| 1. |
- Rahman, Hafizur, Research Engineer, 1978-
(författare)
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Aspects of optimizing pulp fibre properties for tissue and packaging materials
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To improve the competitive advantages of pulp fibre-based materials for tissue and packaging over fossil-based products, it is essential to increase knowledge of the selectivity of the cooking and the chemimechanical processes by optimizing the unit operations of impregnation, cooking and refining. A general goal in pulping processes is to achieve as efficient and even fibre separation as possible. A key to achieving this is to improve impregnation uniformity. In the case of chemical pulping, we need to study how a more even distribution of lignin at the fibre level via easily impregnated wood chips can be achieved using classic measures such as equalized hydroxide ion concentration, increased initial sulphide ion concentration, low sodium ion concentration and a low cooking temperature combined with an oxidative and reductive environment. In the case of chemithermomechanical pulp (CTMP) manufacturing, we need to achieve as even a degree of sulphonation as possible at the level of the individual fibres by means of improved sulphite ion distribution within the wood chips before they are pre-heated prior to entering the refiner. Firstly, we have studied selective cooking systems for sulphate pulp manufacturing in oxidative (polysulfide) and reductive (sodium borohydride) environments. The yield increased from 48% to a maximum of 53%, which resulted in faster dewatering when mimicking a tissue papermaking process. This could explain how the advantage of the increased yield (fewer fibres and a more open sheet structure) outweighs the negative effects of the higher hemicellulose content on the dewatering properties. Moreover, the increased proportion of hemicellulose in the fibre walls resulted in improved bonding and increased tensile index at a certain refining energy. Secondly, we have studied the uniformity of impregnation at the fibre level by developing an accurate way of measuring sulphur and sodium content in measuring points that are 5-10 µm in diameter with miniaturized X-ray-based technology. This technology is considered cheap and efficient enough to be introduced in industrial labs and/or in online equipment. Our newly built miniaturized energy dispersive X-ray fluorescence (ED-XRF) demonstrates the capability of imaging sulphur and possibly sodium distribution in wood chip fibres or individual fibres on a micro scale. In parallel, to the above research we have studied a new catalytic lignin-selective cooking method where a substantial portion of the dissolved lignin can be extracted as vanillin, creating significant value and opportunities for new cost-efficient wood biorefinery systems.
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| 2. |
- Björk, Elisabeth
(författare)
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Production and application of fine fractions made of chemical pulp for enhanced paperboard strength
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For all kinds of paperboard packages, the bending stiffness of the paperboard is a crucial property. In multi-ply folding boxboard (FBB) grades, this is obtained by placing different stocks in the outer and centre plies of the board. In the outer plies, a stock with a high tensile stiffness is used, typically made from refined kraft pulp fibres. In the middle ply/plies a stock with more bulky properties is placed, typically comprising of a high proportion of CTMP (chemi-thermomechanical pulp). CTMP fibres are stiffer and more inflexible with poor bonding abilities resulting in low strength properties. To increase the bonding strength in the middle ply, broke, containing chemical pulp is added, and sometimes refined chemical kraft pulp as well. Both fibres and fines, i.e. smaller fibre fragments, in a pulp have a significant contribution to the properties of the product. Fines produced during refining of chemical pulp are especially beneficial for increasing the strength.To achieve pulp fraction with higher fines content the pulp can be fractionated with a micro-perforated screen basket; a fine fraction produced from a screen with very small holes will contain a large proportion of fines. By adding such a fine fraction to a middle ply stock, the bulk properties of the main pulp, for example a CTMP, can be conserved as less refining of this pulp is required to achieve the targeted strength properties. However, a drawback is that the fine fraction usually has a very low mass concentration after the screening process as a lot of water pass through the screen together with the fines and fibre fragments. The excess water must be removed to maintain the water balance of the papermaking process. Further, the larger volumes require extra pumping capacity. A resource-efficient production of a fine fraction must target a high fine fraction mass concentration and a high content of fines and short fibre fragments in order to be implemented industrially.The focus of the present work was on separation efficiency (i.e. the difference in fibre length distribution caused by screening) and process efficiency (i.e. the concentration of the fine fraction) for production of a fine fraction of chemical pulp by screening, and the utilisation of the fine fraction as strength agent.Pilot-scale fractionation trials with a pressure screen with different microperforated screen baskets were performed in order to evaluate how the separation efficiency and process efficiency were affected by parameters such as feed concentration, pulp type (hardwood or softwood kraft pulp), hole size of the screen, and refining treatment prior to screening. The trials were evaluated using fibre length distributions, flow rates and concentrations of viii the feed flow and the fractions. Here, two complementary quantitative measures, Proportion in fine fraction (for process efficiency) and Fine fraction enrichment (for separation efficiency), were developed. To evaluate the strength enhancing effect of the obtained fine fraction, a lab scale study was performed where the fine fraction of a highly refined pulp was compared with the highly refined pulp as strength agent for a CTMP. The results of this study were verified in a pilot paper machine trial. In a second pilot paper machine trial, sheets with different CTMP proportions in the middle ply were studied in order to find out if the bulk could be increased while maintaining strength, by using a fine fraction made from refined chemical pulp.Regarding process efficiency, it was found that the most important parameter to obtain a high fine fraction concentration was a high feed concentration. Further, a higher fine fraction concentration for a given screening process was also obtained when using hardwood pulp and refining the pulp prior to the screening process. A higher feed concentration also had a positive effect on the separation efficiency. Small holes and a smooth surface of the screen basket were also important to improve the separation efficiency.It was shown that, when used as a strength agent in a CTMP pulp, the fine fraction of highly refined kraft pulp was twice as efficient as the highly refined kraft pulp, when added at equal mass proportion. However, both in the lab and pilot trial the strength increase was accompanied by a decreased bulk. This was expected, and to avoid this the proportion of the bulky CTMP had to be increased. The pilot paper machine trial with an increased CTMP proportion in the middle ply and a fine fraction of refined kraft pulp as strength agent demonstrated that it was possible to produce sheets with an increased bulk and maintained z-strength.
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| 3. |
- Ferritsius, Olof
(författare)
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Beyond averages – some aspects of how to describe a heterogeneous material, mechanical pulp, on particle level
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For a more profound understanding of how a process works, it is essential to have a relevant description of the material being processed. With this description, it will be easier to evaluate and control processes to produce more uniform products with the right properties. The focus of this thesis is on how to describe mechanical pulps in ways that reflect its character.Mechanical pulps are made from wood, a highly heterogeneous material. Common practice within the pulping industry and academy is to describe mechanical pulps and its wide variety of particles in terms of averages. The energy efficiency of the mechanical pulping process is usually calculated without taking into account the characteristics of the wood fed to the process. The main objective of the thesis is to explore ways to make more detailed descriptions of mechanical pulps. A second objective is to propose useful ways to visualise these descriptions.The studies were carried out in full-scale mill operations for TMP of publication grades and CTMP for board grades with Norwegian spruce as raw material. The particles in the pulps were analysed in an optical particle analyser for several properties such as length, curl, wall thickness, diameter,and external fibrillation for 10,000 to 60,000 particles per sample to cover their wide property variation. The data was analysed by factor analysis, a method to reduce the multidimensional data space, and also compared with data simulations.Several examples were identified where averages based on wide and skewed distributions may hide useful information and therefore result in misleading conclusions regarding the fibrous material and process performance. A method was developed to calculate the distribution of a common bonding factor, BIND (bonding indicator) for individual particles. This factor is calculated from external fibrillation, wall thickness and diameter measured in an optical particle analyser. Distributions of BIND is one way to characterize and visualise the heterogeneity of mechanical pulp. A characteristic BIND-distribution is set in the primary refiner stage, depending on both wood and process conditions and remains mostly intact through the process.It was demonstrated that both BIND-distributions and 4D maps of the measured property distributions could be used to assess the tails of the distributions (extreme values), energy efficiency, and fractionation efficiency in a new way. It was even possible to get a measure for energy efficiency for a primary stage refiner, since a method was developed where the wood raw material was evaluated in the same way as the pulp discharged from the refiner.It was demonstrated that the average length-length-weighted fibre length, commonly referred to as the average weight-weighted fibre length, is a relevant way to express the amount of long fibres, i.e. “length factor”. The commonly used average length-weighted fibre length may lead to erroneous conclusions. Through data simulations of curl and fibre length on particle level it was found that today’s analysers may underestimate the true length of the particles, especially if they are prone to be curled. As a result, theranking of pulps may be altered.It was concluded that although there is an ISO standard, or long-time used property, it does not necessarily imply that it is a relevant method. Misleading conclusions may be drawn based on current methods; here, modifications of these methods are suggested.The main contribution of this study is the finding that that a highly heterogeneous material such as mechanical pulps could be described in new ways through visualisation of data in 4D maps. These maps reveal casualconnections and more pertinent questions may be raised in thecommunication along the chain product-pulp-wood.Going beyond averages may reveal discrepancies in the process and material that were previously unknown, and lead to a more profound understanding. It seems that the mechanical pulping process can be even further simplified than previously expected. It has been concluded that to operate the process more efficiently, and for make products with just the right quality, the main focus should be on the raw material and the primary refiner stage from a heterogeneity point of view.
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| 4. |
- Joelsson, Tove
(författare)
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The influence of Pulp Type and Hot-pressing Conditions on Paper Strength Development
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The hot-pressing technology has proven to have the potential for manufacturing of strong, wet stable materials based on eco-friendly renewable and recyclable lignocellulose. The purpose of this work was to study how the pulp characteristics and the hot-pressing conditions affect the dry and wet strength properties of paper. Two different devices for hot-pressing were used. One using felted nip and a heated cylinder with a temperature limit at 200°C and one new design using a hard nip and an IR-heated steel belt with a temperature limit of 300°C.The results showed that dry strength can increase up to 150% for high yield pulp (HYP) based sheets at pressing temperatures well above the softening temperature of lignin. The maximum dry tensile strength obtained was 70 kNm/kg at 200°C pressing temperature and the corresponding value for a lignin-rich kraft pulp was about 130 kNm/kg, an increase of 30%. For all lignin-rich pulps the dry strength increased linearly with density up to 200°C whereafter it levelled off and was reduced.The wet tensile strength for paper based on HYP increase from 2 to 28 kNm/kg and for paper based on unbleached kraft pulp from 5 up to 60 kNm/kg in the temperature interval 20-270°C. The increase in wet strength independently of pulp grade seemed to be exponential to the pressing temperature with the steepest slope above 150°C. For unbleached kraft pulp a lignin content of minimum 7% seemed to be necessary for improved wet strength but 12% gave the highest value within the studied interval. In HYPs the lignin content is 25-28% depending on the pulping process but the level of wet strength was lower which is probably related to the lower density and lower dry strength compared to unbleached kraft pulps.Dry strength of lignin-rich paper is enhanced by improved fibre-fibre contact that can be improved by compression at high temperature, well above softening temperature (Tg) of moist lignin, native or chemically modified. It is known that sulfonation of lignin lowers the Tg in moist conditions. It was observed that at 150°C temperature the dry strength increased by 15% to a level of 71 kNm/kg for the high sulfonated pulp compared to the lower sulfonated pulp that had a dry strength of 60 kNm/kg at the same density. The level of wet strength was however not found to be affected by the sulfonation.Paper strength is to a large extent related to pulp fibre morphology and fines content. In this work studied these aspects where briefly studied with respect to hot-pressing and the results indicate that the relative influence of fibre morphology seems to be reduced with increasing pressing temperature. Hot-pressed sheets based on a coarse fines free fibre fraction showed 100% dry strength increase and wet strength increase up to 20 kNm/kg. The dry and wet strength were however also shown to be favoured by the presence of fines fraction.Wet strength development as a function of temperature was fitted to an Arrhenius type of equation and activation energies were found to be similar for very different pulp grades provided that the lignin content is above 7%. This could indicate that the process(es) giving wet strength were similar.It was found that the ratio wet:dry strength was about 35-60% for all lignin containing pulp grades. A rule of thumb for an efficient wet strength resin is that the wet: dry strength ratios are 15%. This means that it should be possible to manufacture wet-strong paper from lignin-rich pulps by means of hot-pressing without using wet strength chemicals. The concern regarding repulpability of such material led to an initial test to disintegrate this paper showing that re-pulping under vigorous mixing at room temperature is possible.The connection between dry and wet strength, high pressing temperature, and lignin content of pulp fibres is suggested to be related to some redistribution mechanisms of surface lignin between adjacent fibres. The improved wet strength and water resistance could be due to intermixing of lignin polymers across the interface between contacting fibre surfaces, or it could be lignin sufficient to cover the fibre-fibre bonds and/or chemical modifications, but these remain open questions.
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| 5. |
- Norlin, Börje, associate professor, 1967-, et al.
(författare)
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Visualisation of sulphur on single fibre level for pulping industry
- 2023
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Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 18:01, s. C01012-C01012
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Tidskriftsartikel (refereegranskat)abstract
- In the pulp and paper industry, about 5 Mt/y chemithermomechanical pulp (CTMP) are produced globally from softwood chips for production of carton board grades. For tailor making CTMP for this purpose, wood chips are impregnated with aqueous sodium sulphite for sulphonation of the wood lignin. When lignin is sulphonated, the defibration of wood into pulp becomes more selective, resulting in enhanced pulp properties. On a microscopic fibre scale, however, one could strongly assume that the sulphonation of the wood structure is very uneven due to its macroscale size of wood chips. If this is the case and the sulphonation could be done significantly more evenly, the CTMP process could be more efficient and produce pulp even better suited for carton boards. Therefore, the present study aimed to develop a technique based on X-ray fluorescence microscopy imaging (µXRF) for quantifying the sulphur distribution on CTMP wood fibres. Firstly, the feasibility of µXRF imaging for sulphur homogeneity measurements in wood fibres needs investigation. Therefore, clarification of which spatial and spectral resolution that allows visualization of sulphur impregnation into single wood fibres is needed. Measurements of single fibre imaging were carried out at the Argonne National Laboratory’s Advanced Photon Source (APS) synchrotron facility. With a synchrotron beam using one micrometre scanning step, images of elemental mapping are acquired from CTMP samples diluted with non-sulphonated pulp under specified conditions. Since the measurements show significant differences between sulphonated and non-sulphonated fibres, and a significant peak concentration in the shell of the sulphonated fibres, the proposed technique is found to be feasible. The required spatial resolution of the µXRF imaging for an on-site CTMP sulphur homogeneity measurement setup is about 15 µm, and the homogeneity measured along the fibre shells is suggested to be used as the CTMP sulphonation measurement parameter.
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| 6. |
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| 7. |
- Rahman, Hafizur, Researcher, 1978-, et al.
(författare)
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Improved CTMP impregnation by the use of X-ray fluorescence measurements
- 2023
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Defibration of wood chips in high-yield pulping such as CTMP production involves sulfonation of wood chips using (Na2SO3). When aiming to improve product properties, one key issue to investigate is the evenness of the sulfonation, i.e., the distribution of the sulfite (SO32-) ions. The challenge is that the inner parts of the wood chips absorb much less sodium sulfite than the outer parts. As a result, less sulfonated wood fibers have different bonding properties. It is likely that the efficiency and evenness of fiber separation in a chip refiner depend greatly on how evenly the chips have been sulfonated. Uneven sulfonation then results in higher shives (unseparated fibers) content which impairs product properties. We suggest a laboratory-scale miniaturized X-ray fluorescence (XRF) scanner for measuring sulfur distribution in the wood chips on-site. By minimizing the differences in sulphonate content between fibers, we can minimize the requirement for sulfite (SO32-) dosage to a certain degree of fiber separation, thereby reducing the total amount of electricity used in chip refining. There has been a significant improvement in commercial XRF microscopy scanners over the last few years, but the spatial resolutions achieved are insufficient. We have developed an XRF scanner optimized for sulfur fluorescence energies [1], and further continued this development by implementing frontier technology polycapillary X-ray optics. We present spatial resolution measurements and discuss the relevance and usability of the proposed measurement methodology to demonstrate its performance.[1] Rahman, H., et.al, ACS Omega 2022, 7, 51, 48555–48563, DOI: 10.1021/acsomega.2c07086
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| 8. |
- Rahman, Hafizur
(författare)
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Modifying kraft pulping to produce a softwood pulp requiring less energy in tissue paper production
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modification of softwood kraft pulp by the addition of either polysulfide (PS) or sodium borohydride (NaBH4) has been shown to increase the pulp yield due to a higher retention of glucomannan. The pulps with higher yield gave a paper with higher tensile index than reference pulp, especially at lower degrees of refining. The higher yield pulps also showed a greater porosity of the fibre wall, indicating an increase in the swelling potential of the fibres. This can lead to increased fibre flexibility and increased joint strength between the fibres and to the higher handsheet tensile index. However, the swelling increase associated with the higher hemicellulose content could also make dewatering more challenging because of the higher water retention of the pulp. The results of this study show however that the positive influence of the increase in yield (fewer fibres and a more open sheet structure) dominates over the negative influence of the higher hemicellulose content on the dewatering properties, especially at lower refining energy levels. Studies simulating full-scale tissue machine dewatering conditions showed that pulps with a higher yield and a higher hemicellulose content had a higher tensile index at the same dryness. Moreover, the same dryness level was achieved in a shorter dwell-time. A given tensile index was also achieved with less refining energy.Increasing the yield and hemicellulose content by the addition of either an oxidizing or a reducing agent in the softwood kraft pulping process thus has a potential for giving high quality fibres for tissue paper production with less refining energy and lower drying energy costs.
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| 9. |
- Rahman, Hafizur, Researcher, 1978-, et al.
(författare)
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On-Site X-ray Fluorescence Spectrometry Measurement Strategy for Assessing the Sulfonation to Improve Chemimechanical Pulping Processes
- 2022
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 7:51, s. 48555-48563
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Tidskriftsartikel (refereegranskat)abstract
- Minimizing the fiber property distribution would have the potential to improve the pulp properties and the process efficiency of chemimechanical pulp. To achieve this, it is essential to improve the level of knowledge of how evenly distributed the sulfonate concentration is between the individual chemimechanical pulp fibers. Due to the variation in quality between pulpwood and sawmill chips, as well as the on-chip screening method, it is difficult to develop an impregnation system that ensures the even distribution of sodium sulfite (Na2SO3) impregnation liquid. It is, therefore, crucial to measure the distribution of sulfonate groups within wood chips and fibers on a microscale. Typically, the degree of unevenness, i.e., the amount of fiber sulfonation and softening prior to defibration, is unknown on a microlevel due to excessively robust or complex processing methods. The degree of sulfonation at the fiber level can be determined by measuring the distribution of elemental sulfur and counterions of sulfonate groups, such as sodium or calcium. A miniaturized energy-dispersive X-ray fluorescence (ED-XRF) method has been developed to address this issue, enabling the analysis of sulfur distributions. It is effective enough to be applied to industrial laboratories for further development, i.e., improved image resolution and measurement time.
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| 10. |
- Sandberg, Christer, 1962-
(författare)
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Process intensification in mechanical pulping : Reduced process complexity and improved energy efficiency
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work shows that, for newsprint quality grades, the production processes for mechanical pulp can be simplified, and the specific electrical energy demand can be reduced with around 600 kWh/ton (30%). The purpose of the work is to demonstrate how the production cost for mechanical pulps can be decreased through increased energy efficiency and reduced number of unit operations. The idea was to improve the main line refining conditions so that no additional fibre development or shive reduction is needed and thereby, the normal screening and rejects treatment system could be omitted.Mechanical pulp is used to produce a variety of products, where the two largest categories are printing papers and paperboard for packaging. The pulp is mainly produced by the breakdown of wood chips between rotating metal discs in machines called refiners with the product and process generally referred to as thermomechanical pulp(ing) (TMP). The refiner process requires high specific electrical energy to separate and develop the fibres to a pulp intended for the production of printing papers. Today, many processes need over 2000 kWh/ton of refining energy plus 200-300 kWh/ton of auxiliary energy (to drive pumps, agitators, screw conveyors, screens, presses, etc.).During the last two decades of the 20th century, the chemical processing industry underwent a transformation. The process development changed from being unit operation focused to function focused. The result is more compact processes with less equipment, higher yield and lower energy demand. When the development is made in an innovative way with such large effects on process performance, it is referred to as process intensification. My work is inspired by the concepts of process intensification, especially the striving for more compact processes with higher efficiency. This work is focused on mechanical pulp, intended for the manufacture of printing paper, produced in refiners with Norway spruce (Picea abies) as raw material. However, this approach could also be applied to mechanical pulp production in integrated paperboard mills and also using other raw materials e.g., pines or hardwoods. The investigated pulps and processes in this work are mainly intended for uncoated paper grades (newsprint, improved newsprint and book paper) printed by the offset printing process. In all studies, the pulps have been produced with full scale mill equipment and evaluated using laboratory measurements. However, in two studies, the produced pulps were evaluated on paper machines and at printing houses.A large number of process concepts have been evaluated in which different approaches have been used to reduce the specific energy and, in some cases, improve pulp quality. The approaches include:1. Impressafiner chip pretreatment 2. Primary high consistency (HC) refiner type (DD, RTS, CD, SD)3. Addition of low doses of sodium sulphite 4. Increased refining temperature (housing pressure)5. Refiner segments and centre plate design6. Increased production rate7. Low consistency (LC) refining in different process positions and in combination with different HC refiner typesThe separate effects of all these techniques have not been evaluated systematically neither have potential synergistic effects of all possible combinations been investigated. Even though a large number of combinations of unit operations have been studied, the emphasis has been on trying to do as much fibre development as possible in a single HC refining stage.The mill trials with spruce as raw material have shown that a low shive content and appropriate fibre development can be attained in a process without separate treatment of long fibres. High intensity primary stage refining (RTS and DD) was necessary to reach a low shive content at a low specific refining energy (SRE), with DD refiners appearing to be the most suitable for simplified processes. DD and RTS refining produced pulps with fibres exhibiting a higher degree of external fibrillation and share of split fibres than SD refining. DD refining produced fibres with lower cell wall thickness and higher light scattering at given fibre length than RTS refining. The lowest specific refining energy was attained for one of the trials using the process, denoted as S:HT:DD-LC-LC, consisting of DD refining at increased production rate, 18 adt/h, increased housing pressure, 6.6 bar(g), and with 5 kg/adt sodium sulphite added to the chips immediately before the refiner. After DD refining the pulp was refined in two LC refining stages. This process required only 1280 kWh/adt SRE to reach a tensile index of 52 Nm/g (Rapid-Köthen). This is 900 kWh/adt lower than the final pulp for newsprint based on SD HC refining, and over 500 kWh/adt lower than Scandinavian BAT processes (2014). Additionally, the auxiliary energy was around 150 kWh/adt lower for the processes without a conventional rejects treatment system. At 52 Nm/g tensile index, the light scattering coefficient was 2-3 m2/kg higher, and the length-weighted average fibre length was around 0.1 mm lower for this process than for SD TMP final pulp. The fibre bonding, indicated by density, tensile index and Z-strength of fibre fraction handsheets, was similar or higher for the S:HT:DD-LC-LC process than the reference SD TMP process with a rejects treatment system. Other interesting process configurations, with somewhat lower efficiencies, included:1. Impressafiner pretreatment of the chips with sodium sulphite before DD refining, with or without subsequent LC refining. Chip pretreatment with the Impressafiner enabled operating the DD refiner at higher intensity (feeding segments and increased production rate) without significant loss of quality and LC refining enabled increased production rate which increased the overall efficiency.2. RTS-SD refining with sodium sulphite added before the second stage SD refiner referred to as RTS-S:SD. The pulp from the RTS-S:SD process had similar fibre length as the S:HT:DD-LC-LC process but lower light scattering coefficient.3. A single-stage DD refiner operating at 15.5 adt/h and 4 bar(g) housing pressure (no sodium sulphite addition), which produced pulp with lower fibre length but higher light scattering coefficient than the S:HT:DD-LC-LC process. Two simplified processes were evaluated on paper machines and in printing houses. The first, denoted DD-LC-F, involved a combination of DD primary refining followed by LC refining and fractionation (screening). The screen rejects were mixed with the main line DD pulp before the LC refiner. The second process was the CPT:S-DD-LC process (№1 above). Good runnability was attained both on the paper machines and in the offset printing presses and the paper quality was similar to the reference paper.For printing paper applications, the proportion of fibre development in LC refining should preferably be relatively low, since it was shown that LC refiners have limited capacity to reduce fibre wall thickness and thereby develop light scattering and fibre fraction Z-strength.Explicit effects on the number of unit operations and production cost have not been evaluated in this work, but clearly both investment and variable costs as well as fixed costs can be reduced with a simplified process.
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