As a material, carbon fiber has fundamentally changed many of the products used every day, making them lighter, stronger and more durable. The manufacturing process is typically unique to each supplier, and it can be as complex as the fiber molecules themselves. Equally as challenging are the air pollution control systems used on the production equipment.

When the first carbon fiber conversion plants came online, operating costs were not critical design parameters and neither were the environmental effects of production. Today, the manufacturing of carbon fiber is heavily regulated by the environmental community, and producers are continually looking to reduce energy demands of this heat-intensive process. The oxidation and carbonization furnaces and industrial ovens have the potential to emit hydrogen cyanide (HCN), ammonia (NH3) and volatile organic compounds (VOCs). Some of these pollutants are immediately dangerous to human health even in very small quantities. Other pollutants of concern for carbon fiber producers include greenhouse gases such as carbon monoxide and nitrogen oxide (NOX).

With help from Milwaukee-based Anguil Environmental Systems, two institutions on opposite sides of the world rolled out new processing techniques that utilize different yet effective air pollution abatement technologies that also drive down production costs.

Recycling at the Forefront in the United Kingdom. The strength, durability and lightweight characteristics of carbon fiber make it useful many manufactured products, but most waste ends up in landfills, where those same attributes do not allow the carbon fiber to break down like other organic material. The University of Nottingham in the United Kingdom opened a new facility to reuse the former waste stream.

In conjunction with industry partners, Nottingham University has developed a pilot-scale carbon fiber recycling plant. The team at Nottingham knew that an air pollution control device would be necessary to meet the local emission requirements for hydrogen cyanide (HCN) and ammonia (NH3). They also realized that there was the potential to reuse some of the energy released during the combustion of these carbon fiber processing emissions.

Anguil Environmental Systems provided the air pollution control system for the University of Nottingham, delivering a 1,500 scfm thermal recuperative oxidizer with dual heat recovery. A stainless-steel heat exchanger within the oxidizer reduces the amount of supplemental fuel required to bring the process emissions up to combustion temperatures. In addition, a secondary heat recovery system downstream of the oxidizer captures 95 percent of the remaining heat ―enough energy to preheat the air for the process equipment. When in operation, no external heating source is required to fuel the Anguil oxidizer or carbon fiber oven, making the entire system self-sustaining. The Anguil oxidizer has been achieving greater than 99 percent destruction rate efficiency at the Nottingham facility. 

Technology Transfer in the United States. Recognizing the need for this industry to develop a lower cost carbon fiber material, the U.S. Department of Energy built a custom-designed conversion process at Oak Ridge National Laboratories (ORNL). The process equipment was designed by Harper International, Lancaster, N.Y. The carbon fiber technology line in Oak Ridge, Tenn., allows industry partners to test the scalability of emerging carbon composite materials before commercial production.

To treat the exhaust streams coming from the carbon fiber process, Anguil Environmental Systems was commissioned to design, manufacture and install a multi-stage direct-fired thermal oxidizer (DFTO). The 1,200 scfm abatement system is capable of destroying nitrogen compounds without the formation of NOX that is a typical byproduct in conventional oxidation processes. Gases move through zones within the oxidizer under varying conditions where the total emission destruction efficiencies are greater than 99 percent with minimal NOX generation.

The system incorporates a secondary heat exchanger to further reduce operating expenses and carbon emissions from the process. Even though this application does not warrant additional NOX reduction, selective non-catalytic reduction could be added to further reduce the environmental impact if needed.

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