acid cleaning ppt
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OBJECTIVE THE OBJECTIVE OF THIS PROCEDURE IS TO CLEAN THE
INTERNAL SURFACE OF STEAM GENERATINGPORTION AND HEATING SURFACE(ECONOMISER)
USING SPECIFIED CHEMICALS.BY CARRYING OUT AN
EFFECTIVE ALKALI BOIL-0UT GREASE AND ANY
OTHER PROTECTIVE COATING APPPLIED ON THEINNER SURFACES OF PRESSURE PARTS ARE
REMOVED.THEN IT IS SUBJECTED TO ACID CLEANING
FOR THE REMOVAL PATCHY MILL SCALE AND
RUST.FINALLY THE ACID PICKLED SURFACE IS
PASSIVATED FOR THE FORMATION OF UNIFORM AND
COHERENT MAGNETITE LAYER
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STATE OF PLANT THE FLAP OF NRV PROVIDED IN
ECONOMIZER FILLING LINE IS REMOVED TOFACILITAE FAST FILING AND DRANING.
ALL THE AUXILLARIES ARE MADE READYAND AVAILABLE FOR BOILER LIGHT UP.THIS
INCLUDES AUXILLARY STEAM,CHEMICALDOZING PUMPS,TANKS CC PUMPS,FANS OILPUMP ETC.
NITROGEN CAPING SYSTEM AT SUITABLELOCATION FOR EASE OF PPERATION.
PROPER NEUTRALIZATIN ARRANGEMENT TONEUTRALIZE EFFLUENT BEFORE DISPOSAL
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FOR ABO ONLY PRIMARY SEPARATOR ARE ERECTEDIN UPPER DRUM AND BAFFLE PLATE IN LOWERDRUM.SECONDARY SEPARATORS AND DRYER NOT
ERECTED IN THE UPPER DRUM AND ORIFICE NOTERECTED IN LOWER DRUM.FOR ACID CLEANINGPRIMARY SEPARATOR IS ALSO REMOVED.
BOILER TUBE COUPONS ARE TO BE PLACED AT TWOENDS INSIDE BOILER UPPER AND LOWER DRUMS TOEFFECTIVENESS OF CLEANING.
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MINIMUM REQUIREMENT
ONE SET ID,FD FAN,ONE SAPH ALONG WITH OIL
CARRY OVER PROBE,SOOT BLOWING SYSTEM,FIRE
DETECTION SYSTEM,ROTOR STOPPAGE ALARMAND
AIR MOTOR,LDO,SCANNER FAN,HP DOSING AND LP
DOSING SYSTEM,ALL BCW PUMP,BAH,COMPLETION
OF ATT FOR URNACE.
PROVISION FOR FREE EXPANSION OF BOILER AND
EXPANSION MARKER.BLOW DOWN SYSTEM.
PERSONAL SAFETY EQUIPMENTS.
PURGE WATER FOR CC PUMP.
READINESS OF TWO ESP PASS IN ALL RESPECT.
EYE WASH BOTTLE AND EYE SHOWER.
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CHEMICAL USEDSL NO ACID
Blr water
Concentr
ation in
%Quantity
required Used forProcess SL NO ACIDBlr water
Concentr
ation in
%
Hydrochl
oric acid
(HCL) 5 % + 1 % 70 tons Acidpickling
& soaking
Hydrochl
oric acid
(HCL) 5 % + 1 %Rodine 0.20 % 800 lts Rodine 0.20 %Ammoniu
m
Bifloride 0.25 % 1000 kgAmmoniu
m
Bifloride 0.25 %
Ammonia
ted Citric
Acid0.2 % 800 kg Ammoniated citric
acid rinseAmmonia
ted Citric
Acid0.2 %
Di/Trisod
ium
phosphat
e
0.1 % &
0.2 % in
the boiler800 &
1500 kgs
Neutraliz
ation
processDi/Trisod
ium
phosphat
e
0.1 % &
0.2 % in
the boiler
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STEPS FOR ABO
Prepare chemical water in chemical
preparation tank of 60 m3 DM water
through boiler fill pump ,add TSP 60 kg ,add
DSP 30 kg ,start heating through steam from
aux PRDS and run chemical pumps onrecirculation till a temp of 50 deg is
achieved.
Check the chemical solution concentrationof 500 ppm of DSP and 1000 ppm of TSP is
achieved.
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Fill the boiler through bottom ring header drain, eco linedrain ,eco inlet header drain, BCW suction lines ,( BCWdischarge valve closed ) by chemical dosing pump till
the minimum level of tank as marked at view glass oftank .
Raise the drum pressure up to 40 ksc in steps of 10kscand take expansion readings,maintain it at 40 ksc , takeboiler expansion reading, hold 40 ksc for 4 hrs.Collectwater samples from CBD sample point for analysis ofalkalinity ,phosphate content ,dissolved silica and oil
content
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Kill the fire in the boiler ,give blow down of 1 minutethrough bottom ring header drain to
IBD(front).Ensure drum level does not go out ofvision in gauge glass.(DWLG at drum)
Raise the drum level through MDBFP, Repeat the
operation of raising the drum pressure to 40 ksc,then hold it for 2 hrs.give blow down through bottomring header drain to water wall drain header, for 1minute after killing fire
Repeat the same procedure and give blow downthrough ECO line drains & ECO inlet header drain
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During this process if phosphateconcentration drops to half of the initial value,
dose additional chemicals through phosphatedosing system to achieve originalconcentration.The boil out is declared complete when the oil
contained in analyzed sample is less than 5PPM or minimum eight blow downs (in samesequence) are completed whichever is latter.
Box up the boiler keeping BCW pumps inservice. Allow the boiler to go under naturalcooling ( ID suction & FD discharge open.).
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Fill the boiler with hot 80 deg DM water throughchemical feeding pump upto lowest port of drum.
Back flush the S/H with DM water containing200ppm hydrazine and PH raised to 10 withammonia till it overflows into drum. Collect thesample from the sampling points of S/H Headerand low point drains for testing.
Drain the boiler through IBD.
Continue the filling & draining for rinsing till thephosphate contain in sample is less than 2 ppm.
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Steps for acid cleaning
MOCK TRIAL:
Mock trial is to be conducted one day in
advance so as to check the healthiness of
various pumps, valves and other connected
system. Boiler filling in 1 hr (approx) and
draining in 1 hr(approx) are to be achieved.
Boiler filling with DM water & lighting up the
boiler to raise the temp. to 80 0c before going
for acid injection.
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Filling of Boiler along with Acid injection(Picking/Soaking)Fill the boiler with 60-70 0C water from the 250
mm temporary header through water walls lowpoint drain hdr. / Eco filling line/ BCW pumpsunction manifold)Once the boiler drum level is at the bottom port
stop filling through BCW suction manifoldContinue filling through other sources.
Fill the boiler up to the drum level is 100 mm
above center line.
Start Boiler Water Circulating (BCW) pumpB
,center pump.
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Take sample at every 10 min interval.Continue this process till the iron content is inequilibrium for 3 consecutive sample .Start draining the boiler under N2 capping to theneutralization PitDM water rinse, after Acid pickling/Soaking is
completed: Refill the boiler with DM water at 60-70 0C.Fill up to 50 % of the gauge glass .Then startback flushing of the SH through the LTSH drain
till the water level is raised in the drum up to 8-9ports. Continue this operation till the sampleresult pH is upto 4.0
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Ammoniated Citric Acid rinse after DM waterrinse: Start injection of citric acid solutionprepared at temporary DM filling pump discharge
through the acid injection pump & regulation valveat the acid pump dischargeAdjust the pH at thefilling point around 3.5-4.0. Collect sample from BCW pump discharge
header after stopping the pump & analyze foracid strength & iron concentration .Continue this operation till 3 consecutivesamples read the acid % & iron content are
steady .This operation shall be minimum 4 hrs &maximum 5 hrs duration .
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Demineralised water rinse: Continue the boilerfilling & draining operation till the sample at pointB is having IRON < 25 ppm
Neutralisation of the boiler system:To removeacid pockets and neutralized acid.
Fill the boiler with TSP AND DSP Solun. Light upthe boiler & raise the pressure to 10 ksc .Hold the pressure for about 6 hrs. After 6 hrs killthe fire .
Allow the boiler to cool naturally .Drain the boiler after metal temperature of < 90 0Cis achievedBoiler is drained with drum vents open to
atmosphere & no N2 capping is used .
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Passivation of Boiler :TO MAKE A LAYER OFMAGNETITE COATING ON PICKLED SURFACEFill the boiler with DM water & inject the preparedblended solution so that the final water having 200ppm of N2H4 & pH of 10 is feed to the boiler .Lightup the boiler at slow rate .
Raise the drum pressure to 40 ksc & hold it for 24hrsAfter 24 hrs shut down the boiler & allow it to cooldown slowly .
Neutralisation of boiler effluentsAs soon as the acid is drained to the neutralizing pitcaustic soda is added to neutralize .As soon as the citric acid is drained to the
neutralizing pit caustic soda is added to neutralize .
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