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Intermittent Blowdown For Boilers

intermittent blowdown boiler steam generator tds silica hardness mud drum steam drum

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#1 Cwsrt

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Posted 04 February 2013 - 10:09 PM

Hi good morning,

 

I had been searching the net regarding the recommended frequency of the intermittent blowdown, however, I've only come upon recommendations that indicate that "shorter, more frequent blows are better than longer, less frequent blows," and proposed blowdown periods of anywhere between 10 seconds and 2 minutes. Some sources only say that a cleaner boiler feed water would require less frequent manual blowdown.

 

I would like to have a more specific and objective indication on how frequent the intermittent blowdown should be.

 

Just a brief history of our water treatment facility, we once used hot lime softener for our boiler feed water wherein we conduct intermittent blowdown once a day. A few years ago, we switched to RO water treatment for a better boiler water quality. However, IBD is still being conducted daily. With the improvement in water quality, I was thinking of the possibility to reduce the frequency of IBD for energy related and economic purposes.

 

Below are our current boiler water quality at our 600 psi boilers:

 

Conductivity:           ~750 uS/cm

pH:                            10.5-11.5

Silica:                        <10 ppm

Hardness at BFW:   <0.5 ppm

 

When conducting IBD, we monitor the level of the boiler steam drum and let it drop by 10%.

 

 

Can you give me your insights regarding this matter?

 

Given the quality of our boiler water, can we reduce the frequency of IBD to around once a week?

 

 

Thank you and best regards,

Cwsrt



#2 breizh

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Posted 04 February 2013 - 11:01 PM

Cwsrt,

 

Talk to the company which is supplying the chemicals for your boiler , it should be part of the technical service offered  to your company .

 

Breizh



#3 thorium90

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Posted 04 February 2013 - 11:28 PM

10% level? I dont know how big your drum is but that sounds like alot... I assume your specs imply you dont use the steam for a steam turbine?

 

From the nalco water handbook,

Attached Files


Edited by thorium90, 04 February 2013 - 11:38 PM.


#4 Cwsrt

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Posted 05 February 2013 - 12:08 AM

Thanks Breizh



#5 Cwsrt

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Posted 05 February 2013 - 12:17 AM

Thanks thorium90.

 

We maintain our steam drum at 50% which is about 10m3. We blowdown around 2m3 when conducting IBD.

 

Also, we use the steam to drive turbo generators. The specs i've given are for boiler water which is already recirculated by around 50-80 times. We do not experience any issues with carry-over on our steam generation system.

 

Is there any other reason why you assumed that we do not use the steam to run a steam turbine?

 

 

Thanks.



#6 thorium90

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Posted 05 February 2013 - 02:20 AM

Its a guess since most places that run steam turbines wont be near 10ppm of silica. pH 10.5-11.5 does seem excessive. Do you employ continuous blowdown too? It might be good to start. continuous is more effective in maintaining continuous water quality


Edited by thorium90, 05 February 2013 - 02:29 AM.


#7 Cwsrt

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Posted 05 February 2013 - 03:34 AM

As I've mentioned earlier, we do not experience any issues on carry-over. I don't think the silica content nor the alkaline pH of 11 affects the throttle steam of the generators.  

 

Yes we also have continuous blowdown. We adjust CBD to correct conductivity of boiler water. Unlike CBD, the conducting of daily IBD is based on the decreasing of steam drum level by 10%.

 

In your opinion, do you think reducing the frequency of IBD to once a week will maintain the quality of the boiler water?

 

 

Thanks.



#8 breizh

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Posted 05 February 2013 - 04:02 AM

http://www.paptac.ca...NewTurbines.pdf

 

You may find some interest reading this document about impurities content in the steam for turbine application .

 

Hope it helps to support your query

Breizh



#9 thorium90

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Posted 05 February 2013 - 04:50 AM

the pH 11 doesnt affect the throttle steam of the generators but its just a waste of chemicals to keep it that high. Most places keep it around 10



#10 kkala

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Posted 05 February 2013 - 06:24 AM

Although not aware of local boiler operation (~40 barg steam, demi water feed), some coming info suggests that it is continuous blow down (CBD) that mainly contributes to make-up water and boiler water quality. Intermittent blow down (IBD) is mainly used for flushing, aiming at removing (suspended or not) solids from rather stagnant areas, not removed  through CBD.  Probably IBD occurs 1-2 times per day here, but this info is too vague.

In this sense you could try to see results "experimentally", by increasing the time between two successive IBDs gradually. E.g. what are the consequences, if IBD occurs every two days? Then proceed according to results.

Note: Composition of boiler water / blowdown in local boilers (feeding also turbines) is not higher than SiO2=10 ppm, suspended solids = 100 ppm, total solids = 2000 ppm, and pH=10.5-11.5, according to their requisition.



#11 Cwsrt

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Posted 07 February 2013 - 08:48 PM

Thank you very much for the helpful and informative suggestions.



#12 abhishek0990

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Posted 08 February 2013 - 08:11 AM

nice information. thank you for sharing it.

 

thanks

packersm



#13 Cwsrt

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Posted 13 February 2013 - 12:33 AM

Just an additional question.

 

Should the limits for the parameters (i.e. conductivity, hardness, etc) of the continuous blowdown samples be different from the limits of the samples taken from the mud drum?

 

We are currently conducting a series of tests for the mud drum boiler water quality and found that the quality from the CBD and IBD are different.

 

Thank you.



#14 thorium90

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Posted 13 February 2013 - 01:16 AM

Well they should be different, normally they are from different points in the steam drum



#15 anuj0990

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Posted 15 April 2014 - 10:36 PM

This is very useful information shared here. I am really thankful for this.

http://www.99th.co.in



#16 sbalikota

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Posted 26 July 2014 - 01:13 AM

Cwsrt:

 

What is the present status of your boiler water?  What system are you following now - or do you have any issue as of this date?






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