Kinetic Energy Recovery from the Chimney Flue Gases Using Ducted Turbine System

An innovative idea of extracting kinetic energy from man-made wind resources using ducted turbine system for on-site power generation is introduced in this paper. A horizontal axis ducted turbine is attached to the top of the chimney to harness the kinetic energy of flue gases for producing electricity. The turbine system is positioned beyond the chimney outlet, to avoid any negative impact on the chimney performance. The convergentdivergent duct causes increase in the flue gas velocity and hence enhances the performance of the turbine. It also acts as a safety cover to the energy recovery system. The results from the CFD based simulation analysis indicate that significant power 34 kW can be harnessed from the chimney exhaust. The effect of airfoils NACA4412 and NACA4416 and the diffuser angle on the power extraction by the energy recovery system using a 6-bladed ducted turbine has been studied with the CFD simulation. It is observed that the average flue gas velocity in the duct section at the throat is approximately twice that of the inlet velocity,whereas maximum velocity achieved is 2.6 times the inlet velocity. The simulated results show that about power may be extracted from the chimney flue gases of 660 MW power plant. The system can be retrofitted to existing chimneys of thermal power plants, refineries and other industries.     

PIV measurements over a double bladed Darrieus-type vertical axis wind turbine: A validation benchmark

Vertical axis wind turbines (VAWTs) are very attractive for in-home power generation since they can be adopted even at low wind speeds and highly variable wind direction. Even if significant experimental research activity has been carried out to improve VAWTs performance, the ability to accurately reproduce flow field characteristics around turbine blades by CFD (computational fluid dynamics) techniques represents a powerful approach to further enhance wind turbines performance. Thanks to CFD, in fact, it is possible to reproduce flow characteristics with a detail level impossible to achieve by experiments. Nevertheless, in order to appropriately analyze the flow structure by CFD application, an accurate validation is essential, and high-quality measurements of some main flow characteristics are required. In recent publications the authors investigated, both experimentally and numerically, the performance of an innovative double bladed Darrieus-type VAWT, with the aim to define an optimal configuration also focusing on self-starting ability of the prototype by employing CFD technique. Nevertheless, comparison between experiments and numerical results was made only in terms of power and torque coefficients. To overcome such limitation, in this paper the authors propose an experimental benchmark case for CFD results validation, describing detailed flow field in correspondence of one pair of blades of the innovative Darrieus-type VAWT in static conditions. Measurements were performed employing Particle Image Velocimetry (PIV) technique on a scaled model of the turbine blades realized by 3D printing. An uncertainty analysis was also performed which showed a high accuracy of the obtained experimental results. The measurements of the main flow characteristics (bi-dimensional velocity components) were then used for a test case CFD validation of two different turbulence models.     

涡轮搅拌器搅拌特性数值模拟与实验研究

针对工业常用的涡轮搅拌器,就典型的平直叶开启涡轮式、45°斜叶开启涡轮式和平直叶圆盘涡轮式3种搅拌器形式,分别进行了流场数值模拟和对比搅拌实验.基于Fluent软件的CFD数值模拟,获得的速度场分布,反映了搅拌器的结构特点.使用Fluent软件的Report功能输出模拟扭矩值,换算成的功率曲线和实测的搅拌功率曲线有很好的一致性,证明了CFD技术不仅能对速度场进行模拟,还可有效模拟搅拌功率,对搅拌设备优化设计和实物实验有进一步的指导作用.     

Developing a model for prediction of helical turbine flowmeter performance using CFD

In this article, a numerical model for prediction of turbine flowmeter performance is proposed. This model is consists of a novel iterative algorithm, based on torque balance theory. Despite previous studies, the effect of bearings drag torque on finding balance point is considered. Using an in-house code, the bearings torque of the flowmeter is calculated based on the finite difference method. The three-dimensional steady state internal flow field of turbine flowmeter is obtained from the Computational Fluid Dynamics (CFD) simulations. For evaluation of the model׳s accuracy the experiments on a 6 in. helical turbine flowmeter has been carried out for crude oil and water. Consequently, the K-factor and also linearity error for cases of fluids are achieved. The results were compared with experimental data and it is found that the numerical model results are reasonably accurate. Therefore, by using the proposed model, the heavy cost of design and optimization of turbine flowmeters can be reduced.     

竖轴固定直叶片潮流水轮机自启动性能研究

竖轴固定偏角直叶片潮流水轮机具有结构简单、系统稳定可靠、造价低的特点,具有广阔的应用前景。但是由于该机构在水流场中的自启动能力较差,低流速下很难启动,故在实际工程应用中有着明显的劣势。提高竖轴固定叶片水轮机自启动性能是目前研究的重点。本文根据叶片在流场中的水动力特点,利用数值模拟的方法在CFD中计算了不同流速下,叶片在不同位置时的自启动性能,同时计算出加装叶栅附体的水轮机的自启动性。进行对比后,得出加装叶栅附体可以提高水轮机自启动性能。初步总结了在设置不同角度、栅距后,不同类型的叶栅对水轮机自启动性能的影响。     

Failure analysis of gas turbine generator cooling fan for 14° and 19° — blades angle of attack

In gas turbine power plants, a fan is used as a cooling system to dissipate generated heat in coils (copper conductors) and generator electric circuits at the end sides of its rotor. In some cases, fracture of blades causes short circuit between rotor and stator and consequently generator explosion and made lot of financial problems. The fracture of cooling fan blades has been occurred five times at the turbine side of the generator in our case of study, just 100 hr after resuming operation after overhaul. Using numerical analysis as well as laboratory investigation — includes visual inspections, metallography and SEM — can help better finding failure problems that cause blade failures. A series of numerical analysis was performed to diagnose the cause of failure possibility. CFD analysis is used to study the airflow distribution in order to observe probable separation phenomenon and pressure forces that they are imposed to fan blades due to operation. A finite element method was utilized to determine the stresses and dynamic characteristics of the fan blade (natural frequencies, stresses and vibrations).     

开式燃气轮机中冷循环热力学优化

调整质量流率(或沿通流路径压力损失)和中间压比的分配可以优化开式燃气轮机中冷循环的热力学性能。分析表明,分别存在最佳的燃料流率(或沿通流路径压力损失)和中间压比使循环输出功率最大,最大功率输出对总压比有附加的最大值。给定质量流率和动力装置尺寸的情况下,通过合理分配压气机入口和透平出口之间的流通面积,循环输出功率和效率可以再次得到优化。     

Optimization the design of venturi gas mixer for syngas engine using three-dimensional CFD modeling

A venturi mixer prototype is developed for mixing air and synthesis gas or “syngas” as a fuel. Syngas is recognized as a viable energy source worldwide, particularly for stationary power generation. It has a very low energy density, so a mixer with λ (ratio of actual to stoichiometric air-fuel ratio) in the range of 1.1 to 1.7 is expected. In this study, three-dimensional computational fluid dynamics (CFD) modeling is used to investigate and analyze the influence of the throat diameter, gas chamber thickness and gas exits diameter on mixer characteristics and performance. Attention is focused on the effect of venturi mixer geometry on the air-fuel ratio, pressure loss and mixing quality. Based on the numerical results, an optimized design of venturi gas mixer is made. The optimized design has λ in the range of 1.2 to 1.3, and gives very good mixing quality and acceptable pressure loss. The CFD results are validated with experimental data. The CFD results show good agreement with experimental data.     

Performance investigation of a counter-rotating tidal current turbine by CFD and model experimentation

Global warming is one of the issues in the world, which is mainly due to the burning of fossil fuels. Thus, alternative energy is now paramount in the 21st century. In Korea, the tidal currents in the southwestern sea have a wide range of currents that are available for tidal current power generation. Single rotor turbines can obtain a theoretical maximum power coefficient of 59.3%, whereas dual rotor turbines can attain a maximum of 64%. In this study, the performance and efficiency of a counter-rotating tidal current turbine is investigated when changing the front and rear blade angles at different water velocities. The investigation was conducted by using Computational fluid dynamics (CFD) and experimental methods highlighted in this study. When varying these parameters, changes in the streamlines were observed in the CFD results. The changes in flow stability over the blade surfaces observed in the numerical results were reflected in the power and power coefficient graphs presented in this study. The results obtained by the experiments were also shown to be in good agreement with the CFD results.     

A performance study on a direct drive hydro turbine for wave energy converter

Clean and renewable energy technologies using ocean energy give us non-polluting alternatives to fossil-fueled power plants as a countermeasure against global warming and growing demand for electrical energy. Among the ocean energy resources, wave power takes a growing interest because of its enormous amount of potential energy in the world. Therefore, various types of wave power systems to capture the energy of ocean waves have been developed. However, a suitable turbine type is not yet normalized because of relatively low efficiency of the turbine systems. The purpose of this study is to investigate the performance of a newly developed direct drive hydro turbine (DDT), which will be built in a caisson for a wave power plant. Experiment and CFD analysis are conducted to clarify the turbine performance and internal flow characteristics. The results show that the DDT obtains fairly good turbine efficiency in cases with and without wave conditions. Most of the output power is generated at the runner passage of Stage 2. Relatively larger amount of the decreased tangential velocity at Stage 2 produces more angular momentum than that at Stage 1 and thus, the larger angular momentum at the Stage 2 makes a greater contribution to the generation of total output power in comparison with that at Stage 1. Large vortex existing in the upper-left region of the runner passage forms a large recirculation region in the runner passage, and the recirculating flow consumes the output power at Region 2.     

一种轴流式涡轮的优化设计

利用CFD方法对一种轴流式涡轮的内流场作了详细的三维紊流数值模拟.分析不同叶片结构对流场的影响情况.试验表明改进后的扭曲叶片涡轮比直叶片涡轮的水力性能高,从而验证了CFD软件是一种很有效的流体模拟软件,对改进涡轮的机械性能指明了途径.     

Parametric simulation and performance analysis of a solar gas turbine power plant from thermodynamic and exergy perspectives

Using solar energy in gas turbine cycles is a new method that can improves the efficiency of gas turbines. Placing a solar receiver before a combustion chamber can raise the temperature of the air coming into the chamber and reduce the consumption of fuel in the chamber. The system that combines a solar energy receiver with a gas turbine cycle is technically called a “solar gas turbine”. The goal of this paper is the parametric simulation and performance analysis of a gas turbine cycle equipped with a solar receiver from thermodynamic and exergy aspects of view. The selected parameters in this study, include the pressure ratio of compressor, the temperature of gases at the turbine inlet and the direct normal irradiance. The obtained results indicate that the fuel consumption of this combined system is reduced by using a solar receiver and the temperature of gases entering the combustion chamber increased. The reduction of consumed fuel, in turn, reduces the rate of exergy destruction in the combustion chamber. Another important point is that the solar receiver itself has the least amount of exergy destruction. The net power generated by a solar gas turbine cycle is 10 % higher than that produced by a simple gas turbine cycle. Also, the studies show that the electrical efficiency of a solar gas turbine cycle is about 41 % higher than the simple gas turbine cycle.

     

Simulation of hydropower turbine performance in duct for system utilizing tidal jet generator

The marine hydropower system proposed in this study creates a tidal jet generator from a seawater exchange type breakwater, with empty space similar to a basin to store ocean water. Due to the water level difference between the inner and outer sides of the breakwater, strong and uni-directional jets are generated. The energy from the jets is captured by turbines in the breakwater ducts.

In this study, the proposed system is first introduced. The design process for a new turbine and its preliminary performance in openwater conditions, estimated using Computational fluid dynamics (CFD), are presented. Experiments with the turbine in a Circulating water channel (CWC) at Pusan National University were also carried out. The results from the simulations and experiments with the same conditions were compared to verify the CFD accuracy. The turbine performance in a duct is estimated; the target power can be generated using the newly developed turbine.

     

一种耦合燃气轮机的富氧燃烧系统技术经济性能分析

提出一种燃气轮机与富氧燃烧耦合的动力系统,该系统利用烟气排烟余热和锅炉内设高温受热面加热压缩空气,使其推动燃气轮机涡轮做功,用燃气轮机的压气机替代空分系统的压缩机,实现空分系统和动力系统耦合,同时燃气轮机也是烟气CO2压缩机的原动机。对新系统进行热力学与经济性分析,对应计算系统净供电效率和供电成本。结果显示当工质在锅炉高温受热面中的吸热量占燃气轮机热耗的比β为0.8、燃气轮机效率ηgt为0.32时,新型耦合系统净效率可比常规富氧燃烧系统增加4.2%,供电成本降低0.044元/(k W·h)。     

Influence of steam injection and hot gas bypass on the performance and operation of a combined heat and power system using a recuperative cycle gas turbine

The influence of steam injection and hot gas bypass on the performance and operation of a combined heat and power (CHP) system using a recuperative cycle gas turbine was investigated. A full off-design analysis was used to investigate not only the change in performance but also the variation in engine operation caused by steam injection. The performance improvement capability and operating limitations of full steam injection was examined. Selected operations (partial steam injection and underfiring) that secure minimum compressor surge margin were comparatively analyzed. Partial steam injection was found to be a better option than underfiring in all thermodynamic aspects. Under ISO condition, power and efficiency improvements in the partial injection targeted at a 10% surge margin are 27% and 7.4%, respectively. This study also investigated the increase in steam generation brought by the bypass of turbine exhaust gas around the recuperator. This bypass provided high operational flexibility by varying the capacity of thermal energy supply in both the pure CHP operation and the steam-injected operation. In particular, in the steam-injected operation, the capacity of thermal energy supply can be largely increased by the said bypass, while producing a greater power output than the pure CHP system.     

Numerical and experimental analysis of a counter-rotating type horizontal-axis tidal turbine

In order to exploit renewable energies form tidal currents, a unique counter-rotating type horizontal-axis tidal turbine was proposed in this paper. Although a counter-rotating type horizontal-axis wind turbine can be taken as a reference in designing the proposed counterrotating tidal turbine, there are some different characteristics such as the effects of the free surface and the occurrence of cavitation. The unique tidal turbine in this paper was preliminarily designed on the basis of the in-house wind turbine, and then CFD analysis and experimental test were carried out to evaluate its performance. For the extreme conditions where severe flow separation and vortex exist, the comparison of the power coefficients generated by the turbine between the CFD predictions and the experimental data shows not so good. However, good agreement has been obtained for the comfortable blade pitch setting angles and over a range of tip speed ratios, which provides an evidence of validation of CFD analysis. Such results give sufficient confidence that the CFD model set up here is suitable for the further works.     

半浸式螺旋桨水动力性能的数值模拟研究

针对半浸式螺旋桨的水动力性能问题,应用CFD方法对其流场进行了数值模拟研究,并把结果与实验进行比较。通过求解雷诺平均方程(RANS)来模拟流场,采用SST k-ω湍流模型来计算RANS方程中的雷诺应力。利用Fluent中的明渠流动(Open Channel Flow)功能模拟空泡水筒中的气液两相流动,采用VOF方法捕捉自由液面。应用滑移网格法完成搅拌桨的转动,实现了对一个五叶右旋半浸式螺旋桨的数值模拟。研究结果表明,桨的尾流场形态与实验结果吻合地较好,证明了CFD方法预测半浸式螺旋桨性能的有效性。在较低浸入深度时,数值模拟可以很好地预测半浸式螺旋桨的性能。随着浸入深度的增加,推力系数和效率的预测结果基本准确,扭矩系数的预测结果有一定偏差。从数值计算结果中,可以获得宏观力的脉动曲线和完全入水桨叶的压力分布,并且可以对桨叶出水和入水过程进行详细的研究。     

Comparative thermodynamic analysis on design performance characteristics of solid oxide fuel cell/gas turbine hybrid power systems

This paper presents analysis results for the hybrid power system combining a solid oxide fuel cell and a gas turbine. Two system layouts, with the major difference being the operating pressure of the fuel cell, were considered and their thermodynamic design performances were compared. Critical temperature parameters affecting the design performances of the hybrid systems were considered as constraints for the system design. In addition to energy analysis, exergy analysis has been adopted to examine the performance differences depending on system layouts and design conditions. Under a relaxed temperature constraint on the cell, the ambient pressure system exhibits relatively larger power capacity but requires both higher cell temperature and temperature rise at the cell for a given gas turbine design condition. The pressurized system utilizes the high temperature gas from the fuel cell more effectively than the ambient pressure system, and thus exhibits better efficiency. Under a restricted temperature constraint on the cell, the efficiency advantage of the pressurized system becomes manifested.     

用流线曲率法计算透平的变工况性能以及可转导叶对机车燃气轮机牵引特性影响的研究

介绍了用流线曲率法计算轴流式透平变工况性能的方法。对4000马力机车燃气轮机透平进行了计算,计算结果与机组的试验结果吻合较好。还计算了具有可转导叶的透平特性,探讨了可转导叶对机车燃气轮机牵引透平的特性及机组变工况运行的影响。