Brownstock Washing Research Articles

Understanding the energy and emission implications of new technologies in a kraft mill: Insights from a CADSIM Plus simulation model

Kraft mills play a vital role in energy transition because they have significant potential to reduce their own energy utilization and produce energy/products to decarbonize other sectors. Through biomass combustion and potential biogenic carbon emissions capture, these mills can contribute to offsetting emissions from other sectors. This research investigates the departmental and cross-departmental implications of technology upgrades on energy, steam, emissions, water, and chemicals using a CADSIM Plus simulation model. The model provides a comprehensive analysis of mass and energy balances, offering valuable insights into the benefits and limitations of each technology. The model facilitates scenario analysis and comparisons of process configurations, enabling data-driven decision-making for sustainable and competitive operations. Six high-impact technologies, including additional evaporator effects, weak black liquor membrane concentration, belt displacement washer for brownstock washing, oxygen delignification, and improvements to the pulp machine shoe press and vacuum pumps, are evaluated. Individual technologies resulted in energy savings of 1.2% to 5.4%, biomass consumption reductions of 8.6% to 31.6%, and total emissions reductions of 1.6% to 5.9%. Strategic decision-making must consider existing mill limitations, future technology implementation, and potential production increases. Future research will explore product diversification, biorefineries, and pathways to achieve carbon-negative operations, aiming to reduce emissions and secure a competitive future for kraft mills.

Industrial Data-Driven Processing Framework Combining Process Knowledge for Improved Decision-Making—Part 2: Framework Application Considering Activity-Based Costing Concepts

Operating time series data collected and stored in historian must be managed to extract their full potential. Part 1 of this paper proposed a structured way (a sophisticated approach) to process industrial data; this first part explains in detail the data processing framework used as the basis for the costing analysis present in the second part of this series. The framework considers the analysis scope definition, data management steps, and operating regimes detection and identification. The added value of this proposed framework is demonstrated in Part 2 via the use of cost accounting for operational problem-solving (debottlenecking), i.e., its practicality is validated via its application alongside a cost analysis on the brownstock washing department of a kraft pulp mill. The traditional debottlenecking approach assumes a single operating condition considering that operating regimes allow for a much more sophisticated debottlenecking study of the washing department. With the use of operations-driven cost modeling (contingent on activity-based costing concepts) and processed time series data corresponding to steady-state operation, incremental profit can be assigned to each operating regime in order to identify the most cost-efficient one. The overall objective of this two-part series is to convert processed industrial steady-state data and cost information into knowledge that can be used to optimize the washing department of a chemical pulp mill. More specifically, different operating regimes are assessed, and the most suitable operating strategy is defined. The application of activity-based costing on a large amount of historically processed industrial data led to the improvement in the operation. The identified optimal way to operate (pulp throughput, pulp conductivity, defoamer and bleaching chemical quantity, etc.) led to a profit of CAD 49 M per year. Lastly, a contribution analysis of the regimes based on PCA highlighted how the process was operated when the preferred performances happened.

Industrial Data-Driven Processing Framework Combining Process Knowledge for Improved Decision Making—Part 1: Framework Development

Data management systems are increasingly used in industrial processes. However, data collected as part of industrial process operations, such as sensor or measurement instruments data, contain various sources of errors that can hamper process analysis and decision making. The authors propose an operating-regime-based data processing framework for industrial process decision making. The framework was designed to increase the quality and take advantage of available process data use to make informed offline strategic business operation decisions, i.e., environmental, cost and energy analysis, optimization, fault detection, debottlenecking, etc. The approach was synthesized from best practices derived from the available framework and improved upon its predecessor by putting forward the combination of process expertise and data-driven approaches. This systematic and structured approach includes the following stages: (1) scope of the analysis, (2) signal processing, (3) steady-state operating periods detection, (4) data reconciliation and (5) operating regime detection and identification. The proposed framework is applied to the brownstock washing department of a dissolving pulp mill. Over a 5-month period, the process was found to be in steady-state 32% of the time. Twenty (20) distinct operating regimes were identified. Further processing with the help of data reconciliation techniques, principal component analysis and k-means clustering showed that the main drivers explaining the operating regimes are the pulp level in tanks, its density, and the shower wash water flow rate. Additionally, it was concluded that the top four persistently problematic sensors across the steady-state spans that would need to be verified are three flow meters (06FIC137, 06FIC152, and 06FIC433), and one consistency sensor (06NIC423). This information was relayed to process experts contacts at the plant for further investigation.

Removal of Sulfide Ions from Kraft Washing Effluents by Photocatalysis with N and Fe Codoped Carbon Dots.

N and Fe codoped carbon dots (N,Fe-CDs) were fabricated from citric acid, L-glutamic acid and ferric chloride via a hydrothermal method for the photocatalytic removal of S2- from kraft washing effluents (KWE). The N,Fe-CDs were fluorescent nanoparticles (average size of 3.18 nm) and catalyzed the oxidation of S2- following a first-order kinetic model with an activation energy of 33.77 kJ/mol. The N,Fe-CDs tolerated elevated temperatures as high as 80 °C without catalyst deactivation. The N,Fe-CDs catalysts were reusable for at least four cycles, preserving over 90% of the activity. In the treatment of KWE from the kraft pulping of eucalyptus, the concentration of S2- was decreased by the N,Fe-CDs from 1.19 to 0.41 mmol/L in 6 h. Consequently, near complete remediation was obtained in 24 h. In addition, half of the chemical oxygen demand was removed after treatment with 500 mg/L of the N,Fe-CDs. In addition, the present photocatalyst was safe within a concentration of 200 mg/L, as indicated by the acetylcholinesterase inhibition test. Our findings may help develop a cleaner production process for kraft brownstock washing.

THE INFLUENCE OF PROCESS PARAMETERS ON BROWN STOCK PULP WASHING AT NATRON-HAYAT MAGLAJ

Brown stock washing is one of the major unit operations within the pulp manufacturing business. Poor operating washers have the potential to significantly and negatively affect almost every other area of a pulp and paper mill, including the mill’s environmental performance. The objective of the pulp washing is to remove the soluble impurities such as organic solids (lignin), fines, inorganic solids (Na, Mg, Ca, and K ions), and byproducts after each processing step. The present paper attempts to look at various parameters influencing pulp washing at Natron-Hayat Maglaj to ensure a complete understanding of the process. The results showed for this mixture of raw materials (15 % pine and 85 % fir) that the most influential parameters are Kappa number and dilution factor. Working with a high Kappa number above 50 requires additional equipment. Online control of the dilution factor would further improve the quality of the washing process and provide additional saving water and savings at the Evaporation plant. The First step for the future to improve the washing of unbleached kraft pulp is the optimization of the washing process through advanced control.

Addressing production bottlenecks and brownstock washer optimization via a membrane concentration system

Advancements in membrane systems indicate that they will soon be robust enough to concentrate weak black liquor. To date, the economic impact of membrane systems on brownstock washing in kraft mills has not been studied and is necessary to understand the viability of these emerging systems and their best utilization. This study investigated the savings that a membrane system can generate related to brownstock washing. We found that evaporation costs are the primary barrier for mills seeking to increase wash water usage. Without these additional evaporation costs, we showed that our hypothetical 1000 tons/day bleached and brown pulp mills can achieve annual savings of over $1.0 MM when operating at higher dilution factors and fixed pulp production rate. We then investigated the impact of increasing pulp production on mills limited by their equipment. In washer-limited mill examples, we calculated that membrane systems can reduce the annual operating cost for a 7% production increase by 91%. Similarly, in evaporator-limited mill examples, membrane systems can reduce the annual operating cost for a 7% production increase by 86%. These results indicated that membrane systems make a production increase significantly more feasible for these equipment-limited mills.

Using multistage models to evaluate how pulp washing after the first extraction stage impacts elemental chlorine-free bleach demand

Steady-state models were constructed to predict the response of a southern U.S. softwood brown¬stock to three- and five-stage elemental chlorine-free (ECF) bleach sequences. The models provided insight into how typical (EO) washing efficiencies from a vacuum drum unit affected pulp brightening and total chlorine dioxide con¬sumption. When (EO) carryover was between 15% and 30%, the chlorine dioxide needed to reach target brightness increased by 8% to 15% for the D0(EO)D1(EP)D2 sequence (89% ISO) and by 15% to 23% for the D0(EO)D1 sequence (86% ISO) versus perfect washing. Use of (EO) filtrate as D0 shower water, such as in split-flow countercurrent wash¬ing, caused the bleach uptake to increase by 1.5 to 3.0 kg chlorine dioxide (ClO2)/ton pulp when compared to using cleaner D0 shower water sources. The ClO2 consumed by 15% to 30% (EO) washer carryover is comparable to that consumed by typical carryover levels from brownstock washing (~10 kg Na2SO4/ton pulp). High (EO) carryover made ECF bleaching to higher brightness targets more difficult.

Importance of Brownstock Washing Process and Andritz Brownstock Washing Technology

Importance of Brownstock Washing Process and Andritz Brownstock Washing Technology

Fundamentals of KP Brownstock Washing and Technical Trend of Washing in Japan

洗浄に関する脱水性，吸着などの基本的事項や基本的な洗浄型式である希釈，抽出（脱水），置換，拡散について説明した後，洗浄でよく用いる用語である単位面積負荷量，希釈係数，洗浄効率，置換比率，芒硝ロス（ソーダロス）および電気電導度について解説する。さらに，釜内で行われるHi-heat洗浄，蒸解後の加圧ディヒューザー，常圧ディヒューザーおよび洗浄最終段でのプレス洗浄機あるいは回転式ドラム洗浄機などの種々の洗浄装置の特徴と変遷について紹介する。また酸素漂白前後の洗浄での黒液キャリオーバーの脱リグニン性および粘度への影響あるいは漂白段での洗浄の変遷についても述べた後，最後に洗浄段から漂白あるいは抄紙工程に黒液がキャリオーバーした場合の環境への影響についても言及する。

Understanding conductivity and soda loss

For more than 40 years, conductivity has been the inline measurement of choice for inferring black liquor/soda losses from brownstock washing. If properly applied, conductivity can provide a benefit in tracking changes in black liquor filtrate concentration. The implied concentration changes in turn can be used to provide feedback for dilution factor or shower flow control on the last stage of a brownstock washing system. A further extrapolation of this application is the correlation (or lack of correlation) of conductivity to soda loss. For each type of conductivity-based application, there are fundamental principles and assumptions that must be understood and managed to achieve the expected outcomes. The fundamentals of conductivity, the application of conductivity to measure black liquor losses during brownstock washing, and laboratory considerations when attempting to correlate inline process conductivity to absolute sodium content are reviewed and investigated. Finally, the operational objectives and measurement alternatives for employing conductivity measurements are discussed.

Determining wash loss levels in the brownstock pulp washing line using different methods

The purpose of brownstock pulp washing is to recover the maximum amount of dissolved inorganic and organic material using a minimal amount of water. Brownstock washing is a notable subprocess in chemical pulping because it has effects on the subsequent treatments of the pulp and is also the first step in the chemical recovery cycle. Without effective washing, the economic viability of chemical pulp production is affected. The performance of washing can be described in two main ways: using wash loss, which describes the amount of washable compounds in the pulp suspension that could have been removed in washing; or the dilution factor, which represents the net amount of water that is added during washing. The amount of sodium in the pulp suspension after washing has typically been used as an indicator of wash loss, usually expressed as kg sodium sulfate/ovendry ton of washed pulp. Other common measurement methods are conductivity, chemical oxygen demand (COD), total organic carbon (TOC), dissolved dry solids (DDS), and lignin concentration. Scandinavian pulp mill softwood and hardwood fiber lines were investigated using various measurement methods in the pulp phases to gain better understanding of wash loss. The concentration of DDS in the streams was measured using a refractometer and laboratory scale. The pH, conductivity, lignin content, TOC, and COD were measured to look for any correlations. Using different methods, the level differences remain constant, but it is difficult to control the washing process with sufficient precision using individual measurements. The measurement methods must also be continuous and reliable to be used to monitor and control washing.

Commissioning brownstock washing controls for an evaporator limited mill

An automated shower water control system has been implemented to reduce the volume and variability of weak black liquor being sent from the pulp mill to the evaporators. The washing controls attempt to balance the need for consistent and low soda carryover to the bleach plant with consistently high weak black liquor solids being sent to the evaporators. The washer controls were implemented on two bleachable grade hardwood lines (one with oxygen delignification, one without oxygen delignification) and one pine line. Implementation of the control program resulted in an increase in black liquor solids of 0.6 percentage points for the hardwood lines. Significant foam reduction was realized on the pine line since the pine black liquor solids were able to be consistently maintained just below the soap separation point. Low black liquor solids excursions to the evaporators were eliminated. Bleach plant carryover was stabilized and no negative impact on chemical consumption was noticed when controlling weak black liquor solids to recovery.

Optimization of a brownstock washing line

The objective of this study was to improve the efficiency of a certain Scandinavian chemical pulp mill’s brownstock washing line. The information was collected by using online devices (a refractometer and a conductivity meter), and the whole line was controlled by an upper level control system. The results indicate that it is possible to reduce the amount of brownstock washing loss by controlling the dilution factor (DF) of the entire brownstock washing line, via the use of torque control of washers and real time wash loss measurements. Simultaneously, the amount of used wash water is decreased, thus significantly improving the economic efficiency of the fiber line, especially in the evaporation and bleaching plant. Real time dissolved dry solids (DDS) measurements proved useful for controlling and monitoring the wash loss and water consumption.

Synthesis of Resource Conservation Networks in an Integrated Pulp and Paper Biorefinery

Pulp and paper production consumes a large amount of water and steam. In particular, water is used in brown stock washing system (BSWS) to separate spent white liquor from the pulp stream. The wastewater stream generated from BSWS, known as black liquor, is a potential biomass. In the current practice, black liquor is concentrated and burned in a recovery boiler to produce steam and electricity. However, recent development in an integrated biorefinery offers increased marketability in pulp and paper mills through the generation of both bioproducts and bioenergy. It is common practice for steam generated from the combustion of black liquor to be integrated with pulp and paper mill to satisfy its heating demands. Note that the water consumption in BSWS directly affects the quantity and quality of black liquor. This will later affect the potential for steam generation and integration in pulp and paper mill. Thus, in this work, water and heat integration is performed for a pulp and paper mill with biorefinery. An integrated pulp and paper biorefinery (IPPB) is proposed which accounts for different conversion pathways of pulp and paper mill biomass. Apart from combustion, several gasification pathways are considered. A nonlinear program (NLP) is formulated to synthesize an optimum IPPB with maximum resources conservation. Sensitivity analysis is then carried out based on the most significant parameters to analyze the robustness of the proposed IPPB.

Brownstock washing fundamentals: Enhancing drainage through chemistry — Part 2

The drainage of filtrates during mat formation in a brownstock washer directly impacts the washer’s productivity and indirectly affects its efficiency. In this paper, the role of entrained air on filtration through a formed mat during displacement as it occurs in brownstock washing was investigated. It was shown how chemical treatments, such as wash aids and fiber surface chemistry, influence air entrainment and, thereby, washer productivity and efficiency. By minimizing air entrained within a formed mat, displacement filtration rates and wash ratios were shown to improve. With this knowledge, washer operations can be improved through the design and selection of better treatments.

Brownstock washing: A review of the literature

Brownstock washing is a complex, dynamic process in which dirty wash water or weak black liquor (dissolved organic and inorganic material obtained from the pulp cooking process) is separated from pulp fibers. The use of material balance techniques is of great importance to identify potential problems and determine how well the system is operating. The kraft pulping industry was the first known to combine pulp washing with the recovery of materials used and produced in the wood cooking process. The motivation behind materials recovery is economic, and more recently, environmentally driven. The chemicals used in the kraft process are expensive as compared to those used in the sulfite process. For the kraft process to be economically viable, it is imperative that a very high percentage of the cooking chemicals be recovered. To reach such high efficiency, a variety of washing systems and monitoring parameters have been developed. Antifoam additives and processing aids have also played an important role in increasing washing effectiveness. Antifoam materials help attain washing effectiveness by preventing entrapped air from forming in the system, which allows for an easier, unimpeded flow of filtrate through the screens and washers.

Brownstock washing fundamentals: enhancing drainage through chemistry: Part 1

Filtrate drainage during mat formation in a brownstock washer directly affects the washer’s productivity and indirectly affects its efficiency. In this paper, we demonstrate the role of entrained air on mat formation and filtration as they occur in brownstock washing. We further show how chemical treatments, such as defoamers and wash aids, and fiber surface chemistry influence air entrainment and thereby washer productivity and efficiency.

A model-based approach for simultaneous water and energy reduction in a pulp and paper mill

Pulp and paper mills receive much attention from environmentalist and authority due to their impact on natural resources, particularly in water and energy consumption. Many research works have been reported for water and energy savings for the pulp and paper mill. However, none of them were targeted at the brown stock washing system (BSWS), where significant water and energy are consumed to perform pulp cleaning and black liquor concentration. This paper presents an optimization model aiming for simultaneous water and energy saving for BSWS in the pulp and paper mills. A mixed integer non-linear programming (MINLP) model has been developed to optimize the water network design. The synthesized water network results in significant reduction in energy and water consumption. Sensitivity analysis is performed to analyse the relationship between washing efficiency and utilities (water and energy) consumption.

Optimization of wash water usage in brown stock washing

Optimum wash water usage level, at which washing losses are satisfactory, was determined by using 12 separate real-time refractometer measurements and advanced process data analysis tools. Refractometers measure total dissolved solids with high reliability. We analyzed the results with the WEDGE trademarked software tool to calculate various parameters of washing performance. All tests were performed on a mill-scale brown stock washing operation at a Finnish pulp mill. Total dissolved solids changes in the incoming flows (liquid and pulp suspension) to the washer were detected immediately and reliably by using refractometer measurements. The changes also had a clear effect on washing loss in the brown stock line’s oxygen delignification performance. Real-time measurement enabled high-level control of the washing line, instant information made it possible to control the amount of fresh water to the washer, and proper control of such a system optimized water usage.

The chemical versus energy cost tug of war: A pulp mill perspective

As the cost of energy and processing chemicals changes, the optimal, lowest cost operating conditions within a pulp mill also change. Additionally, the optimal cost operating point within one area of the mill may not result in a total mill low cost operation. Three practical pulp mill examples have been analyzed under varying cost constraints for energy and chemicals to determine the impact of energy and chemical cost changes on the low cost operating point. These examples include changing the digester kappa number target, changing the brownstock washing dilution factor, and the conversion of a continuous digester from one type of cooking process to a lower energy cooking process. Selected mill operating results and laboratory data were employed to tune various process simulation models to obtain cost predictions over a wide range of operating conditions.