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WELCOME
TOPIC- STEAM BLOWINGBy- ANKIT GOYAL
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
PRECONDITIONS FOR STEAM LINE BLOWING1) Chemical cleaning should be completed2) SH primary and secondary de-
superheater piping and RH’s emergency de-superheater piping ready for operation
3) All permanent piping & temporary piping insulated and supports/hangers are released with cold setting
4) Silencer should be connected at temporary pipe exit
5) Soot blowing for APH should be available6) Make up for deaerator made ready7) Motor Driven BFP with all controls made
ready
PRECONDITIONS …7) Hydraulic test of the following lines
completed:Feed Lines MS, HRH, CRH Lines MS to Aux. PRDS Line All 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 system- Compressors & Atomizing steam system- Start-up system ( for continuous system)- Coal Mill system (for continuous system)- CHP readiness- Economizer 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 reheaters
11) 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
BASIC TECHNIQUE USED
1) PUFFING METHOD
2) PURGING METHOD / CONTINEOUS BLOW METHOD
PUFFING METHOD
To 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 atmosphere with high velocity carrying with it the loose debris.
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 1(a) 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.
ONLINE TARGET PLATE CHANGE ARRANGEMENT
GLAND PACKING ARRANGEMENT
GLAND PACKING ARRANGEMENT
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.
ADVANTAGES- Required less time for completion of the total
process- Less 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 METHOD CONTINEOUS METHOD
More 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 required
Quality 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 supports
Repeated light-up and shutdown
There is a time gap between the blows to make-up DM water
System normalization time after steam blowing is more
Silencer use is optional
Steam velocity or Removal force is the driving force
Less thermal stress on tube material
Light-up only once in the beginning of the steam blowing
DM water make-up to the system during steam blowing is a challenge
System normalization time after steam blowing is less.
Silencer use is compulsory.