WELCOME TOPIC- STEAM BLOWINGBy- Operation TeamADANI POWER MAHARASHTRA LTD,TIRODA,5 X 660 MW

INTRODUCTIONPURPOSE :

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 shock2) Removal force of steam3) Cleaning force of steam

REMOVAL FORCE OF STEAM

Blowing Mass Flow ,Q flow= 1.25 * Qmcr (Vmcr /Vblow)

Qmc= mass flow at MCR Vmc= velocity at MCRVblow=blowing velocity

CLEANING FORCE OF STEAM

The necessity to create in the system, the steam velocity greater than that is possible at MCR condition is obvious. These two velocities are expressed as a ratio Cleaning factor or Distribution factor or Cleaning Force Ratio denoted by X or K.

CLEANING FORCE REQUIRED (CFR)OR DISTRIBUTION FACTORa) K=Velocity of steam during blowing / Velocity of steam at MCR

b) K= (Steam flow during blowing)2 *(Sp.vol of steam at blowing (Steam flow at MCR) * ( Sp.vol of steam at MCR)Steam flow can be measured by the net feed water flowCFR & velocities of the steam should be verified to avoid Over BlowingThe recommended value K > 1.25 ( between 1.25 and 1.4)

PRECONDITIONS FOR STEAM LINE BLOWINGChemical cleaning should be completedSH primary and secondary de-superheater piping and RHs emergency de-superheater piping ready for operationAll permanent piping & temporary piping insulated and supports/hangers are released with cold settingSilencer should be connected at temporary pipe exitSoot blowing for APH should be availableMake up for deaerator made readyMotor Driven BFP with all controls made ready

PRECONDITIONS 7) Hydraulic test of the following lines completed:Feed LinesMS, HRH, CRH LinesMS to Aux. PRDS LineAll other auxiliary lines identified for steam blowing 8) Sampling system made ready

PRECONDITIONS 9) Boiler auxiliaries proved serviceable and ready after pilot operation like:Fuel oil systemCompressors & Atomizing steam systemStart-up system ( for continuous system)Coal Mill system (for continuous system)CHP readinessEconomizer hopper and bottom ash hopper and its evacuation system (for continuous system)

PRECONDITIONS 10) All safety valve disc installed after removing hydro-static plug in drum(sub-critical), superheaters and reheaters11) Adequate communication between control room, boiler and TG area ensured. 12) Flow nozzle, control valves and NRV flaps wherever applicable should be not erected before steam blowing and suitable spool pieces are erected. Strainers in the path should be removed.13) Required number of Target Plates and holder made available

CHEMICAL CLEANING PROCESSBOILER FRONT SYSTEM ALKALINE FLUSHINGMass FlushingHot water RinsingAlkaline FlushingHot DM water Rinsing

MAIN BOILER SYSTEM ACID CLEANIGSuper Heater FillingMass FlushingAlkaline FlushingHot DM water RinsingAcid CleaningPassivation

CHEMICAL CLEANING

ACID CLEANING ( BY CITRIC ACID METHOD )will be done by circulation method for effectiveness of the cleaning process.

Acid cleaning will be followed by PASSIVATION, so that the uniform protective coating of GAMMA FERRIC OXIDE is formed on the metal surface and corrosion / oxidation damage to metal surface is prevented and continue during normal operation by dosing oxygen. The gamma ferric Oxide formed by using the chemical 1-2 % sodium Nitrite(NaNO2)

BASIC TECHNIQUE USEDPUFFING METHOD

PURGING METHOD / CONTINEOUS BLOW METHOD

PUFFING METHODTo give a thermal shock to the contour being purged, to dislodge the scale etc.Procedure: Raise the boiler pressure to a pre-determined value (40-60 kg/cm2), shut off firing and at the same time open the quick opening valve(EOTV), thus allowing the steam to escape to atm. with high velocity carrying with it the loose debris.

PRECAUTIONThe Pressure drop allowed in drum is limited to corresponding saturation temp. change of 40 OC.

SCHEMESteam blowing done in stagesStage-1(a)- SH, MSL, ESV, temporary lines from ESV to EOTV, EOTV to CRH line, CRH lines upto boiler end with temporary exhaust pipe. Tap off lines from CRH to deaerator, auxiliary PRDS, HP heater 6a & 6b, gland sealing, etc. shall be remain closed/isolated. stage 1a end point will be concluded by observing the indents on the target plate.

STAGE- 1(a)

STAGE- 1(b)

SH,MSL, HP bypass inter connection, hand operated valve mounted in place of HP bypass valve and CRH lines upto Boiler end with temporary exhaust piping. In this stage 6 to 8 blows will be given through HP bypass lines to ensure cleanliness of the limb. Boiler MS stop valve will be used for stage 1b. EOTV will be kept closed. Manually Operated Isolation Valves in HP bypass lines will be kept opened fully.

STAGE- 1(b)

STAGE-2(a)

1a plus reheater, HRH lines , Interceptor Valve and temporary pipe.

CRH line along with attemperator shall be welded with reheater before start of stage 2a. LP bypass lines shall be blanked during stage 2a. Stage 2a end point will be concluded by observing the indents on target plates

STAGE- 2(a)

STAGE- 2(b)

2a upto IV + LP bypass lines with temporary exhaust pipe.

Stage 2b blowing will be parallel blow in the path 2a & 2b. LP Bypass blanks shall be removed for stage 2b. 4 blows will be given through L.P. Bypass line to ensure cleanliness of the limbs

STAGE- 2(b)

STAGE-3

Auxiliary Steam Lines covered in steam blowing are listed below.

3a) Main steam line to Aux PRDS3b) CRH to Deaerator3c) CRH to HPH-6.All auxiliary steam lines will be steam blown by continuous blowing method

STAGE-4

The following Aux steam lines, connected to deaerator are steam blown using auxiliary steam from Aux PRDS header.

4a)PRDS to Deaerator.

4b)Extraction 4 to Deaerator. 4c) PRDS to Gland steam header.

CONTINEOUS BLOWING METHODThe initial procedure is same as puffing method except:

Continuous firing till the completion of steam blowing. No need to shut of the firing during blowing.

Maintain constant pressure during the blow

Recommended blowing parameters

Dynamic steam pressure= 3.5 MPaMS temp= 420(not to exceed)HRH temp= 480( not to exceed)Steam flow= 845 TPHCorresponding Drum pr.= 40 KscFurnace load 39%

METHODSet the Temporary purging valve, by-pass valve and drain valve and granulating device behind the temporary pipes

Check the tightness, support and expansion of the temporary system

Section by section rinse of condensate water piping, feed water piping and boiler through the start-up system to CW system

METHOD: Circulation begins when Fe+ in the water of main feed water pipe and separator outlet will be less than 100 ppm. - Maintain the circulation flow or start-up flow at minimum set valueStart oil firing and raise the temp and press. according to the cold start-up. Temp. rise rate of water wall = less than 2OC / minTemp. rise rate of main steam = 4 ~ 5 OC / min

METHOD:Before MS press reaches 1.0 Mpa , open the bypass valve of temporary purging valve to warm the piping with all water drain valves of the system open.

-The blowing system divided into two parts Preliminary Steam Blowing

B) Final Steam Blowing

PRELIMINARY CLEANINGPORPOSE-Primary cleaning out sundries and bulky grain deposited in the RH and main steam systemTo ensure fastness of supports and hangers with proper expansionKnow well about the operation property of oil burning system, condensate water and feed water systemsMETHOD

PRELIMINARRY STEAM BLOWINGStart the oil firing with max. rating of 15% Control the gas temperature at furnace outlet below 500 OC (max.538 OC )Raise the SH outlet press to 1.6 1.8 Mpa with steam temperature around 350 OC.Open the temporary purging valve for 15-20 min to blow in MS systemMaintain K around 0.5.SH & RH desuperheater water system also cleaned

FINAL STEAM BLOWINGMain steam and reheated steam system are purged in seriesStart 2-3 coal mills when oil burner hits the rated firing rate of 15%Increase the SH outlet press. to 3.5 Mpa.Maintain the MS temp < 420 OC.Keep HRH steam temp around 480 OC.When the steam line blowing parameter reaches , open the temporary purging valve gradually and increase the fuel and feed water volume to sustain parameter stability.

FINAL .Establish the MS flow around 40% of the MCR (max.- 50%)Ensure CFR (K) should be 1.25 to 1.3 for MS and 1.05 to 1.1 for reheated steamBlow under this operating condition for 20 to 30 minGradually reduce coal firing and close the purge valve at 0.5MPa . Remove the target plate and check itBy estimation, target may satisfy the requirements after 15 to 20 times in-series purging

- When the steam line temp is above the sat. temp of MS press, close all drains and Open the boiler MSSV fully. Maintain the press. through controlled firingInsert a reference targetCheck the CFRAllow to run for 30-60 min

TARGET PLATE Generally Stainless steel panel Target plate set at the first, sixth, ninth, twelfth purging, thereafter set target for each purging until purging results qualified . Width about 8% of the steam vent tubes inner diameter(ID) and length equal to ID Brinell hardness < 90 Steam velocity 258 m/sec Target plates to be introduced just before steam blowing / light upto be removed soon after blowing is completed.

ONLINE TARGET PLATE CHANGE ARRANGEMENTGLAND PACKING ARRANGEMENTGLAND PACKING ARRANGEMENT

DEBRIS FILTER

AUX BOILER TO AUX STEAM HEADER

TDBFP INLETBOILERHPSVHPSVTEMPORARY PURGING VALVEHPBPTDBFP-1 SVCRH LINEMS LINETDBFP-2 SVTEMPORARY LINEPERMANENT LINE

HP,CRH,REHEATER & HRHBOILERHPSV2HPSV1HPBPCRH LINEIPSV1IPSV2HRH LINETEMPORARAY LINEPERMANENT LINE

HP BYPASS TO CRH NRVBOILERHPSV2HPSV1HPBPCRH LINEIPSV1IPSV2HRH LINETEMPORARAY LINEPERMANENT LINE

LP BYPASS VALVE INLETBOILERHPSV2HPSV1HPBPCRH LINEIPSV1IPSV2HRH LINELPBPTEMPORARAY LINEPERMANENT LINE

STEAM BLOWING COMPLETION CRITARIA At least 2 continuous target plates should not have ORIFICE GRANULARITY on the target shall be not larger than 0.8 mm.

CFR should be 1.25 to 1.4

No. of orifice granularity shall not supass 08 nos.

ADVANTAGESRequired less time for completion of the total processLess time required to normalize the system for final light-up to synchronisation

This reduces the reactionary forces on the temporary pipes

Stresses on the boiler system are lower

PUFFING METHODCONTINEOUS METHODMore time required for complete steam blowing due to stage wise blowing(8-10 days)More time required for stage wise temporary pipe erection and shifting of blowing device

No mill required

Quality of cleanliness is better than continuous process

Less time required for completion (3-4 days)

Less time required as only valves to be opened for different systems

Minimum 02 nos. of mill requiredQuality of cleanliness is slightly less than Puffing.

Comparison between Puffing & Contineous Method

Comparison PUFFING METHOD

CONTINEOUS METHODThermal shock is the driving force of cleaningMore thermal stress on tube material and sudden loading on supportsRepeated light-up and shutdown

There is a time gap between the blows to make-up DM waterSystem normalization time after steam blowing is more Silencer use is optional

Steam velocity or Removal force is the driving forceLess thermal stress on tube material

Light-up only once in the beginning of the steam blowingDM water make-up to the system during steam blowing is a challenge System normalization time after steam blowing is less.Silencer use is compulsory.