| 1. |
- Berg, Jan-Erik, 1957-, et al.
(författare)
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Refining gentleness - a key to bulky CTMP
- 2022
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 37:2, s. 349-355
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Tidskriftsartikel (refereegranskat)abstract
- Chemithermomechanical pulp (CTMP) is often used in middle layers of multiply paperboards due to its high bulk at specified strength. Such a CTMP should consist of well-separated undamaged fibres with sufficient bonding capacity. The basic objective of this work is to examine the effect of refining on bulk, taking into account conditions such as temperature, sulphonation, refining gap and refiner size. First stage CTMP made from Norway spruce (Picea abies) were produced in pilot and mill scale trials. Two new parameters, Equivalent temperature related to softness and Refining gentleness are introduced that take into account refining conditions as actual temperature, softening temperature, bound sulphonate content, refining gap and refiner diameter. The results show that bulk increases linearly with refining gentleness.
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| 2. |
- Sandberg, Christer, et al.
(författare)
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Effects of chip pretreatment and feeding segments on specific energy and pulp quality in TMP production
- 2018
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 33:3, s. 448-459
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Tidskriftsartikel (refereegranskat)abstract
- Increased wood softening and refining intensity have earlier been utilized to improve refining efficiency in mechanical pulping. We have evaluated a combination of increased softening by low dose sulphite chip pretreatment and increased intensity by feeding segment design in a TMP line for production of high quality printing papers. Norway spruce wood chips were preheated, compressed in an Impressafiner and impregnated with water or sodium sulphite solutions (Na2SO3 charges 3.6 and 7.2 kg/t). Chips were refined in two parallel 68" double disc refiners using two different refining conditions: standard bidirectional segments at normal production rate (9 t/h) and feeding segments at increased production rate (11.1-12.1 t/h). The feeding segments enabled a 30 % increase in production rate. Refining with feeding segments at 12.1 t/h production rate combined with chip pretreatment with 3.6 kg/t sodium sulphite reduced the specific energy 360 kWh/t (19 %) compared to refining with standard segments and no pretreatment. Pulp properties were similar for the two configurations. The combination of feeding segments and chip pretreatment with water reduced the specific energy 180 kWh/t (9 %). Implementation of most of the technology presented has reduced the electrical energy use for the mill by approximately 80 GWh/year.
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| 3. |
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| 4. |
- Berg, Jan-Erik, 1957-, et al.
(författare)
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Fibre wall crack development
- 2009
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Ingår i: Proceedings - 2009 International Mechanical Pulping Conference, IMPC 2009. ; , s. 340-343
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Konferensbidrag (refereegranskat)abstract
- An analytical model has been applied to calculate the energy to achieve a certain damage state in a softwood fibre wall by uniaxial tension or shear load. At conditions such as prevailing at the entrance of the gap between the plates in a refiner less energy was needed for earlywood compared to latewood fibres. The energy was lower for loading in shear compared to tension for both earlywood and latewood fibres with a low microfibril angle. This implies that it would be preferred to refine earlywood and latewood fibres separately.
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| 5. |
- Berg, Jan-Erik, 1957-, et al.
(författare)
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LC Refining Intensity In The Light Of Forces On Fibres
- 2014
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Ingår i: International Mechanical Pulping Conference, IMPC 2014. - Espoo : Paper Engineers' Association (PI).
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Konferensbidrag (refereegranskat)abstract
- The aim of this investigation was to find new approaches to evaluate the performance of a full sized two-zoned low-consistency refiner i.e. a refiner with two stators and one rotor in between. Data from a paper mill producing TMP from Norway spruce was used in order to find a possible way to calculate the power split between the two zones. An assumption of equal amount of fibres captured between overlapping bars was found successful in order to develop equations for the power split. The equations predicted equal power in both zones at equal disc gaps. The power was found to correlate approximately linearly with the disc gap. The power split was essential to know for calculating refining intensity expressed as specific edge load and forces on fibres in the two zones. The reduction in fibre length was about 5% at 0.17 mm disc gap corresponding to 0.03 N force on fibres and 0.7 J/m specific edge load. Disc gap, force on fibres and specific edge load was found to predict the fibre shortening with approximately equal sufficiency upon changes in power and flow rate through the refiner.
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| 6. |
- Berg, Jan-Erik, 1957-, et al.
(författare)
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Low-consistency refining of CTMP targeting high strength and bulk : effect of filling pattern and trial scale
- 2021
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Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open. - 0283-2631 .- 2000-0669. ; 36:1, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- Chemithermomechanical pulp (CTMP) is often used in central layers of multiply paperboards due to its high bulk and strength. Such a CTMP should consist of well-separated undamaged fibres with sufficient bonding capacity. The basic objective of this work is to optimize process conditions in low-consistency (LC) refining, i. e. to select or ultimately develop new optimal LC refiner filling patterns, in order to produce fibrillar fines and improve the separation of fibres from each other while preserving the natural fibre morphology as much as possible. Furthermore, the aim is to evaluate if this type of work can be done at laboratory-scale or if it is necessary to run trials in pilot- or mill-scale in order to get relevant answers. First stage CTMP made from Norway spruce (Picea abies) was LC refined in mill-, pilot- and laboratory-scale trials and with different filling patterns. The results show that an LR1 laboratory refiner can favourably be used instead of larger refiners in order to characterize CTMP with regard to tensile index and z-strength versus bulk. A fine filling pattern resulted in CTMP with higher tensile index, z-strength and energy efficiency at maintained bulk compared to a standard filling pattern.
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| 7. |
- Berg, Jan-Erik, 1957-
(författare)
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Wood and fibre mechanics related to the thermomechanical pulping process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner. The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner. The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given. The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.
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| 8. |
- Engberg, Birgitta, et al.
(författare)
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A comparative study of models describing high consistency refining
- 2011
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Ingår i: Proceedings of International Mechanical Pulping Conference. - : Pulp and Paper Technical Association of Canada. - 9787501982516 ; , s. 96-100
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Konferensbidrag (refereegranskat)abstract
- By using the same selected input data in three different refining models the model predictions could be compared both in relation to each other and related to experimental data. Predictions delivered by the Miles and May model deviated most from the estimates based on measured values. The fluid dynamical model and especially the entropy model showed good agreement both when it came to describing the specific energy distribution and the local refining intensity distribution over the refining radius. However, the entropy model had problems with predicting the mean fibre velocity close to the refiner inlet while the fluid dynamical model had a tendency to overestimate the fibre velocity when approaching the periphery. In conclusion, the modelscould deliver realistic estimates. Still, the models need to be developed to be able to depict refining actions even better. To validate new or improved models, more research involving measurements from refiner gaps are needed.
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| 9. |
- Fallahjoybari, Nima, et al.
(författare)
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CFD Simulation Of Pulp Flow In Rotating And Non-Rotating Grooves
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 24-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present study deals with the numerical simulation of softwood pulp flow in the rotating and non-rotating grooves in an aim to investigate the fluid flow and forces acting on a representative surface mounted in the groove. The viscosity of softwood pulp in different consistencies is available from the experimental measurements reported in the literature providing the opportunity to examine the effects of fiber consistency on the velocity and pressure distribution within the groove. The simulations are carried out in OpenFOAM for different values of gap thickness and angular velocity from which the pressure coefficient and shear forces values are obtained. It is found that the pressure increases at the stagnation point located at the gap entrance in the non-rotating groove due to tangential motion of the upper wall which induces the helical motion of the pulp flow in the groove’s cavity. However, such an effect is not observed in the rotating cavity close to the groove inlet. Meanwhile, by moving further along the channel length toward the outlet the helical motion is enhanced and an increase in the pressure is observed at the stagnation point. The shear forces over the representative surface are found to be independent of representative surface’s location and it is in the same level in the rotating and non-rotating grooves. In addition to the numerical simulations, an analytical discussion is also presented to provide a deeper understanding of pressure coefficient and shear forces variations with different parameters in the rotating and non-rotating grooves.
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| 10. |
- Fallahjoybari, Nima, et al.
(författare)
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Investigation of pulp flow helicity in rotating and non-rotating grooves
- 2021
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Ingår i: Proceedings of the Institution of mechanical engineers. Part E, journal of process mechanical engineering. - : SAGE Publications. - 0954-4089 .- 2041-3009. ; 235:6, s. 2045-2058
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Tidskriftsartikel (refereegranskat)abstract
- Numerical simulation of pulp flow in rotating and non-rotating grooves is carried out to investigate the effect of pulp rheological properties and groove geometry on the rotational motion of the pulp flow. The eucalyptus pulp suspension is considered as a working fluid in the present study whose apparent viscosity correlation is available from the experimental measurements reported in the literature. The simulations are carried out with OpenFoam for different values of pulp material, fiber concentrations, and groove cross-section. Helicity is introduced to measure the turnover rate of pulp flow in the groove due to the importance of such motion on the final properties of the pulp flow. A measurement of helicity magnitude and its distribution along the groove revealed that a change in the pulp material would significantly affect the flow structures within the groove. Further investigation on the effects of fiber concentration, c, showed that this parameter does not have a significant effect on the averaged helicity magnitude for c = 2.0 and 2.5, whereas the helicity distribution over the groove cross-section changes clearly for c = 1.5. The results showed that the helicity level is negligible for almost half of the cavity cross-section in the non-rotating groove simulations, which can be considered as a shortcoming of the original geometry of the groove. Therefore, a smaller cross-section for the groove is considered through which an enhancement in the helicity magnitude is observed.
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| 11. |
- Gradin, Per, et al.
(författare)
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Measuring forces in a refiner plate gap
- 2011
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Ingår i: Proceedings of International Mechanical Pulping Conference. - 9787501982516 ; , s. 81-83
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Konferensbidrag (refereegranskat)
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| 12. |
- Gradin, Per, et al.
(författare)
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Measuring Tangential Forces in a Pulp Refiner : A Novel Approach
- 2016
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Ingår i: Experimental techniques (Westport, Conn.). - : Springer Science and Business Media LLC. - 0732-8818 .- 1747-1567. ; 40:2, s. 789-793
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Tidskriftsartikel (refereegranskat)abstract
- To get some insight into the processes that are active during the refining of wood, the tangential force distribution in the plate gap is of interest. Over the years several designs of force sensors have been developed for this purpose. One drawback with these designs is that each sensormeasures forces over quite a small area such that in order to cover the whole disc with a reasonably good resolution, many sensors have to be used. Also, there are problems to protect the active parts of the sensors from the harsh environment in the plate gap. In this paper a different concept is presented, in that the sensor is continuous and consists of a hollow radial bar equipped with strain gages on the inside. The force sensor was calibrated before mounting by loading it with a known load in the tangential direction and in different positions while measuring the strains in the points where the gages are located. This makes it possible to determine the so-called influence (or Green) functions. Knowing these it is possible to determine the tangential force distribution from strain values measured during operation of the refiner. Guidelines for doing this are presented together with a detailed description of the load sensor and some experimental results.
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| 13. |
- Joelsson, Tove, et al.
(författare)
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Unique steel belt press technology for development of high strength papers from HYP
- 2021
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Ingår i: TAPPICon Virtual 2021. - : TAPPI Press. - 9781713829683 ; , s. 523-531
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Konferensbidrag (refereegranskat)abstract
- The dry strength properties of hot pressed moist paper improved as stiff high-yield pulp (HYP) fibers soften and the sheet density increased. Very high wet strength was also achieved without adding strengthening agents. This research focuses on a new hot-pressing methodology based on a steel belt-based pilot cylinder press with infrared heating. The heated steel belt transports the moist paper into the cylinder nip with two adjacent steel rollers with adjustable nip pressure. The temperature ranges up to 300°C, maximum speed is 5 m/min, maximum pulling force from the steel belt is 70 kN and the line load in the two press nips is 15 kN/m each. High peak pressures are possible due to the hard press nip between steel rolls and steel belt, allowing a good heat transfer to the paper. The long dwell time allows strained drying of the paper which results to high density and high wet strength. Paper samples from high-yield pulps were tested at different nip pressures, temperatures and machine speeds while the dry content was kept constant at about 63%. High nip pressure showed the largest effect on densification and dry strength. While high temperature and long dwell time seem to be most important in achieving high wet strength.
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| 14. |
- Joelsson, Tove, et al.
(författare)
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Unique steel belt press technology for high strength papers from high yield pulp
- 2021
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Ingår i: SN Applied Sciences. - : Springer. - 2523-3963 .- 2523-3971. ; 3:5
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Tidskriftsartikel (refereegranskat)abstract
- The dry strength properties of hot-pressed moist paper improved as stiff high-yield pulp fibers soften and the sheet density increased. Very high wet strength was also achieved without adding strengthening agents. This research focuses on a new hot-pressing methodology based on a steel belt-based pilot cylinder press with infrared heating. The heated steel belt transports the moist paper into the cylinder nip with two adjacent steel rollers with adjustable nip pressure. The temperature ranges up to 300 °C, maximum speed is 5 m/min, maximum pulling force from the steel belt is 70 kN and the line load in the two press nips is 15 kN/m each. High peak pressures are possible due to the hard press nip between steel rolls and steel belt, allowing a good heat transfer to the paper. The long dwell time allows strained drying of the paper which results to high density and high wet strength. Paper samples from high-yield pulps were tested at different nip pressures, temperatures and machine speeds while the dry content was kept constant at about 63%. High nip pressure showed the largest effect on densification and dry strength. While high temperature and long dwell time seem to be most important in achieving high wet strength.
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| 15. |
- Jouybari, Nima Fallah, et al.
(författare)
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An investigation of forces on a representative surface in a pulp flow through rotating and non-rotating grooves
- 2023
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Ingår i: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer. - 1678-5878 .- 1806-3691. ; 45:5
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Tidskriftsartikel (refereegranskat)abstract
- Softwood pulp flow in rotating and non-rotating grooves is numerically simulated in the present study to investigate the fluid flow and the forces acting on a representative surface mounted in the groove. The viscosity of softwood pulp with various consistencies is available from the measurements reported in the literature providing the opportunity to examine the effects of fiber consistency on the velocity and pressure distribution within the groove. The simulations are carried out in OpenFOAM for different values of gap thickness, angular velocity and radial positions from which the pressure coefficient and shear forces values are obtained. It is found that the shear forces within the gap increase linearly with the angular velocity for all fiber consistencies investigated and in both grooves. Also, this behavior can be successfully predicted by modeling the gap flow as a Couette flow in a two-dimensional channel. Meanwhile, a more detailed analysis of the flow kinetic energy close to the stagnation point using Bernoulli’s principle is carried out to provide a better understanding of the pressure coefficient variation with angular velocity in the non-rotating groove. A comparison of pressure coefficients obtained numerically with those calculated by considering the compression effects revealed that the comparison effects are dominating in the pulp flow within the groove.
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| 16. |
- Lindström, Stefan B, Professor, 1974-, et al.
(författare)
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Pulp Particle Classification Based on Optical Fiber Analysis and Machine Learning Techniques
- 2024
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Ingår i: Fibers. - : MDPI AG. - 2079-6439. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- In the pulp and paper industry, pulp testing is typically a labor-intensive process performed on hand-made laboratory sheets. Online quality control by automated image analysis and machine learning (ML) could provide a consistent, fast and cost-efficient alternative. In this study, four different supervised ML techniques—Lasso regression, support vector machine (SVM), feed-forward neural networks (FFNN), and recurrent neural networks (RNN)—were applied to fiber data obtained from fiber suspension micrographs analyzed by two separate image analysis software. With the built-in software of a commercial fiber analyzer optimized for speed, the maximum accuracy of 81% was achieved using the FFNN algorithm with Yeo–Johnson preprocessing. With an in-house algorithm adapted for ML by an extended set of particle attributes, a maximum accuracy of 96% was achieved with Lasso regression. A parameter capturing the average intensity of the particle in the micrograph, only available from the latter software, has a particularly strong predictive capability. The high accuracy and sensitivity of the ML results indicate that such a strategy could be very useful for quality control of fiber dispersions.
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| 17. |
- Sandberg, Christer, 1962-, et al.
(författare)
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LC refining combined with screen fractionation – Reduction of system complexity for mechanical pulping
- 2018
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Ingår i: IMPC 2018. - Trondheim, Norway.
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Konferensbidrag (refereegranskat)abstract
- Process intensification - a process development method used in the chemical process industry has been appliedto mechanical pulping process design. Process intensification is characterized by significant reduction of energyconsumption and process complexity.A process with single stage high consistency (HC) refining followed by low consistency (LC) refining andscreening was evaluated in mill trials at the Holmen Paper Braviken mill, Sweden. After LC refining, pulp wasscreened and the reject was fed back to LC refining. The process is called HC-LC-S. Two different HC primaryrefiner types were evaluated – single disc (SD) and double disc (DD).High intensity DD chip refining was more suitable than single disc refining for the process due to higher lightscattering and lower shives content of the final pulp. It was also easier to reach high enough tensile index beforeLC refining with the DD refining. The DD-LC-S process required 1940 kWh/adt total specific energy for newsgrade TMP, which was 300 kWh/adt lower than the reference TMP line; DD chip refining and HC rejectrefining. The auxiliary specific energy was reduced with 100 kWh/adt.Six unit operations and three chests with agitators and pumps were omitted compared to a conventional TMPline.
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| 18. |
- Sandberg, Christer, 1962-, et al.
(författare)
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Low Consistency Refining Combined with Screen Fractionation : Reduction of Mechanical Pulping Process Complexity
- 2019
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Ingår i: BioResources. - 1930-2126. ; 14:1, s. 882-894
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Tidskriftsartikel (refereegranskat)abstract
- Process intensification is a process development methodology aimed at a considerable reduction in the energy consumption and process complexity. The approach has been applied to mechanical pulping process design. A process denoted as HC-LC-S consisting of single stage high consistency (HC) refining, followed by low consistency (LC) refining and screening was evaluated in mill trials at the Holmen Paper Braviken Mill in Sweden. After LC refining, the pulp was screened, and the reject fraction was fed back to LC refining. Two HC primary refiner types were evaluated, namely single disc (SD) and double disc (DD). Double disc chip refining was more suitable than SD refining for the HC-LC-S process because of the higher light scattering and lower shives content of the final pulp. The tensile index and shives content of the pulp produced with the DD-LC-S process was similar to that of the reference process, consisting of single stage DD refining and HC reject refining, but the fibre length and light scattering were somewhat lower. The specific refining energy was approximately 200 kWh/adt lower for the DD-LC-S process compared with the reference. Additionally, the auxiliary specific energy was 100 kWh/adt lower for the HC-LC-S processes, since a number of equipment units were omitted.
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| 19. |
- Sandberg, Christer, 1962-, et al.
(författare)
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Low consistency refining of mechanical pulp - system design
- 2017
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Ingår i: TAPPI Journal. - 0734-1415. ; 16:7, s. 419-429
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Tidskriftsartikel (refereegranskat)abstract
- Many mechanical pulping mills use low consistency (LC) refining for energy efficient fiber development. In this study, energy efficiency and pulp quality were evaluated for six processes, of which four included LC refining. We studied two different types of chip refiners - single disc (SD) and double disc (DD) - with LC refining in the main and reject lines. All process combinations have been used in the Holmen Paper Braviken mill, Sweden, to make thermomechanical pulp for printing papers. LC refining was more energy efficient than high consistency (HC) refining at certain tensile index increases in all evaluated combinations. LC refining in the main line had somewhat higher energy efficiency than did LC refining in the reject line. The type of chip refiner (DD or SD) did not affect the efficiency or pulp property development in LC refining. The process with a combination of DD chip refining and LC refining had the highest energy efficiency (tensile index at certain specific energy consumption). All processes with LC refining produced pulp with somewhat lower light scattering and fiber length than did the corresponding system with only HC refining. Thus, for printing papers, the best combination was LC refining with DD chip refining. LC refiners seem to have a narrow range in specific energy for maximum energy efficiency and a good balance between tensile index increase and fiber length reduction. Much higher specific energy was applied on reject pulp. However, the reject share was only around 30%. The LC refining specific energy, based on main line production, was around 80 kWh/air-dried metric ton (a.d. metric ton), whereas up to 180 kWh/a.d. metric ton was applied in main line.
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| 20. |
- Sandberg, Christer, et al.
(författare)
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Mill evaluation of an intensified mechanical pulping process
- 2017
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 32:2, s. 204-210
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Tidskriftsartikel (refereegranskat)abstract
- Mill-scale demonstration of a process concept inspired by Process Intensification (PI) principles was performed in Holmen Paper Braviken mill, Norrkoping, Sweden. The intensified process consists of wood softening by means of chip pretreatment with sodium sulphite, high intensity refining followed by low consistency refining. This process yields very low shives content and thus the unit operations screening and reject refining can be eliminated and the pulp is fed directly to the paper machine. Thorough evaluation of key paper-and print quality data showed that it is possible to produce pulp for newsprint at 1500 kWh/adt total specific energy (including auxiliary drives such as pumps, screw feeders, etc.). The total specific energy consumption was 900 kWh/adt lower compared to the normal process used for newsprint in Braviken, and 500 kWh/adt lower compared to today's best available technology. The auxiliary equipment energy demand was 120 kWh/adt, which was less than half of that of the reference TMP line. The PIinspired process reduces the number of machines drastically compared to a conventional TMP line, as well as the number of pumps, chests and other auxiliary equipment.
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| 21. |
- Sandberg, Christer, 1962-, et al.
(författare)
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Process intensification in mechanical pulping
- 2017
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 32:4, s. 615-622
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Tidskriftsartikel (refereegranskat)abstract
- Process intensification is a term used in the chemical process industry for major improvements in the process design leading to radical changes in process complexity, equipment size and efficiency. We suggest that a similar approach is applied in the pulp and paper industry. We have focused on the production of mechanical pulp, but a similar approach can be applied to other areas within the pulp and paper industry. Inspired by process intensification methodology, we suggest five principles for development of the mechanical pulping process. Three fundamental principles; 1. Break up the wood and fibre wall structure in the right positions. 2. Give each fibre, of certain morphology, the same processing experience. 3. Optimize the applied mechanical forces and the physiochemical state of the wood and fibre material. and two system oriented principles; 1. Select wood raw material based on final product specifications. 2. Design the process to facilitate observability, controllability and maintenance. Implications of these principles on process design and future challenges for mechanical pulping are discussed.
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| 22. |
- 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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- Sandberg, Christer, 1962-, et al.
(författare)
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System Aspects on Low Consistency Refining of Mechanical Pulp
- 2016
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Ingår i: TAPPI 2016 International Mechanical Pulping Conference (IMPC). - : TAPPI Press. - 9781510830738 ; , s. 485-495
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Konferensbidrag (refereegranskat)abstract
- Several combinations of high consistency (HC) and low consistency (LC) refiners were evaluated both in main line and reject line for production of pulp for printing papers. HC-LC processes were compared with processes with only HC refining. Processes with two different types of chip refiners were studied – single disc (SD) and double disc (DD). All process combinations were evaluated during continuous production in the Holmen Paper Braviken mill, Sweden. The purpose of this work was to evaluate energy efficiency and pulp quality for the processes.LC refining was more energy efficient than HC refining for certain tensile index increase in all evaluated combinations. The highest energy efficiency was attained when LC refining was utilized in main line, but the difference was small compared to application on reject. Much higher specific energy was applied on reject pulp, but since the reject share was only around 30%, the LC refining specific energy, based on main line production, was around 80 kWh/air dry ton (adt) whereas up to 180 kWh/adt was applied in main line.The combination of DD chip refining and LC refining had the highest energy efficiency (tensile index at certain specific energy consumption) and produced pulp with somewhat lower fibre length but higher light scattering and lower shives content compared to a line with only SD HC refining. Thus, for printing papers it seems beneficial to combine LC refining with high intensity HC chip refining. All processes with LC refining had lower light scattering and fibre length compared to the corresponding system with only HC refining.
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