Flocculation Monitoring: Focused Beam Reflectance Measurement as a Measurement Tool

Abstract

1I n paper manufacturing flocculation can be defined as the formation of aggregates or flocs from the raw materials presented in a papermaking furnish. These interactions include fibres-fibres; fines-fibres; fillers-fibres; fillers-fines; and dissolved and colloidal fraction with all other furnish constituents. Fibre flocculation is mainly due to mechanical processes and it has an important influence on formation. However, fines and fillers interaction is dominated by the electrostatic interactions between particles and chemicals, and are the main influence on retention. Adhesion and occlusion of fines and fillers in the mechanical network mainly affect drainage. Dissolved and colloidal material flocculation is also due to electrostatic interactions with the added polyelectrolytes and it will mainly affect the efficiency of the chemicals and the runnability of the process and the quality of the final product when deposits are formed. Flocculation is extremely important in papermaking and it can be considered the intermediate state between the raw materials and the final product. For this reason, flocculation control has become an increasingly important issue in the paper industry over the years. The goal is to achieve the optimum flocculation that allows papermakers to obtain good retention and drainage at the same time as good formation. In the past, the optimum was considered the right equilibrium between these opposite effects; however, nowadays, the aim is to optimize these opposing effects in a sequential way. In other words, manipulating the chemicals and the turbulence in order to first flocculate the suspension, then break down the flocs, and then to re-flocculate the suspension in an optimum manner. This approach facilitates low mechanical flocculation and high chemical flocculation. Considering that the raw materials and the papermaking conditions are fixed for a given product and paper machine, there are only a few variables that can be controlled to improve flocculation, from the point of view of floc properties, size and strength to shear stress. Among these variables are consistency, type of chemical additive and addition point (Gess, 1998;Blanco, 1994).On the other hand, trends in papermaking such as a move towards closed-water systems, a higher use of recovered paper, faster machines, etc., also affect flocculation. For example, accumulation of anionic trash, fluctuating pH and temperature, increase of conductivity and turbulence, and so forth. These changes may affect pulp fractions, polymer characteristics, flocculation mechanism and floc properties. Therefore, the efficiency of the polymer can be dramatically affected. These effects most often result in a degradation of the additive efficiency and sometimes hinder the effectiveness of the various additives (Blanco et al., 1998;Vendries and Pfromm, 1998 One of the most important parameters that influences flocculation and, therefore, floc properties, is the flocculant characteristics. Flocculant additives operate via different flocculation mecha...

Efficiency of chitosans for the treatment of papermaking process water by dissolved air flotation

“…FBRM technique monitors in real-time the chord length distribution and the number of particles in a suspension. The data can be used to analyze the flocs properties and the flocculation mechanisms allowing the selection of both the best chemicals and the optimal chemical dosages [26]. FBRM technique has been previously used for the chemical optimization of the DAF treatments in papermaking processes [8][9][10][27][28][29].…”

Silica removal from newsprint mill effluents with aluminum salts

“…From these data, the total number of counts (TNC), counts in a specific size region, mean chord size (MCS) and other statistical parameters can be calculated. The use of FBRM technique to monitor flocculation has been thoroughly described previously by the authors [26,27]. In a typical trial, the probe is submerged into a 100 ml and the stirring speed was fixed at 200 rpm.…”

Increase of Paper Strength and Bulk by Co-Flocculation of Fines and Fly Ash-based Calcium Silicate

“…It is generally believed that CPAM, with a high molecular weight and a low charge density, flocculates fillers through a bridging mechanism (Biggs et al 2000;Blanco et al 2002;Rasteiro et al 2008). The CPAM adsorbs on the surface of FACS particles or fines randomly, and its loops and tails extended far beyond the particle surface to interact with other particles, forming FACS-fines composites.…”