The search for sustainable solutions in the heat treat industry is at the forefront of research for industry experts. Michael Stowe, PE, senior energy engineer at Advanced Energy, one such expert, offers some fuel for thought on the subject of how heat treaters should prioritize the reduction of their carbon emissions by following the principles of reuse, refuel, and redesign.
This Sustainability Insights article was first published in Heat Treat Today’sJanuary/February 2024 Air & Atmosphereprint edition.
Reduce
Michael Stowe PE, Senior Energy Engineer Advanced Energy
We explored why the question above has come to the forefront for industrial organizations in Part 1, released in Heat Treat Today’s December 2023 print edition. Now, let’s look at the four approaches to managing carbon in order of priority.
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The best way to manage your carbon footprint is to manage your energy consumption. Therefore, the first and best step for reducing your carbon footprint is to reduce the amount of energy you are consuming. Energy management tools like energy treasure hunts, energy assessments, implementation of energy improvement projects, the DOE 50001 Ready energy management tool, or gaining third party certification in ISO 50001 can all lead to significant reduction in energy consumption year over year. Lower energy use means a smaller carbon footprint.
Additionally, ensuring proper maintenance of combustion systems will also contribute to improved operational efficiency and energy savings. Tuning burners, changing filters, monitoring stack exhaust, controlling excess oxygen in combustion air, lubricating fans and motors, and other maintenance items can help to ensure that you are operating your combustion-based heat treating processes as efficiently as possible.
Reuse
Much of the heat of the combustion processes for heat treating goes right up the stack and heats up the surrounding neighborhood. Take just a minute and take the temperature of your exhaust stack gases. Chances are this will be around 1200–1500°F. Based on this, is there any effective way to reuse this wasted heat for other processes in your facility? One of the best things to do with waste heat is to preheat the combustion air feeding the heat treating process. Depending on your site processes, there are many possibilities for reusing waste heat, including:
Space heating
Part preheating
Hot water heating
Boiler feed water preheating
Combustion air preheating
Refuel
Once you have squeezed all you can from reducing your process energy consumption and reusing waste heat, you may now want to consider the possibility of switching the fuel source for the heat treating process. If you currently have a combustion process for a heat treat oven or furnace, is it practical or even possible to convert to electricity as the heating energy source? Electricity is NOT carbon free because the local utility must generate the electricity, but it typically does have lower carbon emissions than your existing direct combustion processes on site. Switching heating energy sources is a complex process, and you must ensure that you maintain your process parameters and product quality. Typically, some testing will be required to ensure the new electrical process will maintain the metallurgical properties and the quality standards that your customer’s specific cations demand. Also, you will need a capital investment in new equipment to make this switch. Still, this method does have significant potential for reducing carbon emissions, and you should consider this where applicable and appropriate.
Redesign
Finally, when the time is right, you can consider starting with a blank sheet of paper and completely redesigning your heat treating system to be carbon neutral. This, of course, will mean a significant process change and capital investment. This would be applicable if you are adding a brand-new process line or setting up a new manufacturing plant at a greenfield site.
In summary, heat treating requires significant energy, much of which is fueled with carbon-based fossil fuels and associated-support electrical consumption. Both combustion and electricity consumption contribute to an organization’s carbon footprint. One of the best ways to help manage your carbon footprint is to consider and manage your energy consumption.
For more information: Connect with IHEA Sustainability & Decarbonization Initiatives www.ihea.org/page/Sustainability Article provided by IHEA Sustainability
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On site at heat treat operations, gas-fired furnaces can be a significant source of carbon emissions. But depending on the desired heat treatment, an alternative approach that combines induction through heating and intensive quenching could be the “green ticket.” Learn about the ITH + IQ technique and discover how certain steels may benefit from this approach.
This Technical Tuesday article was composed by Edward Rylicki, Vice President Technology, and Chris Pedder, Technical Manager Heat Treat Products and Services, at Ajax TOCCO Magnethermic Corp., and Michael Aronov, CEO, IQ Technologies, Inc.It appears in Heat Treat Today's May 2023 Sustainable Heat Treat Technologiesprint edition.
Introduction
Chris Pedder, Technical Manager Heat Treat Products and Services, Ajax TOCCO Magnethermic Corp. Source: Ajax TOCCO Magnethermic Corp.
Induction heating is a green, environmentally friendly technology providing energy savings and much greater heating rates compared to other furnace heating methods. Other advantages of induction heating include improved automation and control, reduced floor space, and cleaner working conditions. Induction heating is widely used in the forging industry for heating billets prior to plastic deformation. Induction heating is also used for different heat treatment operations such as surface and through hardening, tempering, stress relieving, normalizing, and annealing. However, the amount of steel products subjected to induction heating in the heat treating industry is much less compared to that processed in gas-fired furnaces.
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Gas-fired heat treating equipment is a major source of carbon emissions in the industry. As shown in Reference 1, induction through heating (ITH) followed by intensive quenching (IQ) (an “ITH + IQ” technique) eliminates, in many cases, the need for a gas-fired furnace when conducting through hardening and carburizing processes — the two most widely used heat treating operations for certain steel parts. Eliminating gas-fired furnaces will result in significant reduction of carbon emissions at on-site heat treat operations.
Dr. Michael Aronov, CEO, IQ Technologies, Inc. Source: Ajax TOCCO Magnethermic Corp.
The goal of this article is twofold: 1) to evaluate carbon emissions generated during through hardening of steel parts and carburizing processes when conducted in gas-fired furnaces, and 2) to discuss how these emissions can be reduced to zero using the ITH + IQ process.
Evaluation of Carbon Emissions for Through Hardening and Carburizing Processes
Ed Rylicki, Vice President Technology, Ajax TOCCO Detroit Development & Support Center Source: Ajax TOCCO Magnethermic Corp.
Most through hardening and carburizing operations for steel parts are conducted in batch and continuous integral quench gas-fired furnaces. Assumptions made for evaluating CO2 emissions produced by a typical integral quench furnace are presented in Table 1. Note: The values of carbon emissions presented Table 1 are conservative since they don’t consider the amount of CO2 produced by furnace flame screens and endothermic gas generators used to provide a controlled carburizing atmosphere in the furnace. Also, it’s assumed that the furnace walls are already heated through when loading the parts, so there are no heat losses associated with the thermal energy accumulated by the furnace walls.
Table 1. Assumptions for calculating of carbon emissions by integral quench furnace Source: Ajax TOCCO Magnethermic Corp.
Emissions Generated During the Through Hardening Process
A furnace time/temperature diagram for the through hardening process considered is presented in Figure 1. Carbon emissions Ehard produced by the furnace considered during heating of the load to the austenitizing temperature prior to quenching are calculated by using the following equation,
(Equation 1) Ehard = k • Qhard
where:
■ k = the emission coefficient (equal to 0.050 • 10-3 kg per 1 kJ of released energy when burning natural gas (see Reference 2) ■ Qhard = thermal energy required for heating up the above load from ambient to the austenitizing temperature
A value of Qhard is calculated by the equation below,
■ M = load weight, kg ■ C = steel specific heat capacity (kJ/kg°C) ■ Ta = part austenitizing temperature (°C) ■ To = part initial temperature (°C) ■ Eff = furnace thermal efficiency (a ratio of the furnace thermal losses to the gross heat input)
From equations (1) and (2), the amount of carbon emissions produced by the above furnace during one hardening operation is 40.2 kg. To determine an annual amount of carbon emissions, calculate the number of hardening cycles per year (Nhard) run in the furnace. From Figure 1, a duration of one hardening cycle is 4 hours (3 hours for austenitizing of the parts plus 1 hour for quenching the parts in oil and unloading/loading the furnace). Thus, Nhard is equal to:
Nhard = 360 day • 24 hour • 0.85 / 4 hour = 1826
Figure 1 Source: Ajax TOCCO Magnethermic Corp.
Annual CO2 emissions from one integral quench batch gas-fired furnace are 40.2 • 1836 = 73,807 kg, or more than 73 t
Emissions Generated During Carburizing Process
A simplified furnace time/temperature diagram for the carburizing process considered is presented in Figure 2. Carbon emissions (Ecarb) produced by the above furnace during the carburizing process are calculated by the following equation,
(Equation 3)
Ecarb = k • Qcarb
where:
■ Qcarb = a thermal energy expended by the furnace during the carburizing process. A value of Qcarb amounts to two components:
(Equation 4)
Qcarb = Qcarb1 + Qcarb2
Qcarb in the following equation is:
■ Qcarb1 = energy required for heating up the load to the carburizing temperature
■ Qcarb2 = energy needed for maintaining the furnace temperature during the remaining duration of the carburization process (for compensation of the furnace thermal losses since the parts are already heated up to the carburizing temperature)
A value of Qcarb1 is calculated using equation (2) where the part carburizing temperature Tc is used instead of part austenitizing temperature Ta (see Table 1):
A value of Qcarb2 is a sum of the flue gas losses and losses of the thermal energy through the furnace walls by heat conduction. Qcarb2 is evaluated from the following considerations. Since the assumed furnace thermal efficiency is 65%, the furnace heat losses are equal to 35% of the gross heat input to the furnace. Hence, the furnace heat losses Qloss1 during the load heat up period (the first 3 hours of the carburizing cycle, see Figure 2) are the following:
Thus, the total amount of the thermal energy expended by the furnace during the carburizing cycle is Qcarb = 0.887 • 106 + 0.827 • 106 = 1.71 • 106 kJ. The total amount of the CO2 emissions from carburizing of the load in the furnace considered according to equation (3) is: Ecarb = 0.050 • 10-3 • 1.71 • 106 = 85.7 kg. To determine an annual amount of carbon emissions from one carburizing furnace, calculate the number of carburizing cycles run in the furnace per year. Per Figure 2, a duration of one carburizing cycle is 12 hour (1 hour for the furnace recovery plus 10 hour for carburizing of parts at 927°C plus 1 hour for quenching parts in oil and for unloading and loading the furnace). Thus, the number of carburizing cycles per year Ncarb is:
Ncarb = 360 day • 24 hr • 0.85 / 12 hr = 612
Figure 2 Source: Ajax TOCCO Magnethermic Corp.
Annual CO2 emissions from one integral quench batch carburizing furnace is about 85.7 • 612 = 52,448 kg, or more than 52 t.
Reducing Carbon Emissions Using the ITH + IQ Process
Reference 1 presents results of two case studies of the ITH + IQ process on automotive input shafts and drive pinions. The study was conducted with a major U.S. automotive part supplier. A two-step heat treating process was used for the input shafts, consisting of batch quenching parts in oil or polymer using an integral quench gas-fired furnace for core hardening followed by induction hardening. This two-step method of heat treatment is widely used in the industry for many steel products. It provides parts with a hard case and tough, ductile core.
Substituting the “ITH + IQ” method for the two-step heat treating process not only eliminates the batch hardening process, but also requires less alloy steel for the shafts that don’t require annealing after forging. Thus, in this case, applying the ITH + IQ technique eliminates two furnace heating processes for the input shafts, resulting in the reduction of the CO2 emissions to zero for the shafts’ heat treatment. Per client evaluation, as mentioned in Reference 1, the hardness profile in the intensively quenched input shafts was similar to that of the standard shafts. Residual surface compressive stresses in the intensively quenched shafts were greater in most cases compared to that of the standard input shafts, resulting in a longer part fatigue life of up to 300%.
Per Reference 1, the environmentally unfriendly carburizing process can be fully eliminated in most cases for automotive pinions when applying the ITH + IQ method and using limited hardenability (LH) steels that have a very low amount of alloy elements. A case study conducted for drive pinions with one of the major U.S. automotive parts suppliers demonstrates the intensively quenched drive pinions met all client’s metallurgical specifications and passed both the ultimate strength test and the fatigue test. It was shown that the part’s fatigue resistance improved by about 150% compared to that of standard carburized and quenched in oil drive pinions. In addition, distortion of the intensively quenched drive pinions is so low that no part straitening operations were required.
Conclusion
Coupling Ajax TOCCO’s induction through heating method with the intensive quenching process creates a significant reduction of CO2 emissions produced during heat treatment operations for steel parts. For the through hardening process, eliminating just one batch integral quench gas-fi red furnace will reduce carbon emissions by more than 73 ton per year. For the carburizing process, eliminating just one batch carburizing furnace will reduce carbon emissions by more than 52 ton per year. Note that for continuous gas-fired furnaces, the carbon emission reduction will be much greater due to higher continuous furnaces production rates (hence a much higher fuel consumption).
Per our experience, the ITH + IQ process can be applied to at least 20% of the currently through-hardened and carburized steel parts. Per two major heat treating furnace manufacturers in the U.S., there are thousands of atmosphere integral quench batch and continuous furnaces in operation in the U.S. That means hundreds of gas-fired heat treating furnaces can be potentially eliminated, drastically reducing carbon emissions in the U.S., supporting a lean and green economy.
Ed Rylicki has been in the induction heating industry for over 50 years. He is currently Vice President Technology at Ajax TOCCO Detroit Development & Support Center in Madison Heights, Michigan.
Mr. Chris Pedder has over 34 years of experience at Ajax Tocco Magnethermic involving the development of induction processes in the heat treating industry from tooling concept and process development to production implementation.
Dr. Michael Aronov has over 50 years’ experience in design and development of heating and cooling equipment and processes for heat treating applications. He is CEO of IQ Technologies, Inc. and a consultant to the parent company Ajax TOCCO Magnethermic.
On site at heat treat operations, gas-fired furnaces can be a significant source of carbon emissions. But depending on the desired heat treatment, an alternative approach that combines induction through heating and intensive quenching could be the “green ticket.” Learn about the ITH + IQ technique and discover how certain steels may benefit from this approach.
