Drying Characteristics-Property Correlationships in Gas-Fired Infrared Drying of Paper Obtained by Diffuse Reflectance FT-IR Spectroscopy

Introduction

Infrared (IR) drying of paper in a pilot scale has been investigated by several researchers in the past [1–3]. Both high-intensity electric heating and medium-intensity gas heating are now being used industrially either to preheat wet paper before conventional steam drying [1] or as a moisture-profile corrector just before paper sizing press [2]. Our own investigation [3] on the use of radiant energy from a gas-fired IR radiator have revealed that the drying efficiency of IR radiation is influenced by the nature of association of water molecules with cellulose in wet paper. Depending on the total moisture content of a paper, the free and bound moisture contents of paper will vary in wet paper sheet. Our previous study [3] has also confirmed that it is possible to remove free moisture more efficiently using gas-fired IR emitter operated at 1373 K rather than as 1223 K. It is reported that besides emitter temperature, the efficiency of drying also depends on the location of the emitter. In general, the efficiency is high if the emitter is installed near the preheating zone and the efficiency changes in the following order: falling rate < constant rate < preheating. Pikulik [4] compared the efficiency of hot gas impinging drying with conventional steam drying emphasizing the paper properties. The properties of a high-intensity hot gas-dried paper has been reported to be better than those of conventionally steam dried paper. An immediate quality improvement in terms of reduced moisture steaks and superior resistance to paper embrittleness was also observed when installing a high-intensity infrared drying system [5,6].