High Emission of ESP

7/28/2019 High Emission of ESP

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PROJECT : WCPML / DANDELI ( 500 TPD CHEMICAL

RECOVERY BOILER)

SUBJECT : HIGH EMISSION OF ESP

IN WCPML / Dandeli, 500 TPD recovery boiler, BHEL / Ranipet,supplied two pass ESPs with each pass having two fields. We have toprove at MCR fired with 32.05 T / Hr of black liquor with 65 % drysolids, the emission of dust less than 80 mg / Nm3.

PROBLEM:

1. After the erection and commissioning of the ESP along withassociated systems, the GD test was carried out along with BHEL /Ranipet. The coefficient of cold air distribution during the test waswell within the limit. However, when the unit was taken into service,the emission of dust concentration increased from 80 mg / N cub m to300 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 entryof flue gas into the ESP funnel might have caused the above problemof high emission. Repeat GD test conducted confirmed air bypassingover and below the collecting and emitting frame (just above thescrapper conveyor) with a velocity of around 1.2 to 1.5 m / sec.The air bypassing the treatment area was corrected with suitablethrottling and diversion plates. After this ESP emission was broughtwell below 80 mg / N cub m with 26 to 28 KL of black liquor fired in

the boiler.


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SUGGESTIONS:1. The gas entry inlet of ESP be symmetrical and top entry of gas

into the ESP inlet funnel be avoided as shown in the attachedsketch. (Refer attached sketch).

2. Whenever the GD test is carried out, the air flowing over andbelow the CE & EE frames are to be recorded and the velocity ofair in this region is presently less than 0.2 M/sec. Thecoefficient of distribution of air velocity may be separatelycomputed above and below the frame and to be verified during GDtest.

3. Wherever standby ID fan is supplied, the duct after the ESPoutlet duct is to be laid out to have symmetrical flow of gas inboth passes.

4. Above phenomenon is to be studied in flow model test to ensureenvisages performance of ESP.

ACTION TAKEN :

Following works were carries out to resolve the problem during unitshut down from 23.2.2002 to 30.3.2002 by BAP, BHEL (T) and siteteam.

1. 3 nos. of inlet guide vanes provided at inlet of both ESP passes inline with flow model test at BAP, Ranipet.

2. Control damper provided at ESP A pass outlet and flow equalizedto within 2% with ID fan A in service by control damperadjustment.

3. Additional screen sheets provided at bottom of second field atfront and rear side in both passes.

4. GD test conducted and CV found improved.


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5 Eco baffle plated found dislodged fixed back and additional

stiffeners provided.6. O2 sensor relocated at Eco outlet.

OBSERVATION :

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 51.74m3/sec.

3. ESP emission test conducted and the ESP outlet concentration hasreduced to 74 mg/Nm3 (well within permissible limits) andconfirmed with customer measurement.

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High Emission of ESP