Emerson’s Zach Brooks and Steven Kormann described how compliance with National Fire Protection Association (NFPA) with modern burner management and combustion control hardware systems has been simplified. They explored how recently released (and upcoming) standard changes have forced the evolution of best practices based on modern hardware solutions. The acceptance of SIL-capable instrumentation has become more commonplace, leading the industry to a more reliable burner.
The specific NFPA codes include 85, 86, and 87. NPFA says burner management systems (BMSs) need to include logic systems independent of the control system with hardwired operator-initiated shutdown, diagnostics & fault monitoring and field devices.
General purpose PLCs have been used in BMSs. The processor needs to be separate from the control system. The hardwired shutdown needs to go through MFT relays and not through the logic system. Externally wired watchdog timers have traditionally been used to shut down the PLC if it stopped sending reset commands to the timer. Diagnostics/fault monitoring needs to perform critical I/O checking to make sure the I/O signal has not been lost or frozen.
For NFPA 86 applications, a high-temperature interlock is there to cause a shutdown on high temperature conditions. Putting everything together makes the BMS complex and hard to implement per the NFPA standards.
NFPA 86 or 87 require a logic solver made for burner management or a logic solver rated for SIL 2 applications. The DeltaV SIS logic solver does not require a separate watchdog timer. Critical I/O checking is also built in. For 86, the high temperature interlock can go away with the DeltaV SIS design. Line faults can also be detected in the wiring with the diagnostics built into each DeltaV SIS I/O channel.
With smart commissioning built into the DeltaV system, commissioning time per SIS sensor can be reduced from around 2 hours to 5 minutes. With the latest release of the NFPA 86 2019 edition, the manual shutdown button logic can now be performed in the logic solver instead of a separate relay. The BMS architecture becomes greatly simplified.
Modern hardware simplifies the hardware design, futureproofs the installation, simplifies integration between systems and offers expanded diagnostics.