Propylene recovery by gas fractionation
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The propylene content in the vent tank of our deethanizer usually ranges around 70. I’d like to know what it is for everyone else – are your vent valves set to be open at 100? Will this result in significant loss of propylene? The volume fraction of propylene in the liquefied gas used as raw material in our plant is 30%, and the mass yield of propylene in our plant is 20%, not exceeding 23%. Is this reasonable? Also, the temperature at the top of the deethanization tower in our plant is around 52 degrees. Yet even after cooling, the temperature remains around 52 degrees. Is this reasonable? Could poor cooling performance be the reason why the reflux pump in the deethanization tower of our plant isn’t able to operate properly? I hope everyone can help me :handshake Last edited by Xiao Yue Can Yun on 2009-2-25 23:31 ]
Generally, levels within 50–80% are not considered high, because although the propylene removed by the deethanizer accounts for a large volume, its mass is not significant. . . The upper one is acceptable. . . During actual operation, the tower pressure can be adjusted appropriately according to the specific circumstances, in order to minimize the amount of propylene lost at the top of the tower; it’s a pity. . . In fact, it is usually the control valve used to stabilize the tower pressure that releases it. . . :lol
The propylene yield is not high. Is the temperature at the top of the deethanizer a bit high? It’s best to keep it below 40 degrees. I’m not sure what pressure level is maintained in your deethanizer; the venting from the top of the deethanizer should be done intermittently – continuous venting isn’t reasonable, and it’s necessary to find out why. The carbon dioxide content in the feed gas also needs to be controlled. The propylene yield is generally 3-5 percentage points lower than the propylene content in the feedstock.
The propylene released at the top of the tower can be sent back to the inlet of the catalytic compressor for recovery; the propylene content at the top of our tower is over 98%.
The propylene content in the vent from the reflux tank of the deethanizer is generally around 60-70%. If the control team maintains an appropriate level of C2 content in the liquefied gas, it will not be necessary to keep the vent valve open. Additionally, the vent stream can be directed to the condensate oil tank in the absorption system, where propylene can be recovered； Going to the compressor inlet on the 4th floor for recovery is not a good idea; the pressure in the deethanizer is too high, which has a significant impact on the reaction pressure ； The top temperature of the deethanizer is 52 degrees, which is slightly high; however, it becomes too high after cooling – it doesn’t cool down at all. There is a lot of non-condensable gas at the tower top, making it difficult to regulate the flow rate on the reflux pump.
If the operating parameters are not selected properly, the loss of propylene at the top of the deethanizer accounts for about 50% of the total losses in the absorption and stabilization unit as well as in the gas separation unit. Therefore, it is necessary to adjust the operations in the absorption and stabilization section in order to keep the C2 components below 0.5%； Otherwise, the deethanizer should have its operating pressure increased to at least 25 kilograms, the reflux ratio should be raised, and the top temperature of the tower should be kept below 40°C; this will help to effectively reduce the loss of propylene
The deethanization system is under pressure, and cooling isn’t effective. It cannot cool down, and the backflow fails to exert its intended effect. Vicious cycle.
It can be sent to the inlet or outlet of the compressor for recycling; the cooler is not very effective when the temperature does not drop, but this will not cause evacuation
Agree with what was said on floor 4. At the same time, the temperature after cooling should be kept below 40°C.
1. What is the design top pressure of the deethanizer at your plant? If the pressure at the top of the tower is too low, there is significant loss of propylene; our operating pressure must remain above 2.78 MPa. If it is too low, the deethanization process does not work effectively, and propylene loss increases.
Reason 1: The C2 content in your raw materials may be too high, exceeding 3%; this could be related to the quality of the catalysts used or of the externally purchased materials. Reason 2: There may be issues with your operating procedures – perhaps the reflux rate is too high; it is recommended to adjust this value. Reason 3: The tower pressure is too low; increase it, with the pressure should be maintained between 2.7 and 2.85. 4. If the temperature after cooling is too high, it is recommended to check for leaks, severe scaling, insufficient circulation water volume, or high inlet water temperature. You can contact the circulation water department to adjust the water temperature to 26 degrees. If the equipment is overloaded, it is advisable to add another heat exchanger in order to reduce propylene losses.
The pressure in our deethanization tower is around 2.3, with a top temperature of 50 degrees and a bottom temperature of 57 degrees; it seems that the tower does not perform any distillation function. The ethane content in our mixture of C2 and C3 compounds is between 2-3%, while in the catalytically liquefied gas, the ethane content is mostly between 0.02-0.03%
The components separated at the top of the tower can be recycled to the outlet of the compressor, and then passed through the absorption stabilization system again; this allows for the recovery of some of the dry gas as well as gasoline components.
The temperature after cooling is too high, usually around 35 degrees. When the temperature is lowered, emissions decrease, and the ethane content increases.