Decarbonizing Process Heating: Strategies and Challenges

The industrial sector’s carbon footprint represents about a third of all greenhouse gas (GHG) output globally or nationally. Many of these emissions are the result of process heating. In the U.S. industrial sector, process heat accounts for about half of all onsite energy use, with the majority generated by fossil fuels.

Because temperatures vary widely, from below 400°C to 1000°C and above, there is no one-size-fits-all-solution. Any new solution must be compatible with both the specific process and its equipment.

Current and future options

The industry can first optimize heat usage and minimize waste. Implementing energy efficiency tools (energy management) and technologies (smart manufacturing) can significantly reduce carbon footprints. Waste heat recovery is another low-cost option; by electrifying this option, higher efficiencies can be achieved.

Options for low-temperature processes include:

• Solar thermal systems. Used to preheat boiler feedwater and other similar applications.
• Biomass boilers. Organic feedstock (such as agricultural waste) is converted into syngas (synthetic gas), replacing natural gas.
• Electrification. Equipment includes industrial heat pumps, electric furnaces, among others. Heat pumps are being used to dry lumber for flooring.

Initial investments are offset by long-term operating and maintenance cost savings for a lower total cost of ownership. For high-temperature processes, new technologies are emerging. Fossil-fuel steam crackers that produce high-value chemicals may eventually be replaced with electric counterparts. The cement industry is developing kilns with plasma-generated heat. The steel sector is piloting new electrolytic reduction processes using mixed carbon.

Fuel with a low carbon footprint, such as hydrogen and ammonia, can also generate process heat. Hydrogen shows promise for very high-temperature processes where no other alternatives currently exist.

Multiple technologies are better than just one

Whether it be low or high temperature, companies are finding ways to decarbonize. California Dairies, Inc. partnered with an energy-as-a-service (EaaS) company to complete a total of six decarbonization projects across their two largest facilities in 2023. Three technologies were implemented:

• A rooftop-mounted solar thermal system preheats the boiler feedwater to 180°F, reducing the amount of natural gas used to generate steam.
• Smart steam traps with internet-connected sensors reduce steam loss.
• Boiler heat recovery uses a condensing economizer to transfer heat from the boiler flue gas to preheat boiler feedwater, increasing boiler efficiency by nearly 10%.

Together, these technologies avoided 7,000 metric tons of carbon emissions and more than 110,000 MMBtu of natural gas consumption per year, resulting in net savings of $419,659 as of April 2024.

Steel manufacturer Cleveland-Cliffs Inc. also took a multi-pronged approach:

• Installed two state-of-the-art walking beam reheat furnaces, resulting in estimated savings of 2.1 million MMBTU of natural gas.
• Recovered energy from byproduct gases to generate electricity and steam, reducing the amount of purchased electricity and associated Scope 2 emissions.
• Initiated or completed energy-saving projects during 2023, reducing the annual energy consumption of electricity and natural gas by over 70 million kWh.

In addition, Cleveland-Cliffs completed successful hydrogen injection trials at several blast furnaces and is developing heating elements for slab reheat furnaces.

Despite the potential, challenges do remain. Electricity consumption could increase significantly. And, for longer processes, electrification may be less efficient than fossil-fueled technologies. With strong policy support and funding, however, energy efficiency and electrification could revolutionize sustainable manufacturing.