Hi all!
Even thouhg this question address a pitch oil burner for a lime kiln, I Think the principles remain similar for other applications as well.
I've started to look into how we control the primary air to our lime kiln burner. See the attached P&ID for information.
For clarification, the primary air is the air delivered directly to the burner, which surrounds the pitch oil lance. The secondary air is drafted into the flame zone, and is not a part of managing the burner operation itself (hence, it will not be considered further here).
The general rule of thumb (from a burner vendor) say between 15 and 20% of the total air supply should come from the primary air, the rest coming from the secondary air.
As I see it, there are two important parameters for the primary air: pressure of the air delivered to the burner, and the amount of air delivered. By looking at the amount of fuel delivered, one can pair the desired amount of primary air stochiometrically to the fuel flow.
The pressure in numbers, however, is not mentioned from the vendor side, even though, they state the importance of "correct pressure". The problem for me is to find this pressure, without any useful vendor input.
For the primary air supply, we have two degrees of freedom (seen in the attachment):
- Adjusting the pressure by controlling the primary air fan speed
- Adjusting the air flow by controlling a valve
Question 1:
Is the arrangement of the degrees of freedom (as in the attachment) correct, or should it be the other way around, i.e., flow control by fan, and pressure control by valve?
Question 2:
How can one find an optimal pressure for the primary air supply?
As I stated earlier, vendor input has been useless, and I'm also struggling in finding scientific articles of interest. Assuming a constant fuel flow.
Question 3:
If trial and error seems to be the only way forward, how should one proceed?
Setting a constant airflow, and adjusting pressure in small steps either up or down?
Or the other way around, i.e., fixed pressure and varying airflow? Assuming a constant fuel flow.
Keep in mind that the main goal of this task is to find the optimal air pressure.
Hope for some enlightning answers!
Best regards,
Andreas
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