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首页> 外文期刊>Energies >Development of an Exergy-Rational Method and Optimum Control Algorithm for the Best Utilization of the Flue Gas Heat in Coal-Fired Power Plant Stacks ?
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Development of an Exergy-Rational Method and Optimum Control Algorithm for the Best Utilization of the Flue Gas Heat in Coal-Fired Power Plant Stacks ?

机译：开发能最佳利用燃煤电厂烟气烟气热量的火用比方法和最优控制算法？

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摘要

Waste heat that is available in the flue gas of power plant stacks is a potential source of useful thermal power. In reclaiming and utilizing this waste heat without compromising plant efficiency, stacks usually need to be equipped with forced-draught fans in order to compensate for the decrease in natural draught while stack gas is cooled. In addition, pumps are used to circulate the heat transfer fluid. All of these parasitic operations require electrical power. Electrical power has unit exergy of almost 1 W/W. On the contrary, the thermal power exergy that is claimed from the low-enthalpy flue gas has much lower unit exergy. Therefore, from an exergetic point of view, the additional electrical exergy that is required to drive pumps and fans must not exceed the thermal exergy claimed. Based on the First-Law of Thermodynamics, the net energy that is saved may be positive with an apparently high coefficient of performance; however, the same generally does not hold true for the Second-Law. This is a matter of determining the optimum amount of heat to be claimed and the most rational method of utilizing this heat for maximum net exergy gain from the process, under variable outdoor conditions and the plant operations. The four main methods were compared. These are (a) electricity generation by thermoelectric generators, electricity generation with an Organic-Rankine Cycle with (b) or without (c) a heat pump, and (d) the direct use of the thermal exergy that is gained in a district energy system. The comparison of these methods shows that exergy-rationality is the best for method (b). A new analytical optimization algorithm and the exergy-based optimum control strategy were developed, which determine the optimum pump flow rate of the heat recovery system and then calculate how much forced-draft fan power is required in the stack at dynamic operating conditions. Robust design metrics were established to maximize the net exergy gain, including an exergy-based coefficient of performance. Parametric studies indicate that the exergetic approach provides a better insight by showing that the amount of heat that can be optimally recovered is much different than the values given by classical economic and energy efficiency considerations. A case study was performed for method (d), which shows that, without any exergy rationality-based control algorithm and design method, the flue gas heat recovery may not be feasible in district energy systems or any other methods of utilization of the heat recovered. The study has implications in the field, since most of the waste heat recovery units in industrial applications, which are designed based on the First-Law of Thermodynamics, result in exergy loss instead of exergy gain, and are therefore responsible for more carbon dioxide emissions. These applications must be retrofitted with new exergy-based controllers for variable speed pumps and fans with optimally selected capacities.
机译：发电厂烟气中可利用的废热是有用热能的潜在来源。在不浪费工厂效率的情况下回收和利用这些废热时，通常需要为烟囱配备强制通风风扇，以补偿烟囱气体冷却时自然通风量的减少。另外，使用泵来循环传热流体。所有这些寄生操作都需要电源。电功率的单位能值几乎为1 W / W。相反，低焓烟道气所要求的热能的火用具有较低的单位火用。因此，从积极的角度出发，驱动泵和风扇所需要的额外电能不能超过所要求的热能。根据热力学第一法则，所节省的净能量可能为正，且具有明显较高的性能系数;但是，对于第二法律而言，通常情况并非如此。这是确定要索取的最佳热量的方法，以及在可变的室外条件和工厂运营条件下利用该热量以最大程度地从过程中获得净本能收益的最合理方法。比较了四种主要方法。这些是（a）由热发电机产生的电力，有（b）有无（c）有热泵的有有机朗肯循环的电力，以及（d）直接利用区域能源获得的热能系统。这些方法的比较表明，本能理性是方法（b）的最佳选择。开发了新的分析优化算法和基于火用的最优控制策略，确定了热回收系统的最佳泵流量，然后计算了在动态运行条件下烟囱中需要多少强制通风风扇功率。建立了稳健的设计指标，以最大程度地提高净火用收益，包括基于火用的性能系数。参数研究表明，通过充分利用热量，可以最佳回收的热量与经典经济和能源效率考虑因素所给出的值相差很大，从而提供了更好的见解。对方法（d）进行了案例研究，结果表明，如果没有任何基于火用合理性的控制算法和设计方法，烟气的热回收在区域能源系统或任何其他利用回收的热量的方法中可能不可行。 。该研究具有实际意义，因为工业应用中的大多数废热回收装置都是基于热力学第一法则设计的，导致了火用损失而不是火用增加，因此导致了更多的二氧化碳排放。这些应用必须使用新的基于火用的控制器进行改装，以用于具有最佳选择容量的变速泵和风扇。

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