Ultra-supercritical Unit Research Articles

The role of output-based emission trading system in the decarbonization of China's power sector

The emission trading system (ETS) is a key policy for China to achieve carbon neutrality. China's national ETS started operation and covered the power sector first, which will promote its transformation. This study explores how China's national ETS can support the future decarbonization of the power system. With benchmark tightening, China's ETS can cost-effectively peak CO2 emissions of the power sector before 2030 and reduce 13% of the total emissions by 2035, compared to a No-Carbon-Pricing Scenario. Under the ETS, the allowance price would rise gradually to 350 yuan/tCO2 by 2035. The main driving factor for emissions reduction would be improving the efficiency of coal-fired power generation between 2020 and 2025 and deploying carbon capture and storage (CCS) from 2030, respectively. Fuel-switching away from coal is limited under the ETS with technology-specific benchmarks and free allocation. Regional distributional effects could arise under the ETS. Regions with a higher share of ultra-supercritical units could have allowance surpluses at the beginning, while only regions with CCS-equipped coal-fired units have the potential to gain high allowance surpluses by 2035.

Impacts of carbon markets and subsidies on carbon capture and storage retrofitting of existing coal-fired units in China

Carbon capture and storage (CCS) is a feasible technology option to reduce carbon emission in the power industry. However, the high cost of CCS deployment in power plants precludes its large-scale application. Carbon markets may act as an incentive for CCS, but the impact of auction and quota allocation mechanisms in carbon markets on CCS is unclear. In order to investigate the roles of the auction and quota allocation mechanism on the CCS retrofitting in coal-fired units, the life-cycle cost method was used to evaluate the CCS retrofitting cost of China's coal-fired units in the carbon market after supplementing the existing database. The impact of subsidies on stimulating CCS retrofitting was jointly considered. The results show that most units have a CCS retrofit Levelized additional cost of electricity (Lacoe) of $25.24/MWh to $64.57/MWh, making the CCS retrofitting burdensome, even for ultra-supercritical unit that has a low cost. The combination of grandfathering quota allocation mechanism and subsidy will effectively promote CCS retrofitting of coal-fired units, especially when the auction ratio is 30%–40%, about 400–540 GW units will be retrofitted under the carbon market using grandfathering and 12.05$/MWh-22.77$/MWh subsidies. Additionally, there are significant differences among provinces in terms of the lifetime costs of the CCS retrofitting of coal-fired units. Xinjiang, Guangdong, and Jiangsu, with retrofitting potentials of respectively 20.68 GW, 10.58 GW–43.00 GW and 15.00 GW–52.27 GW are best suited for the CCS retrofitting of coal-fired units.

Theoretical and technical analysis of the photo-thermal energy cascade conversion for fuel with high-temperature combustion

This study theoretically reveals the advantages of the photo-thermal energy cascading conversion over single thermal energy or a radiative energy conversion. It also analyzes the potential of the photo-thermal energy cascading conversion relying on typical power generation units with different parameters and considers the research outlook. The results demonstrate that the cascade conversion is more critical for high-temperature conditions since there are limitations for single radiation energy; thus, oxy-fuel combustion at a high temperature is more suitable. In consideration of technology conditions, the cascade system based on ultra-supercritical units can theoretically increase efficiency by more than 20% points under oxy-fuel combustion, whereas the efficiency of the cascade system based on combined cycle units can be theoretically increased by 15% points. The efficiency of the cascade system based on the small-parameter organic Rankine cycle unit can be increased by over 30% points according to the actual technology, and the small-scale unit could be applied in distributed energy systems. It is also pointed out that the further improvement of the system lies in the design of staged thermo-photovoltaic and complex thermal cycles to realize the cascade utilization of photo energy or thermal energy.

Application of ECS-700 control system in ultra-supercritical units

Application of ECS-700 control system in ultra-supercritical units

Microstructural evolution in S31042 heat-resistant steel after service and the effect on hardness

The ultra-supercritical power generation technology with high energy efficiency and low emissions is one of the important ways to solve the current increasingly prominent energy problems in the context of international development requirements for carbon neutrality and the increasingly prominent energy shortage. Because of its excellent resistance to high temperature corrosion and organizational stability, S31042 is commonly employed in the most severe working environment of ultra-supercritical units. Due to its great resistance to high-temperature corrosion and organizational stability, S31042 is commonly employed in the most demanding components of ultra-supercritical units such as high-temperature reheaters and high-temperature superheaters. Various characterisation approaches were employed in this research to reflect the microstructure of S31042 heat-resistant steel in service under various time length conditions, and the hardness of S31042 heat-resistant steel was assessed under the corresponding service conditions. The results showed that the hardness of S31042 increased significantly with increasing service time, from around 160 Hv at the time of non-service to nearly 220 Hv after 75360 hours of service. The continuous distribution of uniformly sized M23C6 phase on the grain boundaries of S31042 developed toward grain coarsening after service, but the precipitation strengthening effect produced by the nanoscale secondary NbCrN phase appearing in the grains was the main reason for the increase of the hardness value of S31042, according to the microstructure of the material.

Nonlinear model predictive control of USC boiler-turbine power units in flexible operations via input convex neural network

Coordinated control of an ultra-supercritical (USC) boiler-turbine unit in the flexible-operation mode is challenging because of internal nonlinearity, various unknown disturbances, and the strong-coupled multivariable behavior of the unit. A novel nonlinear model predictive control (NMPC) approach is proposed to improve the flexibility of the USC unit, which introduces an input convex neural network (ICNN) to model the dynamics of the USC unit, and then computes the optimal control decisions by solving a convex model predictive control problem. Simulations are conducted on a 1000 MW USC boiler-turbine unit. The results demonstrate that the ICNN exhibits equivalent performance to a conventional neural network in learning the system dynamics. The root mean square errors of the throttle steam pressure, the separator steam enthalpy, and the power are 0.003 MPa, 0.162 kJ/kg, and 0.513 MW, respectively. In load tracking and disturbance rejection simulations, the proposed ICNN-based NMPC outperforms the linear model predictive control and conventional neural network-based NMPC. The ICNN-based NMPC provides a fast and stable load tracking capacity at a ramp rate of 10.8% MCR/min. Moreover, the superiority of the proposed approach is further confirmed by comparison with the internal-model robust adaptive control method, which is a state-of-the-art method. The proposed approach has good potential to improve the operational flexibility of USC power units.

The microstructure and tensile property changes of S31042 steel after long time service

Abstract Ultra-supercritical power generation technology is one of the main solutions to the many contradictory problems of carbon emissions and environmental protection in coal-fired power plants. S31042 austenitic heat-resistant steel has become a typical material for high-temperature components used in ultra-supercritical units because of its good high-temperature creep properties and high-temperature corrosion resistance. In this study, typical characterization techniques such as SEM (Scanning Electron Microscopy), TEM (transmission electron microscopy), and EBSD (Electron Backscattered Diffraction) were used to observe the microstructure of S31042 austenitic heat-resistant steel, while the room-temperature tensile and high-temperature tensile properties of the material were tested under the corresponding conditions. The results show that the grain of S31042 heat-resistant steel after service is the same as that of the non-service samples, which is still twinned austenite. The room-temperature tensile properties and high-temperature tensile properties of S31042 after long service were almost unchanged.

Cause analysis on tube brust of T23 steel water-wall in a ultra-supercritical unit

During the hydrostatic test of an ultra supercritical unit, the water wall burst occurred. The causes of leakage were analyzed by means of macro observation, chemical composition analysis, metallographic examination and hardness test. The results show that the formation of cracks is related to fatigue, extending from the inner wall to the outer wall, accompanied by corrosion and oxidation. Fatigue is the main cause of transverse crack formation.

Flexibility Improvement of 1000mw Ultra-Supercritical Unit Under Full Operating Conditions by Error-Based Adrc and Fast Pigeon-Inspired Optimizer

Flexibility Improvement of 1000mw Ultra-Supercritical Unit Under Full Operating Conditions by Error-Based Adrc and Fast Pigeon-Inspired Optimizer

Discussion on energy saving optimization of supercritical secondary reheat unit

It aimed at the secondary reheat ultra-supercritical unit to study the direction of energy saving, through comparing the design reasonable optimization and energy saving, improve the cycle thermal efficiency, reduce the coal consumption, achieve the goal of saving energy and reducing consumption. From the traditional heat extraction scheme, by setting the cooler, increase the heat series to design a new solution method, such as energy saving optimization scheme of different performance, investment, such as comparative analysis, finally to determine the best solution. Through the design of a series of studies show that for secondary reheat ultra-supercritical unit, can adopt the following means to improve the efficiency of generating units: one is to increase external steam cooler, make full use of the extraction period of heat; The second is to increase the steam recovery series and rationally distribute the enthalpy drops at all levels. After the above energy-saving optimization and transformation technology, the generating efficiency of the unit is increased by 1.6%, and the coal consumption of power supply is reduced by 6.6g/kWh, achieving a good energy-saving effect.

Creep deformation and rupture behavior of 10Cr-3Co-2W heat-resistant steel weldments in ultra supercritical power units

Creep deformation and rupture behavior of a martensitic heat resistant steel (10Cr-3Co-2W) welded joints prepared by vacuum electron beam welding for supercritical power generation unit are investigated employing traditional uniaxial tensile creep, 898 K (625 ℃) to 948 K (675 ℃) and 105 MPa to 250 MPa, and room temperature nanoindentation on different welding micro-zones. The rupture location shifts from base metal (ductile rupture) for the shortest creep time of 74 h, to heat affected zone (brittle Type IV rupture) for the rest crept specimens. Accordingly, a softening phenomenon is observed in fine grain heat affected zone in crept specimens for longer creep times, where voids, precipitates and reduced dislocation density are found and further discussed. The extrapolating creep rupture time under various creep temperature and stress combinations and the 100,000 h creep rupture strength for different temperatures are predicted employing the Larson-Miller parameter method, which satisfies the industry service condition. Compared with tensile creep the nanoindentation creep yields faster creep rates and higher stress exponents; and the largest strain rate sensitivity value (m) in weld metal implies that weld metal has the best creep resistance while heat affected zone and base metal are more likely to appear creep rupture.

Research and Design on the Coordinate Control System of Once-through Boiler Power Unit

Taking the 1000 MW ultra supercritical unit as an object of study, The nonlinear model is builded through mechanism analysis, which is linearized based on small error, the multi-variable decoupling controller is designed to achieve full decoupling of the input and output variables, and finally the three-input-three-output coordinated control system (CCS) is established. The control system is verified by coal quality and the specific enthalpy of feed water disturbance when load changing, the simulation result shows that the improved CCS has good control performance.

Application of extraction steam graded heat storage in peak shaving of condensing units

In order to alleviate the peak shaving pressure of power grid and further improve the deep peak shaving capacity of coal-fired units, this paper applies staged heat storage to condensing units. Under the condition of constant boiler load, the heat of regenerative steam extraction is stored to reduce the electrical load output of the unit. Taking a 660MW ultra-supercritical unit as an example,30%THA,40%THA and 50%THA were taken as the initial conditions of heat storage respectively to discuss the peak shaving range and power regeneration efficiency of different extraction steam positions for heat storage. The results show that the “storage 1# HP heater extraction steam” scheme with “two-stage three tank” heat storage and release structure has the largest peak shaving range of 37.3%~56.9% under 50% initial conditions. When the “two-stage three tank” heat storage and release structure selects the “storage 1# HP heater extraction steam ”scheme under 40% initial working condition, the “power regeneration efficiency” reaches the highest——78.3%. And the “power regeneration efficiency” of “two stage three tank” storage structure are always higher than the “single-stage” storage structure.

Failure analysis of exhaust valve bolt of Ultra Supercritical Unit

The exhaust valve bolt of an ultra supercritical unit broke during its service. This paper makes an all-round study on the fracture reason through macro fracture analysis, chemical composition and material analysis, metallographic structure analysis and hardness analysis. The research shows that the bolt is made of 25Cr2MoV, and the main reason for the fracture of the bolt is the insufficient strength caused by low hardness and uneven structure.

Research on the Application of Thermoelectric Potential Technology in Austenitic Heat-resistant Steel During Aging

HR3C heat-resistant steel is an important material for ultra-supercritical units. The results of the current study show that HR3C heat resistant steel suffers from a significant short term reduction in impact power under long term high temperature conditions. In this paper, through the austenitic heat-resistant steel HR3C through a long time high-temperature aging heat treatment, the results show that after high-temperature aging HR3C significant characteristics of its grain boundaries precipitation of a large number of M23C6 phase, the austenite grains will be closely wrapped, is the main cause of the HR3C impact power found to be significantly reduced. In addition, the thermoelectric potential non-destructive testing technique can better characterise the changes in the characteristics of HR3C heat resistant steel during the long term thermal ageing process and has a greater engineering application in monitoring changes in the properties of HR3C materials, affecting the results of HR3C thermoelectric potential testing in relation to the second phase produced during its thermal ageing process.

Analysis on microstructure and properties evolution and life prediction of P92 steel in high temperature service

P92 steel (10Cr9MoW2VNbBN) is widely used in high-temperature steam piping and high-temperature header fabrications of ultra-supercritical units. In this paper, a follow-up study on the microstructure, mechanical properties and life of P92 steel steam pipes which are virgin, 31,000 h in service, 49,000 h in service and 71,000 h in service was carried out. The results show that the mechanical properties of the P92 steel drop significantly after 31,000 h of service, then decrease slowly with the increase of the service time. When the service time reaches 71,000 h, the high temperature yield strength, percentage elongation, and impact absorbed energy are all close to the lower limit regulated by the ASME standard. Moreover, the morphology of lath martensite becomes fragmentary, the width of the martensitic lath increases and carbide particles cluster and grow at the grain boundary. M23C6 phase coarsens and local Laves phase precipitates. Meanwhile, the dislocation density decreases to some degree. Furthermore, there is a good corresponding relationship between the room temperature hardness and the high temperature tensile strength of the P92 steel after a long period of service. The prediction model of the remaining endurance life of P92 components is proposed on the basis of the room temperature hardness.

Coordinated control system modeling of ultra-supercritical unit based on a new fuzzy neural network

The coordinated control systems (CCS) in ultra-supercritical thermal power unit, like many other industrial systems, is a complex multivariable system with severe nonlinearity, strong multivariable coupling and uncertainties. In order to meet the requirements of operational stability, economy. etc in ultra-supercritical unit, it is necessary to establish its accurate mathematical model and further design the advanced controller. Against this background, a new fuzzy neural network modeling method is proposed in this paper. First of all, the incremental model is considered separately to improve the rationality of the local linear model structure. Then, the parameters in antecedent part is initialized by a kernel k-means++ algorithm, in which Xie-Beni index is used to optimize the number of fuzzy rules. Finally, supervised adaptive gradient descent algorithm and artificial immune particle swarm optimization algorithm work in stages to complete the training of the consequent part parameters. The proposed modeling method in this paper is applied to a 1000 MW unit in China and shows satisfactory accuracy. In the established model, the MSE of power output, main steam pressure and separator outlet steam temperature are 0.0099, 1.21E-4, 0.0023, respectively. Both numerical and graphical simulation results confirm the effectiveness of the presented fuzzy neural network in modeling.

Temperature prediction of combustion level of ultra-supercritical unit through data mining and modelling

This paper presents the dynamic prediction model of different combustion levels temperature in the furnace based on the data mining and modelling. The temperature of the combustion level is the important parameter to characterize the combustion state. The infrared temperature measuring device is developed to measure the temperature of different combustion levels. Based on the operation data of 660 MW ultra-supercritical coal-fired unit, the dynamic prediction models of different combustion levels (bottom, middle and upper) temperature under different load conditions are proposed by using the autoregression integrated moving average with external input model and autoregressive distributed lag model. For the different load conditions, including high-load, middle-load and low-load, variable importance in the projection algorithm is used to obtain the key variables that affect the combustion temperature of different levels. The different prediction models are compared and analyzed. The feasibility and effectiveness of the developed dynamic model for predicting the combustion level temperature using industrial data is validated. Results demonstrate that the proposed approach provides an effective tool for predicting temperature of combustion level and the potential of further improving combustion optimization.

Mechanical Properties of Main Steel Pipeline P92 Steel in Ultra-Supercritical Unit after 50,000 h Service

The mechanical properties of P92 steel after 50,000 h service were explored using the mechanical property tests, such as tensile test, bending test, and impact test by means of scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS), etc. The results show that the strength, elongation, and plasticity of P92 steel after the 50,000 h high-temperature service meet the requirements specified in the related standards, with a certain aging embrittlement phenomenon, which is closely related to the structure aging after the service. The precipitates after the high-temperature service are mainly M23C6, Laves, and compounds of Nb, where the first two phases, which are large, present weak binding force to the matrix with embrittled grain boundary, but the dispersed fine compounds of Nb can be effectively pin the dislocations, and have outstanding solid solution strengthening effect, which is good for improving the strength, plasticity, and toughness of P92 steel.

Investigation on control in oxide scale formation and prevention of peeling off in ultra-supercritical unit

It is a common problem that oxide scale of boiler tube peels off in supercritic al unit. In recent years, many boiler tube burst accidents have been caused by oxide sc ale peeling off and blocking. Therefore, the analysis and research of oxide scale is of g reat significance. In order to control the occurrence of such accidents and reduce the ec onomic losses of thermal power plants, this paper mainly analyzes the factors influenci ng the oxide scale growth rate, peeling off condition and puts forward corresponding p revention and treatment measures.