Effect of High Temperature Drying of Recycled Paper on Heat TRansfer Rates and Sheet Properties, 2007 TAPPI 8th Research Forum on Recycling

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This paper presents a study on the effect of high temperature on paper drying rates and properties for both virgin and recycled pulp. Recently, there has been considerable interest in increasing the rate of paper drying to increase production. The use of gas-fired dryers (high temperature drying) is one method to increase the drying rate. With gas-fired dryers, one or more conventional dryers are replaced with a gas-fired dryer. The gas-fired dryer can provide internal shell temperatures in excess of 200 oC, which significantly increases the drying rate. However there are several issues with such an installation. These include, the change in the heat transfer rates (drying rates), the effect on paper properties especially curl and strength properties and the ideal location of such dryers. The process variables studied include the effects of temperature, moisture level, recycling, refining and basis weight on heat transfer and paper properties. The results of this study provide information that optimizes the location of the high temperature dryers. In the ideal location, the heat transfer rates are maximized with minimum effect on sheet properties. Sheet curl was found to be a function of recycling, refining, basis weight and drying temperatures.