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OPTIMAL DEWATERING WORLD PULPPAPER52 1. INTRODUCTION The efficiency of overall water removal during papermaking is critical for good runnability quality and cost-effective paper production. Water removal occurs in three areas on the paper machine the forming press and drying sections. It has long been accepted that the most cost-effective dewatering takes place in the forming section. As a result it is advantageous to remove as much water as possible during web formation. The cost and effort of removing water increases considerably throughout the production process so it is imperative though often difficult to find the right balance. 2. BACKGROUND 2.1. Optimal dewatering is dependent on the size of the flocs created at various stages of the process. Large flocs in general have the potential to drain well in the wire section but tend to hold a substantial amount of water when entering the press section. This water can be very difficult and crucially expensive to remove in the pressing and drying sections of the paper machine. By Wim van den Brink Applications Project Manager Luc VanderAuwera Laboratory Team Manager Patric Bierganns RD Manager and Paul Knight Market Manager Solenis Novel total dewatering concept improves water removal and paper machine runnability A well-designed laboratory test can provide useful information about the dewatering process without incurring the high cost and risks associated with full-scale evaluations Therefore one has to consider a certain balance between floc size and water removal in the wire section and press dryer sections. In particular small micro flocs or flocs with a more open structure tend to favour water removal in the press and dryer sections. Controlling floc size with the aim of optimising dewatering becomes even more difficult when producing high basis weight paper and board 250 gsm. A well-designed laboratory test can provide useful information about the dewatering process without incurring the high cost and risks associated with full-scale evaluations of many different retention and drainage programs. 2.2. Test Methodologies Traditional laboratory retention and drainage testing can be done with tools such as Drainage Freeness Retention DFR Dynamic Drainage Analyser DDA see Figure 1 and Vacuum Drainage Tester VDT. In general VDT differentiates itself from gravity drainage testing Schopper Riegler Britt Jar DFR by providing information related to the sheet moisture content as it enters the press section of the paper machine. For cases where one is most interested in obtaining highly reproducible dewatering rate data following treatment with different chemical programs DDA is the recommended tool. Unfortunately none of the described methodologies provides accurate predictive values regarding the potential of efficient water removal in the press and dryer sections during full-scale machine trials. Nor do they fully capture or predict the behavior of polymer programs. Hence there is a need for a predictive laboratory or field method that can simulate wet-end drainage press dewatering and water removal in the drying section. 3. TOTAL DEWATERING CONCEPT 3.1. The Challenge Polyethyleneimine PEI has been the benchmark for retention and drainage for higher basis weight recycled packaging grades. In an effort to reduce total operating costs heavy weight paper and board producers have been searching for new technologies that allow them to Simulation of overall water removal in heavy weight paper and board