Reduction of CO level in flue gas

[ProcessJim]

I have been asked to investigate meands of reducing the CO level in flue gas from our rotary furnace. The options we are looking into are:

Provision of a controlled excess of O2 to the burner nozzle (Simplest option but concerns over product quality)
Installation of afterburner in exhaust chamber, and, the prefered option currently owing to cost and simplicity, that is, injection of pure O2 into the furnace exhuast gas stream.

I believe I have done necessary theoretical calcs to establish O2 qty required and heat evolved but I have no practical experience of this kind of system. I understand that ensuring that there is sufficient temperature in exhaust gas for reaction to occur is important.

Can anyone advise on potential pitfalls of such a system or matters to be taken into consideration?

Many thanks,
James

 

[ash9144]

The best means for CO control is as you state to control your excess O2 and ensure you have good combustion control.

Adding pure O2 may effect CO levels but could have impact on other combustion products as well, such as NOx.

 

[ProcessJim]

Thanks for that, hadn't considered NOx. Not sure that NOx would be a problem in this case as we are way off our limits for NOx at the moment and the burner runs pure O2 so not much present immediately downstream of furnace. The only air ingress happens on charging furnace when the door is open.

My suspicion is that the exhaust gas temp will not be high enough at all times, particularly when charging furnace, to ensure reaction. Would this present hazards in the form of oxygen enrichment in bag houses etc? my feeling is that the volumes of air getting dragged through system will dilute to safe level, current O2 in stack around 17%.

What safety precautions would need to be taken before running a crude trial? I am currently attempting to measure temperature in immediate vicinity of furnace exhaust to gain some idea of conditions.

 

[AggieCHEN04]

I believe there are oxidation catalysts out there for converting CO into CO2 in flue gas, similar to the catalytic converter on your car. Probably pretty expensive though.

 

[rmw]

Is the furnace air FD or ID? If ID, check your seals. If you are leaking a lot of air through the seals, you are getting less through your burner where you are creating the CO.

rmw

 

[ProcessJim]

The burner runs on pure O2, we have no reason to suspect that the control system for the burner ratio is not controlling properly.

The furnace is used for reduction of metal oxides which is where a significant proportion of the CO is coming from. It is possible to control the CO level by running with the required excess of O2 at the burner but the afterburner method would be prefered due to concerns over product quality resulting from an oxidising atmosphere in the furnace.

I know that we could install an actual burner in exhaust chamber to ensure that CO is oxidised but we are looking into the possibility of adding O2 with no burner due to cost, plus it would be relatively simple to provide an extra O2 line from the existing burner skid.