Ultra-supercritical Power Unit Research Articles

Methods for Competitiveness Improvement of High-Temperature Steam Turbine Power Plants

The paper is concerned with the problem of the development of high-temperature steam turbine power plants with ultra-supercritical (USC) initial parameters. One of the main disadvantages of the USC power unit’s creation is high price due to the application of expensive heat-resistant materials for boiler, live and reheat steam pipelines in turbines. To solve this problem, the following technical improvements to reduce the application of the heat-resistant materials and equipment metal consumption are proposed: horizontal boiler layout, high temperature steam turbine with a cooling system, oxy-hydrogen combustion chambers, and two-tier low-pressure turbine. The influence of the above-mentioned solutions on the high-temperature steam turbine power plant efficiency was estimated using thermodynamic analysis. The promising equipment design was developed based on the results of numerical and experimental research. The analysis of the proposed solutions’ influence upon the economic parameters of a high-temperature power facility was investigated based on the developed cost analysis model, which included the equipment metal and manufacturing expenses. The introduction of all the mentioned cost reduction methods led to a decrease in the facility’s price by RUB 10.5 billion or 15%. The discounted payback period was reduced from 27.5 to 10 years and the net present value increased by RUB 9.6 billion or 16 times.

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.

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.

The influence of the temperature on the mechanical properties of Sanicro 25 steel

Austenitic steel 22Cr25NiWCoCu (Sanicro 25) is one of the newest and most promising steels for use in supercritical and ultra-supercritical power units. High resistance of Sanicro 25 steel to corrosion and oxidation in the steam atmosphere at up to 700 °C is ensured by chromium content at 21.5-23.5 wt%. Also, higher chromium content provides less mass decrement during high-temperature corrosion at 700 °C. Currently, the Sanicro 25 steel is characterised by the highest creep strength among the commercially used creep-resistant stainless steels. In this work, the study of precipitation processes and microstructure stability in the delivery state and after the ageing process in time up to 20,000 h at 750 °C was performed. Identification of secondary phases was performed using electron diffraction on thin films using transmission electron microscopy and X-ray phase composition analysis. Long-term ageing depending on time and temperature showed that there are four secondary phases in Sanicro 25: M23C6, MX, NbCrN, σ-phase and Cu_rich. The precipitation and increase in the size of secondary phase particles during ageing results in a decrease in matrix saturation with alloying elements, which leads to a reduction in hardening by solid solution mechanism. These processes and effects result in changes in mechanical properties. The alloy overageing effect observed for the ageing temperature of 750 °C results in obtaining strength properties similar to those of the steel in the as-received condition.

Overview of Foreign Boiler Designs for Ultra Supercritical (USC) Boilers and Prospects for Development of USC Power Units in Russia

Overview of Foreign Boiler Designs for Ultra Supercritical (USC) Boilers and Prospects for Development of USC Power Units in Russia

Research on the status and priority needs of developing countries to address climate change

Abstract Identifying what developing countries need to address climate change is of great significance for promoting North-South and South-South climate cooperation and implementing the Paris Agreement. In this study, based on questionnaires surveys of 143 representative government officials, experts, scholars, and industry engineers from developing countries who have been engaged in climate change, the current situation and priority requirements of developing countries in terms of policies and actions, technology, financing, capacity building, and international cooperation for addressing climate change were systematically analyzed. We found that 1. Most developing countries have already taken national general actions and sectoral and industry-level actions focus on renewable or clean energy, waste management and recycling, sustainable urban transport and forestry carbon sequestration. 2. The demands for climate change mitigation are mainly concentrated in technology and capital, and the priority areas are energy and electricity and waste management; for climate change adaptation, the demands differ significantly among regions. 3. Developing countries show high preferences for emission reduction and energy-saving technology, solar energy, wind energy and bio-energy, whereas a low preference for supercritical and ultra supercritical power units, nuclear energy and tidal energy. 4. Agroforestry, energy conservation and efficiency, renewable energy and water resources are priority areas for climate change financing. 5. Building institutional capacity, improving technology R&D networks and institutions, formulation and implementation ability of planning schemes, and data statistics and verification are priority areas needed for capacity building. To better address climate change, developing countries need to establish and improve information exchange channels or platforms and strengthen South-South climate cooperation while optimizing the allocation of climate change resources according to the priority needs.

Improved internal-model robust adaptive control with its application to coordinated control of USC boiler-turbine power units in flexible operations

ABSTRACTCoordinated controllers for coal-fired ultra-supercritical (USC) boiler-turbine power units in the new flexible-operation mode face many challenges, such as faster load-following rate over wider-range operations, nonlinear dynamics with long time delay and multiple disturbances from strong-coupled multivariable processes. Hence, to improve the coordinated controller of the USB power unit, this paper proposes an internal-model robust adaptive control (IM-RAC) approach to handle nonlinearity, multiple variables, unknown uncertainties and long-time delay. The proposed IM-RAC augments an internal model with the framework of an L1 robust adaptive control to predict the time-delay variable. In addition, the proposed IM-RAC uses a dual-feedback adaptive law instead of a single-feedback adaptive law. Based on the proof by contradiction, the stability of the IM-RAC control loop is proved, and stability conditions and performance bounds are derived. Furthermore, an IM-RAC coordinated controller is designed for a 1000 MW coal-fired USC power unit. By simulations, we show that the proposed IM-RAC outperforms an advanced model predictive controller in the presences of fast and wide load-following, long-time delay and uncertainties. With less modelling requirements, the IM-RAC control approach is a promising solution to improve the operational flexibility of USC power units.

Microstructure and mechanical properties of HR6W alloy dedicated for manufacturing of pressure elements in supercritical and ultrasupercritical power units

The article presents the results of research on the microstructure and selected mechanical properties of HR6W nickel-base alloy. The test alloy was subjected to isothermal ageing at 700°C and for up to 10000h. The tests of the HR6W microstructure were performed using the scanning electron microscopy (SEM) and the transmission electron microscopy (TEM). The performed microstructural tests of the HR6W alloy showed that in the as-received condition it was characterised by the structure of nickel austenite with numerous primary precipitates of NbC and TiN. Ageing of the investigated alloy contributed to the precipitation of numerous particles of varying morphologies inside the grains and at the grain boundaries, as well as at the boundaries of twins - they were the secondary precipitates of M23C6 and Laves phase. The number of the particles precipitated at the boundaries was so large that they formed the so-called continuous grid of precipitates. Inside the grains, the presence of compound complexes of precipitates was observed. These complexes consisted of the TiN particles, as well as the M23C6 carbides and Laves phase nucleating on them. The tests of the mechanical properties of HR6W alloy showed that in the as-received condition the alloy showed high plastic properties, with relatively low strength properties - in particular, the yield strength. Ageing of the HR6W alloy, as a result of precipitation of numerous particles in the matrix, through the strengthening with the precipitation mechanism, resulted in a considerable growth of the strength properties - inter alia the yield strength by over 60%, with the reduction of the plastic properties - elongation decreased by around 40%. Similar growth in the test alloy was observed for hardness.

Analysis of an improved economizer system for active control of the coal-fired boiler flue gas temperature

The use of a low pressure economizer (LPE) is an effective way to recover waste heat from the exhaust flue gas in thermal power plants. In this paper, an improved bypass staged economizer scheme is presented for China's 600-MW ultra-supercritical power units. The simulation models of the bypass staged economizer and traditional LPE were established based on a 600-MW unit. The simulation results showed that when the presented economizer system was adopted, the temperature of the exhaust flue gas was reduced to near the flue gas acid dew point, thereby greatly improving the energy-saving effects. Compared with the traditional LPE system, the improved economizer system can reduce standard coal consumption rate by an additional 1.1 g/kWh. The bypass ratio under different loads could be adjusted to achieve the best energy-saving effect. The optimum bypass ratio was analyzed under different loads. The results showed that the improved economizer system had a better energy-saving effect by actively controlling the exhaust flue gas temperature.

Analysis of efficiency of 'zero-emission' oxy-type ultra-supercritical power unit based on high-temperature membranes

Analysis of efficiency of 'zero-emission' oxy-type ultra-supercritical power unit based on high-temperature membranes

Analysis of efficiency of 'zero-emission' oxy-type ultra-supercritical power unit based on high-temperature membranes

Oxy-combustion technology by eliminating, in the stage of preparation of oxidant, atmospheric nitrogen from combustion process is characterised by a high concentration of carbon dioxide in the exhaust gas, and thus, facilitates its sequestration. Power unit that operates in classic (air) combustion technology with a gross power output similar to the power of the investigated model is characterised by a CO2 emission of 860 kg/MWh. The use of oxy-combustion allows to reduce the carbon dioxide emissions by more than 90%, so it is worth to present both thermodynamic and economic consequences of the introduction of this technology. Thermodynamic analysis of the model assumed investigation of the impact of changes in the oxygen recovery rate on the basic characteristics of the power unit. In the next stage of calculations the estimated capital expenditures and a break-even price of electricity under the assumption that NPV is equal to zero were determined.

The microstructure evolution and element segregation of Inconel 617 alloy tungsten inert gas welded joint

Abstract

Gradient-free methods applied to optimisation of advanced ultra-supercritical power plant

Thermo-economic analysis and optimisation of thermal systems have become a key solution in providing a better system configuration on the design stage and in modification of already-working installation. Nowadays, there are many commercial software packages allowing one to perform 0-dimensional (0D) analysis of any power plant system. Some of these programs are equipped with their own optimisation tools; however, as is often the case, most of them are not able to carry out a multi-variable optimisation with a large number of decision variables. This paper presents application of the integrated package containing the IPSEpro and MATLAB software for numerical optimisation of advanced ultra-supercritical steam power plant. Searching for new technology makes it necessary to analyse the structure of the thermal cycle. This can be obtained by combining the numerical modelling with the multivariable optimisation of such an object. For that purpose a new concept of 900 MW advanced ultra-supercritical power unit was examined. To increase the efficiency and flexibility of calculations three different non-gradient methods were introduced into the code, i.e., Nelder–Mead, Hooke–Jeeves and Rosenbrock. It was shown that all of the three considered methods can find their usefulness in the optimisation process of power plant thermal cycle giving the rise in the efficiency by about 0.34 percentage points. The additional significant advantage of the Rosenbrock method is the lowest cost of computation, almost independent of the number of decision variables considered. It was shown that the gained efficiency improvement was accompanied with serious intervention into the thermal cycle configuration (in particular into operating pressures) which can lead to necessity of modifying the major power plant components.

Tempospacial energy-saving effect-based diagnosis in large coal-fired power units: Energy-saving benchmark state

The energy-saving analytics of coal-fired power units in China is confronting new challenges especially with even more complicated system structure, higher working medium parameters, time-dependent varying operation conditions and boundaries such as load rate, coal quality, ambient temperature and humidity. Compared with the traditional optimization of specific operating parameters, the idea of the energy-consumption benchmark state was proposed. The equivalent specific fuel consumption (ESFC) analytics was introduced to determine the energy-consumption benchmark state, with the minimum ESFC under varying operation boundaries. Models for the energy-consumption benchmark state were established, and the endogenous additional specific consumption (ASFC) and exogenous ASFC were calculated. By comparing the benchmark state with the actual state, the energy-saving tempospacial effect can be quantified. As a case study, the energy consumption model of a 1000 MW ultra supercritical power unit was built. The results show that system energy consumption can be mainly reduced by improving the performance of turbine subsystem. This nearly doubles the resultant by improving the boiler system. The energy saving effect of each component increases with the decrease of load and has a greater influence under a lower load rate. The heat and mass transfer process takes priority in energy saving diagnosis of related components and processes. This makes great reference for the design and operation optimization of coal-fired power units.

Sensitivity Analysis of a 50+ Coal-Fired Power Unit Efficiency

The coal-fired power unit integration with a CO2 capture and compression installation involves a considerable rise in the costs of electricity generation. Therefore, there is a need for a continuous search for methods of improving the electricity generation efficiency in steam power plants. One technology which is especially promising is the advanced ultra-supercritical (A-USC) power unit. Apart from steam parameters upstream the turbine, the overall efficiency also depends on the efficiency values of individual elements of the plant and the size of energy consumption of the process of CO2 sequestration from the boiler flue gases. These problems are considered herein to emphasize that without specifying the efficiency values of the power plant main elements the information concerning its electricity generation efficiency is incomplete. This paper presents the influence of the efficiency of individual elements of the power plant on its electricity generation efficiency. The lack of information of the efficiencies of the power plant individual elements, by presenting its overall efficiency, may lead to the false conclusions.

Heat transfer characteristics and energy-consumption benchmark state with varying operation boundaries for coal-fired power units: An exergy analytics approach

The energy-saving analytics of coal-fired power units in China is confronting new challenges especially under varying working conditions and operation boundaries, such as load rate, coal quality and ambient temperature. Compared with traditional optimization of specific operating parameters, the idea of energy-consumption benchmark state was proposed. The exergy analytics was introduced to determine the energy-consumption benchmark state, with the minimum exergy destruction under varying operation boundaries. The heat transfer coefficient and condenser vacuum were calculated by considering the influence of operation boundaries in different coal quality and ambient temperature. The coal rate was figured out for the coal fuel in different composition and calorific values, for the circulating water condition in different temperatures and cooling modes with different load rate. As a case study, the energy consumption model of a 1000 MW ultra supercritical power unit was built on the platform of Ebsilon and tested by practical operation data of power unit. The results show that the heat transfer coefficient and condenser vacuum change greatly with different coal composition and circulating water temperatures under different working conditions. The energy-consumption benchmark state of power unit is also operation condition and boundary-dependant. The coal rate of such benchmark state is considerably less than that of the actual state with the same operation boundaries. This makes great reference for the operation optimization of coal-fired power units.

Multi-model Predictive Control of Ultra-supercritical Coal-fired Power Unit

The control of ultra-supercritical (USC) power unit is a difficult issue for its characteristic of the nonlinearity, large dead time and coupling of the unit. In this paper, model predictive control (MPC) based on multi-model and double layered optimization is introduced for coordinated control of USC unit. The linear programming (LP) combined with quadratic programming (QP) is used in steady optimization for computation of the ideal value of dynamic optimization. Three inputs (i.e. valve opening, coal flow and feedwater flow) are employed to control three outputs (i.e. load, main steam temperature and main steam pressure). The step response models for the dynamic matrix control (DMC) are constructed using the three inputs and the three outputs. Piecewise models are built at selected operation points. Double-layered multi-model predictive controller is implemented in simulation with satisfactory performance.

Selection of the cooling system configuration for an ultra-critical coal-fired power plant

The appropriate selection of the condenser pressure, apart from raising the live steam parameters, is a factor which could have a decisive impact on the improvement in the efficiency of the thermal cycle. The pressure value depends both on the parameters and configuration of the cooling system. The condenser cooling system configuration is particularly important in the case of newly designed high-capacity ultra-supercritical power plants. The presented study comprises a comparison of two variants of a cooling system for a 900MW ultra-supercritical power unit. The serial and parallel configurations of the condenser are considered. A thermodynamic analysis which takes account of the exhaust loss of the LP turbine is performed. Additionally, an economic analysis based on the NPV method is conducted for all investigated cases.

Optimal Control System Based on Advanced Control Technology in Ultra Supercritical Power Units

Optimal Control System Based on Advanced Control Technology in Ultra Supercritical Power Units

Calculation of an advanced ultra-supercritical power unit with CO2 capture installation

An efficiency enhancement of coal-fired power units becomes a basis for the reduction in the consumption of primary fuels and as a result in CO2 emissions. Steam parameters increasing is an effective way to improve the efficiency of electricity generation. The progress in materials engineering has led to the more and more common implementation of the technology of power units for ultra-supercritical parameters. The next generation of this technology – the advanced ultra-supercritical parameters A-USC – opens new perspectives. Obtaining a higher efficiency of electricity generation and exceeding the 50% net efficiency barrier, apart from the increase in the steam parameters, requires an optimisation of the thermodynamic cycle, together with the modernisation of the flow system of steam, condensers, regenerative water heaters. The development of the advanced ultra-supercritical technologies is the subject of European, Japanese, American and Chinese projects, which aims at the completion of a power unit with the live steam parameters of 700°C and 35MPa and the net efficiency exceeding 50%. The paper presents the results of the calculations which were performed for a conceptual power unit in two configurations – with single and double steam reheat. The CCS Directive contains a clause providing for the new construction of power installations as “capture ready”. Newly built power unit gives possibility of optimized integration with CO2 capture installation. The power and efficiency loss related with the integration with CO2 capture process can be reduce. Due to the state of knowledge of CO2 capture methods and the ability of its application into the high power unit only the chemical absorption was considered in the paper. The CO2 capture installation requires large amount of heat to solvent regeneration in appropriate quantity and quality, cooling system to discharge waste heat and power to drive CO2 compressor and auxiliary equipment (pump, fans). In the paper the steam to CCU is extracted from IP/LP crossover pipe. The design IP/LP crossover pressure has very significant impact on the power unit efficiency. Its reduction to the level which is required by the CCU can improve power unit efficiency. However, lower crossover pressure results in efficiency looses in part-load operation. Therefore, the analysis of power unit operation with partial load for various design crossover pressure was considered. The slight improvement of power unit efficiency can be gained also through the recovery of waste heat from the overhead condenser and CO2 compressor intercoolers in the feed water preheating system.