Pulp Mill Process Research Articles

Comparison of thermal, rheological properties of Finnish Pinus sp. and Brazilian Eucalyptus sp. black liquors and their impact on recovery units

Black liquor (BL) is the major bioproduct and biomass fuel in pulp mill processes. However, the high viscosity of BL makes it a challenging material to work with, resulting in issues with evaporators and heat exchangers during its transport and processing. The thermal and rheological properties of BLs from Pinus sp. (PBL) and Eucalyptus sp. (EBL) were studied. FTIR spectra revealed the presence of the characteristic functional groups and the chemical composition in liquors. TGA/DTG curves showed three characteristic degradation stages related to evaporation of water, pyrolysis of organic groups, and condensation of char. Rheologically, liquors are classified as non-Newtonian and with comportment pseudoplastic. Their rheological dynamic shear properties included a linear viscoelastic region up to 1% shear strain, while frequency sweeps showed that storage modulus (Gʹ) > loss modulus (Gʹʹ), thus confirming the solid-like behavior of both BLs. The rheological study demonstrated that increasing the temperature and oscillatory deformations of PBL and EBL decreased their degree of viscoelasticity, which could favor their pumping and handling within the pulp mill, as well as the droplet formation and swelling characteristics in the recovery furnace.

Characterization and recognition of three-dimensional excitation-emission matrix spectra of wastewater from six typical categories

In this study, we analyzed the characteristics of three-dimensional excitation-emission matrix spectra (EEMs) of 150 samples from five industrial wastewater types and domestic sewage to track water pollution sources effectively. We then developed a recognition model for wastewater EEMs by establishing a feature dataset containing fluorescence peak values and parameters derived from EEMs, integrated with machine learning techniques. This model enables the rapid and precise identification of pollution sources. Our findings suggest that although the EEMs of the six wastewater categories are distinct, visual differentiation is challenging. This was confirmed by cosine similarity assessments, showing some samples with low within-group (< 0.8) and high between-group (> 0.95) similarities. Despite significant variations in EEMs features across wastewater categories, identifying specific pollutants remains difficult, especially for pulp mills and leather effluents. Among the tested classification algorithms, Support Vector Machine (SVM) achieved the highest performance with 91.7 % accuracy, 94 % precision, 91 % recall, and 92 % F1-score, outperforming K-Nearest Neighbors and Partial Least Squares Discriminant Analysis. The SVM significantly improved identification accuracy for pulp mill and leather processing wastewaters compared to other models. To enhance identification accuracy, further exploration of EEMs features and expanding the training dataset are recommended. Combining EEMs features with machine learning presents a promising method for improving water pollution supervision and source tracing in environmental management practices.

Novel pulp mill wastewater recovery process for CO2 and SOx utilization

Pulping industry has a pulp mill process that emits a significant amount of carbon dioxide (CO2) and sulfur oxides (SOx). The pulp mill wastewater has a high potential for reducing pollution caused by CO2 and SOx because it contains useful mineral ions in high concentrations, such as Ca2+, Mg2+, Na+, and K+ that react with carbonate and sulfate ions. In this study, we develop a novel pulp mill wastewater recovery process for CO2 and SOx utilization. To design the CO2 and SOx capture and utilization process using pulp mill wastewater, a process model is developed based on validated experimental data. The developed process model comprises the following three steps: (1) metal ion separation of pulp mill wastewater to produce KClO4, Mg(OH)2, and Ca(OH)2; (2) SOx capture and utilization using Ca(OH)2 and SOx, utilized as desulfurization gypsum; (3) CO2 capture via generated KClO4, and the captured CO2 is utilized as carbonate using Mg(OH)2 and Ca(OH)2. Accordingly, the economic feasibility of the suggested process model is demonstrated by calculating the pay-back period in economic assessment. As a result, the desulfurization efficiency was 99% with high-purity gypsum production. In addition, ∼98.2% CO2 was captured. Furthermore, the annual profit was increased by USD 94,469, and thus, the pay-back period was determined as 8.4 y.

Decision fusion for reliable fault classification in energy-intensive process industries

Heavy industries such as oil & gas, steel & iron production, the cement industry, chemical processes, and pulp & paper mills are among the industries that contribute most to greenhouse gas emissions. The operation of processes in these industries requires massive amounts of energy, which is mainly generated through the consumption of natural resources, leading to the emission of harmful gases. These emissions can be reduced by improving the efficiency of process operations and with better management of abnormal events/faults through accurate fault classification. Managers and operators of these industries need intelligent fault classification strategies that provide accurate information and decisions on faulty situations management, thus helping day-to-day processes operate in safe, reliable and energy-efficient ways. This paper proposes a decision fusion approach that combines outputs produced by diversified machine learning fault classifiers, each with distinct pattern representations. The proposed approach mainly adopts the behavior knowledge space (BKS) method and updates the corresponding lookup table based on the F1-scores calculated for every single fault classifier based on historical data. The concept is based on the exploitation of the advantages of each fault classifier as a complementary information source to effectively classify faults and provide plant operators and engineers with unified, accurate and comprehensive decisions. The proposed approach is validated through two case studies in the pulp and paper industry. The first one is the pulp mill process benchmark using simulated data and the second case is on a reboiler in a Canadian thermomechanical pulp mill. The results obtained demonstrate that the accuracy of the proposed approach is higher than the accuracy of every single classifier and other comparable methods applied to such complex industrial processes. The results have helped the mill operators correctly identify the causes of abnormal events and have contributed to significant energy savings and reduction in Greenhouse Gas (GHG) emissions.

Development of Antifouling Polysulfone Membranes by Synergistic Modification with Two Different Additives in Casting Solution and Coagulation Bath: Synperonic F108 and Polyacrylic Acid.

This study deals with the development of antifouling ultrafiltration membranes based on polysulfone (PSF) for wastewater treatment and the concentration and purification of hemicellulose and lignin in the pulp and paper industry. The efficient simple and reproducible technique of PSF membrane modification to increase antifouling performance by simultaneous addition of triblock copolymer polyethylene glycol-polypropylene glycol-polyethylene glycol (Synperonic F108, Mn =14 × 103 g mol−1) to the casting solution and addition of polyacrylic acid (PAA, Mn = 250 × 103 g mol−1) to the coagulation bath is proposed for the first time. The effect of the PAA concentration in the aqueous solution on the PSF/Synperonic F108 membrane structure, surface characteristics, performance, and antifouling stability was investigated. PAA concentrations were varied from 0.35 to 2.0 wt.%. Membrane composition, structure, and topology were investigated by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The addition of PAA into the coagulation bath was revealed to cause the formation of a thicker and denser selective layer with decreasing its pore size and porosity; according to the structural characterization, an interpolymer complex of the two additives was formed on the surface of the PSF membrane. Hydrophilicity of the membrane selective layer surface was shown to increase significantly. The selective layer surface charge was found to become more negative in comparison to the reference membrane. It was shown that PSF/Synperonic F108/PAA membranes are characterized by better antifouling performance in ultrafiltration of humic acid solution and thermomechanical pulp mill (ThMP) process water. Membrane modification with PAA results in higher ThMP process water flux, fouling recovery ratio, and hemicellulose and total lignin rejection compared to the reference PSF/Synperonic F108 membrane. This suggests the possibility of applying the developed membranes for hemicellulose concentration and purification.

Development of polysulfone ultrafiltration membranes with enhanced antifouling performance for the valorisation of side streams in the pulp and paper industry

One-stage method of polysulfone (PSf) membrane modification by the addition of polyacrylic acid (PAA, Mn = 250 kg·mol−1) to the coagulation bath during membrane preparation via non-solvent induced phase separation (NIPS) was proposed. The effect of PAA concentration on the membrane structure, hydrophilicity, zeta potential, separation performance and antifouling stability in ultrafiltration of lysozyme, polyvinylpyrrolidone (PVP K-30, Mn = 40 kg mol−1) and humic acid model solutions as well as thermomechanical pulp mill process (ThMP) water was studied. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), measurements of the tangential flow streaming potential and water contact angle were used for membrane characterization. It was found that addition of PAA into coagulation bath resulted in decreasing pore size and porosity of the selective layer as well as the formation of a thicker and denser selective layer. Water contact angle of the modified membranes was found to decrease significantly and zeta potential of the selective layer was shown to become more negative in the studied pH range 3–10, all compared to the reference membrane. It was revealed that pure water flux (PWF) decreased and lysozyme and PVP K-30 rejection increased with the increase in PAA concentration in the coagulation bath. It was found that membranes modified with PAA demonstrated better antifouling stability in ultrafiltration of humic acid solution and ThMP process water. Modified membranes were found to have higher flux, fouling recovery ratio and hemicelluloses rejection in ThMP process water ultrafiltration compared to the reference PSf membrane that allows application of these membranes for hemicelluloses concentration and purification.

Thermal evaluation of the use of porous ceramic plates on ventilated façades – Part I: Effect of composition and firing temperature on porosity and bending strength

AbstractThe effect of composition and firing temperature on porosity and bending strength of porous ceramic plates for using in ventilated façades were investigated. Two byproducts, basalt and lime mud, were used to obtain porous ceramic plates in accordance with the circular economy concept. Basalt, which is a fine powder‐based byproduct generated from the processing of basaltic rock, was used to replace feldspar as the flux mineral in a ceramic composition. Lime mud, a byproduct of the pulp and paper mill process and containing a high content of calcium carbonate (CaCO3), was incorporated in the ceramic composition to generate pores. The specimens were prepared using three different amounts of lime mud (20, 30, and 40 wt%) and three firing temperatures (900°C, 1000°C, and 1100°C), and their porosity and bending strength were determined. The highest performing specimen (5.1 ± 1.3 MPa bending strength and 42.6 ± 0.5% porosity) was obtained by using 40 wt% of lime mud and a firing temperature of 1100°C with potential for further thermal tests in a ventilated façade in comparison with a commercial porcelain ceramic tile as reference material.

On-line characterization of wood chip brightness and chemical composition by means of visible and near-infrared spectroscopy

Abstract Historically, on-line and real-time measurement of wood chip properties in the pulp and paper industry has been a challenge and has hampered the development of advanced process control strategies. In this study, visible and near-infrared (VIS-NIR) spectroscopy is investigated as a means to characterize wood chip brightness and chemical composition (i.e. extractives, lignin and holocellulose content) on-line. The estimated standard error on the holocellulose reference measurement was significantly reduced using data reconciliation. VIS-NIR calibration models were developed using partial least square regression. Derivative and baseline correction were found to be the most appropriate pre-processing methods. Model desensitization to the influence of moisture content and temperature by means of external parameter orthogonalization resulted in more robust models critical for on-line applications under harsh industrial conditions. Wavelength selection improved model accuracy for all properties. A comparison of two different spectrometer and probe combinations demonstrated that, after wavelengths selection, a non-contact measurement of wood chips performs as well as a contact measurement of wood powder for monitoring chemical composition. On-line prediction of wood chip brightness and chemical composition using the developed VIS-NIR models was demonstrated over 7 months in a kraft pulp mill processing both hardwood and softwood chips.

Effect of polysulfide pulping process on the energy balance of softwood and hardwood kraft pulp mills

Abstract Polysulfide pulping is a method to increase the pulp yield in a kraft pulp mill. Higher production is in the core of pulp mill process development, but modifications in cooking raise questions on their effects on the other parts of the process. This study focuses on the impacts of polysulfide pulping on the energy use and production of kraft pulp mills. The impacts are estimated by calculating and analyzing the steam and electricity balances of reference softwood and hardwood mills. Energy generation using residual biomass is an essential part of the operation of a kraft pulp mill, and often a notable source of income. The results show that implementation of polysulfide cooking affects both energy consumption and production. Higher hemicelluloses content of pulp cooked using polysulfide liquor means that less organic material ends up in the black liquor. Subsequently, the recovery boiler energy production suffers. The reduced steam production together with increased steam consumption decreased electricity production, corresponding to a decline in sellable electricity of 22.4 % in the hardwood mill and 28.4 % in the softwood mill. The study shows that increasing the pulp production by investing in polysulfide cooking in stand-alone kraft pulp mills can be economically feasible.

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.

The Modification of Polyethersulfone Membranes Using a Synperonic F108 Block Copolymer and Their Application for the Fractionation of Thermomechanical Pulp Mill Process Water

The effect of additions of a Synperonic F108 amphiphilic triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) to casting solutions on the structure and properties of polyethersulfone (PES) membranes was studied. It is found that the introduction of small amounts (0.3–0.5%) of Synperonic F108 leads to an increase in the pure water flux of membranes from 50 up to 120–200 L m−2 h−1 at the same time membranes showed constant selectivity and enhanced hydrophilicity. The water contact angle decreases from 65° down to 41°–42°. Infrared (IR) spectroscopic studies show that Synperonic F108 is predominantly localized on the selective layer of membranes. The investigation of the morphology of membranes by scanning electron microscopy (SEM) shows that the introduction of Synperonic F108 promotes an increase in the total width of the transition layer and suppressed the macrovoids formation in the membranes supporting layer. Modified membranes are tested in the process of fractionation of thermomechanical pulp mill process water in order to isolate hemicelluloses for further processing. It is shown that the modified membranes obtained with the addition of 0.5% Synperonic F108 are characterized by two- to sixfold higher flux and 40% higher flux recovery ratio. The hemicellulose rejection for the initial and modified membranes varies within 95–97%, while lignin rejection is slightly lower in the case of modified membranes (14–19%, 21% for the nonmodified membrane).

Recovery of lignin and lignans enriched fractions from thermomechanical pulp mill process water through membrane separation technology: Pilot-plant study and techno-economic assessment

Membrane process is a viable option for valuable compounds such as lignin and lignans recovery in aqueous discharges of thermomechanical pulp industries. Recovery of lignin and lignans with continuous mode ultrafiltration/nanofiltration installation has not been studied in detail previously. After flotation used to remove lipophilic matter of pulp mill effluent, the three steps membrane process was composed of a clarification step by a 150 kDa ultrafiltration used to remove suspended matter, followed by two nanofiltrations of 1 kDa and 300 Da to respectively retain lignin and lignans. A techno-economic evaluation of this process has been performed. The process with a plant capacity of 60 m3 h−1 was able to produce 12 tons of lignin and 825 kg of lignans per month. The influence of plant capacity between 0.1 and 60 m3 h−1 on extracts production cost allows determining a production cost equal or below 10 €.kg−1 as plant capacity reached 10 m3 h−1. Valorization of lignin and lignans as parts of the formulas of high added value products could allow thermomechanical plants to head towards biorefinery and cleaner production concepts. Furthemore, the 300 Da permeate possessed the required characteristics to be re used and save fresh water utilization.

The influence of gas diffusion mechanisms on foam stability for foam forming of paper products

Foam forming is an innovative process for papermaking that yields various paper products with excellent formability and porosity. The stability of the foam is a critical factor in foam forming technology. The effects of different surfactants and gases (N2 and CO2) on the ability of the foams to coalesce and the stability of the foams were studied. The properties of the liquid film were investigated via high-speed camera observation and infrared spectrum. The CO2 foam was less stable than the N2 foam under the same conditions, especially for the polyvinyl alcohol surfactant. The infrared spectra and high-speed camera observation showed that the main factor that resulted in CO2 foam instability was the bubble coalescence caused via the gas diffusion in the foam column, although the process of liquid film thinning was performed simultaneously. The greater the liquid film permeability coefficient of the foam, the easier the gas was able to spread throughout the liquid film. Foam forming technology will likely be employed in many potential pulp and papermaking mill processes.

On-Site Recovery of Hemicelluloses from Thermomechanical Pulp Mill Process Water by Microfiltration and Ultrafiltration

During mechanical defibration of wood, a minor fraction of the wood mass is dissolved in the process water. These dissolved substances represent an extra energy demand when they are treated in the mill’s wastewater treatment plant. Galactoglucomannan, the main hemicellulose in spruce, can be recovered from thermomechanical pulp mill process water by a process based on microfiltration (MF) and ultrafiltration (UF). The purpose of this work was to study the scale-up of the process from laboratory scale to continuous industrial scale. MF was first studied in the laboratory, and then combined with UF in a continuous pilot process on-site at a pulp mill. The data obtained were used to estimate the cost of the membrane processes for galactoglucomannan recovery which was found to be about €1160 per ton hemicelluloses.

Separation of hemicelluloses and lignins from synthetic hydrolyzate and thermomechanical pulp mill process water via liquid-liquid extraction

The separation of hemicelluloses from thermomechanical pulping (TMP) process water is of particular interest because it yields a biopolymer suitable for various value-added biomaterials production and reduces the organic loading on the water treatment facility. However, during the TMP process, hemicellulose is released in the process water at relatively low concentrations that are difficult to recover by many methods efficiently. Liquid-liquid extraction (LLE) has been deemed as a potentially viable separation technique in modern industrial processes for valuable materials recovery and undesirable impurities removal. In this work, the extraction of hemicellulose from the process water and synthetic hydrolyzate using LLE was investigated. In particular, the effects of the major experimental variables (the type of solvent, hydrolyzate to solvent volume ratio, and pH) on extraction performance were explored. The tested solvents have shown varying affinity and selectivity for the recovery of hemicellulose. It was found that the hemicellulose extraction efficiency of n-hexane (71.03%) and tributyl phosphate (TBP) (72.34%) was higher than that of 1-butanol (62.36%), and toluene (67.03%) at a solvent: hydrolyzate volume ratio of 1:3. Although TBP showed a high degree of hemicellulose extraction (72.34), it was characterized by a low selectivity coefficient, while n-hexane achieved the highest selectivity. The average selectivity coefficients of n-hexane were 7.3, 5.1, and 8.7 followed by toluene 2.7, 2.7, and 2.9 for pH values of 9.5, 7, and 4.3, respectively. Changing the pH of the hydrolyzate has resulted in varying effects depending on the type of the solvent used. The optimum extraction pH, phase ratio, and extraction time were at 4.3, 1:3 mL/mL and 30 min, respectively.

Periodate oxidation of xylan-based hemicelluloses and its effect on their thermal properties

Hemicellulose from pulp mill process water and crop residuals from food production often end up in waste streams or burnt for energy contribution. These waste products contain valuable biopolymers but lack many attributes needed for use in applications such as food and medical or consumer products. This study reports on an investigation of the periodate oxidation of hardwood xylan and arabinoxylan (AX) from wheat bran to produce materials with new functionalities. The study explores how to control the oxidation degree and describes structural differences between the two xylan-based polymers. For the xylan samples, the oxidation resulted in a lowering of the glass transition temperature (Tg), indicating a more flexible chain due to ring-opening of the xylan anhydro-sugar units. For the AX samples, the arabinose side-groups were instead oxidized, hindering oxidation on part of the xylose units, which resulted in a crosslinked network with an unchanged Tg but reduced intrinsic viscosity.

Characterization of Irreversible Fouling after Ultrafiltration of Thermomechanical Pulp Mill Process Water

Large volumes of wastewater with dissolved wood components are treated in wastewater treatment plants at thermomechanical pulp mills. It has been shown previously that hemicelluloses in these wastewater streams can be recovered by membrane filtration. A serious obstacle when treating lignocellulose process streams is fouling of the membranes. Fouling not only increases operating costs but also reduces the operating time of the membrane plant. When optimizing the membrane cleaning method, it is important to know which compounds cause the fouling. In this work fouling of an ultrafiltration membrane was studied. The fouling propensity of untreated process water and microfiltrated process water was compared. Fouled membranes were analyzed using scanning electron microscopy and attenuated total reflection Fourier transform infrared spectrometry. Acid hydrolysis of membranes exposed to untreated process water and microfiltration permeate revealed that 508 mg/m2 and 37 mg/m2 of polysaccharides, respectively, remained on the membranes even after alkaline cleaning.

Fractionation of polyphenols from thermomechanical pulp mill process water by flotation and membrane integrated process

ABSTRACTFractionation of phenolic compounds in thermomechanical pulp mills was performed with a coupling of a prior treatment realized by flotation and a ceramic membrane process. Two lines of membranes filtration were tested. After a common 150 kDa clarification, 1 kDa filtration was performed with or without previous 5 kDa filtration. Flotation was shown to be inevitable to retain lipophilic compounds which cause severe membrane fouling. 150 kDa permeate flux was 20% higher when process water was firstly floated and was around 260 L h−1 m−2. 1 kDa membrane was fouled with 31% of irreversible fouling without previous 5 kDa filtration and phenolic compounds purity reached only 26% in this 1 kDa permeate. Phenolic compounds as lignin-like substances which might be attached to hemicelluloses were recovered in 5 kDa retentate. Retentate of 1 kDa might contain a major fraction of lignin derivatives with molecular weights around 1 kDa free or linked with phenolic acids. Permeate of 1 kDa contained 14% of phenolic compounds such as lignans and free phenolic acids purified at 50%.

Ultrafiltration for hemicelluloses recovery and purification from thermomechanical pulp mill process waters

Ultrafiltration for hemicelluloses recovery and purification from thermomechanical pulp mill process waters

An Analysis of the Cost Effectiveness for Energy Efficiency Technology in Thailand Pulp and Paper Industry

Green Energy efficiency is becoming more important because of the resulting cost reduction and image of green society which helps to enhance competitiveness in a globalized green market. Pulp and paper manufacturing is a large-scale industry which is generally regarded as important for national development. The Pulp and Paper industry consumes approximately 2.5% of total industrial energy consumption in Thailand by 44 factories distributed throughout the country. Therefore, energy efficiency improvement can play a significant role in the industry. Investigations of the cost effectiveness of energy efficiency measures and technologies using bottom-up Conservation Supply Curve (CSC) in the pulp and paper mill process are required. This study examines the concept, methodology, and the usefulness of the energy conservation supply curve, and the potential to create the appropriate energy policies to the Thai Pulp and Paper Industry.