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Thursday 16 May 2013

SEAL AIR FAN , SCANNER AIR FAN ERECTION PLAN SEQUENCE IN THERMAL POWER PLANT

Major Fans like ID ,FD and PA fans are already been discussed in my previous articles. However

two more fans are required to be discussed . The name of the fans are Seal air fans and Scanner air

fans . Scanner air fans are small fans ( Both AC & DC) for supplying cooling air to scanner head.

Scanner heads are placed near the fuel nozzle of every elevation to monitor the fireball of the furnace.

For AC motor driven fans the suction is taken from FD discharge and for DC motor driven fans

( only for emergency suction is taken from atmosphere.) Complete sets of dampers suction &

discharge are attached on the ducts as per requirement . This fans are located rear side of the

boiler operating floor and do not need any civil foundation. It is mounted on structural items

and standard erection procedure can be adopted.

Seal are fans are bigger fans and need civil foundations at Zero metre level. It is generally

located  below the second pass of the furnace. Therefore it can not be erected in the

beginning . It has to follow a sequence to start the civil work. It will be prudent to complete

piling work in the beginning that is before the start of boiler erection and pile cap can also

be completed along main boiler column foundations and if possible first lift can also be

completed the elevation of first lift should be at least 800 mm below the zero metre level. This

will reduce interference problems at later stage as the same area lot of structural work , duct

work , insulation work will be carried out. After completion of first stage civil work the

area to be back filled with soil and compacted to enable movement of heavy duty crane

for boiler work. The area to be again excavated after completion of boiler pressure part

work , Boiler structural work rear side , structural work and hopper work below economiser

and air heater. Requirement of passage  from rear  and sides ceases . The area required to

complete the seal air foundations , duct foundations , compressed air storage vessels for

air heaters etc . This area to be completed in war footing as other mechanical work at that

time will be peak therefore movement of dumper , transit mixer , placement of concrete

pumps etc will be on priority. Zero metre paving can be planned at that time . It is

assumed that all other small foundations etc like dirty oil tank ,pumps etc will be

completed. After completion of civil work mechanical work of equipment erection ,ducting

integral piping work etc   will be carried out.


SEAL AIR FANS

The Seal air fan system consists of the following items:-


Cold Primary air Suction duct.

2 Number of vane type filters & its associated dampers & bleed air lines.

2 Number fans with motors.

Suction Dampers of Seal Air Fan

Discharge Dampers of Seal Air Fan

Discharge Ducts up to Mill Seal air points

Seal Air Fan basically functions as booster fan taking suction from primary air fan discharge (cold 

primary air before AH-A&B) boosting up the air pressure and supplying seal air to various sealing 

points of Bowl Mills.

Seal Air Fan Suction Pressure       : 580 mmwc ( approximately)

Seal Air Fan Discharge Pressure  :  1088 mmwc

Vane filters are provided in the Suction line of the Seal air fan with a provision to continuously bleed any dust laden air in to furnace through Secondary air duct-wind box.

-Foundation checking with reference axis and starting of chipping work on foundations

-Alignment of base plates and bearing pedestals.

-Grouting of base plates and bearing pedestals.

-Pre-assembly of spiral casing

-Alignment of spiral casing with respect to fan centre line.

-Ensure vertical of spiral casing.

-Elevation and horizontal at the parting plane of bottom half of spiral casing at four corners.

-Ensure proper seating of the locating groove in the shaft flange with the impeller.

-Torque tightening of bolts for shaft, conical cover plate, flange and impeller.

-Seating of flange of conical cover plate and impeller

-Fan bearing face out
-Fan bearing clearances

-Fixing of labyrinth seals at expansion and non-expansion end of shaft

-Adjustment of duct supports of suction and discharge ducts to avoid loading / pulling of fan

-Alignment of coupling with motor & fan and ensure tightness of bolts fixing coupling with shaft

TOLERANCES FOR SEAL AIR FAN


Gap between shaft flange and impeller mating face <0.05 mm .

Ensure 80% colour matching between bearing housing and the bearing pedestals.

Horizontal of bearing housing to 0.04 mm / M.

The shaft at fixed end bearing should be levelled to within 0.04 mm / M.


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