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首页> 外文会议>Clearwater clean coal conference;International technical conference on clean energy >Development of PCHE Off-design Performance Model for Optimizing Power System Control Strategies in S-CO_2 Brayton Cycle
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Development of PCHE Off-design Performance Model for Optimizing Power System Control Strategies in S-CO_2 Brayton Cycle

机译：用于优化S-CO_2布雷顿循环中的电力系统控制策略的PCHE非设计性能模型的开发

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Recently, there has been a growing interest in the supercritical carbon dioxide (S-CO_2) Brayton cycle due to many advantages as one of the promising power systems. That is because it can achieve high thermal efficiency at moderate turbine inlet temperature range (450°C - 750°C) with simple layout and compact footprint due to small-sized turbomachinery and compact heat exchanger technology like a Printed Circuit Heat exchanger (PCHE). PCHE is a potential candidate for the S-CO2 system because it has excellent structural rigidity and high compactness due to extremely large heat transfer area owing to a micro-sized channel. The conventional heat exchanger analysis methods (e.g. LMTD, ε-NTU) cannot be directly applied to a pre-cooler of an S-CO_2 system owing to substantial change of properties near the critical point. To solve non-ideal gas property of CO_2 near the critical point, the PCHE analysis tool, which divides flow channel into several nodes, was developed in KAIST previously. This discretized method has a high accuracy by solving energy and momentum equation for each node under any operating conditions However, this method assumes cold side outlet temperature and pressure to calculate the node sequentially when a PCHE is counter-current type. Thus, a numerical method to find a solution is applied. The selected numerical method sometimes causes non-convergence issues and consumes a lot of computational resource due to iterative process This leads to a difficulty in establishing control strategies under off-design condition because optimum control strategies has to be obtained by repetitive quasi-steady state analysis under the change of control parameters (eg. bypass valve fraction, throttle valve fraction, inventory of working fluid, and turbomachinery RPM). An optimum control strategy means maximizing the cycle efficiency while preserving integrity of system by adjusting control parameters. Accordingly, significant computational resource is required to obtain the optimized results because the higher the number and sensitivity of the control parameters are, the better the results are. Therefore, reducing pre-cooler analysis time and computational resources while maintaining similar order of accuracy becomes imperative for establishing the control strategies of the S-CO_2 power cycle. This issue can be re-solved by modifying the existing LMTD method and using the method instead of the discretized numerical approach. In this study a new PCHE type pre-cooler model for the S-CO_2 power cycle is developed and evaluated for it accuracy and simplicity under various flow conditions, which can be used for the future optimization of the power cycle.
机译：近来，由于作为有前途的电力系统之一的许多优点，对超临界二氧化碳（S-CO_2）布雷顿循环的兴趣日益增长。这是因为由于小型涡轮机械和紧凑型换热器技术（如印刷电路换热器（PCHE）），在中等涡轮机入口温度范围（450°C-750°C）下，它可以在简单的布局和紧凑的占地面积内实现高热效率。 PCHE是S-CO2系统的潜在候选者，因为由于微尺寸的通道，传热面积非常大，它具有出色的结构刚度和高致密性。由于临界点附近性质的实质性变化，传统的热交换器分析方法（例如LMTD，ε-NTU）无法直接应用于S-CO_2系统的预冷器。为了解决临界点附近的CO_2的非理想气体特性，以前在KAIST中开发了PCHE分析工具，该工具将流道分为几个节点。通过在任何工作条件下求解每个节点的能量和动量方程，该离散化方法具有很高的精度。但是，此方法假定冷侧出口温度和压力在PCHE为逆流型时按顺序计算该节点。因此，应用了寻找解的数值方法。所选的数值方法有时会导致不收敛问题，并且由于迭代过程而消耗大量计算资源。这导致在非设计条件下建立控制策略非常困难，因为必须通过重复的拟稳态分析来获得最佳控制策略。在控制参数（例如，旁通阀分数，节气门分数，工作流体清单和涡轮机械RPM）的变化下。最佳控制策略意味着在调节控制参数的同时保持系统完整性的同时最大化循环效率。因此，需要大量的计算资源来获得优化的结果，因为控制参数的数量和灵敏度越高，结果越好。因此，在建立相似的精度顺序的同时，减少预冷器的分析时间和计算资源对于建立S-CO_2动力循环的控制策略变得势在必行。可以通过修改现有的LMTD方法并使用该方法代替离散数值方法来解决此问题。在这项研究中，针对S-CO_2功率循环开发了一种新的PCHE型预冷器模型，并对其在各种流量条件下的准确性和简单性进行了评估，可用于将来的功率循环优化。

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