CONCLUDING PART STEAM BLOWING PART -IV ABC OF THERMAL POWER PLANT

PART -IV

COMPLETION CRITERIA

Stages 1a, 2a, 1c, 3a, 3b, 4a,4b

For the first few blows Target plates need not be kept. Afterwards Target plates made of Stainless steel of mirror finish are to be used.

Target plates are mounted in the temporary exhaust pipes nearer to the permanent line.

Steam blowing can be declared complete only after ensuring cleanliness of target plates. Following criteria is followed for declaring completion of steam blowing:

 Stage 1c & 2b

Minimum 8 (eight) numbers of blows are to be given.

Stages 4c to 4i

Steam blowing is declared complete based on visual observation. Minimum three nos. of blows shall be given for each sub stage.

No of impact >= 1 mm

Less than 4 impacts >= 0.5mm

less than 10 impacts >= 0.2mm

Total impact above 2mm size not exceeding 10 nos at the end of steam blow.

Impacts below 0.2mm size at the end of steam blow can be accepted provided they are well dispersed and uniform in distribution without creating a rough surface.

Minimum number of consequtive target plate is two.

The above criteria has been fixed by BHEL for  660 MW Boiler. However there are difference of opinion regarding completion  criteria. The First difference of opinion arises on metal of target plate. Earlier days we have seen use of bronze target plate and it is malleable material therefore slightest impacts are visible. Therefore steam blowing operation gets continued longer time and disturbance factor calculation was not available with us. For any 200 to 250MW plant steam blowing operation took around 30 to 40 days. After that target plate changed to Mild steel and now stainless steel. As per CEA guidelines it is written as steel. Therefore all personnel carrying out steam blowing should agree with the material.

A Few points to be noted during steam blowing :

1.  Four number Electrical operated trip valves with quick opening and closing are needed to conduct steam blowing.  To standardize the requirements 12”/1500 class for 250 MW and below and 14”/1500 class for 500MW and above are selected. Material of valve body selected is WC9.

2. Special precaution to be taken in cleaning of CRH lines . As it is seen that Reheater tube failures happened due to debris deposited in reheater tubes. Lines are to be checked thoroughly and some time it may happen a small portion of pipe not cleaned during steam blowing operation. Therefore pre cleaning and to maintain a log on that is necessary to avoid complication at later dates.

3. The steam blowing operation produces tremendous noise and certainly does noise pollution to the maximum effect. In earlier days people are not bothered about such pollution but now all are aware therefore steps to be taken to reuce this noise pollution . Earlier days only ear caps were provided but now a days silencer has been designed to reduce the noise.      

 The Steam Blowing Silencers are used to reduce the noise produced by the valve (Structure born noise and Air born noise) , when venting of pressurized and high velocity gas to the atmosphere, especially , steam, air and nitrogen.

4. The low point drain will be getting chocked at the time of initial operation. Therefore the same to be cut and debris to be cleared immediately and again re –weld the same after ensuring that steam flows through the drain.

5. Tools and other materials should be kept ready for cleaning of BFP and CEP strainers. As initially there will be frequent choking of strainer one after another 

with  minimum    time gap. If you are not prepared you can not keep the boiler running.

6. As we will running the boiler through oil firing then Air heater soot blower is must.

7. Drum level should be on manual to take care of swelling during blow off.

Disturbance Factor   =               Qb² x Vb

or

clearing force ratio               Q² MCR x VMCR

Qb                   -           Steam flow during blowing

QMCR            -           Steam flow at MCR

Vb                    -           Sp. Volume of steam during blowing

VMCR              -           Sp. Volume of steam at MCR

                         Qb = 1.13 x A x sq.rt of P/V

                        A = Area of Blow out pipe at the end ( cm2)

                        P= Pressure at blow at blow out piping end.

                        V= steam specific volume at blow out piping end.

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

ELECTRICAL SYSTEM (LT) INSTALLATION , PRE-COMMISSIONING , COMMISSIONING OF DIFFERENT LTMCC -ABC OF THERMAL POWER PLANT PART -III

COMMISSIONING

Carry out functional checks to prove the operation of interlocks/inter-tripping between the 415 Volts incoming and bus coupler breakers in each switchboard & MCC.

Carry out functional checks to prove the operation of interlock and inter tripping between the 11 KV upstream and 415 Volts circuit breaker wherever required.

GENERAL CHECKS:

Inspect any physical damage in the bus bar, insulation, panel doors, power & sliding contacts  etc. And to be rectified if found and make individual unit ready for commissioning.

Making the panel inside dust free & free from foreign materials.

Checking the tightness alignment & clearance of bus bars ,smooth ness in racking in & racking out of modules, proper making of sliding contacts, tightness of input power cables and module power control o/ps & control internal wire connection.

Inspect all contacts , relays and make sure that any blocking used for shipping purpose is removed. This is a must check before commissioning .

Check all doors for proper mounting with respect to the switch handle.

Check door interlock mechanism.

Test the pts,cts & relays involved. Keep the recommended settings for the relays like over-current, under-voltage & overload protections, calibrate the meters (ammeters, voltmeters, power meters & energy meters etc)

Test the insulation of boards with 500 v dc megger & the value should be as per the relevant is specification (more than 5 mega ohms)

Check closing & tripping interlocks , overload release setting of all air circuit breakers in the panel.

Check the protection circuit wiring connections by conducting primary injection current

Check  the input power cable terminations from transformer secondary

Ensure  the phase sequence and ct links are proper before charging the panel.

check closing & tripping mechanism operates smoothly both manually and electrically

Space heaters & thermostat shall be in good and running condition.

Energising checks

Check that communications have been established between 11 KV 

switchgear,415 Volts switchgear and the UCB. Also check the safety 

clearance available before charging.

Ensure that the 11 KV and 415 Volts circuit breakers for charging are in isolated position. Also tie breakers between Emergency switchboard No-1 and bus coupler breaker at unit service switchboard No-1 are OFF and isolated.

Ensure that the 415 volts V.T.s for Section A & B are in position and  fuses  in service.

Ensure that all the outgoing feeder breakers, contactors and Isolators of 415 Volts switchgear are off and isolated.

Ensure that the control circuit fuses for 11 KV and 415 volts circuit breakers for the power transformers and those for the 415 volts buscoupler breaker of switchboard are put on.

Ensure that protection relay settings are correct for feeder VCBs at HT switchgear and incomers at LT switchgear.

ENERGISING PROCEDURE:

Energise the 415 volts switchgear control circuit bus  from its normal source of supply.

Put the 415 volts circuit breaker(Incomer 1) in test      position with selector switch in LOCAL.

Close and open the breaker from local and check that the status indications are correct.

Carry out the tests for the next Incomer and     buscoupler for the same LT Switchgear.

Put the 11 KV breaker for power transformer - A in test position with the selector switch to interlock ‘OUT” position.

Close and open the 11 KV breaker from local and      check status indications are correct.

Put the selector switch to interlock IN and close and open the breaker from UCB and check that status    indications are correct.

Carry out the tests for 11 KV breaker Transformer – B.

Put the 11 KV breaker transformer A in service position with the selector switch to interlock ‘IN’     position.

Close the 11 KV breaker from UCB to first  energise the Power Transformer A.

Open and close the 11 KV breaker

Note the ammeter for the transformer H.V side for any abnormal current. Check the transformer   externally for any abnormality.

If 8.3.13 ( bus coupler breakers )is O.K.,put the 415 Volts breaker (Incomer 1) for Transformer A in SERVICE position with the    selector switch in REMOTE.

Close the 415 Volts Incomer 1 breaker from UCB to first energise the section A of LT switchboard.

Check the ammeter and voltmeter reading and noted in the register.

voltage relays are in picked up(energised) condition. Check phase rotation.

Check externally for any abnormality with the 415    Volts LT switchboard.

Initiate tripping through overcurrent relay on the   11 KV side and check that both the 11 KV and 415 Volts breakers of the power transformer A trip.

Put the 415 Volts bus coupler breaker for LT switchgear in SERVICE      position with the selector switch in ‘REMOTE’  

Close the 11 KV and 415 Volts breakers(Incomer 2)    for power transformer B in “TEST” position

Close the 415 volts bus coupler breaker from UCB to first energise the section B of the LT switchgear

Note the ammeter in incomer-A panel for any abnormal      current. Also note the voltmeter in bus section B   for correct bus voltages.

Check that the under voltage relays in section B are in energised condition.

Check externally for any abnormality with the 415    Volts in bus section B

Switch off the bus coupler breaker

Put the 11 KV breaker   for power transformer B in ‘SERVICE’ position with its selector switch to interlock ‘IN’.

Close the 11 KV breaker for power transformer B from      UCB to first energise the transformer.

Open and reclose the 11 KV  breaker

Note the ammeter on the 11 KV side of the transformer for any abnormal current

Check externally for any abnormality with the transformer.

Put the 415 Volts breaker(Incomer 2) for Transformer B in SERVICE       position with its selector switches in ‘REMOTE’

Close the 415 volts breaker for the transformer to   energise the bus section B

Note the ammeter and voltmeter in bus section B for any abnormal current and voltage.

Check phase rotation of B section and phase in &     phase out between section A & B

If everything with the transformers and the LT switchgear are O.K. keep the transformers and the     415 volts bus energised for 24 hours.

After 24 hours check that there is no abnormality    with the transformers and the 415 Volts LT    switchgear. Also check periodically bucholtz relay      for any chapped gas on in.

For MCCs & Aux. Control panels ,Upstream breakers    and interconnecting cables will come into picture in stead of 11 KV outgoing feeder and power      transformers.

Few  portion of SLD are given to understand the flow of power to different LTMCC.

wish all my readers happy new year 2017.

ELECTRICAL SYSTEM (LT) INSTALLATION , PRE-COMMISSIONING , COMMISSIONING OF DIFFERENT LTMCC -ABC OF THERMAL POWER PLANT PART -II

415 Volts LT switch gear consists of two bus sections A&B with a bus coupler between them. The two sections are fed from two individual power transformers 1A and 1B in case of switchboard & up stream breakers in case of MCCs & ACPs.The Transformers get their supplies from 11 KV unit switchgear feeders TRF1 & TRF2.  415 Volts Unit service switchboard feeds the boilers and turbine auxiliaries,(MCCS) Soot blower MCCs,Battery chargers(220 V ,24 V DC) Emergency switch gear and other unit auxiliaries.The single line diagram of the Unit service switchboard is given below :

LT SWITCHGEARS in typical 500 mw Project:     

I.SWITCHBOARDS

1.  Unit emergency switchboard

2.  Unit Service Switchboard

3.  ESP-1 to 4 LT Main switchboard

4.  Station service switchboard

5.  Ash system compressor switchboard

6.  Ash water Power House switchboard

7.  Off side plant services switchboard

8.  Switch yard Service Switchboard

9.  CHP Switchboard-1

10.    CHP Switchboard-3

11.    CWPH Switchboard

12.    ADM Bldg. Switchboard

13.    Raw Water Pump House Switchboard

14.    Ash Water Re circulation Service switchboard

15.    Sea Water Power House switchboard

16.    Bunker service switchboard

17.    Sweet Water Makeup Power House switchboard

II Motor Control Centres

1.  Turbine MCC

2.  Turbine valves MCC

3.  Coal mill MCC

4.  Boiler MCC

5.  Boiler Valve MCC

6.  Boiler Damper MCC

(

7.  Boiler AC Distribution Board

8.  Track Hopper MCC

9.  PT MCC

10.    DM Plant MCC

11.    CMB MCC

12.    ETP MCC

13.    Hydraulic Generation Plant MCC

14.    Chimney lighting MCC

15.    Emergency Chimney board

16.    ESP Area MCC

17.    ESP A/C & Vent MCC

18.    Ash SILO MCC ()

19.    Air Washer MCC

20.    AC & Vent MCC (

21.    Aux. Boiler MCC

22.Station AC Distribution Board

III.Aux Control Panels:

ESP – 1 to 4 Aux Control Panels 

FOUNDATION OF MCC ROOM WHERE PANEL WILL BE INSTALLED . PANELS ARE BEING SHIFTED FOR ERECTION. TRAYS FOR CABLE IS RUNNING BELOW THE  PANEL.

LOCATION OF MCC ROOM IN THE POWER HOUSE 

PANEL LINED UP FOR ERECTION.

Every 415 V LT  switch gear consists  of a number of equipment and it is proposed that these will be checked individually using standard check lists and test procedures which will be recorded in the testing schedule. Items like transformers (LT and HT side) , Breaker and its circuit, different type of relays and their settings , Bus bars etc. If these equipments are checked individually then commissioning of the particular system will take very less time. All organisation prepared detailed documentation for checking the same . Some of the organisation also outlined about the IMTE required for the testing and also tools are required to do testing work.

STATUS OF THE PLANT.

All panels are erected , aligned and individually tested for any mechanical damage . Also check all the power contractors ( a waring was issued in last despatch.

Testing equipment required.

1. Variable 03 phase 415 v AC supply and also 220 v DC supply.

2. Insulation tester (megger) hand operated / electronically operated 500V

3 Digital multimeter ( 3 and half digit).

4. Analogue multimeter , Ampere meter , voltmeter 

5. Phase sequense meter.

6. Injection test kit for injecting current /voltage to relays for testing cut in and cut out

7. Micro ohm meter 

8. Battery operated continuity tester .

9. Hand tools of standard size and make.

All IMTE must calibrated and certificate should be available with leader .Cross reference to be mentioned in the testing report.

continued to PART -III