THERMAL POWER PLANT BOILER PRESSURE PART DESCRIPTION

We have discussed about the spiral wall with different pictures and illustration . We will leave

spiral wall there and proceed further on pressure parts of Boiler.

                                                          Furnace Vertical Walls:

The vertical wall panels are after the steam or steam and water mixture (as the case may be) comes out 

of intermediate headers. The tube size is 38.1 tubes @ 50.8 mm spacing. All the panels are of Alloy 

Steel tubes and are fin welded construction. The vertical wall transfer the total load of spiral walls to 

the ceiling by the means of Finger Strap plate welded to the spiral walls on all four sides. The walls are 

separately supported from the ceiling and the outlet headers are supported separately. The bent tubes at 

the end of vertical panels have lug welded as in case of Roof Panels in 210 / 250 MW designs.

                                         Furnace Vertical Wall Outlet Headers:

The vertical walls deposit the steam or steam and water mixture in outlet headers. The headers on front 

and sides are offset from the centre line of walls. Hence, the total loads of the walls are not transported 

through the header except the rear wall header, when the header takes the total load. This is no separate 

header in once through boiler for screen and hanger because the screen and hangers are at the same 

location and are inline with the rear wall. Hence, the rear wall header takes the total load. In some   

cases , there are two tubes for load carrying. Headers are supported by ‘U’ Rods separately.

                                           Furnace Wall Rear Arch Panels:

In Once Through Designs, the rear arch tubes are sent as panels. There are generally 6 rows of tubes 

forming the screen and one of the tubes (the rear one) is the hanger tube. This tube size is made bigger 

for load carrying purposes. In our project  this tube is 57.2 x 12.7 – SA213 T23 to take care of load.

                                              Furnace Riser Pipes to Separator:

As against in Conventional designs, the risers are in very less in number but are of bigger sizes. The 

sizes vary from 219.1 to 323.9 based on the capacity. The number of risers is totally 16 in our 

project. The risers from each of the 4 outlet headers are connected to each separator vessel. In

case of subcrtical boiler of 500 MW capacity the quantity approximately 61 nos of lower size

and length.

                                                          Burner Panels:

Without any doubt, the Burner Panel is the MOST Complicated piece of item in Once Through Boiler 

Pressure Parts. The burner panels are made in the spiral wall area. The boilers are tangential fired 

designs and the burner panels are positioned at four corners in our conventional designs. The main 

difference between our conventional design and once through spiral wall designing that in our 

conventional designs, we have single opening in burner panel through which the total wind box is 

inserted. But, in once through spiral wall designs, the opening for each nozzle is made separately by 

arranging tubes. The sizes of tubes in burner panels are 41.3 x 7.4 – SA213 T22. 

                                                             SOFA Tube Panels:

The extra air is fed into the furnace to control the Nox emissions through openings called SOFA

(Separate Over Fire Air) openings. For our project, these are located on the all  side walls.

Conceptually, the SOFA Panel Arrangement is similar to Burner Panel. The height is smaller as

compared to Burner Panels. Thus we can now sketch the flow of steam or steam and water mixture in

the furnace system:-

Economizer outlet links to Evaporator Inlet Header
               |
Spiral Hopper Loose Tubes
               |
Spiral Hopper Wall Panels
               |
Spiral Hopper to Wall Transitions
               |
Spiral Walls (including Burner & SOFA Panels)
               |
Intermediate Headers (including Spiral to Vertical wall transitions)
              |
Vertical Wall Panels (including Rear Arch tubes)
             |
Furnace Outlet Headers
             |
Furnace risers

Above picture shows the pressuse parts items are hanging from welded beam through suspension

rods. Some of the link pipes are visible here . These links pipes are to be erected first after

erection od suspension as these pipes big in length and having bends at different place to

avoid fouling with other members ,rods etc.

Some of the water wall panel ( vertical ) erection and alignment under progress. 

SOFA panel . In my next dispatch we will give the picture of Burner panel and its crticality .

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SPIRAL WALL -3( PR.PARTS OF BOILER) PICTURES

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SPIRAL WALL-2 CONTINUE FOR BOILER

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We have attached photographs for spiral wall for ready references .


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PR.PARTS OF BOILER ( SPIRAL WALL -I) ABC OF THERMAL POWER PLANT

Spiral Wall

Introduction of Spiral wall in very new in India . This is now being used by foreign manufacturer

for Super critical boiler. From hopper, the water raises in the spiral wall system of furnace. In the

spiral wall, the slope can be any value from 13° to 20°. In case of Barh, this value is 20°. The 

spiral walls  are constructed on the concept of fin welded panels. They have stepped weld so

as to join with the other adjoining panels. The size in spiral wall chosen for Barh is 41.3mm

tubes. The material is selected as T22/ T12. The walls are provided with many openings for the 

following items:-

i) Wall blowers.

ii) LRSB.

iii) Observation Doors.

iv) APM (Acoustic Pyro Meter)

v) FMS System (Flame Monitoring System).

vi) ASLD (Acoustic Steam Leak Detector).

 Furnace Spiral Wall to Vertical Wall Transition Panels

The spiral walls on all four sides terminate below the screen and rear arch. The spiral wall terminates at 

the designated level with forged fittings. These are small individual forged elbows with Integral Fins

and are made of Alloy Steel SA182 F12 Cl.2 or SA182 F22 Cl.3. All the spiral wall fittings are welded

on the panels at shop. Similarly, there are forged fittings for the vertical wall to intermediate header

terminal tube connections. These are combined formed fittings. i.e. one fitting takes care of 3 or more

tubes. These tubes are directed by the spiral to vertical wall tube ratio. Hence, most of the vertical wall

fittings are made up for 3 Nos. of tubes except at ends when there may be variation in number of tubes.

All the forged fittings for spiral wall as well as the vertical walls are welded at the shop floor.

From this dispatch onwards we will provide more details on Spiral wall as its is absolutely new.

Construction workers ,supervisor and engineers should have an overall idea of the system.

Both type of  furnace arrangement has been shown vertical type we are using sub critical boilers

also in super critical ( with improved version of tubes) and spiral wall we are using in super critical

boiler ( the spiral wall type we worked) . As already mentioned There are two zones one is  spiral

wall up to 59+ metres and ended above burner nozzle and then transition header and vertical wall.

Tube arrangements of spiral wall in comparison to vertical wall. Inclination has already been

mentioned above. Forged fittings used for connection spiral to vertical through transition header.

Pre-assembly of spiral wall is under progress with Tension. Fixing of Tension Bar is very important

for matching of the spiral wall. Please note this matching cannot be done in situ at working place like

other vertical Wall ( Tension Bar is not there in vertical wall panel)

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FURNACE AND EVAPORATOR SYSTEM OF BOILER

In last dispatch we have discussed what are the major components constitutes the Furnace

/ Evaporator System. Today we will describe the system individually in brief.

Furnace wall inlet Headers. 

1. The headers form a ring header   pattern link in all conventional designs. The basic difference

is in the arrangements of  headers. Basic points which make the header unique are that the side

wall headers donot have any stubs as they have only the economiser water connection and the

other point is headers on front and rear do not extend up to the wall as it in subcritical utility

boilers. As the spiral wall construction begins at hopper iyself , the stub arrangement is

staggered both front and rear headers.

Spiral wall inlet tubes

The spiral hopper formation starts at the hopper inlet tubes. The pitching and arrangement

 is such that the required angle of spiral hopper and pitching of tubes is achieved at the 

loose tubes.

Furnace Hopper Spiral Walls

The water from the bottom inlet header enters the spiral hopper walls. The hopper walls are slanted to 

the hopper angle on front and rear and are vertical on sides. The hopper walls on front and rear have 

two inclination angles to accommodate the tubes and to facilitate the formation of helix. All the end 

connections are with loose tubes only and there is no spiral panel gang bending requirement. These 

loose tubes at all the four corners are welded at site. Furnace hopper side walls have the large access 

door opening (610 mm x 762 mm), which is given for taking equipments like scaffold door, etc. inside 

the furnace. The tubes are to be bent in multi plane to arrive at all openings.

Furnace Hopper to Vertical Transition

On the front and rear sides of the furnace hopper, the tube panels are at angle of 50° to the vertical. To

match the vertical spiral wall, these transition panels have a bend in the vertical plane. These bends are

provided by the number of loose tubes in the matching panels.

This is typical status of erection site at the beginning of pressure part erection. Any body can observe

that roof sheeting work is over. It will benefit the erection work during monsoon season, As you

know structural work starts from bottom but Pressure parts work starts from Top.  Therefore

suspension work , lifting of link pipes , roof panel , top headers etc can be lifted. Suspended

suspension and a few headers can be seen. It also observed that lot of horizontal buck stay has

been lifted and kept in position . There are two schools of thought regarding lifting of buck stay

one is buck stay to be lifted along with the wall panel because bigger length and avoid bending

during lifting and other school is buck stay to be lifted separately and attached after lifting of

panel. Both the theories have their advantage and disadvantage therefore it will be the decision

of erectors and material position that will guide. We have followed mixed rout of both the system.

It can be observed that all silencers are erected on the roof .

As described earlier transition header with spiral panel and vertical panel pre-assembled and

getting lifted.

Furnace wall vertical is taking it shape . Buck stays were attached now and helping in formation of

furnace.

PRESSURE PARTS ( FURNACE AREA) FOR BOILER.

The Economiser outlet connection are made with the furnace inlet headers. The total furnace

system consits of the following system.

a. Furnace wall inlet headers -------------  Front , Rear and sides.

b. Furnace inlet loose tubes  --------------  Front and Rear.

c. Furnace Hopper Spiral wall ------------- Front ,Rear and sides.

d. Furnace Hopper to  Spiral wall  Transition -------------  Front , Rear and sides.

e. Furnace wall Spiral ------------------------ Front , Rear and side attachments.  

f. Furnace wall Transition panels ---------- Front , Rear and sides including  spiral & vertical

   fittings and forged fitting used  for  transition.      

g. Furnace wall intermediate headers ----------------- Front and Rear.



h. Furnace vertical wall ----------------------------------Front and sides.

i. Furnace wall rear arch tube panels and Furnace rear hanger tubes.

j. Furnace vertical wall outlet headers ---------------- Front , rear and sides.

k. Burner Tubes bundles at four corners.

l. Sofa panel on the side walls.

m. Furnace outlet riser pipes to seperator.------------------- Front , rear and sides.

n. Rear Arch Supports  ( Special for once through Boiler)

A picture of pressure erection is added to explain some basic points. This is Sprial panel with

transition header pre-assembled and lifted . You can see the vertical Panel on the top . Vertical

panel got assembled with loose tubes and header .  Also notice the Y shape alloy steel plate for

supports. This plates are fitted during pre -assembly of panel and  keep the continuty of the plate

during susequent panel fitting. Header is 60 + elevation.

Same panels are getting positioned at respective elevation and giving a birds eye view  for furnace

formation.

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BOILER ERECTION (ECONOMISER) CONTINUED WITH PICTURES

Two pictures given to show the pre-assembly can be for header and terminal tube. Also show the

after erection look. We will not discuss about erection of the coils header etc as the same will be

during erection sequence. etc. There are two theory of lifting economiser coil  1. by doing pre-

-assembly of two coils . 2. lifting it by one by one. There is advantage and disadvantage of both

the system which we will discuss later.

We conclude the discussion about economiser loose tube with header pre-assembly at site.

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