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.