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当精馏塔釜温度较高、且蒸汽温位过低而不能用做重沸器热源时,炼油厂通常采用高温导热油、工艺液体等不发生相变的介质作为精馏塔重沸器热源。当这些加热介质温度高至使重沸器传热处于过渡沸腾区时,重沸器传热速率则会随传热温差的增大而下降,造成精馏控制不稳定及产品质量不合格。本文结合重沸器传热过程原理,提供了一种可以避免重沸器在不稳定的过渡沸腾区传热的控制方法,即“加热介质部分循环、部分补充”的控制方法。该方法将来自重沸器出口的、温度较低的加热介质,与来自系统的、温度较高的加热介质按一定比例混合,以降低重沸器入口的加热介质温度,确保重沸器在稳定的泡核沸腾区操作,并使精馏塔在平稳的状态下运行。应用实例表明,应用本方法,系统总能耗增加很少,甚至会有所降低,精馏塔的操作性能得到明显改善,产品质量大幅提高。
When the distillation column temperature is high, and the steam temperature is too low and can not be used as a reboiler heat source, the oil refineries usually use high-temperature heat-conducting oil, the process of liquid and other non-phase change medium as distillation column reboiler heat source . When the temperature of these heating media is so high that the reboiler heat transfer is in the transition boiling zone, the heat transfer rate of the reboiler will decrease as the heat transfer temperature difference increases, resulting in unstable distillation control and unqualified product quality. Based on the principle of reboiler heat transfer process, this paper provides a control method that can avoid the reboiler heat transfer in the unstable transition boiling zone, namely “part of heating medium cycle, partial replenishment” control method. The method mixes the lower temperature heating medium from the outlet of the reboiler and the higher temperature heating medium from the system in a certain proportion to reduce the temperature of the heating medium at the inlet of the reboiler to ensure that the reboiler is stable Bubble boiling zone operation, and the distillation column in a steady state operation. The application example shows that with this method, the total energy consumption of the system increases little or even decreases, the operation performance of rectification tower is obviously improved, and the product quality is greatly improved.