Estudio de la flotación para el destintado de la fracción de fibra corta en pulpa procedente de papel recuperado

Optimización de las variables para el destintado por flotación de la fracción de fibra corta en un proceso de destintado de pasta de papel con fraccionamient

Comparison of pin mill and hammer mill in the fine grinding of sphagnum moss

Abstract Dried sphagnum moss was ground using a pin mill and a hammer mill under various operating conditions, i.e., changes in the rotor frequency and feed rate. The specific energy consumption of the size reduction was recorded. The ground powder was characterized by median particle size, width of size distribution (span), loose and tapped bulk densities, and the Hausner ratio. Pin milling used less energy for size reduction than hammer milling, especially when the target size was below 100 μm. In both milling methods, the specific energy consumption was mainly caused by the rotor frequency used. However, in pin milling, the specific energy consumption was also dependent on the production rate: the higher the rate, the higher the energy consumption. No such dependence was observed with the hammer mill. The span was wider in pin milling than hammer milling in the intermediate product size range although the difference decreased at the fine and coarse ends. A similar pattern was found for bulk densities. However, the flowability of powder, as characterized by the Hausner ratio, was comparable between the grinding methods

Fractionation of thermomechanical pulp in pressure screening:an experimental study on the classification of fibres with slotted screen plates

Abstract Pressure screening, nowadays the most widely used method for cleaning pulp, has been traditionally investigated as a debris removal process. The aim of this thesis, however, was to study it with a view to the fractionation of pulps, examining systematically and extensively the effects of screening parameters on fractionation under actual working conditions in order to provide an insight into its possibilities and limitations as a fractionation method. The experimental work was performed with a full-scale two-stage pressure screen connected to an industrial TMP process. Fractionation of the pulp was analysed in terms of consistency, freeness, optical fibre length distribution, coarseness index and Bauer-McNett fractions. Two sampling systems were used during the screening experiments, manual and semiautomatic. The latter was assessed to be more reliable, as reflected in lower stochastic variation and the absence of a systematic bias in the mass balance errors over the screen. The poorer reliability of the manual sampling system was offset by the large number of screening tests, however. The results of the screening experiments showed that with a given design of the screen plate, the separation of each fraction was dependent almost exclusively on the mass and volumetric reject rates. The mass flow of fines, defined as the Bauer-McNett P200 fraction, was dependent mostly on the volumetric reject rate, while the mass flow of fibrous fractions (R200, R50, R30, R16) depended mostly on the mass reject rate. The mass reject rate obtained in pressure screening was a result of the choice of operating parameters, but fractionation efficiency could not be affected by using different combinations of these parameters (feed consistency, rotor tip speed and slot velocity) if the mass and volumetric reject rates were kept constant. The slot width together with the contouring of the screen plate affected the fractionation efficiency as compared with the situation at constant mass and volumetric reject rate. Increased fractionation was obtained by reducing the slot width and contouring. The pulp passage ratio, which combines the mass and volumetric reject rates into one parameter, was found to be a expedient way of expressing the fractionation of pulp, as it was possible to present fractionation uniformly as a function of this ratio. The change in freeness was found to correlate quite well with that in Bauer-McNett fractions, and it was a good indicator of fractionation efficiency in screening. Apart from fractionation according to length (or Bauer-McNett fractions), the slotted pressure screen was also found to classify the fibres according to their coarseness. The coarseness difference was partially dependent on the fibre length, but additionally the coarseness in the accept pulp for any given fibre length class was always lower than that in the reject pulp. The difference obtained seemed to depend on the passage ratio of the pulp. This thesis provides new information for the modelling of pulp quality and the design of fractionation experiments, fractionation processes and screen room control strategies

METHOD FOR AUTOMATIC ANALYSIS OF WHEAT STRAW PULP CELL TYPES

Agricultural residues are receiving increasing interest when studying renewable raw materials for industrial use. Residues, generally referred to as nonwood materials, are usually complex materials. Wheat straw is one of the most abundant agricultural residues around the world and is therefore available for extensive industrial use. However, more information of its cell types is needed to utilize wheat straw efficiently in pulp and papermaking. The pulp cell types and particle dimensions of wheat straw were studied, using an optical microscope and an automatic optical fibre analyzer. The role of various cell types in wheat straw pulp and papermaking is discussed. Wheat straw pulp components were categorized according to particle morphology and categorization with an automatic optical analyzer was used to determine wheat straw pulp cell types. The results from automatic optical analysis were compared to those with microscopic analysis and a good correlation was found. Automatic optical analysis was found to be a promising tool for the in-depth analysis of wheat straw pulp cell types

Pine sawdust modification using Fenton oxidation for enhanced production of high-yield lignin-containing microfibrillated cellulose

Abstract Sawdust is an abundant high-quality residue from sawmills, representing 20–30 % of sawn products by volume. In this study, the chemical pre-treatment of pine sawdust with Fenton’s reagent, formed from hydrogen peroxide and iron catalyst under moderately acidic conditions, was found to intensify the microfibrillation process in terms of energy consumption and improve the grade of the high-yield lignin-containing microfibrillated cellulose (LMFC) produced. With a minor yield loss of 5.5 wt.%, Fenton pre-treatment increased the microfibrillation rate and bonding potential of LMFC, indicating that the ultrastructure of the lignocellulose cell walls had been modified. Linear dependency between the growth of specific surface area and energy consumption was seen, i.e. microfibrillation followed Rittinger’s law of comminution. In comparison with the reference without any pretreatment,the total grinding energy consumption to a particle size of 14 µm was about 30 % lower (10.7 vs. 15 MWh/t) while the tensile strength and stiffness of LMFC films were 50 % (100 vs. 66 MPa) and 35 % higher (6.6 vs. 4.9 GPa), respectively. The advantageous effects of Fenton chemistry were assumed to originate from the cleavage of lignin-carbohydrate bonds, mainly between lignin and hemicelluloses. This phenomenon was supported by the substantially increased solubility of polysaccharides in dilute alkali. The calculated manufacturing costs of LMFCs (using the above-mentioned specifications) was € 850/t, of which the raw material, chemical and electricity costs accounted for 10 %, 2 % and 88 %, respectively. Without any chemical pre-treatment, manufacturing costs were € 1100/t of which raw material accounted for 7 % and electricity 93 %

Role of screen plate design in the performance of a rotor impact mill in fine grinding of biomass

Abstract The role of rotor impact mill screen plate design in biomass grinding has attracted limited interest. This study aimed to clarify the effect of operational parameters and various screen designs on the fine grinding of Sphagnum moss. Contoured screens having forward (rasp) and backward (inverse rasp) inclined trapezoidal apertures of nominal sizes 0.2, 0.3, 0.4, and 0.5 mm were studied. A smooth screen plate having circular perforations (0.5 mm) was used as a reference. Flow phenomena were modeled with Computational Fluid Dynamics (CFD) using 2D geometry for the screen apertures. Product particle size and capacity were mostly dependent on the equivalent diameter of the screen apertures together with rotor frequency and also on the screen design, while the aspect ratio was solely a function of particle size. Among the screens having nominal sizes of 0.3, 0.4, and 0.5 mm, the smooth screen produced the smallest particle size; followed by the rasp screens and the inverse rasp screens. The smooth screen had higher capacity than the rasp or inverse rasp screens, and a narrower operating range. In the case of 0.2 mm apertures, higher capacity was achieved with the inverse rasp than with the rasp screen. The net energy consumption (SEC) of grinding with the rasp screens was at a lower level than with the inverse rasp screens (or the smooth screen). No difference was seen in the case of the smallest size apertures, however. The results, supported by CFD modeling, indicate that the incidence angle of particles does not explain the passage of particles through screen apertures. The passage is affected by the flow patterns above and within the apertures, and the pressure difference over the screen plate. The eddies within the apertures reduce their effective open area, resulting in product particles much smaller than the aperture size. When the aperture inclination is toward the tangential flow (rasp), an eddy is also generated in front of the aperture that turns the flow perpendicular to the screen surface within the aperture. In contrast, when the aperture inclination is against the tangential flow (inverse rasp), an eddy is generated above the aperture that guides the flow smoothly into the aperture, although the flow has to make a U-turn first. A design of inverse rasps seems to be beneficial when very small apertures are used, as it appears that the eddies formed above the apertures prevent blocking by dislodging accumulated particles. The low SEC with rasp screens does not seem to make the passage of particles through apertures easier, but it does enable more efficient size reduction because of the ability of rasps to serve as a grinding track

Study of butyl-amine nanocrystal cellulose in the flotation of complex sulphide ores

Froth flotation is a widely used process for the beneficiation of complex sulphide ores. Thiol collectors (mostly xanthates) are usually effective collectors for sulphide minerals but may have a low selectivity between different sulphide minerals when associated in complex sulphide ores. Additionally, a concern is their suggested harmfulness on human health and impact on the environment. In this study, a green sustainable reagent, butyl-amine cellulose (BAC), was synthesized from hardwood kraft pulp, a renewable abundant resource, for the selective separation of chalcopyrite and sphalerite. The performance evaluation was made using samples of two ores containing chalcopyrite and sphalerite, one was from Panasqueira mine (Portugal) and the other with a different mineral association (from the massive sulphide deposits of the Iberian Pyrite Belt). The study demonstrated that when chalcopyrite is associated with sphalerite, BAC is selective for chalcopyrite, i.e., it is a collector for this mineral and not for sphalerite. The recovery of chalcopyrite in the floated product was a function of interaction between BAC concentration and pulp pH. The study showed that the novel cellulose-based collector had a better performance than the reagents used in the industrial flotation of Panasqueira ore.Peer reviewe

Energy consumption, physical properties and reinforcing ability of microfibrillated cellulose with high lignin content made from non-delignified spruce and pine sawdust

Abstract The production of MFC and CNF has recently been focused on fiber raw materials which, still contain residual lignin instead of bleached chemical pulp fibers. The target of this study was to assess the energy consumption and microfibrillation rate for high lignin containing microfibrillated cellulose (LMFC) produced from non-delignified pine and spruce sawdust directly or after lignin-preserving sulfonation, and evaluate their grade by measuring strength properties of self-standing films made from the LMFCs and by determining their ability to reinforce fluting board. MFC from bleached softwood was used as a reference. Microfibrillation rate at 80 °C was faster for spruce sawdust than for pine sawdust, i.e., bonding ability (measured as tensile strength of self-standing films) developed faster in spruce LMFC than in pine LMFC. By mild pre-sulfonation of sawdust, corresponding to the sulfonation degree of 0.5−0.6 %, the rate increased further with both softwood species. In similar grinding conditions and equal grinding time, pre-sulfonation did not affect much energy consumption but at a given specific energy consumption the grade of LMFC was better. Due to the high lignin content, mechanical properties of LMFCs could not been developed at as high level than MFC. However, the tensile strength of 100 MPa was possible to achieve for LMFC films using either the equivalent (spruce and sulfonated pine) or even clearly lower amount (sulfonated spruce) of grinding energy than in microfibrillation of bleached Kraft pulp to the same strength. By comparing the pre-sulfonation of sawdust and the post-sulfonation of LMFC, it was concluded that the main sulfonation effect in grinding was lignin softening, which enhanced cell wall disintegration in microfibrillation. The increased bonding ability of sulfonated lignin and the dissolution of extractives were seen to be secondary effects but not without significance. Pre-sulfonation also improved redispersibility, i.e., the recovery of the mechanical properties of dried LMFCs. The reinforcing potential was evaluated by dosing LMFCs and MFC without a retention aid into the handsheets made from fluting pulp. The tensile strength of fluting increased almost linearly with an increasing dosage and increasing microfibrillation time. Although the grade of LMFCs, in terms of viscosity and mechanical properties of LMFC films, was lower than that of MFC from bleached softwood, their ability to reinforce fluting board was shown to be equal, indicating lignin present did not interfere the formation of hydrogen bonds. With a 4 % dosage (equaling to the amount of 2–2.5 % within the handsheets) of each LMFC microfibrillated for 120 min, the tensile strength improved by 20 %. Among the tested raw materials, LMFC from spruce sawdust without pre-sulfonation has the greatest potential as a cost-effective reinforcing agent for the paper and board industry. For sulfonated LMFCs should be found applications where their better bonding ability could be better utilized

Fine grinding of wood:overview from wood breakage to applications

Abstract Due to its abundance, wood is the pre-eminent lignocellulosic raw material for a sustainable bioeconomy based society. Wood is widely used as fuel, construction material, and raw material in cellulose and lignocellulose based products. Besides the established uses of wood powder, like co-firing with coal and biofuel production, there are also novel uses and process applications, e.g., advanced wood-plastic composites and biochemical production are emerging for which the pulverization or fine grinding of wood is an essential pre-treatment step. Due to the tenacious nature of the wood matrix, size reduction is an energy intensive process and thermal or chemical pre-treatment may be needed to improve economy. This paper provides a broad overview of the fine grinding of wood. First, wood breakage mechanisms and the mechanisms of size reduction are presented, followed by fine grinding techniques and wood pre-treatment methods. A comparison of the specific energy consumption of wood fine grinding in both a gaseous and liquid environment is illustrated. Additionally, examples are given of the role played by pre-treatment methods in decreasing energy consumption. The particle aspect ratio is discussed briefly. Finally, the use and requirements of wood powders in various applications are discussed

Key role of mild sulfonation of pine sawdust in the production of lignin containing microfibrillated cellulose by ultrafine wet grinding

Abstract Cheaper methods and raw materials are currently being sought for the production of microfibrillated cellulose. Presently microfibrils with high lignin content have attracted increasing interest. Wood residues, like sawdust, are good candidates due to their abundancy and low price but the recalcitrant nature of the lignocellulose complex is an obstacle for the mechanical separation of microfibrils directly from wood. The purpose of this study was to investigate whether the mild sulfonation pretreatment of pine sawdust with sodium sulfite in neutral and mild alkaline conditions could enhance mechanical fibrillation in ultrafine wet grinding. Sawdust sulfonated at pH 7 and 9 resulted in a lignin sulfonation degree of 0.5–0.6% with a yield loss of 5–6%, approximately half of which was due to the dissolution of extractives from the initial content of 4.7% to 1.3–1.5%. Sawdust (with and without sulfonation) was pre-ground first in a twin-screw extruder, followed by ultrafine grinding with a friction grinder at a temperature of 80 °C. The viscosity and size distribution of the microfibrillated sample suspensions were determined. Additionally, the samples were filtered on a membrane, dried, and the mechanical properties of the sheets made from the samples were measured. The results showed that the sulfonation of softwood sawdust is a promising economic and environment-friendly method to produce microfibrillated cellulose with high lignin content (above 28%), having excellent strength properties, low viscosity, and fast dewatering rates. The sheets made from the sulfonated samples yielded an almost twofold increase in tensile strength and Young’s modulus (100 MPa and 7–7.5 GPa, respectively) compared to the reference sample without sulfonation (52 MPa and 4.3 GPa) at an applied net grinding energy of 7 MW h per ton. It was found that the size of the fibrils was at a similar level with and without sulfonation, but the bonding ability of the sulfonated samples was clearly better