Effectively Drying Textiles
In search of high productivity, problems can arise when trying to increase production line speed. The available infrared technology (ceramic tile burners or radiant tubes) may not provide enough power to thoroughly dry carpet. However, increasing the power of hot air equipment can lead to an efficiency loss. Other carpet drying problems include:
- Inefficient drying when using hot air.
- Considerable energy consumption.
- Limited infrared power output.
- Problems reaching the desired moisture profile.
- Limited production line speed.
Metal fiber burner technology, created in response to these problems, places radiant burners above the carpet. The rectangular metal fiber burners range in size, and each burner's power output can be modulated between 200,000 and 1.1 million BTU/hr. Each burner has a single central inlet tube and homogeneously distributed combustion over its surface. The technology allows a burner to be designed according to the treated carpet's dimensions.
Burners in Textile MillsIn the winter months, some textile mills switch from natural gas to a mixture of propane and air to reduce operating costs. However, ceramic infrared burners are sensitive to this switch and may be able to handle only a narrow input band (BTU/ft2). If the burners are under-fired for a few minutes, they will flashback. Flashback occurs when a flame front moves through the burner deck or flame holder. Propane, having a lower ignition point and higher flame speed than natural gas, increases the risk of flashback in this situation. Flame speed is the rate at which a flame progresses into a combustible mixture relative to the speed of the mixture.
As a result of the shock wave created by a flashback, cer-amic tiles can literally break and fly out of the burner, resulting in a line shutdown, lost production time and replacement ex-penses. By introducing metal fiber gas burners into textile applications that use ceramic burners, flashbacks and line shutdowns can be eliminated.
Another textile application that may benefit from gas-fired infrared is a textile coating line where minimal heating of cloth is required. Often, electrical infrared radiant elements are used. After coating, a continuous band of textile cloth is heated using electrical infrared heaters to melt the powder or granulate. Metal fiber burners allow natural gas or propane to be used as an alternative energy source.Textile manufacturers also have complete cloth-coloring lines that combine handling, coloring and drying machines. The cloth is placed in a bath with coloring liquid and pressed between two rolls to remove as much moisture as possible. The cloth then is introduced into an infrared drying installation for preheating and a first drying step. Finally, the cloth goes into a convection drying oven, where it is dried completely. Following drying, it is rolled up for further processing.
In dying pro-cesses, operators must clean the rolls when changing colors. This application poses two potential problems for cer-amic tile burners: acid, used to clean the rolls, can eat away the ceramic, and as a result, the ceramic has to be protected by placing plastic covers over the burners, which is time consuming and results in less production. Also, operators must take precautions to avoid breaking the ceramic tiles. Metal fiber burners can be splashed with acid solution before or during an application and receive no damage.
Metal fiber burner elements are available for both the retrofit of ceramic tile burners and new infrared installations. A typical ceramic burner is approximately 12 x 5" (360 x 130 mm) with a number of tiles, and a typical power output around 23,000 BTU. Metal fiber burners can have the same dimensions and functionality, but the system can employ bigger burner elements such as a 40 x 8" (1,000 x 200 mm) burner with a power output between 67,000 and 670,000 BTU.
Metal fiber burners are suited for use in textile mills because they resist rough handling and thermal shocks, are flexible and will not crack in high temperature environments. By reusing existing mixing equipment, simple conversion of existing units can be accomplished. For all of these reasons, metal fiber burner technology is gaining in popularity.