2017 Volume 1
Oxfordpp 281-298Experimental Study of Filtration of Fiber Suspensions: Part II: Combined PIV and Pressure Drop Measurements.AbstractPDF
The filtration of a fiber suspension has been studied experimentally. Typical application where pressure filtration occurs are: papermaking, air cleaners, production of composite materials, etc. In particular, in papermaking, the quality of the final product depends on the fiber orientation and mass distribution in the filtered materials Micro-variations of there properties can strongly affect the quality of the final product and they can occur during filtration, thus it is important to predict how this can happen. However, this is not an easy task, first because the filtered cake is a non-homogeneous compressible porous media, second because the filtration flow is non-stationary, since the cake is continuously evolving in time. Therefor in this work we focus on the filtration flow through formed steady fiber networks. For each grammage (i.e. mass of fibers per unit area), we simultaneously measure the pressure drop across the network and velocity field on top and below the fiber network using Particle Image Velocimetry (PIV). Compression of the fiber network can also be extracted form the PIV images normalized filtration resistance was found to be decreasing with increasing network thickness, as well as network compressibility. From the PIV data the influence of the formed fiber network on the flow field was analyzed and characteristic scales of the flow structure are quantified.
Oxfordpp 299-322Characterization of Fines Quality and Their Independent Effect on Sheet PropertiesAbstractPDF
It is widely accepted that pulp fines (particles passing a 200 mesh screen) largely affect pulp properties, sheet consolidation and the final paper properties. Especially fines produced during refining – so called secondary fines- showing a more fibrillar character compared to primary fines already present after the pulping process, have a positive effect on strength properties. Although this is common knowledge within the paper physics community, it is still largely unclear which detailed properties of fines influence pulp and paper properties to what extent. As fines show some similarity to MFC, this question is also of interest regarding the sue of MFC as an additive in papermaking. We apply established and new methods for fines characterization, such as the secondary fines content, the swelling ability and data on fibrillation and fibrillary material together with a suitable experimental setup t isolate the technological impact of fines in the final product Thus we are able to evaluate the technological effect of fines with different characteristics in therms of the above mentioned properties. Our results clearly show that categorizing primary and secondary fines is not sufficient when it comes to their technological impact and only in depth analysis of the fines present in a given pulp allows to understand their effect on paper properties.
Oxfordpp 323-343The Effect of Press Nip Geometry on Dryness, Density and Paper PropertiesAbstractPDF
Oxfordpp 345-365Chemical Modification of Pulp Fibres for the Production of Thermoformable PaperAbstractPDF
Enhancing the usability of paper based materials in forming processes is one major objective to pave the way for a sustainable and bio-based economy. Therefore, modifications of either the forming process or the paper material will provide future opportunities. The present study focuses on the concept of chemical pulp fibre modification as a factor influencing the formability of paper materials made thereof.Specifically, covalent attachment of ester moieties with different chain lengths onto cellulose onto fibres, a surface polymer grafting and a two-step glycol cleavage-reduction approach were characterised regarding their chemical composition and thermomechanical properties. To evaluate their formability, a temperature controlled tensile test was used.
Microfibrillated cellulose (MFC) has unique properties which can lead to interesting new paper applications. Some applications strongly rely on defined pore structure, like filter paper for water purification or separator paper in batteries. The pore structure modification of a paper sheet through MFC is investigated, the combination of MFC and polyelectrolytes (PEs) enables a pore dimension reduction of an existing softwood softwood base layer. In both handsheet and pilot paper machine trials this effect was accomplished and reproducible. It was shown that MFC grammage, MFC consistency and PE type are significant factors that affect the pore dimension.
Oxfordpp 383-407Simulation of Sloshing of Condensate Water Inside a Drying Cylinder Using Particle Finite Element MethodAbstractPDF
Energy consumption is a key issue in paper making due to its high costs and for ecological reasons. In this paper, we focus on the simulation of the drying section, with a special emphasis on the heat transfer inside a steam-heated drying cylinder, accounting for the sloshing of condensate water inside the cylinder. It is known that the condensate creates a barrier reducing the efficiency of heat transfer through the cylinder surface, a shortcoming that can be overcome by the addition of turbulator bars that increase the convective heat transfer through the water layer. In this study, we simulate the fluid flow and heat transfer in the drying roll for both the water and steam phase, but for simplicity, neglect the phase change.The Particle Finite Element Method with a fixed mesh (PFEM-2) is used to compute the numerical solution. Our aim is to show the capability of this method for solving complex sloshing phenomena with adequate qualitative accuracy and computational efficiency.
Oxfordpp 409-449Quantitative Studies of Ambient Gases in Pulp and Paper Mills and Their Degradation with Photo-catalytic Oxidation Technology.AbstractPDF
In order to reduce gaseous pollution emissions and achieve the goal of cleaner production in paper industry, in this study, (I) First, the concentrations of four potential compositions of gaseous pollutants, TVOC, HCHO, H2S and CxHy, in the ambient air on 30 sampling sites in 5 pulp and paper mills were analysed. The analysed results were discussed in the following aspects: (a) the levels of four gaseous pollutants on all the sampling sites in five mills; (b) gaseous pollution differences due to different production processes; (c) gaseous pollution comparisons on the common sites. (II) Secondly, the compositions of VOCs in a secondary fiber paper mill were determined with GC-MS method. The main identified substances in the four sites were as follows: (a) waste paper sorting room: alkanes, phenols and esters; (b) paper machine hall: benzene homologues, alkanes, ethers and phenols; (c) vacuum pulp outlet: benzene homologues and phenols; (d) office area: benzene homologues and phenols. (III) Third and last, aiming a the detected formaldehyde and benzene pollutants, a photo-catalytic reactor was developed and its performance with respect to degradation was studied. The performance tests of reactor showed that both formaldehyde and benzene could be completely degraded, but the degradation time for benzene was much longer than that for formaldehyde.
Oxfordpp 451-485Prediction of Mineral Deposits in Kraft Pulp Bleaching Lines Through Chemical Process SimulationAbstractPDF
The general tendency in the pulp industry towards reduced fresh water consumption and minimum effluent causes major deposit problems in mills. Chemical pulp bleach plants are affected by several types of mineral deposits, the most frequent being calcite, calcium oxalate and barite. We present a coupled chemical process simulation of kraft pulp bleaching line, which handles chemical equilibria, together with dissolution and precipitation effects. The simulation could adequately predict formation of mineral deposits throughout a D0(EP)D1D2 bleaching line. Strategies to help reduce formation of calcium oxalate and barite scales could be evaluated. Partial substitution of sodium hydroxide by a magnesium source at extraction stage is anticipated to inhibit formation of calcium oxalate throughout the line. Also, using sulfuric acid instead of spent acid for pH regulation at D0 would reduce but not suppress barite deposits.