What should be done if C2 is introduced into the feed of the propane-propylene distillation column?

There will be ethane in propylene, as a portion of ethane dissolves in it; monitoring the product quality through online analysis of propylene is sufficient as long as the quality requirements are met. The most effective way to remove the carbon dioxide component from the propylene column is to vent it from two locations: the top of the reflux tank and the exhaust line at the column top condenser (where the effect is best). If it is vented through the gas phase at the column top, this will result in significant losses of propylene, and the effectiveness of this method will not be good.

Agree with the view from Building 3#; the unqualified propylene product at the top of the tower needs to be sent back to the C2 removal tower for further processing.

I work in a catalytic liquefied gas gas fractionation system, and propane separation is a routine operation for us. I have been working in this field for over 10 years. To be honest, we do not use heat pump operations; instead, we will explain the issue of carbon dioxide appearing during propane separation, in the hope that this can help you. When carbon dioxide gets into the propylene distillation system, releasing pressure from the reflux tank can indeed solve this problem, but it takes a long time to do so (during this process, it’s impossible to ensure that the propylene product is of high quality – in other words, the propylene product will definitely contain a small amount of carbon dioxide). When there is 0.03% carbon dioxide at the bottom of the decarboxylation tower, the propylene product will still contain carbon dioxide. Of course, our operating pressure is 1.8 MPa, and even then carbon dioxide is present in the product; imagine then what happens at a pressure of 1.3 MPa. The prolonged pressure release we employ does not involve releasing pressure into the gas system, but rather into the raw material buffer tank, which helps to maintain the efficiency of the system. Another suggestion: if your propylene product contains a high amount of ethylene dichloride, it is recommended to use a bypass line connected to the tower top safety valve to release pressure. By using this two-pronged approach, it is possible to remove the ethylene dichloride components as quickly as possible, ensuring that the propylene product meets the required standards in the shortest time possible. After all, it is the product’s compliance with standards that is the most important. This suggestion hopes to be adopted! I also hope to win the Ruyi Trophy from Haichuan Chemicals {:9001:}.

But I checked and found that the saturated vapor pressure of ethane is very high; under the conditions at the top of the tower, ethane should be in a supersaturated gas phase. So how can it appear in the liquid propylene?

This is a continuous production process, and without ensuring adequate separation between the gas and liquid phases, it is not possible to guarantee that the propylene product delivered does not contain carbon dioxide. Do you understand? ?

This comes from over a decade of practical experience, without much theoretical analysis.

Under normal conditions, the non-condensable gas is vented from the top of the reflux tank at point C2; it is important to maintain a pressure in the tank that ensures the propylene is in a fully condensed state (at the saturation temperature corresponding to its saturated vapor pressure), thereby preventing any gaseous propylene from being vented to the flare and wasted. Normal propylene product contains a small amount of ethane, and our exported propylene product is subject to online analysis (for the detection of propane, ethane, ethylene, and MAPD).

Some of this ethane will dissolve, but as long as the product is of good quality it will be gradually removed; if it is vented from the gas phase, the removal rate should be faster, based on conventional operating experience with propylene towers