Infrared Imager Helps Evaluate Papermaking Process
Ruth A. Mendonsa
The papermaking industry is among the highest consumers of energy in the US, and researchers at the Institute of Paper Science and Technology (IPST) in Atlanta are working to make the process more energy efficient. They chose Secaucus, N.J.-based AGEMA Infrared Systems' Thermovision 900 imaging system to help.
In papermaking, the energy consumption comes from the need to remove the water from a continuous wet paper web. Put simply, the water is removed in two steps: First it is fed through a press where the water is pushed into the press felt; next the paper web is transferred to a dry press felt for drying by evaporation, the more energy-intensive part of the process. The key to saving energy lies in removing more moisture from the paper sheet in the pressing phase. For every 1 percent increase in water removed in the pressing section, there is a 4 percent energy savings in the drying section.
The researchers are trying to do this by using a heated roll as part of the press, a method they call impulse drying. A plasma-sprayed coating is applied to the steel roll to control the amount of energy transferred to the sheet. The scientists needed to determine what combination of ceramics and metal would provide the ideal coating.
To determine how and under what conditions a particular coating begins to fail, the researchers are using the thermoelectrically cooled Thermovision 900. It evaluates a test roll coated with four different coatings arranged side by side. The institute's roll coating durability test stand comprises a roll press that runs at 400 rpm, an induction heater, the Thermovision 900 and a data acquisition and control system. It tests the durability of the coatings as they are subjected to cyclic mechanical and thermal loads.
The 900 is mounted in an air-cooled enclosure opposite the test stand on a track assembly. The track allows the distance between it and the roll to be varied. The researchers use the camera in two ways. In the full image mode, it monitors the entire surface of the roll from 18 in. away, looking for hot spots. As a section of the coating starts to fail, it begins to separate from the base metal of the roll and will be heated differently from the surrounding areas of coating.
The researchers also use the 900 in its line-scanning mode, now from a distance of 31/2 in. They synchronize the image capture with the roll rotation to get a series of high-resolution close-up looks at a full revolution of each coating for evaluation. Tim Patterson of IPST said the 900, which operates at up to 3500 Hz, is the only imager they looked at that was fast enough for the job.
The data will be correlated with existing shear and tensile strength tests of the various components of the coatings. Once the optimum coating formulation is determined, it will be applied to a larger-diameter roll and installed in a pilot plant paper machine at Beloit Corp. of Rockton, Ill. Beloit and the US Department of Energy's Office of Industrial Programs are funding the research project.
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