This case study describes a compressor (C-1714) tripping due to low surge flow. The surge flow dropped to 0 Nm3/Hr below the alarm limit of 700 Nm3/Hr. Potential causes identified include condensate not being released from the air trap, high ambient temperatures, and foreign material choking the air trap valve port. Permanent countermeasures proposed include installing a new ball float type air trap to replace the existing inverted bucket type, cleaning the compressor impeller blades, and conducting a performance test.

1. Case Study:
C-1714 Compressor low surge flow
Presented By:
Md.Aminul Islam
Reliability Engineer

2. Compressor Design Data
Type : 4th stage centrifugal compressor
Atm Pr : 0.1013 MPaA
Suction Temp : 34.0 deg C
Relative Humidity : 100%
Disc Pr : 1.71 MPaG
Disc Flow rate : 10KNm3/Hr
Disc temp : 161 deg C
Motor rating : 1670 KW
Speed : 3000 RPM
Problem: Compressor (C-1714) trip due to low surge flow

3. Compressor( C-1714 ) Trip
Surge flow became '0' Nm3/Hr as air flow reduced
( Surge Alarm: <700Nm3/Hr and Interlock : "0" Nm3/Hr)
Condensate not released
Ambient temp high
Compressor air trap
choked
Suction air density
decreased
Foreign material came into
air trap & choked the valve
port (port size less- φ 2mm)
It is designed for
34 deg CPaint,Dust accumulated at
strainer of trap
Flow decreasesFlow decreases & inter stage temp
increases
Air not cool properly as
heat transfer not proper
Air filter damage & dust
ingress through suction filter.
Flow decreases as dust
accumulation on impeller blade
Air filter damage & dust
ingress through suction
filter .
Modified type air trap
will be install, from
Inverted Bucket type
to ball float type (Port
size 7mm)
1. Inter cooler
cleaning to be done
2. WRS given to
process to monitor
air filter del pr from
DCS
1. 1.Impeller Blade cleaning
to be done.
2. Compressor performance
test will be done
Countermeasure:
Dust accumulation on tube
of inter cooler

4. Counter Measure
Temporary:
1. Air trap remove from site, overhaul/clean & reinstallation done.
2. Surge flow monitoring from DCS,If surge flow < 200 Nm3/Hr
a) Bypass purging done.
b) Air trap checking done.
Permanent:
1. New type air trap to be install (PR already done)
2. Compressor impeller blade cleaning to be done &
performance test will be done in next SDM Nov'13
3. Communicated with OEM (MHI) regarding low surge flow

6. When Temperature increases Surge flow decreases
Temperature Graph Surge Flow Graph
Surge Flow vs Temperature

8. Modified type trap (New)

10. C1714 1st Stage trap
Existing New
1 Type Inverted Bucket type Ball Float
2 Capacity
460Kg/hr at 0.2Mpa pr diff. 2267Kg/hr at 0.2Mpa pr diff.
402Kg/hr at 0.165Mpa pr diff.
2041Kg/hr at 0.165Mpa pr
diff.
3 Pr difference 0.2Mpa 0.2Mpa
4 Flange size 1" 1"
5 Orifice size 2mm 7mm
6 Strainer 20 mesh Not available
7
Flange to flange
distance
215mm 264mm
8 Problem
If orifice /mesh/Inverted bucket
orifice clogged by foreign particle
then trap will not work.
This trap will not have this
type of problem