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Materials performance considerations in hydrothermal liquefaction conversion of biomass, TAPPI Journal June 2025

ABSTRACT: Hydrothermal liquefaction (HTL) is a promising thermochemical route developed to convert woody biomass and biowaste to biochemicals and bio-oils. However, the operating conditions are rather harsh to biorefinery structural metallic components. These conditions include alkaline catalysts such as potassium carbonate (K2CO3); hot, pressurized (sub-critical) water reaction; and medium and aggressive anions chlorine (Cl•) and hydrogen sulfide (H•) released from biomass feedstocks. Thus, selection of suitable structural alloys for biorefinery components involves striking a balance between mechanical properties, corrosion resistance, and cost. Alloys currently being considered for this application include ferritic-martensitic steels and austenitic stainless steels. From a corrosion perspective in hot pressurized water, the former typically exhibits higher stress corrosion cracking resistance, whereas the latter exhibits higher corrosion resistance. This study reviews cost-effective corrosion control strategies aimed at increasing the chromium (Cr) content for protective surface oxide formation, as screened by testing in simulated HTL alkaline water, to support materials selection and design. Corrosion control strategies include surface modification (increasing surface Cr content), alloying (increasing bulk Cr content), and stainless-steel type (ferritic vs. austenitic). Of the alloys considered (including those subjected to surface modification), ferritic stainless steels exhibit a promising balance between corrosion and stress corrosion cracking resistance, adding another family of candidate alloys for structural biorefinery component materials selection and design.

Effect of xylan on the mechanical performance of softwood kraft pulp 2D papers and 3D foams, TAPPI Journal March 2025

ABSTRACT: Pulp fibers are paramount in paper products and have lately seen emerging use in fiber foams. Xylan, an integral component in pulp fibers, is known to contribute to paper strength, but its effect on the strength of pulp fiber foams remains less explored. In this study, we investigate the role of xylan in both 2D handsheets and 3D foams. For a softwood kraft pulp, we enzymatically removed 1% from pulp fibers and added 3% xylan to them by adsorption, corresponding to approximately a decrease of a tenth and an increase of a third of the total xylan content. The mechanical properties of 2D fiber networks, i.e., handsheets, made using the xylan-enriched pulp improved, particularly regarding tensile strength and Young’s modulus; however, the decrease in mechanical properties of handsheets made from enzymatically- treated xylan-depleted pulp was more pronounced. In 3D networks • pulp fiber foams, much less fiber-fiber contacts formed, and thus the mechanical properties were not as much influenced by removal of xylan. Furthermore, the presence of the required surfactant on the fibers, acting as debonding agent, overshadows any positive effect xylan might have on fiber-fiber bonding. We propose that the improved mechanical properties for the sheets result from a combination of an increased number of fiber-fiber bonds and higher sheet density, while the deterioration in mechanical properties of handsheets comprising enzymatically-treated fibers is caused by the opposite effect.

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.

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.

MOISTURE PICKUP IN CALCIUM CARBONATE COATING STRUCTURES: role of surface and pore structure geometry, 2008 Advanced Coating Fundamentals Symposium

MOISTURE PICKUP IN CALCIUM CARBONATE COATING STRUCTURES: role of surface and pore structure geometry, 2008 Advanced Coating Fundamentals Symposium

A theoretical approach to understanding microstructure-tensile modulus relations in paper coatings , 2008 Advanced Coating Fundamentals Symposium

A theoretical approach to understanding microstructure-tensile modulus relations in paper coatings , 2008 Advanced Coating Fundamentals Symposium

Real Measurements Lead to Real Understandings and Better Operating Control of the Recovery Liquor Cycle, 2023 PEERS Conference

Setting priorities in CNF particle size measurement: What is needed vs. what is feasible, TAPPI Journal February 2023

Predictive advisory solutions for chemistry management, control, and optimization, TAPPI Journal March 2025

ABSTRACT: Process runnability and end-product quality in paper and board making are often connected to chemistry. Typically, monitoring of the chemistry status is based on a few laboratory measurements and a limited number of online specific chemistry-related measurements. Therefore, mill personnel do not have real-time transparency of the chemistry related phenomena, which can cause production instability, including deposition, higher chemical consumption, quality issues in the end-product and runnability problems. Machine learning techniques have been used to establish soft sensor models and to detect abnormalities. Furthermore, these soft sensors prove to be most useful when combined with expert-driven interpretation. This study is aimed at utilizing a hybrid solution comprising chemistry and physics models and machine learning models for stabilizing chemistry-related processes in paper and board production. The principal idea is to combine chemistry/physics models and machine learning models in a fashion close to white box modeling. A cornerstone in the approach is to formulate explanations of the findings from the models; that is, to explain in plain text what the findings mean and how operational changes can mitigate the identified risks. The approach has been demonstrated for several different applications, including deposit control in the wet end, both raw water treatment and usage, and wastewater treatment. This approach provides mill personnel with knowledge of identified phenomena and recommendations on how to stabilize chemistry-related processes. Instead of using close to black box machine learning models, a hybrid solution including chemistry/physics models can enhance the performance of artificial intelligence (AI) deployed systems. A successful way of gaining the trust from mill personnel is by creating a plain text explanation of the findings from the hybrid models. The correlation between the likelihood of a phenomena and disturbance and the explanations are derived and validated by application and chemistry and physics experts.

Energy saving potential of interstage screen fractionation for production of board grade BCTMP, TAPPI Journal August 2023

Over the last few decades, the continuing decline in mechanical pulp-based grades has led pulp producers to modify operations and implement measures to reduce production costs in order to stay competitive. In spite of a considerable effort to reduce energy consumption, the latter is still a major portion of production costs in the process of making bleached chemithermomechanical pulp (BCTMP). In this study, we evaluated the impact of interstage screening fractionation (ISSF) and secondary refining strategy for producing BCTMP with the objective of reducing refining energy consumption while maintaining or improving bulk and strength properties. In the first step and to establish a baseline for a mill’s existing configuration, the collected primary refined pulp and reject streams from the ISSF were refined in a high consistency (HC) refiner to target freeness levels. The accepts and refined rejects streams were recombined, and their properties were compared to those of the refined primary pulp. The results showed that, at a given freeness of 400 mL and compared to the control case (without fractionation), the ISSF using an 0.070 in. basket followed by rejects refining could lead to about 25% energy saving in the second stage HC refining. Handsheet properties showed that utilization of ISSF could produce BCTMP with higher bulk and similar average fiber length and tear index. However, a slight reduction in tensile strength was observed. In the second set of trials, the primary refined pulp and the rejects from the ISSF using the 0.070 in. basket were refined by a low-consistency (LC) refiner. The results showed that, at the same freeness of 400 mL and compared to refined primary pulp, the ISSF saved about 26% in net LC refining energy. At a specific edge load (SEL) of 0.4 J/m, the produced pulp had similar bulk and strength properties compared to those of the control sample. A higher SEL of 0.6 J/m in LC refining could further decrease net refining energy consumption; however, it also led to reduction in fiber length, bulk, and strength properties.