Air preheater
Air preheater
(OP)
To what temperature must the combustion air be heated in an airpreheater
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RE: Air preheater
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RE: Air preheater
This temperature will set preheated air temperature.
Regards,
Milutin
RE: Air preheater
Rgds,
rokkam
RE: Air preheater
I think you are asking the wrong question and that Milutin has already provided you with the "best" answer. Even if you are firing a difficult to burn fuel, I can't imagine it being necessary to achieve some minimum air temperature in order to sustain the combustion. Is that the question you are asking? There are a variety of factors, such as efficiency, that would suggest certain operating ranges be maintained. But you could likely operate outside those ranges if you acceptt he associated economic penalty. There could even perhaps be environmental constraints that could drive your operations into a constrained range.
HTH,
Doug
RE: Air preheater
So find out your air flow and fuel flow and do the calculations.
One comment; since you have to run with some excess air, the more the burners have to make up for the inadequacies of the APH, the more air they will need to support combustion, all of which will have to be heated with more fuel.
rmw
RE: Air preheater
Assuming what you want to do is maximize the thermal efficiency of the combustion furnace (or steam generator) so as to decrease the furnace fuel consumption, then the combustion air preheater exit temperature should be as high as:
(a) technically possible to achieve and
(b) can be economically justifed.
If you are preheating the combustion air by heat exchange with the furnace flue gas, then you must not lower the flue gas temperature to below the sulfuric acid dewpoint (as pointed out above by milutin) to avoid serious corrosion.
Milton Beychok
(Visit me at www.air-dispersion.com)
.
RE: Air preheater
Just to get a rough idea, the temperature loss (500oF→370oF) equals about 17.5 kcal/kg air.
Assuming you are burning a 10,000 kcal/kg NCV fuel, and are using about 17.1 kg air per kg of fuel, the loss is about 300 kcal/kg fuel.
RE: Air preheater
The maximum possible (technicaly and economically) outlet temp for combustion air is available. Whatever the APH fails to do is now done by the burners. I can now calculate the extra fuel expended.
Rgds,
Rokkam