氢燃料电池氢气利用率提升策略研究

针对燃料电池堆再循环管线的再循环速率低的问题,提出用于燃料电池的氢气供应系统的循环控制方案,根据再循环管线中再循环的气体量精确估计由吹扫阀吹扫的氢体浓度,通过反馈每种气体的吹扫量,调节吹扫阀的开度,提升氢气利用率,并对该方案进行仿真分析。仿真结果表明,燃料电池阳极侧氢气利用率明显提升,最高可达92.733%,可提高燃料电池堆的耐久性。     

汽轮机空心静叶吹扫性能的试验研究和数值计算

在气-液两相流试验装置上研究了汽轮机空心静叶缝隙热气吹扫对二次水滴尺寸的影响,并结合数值方法分析了热气吹扫对叶栅气动性能的影响.试验结果表明:热气流吹扫使二次水滴的尺寸显著减小,尾缘处的缝隙吹扫对减小二次水滴的尺寸最明显,而压力面时二次水滴尺寸的影响最小,并且提高吹扫压比有助于提高吹扫效果.数值分析表明:压力面和吸力面吹扫缝隙后出现严重的流动分离;扩压区增大,使压力损失增大;尾缘吹扫需对叶片尾缘加厚,但这却导致了严重的尾迹损失;热气吹扫造成叶栅效率降低高达4%.     

氢燃料电池氢气管道吹扫系统冷启动策略研究

针对现有车载燃料电池管道在吹扫过程中氢气侧管道由于低温结冰易受阻,从而导致冷启动困难的问题,提出氢气管道两级吹扫方案,以实现对燃料电池堆氢管中剩余水、蒸汽含量的独立控制,降低冷启动时的加热能耗,避免冷启动失效。通过三维仿真对4种不同工况下阴极中段在不同时间的温度、阴极中段在不同时间的冰体积分数、电池纵向截面表面不同时间的温度进行分析,结果表明该方案可实现在-20 ℃温度下20 s内的平稳冷启动,既解决了低温冷启动困难问题,又保证了冷启动后的电堆输出性能。     

辅助蒸汽吹扫锅炉末级再热器的应用研究

某电厂锅炉末级再热器大面积换管后,投运前须对再热器及其管道进行吹扫,目的 是去除在大面积换管过程中产生的杂质(金属屑、切割物、焊渣等杂物),以提高机组的安全性,改善运行期间的蒸汽品质.通过主蒸汽吹扫及辅助蒸汽吹扫两种方案的比较,确定了最适合吹扫方案.     

二次吹扫条件下PEMFC电堆冷启动特性实验研究

为探究燃料电池低温启动性能,利用自搭建的实验平台,对稳态运行后的PEMFC电堆进行二次吹扫实验,考察吹扫气体温度、流量对吹扫实验中电堆内阻的影响,对经过二次吹扫后的电堆进行多次启动试验,研究进气温度对电堆冷启动性能的影响.实验结果表明:增大吹扫气体温度和流量都可降低电堆内阻,但进气温度影响较小;从启动时间上来看,二次吹...     

影响气质联用测定水质挥发性有机物实验结果的因素

采用吹扫捕集/气相色谱质谱法对水质57种挥发性有机物分别在不同的吹扫温度、盐浓度及pH条件下进行分析.实验结果表明,提高吹扫温度及盐浓度可以增加化合物的灵敏度获得更好的富集效果,将样品pH调至中性或酸性可以使得替代物及加标回收率正常.     

连续蒸汽吹扫技术在乌奇工程上应用浅析

针对巴基斯坦乌奇560MW联合循环电站工程蒸汽吹扫方案的成功案例,分析了连续中压蒸汽吹扫技术的特点,为蒸汽吹扫参数的选择提供了参考依据。     

锅炉飞灰采样装置结露堵灰的原因分析及其对策

锅炉飞灰采样装置常出现堵灰,影响飞灰含碳量测量装置的工作.为此,以自吸式飞灰等速采样装置为例,对结露堵灰问题进行了分析和计算,并提出了合理进行取样管线保温.压缩空气吹扫及吹扫空气预热等解决措施,取得了良好的运行结果.     

浅议烟气脱硫GGH吹扫方式的选择

GGH的堵塞直接关系到脱硫系统的运行阻力以及电站主机的运行稳定性,分析说明GGH堵塞可能产生的原因,阐述GGH蒸汽吹扫方式的优势以及压缩空气吹扫的弊端。结合老挝HONGSA 3×626MW烟气脱硫工程,论述蒸汽吹扫与压缩空气吹扫在能耗、运行稳定性、机组投运率、设备维护量、设备维护费用、换热元件寿命等方面的对比情况。综合各项性能指标,在湿法脱硫系统入口烟气灰份较大时,GGH采用蒸汽吹扫明显要优于采用压缩空气吹扫。     

700MW级多轴燃气蒸汽联合循环机组余热锅炉的蒸汽冲管

针对1台700MW级多轴燃气-蒸汽联合循环余热锅炉,采用两炉单独吹扫、降压法与稳压法相结合的冲管方案,以燃机点火后余热锅炉的自产蒸汽作为冲管汽源.由于余热锅炉的高中低压系统参数不同,三路系统分别吹扫并分别打靶;三路临时系统在临吹门前合并.只使用一套打靶装置和消音器,简化了临时系统,降低了冲管费用和工作量.详细介绍了冲管时为防止三路临时管道间产生过高热应力而采取的暖管和吹扫步骤,并讨论了冲管过程中出现的问题,可为同类型机组的冲管提供借鉴.     

A dynamic model for hydrogen consumption of fuel cell stacks considering the effects of hydrogen purge operation

The actual hydrogen consumption of a fuel cell stack varies with a fixed time delay under the step load change. For each individual stack, the delay time in the step-up load stage is generally shorter than in the step-down stage. Due to the hydrogen purge operation, transient overshoots take place intermittently after the actual hydrogen consumption reaches the steady state, and the duration and peak value of such overshoots are distributed approximately within a fixed range. Based on the performance investigation mentioned above, an improved dynamic model for hydrogen consumption of a fuel cell stack considering the effects of hydrogen purge operation is introduced in this paper. Compared with the previous model, the suggested model indicates a better agreement between test and simulation, especially in the working condition of hydrogen purge operation.     

An investigation into the effect of anode purging on the fuel cell performance

The anode purge is a crucial process for the fuel cell long time operation because when the hydrogen is supplied in a circulation mode, any impurities present in hydrogen will gradually accumulate which lead to output voltage loss. A mathematical model is proposed for the purge process based on some operational purge parameters. The governing equations are solved and the effect of purge process on the stack working parameters is analyzed. Purge operational parameters are determined in such a way that the minimum pressure fluctuations in the anode compartment and a compromise between the minimum voltage loss and minimum hydrogen waste are achieved. A semi-stable condition is introduced and indicated that the behavior of voltage loss and hydrogen waste at this condition with respect to purge stop time (duration which the purge valve is closed) is semi-logarithmic.     

Effective purge method with addition of hydrogen on the cathode side for cold start in PEM fuel cell

The purge process is essential for successful cold start of fuel cell vehicles during winter, and it plays an important role in the removal of the residual water inside the fuel cell in a short time. In this study, a new purge method is introduced by adding a small amount of hydrogen to the cathode gas flow in order to increase the purge performance. The experimental results demonstrate that the hydrogen addition purge method is very effective in removing the residual water near the catalyst layer. The water removal is verified by measuring the resistance of the fuel cell, dew point temperature of the outlet purge gas, and weights of the membrane electrolyte assembly (MEA) and gas diffusion layer (GDL). In addition, the image of the GDL after the purge process is captured to show the advantage of the hydrogen addition purge method. Cold start experiments are also conducted after the optimal purge process. It is also found that the degradation of the catalyst layer is not serious after the hydrogen addition purge process.     

Optimization of purge cycle for dead-ended anode fuel cell operation

Dead-Ended Anode (DEA) operation of Proton Exchange Membrane Fuel Cells (PEMFCs) yields a system with lower complexity and the potential to reduce system cost as fewer external components are required. Optimization of the purge interval and cycle duration, for a given operating power, can increase the fuel cell efficiency which depends on three interrelated objectives, namely, the hydrogen loss during the purge, the average voltage output between the purges, and the voltage decrease due to the carbon corrosion caused by hydrogen starvation over the lifetime of the DEA operation.In advancing past results, this paper shows how the purge cycle can be optimized for better efficiency in DEA operation by considering the impact of carbon corrosion. For this optimization, a model capturing the liquid water and nitrogen accumulation in the anode is needed to accurately describe the evolution of corrosion rate and the amount of hydrogen wasted during the purge. The optimization process is first defining a target range of purge intervals based on the physical constraints of the actuator and the model-based prediction of the species concentration distributions. The search of optima is performed then by scanning the target domain to quantify the trade-off between wasted hydrogen and reducing the corrosion rate over a long time horizon.     

Transient characteristics investigation of the integrated ejector-driven hydrogen recirculation by multi-component CFD simulation

The hydrogen supply of the fuel cell system is realized by the cooperation of multiple components. Transient characteristics of a single component can affect the performance of other components. In this study, a three-dimensional multi-component computational fluid dynamics (CFD) model was developed to investigate the synergistic transient characteristics of the hydrogen recirculation components such as hydrogen injector, ejector, and purge valve in an 80 kW PEMFC. The results show that the entrainment performance of the ejector is reduced under unsteady purge conditions compared with steady conditions. The pressure fluctuation of the secondary flow is significant even under purge closed durations. There are drastic changes in velocity and pressure in the ejector, especially in the mixing chamber. Moreover, an abundant hydrogen supply capacity of the injector is necessary to deal with the excessive anode pressure fluctuation. The feedforward-feedback integrated control of the injector is a more efficient strategy to reduce pressure fluctuations compared with the feedback control.     

Experimental study on enhancing the fuel efficiency of an anodic dead-end mode polymer electrolyte membrane fuel cell by oscillating the hydrogen

This paper investigates how to improve the fuel efficiency of an anodic dead-end mode fuel cell for portable power generation. Generally, a periodic purge process in anodic dead-end operation is required to avoid anode flooding caused by back diffusive water from the cathode. However, during the purge process, small amounts of the hydrogen are discharged with the water, lowering the fuel utilization efficiency. Therefore, hydrogen pulsations are introduced and experimental attempt to minimize the purge frequency is conducted in this study. The experimental results indicate that pulsation reduces partial pressure of the water vapor in the anode channel, increasing the interval between purges by approximately three times, thus improving overall efficiency.     

Hydrogen utilization enhancement of proton exchange membrane fuel cell with anode recirculation system through a purge strategy

Proton exchange membrane (PEM) fuel cells are widely considered as potential alternative energy candidates for internal combustion engines because of their low-temperature start, high energy density, and ease of scale up. However, their low hydrogen utilization rate is one of the main reasons for the limited commercial development. This study focuses on improving the hydrogen utilization rate of PEM fuel cells and system efficiency using optimal active recirculation system (ARS). An anode ARS and purging strategy are introduced to enhance the hydrogen utilization rate of PEM fuel cells. An ARS simulation model with purge strategy model is developed in a MATLAB/Simulink environment. A control-oriented dynamic model is developed to study the hydrogen recirculation system characteristics. The dynamic model is used as basis to propose a proportional integration differentiation controller to maintain the anode hydrogen concentration and increase the hydrogen utilization rate. Several experiments are performed using different purging strategies in conjunction with ARS. The hydrogen utilization rate is the highest when the purge time is 0.3 s and the purge period is 10 s. Simulation results show that the PEM fuel cells with an anode recirculation configuration exhibit a better performance than other configurations in terms of hydrogen utilization. Experimental results also demonstrate the feasibility of the proposed system, the performance of which is also superior to that of other hydrogen supply system.     

Development of a polymer electrolyte fuel cell dead-ended anode purge strategy for use with a nitrogen-containing hydrogen gas supply

The effect of nitrogen content within the hydrogen fuel supplied to a polymer electrolyte fuel cell (PEFC) operating in dead-ended anode mode is examined, with a view to using an ammonia decomposition product gas mix (containing 75H₂:25N₂) as the hydrogen-containing fuel. The impact of this impure hydrogen stream, supplied to the anode, was evaluated in terms of mean cell voltage and in relation to actual operating conditions (purge interval, dead-ended interval and fuel cell load). Design of Experiments (DoE) methodology, using multi-linear models, assessed hydrogen utilisation in terms of stack efficiency and identified an effective and viable dead-ended anode purge strategy for this nitrogen-containing hydrogen fuel.     

Stack shut-down strategy optimisation of proton exchange membrane fuel cell with the segment stack technology

In the previous researches, researchers mainly focus on the single cell which is far away from the practical application. In this paper, shut-down process is studied in a 5-cell stack with segment technology. In the unprotected group, the hydrogen/air boundary is observed, and the output voltage performance degrades greatly after 300 start-stop cycles. A 2-phase auxiliary load strategy is proposed to avoid the hydrogen/air boundary. The lifetime is extended. But a serious local starvation is observed during the shut-down process. And corrosion happened in the inlet region. To avoid the starvation, the second strategy is designed, which combines 2-phase auxiliary and air purge (2-phase load& air purge strategy). With the new strategy, the degradation of the stack after 1500 cycles is acceptable, and the carbon corrosion in the inlet is effectively reduced. It could conclude that the hydrogen/air boundary is the main cause of the degradation of fuel cell during an unprotected shut-down process. And a strategy only with auxiliary load may suffer from the local starvation. The purge process can avoid the vacuum effect in the fuel cell caused by the auxiliary load. Therefore, adding an air purge during the shut-down process is promising in vehicle fuel cell.