Parameter control during self-circulation of propylene refrigeration

The propylene gas from the low-temperature methanol wash unit (-40°C, 0.04 MPa(G)) enters the inlet of the first stage of the compressor after the entrained liquid propylene is separated in the compressor inlet separator (142V101). The compressed propylene gas (at 90°C and 1.6 MPa(G)) is condensed into liquid propylene by the propylene condenser (142E101) using circulating water, and then reduced in pressure to 0.51 MPa(G) before entering the propylene flash tank (142V103). The propylene gas that emerges from the flash tank is separated from any entrained liquid propylene in the three-stage inlet separator (142V105), after which it enters the compressor’s three-stage inlet. The liquid propylene (1.2℃, 0.651 MPa(G)) coming out of the bottom of the propylene flash tank (142V103) is divided into two streams: one stream enters directly the tube side of the propylene subcooler (142E102), while the other stream is depressurized to 0.15 MPa(G) and then used to cool the propylene in the shell side of the propylene subcooler (142E102) to -20℃, after which it is sent to the low-temperature methanol washing unit for use. The gaseous propylene (-25°C, 0.15 MPa(G)) exiting the shell side of the propylene subcooler (142E102) enters the compressor’s second-stage inlet after the entrained liquid propylene is separated in the two-stage inlet separator (142V104). The two refrigeration systems share one propylene storage tank (142V102), which collects the liquid propylene discharged from this unit and the low-temperature methanol washing unit; meanwhile, the two refrigeration systems also use one oil boiling unit (142V106) to remove impurities from the system.

This is a brief introduction to the process. By the way, have you ever encountered a situation where the level in the inlet separator is high, the make-up valve closes, yet the level remains high?

Based on the load of the equipment, and also, what is the volume of gas that you guys feed into the conversion scrubber tower? What is the speed of the chiller? What is the opening degree of the anti-surge valve? As a general principle, when operating in self-circulation without a load, it is necessary to reduce the speed and open the anti-surge valve simultaneously, while replenishing liquid level in the inlet separator to ensure that the compressor outlet temperature does not rise too high. The process parameters differ slightly from normal operation. If you have any more questions, let’s continue discussing them

The rotational speed is less than 5000; it shouldn’t have anything to do with the flow rate in the washing tower, right? I’m not very familiar with driving either, so I’d like to know what appropriate pressure levels for exits and entrances are when driving.

By changing the gas flow rate, we aim to determine the size of your installation. After driving, some of the data and process parameters differ. For example, in the design of our propylene compressors, the cooling load is set higher than what is required under actual operating conditions; currently, only 50% of the designed amount of liquid propylene is output. So all the data differs from the design data; our inlet temperature is currently around 0 degrees, while the design value is -40 degrees. The above is just an example. But remember to keep all interlock values and high/low alarm levels in mind, and go over the procedures that trigger interlocks in your head. This is the key point. I hope this is helpful to you.

Yes, we have encountered this before. The main reason is likely the excessively low temperature and high volume of propylene gas entering the compressor inlet separator after low-pressure washing, coupled with the fact that the anti-surge valve in the first stage cannot be fully closed (approximately 30% of its opening must remain). The cold gas returning from the low-pressure washing process condenses the hot gas from the anti-surge system into propylene liquid, causing the liquid level in the inlet separator to rise rapidly – it can fill up within 10 minutes. Solution: When starting up the low-temperature methanol wash unit, the amount of cooling capacity should not be increased too quickly, nor should it be excessive; excessive subcooling can lead to liquid entrainment. At the same time, the low-wash propylene cooler does not have a liquid level control, which allows for a rapid reduction in cooling capacity; otherwise, if the cooling is not carried out promptly, it is easy for the liquid level in the compressor inlet separator to rise to its maximum level.

Can you all bring enough? So high? While we were driving, the level of the cryogenic fluid remained around 50%. Inlet separator level 40%. Forced to modify the chain.