Modelling of automated steam coal transportation and enrichment systems for efficient operation and cost reduction of thermal power plants

. This paper investigates the efficiency of fuel enrichment to reduce the costs of thermal power plants (TPPs). An objective function is formulated to define and measure the desired results. The annual costs of TPPs and additional costs associated with the use of highly abrasive coal are analyzed. The costs of enrichment, in particular, flotation enrichment, are considered. A cost analysis and a transportation problem are presented to demonstrate the results. In general, this paper provides insight into the financial implications of fuel enrichment strategies for thermal power plants

offers a comprehensive analysis of fuel enrichment strategies and their impact on reducing TPP costs.
Setting the objective function The objective function of TPP costs is given: to the delivery point [km]. The efficiency is based on complete fuel combustion [2].
Since coal was considered the main fuel, in addition to the main components, it was also necessary to take into account non-combustible ash-forming additives. Ash pollutes the environment and is sintered into slag, which makes it difficult to burn coal, and also has an abrasive destructive effect on the furnace tubes, superheater, economizer, etc. Depending on the type and conditions of coal mining, the amount of minerals in it varies. For example, the ash content of hard coal is 14-35%, and for anthracite, it is 5-20%.
At this stage, it is important to investigate to what extent an increase in ash content affects fuel consumption at power plants. When considering the hypothetical scenario represented by formula (1), it is necessary to provide a new formulation that will facilitate the determination of the daily demand of the power plant.
The formula (1) for daily fuel consumption, taking into account ash content, is as follows: Additional costs are caused by the wear and tear of TPP equipment Abrasive wear is characterized by the continuous cutting action of large ash particles with a sufficient hardness on the surface of heat exchanger tubes. This erosion process leads to a gradual decrease in the wall thickness of the pipe in the affected area. In addition, particles of unburned fuel, especially in anthracite coal, cause wear and tear of dust collection systems, and the abrasiveness of ash leads to degradation of convective heating surfaces in the boiler, such as the water economizer (WEC) and superheater (SH). Therefore, the annual costs associated with the repair of the main and auxiliary equipment of the boiler, taking into account the abrasive properties of both coal and ash, include the cost of repairing dust collection systems and convective heating surfaces of the boiler.
It is important to note that these costs are part of the total annual costs of a thermal power plant (TPP) and depend on regular equipment replacement: C TPP = U eq.rep. +U ash collectors rep. +U ash removal. +U ash collector rep. +U storage 365 . ( These costs will remain unchanged, except for the cost of repairing steam preheater equipment, furnace screens, and festoon [1].
These costs were included in the objective function: The following formula is used to calculate the operating No 159 The coefficient of the relative content of SiO 2 in the transported material is determined as follows: where 2 -the percentage of quartz content in the material: where ℎ -percentage content of other ash minerals in the transported material.
Therefore, the costs of TPPs will also be a function of this indicator.
C TPP = C TPP (T(n SiO 2 )) (14) The efficiency of ash collectors is characterized by the following indicators: where h -level of ash captured in ash traps; G in , G out -amount of ash at the inlet and outlet of the ash collector per unit of time; с in , c out -ash concentration at the inlet and outlet of the ash collector [5].
To calculate the volumetric flow rate of gas resulting from the reaction, the chemical formula of coal and air in the form of an air-coal mixture is given.
-coal fuel, where 2 + 2 ⋅ 3 = , and 2 = 2 , while carbon and oxygen are involved in the reaction (for a simplified air formula, we use the ratio 20%/80% oxygen/nitrogen Fuel enrichment It is necessary to check the feasibility of using flotation fuel enrichment directly at TPPs. The mechanical flotation machine MFU-25 was used as a prototype [3]. According to the equipment specifications, the concentrate extraction is I conc = 87,6% (hence the tailings extraction is 12.4%). The recovery of valuable components into the concentrate during mineral processing ranges from 60 to 95% and above. For example, we took the recovery of =95% and calculated the mass of concentrate, tailings mass, and variable ash content per 100 tons of coal at the initial Ad=30%. (17)

Inclusion of TPP fuel enrichment costs in the objective function
The purchase of coal depends on the cleaning procedure and can be carried out in the following ways: Below (Table 1), we present a study of how the dynamics of coal purchases change with increasing ash content and subsequent cleaning. Table 1 Changing the volume of fuel purchases depending on the value of the Ad Where Ad is ash content, %; d МFU -a fraction of the initial fuel mass after fuel enrichment, %; -ash content after enrichment step, %; k МFU -number of enrichment iterations; M МFU -is the final mass of fuel after enrichment, tons; Q МFU -is the amount of energy consumed for fuel enrichment, kWh; B МFU -should be procured with the calculation of the loss of fuel during enrichment, tons; K МFU -the number of MFU-25s for round-the-clock operation; P МFU -the cost of electricity consumed, UAH.
Examples Transportation problem. To solve the problem, three TPPs were taken: A1, A2, and A3, with Zaporizhzhia TPP, Vuhlehirsk TPP, and Burshtyn TPP as examples. These TPPs operate on coal. Since the specific heating value of coal is taken as 31 MJ/kg, the fuel consumption will be as follows. The Ukrainian mines were considered as a prototype of suppliers in the transportation problem (information was taken from statistics for 2008 and 2009). The option of a fuel shortage in the domestic market was also considered. In this case, the possibility of importing coal from South Africa was taken into account. The average cost per tonne for 2020 on CIF port of Odesa was taken as the price, which was equal to UAH 2'724.96. The average distances from the ports of the Odesa region to TPPs A 1 , A 2 , and A 3 are 555 km, 845 km and 764 km, respectively.
The transportation problem was solved by taking into It was assumed that coal from South Africa was purchased for the supply, which turned out to be of poor quality with a high ash content of 50%. Consequently, twice as much coal would be needed to be delivered via this route. Given the high coal consumption due to high ash content, TPP A 3 lacks 4.06 thousand tons per day. By using source B 2 , it turned out that the coal from this mine also has a high Ad=30%. Of the 8.125 thousand tons produced daily, only 5.6875 thousand tons are useful fuel, excluding ash impurities. Due to the shortage of 4.06233 thousand tons of ash-free fuel, the actual carbon demand, including ash content, will be 5.80333 thousand tons. It is worth noting that neither the purchase price nor the transportation costs are affected in this scenario, as the actual weight remains unchanged.
Three MFU-25 mechanical flotation machines were installed, and the recovery procedure was carried out three times. At each stage of cleaning, the concentrate will be 67.2% of the initial mass, and the tailings will be 32.8%. In the above problem, given the initial ash content of 30% for 100 tons of coal, the cleaning process will produce a concentrate with an ash content of 10.8% for 67.2 tons. The production capacity of the MFP-25 is 67.2 tons of enriched fuel per hour, resulting in a daily output of 1'612.8 tons from 2,400 tons of supplied coal.
With a capacity of 30 kW per unit, the enrichment equipment has a total capacity of 90 kW, consuming 2'160 kWh per day.
The electricity tariff for thermal power plants in Ukraine is UAH 0.67/kWh. Thus, the cost of processing 2'400 tons of coal per day, based on the average electricity cost of 173.6 kopecks per kWh, is UAH 3'749.76.
With a capacity of 30 kW per unit, the enrichment equipment has a total capacity of 90 kW, consuming 2'160 kWh per day.
The electricity tariff for thermal power plants in Ukraine is UAH 0.67/kWh. Thus, the cost of processing 2'400 tons of coal per day, based on the average electricity cost of 173.6 kopecks per kWh, is UAH 3'749.76.
A comparison of objective functions (15)  transportation problem shows that fuel enrichment to an ash content of 30% is more profitable than relying on regular repairs and replacement of equipment at TPPs. In addition, taking into account the operation of the K-300 turbine for 10 years, the savings amount to an average of more than UAH 25.5 million.
As a result, the ash content has decreased from 30% to 24.1%, and the total weight of fuel has decreased from 100 tons to 87.6 tons. Analysis of the optimal plan (Table 4). 1) From the 1st mine, all the cargo should be sent to the 3rd TPP.
2) From the 2nd mine, all the cargo must be sent to the 3rd TPP.
3) From the (2*) port warehouse, all the cargo must be sent to the 3rd TPP. 4) From the 3rd mine, the cargo must be sent to the 2nd TPP (1.073928417 thousand tons), to the 3rd TPP (1.660318158 thousand tons) 5) From the 4th mine, the entire cargo must be sent to the 2nd TPP.
For the purposes of the analysis, we will assume that the average ash content of Donbas coal is 15-20%. Assuming that Ad is 20%, and quartz (SiO 2 ) makes up 60% of the ash content, we have Ad = n SiO2 + n rock = 12% + 8% = 20%.
Using the example of TPP A1 turbines: two K-300-240-2 and two K-325-23.5 turbines with a total electric capacity of 317 MW and 337.3 MW, respectively, the total capacity of the four turbines will be W = 1308.6 MW. Assuming that the efficiency of the TPP is 40%, the consumption of "ideal coal fuel" for TPP A1 will be 379.91 tons per hour. Consequently, the electricity generated per day, assuming 40% efficiency and combustion of "ideal" fuel, will be q = W * 40% * 24 = 12`565.56 MWh.
For Donetsk G-grade coal, the fuel consumption is B = 25.08 tons/d, where 80% = 31.3545 tons/d. At Ad = 20%, consisting of 12% abrasive material and 8% rock, the ash content is compensated by increasing the volume of fuel burned, thereby maintaining the same turbine power, resulting in q = 12`565.56 MWh/day. The abrasive wear per ton of dry The ash removal rate of 31.23% was obtained. When burning coal with an ash content of 20%, of which 12% is abrasive, the boiler tubes wear out in 6.2 years (with a normal service life of 10 years).
Conclusions. This study addresses the issue of ash impurities and their abrasive impact on thermal power plant (TPP) equipment. By considering the financial aspects of equipment failures, including repair and replacement costs, as well as additional fuel purchases, the importance of fuel enrichment to reduce TPP costs was emphasized. The analysis showed that, despite the initial costs associated with enrichment, the extended equipment life as a result of reduced wear and tear outweighs the investment.
In addition, the analysis of the optimal plan for the transportation problem provided valuable information on the distribution of cargo between different mines and thermal power plants. The identified optimal plan ensures efficient use of resources and transportation, contributing to cost optimization in the overall supply chain. By implementing fuel enrichment strategies and optimizing freight distribution, thermal power plants can achieve significant cost savings, extend equipment life and improve operational efficiency. These findings contribute to ongoing efforts in the energy sector to improve the financial sustainability and reliability of thermal power plants.
It is important to keep in mind that this study focused primarily on the financial perspective and did not take into account operational constraints related to scheduled maintenance and grid capacity. Traditionally, TPPs do not have the laboratory infrastructure to test every batch of fuel, but periodic deviations in fuel quality from documented specifications require methods for timely detection.
Future research could explore methods for accurately determining the need for fuel enrichment given periodic fluctuations in fuel quality.