ESP MECHANICAL WORK PART-IV FOR THERMAL POWER STATION.

Till date i have discussed ESP mechanical work up to inner roof panel.

ESP supplied by BHEL requires enormous quantity of welding (structural)ired 

at site . Therefore vendor should have adequate number of qualified welder

for the job . For 500MW and above unit at least 35 to 40 welders and around

20 tack welders are required at the peak time. As ESP jobs mostly sequential

in a pass therefore any delay on welding will delay the subsequent activities.

-Once all electrodes were loaded on temporary J- bolt then alignment work

for frames and shifting the load to permanent supports starts.

- Parallel erection of hopper wall also start once electrodes are fixed with

  frame by   bolts and this bolts are fixed by Huck bolting machine.

- Once should check the compatibility of the machine and bolts.

- All inner roof welding ,insulator housing work etc is complete then go

for insulation of inner roof and outer roof fixing.

- Funnel pre=assembly outlet and inlet to be done separately with from

the beginning as these activity will take about an year due to interfaces

Inlet funnel and outlet funnel requires huge space for assembly and at

site to get those space is difficult .However with proper planning same

could be achieved . 

ESP wall erection, roof erection and GD screen erection can be viewed.

Inlet funnel erection under progree with heavy duty crane.

Outlet funnel erection  under progress.

continued part-v

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ELECTROSTATIC PRECIPITATOR ERECTION PLAN ,TOLERANCES PART-III FOR ATHERMAL POWER STATION

I  have discussed about the column and bracing erection ( horizontal and

diagonal) in ESP erection Part -II. There is sizing calculation for choosing

ESP size and the same will be discussed at later date. In this dispatch we

will discuss about other structural part.

CASING

- Pre -assembly of casing intermediate column individually and as a frame.

- A pre-assembly bed is required very near to ESP preferably any side of the

  ESP as frames are very big in size but not in weight.

- Transfer the foundation centre line to the top of the bearing through base 

  column.

-Transfer the centre line from bearing bottom plate to centre line of inter

 mediate column.

- Tolerance of distance variation is +/- 5 mm.

- Start erecting casing plate one by one between two intermediate columns .

- It is preferable to start erection from centre then come to side.

- It is also preferred to erect adjacent sides of two pass first then the free end.

- Once casing erection under progress then erection of roof beam horizontal

 ( longitudinal and transverse beams ) are erected  to lock all the casing and 

making it as a box. 

- After erection checking of beams , distances and diagonal measurement

  all are welded.

- After completion of roof structure measurement are made from Gas path

  centre line and recorded.

- Start erecting emitting frame and collecting electrode frame. This is a

  repetitive job needs to be done attentively. All measurements are to done

  with reference to GPCL. 

- All measurements are recorded  for reference.

- Collecting electrode erection either through bottom or using heavy duty

  crane from top that is roof. Both  process are having advantage and 

  disadvantages. If we don from the top progress will be more but we require

  deployment of 250MT crane exclusively for electrode erection. We also need

  a frame (sliding on rail ) to be fabricate at least for one packet of electrode 

 ( 30 nos). Its also advantage is hopper work can go simultaneously. However

  roof work will be suspended at that time. But inserting from the bottom 

  we need only a 1MT winch and nothing else . But progress will be slow.

casing erection , intermediate column erection with some roof beeam erection

under progress.

Roof erection and emitting frame erection under progress.

contd to part-iv.

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ELECTROSTATIC PRECIPITATORS FOR A THERMAL POWER STATION OVERVIEW, ERECTION PLAN & CONSTRUCTION FEATURE PART -II

There are many types of electrostatic precipitators but I will describe only

BHEL make ESP.

- ERECTION PLAN AND SEQUENCE.

- Check the foundation of ESP column .

- Mark the centre line .

- Check the distance between centre lines of ESP foundations.
  Tolerance +/- 10mm.

-Top elevation of ESP foundations to be measured.

- Spacing between its foundation and diagonal difference.

- Bolt to Bolt pitches distance and diagonal distance to be measured
  Tolerances for pitch +/-03mm and diagonal +/- 05 mm.

- Some of the foundation will have shear lugs also .All those measurement
  are to be taken.

Top of the elevation and dimension of shear lug pocket is very important

for carrying out the secondary grouting by Ready  Mix concrete like

conbextra , pagel , sikka , five star etc. Gap between foundation and  column

pedestal will determine the volume of RMC required. Generally GAP is

restricted to 30 mm to maximum 70 mm. Secondary grout can be done

by one grade higher concrete but the curing time and settling time will be

21 days where as the same value can be achieved within 3 days of  RMC

concreting. Cost of RMC is much more therefore optimum dimension should

be achieved during pre-concreting check of foundations.

Once all foundations are checked then we can start preparing for column

erection. For any 500MW ,600 MW or 660MW set either there will be

04 pass ESP or 06 pass ESP. The work involved in each pass will be the

same and repetitive. Erection should start from the centre pass of the ESP

then move out to outer side. This help us in optimisation of crane capacity

any deviation from this may attract the requirement of higher capacity crane

for erection of  wall , inlet nozzle , roof truss etc. Interface with boiler erection

CHP , AHP and Duct structure will obstruct ESP erection. Therefore careful

planning is required to erect ESP .

- Sweep and camber of the columns to be checked .

- After erection column to be vertical. Tolerance 1mm/M ,max 10 mm.

- Horizontal bracing and diagonal bracing to be erected.

- Checking of orientation of column is must before erection.

we donot erect all the digonal bracing  to allow movement of Hydra crane

between the columns . Otherwise same is not possible . Bracing are erected

when our requiremnent of Hydra crane reduces.

- After welding of all bracings etc bearing /slide supports are placed on the

 top of the column.Diagonal Distance are measured from the top of the fixed

foot column to other bearing top and recorded.

contd to part-3

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ELECTROSTATIC PRECIPITATORS FOR A THERMAL POWER STATION OVERVIEW, ERECTION PLAN & CONSTRUCTION FEATURE PART -I

Air pollution is the presence of some substances added directly or indirectly

by different operations in such quantity and of such duration so as to affect

or try to affect human beings ,animal , vegetations , materials , climates etc

adversely. Example of primary air pollutants are CO;SO2,NO2 etc , second-

ary pollutants are O3, NO2, H2SO4,HNO3 etc. Thermal Power station

operation with oil and coal as fuel are source of these pollutants and also ash

from burnt out coal. On average if two and half rake of coal are used in the

power station then there will be one rake of ash to be cleared.

NATIONAL AMBIENT AIR QUALITY STANDARDS ( NAAQS)

                                                                        Land Use.

Pollutants         Average time    Industrial      Residential, Rural    Sensitive

SO2                    ANNUAL          80                         60                    15

NO2                   --DO----             80                         60                    15

SPM                   --DO----           360                       140                    70

RPM (<10microns) - do --          120                         60                   50

LEAD (Pb)           --do---                 1.0                    0.75               0.60

(All values are micro gramme / metre cube. )

AMMONIA          ---do---                0.1                     0.1                0.1

( All values are milligramme / metre cube)

In earlier days i.e. before the use of ESP mechanical devices like i) Settling

chamber  ii) Cyclone Separator  iii) Bag House Filter iv) Wet scrubber.

Out which Bag House Filter type of precipitators are still in use specially by

Chinese suppliers.

However once technology of ESP comes into force all other separators

became obsolete. The performance of ESP can now be guaranteed up

to 99.97%.

Electrostatic precipitators is most widely used device to control particulate

emission in Industry now.

Electrostatic Precipitation is physical process by which particles suspended

in gas stream  are charged electrically and  under the influence of electric

field  are separated from the gas stream. The precipitation system consist of

positively charged collecting surface ( Termed as collecting electrode ) and

high voltage negative charged wire suspended from the top of the frame to

bottom the frame hook ( Termed as emitting electrode). The total frame was

suspended from the top through a high voltage insulator. At a very high DC

voltage to the tune 50 KV to 70 KV are applied  between emitting and

collecting electrode and a corona discharge occurs close to emitting

electrode . This will charge the whole gas path across the electrode and

particulate charged with negative charge will attract towards the +ve

collecting electrode and gets deposited on the surface.

A Typical ESP area  foundations are getting ready for start of erection.

 



Base Column erection under progress for an ESP pass.

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MISC. PICTURES ,INSULATION WORK AND ERECTION PLAN OF BOILER

In my last two or three dispatches we have discussed miscellaneous items

erected in a steam generation and there strategies to be adopted. I am enclosing

some pictures to bring clarity about earlier topics.

The above two works are for ducts .One is getting erected in position and

other is getting assembled with subsequent duct on bed before erection.

We will now discuss about insulation work in boiler . In 500MW or

660 MW boiler around 4000 MT + insulation work to be executed.

Insulation work in India is not getting much importance compare to

main Boiler work. This job is extremely labour oriented and requires

experienced manpower to execute them. Insulation work in boiler

can be divided into three categories  e.g.  1) Castable  2 ) Pourable

3) Wool mattress . beside that there are work of iron parts and overall

sheathing.

In general boiler insulation work starts after conductance of Hydraulic

test ( preferably drainable) . If we conduct non drainable Hydraulic test

then it is mandatory to light up the boiler within 21 days to 30 days other

wise wet preservation is required for non drainable portion. This will open

a new area which is not a part of this topic. It has been observed that after

successful Hydro Test a unit takes 03 to 05 months  time for Light Up and

majority of the insulation to be completed. This becomes a very big problem

for erectors to race against time . Therefore a few steps to be taken to work

on parallel path .

- Most of the time it is found that leakage do occurs from water wall panel

while making gas cut on fins for fixing lifting lugs. This can be altogether

avoided by use of specially designed fixture or gas cutting to be done in

front of responsible supervisor.

- Regular inspection to be done during fin welding . Tube may get

punchered during striking an arc. All welding joints of pressure parts

are subjected to various NDE and inspected by various persons . Therefore

failure of High pressure joints are very minimal. But fin welding which

is to be done in Kilo meters without any major inspection needs to be

improved to pass through the hydraulic test in one go.

- Welding of insulation hooks is another area where mistake may happen.

Welding hooks to welded either on fins or on tubes. There are two school

of thought on this. If it is to be welded on tubes then 100% welding to be

completed before Hydro test . But if it is to be welded on fins then same

are to be done before Hydro test but risk are less.

- Duct insulation work can be done once kerosene test of duct is over . A

portion of both side can be kept open for final welding between two ducts.

This will help to achieve boiler light up and sub sequent activities.

A typical data of insulation used in 660MW Super critical Boiler.

s/n       area           temp C     thickness             sheathing          density

01. Furnace wall   439       310 mm  Al.sheathing 1.6mm       150kg/m3

02. Pent house      482       360 mm          do                            -do-

03. Separator        427       250                  do       1.2mm         150kg/m3

04. Flue gas Duct  343       210                  do       0.914mm    100kg/m3

05. ID duct            138         40                 do            do              do

06. Hot air Duct     321       140                do             do             do

07.  Cold air Duct  acoustic 200                do            do              do.

08. Misc. items                      50                do            do              do.

-Insulation Material as IS 8183 group 3&4 lightly resin bonded Mineral

 rock wool.

- Any surface more than 60 deg.C temp will be insulated.

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