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.
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 to0.04 mm / M.
The shaft at fixed end bearing should be levelled to within0.04 mm / M.
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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 <
Ensure 80% colour matching between bearing housing and the bearing pedestals.
Horizontal of bearing housing to
The shaft at fixed end bearing should be levelled to within
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