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Friday, 15 March 2013

THERMAL POWER PLANT PRESSURE PARTS SUPERHEATERS.

                                                                         Super heater System:



The steam from riser comes to the separator vessels. The steam is taken to the radiant

super heater inlet header. The super heater links are 8 in numbers and are generally of the size

219.1 to 273.0. These are connected to the header by means of nozzle (forged) or by reduced

branch end tees. The selection is based on the header size and connecting nozzle size. From the

Radiant Roof inlet header, Roof tubes start and they cover for the furnace and extended pass.

As the project designs are without super heater divisional panels, the SH Radiant Roofs are in

the form of fin welded panel in this portion. The second part of the roof is saw cut fin welded

loose tubes. These tubes go to the SH Radiant Roof outlet header. There are 8 Nos. of SH By

pass pipes which connect the SH Radiant Roof inlet and outlet headers. Steam from the SH

Radiant Roof outlet header is bifurcated into two items:- (1) One portion goes to side walls & (2)

The second goes to the extended wall inlet headers. The arrangement of headers is in the shape

of English letter ‘H’ in the plan view. The steam in the extended walls flows through the vertical

walls through the bottom panels to the extended side wall outlet header placed on the centre line

of unit. The basic difference between our conventional design of 210 / 250 MW and this unit is

that the steam flow is upward in our designs where as the steam flow is downward in this

design.


The steam from extended wall outlet header then flows to the set of two extra headers used in

the specific project design. In between the two headers, there are 18 Nos. of pipes size 168.3 x 47.0

thick Alloy Steel, which take load and also complete the steam circuit. From the bottom header

steam is taken to the 2nd Pass Bottom Front wall inlet header by 2 Nos. of links. The second

part of steam flows from the 2nd pass side walls to the outlet bottom headers. From the side wall

outlet headers, the steam in correct proportion flows to Front Wall Inlet Header and Rear Wall

Inlet Header. Also, the steam cooled Hanger tubes are taken from both of these headers (as

against our 500 MW designs, where there are taken only from the front wall header). The fin

welded panels are made of Alloy Steel tubes. The Radiant Roof tubes and extended panel tubes

are of SA213 T23 material. The steam flows through the front walls, SH Screen tubes and also

through the Economiser / LTRH coil hanger tubes and Economiser outlet header support tubes

and gets connected to the Back pass front wall outlet junction header and hanger tube outlet

header respectively. Similarly, the steam in the Back pass rear walls goes through the roof tube

and also through the hanger tubes of Economiser / LTRH coils and LTRH inlet header support

tubes and finally gets connected to the Back pass front wall junction header and the hanger

outlet header respectively. The hangers tubes include:-



i) Economiser coil hanger tubes.

ii) LTRH coil hanger tube (continuation of same economiser hanger tubes)

iii) Economiser outlet header support tubes.

iv) LTRH inlet header support tubes.



From the both hanger outlet header and front wall junction header links are taken and they join

together in the pent house before carrying the steam to the Platen super heater. Platen super heater in

the sole pendent section is in furnace radiant zone. The design of the project has 24 elements. The

platen SH is made of tube 44.5 and the main material used is  SA213 TP347H  and  SA213 T91.

The headers are Short Stub headers.

From the platen SH coils the steam goes through the Platen outlet header, which is, split type (two

headers separately positioned and connected by mechanical means), the steam is carried by two links to

the final SH section. The SH DESH is placed in these links. These links are crissis crossed .The

finishing super heater coils are put in the extended super heater pass. This arrangement is more or less

similar to the 210 / 250 MW designs. There are two vertical banks of coils. The connection between

them by criss crossing the tube above the roof, The finishing SH coils are of 44.5 tubes and mainly

SA213 TP347H material. All the terminal tubes are SA213 T91. The steam reaches the main steam

outlet header, which is split header with end outlets and goes to HP Turbine.








Platen super heater coils in erected conditions .

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