太阳能烟囱发电装置的CFD模拟

用Fluent软件对太阳能烟囱发电装置内的气流进行了数值模拟，获得了太阳能烟囱发电装置内气流流速、温度等分布，并将温度场模拟计算值和试验检测值进行了比较。结果表明：气流在集热棚中从四周向中部汇流是一个加速的过程；从地面到烟囱，随着高度的增加温度呈递减分布。温度分布模拟与试验检测结果的规律基本相似。但由于进行了稳态假设，也存在一定差别。数值模拟结果以集热棚中心呈对称分布。然而，由于集热棚南部接收的太阳辐射大于北部，在试验检测中南边的温度明显高于北边的温度，温度的峰值向南边偏移，呈不对称分布。     

烟囱阴影对风力增压太阳能烟囱电站性能的影响:基于西班牙原型电站规模的数值案例研究

为研究烟囱阴影效应,本文采用太阳射线追踪算法对基于西班牙原型电站规模的太阳能烟囱电站(SCPP)和风力增压型太阳能烟囱电站(WSSCPP)进行了三维数值模拟.烟囱阴影区面积随着太阳光线入射角的增加而增加,本文研究了入射角从0°变化到30°下系统的温度和速度分布;还研究了在几个SCPP综合系统中的烟囱阴影效应.结果表明:...     

烟囱阴影下风力增压式太阳能烟囱电站性能探究

文章以西班牙太阳能烟囱电站为原型,采用太阳射线追踪法加载太阳辐射,对太阳能烟囱电站和风力增压型太阳能烟囱电站进行三维数值模拟,探讨烟囱阴影下系统的流场特性和太阳入射角度对系统性能的影响。研究结果表明:烟囱阴影区蓄热层表面、集热棚表面温度突降,导致热气流与蓄热层表面、集热棚表面进行对流换热,造成热量损失;随着太阳入射角增加,系统轴功率和集热棚效率均明显下降;风力增压装置形成的出口负压可以削弱阴影所造成的气流掺混等不利影响,因而风力增压型太阳能烟囱电站涡轮机轴功率的变化幅度相对常规太阳能烟囱电站较为平缓。     

太阳能热气流发电系统仿真与实验研究

太阳能热气流发电系统是一种新型的可再生能源发电系统。文章利用COMSOL Multiphysics软件构建了该系统的CFD模型,并对该系统中集热棚和烟囱内的温度和压强,以及烟囱内浮升气流的风速变化情况进行了模拟研究。同时,利用搭建的太阳能热气流实验装置测量了集热棚内气流温度和烟囱内风速,并将实验结果与仿真结果进行对比分析。分析结果表明,集热棚内气流温度和烟囱内风速实测值的变化趋势与仿真结果基本一致,集热棚内气流温度实测值的平均值与仿真值平均值之间的相对偏差为2.9%,烟囱内风速仿真值与实测值之间绝对偏差的平均值以及标准差分别为1.21 m/s,0.4。     

集热棚高度对太阳能热气流发电性能的影响

以内蒙古乌海金沙湾太阳能烟囱热气流发电站为研究对象,应用ANSYS-Fluent软件对电站系统进行了稳态数值计算,模拟不同集热棚高度下系统内部流场和压力场的分布规律。模拟结果的对比分析显示,对该电站而言,集热棚高度以6⁸ m为宜。     

太阳能热气流发电流道优化分析

以西班牙太阳能热气流电站为原型进行数值模拟,得出了太阳能烟囱内的速度场、压力场和温度场分布;研究了集热棚坡度、分流板高度和弧度等因素对系统发电性能及涡轮机位置的影响。研究结果表明:集热棚坡度增加时,烟囱的抽吸作用增强,空气流速增加,有利于提高太阳能热气流发电的输出功率;当集热棚坡度约为0.5°时,其作用最为明显,对于提高系统发电性能最为有利;增加分流板有利于气流发电站的优化,当分流板高度略微高于集热棚高度时,优化效果较好;分流板弧度越小,越有利于系统的优化;集热棚坡度对涡轮机位置有影响,改变分流板的几何因素对涡轮机位置没有影响。     

辅助加热气体焓值与太阳能热气流发电系统烟囱特性的数值模拟

针对辅助加热太阳能热气流发电系统,采用数值模拟的方法对辅助加热烟囱特性进行了数值模拟,研究了辅助加热气体的焓值变化对烟囱速度场分布的影响。研究表明,辅助加热气体的焓值在6×104~8×104 k J/s内变化时,烟囱底部的气流速度比无辅助加热增大了60%~73%,提高了烟囱的抽吸能力,而且辅助加热气体的焓值有一个最优区间,可使烟囱底部动能的增加达到一个最优值。     

立式太阳能热气流电站系统运行机理研究

由于立式太阳能热气流电站系统中气流的流动过程温度及压力的耦合作用,气流的密度随电站系统高度的增加而不断变化,利用UDF编程工具对密度与温度和压力的关系式及密度随高度的变化关系式进行编程,并导入Fluent计算软件中,通过数值计算得到太阳能热气流电站系统内的流动传热特性,并将该结果与设置恒空气密度模型的数值计算结果及实验结果进行比较,结果表明:当温压耦合下的数值计算结果与实验值差28%,较设密度为恒定值与实验值差41%,因此采用温压耦合模型,更符合系统实际运行情况。     

太阳能热气流电站透平布置位置研究

基于相对压力概念,建立了太阳能热气流电站系统的新数学模型,并通过数值模拟得到系统内的相对压力分布。根据系统相对压力的分布特点确定了透平布置的最佳位置：在烟囱的底部区域,相对压力最小,压力梯度最大,最适于布置透平;在技术容许的情况下,为实现能量转换效率最高,不宜采用能量梯级利用方案。     

间接冷凝换热制备淡水的联合海水淡化太阳能烟囱电站初探

文章设计了一种专门用来制备淡水的冷凝器,以及一种间接冷凝换热制备淡水的联合海水淡化太阳能烟囱电站(SCPPSDIC)。以西班牙太阳能烟囱电站的几何参数为基础,对SCPPSDIC系统进行三维建模和数值模拟,并将模拟结果与单一太阳能烟囱电站(SCPP)的模拟结果进行对比分析。研究结果表明:SCPPSDIC的温度场、压力场沿烟囱中轴线呈对称分布,且变化较为平缓;相比于SCPP,SCPPSDIC的输出功率虽有4.2 k W的小幅度下降,但冷凝器区域能够析出3.95 t/h的淡水,淡水产出量极其可观,这使得太阳能综合利用率由1%以下提高到3.43%;冷凝器在制备淡水的同时,所放出的凝结热也会对流入蒸馏池的海水起到预热作用,从而使系统的能量得到充分利用。     

3D modeling of a 200 cm HT-PEFC short stack

A computational fluid dynamics (CFD) model of a five cell short stack is presented in form of a multi-domain and multi-scale model, which allows the simulation of an entire stack with reasonable computational power and time. The model comprises an averaged volume (porous volume) approach to mimic the flow distribution in the cell flow fields. Electrochemical conversion is described by a standard approach which is based on the Tafel equation. The results are validated against local measurement of temperature and current density inside a HT-PEFC short stack consisting of 5 cells with an active area of 200 cm².     

Characterization of a novel, highly integrated tubular solid oxide fuel cell system using high-fidelity simulation tools

A novel, highly integrated tubular SOFC system intended for small-scale power is characterized through a series of sensitivity analyses and parametric studies using a previously developed high-fidelity simulation tool. The high-fidelity tubular SOFC system modeling tool is utilized to simulate system-wide performance and capture the thermofluidic coupling between system components. Stack performance prediction is based on 66 anode-supported tubular cells individually evaluated with a 1-D electrochemical cell model coupled to a 3-D computational fluid dynamics model of the cell surroundings. Radiation is the dominate stack cooling mechanism accounting for 66-92% of total heat loss at the outer surface of all cells at baseline conditions. An average temperature difference of nearly 125 °C provides a large driving force for radiation heat transfer from the stack to the cylindrical enclosure surrounding the tube bundle. Consequently, cell power and voltage disparities within the stack are largely a function of the radiation view factor from an individual tube to the surrounding stack can wall. The cells which are connected in electrical series, vary in power from 7.6 to 10.8 W (with a standard deviation, σ = 1.2 W) and cell voltage varies from 0.52 to 0.73 V (with σ = 81 mV) at the simulation baseline conditions. It is observed that high cell voltage and power outputs directly correspond to tubular cells with the smallest radiation view factor to the enclosure wall, and vice versa for tubes exhibiting low performance. Results also reveal effective control variables and operating strategies along with an improved understanding of the effect that design modifications have on system performance. By decreasing the air flowrate into the system by 10%, the stack can wall temperature increases by about 6% which increases the minimum cell voltage to 0.62 V and reduces deviations in cell power and voltage by 31%. A low baseline fuel utilization is increased by decreasing the fuel flowrate and by increasing the stack current demand. Simulation results reveal fuel flow as a poor control variable because excessive tail-gas combustor temperatures limit fuel flow to below 110% of the baseline flowrate. Additionally, system efficiency becomes inversely proportional to fuel utilization over the practical fuel flow range. Stack current is found to be an effective control variable in this type of system because system efficiency becomes directly proportional to fuel utilization. Further, the integrated system acts to dampen temperature spikes when fuel utilization is altered by varying current demand. Radiation remains the dominate heat transfer mechanism within the stack even if stack surfaces are polished lowering emissivities to 0.2. Furthermore, the sensitivity studies point to an optimal system insulation thickness that balances the overall system volume and total conductive heat loss.     

An analysis of the control and operation of a solid oxide fuel-cell power plant in an isolated system

The concept of a feasible operating area for a solid oxide fuel-cell power plant is introduced by establishing the relationship between the stack terminal voltage, fuel utilization, and stack current. The analysis shows that both the terminal voltage and the utilization factor cannot be kept constant simultaneously when the stack current changes. This leads to the two possible control strategies as constant utilization control and constant voltage control. By controlling the input hydrogen fuel in proportion to the stack current, constant utilization control can be accomplished. By incorporating an additional external voltage-control loop, stack terminal voltage can be maintained constant. The detailed design of the control schemes is described. The effectiveness of the proposed schemes is illustrated through simulation. Using the numerical results, the maximum value of load power change that the plant can handle safely is predicted.     

Numerical analysis of an SOFC stack under loss of oxidant related fault conditions using a dynamic non-adiabatic model

This paper presents a numerical analysis of a 1000 W-class solid oxide fuel cell stack. The study includes simulation of dynamic operation of the unit under conditions which are qualified as faults. The simulation tool was developed to address the effects of oxidant-related faults on the operating parameters of the stack. Additionally, a control system was proposed in order to mitigate the effects of the sudden reduction in the flow of oxidant and passivation of the cells inside a 60-cell stack. In the current study, those occurrences were related to the loss of tightness of the sealants in the stack of planar cells. The model of an adiabatic-stack was used to generate the temperature profiles and was used in two reference cases. In the first case, the control system was activated in order to maintain the key parameters within the safe range, in the second case the simulations with deactivated controls enabled prediction of the temperature, voltage and power in the stack which continues operation without counteractions oriented toward minimizing the negative impacts on the performance due to exceeding the given limiting values of parameters. In the current study, two scenarios were analyzed: partial loss of oxidant and partial failure of stack modules resulting in decrease of the generated electric power. The results of both cases are presented, with and without the fault prevention control modules considered. Adjustment of the operating parameters can effectively limit the rapid increase in thermal gradients inside the stack. To complement the discussion, a classification of the typical faults of SOFC stack is presented.     

Numerical based design of exhaust gas system in a cogeneration power plant

Among the various aspects that have to be analysed in a cogeneration and combined cycle plant design, the exhaust gas stack design can represent a critical aspect, in particular when a by-pass stack, which allows the modulation of heat-to-power generation, is present, since it may influence the entire system working condition. To properly take into account the large number of the different requirements which enter in an exhaust gas system design, a multidisciplinary analysis involving numerical integrated approaches can be adopted in order to obtain an optimally designed stack system. In this paper, the design of the exhaust gas system in a cogeneration plant is analysed. The design is performed numerically through a three-dimensional integrated numerical code. Different design solutions are simulated and the results discussed in detail.     

Thermochemical model and experimental validation of a tubular SOFC cell comprised in a 1 kWel stack designed for μCHP applications

Being aware of the needs for clean highly efficient micro combined heat and power (μCHP) systems for single and multifamily households, the Italian Ministry of Industry launched in 2009 the EFESO Project aiming to develop and operate four SOFC prototypes. An imperative part of the project foresaw computational modeling to optimize operating conditions of the power modules and pinpoint potential drawbacks in its design. This article deals with a 3-dimensional thermochemical model of a single SOFC tubular geometry cell comprised in a 1kW_el stack operating under similar conditions to the characterized power module. An analysis is presented on the effects of current density distribution, temperature distribution in the cell and pressure drop in the air and fuel channels, being these the most critical variables when operating the SOFC-powered μCHP system. This model will serve as a platform to generate a model of the whole stack which will be further validated by means of experimental activities.     

带脱硫系统的火电厂烟囱低温腐蚀模拟实验研究

采用人工加速腐蚀实验方法,研究了电站尾部烟气对烟囱混凝土的影响。对在H2SO4、HCl和HF酸液下的低温腐蚀进行了比较研究。结果表明:3种酸液对混凝土腐蚀的发展规律符合幂函数的变化关系;在H2SO4和HCl腐蚀下,抗压强度随腐蚀时间的延长而降低,但在HF酸中,抗压强度增加;抗压强度的变化值随着中性化深度增加而增加。混凝土中CaO含量下降是引起强度降低的主要原因;强度大幅度降低(HF酸除外)的根本原因,是由于混凝土中Ca(Al2Si2O8)·4H2O、Na6AlSi2O7和Ca2SiO4·4H2O等组分大量减少。     

3D modeling of an HT-PEFC stack using reformate gas

A computational fluid dynamics model is presented, which is suitable to perform full stack simulations of a high temperature polymer electrolyte fuel cell with reasonable computational power and time. The model is based on a previously presented multi-domain and multi-scale model and is extended by electrochemical equations suitable for operation with reformate gas. Model results show very good agreement with the local current density and temperature distributions which were obtained by stack experiments. A general analysis of possible flow configurations regarding anode, cathode and cooling fluid inside a stack is performed. The most favorite configuration with regard to current density homogenization is anode and cathode in counter-flow with cooling and anode in co-flow. This result is confirmed by stack experiments.     

1000MW超超临界锅炉NOx生成特性的数值模拟研究

新建的大型燃煤电站锅炉设计中均采用了低NOx燃烧系统,通过对炉内燃烧过程的合理组织来实现低NOx生成和排放.采用计算流体力学(CFD)模拟的方法,完成了对某电厂采用先进低NOx燃烧系统的1000 MW超超临界锅炉的计算和分析.对通过数值模拟计算获得的炉膛温度场、CO浓度场、O2浓度场和NOx浓度场进行分析,证明锅炉主燃...     

无旁通烟囱燃气_蒸汽联合循环机组的运行维护和停运

论述了无旁通烟囱燃气－蒸汽联合循环机组运行维护和停运的特点,探讨了它与火力发电厂和有旁通烟囱联合循环的不同之处,总结了机组运行维护和停动的经验,可供运行人员和设计人员参考。