We have a compressor (two stage doube acting)that has been sized for a Suction Pressure=250 psig, Discharge Pressure=1250 psig and a Gas Volume Handling Capacity=10 MMSCFD. This compressor is to be installed as Front End Compressor to boost gas pressure (coming from wellhead) to the desired discharge pressure in order to maintain facilities operating pressure. The compressor shall be installed downstream of a 3-phase separator to ensure single phase entry into the compressor machine.
The query is that the upstream pressure at the inlet of compressor is high initially i.e. in the range of 700-750 psig. Now we have two ways of controlling this pressure and ensuring optimum machine performance.
1. One way to do this is to install a PCV (pressure control valve) and limit the outlet pressure of PCV to 250 psig to operate the compressor. Then the machine inherent controls like VVCP and RPM can be brought into play to adjust the required flow alongwith recycling if required.
2. The second way is to use unloader valves to blow by the 1st stage completely and introduce the high pressure directly into the 2nd stage.
Although both options are theoretically possible and have been confirmed by the vendor/packager as doable, I personally believe that putting a valve upstream of compressor with valve sensing to maintain a constant suction pressure is more doable and practical rather than opting for option 2.
I would like to have inputs by senior members of the forum and what options are practical and doable and what is the industry norm in this matter. Any references in the matter shall also be appreciated.