STEAM BLOWING STAGES PART-III (BOILER COMMISSIONING) ABC OF THERMAL POWER PLANT

STEAM BLOWING  PART -III

Stage 3a -- Steam inlet line from COLD RE HEAT to TURBINE DRIVEN BOILER FEED PUMP  A ESV. Steam valve of PRDS line will be kept closed. Electro hydraulic control valve will not be erected and steam blowing arrangement (Blanking device) shall be used. This stage shall be concluded by observing the indents on target plates.

Stage 3b -- Steam inlet line from CRH to TDBFP B ESV. Steam valve of PRDS line will be kept closed. Electro hydraulic control valve will not be erected and steam blowing arrangement (Blanking device) shall be used. This stage shall be concluded by observing the indents on target plates.

Operation  during Stage 3a & 3b

Boiler is lighted up and Separator pressure raised to 20 Kg/cm2 and steam lines charged from Boiler outlet up to dummies provided in the temporary piping of stages 2a and 2b. (Alternatively, after restoration of ESV, IV, HPBP, LPBP, 3a & 3b stages blowing can be taken up at a later date prior to commg of TDBFP turbine)

Temporary steam valve or Dummy provided in the Temporary exhaust lines connected to permanent steam lines to TDBFPs is kept open.

CRH-1 & CRH-3 are gradually opened to full. Steam blowing is carried out for 20-30 minutes at about 50% of system operating pressure. Blowing is continued with a gap of two hours between the blows.

After few blows, Target Plates are put and further blowing continued. Termination of stage 3a and 3b are as per Target plate results as given in Section 9.0.

Stage 4 -- Auxiliary Steam Lines

4a – From PRDS to TDBFP A ESV

4b --From PRDS to TDBFP B ESV

4c -- From CRH to Turbine extraction lines

4d -- From CRH to extraction line to Deaerator

4e -- From CRH to Deaerator / FST

4f -- From CRH to HP Heaters

4g -- From CRH to Turbine gland sealing header

4h -- From CRH to PRDS to Aux Steam Header

4i -- From Main Steam line to PRDS to Aux Steam Header

Steam blowing of sub-stages 4h & 4i shall be done prior to blowing of sub-stages 4a & 4b.

Operation Stage 4

Temporary steam valve or Dummy provided in the Temporary exhaust line connected to permanent steam line to BFP Turbine is kept open.

Steam blowing for sub-stages 4a & 4b is carried out for 20-30 minutes. Blowing is continued with a gap of two hours between the blows.

After few blows, Target Plates are put and further blowing continued. Termination of stage 4a and 4b are as per Target plate results as given in Section 9.0.

Minimum three nos. of blows are given for each of sub stag 4c to 4i. Blows are given at intervals of one hour.

continued to part-iv

STEAM BLOWING STAGES PART-II (BOILER COMMISSIONING) ABC OF THERMAL POWER PLANT

STEAM BLOWING -II

Stage 1b --  Super heater, Main Steam Lines up to ESVs, temporary lines from ESVs to EOTVs, temporary loop from EOTV exit temporary line to overload lines and from there to exhaust. Tap off lines from CRH for Deaerator, TDBFPs, PRDS, HP Heaters 6A & 6B, Gland sealing etc., shall remain closed / isolated. Blowing of this stage shall be concluded by observing the indents on the target plates.

Stage 1c -- Superheaters, Main Steam Lines, HP bypass lines and CRH lines upto Reheater inlet and temporary lines upto exhaust. EOTV provided in temporary loop in HPBP lines will be used for steam blowing. 8 (eight) nos. of blows shall be given through HP Bypass lines to ensure cleanliness of the limbs.

Stage 2a -- Superheaters, Main Steam Lines upto ESVs, temporary lines from ESVs to EOTVs, temporary lines from EOTVs to CRH lines, CRH lines, Reheater, HRH Lines to IVs, temporary lines from IVs to exhaust. RH Desuperheater shall be replaced by temporary spool piece before start of stage 2a  blowing. LP bypass lines shall remain blanked. Blowing of this stage shall be concluded by observing the indents on the target plates.

Stage 2b -- Superheaters, Main Steam Lines upto ESVs, temporary lines from ESVs to EOTVs, temporary lines from EOTVs to CRH lines, CRH lines, Reheater, HRH Lines, LP bypass lines with temporary exhaust pipe. RH Desuperheater shall be welded prior to this stage. 8 (eight) nos. of blows shall be given through LP Bypass lines to ensure cleanliness of the limbs.

The Boiler is started in a normal manner following start up procedure.

Stage  1a, 1b, 1c, 2a & 2b

First steam blow for each of stage 1a, 1b, 1c, 2a & 2b is given at a lower pressure (Drum pressure 25 kg / cm2) and the pipe lines including temporary piping are surveyed for proper expansion and supports. Subsequent blows are given at 50 kg / cm2 Drum pressure.

Boiler pressure is raised to 50 kg / cm2.  The steam lines to be steam blown are warmed up prior to blowing. Firing is shut off and at the same time EOTVs are opened. The opening of temporary valve allows steam to escape to atmosphere at high velocity carrying with it loose and dislodged debris. To prevent thermal stresses in the thick walled shell like Separator and headers the saturation temperature change in Separator is limited to maximum 400C. Hence, for the purpose of steam blowing of all critical piping, the valve is opened at 50 kg / cm2 and closed at 25 kg / cm2 Separator pressure.

The water level in the Separator swings beyond visible limits at the start, during and at the end of steam blowing. There are chances of water droplets getting carried over to superheaters. Hence optimum water level is maintained in the Separator.

The furnace exit gas temperature should be limited to 560 deg. C to safeguard superheaters and reheaters.

Boiler water treatment is carried out with liquid ammonia and hydrazine hydrate to maintain pH above 9 in Boiler water and 5 to 25 ppm of N2H4 in feed water.

Hot tightening of flanges, studs / bolts is done wherever such connections have been made.

During steam blowing MS, CRH & HRH line drains are kept open to atmosphere without any valve for achieving free and uninterrupted flow.

While carrying out stage 2a blowing, suitable dummies are put at LPBP outlet temporary line. Similarly, during stage 2b blowing, suitable dummies are put at IVs outlet temporary lines. Drains of suitable size are provided at the upstream of flange local blanks for the purpose of warming up.

CONTINUED PART-III

STEAM BLOWING PART -/I ABC OF THERMAL POWER PLANT

Steam blowing of MS lines, CRH,HRH,SH,RH,HP & LP bypass pipe lines of turbine is carried out in order to remove welding slag, loose foreign materials, iron pieces, rust etc. from the system, generated during manufacturing, transportation & erection.

EFFECT OF BLOWING DEPENDS ON

1)     Thermal shock

2)     Removal force of steam

3)     Cleaning force of steam

In earlier days steam blowing was done in puffing method . Boiler is being pressurized up to 40 kg/cm2 then blowing valve was opened and blowing starts . It gets completed when pressure drops down to 20 kg /cm2. Target plate was kept after some initial blows. Steam blowing operation starts in early morning to late evening. Night is being kept for cooling. In  this operation fire was killed during blowing and lighted up after one cycle of blowing is over. Drum level  has to be watched very minutely during blowing.

Around four year back before my retirement we conducted steam blowing on a 660MW boiler I will describe the same. Steam blowing procedure will be more or less same for an utility boiler. Now a days engineering software is available with the consultant to calculate disturbance factor etc of the blowing.

The Steam Generator is a once through supercritical plus Radiant Reheat Boiler. Major auxiliaries of the Boiler are Pulverisers, Feeders, Fans and miscellaneous valves. Boiler Recirculation Pump is provided to ensure proper circulation of water in the furnace wall circuits during initial subcritical mode operation.

The circuits which are subjected to steam blowing are Superheat sections of Boiler, Main steam lines up to HP Turbine inlet, Cold Reheat lines up to Reheater inlet, Reheater sections, Hot Reheat lines upto IP Turbine inlet, HP and LP bypass sections and all auxiliary steam lines.

Line Sizes

1.  SH Outlet Pipes                            : ID 350 x 60

2.  MSL                                              : ID 460 x 85

3.  CRH                                              : 864 x 29

4.  CRH to Reheater inlet                   : 660 x 23

5.  RH to HRH                                    : 711 x 42

6.  HRH                                               :  864 x 50

7.  HP BP line                                     : 323.9 x 48 / 508 X 27

8.  LP BP line                                            : 711 x 42 

To remove scales, loose material, iron cuttings etc that might have remained entrapped in Super heaters , Reheater & Steam pipings during manufacture, storage and erection. Failure to remove the debris may result in damage to Turbine blades, valves etc.

Steam blowing shall be done in eight stages viz Stage 1a, 1b, 1c, 2a, 2b, 3a, 3b, 4.

Electrically Operated Temporary Valves (EOTVs) shall be located as shown in the scheme. Loop pipes from ESV and IV (if any) to Turbine shall not be steam blown. Hence proper care shall be taken for cleanliness of these pipes before erection.

All critical pipelines covered in stages 1a, 1b, 1c, 2a, 2b shall be steam blown using EOTVs.

Puffing method shall be adopted for carrying out Steam blowing of stages 1a, 1b, 1c, 2a, 2b  in which Boiler Separator pressure shall be raised to 50 Kg/cm2 and released through a quick opening valve and steam blowing done till the Separator pressure drops from 50 Kg/cm2 to 25 Kg/cm2.

Steam blowing for stages 3a, 3b and 4 shall be carried out by continuous blowing method. Steam blowing by continuous method shall be done at 50% of normal operating pressure of the respective system. .Duration of each blow shall be 20 to 30 minutes. The time gap between two blows shall be  1 ½ to 2 hours.

The effects of steam blowing shall be evaluated and steam blowing concluded as per the completion criteria  given .

Stage 1a --  Superheaters, Main Steam Lines upto ESVs, temporary lines from ESVs to EOTVs, temporary lines from EOTVs to CRH lines, CRH lines upto Reheater inlet and temporary lines upto exhaust. Tap off lines from CRH for Deaerator, TDBFPs, PRDS, HP Heaters 6A & 6B, Gland sealing etc., shall remain closed / isolated. Blowing of this stage shall be concluded by observing the indents on the target plates.

CONTINUED PART-ii