Flue Gas Recirculation
Flue Gas Recirculation
(OP)
Hi All,
Does anyone here have experience of recirculating flue gas back into the furnace chamber as a means of heat recovery? The concept is that combustion is only required to raise the exhaust temperature back up to furnace temperature set point, the gas will continuously recirculate with only the excess combustion products being vented from the stack to atmosphere.
I'm putting the feelers out to see if this is a well known application. If anyone has any experience to share that would be very helpful.
Cheers,
PR
Does anyone here have experience of recirculating flue gas back into the furnace chamber as a means of heat recovery? The concept is that combustion is only required to raise the exhaust temperature back up to furnace temperature set point, the gas will continuously recirculate with only the excess combustion products being vented from the stack to atmosphere.
I'm putting the feelers out to see if this is a well known application. If anyone has any experience to share that would be very helpful.
Cheers,
PR
The scientist describes what is; the engineer creates what never was.
RE: Flue Gas Recirculation
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Flue Gas Recirculation
It's not a boiler or a steam generator. In an ideal world, yes the system original design should have considered this but unfortunately that was not the case. Now I retrofit to improve.
Regards,
PR
The scientist describes what is; the engineer creates what never was.
RE: Flue Gas Recirculation
I've copied my response below:
On fired boilers, I typically see flue gas recirculation into the inlet of the forced draft fan utilized as a means to lower NOx production in the furnace - you add in the necessary turbulence for mixing the air and fuel without adding in more oxygen than you require for complete combustion. Heating the incoming air is somewhat of a side effect. If you're concerned about the temperature of your combustion air, you'd be better off with a steam coil air heater, or something similar. I've not heard of flue gas recirculating directly into the furnace or windbox - and would not recommend doing so as it would disrupt the uniformity of your air flow and destabilize your flame.
If you utilize flue gas recirculation, you'll need to retune your burner(s) to account for the impact to your air flows and O2.
P.S. Since it isn't a boiler or steam generator, can you give us an idea of what application you're dealing with?
RE: Flue Gas Recirculation
Apologies, I didn't know about the double post faux pas, thought I might reach a different audience there. Deleted now.
Thanks for your response here, interesting and helpful.
The reason we have a problem with high gas consumption is that we are using ambient 'dilution' air to create the velocities needed in the furnace chamber for heat transfer. My concept is to replace the ambient dilution air hot exhaust gas, therefore reducing the heat required to raise the temperature. To be honest, flame stabilisation is my main concern but I plan on taking care of that by feeding the exhaust gas into a mixing chamber downstream of the burner & combustion chamber and upstream of the furnace. There should be sufficient distance between exhaust gas entry and flame to negate the chance of a problem, and anyway we would only be replacing an existing flowrate for a new one albeit at a higher temperature.
I can't/won't give anymore detail on my application and don't think it is appropriate. Purely looking for sound advice based on logic and/or experience.
The scientist describes what is; the engineer creates what never was.
RE: Flue Gas Recirculation
RE: Flue Gas Recirculation
Thanks for your time. My takings from this is that it is a novel application and should be handled with care. We start with an R&D trial only and judge results before proceeding.
Thanks
The scientist describes what is; the engineer creates what never was.
RE: Flue Gas Recirculation
RE: Flue Gas Recirculation
Not perpetual motion, as heat & flow will be added from the burner, just less than at present. And excess flue gas will be bled through the chimney. I'll look into those options.
Mine's is an unconventional application, and as such I don't have the luxury to use typical heat recovery options which is why I'm exploring this. I must say I can't see any firm reason from the comments as to why this won't work.
The scientist describes what is; the engineer creates what never was.
RE: Flue Gas Recirculation
RE: Flue Gas Recirculation
RE: Flue Gas Recirculation
Gas leaves furnace @ 400C>
Gas blown back into mixing chamber upstream of furnace @ 400C
ENERGY ADDED via combustion of SEPARATE fuel and air stream to raise mixed gas to 600C
Gas leaves furnace @ 400C
Repeart
Please tell me how that is silly? It's using the recirculated gas as a medium which is heated in order to achieve velocity required for heat transfer.
Your statement does not make sense, perhaps you have not understood the thermodynamics of the problem. Calling an idea "silly" without offering logic or a well reasoned argument is not productive.
Hi Quark,
I'm looking at air preheaters too but cost is much higher per energy saving as per my calculations. The flue gas will enter a mixing chamber downstream of the burner, this will be designed to prevent flame quenching.
The scientist describes what is; the engineer creates what never was.
RE: Flue Gas Recirculation
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick