Safety System Considerations for Process Fired Heaters

The American Fuel & Petrochemical Manufacturers (AFPM) will hold their 2013 annual meeting next week, just down the road from here in San Antonio Texas. This March 17-19 conference assembles key executives, decision-makers, and technical experts from refining businesses, technology providers, contracting and consulting firms, and equipment manufacturers around the world.

Emerson’s Nikki Bishop will be presenting the paper co-authored by Dave Sheppard, “The Bottom Line: What Role Do Fired Heater Safety Systems Play?” at 2:30pm on March 18. Here’s the presentation abstract [hyperlinks added]:

Safety and risk mitigation has always been and will always be an important topic for any operating company. Common in refineries and chemical facilities, process fired heaters present significant safety risks with potentially serious consequences. Accumulated fuel or a leak of combustible process fluid presents the ideal conditions for catastrophic combustion, resulting in the potential for the loss of life. Even minor incidents can result in costly shutdowns for repair. Minimizing the risk of such events means selecting a safety system that inhibits startup when unsafe conditions exist and initiates a safe state when unsafe conditions arise. This sounds simple enough but with so many standards and recommendations out there, it can be a daunting task to determine the safety system that meets both financial and safety targets.

RP 556, issued by API in April 2011, provides guidelines that specifically apply to instrument, control and protective system installations in gas fired heaters in petroleum production, refineries, petrochemical and chemical plants and recommends a Safety Instrumented System (SIS) for protective action. Safety-instrumented systems adhere to the IEC 61511 standard and ensure that these systems are designed, maintained and tested per both the applicable prescriptive standards (API, NFPA, etc.) as well as the latest SIS performance based standards.

This presentation will discuss the benefits of an SIS implementation for protective actions on fired heaters, including the financial returns of a safer heater. The profile of a major chemical company will be used to show the return on investment from a burner management system SIS implementation.

I had the opportunity to get a sneak peak of the paper, so I’ll highlight some points from it. Nikki and Dave open making a point that while minimum safety requirements must be met, that there is an opportunity to also improve operations, energy efficiency, and profitability.

Process fired heaters are used in heating, vaporization, and thermal cracking processes and are common in refining and chemical plants. The have inherent safety risks since fuel is combusted to provide heat energy to the process. The control strategy typically involves maintaining the desired outlet temperature at the desired charge rate, while being as energy efficient as possible through the full range of operation. The safety system’s role is to take the fired heater to a safe state in the event of an unsafe condition or process state.

Typical Process Fired Heater

Typical Process Fired Heater

The authors note the challenges in controlling the fired heater. Fuel must not be allowed to accumulate in the firebox, where an ignition could be catastrophic. Beyond the combustion risks, there are risks on the process side that must be addressed. Overheating/over firing can lead to ruptured tubes, which can threaten lives, destroy equipment, and cause environmental damage. Extended downtime may also result.

The safety instrumented system’s role is to mitigate these risks. Safety instrumented functions continuously monitor for any unsafe conditions around process conditions such as fuel gas pressure and flow, furnace draft pressure, flame detection, process stream flow, combustion air flow, tube skin temperature, stack temperature, percent oxygen and combustibles.

I’ll address other major parts in this paper, including safety system design and selection and estimated savings in startup time reductions in a future post.

If you’ll be in San Antonio next week for the AFPM Annual Meeting, make sure you catch this important presentation on process fired heaters and their associated safety systems.

MP3 | iTunes

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