boiler superheater

[mzferr]

I'm am a boiler engineer.
I have one boiler currently in commissionig phase.
since beginning I have noticed that superheater bundle installed surface is too much and steam temperature exceed design limit.

Is ther any possibility to carry out a sort of artificial fouling (like as some coatings , special high temperature painting) to reduce heat exchange coefficent ?

Consider that metal temperature of tubes is lower than 550 °C.
Thanks

 

[dougarthur42]

Usually superheater sections are made this way. Mostly this is done so you can get full superheat at all boiler loads. At lower loads(30%) or so the is less heat picked up by the superheaters, hense the need for larger superheaters. And then at high loads it is attemperated down so that final super heat temperture is exactly what is needed. This will also control metal temperature. Thanks Doug

 

[mzferr]

Doug,
you're right.
In my case superheater bank is splitted in two sections: primary and final with intermediate desuperheater to control steam temperature at final superheater outlet.
During design phase i "overdesign" super heater surface to take into account boiler operation at minimum load.

But during commissioning i noticed that steam temperature at primary outlet exceeds design value and consequently the use of desuperheater , which is placed in between, is ineffective.

I should find some ways to get less efficiency in primary heat exchange. This is reason why i'm asking for some method to create artificial fouling on primary.

Thanks
Mzfer

 

[StrykerTECH]

How much of a reduction in heat transfer coefficient is needed? 10% 20%?
What is the material? Stainless? Inconel? Coating it probably isn't the answer if you need a substantial reduction in heat transfer coefficient.

Is there a way you could re-route some of the Superheater so a portion of it is bypassed?

StrykerTECH Engineering Staff

http://www.stryker-tech.com/

 

[mzferr]

Approximately I need a reduction of 20% of heat transfer or alternatively a reduction of effective surface of same amount.
Unfortunately superheater geometry does not allow any kind of mak good (like as tubes removal or flue gas bypass).
Material of tubes is A-213 T11.
Thanks.
MZF