| Abstract |
The Rosemount 3051S pressure transmitter was tested to verify if the Standard Deviation signal (Std-Dev) could be utilized as a means to define an alarm point for Draft Oscillation in fired heaters. This test included peak-to-peak pressure pulses from 0.5 in-w.c. to 2.0 in-w.c., and frequencies from 1 Hz to 10 Hz. The Std-Dev signal provided by the pressure transmitter via HART is converted to 4-20 mA signal. The Std-Dev signal was shown to meet the intent of this application, and not likely to cause nuisance alarm concerns if due diligence is used in selecting the alarm point. The purpose of the firebox pressure alarm is to provide an early alert that the burners are outside of the desired, or historical, operating envelope. If this value becomes a nuisance alarm, then it can be increased by one standard deviation. The recommended action for this alarm is to check the operating parameters, such as the O2, damper position, firebox pressure, fuel gas pressure and fuel gas flow. A proactive response to such an alarm would be to automatically reduce the firing rate - an approach that has been implemented at some locations. If the operating parameters are normal, then a visual check of the burners should be conducted to see if one or more burners are becoming unsteady. The affected burner may need to be cleaned. |
