Intermittent Blowdown Requirements

Use an on-line bookselling service to find texts on boiler management, perhaps?

The frequency of blowdown is related to the level of total dissolved solids [TDS] in the feed water, the TDS setpoint for blowdown, the volume of water in the boiler and the rate of generation of steam. It is a back-of-the-envelope calculation that gives a near-enough sort of answer.

Boiler feed water needs to be scavenged of oxygen and held at a slightly alkaline pH to ensure boiler longevity.

There’s loads more in the many texts to be found.

Thank you so much.

TDS is usually fudged by using conductivity, which is easily measured in real time.

TDS is usually fudged by using conductivity, which is easily measured in real time.

GA, similarly on a cooling tower the same can be done, water quality can pretty consistent, it can be put on a timer.

any adjustment can be done after periodically inspections with your chemical rep.

So the limit of feedwater solids is perhaps set by the actual boiler manufacturer, tube metallurgy and design, and not set at all by ASME or ABME? Lots of good advice on how to control solids, but not much about the actual target, the original question...

Actually in the power stations where I worked they did not scavenge the O2 but added it to the water to change the chemistry so that the inside of the tubes became coated with ferric oxide as it had been found that the ferric oxide, I believe it was Fe3O4 coated the tubes and reduced the pitting of the tubes at the boiling interface.

These were subcritical water tube boilers. The feed water had been feed through a RO plant and then treated with anionic and cationic resins to remove any unwanted particles before the actual boiler chemistry additions were added.

Boiler blow downs were only conducted when a boiler was brought on line after a repair or shutdown and the blowdown was checked for foreign matter.

<...Lesser TDS [setpoint] means more blow-down quantity...>.

One also needs to look at silica content in the feedwater. A bu&&er to get rid of, silica contributes nothing to conductivity and coats heat exchange surfaces that are subject to evaporation. Although silica is mildly soluble in steam, it tends to remain in the boiler and appear in the sludge during blowdown and washout.

It's all in the many boiler management texts to be found.

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Thank you everyone for your comments.

Supposedly I am a boiler manufacturer and I have the feed water TDS details provided by the proprietor. Boiler water TDS limits are determined based upon the operating pressure of the boiler. So, I can determine Blowdown %.

Let's say my operating pressure is 126.033 kg/cm2 and feed water TDS is 0.55 ppm. So the blowdown % shall be (0.55/(50-0.55))*100 = 1.11. Also, the steam flow rate is 354960 kg/hr. Under these circumstances, how can we decide whether continuous blowdown shall be better or manual blowdown shall be better?

If at all we choose continuous blowdown, is it still essential to periodically go for manual blowdown?

Plz correct me if am wrong anywhere.

You could set a baseline continuous blowdown, provide heat recovery equipment sized for that flow, and then use intermittent blowdown to handle variations in feedwater quality. If the quality is really consistent, you can size your heat recovery equipment to minimize the heat loss & fuel cost for blowdown, and trim the blowdown rate as needed. For large upsets, manual blowdown can be used, and you haven’t invested in heat recovery equipment that will be underutilized. You really need to know the value of your feedwater, and invest according to your financial guidelines, as stated by DHAYANANAHN.S

Okay. Thank you so much sir.