WELCOME ADANI POWER MAHARASHTRA LTD,TIRODA, 5 X 660 MW TOPIC- STEAM BLOWING By- Operation Team
INTRODUCTION PURPOSE : 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
REMOVAL FORCE OF STEAM Blowing Mass Flow , Q flow = √1.25 * Q mcr √(V mcr /V blow ) Q mc = mass flow at MCR V mc = velocity at MCR V blow =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 FACTOR a) 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)² * ( Sp.vol of steam at MCR) Steam flow can be measured by the net feed water flow CFR & velocities of the steam should be verified to avoid “Over Blowing” The recommended value K > 1.25 ( between 1.25 and 1.4)
PRECONDITIONS FOR STEAM LINE BLOWING Chemical cleaning should be completed 1) 2) 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 available 6) Make up for deaerator made ready 7) 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
CHEMICAL CLEANING PROCESS BOILER FRONT SYSTEM ALKALINE FLUSHING Mass Flushing Hot water Rinsing Alkaline Flushing Hot DM water Rinsing MAIN BOILER SYSTEM ACID CLEANIG Super Heater Filling Mass Flushing Alkaline Flushing Hot DM water Rinsing Acid Cleaning Passivation
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(NaNO 2 )
BASIC TECHNIQUE USED PUFFING METHOD 1) 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/cm 2 ), 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.
PRECAUTION The Pressure drop allowed in drum is limited to corresponding saturation temp. change of 40 O C.
SCHEME Steam blowing done in stages Stage-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 PRDS 3b) CRH to Deaerator 3c) 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 METHOD The 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 MPa MS temp = 420(not to exceed) HRH temp = 480( not to exceed) Steam flow = 845 TPH Corresponding Drum pr. = 40 Ksc Furnace load ≈ 39%
METHOD - Set 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 value - Start oil firing and raise the temp and press. according to the cold start-up. Temp. rise rate of water wall = less than 2 O C / min Temp. rise rate of main steam = 4 ~ 5 O C / 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 A) Preliminary Steam Blowing B) Final Steam Blowing
METHOD PRELIMINARY CLEANING PORPOSE- a) Primary cleaning out sundries and bulky grain deposited in the RH and main steam system b) To ensure fastness of supports and hangers with proper expansion c) Know well about the operation property of oil burning system, condensate water and feed water systems
PRELIMINARRY STEAM BLOWING - Start the oil firing with max. rating of 15% - Control the gas temperature at furnace outlet below 500 O C (max.538 O C ) - Raise the SH outlet press to 1.6 – 1.8 Mpa with steam temperature around 350 O C. - Open the temporary purging valve for 15-20 min to blow in MS system - Maintain K around 0.5. - SH & RH desuperheater water system also cleaned
FINAL STEAM BLOWING - Main steam and reheated steam system are purged in series - Start 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 O C. - Keep HRH steam temp around 480 O C. - 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 steam - Blow under this operating condition for 20 to 30 min - Gradually reduce coal firing and close the purge valve at 0.5MPa . - Remove the target plate and check it - By estimation, target may satisfy the requirements after 15 to 20 times in-series purging
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