Guest Post: Atmosphere Furnaces & Temperature Uniformity

Nate Sroka, Mechanical Design Engineer
As a Mechanical Design Engineer, Nate Sroka focuses on the mechanical design of atmosphere heat-treating systems. Before joining Ipsen in 2014, he received his Bachelor of Science in mechanical engineering from Northern Illinois University.

Nate also brings with him a significant amount of knowledge and training on combustion safety, NFPA 86, furnace maintenance and heat treatment evaluations.


Part One: Why Your Burners Matter

The backbone of any atmosphere furnace is the heating system. Part of ensuring part quality and maintaining temperature uniformity, the heating system plays an essential role in keeping the furnace operating at peak performance.

The ATLAS atmosphere furnace, for example, has a robust system that inputs energy, in the form of heat, to elevate the temperature inside the heat zone to a level necessary to process metals. This demands power, efficiency, precision and durability.

To maintain temperature uniformity throughout the heating system, the burners must all be tuned together within a tight temperature range. To satisfy those needs, Ipsen developed the Recon® III Burner, which is coupled with a safe, reliable fuel delivery and burner management system.

However, to keep your system running at optimal performance and ensure consistent temperature uniformity, it is important to understand some key concepts and best practices when it comes to your atmosphere furnace’s burners and heating system. Today’s post will examine how the burner functions, as well as discuss key components of the fuel delivery and air supply that will help you better achieve production and cost efficiency.

Burner Specifications

The Recon III Burners are a single-ended, self-recuperative radiant tube (SERT) style burner. These differ from other burners in that they have more uniform heating down the length of the tube. This is accomplished with a high-velocity flame that pushes the heat further down the tube, and much more uniformly.

These burners also use gas more efficiently, resulting in fewer NOx emissions, and they use any waste heat to heat up the cold air entering the system. As such, they offer up to 50% more energy savings than a burner without heat recovery (which has approximately 25% energy savings), resulting in 75-80% efficiency.

The exhaust gases preheat the incoming combustion air through means of a smooth tube heat exchanger. Fuel and air then come together in a mixing head. An electrode connected to an individual transformer ignites this mixture. This single electrode and a burner control unit also monitor the ionization current.

A high exit velocity from the burner and a set maximum load as a function of the outer tube length provides good thermal uniformity over the outer tube surface. This thermal uniformity transfers over to the heating chamber as a whole.

Fuel Delivery

Natural gas is supplied to the furnace at a single-point location. From there, it is piped to the burners, pilots and enriching gas on the mixing panel. An NFPA 86 compliant valve train monitors and controls the main gas supply.

The gas supply first passes through a strainer to ensure that no large particles can affect downstream components. From there, it is regulated to a lower pressure determined by the manufacturer and passes through a series of safety shutoff valves. The pressure in that line is monitored to be under a set upper limit and above a set lower limit.

The safety shutoff valves consist of a main valve and a blocking valve. A proof-of-closure switch confirms the position of the main valve. Gas is then transported to the manifold and evenly distributed to each individual burner.

You can also adjust the gas at each burner with individual metering controls. These controls are supplied at each burner to ensure the proper air-to-gas ratio of 10:1 is maintained.

Air Supply

A regenerative-type blower located atop the furnace supplies the combustion air. It provides air to the burners, as well as cooling air to the heat fan bearing pack and process air to the mixing panel. Air is pulled from the surrounding environment through a filter and into the blower inlet. There, it is pressurized and directed into the air manifold. A low-pressure switch and a spring-operated overpressure valve monitors the pressure in this manifold. Each individual burner feeds from this manifold and has individual metering devices. Typically, once the air and gas metering valves are set, the burners should continue to function efficiently.

It is crucial to maintain the 10:1 air-to-gas ratio at all times to ensure maximum efficiency. As such, it is important to check the ratio with a combustion analyzer every six months. You should also maintain a clean air filter on the regenerative blower as any blockage can significantly reduce efficiency. How often you need to replace the filter depends on the surrounding environment, but you should check it at least once a month.

Overall, the heating system and burners play an essential role in maintaining part quality and maximizing furnace operation. Understanding how different system components function and interact will help you better identify when something isn’t performing as it should.

Make sure to check back! Our next post on this topic will discuss how to safely and effectively manage the burner control unit.