Case Study:

C-1714 Compressor low surge flow

Presented By: Md.Aminul Islam

Reliability Engineer

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

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 C Paint,Dust accumulated at

strainer of trap

Flow decreases Flow 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

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

When Temperature increases Surge flow decreases

Temperature Graph Surge Flow Graph

Surge Flow vs Temperature

Modified type trap (New)

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