Boiler Drum And Internals

BOILER DRUM AND INTERNALS  DRUM:

Drum is a closed cylindrical vessel used for steam generation. *Purpose of Boiler Drum:  Drum is used for seperating the steam from a mixture of steam & water.  It is used to store a little part of total circulating water as a buffer stock during normal operation of boiler.  It also has provision for chemical dozing & blow down for removal of sludge, mainly silica.  The boiler drum forms part of water circulation system

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SPECIFICATIONS OF BOILER DRUM: Length-15.76 m Internal diameter- 1676 mm Thickness- Bottom half=133mm Top half= 155 mm  Weight- 123 Tons  Material- Carbon Steel (SA – 515 GR 70 or 299)  Design Pressure – 158.2 kg/cm2  Operating Pressure- 150 kg/cm2  Drum filling capacity- 1)Entire- 37.20 m3 2) Operating level- 11.53 m3 The thickness of the top half is more because the top side of the drum contains steam and pressure of the top side is more than bottom side.

MANUFACTURING OF DRUM :  The top half & bottom half plates are heated

in aplate heating furnace at a very high temp. & are pressed to form a semi cylindrical shape.  The top & bottom semi cylinder with hemi spherical dished ends are fusion welded to form the boiler drum.

DESCRIPTION :  The boiler drum is located at a height of 53 m.  In250 MW (KWU) units, the drum is located at 58 m.  Modern high capacity boilers are top supported units. The main

supporting structure of the boiler consists of 18 main columns & 12 auxiliary columns. The main column supports the main boiler components i.e. drum, water wall, membrane plate, super heaters etc.  The drum is provided with stubs for welding all the connecting tubes i.e. down comer stubs, riser tube stubs, s/h outlet tube stubs.  The drum is provided with manhole & manhole covers. Manhole is used for facilitating the maintenance persons to go inside drum for maintenance.

WATER AND STEAM CIRCUIT  The drum forms part of boiler circulation system i.e. movement of

the fluid from drum to the combustion zone & back to boiler drum.  Feed water is supplied to drum from economiser through feed nozzles. *DOWN-COMERS: Water from the drum goes to water walls through six down comers. There are total eight no. of down comers for 210 MW*CONNECTIONS:  2 down comers- to front side of bottom ring header.  2 down comers- to rear side of bottom ring header.  1 down comer- to left side of bottom ring header.  1 down comer- to right side of bottom ring header.  2 down comers- to water wall platen inlet header.

DRUM INTERNALS  The saturated steam is led to the super heater through super heater connecting tubes, provided at the top of the drum.  The feed nozzles are connected to internal feed distributing header.

* FEED NOZZLE ASSEMBLY Feed nozzles are connected to internal feed distributing header.  The feed header is located below the water level & runs through the entire length of the drum.  One row of feed distributing tubes on one side of this headers directs the feed water towards the down comer. * RISER TUBES• The steam water mixture enters the drum through riser tubes. • There are six levels of riser tube connections welded to the drum. • 6 x 23 – rows of riser tube connections. • Dia. Of riser tubes- 127 mm.

VARIOUS PARTS: Feed pipe Baffle plate Separating chamber

Turboseperator Screen dryers Anti-vortex spider

BAFFLE PLATE:  These surfaces direct the flow of substances either to prevent or

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improve its flow. Functions of baffle plateThe shrouded drum arrangement provides uniform heating & cooling which maintains entire drum surface at an even temp. Guide the steam/water mixture from the riser tubes to the turboseperators. SEPERATING CHAMBER : From the riser tubes stem & water mixture flows into the drum through a narrow annulus formed by a shroud extending along the length of the drum shell called the seperating chamber. This is a welded construction framed by baffles.

TURBOSEPERATORS :  From the lower end of the seperating chamber, the steam &

water mixture is forced upward in the turboseperator.  It is a main seperating device. * Primary stage The fixed spinner blade of turboseperator which is located inside the inner can imparts a centrifugal motion to the mixture of steam & water flowing upward through the inner can. * Principle of working of turboseperator Water particles, being heavier, are thrown to the outer periphery & steam remains in the centre.  The water is arrested by a skin off lip above the spinner blade & flows down through the annulus between the two cans.  The steam then proceeds into the secondary seperator.

• Stages of separation of water & steam: • The first stage of separation takes place in the

concentric cylinder of turboseperator. • The second stage of separation takes place in corrugated sheets connected to the top of the turboseperator. • The third & final stage of water & steam separation takes place in the screen dryers.(i.e. dry saturated steam) • 2 rows of 50 turboseperators are there along the length of drum.

SCREEN DRYER :  Screen dryers are acting as eliminator (eliminate water     

particles). It removes residual moisture from the steam leaving turboseperator. The screen dryer box consists of wire mesh of different gauges. Exterior meshes are of thicker wire rod, which have better mechanical rigidity to the screen box. It consists of closely packed strips of steel ‘V’ or ‘W’ sections. The steam passing between the strips making one or more sharp changes of direction & throwing the heavier water particles coming in contact with strips.

* Dryer arrangement: • 49 screen dryers are arranged along the entire length of drum. • The steam coming out from the dryer is totally moisture free saturated steam. • Dryers are held by bolts & nuts for easy dismantling & assembly.

Cont. Blow Down/E.B.D.  C.B.D. is done for the removal of silica.  Phosphate dozing is done in boiler drum for removal

of silica.  Drum is slightly tilted to the right side, so that silica comes down to the right side, so the connections for C.B.D. are given to right side.  E.B.D. is done only when drum goes certain high.

SAFETY VALVES:  As per boiler act, the safety valves are provided at different locations in

boiler.  The safety valves are employed to relieve excess pressure over & above the permissible working pressure in boiler drum.  There are 3 safety valves to the drum, one at right side & two at left side.  Following table shows the setting pressures of safety valvesLocation

Operating pressure of drum

Safety valve

Set pressure Kg/cm2

Drum

150 kg/cm2

SV1 SV2 SV3

158.2 160.3 162.4

 Tapping's for various measurements on the drum:  3 pairs-Remote drum level indicators.  2 pairs- Local drum level gauges.

 2 pairs- Conductivity measurement.  2 pairs- connections for steam/water sampling.  1 pair- for pressure measurement.  3 pairs- thermo pads for measuring drum metal temp.

measurement.  1 pair- high & low level drum trips.

THANK YOU !