Investigation of factors contributing to the deposition of contaminants on dryer cylinders
Clarke, Andrew Edward
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Pulp from recycled paper products contains various waxes, glues, adhesives, filler, and inorganics that are collectively referred to as contaminants. Contaminants that are not drained out during the forming process are trapped in the sheet and carried down the paper machine. These contaminant particles and contaminants in solution can become deposited on the dryer cylinders. The contaminants which deposit on the dryer cylinders lead to reduced quality and production of paper on the machine. The process by which contaminants are deposited on a dryer cylinder has not been explored at a fundamental level. Rather, quick industrial fixes have been tested to try and eliminate the contaminant deposition and only reductions in deposition have been achieved. The literature reviewed does not relate the flow of particle suspensions through porous media to the heat transfer and fluid dynamics processes associated with drying paper. The experiments in the literature showed the general trends of particle and dye distributions across the thicknesses of different porous media during forming or filtration processes. Filler and fines distribution were not able to be changed by flows induced by pressing a sheet. The mechanisms for how particles move through porous media found in the literature were a basis for what kind of phenomena would be expected in the particle flow experiments. A means of completely eliminating sticky deposits could be found by examining the parameters which contribute to the deposition process. The hypothesis proposed in this thesis is that contaminant particles and liquid containing contaminants are transported to the dryer can surface by liquid flows induced by the drying process. By performing particle flow experiments during drying, bounds for the particle size, initial drying surface temperature, drying time, and initial solids content will be determined for which the hypothesis is true. The particle and dye transport studies performed showed an array of processes at work simultaneously. The results from the particle and dye transport studies show that a particle diameter of ~1.0 and #956;m or less, handsheet solids content of less than 30%, open sheet structure and a high surface drying temperature (200C) were needed to create a significant change in filler and dye distribution across the thickness of a handsheet.