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Neutralization Of Caustic Soda After Boiler Cleaning


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#1 isbarqi

isbarqi

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Posted 06 October 2014 - 02:18 AM

Hi all,,

What is the best acid to neutralize caustic soda waste from boiler cleaning in term of efficiency, safety handling and cost??

 

1. I consider HCl, but it might need huge amount of HCl to neutralize since industrial grade HCl only available 32% solution.

 

2. 2nd option is H3PO4, with reaction : 3NaOH + H3PO4 = Na3PO4 + H2O. but I wonder if I have enough H3PO4 to complately neutralize NaOH. the reaction result, trisodium phosphate, as far as I know is an alkali salt, which still have alkali pH. Is that correct? does that mean I need more acid?

 

3. H2SO4, cheap and available in 98% concentration. but I worry Na2SO4 salt will precipitate at boiler tube since it have lower solubility in water than other salt. 

 

Please give me some advice.



#2 breizh

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Posted 06 October 2014 - 04:36 AM

Hi ,
To me your query is unclear , is it waste (spent) caustic recovered let say in a pit or somewhere else because you mention deposit on the tubes ? Another issue is the exothermic reaction when you neutralize strong base with acid .

Note : After cleaning with Caustic , you should use good water to flush the equipment and transfer the spent caustic to the pit !

Hope this helps

Breizh

#3 Art Montemayor

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Posted 06 October 2014 - 11:11 AM

Breizh's recommendation is the best that I've used on process equipment.  It is also the cheapest and safest (if employed with scrutiny and safe procedures.

What type of boiler are you referring to?  what was the procedure for applying caustic - and why?

How much caustic was left in the boiler?  The obvious concern is that there may be "dead" spaces where access to the caustic may be difficult.  A thorough, planned rinsing circulation should be applied with water and a careful and accurate monitoring of the caustic (pH) of the circulating, hot water should be done.  How and where you apply the circulation depends on the type and size of boiler.

 

You may even consider firing up the boiler and heating a complete water content while circulating.

I would certainly not apply any mineral acid!  Depending on how much caustic you left behind, you may not need to neutralize.   I would simply hot rinse and test.



#4 isbarqi

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Posted 08 October 2014 - 08:05 AM

Thanks all,
mr Breizh, I see you live at Thailand, me too.

 

I'm a contractor, and i'm gonna perform a boiler cleaning at sugar factory. they have problem because the boiler feed water is contaminate with sugar. so, we gonna perform the alkali cleaning and acid cleaning at the boiler tube. and we need to neutralize all the waste water before entering the pit.






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