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Thermodynamic evaluation of combined cycle plants

机译：联合循环装置的热力学评估

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The application of the exergy concept for the thermodynamic evaluation of energy conversion systems and chemical plants is steadily growing. However the general application of this concept is complicated by the large variety of parameters that is used to present the results of such evaluations. Easily understandable diagrams that offer a quick overview of the main results of such an evaluation will be very helpful.rnLarge power plants, as for example combined cycle plants, consist of a large number of apparatuses. The thermodynamic modeling of these plants requires the computation of the thermodynamic properties at inlets and outlets of all apparatuses. These results allow for the calculation of the exergy values at all considered points after defining an appropriate environment Using these exergy values exergy losses and efficiencies of all considered apparatuses can be determined.rnHowever, additional parameters and methods for presenting losses are necessary to understand the origin of exergy losses and the options for further improvements. Exergy efficiencies of power cycles show the actual losses but do in general not clearly indicate the potential for improvement. The use of the so-called internal exergy efficiency of a power cycle will be helpful to understand this potential. Also value diagrams and exergy flow diagrams are very useful to understand the thermodynamic performance of complicated systems.rnIn this paper the application of these tools is demonstrated for the evaluation of alternative designs of combined cycle plants. Three system designs are established for this purpose and modeled using the computer program Cycle-Tempo. The considered combined cycles use the same gas turbine but have different steam bottoming cycles. Differences do originate from the number of pressure levels at which steam is generated in the HRSG (Heat Recovery Steam Generator). The evaluation includes respectively a single pressure, double pressure and triple pressure HRSG. The steam pressures are optimized with regard to overall plant efficiency using a multi-parameter optimization procedure.rnThe evaluation shows that the application of the internal exergy efficiency of a power cycle is in particular useful if the temperature of heat transfer from the cycle will be affected by the cycle performance, i.e. in the case of gas turbine cycles. The value diagrams show how the increasing number of pressure levels of steam generation will reduce the losses due to heat transfer in the HRSG but also the exergy loss due to the exhaust of flue gas to the stack. The exergy flow diagrams show that the main exergy losses of combined cycle plants occur in the combustion process. Possibilities to reduce these losses are limited. Serious improvement of the efficiencies of future combined cycle plants is conceivable by applying high temperature fuel cells.
机译：火用概念在能量转换系统和化工厂的热力学评估中的应用正在稳步增长。但是，此概念的一般应用由于用于呈现此类评估结果的大量参数而变得复杂。易于理解的图表提供了这种评估的主要结果的快速概览将非常有帮助。大型发电厂，例如联合循环发电厂，由大量设备组成。这些设备的热力学模型要求计算所有设备入口和出口的热力学性质。这些结果允许在定义适当的环境后计算所有考虑点的火用值。使用这些火用值，可以确定所有考虑的设备的火用损耗和效率。然而，为了解起因，需要额外的参数和表示损耗的方法火用损失和进一步改进的选择。动力循环的火用效率显示实际损失，但通常并不能清楚地表明改进的潜力。功率周期的所谓内部（火用）效率的使用将有助于理解这种潜力。值图和火用流程图对于理解复杂系统的热力学性能也非常有用。本文证明了这些工具在联合循环电厂替代设计评估中的应用。为此建立了三种系统设计，并使用计算机程序Cycle-Tempo对其进行了建模。所考虑的联合循环使用相同的燃气轮机，但具有不同的蒸汽底部循环。差异确实源于HRSG（余热回收蒸汽发生器）中产生蒸汽的压力水平数。评估分别包括单压力，双压力和三压力HRSG。蒸汽压力通过多参数优化程序针对工厂整体效率进行了优化。rn评估表明，如果会影响动力循环的传热温度，则动力循环内部火用效率的应用特别有用取决于循环性能，即在燃气轮机循环中。数值图显示了越来越多的蒸汽产生压力水平将如何减少由于HRSG中的传热而造成的损失，以及由于烟道气排放到烟囱而产生的本能损失。火用流程图显示，联合循环电厂的主要火用损失发生在燃烧过程中。减少这些损失的可能性是有限的。通过应用高温燃料电池，可以想象到未来联合循环电厂效率的大幅提高。

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