The pre-carbonization and carbonization of Carbon Fiber is achieved through an LT (low temperature, typically at 700-900°C) and HT (high temperature, typically at 1450-1800°C) furnace. It is during these steps that the majority of the volatile organic components and contaminants are released.
At the industry’s inception, the designs routed off-gases from the LT and HT furnaces to be blended with air at the discharge from the furnace. This allowed for combustion locally but resulted in large environmental impact. Localized destruction of the volatile organic components (VOCs) helped to keep off-gas fumes from fouling, but this localized destruction led to high nitrogen oxide (NOx) generation. As systems integrations and environmental expectations matured, modern plants have transitioned toward closed pipe transport of these off-gases to an incinerator. Transport of the VOCs to a incinerator allows for low NOx destruction of these gases.
Modern furnace designs have addressed energy utilization in each stage. The modern LT and HT include insulation or refractory packages focused on eliminating the need for shell cooling at temperatures up to 1600°C and beyond. A marginal increase in cost of manufacturing leads to a sustained, continuous decrease in cost of operation through elimination of cooling water. Advances in power systems and coordination of the overall electrical interface with the facility designer and electrical utility provider also allow for decrease of harmonic losses and power factor over historical designs. Harper pioneered the development of a robust muffle design that delivers increased line sizes with the same gas flow rate as smaller lines. This means no increased gas consumption at a higher production rate.
Since its inception, Harper has guided the industry through its major capacity expansions. These include the standardazation of the 2 meter wide design, the development of the 2 meter double wide design deployed in the 1980s, and most recently, the establishment of the highly efficient 3 meter design as the preferred method for efficient high volume production. Learn more about cost economics of each of these designs in our Resource Center.