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Saving Money in Wastewater Treatment, Paper360º March/April 2024

Summaries from TAPPI Journal, Paper360º May/June 2024

In-situ green synthesis and adsorption on methylene blue of copper-based metal organic framework/cellulose/chitosan (CCTSA/HKUST-1) composite aerogel, TAPPI Journal October 2024

ABSTRACT: In order to explore the application of metal-organic frameworks (MOFs) in environmental and water treatment fields, a new composite aerogel of HKUST-1/cellulose/chitosan (CCTSA/HKUST-1) with better hydrostability was synthesized by an in-situ synthesis method combining covalent cross-linking and solvothermal methods as an efficient adsorbent for methylene blue (MB). The composite aerogel (CCTSA) obtained by covalent cross-linking of cellulose (CE) and chitosan (CTS) exhibited excellent stability under strong acid and solvent-thermal conditions. With the increase of CTS content, it was beneficial to the in-situ synthesis of HKUST-1, as well as to increase the mass loading rate of HKUST-1 to 37.06%, while the Brunauer-Emmett-Teller (BET) specific surface area of CCTSA/HKUST-1 composite aerogel reached 945.123 m2·g-1, which was much higher than that of the CCTSA composite aerogel (14.489 m2·g-1). The CCTSA/ HKUST-1 composite aerogel exhibited excellent adsorption capacity (537.6 mg·g-1) on MB solution, and cyclic adsorption could be achieved. This study proposes a concept of valorization of alkaline peroxide mechanical pulping (APMP) waste liquor to hemicellulose-based hydrogel. This hemicellulose-based hydrogel exhibits a sensitive temperature/pH dual response. Hemicellulose-based hydrogels swell or shrink through the change of hydrogen bond/electrostatic repulsion/charge screening. They also show good water absorption and water retention properties.

CFD and predictive modeling of temperature and calcination in a rotary lime kiln • Potential for steadier kiln operation, TAPPI Journal October 2024

ABSTRACT: Rotary lime kilns are used in the pulp and paper industry to calcine lime mud to lime. Lime kiln models provide a means to understand the complex phenomena occurring within the kiln to aid in problem-solving during operation. A two-dimensional (2D) computational fluid dynamics (CFD) and one-dimensional (1D) bed model was previously developed for steady-state and transient analysis. This study explores data extracted from the model over a longer time period. The simulated outlet gas and shell temperature are compared to measured data for validation. The capability of using the model to estimate the production rate, accounting for the residence time within the kiln, is discussed. The maximum refractory wall temperature is analyzed during operation. Fluctuations in the calcination location are compared to outer shell heat-map data to correlate the calcination location and ring formation and growth. The model results to date indicate that fluctuations in the calcination zone may contribute to problematic ring growth, though a direct correlation has yet to be established. Additionally, a method for steadier kiln control is introduced and discussed. A machine learning model is also developed to predict the calcination start location from industrial data and is compared to the CFD model for validation. This model can generate results quickly and without the need for knowledge in CFD software and theory. Good agreement is found between the CFD and machine learning model during operation, with a mean absolute error (MAE) of 0.46 m, a mean absolute percentage error (MAPE) of 0.92%, and a root mean square error (RMSE) of 1.17 m.

Biofuels in lime kilns • Operating experience in the Nordic pulp and paper industry, TAPPI Journal October 2024

ABSTRACT: The lime reburning process is a central part of the chemical pulp mill. It is energy intensive and consumes large amounts of fossil fuel, globally consuming about 50 terawatt-hours (TWh) of fuel per year. Conversion to operation with biofuel is interesting, both to reduce carbon dioxide emissions and to reduce costs. Researchers interviewed managers in mills that use solid, liquid, or gasified biofuels to replace fuel oil or natural gas in their lime kilns, and they conducted surveys related to fuel consumption and operations and maintenance. In Sweden and Finland, there were ten mills in 2020 using biomass powder or gasified biomass as the primary fuel, and two more installations were under construction. There were also nine installations in operation or under construction outside the Nordic countries. Fourteen mills in Sweden and two mills in Finland used tall oil pitch as the main fuel. Fuel consumption in Swedish lime kilns was 3.8 TWh in 2020, and 90% of this energy was supplied with biofuels. Of about 4.2 TWh used in Finnish lime kilns, approximately 45% was supplied with biofuels. Developments in the design of the fuel supply system include belt dryers being used in all new installations and mass flow metered dosing systems being used in most new pulverized fuel installations. Bark gasifiers have increased considerably in size. Lignin powder firing has been established as a proven option. A solution for many Swedish and Finnish mills is the use of tall oil pitch as a replacement for fuel oil.

Model development for real oxygen delignification processes, TAPPI Journal October 2024

ABSTRACT: Previous extensive work has been done on modeling the oxygen delignification process, based on how the basic parameters, i.e., temperature, kappa number, concentration of alkali, and concentration of oxygen, affect the delignification rate. However, these models are not used extensively to evaluate the performance of real processes, primarily because they have not been able to properly consider all the essential issues affecting delignification in practice. Such issues include the mass transfer and consumption of oxygen, which defines the concentration of dissolved oxygen in the process, and the effect of that concentration on the delignification rate. In this paper, a new way to model the oxygen delignification process is used in which these parameters, among other smaller matters, are taken into account. The basic model and its parameters were defined by the information obtained from the literature, delignification made in the laboratory tests, and mill processes and mill tests. An essential aspect of these studies was the information obtained from the oxygen concentration measured in the residual gas obtained from the top of the reactor. With the aid of this measurement, it was possible to define more accurately the consumption of oxygen and partial pressure of oxygen that define the concentration of dissolved oxygen in the reactor. Using mill experiments, a model was formed that predicts the operation of the oxygen delignification process. The model was used to show how much the process could be improved by optimizing the charge of the oxygen. The mill experiments also confirmed that mass transfer of oxygen is modeled correctly enough, except when the charge of oxygen is very low and/or the mixing is not efficient enough. In that case, there is variation in the concentration of oxygen in the process that should be taken into account in the modeling.

Pixelle Mill in Jay, ME, Jay, ME, Paper360º September/October 2024

Assessing lignin content in Nordic hardwood and softwood species using models based on near-infrared (NIR) spectral data and partial least squares regression (PLSR), TAPPI Journal September 2025

ABSTRACT: Continuous kraft cooking digesters face challenges affecting product quality, making it valuable to improve control through advanced techniques like near-infrared (NIR) spectroscopy, model predictive control, and machine learning models. The primary goal of this study was to use NIR spectra to predict the amount of lignin in hardwood and softwood samples. This study investigated the correlation of NIR derivative spectra with the amounts of lignin relative to other constituents, namely cellulose, hemicellulose, and water, in wood chip samples of varying chip sizes and shapes from six Nordic wood species. It employed partial least squares regression (PLSR) on the NIR data to construct a model that predicted the lignin fraction and the relative fraction of acid-soluble lignin. When trained on a group of five wood species, the model achieved a satisfactory predictive ability, striking a balance between a wide range of lignin content and a consistent chemical environment. The accuracy increased further when the model was restricted only to spruce and pine, reflecting the benefits of a more homogenous dataset. Additionally, the optimal number of latent variables was identified as two, indicating that three distinct chemical components — cellulose, lignin and water — can be effectively differentiated using NIR.

Optimization of energy efficiency and condensate production in evaporation plants for a modern softwood pulp mill, TAPPI Journal April 2026

ABSTRACT: To meet the need to further improve thermal efficiency and environmental performance of kraft pulp mills, new systems and techniques have been developed within the evaporation plant. This paper describes these novel approaches and how they were implemented in a project completed in 2018 for a new evaporator and condensate treatment system supplied by Valmet at the SCA Östrand market pulp mill in Sweden. This project was part of a stepwise upgrade of the complete mill to increase the production capacity of the mill from 430,000 to 900,000 air-dried metric tons/year (ADt/y). As part of this upgrade, the mill had the objectives to increase the energy efficiency of the pulp mill and to minimize the air emissions as much as possible, the effluent volume, and the water usage in the mill. The mill also wanted to have the disposal of the biosludge in the black liquor, and the production of tall oil from black liquor soap, liquid methanol, and turpentine. This required that the new evaporation and condensate treatment system be very closely integrated into the other process departments of the mill, including integration of the hot weak black liquor flash vapor from the digester directly into the evaporator train and the production of multiple streams of clean evaporation plant condensate at the correct temperature for the bleach plant. Heat and mass balance calculation values, which were found to do very well in predicting the effect on actual mill operation, are also presented in this paper.

Utilization of inline total dissolved solids measurement system in a pulp mill's brownstock washing line, TAPPI Journal January 2026

ABSTRACT: Efficient washing improves the recovery of sodium (Na) and sulfur (S) cooking chemicals, as well as wood-based dissolved organic material. It also reduces the additional consumption of chemicals in the subsequent bleaching stages. The operation of the brownstock washing of the pulp mill’s fiber line has a significant impact on the mill’s energy economy, material efficiency, and environmental emissions. Process refractometers can be used to measure the total dissolved solids (TDS) from both the washing liquor and the pulp suspension filtrate part directly from pipelines or pipe bypass loops. In addition, by measuring the three or four incoming/outgoing dissolved solids streams to the washers, together with consistencies and flow rate measurements, it is possible to build the real-time effectiveness calculation of the washer(s). In this work, an online efficiency calculation based on TDS measurements was built for a pressure filter after cooking and oxygen (O2) delignification. The washing performance was monitored over a longer period, and stepwise tests were conducted to find the optimal operating mode. The feed and washing consistencies, the washer’s torque, and the washing liquid distributions varied, and the washer’s efficiency values were monitored using realtime measurements. From the long-term trends of the efficiency calculation, process disturbances could be detected, and their causes could be found. Based on the results of the stepwise tests, an optimal operating model for the washer was found. By optimizing the washing consistency, the Y10 washing yield could be increased. More efficient washing with the same or even a smaller amount of washing liquid can relieve the operation of the evaporator, which is often a bottleneck in the mill. The study also found the effect of cooking-related carryover on the operation of the oxygen stage, as well as differences in the washability of softwood and hardwood.