High Emission at ESP Outlet

7/28/2019 High Emission at ESP Outlet

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FEED BACK No. 5

PROJECT: WCPML/DANDELI (500TPD CHEMICAL RECOVERY BOILER)

SUBJECT : HIGH EMISSION AT ESP OUTLET

In WCPML/Dandeli 500 TPD Recovery boiler, BHEL/Ranipet supplied two pass

ESPs with each pass having two fields. We have to prove at MCR firedwith 32.05T/Hr. of black liquor with 65% dry solids, the emission of dust

less than 80 mg/Nm3.PROBLEM:1. After the erection and commissioning of the ESP along with associated

systems, the GD test was carried out along with BHEL/Ranipet. The

coefficient of cold air distribution during the test was well within the

limit. However, when the unit was taken into service, the emission

of dust concentration increased from 80 mg/N cub m to 300 mg/N

cub m from 24 T/hr. to 26 T/hr. of black liquor fired in the boiler.

Subsequently, it was suspected that the top entry of flue gas into the

ESP funnel might have caused the above problem of high emission.

Repeat & D test conducted confirmed airbypassing overandbelow the

collecting andemitting frame (Just above the scrapper conveyor) with

a velocity of around 1.2 to 1.5 m/sec. The air bypassing the

treatment area was corrected with suitable throttling and diversion

plates. After this, ESP emission was brought well below 80 mg/N cub

m with 26 to 28 KL of black liquor fired in the boiler.2. Pass nearer to the running ID fan was found to have more flow of flue

gas than the other during Boiler operation affecting ESP performance

and resulting in high emission of dust.


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14SUGGESTIONS:1. The gas entryinlet of ESP be symmetrical andtop entry ofgas into

the ESP inlet funnel be avoided as shown in the attached sketch.

(Referattachedsketch).

2. Whenever the GD test is carried out, the air flowing over and below

the CE & EE frames are to be recorded andthe velocity ofair in this

region is presently less than 0.2 M/sec. The coefficient of distribution

of air velocity may be separately computed above and below the

frame and to be verified during GD test.

3. Wherever standby ID fan is supplied, the duct after the ESP outlet

duct is to be laid out to have symmetrical flow of gas in both passes.

4. Above phenomenon is to be studied in flow model test to ensure

envisaged performance of ESP.

ACTION TAKEN :Following works were carriedout to resolve the problem during unit shut downfrom 23.3.2002 to 30.3.2002 by BAP, BHEL (T) and site team.1. 3 nos. of inlet guide vanes provided at inlet of both ESP passes in line

with flow model test at BAP, Ranipet.

2. Control damper provided at ESP 'A' pass outlet andflow equalized to

within 2% with ID fan A in service by control damper adjustment.

3. Additional screen sheets provided at bottom of second field at front

and rear side in both passes.

4. GD test conducted and CV found improved.

5. Eco baffle plates found dislodged fixed back and additional stiffeners

provided.

6. O2 sensor relocated at Eco outlet.


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15OBSERVATION :1. ID fan B taken in service for operation and ESP 'B' outlet

damperadjusted for equal flow in both passes.

2. Boiler was full loaded and gas flow was measured to be 51.74m^/sec.

3. ESP emission test conducted and the ESP outlet concentrationhas

reducedto 74 mg/Nm^ (well within permissible limits) and

confirmed with customer measurement.

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High Emission at ESP Outlet