Commissioning of the ethylene distillation tower and ethylene circulation system
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The open heat pump cycle formed by the ethylene distillation tower and the three stages of the ethylene compressor in the Linde process. At startup, the recycled ethylene passes through the third-stage outlet of the ethylene compressor and is sent to the counterflow heat exchanger in the ethylene distillation tower; after passing through the reboiler, it goes through the counterflow heat exchanger again to serve as the reflux for the ethylene distillation tower. The ethylene gas from the ethylene compressor expands from the three-stage outlet to the three-stage inlet; the gas is cooled, leading to further condensation. (Ethylene gas gradually condenses at the bottom of the ethylene distillation tower). During this cycle, the return valve acts as a throttling expansion valve to produce a cooling effect. Question: Is it beneficial for ethylene to condense rapidly if this valve is opened wider or fully open, or is it better to keep it at a low opening degree to facilitate ethylene condensation?
Heat is absorbed only during throttling expansion; does increasing the throttle size make it smaller or larger?
According to the Joule-Thomson equation, it depends only on the pressures before and after. Increasing or decreasing the size has little impact on the pressure in the front and rear systems. However, when it is opened wide, the flow rate is high, resulting in a greater cooling effect.
At the beginning of operation, use the cold reflux from the buffer tank together with the hot reflux you mentioned to operate the cooling tower; start with the cold reflux first, and then use both simultaneously once liquid is present. It’s quite difficult to keep the heat pump system running in balance without any feedstock. Under normal operating conditions, since this stream of hot reflux passing through the heat exchanger is related to reboiling and reflux, generally no significant adjustments are made based on the feed load; instead, adjustments are primarily made using cold reflux. However, under any operating condition, there is no scenario in which both the cold and hot return valves are fully open.
After driving a few times, it was found that as long as the system pressure is sufficient, the distillation tower can be ignored while driving.
The opening degree of this valve must ensure that there is a liquid level in the heat exchanger; otherwise, increasing its opening will not help start up the ethylene plant. It is necessary to ensure that ethylene undergoes a phase change; otherwise, if the gas phase enters the ethylene column, it will create a vicious cycle that makes it even more difficult to start up the ethylene plant.