In this month’s column, John Clarke will expand his discussion beyond combustion safety to include the economic issues that are concerns to all equipment owners and operators.
This column appeared in Heat Treat Today’s 2021 Induction May print edition.
John Clarke is the technical director at Helios Electric Corporation and is writing about combustion related topics throughout 2021 for Heat Treat Today.
Technical Director
Helios Electric Corporation
Source: Helios Electric Corporation
The furnace's or oven’s burner management system (BMS) and its associated components are all that stand between us and an incident. The severity of these incidents ranges from the very expensive — a damaged furnace or oven — to the tragic — loss of a human life. It is a testament to the good work of hundreds of people that combustion system explosions are so rare. That said, the risk to life and property mandates that we revisit this subject frequently, and the risk to profitability dictates we expand our consideration beyond safety to include uptime and quality, as well.
National Fire Protection Association Standard 86 (NFPA 86), or “Standard for Ovens and Furnaces,” provides a standard that is the most common guide to the application of combustion components used in the US. This excellent prescriptive standard reflects the common thinking of people with hundreds of years of combined experience; but it still requires expertise to properly interpret and apply its requirements. It is important to not only understand what component must be provided, but also why.
NFPA 86 is used as a guide for the design of your BMS which includes the various control components to properly monitor the startup and operation of the burner. NFPA 86 also applies to the fuel train, constructed of components that regulate the flow of fuel and air and includes blowers, regulators, valves, filters, and sensors. What BMS and fuel train safety system issues should most concern an end user? An end user must know what it really means when your system is stamped “NFPA 86 Compliant.” To paraphrase Clint Eastwood: The end user needs to know their system’s limitations.
The NFPA 86 standard has been developed to protect life and property, but not production and profits. It is also a prescriptive standard, providing specific guidance to what components need to be applied and in what order. The shortcoming of a prescriptive code is that it must be mostly generic, that is, it applies to types or classes of equipment as opposed to specific applications. Given the variety of burner applications used in industry, it would be impractical to specify every component, order, and wiring for every conceivable process heating application.
Why is this a concern for end users? A specific application may have unforeseen risks or are out of the scope of NFPA 86 . Critical failure modes may be indirectly associated with a burner failure. For example, loss of a process air flow may allow a heat exchanger to overheat before a high temperature limit instrument detects the temperature rise. In this case, the process air flow must be monitored, and the flow or pressure switch monitoring the air flow must be added to the interlock string. This way, the burner will shut off as soon as the air flow failure is detected and not wait for the heat exchanger’s temperature to rise to an unsafe temperature. Another reason to “exceed” the code is that often ovens or furnaces are one element in a much larger manufacturing system. An example would be a continuous paint line, where a failure of the curing oven might shut down an entire facility.
What should an end user do? Ensure the system provided meets the standards and codes, NFPA 86, the Fuel Gas Code (NFPA 54), NEC, etc. This level of compliance is the minimum – and is often not the optimal. Additionally, invite the OEM who built the system to apply their experience and exceed the standards if it provides a more robust system. It may cost a few dollars up front, but it will be pennies when compared to the cost of an incident or, in many cases, an outage.
Encourage your supplier to apply a recognized process to the system review, perhaps a failure mode effects analysis (FMEA) and factor in not only the cost of an incident, but the cost of lost production or quality rejects as well. Consider an independent third-party review – it never hurts to get a second opinion. Review the cost of redundancy, be it online or near online . What is the cost of a second flame rod and flame safeguard when compared to the value of four hours of production?
Next, review the steps to service the system. Look at the mean time to replace (MTTR) a failed component. Has the system been designed to be easily serviced? Are there pipe unions on either side of all critical valves? Where are the spare parts located? What skill trades are required to make the repair? Is post replacement calibration or testing required? And if so, has it been documented?
Ask if the BMS provides a clear indication of the reason for a shutdown. The interlock string, a logical series wiring of critical components where any one component indicating a fault will disable the combustion system, should be monitored in a way where the “first out” or component that will shut down the system, is clearly identified.
Lastly, it is the end user’s responsibility for periodic inspections and equipment maintenance. NFPA 86 prescribes that the BMS and fuel train components are inspected per the manufacturer’s recommendation, but at least once a year.
The annual inspection is a critical step for safe operation but is viewed by many end users as simply a cost. Add to this the relative reliability of most components and we are presented with the ironic risk that maintenance personnel may take short cuts during the periodic inspection. One such person may say, “I always check the low gas pressure switches and they always pass, so I thought, what would it hurt if I skipped the test this year?”
For a more robust inspection, consider adding more value to the process. Combine the safety inspection with an extensive equipment calibration and service: Replace the filters, change the thermocouples, calibrate the control instruments, tune the burner, check the fuel-to-air ratio of the burner, and inspect the BMS components. This adds value to the process and makes it more palatable for the maintenance department.
When the cost of downtime of a key piece of equipment is high, practice the repair, at least on paper. However, if a failed burner shuts down an automotive assembly line, isn’t it worth the time to run actual drills?
In general, most burner trips are the result of a failed sensor, a UV scanner, dirty flame rod, an open thermocouple, or the vibration from an unbalanced fan tripping a pressure switch. In other words, when this type of trip occurs, the greatest cost is lost production, followed by the labor to diagnose the problem and then the cost to replace the component. Generally, the purchase price of the component is far less than the other costs associated with the system trip. Do not be penny wise and pound foolish. Spare parts are a pretty good investment.
If you need the heat from a burner to make your product, it makes sense to not only consider safety, but also plan reduced downtime as well. In the coming articles, we will examine these issues in greater detail, so stay tuned.
References:
[1] https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=86
About the Author:
John Clarke, with over 30 years in the heat processing area, is currently the technical director of Helios Corporation. John’s work includes system efficiency analysis, burner design as well as burner management systems. John was a former president of the Industrial Heating Equipment Association and vice president at Maxon Corporation.
