Abstract

The optimization of heat exchangers used in heat-recovery systems of heated media exiting process plants is considered. Such systems are widespread and used in various industries: energy, engineering, ferrous metallurgy, engineering systems of buildings. The authors propose an optimization method that uses target functions that take into account the mass and size characteristics of heat exchangers as well as the difference between the heat returned to the installation and the heat equivalent of electric energy required for pumping heat carriers through heat exchangers. Independent variables are total heat capacities of the mass flow rate of the heat carriers. Possible limitations are the maximum speeds of the heat carriers causing a large hydraulic resistance along the path. It is established that the target functions have a pronounced maximum. At certain values of the operating parameters, the target function acquires negative values and the use of heat exchangers becomes impractical. To correctly select the operating parameters of a specific heat-recovery unit, it is proposed to use thermohydraulic characteristics—graphs that represent the dependence of the target function on the heat-transfer heat capacities of the mass flow rate. Such dependences are obtained as a result of multiple thermal and hydraulic checking calculations for heat exchangers. Thermohydraulic characteristics can be built for each possible temperature mode of operation of the heat exchanger. They can be attached to the technical data sheet of devices and allow to determine the optimal flow rates of heat carriers, providing maximum economy of energy recourses. They can also be used to select the desired apparatus from the standard design list. The thermal-hydraulic characteristics calculated for the devices of the most common designs are presented: a plate heat exchanger with water–water heat carriers, a tubular finned gas-liquid heat exchanger, and a plate gas-air heat exchanger. It is shown that the maximum value of the target function when using the same heat carriers lies near the diagonal of the characteristic, i.e., at approximately equal values of the heat capacity. It is also shown that the use of thermodynamic criteria for optimizing heat exchangers of heat-recovery plants is not always advisable.

中文翻译：

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优化热回收系统中热交换单元的方法

摘要

考虑了用于离开加工厂的加热介质的热回收系统中使用的热交换器的优化。这种系统是广泛使用的，并用于各种行业：能源，工程，黑色冶金，建筑工程系统。作者提出了一种使用目标函数的优化方法，该函数考虑了换热器的质量和尺寸特性以及返回到设备的热量与通过换热器泵送热载体所需的电能的热量当量之间的差。自变量是热载体质量流量的总热容量。可能的限制是，热载体的最大速度会导致沿路径产生较大的液压阻力。确定目标函数具有明显的最大值。在一定的运行参数值下，目标函数获取负值，并且使用热交换器变得不切实际。为了正确选择特定的热回收单元的运行参数，建议使用热工水力特性曲线图，这些曲线图表示目标函数对质量流量传热热容量的依赖性。这种依赖性是通过对热交换器进行多次热力和水力检查计算得出的。可以为热交换器的每种可能的温度模式建立热工液压特性。它们可以附在设备的技术数据表上，并可以确定热载体的最佳流速，从而最大程度地节省能源。它们也可以用于从标准设计列表中选择所需的设备。给出了针对最常见设计的设备计算出的热工水力特性：带水-水热载体的板式热交换器，管式翅片式气液热交换器和板式气-气热交换器。结果表明，当使用相同的热载体时，目标函数的最大值位于特性曲线的对角线附近，即热容量近似相等。还表明，并非总是建议使用热力学标准来优化热回收设备的热交换器。管状的翅片式气液热交换器和板式气-气热交换器。可以看出，当使用相同的热载体时，目标函数的最大值位于特性曲线的对角线附近，即热容量近似相等。还表明，并非总是建议使用热力学标准来优化热回收设备的热交换器。管状的翅片式气液热交换器和板式气-气热交换器。结果表明，当使用相同的热载体时，目标函数的最大值位于特性曲线的对角线附近，即热容量近似相等。还表明，并非总是建议使用热力学标准来优化热回收设备的热交换器。