BURNERS & COMBUSTION SYSTEMS TECHNICAL CONTENT

Heat Treat Tips: Effect of Exhaust Gas Temperature vs. O2 on Efficiency

During the day-to-day operation of heat treat departments, many habits are formed and procedures followed that sometimes are done simply because that’s the way they’ve always been done. One of the great benefits of having a community of heat treaters is to challenge those habits and look at new ways of doing things. Heat Treat Today‘s 101 Heat Treat Tips, tips and tricks that come from some of the industry’s foremost experts, were initially published in the FNA 2018 Special Print Edition, as a way to make the benefits of that community available to as many people as possible. This special edition is available in a digital format here.

Today, we offer one of the tips published under the Combustion category. 


Combustion

Heat Treat Tip 50

Effect of Exhaust Gas Temperature vs. O2 on Efficiency

Tuning a burner properly is important for safety. Tuning can also have a significant effect on efficiency in some but not all cases.

The efficiency of a conventional cold air burner varies significantly with the amount of excess air (related to % O2 in the exhaust products). Since a cold air burner does not use the exhaust gas to preheat the combustion temperature, the exhaust gas temperature is essentially equal to the furnace temperature. For a cold air burner operating at a 1,850°F, reducing excess air from 20% to 10% (reducing O2 from 4% to 2%) will increase efficiency by almost 5%.

Modern high-efficiency burners use the exhaust gas to preheat the combustion air as it enters the burner. Therefore, the temperature of the exhaust gas leaving the burner is significantly lower. The lower the exhaust gas temperature, the smaller the effect of a change in excess air on efficiency. For example, a self-regenerative burner operating at 1,850°F may have an exhaust gas temperature around 480°F. In this case, reducing excess air from 20% to 10% (reducing O2 from 4% to 2%) will only increase efficiency by about 1%.

As a general rule of thumb, reducing exhaust gas temperature by 180°F will increase efficiency by about 5%. So while proper tuning is important for many reasons, it does not have a significant effect on the efficiency of burners with advanced heat recovery systems.

This tip was submitted by WS Thermal.

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Heat Treat Tips: Burner Tuning & Calibration – It’s Not Your BBQ Grill . . .

During the day-to-day operation of heat treat departments, many habits are formed and procedures followed that sometimes are done simply because that’s the way they’ve always been done. One of the great benefits of having a community of heat treaters is to challenge those habits and look at new ways of doing things. Heat Treat Todays 101 Heat Treat Tips, tips and tricks that come from some of the industry’s foremost experts, were initially published in the FNA 2018 Special Print Edition, as a way to make the benefits of that community available to as many people as possible. This special edition is available in a digital format here.

In today’s Technical Tuesday, we continue an intermittent series of posts drawn from the 101 tips. The category for this post is Combustion, and today’s tip is #23.


Combustion

Heat Treat Tip #23

Burner adjustment to nominal gas and air ratios is a typical component of your combustion equipment maintenance. However, this process cannot be minimized in importance as any adjustment can affect operation, efficiency, exhaust emissions & equipment life. Factors to consider and address during any burner adjustment:

  • Burner adjustment should always be done when possible at normal furnace operating temperature under typical production to maintain best conditions for final calibration.
  • Provide clean combustion air: maintain blower filter & consider the source of any plant air.
  • An increase of gas may not increase power to the system due to heat transfer or throughput issues.
  • A decrease in combustion air will not create a hotter flame or add power to the system as this may only create a gas-rich operation resulting in reduced power and CO in the exhaust.
  • Verify gas & combustion supply pressures & consider creating a monthly log of incoming pressures.
  • While a visual inspection of flame can help to verify operation or proper combustion, burner gas /air adjustment can not accurately be performed by simply looking at color or size of a flame.
  • A working understanding of burner system is important to determine and verify values to gas/air and excess O² to a specific application.

This tip was submitted by WS Thermal.


If you have any questions, feel free to contact the expert who submitted the Tip or contact Heat Treat Today directly. If you have a heat treat tip that you’d like to share, please send to the editor, and we’ll put it in the queue for our next Heat Treat Tips issue. 

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Burners 101 for Heat Treating Efficiency and Safety

 

 

Source: Control Engineering

 

Running a heat treat shop is more than just firing up a furnace to treat components; it’s doing so in a way that is both efficient and safe.

Today’s Technical Tuesday is a helpful article from Control Engineering about burners for gas-fired heat treating furnaces, their differences and how they are best utilized in different heat treating applications, technological advances in controls engineering, and combustion safety. The article draws on the skills and knowledge of several in the industry who have contributed to the advances and development in burner manufacturing, operation, and safety.

A couple of excerpts:

“With a careful engineering analysis, it often is possible to obtain more efficiency by optimizing either process or system control. As an added benefit, in many cases, such optimization does not require substantial physical hardware upgrades.” ~ Michael Cochran, marketing engineer, combustion systems at Bloom Engineering Company Inc.

“The goal of both regenerative and recuperative designs is to capture heat energy that would otherwise be wasted.” ~ Control Engineering

 

Read more: “Understanding Burners for Heat Treating Furnaces”

 

 

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Radiant Tubes Longevity Improves Heat Treating: An Analysis

 

Source: heat processing online

 

Photo Credit: heat processing online

Nico Schmitz, Christian Schwotzer, and Herbert Pfeifer with the Department for Industrial Furnaces and Heat Engineering (IOB) in Germany have collaborated on an analysis of metallic recirculating radiant tubes, their purpose in the heat treating process, and their design and installation. In particular, the authors, with access to a furnace-equipped pilot plant operated by IOB, investigate the factors that affect tube productivity and contribute to tube failures. They have reported on these findings in an exclusive paper published at heat processing online, the official publication of the European Committee of Industrial Furnace and Heating Equipment Association (CECOF).

An excerpt:

“It is common to assume a homogeneous temperature distribution for construction calculations. In real operation, inhomogeneous temperature distributions occur. The temperature gradients induce thermal stresses that can substantially influence the lifetime of the tubes. In addition to that, higher furnace temperatures come along with an increasing thermal load.”

 

Read more: “Increasing Lifetime of Metallic Recirculating Radiant Tubes”

Photo credit: heat processing online. Caption: Radiant tube test furnace at IOB

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