Ultra-supercritical Pressure Research Articles

Experimental investigation of heat transfer characteristics of water in a vertically–upward tube under ultra-supercritical pressure and ultrahigh-temperature conditions

Advanced ultra-supercritical (A-USC) steam power generation technology is characterized by main steam conditions of > 700 °C and > 35 MPa, enhanced cycle efficiency, and reduced environmental footprint, and is one of the important development goals of the thermal power plants today. However, scarce studies were conducted on the heat transfer characteristics of supercritical water (SCW) under A-USC operating conditions. An experimental platform to safely measure the heat transfer of SCW flowing in a vertical tube at temperature up to 760 °C and pressure up to 42 MPa was designed and built in this study. Experimental measurements of the heat transfer characteristics of SCW were performed on this platform in a wide range of temperature and pressure, up to a maximum bulk fluid temperature of 750 °C and a maximum pressure of 38 MPa. The effects of pressure, mass flux, and heat flux on the heat transfer characteristics of SCW in the ultrahigh enthalpy region (over 3200 kJ·kg−1) were then analyzed based on the experimental data. Results show that in the ultrahigh enthalpy region, the bulk fluid temperature and wall temperature increase approximately linearly with increasing bulk fluid enthalpy. The heat transfer coefficient decreases gently and then gradually stabilizes in the same range, with values in the range of 4–10 kW·m−2·K−1. In the ultrahigh enthalpy region, increasing the mass flux or decreasing the heat flux will improve the heat transfer performance. And at a pressure of > 35 MPa, increasing the pressure will improve the heat transfer performance moderately. By comparing with experimental data, the Gupta’s correlation has acceptable accuracy in predicting the heat transfer coefficient and inner wall temperature.

State-of-the-art ultra-supercritical variable pressure once-through boiler with improved dynamic characteristics and reliability by reducing mass velocity of furnace wall

State-of-the-art ultra-supercritical variable pressure once-through boiler with improved dynamic characteristics and reliability by reducing mass velocity of furnace wall

Characteristics and Typical Problems Analysis of Laizhou 1000MW Double Reheat Tower Boiler

The boilers of no. 3 and no. 4 units of laizhou power plant phase II project are 1000MW ultra-supercritical pressure double reheat tower boilers. The units 3 and 4 have been puted into operation in august and november 2019 respectively, and several typical problems of tower boiler are encountered during boiler commissioning. This paper mainly introduces the characteristics of the boiler and some typical problems and their solutions encountered during commissioning.

Analysis of creep behavior of welded joints of P91 steel at 600 °C

The martensitic P91 steel (9Cr-1Mo-V-Nb) has been developed for ultra-supercritical pressure application in steam power plants. The creep rupture strength of the welded joint of this steel is limited by the fine-grained region of its heat affected zone (HAZ). The factors which result in the reduction of the creep rupture strength of the fine-grained region of HAZ were discussed. It was found that the most effective factor reducing the creep rupture strength of the fine-grained region of the HAZ of the welded joint of P91 steel, in comparison with other regions of the welded joint, is the finer prior austenite grain size. These fine prior austenite grains of the fine-grained region of the HAZ accelerate the rate of growth of martensite lath subgrains which results in a softer martensite matrix.The minimum creep rate dependence on applied stress for base metal, welded joints and the samples simulating the fine-grained region of the welded joints was described by means of the conventional power-law equation. The experimental results, both in the form of strain versus time creep curves and of minimum creep rate versus time creep curves were used to study the creep behavior of the welded joints of P91 steel at 600 °C.

Experimental investigation on flow instabilities of ultra-supercritical water in parallel channels

An experimental study on the flow instabilities of ultra-supercritical water in the water wall tubes of an ultra-supercritical circulating fluidized bed (CFB) boiler was conducted. The material of the tubes is 1Cr18Ni9Ti. The scope of experimental parameters is as follow: pressure from 23 to 30 MPa, mass flow rate from 0.05 to 0.2 kg·s−1; inlet water temperature from 200 to 390 °C, inlet pressure drop coefficient from 0 to 5.5, and heat flux from 0 to 500 kW·m−2. Variations of mass flow rate and pressure in the parallel channels were recorded with the occurrence of flow instability, and oscillation curves of the wall temperature were obtained. The starting points and factors that affect various types of oscillations were analyzed to derive a stability map. Results show that pressure and mass flow rate display a reverse phase pulsation during oscillation. With the increase in heat flux, three regions of oscillations, namely, region1, region2 and region3, appeared. The oscillations in region1 and region2 are observed for the first time under ultra-supercritical pressure. Among them, oscillations in region1 and region2 are system oscillations, and they have long periods and large amplitudes. Oscillation in region3 belongs to density wave oscillation (DWO), which is the intertube oscillation and has a short period and small amplitude. Increases in system pressure, inlet mass flow rate, inlet pressure drop coefficient or decreasing the inlet water temperature are conducive to system stability.

Experimental study on temperature distribution of membrane water wall in an ultra-supercritical pressure once-through boiler burning zhundong coal

Taking an ultra-supercritical pressure once-through boiler as an example, the temperature distribution of the lower membrane water wall is investigated experimentally, the conclusion reveals that increasing the proportion of Zhundong coal can effectively reduce the district heat load, which benefits the temperature uniformity in the lower membrane water wall. When the boiler being operated at middle load, the temperature deviation in lower membrane water wall increase simultaneously, one of the reasons is that the restriction orifice could not adjust the flow rate of working fluid as expected. By adjusting boiler performance, the temperature uniformity of lower membrane water wall can be improved to a certain degree.

Experimental investigation on two-phase flow instabilities of ultra supercritical pressure boiler with spirally water wall tubes

For a better design of 1000MW ultra supercritical pressure boiler with spirally water wall tubes, an experimental study has been performed in the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University to investigate the instability of the steam-water two-phase flow inside a smooth tube with an inclined angle of 20degree from the horizon. The static hydrodynamic characteristic curves are obtained and the dynamic instabilities are also analyzed. The boundary conditions of the pressure drop oscillation and the density wave oscillation are proposed. The effects of pressure, mass flux, inlet and outlet throttle, inlet subcooling and the compressible volumes are analyzed primarily. The results demonstrate that the above parameters significantly influence the critical heat flux for the mentioned two types of oscillations and the density wave oscillations are the major type of oscillations in boilers and steam generators. The density wave oscillations occur at a higher heat flux than the pressure drop oscillations with the other operating parameters remaining constant. The inducing mechanisms of the above two types of oscillations are clarified. The variation ranges of critical heat flux and critical vapor quality are illustrated. Two empirical correlations predicting the onset of pressure drop oscillation and density wave oscillation are derived from the experimental data.

A study of the hydrodynamic characteristics of a vertical water wall in a 2953t/h ultra-supercritical pressure boiler

A simulation was carried out to study the hydrodynamic characteristics of a vertical water wall in a 2953t/h ultra-supercritical pressure boiler. A hydrodynamic model was established by using the Chebyshev polynomial fitting method. The restriction orifice at the entrance of the water wall was designed at 50% of the boiler maximum continuous rating (BMCR) to minimize the differences in outlet fluid temperature. The hydrodynamic characteristics, including the distributions of the mass flows and pressure drops and the temperature of the metal of the water wall tubes, were studied. It was found that the mass flow within the water wall can be designed to match the heat absorption from the surface that is transferring heat from the furnace at different boiler loads when using this restriction orifice. The variation in the total drops in pressure is related to the variation in the boiler load. However, the proportions of the main components of the overall pressure drop are different at different boiler loads. For weakly heated circuits, the gravitational pressure drop forms a greater part of the total pressure drop than the frictional pressure drop. However for heavily heated circuits, the frictional pressure drop is larger than the gravitational pressure drop, making forced circulation inevitable. The pressure drop induced by the restriction orifice is more pronounced in weakly heated circuits, indicating that it is necessary to use the restriction orifice to adjust the mass flow in weakly heated circuits. Under the normal working conditions of the boiler, the temperatures of the metals did not exceed their safety limitations, suggesting that the reliability of the boiler unit can be ensured.

HTR-Based Power Plants’ Performance Analysis Applied on Conventional Combined Cycles

In high temperature reactors including gas cooled fast reactors and gas turbine modular helium reactors (GT-MHR) specifically designed to operate as power plant heat sources, efficiency enhancement at effective cost under safe conditions can be achieved. Mentioned improvements concern the implementation of two cycle structures: (a), a stand alone Brayton operating with helium and a stand alone Rankine cycle (RC) with regeneration, operating with carbon dioxide at ultrasupercritical pressure as working fluid (WF), where condensation is carried out at quasicritical conditions, and (b), a combined cycle (CC), in which the topping closed Brayton cycle (CBC) operates with helium as WF, while the bottoming RC is operated with one of the following WFs: carbon dioxide, xenon, ethane, ammonia, or water. In both cases, an intermediate heat exchanger (IHE) is proposed to provide thermal energy to the closed Brayton or to the Rankine cycles. The results of the case study show that the thermal efficiency, through the use of a CC, is slightly improved (from 45.79% for BC and from 50.17% for RC to 53.63 for the proposed CC with He-H2O operating under safety standards).

J0310301 A-USCボイラ用具材溶接継手のクリープ強度

The commercialization of a 700℃ class pulverized coal power system, advanced ultra-supercritical (A-USC) pressure power generation, is the target of an ongoing research project in Japan. In the A-USC boiler, Ni or Ni-Fe base alloys are used for high-temperature parts at 650-700℃, and advanced high-Cr ferritic steels are planned to be used at temperatures lower than 650℃. In the dissimilar welds between Ni base alloys and high-Cr ferritic steels, Type-IV failure in the heat-affected zone is a concern. The high B-9Cr steel developed at the National Institute for Materials Science, which has improved creep strength in both base metal and weldment, is a candidate material for the Japanese A-USC boiler. In the present study, long-term creep tests were conducted on the dissimilar welded joints between Ni base alloys and high B-9Cr steels. Microstructures and creep damage in the dissimilar welded joints were investigated. The creep rupture life of the dissimilar welded joints using high B-9Cr steel was 5-10 times longer than that of the conventional 9Cr steel welded joints at 650℃. The effect of welding procedure was also investigated.

百万等级电站锅炉给水泵径向弯叶片空化性能研究

本文以百万等级超超临界电站锅炉给水泵为研究对象，通过CFD技术对叶片空化性能进行数值研究。提出一种基于样条函数思想的径向弯叶片几何参数设计方法，引入“正弯叶片”和“反弯叶片”两种叶片径向弯曲结构。结果表明：“直叶片”必需空化余量为22.8 m，与试验值误差仅为0.2 m，预测结果具有一定的精度，“反弯叶片”必需空化余量为21.7 m，空化性能最优；“正弯叶片”在叶片进口处压力面最先出现空泡，吸力面空化面积最大，而“反弯叶片”吸力面空化面积最小。 Numerical simulation of cavitation performances of 1000 MW ultra-supercritical pressure boiler feed pump was carried out through CFD applications. A new design method of geometric profile parameters based on Spline function was proposed. Two types of radial bending blades were in-troduced, i.e. “Forward Curved Blade” and “Reversed Curved Blade”. Results indicate that the NPSH (net positive suction head) of “Straight Blade” is 22.8 m, then the absolute error is 0.2 m. Compared with “Straight Blade” and “Forward Curved Blade”, “Reversed Curved Blade” has the best cavitation performance, and NPSH is 21.7 m. The vapor generated at pressure surface of “Forward Curved Blade” near the leading edge at first, and the cavitation region of suction surface is the largest, but the “Reversed Curved Blade” is opposite.

超々臨界圧ボイラ給水中の鉄定量における前処理としての2段フィルター濃縮法

超々臨界圧ボイラ給水中の鉄定量における前処理としての2段フィルター濃縮法

Creep Strength of Dissimilar Welded Joints Using High B-9Cr Steel for Advanced USC Boiler

The commercialization of a 973 K (700 °C) class pulverized coal power system, advanced ultra-supercritical (A-USC) pressure power generation, is the target of an ongoing research project initiated in Japan in 2008. In the A-USC boiler, Ni or Ni-Fe base alloys are used for high-temperature parts at 923 K to 973 K (650 °C to 700 °C), and advanced high-Cr ferritic steels are planned to be used at temperatures lower than 923 K (650 °C). In the dissimilar welds between Ni base alloys and high-Cr ferritic steels, Type IV failure in the heat-affected zone (HAZ) is a concern. Thus, the high B-9Cr steel developed at the National Institute for Materials Science, which has improved creep strength in weldments, is a candidate material for the Japanese A-USC boiler. In the present study, creep tests were conducted on the dissimilar welded joints between Ni base alloys and high B-9Cr steels. Microstructures and creep damage in the dissimilar welded joints were investigated. In the HAZ of the high B-9Cr steels, fine-grained microstructures were not formed and the grain size of the base metal was retained. Consequently, the creep rupture life of the dissimilar welded joints using high B-9Cr steel was 5 to 10 times longer than that of the conventional 9Cr steel welded joints at 923 K (650 °C).

Long term creep behaviour of welded joints of P91 steel at 650 °C

The martensitic P91 steel (9 Cr–1Mo–V–Nb) has been used for high temperature components in the highly ultra super critical pressure steam power plants. The creep behaviour in terms of creep rupture strength and minimum creep rate of the welded joints of this steel is controlled by that of the fine-grained heat affected zone (FGHAZ). The factors which results in the reduction of the creep rupture strength and the increase in the minimum creep rate of FGHAZ at 650°C were determined and discussed. It was found that the main difference between the welded joint zones is the prior austenite grain size. The finer the prior austenite grain size as in FGHAZ, the higher is the rate of recovery of dislocations, the rate of coarsening of the subgrain structure and coarsening of the intergranular Cr-rich carbide particles, consequently, the lower the creep resistance.

Status and Prospect of Large-Scale Circulating Fluidized Bed Boiler

The paper is focused on the present situation and the development of large-scale circulating fluidized bed (CFB) boilers. Several developed technology of CFB such as supercritical and ultra supercritical pressure CFB boilers for power plants, oxy-fuel CFB boiler for CO2 capture and high-density circulating fluidized bed gasifier for advanced IGCC/IGFC are introduced in this paper.

Trend of technology innovation in China's coal-fired electricity industry under resource and environmental constraints

This research builds a technology-based bottom-up model to estimate the performance of China's coal-fired electricity industry on resource consumption and environmental emissions. From the integrated estimation of three scenarios characterizing different stages of technology innovation in 2007–2030, technology innovation is proven to be the determinant in decreasing resource use and environmental effects from electricity production, but analysis based on current policies reveals some doubt in achieving the coal consumption intensity control target. Constrained with national control targets, the best route of technology innovation is calculated by integrated benefit targeting optimization. Supercritical (SC) and ultra-supercritical (USC) pressure boilers, flue gas desulfurization (FGD) and closed-cycle wet cooling with a high circulation ratio will be the mainstream technologies before 2030 based on current policy. It is inevitable to close or reconstruct small power plants from the late 2010s, and integrated gasification combined cycle (IGCC) and pressurized fluidized bed combustion combined cycle (PFBC-CC) plants will show a competitive advantage in the late 2020s. However, air cooling and FGD systems will expand slower than the authorities' expectation, while higher water prices and SO2 charges promote the expansion. Stricter restrictions are also found to be positive for technological progress.

PRECIPITATES IN HR3C STEEL AGED AT HIGH TEMPERATURE

HR3C steel(Fe-25Cr-20Ni-Nb-N)is a new type of austenitic heat-resistant steel which has been widely used for super-heater and re-heater tubes in the ultra supercritical pressure (USC)boiler.The mechanical properties of HR3C steel were dependent on the stability of the microstructure, particularly the large amount of precipitates formed during service.This work was focused on the change of microstructure and the precipitations of HR3C steel after thermal aging for 500 h at 750℃.The results indicated that the major precipitates were variform M_(23)C_6 carbides and NbCrN nitrides.M_(23)C_6 carbides precipitated on grain boundaries and in intragranular.Fine and dispersed NbCrN nitrides were found to precipitate in intragranular.The hardness of HR3C steel had been improved through dispersed M_(23)C_6 and fine NbCrN precipitates after thermal aging for 500 h at 750℃.All the M_(23)C_6 carbides,with lattice parameter of three times of the austenite matrix,grown in a cube to cube orientation relationship with the matrix.Some of the M_(23)C_6 carbides which precipitated on grain boundaries were transformed intoσphase.

Research and Development of Advanced Steam Turbine Systems with the Ultra Super Critical Pressure Steam Condition for Future Generation (Optimization of Advanced Turbine Systems and Development of Heat Resistant Ferritic Rotors)

Application of advanced steam condition for the old oil fired units is very useful to improve the plant thermal efficiency, as a result, it reduces CO2 emission and achieves the economical generating cost. Development of the heat resistant ferritic rotor combined with rotor surface cooling system is very important to realize the steam turbine with the advanced steam condition. The full scale ferritic turbine rotor has been manufactured to verify the producibility and the quality of materials. This paper describes how to develop heat resistant ferritic turbine rotors for advanced steam condition for future.

Microstructural instability of a welded joint in P91 steel during creep at 600°C

The martensitic 10CrMoVNb 91 (P91) steel has been developed for applications under high ultra supercritical pressure for steam power plants. The creep rupture strength of welded joints of this steel is limited by the fine grained region of its heat affected zone (HAZ). The microstructural changes occurring in this region during long term creep tests at 600°C and 70 MPa were examined using optical microscopy and scanning and transmission electron microscopy for comparison with the microstructure of this region after post-weld heat treatment. The factors which result in the reduction of creep rupture strength of the fine grained region of HAZ are discussed. It was found that the most effective factors reducing the creep rupture strength of the fine grained region of the HAZ of a welded joint in P91 steel, in comparison with the coarse grained region of the HAZ and the base metal of the welded joint, are the finer prior austenite grain size of the fine grained region, which accelerates the rate of growth of martensite lath subgrains and enhances creep cavitation, and also the lower peak temperature during welding, which results in a softer martensite matrix.

Properties of weldments in high-strength ferritic heat-resistant steels

In recent years, the preservation of natural resources and the reduction of the pressure on the environment have become important tasks. In fossil-fuelled power plants, efforts have been made to improve the efficiency in electricity generation by raising the temperature and pressure of steam. The main conditions for the steam used with the ultra-super critical pressure (USC) boiler of the most recent design in Japan have reached 600°C and 31 MPa. To realise these steam conditions, it is essential to use materials with excellent high-temperature creep strength in the areas subjected to the highest temperature, such as steam and heat conduction pipes. It is not an exaggeration to say that these conditions had not been achievable until high-strength ferritic steels and austenitic stainless steels were developed.1 Incidentally, in pressure-resistant sections of a boiler like the above-mentioned pipes are welded structures of a large scale, and hence, not only base materials but also the properties of weldments affect the life and reliability of pressure-resistant sections. This article deals with the properties required for welded joints of high-strength ferritic heat-resistant steels which have been used for the most recently designed boilers for fossil power plants. It also describes the creep strength properties at the most important joints and the issues of welding consumables for high-strength materials, together with future tasks.