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Liquid Trap / Auto Drainer
- Thread starter reiszal
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I would look at the consequences if you do lose all the liquid level in the drum and blow gas into the drain line and whatever other equipment it goes to. Will that system be able to handle the pressure and simply having fuel gas in it instead of liquids.
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Hi TD2K,
Thanks for your input. We design the vessel (fuel gas scrubber) with a liquid trap/auto drainer on the liquid line instead of putting LCV with on/off operation based on the liquid level inside the vessel. This is because the liquid drop off from the gas stream is fairly small in the vessel. The recovered liquid from the vessel we route it to Closed Drain Vessel which is also acts as LP Flare Knock-out drum. We size the vessel to cater for 7 MMSCFD gas max and 420 blpd max. These two flowrates is not coincident. The maximum gas going to the scrubber is 5 MMSCFD. The design pressure of the closed drain vessel is 7 barg and the max OP of the fuel gas scrubber is 5.2 barg. Hence i believe the gas blowby scenario occured in the fuel gas scrubber can be handled by the downstream equipment, i.e piping and closed drian vessel (LP Flare KO drum).
And thinking back, since the liquid drop off is fairly minimal, how do I set the set point of the LSLL because the minimum liquid amount will varies and i might experience frequent unit tripping of the vessel which will of course disturb the process flow.
Thanks for your input. We design the vessel (fuel gas scrubber) with a liquid trap/auto drainer on the liquid line instead of putting LCV with on/off operation based on the liquid level inside the vessel. This is because the liquid drop off from the gas stream is fairly small in the vessel. The recovered liquid from the vessel we route it to Closed Drain Vessel which is also acts as LP Flare Knock-out drum. We size the vessel to cater for 7 MMSCFD gas max and 420 blpd max. These two flowrates is not coincident. The maximum gas going to the scrubber is 5 MMSCFD. The design pressure of the closed drain vessel is 7 barg and the max OP of the fuel gas scrubber is 5.2 barg. Hence i believe the gas blowby scenario occured in the fuel gas scrubber can be handled by the downstream equipment, i.e piping and closed drian vessel (LP Flare KO drum).
And thinking back, since the liquid drop off is fairly minimal, how do I set the set point of the LSLL because the minimum liquid amount will varies and i might experience frequent unit tripping of the vessel which will of course disturb the process flow.
The LSLL is to trip the drain line shut-off valve if you should install it?
I'd install it a minimum distance above the bottom tangent line. 6" inches is a pretty common figure I've seen. I've also seen people mount the top connection off the bottom of the drum and then the lower connection off the drain pipe. I've not crazy about that as it seems more prone to pluggage.
Why is frequent tripping of the LSLL going to disturb the process? The gas flow is just going to continue through the process and you simply stop the liquid flow out of the drain line which is an intermittant service anyway.
As I agree that sizing an LV for low liquid flows can be difficult and they are prone to plugging with very small Cvs, I've also seen an orifice installed in the line with an on/off valve. A 'high' level in the vessel opens the valve and a 'low' level closes the valve. The orifice is sized to control the flow rate.
I'd install it a minimum distance above the bottom tangent line. 6" inches is a pretty common figure I've seen. I've also seen people mount the top connection off the bottom of the drum and then the lower connection off the drain pipe. I've not crazy about that as it seems more prone to pluggage.
Why is frequent tripping of the LSLL going to disturb the process? The gas flow is just going to continue through the process and you simply stop the liquid flow out of the drain line which is an intermittant service anyway.
As I agree that sizing an LV for low liquid flows can be difficult and they are prone to plugging with very small Cvs, I've also seen an orifice installed in the line with an on/off valve. A 'high' level in the vessel opens the valve and a 'low' level closes the valve. The orifice is sized to control the flow rate.
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