Coal-fired Power Units Research Articles

Policy Effect on Clean Coal-Fired Power Development in China

The coal power policy has been influencing the development of China’s coal power industry from the aspects of quantity control, technological progress, and market-oriented reform. Meanwhile, the strategic coal power policy of the mid- and long-term future is yet to be well-designed under the carbon peak and neutrality targets. Therefore, it is necessary to have a comprehensive overview of the coal power policy during the past and give targeted prospects for policy-makers. This paper discusses the policy effect on the development and technological progress of the coal power industry by giving an overview of the policy and reform processes of the coal power industry in China in the past 20 years. The results indicate that China’s coal power policy has promoted the progress of coal power generation technology, optimized the coal power structure, accelerated the diversified investment in the power industry, and alleviated the overcapacity problem of coal power generation. After discussion, we conclude that: (1) It is necessary to gradually reduce the average generation hours of coal-fired power units while retaining high-quality coal-fired power units. (2) The renewable energy enterprises that adopt the support services of coal power enterprises should provide reasonable capacity compensation costs to create favorable conditions and achieve sustainable development for China’s coal power industry. (3) To deploy coal power units combined with large-scale renewable energy in the western and northern regions will achieve efficient energy utilization. (4) Different strategies should be adopted for different coal power units, and the peak regulation potential of coal power units with low-capacity parameters should be explored.

CFD modeling for NOx absorption accompanying with SO2 in wet flue gas desulfurization scrubber based on gas-phase ozone oxidation

NOx removal performance accompanying with SO2 is investigated in a two-step process containing O3 pre-oxidation of NO and NOx post-absorption in the scrubber of wet flue gas desulfurization (WFGD) unit. Based on EulerianLagrangian framework, a comprehensive CFD model is established to describe the reactions of NO2 and N2O5 with S(IV) in droplets coupled with NOx transfer process and hydrodynamics in the scrubber. Taking the WFGD scrubber of 330 MW coal-fired power unit as case study, the results indicate NOx absorption efficiency in scrubber is increased by increasing O3/NO molar ratio from 1.0 to 2.2 and decreasing reaction temperature from 423 K to 363 K in O3 pre-oxidation process. The obtained highest removal efficiency is 85.79% for pH of 5.5 or 96.32% for pH of 9.0 in droplets. NO2 absorption is much slower than N2O5 and more sensitive to chemical compositions in droplets or hydrodynamics in scrubber. The overall mass transfer coefficient (KG) for NO2 is mainly determined by pH and S(IV) concentration in droplets, while the specific interfacial area (a) is largely influenced by gasdroplet hydrodynamics in scrubber. Finally, a correlation is proposed to predict the volumetric mass transfer coefficient (KGa) for NO2 absorption accompanying with SO2 in WFGD scrubber.

Performance Analysis of a Waste-to-Energy System Integrated with the Steam–Water Cycle and Urea Hydrolysis Process of a Coal-Fired Power Unit

An innovative hybrid energy system consisting of a waste-to-energy unit and a coal-fired power unit is designed to enhance the energy recovery of waste and decrease the investment costs of waste-to-energy unit. In this integrated design, partial cold reheat steam of the coal-fired unit is heated by the waste-to-energy boiler’s superheater. The heat required for partial preheated air of waste-to-energy unit and its feedwater are supplied by the feedwater of CFPU. In addition, an additional evaporator is deployed in the waste-to-energy boiler, of which the outlet stream is utilized to provide the heat source for the urea hydrolysis unit of coal-fired power plant. The stand-alone and proposed designs are analyzed and compared through thermodynamic and economic methods. Results indicate that the net total energy efficiency increases from 41.84% to 42.12%, and the net total exergy efficiency rises from 41.19% to 41.46% after system integration. Moreover, the energy efficiency and exergy efficiency of waste-to-energy system are enhanced by 10.48% and 9.92%, respectively. The dynamic payback period of new waste-to-energy system is cut down from 11.39 years to 5.48 years, and an additional net present value of $14.42 million is got than before.

Wind integration cost in China: A production simulation approach and case study

The integration cost of large-scale variable renewable energy (VRE) in China’s coal-dominated inflexible power systems is of significant concern when studying the generation cost of VRE. One key component of studies about integration cost is the question of how to estimate the impact of large-scale VRE integrated into power systems on the operation mode of conventional generators. It is intuitive to compare system-level costs with and without VRE under a benchmarked system. In this study, we employ a unit commitment (UC) model to simulate the output of various types of units based on minimizing the total power system cost. Then, we estimate the conventional generator operation cost change caused by the change of operation mode. Using the power system in Jilin province as a typical case, the integration cost will increase with increased VRE penetration, reaching 123.5 CNY/MWh at 40% penetration level. The idle cost of the coal-fired power units accounts for 69% of the integration cost at 40% VRE penetration, the highest proportion; wind curtailment cost ranks second for 26%, while the incremental operating cost of coal power accounts for 4.7%. With a long-term perspective, establishing a complete power market and adopting an appropriate pricing mechanism to incentivize system flexibility is the best solution for adopting VRE.

Thermal System for Comprehensive Utilization of Boiler and Steam Turbine Energy of Coal-Fired Power Units Based on the S-Co2 Cycle

Thermal System for Comprehensive Utilization of Boiler and Steam Turbine Energy of Coal-Fired Power Units Based on the S-Co2 Cycle

A Thermodynamic System of Coal-Fired Power Unit Coupled S-Co2 Energy-Storage Cycle

A Thermodynamic System of Coal-Fired Power Unit Coupled S-Co2 Energy-Storage Cycle

Nox Emission Prediction of Coal-Fired Power Units Under Uncertain Classification of Operating Conditions

Nox Emission Prediction of Coal-Fired Power Units Under Uncertain Classification of Operating Conditions

Effects of the Changes of Load and Flue Gas Temperature on the Emission of Particulate Matter from the Coal-fired Unit

Due to the rapid development of new energy power generation, most coal-fired power plants cannot always operate at full capacity. The changes in flue gas temperature at the inlet of low-low temperature electrostatic precipitator and unit load are the important factors affecting the emission of condensable and filterable particulate matter (CPM and FPM). CPM and FPM were sampled from a typical ultra-low emission coal-fired power unit with different operating loads (650, 850, and 1000 MW) and flue gas temperature (90 and 100°C). The emission concentration of FPM, organic and inorganic components of CPM were obtained. The representative organic matter n-alkanes and phthalates in CPM (C-N and C-P) were quantified. The concentrations of CPM emitted from the coal-fired unit ranged from 6.66–8.93 mg Nm–3, which was 2.4–6.2 times higher than FPM. The emission concentration of CPM was the lowest from the unit under high load and low flue gas temperature. The decrease of flue gas temperature increased of SO42– emission concentration, which was the soluble ion with the highest concentration in CPM. The effect of unit load and flue gas temperature changes on monocomponent C-N and C-P was limited; however, the effect on its total emission concentration was consistent with that on CPM. The concentrations of n-alkanes and phthalates in CPM accounted for more than 20% at all four stages.

Thermal System for Comprehensive Utilization of Boiler Flue Gas and Steam Extraction Energy of Coal-Fired Power Units Based on S-Co2 Cycle

Thermal System for Comprehensive Utilization of Boiler Flue Gas and Steam Extraction Energy of Coal-Fired Power Units Based on S-Co2 Cycle

Steam-Water Modelling and the Coal-Saving Scheduling Strategy of Combined Heat and Power Systems

China aims to peak carbon emissions by 2030. As a result, small-scale coal-fired combined heat and power (CHP) units and self-provided units are gradually shut down, and large-scale coal-fired CHP units are a solution to undertake the industrial heat loads. From the perspective of the industrial heat load allocation during the non-heating season, the problems regarding the coal-saving scheduling strategy of coal-fired CHP units are addressed. The steam-water equations of CHP units are established to analyze the heat-power coupling characteristics. The energy utilization efficiency, exergy efficiency and the coal consumption are analyzed. The optimization model of saving coal consumption is established and the adaptive mutation particle swarm optimization (AMPSO) is introduced to solve the above model. The 330 MW coal-fired CHP unit is taken as an example, and the results show that for the constant main flow rate, each increase of 1 t/h industrial steam extraction will reduce the power output by about 0.321 MW. The energy utilization efficiency and the exergy are mainly influenced by industrial steam supply and the power load, respectively. For the CHP system with two parallel CHP units, the unequal allocation of industrial heat load between two units saves more coal than equal allocation. The coal consumption can be reduced when the unit with lower power load undertakes more industrial heat load. In the typical day, the total coal consumption after optimization is 3203.92 tons, a decrease of 14.66 tons compared to the optimization before. The two CHP units in the case can benefit about 5,612,700 CHY extra in one year.

Technical and Economic Evaluation on the Integrated Heating System With Coupled Heat Pump and Backpressure Turbine

Abstract The increasing depletion of fossil energy and the gradual aggravation of environmental pollution have increased the necessity of renewable energy applications. However, the intermittent characteristics of renewable energy power generation need to increase the flexibility of the original coal-fired power unit for balancing the supply and demand of the power system. In this work, two 350 MWe condensing units (CUs) were taken as examples and the thermodynamic simulation models were built by the ebsilon software to evaluate their technical and economic characteristics. At the same time, the system is coupled with heat pump (HP) and backpressure turbine (BT) for heating. Among them, the rated steam intake of HP is 194.9 t/h, and the rated steam intake of BT is 214.5 t/h. Results show that under the same requirements, the energy consumption with the backpressure turbine priority principle (BTtlp principle) is smaller than that with the heat pump priority principle (HPtlp principle). However, under the same thermal load conditions, the electrical load with the HPtlp principle can drop lower than that with the BTtlp principle. Meanwhile, there is an optimization interval for the output distribution of HP and BT. From the energy current diagram, it can be found that under the design main steam and given thermal load condition, the power generation efficiency of coupled mode is 0.74% more than that of HP mode and is 1.93% more than that of direct mode, while under the given thermal and electrical load condition, the system’s boiler output with direct mode is 3.37% more than that with HP mode and is 5.34% more than that with coupled mode. This provides a theoretical basis for the subsequent comprehensive evaluation of heating reformation.

SOx removal and emission characteristics of WFGD system applied in ultra-low emission coal-fired power plants

In this paper, SOX (SO2 and SO3) removal and emission characteristics of wet limestone-gypsum flue gas desulfurization (WFGD) are investigated based on the data collected from 95 ultra-low emission coal-fired power units. The study shows that the overall removal efficiency of single-absorber is above 97.5%, in which the SO3 removal efficiency is between 31% and 70%. When the inner structures are installed into the spray absorber, the correlation between the inlet SO2 concentration and SOX removal efficiency becomes more obvious, however, with a tray absorber, the maximum SO2 removal efficiency of double-absorber reaches 99.74%, in which the SO3 removal efficiency is between 27% and 81%. With a normal spray absorber, the higher inlet concentration, the higher removal efficiency it reaches, while with a tray absorber, the result is opposite. With a single-absorber, there is little correlation between flue gas temperature drop and SO2 removal efficiency. Large temperature drop harms the improvement of overall SO2 removal efficiency but is beneficial to SO3 removal. By the calculation of SOX emission performance model, average emission performances of SO2 and SO3 are acquired, which are about 90–107 mg/(kW·h) and 81–97 mg/(kW·h), respectively.

Flexibility improvement method of coal-fired thermal power plant based on the multi-scale utilization of steam turbine energy storage

In order to achieve the large-scale grid connection of renewable energy, flexibility of the power generation system operation needs to be improved. The coal-based power supply structure indicates that coal-fired generating units are gradually becoming the main force of power regulation in China. However, the coal-fired power unit load regulation capacity requires significant improvement. Based on the energy storage characteristics of the coal-fired power unit, a load regulation method based on the multi-scale energy storage utilization is proposed. The method is based on the combination of feedwater bypass throttling and feedwater heater extraction steam throttling. The coal-fired power unit mathematical model is established and verified against the field tests, and simulation relative error is approximately 7%. Based on the mechanism mathematical model, the load coordinated controlled model is obtained. Moreover, the load response time of feedwater bypass throttling method is nearly 125 s longer than that of high-pressure heater extraction steam throttling method, the load command is decomposed by multi-scales, and the load regulation method based on the feedwater bypass and extraction steam throttling is proposed. The simulation results indicate that the proposed method is superior to the conventional control method. Furthermore, it can effectively improve the unit load flexibility.

On-Line Control of Stresses in the Power Unit Pressure Elements Taking Account of Variable Heat Transfer Conditions

Coal-fired power units, now balancing power shortages in the power system, must be characterised by increasingly higher flexibility of operation. This means faster start-ups and the capacity for frequent decreases and increases in the power output. These processes cause large temperature gradients in elements of the power unit and the turbine and lead to an increase in the stress level. At such an operating regime it is impossible to ensure safety based on start-up characteristics only—it becomes necessary to constantly monitor stress levels in critical areas of machinery and equipment elements. The stress level in turbine elements can be monitored on-line using algorithms based on Green’s functions and Duhamel’s integral. This paper presents examples of modifications of stress calculations in turbine valves and casings during start-ups. By modifying basic algorithms, it is possible to take into account the impact of the variability of heat transfer coefficients on the thermal stress level. Additionally, individual Green’s functions and correction factors were determined for specific stages of start-ups. Due to modifications, it is possible to obtain satisfactory agreement with the results obtained from FEM-based calculations for the entire heating process. Equations are also given that enable estimation of values of the heat transfer coefficient in turbine valves. The proposed modification of the algorithm will substantially improve the accuracy of stress modelling in transient states of the turbine operation. On-line stress monitoring will enable an increase in the flexibility of the power unit operation and facilitate operational control, ensuring safety of individual elements at the same time. The stress values calculated in the on-line mode can also be used to estimate fatigue life consumption and forecast the residual lifetime of individual components.

Numerical Analysis on the Flue Gas Temperature Maintenance System of a Solid Fuel-Fired Boiler Operating at Minimum Loads

Currently, energy policy is associated with the increase in the share of renewable sources in systemic energy production. Due to this trend, coal-fired power units must increase their work flexibility. Adapting a coal power plant to work with a lower load often causes the issue of maintaining the temperature before the selective catalytic reduction (SCR) installation at a sufficiently high level. This paper presents a CFD analysis of the mixing area of two flue gas streams before the SCR installation with various methods for mixing flue gas streams. The novelty of the work is mixing the flue gas streams of different temperatures using a flap shape developed by the authors. A series of numerical simulations were performed to develop the location and method of introducing the higher temperature gas, obtaining a uniform distribution of the exhaust gas temperature. The simulation scheme was applied to a series of geometrical modifications of the boundary conditions. The tested solution using only a single, straight flap in the flue gas duct allows the amplitude to be reduced from 298 K to 144 K. As a result of the research, a mixing flap design was developed to reduce the initial temperature amplitude of the flue gas streams from 298 K to 43 K.

Quantifying stranded assets of the coal-fired power in China under the Paris Agreement target

ABSTRACT Coal-fired power plays a critical role in China’s compliance with the Paris Agreement. This research quantifies China’s stranded coal assets under different coal capacity expansion scenarios with an integrated approach and high-precision coal-fired power database. From a top-down perspective, firstly, the pathway of China’s coal-fired power capacity consistent with the global 2°C scenario is outlined and then those stranded coal-fired power plants are identified with a bottom-up perspective. Stranded value is estimated based upon a cash flow algorithm. Results show that if coal capacity stabilizes during 2020–2030, China will only incur a sizeable yet manageable stranded asset loss (USD 55 billion, 2020–2045). However, a continued increase of coal-fired capacity, of another 200∼400 GW, would significantly enlarge the loss by 2.7∼7.2 times. Further, once commissioned coal-fired power would form a resource lock-in effect. Thus, it will miss a short-term opportunity to develop new energy sources and induce a long-term need to invest in coal-fired power negative emission technology. Therefore, halting the construction of new coal-fired plants is a low-cost and no-regret option for China. Key policy insights Even with the largest coal-fired power capacity in the world, China still has the chance to decommission the coal-fired power units gradually at a relatively low cost. Continuing to build new coal-fired power units in China will increase the risk of stranded assets, especially for North China Grid and Northwest China Grid. Taking immediate action to stop building new coal-fired power units would be the low-cost and no-regret option for China. The local financial sector needs to work with the energy sector to gradually withdraw from the coal sector and support clean and renewable energy.

Mass transfer process intensification for SO2 absorption in a commercial-scale wet flue gas desulfurization scrubber

To intensify SO2 absorption process in wet flue gas desulfurization (WFGD) spray scrubber, a comprehensive CFD model coupled transfer process with chemical reactions is established by Eulerian‒Lagrangian method and verified in a commercial-scale device of 330 MW coal-fired power unit. The desulfurization performance is significantly affected by both the property of each droplet and the dispersion of droplet swarm, which are determined by the spray behaviors. Three dominant factors, including droplet diameter, injection direction and spray morphology, are explored to optimize the spray conditions for intensifying SO2 absorption process. Differing from the ideal plug flow, the optimal diameter of droplet in non-ideal flow is obtained by considering the synergistic effect of the uniformity of gas–slurry distribution and the dynamics of SO2 mass transfer. Compared with the single-direction spray with downward or upward injection, the dual-direction spray reaches a great balance between the competitive effects of the uniformity of gas‒slurry flow and the interfacial area for mass transfer. The influence of spray morphology on mass transfer process is essentially the difference of dispersion characteristics of droplets in the middle part of scrubber. A design scheme combining full-cone and hollow-cone nozzles is suggested for improving the overall SO2 removal efficiency.

Emission of organic components and distribution characteristics of PAHs in condensable particulate matter from coal-fired power and industrial plants

Fine particles, especially condensable particulate matter (CPM) emitted from coal combustion, is one of the hidden trouble to the ecological environment and human health. In this study, CPM and filterable particulate matter (FPM) were sampled in four coal-fired units. The emission concentrations of CPM and FPM, organic fractions in the emitted CPM were obtained. The effects of air pollution control devices (APCDs) on the distribution of polycyclic aromatic hydrocarbons in CPM (C-PAHs) were investigated by analyzing samples from inlets and outlets of APCDs. The concentrations of CPM emitted from the four units were all higher than that of FPM. Organic fractions were dominant in CPM, especially saturated hydrocarbons accounted for a relatively high proportion (49.19–67.47%). The removal effect of the bag filter for C-PAHs was excellent. The emission concentration of C-PAHs was significantly reduced from the low load unit (350 MW) to the high load unit (600 MW). The 4-ring C-PAHs contributed the largest percentage (nearly 80%) in the emission concentrations of C-PAHs from the four units. The concentrations of C-PAHs emitted from coal-fired power units (1.43 and 2.08 μg/Nm3) were higher than that of coal-fired industrial units (0.17 and 1.31 μg/Nm3).

Catchment-level water stress risk of coal power transition in China under 2℃/1.5℃ targets

Coal power production is the second largest source of water demand in China. However, as coal power would undergo significant changes under ambitious climate goals (2℃ or 1.5℃), it’s not clear how the low-carbon transition of the power sector made at the provincial level would affect the catchment-level water resources in the future. With a power system model (MESEIC) and a unit-level coal-fired power unit dataset, this study explores different power sector transition pathways from 2020 to 2050, and maps out the catchment-level water stress risk of China’s coal power with Monte Carlo method. Results show that the future power supply mix varies much under the shared socio-economic pathways (SSPs) and carbon emission targets. Without carbon emission targets, coal power would continue to dominate the power supply mix advantage and would cause severe risk of water stress. Under SSP1-5, the national water withdrawal from coal power in 2050 would be 12.2–176.2 billion m3 under the reference scenario, but would decline to 10.7–59.2 billion m3 with 2℃ target and 0.11–35.5 billion m3 with 1.5℃ target. Compared with the 2℃ target, the catchment-level water stress risk generated by coal-fired power plants in north China would be significantly reduced under the stricter target of 1.5℃. However, the benefits would be reduced under SSP5 because of the application of carbon capture and storage. This study reveals the strong synergies between reducing carbon emissions and alleviating water stress risk in China’s power sector, but regional risk should be noted while achieving the carbon reduction targets.

Techno-Economic Assessment of Coal-Fired Power Unit Decarbonization Retrofit with KP-FHR Small Modular Reactors

The near and mid-term future of the existing Polish coal-fired power fleet is uncertain. The longer-term operation of unabated coal power is incompatible with climate policy and is economically challenging because of the increasing price of CO2 emission allowances in the EU. The results of the techno-economic analysis presented in this paper indicate that the retrofit of existing coal-fired units, by means of replacing coal-fired boilers with small modular reactors, may be an interesting option for the Polish energy sector. It has been shown that the retrofit can reduce the costs in relation to greenfield investments by as much as 35%. This analysis focuses on the repowering of a 460 MW supercritical coal-fired unit based on the Łagisza power plant design with high temperature small modular nuclear reactors based on the 320 MWth unit design by Kairos Power. The technical analyses did not show any major difficulties in integrating. The economic analyses show that the proposed retrofits can be economically justified, and, in this respect, they are more advantageous than greenfield investments. For the base economic scenario, the difference in NPV (Net Present Value) is more favorable for the retrofit by 556.9 M€ and the discounted payback period for this pathway is 10 years.