Increased stack air flow - fuel efficiency?
Over the years our stack flow rate has run at about 80k wet scfm, during this year the flow gradually increased until it became constant at a rate of 100k wet scfm. At the same time, we experienced a loss in production of about 14%. The oxygen level has not increased so I would have to rule out inleakage. Flue gas temperature has remained constant, so I do not believe is an air density problem. Of course there has been an increased specific fuel consumption of ~ 11%. Clinker temperature remained normal, cooler exhaust and tower exit temperatures normal as well. We really can not explain the loss in efficiency but I suspect that the increased air flow is related to it.
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Re: Increased stack air flow - fuel efficiency?
It seems very unlikely that you could have an increase of heat consumption without having one of the exhaust temperatures (preheater top, clinker, clinker exhaust air) increasing as well. False air could mitigate a gas temperature increase, but should show up on the gas analyzer. It seems that you would have to crosscheck all your measurements.
What is the bottleneck that is limiting your production ?
In last resort, establishing a full heat and mass balance of your kiln line should provide a clearer picture. It is unfortunately quite a difficult task as a lot of measurements are needed.