Why is a differential pressure between the primary seal gas and the flare required in cascade seal control?
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In dry gas seal control, in addition to the primary seal and the differential pressure across the balance line, why is a differential pressure related to the flare also required? Another issue is that the flow rate of the torch is too high, which is caused by severe leakage in the primary seal. What exactly leads to this leakage? Could it be that the path through which the air from the primary seal enters the machine chamber has become distorted, resulting in increased resistance?
Actually, venting the gas is meant primarily for the secondary seal. Strictly speaking, people don’t want the gas from the primary seal to be vented as well. But in order to prevent the gas from the secondary seal from entering the primary seal, a small amount of gas from the primary seal is allowed to leak toward the secondary seal, thereby preventing that gas from entering the primary seal and mixing inside the chamber. In my understanding, the function of the flare differential pressure is to prevent secondary gas from entering the primary sealing chamber and damaging the primary seal. What causes the reversal of the process is high pressure followed by low pressure; this is just my personal understanding, and I’m not sure if someone more knowledgeable can provide a reasonable assessment of it.
A high leakage rate indicates that the gap between the dry gas seal surface and the main shaft has increased, resulting in a reduced effectiveness of the dry gas seal or even damage to it. Flow control is generally used, while differential pressure control is used less often.
The original poster seems to have a misunderstanding regarding dry gas sealing. In a series-connected primary seal system, the pressure of the sealing gas is typically much higher than that of the flare; it is used to control the internal pressure of the equipment. The pressure in the flare chamber is what is used to determine whether there is a seal leakage. I’ll stop talking; there’s tons of information on the forum