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Tchoryk, C.; Paul Stuart, P.R. NSERC Environmental Design Engineering Chair, Department of Chemical Engineering, Ecole Polytechnique, Quebec, Canada paul.stuart@polymtl.ca INTRODUCTION It is widely used practice in the pulp and paper industry to burn its waste water sludge after mechanical dewatering as it allows the recovery of energy and reduces landfilling [1]. However, the sludge’s low dryness has a big impact on the energy recovered from the boiler [3,5]. A novel biodrying process is evaluated as a solution to add value to the sludge. In biodrying, heat is produced by the exothermic metabolism of microorganisms present in the sludge. Aeration of the biological material serves two purposes; keeping microorganisms in an aerobic state and removing water from the system. Biodrying is similar to composting, but has a different goal; where composting looks at degrading biological matter; biodrying looks at maximizing the low heating value The goal of this study was to assess the economic viability of a vertical continuous biodrying process. This was done by showing the economic benefits of the process in a pulp and paper mill and by demonstrating that full scale operation can be attained based on pilot plant experiments. This study required a variety of skills essential for process engineers. This paper will show the importance of multidisciplinary that can be found in a chemical engineering master’s degree project. METHOD The first step of the study was the commissioning of a novel vertical continuous biodryer. Unforeseen difficulties had to be worked out with the pilot plant. The first main issue encountered was an uneven sludge residence time that caused gaps and bridging. This was resolved by re-engineering the discharge screw. The second issue was the condensation of moisture before and on measurement instruments from air exiting the dryer. Better insulation and heating were installed to remediate this. Large volumes of sludge, limited storage area, and long experimental runs of 8 to 12 days, required management skills. Logistics were needed to coordinate experiment scheduling and sludge shipping from and to a pulp and paper mill. With the results from the experiments, an empirical model was created to predict sludge characteristics based on dryer operating conditions. Scale-up of the process was done using basic experimental data analysis and comparing the new process with similar industrial processes, either other biodrying designs [4,2] or in-reactor composting, The data for this comparison originated mostly from the grey literature, such as companies’ website. Table 1: Summary of case study mills

Design Of Novel Biodrying Process For Pulp And Paper Mill Sludge, And Impact On Fluidized Bed Boiler Efficiency