In our FPSO we have 2 export compressor running parallel, sharing controller using CCC 3++.
Once upon a time, we have Compressor SD due to power supply to UCP lost and also to CCC module lost. Therefore MPIC mode restore to Local Setting and Suction pressure became 0 psig.
This condition unrealized after several days running.
It just realized by panel operator when they tried to reduce feeding gas from well and then suction pressure going lower, as operator know, suction pressure should be constant at desired point since we using suction pressure control mode.
Another anomaly reported by operator was suction pressure went lower then operator decided to open Anti Surge Valve (manually open ASV) to compensate suction pressure getting lower.
And here we come our summary troubleshoot ....................... special Thanks to Allah to give me opportunity to develop and elevate my knowledge by doing troubleshoot.
As informed by panel
operator we have MPIC at EGC A at local set point mode, and local set point
value at 0 psig.
This condition occurred since last SD EGC A due to DCS blank
at 27 October 17 @ 11:28 with Detail of event: Gas Compressor EGC-A Blank indication /
UCP down.
By this UCP down then MPIC setting restore back to Local Set
point and its value = 0 psig.
Then when unit back on line and during running after Total
SD program until last night, this MPIC condition keep running at MPIC
local set point 0 psig.
MPIC set point at 0 psig while PV at 219 psig.
This means that control controlled by LSIC (Load share Indicating Controller) to reach suction pressure = 0 psig, therefore Speed N3 will be
maximize.
This condition shown by TRACK led illuminated at LSIC.
By this condition Controller will be command the N3 speed
goes high regardless Suction pressure, this not wanted by operator due to we
have Ps LL at 170 psig.
Then to secure process we manually increase setting the set
point by press increase button (triangle) at local module CCC 3++ at EGC A UCP.
When we reach at set point 211 psig, then the speed N3
decrease from 4800 rpm to 4600 rpm.
Then we standby for a while and N3 back to 4800 rpm due to
set point still below the PV.
Then finally we put set point at 232 psig at N3 speed 4800
rpm and we keep it until this morning.
On the next day, this morning change local set point mode to
Remote set point by press REMT SP.
And then remote set point went to 238 psig as per shown at
DCS display : Suction Press SP from PCS 238 psig
Finally we run EGC with MPIC remote set point mode and
suction pressure control at 238 psig normally and safely.
Special thanks to Allah
Alhamdulillah
