We will now discussing the erection of Steam Generator structures . Our discussion will be mainly on super critical boiler which is now being introduced in India. The unit capacity is 660 MW onwards. Capacity less than 660 MW units are all sub critical and available in plenty in India.
Structures for Sub critical and super critical do not have major difference in construction. Structure can be divided in to following parts .
1. Structure which is holding the furnace 6780 MT
2. Structure which is holding platforms ,Air heaters and auxiliaries 3600 MT
3. Structure which is holding ducts of boiler , BOF to ESP and ESP to chimney 2340 MT
4. Misc. inter connecting structures ,platforms ,handling ,elevator etc 1200 MT
The above tonnages are approximate tonnage of a 660 MW boiler . Quantity of smaller unit will be less than what it is indicated. However the tolerances followed will be the same. Some of the common tolerances followed not only for Boiler but also civil structure is given below.
he surface1. Individual column piece sweep and camber 1 mm / M max up to 10 mm
( Individual columns are placed on the pre-assembly bed to check the sweep and camber. Pre-assembly
bed need to be prepared carefully so there is no undulation on top of the surface. Beds are prepared
by using concrete blocks and beams . Dimension check ,cleat angle welding , Marker fixing , Bolt
Hole cleaning etc are done at Pre - assembly bed.)
2. Camber and Sweep for assembled column 1 mm / M max up to 10 mm
3. Total length of column + / - 15 mm
4. Top elevation of column with reference point + / - 5 mm
5. Position with reference axis + / - 5 mm.
( Measurement of the total length was done at manufacturing time . However during erection same
check is being carried out after erecting the piece of column and dropping plumb from the top to the
reference point at regular interval ( thrice up to the 7 th tier ). Final check has been done after 6th tier
column erection and before seventh tier erection. Seventh tier measurement done at ground. )
Grouting Gap below the column base minimum 20 mm to 70 mm max.
( Ideal gap is 35 mm to 45 mm ) for easy free flow secondary grouting)
Elevation of Top of pedestal + 30 mm to - 20 mm.
( All the pedestal need to be cleaned from loose concreting on the surface. At least 10 mm /15 mm
to be chipped of to position the packer plate below the column base plate . If the pedestal is more
on positive side then we have to chip more and doing it manually as it is being done in India will be
taking extra time. It is all time better to have pedestal elevation on negative side.) .
Typical floor plan ( foundation detail ) of Steam Generator is given above. Column no 7 to 17 L & R (
except 17 all other columns having two numbers i.e . one in right side and other is on left side) are the
main columns and column number one to six ( L& R) auxiliary column. Distance between 7R and 7L
will give an idea of space availability in Boiler cavity. This area inside the boiler is very important for
erection of steam Generators. Inside the Boiler Cavities there are column no (14 ,15 and 16 ) L &R .
These columns are shorter columns in height and need to be erected afterwards i.e. only after erecting
the ceiling Girders. However these column foundations need to be protected until and unless we start
erection on these columns../
Continued to part III
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