November 2022 Volume 4

EQUIPMENT & TECHNOLOGY

Decarbonization Techniques for Gas Fired Forge and Heat Treat Thermal Processes By Justin Dzik and Alexis Omilion

Recently, a focus has been placed on the decarbonization of industry. Energy intensive processes are being analyzed to find the best way to minimize carbon-based energy sources or best case, remove them all together. Forge and heat treat thermal processes are one of the most energy intensive and therefore, have a large carbon footprint per unit of production. Some heating approaches are already electric, specifically the applications that utilize induction heating. In those cases, the electricity production will need to be evaluated to make sure that green power is being used to run the units. Regarding existing gas fired furnaces, electric resistive heating may be considered. However, modifying an existing natural gas fired furnace to electric heating may prove troublesome when looking at temperature uniformity and power density. Additional considerations would need to be made regarding furnace geometry, possible sources for circulation, and atmosphere inside the furnace. It is unlikely to be a “plug and play” change in retrofit cases. For new furnaces, electric resistive heating may be an option for furnaces properly designed to meet temperature uniformity and production specifications. The two best options for decarbonization of existing gas fired processes are: reduction of fuel usage through increased efficiency and use of non-hydrocarbon fuels, such as hydrogen. Reduction of fuel usage can be accomplished by increasing the efficiency of the combustion systems through use of recuperators or regenerators. Regarding non-carbon fuels, Hydrogen is currently regarded as the best non-hydrocarbon option for industrial fuel source. How is CO2 Formed and How Can It Be Reduced? Carbon Dioxide (CO2) is a major species in the combustion of hydrocarbon fuels, as given by the following general reaction for the combustion of any hydrocarbon in air:

The amount of CO2 produced is directly proportional to the number of carbon atoms in the fuel. Therefore, the amount of CO2 formed in the combustion process depends only on the fuel composition and the amount of fuel consumed by the process. The combustion system CO2 emissions can therefore be reduced by improving efficiency and/or using an alternative fuel with lower carbon content. Process efficiency can be improved through maintenance and operational practices, such as maintaining proper air/fuel ratio, effective furnace pressure control, regularly inspecting/repairing furnace refractory, doors, and optimizing operational practices. Heat recovery canbe used to further increase efficiency by reclaiming heat from the exhaust gases and using it for useful heating, either in the same process or in another process within the plant. This can be done by strategically designing the flow of products of combustion within a furnace, diverting flue gases to another process within the plant, or using a heat recovery device, such as regenerative burners. Other than improving process efficiency, the only other means of reducing the CO2 emissions from a combustion system is to use an alternative fuel with lower carbon content, such as hydrogen or hydrogen-enriched natural gas. Although hydrogen is a high-quality fuel, firing burners with hydrogen poses several challenges compared to natural gas, including hydrogen’s higher flame temperature and faster flame speed. The flame temperature of hydrogen is 150-200°C hotter than a methane (the main constituent of natural gas) flame across all air/fuel ratios. This implies elevated NOx emissions when firing hydrogen fuels with conventional burners. The flame speed of hydrogen is also significantly faster than methane, especially when operating under rich conditions or with minimal excess air. This fast flame speed means the likelihood of flashback of a premix flame into the burner body greatly increases. Rather than using pure hydrogen as a fuel source, there is also the option of blending hydrogen with natural gas to lower CO2 emissions. Achieving significant CO2 reduction requires blends that are in the steeper nonlinear regions. As shown in Figure 2, achieving only a 25%CO2 reduction will require 50% hydrogen blended with natural gas and a 50% CO2 reduction will require 76% hydrogen blended with natural gas.

FIA MAGAZINE | NOVEMBER 2022 18