Optimizing Powder Coat Curing to Improve Your Carbon Footprint

By Michael Stowe

More and more policies, plans, goals, corporate mandates, and even regulations are pushing organizations to take a closer look at sustainability and decarbonization. There is a direct connection between energy and carbon footprint. If you consume energy, then you have a carbon footprint. In this article, we will explore the sources of carbon emissions from powder coating processes and ways to reduce and optimize your carbon footprint.

1. Natural gas fired convection oven.
2. Natural gas or electric infrared oven.
3. A hybrid combination of 1 and 2.

We will focus on the curing process and how to optimize its energy efficiency and carbon emissions, but first let us get a little background information on carbon emissions.

Greenhouse gas (GHG) emissions refer to all types of gases, including carbon dioxide, which can cause global warming due to their greenhouse effect. GHGs insulate the earth. In other words, gases that trap heat in the atmosphere are called greenhouse gases. Figure 1 shows a table of some of the most common GHGs. The impact of various GHGs can be compared to carbon dioxide, which is set as the baseline with a 100-year global warming potential (GWP) of 1. Take for example sulfur hexafluoride. This gas has an impact 22,800 times more than that of carbon dioxide. For the powder coat curing process, we will focus on carbon dioxide emissions.

For a specific industrial process like powder coat curing, the carbon dioxide produced from the process falls into two categories, Scope 1 and Scope 2 emissions.

Scope 1 emissions are direct emissions that occur on site by processes controlled by the organization. These emissions are associated with the combustion of fuels such as natural gas, diesel, fuel oil, etc., in ovens, furnaces, boilers, vehicles, building heating, or other systems. A good way to remember this is: If you are burning something, then you are generating scope 1 emissions.

Scope 2 emissions are indirect emissions that an organization causes based on the energy that it purchases. The most common form of scope 2 emissions is from purchased electricity. When your organization consumes electricity, that electricity had to be generated at an electrical utility and some amount of fossil fuels were used to generate that electricity. Scope 2 emissions vary geographically based on the fuel usage of the local electrical utility that supplies your site. Figure 2 shows the diverse mix of energy resources used to generate electricity. A good way to remember this is: If you are buying and consuming electricity, then you are generating scope 2 emissions.

Now let us go back to the powder coat curing process. Where does the carbon dioxide come from? A chemical reaction occurs in the combustion of natural gas (methane— CH₄) in the curing oven. The methane is combined with oxygen, and during combustion, is converted into carbon dioxide and water. (Remember, if you are burning anything, then you are producing scope 1 carbon emissions.) The natural gas flows into one or more combustion burners on the powder coat curing oven. The combustion creates heat that is circulated around the parts in the oven to cure the powder. The water vapor and carbon dioxide go up the flue stack to the earth’s atmosphere.

Combustion heating for powder coat curing ovens also consumes electricity for combustion air supply fans, exhaust fans, air recirculation fans, conveyor chains or trolleys, etc. All the electrical energy consumed for a natural gas convection oven would be considered scope 2 emissions and the carbon content of the electricity consumed at your site would be based on the electrical generation fuel mix for your local electric utility.

In the case of an electric infrared powder coat curing oven, also with fans and conveyors, all the carbon for this would be considered scope 2 (i.e., all from purchased electricity).

Now that we have learned about how carbon emissions are related to the energy consumed in the powder coat curing process, what are some things that can be done to reduce our carbon footprint?

Energy Efficiency
Since we know that our carbon emissions are directly proportional to our energy consumption, improving the energy efficiency of our powder coat curing process will reduce our carbon footprint.

The goal is to both minimize energy in and minimize losses. In this way, most of the energy consumed by your powder coat process will go to add value to your parts.

Here are some ideas to consider for improving energy efficiency in the powder coat curing process:

1. Combustion burners
   a. Make sure that your combustion burners are cleaned, tuned, and balanced at least annually.
   b. Ensure the proper amount of combustion air is supplied and excess air is optimized.
   c. If you have very old burners, consider upgrading to new, more efficient burners.
   d. Ensure that your burner controls are operating properly and that the burners are used at, or close to, design capacity.
   e. Ensure good air circulation within the oven and good, calibrated temperature measuring devices (e.g., thermocouples). This will provide the best temperature feedback to the burner controllers.
   
   
2. Oven envelope
   a. Ensure that the oven is properly insulated, and that the insulation is periodically inspected and repaired as needed.
   b. Periodically inspect the oven walls with a thermographic camera to check for hot spots.
   c. Ensure oven openings are as tight as possible to reduce heat loss.
   
   
3. Waste Heat Recovery (WHR)
   a. Most of the heat of combustion in a typical powder coat curing oven goes right up the flue stack.
   b. Consider using hot flue gas to preheat oven combustion air.
   c. Consider using the hot flue gas for heating other site processes like building or hot water heating.
   d. Many powder coat lines have heated wash tanks. Consider using hot flue gas for preheating wash tank water.
   
   
4. Electrical motors
   a. Consider the use of variable frequency drives (VFDs) on motors for combustion and recirculation fans.
   b. Always use NEMA Premium® efficient motors to ensure the maximum efficiency of your motor population.
   c. Ensure proper maintenance and alignment of motors.
   
   
5. Electric infrared ovens
   a. Infrared oven vendors will help to optimize the heating element type and position within the oven to ensure proper heating of the parts and curing of the powder coat.
   b. Typically, recipes are developed for each family of parts to be coated.
   c. Electric infrared ovens are very energy efficient and can also increase line speed.
   
   Remember that energy efficiency is directly tied to your carbon footprint. The more efficient that you can make your powder coat curing oven, the more reduction you can see in your carbon footprint.
   

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NEMA Premium^® labeled electric motors will assist purchasers to optimize motor systems efficiency, reduce electrical power consumption and costs,and improve system reliability. It is estimated that the NEMA Premium^® efficiency motor program would save 5,800 gigawatts of electricity. This translates to preventing nearly 80 million metric tons of carbon dioxide into the atmosphere over the next 10 years—equivalent to keeping 16 million cars off the road.

Energy Intensity
Energy intensity is a ratio that measures the specific amount of energy consumed to produce one logical production part or process parameter. For a powder coating processes, this energy intensity could be the total energy per pound of powder applied, or total energy per item coated, or some other similar ratio. The key here is that energy efficiency and energy intensity go hand in hand. As you improve the energy efficiency of your process by making improvements, this reduces the total energy consumed, i.e., the numerator of the energy intensity ratio. Now, with this improved energy efficiency and smaller numerator, if you make the same number of parts, your energy intensity will go down. In other words, you want to increase your energy efficiency to reduce your energy intensity.

Energy intensity provides a good measure of how your energy consumption is trending on a per production part basis. Figure 3 shows an example of an energy intensity trend with a goal line (in blue) and the monthly energy intensity of total energy in MMBTUs per gear set in red. Additionally, you can track and trend your carbon intensity, the amount of carbon dioxide released to produce a kilowatt hour (kWh) of electricity, as well. Establishing goals for energy efficiency and energy intensity and tracking these trends over time can go a long way to helping manage your carbon footprint.

Alternative Energy Sources
In addition to energy efficiency and energy intensity, there are several other ways to improve the carbon footprint of your powder coat curing process. Here are several possibilities to consider for alternative energy sources:

1. If you are currently curing your powder in a natural gas convection oven, consider the possibility of using electric infrared as an alternative or as a hybrid enhancement to the natural gas oven. This can reduce your natural gas (e.g., carbon scope 1) consumption and in many cases can increase your line speed, which would improve overall energy intensity. The added electrical consumption for the infrared heating would increase your scope 2 carbon emissions.
   
   
2. Many existing combustion burners can be adjusted to burn hydrogen as a heating fuel. Using hydrogen as an alternative fuel could allow you to use the same equipment and at the same time considerably reduce your carbon scope 1 emissions. The combustion of hydrogen does not release any carbon dioxide. There are many forms of hydrogen production, most of which are not yet commercially available, but as hydrogen availability improves, this could be a consideration.
   
   
3. The cleaner the electricity that you consume, the less scope 2 carbon emissions you will have. Solar, wind, and hydroelectric power generation are all very clean and essentially carbon free. If you have available space, consider the possibility of adding these clean electrical generation methods to your site.

In summary, the powder coat curing process creates scope 1 and scope 2 carbon emissions. The amount of energy you consume for this process is directly related to the amount of your carbon footprint. There are many ways to optimize, update, and innovate your powder coat curing process through energy efficiency and energy intensity improvements, and through the thoughtful consideration of possible energy source alternatives.

Michael Stowe is senior energy engineer at Advanced Energy.