NDCT CW SYSTEM CIVIL WORK IN SHORT FOR THERMAL POWER STATION.

Minimum test on concrete should be carried out as per codes and standard practise. However at least these tests are to be carried out.

1 Test for comprehensive strength - one cube per column.

2. Test for comprehensive strength - two cubes per climbing section of the shell.

Some of the cooling water construction is given below.

a) Shell wall centre line in horizontal plane measured radially at mid point on a 3m wide chord : +/- 15 mm.

b) Shell wall centre line in vertical plane measured over a height of 1m : +/- 10 mm

c)  Shell thickness : + 10 mm or- 5 mm

d) Horizontal radius of shell at any section other than shell base : +/- 50 mm.

e) Horizontal radius at shell base : +/- 40 mm

Beside chimney  and  NDCT the major civil work at thermal power is CW system comprising of  CW pump houses , CW ducts and CW channels etc.

- The Sub structures of all the pump houses , forebay etc will have RCC of M-30 concreting.

- Super structure building may have structural steel building .

- Sizing of Pumps , sizing of Forebays etc is to be decided by the model study . The model study will be conducted by reputed Hydraulic Research Institutes.

- Design of substructure  consist of two parts  1. Stability Analysis  2. Structural Analysis.

- Stability analysis is to be done for following load conditions.

Under operation stage :- Maximum load of super structure + equipment load + subs structure + earth pressure + ground water pressure etc.

2. Loads as above + Seismic Load.

3  Under construction stage loading and seismic load.

Following stability conditions to be checked on above load conditions .

a. Check for overturning.

b. Check for sliding.

c. Check for uplift.

Structural Analysis will be done in following areas.

1. Base slabs  2. Intermediate Piers 3.End Piers  4. Back Walls  5. Operating floor slabs .

Analysis will be done in different load conditions 

- CW ducts are made of steel liner and encased it concrete.

- Minimum thickness of the pipes is given below.

For pipes less than or equal to 2200 mm                                                       12mm

For Pipes more than 2200mm but less than or equal to 32oomm                  14mm.

For pipes greater than 3200mm                                                                     16mm.

Maximum velocity in the ducts should not exceed 2.2 M / sec.

These pipes are generally fabricated at site from steel plate and welded. After all pipes are manufactured , laid and welded hydraulic test was carried out  pressure. After successful Hydraulic test the pipes were encased. Special care should be taken during hydraulic test with an eye to venting about the system to avoid damage of the pipes.

Raw water Reservoir shall have net usable capacity of 17,76,000 cu m . Over and above evaporation loss is to be considered. To calculate the sizing of the reservoir  last 500mm depth is taken as dead storage for deposition of slits. Embankments will have side slope of 1(V) : 2 .5 (H).  Minimum top width of embankment will 6 M.

  

    NDCT SHELL

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