GAS PROCESSING

Gas from 58 different wells enters Qadirpur Gas Field via two headers at a pressure of 310-340 psig.

  1.    Northern Header’s 30”
  2. Eastern Header’s 26”

 

From these headers, gas and water-condensate mixture is separated in SLUG CATCHER.

Slug Catcher

The function of slug catcher is to separate the mixture of water-condensate and gas. On the plant we have two types of slug catchers

 

Finger Type: It separates the mixture by varying the velocity of the mixture. Gas first moves up in an inclined pipeline and the moves down via 4 parallel distributed lines. This separates the gas from the mixture by breaking the momentum. Gas moves up through a line while the liquid being heavy, moves along the line.

 

Vessel Type: It separates on the basis of density difference. Mixture enters from the side of the vessel and gas leaves from the top. A level of liquid is maintained in the vessel so that gas may not slip into the liquid line.

 

After moving from the slug catcher it is required to compress the raw gas at a high operating pressure of 720 psig for further processing. For this it is sent to 14 double acting reciprocating positive displacement compressor and 3 centrifugal turbine driven compressors. About 250-280 MMSCFD of the raw gas is compressed in the centrifugal compressor while the rest of the gas is compressed in the reciprocating compressors

 

Compressor (Aerial Valerus)

There are 14 double acting reciprocating positive displacement compressors (K1301-K1314) that are installed in parallel fashion on the common suction line. Gas from the suction line enters the compression unit. This is also known as front end compression unit (FECP). The first vessel in the compression unit is the scrubber. Liquid and gas is further separated by expansion of the gas in the scrubber. Gas moves up the column while the liquid drops down. A level of liquid is maintained in the vessel so that gas may not slip along with the liquid. Gas from the scrubber enters the suction bottle. The function of the suction bottle is to minimize the pulsation in the compression chamber. From here gas enters the compression chamber and is compressed to a high pressure. There are 2 suction chambers with the suction bottle and both are the connected with the discharge bottle. Function of the discharge bottle is to minimize the pulsation in the line. In each compression chamber there are 4 valves, 2 suction valves and 2 discharge valves. As the shaft moves in the chamber alternate suction and discharge valve opens. Same phenomenon occurs in both the chambers. Gas from the discharge bottle then further moves to the fin tube air cooler to remove the heat of compression and after being cooled down it is then sent to the second scrubber of the unit for the removal of any liquid if present, in high pressure cooled gas. Gas is then passed through the other two compression cambers of the unit via suction bottle and then again moves to the fin tube air cooler for cooling via discharge bottle. Now this cool gas is entered in the discharge header. Discharge from all the compressors enters the same discharge header (Common Point).

SUCTION PRESSURE: 310-320 psig

DISCHARGE PRESSURE: 710-720 psig

 

In the main process it is required to reduce the amount of carbon dioxide and hydrogen sulfide along with water and heavier hydrocarbons. This is done by membrane selective permeation. For the proper working and safety of the membrane, water and other heavier hydrocarbons should not enter the membrane tubes. For this reason, pretreatment is required. In the pretreatment process gas first enters the inlet separator. After the compression phase we have two pre-treatment trains. Train 2 is not working as the load is low but was operational a few months ago when the load was high. Now only train 1 is in operation. Pretreatment train 2 starts with the inlet separators

Aerial Valerus Compressors

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