cycle number

[djoko]

Hi,
Can we calculate the cycle number of boiler based on conductivity?
If I calculate it based on Silika content, the cylce number of my boiler with P 35 kg/cm2 only 6. SiO2 inlet 0.1 ppm, silica in boiler water 0.6 ppm. the maximum silica permitted in boiler water is 10 ppm. I think that the blow down is too high. but the chemical supplier suggest another calculation methode based on conductivity. If I calculate it based on conductivity, I got 30 for cycle number.

regards

dj

 

[DeltaCascade]

If its a drum type boiler, I would base your calculations on phosphate (using a number of feed water samples over a period of time):

ppm PO4 in boiler water / ppm PO4 in feed water = cycles.

Get the total PO4 concentration in the treatment chemical that you feed, from the treatment chemical supplier (don't try a simple wet-lab PO4 test on the drum (or whatever) of phosphate-polymer treatment product as most of of the PO4 may be in complex polyphosphate form and not detectable, until it degrades to PO4 in the hot boiler).

Silica is tricky because colloidal silica may not show up in your feed water silica test (only reactive SiO2 will, unless you do a more involved total silica test), yet the colloidal silica will break down to reactive silica in the hot boiler. So this may give you erroneously high results (dont understand your numbers, unless you really are at really low cycles). Besides, accuracy may suffer at << 1 ppm silica in feed water sample.

10 ppm silica control range in boiler water suggests operation at high pressure. So watch for phosphate hideout during load swings, but that is another topic.

(Using conductivity, particularly neutralized conductivity (with gallic acid), may have been used in the old days but make-up and feed water qualities are typically better today ... indeed, if you have dealkalized make-up water, most of the boiler water conductivity may be from the treatment chemicals that you feed ... but conductivity can be misleading unless the system is well characterized).

Testing for chloride ion in boiler feed water (not the make-up of course, but the blended deaerated feed water) and in boiler water may also help .. unless you have chloride free or demineralized make-up. Of course, feed water chloride concentration would change as % make-up (% condensate returns) change.

I guess you don't have a steam AND a blowdown meter, which would of course provide another means of calculating cycles (and/or % blowdown).

Of course, as per ASME guidelines, you never want to go higher than 100 cycles (1% blowdown).

Hope this helps. Good luck.

 

[quark]

Hi DC,

Long time no see, seems you are very busy at work. Welcome back.

djoko,

How did you get 6? Shouldn't it be 16(10/0.6)

 

[djoko]

dc,
thanks for your comment.

quark,
i got 6 from silica in boiler water/silica in boiler feed water (0.6/0.1). 10 ppm is the maximum silica permitted in boiler water, not the actual silica in boiler water.

sorry for the long reply,

djoko

 

[DeltaCascade]

Hello Quark. Thank you for the greetings.
Yes, we are fortunate here in Calgary recently in that there is lots of engineering activity

Djoko .. my pleasure. And, oops, above, I meant a number of boiler water samples; the feedwater PO4 content is calculated based on gram PO4 in phosphate-polymer treatment chemical fed per Mg of feedwater... divide that ppm into boiler water ppm PO4 to get cycles.
Yes, 35 Kgf/cm2 = 498 psi (3.4 MPa) ... ASME guidelines say <40 ppm SiO2 for boiler water (eg: as per table in an old edition Betz Handbook for 451-600 psi boiler).
Looks like you've come across a good opportunity for process improvement; improving measurement of a key boiler system operating parameter itself is of high value.
Cheers//