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Predicting strength characteristics of paper in real time using process parameters, TAPPI Journal March 2022
ABSTRACT: Online paper strength testing methods are currently unavailable, and papermakers have to wait for manufacture of a complete reel to assess quality. The current methodology is to test a very small sample of data (less than 0.005%) of the reel to confirm that the paper meets the specifications. This paper attempts to predict paper properties on a running paper machine so that papermakers can see the test values predicted in real time while changing various process parameters. This study was conducted at a recycled containerboard mill in Chicago using the multivariate analysis method. The program provided by Braincube was used to identify all parameters that affect strength characteristics. Nearly 1600 parameters were analyzed using a regression model to identify the major parameters that can help to predict sheet strength characteristics. The coefficients from the regression model were used with real-time data to predict sheet strength characteristics. Comparing the prediction with test results showed good correlation (95% in some cases). The process parameters identified related well to the papermaking process, thereby validating the model. If this method is used, it may be possible to predict various elastic moduli (E11, E12, E22, etc.) in the future as the next step, rather than the traditional single number “strength” tests used in the containerboard industry, such as ring crush test (RCT), corrugating medium test (CMT), and short-span compression strength test.
Journal articles
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Impact of different calendering strategies on barrier coating pickup, TAPPI Journal November 2023
ABSTRACT: Paper was pre-calendered in a pilot scale configuration with a traditional soft nip calender and a metal belt calender. All calendering strategies reduced surface roughness and permeability of the samples, but different strategies affected the surface roughness and permeability differently. The metal belt calender seemed to have a larger effect on the large-scale variations compared to the soft nip calender. Six test points from the pilot calendered papers were chosen for laboratory coating studies. Uncalendered paper was included as reference samples. The calendered samples and the reference were pre-coated with a regular pigmented coating consisting of a ground calcium carbonate (GCC) pigment and a styrene acrylate (SA) latex. Both uncoated and pre-coated substrates were barrier coated with a polyvinyl alcohol (PVOH) in one and two layers. The coating pickup was determined gravimetrically, and the barrier properties were evaluated with TAPPI Standard Test Method T 454 grease resistance test. All samples needed two PVOH coating layers to form a grease barrier. The uncalendered sheets showed the best results with one coating layer, but this was at the expense of a higher coating pickup compared to the calendered sheets. The barrier coating pickup could be reduced by a combination of high temperature metal belt calendering and pre-coating. The high temperature and long residence time in the nip enabled plasticization of the fibers. This led to an irreversible deformation, even after water application. This meant that the smoothness obtained during calendering would be less affected by water-induced roughening during the coating operation.
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Use of kaolin clay in aqueous barrier coating applications, TAPPI Journal November 2023
ABSTRACT: Paper-based packaging with barrier effect, as opposed to single use plastics, is gaining more prominence for sustainability reasons. At the same time, latex- or biopolymer-based aqueous barrier coating dispersions are increasingly being adopted as a better alternative to the traditional barrier coating materials, such as wax, surface active chemicals, and polyethylene. In this work, studies were performed to determine the influence of different kaolin clays in latex binder-based aqueous coatings on barrier properties, namely, oil and grease, water resistance, and water vapor transmission rate, by applying coatings to solid bleached sulfate (SBS) paperboard substrate in the laboratory. The aim was to explore potential benefits of using kaolin clay to replace some of the latex binder in coating and improve or maintain various types of barrier performance and blocking without negatively influencing the other performance attributes, including heat seal. The delaminated clay with the highest shape factor provided improved barrier properties over the clays of low shape factor. The ultrafine and non-delaminated clays required significantly higher coat weights to reach satisfactory barrier properties. Coatings with different latex levels indicated that a considerably high proportion of coarse delaminated clay can be incorporated to replace latex binder, while still achieving exceptional barrier properties. Furthermore, a change in binder system was found to significantly alter the barrier properties and the role that a mineral pigment can play. The results indicate that a proper selection of binder systems for each barrier property would be required while considering the clay/latex coating systems.
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Pulp and paper mills: The original biorefineries — past performance and limitations to future opportunities, TAPPI Journal October 2023
ABSTRACT: Pulp mills have been biorefineries since the invention of the Tomlinson recovery boiler. Unfortunately, the paper industry has done a poor job explaining that concept to the general public. A number of bioproducts in everyday use have been produced by pulp mills for several decades, and new products are routinely being developed. Modern research efforts over the last couple of decades have focused on producing even more products from pulp and paper mills through capacity enhancement and the development of value-added products and liquid transportation fuels to enhance paper mill profitability. Some of these efforts, often referred to as modern biorefineries, have focused so heavily on product development that they have ignored operating and process realities that limit the transformation of pulp and paper mills from the current limited number of bioproducts produced today to economic scale production of these value-added products. In this paper, several of these limitations are addressed. In addition, there are several supply chain, marketing, product quality, and economic realities limiting the value potential for these wholesale conversions of pulp mills into multiproduct modern biorefineries. Finally, the conservative nature and capital intensity of the pulp and paper industries provide a difficult hurdle for conversion to the modern biorefinery concept. These issues are also reviewed.
Journal articles
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Kraft recovery boiler operation with splash plate and/or beer can nozzles — a case study, TAPPI Journal Octobr 2021
ABSTRACT: In this work, we study a boiler experiencing upper furnace plugging and availability issues. To improve the situation and increase boiler availability, the liquor spray system was tuned/modified by testing different combinations of splash plate and beer can nozzles. While beer cans are typically used in smaller furnaces, in this work, we considered a furnace with a large floor area for the study. The tested cases included: 1) all splash plate nozzles (original operation), 2) all beer can nozzles, and 3) splash plate nozzles on front and back wall and beer cans nozzles on side walls. We found that operating according to Case 3 resulted in improved overall boiler operation as compared to the original condition of using splash plates only. Additionally, we carried out computational fluid dynamics (CFD) modeling of the three liquor spray cases to better understand the furnace behavior in detail for the tested cases. Model predictions show details of furnace combus-tion characteristics such as temperature, turbulence, gas flow pattern, carryover, and char bed behavior. Simulation using only the beer can nozzles resulted in a clear reduction of carryover. However, at the same time, the predicted lower furnace temperatures close to the char bed were in some locations very low, indicating unstable bed burning. Compared to the first two cases, the model predictions using a mixed setup of splash plate and beer can nozzles showed lower carryover, but without the excessive lowering of gas temperatures close to the char bed.
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Dynamic CFD modeling of calcination in a rotary lime kiln with an external dryer, TAPPI Journal August 2023
ABSTRACT: Mid-kiln ring formation is a problem in lime kilns that may be related to fluctuations in the start location of calcination. To calculate fluctuations in bed and gas temperature profiles within a lime kiln with an external dryer, a dynamic two-dimensional (2D) axisymmetric computational fluid dynamics (CFD) gas model with a methane burner implemented in ANSYS Fluent, coupled by mass and heat balances to a one-dimensional (1D) bed model, was developed. The dynamic model was used to calculate changes in the location where calcination starts with fluctuations in operational conditions using pulp mill data. This model simulates radiative, convective, and conductive heat transfer between the gas, wall, and bed to determine the axial bed temperature in the kiln. The calcination reaction is described using a shrinking core model that allows for the prediction of the location at which calcination begins and the degree of calcination achieved. The solid motion within the kiln is modeled using Kramer’s equation modified for transient response. Steady-state and dynamic simulation results were compared to data from an industrial dry lime kiln, and good agreement was found. A sensitivity analysis was also performed to provide insight on how operating conditions and model variables impact the calcination location and degree of calcination. Of the variables examined, the fuel rate and the feed temperature had the largest impact on both the calcination location and degree of calcination in the kiln. Model predictions of a period of ring formation in the industrial kiln showed that the start location of calcination fluctuated by more than 2 m on either side of the mean of regular operation, warranting further investigation of the importance of these fluctuations on mid-kiln ring formation.
Journal articles
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In-process detection of fiber cutting in low consistency ref
In-process detection of fiber cutting in low consistency refining based on measurement of forces on refiner bars, TAPPI JOURNAL April 2017
Journal articles
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Photo-catalytic degradation of gaseous pollutants in paper mills of southern China, TAPPI JOURNAL March 2018
Photo-catalytic degradation of gaseous pollutants in paper mills of southern China, TAPPI JOURNAL March 2018
Journal articles
Magazine articles
Use of vent stack temperature as a feedforward variable for dissolver total titratable alkali (TTA) control, TAPPI JOURNAL May 2018
Use of vent stack temperature as a feedforward variable for dissolver total titratable alkali (TTA) control, TAPPI JOURNAL May 2018
Journal articles
Magazine articles
Operational limits of blade coating associated with high aspect ratio pigments: Part I—bench top blade coater, TAPPI Journal February 2019
Operational limits of blade coating associated with high aspect ratio pigments: Part I—bench top blade coater, TAPPI Journal February 2019