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Abstract We propose a maximum likelihood estimation approach for the identification of symmetric noncausal models. Such models are used to represent the cross-directional dynamic response of many industrial processes that are generally modeled with a high-dimensional gain matrix. Reducing the number of parameters in a noncausal model can significantly reduce the uncertainty associated with parameter estimates. We adapt the maximum likelihood method to treat symmetric noncausal models by showing that every symmetric noncausal process admits a spectrally equivalent causal model. It is then proved that the maximum likelihood estimate of this causal model converges to that of the original noncausal model. We present an iterative identification algorithm to efficiently estimate the parameters in noncausal models. Finally, we show that the parameter covariance estimate obtained from the causal model also converges to that of the noncausal model, which lays a foundation for optimal input design in noncausal processes. Several numerical examples illustrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Highlights • scanner path utilized as a manipulatable variable in paper machine cross-directional control. • faster response to load disturbances. • estimation of process noise and basis weight estimate uncertainty based on web-wide transmittance measurement. • adaptive model between transmittance and basis weight. ABSTRACT The cross-directional (CD) basis weight control on paper machines is improved by optimizing the path of the scanning measurement. The optimal path results from an LQG problem and depends on how the uncertainty of the present estimate of the basis weight and the intensity of process noise vary in CD. These factors are assessed by how accurately the CD basis weight estimate predicts the measured optical transmittance with a linear adaptive model on synchronized basis weight and transmittance data. Simulations on optimized scanner path in disturbance scenarios are presented, and the practical implementation of scanner control is discussed. [ABSTRACT FROM AUTHOR]

Globally, small and medium-sized enterprises (SMEs) constitute a significant industrial segment. However, their energy-efficiency potential has remained largely untapped due to several barriers. The prevailing approaches on energy optimization in the energy-intensive SMEs are focused on the technological improvements at the operational level and lack a strategic approach. This study developed an energy management system (EnMS) for SMEs by integrating technical and managerial energy saving activities (ESAs), suggested in energy management literature. The proposed EnMS adopted a PDCA (Plan-Do-Check-Act) process approach for consistent energy efficiency and cleaner production. For the validation of the proposed EnMS, a case of small-sized Indian paper mill was selected. The case exhibited the ramp of continuous improvement in the energy efficiency at the mill by illustrating two PDCA cycles. Step I (Plan) involved creating energy management roles with management support, energy auditing, identifying energy-saving opportunities and developing action plan; step II (Do) was about creating communication, awareness and motivation before the implementation of the action plan; step III (Check) involved periodic monitoring, analysis and reporting of the energy key performance indicators (KPIs), and benchmarking enterprise energy performance. The case analysis showed a 35% reduction in specific energy consumption (SEC) of one of the Paper Machine's (PM) vacuum system by the implementation of ESAs for vacuum optimization, generating an annual energy-saving of 0.3 GJ/t. In step IV, the subsequent PDCA cycle was triggered by the biannual management review for exploring the new energy saving opportunities at the enterprise. The next improvement cycle targeted at steam and condensate system optimization in another PM resulted in an additional energy cost saving of USD 26,900. [ABSTRACT FROM AUTHOR]

Previously, plant-wide disturbance analysis has looked into the propagation of faults through an industrial production process by investigating process measurements. However, the extent of the analysis has mostly been limited to a section of a plant. In this work, we propose a top-down approach which investigates measurements of the complete plant and identifies a section where the disturbance originates. Root cause analysis is carried out thereafter to pinpoint the faulty asset. The proposed approach has three novel elements: Using key performance indicators (KPI) as reference and starting point of the analysis, restricting measurements to a measurement type (e.g. flow) thus focusing on a section and applying the novel method of contribution plots of spectral PCA T 2 statistic to find the contribution of each measurement towards the disturbance observed in the KPI. The approach is described and carried out on a paper machine where a quality KPI showed an established oscillation. [ABSTRACT FROM AUTHOR]

In this work, the performance assessment study is done on a paper mill using an in-house analytics tool capable of data mining. The tool proposes a generic methodology for performance analysis and then shows its application on an industrial multi-grade paper making process. The tool framework facilitates data preprocessing and data mining, configuration and calculation of key performance indices (KPIs), benchmarking and gap analysis for benefit estimation. It also helps in better performance visualization and identification of the root cause of variations in performance in paper mills. To illustrate the concept, key results from performance analysis study done on a paper machine are presented and suggested measures to improve performance are discussed. [ABSTRACT FROM AUTHOR]

Oscillations in control loops are one of the most prevalent problems in industrial processes. Due to their adverse effect on the overall process performance, finding how oscillations propagate through the process units is of major importance. This paper presents a method for integrating process causality and topology which ultimately enables to determine the propagation path of oscillations in control loops. The integration is performed using a dedicated search algorithm which validates the quantitative results of the data-driven causality using the qualitative information on plant connectivity. The outcome is an enhanced causal model which reveals the propagation path. The analysis is demonstrated on a case study of an industrial paperboard machine with multiple oscillations in its drying section due to valve stiction. [ABSTRACT FROM AUTHOR]

In this paper a new process to manufacture unidirectional reinforcements for eco-composite materials, made of natural fibers, is presented. Starting with flax rovings of different sizes, an apparatus was developed to feed and align the rovings over the wet-end section of a paper machine. The short kraft paper fibers are therefore mixed with the long flax roving as the machine is running, and at the end of the process, a sheet of the hybrid dry reinforcement is obtained and cut to size for impregnation with various resins, using different processes. This novel manufacturing process allows for high volume production of reinforcement. It is very flexible, and many different combinations of long and short fibers can be exploited for the production of a vast variety of dry reinforcements. In this paper, composite samples are obtained out of these reinforcements, using the resin infusion (RI) molding process with a commercial epoxy resin. The results are compared with those of usual glass fiber reinforcement. An interesting aspect is that the large variability, typical for natural fibers, is largely reduced when the short kraft fibers are present in the composite. In terms of permeability to resin, reasonably comparable values can be obtained compared to that of glass fabrics, if a low surface density of reinforcement is chosen. [ABSTRACT FROM AUTHOR]

Abstract: Calculations on the global energy consumption used to overcome friction in paper machines in terms of friction in motors, transmissions, pumps, blowers, agitators, pipes and the roll systems are presented. The following was concluded: [–] The energy consumed to overcome friction in a paper mill is in the range 15–25%. [–] Globally there were 8525 paper and paperboard machines in operation in 2012. One paper machine uses on an average 140TJ of electrical energy per year. Of this 32% is consumed to overcome friction, 36% is used for the paper production and mass transportation and 32% is other losses. [–] The friction losses in an average paper machine are in total 44.8TJ per year, and they are distributed as 32% due to friction in water-lubricated sliding in seals, doctor blades and fabric/support contacts, 23% due to friction in elastohydrodynamic rolling contacts, 22% due to friction in elastohydrodynamic rolling–sliding contacts, 15% due to friction in oil-lubricated seals and 8% due to friction in hydrodynamically lubricated contacts. [–] Worldwide 105,000GWh electrical power was used in 2009 to overcome friction in paper machines. This equals to 381,000TJ of annual energy consumption. [–] By taking advantage of new technology for friction reduction in paper machines, friction losses could be reduced by 11% in the short term (about 10 years), and by 23.6% in the long term (20–25 years). This would equal to annual worldwide economic savings of 2000 million euros and 4200 million euros; electricity savings of 36,000 and 78,000GWh; and CO2 emission reduction of 10.6 million and 22.7 million tonnes. Potential mechanisms to reduce friction in paper machines include the use of low-friction and highly durable coatings, surface engineering including texturing, low-viscosity and low-shear lubricants and fluids, novel additives, new materials in seals, doctorblades and fabrics, as well as new designs. [Copyright &y& Elsevier]

Abstract: Paper raw materials contain impurities, such as waxes, coating binders, hot melts and pressure-sensitive adhesives, that have a tendency to attach to the surfaces of machinery during paper production. Drying cylinders located at the beginning of the drying section are in an especially challenging position because sticky materials can easily transfer from the paper web to the hot cylinder surfaces at this point. Usually, one to four drying cylinders are coated with a nonstick coating material in order to decrease contamination. The nonstick properties of coating materials are at their best when the coatings are new, but their performance usually decreases as the materials age. To date, there is no practical method available for the on-site evaluation of the nonstick properties of coating materials or a method to monitor the condition of the coating during its life cycle. A new practical method for the on-site evaluation of nonstick cylinder coating materials has been developed. This method also provides the opportunity to compare the performance of different drying cylinder coating materials. The analysis is performed using an adhesive tape attached to a clean cylinder surface. The tape is immediately peeled off of the surface at a constant speed and peel angle. The temperature compensation is used to facilitate the comparison of surfaces at different temperatures. The force required to peel off the adhesive tape is monitored with a force meter. Our results show a linear relationship between the release force and the nonstick qualities of the coating. In this paper, a method for testing drying cylinder coatings and the results of mill tests are presented. [Copyright &y& Elsevier]

Abstract: There is a large value in making Pulp and Paper mills more energy efficient. ABB has developed an energy assessment service where opportunities to save energy in the paper machine are identified. The energy assessment is done by quantifying energy flows, benchmarking energy users, data mining and steam sensitivity analysis and by experiments and additional measurements at the paper machine. Energy quantification helped in identifying main energy consumer, benchmarking was useful to assess the gap between operating performance and best performance whereas data mining and steam sensitivity analysis helped in studying the impact of key operating variables on performance of paper machines. After the assessment an action plan was presented to the mill for energy efficiency improvement together with a return on investment. [Copyright &y& Elsevier]

Abstract: Superhydrophobic flaky γ-alumina coating was prepared on AISI 316 2B stainless steel and was field-tested near size roll at a paper machine in a paper mill for 6 weeks consisting of two running periods of machine to check the easy-to-clean property and durability, as compared to an uncoated reference stainless steel. In the end of the field test, both the superhydrophobic and the reference stainless steel were fully covered with substances from the testing environment. Major part of the collected substances on the superhydrophobic stainless steel can be washed away by pressurized water; however, the collected substances remained on the reference stainless steel after washing. The field-tested samples were characterized visually and by stereomicroscopy, field emission scanning electron microscopy, laser profilometry and contact angle tester. The field test revealed the easy-to-clean property of the superhydrophobic surface and the superhydrophobic coating survived rather well after the first running period of 16 days in the field test. The resistance and durability of the superhydrophobic surface still needs to be further improved for longer term application in paper industry. Nanoindentation was used to further study the mechanical properties of the γ-alumina coating. It was found that the γ-alumina coating became much softer after transforming from flat to flaky form. In addition, the flaky γ-alumina coating demonstrated a phenomenon of time-dependent plasticity and some flexibility. [Copyright &y& Elsevier]

Abstract: Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used as the tools to study the adsorption of bacteria onto surfaces of silica and polystyrene coated with materials related to papermaking. Cationic polyelectrolytes used as fixatives and retention aids in paper industry were found to promote irreversible adsorption of the ubiquitous white water bacterium, Pseudoxanthomonas taiwanensis, onto model surfaces of cellulose (pH 8). The high charged low molecular weight polyelectrolyte, poly(diallyldimethyl) ammonium chloride (pDADMAC) adsorbed to silica surface as a flat and rigid layer, whereas the low charged cationic polyacryl amide (C-PAM) of high molecular weight adsorbed as a thick and loose layer. AFM images showed that the polyelectrolytes accumulated as layers around each bacterial cell. In the presence of wood hemicellulose (O-acetyl-galactoglucomannan) the bacteria adsorbed massively, as large, tightly packed rafts (up to 0.05mm in size) onto the polystyrene crystal surface coated with wood extractives (pH 4.7). AFM and FESEM micrographs also showed large naked areas (with no bacteria) in between the bacterial rafts on the crystal surface. In this case, QCM-D only incompletely responded to the massiveness of the bacterial adsorption. The results indicate that cationic polymers can be used to increase the retention of bacteria from the process water onto the fibre web and that, depending on the balance between hemicelluloses and wood extractives and pH of the process waters, bacteria can be drawn from process waters onto surfaces. [Copyright &y& Elsevier]

Abstract: This paper presents a new strategy for steam pressure control during web breaks in the paper machine. The aim was to restart paper production with the same drying properties of the cylinder as before the break. A detailed physical dynamic model of the drying cylinder has been developed. The accuracy of the model has been verified through experiments made at the M-real paper mill in Husum, Sweden. Verifications are made both during normal operation and during web breaks. The dynamic model has been reduced in order to derive simple transfer functions which were used to find the optimal steam pressure trajectory during web breaks. The resulting strategy has been tested on a paper machine with good results and it has been well received at the mill. [Copyright &y& Elsevier]

Abstract: This paper presents a novel dynamic causal digraph reasoning method for fault diagnosis and its application to the short circulation process of a paper machine. In order to improve the fault detection ability of the original causal digraph method, a residual modification approach that takes into account the direction of different fault effects is presented. An improvement of the isolation capability of the original method, an inference mechanism between the arcs of the graph, is also proposed to locate process faults on the arcs. The results from the application show that the proposed method, compared to the conventional method, is able to detect the correct nodes and to identify the responsible arcs when the system is affected by a process fault. [Copyright &y& Elsevier]

The aim of this study was to determine the effect of varying nutrient conditions on biofilm formation of a Pseudomonas putida strain isolated from a paper machine under controlled conditions. Biofilm accumulation, was investigated using a laminar flow cell reactor in a defined mineral medium. Our results indicate that increasing nutrient concentration (from 0.1 to 0.5gl−1 glucose, C/N=40, C/P=100) or phosphate concentration (from C/P=200 to C/P=100) increased the rate and extent of biofilm accumulation, however, higher nutrient (1gl−1 glucose, C/N=40, C/P=100) or phosphate (C/P=50) concentration reduced biofilm accumulation rate because of a higher detachment. The rate and extent of biofilm accumulation increased with nitrogen concentration (from C/N=90 to C/N=20). Detachment is a key parameter that influences biofilm accumulation since the early stage (2h) of colonisation and strongly depends on nutrient conditions. In practice, controlling nutrient levels may be interesting to reduce biofilm formation in the paper industry. [Copyright &y& Elsevier]

Abstract: The spreading kinetics and adhesion of liquid alkenyl succinic anhydride (ASA) on hydrophilic and hydrophobic SiO2 surfaces was studied. Contact angles were measured both in air and in aqueous environment. ASA spread fairly well on both surfaces in air, but when immersed in aqueous solution it spread only on the hydrophobic surface. The contact angle in water on the hydrophilic surface was ≉170°. The work of adhesion of ASA to both surfaces in air was about 60mJ/m2. When immersed in water the work of adhesion of ASA on the hydrophobic surface was 22mJ/m2, and less than 1mJ/m2 on the hydrophilic surface. In the pH range used in papermaking there was no significance of pH on spreading of ASA, but at high pH effects on the surface tensions due to hydrolysis of ASA were observed. Ca2+-ions had no effect on the spreading of ASA on the hydrophilic surface but strongly influenced spreading on the hydrophobic surface. ASA is extensively used as a hydrophobing agent and tends to form detrimental deposits on equipment used for manufacture of paper. From the results it can be concluded that best way to prevent fouling on paper machines by hydrophobic substances is to maintain the process surfaces wetted by water and to choose surface materials that stay hydrophilic as consistently as possible. [Copyright &y& Elsevier]

A mechanistic nonlinear model of the wet end of paper machine 6 (PM6) at Norske Skog Saugbrugs, Norway has been developed, and used in an industrial MPC implementation. The MPC uses an infinite horizon criterion, successive linearization of the model, and estimation of states and parameters by an augmented Kalman filter. Variation in important quality variables and consistencies in the wet end have been reduced substantially, compared to the variation prior to the MPC implementation. The MPC also provides better efficiency through faster grade changes, control during sheet breaks and start ups, and better control during periods of poor measurements. From May 2002 of the MPC has been the preferred controller choice for the process operators at PM6.In this paper we also study if the model can be applied to PM4 at Norske Skog Saugbrugs, and PM3 at Norske Skog Skogn, Norway. No structural changes were necessary in order to fit the model to PM4 and PM3 data. The time spent on fitting the PM6 model to PM4 and PM3 is approximately 1% of the time spent on developing the original model. This should be a strong incentive for focusing on mechanistic modeling in industries were there are many similar production lines or units. [Copyright &y& Elsevier]

This paper presents consistent criteria for evaluating the selection of tuning parameters for an industrial model predictive control of large-scale cross-directional (CD) processes using a two-dimensional (temporal and spatial) frequency analysis technique. The concept of rectangular circulant matrices (RCMs) and their properties are presented. It is shown that large-scale CD processes can be approximated as RCMs and then diagonalized by complex Fourier matrices, allowing analysis in terms of a family of SISO transfer functions across the spatial frequencies. Familiar concepts from control engineering such as bandwidth and stability margin are extended into the two-dimensional frequency domain, providing intuitive measures of closed-loop performance and robustness. [Copyright &y& Elsevier]

Pick-up felts and deposits in wet end splash areas and in storage tanks of paper machines contained large amounts of thiosulfate (80–16 000 mg kg−1, wet weight) and oxalate (20–2300 mg kg−1, wet weight). These anions were absent (<5 mg l−1) in process water and found in raw materials only in low concentrations (5–10 mg kg−1, wet weight). Similar and larger amounts of thiosulfate, sulfite and oxalate were generated de novo from sulfate and sheets of chemical pulp in a splash area simulator fed with artificial paper machine white water in the laboratory. Stainless steel UNS S30400 coupons placed in the simulator developed significant corrosion pits within 4 weeks. Pitting was most extensive under or vicinal to patches where large amount of thiosulfate and oxalate accumulated in the pulp sheet. Pitting of UNS S31600 occurred only vicinal to the pulp sheet. The pitted steel surfaces accumulated large amounts of silicon containing material. The biogenic conversion of sulfate into compounds of lower oxidation states occurred more extensively on stainless steel UNS S30400 than on UNS S31600. [Copyright &y& Elsevier]

A drainage model for heterogeneous pulp suspension has been developed using a mathematical correlation between the Canadian standard freeness, the consistency, the density of the pulp, the fiber diameter and the porosity of the fiber mat deposited over the wire. The concept of tortuosity factor has been introduced in several equations describing the drainage phenomena. Introducing these parameters in mass balance equations, software was created. The model was validated based on the data from a paper mill using a blend of pulp of low freeness. [Copyright &y& Elsevier]

• Paper machine manufactured photocatalyst papers were investigated. • The photocatalyst papers were soaked by indicator solutions in a laminate structure. • Lateral variations of the photoconversion were followed by reflectance measurements. • Lateral variations show maximum values during the conversion. • The catalyst loading does not influence the overall conversion rate significantly. Paper machine manufacturing of photocatalysts can enable low cost devices for removal of low concentrated pollutants. Lateral variations originating from the paper making process leads to variations of the catalytic activity over the paper area. Paper machine manufactured papers made from tetrapodal ZnO whiskers and kraft pulp were investigated in this test geometry using simulated solar light. Photocatalytic ZnO papers were laminated between polyethylene sheets and an indicator solution seeped into the laminated photocatalytic paper, to create a test geometry where the indicator ink is confined to a small volume between the polyethylene sheets. The photocatalyst papers exhibited surprisingly similar photocatalytic behavior although having different catalyst loading 15, 30 and 45 wt percent. All papers exhibited lateral variations that peaked during the conversion. The results show that production of effective photocatalytic composite papers can be scaled. Further, the results show that variations must be considered for photocatalytic papers. [ABSTRACT FROM AUTHOR]