Gas Compression Station

Although it seems some of your questions is not related to the discussion but my answes are:

1. What is the suction drum for? The suction drum have to installed to protect (centrifugal) compressor from probable liq. Droplets in gas flow.

2. Is there a posibility for condensation between the drum and the compressor? No, I have not come across with cases in which condensation occurred between the drum and compressor.

3. If the dump valve fails can you afford to lose both units? What do you mean "dump valve"?

4. Is the amount of steel used on a single drum more or les than on two drums? Suction drum is not considered alone, it should also considered other accessories ( piping, controllers, level switches, …) related to the vessel. EPC Cost of common suction drum arrangement is lower than separate suction drums.

5. Why does the shutdown have to be uptream of the drum when there are two? Location of shutdown valve is my main question and can be discussed. Although It's obvious that it is more economic if the valve be installed downstream of the drum but really it is not clear for me which location of the shutdown valve is suitable in view of technical points or other consideration( starting compressor, …).

6. Why would you not design the suction drum to match the compressors rated pressure? There is no obligation for doing this. Design pressure is determined based on the operating pressure plus a constant value not rated pressure of the compressor.

7. Will the compressor have recycle (min flow/anti surge/pressure control). It is very obvious that the anti-surge control system is obligatory for protection of centrifugal compressor.

But as I mentioned above( 5), I'm not sure which location of the shutdown valve is right( or better ).

Very nice.

The dump valve is the valve that allows the liquids captured to be removed. If it fails the vessel will fill up. There should be a level alarm or switch that will shut the compressor down. If you only have 1 drum, then both units shutdown

There is not eneough information on the gas to decide if there will be liquids formed at any point upstream of the compressor or downstream or in the antisutge loop. I've seen liquids for coming out of a surge drumm after only a couple of meters of pipeing when the outside air temperatures were low and the gas was at vapour/liquid equalibrium.

The antisurge loop can form liquids, again, it depends on the gas stream composition.

Do some pressure temperature runs on the gas and if the probability is low that there will no condensation of liquids, then a single drum can be used. In large refrigeration systems where the properties of the gas is well known, single drums are used. The same with pipeline quality gases. For produced gas where it is always at or near it's dew point, individual drums are perfeered.

The shutdown valve just needs to be outside of the recycle/anti surge valve. If the gas is at dew point, liquids could form in the gas while the unit is down and if the valve is after the drum, those liquids will go into the compressor, so the location is dependant on the gas.

Thank you vicini,

As you know, the anti-surge line end connection is where in the downstream of the shutdown valve. Now, Let me please to rewrite your explanation stated in
paragraph 2 -4: if there is possibility of liquid formation in the gas flow in antisurge line, the shutdown valve have to be installed before the suc. drum, and the end of the anti-surge line shall be connected between the sutdown valve and the drum. With no doubt, In this case individual suc. drums for each train shall be considered. But, if there is no probability of liquid condensation, the shutdown valve(& consequently anti-surge line end con.) is installed after the drum. So, one suction drum is enough for all of the trains. so, the probability of liquid formation in the antisurge line is the governing factor to select one of these two options( common & individual suc. drum). your reply is good and acceptable.

By the way, In 1^st paragraph you've written : If you only have 1 drum, then both units shutdown But As I mentioned before, there is a 1+1 configuration for compression system. i.e. one train works while other train as spared(out of service). If one(common) suction drum to be considered for both trains, one train will be only shutdown in case of high liquid level in suction drum.

Based on the your definition of dump valve, the Term of Level control valve( LV or LCV) is an another similar term that is usually used in the design works that I have seen.