Subcritical Coal-fired Power Plant Research Articles

Thermodynamic modeling and analysis of a Carnot battery system integrating calcium looping thermochemical energy storage with coal-fired power plant

Long-term energy storage and carbon capture technologies are pivotal in managing renewable energy surpluses and achieving carbon neutrality. This paper proposes a Carnot battery system integrating calcium-looping thermochemical energy storage with a coal-fired power plant. The system utilizes excess electricity from the grid for energy input, facilitating long-term energy storage, achieving carbon capture, and reducing coal consumption in the power plant. An optimization framework is developed, incorporating component thermodynamic models and optimization algorithms, to maximize the coal savings in plants and energy efficiencies of the Carnot battery system. During the energy release process, the carbonator partially replaces the reheat load of the boiler, necessitating retrofitting of the boiler’s heating surface to ensure normal operation. The base system demonstrates a CO2 capture capacity of 3.23 MJ/kg and a reduction in coal consumption by 7.07 %. The round-trip efficiency and comprehensive efficiency of the base system are 36.93 % and 37.91 %, respectively. The relatively low energy efficiency is primarily due to the deactivation of circulating adsorbents and the limited efficiency of the subcritical coal-fired power plant. By incorporating an additional recarbonation step to mitigate adsorbent deactivation, the system’s comprehensive efficiency is improved to 42.20 %. Further improvements in system efficiency can be achieved by using modified adsorbents with high cycling stability instead of natural limestone and by coupling the system with more efficient ultra-supercritical units instead of the investigated subcritical units. This study offers valuable insights into the development of long-term energy storage solutions and multifunctional Carnot battery technology.

Sustainable energy storage solutions for coal-fired power plants: A comparative study on the integration of liquid air energy storage and hydrogen energy storage systems

With the majority of the world's energy demand still reliant on fossil fuels, particularly coal, mitigating the substantial carbon dioxide (CO2) emissions from coal-fired power plants is imperative for achieving a net-zero carbon future. Energy storage technologies offer a viable solution to provide better flexibility against load fluctuations and reduce the carbon footprint of coal-fired power plants by minimizing exergy losses, thereby achieving better energy efficiency. This work focuses on developing two such energy storage technologies: Liquid Air Energy Storage (LAES) and Hydrogen Energy Storage (HES), and their integration strategies with a sub-critical coal-fired power plant. The performance of the integrated systems is analyzed based on key parameters like energy storage capacity, net unit power output during charging and discharging, round-trip efficiencies, and net unit efficiencies at different operating load conditions of the plant. Our results show that during the charging cycles, by increasing the air flow rate in LAES and the hydrogen production rate in HES, the net unit efficiency of the integrated plant decreases by 3–10% at different load conditions, while the energy-based round-trip efficiency increases with increasing liquid air and hydrogen flow rates during the discharge cycles. For the HES system, utilization of the produced hydrogen in the fuel cells gives 40–50% better roundtrip efficiencies than co-firing hydrogen in the boiler at full and minimum load and it increases with increasing hydrogen flow rates. While HES has shown a better overall net unit efficiency (41.5%, in fuel cell scenario) of the integrated unit than the LAES system (40%) for the base case operation, LAES shows superior round-trip efficiencies when operated at higher liquid air discharge flow rates (>80 kg/s). The results provide insights into the system modeling of LAES and HES integrated with a sub-critical coal power plant, contributing to the advancement of sustainable energy storage solutions.

Mercury in coal from south eastern coalfield and mercury partitioning at sub-critical coal-fired power plant

Mercury in coal from south eastern coalfield and mercury partitioning at sub-critical coal-fired power plant

Model predictive control of power plant cycling using Industry 4.0 infrastructure

This work involves the Industry 4.0 infrastructure developed at West Virginia University (WVU) for process systems applications. This infrastructure emulates an interconnected environment, enabling communication and data sharing among different components for use in academic and industrial settings. The current infrastructure encompasses a power plant model interacting with online load demand, distributed control systems, and data analytics components. The developed model of a sub-critical coal-fired power plant is employed to evaluate classical and advanced control strategies using this infrastructure under different operating conditions. Specifically, the control strategies evaluated include classical proportional–integral–derivative (PID) and advanced model predictive control (MPC) structures, focusing on the dynamic matrix control (DMC) approach with an in-house modified sequential quadratic programming (SQP) solver. The MPC approach is developed and simulated in closed loop to address setpoint tracking and load-following scenarios under power plant cycling conditions. In this infrastructure, the PI System centralizes all the information received from the power plant model and the online power demand and sends the control actions calculated by the MPC back to the power plant model for implementation. Results of the implementation of these control strategies are discussed focusing on power plant operating regions associated with cycling.

Effects of integration mode of the molten salt heat storage system and its hot storage temperature on the flexibility of a subcritical coal-fired power plant

To match the fast-developing renewable energy, it is necessary to improve the flexibility of the existing coal-fired power plants to maintain power grid stability, and integrating heat storage systems to coal-fired power plants is an easy and prospective solution. Four integration modes were proposed by extracting the main or reheated steam to store energy and looping steam back to the low-pressure turbine or condenser. Peak shaving performances under various cases were evaluated based on the first and second laws of thermodynamics. Simulation results showed that the mode of extracting reheated steam and looping steam back to the low-pressure turbine (mode RtLP) is optimal for economy, with the highest round-trip efficiency of 36.25 % and a low discharging time of 0.11 h. From the point of flexibility, discharging time under the mode of extracting main steam and looping steam back to the condenser (mode MtCON) increases to 0.48 h, over 4 times of the one achieved under mode RtLP, while the equivalent round-trip efficiency under mode MtCON is nearly 10 % lower. The minimum power load is achieved under mode MtCON by decreasing power load from 30 % to 14.23 %. Furthermore, peak shaving performance of the integrated system under mode MtCON is enhanced by reducing the hot storage temperature of molten salt. As the hot storage temperature declines from 480 °C to the critical one of 309 °C, the discharging time and round-trip efficiency increase by nearly 2 times and 1.7 times, respectively. This work is expected to provide meaningful guidance for the efficient integration between coal-fired power plant and molten salt heat storage system to achieve the targeted benefits.

Emission Characteristics of Gaseous and Particulate Mercury from a Subcritical Power Plant Co-Firing Coal and Sludge

Field tests were carried out in a subcritical coal-fired power plant co-firing coal and sludge to analyze the emission characteristics of gaseous and particulate mercury. EPA30B method was applied to determine the mercury speciation in different positions of the flue gas, including the inlet and outlet of the selective catalytic reduction DeNOX system (SCR) and electrostatic precipitator (ESP); PM10 (with aerodynamic diameter ≤10 μm) was collected using a cyclone and a Dekati low-pressure impactor (DLPI). Before accessing the SCR, Hg in flue gas from both single coal combustion and co-firing mainly existed as Hg0; the higher content of Hg in sludge than coal led to the much higher Hg0 concentration for co-firing. The total Hg concentration at not only the SCR inlet and outlet but also the ESP inlet did not change obviously. However, Hgp concentration at the ESP inlet increased significantly, accompanied by a decrease in Hg0. The transformation of Hg0 to Hgp appeared to be more distinct for co-firing. The higher HCl concentration of co-firing derived from the much higher Cl content of sludge than coal, and together with the higher ash content of sludge containing more minerals capable of adsorbing Hg0, may lead to the greater transformation from Hg0 to Hg2+ and Hgp when co-firing. After the ESP disposal, nearly all Hgp was removed along with PM10, and most Hg0 was also removed. The removal efficiency of mercury after the ESP was 92.12% under coal firing and 92.83% under co-firing conditions, respectively. The slightly higher mercury removal efficiency under co-firing should be attributed to the complete removal of the higher concentration of Hgp.

Research on influence of steam extraction parameters and operation load on operational flexibility of coal-fired power plant

The operational flexibility of coal-fired power plant is very important for the integration of large-scale renewable energy to the grid. In order to increase the operational flexibility of coal-fired power plant, a 600 MW subcritical coal-fired power plant was selected as research example to analyze the influence of steam extraction parameters and operation load by simulation. A novel main steam extraction system was proposed to adjust the power output under the low load period. The sensible and latent heat of the extracted steam was stored in molten salts and phase change materials, respectively, during the load reduction process. While the stored heat was reused again to heat the feed water and condensate water during the load raising process. The 50% rated load (300.03 MW) of the unit was used as the research benchmark to further adjust the load. The results show that the proposed steam extraction system can improve the operational flexibility of coal-fired power plant. The power output can be reduced to 204.51 MW from 300.03 MW when the main steam extraction mass flow rate is 250 t/h during the load reduction process. The sensible heat storage power factor and the operation load of the unit can affect the power output increment of coal-fired power plant during the load raising process. Under the condition of the maximal sensible heat storage power factor is 0.2462, the power output can be increased to 325.47 MW from 300.03 MW when the bypassed feed water mass flow rate of 251 t/h was heated by the stored heat during the load raising process. Using such operation model, the coal-fired power plant can achieve the maximum deep peak shaving time of 8.4 h/d, and its equivalent thermal efficiency is increased by 2.28%. With the same stored thermal energy to heat the bypassed feed water of 308.65 t/h, the power output can be increased to 394.2 MW from 360.07 MW (60% rated load) at the same sensible heat storage power factor of 0.2462 during the load raising process, and the coal-fired power plant can achieve the maximum deep peak shaving time of 9.86 h/d with its equivalent thermal efficiency increase of 2.55%. The results show that the proposed steam extraction method can make the unit operate in the lowest stable load and provide a wider renewable energy access space below the minimum stable load. The research provides a theoretical guidance for the flexibility design of coal-fired power plant, especially suitable for the large-scale renewable energy access to the grid in China.

Off-Design Dynamic Performance Analysis of a Solar Aided Coal-Fired Power Plant

Coal consumption and CO2 emissions are the major concerns of the 21st century. Solar aided (coal-fired) power generation (SAPG) is paid more and more attention globally, due to the lesser coal rate and initial cost than the original coal-fired power plant and CSP technology respectively. In this paper, the off-design dynamic performance simulation model of a solar aided coal-fired power plant is established. A 330 MW subcritical coal-fired power plant is taken as a case study. On a typical day, three various collector area solar fields are integrated into the coal-fired power plant. By introducing the solar heat, the variations of system performances are analyzed at design load, 75% load, and 50% load. Analyzed parameters with the change of DNI include the thermal oil mass flow rate, the mass flow rate of feed water heated by the solar energy, steam extraction mass flow rate, coal consumption, and the plant thermal efficiency. The research results show that, as DNI increases over a day, the coal saving rate will also increase, the maximum coal saving rate reaches up to 5%, and plant thermal efficiency reaches 40%. It is analyzed that the SAPG system gives the best performance at a lower load and a large aperture area.

Flue Gas Desulfurizer mass and energy balance in 300 MW class subcritical Coal-Fired Power Plant for retrofit application

Based on the recent implementation of the Ministry of Life and Environment (MOLE) Regulation No. P.15/MENLHK/SETJEN/KUM.1/4/2019 regarding Power Plant Flue Gas Emission, which supersedes MOLE Regulation No. 21 year 2008, there is a reduction of maximum Sulfur Dioxide (SO2) concentration in flue gas emission of Coal-Fired Power Plant (CFPP), from 750 mg/Nm3 @7% O2 content (dry basis), to 550 mg/Nm3 in existing CFPP, and 200 mg/Nm3 in CFPP constructed after the implementation of the regulation. Thus, arises the necessity for the consumption of Coal with lower Sulfur (S) content and/or retrofitting of Flue Gas Desulfurizer System (FGD) system in CFPP, not yet equipped with the FGD system. One of the applicable systems for retrofit is Sea Water FGD (SWFGD). This paper explores the energy and mass balance aspect of the SWFGD system for application in 300 MW subcritical reheated steam CFPP. Operational aspect is the increase of allowable sulfur content in consumed coal up to 1,162%, when the plant is retrofitted with SWFGD, and an increase in condenser cooling water of 0.6 °C due to SWFGD Absorber interface.

A study on the Performance and Reliability Effect of Low-Rank Coal to the Steam Power Plant

The main purpose of utilizing lignite coal in Indonesia is to decrease fuel costs in electricity and Greenhouse Gas emissions. Still, on the other hand, it will affect the reliability and plant performance. This paper attempts to evaluate 340 MW subcritical coal-fired power plant’s performance and reliability by comparing the impact of coal utilization below boiler design toward the baseline and identifying the significant factors that lead to plant efficiency and reliability. Performance tests conducted using the standard procedures at four segments of load, i.e., 50%, 65%, 80%, and 95%, with two scenarios: (1) use 3500 kcal/kg of coal calorific value, and (2) use 4500 kcal/kg of coal as the baseline. There are no adjustments during the test and all measurements, including pressure, temperature, flow, bomb calorimeter, etc., already calibrated. The results show that during 3500 kcal/kWh, 100% of the load is unable to reach. Plant performance becomes higher up to 2930 kcal/kWh, boiler efficiency decrease to 80.4%, and fans current increase to maximum capacity. The study’s conclusion suggests that the utilization of LRC must be considering the energy amount to the boiler.

A Study of Reducing Waste Heat Rejected By Condenser Using Thermoelectric Heat Pumps to Decrease Net Plant Heat Rate of Coal Fired Power Plant

Paiton 1-2 subcritical coal-fired power plant applied coal switching program in order to can compete at Jawa-Bali electrical system. The calorific value of coal consumed is switched from 5200 kcal/kg to 4500 kcal/kg. As the result, it increases the net plant heat rate (NPHR) as well as the coal flow and produce more CO2 emissions. Increasing final feed water temperature can reduce NPHR because less heat needed to produce steam. One of promising method to increase feed water temperature is reusing wasted energy being rejected to environment through condenser. There is opportunity to reuse this waste heat by use of thermoelectric heat pumps (THPs). THPs convert electrical energy into thermal energy using Peltier effect. It can capture the heat released by condensation process and reused for increasing the feed water temperature, which can increase the cycle efficiency. Furthermore, it will reduce coal flow, decrease NPHR and aid the reduction of CO2 emissions. To maximize the energy recovery, a number of heat pumps can be used in series. This paper focused on finding the optimum number of heat pumps array. The expected feed water temperature rise gained from THPs arrangement is 19.81°C and potentially will contribute to 0.66% reduction on NPHR.

Data analytics for leak detection in a subcritical boiler

For decades, boiler leaks have been the leading cause of forced outages in the coal-fired unit. The leak occurrences are currently escalating since the existing plants must satisfy faster-ramping rates to support grid operation. Data analytics including Principal Component Analysis (PCA), Canonical Variate, and Fisher Discriminant Analysis (CV-FDA) were combined for detecting and characterizing the leak in a commercial 650 MW subcritical coal-fired power plant. The combined approach was shown to be highly effective in the fault investigation that would not have been easily achieved by an individual technique. The variability in both training and validation datasets was first evaluated using PCA. Then, the CV-FDA was employed to discriminate among faults, and to categorize the processed data into two main groups: no-leak (0) and leak (1), providing the timeframe and location of the leak occurrence. About 8,014 observations from 81 process variables were initially included in the calculation, while the variable count was reduced to 4 with less than 1% misclassification rate in total observations. Finally, the leak was isolated in the waterwall section. Thus, the outcome of this research may provide early detection and isolation of faulty operations in the coal-fired power plant that involves a considerable number of process variables.

Exergy and exergo-environmental analysis of a 660 MW supercritical coal-fired power plant

This paper presents the exergy and exergo-environmental analysis of the 660 MW supercritical coal-fired unit situated in western India. The study is based upon the SPECO approach, which is followed in the case of exergoeconomic analysis. The proposed research includes evaluating values of exergy of each stream, using F and P principal to find out exergy of fuel, the product of each component, and its exegetic efficiency. It further includes allocation of Eco-indicator 99 assessment grading values to perform life cycle assessment of each component, solving simultaneous equations by suitable solver formed from the environmental impact of components to calculate the exergo-environmental factor of each stream. The exergy efficiency obtained for the supercritical unit is 35.54%. The effect of variation of exergetic efficiency with an inlet pressure of high-pressure turbine for major components is studied. The major components such as steam generator, high-pressure turbine, intermediate-pressure turbine, low-pressure turbine, condensate extraction pump, and boiler feed pump exhibit higher exergetic efficiency at 247 bar. An increase in environmental impact in the exergy flows has been identified for components with having heat, work or fuel at the inlet. The cooling water used in condenser and flues gases exhausted from the supercritical power plant represent the environmental impact rate per unit electricity generated of 2.89 and 3.689 mPts kWh−1. The electricity generated had an environmental impact rate of 39.71 mPts kWh−1. The environmental impact per unit of electricity generated for 660 MW supercritical power plant is evaluated as 46.29 mPts kWh−1. The result obtained from semi-empirical model for environmental impact per unit of electricity is validated by comparing with subcritical and ultra-critical coal-fired power plant. The supercritical coal-fired power plant is proved to be better technology as compared with subcritical coal-fired power plant. The exergo-environmental variable for the steam generator offers high potential to reduce environmental impact by introducing an exhaust gas treatment unit.

Modeling and Energy Efficiency Analysis of Thermal Power Plant with High Temperature Thermal Energy Storage (HTTES)

This paper presents the recent research on the study of the strategies for the flexible operation of the thermal power plant to meet the requirement of load balance. The study aimed to investigate the feasibility of bringing the High Temperature Thermal Energy Storage (HTTES) to the thermal power plant steam-water cycle, to identify the suitable HTTES in the cold (hot) section of the reheating pipeline and to test the efficiency of the HTTES integration to increase the flexibility of peak shaving and energy efficiency via thermal power plant with HTTTES modelling and simulation. Thermoflex was adopted to perform the simulation and a 300 MW subcritical coal-fired power plant model was implemented onto the software platform. The simulation results show that it is feasible to extract steam from the steam turbine to charge the HTTES, and to discharge the stored thermal energy back to the power generation process, and to analyse the improved capability of the plant flexible operation with HTTES. Then the study was extended to analyse the effect of thermal energy temperature, the opening of the regulating valve, and the pipeline pressure loss aspects on thermal efficiency of the whole plant. The study is beneficial to achieve more economic operation of the thermal power plant with HTTES integration. It is concluded that the introduction of the HTTES can improve the consumption of wind power, and these ideas and methods for solving the energy consumption of the renewable energy and reducing the peak energy consumption are provided.

A novel approach to improving load flexibility of coal-fired power plant by integrating high temperature thermal energy storage through additional thermodynamic cycle

This work presents a novel approach to improving the load flexibility of coal-fired power plant by integrating high temperature thermal energy storage (HTTES) through additional thermodynamic cycle. It aims to investigate the feasibility of introducing an HTTES-aided additional cycle into the steam-water cycle of conventional coal-fired power plant and to test how a high round-trip efficiency can be achieved with the HTTES integration. The thermal system and operation mode of an HTTES-aided coal-fired power plant were described. The performance evaluation model was built and its performance was discussed based on a 600 MW subcritical coal-fired power plant model. The results show that the proposed approach is feasible to improve the load flexibility of the conventional coal-fired power plant. An additional net power can be obtained while the original unit works at its rated condition. The initial steam pressure of the additional cycle is the determining factor for the round-trip efficiency and a round-trip efficiency of 44.18% can be obtained. This work is expected to provide a detailed reference on the use of HTTES system to improve the load flexibility of coal-fired power plants and further to relieve the serious problem of the curtailment for fluctuating renewable power generation in China.

Hybrid membrane process for post-combustion CO2 capture from coal-fired power plant

Post-combustion CO2 capture is a promising way to reduce CO2 emissions at the coal-fired power plants. Even though several studies have been conducted regarding a wide variety of CO2 capture techniques, gas separation membrane process has shown potential as an energy-efficient, low-cost CO2 capture option. However, most of the previous researches focused only on CO2-selective membrane, and there's limited literature about the application of N2-selective membrane.In this study, both CO2-selective and N2-selective membranes are considered and relevant issues regarding the CO2-selective membrane, such as pressure ratio, attainability, and multistage configuration, are studied and extended to the N2-selective membrane. Polaris® membrane is served as a typical CO2-selective membrane; on the other hand, membrane properties of N2-selective membrane with selectivity up to 200 are considered. Hybrid membrane process applying both CO2- and N2-selective membranes for capturing at least 90% CO2 from a typical 550 MW subcritical coal-fired power plant is designed, simulated and analyzed using Aspen Plus® simulation software. The optimization and economic analysis are also applied with the cost factor defined in this work, which is a comprehensive index to evaluate the applicability of the membrane, including permeance, membrane lifetime and membrane price. The results reveal the relationship between the optimal design variables and membrane properties. Moreover, the selectivity-limited region is identified, which leads to two different dominant strategies for the cost reduction in a different region, either by the increase in selectivity or the reduction of the cost factor.

Dynamic Simulation and Plant-Wide Control for Flexible Operation of Subcritical Coal-Fired Power Plant Integrated with Solvent-Based Post-Combustion Co2 Capture

Dynamic Simulation and Plant-Wide Control for Flexible Operation of Subcritical Coal-Fired Power Plant Integrated with Solvent-Based Post-Combustion Co2 Capture

Energy and Exergy Analysis of a Coal Fired Power Plant

In this paper, energy and exergy analysis has been conducted on a subcritical coal fired power plant of Wisconsin Power and Light Company, USA to investigate the steam cycle energy and exergy efficiency. The cycle is analyzed by developing a mathematical model using its operating and design parameters. The analysis is performed using EES (Engineering Equation Solver). The energy analysis shows that major share of energy loss occurs in condenser i.e. 72% of total cycle energy loss, whereas, exergy analysis shows that 83.09% total exergy destruction of cycle occurs in boiler.Furthermore, the simulation results are compared with actual with an absolute error of 3.1%. Additionally, the parametric study is performed to examine the effects of various operating parameters such as main steam pressure and temperature, condenser pressure, terminal and drain cooler temperature difference on net power output, energy andexergy efficiency of cycle. The parametric study shows that the plant has maximum energy and exergy efficiencies at steam pressure of 2500psi, condenser pressure of 1.0psi and main steam temperature of 1100oF. Furthermore, these parameters do not seem to change energy and exergy efficiencies significantly.

Operating Parameter Optimization using DOE Method to Reduce Unburned Carbon of Fly Ash for Tangential Fired Subcritical Coal Fired Power Plant

As electric demand increasing due to rapid economic growth, most developing country are sourcing for cheap fuel and low maintenance power plant which coal fired power plant become the more preferable plant. The cheap and abundant coal resources have played a major factor for coal power plant selection compare to other type of power plant. Although this plant type has low maintenance and operating cost but its emission of by product has a great effect on daily plant operation and environment. The one of the major emission was unburned carbon which by product of incomplete combustion where remaining of coal that unburned exits the furnaces with ash. Presence of higher percentage of unburned carbon indicates the low efficiency of furnace combustion and this directly affects financial status of the power plant operators. This condition causes severe damages on the boiler tube by formation of slagging and clinkering which reduces heat transfer and efficiency of the furnace. Current method proved to be more time consuming and plant operator facing difficulty to reduce unburned carbon in real time. As a solution for this problem, a best parameter was predicted to achieve low percentage of unburned carbon.

Life cycle assessment of post-combustion CO2 capture: A comparison between membrane separation and chemical absorption processes

Carbon capture technologies are regarded as promising options to mitigate CO2 emissions from large point sources, such as power generation facilities and energy intensive industries.However, CO2 capture technologies have several environmental impacts, from the system infrastructure production stage to the end of their lifetime, because of the consumption of resources in the form of materials and energy, as well as the formation of chemical by-products. All these aspects should be taken into account in order to assess and compare the real environmental sustainability of the CO2 capture processes.It is well established that life cycle assessment (LCA) represents a powerful tool to evaluate the most significant environmental impacts of CO2 capture technologies throughout their lifetimes.Using LCA methodology, this study aimed to compare life cycle emissions of membrane separation and chemical absorption processes for the post-combustion capture of one tonne of CO2 from a subcritical coal-fired power plant. Environmental impacts were evaluated considering a hybrid approach for the life cycle inventory, combining physical and economic input data.Simulation results highlighted that life cycle emissions of CO2 capture based on membrane separation process were strongly related to membrane material and thickness of the dense active layer, influencing the net power consumption and membrane area requirement. Membrane configurations investigated allowed to reduce to such an extent environmental impacts compared to CO2 capture based on monoethanoalmine (MEA) absorption. The greatest reduction potential was observed for human toxicity and impacts on freshwater and marine ecosystems, because of the elimination of environmental concerns related to solvent manufacturing and disposal of amine reclaimer wastes.