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Currently, there is a scarcity of studies exploring the safe operating parameters for coal-fired power units at loads below 30%. To accurately understand the operating characteristics of coal-fired units under low load conditions, and to provide a design basis for flexibility modifications, a simulation model coupled with boiler and turbine was established, which includes the flue gas and air system, steam and water system, steam turbine, and steam extraction heat recovery system, and the iterative calculation strategy for low load conditions was proposed. The simulation calculation was performed on a 350 MW supercritical coal-fired unit, with the model results showing a high degree of alignment with the unit's design and operational parameters. Under the condition of 269MW, the maximum calculation error between the model's predicted exit flue gas temperature of the air preheater and the actual operational results was 8.84%. This discrepancy was due to a sudden increase in the operating flue gas temperature, which may be associated with a blockage in the air preheater. And the simulation results under low load conditions indicate that when the unit load is below 20%, the furnace total airflow is controlled to no less than 30% of the airflow at Maximum Continuous Rating (BMCR) and the minimum feedwater flow rate can be reduced to 20% of that in Turbine Heat Acceptance (THA) load, and the unit switches to wet state operation around 20% load. As the unit load decreases, the coal consumption rate for power generation and steam turbine heat consumption rate both increase significantly. The coal consumption rate for power generation at 30% load is increased by 13.3% compared to BMCR load, and it is increased by 32.5% at 15% load which is operated in wet state. Under low load conditions, the coal consumption rate of the unit can be reduced by decreasing the oxygen content in the flue gas, reducing the minimum feedwater flow rate, and implementing boiler water recirculation. [ABSTRACT FROM AUTHOR]

This paper presents the results of the first stage of the project, aimed at the assessment of the applicability of the new apparatus for disintegration of excess waste activated sludge. It was documented that the analysed device allows for disintegration of sewage sludge with an efficiency comparable to that obtained in other devices dedicated for mechanical disintegration of sewage sludge described in the literature. The disintegration process at energy density in a range of 35–210 kJ/l resulted in the release from activated sludge flocs of 219–515 mg SCOD/l for 35 kJ/l to 2138–4884 mg SCOD/l for 210 kJ/l.

The paper presents the influence of selected components parameters on the performance of supercritical carbon dioxide power unit. For this analysis mathematical model of supercritical recompression Brayton cycle was created. The analysis took into consideration changes in the net cycle power and efficiency for different compressor inlet temperatures. The results were obtained for a fixed minimum pressure of 7.4 MPa and fixed recompression split ratio. The studies conducted in this paper included also consideration of sensitivity of the cycle efficiency to a change in recuperators heat transfer area. In order to determine how each recuperator influences the cycle performance, an analysis of efficiency dependence on the recuperators area was made. Another parameters that were investigated are to a change in turbine and compressors isentropic efficiency and their influence on the cycle efficiency. In the reference cycle, isentropic efficiencies were set up as 88% for both the main and recompression compressor, and 90% for the turbine. Since isentropic efficiency is a sort of measure of broadly defined quality of a turbine or compressor, including airfoil shape, sealing, etc., it may be a significant cost factor that should be considered during cycle design. Therefore, a sensitivity analysis of cycle efficiency to both compressors and turbine isentropic efficiencies was conducted.

The paper aims to compare the models of working fluids against experimental data for carbon dioxide close to its critical conditions. Fortunately, most of the work is already done and published where the authors compared the models based on the equation of the state (EoS). There are a few other models which were not investigated, thus we would like to add a few new results here and focus only on near-critical properties where the biggest deviation between experimental and calculated properties can be observed. The area of interest was pressure range of 7.39 – 20 MPa and temperature range of 304-340 K just above fluid critical point (7.39 MPa, 304.25 K). Model validation was performed for density and heat capacity as one of the most important parameters in preliminary cycle analysis.

This paper presents models of three elements: heat exchanger, compressor and expander dedicated to supercritical CO2 cycles (Brayton). The models are built using Ebsilon software and validated against experimental data from available literature. Radial turbomachinery and thin plate heat exchangers were used to meet the demands of the relatively compact design of the S-CO2 cycle elements. It seems that there are no general relationships for the turbomachinery and real characteristics need to be used for constructing the models. [ABSTRACT FROM AUTHOR]

This paper focuses on and discusses the concept of hot windbox repowering in an existing steam cycle power plant. Using commercial software, for that process based on the fraction of oxygen in exhaust gases, nine different models of gas turbines were tested in power plant model with a fossil fuel boiler. Then thermodynamic analysis of the power plant model before and after hot windbox repowering was conducted. This work seeks to select the best fit gas turbine for hot windbox repowering for a 200 MW fossil fuel power plant and to gain a deeper understanding of the effect of hot windbox repowering. To this end nine models of gas turbines with different net electrical power (from 50 to 125 MW) were tested and General Electric production GE Energy Oil&Gas MS9001E SC (GTW 2009) 123 MW gas turbine was selected as the most suitable for the model of the power plant and, after repowering, the total power of the power plant rose to 398 MW. Calculations were performed in 2 stages: 1) calculation and comparison of the thermodynamic parameters as well as carbon dioxide emissions of power plant model before and after repowering with nine different gas turbines, 2) calculation of thermodynamic parameters of the combined cycle power plant model before and after repowering in values 100%, 90%, 80%, 70%, 60% of fossil fuel boiler heat loads. [ABSTRACT FROM AUTHOR]

The paper presents a variant analysis of the structures of closed gas turbines using supercritical carbon dioxide (super-CO2) as a working fluid. Several configurations covered in the available literature were collected, commented on and compared. The parameters of the cycles, such as operating temperature and heat supply are noted and commented on. There are three main configurations considered in the available literature: the precompression cycle, partial cooling cycle, and recompression cycle. [ABSTRACT FROM AUTHOR]

The paper presents the concept of using hot exhaust gases from gas turbines with different power output to heat up feedwater in a supercritical power plant unit. The gas turbine is connected to the system, bypassing a high pressure regenerative heat exchanger. The benefits of this solution are discussed and the factors to be taken into account are listed. The criteria to be met by the gas turbine to ensure safe and optimal connection to the steam system are discussed. A reference unit model with 800 MW electric power (an existing super-critical power unit in Poland-Belchatow II) was created and presented in a previous paper by the same authors. This model was later supplemented with a gas turbine (three different models with different levels of power production are taken into consideration). The system with a gas turbine enjoys greater power and efficiency over the steam cycle alone. The power increase is due to the extra power generated by the gas turbine and the higher output of the steam system caused by increasing the steam flow through the turbine (closed extraction to the "bypassed" high-pressure heat exchanger). System power is changed linearly with the steam flow and reaches the nominal point 40..50% higher than without an added gas turbine (depending on gas turbine power and efficiency). The efficiency characteristics of the whole system are flatter, with higher values. [ABSTRACT FROM AUTHOR]

This article presents the off-design operation of a 900 MW-class steam turbine cycle upgraded with utilization of lowtemperature waste heat taken from boiler flue gas. The low-temperature heat contributes to increasing the efficiency of power plants without introducing many complex changes to the whole system. The base for investigations was a power unit operating in off-design conditions and supplied with steam from a BB-2400 boiler. Modifications to the model were made using commercially available software and by applying the Stodola equation and the SCC method. Calculations for off-design conditions show that, after making some modifications to the system, both heat and electricity generation could be increased through the addition of a low-temperature heat exchanger. [ABSTRACT FROM AUTHOR]