6. Chemical cleaning procedure................................................................................................................................. 4 6.1 Start..................................................................................................................................................................... 4 7. Appendix1 Chemical cleaning water quality record............................................................................................ 7 8. Appendix 2 HRSG pressurization curve................................................................................................................. 8 9. Appendix 3 HRSG chemical cleaning technical data record............................................................................. ... 9
1. Purpose HRSG alkali chemical cleaning is injecting NaOH and Na 3PO4 into drums and tubes to clean oiland rust inside drums and tubes, and passivation coat would be formed on inner surface after chemical cleaning.
2. Reference HRSG operation and maintenance manual YL57 SM.2 Chemical cleaning guide for thermal power plant DL/T 794-2001
3. Condition 3.1 Chemical cleaning should be carried out after hydraulic test completed. 3.2 Feed water pipeline and de-superheat water pipeline should be flushed in order to clean impurity and rust. Flow orifice would be installed after feed water pipe and de-superheat water pipe flushed. 3.3 Deminerlized water is available, during chemical cleaning de-mi water pump could be used to feed water to deaerator system. De-mi water common pipe and condensate water common pipe would be connected with temporary pipe on pipe rack. 3.4 Temporary sampling device would be installed at 0m on HRSG drain system.
4.7 Operator should wear protection clothes and glassed during chemical transportation. 4.8 Clean water, towel, absorbent cotton, 0.2% boric acid solution would be prepared at mixing and dosing point.
5. Dosing 5.1 Dosing amount According to HRSG operation manual, dosing amount would be NaOH and Na3PO4.12H2O 3-5 kg/m3 , HP system volume is 33m 3, dosing amount is 135kg; LP system volume is 14m3, dosing amount is 60kg; DA system volume is 28m3, dosing amount is 115kg. Total dosing amount is 310kg. In consideration of leakage and volatilize, certain quantity chemical would be stored at site. 5.2 Dosing method One 6m3 steel tank would be placed beside HRSG, put solid chemical and calculated water into the tank, mix chemical and demi-water, the dosing solution would be put into bottle cleaned by de-mi water and lifted to drums platform. Dosing solution would be pumped into drums from manhole with electrical dosing pump. After dosing manhole should be closed and sealed, feed water to drums and the level should be 50-100mm below normal level.
solution)
Do chemical cleaning for 26 hours continually .(Please mention the time for HP also) Drain 1 minute every 8 hours. (Which drain should be open, IBD, CBD?) After 28 hours cleaning flushing the system and drain. Feed de-mi water into LP system to replace water. Maintain LP system pressure at 0.1-0.4Mpa until HP system cleaning completed. LP system water PH should be maintained more than 9 during this period. 6.4 DA system After dosing DA system would be pressurized to 0.1Mpa. Drain 1 minute after 8 hours. (which Drain?) Drain and flush system after 8 hours, feed de-mi water into DA system to replace dosing water. Maintain DA system pressure at 0.1Mpa until HP system chemical cleaning completed, during this period DA system water PH should be more than 9. Note: Detail chemical cleaning time would be depend on sampling results. 6.5 Caution
every 2 hours. Visual inspection would be carried out to confirm no oil on drum inner surface. Visual inspection would be carried out to confirm no new rust point on drum inner surface. Clean impurity inside drums and take photos for record. NOTE: Please mention the boiler operation, how you would maintain the pressure and temperature. •
Normally Super heater is not used in chemical cleaning but as per your P&ID you are venting the steam through LP and HP super heaters vents
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HP and LP feed water pumps cannot be used during chemical cleaning to avoid dirty water gets in the Impeller.
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If use the HP and LP Feed water Pump, then what about the Motor testing..
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How we make sure proper mixing of chemical in HP and LP drums
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Chemical Injection point is not mentioned in the procedure
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Initial stage and during chemical cleaning how would you maintain Chemical levels.
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Control Philosophy of Drum Levels.
7. Appendix1 Chemical cleaning water quality record
