Numerical Analysis of Labyrinth Seal Performance for the Impeller Backface Cavity of a Supercritical CO_(2) Radial Inflow Turbine

For a radial inflow turbine(RIT),leakage flow in impeller backface cavity has critical impacts on aerodynamic performance of the RIT and axial force acting on the RIT impeller.In order to control this leakage flow,different types of labyrinth seals are numerically studied in this paper based on a supercritical carbon dioxide(S-CO_(2))RIT.The effects of seal clearance and cavity outlet pressure are first analyzed,and the impacts of seal design parameters,including height,number and shape of seal teeth,are evaluated.Results indicate that adding labyrinth seal can improve cavity pressure and hence adequately inhibits leakage flow.Decreasing the seal clearance and increasing the height of seal teeth are beneficial to improve sealing performance,and the same effect can be obtained by increasing the number of seal teeth.Meanwhile,employing seals can reduce leakage loss and improve RIT efficiency under a specific range of cavity outlet pressure.Finally,the influences of seal types on the flow field in seal cavity are numerically analyzed,and results demonstrate that isosceles trapezoidal type of seal cavity has better sealing performance than triangular,rectangular and right-angled trapezoidal seal cavities.

Application of Supercritical CO2 Gas Turbine for the Fossil Fired Thermal Plant

A supercritical CO2 gas turbine cycle can produce power at high efficiency and the gas turbine is compact compared with the steam turbine. Therefore, it is very advantageous power cycle for the medium temperature range less than 650 ℃. The purpose of this paper is to show how it can be effectively applied not only to the nuclear power but also to the fossil fired power plant. A design of 300 MWe plant has been carried out, where thermal energy of flue gas leaving a CO2 heater is utilized effectively by means of economizer and a high cycle thermal efficiency of 43.4 % has been achieved. Since the temperature and the pressure difference of the CO2 heater are very high, the structural design becomes very difficult. It is revealed that this problem can be effectively solved by introducing a double expansion turbine cycle. The component designs of the CO2 heater, the economizer, supercritical CO2 turbines, compressors and the recuperators are given and it is shown that these components have good performances and compact sizes.

Performance Analysis and Retrofit on 350-MW China-Made Supercritical Steam Turbines

In this paper the development status and background of 350-MW China-made supercritical steam turbines are introduced.Through the study on the eight turbines that are put into operation,their technical performances are compared and summarized.The major factors affecting the heat consumption rate are analyzed in details and the technical measures to reduce the heat consumption rate are put forward.These measures have been applied to several such units with significant improvements,which can provide important references for the maintenance and retrofit of 350-MW super critical steam turbines.

Demonstration of a small‐scale power generator using supercritical CO_(2)

The supercritical CO_(2)(sCO_(2))power cycle could improve efficiencies for a wide range of thermal power plants.The sCO_(2)turbine generator plays an important role in the sCO_(2)power cycle by directly converting thermal energy into mechanical work and electric power.The operation of the generator encounters challenges,including high temperature,high pressure,high rotational speed,and other engineering problems,such as leakage.Experimental studies of sCO_(2)turbines are insufficient because of the significant difficulties in turbine manufacturing and system construction.Unlike most experimental investigations that primarily focus on 100 kW‐or MW‐scale power generation systems,we consider,for the first time,a small‐scale power generator using sCO_(2).A partial admission axial turbine was designed and manufactured with a rated rotational speed of 40,000 rpm,and a CO_(2)transcritical power cycle test loop was constructed to validate the performance of our manufactured generator.A resistant gas was proposed in the constructed turbine expander to solve the leakage issue.Both dynamic and steady performances were investigated.The results indicated that a peak electric power of 11.55 kW was achieved at 29,369 rpm.The maximum total efficiency of the turbo‐generator was 58.98%,which was affected by both the turbine rotational speed and pressure ratio,according to the proposed performance map.

Simulation Modelling and Techno-Economics of Supercritical Carbon Dioxide Recompression Closed Brayton Cycle

In recent years, there has been global interest in meeting targets relating to energy affordability and security while taking into account greenhouse gas emissions. This has heightened major interest in potential investigations into the use of supercritical carbon dioxide (sCO2) power cycles. Climate change mitigation is the ultimate driver for this increased interest;other relevant issues include the potential for high cycle efficiency and a circular economy. In this study, a 25 MWe recompression closed Brayton cycle (RCBC) has been assessed, and sCO2 has been proposed as the working fluid for the power plant. The methodology used in this research work comprises thermodynamic and techno-economic analysis for the prospective commercialization of this sCO2 power cycle. An evaluated estimation of capital expenditure, operational expenditure, and cost of electricity has been considered in this study. The ASPEN Plus simulation results have been compared with theoretical and mathematical calculations to assess the performance of the compressors, turbine, and heat exchangers. The results thus reveal that the cycle efficiency for this prospective sCO2 recompression closed Brayton cycle increases (39% - 53.6%) as the temperature progressively increases from 550˚C to 900˚C. Data from the Aspen simulation model was used to aid the cost function calculations to estimate the total capital investment cost of the plant. Also, the techno-economic results have shown less cost for purchasing equipment due to fewer components being required for the cycle configuration as compared to the conventional steam power plant.

Hopf Bifurcation Research of Hydraulic Turbine Governing System with a Saturation Nonlinearity

A nonlinear mathematical model for hydro turbine governing system with saturation nonlinearity in small perturbation has been proposed with all the essential components, i.e. turbine, PID t^^pe governor with saturation part and generator included in the model. Existence, stability and direction of Hopf bifurcation of an example HTGS are investigated in detail and presented in forms of bifurcation diagrams and time ＂wavefomis. The analysis show,that a supercritical Hopf bifurcation may exist in hydraulic turbine systems in some certain conditions. Moreover, the dynaiidc behavior of system with different parameters such as Tw, Tab, Ty and 尺 are studied extensively. An example with numerical simulations is presented to illustrate the theoretical results. The researches provide a reasonable explanation for the Hopf phenomenon happened in operation of hydroelectric generating unit.

Feasibility Analysis of Back-Pressure Steam Feeding Water Pump for Direct Air-Cooled Unit

As the performance of an air-cooled condenser is apt to be affected by the fluctuating ambient condition, some difficulties are brought to the use of a steam feeding water pump in an air-cooled unit. This paper introduces a new design of for steam feeding the water pump of an air-cooled unit using the back-pressure steam turbine as the prime motor. Using variable condition analysis on a 600 MW direct air-cooled unit, and with consideration of the effect on the ambient conditions, the feasibility, economy, and adaptability of the design are verified.

Aerothermodynamic Design and Flow Characteristics for a S-CO_(2) Radial Inflow Turbine

In this paper,a radial inflow turbine is designed for the 150 kW S-CO_(2) Brayton cycle system,and flow characteristics and off-design performances are analyzed.The design results are accurate and high performances can be achieved for the S-CO_(2) power system,and the total-static efficiency of 86%and net output power about 285.2 kW can meet the design requirements of S-CO_(2) cycle system.The results of the flow characteristics show the streamlines of radial inflow turbine distribute uniformly,and the vortexes generated at the shroud of the blade suction surface have little influence on the turbine performances.The off-design performances show the total-static efficiency remains above 80%in the pressure ratio range of 1.6~2.9,and the output power and mass flow rate increase with the pressure ratio increasing.It is indicated that the designed turbine has excellent off-design performances and can meet the operation requirements.The study results can provide guidance for S-CO_(2) radial inflow turbine design and operation.

Machine learning-based multi-objective optimization and thermal assessment of supercritical CO_(2) Rankine cycles for gas turbine waste heat recovery

Technologies for utilizing waste heat for power generation have attracted significant attention in recent years due to their potential to enhance energy efficiency and reduce greenhouse gas emissions.This research focuses on the comparative and optimization analysis of three supercritical carbon dioxide(sCO_(2))Rankine cycles(simple,cascade,and split)for gas turbine waste heat recuperation.The study begins with parametric analysis,investigating the significant effects of key variables,including turbine inlet temperature,condenser inlet temperature,and pinch point temperature,on the thermal performance of advanced sCO_(2) power cycles.To identify the most efficient cycle configuration,a multi-objective optimization approach is employed.This approach combines a Genetic Algorithm with machine learning regression models(Random Forest,XGBoost,Artificial Neural Network,Ridge Regression,and K-Nearest Neighbors)to predict cycle performance using a dataset extracted from cycle simulations.The decision-making process for determining the optimal cycle configuration is facilitated by the TOPSIS(technique for order of preference by similarity to the ideal solution)method.The study's major findings reveal that the split cycle outperforms the simple and cascade configurations in terms of power generation across various operating conditions.The optimized split cycle not only demonstrates superior power output but also exhibits enhanced net power output,heat recovery,system and exergy efficiency of 7.99 MW,76.17%,26.86%and 57.96%,respectively,making it a promising choice for waste heat recovery applications.This research has the potential to contribute to the advancement and widespread adoption of waste heat recovery in energy technologies boosting system efficiency and economic feasibility.It provides a new perspective for future research,contributing to the improvement of energy generation infrastructure.

BEM/FDM Conjugate Heat Transfer Analysis of a Two-dimensional Air-cooled Turbine Blade Boundary Layer

A coupled boundary element method （BEM） and finite difference method （FDM） are applied to solve conjugate heat transfer problem of a two-dimensional air-cooled turbine blade boundary layer. A loosely coupled strategy is adopted, in which each set of field equations is solved to provide boundary conditions for the other. The Navier-Stokes equations are solved by HIT-NS code. In this code, the FDM is adopted and is used to resolve the convective heat transfer in the fluid region. The BEM code is used to resolve the conduction heat transfer in the solid region. An iterated convergence criterion is the continuity of temperature and heat flux at the fluid-solid interface. The numerical results from the BEM adopted in this paper are in good agreement with the results of analytical solution and the results of commercial code, such as Fluent 6.2. The BEM avoids the complicated mesh needed in other computation method and saves the computation time. The results prove that the BEM adopted in this paper can give the same precision in numerical results with less boundary points. Comparing the conjugate results with the numerical results of an adiabatic wall flow solution, it reveals a significant difference in the distribution of metal temperatures. The results from conjugate heat transfer analysis are more accurate and they are closer to realistic thermal environment of turbines.

Performance Assessment of a Novel Polygeneration System Based on the Integration of Waste Plasma Gasification,Tire Pyrolysis,Gas Turbine,Supercritical CO_(2)Cycle and Organic Rankine Cycle

In this paper,a novel polygeneration system involving plasma gasifier,pyrolysis reactor,gas turbine(GT),supercritical CO_(2)(S-CO_(2))cycle,and organic Rankine cycle(ORC)has been developed.In the proposed scheme,the syngas is obtained by the gasification and the pyrolysis is first burned and drives the gas turbine for power generation,and then the resulting hot exhaust gas is applied to heat the working fluid for the supercritical CO_(2)cycle and the working fluid for the bottom organic Rankine cycle.In addition to the electrical output,the pyrolysis subsystem also produces pyrolysis oil and char.Accordingly,energy recovery is achieved while treating waste in a non-hazardous manner.The performance of the new scheme was examined by numerous methods,containing energy analysis,exergy analysis,and economic analysis.It is found that the net total energy output of the polygeneration system could attain 19.89 MW with a net total energy efficiency of 52.77%,and the total exergy efficiency of 50.14%.Besides,the dynamic payback period for the restoration of the proposed project is only 3.31 years,and the relative net present value of 77552640 USD can be achieved during its 20-year lifetime.

汽流激振下超超临界汽轮机碰摩转子的油膜力特性分析

为探究汽流激振与碰摩故障耦合下超超临界汽轮机组轴系油膜力特性的变化特点,以高压缸转子为研究对象,计算各非线性因素影响下各向异性转子两端的油膜力特性,并结合力的矢量图分析转子两侧的滑动轴承油膜力参数不同时的矢量变化。结果表明:交叉刚度会引发油膜力矢量图出现椭圆化趋势,通过油膜力矢量图边缘的波动情况可间接表征转子在不同运行工况下的振动特点,该现象可作为轴系故障诊断的一个判别方向。

非线性动态特性系数对汽轮机转子-轴承-密封系统运动特性的影响

为准确地反应汽流激振下汽轮机转子-轴承-密封系统的运动特性,推导了包含非线性动态特性(非线性刚度、阻尼)的转子运动微分方程,将数值模拟获得的非线性汽流激振力拟合成方程耦合到运动方程中,采用龙格-库塔法求解对应的运动方程,基于试验对比验证了考察非线性因素的必要性与运动微分方程的准确性。在此基础上,分析汽流激振力作用下不同非线性动态特性系数对转子运动特性与稳定性的影响。结果表明:系统中的非线性动态特性会改变转子不同类型的混沌运动区域与位移,使1/2、1/3、2/3工频的出现范围及幅值改变,密频现象增加;耦合热、动载荷后高负荷区域转子位移减小。对比Lyapunov指数,考虑非线性动态特性后其均值有所上升;合理的非线性刚度能够改善系统的稳定性,高非线性阻尼值能提高系统稳定性;耦合热、动载荷后的系统高负荷运行时更稳定。

某1000MW超超临界机组不同配汽方式对经济性的影响研究

基于某1000MW超超临界机组,分别对喷嘴调节、全周进汽+节流调节、全周进汽+补汽阀调节等配汽方式进行了变工况计算分析,结果表明不同配汽方式对机组变工况性能影响主要体现在主汽压力和高压缸效率变化上,进而影响机组热耗率。针对该机组全年负荷率分布情况进行了综合经济性分析,得出了该机组经济性最优的配汽方式。

水下S-CO_(2)循环部分进气轴/径向涡轮机对比研究

将超临界二氧化碳(S-CO_(2))循环动力系统合理应用于无人水下航行器(UUV),有助于解决现有UUV蒸汽动力循环系统尤其是针对小功率等级应用效率低的问题。为合理选型水下S-CO_(2)系统涡轮机,结合损失模型的一维方法获得了设计空间内的最佳几何参数,并基于RANS方程的三维数值仿真方法验证了一维设计方法的合理性,进一步对比分析了轴/径向涡轮机的气动性能及流动特性。结果表明,设计工况下径向涡轮机内效率比轴向涡轮机高5.41%,但尺寸较大,约为轴向涡轮机的2倍;径向涡轮机的主要损失集中在喷管和转子非工作段,而轴向涡轮机则主要为转子处产生的二次流损失。通过变工况分析发现,轴向涡轮机更适用于低速比工况,但在同一转速下径向涡轮机效率更高。文中研究结果可为应用于UUV的S-CO_(2)系统动力主机的研制提供参考。

600℃及以上等级高参数汽轮机组主要部件选材及应用

综合近年来国内外先进超超临界汽轮机主要部件材料方面的资料,分析了国内外600℃及以上等级超超临界汽轮机主要部件的选材及材料性能情况,给出了我国600℃及以上等级超超临界汽轮机主要部件的使用材料。

汽轮机高位布置超超临界燃煤发电系统变工况㶲经济性分析

可再生能源的迅速普及给电网的稳定性和可靠性带来了挑战,为了解决此问题,燃煤机组承担了调峰调频的主要任务。汽轮机高位布置技术可大幅减少耐高温材料的用量,从而提高超高参数机组的经济性。为获得汽轮机高位布置超超临界燃煤发电机组的变负荷性能,建立了㶲分析和㶲经济性分析模型,分析了不同负荷下机组的㶲经济性,获得了机组变负荷的不可逆性分布。分析结果表明:通过对系统参数进行优化,可以改善高压加热器的㶲效率;采用汽轮机高位布置技术的燃煤机组的度电成本为0.3324元/(kW·h);发电的㶲价格随着负荷的升高而降低。

东方汽轮机补汽阀与协调变负荷技术性研究

东方汽轮机有限公司生产的1000 MW超超临界、一次中间再热、单轴、四缸四排汽、双背压、间接空冷凝汽式汽轮机,型号为NJK1000-28/600/620;机组设计一路补汽阀,目的是通过补汽阀将主蒸汽从汽轮机高压缸的第五级进入高压缸,以便加快协调变负荷的速率。

汽轮机部件多轴蠕变-疲劳寿命评估方法

汽轮机汽缸、转子等高温部件运行中受到疲劳损伤和蠕变损伤,二者的损伤机制会互相影响,有必要对疲劳损伤和蠕变损伤以及二者的耦合作用进行评估。在Ohno-Wang循环塑性模型基础上进行了拓展,提出了一种统一黏弹塑性循环材料本构模型,在ABAQUS平台上采用UMAT用户子程序开发了多轴蠕变-疲劳耦合分析程序。采用该程序对1 000 MW超超临界机组高温转子进行了多轴蠕变-疲劳寿命评估,结果显示损伤最大的位置出现在第1级动叶叶根轮槽位置。研究成果可为汽轮机高温部件的寿命评估提供技术支撑。

某1000MW超超临界机组低压通流优化方法研究

指出了某1000MW超超临界机组低压通流效率较低的原因,据此针对低压通流的级做功型式、级数、焓降分配及末级叶片提出了优化方法并确定最终优化方案;最后对优化前后的低压通流进行了三维气动分析,结果表明,优化后通流效率明显提升。