PART -V MAIN CIVIL WORK THERMAL POWER PROJECT.

BOILER /ESP SUPPORTING STRUCTURE 


Boiler/ESP ( Electrostatic Precipitator) support structure shall be designed for  1. Dead load   2. live /

imposed loads  3. Static and Dynamic loads for piping , rotating equipment etc.  4. Cable trays and

walkways supported on columns.  5. Ash water piping support   6.  ESP hopper ash filled up condition

to  the extent of top of the hopper .  7.  To calculate the load the ash density to be taken 1350 kg/ m3 

8. Ash load at the bottom of hopper  and pent house as specified in the mechanical contract. 9. Wind

load  and seismic load . 10. Temperature load ( +/- 25 c ) for atmospheric temperature variations. 11.

Temperature load for variation of temperature due to ESP operating conditions.

Boiler structure should be so designed that temperature of the structure should not go beyond 60 deg.

Bracing for pipe supports on ESP should be less than 10.0 Mtr height.

Plinth level of Boiler area will be 500mm higher than FGL ( Finished Grade Level).


Finished floor level of boiler area paving shall be kept about 200 mm lower than the finished floor

level of Main Plant buildings.

Foundation System General requirements are -

A. Foundations can be open ( isolated footing /raft)  or pile foundation depending on soil report.

B. The design of foundations should be as per different IS codes.

C. No Major foundations should be on filled up soil.

D. Open foundations and pile foundations should not be combined in same structure.

E. Foundations should be designed on worst combination of loads.

F. For open foundations minimum width is 1.0 M and depth is 1.0M below NGL.

G. Permissible settlement of open foundation of 6.0 M and below  span is  40mm

     Permissible settlement of open foundation of 6.0 M and  span(raft) is  75mm

     Permissible settlement on weathering rock is 12mm.

H. For pile foundations the diameter of pile shall be 600mm diameter minimum . Vertical compression load will be 140MT. The uplift and lateral load capacity will be  20% and 5% respectively.

I. Initial Pile Load test to be carried out for each diameter.

   Vertical (Compression) - 3

    Lateral (Horizontal) -     3

    Uplift (Tension) -           3    

MAIN PLANT AND  AUXILIARY PLANT BUILDING AND STRUCTURES.


-Main plant building shall consist of TG bay, De aerator bay, service

building / Control room 

and all the auxiliary structures/facilities located there

.

- Mill and bunker bay.

AUXILIARY BUILDINGS

- Air compressor building

- Ash water pump house building.

-Air washing Building.

-Ash Slurry Pump House

-AC Plant Equipment Building

-Air handling Unit.

-CPU regeneration Unit.

- Fire water tank and Pump House Building.

- D.G Set.

- Compressor House Building.

- ESP control Room and VFD Room ( if required.)

- RCC twin compartment Potable overhead tank capacity 50 M3.


CHIMNEY

- Height of the chimney will be 275 M as per direction of Pollution Control Board.

- Intermediate platforms shall be placed at minimum spacing of 45 M.

- Outside the chimney to be painted with Red and white paint  band alternatively . However last 50 M to be painted with acid and heat resistance paint.

- All components of chimney shall be designed for 5KN/M2.

- 25% additional loading to be taken as impact loading during liner erection.

-  Limit of  deflection of Girders shall be  span/325 mm.

- Seismic and wind loads reference to be drawn from IS codes.

- Grade of concrete for chimney shell will be M30.

- Chimney design to be verified by " Wind Tunnel Test" conducted by reputed institution.

- Chimney flue duct shall be so designed that the flue gas velocity at exit point remain 20-25 m/sec at

  normal operating conditions.

- Chimney is connected with flue gas duct through a transition piece having one end circular and other

 end rectangular. Liner of the chimney is insulated either by resin bonded glass wool ( density 64 

 kg/cum  ) or rock wool ( density 100kg/cu m/)

- Insulation thickness shall not be less than 100 mm overall.

- Chimney is provided with Rack and Pinion Elevator and aviation light on selected locations.

- A temporary lighting protection  system shall be installed during construction after that permanent

  system will  be installed.

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MAIN CIVIL WORK FOR THERMAL POWER PLANT. part iv

We have discussed about the loading pattern on structure of Thermal Power Plant. Now we will give a few conditions for calculating the load.

We like to mention that these blogs will cover all the aspect of thermal power plant and the information provided are typical . This information will be eye opener and interesting for new comers in the construction field . Therefore all the blogs may be judge accordingly.

The different load conditions are to be taken from (IS:875 part-5) and other relevant IS codes.

1. Wind and Seismic force shall not be considered to act simultaneously.

2. The design of PH structure during Seismic conditions FST ( Feed Storage Tank ) should be considered full up to operating conditions. For other load condition it should be taken as flooded condition.

3. During Seismic condition lifted load of crane should not be considered.

4. For two crane operation ( not in tandem ) one crane considered to be fully loaded and  other crane in no load condition standing side by side . For tandem operation both the cranes considered to be full load conditions standing side by side.

5. For pipe and cable rack structure frictional forces on longitudinal direction , Seismic and wind load are not considered.

6. Clearance of 600 mm to be kept clear from nearest crane structure to B row column. The same clearance for A row will be approximately 1000 mm.

7. Where ever bolting connection is there High tensile bolts of 8.8 grade (min) provided.

8. For nominal connections ( perlins , stairs , wall beams etc) 4.6 grade black MS bolts are used.

9. Permissible deflection of lattice structure and frame except drive floor is span/325 mm.

10. Beams directly supported equipment is span/500 mm.

11. For manual operated cranes and hoist etc the beams deflection is beam span /500 mm in general.

12. EOT crane less than 50T the deflection is span /750  mm. and Crane more than 50T the deflection is  span/1000.mm

13. Bunker capacity to be designed 16 hrs operation on BMCR duty.

14. For all capacity calculation and structural design the unit weight of coal shall be 800 Kg/cu.m and 1200 Kg/cum respectively.

                                                         1.6x Rated capacity on conveyor  x 1200

15 The load on moving corridor  = ----------------------------------------------------

                                                           conveyor speed  x 800

16. Static and dynamic Analysis to be done for all major rotating parts  foundations like  TG , MILLS . ID ,  FD  AND PA FANS , BFP ,CEP CWP ETC. A. fatigue factor 2.0 to be assumed  for above foundations

17. Design criteria of CW duct :Following cases are considered  

-  Maximum design water pressure.

- Surge water pressure to be considered as 5.0 kg/cm2

- External surcharge loading will be 2.0 T / sq.m.

- Minimum headroom (clearance ) will be kept for cable racks and pipe racks.

Switch yard Structure. 

- Switch yard structure should be designed considering worst condition of following loans.

1. Dead Loads .          2. live loads           3. Wind loads        4. Seismic loads    5. Temperature  load

6. Loads due to deviation of conductor.   7. Loads due unbalanced tension of conductor. 8. Torsional

loads  9. Erection loads   10. Short Circuit including Snap of conductor. 

The factor safety for the design of  members is generally taken as 2.0. for normal and broken wire conditions. The factor of safety for short circuit and broken wire condition will be 1.5. These two conditions the factor of safety for designing the foundations will be 2.2 and 1.65 respectively.

Structural work at Power House Building under progress

  

 Bunker House Supporting structure and coal Gallery supporting structure under progress.

(to be continued).

LOAD CONSIDERED ON CIVIL STRUCTURE FOR THERMAL POWER STATION.

To calculate the total load reference of IS 875 ( Part _II) is necessary however for ready reference following values are Given below.

Materials                                                                                                     Unit Weight

Plain Cement Concrete                                                                                24 kN/m³

Reinforced Cement Concrete                                                                       25 kN/m³

Structural Steel                                                                                            78.5 kN/m³

Brick work                                                                                                   19 kN/m³

Cement Plaster                                                                                             21 kN/m³

Floor finish                                                                                                  24 kN/m³

The above value will help to calculate the dead load. Now let us go back to reference value of imposed load of other places than TG area.

 LOCATION                                                                                                VALUE IN T/m2.

Deaerator     and  HP/LP Heater Floor                                                           1.50

Cable Gallery  ( without cable weight)                                                           0.75

MCC and Control Building                                                                            1.00

Roof ( equipment and no equiment)                                                                0.5 - 0.15

Battery room , AHU room , Air Washer Room                                                1.5

Mill ,Bunker bay Ground floor                                                                        2.5

Tripper floor and other floor including Pump house                                        1.5

Roof  ( similar to TG roof)                                                                                0.5-1.5 

Underground ducts, channels , structures , sump ,trenches reservoirs etc  in addition to ground earth pressure and ground water pressure an additional   2T/m2 load has to be added.

For  Boiler and ESP                                                                                          0.5   

For all other areas like , walk way , floor , toilets roof , road culvert etc           0.15 -0.5

( depends upon the nature of use and loading on it. )

* Above imposed loads are indicative it may change sometimes according to the size and type of the power station. For example let us take Ground floor ( lay down area) where we have shown 3.5T/m2

imposed loading but for lesser size plant 2.5T/m2 imposed loading will be sufficient as equipment loading will be less on it.

Equipment loading , piping and other associate loading will be taken over and above the imposed load. The value of this load should be taken from the manufacturer .

Seismic load should be taken from geological survey and varies place to place. 

Wind load also to be taken from IS- 875 ( part-3) and meteorological data.

Temperature load shall be taken as 2/3 of average minimum annual variation . The average

maximum annual variation in temperature for this purpose shall be taken as the difference between the mean of the daily minimum ambient temperature during the coldest month of the year and mean of daily maximum ambient temperature during the hottest month of the year. The structure shall withstand the stress of 50% temp variation. 

 For Crane load on structure frame 25% impact factor ,10% lateral load surge , 5% longitudinal of static wheel load will be considered.

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MAIN CIVIL WORK OF THERMAL POWER PLANT.

E. Switch yard with associated civil foundations.

It has been observed that beside civil and structural work of main plant package there are number of packages (small) in BOPs. Earlier time the equipment supplied by the company ,usually did the civil work associated with it. As a result number of small civil vendors were present at site. These creates number of problems during interface with other package. However now a days big companies or consortium are coming up to resolve the issue. There  may be one company which is handling the project as EPC or some company may supply two or three system. These BOP vendors were mobilised at a later date and found not up to the mark regarding civil work. Generally civil scope is very less for individual package  therefore it does  not attract bigger companies to quote. It is a source of delay for the project. To overcome the difficulties all the civil vendors of BOP should be under the fold of one umbrella . This will help us to reduce the time, cost and can maintain quality. This can only achieve by the insistence of owner to all the bidders quoting for BOPs. Our motto will be to bring competent vendor for the civil work . This will have added advantage also during execution . If there delivery delay in one package in terms of material , drawing and other resources then manpower can be diverte ed to do the job of other package. This will reduce the idle labour problem also to individual equipment supplier. But this type of proposal yet to come in force in our construction field as on date.

It was told earlier that owner will float the civil package tender with all boundary conditions the bidder will carry out all detailed drawing indicating all necessary input and submit to owner/consultant for review and acceptance.

The bidders need to perform following jobs under their scope of work.

"

The work to be performed under this specification consists of design,engineering and providing all labour, materials, consumables, equipment, temporary works, temporary storage sheds, temporary colony for labour and staff, temporary site offices, constructional plants, fuel supply, transportation and all incidental items not shown or specified but reasonably implied or necessary for the completion and proper functioning of the plant, all in strict accordance with the specifications including revisions and amendments thereto as may be required during the execution of work. "

Design Criteria : The design criteria given here will be applicable to all civil and structural work of the plant.

Dead Load : All structural load complete as per IS -875 ( Part- I)

Imposed Load : Imposed loads of different area include live loads , erection ,operation and maintenance loads . Equipment loads which are coming on the floor is not considered. For calculation of Imposed equipment loads are to be added. For reference and Guidance pl. refer IS 875 ( Part -2) Some of the imposed load in critical areas are mentioned below to be considered for design.

SERIAL NO.                                       LOCATION                                       IMPOSED LOAD T/m2

A.                                                   TURBINE BUILDING.:-

                                                       1. Ground Floor  (general)                         2.50

                                                       2. Ground Floor ( unloading )                    5.00

                                                       3. Operating & equipment lay down          3.50

                                                       4. Intermediate floor and other areas         1.50

                                                       5. Grating , roof ,stair ,chequered pl          0.50

Turbine Deck casting inside the Powerhouse area

(to be continued)

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MAIN CIVIL WORK IN A THERMAL POWER PLANT.

We will discuss the main civil work of the power . We will try to provide you the design criteria etc the work and relevant to civil work. But before we should discuss the civil work let us understand the process on which civil work gets performed. We will discuss about the two types of project . One type is public sector owned ( central or state ) and other one is privately owned project. In both the cases owner ( either in house  or through consultant ) made the specification for civil works and eligible vendors quote for the same.

The vendor may be a public sector undertaking or a private one . In both the cases the vendors /associate are big companies with adequate resources . However they again sub let the job to lesser category vendors . It is seen that these vendors also sublet portion of the jobs to petty contractors. They are reduced to only manpower supplier using the resources of the 2nd line vendors and 2nd  line vendors are using the resources of prime vendor to execute the jobs. All these su letting only cause the quality of the job to suffer and also cause numerous administrative problem of managing the site. Government have number rules and regulation for the construction worker and all the inspection agencies descend on owner to check the records as they are principal employer . In all this fair amount of malpractice take place and the same cannot be routed totally from the system. You can understand that all the vendors including the owner have one objective i.e. complete the in time safely. But the priorites of all interested agencies are different and to bring them to one fold is not only 

difficult but some time it is felt that impossible. We are discussing here political influence and strong arm tactice . It is causing the project only harm. It is observed that most of the petty contractors are strong man of that   area so that they can arrange manpower ( specially unskilled and semiskilled). Invariably there will be mistrust between the petty contractor and actual labour working in the field regarding payment.There will be problem in execution because  of  conflict of interest. As a whole quality of work gets  beating . Who so ever control this they can control the project. Civil work still in India is labour intensive jobs . It getting mechanised slowly but badly affected due to resource crunch and absence of skilled manpower.
Project delays start from civil work . Majority of the work force who belongs to the area  within 100kms of the project knew that their wages will be stopped as soon as project work is completed. If there is oppertunities to work somewhere else they will move but majority will not move as money provided to them is not  sufficient to sustained elsewhere. Therefore there will be tendency to prolong the work as long as they can and there conflict of interest starts. There are many other reasons as this sector is called un- organised sector. This problem can only be resolved if the construction worker is having social sequirities during lay off period. The workers belong to prime vendor does not get affected with this condition as they are permanent employee of the company and governed by the permanent rules and regulation. But this ratio is 1:100 .

A  construction man should understand this as early as possible . We should now move towards the technical section . The civil work of a power plant can be divided into a few categories

A. Civil work associated with Main Package like Boiler , Turbine Generator , Power House struc-
ture etc.

B. Civil work related to chimney.

C. Civil work related to ASP , CHP and Ash Pond.

D. Misc civil works associated with BOP ( Balance of Plants) . Beside Boiler and TG all other plants required for a thermal power station is termed as chimney.

(to be continued)

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FIELD & LABORATORY TEST OF SOIL INVESTIGATION FOR THERMAL POWER PLANT

We have attached two photographs only to make aware of the site situation and try to give the picture of scope . First picture shows the amount of structural work ( fabrication and erection ) to be done only for Power House Building. It also shows the stages of civil work i.e pile cap , foundation raft and foundation . Preparation of foundation casting etc. 2nd picture shows that the piles are exposed through excavation now pile head has to be removed and cap to be made as shown in the picture.  

We have discussed about Boreholes to be done in the powerhouse. In fact all the boreholes and specific feild test to be carried out at site will be marked in the GLP ( General Layout Plan) with marked  latitude and longitude. Even the bench mark to be established from GSI bench mark. Other field tests are to be carried is given below. Please note that i have chosen a site where piling is necessary there may be other sites where piling is not necessary but rock cutting is required then specification and requirement will be altered.

S.N0                                           TEST UNIT                                                    

1                                     STAND PIPES                                            METRE 

2                                     PIEZOMETERS                                          NOS 

3                                     TRIAL PITS                                                CUM 

4                                     FIELD PERMEABILITY

a                                       PUMP IN TEST                                        NOS 

b                                       PERCOLATION TEST                            NOS  

c                                       PERMEABILITY IN ROCK                    NOS 

5                                     SCPT                                                         METRE   

6                                     DCPT                                                        METRE             

7                                     PLT                                                            NOS

8                                     CPLT                                                         NOS 

9                                     ERT                                                           NOS 

10                                   SRT                                                           METRE                                

11                                   PMT                                                          NOS 

Above field tests are to be conducted in most of the power station. Quntity will be differed site to site and Size of the station . Beside that lot of laboratory tests are performed on sample collected from field. The details are given below. 

S.N0                                                               TEST                                                     UNIT 

1                                         BULK DENSITY & MOISTURE CONTENT                  NOS 

2                                         SIEVE ANALYSIS                                                           NOS 

3                                         HYDROMETER ANALYSIS                                           NOS 

4                                         LIQUID LIMIT & PLASTIC LIMIT                                  NOS 

    a                                     SHRINKAGE LIMIT                                                         NOS 

    b                                     SPECIFIC GRAVITY                                                       NOS 

    c                                     STANDARD PROCTOR COMPACTION TEST             NOS 

   d                                      MODIFIED PROCTOR DENSITY TESTS                     NOS 

5                                         SWELL PRESSURE                                                        NOS 

6                                         FREE SWELL INDEX                                                     NOS 

7                                         RELATIVE DENSITY                                                     NOS 

8                                         UNCONFINED COMPRESSIVE STRENGTH               NOS 

9                                         DIRECT SHEAR TEST                                                    NOS 

10 TRIAXIAL SHEAR TEST

  a                                       UU TEST                                                                           NOS  

  b                                       CU TEST

  c                                       CD TEST                                                                           NOS  

11                                       ONE DIMENSIONAL CONSOLIDATION TEST           NOS 

12 CHEMICAL ANALYSIS

  a                                       SOIL SAMPLES                                                               NOS

  b                                      WATER SAMPLES                                                          NOS 

ROCK SAMPLES

13                                     MOISTURE CONTENT,POROSITY AND DENSITY     NOS

14                                     SPECIFIC GRAVITY                                                        NOS 

15                                     HARDNESS                                                                       NOS 

16                                     SLAKE DURABILITY                                                       NOS 

17                                     UCC                                                                                    NOS 

18                                     POINT LOAD STRENGTH                                                NOS 

19                                     DEFORMABILITY TEST                                                  NOS    

Above are the laboratory test to be conducted as per requirement . The detail of conducting field test and laboratory test can be acquired from any test book on soil investigation. We will not discuss the same here. However i will try to provide you IS code number to relate the above test for further working knowledge and also what we derive from Geo technical investigation and Topographical Survey will be our objective.

IS 2720                                : Guideline of test for Soils.

IS 1892                                : Suitable mechanical rigs for boring.

IS 2131 & 2131                   : Sampling procedures and SPT ( standard Penetration Test)

IS 4078                                : Specification of core boxes to keep samples ( rocks)

IS 4968 ( part III)                 : Static Cone Penetration Test

IS 4434                                : Apparatus for Vane Shear Test

IS 1892-1979                       : Electrical Resistivity Test ( Appendix B clause 3.2)

IS 2720 (Part -V)                  : Attenberg Test 

IS 2720 (Part-III)                   : Specific Gravity

IS 2720 ( Part-10)                  : Unconfined compressive test

IS 2911 ( Part-III)                   : Free Swelling test.

Above list of IS codes are informative but not exhaustive there may be some other codes which I have missed . I request readers of the blog from India or abroad may do value addition.

( to be continued.)  

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