Importance of Performance in Carbon Fiber Processing – Oxidation Furnace Technology

James Fry / Applications Engineer - Harper International

Since the carbon fiber market's establishment in the 1970s, fiber producers have achieved increasingly significant technological advances to keep pace with market demand. Harper offers advanced carbon fiber oxidation furnace technology to complement its industry-leading furnaces for carbon fiber processing. Our latest furnace designs are available from 300 mm to over 4000 mm draw belts. Harper's designs incorporate numerous improvements beyond what is currently available in the market today, including designs that deliver energy efficiency. The latest model developed by Harper, a production-scale oxidation furnace with 3 meters width (a section of which is visible in the photograph), demonstrates superior performance by maintaining air velocity uniformity of 2% at key dimensions and temperature uniformity of +/- 2.5°C across the entire heated area. This innovative design, combined with improved performance, delivers significant productivity gains in production rates. For the customer, our technological advances mean faster oxidation through elimination of stack effect, improved uniform velocity distribution and distance, guaranteed uniform temperature distribution across varying flow rates, and ultimately improved fiber quality through optimal reaction control. These improvements come in the form of clearly stated performance guarantees. Some of these design improvements are: • Superior atmospheric seal materials, • Continuous monitoring of feed, circulation and exhaust flow rates, • Patent-pending improved nozzle design, • Process-based indicator array, • Improved dial structure for better installation. The innovative atmospheric end seal, the defining feature of Harper's latest technology design, reduces fugitive emissions, increases the furnace's active volume, and reduces energy consumption compared to alternatives. The seal materials have independent adjustment from upper and lower inner and outer openings.

On each pass, there is independent, adjustable draw-controlled ventilation and the exhaust box is connected to a dedicated fan/VFD. Thanks to these innovative design features, there is no vertical mixing in the seal material, less air ingress, and no process gas leakage.

Harper's indicator improvements include a two-tier balancing methodology, a reactive quench system and fast cooling system, emission monitoring, and by design a safer pressure relief system. Additionally, Harper's modular design structure is another development that sets us apart from our competitors. Our furnaces deliver 90% reduction in labor compared to installation times for a comparable full-line pilot system (300 mm) in the same space. Furthermore, Harper's proprietary multi-flow Research Furnace, part of our Microline system, provides parallel, cross, and downward air flow directions in a single furnace, enabling accurate evaluation of different flow techniques. Furnace uniformity characteristics provide or exceed class-best values for each flow regime.

Innovations in Alternative Precursor Processing

While carbon fiber is largely made from polyacrylonitrile (PAN) and pitch, as the industry expands to encompass applications such as automotive, there is increasing demand for alternative, lower-cost and renewable precursors. Harper has the capability to adapt its technology to process non-conventional precursors throughout the entire thermal process. Our customers can reduce operating costs and decrease furnace residence time by using non-conventional precursors such as wood pulp, synthetic silk, polyethylene and blends. To customize equipment to unique process requirements, we consider the precursor chemistry to determine production materials. Whether the precursor requires a belt furnace because it cannot be self-supporting, or whether it is a draw-type furnace, Harper provides solutions throughout the entire process for these emerging precursors. We have designed our equipment to process these emerging precursors at every line size from research lines to full production scale, which can be seen in our complete line established at Oak Ridge National Laboratory's Carbon Fiber Technology Center.

Innovations in Gas-Fired Heating Systems

In addition to our innovations in handling alternative precursors, Harper supports the development of the carbon fiber market through the design of gas-fired furnaces at production scale and sizing dryers and air pollution reduction systems that utilize the advantages of natural gas. Today's energy markets and environmental regulations have provided significant advantages for thermal processing equipment using natural gas as fuel, and Harper possesses unique experience in producing reliable combustion-heated processing equipment for various industries and applications. Capital cost for gas-fired equipment comes with a small premium, and return on investment (ROI) varies by installation location. However, compared to electrically heated equipment in North America, ROI of less than two years has been observed. In other regions of the world where fuel gas prices are higher, additional heat recovery options can be implemented to increase efficiency. Harper's philosophy is to support our customers with a unique portfolio, service and capabilities while also providing the latest technology across all stages of carbon fiber production. With Harper, you will have a unique partner to meet the carbon fiber market's growing needs. Our highly skilled and experienced technical team offers deep and broad experience that no other partner can provide.