Ultra-supercritical Coal-fired Power Plants Research Articles

Dynamic modeling and comprehensive analysis of an ultra-supercritical coal-fired power plant integrated with post-combustion carbon capture system and molten salt heat storage

Reducing carbon footprints and enhancing operational flexibility are crucial for the future development of coal-fired power plants (CFPPs). This necessitates the deployment of post-combustion carbon capture (PCC) and molten-salt heat storage (MSHS) systems. Given the various integration schemes and complex interactions, understanding the comprehensive performance of the integrated CFPP-PCC-MSHS system is important. This paper proposes an integration scheme for 1000MWe ultra-supercritical CFPP, solvent-based PCC and MSHS, achieving cascade energy utilization. A dynamic simulation model for the CFPP-PCC-MSHS system is developed to understand the dynamic couplings between subsystems. Comprehensive performance analyses are conducted to evaluate the thermodynamics, flexibility and safety of the integrated system under various operating conditions. Simulation results indicate that deploying MSHS reduces the thermal and exergy efficiencies of the CFPP-PCC system by 0.18 % and 0.19 %, respectively, but effectively expands the adjustable power load range by 6.08 % under the fixed 90 % CO2 capture rate mode. Meanwhile, the integration of MSHS offers alternative pathways to improve the power ramping rate to 13.33 MW/min. The heat charging/discharging process of MSHS induces fluctuations in temperature and pressure within the turbine, potentially affecting plant operating safety. This paper provides useful insights for the design, retrofit and operation of new generation of CFPPs.

Life cycle assessment of post-combustion carbon capture and storage for the ultra-supercritical pulverized coal power plant

In this paper, different emerging post-combustion technologies, i.e., monoethanolamine (MEA), aqueous ammonia, pressure swing adsorption (PSA), temperature swing adsorption (TSA), membrane and calcium looping, were applied to an ultra-supercritical coal-fired power plant for carbon capture. A ‘cradle-to-grave’ life cycle assessment (LCA) was conducted to evaluate the technical performance and environmental impacts of the power plant with six emerging carbon capture technologies. Carbon capture significantly influences the impact categories directly associated with flue gas emission. The application of carbon capture reduced the GWP in the range of 49–75 %. TAP also reduced in the range of 18–51 %. However, the human toxicity potential, eutrophication potential, ecotoxicity potential and particulate matter formation potential increased due to energy and resource consumption in the upstream and downstream processes. For the life cycle water consumption potential, it decreased by 8 % with calcium looping, whereas it increased in the range of 36–75 % with other post-combustion technologies. The highest reduction in GWP and the least reduction in power efficiency was observed in calcium looping because of the high-temperature heat recovery from flue gas and elimination of complex solvent manufacturing. The plant with aqueous ammonia and membrane separation had the second and third highest reductions in GWP. In addition, the lowest values for TAP, FEP, and MEP were obtained in the membrane system. With MEA for CO2 capture, the total GWP value of the plant is slightly higher than these three technologies mentioned above, and the highest HTPc, FETP, and METP can be observed in this case. TSA and PSA have the most significant environmental impacts in most categories due to higher energy requirements.

Rated load state performance assessment and analysis of ultra-supercritical coal-fired power plant

ABSTRACT To address the problems of unclear assessment standards and incomplete assessment systems in the performance assessment of ultra-supercritical coal-fired power plants. This study utilized the running dataset from a 660 MW ultra-supercritical coal-fired power plant in Xinjiang, China. By combining the analytic hierarchy process and the entropy weight method, a system of assessment indicators was established that used three layers of criteria. A running line graph representing power plant performance and containing 149 moments was obtained, which provided a theoretical basis and optimization direction for improving the power plant. The results show that the 149 running states of the power plant performance are all at level I. The boiler running level had 143 moments (95.97%), the steam-turbine level had 135 moments (90.60%), the power consumption rate level had 148 moments (99.33%), and the environmental performance level had 143 moments (89.94%) of running states at level I.

Finite element modelling of ultrasonic backscattered waves for improving creep void detection

ABSTRACT Ultra-supercritical coal-fired power plants in Japan and globally experience creep damage in the welded parts of their high-chromium steel assets. As the creep damage advances, voids develop at depth by preference and become dense and cause accidents. The voids cannot be detected using existing non-destructive methods, causing the unreasonable and uneconomic management of plants. To establish a non-destructive examination method that can be used for practical and economic maintenance, a detection method for dense creep voids using ultrasonic backscattered waves is proposed herein. The creep-damaged structures are modelled using a transducer and the transmission and reception characteristics are discussed. These characteristics are considered using the finite element method, as they cannot be measured through normal experiments. The results show that without a focusing process at the time of reception, changes in the amplitude of backscattered waves cannot be confirmed; thus, the contribution of transmission focus to creep void detection is limited. Conversely, it is confirmed that when the received backscattered waves in the direction normal to the transducer are integrated and the phase matching is reflected, the amplitude of the scattered waves increases with creep void density. The reception focus considerably contributes towards dense creep void detection.

Modal decomposition integrated model for ultra-supercritical coal-fired power plant reheater tube temperature multi-step prediction

Overheating of reheater tubes in ultra-supercritical coal-fired power plants can affect the efficiency and safety of power generation (PG). To avoid reheater tubes overheating and bursting, this study proposes a modal decomposition integrated model (MDIM) for multi-step prediction of the reheater tube temperature to help managers adopt appropriate measures based on the predicted temperature changes. Considering the non-smooth and non-linear nature of the original temperature data, this study applies complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) to decompose the temperature data to remove noise and extract non-linear features effectively. In this study, the residual network18-convolutional block attention module (ResNet18-CBAM), transformer, gate recurrent unit (GRU), and temporal convolutional network (TCN) are applied to predict each component with different degrees of complexity after decomposition. The results of each component are integrated by the multilayer perceptron (MLP). The proposed MDIM is evaluated with various metrics. For single-step prediction, mean absolute error (MAE), mean absolute percentage error (MAPE), and root mean square error (RMSE) are 0.037, 0.0062, and 0.066, respectively. In the case of 48-step prediction, the corresponding values are 1.97, 0.33, and 2.4. Therefore, the proposed MDIM achieves outstanding results in both single-step and multi-step prediction.

The mechanism and regulation of hot cracking in a new complex-concentrated alloy by a novel integrated directed energy deposition

Improving thermal efficiency in advanced ultra-supercritical coal-fired power plants relies on increased steam temperature and pressure, accelerating the emergence of newly complex-concentrated alloys (CCAs). However, the new developed CCA have a combined Al and Ti content for 4.87 wt%, which indicates a high susceptibility to hot cracking. In this work, the hot cracking problem for the CCA during the laser deposition process was studied. The eutectic of the matrix and carbides with a low melting point liquefied during reheating process. The hot cracking occurred with local unbearable stress concentration. Based on the above analysis of hot cracking, a novel integrated directed laser deposition method was proposed to flexibly adjust the microstructure evolution and stress distribution by thermal cycles to achieve the control of hot cracks. The microstructure evolution and the control of residual stress are realized by gas quenching and preheating substrates, respectively. The evidence was obtained to show that the coupled process with synchronous gas quenching during preheating can eliminate the hot cracks effectively. More specifically, the preheating process relieved the residual stress, and the local gas quenching simultaneously accelerated the liquid film solidification and reduced carbide segregation. Finally, the sample prepared by the integrated directed energy deposition presented superior overall performance with ultimate tensile strength of 991.84 MPa and elongation of 18.28 %. This work provides a meaningful reference for producing crack-free superalloys in metal additive manufacturing.

Development of a three-term MPC and its application to an ultra-supercritical coal fired power plant

Most MPC (Model Predictive Control) algorithms used in industries and studied in the control academia use a two-term QP (quadratic programming), where the first term is the weighted norm of the output errors, and the second term is that of the input increments. In this work, a DMC (Dynamic Matrix Control) algorithm that uses three-term QP is developed and studied, where the third term is the weighted norm of the output increments. A relationship between the three-term DMC and the two-term DMC is established; and based on that, ideal closed-loop response curves are derived. These results are useful for the tuning of the three-term DMC. Then, a method for comparing two control methods is proposed and it is shown that the three-term DMC outperforms the two-term DMC. The findings are verified using simulation studies. Finally, the three-term DMC is successfully applied to a 1030 MW ultra-supercritical coal-fired power plant. According to simulation study using the identified model, in comparison to traditional two-term DMC, there is a roughly 10% reduction in the standard deviation of load tracking error for similar control efforts. In real-life tests on the power plant, the performance of the three-term DMC is compared to that of the existing PID controller. The load rate of change increased from 0.8%/min to 1.5%/min while the standard deviation of steam pressure decreased 38%; the standard deviations of the main steam temperature and reheat steam temperature decreased more than 40% with their mean values increased by more than 2 ∘C and 4 ∘C respectively.

One-Step Ahead Control Using Online Interpolated Transfer Function for Supplementary Control of Air-Fuel Ratio in Thermal Power Plants

Recently, the environmental problem has become a global issue. The air to fuel ratio (AFR) in the combustion of thermal power plants directly influences pollutants and thermal efficiency. A research result was published showing that the AFR control performance of thermal power plants can be improved through supplementary control using dynamic matrix control (DMC). However, online optimization of DMC needs an extra computer server in implementation. This paper proposes a practical AFR control with one-step ahead control which does not use online optimization and can be implemented directly in existing distributed control system (DCS) of thermal power plants. Closed-loop transfer function models at three operating points are independently developed offline. Then, an online transfer function using interpolation of offline models is applied at each sampling step. A simple one-step ahead control with online transfer function is applied as a supplementary control of AFR. Simulations with two different type power plants, a 600 MW oil-fired drum-type power plant and a 1000 MW ultra supercritical (USC) coal-fired once-through type power plant, are performed to show the effectiveness of the proposed control structure. Simulation results show that the proposed supplementary control can effectively improve the conventional AFR control performance of power plants.

Al–Si–Fe alloy-based phase change material for high-temperature thermal energy storage

Abstract Carnot batteries, a type of power-to-heat-to-power energy storage, are in high demand as they can provide a stable supply of renewable energy. Latent heat storage (LHS) using alloy-based phase change materials (PCMs), which have high heat storage density and thermal conductivity, is a promising method. However, LHS requires the development of a PCM with a melting point suitable for its application. For the Carnot battery, the reuse of a conventional ultra-supercritical coal-fired power plant with a maximum operating temperature of approximately 650°C is considered. Therefore, developing a 600°C-class alloy-based PCM is crucial for realizing a highly efficient and environmentally friendly Carnot battery. Using thermodynamic calculation software (FactSage), we found that Al-5.9 mass% Si-1.6 mass% Fe undergoes a phase transformation at 576–619°C, a potential 600°C-class PCM. In this study, we investigated the practicality of an Al–Si–Fe PCM as an LHS material based on its heat storage and release properties and form stability. The examined Al–Si–Fe PCM melted until approximately 620°C with a latent heat capacity of 375–394 J·g−1. Furthermore, the PCM was found to have a thermal conductivity of approximately 160 W·m−1·K−1 in the temperature range of 100–500°C, which is significantly better than that of conventional sensible heat storage materials in terms of heat storage capacity and thermal conductivity.

Generation of allowable stress for indigenously developed 304HCu Stainless steel

The 304HCu stainless steel (SS) is the candidate material for reheater and superheater tubes in Advanced Ultra Supercritical (AUSC) coal-fired power plants of India. In the present study, the creep design data have been generated for indigenously developed 304HCu SS using the creep properties (creep strain and the rupture life) and tensile properties available at the temperatures 923 K, 973 K and 1023 K. The time dependent allowable stresses were obtained for the above steel according to the stress criteria specified in ASME Section III Division 5 Subsection HB. The allowable stresses were also derived in the creep as well as non-creep regimes as per the guidelines in ASME Section IID. In both the cases, the maximum allowable stress at each temperature was dictated by the stress to cause rupture. The allowable stress determined as per Section IID was the same as that estimated according to section III.5 HB for creep exposure of 100,000 h. Further, it must be mentioned that, at the temperature range 923–1023 K, the indigenously developed 304HCu SS possess allowable stresses that are in par with the corresponding values specified in ASME code case 2328–2.

Assessments of the Emission Contributions from an Ultra-Supercritical Coal-Fired Power Plant to Ambient PM2.5 in Taiwan

Assessments of the Emission Contributions from an Ultra-Supercritical Coal-Fired Power Plant to Ambient PM2.5 in Taiwan

Novel exchanger type vacuum temperature swing adsorption for post-combustion CO2 capture: Process design and plant demonstration

Carbon capture and storage (CCS) is a crucial technology for the mitigation of greenhouse gas emissions while sustaining the energy security during the transition from fossil fuel to renewables. However, one of the biggest challenges to commercialize CCS is to develop an effective and less energy intensive capture technology. In this study, we demonstrate a novel multi-columns-in-column exchanger type adsorption unit (ETAU) for post-combustion carbon capture from a side stream of a 4000 MW ultra-supercritical coal-fired power plant. Using vacuum temperature swing adsorption (VTSA) process and 13X-APG adsorbent, we achieved a CO2 product purity of 94.4 %, and a recovery of 90.6 % on a single column adsorption unit cycle from pre-dehydrated raw flue gas. Another 4-bed 10-step VTSA process was carried out achieving a CO2 product purity and recovery of 93.5 % and 84.3 %, respectively, using the same raw flue gas. For this experimental unit in a much-limited scale, the greatest heat consumption is 3.71 GJ/tonCO2, and the electricity consumption is 128 kWh/tonCO2. Our evaluation indicates that the heat energy consumption by VTSA employing an ETAU design is more economical than that solely using temperature swing process for producing comparable carbon capture purity and recovery. Advanced heat management strategies have been developed to lower the energy consumption of the capture process making the utilization of ultra-low-grade heat viable. Scale-up of this novel multi-columns-in-column exchanger type adsorption unit with water resistant pre-layer is expected to further reduce the energy penalty and accelerate the deployment of carbon capture.

Phase precipitation behavior and its influence on mechanical properties of a solid-solution strengthened Ni-based alloy

Phase precipitation behavior and its influence on mechanical properties of a solid-solution strengthened Ni-based alloy, used to manufacture large casting components in next generation of advanced ultra-supercritical coal fired power plant, were studied during exposure at 700 ℃ for up to 30,000 h. Detailed analysis reveals that only MC carbide exists in solution annealed alloy. During thermal exposure, γ′′, δ and M23C6 carbide precipitate, but γ′′ and MC carbide are metastable phases. γ′′ precipitation precedes δ phase, but it disappears gradually with the precipitation of δ phase. MC carbide gradually degenerates via reaction MC + γ → M23C6 + δ. δ phase first precipitates at grain boundary due to the segregation of Nb at grain boundary and M23C6/γ interface, then tends to form in the vicinity of MC carbide and then appears in the interdendritic region. Its growth expends γ′′ phase or MC carbide. Finally, the precipitation-free zone forms in the dendrite core region. The variation trend of yield strength can be divided into three stages during thermal exposure. It first increases drastically, then increases gradually, and then keeps almost constant. γ′′ phase has a major contribution in first stage, but δ phase gradually becomes the primarily strengthened phase. The elongation decreases steeply at early stage and then has no significant change. After thermal exposure, the impact toughness at room temperature also decreases drastically. The major influence factors of elongation and impact toughness are the increase of grain interior strength and the film-like M23C6 carbide.

Effect of long-term aging on microstructural stability and tensile deformation of a Fe–Ni-based superalloy

The microstructural evolution, tensile behavior and deformation mechanism of a Fe–Ni-based superalloy for advanced ultra-supercritical coal-fired power plant during long-term isothermal exposure at 700–800 °C for 500–3000 h were investigated. The coarsening rate constant of γ′ phase in the alloy exposured at 700 °C, 750 °C and 800 °C were about 47.543 nm3/h, 277.963 nm3/h and 2201.937 nm3/h, respectively. The activation energy for γ′ growing is around 250.24 kJ/mol. The results showed Al, Ti and Ni elements primarily gathered into γ′ precipitates, while Cr and Fe mainly partitioned into γ matrix in Fe–Ni base alloy. After long-term aging, there was no precipitation of harmful phases such as the η and σ phases, but the decomposition of MC + γ → M23C6 + γ′ was observed. The microcracks were prone to initiate and propagate around pores formed by MC decomposition and lamellar M23C6 carbide, which might result in the premature fracture failure of the alloy. The yield strength first remained stable with a slight increase in the γ′ phase diameter and then decreased after further thermal exposure. The variation of tensile strength with precipitate size could be rationalized by the transformation between shearing model and Orowan looping mechanism of γ′ precipitates with increasing the γ′ precipitate size.

Performance analysis of an efficient waste heat utilization system in an ultra-supercritical coal-fired power plant

With the rise of new energy sources in the power industry, improving the efficiency of coal-fired power plants is essential. Currently, the leading main causes of irreversible energy loss are the energy level mismatches of boilers and turbines. An ultra-supercritical coal-fired power plant thermodynamic system was reconstructed based on the first and second laws of thermodynamics to improve the efficiency of power plants, and an efficient condensate water preheating air integrated bypass flue waste heating efficient utilization system is thus herein proposed. Consequently, high and medium steam turbine extraction flow is returned to the steam turbine to do work, and cold source loss is reduced by increasing the extraction steam flow of the low-pressure cylinder. At the same time, the inlet air temperature in the air preheater is significantly increased by preheating the hot air with condensate water, resulting in a reduced heat transfer temperature difference and significantly improved exergy efficiency. Compared with conventional low-temperature economizer and bypass flue waste heat utilization schemes, the results indicate that the heat transfer exergy efficiency increased significantly from 78.49% to 95.88% in the air preheater, and the heat consumption rate of the turbine generator set decreased by 108.06 kJ/(kW⋅h). The generation efficiency increases by 0.74%, while the standard coal consumption rate decreases by 3.92 g/(kW⋅h). In terms of economic investment, the dynamic payback period is 3.31 years and the net present value is $2.20 M/year. This paper provides an effective energy conservation and emission reduction plan for coal-fired power plants to contribute towards achieving national carbon peaking and carbon neutrality goals.

Low-rank coal pyrolysis polygeneration technology with semi-coke heat carrier based on the dual-fluidized bed to co-produce electricity, oil and chemical products: Process simulation and techno-economic evaluation

Pyrolysis polygeneration technology is a good way to realize clean and efficient utilization of low-rank coal and heat carrier is a key factor. Aspen Plus is used to establish low-rank coal pyrolysis staged conversion polygeneration technology with semi-coke heat carrier based on dual-fluidized bed (CPSCPC-DFB), which couples with ultra-supercritical semi-coke powder furnace for power generation. Three processes are simulated to co-produce methanol (CPSCPC-DFB-M), synthetic natural gas (CPSCPC-DFB-S) and hydrogen (CPSCPC-DFB-H). Mass and carbon balance are established, techno-economic, environmental and sensitivity analysis are carried out, and the comparison with ultra-supercritical coal-fired power plant (SCFP) is made. The results show that the comprehensive performances of CPSCPC-DFB-M, CPSCPC-DFB-S and CPSCPC-DFB-H are significantly better than those of SCFP in energy loss (49.37%, 47.33%, 45% and 55.6%), CO2 emissions (2.07, 2.12, 2.22 and 2.52 kg/kgcoal), internal rate of return (23.24%, 21.83%, 29.52% and 17.56%). Although the total investment of CPSCPC-DFB is much higher than SCFP, the net present value is better than SCFP. Comparing the three polygeneration systems, the total investment and CO2 emissions of CPSCPC-DFB-H are slightly higher than those of other two systems, but CPSCPC-DFB-H has absolute advantages in economy. Sensitivity analysis shows that the anti-risk ability of the polygeneration systems are significantly improved.

Effects of boron addition on the microstructure and creep properties of a Ni-Fe-based superalloy weld metal alloy

The role of boron in the creep properties and grain boundary characteristics in a new Ni-Fe-based weld metal suitable for advanced ultra-supercritical (A-USC) coal-fired power plant applications has been investigated. Ni-Fe-based filler wires without boron and boron-doped (50 ppm wt% boron) were prepared for this study. Boron-doped weld metals exhibited longer rupture lives and lower steady creep rates during the creep rupture tests at 750 °C / 380 MPa and 750 °C / 210 MPa. This study explains the improvement mechanism of boron on creep resistance from the perspective of the effect of boron on M23C6. Boron increased the nucleation rate of M23C6 and participated in the formation of M23(C, B)6 type boron-carbides. After creep deformation, boron still existed stably in the M23(C, B)6. The higher density of discrete M23C6 particles due to boron addition could restrain grain boundary crack propagation and grain boundary sliding, and thereby improve the creep fracture resistance of the GH984G weld metal at 750 °C / (380/ 210 MPa).

Development and Qualification of Materials for Indian Advanced Ultra-Supercritical Coal-Fired Power Plant

Abstract India has embarked on an ambitious program of setting up efficient advanced ultra-supercritical (AUSC) technology with steam temperature and pressure of 993 K and 31 MPa, respectively. This article deals with the testing and qualification of indigenously produced materials for the Indian AUSC mission project, the research and development phase of which is currently in the advanced stage of completion. As part of this, exhaustive database pertaining to various mechanical properties including creep, low cycle fatigue (LCF), creep-fatigue interaction (CFI), high cycle fatigue (HCF), fracture toughness, and crack growth has been generated covering important candidate materials such as alloy 617M tubes and forgings, 304HCu stainless steel tubes, and alloy 625 castings. Tubes of both alloy 617M and 304HCu stainless steels are to be used in the boilers, whereas alloy 617M forgings would be used as turbine rotor and alloy 625 castings as turbine casings. The data have been subsequently used to establish design curves identifying safe regimes of operation with respect to creep, LCF, HCF, CFI, and fatigue and creep crack growths. The properties were seen to be comparable with those derived from internationally developed equivalent grades. The bimetallic weld joints between alloy 617M and 10Cr steels were also evaluated to derive the appropriate strength reduction factors under creep and cyclic loadings. Additionally, the influence of thermal aging at service temperature on the microstructural evolution and mechanical properties was investigated based on tensile and fracture properties to account for the service exposure induced degradation and associated embrittlement.

Multi-feature-scale fusion temporal convolution networks for metal temperature forecasting of ultra-supercritical coal-fired power plant reheater tubes

The ultra-supercritical coal-fired power plant has higher reheater steam temperatures. To reduce the possibility of overheating operation and decrease the explosion of reheater, the operating temperature of reheater should be accurately monitored in real-time. Through the real-time prediction of the temperature distribution of the reheater tube, the alarm threshold is set to prevent tube burst and other faults. To accurately predict the metal temperature of the reheater tube in real-time, a multi-feature-scale fusion temporal convolution network prediction model is proposed in this paper. The model has a strong ability of feature extraction and nonlinear function fitting, and can infinitely approximate the mapping relationship between input and output data. Innovative methods feature construction, spatial partition and feature fusion, are proposed to improve the accuracy. Original data are collected from one thermal power plant reheater in the Guangdong province of China. The multi-feature-scale fusion temporal convolution network is applied to study the real-life data from March 2020 to May 2020. Compared with 20 prediction models such as random forest, the proposed model has higher accuracy. The mean absolute percentage error result of the proposed model is smaller 0.16% than the second smallest model and 25.70% smaller than the largest model.

Advanced Ultra-Supercritical Coal-Fired Power Plant with Post-Combustion Carbon Capture: Analysis of Electricity Penalty and CO2 Emission Reduction

This article presents the performance analysis of a 700 MW future planned advanced ultra-supercritical (A-USC) coal-fired power plant fitted with post-combustion carbon capture and storage (CCS) technology. The reference A-USC unit without CCS achieves a net efficiency of 47.6% with CO2 emissions of 700 kgCO2/MWh. Relatively to subcritical units, the net efficiency of the A-USC is 8%-pts higher while CO2 emissions are 16.5% lower. For a CO2 removal rate of 90%, the net efficiency of the CCS integrated A-USC unit is 36.8%. The resulting net efficiency loss is 10.8%-pts and the electricity output penalty is 362.3 kWhel/tCO2 for present state CCS technology. The study continues with the assessment of interface quantities between the capture unit and the steam cycle affecting the performance of the A-USC. Improved CO2 absorbents could alleviate the net efficiency loss by 2–3%-pts, and enhanced CO2 compression strategies and advanced heat integration could further reduce the efficiency loss by 0.5–1.2%-pts and 0.4–0.6%-pts, respectively. The total efficiency gain from CCS technology upgrades is estimated at 3.6%-pts, thus bringing down the net efficiency loss to 7.2%-pts and the electricity output penalty to 241.7 kWhel/tCO2.