Mechanical Pulping Process Research Articles

Towards optimal defibration: Energy reduction by fatiguing pre-treatment

Abstract A motive for fatiguing wood prior to defibration would be to reduce the energy consumption needed in mechanical pulping processes. Therefore, the effects of fatiguing pre-treatment were here studied on wood samples, on defibration and also on produced paper. The results indicate that pre-fatiguing changes the mechanic response of wood to be more favorable for harsh defibration which in turn is positive for the process efficiency.

Energy Use and GHG Emissions in the Quebec Pulp and Paper Industry, 1990–2006

Greenhouse gas (GHG) emissions of the Quebec pulp and paper industry fell by more than 30 percent from 1990 to 2006. We use an energy demand model to analyze the contributions to this decrease of energy prices, product mix, technological change, and biomass use. The product mix is made of pulp, and cardboard, and paper. Pulp is an intermediate product for the industry, but not necessarily so for mills; vertical integration varies across mills and presents different opportunities to transfer heat between stages of production. Chemical and mechanical pulping processes are used to form two groups of pulp and paper mills. We find that changes of product mixes contributed the most to reduce GHG emissions, followed to a lesser extent by increases of fuel prices relative to electricity. The estimated electricity and fuel price elasticities are low. However it is still possible to significantly reduce GHG emissions by substituting natural gas for heavy fuel oil; such a substitution could be brought about by a small change of their relative price.

Significance of fatigue for mechanical defibration

The fatigue induced by high-frequency cyclic loading on the compressibility and tensile properties of wood and wood cell walls was quantified. The non-elastic behavior of fatigued and reference samples was similar, whereas their elastic behavior differed, as expected. Next, the effects of the dynamic fatigue on the mechanical pulping process were quantified by grinding fatigued and untreated samples and by comparing the paper strength produced by the two pulps against the consumed pulping energy. Pre-introducing fatigue increased the energy efficiency of grinding and may allow designing a more energy efficient mechanical pulping process.

Energy Use and GHG Emissions in the Quebec Pulp and Paper Industry, 1990–2006

Au Quebec, l’industrie des pâtes et papiers a reduit de plus de 30 % ses emissions de gaz a effet de serre (GES) de 1990 a 2006. Dans cet article, nous analysons, a l’aide d’un modele de la demande d’energie, les facteurs qui ont contribue a cette reduction : prix de l’energie, portefeuille de produits, changements technologiques et utilisation de la biomasse. Le portefeuille de produits de cette industrie se compose de pâte, de carton et de papier. Si la pâte est, pour l’industrie consideree dans son ensemble, un produit intermediaire, ce n’est pas necessairement le cas pour les usines prises individuellement ; l’integration verticale, qui varie selon les usines, offre differentes possibilites de transferer la chaleur d’un stade de production a un autre. Nous avons reparti les usines en deux groupes sur la base des procedes chimiques et mecaniques utilises pour reduire le bois en pâte. Nos resultats montrent que ce sont les changements dans le portefeuille de produits qui ont le plus contribue a la reduction des emissions de GES. L’augmentation du prix du carburant par rapport a celui de l’electricite a joue un certain role, mais beaucoup moins important. Enfin, selon l’estimation que nous avons faite, l’elasticite des prix de l’electricite et du carburant est faible, mais il est quand meme possible de reduire de maniere appreciable les emissions de GES en remplacant le mazout lourd par l’electricite ; un faible changement des prix relatifs de ces deux types de sources d’energie peut justifier une telle substitution. Abstract: Greenhouse gas (GHG) emissions of the Quebec pulp and paper industry fell by more than 30 percent from 1990 to 2006. We use an energy demand model to analyze the contributions to this decrease of energy prices, product mix, technological change, and biomass use. The product mix is made of pulp, and cardboard, and paper. Pulp is an intermediate product for the industry, but not necessarily so for mills; vertical integration varies across mills and presents different opportunities to transfer heat between stages of production. Chemical and mechanical pulping processes are used to form two groups of pulp and paper mills. We find that changes of product mixes contributed the most to reduce GHG emissions, followed to a lesser extent by increases of fuel prices relative to electricity. The estimated electricity and fuel price elasticities are low. However it is still possible to significantly reduce GHG emissions by substituting natural gas for heavy fuel oil; such a substitution could be brought about by a small change of their relative price.

Fundamental understanding of pulp property development under different thermomechanical pulp refining conditions as observed by a new Simons’ staining method and SEM observation of the ultrastructure of fibre surfaces

Abstract The morphological and chemical characteristics of cell walls govern the response of wood fibre to mechanical pulping processes and thereby influence the energy efficiency of the process and determine most pulp and paper properties. A study has been carried out at the microstructural/ultrastructural level of fibre cell walls by means of a newly developed Simons’ staining (SS) method and scanning electron microscopy to characterize thermomechanical pulps (TMPs) produced under different refining conditions. The SS method allows assessment and quantification of pulp fibre development during the process in terms of cell wall delamination/internal fibrillation (D/IF) under different process conditions, and the degree of D/IF can be statistically evaluated for different TMP types. In focus was never-dried Norway spruce TMP from primary stage double-disc refining running in a full-scale mill, where specific refining energy was varied at different refining pressure levels. Improved energy efficiency was gained at the same tensile index level when applying high pressure (temperature). Under conditions of high pressure and refining energy, a significant enhancement of the degree of D/IF of pulp fibres was observed. The surface ultrastructure of these fibres exhibited an exposed S2 layer with long ribbon-type fibrillation compared to pulps produced with lower pressure and energy input. A given TMP type can be classified in the categories of high-severity and low-severity changes and quasi-untreated concerning the degree of D/IF of its fibres. The relative proportions of these are important for the development of pulp properties such as tensile strength. The presence of higher amounts of fibre fractions in the categories high D/IF and low D/IF will improve the tensile index of a TMP.

Treatment of APMP pulping effluent based on aerobic fermentation with Aspergillus niger and post-coagulation/flocculation

A novel two-stage biological/flocculation process was developed for treating the pulping effluent from the alkaline peroxide mechanical pulping (APMP) process. In the first biological stage, the aerobic fermentation by using Aspergillus niger can decrease the chemical oxygen demand (COD) by about 60% while producing about 7g/l of solid biomass. In the second stage (post-coagulation/flocculation), the residual COD, turbidity and color, can be further decreased by using alum and polyacrylamide (PAM). The overall removal efficiencies of COD, color and turbidity from the APMP pulping effluent by the above two-stage biological-coagulation/flocculation process were 93%, 92% and 99%, respectively, under the conditions studied.

Advanced Step Nonlinear Model Predictive Control for Two-stage Thermo Mechanical Pulping Processes

AbstractIn this work, we use a general nonlinear model predictive control (NMPC) technique for the two-stage (primary and secondary refining) thermo-mechanical pulping (TMP) refining process. The NMPC strategy is based on empirical and first-principle models which describe dynamic behavior and interactions among process variables. The computational burden is one of main drawbacks of NMPC controllers when applied to real systems. In this work, we handle the computational burden of the resulting nonlinear programming (NLP) problem using the IPOPT (Interior Point OPTimizer) solver. This is further improved with the advanced step NMPC (asNMPC) controller concept, a sensitivity based approximation to the solution of the resulting NLP. The simulation study compares the performances of the ideal-NMPC and the asNMPC strategies. The asNMPC controller reduces the CPU time and performs well in the presence of disturbances.

Designing an Economical Membrane Process to Concentrate the Effluent from Alkaline Peroxide Mechanical Pulping Plants

Using a multi-effect evaporation system to concentrate the effluent from alkaline peroxide mechanical pulping (APMP) plants is known to require a high energy consumption. In order to improve the situation, a polyethersulfone (PES) membrane was used to concentrate the effluent of APMP plants beforehand. An orthogonal experimental design was applied and a mathematical model was established to optimize the filtration parameters. An estimation of potential energy and water savings from this new concentration process was developed. The optimal filtration conditions obtained were: molecular weight cut-off at 10,000 Dalton, trans-membrane pressure at 3 bar, feed temperature at 50oC, cross-flow velocity at 420 rpm, and volume reduction factor at 0.93. The average permeate flux under these conditions was 45.31 l/m2.h. The total solids content was increased from 14.74 g/l in the feed to 95.04 g/l in the concentrate. The permeate had low total solid contents of 8.75 g/l, Chemical Oxygen Demand of 6696 mg/l, and Biochemical Oxygen Demand of 4383 mg/l. Such qualities would allow the permeate to be reused in the alkaline peroxide mechanical pulping process. With this new concentration process, about 4840.6 kWh energy can be saved and 23.3 m3 effluent discharge can be reduced for each ton of pulp produced.

Using a membrane filtration process to concentrate the effluent from alkaline peroxide mechanical pulping plants

Using a multi-effect evaporation system to concentrate the effluent from alkaline peroxide mechanical pulping (APMP) plants is known to require a high energy consumption. In order to improve the situation, a polyethersulfone membrane was used to concentrate the effluent of APMP plants beforehand. An orthogonal experimental design was applied and a mathematical model was established to optimize the filtration parameters. An estimation of potential energy and water savings from this new concentration process was developed. The optimal filtration conditions obtained were: molecular weight cut-off at 10,000 Dalton, trans-membrane pressure at 3 bar, feed temperature at 50oC, cross-flow velocity at 420 rpm, and volume reduction factor at 0.93. The average permeate flux under these conditions was 45.31 l/m2.h. The total solids content was increased from 14.74 g/l in the feed to 95.04 g/l in the concentrate. The permeate had low total solid contents of 8.75 g/l, Chemical Oxygen Demand of 6696 mg/l, and Biochemical Oxygen Demand of 4383 mg/l. Such qualities would allow the permeate to be reused in the alkaline peroxide mechanical pulping process. With this new concentration process, about 4840.6 kwh energy can be saved and 23.3 m3 effluent discharge can be reduced for each ton of pulp produced.

Partially Substituting MgO for NaOH as the Alkali Source in the Second-Stage Impregnation of Triploid Poplar P-RC APMP

In the conventional preconditioning followed by refiner chemical treatment, alkaline peroxide mechanical pulping (P-RC APMP) process, sodium hydroxide (NaOH) is used as the alkali source. In this study, magnesium oxide (MgO) was used to partially substitute for NaOH as the alkali source (substitution ratio of up to 50%) in the second-stage impregnation of the triploid poplar P-RC APMP process. The changes in pH values of the residual bleaching liquor, yields, and chemical components of the treated wood chips in the second-stage impregnation and also the physical properties of the resultant P-RC APMP pulps with and without MgO substitution were investigated to explore the potential advantages of the process. The results showed that the partial MgO substitution for NaOH resulted in a lower pH of residual bleaching liquor and a higher treated wood chips yield than those of the NaOH-based process. In addition, the dissolution of benzene alcohol extractives, lignin, pentosans, and carbohydrates were all decreased. The resultantly yielded P-RC APMP pulp has a higher bulk, opacity, and light-scattering coefficient, but lower strength properties and a slightly lower brightness.

Mechanical pulping for manufacture of hand made paper from Date-Palm leaves (Phoenix dactylifera - L)

The present paper highlights the production of pulp from agro-residues by mechanical pulping for the benefit of Indian paper industry. Date-Palm leaf (DPL), a renewable agro-residue is an excellent raw material for making pulp and paper of different grades due to high alpha cellulose (50-58%) and hemi cellulose contents (26-32%). These constituents play a stellar role in mechanical pulping i.e. in beating operation without using any chemical. Ultimate fibre length (1.25 mm to 2.50 mm) is also higher than fibres of other agro-residues, recycled cotton rag and paper. Yield and mechanical properties of the pulp of 100% DPL fibre obtained by mechanical pulping process attained higher values as compared to its blends with recycled cotton rag. Chemo-mechanical process is costly and not environment friendly. Moreover, yield and mechanical properties of the paper obtained in this process are poor. Hemi cellulose (more than 25%) and non-cellulosic polysaccharide which exist in cell wall of fibres contribute to efficient beating operation and fibre bonding. Hemi cellulose also contributes largely towards higher burst index, tensile index and folding endurance to the pulp sheet specially produced without using any chemical in the entire process.

Analysis of chemical changes in Picea abies wood decayed by different Streptomyces strains showing evidence for biopulping procedures

The present study is focused on analysing the suitability of different Streptomyces strains for biomechanical pulping purposes using spruce wood (Picea abies) as substrate. After 2 weeks of incubation, no apparent variations in lignin Klason content of treated woods were detected compared with the control. However, the increase in acid-soluble lignin fraction pointed out chemical alterations in lignin moiety. Through Py-GC/MS analysis enrichment in cellulose and lignin molecule modifications were detected in treated woods. The increase in the relative abundance of the most G-type phenol units with a higher oxidation degree suggests that some oxidation occurred in the lignin C3-alkyl chain. In addition, the decrease in the phenylmethane + phenylethane/phenylpropane (phC1 + ph C2/ph C3) ratio would indicate the ability of Streptomyces strains to breakdown the C3-alkyl chain linkages once carbons had been oxidized. From this study it could be concluded that the assayed strains are able to produce a delignification of spruce wood which may improve mechanical pulping processes.

Refining Energy Reduction and Pulp Characteristic Modification of Alkaline Peroxide Mechanical Pulp (APMP) Through Enzyme Application

Eucalyptus wood chips were subjected to impregnation with various blends of novel fiber modify-ing enzymes before chemical pretreatment and two stages of refining using the preconditioning refiner chemical–alkaline peroxide mechanical pulping (PRC-APMP) process. Wood chip impregnation and pulp processing was con-ducted at a pilot plant in the United States. When compared under constant chemical application and at a constant 350 mL CSF, enzyme treatment reduced specific refining energy by at least 24%. The effect of one versus two stages of impregnation and of enzyme action upon several physical pulp properties was determined.

Evaluation of Various Mechanical Pulping Processes for Mature and Juvenile Loblolly Pine in Lightweight Coated Paper

Although loblolly pine (Pinus taeda) is less costly than northern softwoods, loblolly pine mechanical pulps tend to be of poor quality and are mainly used in low-value grades such as newsprint. We evaluated various mechanical pulping processes for mature and juvenile loblolly pine and their potential for use in value-added grades, especially in lightweight coated (LWC) paper. Results for black spruce were also included for comparison purposes. Pilot plant results have shown that loblolly pine is inferior to spruce in terms of sheet density, brightness ceiling, and long fiber coarseness. To some extent, the quality disadvantages of pine pulps could be offset by proper chemi-cal pre-treatment, high specific-energy application, or both, in the pulping process. With proper chemical pretreat-ment or refining, all the loblolly pine mechanical pulps should have adequate strength and light-scattering ability for LWC and supercalendered grades, compared with the general requirements reported in the literature. However, paper containing pine mechanical pulp is rougher on the surface, less dense, and has higher air permeability than the paper with spruce mechanical pulp. Therefore, proper papermaking strategies, such as precalendering, are essential to reduce sheet surface roughness and pore size before coating. This was confirmed by a LWC dynamic sheet former (DSF) sheet study that used three selected loblolly pine mechanical pulps.

A method for experimental investigation of the wood chipping process

In both the chemical and mechanical pulping process, the logs are cut into wood chips by a disc chipper before fibre separation. To make the wood chipping process more efficient, one have to investigate in detail the coupling between process parameters and the quality of the chips. One objective of this thesis was to obtain an understanding of the fundamental mechanisms behind the creation of wood chips. Another objective with the thesis was to investigate whether it was possible to, in a way tailor the chipping process so as to reduce the energy consumption in a following mechanical refining process.Both experimental and analytical/numerical approaches have been taken in this work. The first part of the experimental investigations, were performed with an in-house developed chipping device and a digital speckle photography equipment.The results from the experimental investigation showed that the friction between the log and chipping tool is probably one crucial factor for the chip formation. Further more it was found that the indentation process is approximately self-similar, and that the stress field over the entire crack-plane is critical for chip creation.The developed analytical model predicts the normal and shear strain distribution and to be more specific, the model can predict the compressive stresses parallel to the fibre direction for an assumed linear elastic and orthotropic material. The analytical distributions were found to be in reasonable agreement with the corresponding distributions obtained from a finite element analysis.To be able to study the chipping process under realistic conditions, which for example means to use chipping rates representative for a real wood chipper, a laboratory chipper was developed. Details regarding the chipper and how to evaluate the force measurements are given together with an example of how the force on the cutting tool (the knife) varies with time during cutting.To investigate the influence of a certain chipping process parameter, the chips were after production in the laboratory chipper, refined in a pilot refiner during conditions optimized for TMP (thermomechanical pulp) and CTMP (chemithermomechanical pulp) processes. It was concluded that the details concerning the chip process had a large impact on e.g. the energy consumption in both first stage and second stage refining. Results showing this are given in this thesis.

Characterizing wood polymers in the primary cell wall of Norway spruce (Picea abies (L.) Karst.) using dynamic FT-IR spectroscopy

Dynamic Fourier Transform Infra-Red (FT-IR) spectroscopy was used to examine the interactions among cellulose, xyloglucan, pectin, protein and lignin in the outer fibre wall layers of spruce wood tracheids. Knowledge regarding these interactions is fundamental for understanding the fibre separation in a mechanical pulping process. Sheets made from an enriched primary cell wall material were used for studying the viscoelastic response of the polymers. The results indicated that strong interactions exist among lignin, protein, pectin, xyloglucan and cellulose in the primary cell wall. This signified a closely linked network structure of the components on the fibre surface. This ultrastructural arrangement in the primary cell wall and the relatively high content of lignin, pectin and protein in it, means that the primary cell wall is more submissive to selective chemical attacks, when compared to the secondary cell wall. A low ratio of cellulose Iα to cellulose Iβ in the primary cell wall was also found.

Biobleaching of banana fibre pulp using Bacillus subtilis C O1 xylanase produced from wheat bran under solid-state cultivation

A cellulase-free xylanase produced by Bacillus subtilis C 01 from wheat bran under solid-state cultivation was tested for its efficacy in biobleaching of raw banana fibre and banana pulp obtained through a mechanical pulping process. Banana pulp samples treated with crude xylanase (450 nkat g(-1) pulp) resulted in a 19.6% increase in the brightness as compared to untreated pulp. The presence of chromophores, hydrophobic compounds and an increased reducing sugar (10.79 mg g(-1) pulp) quantity in the bleached solution after enzymatic treatment indicated the removal of materials that were absorbed at 237 nm from the banana pulp.

The nature of chromophores in high-extractives mechanical pulps: Western red cedar (Thuja plicata Donn) chemithermomechanical pulp (CTMP)

Abstract The utilization of western red cedar mechanical pulp is limited by low brightness caused by a high chromophore content. In this paper we identify these chromophores and provide a possible mechanism for their formation during the mechanical pulping process. Diffuse reflectance ultraviolet (DRUV) and Fourier-transform infrared (DRIFT) spectra were recorded for western red cedar chemimechanical pulp treated with hydrogen peroxide, sodium borohydride and acetic anhydride. Treatment with hydrogen peroxide was conducted over different time periods. The spectra indicate that three carbonyl-containing chromophores contribute to light absorption in the visible region. Two conjugated ortho-quinones contributed most of the color. These quinones were formed by oxidation and polymerization of lignans during the refining process. The third chromophore was coniferaldehyde. There was a large initial time lag for the reaction of peroxide with coniferaldehyde relative to reaction time with the quinones. We ascribe this to differences in topochemistry. It was deduced that coniferaldehyde was mainly associated with lignin in the interior of the fiber wall, whereas the quinones were derived from lignans that had been deposited on the fiber surface. Identification of the three chromophores provides a basis for studies of the kinetics of brightening of western red cedar mechanical pulps.

Tannin-iron impregnated thermomechanical pulp Part II: Bleachability and brightness reversion

Tannins are polymeric, phenolic constituents found in the bark of pine and spruce. When reacting with iron ions, tannins form strongly coloured complexes. Thus, the presence of bark in the mechanical pulping process leads to decreased brightness of the pulp. In order to evaluate the effects of the presence of iron on the properties of pulp, we have impregnated thermomechanical pulp (TMP) with 30 parts per million (ppm i.e. mg/kg) iron either as Fe3+ or as tannin-iron complexes and studied how such treatments affect bleachability and heat-induced brightness reversion. The bleaching agents studied are hydrogen peroxide and sodium dithionite. Treatment of the tannin-iron impregnated pulp with 1% by weight of diethylenetriaminepentaacetic acid (DTPA) before bleaching with 4% hydrogen peroxide almost eliminated the brightness loss caused by the impregnation. Such a treatment also removed all of the added iron from both the tannin-iron and FeCl3 impregnated pulps. Approximately 5% more of the added peroxide was required for oxidation of the tannins in the tannin-iron impregnated pulp. Contrary to what was observed with peroxide bleaching, dithionite bleaching did not reduce the amount of iron in the pulps. Instead, the added iron and tannin-iron negatively affected the dithionite bleaching, even if the pulps were extracted with DTPA before bleaching. It should therefore be advantageous to first bleach with peroxide, which removes most of the iron, and then with dithionite. Compared with dithionite, peroxide yields a more efficient bleaching. The reason for this is that the former reduces the light absorption coefficient, the k-value, more efficiently in the whole visible spectrum, whereas dithionite reduces it mainly at shorter wavelengths. In our experiments, the addition of tannin-iron or FeCl3 to the untreated pulp did not increase heat-induced brightness reversion. This is Supported by the fact that although extraction of the samples with DTPA before bleaching lowered the iron content slightly, it-did not affect the brightness reversion. The initial brightness reversion of the dithionite bleached pulps was larger than that observed for the peroxide bleached pulps.

Effect of impact velocity on the fracture of wood as related to the mechanical pulping process

The fiber separation step in refining is crucial for energy consumption in subsequent refining where the pulp properties are developed. The size reduction of chips during refining is dependent on refining intensity and chip strength. Factors affecting these two parameters are discussed in a literature review. The impact strength of chips and the break down of chips to separate fibers are also discussed. Specifically the effect of impact velocity on the fracture of wood has been studied by use of a falling weight impact tester. Samples were prepared from a freshly cut log of Norway spruce, Picea abies, and the impact strength was measured using an instrumented falling weight impact tester. An increase in impact velocity from about 2.7 to 4.8 m/s resulted in an increase in impact strength of about 50%.