aph lube oil flushing- rajeev

7/30/2019 APH Lube Oil Flushing- Rajeev

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Case Study on APH Lub Oil Flushing (1x500 MW NTPC

Korba)

By: Rajeev Lalwani

PROBLEM IDENTIFICATION

A 500 MW unit boiler consumes 1000 TPH primary and secondary air to burn

300 TPH coal. In order to improve to efficiency of boiler specific heat carried

by flue gases is transferred to secondary and primary air by air pre-heaters.

Two numbers of secondary and two numbers of primary, bi-sector type

rotary air pre-heaters are provided. Each APH has separate lub oil system for

its guide and support bearing. Acid cleaning and lub oil flushing of system is

carried out to clean the lines of these lub oil systems before trial run of air

heater. To remove dirt and debris free from lub oil lines, acid cleaning is

done by HCl. Lub oil flushing is completed in two stages, bypassing bearing

and thru bearing. Customers like NTPC, NSPCL are demanding mechanical

impurities and moisture lesser than 100 ppm to declare completion of oil

flushing and hence takes more time to meet the criteria.

ANALYSIS

SAPH (B) guide bearing lub oil flushing started on 17/09/2009. Oil used for

lub oil flushing was diverted from 1x500 MW Birsinghpur site having 250ppm moisture and 400 ppm mechanical impurity.

The size of filter of oil system is 60 micron and the analysis of oil done by

0.45 micron filter to find the mechanical impurities. So the mechanical

impurities lies between 60 micron to 0.45 micron could be removed by

centrifuge only. A centrifuge of mandatory spares for MDBFP oil flushing was

kept in clarifier mode for oil purification. Atmospheric temperature was

decreasing day by day due to winter and decreasing the purification

efficiency of centrifuge. The available centrifuge was not equipped with

built-in heater. So two numbers of stress reliving heating coils (16 gauge, 20amp each) were wrapped on suction line of lub oil system and maintained 80oC temperature.

A temporary tank (reservoir) is required to start the first stage (bypassing

bearing) oil flushing. Earlier a lower half of 200 lit drum was used as a

reservoir filled approx 100 lit oil. The time consumed in flushing can be


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minimized by using small quantity of oil. So a 275x400 mm pipe was blanked

at one end used as reservoir to minimize the oil used and reduced

purification time.

RESULT

The lab analysis w.r.t time shown in fig 1.

Fig. 1

SOLUTION

The following suggestions are made to speed up the purification of oil during

flushing:

1. Lesser viscosity (SAE 68 or 46) oil should be used for both (thru and

bypassing bearing) flushing.

2. Centrifuge should be used to speed-up the purification of oil.

3. While flushing oil temperature should not be less than 80 oC.

Centrifuge without heater Centrifuge with heaterBypassing flushing declaredThru Bearing Flushing Declared

PPM

Connectionof lub oillines thrubearingwas done.


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Arrangement for heating oil using SR heating coil.

aph lube oil flushing- rajeev

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