Heat Recovery Systems

Emissions Reduction & Sustainability Improvement

Heat recovery from air pollution control systems—such as thermal oxidizers, regenerative thermal oxidizers (RTOs), or catalytic oxidizers—can not only reduce operating costs but also lower greenhouse gas (GHG) emissions. Catalytic Products International (CPI) regularly engages in energy conservation discussions with customers to identify cost-effective heat recovery solutions.

Heat Recovery 101: What Is Heat Recovery?

In this context, heat recovery means using waste heat that would otherwise be released to the atmosphere for a beneficial purpose. While the concept sounds simple, actual implementation can be complex depending on the waste heat gas stream constituents and the process generating it.

CPI’s primary business is engineering solutions that eliminate air pollution from stationary industrial sources—most often using thermal or catalytic oxidizers. These processes operate at elevated temperatures, with exhaust temperatures typically ranging from 200°F to 1,500°F. Other heat sources (boiler exhaust, oven/dryer exhausts, fluid heaters, etc.) may also offer attractive energy conservation opportunities.

Two Basic Forms of Oxidizer Heat Recovery

1. Direct Heat Recovery

Direct heat recovery is less common. In this method, the hot waste gas is used directly in a process without an intermediate heat exchange medium.

Example: An oven or dryer using gas burners can be integrated with a direct heat recovery system that utilizes waste heat from a thermal oxidizer. This approach offers very low capital cost, high recovery value, and rapid return on investment.

Considerations: A clear understanding of oxidizer exhaust constituents is essential. For instance:

• In flexographic or offset printing, byproducts in the oxidizer exhaust may affect printed image color.
• In coating applications containing silicone, silicon dioxide formed in the oxidizer can create particulate that may travel back to the oven.
• If your process requires a contaminant-free heat source, direct heat recovery may not be suitable.

2. Indirect Heat Recovery

Indirect heat recovery is more common and uses a heat exchanger to transfer energy between different mediums—either air-to-air or air-to-fluid.

Example: An oven or dryer can be integrated with an indirect heat recovery system where hot air from the oxidizer exchanges energy with cool fresh air. These systems are more complex, require additional equipment, and typically have higher capital costs. Due to efficiency limitations, lower recovery temperatures are typical.

Benefits: Indirect recovery separates the oxidizer waste heat from the process supply heat, allowing ambient fresh air to be filtered (removing particulates) or humidity-controlled for specific curing requirements.

Common Forms of Indirect Heat Recovery

• Hot air to steam: Often uses a fire-tube boiler connected to a direct-fired thermal oxidizer.
• Hot air to glycol: Glycol hot water systems allow higher water temperatures than traditional water heating.
• Hot air to thermal oil: Provides high-temperature heating with very stable temperature profiles.

Connecting Heat Recovery to GHG Reduction

By recovering waste heat and using it to offset natural gas consumption in process heating equipment, facilities can significantly lower their greenhouse gas footprint. CPI offers expertise in analyzing the most cost-effective energy conservation techniques, reviewing total installed costs, and calculating expected return on investment (ROI).

CPI custom engineers heat recovery solutions—both direct and indirect—to help you achieve your emissions reduction and sustainability goals.