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Boiler Feed Water - Impurities, Treatment, Blowdown And Cycles Of Concentration




Quite sometime back during my tenure in Saudi Arabia, I was involved in a project related to a large-capacity, gas-fired, D-type water tube boiler. The capacity of the boiler was 530,000 lb/h (240 TPH).

During that time I had been studying about the requirement and design calculations for boiler feed water (BFW) for the boiler since it was part of the overall design engineering. For my understanding and clarity I had prepared an excel workbook related to BFW wherein the various natural sources for make-up water, the impurities that need to be addressed for enabling it to be fed to the boiler, the treatments that were required to remove or reduce the impurities, the concept of water blowdown from the boiler and the definition and calculations related to cycles of concentration (CC) were addressed.

An organization called "American Boiler Manufacturer's Association" (ABMA) as well as ASME provides guidelines for the quality of BFW as a function of the steam drum pressure and readers can refer the links provided below for that as well as some some guidelines on water treatment. Refer he link below for ASME guidelines for water-tube boilers:

http://www.cip.ukcentre.com/steam.htm

ABMA provides the following guidelines for BFW quality:

http://www.banksengi...om/blrwater.htm

http://vganapathy.tr...om/dasteam.html

Today, I did some polishing work on the excel workbook and it is now ready to be shared with the readers and members of "Cheresources". Hope you will enjoy this workbook and I am looking forward to your comments on the same.

Reagrds,
Ankur.

The MS Excel spreadsheet can be downloaded here:

Boiler Feed Water Design Notes






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Chris Haslego
Oct 11 2011 03:46 PM
Excellent information that will be useful to many, many folks out there!
Wonderful!

This is simply just the tool I needed!

Thank you so much Ankur.
Great, one stop info for bfw system.
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S.Chittibabu
Oct 11 2011 11:04 PM
It is mentioned that TOC (Total Organic carbon) in HP boilers shoud not go beyond 0.5 ppm. I understand that TOC at higher temp disintegrate in to CO2 and the alkalinity present in the boiler is sufficient to convert into
Sodium compound which can be checked by proper blowdown. Is there any other serious issue if the TOC residual exceed this limit?
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adilameen90
Oct 20 2011 03:34 AM
THAAAAAAANKS
Very useful information package
Dear Ankur,

I have just realized that the ratio (C_BFW / C_BD) is fixed and equal to 0.02 in your spreadsheet.

Could you please automate this calculation so that we can use the spreadsheet in other cases than your example?

Thanks in advance.
Sheiko,

I have automated the spreadsheet for it to be used for other cases. I am sending it to you on your messenger.

Regards,
Ankur.
Dear Ankur,

Can you please let me know the exact location in ASME where I can find the BFW properties used for Boilers. Is there anything specific for the Once though HRSGs.

Regards,
Shaji
Shaji,

BFW chemistry as recommended by the "American Boiler Manufacturer's Association" (ABMA) can be found at the link provided below. Please note that these are for standard boilers with steam drums which are used in most steam generation applications for power boilers and process heating boilers.

http://www.engineeri...its-d_1064.html

Unfortunately there are no standards such as ASME or ABMA for "Once Through Steam Generators" (OTSG) except stating that the feedwater quality need not be as stringent as that for conventional boilers with steam drums. OTSG design is still vendor driven and the feedwater chemistry (quality) is defined by the manufacturer / vendor of the OTSG.

Hope this helps.

Regards,
Ankur.
Ankur,

Thanks for the reply.
I was going through a site
http://www.cip.ukcentre.com/steam.htm
and found that it refers to ASME for water properties, and was wondering which specific code will give me the details of the table mentioned as we cannot give reference to Internet sites.
Is the reference given in this link wrong?

Regards,
Shaji
shaji,

That is a very good site you have referred to. However, the site mentions it as just ASME guidelines for Table 12.1 without mentioning which ASME document has these guidelines. Probably some further search woul be able to provide the ASME publication which mentions the BFW quality guidelines.

Regards,
Ankur.
Ankur,

I could not find the ASME document which gives these guidelines, so was wondering if you will have an answer for the same.

Regards,
Shaji

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