGI are in the range of 15-22% of the mass fraction of total moisture in coal, while the maximum values of HGI are for a total moisture content of 5-13%. In the case of high moisture content in coal, the obtained high values of HGI may not reflect the true grindability of the coal. These values could be misleading and not necessarily indicative of the coal inherent characteristics. Instead, they could be a result of the imperfections in the Hardgrove method used to determine the grindability index of coal with high moisture content. [ABSTRACT FROM AUTHOR]

Wood chips are often used as solid fuel in modern biomass boilers. Experiments were conducted on 22 boilers located in Serbia burning wood chips as fuel. The influence of wood chips characteristics is analyzed in relation to the flue gas losses and the thermal efficiency of the boiler. Measured useful heat output of the tested boilers was 460-2585 kW. Moisture content of the wood chips was 19.21-38.23% with a net calorific value of 10177-14139 kJ/kg and ash content of 0.84-3.59%. Thermal efficiency of the boilers was 88.78-94.06%, flue gas losses 5.84-11.13% and flue gas temperature 121.83-188.44 °C. Experimental research and analysis of the results showed that an increase in moisture content of wood chips lead to a decrease of net calorific value i.e., decrease in flue gas temperature. Moisture content of wood chips has an influence on both useful heat output and boiler thermal efficiency. The experimental results showed that for a given boiler construction, this impact is not negative. Based on regression analysis, mathematical expressions were derived for the calculation of thermal efficiency and flue gas losses. Throughout the experiments, pollutant emissions were measured, NOx, CO, and particulate matter. [ABSTRACT FROM AUTHOR]

To achieve as complete fuel burnout with as little excess air as possible, small wood log boilers (< 50 kW) use stage combustion. The first stage is often a process similar to downdraft gasification that consequently produces a flue gas laden with particulates. To prevent the build-up of solids and promote heat transfer in pipes of the convective part of these boilers, wire coils are used. The paper presents their in-situ examination together with CFD analysis. The analysis is carried out in a 460 mm long pipe, with a diameter of 82.5 mm, equipped with different wire coils for flue gas temperatures in the range between 300 °C and 150 °C. The analyzed coils are with and without a conical spring at their free end. The addition of this conical top is economical and should influence the rotation of the core flow. Proper pipe surface cleaning limited the analyzed wire coil designs to the dimensionless pitch, p/d, in the range between 0.36-0.61, dimensionless wire diameter e/d = 0.04-0.1, and pitch to wire diameter ratios p/e = 3.75-14.3, and three different angles (60⁰, 90⁰, and 120⁰) of the conical top. The goals are to find the optimal flue gas velocity for the given operating conditions, pipe, and wire coil dimensions, and to investigate the addition of the conical top on heat transfer enhancement. Several evaluation criteria are used to achieve the goals. [ABSTRACT FROM AUTHOR]

This paper analyzes the effects of coal grindability and its characteristics on the grinding capacity and power consumption for beater wheel mill during exploitation in thermal power plant TENT B in Obrenovac, Serbia. For this purpose, experiments were made on the mill, before and after its reconstruction. Experiments included the determination of grinding capacity, mill power consumption, and laboratory analysis of coal characteristics and Hardgrove grindability index (HGI). The analysis of experimental results found that the grinding capacity has a negative correlation with the ash content in coal. Moisture content in analysis sample of coal has a positive correlation with the consumption of electricity and grinding capacity. Between the grinding capacity and the value of HGI exists a negative correlation. Analysis of the influence of grindability of coal and coal characteristics on grinding capacity and energy consumption was carried out. Based on coal characteristics and values of HGI, mathematical expressions were derived for the calculation of grinding capacity and electric energy consumption. In addition, ability to predict specific power consumption of the mill on the basis of HGI values, were carried out. Specific power consumption obtained from HGI values showed good agreement with the experimentally determined specific power consumption of the mill. [ABSTRACT FROM AUTHOR]