一种避免重沸器在不稳定过渡沸腾区操作的控制方法

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.

A Method for Preventing Reboiler from Operating in Unstable Transient Boiling Range

When the temperature in the rectifying column reactor is high and steam is unsuitable for use as the heat source of the reboiler due to its excessively low temperature,a refinery usually uses media that do not experience phase changes such as high-temperature heat transfer oils and process liquids as the heat source of the rectifying column reboiler.When the temperature of such heat transfer media rises to a point where the reboiler′s heat transfer is in the transient boiling range,the heat transfer rate of the reboiler will drop as the heat transfer temperature difference increases,resulting in unstable rectification control and production of substandard products.By utilizing the principle of heat transfer of reboilers,this article proposes a method for preventing reboilers from transferring heat in the unstable transient boiling range,which is characterized by partial circulation and partial replenishment of heating medium.This method blends the relatively low-temperature heating medium from the outlet of the reboiler and the relatively high-temperature heating medium from the system in a proportion in order to reduce the temperature of heating medium at the inlet of the reboiler,thus ensuring the reboiler to work in the stable nucleate boiling range and enabling the rectifying column to operate stably.Application shows that with this method,the total energy consumption of the system rises only slightly or even declines,the operating performance of the rectifying column improves considerably and that product quality improves significantly.