ERECTION PLAN AND SEQUENCE FOR AIR PREHEATER PART-V

Air Pre-heater erection Part - V continues

Air pre heater erection sequence and plan is given above. Also this process can be utilised for

monitoring purpose. Electrical ,C&I are left out as the same will be discussed separately. Air

heater erection from start to erection finish is about 4 to 6 months job. Material flow for the

job should be as per sequence mentioned earlier. Around 30 to 40 persons are required to

execute the job in that time frame with adequate T&P and IMTE.


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ERECTION OF AIR PREHEATER FOR SUPER CRITICAL BOILER PART-IV

Air pre heater erection continues part-iv.

continues for part v.

ERECTION OF AIR PREHEATER PART-III OF SUPER CRITICAL THERMAL PLANT

Air Pre Heater erection continues:-

AIR PREHEATER ( LUNJSTORM) FOR BOILER ERECTION PLAN PART-2

Air preheater erection can be started just after erection of last ceiling girder and can be continued

along with Pressure Part erection. However approach for pressure part  should be kept open.

For Boiler where Air heaters are installed in second pass approach from rear and both sides

should be available. Two other issues may crop up i) Construction of fan foundations ( PA & FD)

ii)  Erection of ducts just above Air heater. It is noticed that approach area at the rear gets

congested early because of multi- discipline starting of erection work like ESP , SG , coal

gallery , Ash handling work , duct support , electrical tray work etc. Therefore it needs good

planning and idea about the priorities for all the above work otherwise conflict bound to happen

and derails the time schedule.

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AIR PRE HEATER FOR BOILER IN THERMAL POWER PLANT

We have completed our discussion on Steam Generator structural and Pressure part erection

work. Small tips were also provided to construction worker which i think will be useful during

actual erection work. After completing the structural and pressure parts it is time now to discuss

about other main equipment like AIR PRE HEATER.

An Air Pre heater (APH) is a general term to describe any device designed to heat air, before

another process (for example, combustion in a boiler) with the primary objective of 

increasing the thermal efficiency of the process. They may be used alone or to replace a 

recuperative heat system or to replace a steam coil.

Air pre heaters are mainly two types (i) Tubular Airheater  (ii) Ljunstorm rotary air pre heater

bisector or trisector. Tubular air heater is now becoming an obsolete equipment only can be

seen in old and small capacity power house. However use of Ljunstorm air heater is common

to any size of unit. There are advantages and dis advantages for both type of air pre heater in 

use. We will confine our discussion only on Ljunstorm air preheater erection.

The picture above shows the overall construction feature of Ljunstorm air pre heater'

Names of the main parts of the LJUNGSTROM APH are:-

      1)    Expansion block (08)        

2)    Cold centre section (01)

3)    Main pedestal (02) 

4)    Side pedestal (02)

 5)     Guide bearing Assy (01)   

 6)    Support bearing Assy (01)

 7)    Rotor post (01)

 8)    Cold pocket ring (08)

 9)    Hot pocket ring (08) 

10) Hot centre section (01)

11) Cold end tension rings (08)

12) Hot end tension rings (08)

13) Drive pedestal (01)  

14)  Rotor drive unit

15) Guide bearing oil circulation unit

16)  Support bearing oil circulation unit

17) Rotor stoppage alarm sensor

18) Soot blowing system

19) Leakage control system     

20)  Shop assy modules (09)

21)  Semi modules (09) 

22) Gratings (72)

23) Baskets(heating elements)

24) Duct corner Assy (08)

25) Seismic stoppers (08)        

26) Rolled panels/Casings (16)

27) Field insulation 

28) Thermocouple for temperature Measurement.

Picture shows the location of Air preheater in a boiler ( having mills on the side) . PAPH stands

for Primary Air Preheater ( Left and Right) and SAPH stands for Secondary Air Preheater (Left 

and right)

Picture above shows Air Preheaters are in advanced stage of erection including interconnecting duct.

to be continued.

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CONSTRUCTION TIPS ON PRESSURE PARTS ERECTION FOR A THERMAL POWER PLANT.

Colour Coding of filler wire

Specification                                   Brand Name            Colour Code

RT ½ Mo (ER 80s-D2)                      TGSM                        Green

RT 1 Cr ½ Mo (ER 80s –B2)           TGS 1CM             Silver grey/white

RT2 ¼ Cr 1 Mo (ER90s –B3)          TGS 2CM             Brown /Red

RT 9 Cr 1 Mo ¼ V                            TGS9Cb                     -

RT 347 (ER 347)                               TGS -347             Blue

Low and extra low Hydrogen Electrodes    

As per IIW (Indian Institute of welding) classification of Hydrogen

Content classify electrodes is given below.

High   : greater than 15 ml /100gm

Medium: 10-15 ml /100gm

Low: 5-10 ml /100 gm

Extra low: less than 5 ml /100 gm

Baking, Storage and Handling

The electrodes have tendency to pick up moisture when exposed

to atmosphere and the amount depends on the time, relative humidity

and also the type of coating on the electrode. The recommendation

of baking electrodes are given below.

AWS Classification              Baking temperature & Time   Holding temp

E-7018                                 250-300 & 2 hrs                        100 deg C

E-7018 -1                            250-300 & 2 hrs                        100 deg C          

E-7018- A1                         250-300 & 2 hrs                        100 deg C

E -8018 –B2                       250-300 & 2 hrs                        100 deg C

E-9018- B3                         250-300 & 2 hrs                        100 deg C

E-8018- B2L                      250-300 & 2 hrs                         100 deg C

E-9018 –B3L                      250-300 & 2 hrs                        100 deg C

E309 & E347                      250-300 & 1 hr                          100 deg C     

** - After issue the electrode from site store to welder the temperature

Portable oven should be around 65 to 70 deg C during actual use by welder.

This is not applicable to E309, E347 and E 6013.

Selection of electrodes for non –pressure parts work

Material P1 + P1

A. For butt welds, up to 6mm inclusive:  E6013

                                      

                                       > 6mm            :  E7018

B. For fillet welds up to 8mm inclusive    :  E6013

                                      

                                    > 8mm                   :  E7018

Carbon Steel + P1                                     : E6013 or E7018

Carbon steel + Carbon Steel                     : E8018 –B2

Note: E6013 can be used for all non load carrying welds of all thickness

of IS2062 plates 20mm thickness and 8mm fillets. For structural material

like Ceiling Girders thickness of material is > 63 mm needs preheating (120

Degree C) and stress relieving (600-700 degree C) depends on material.

Common Knowledge required by construction supervisors engaged in boiler work

Weight Calculation for tubes:-

W = (D-1.1425t) x 1.1425t x 0.024466 Kg/M

           

            W= Weight of the tube in kg/M

            D = Specified outside diameter in mm

            t = Specific thickness

Weight Calculation For pipes:-

W = (D-t) t x 0.02466 kg/M

         

           W- Weight of pipes in Kg/M

            D- Specified outside diameter

            t - Specified thickness

Weight Calculation for ID controlled pipes/tubes

  

W = (Dot) t x 0.02466 kg/M

           

            W- Weight of pipes in Kg/M

            D- Specified outside diameter

            t - Specified thickness

 Temperature Measurement

For measuring the stress relieving temperature we generally use

Thermocouples. The thermoelectric voltage in a thermocouple depends

 on the temperature difference between two junctions and is used and

is used for the purpose of temperature measurement when one of the

temperature is known. At project site we use Chromel – Alumel thermocouple

popularly known as “ K “type.

Colour Code of thermocouple is yellow (+) and Red (-) over all Brown.

(Polarity +/- should be known otherwise it will give erroneous reading)

Thermocouple extension wire Yellow (+) and Red (-) overall yellow.

(Thermocouple can only be connected by thermocouple extension wire not

by any other wire)

There are other types of thermocouple but in India “K” type is only used at

the project site. The temperature – milivolt curve is linear. The increase is

4.13 mv per 100 degree C. (approximately)

Radiography Source

In India for industrial radiography we use two type of source i.e Cobalt -60

and Iridium -192. Out of that use of Cobalt -60 is extremely unpopular

because it requires stringent safety precautions to be followed and it

affects the progress of work. Instead of cobalt -60 now a day’s all are

using ultrasonic machine to detect the fault. Ultrasonic machine requires

Test block (made of same material to be tested) to be made as per the

Specification of IIW.

Iridium -192 is having half life of 74.4 days. All our pipes and tubes are

Radio graphed by this source except pipe /structural thickness of > 60 mm.

In those cases only UT is performed. The Iridium source should be more

than 30 Curie strength. It will require less exposure time and time can be

saved. Exposure time is inversely proportional to the strength. In 500MW

/660 MW boiler around 10,000 to 12000 shots are taken.

For surface defects of welds two very simple tests are carried out (i) Magnetic

particle test (ii) Dye Penetration test. 

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