Compressor regarding question

[Aryan@1234]

1. Can someone please give a brief about the HP and LP barrel used in any compressor , what is their purpose to use ?

2. Why do we generally give suction to any compressor from bottom side ?

 

[georgeverghese]

Q1. Compression duty may be split into 2 or more casings, stages or barrels if the overall dp is high. Intercooling is done between stages when discharge temp from one casing approaches 150degC in most gas applications. For H2, believe it is to be limited to 120degC.
In addition, max no of impellers per casing or barrel is limited to about 8 or 9.

Q2. Dont know of any pros or cons for bottom or top feed for compressor suction. When gas is at or could be close to dewpoint, suction piping should slope continuously back to compressor suction drum for either option. Casing drain should be included to drain out the casing of liquids prior to startup if necessary.

 

[SB1976]

[1] Pressure developed by a compressor is not always done in single casing. For high pressure applications, we may need two or more casings which are connected in series. One of these casings develop less pressure as compared to the other, and thus is called LP (Low Pressure) casing, while the other by virtue of higher pressure generation is called HP (High Pressure) casing.
LP casing and HP casing are different in design and construction.
LP casing is usually a single casing (being an axially split design) while HP casing is a double casing design with outer casing (also called as barrel) in radially split design.


[2] Axially split casings are manufactured in two halves with suction / discharge nozzles placed on one of the halves. In case of top nozzles i.e. the nozzles placed in topmost half, there is huge difficulty during maintenance. In that case, the above piping needs to be disconnected with potential for fouling with overhead crane hook. However, nozzles placed in bottom half have easier maintenance. Only the top half of the casing needs to removed.
As such, in view of maintenance easiness, bottom nozzles for suction / discharge are preferred.

 

[georgeverghese]

Bottom inlet and exit nozzles are preferred when high dewpoint gas can condense upon shutdown / cooldown and partially flood the casing. In such cases, casing blowdown (with additional casing drain lines) is also implemented as part of auto start sequence.