Combustion Tuning a Parallel Positioning System

-Dan Wallace, PE

Follow these best practices to tune a Natural Gas burner.

1. Check the burner nameplate for the required gas pressure at the manifold at high fire.

2. Check the burner nameplate for the required supply pressure.

3. Light the burner off, and adjust the main gas pressure regulator until the desired supply pressure is obtained. It is important to do this while the burner is running not when the burner is off.

4. After the boiler is warm, store rough curve points going up in firing rate until high fire is reached.

5. Now, begin decreasing the firing rate and store more points on the way down in firing rate while overriding the rough points that were stored on the way up. Why is this important? A curve point is generally most fuel rich on the way down in firing rate so storing points on the way down will ensure an appropriate O2 value is stored that will also allow the burner to have enough air on the way up in firing rate.

6. Make sure no points are stored at “0” position. There are end effects for electronics, etc. So, it’s best to store values at 1.0 degree or higher.

7. Make sure the deadband setpoint in the controller for servos is set above the inherent deadband of the servo manufacturer. Otherwise, there will be nuisance lockouts!

8. Check the flame appearance at each curve points to ensure stability and flame fit in the furnace.

9. Check to make sure the emissions are below the required threshold at each curve point.

10. Lastly, but very importantly, consult the burner and controls manuals for proper setup before engaging in a combustion startup.

11. When a flowmeter is not present, remember that pressure varies by the square of flow so gas flow rate can be approximated by the following formula: Flow Rate = Sqrt(Current Pressure at Manifold / Manifold Pressure at High Fire) * High Fire Flow Rate.

Dan Wallace, PE is the Vice President of Research and Development at Preferred Utilities Manufacturing Corporation in Danbury, CT, and has been with the company for over 10 years.

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