The Industrial Safety and Security Source blog has a post, Firing Up Burner System, which describes the implementation of a burner management system (BMS) at RockTenn‘s recycled paper mill in St. Paul, Minnesota. Their challenge was to replace an old relay panel-based BMS on the plant boilers. The National Fire Protection Agency (NPFA) 85: Boiler and Combustion Systems Hazards Code standard no longer recognized this supervised manually operated system for burner management.
In the post, RockTenn’s Gary Northam described the BMS modernization goals:
…to bring the BMS to NFPA standards, reduce the potential for unnecessary boiler trips, improve operator visibility to burner interlock and permissives, and capture trip event conditions to reduce the diagnostic time needed to restore the boiler to normal operation. In addition, the solution also had to integrate into the existing boiler control system.
Gary and the mill automation team worked with Emerson local business partner, Novaspect, to plan and execute this project. The project required new valve automation for the pilot gas system, main gas line, oil shutoff, and oil and steam valves for each of the burners.
One of the shortcomings of the old relay panel was the lack of clues it provided as to the cause of boiler trips. This increased the troubleshooting time and length of time it took the operations and maintenance staff to get the boiler back online. It was very important for the new BMS to provide:
…very clear indication of interlock status and the ability to capture the first out when a trip occurs to aid in troubleshooting.
The team’s choice was to use the DeltaV SIS process safety system, integrated with the mill’s existing DeltaV control system. The Novaspect engineers designed operator displays for master fuel trip and purge which displayed all the trip conditions. Clear conditions have black lettering, and active trip conditions are highlighted in red. A left-side arrow points to the condition that caused the last trip. Troubleshooting time was reduced to a quick glance of this operator display. Not only could the operators see the source of the trip, but also any remaining trip conditions that would prevent a boiler restart.
A purge process is required to restart the boiler after a trip condition. Gary described what the operators see on this same master fuel trip and purge display:
The right side of the display showed the purge conditions used for startup. Before a boiler can restart you have to purge it out, which requires all the conditions listed to be good; the display clearly tells what has to happen to achieve purge conditions. The display also shows the combustion control side, so the operator can see what the trim air flow is, and what has to occur to achieve a purge air flow.
To simplify the BMS logic, they used DeltaV SIS state transition diagram, step sequencer, and cause and effect matrix function blocks. Gary noted:
There are state transition diagrams and step sequencers for purge, main gas leak test, oil leak test and burner ignition. Cause and effect matrices are in use (in many cases like permissives) for master fuel trip, oil fuel trip and main gas fuel trip. There are trips controlled by analog voters for furnace pressure, low combustion air flow, high and low main gas pressure and high and low igniter gas pressure.
Two boilers were switched over to the new BMS last summer. Gary summed up the project and operator acceptance:
We now have accurate, repeatable startup procedures, and FM Global has reviewed and acknowledged the system. The operators have accepted it wholeheartedly. Perhaps the biggest fan of the new system is the chief operating engineer. The old system required more finesse to restart a boiler or even change burners thus requiring more of his time.
I also saw some notes from Gary’s BMS presentation at the 2010 Emerson Exchange meeting. They also employed techniques to ensure their instrument health like using Rosemount 3051 pressure transmitters for the gas pressure shutdown detection interlocks which allowed them to use AMS pass through to help maintain these critical inputs. They also installed and used line fault detection for the critical inputs for the BMS, which enhanced their diagnostic abilities in DeltaV SIS for these signals. The BMS gave the boiler superintendent the confidence to trust the operators to start up the boilers without intervention.
Give the post a read to see pictures of the displays and Gary’s full account of RockTenn’s BMS modernization project.