Thermomechanical Pulp Research Articles

Characterisation of hardwood fibres used for wood fibre insulation boards (WFIB)

Wood fibre insulation boards (WFIB) are typically made from softwood fibres. However, due to the rapid decrease in softwood stands in Germany, the industry will be forced to adapt to the wood market. Therefore, alternative approaches for the substitution of softwood with hardwood will be needed in the fibre industry. The objective of this paper is to address the characterisation of hardwood fibres regarding their availability for the WFIB industry. The physico-mechanical properties of WFIB are significantly determined by the length of the fibres. Longer softwood fibres usually generate higher strength properties and a lower thermal conductivity than shorter hardwood fibres. In this paper, the potential application of hardwood fibres (up to 20,500 μm long) produced in a refiner by thermo-mechanical pulping (TMP) to WFIB production was examined. The scanner-based system FibreShape was used for the automatic optical analysis of the geodesic length distribution of fibres. The analysed hardwood fibres contained significantly more dust and were shorter than respectively produced softwood fibres, limiting their applicability for WFIB production. Thus, two analytical approaches were chosen to receive longer fibres and less dust: (1) blending hardwood fibres with supporting softwood fibres (20%, 50 and 80% proportion of softwood), and (2) mathematical fractionation of hardwood fibres based on the fibre length to remove all particles smaller than 500 μm. It was concluded that the practical fractionation seems to be economically and ecologically challenging and that blending hardwood fibres with at least 50% softwood fibres offers a promising approach, which should be further studied.

Energy Efficiency Analysis of the Refining Unit in Thermo-Mechanical Pulp Mill

A refining model is developed to analyses the refining process’s energy efficiency based on the refining variables. A simulation model is obtained for longer-term refining energy analysis by further developing the MATLAB Thermo-Mechanical Pulping Simulink toolbox. This model is utilized to predict two essential variables for refining energy efficiency calculation: refining motor-load and generated steam. The conventional variable for presenting refining energy efficiency is refining specific energy consumption (RSEC), which is the ratio of the refining motor load to throughput and does not consider the share of recovered energy from the refining produced steam. In this study, a new variable, corrected refining specific energy consumption (CRSEC), is introduced and practiced for better representation of the refining energy efficiency. In the calculation process of the CRSEC, recovered energy from the refining generated steam is considered useful energy. The developed model results in 160% and 78.75% improvement in simulation model determination coefficient and error, respectively. Utilizing the developed model and hourly district heating demand for CRSEC calculation, results prove a 22% annual average difference between CRSEC and RSEC. Findings confirm that the wintertime refining energy efficiency is 27% higher due to higher recovered energy in the heat recovery unit compared to summertime.

Effect of Pretreatments on the Enzymatic Hydrolysis of High-Yield Bamboo Chemo-Mechanical Pulp by Changing the Surface Lignin Content.

Hydrogen peroxide chemo-mechanical pulp (APMP), sulfonated chemo-mechanical pulp (SCMP), and chemical thermomechanical pulp (CTMP) were used as raw materials to explore the effects of hydrogen peroxide (HP), Fenton pretreatment (FP), and ethanol pretreatment (EP) on the enzymatic hydrolysis of high-yield bamboo mechanical pulp (HBMP). The surface lignin distribution and contents of different HBMPs were determined using confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS). The correlation between the surface lignin and the enzymatic hydrolysis of HBMP was also investigated. The residue of enzymatic hydrolysis was used to adsorb methylene blue (MB). The results showed that the cracks and fine fibers on the surface of APMP, SCMP, and CTMP increased after FP, when compared to HP and EP. The total removal content of hemicellulose and lignin in SCMP after FP was higher than with HP and EP. Compared to SCMP, the crystallinity increased by 15.4%, and the surface lignin content of Fenton-pretreated SCMP decreased by 11.7%. The enzymatic hydrolysis efficiency of HBMP after FP was higher than with HP and EP. The highest enzymatic hydrolysis of Fenton-pretreated SCMP was 49.5%, which was higher than the enzymatic hydrolysis of Fenton-pretreated APMP and CTMP. The removal rate of MB reached 94.7% after the adsorption of the enzymatic hydrolysis residue of SCMP. This work provides an effective approach for a high value-added utilization of high-yield bamboo pulp.

Online Pre-Treatment of Thermomechanical Pulp with Emulsified Maleated Polypropylene for Processing of Extruded Thermoplastic Composites

The effectiveness of maleated polypropylene (MAPP) in emulsified form for the pre-treatment of thermo-mechanical pulp (TMP) before extrusion with polypropylene fibres was evaluated. MAPP in pellet form, which was applied during the compounding step, served as a benchmark. In addition, commercial softwood flour was included as a reference. The influence of the temperature during the defibration process and the presence or absence of the coupling agent on composite performance were evaluated. Composites were processed with a high wood content of 70 wt.%, which is common for extruded profiles. It was found that TMP based on Robinia (Robinia pseudoacacia L.) conferred higher strength properties to the composites compared to TMP based on Scots pine (Pinus sylvestris L.), which was attributed to the higher length/diameter ratio of fibres in Robinia. However, under the conditions of this study, strength properties were superior and water uptake and swelling were reduced when wood flour was used instead of TMP. On the other hand, in many formulations, larger improvements in flexural and tensile strength due to MAPP were found for the TMP-based composites compared to the wood flour-based composites. This could be due to the larger surface/volume ratio for TMP compared to wood flour and more efficient stress transfer from fibres to the matrix. Results from X-ray photoelectron spectroscopy (XPS) showed that TMP surfaces were more hydrophobic than wood flour due to coverage with lignin, which reduced the effectiveness of MAPP. Esterification between the emulsified MAPP and fibre surfaces was determined using Fourier-Transform Infrared (FTIR) spectroscopy, but some non-activated maleic anhydride remained. Under the conditions of this study, MAPP added during compounding provided better performance compared to MAPP which included a non-ionic emulsifier and which was added during the refining process. Lower temperature (150 °C) during defibration was shown to be beneficial for the strength properties of composites compared to high temperature (180 °C) when MAPP was included in the formulations.

Mass-production of high-yield and high-strength thermomechanical pulp fibers from plant residues enabled by ozone pretreatment

Thermomechanical pulp (TMP) has great potential in packaging paper production. However, the lack of raw materials and relatively low physical performance of TMP due to the high lignin content limit its large-scale application. In this study, we use thermomechanical pulping of plant residues combined with ozone treatment to cut costs and improve the physical performance of TMP. During TMP pulping, the effects of the ozone on the structure and physical properties of fibers were investigated. Changing the ozone dosage showed a distinct effect on the surface lignin content and morphology of fibers. In the oxidation process, the structure of lignin was damaged and the physical properties were improved significantly. Moreover, it also proved the feasibility of the mass production of this approach. The fibers of this type have a great future as complementary raw material to recycled fibers to produce packaging paper in applications of paper products of higher quality.

Monitoring fibrillation in the mechanical production of lignocellulosic micro/nanofibers from bleached spruce thermomechanical pulp

The present work aims at assessing the main characteristics of lignocellulosic micro/nanofibers (LCMNF) from bleached thermomechanical pulp (BTMP) from spruce while glimpsing the suitability of cationic demand (CD) as effective monitoring parameter of the fibrillation process. For this, BTMP was mechanically refined at different times in a Valley beater, aiming at determining the required refining time and fiber length to be later fibrillated in a high-pressure homogenizer. It was found that 150 min treatment is required to avoid clogging in the pressure chambers of the homogenizer. The mechanically treated BTMP was gradually passed through a high-pressure homogenizer, leading to four LCMNF with different fibrillation degree. The main characteristics of the LCMNF were determined, as well as the effect that high-pressure homogenization may generate onto the LCMNF structure. It was observed that CD is a robust parameter to monitor the fibrillation process, as it is a good indicator of the LCMNF characteristics. In addition, it was found that WRV may not be a good indicator of the extent of fibrillation for LCMNF, as the lignin content varies with the homogenization intensity. Finally, the limitations of CD as monitoring parameter and perspectives on this regard are provided to the reader.

Fault classification in the process industry using polygon generation and deep learning

This paper proposes a novel data preprocessing method that converts numeric data into representative graphs (polygons) expressing all of the relationships between data variables in a systematic way based on Hamiltonian cycles. The advantage of the proposed method is that it has an embedded feature extraction capability in which each generated polygon depicts a class-specific representation in the data, thereby supporting accurate “end-to-end learning” in industrial fault classification applications. Moreover, the generated polygons can play a significant role in the interpretation of trained deep learning fault classifiers. The performance of the proposed method was demonstrated using a benchmark dataset in the process industry. It was also tested successfully to classify challenging faults in major equipment in a thermomechanical pulp mill located in Canada. The results of the proposed method show better performance than other comparable fault classifiers.

Coagulation Efficiency of Biomass Fly Ash Leachate in Thermomechanical Pulping (TMP) Pressate

In this study, the coagulation performance of a biomass-based fly ash leachate (FLC) and alum on a thermomechanical pulping (TMP) pressate was compared systematically. Fly ash leachate (FLC) was first produced via mixing fly ash with water and extracting the soluble part of fly ash. Then, the coagulation performance of FLC in TMP pressate was studied and compared with that of alum, as a benchmark. The effects of the dosage of the coagulant and treatment time on the chord length of particles in the TMP pressate as well as the chemical oxygen demand (COD) and lignin content of the TMP pressate were systematically monitored. It was observed that FLC and alum coagulated the dissolved materials of the TMP pressate. The COD and lignin removals were 18.4% and 26.9%, respectively, when FLC was added to a TMP pressate under the conditions of 5060 mg/kg FLC/TMP pressate, 200 rpm, pH 12.5 298 K and 30 min. Calcium ions of FLC were the main contributor to the coagulation performance of FLC for TMP pressate. The chord length analysis of solution revealed that the particles in the 1–10 and 10–50 µm ranges were rapidly coagulated, forming larger aggregates in the 50–150 and 150–300 µm size ranges and reaching the maximum mean chord length within approximately 4 min when the coagulant was an alum. FLC led to the slower conversion of particles in 1–10 µm range and a faster conversion in the 10–50 and 50–150 µm ranges than alum did. As FLC can be readily produced inexpensively onsite, it could be a suitable coagulant for eliminating the dissolved components of the pulp and paper effluents.

Energy simulation and variable analysis of refining process in thermo-mechanical pulp mill using machine learning approach

ABSTRACT Data from two thermo-mechanical pulp mills are collected to simulate the refining process using deep learning. A multilayer perceptron neural network is utilized for pattern recognition of the refining variables. Results show the impressive capability of artificial intelligence methods in refining energy simulation so that the correlation coefficient of 98% is accessible. A comprehensive parametric study has been made to investigate the effect of refining disturbance variables, plate gap and dilution water on refining energy simulation. The generated model reveals the non-linear hidden pattern between refining variables, which can be used for optimal refining control strategy. Considering the disturbance variables’ effect in refining energy simulation, model accuracy could increase by 15%. Removing the plate gape from predictive variables reduces the simulation determination coefficient by up to 25% in both mills, while the mentioned value for removing dilution water is 9–17% in mill 1 and about 35% in mill 2.

Selective addition of C-PVAm to improve dry strength of TMP mixed tissue paper

Abstract During the manufacture of low basis weight tissue paper, it is difficult to efficiently use the dry strength agent (DSA) because a large amount of DSA adsorbed fines releases in forming roll by centrifugal forces. In this study, cationic polyvinylamine (C-PVAm) was used as a DSA in an environment where the retention of fines was weak. Addition of C-PVAm to the thermomechanical pulp (TMP) or TMP mixed with softwood bleached kraft pulp (SwBKP) improved the turbidity of filtrate from sheet former, however, the strength of handsheet paper was similar to that without C-PVAm. When C-PVAm was selectively added to SwBKP as much as 4 %, the tensile index could be improved by approximately 10.6 % without changing the retention of fines. In addition, C-PVAm added before the beating of SwBKP showed better results than C-PVAm added after the beating in terms of fines retention, tensile index, and formation. In particular, the tensile index was improved about 7.7 % by adding of C-PVAm 4 % as is before beating of SwBKP. Consequently, it was found that C-PVAm with a high reaction rate can be added before beating of SwBKP to improve the physical strength.

Development of antifouling ultrafiltration PES membranes for concentration of hemicellulose

AbstractA new approach for one‐stage facile membrane modification during non‐solvent induced phase separation (NIPS)‐process is proposed. The novelty of this study is that cheap and commercially available anionic high molecular polyacrylamide‐based flocculant (AHMPF) is applied for the first time as an additive to coagulation bath (CB). The series of polyethersulfone membranes were prepared using 0.05–0.3 wt% AHMPF aqueous solution as CB at different temperatures (25–50°C) via NIPS. The effect of AHMPF concentration on the structure, composition and hydrophilicity of membranes was investigated. The separation and antifouling performance were evaluated during filtration of bovine serum albumin (BSA) solution and thermomechanical pulp mills process water (ThMP) in order to concentrate hemicellulose. The successful immobilization of AHMPF into the structure of membranes selective layer (not bottom layer) was confirmed by FTIR spectroscopy. It was established that despite the similar rejection of hemicellulose (88.8–93%) and lignin (20–21.4), modified membranes demonstrate 3–8 times higher flux and 2 times higher FRR (43.8% for reference membrane and 86.5% for modified one) in ThMP ultrafiltration. The developed membrane was found to be highly efficient in hemicellulose concentration and purification in pulp industry.

Methane potentials and organic matter characterization of wood fibres from pulp and paper mills: The influence of raw material, pulping process and bleaching technique

During the process of pulp- and papermaking, large volumes of fibre-rich primary sludge are generated. Anaerobic digestion of primary sludge offers a substantial potential for methane production as an alternative approach to the inefficient energy recoveries by commonly used incineration techniques. However, a systematic study of the importance of upstream process techniques for the methane potential of pulp fibres is lacking. Therefore, biochemical methane potentials were determined at mesophilic conditions for 20 types of fibres processed by a variety of pulping and bleaching techniques and from different raw materials. This included fibres from kraft, sulphite, semi-chemical, chemical thermo-mechanical (CTMP) and thermo-mechanical pulping plants and milled raw wood. The pulping technique was clearly important for the methane potential, with the highest potential achieved for kraft and sulphite fibres (390–400 Nml CH4 g VS−1). For raw wood and CTMP, hardwood fibres gave substantially more methane than the corresponding softwood fibres (240 compared to 50 Nml CH4 g VS−1 and 300 compared to 160 Nml CH4 g VS−1, respectively). Nuclear magnetic resonance characterization of the organic content demonstrated that the relative lignin content of the fibres was an important factor for methane production, and that an observed positive effect of bleaching on the methane potential of softwood CTMP fibres was likely related to a higher degree of deacetylation and improved accessibility of the hemicellulose. In conclusion, fibres from kraft and sulphite pulping are promising substrates for methane production irrespective of raw material or bleaching, as well as fibres from CTMP pulping of hardwood.

A case study on the treatment and recycling of the effluent generated from a thermo-mechanical pulp mill in Brazil after the installation of a new bleaching process

A Brazilian thermo-mechanical pulp mill (TMP) was evaluating the installation of a proposed bleaching process, with changes in the qualitative and quantitative characteristics of the wastewaters and the Effluent Treatment Plant (ETP). The objectives of this research were to evaluate the treatment plant configuration for the future industrial effluent, consisting of a flotation unit followed by an upflow anaerobic sludge blanket reactor (UASB), an activated sludge process and nanofiltration (NF) using polymeric membranes, and to study the technical feasibility of recycling the treated effluents in the industrial process. The possible options for recycling the treated effluent were determined through a water balance of the mill. The pulp quality was evaluated in laboratory bleaching assays, based on brightness and brightness reversion tests after the recycling of 50%, 75% and 100% of the treated effluent. The buildup of the non-process elements (NPE) in the industrial water cycle after each effluent recycling proportion was evaluated through computer simulation, using the Aspen Plus® simulator software. The future mill effluent, considering the implementation of a proposed bleaching stage with hydrogen peroxide, was generated in the laboratory and treated in a bench-scale effluent plant, simulating the future configuration. The treatment plant removed 99.8%, 99.2% and 61.6% of soluble COD, BOD5 and color, respectively. The water consumption was highest in the bleaching plant and, therefore, the recycling of 50%, 75% and 100% of the treated effluent for washing the pulp was simulated. The brightness and brightness reversion of the pulp, with 100% of the treated effluent used in the bleaching process, were similar to those provided by fresh water. The recycling of 100% of the treated effluent in the proposed treatment plant was possible in the TMP pulp mill without decreasing the pulp quality.

Energy Modeling of a Refiner in Thermo-Mechanical Pulping Process Using ANFIS Method

In the pulping industry, thermo-mechanical pulping (TMP) as a subdivision of the refiner-based mechanical pulping is one of the most energy-intensive processes where the core of the process is attributed to the refining process. In this study, to simulate the refining unit of the TMP process under different operational states, the idea of machine learning algorithms is employed. Complicated processes and prediction problems could be simulated and solved by utilizing artificial intelligence methods inspired by the pattern of brain learning. In this research, six evolutionary optimization algorithms are employed to be joined with the adaptive neuro-fuzzy inference system (ANFIS) to increase the refining simulation accuracy. The applied optimization algorithms are particle swarm optimization algorithm (PSO), differential evolution (DE), biogeography-based optimization algorithm (BBO), genetic algorithm (GA), ant colony (ACO), and teaching learning-based optimization algorithm (TLBO). The simulation predictor variables are site ambient temperature, refining dilution water, refining plate gap, and chip transfer screw speed, while the model outputs are refining motor load and generated steam. Findings confirm the superiority of the PSO algorithm concerning model performance comparing to the other evolutionary algorithms for optimizing ANFIS method parameters, which are utilized for simulating a refiner unit in the TMP process.

Development of fibre properties in mill scale high- and low consistency refining of thermomechanical pulp (Part 1)

Abstract The aim of this study was to evaluate changes in fibre properties with high (HC)- and low consistency (LC) refining of TMP and determine how these contribute to tensile index. Two process configurations, one with only HC refining and another with HC refining followed by LC refining were evaluated in three TMP mainline processes in two mills using Norway spruce. An increase in tensile index for a given applied specific energy was similar for all LC refiners in the three lines, despite differences in the fibre property profiles of the feed pulps. Compared with only HC refined pulps at a given tensile index, HC+LC refined pulps had greater fibre wall thickness, similar fibre length, strain at break and freeness, but lower light scattering coefficient, fibre curl and external fibrillation. The degree of internal fibrillation, determined by Simons’ stain measurements, was similar for both configurations at a given tensile index. The results indicate that the increase in tensile index in LC refining is largely influenced by a decrease in fibre curl and in HC refining by peeling of the fibre walls. Compared at a given tensile index, the shive content (Somerville mass fraction) was similar for both HC+LC and HC refining.

Analysis of Cellulose Pulp Characteristics and Processing Parameters for Efficient Paper Production

For economic reasons, increasing the use of various fibrous pulps with high lignin contents—i.e., chemothermomechanical pulp (BCTMP and CTMP), thermomechanical pulp (TMP), and semichemical pulp—is desirable. The relatively good quality and increased efficiency of these pulps make them attractive paper semi-products. In particular, they could alleviate the severe shortage of paper semi-products. Although mechanical pulp and semichemical pulp are achieving increasing quality with substantially increased wood efficiency, their production is often characterised by high consumption of electricity to defibre chips or refine high-lignin-content fibrous pulps. Technological, environmental, and economic evaluations of the manufacture and application of increased efficiency cellulose pulps that take into account potential profits from increased cellulose pulp efficiency and losses due to energy costs and degradation in the properties of the resulting paper are relevant and essential to paper mills. This article reports such an analysis. The authors have analysed the usable properties of ten cellulose pulps with various degrees of digestion and identified the optimum pulp that yields the optimum product properties, considering the yield; pulp refining time, which determines the cost of paper manufacture; and strength properties of the obtained paper.

Influence of Chemical and Enzymatic TEMPO-Mediated Oxidation on Chemical Structure and Nanofibrillation of Lignocellulose

Chemically pretreated lignocellulose (CL) from poplar wood and commercial thermomechanical pulp (TMP) were oxidized using a TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)/NaBr/NaClO system an...

In situ real-time investigations on adsorptive membrane fouling by thermomechanical pulping process water with quartz crystal microbalance with dissipation monitoring (QCM-D)

Membrane processes are essential for the success of lignocellulosic biorefineries, but membrane fouling is still a major problem and the single most important reason for the relatively slow acceptance of membrane technology in this industrial application. It is therefore of the utmost importance to find methods that enable the study of the fouling development when processing new types of feed solutions. Although ex situ analysis allows the composition of the fouling layer to be determined, the processes leading to its build-up remain unknown. In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to study adsorptive fouling in situ. By using QCM-D, the development of fouling over time can be studied. Fouling of three fractions of a thermomechanical pulping process water (feed, microfiltration retentate and permeate) were studied on QCM-D sensors coated with a polymer used in commercial polysulfone membranes. The retentate contained mainly colloidal extractives and the permeate hemicelluloses. In the case of the retentate, adsorption was almost immediate and the greatest increase in mass was observed. In case of the permeate, the increase in mass was slowest but at steady state the adsorbed mass was similar to the adsorbed mass of the process water. After rinsing with water, an irreversibly attached network of hemicelluloses remained on the polymer surface while the colloidal extractives were washed away. Overall, the study shows that in situ real-time monitoring of adsorptive membrane fouling combined with additional ex situ analysis generates valuable understanding on the evolution of membrane fouling in lignocellulosic biorefineries.

Modification of PES ultrafiltration membranes by cationic polyelectrolyte Praestol 859: Characterization, performance and application for purification of hemicellulose

Novel approach for membrane modification to improve separation performance and antifouling stability was proposed. It involves using of 0.1–0.3wt.% aqueous solutions of Praestol 859 (cationic polyelectrolyte based on copolymer of acrylamide and 2-acryloxyethyltrimethylammonium chloride) as coagulants upon membrane preparation via non-solvent induced phase separation. It was shown that the addition of small amounts (0.1–0.3wt.%) of Praestol 859 into the coagulation bath leads to an increase in membrane pure water flux from 51 up to 68Lm−2h−1 without decreasing membrane retention. Contact angle for modified membranes decreased from 64° down to 55°. Immobilization of Praestol 859 on the surface of a selective membrane layer was confirmed by FTIR spectroscopy. It was found that the addition of Praestol 859 into the coagulation bath suppressed the macrovoid formation in the membranes supporting layer due to the decrease of “solvent-non-solvent” exchange rate which is attributed to the significant increase of viscosity of the coagulation bath. The separation performance of modified membranes for fractionation of thermomechanical pulp mill process water, for concentration and purification of hemicellulose for further processing was studied. It was found that membrane modification by Praestol 859 leads to 2–6 times increase of flux, increase of fouling recovery ratio and improvement of cleaning efficiency without decreasing membrane rejection with regard to hemicelluloses (91.5–93%) and lignin (21–22%) as reference components.

A Multiagent-Based Methodology for Known and Novel Faults Diagnosis in Industrial Processes

This article proposes a multiagent-based methodology for the real-time fault diagnosis in industrial processes. This articles aims to build a decision support tool that helps process operators identify and better manage abnormal situations. The supervised and semisupervised machine learning methods are widely used to develop such tools. Despite their accuracy in classifying faults, supervised methods have a major limitation: they cannot diagnose novel faults. The semisupervised methods can detect and isolate novel faults but cannot disclose their root causes. The proposed methodology combines both supervised and semisupervised methods in a parallel-serial structure, exploiting their respective strengths. Moreover, it provides the process expert with the meaningful explanations of the detected novel faults or otherwise. Two case studies are used in this article to demonstrate the effectiveness of the proposed methodology. The first case is the Tennessee Eastman process benchmark. The second one uses the real data collected from a heat recovery system in a thermomechanical pulp mill.