Three-Layer Model for Drying of Coating Applied on Silicone-Coated Paper

Abstract

Upon application of water based coating onto silicone-coated paper and during the subsequent drying process, the water permeates through the silicone layer into the paper substrate. At the same time, water evaporates from both the surface of the coated layer and throughout the paper layer. Initially, the evaporation rate from the wet coating surface may be dominant, but at longer times the bulk evaporation from the paper can dominate. Here a three-layer diffusion model for such a system is developed. Solutions obtained by Galerkin's method with finite element basis functions show that the hygroscopic nature of the paper leads to low drying rates at low moisture contents. Further, the model predicts that initially the coating dries to a moderately low residual moisture concentration faster than a coating applied on an impermeable substrate. However, at longer times, the predicted residual moisture of coatings applied on silicon-coated paper is higher than for a coating applied on an impermeable substrate.     

Energy Efficiency and Drying Kinetics of Recycled Paper Pulp

In this work, the influences of the air temperature and velocity on the drying kinetics of recycled paper pulp were analyzed. The increase of both variables positively influences the process, concerning the final moisture content and the drying time. However, optical microscopy and visual observation showed worse quality of the paper for drying conditions of high air temperature and velocity, presenting less uniformity and overdried surfaces. The dryer energy efficiency was evaluated by performance parameters and the results were compared with the ones obtained for other types of industrial paper dryers, presenting good agreement.     

Energy Efficiency and Drying Kinetics of Recycled Paper Pulp

In this work, the influences of the air temperature and velocity on the drying kinetics of recycled paper pulp were analyzed. The increase of both variables positively influences the process, concerning the final moisture content and the drying time. However, optical microscopy and visual observation showed worse quality of the paper for drying conditions of high air temperature and velocity, presenting less uniformity and overdried surfaces. The dryer energy efficiency was evaluated by performance parameters and the results were compared with the ones obtained for other types of industrial paper dryers, presenting good agreement.     

Enhancement of Properties of Diverse Grades of Paper by Superheated Steam Drying

Abstract:

Studies from this laboratory have documented significant changes in properties when paper is dried in superheated steam rather than, as in all current processes, in air. Extending these investigations to additional important pulp types, recycled pulps, and filled papers, and using commercial furnishes from mills, has identified further grades of paper for which drying in superheated steam enhances key properties. For bleached chemithermomechanical pulps and blends with kraft pulp, as used for tissue and toweling, strong paper resulted with 10% higher bulk. Linerboard from 100% recycled old corrugated containers (OCC) is obtained with various strength properties increased by up to 21% with no densification, actually a 4% increase in bulk. Linerboard from high-yield (55–67%) virgin kraft pulps shows a 23 to 37% increase in strength and toughness. Filled papers containing 0–10% clay can be produced with the same brightness but 23% higher tensile index when dried in superheated steam.     

Waste Heat Integration of Coating Paper Machine Drying Process

The paper sheet drying process consumes about 70% of the total energy required in coated papermaking, and almost all the thermal energy used in the process can be found in the exhaust air; thus, it has significant potential to recover the heat. With the aim of saving energy, the recovered energy is usually used to heat different process streams instead of steam.

This article examines the drying process of an operating coating paper machine to demonstrate an optimization method. To study the possibility of improving energy efficiency, thermodynamic analysis was conducted. The reasons why there is so much heat lost during drying were investigated. Based on the results of the energy and exergy analysis, a new waste heat integration scheme is presented. Furthermore, the performance of the proposed scheme has been evaluated. The results of the case study show an energy efficiency improvement of 7.3% and a specific energy consumption reduction of 4.6% with profitable investments.     

Enhancement of Drying Rate in Paper Machines with Multi-Functional Radial Jet Reattachment Blow Boxes — Theoretical Analysis

Multi-functional radial jet reattachment blow boxes deliver a dry air into the pockets of the dryer section of a paper machine by impinging directly onto the unsuppned sheet in the open diaw. The air flow also maintains or improves the sheet swbility.

The iadial jet reattachment blow box technology pmvides a significant enhancement in drying rates. The theoretical drying results are presented in terms of average drying rates, moisture and temperature pmfiles along the drying section with and without the presence of the multi-functional radial jet reaaachment blow boxes. The thcorclical results indicate that enhancements of drying rates within the range of 8% to 25% are feasible depending on ihe operating conditions and machine configuration.     

Finite Element Simulation of Drying of Longan Fruit

A two-dimensional finite element model has been developed to simulate moisture diffusion in longan fruit during drying and moisture diffusivities of the components of longan fruit determined experimentally are used in this simulation. Shrinkage of the flesh of longan during drying is also taken into account. The finite element model is programmed in Compaq Visual FORTRAN version 6.5. This finite element model satisfactorily predicts the moisture diffusion during drying. Moisture contents in the different components in the longan fruit during drying are simulated. Moisture content profiles of the longan fruit are also predicted. Knowledge gained from this study will be useful in the understanding of the transport processes in the different components of the longan fruit.     

Heat and Mass Transfer Mechanisms in Drying of a Suspension Droplet: A New Computational Model

A new computational single-droplet drying model is presented. The model considers heat and mass transfer simultaneously together with the receding evaporation front approach. A spherical droplet under constant drying conditions is considered. Computations are performed to predict the drying of colloidal silica-water suspension and skimmed milk. It is shown that the results agree well with those of experimental observations available in the literature.     

Heat and Mass Transfer Mechanisms in Drying of a Suspension Droplet: A New Computational Model

A new computational single-droplet drying model is presented. The model considers heat and mass transfer simultaneously together with the receding evaporation front approach. A spherical droplet under constant drying conditions is considered. Computations are performed to predict the drying of colloidal silica-water suspension and skimmed milk. It is shown that the results agree well with those of experimental observations available in the literature.     

Use of Superheated Steam Drying to Increase Strength and Bulk of Papers Produced from Diverse Commercial Furnishes

Studies from this laboratory have documented significant changes in properties when paper is dried in superheated steam rather than, as in all current processes, in air. Extending these investigations to additional important pulp types, to recycled pulps and to filled papers, using commercial furnishes from mills, has identified further grades of paper for which drying in superheated steam enhances key properties. For bleached chemithermomechanical pulps and blends with kraft pulp as used for tissue and toweling, strong paper resulted, with 10% higher bulk. Linerboard from 100% recycled old corrugated containers (OCC) is obtained with various strength properties increased by up to 21% with no densification, actually a 4% increase in bulk. Linerboard from high-yield (55-67%) virgin kraft pulps show 23 to 37% increase in strength and toughness. Filled papers containing 0-10% clay can be produced with the same brightness but about 23% higher tensile index when dried in superheated steam.     

紫外光固化纸张涂料的研制

研究合成了聚酯型丙烯酸聚氨酯。讨论了树脂的工艺配方、活性稀释剂、光敏剂的种类及数量对涂料性能的影响。将该涂料用于纸张、纸板、印刷品等，不仅固化速度快，而且性能完全符合要求。     

Use of Superheated Steam Drying to Increase Strength and Bulk of Papers Produced from Diverse Commercial Furnishes

ABSTRACT

Studies from this laboratory have documented significant changes in properties when paper is dried in superheated steam rather than, as in all current processes, in air. Extending these investigations to additional important pulp types, to recycled pulps and to filled papers, using commercial furnishes from mills, has identified further grades of paper for which drying in superheated steam enhances key properties. For bleached chemithermomechanical pulps and blends with kraft pulp as used for tissue and toweling, strong paper resulted, with 10% higher bulk. Linerboard from 100% recycled old corrugated containers (OCC) is obtained with various strength properties increased by up to 21% with no densification, actually a 4% increase in bulk. Linerboard from high-yield (55–67%) virgin kraft pulps show 23 to 37% increase in strength and toughness. Filled papers containing 0–10% clay can be produced with the same brightness but about 23% higher tensile index when dried in superheated steam.     

A Modular Process Modeling Tool for the Analysis of Energy Use and Cost in the Pulp and Paper Industry

A novel process modeling tool to facilitate the study of how various process changes in the paper dryer section affect the mill-wide energy system has been developed. A model library with steady-state block models describing paper dryers, heat recovery equipment, and auxiliary systems on component level have been developed using the software Extend. Process models are then created from these block models using graphical programming. In this article, the characteristics of the developed tool are described and a case study where the tool is shown to be useful for analyzing the energy performance of a hybrid dryer section is presented.     

A Modular Process Modeling Tool for the Analysis of Energy Use and Cost in the Pulp and Paper Industry

A novel process modeling tool to facilitate the study of how various process changes in the paper dryer section affect the mill-wide energy system has been developed. A model library with steady-state block models describing paper dryers, heat recovery equipment, and auxiliary systems on component level have been developed using the software Extend. Process models are then created from these block models using graphical programming. In this article, the characteristics of the developed tool are described and a case study where the tool is shown to be useful for analyzing the energy performance of a hybrid dryer section is presented.     

Shrinkage of Recycled Paper Sheet During Drying

The properties of recycled paper are strongly affected by shrinking during drying, which depends on the drying conditions. An experimental study of the shrinkage phenomenon during drying of paper is presented. Drying experiments were conducted in a drying oven with controlled temperature. The temperature influence on shrinkage extent, porosity, and apparent density of the paper was evaluated. Structural changes on the paper surface after drying were analyzed by scanning electronic microscopy. Thickness contraction, surface, and volumetric shrinkage were correlated as a function of the moisture content. Lower apparent density values and more porous paper samples were obtained for higher temperatures.     

Estimation of the Effect of Shape and Temperature on Drying Kinetics Using MLP

The kinetics of drying is described in the article using artificial neural networks (multilayer perceptron MLP). Drying curves for vegetables are possible to obtain theoretically on the basis of the equations of mass transfer in a porous material. A key role in these equations is played by the effective coefficient of water diffusion in the form of liquid, vapor or jointly as liquid and vapor. The diffusion coefficient which depends both on moisture content in the material and temperature should be determined experimentally. The drying kinetic curve in this article is treated as a time series dependent on the state of material prior to drying and on the constant K characterizing process parameters such as drying temperature and describing the material, e.g., its shape and moisture content. Constant K characterizes the analyzed material from the drying point of view because it contains a diffusion coefficient and depends on the shape of material. The following materials were analyzed: beetroot and potato dried in the form of cubes, slices, chips, and strips. Experiments were carried out in a laboratory oven dryer at process temperature 50, 60, 70, 90, and 106°C.