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Predictive advisory solutions for chemistry management, control, and optimization, TAPPI Journal March 2025
ABSTRACT: Process runnability and end-product quality in paper and board making are often connected to chemistry. Typically, monitoring of the chemistry status is based on a few laboratory measurements and a limited number of online specific chemistry-related measurements. Therefore, mill personnel do not have real-time transparency of the chemistry related phenomena, which can cause production instability, including deposition, higher chemical consumption, quality issues in the end-product and runnability problems. Machine learning techniques have been used to establish soft sensor models and to detect abnormalities. Furthermore, these soft sensors prove to be most useful when combined with expert-driven interpretation. This study is aimed at utilizing a hybrid solution comprising chemistry and physics models and machine learning models for stabilizing chemistry-related processes in paper and board production. The principal idea is to combine chemistry/physics models and machine learning models in a fashion close to white box modeling. A cornerstone in the approach is to formulate explanations of the findings from the models; that is, to explain in plain text what the findings mean and how operational changes can mitigate the identified risks. The approach has been demonstrated for several different applications, including deposit control in the wet end, both raw water treatment and usage, and wastewater treatment. This approach provides mill personnel with knowledge of identified phenomena and recommendations on how to stabilize chemistry-related processes. Instead of using close to black box machine learning models, a hybrid solution including chemistry/physics models can enhance the performance of artificial intelligence (AI) deployed systems. A successful way of gaining the trust from mill personnel is by creating a plain text explanation of the findings from the hybrid models. The correlation between the likelihood of a phenomena and disturbance and the explanations are derived and validated by application and chemistry and physics experts.
Journal articles
Colloidal silica and its effects during formation of paper sheets in the presence of nanofibrillated cellulose, cationic starch, and cationic acrylamide copolymer, TAPPI Journal May 2025
ABSTRACT: This work considered effects of colloidal silica addition during laboratory preparation of paper sheets containing nanofibrillated cellulose (NFC) that had been pretreated with cationic starch. The emphasis was on process performance issues, including dewatering rates, fine particle retention, and the extent of fiber flocculation. In addition, micrographs were obtained to show what was happening to the NFC upon treatments with cationic starch and subsequent application of hydrodynamic shear. Contrasting results were obtained, depending on the charge density of the cationic starch. Pretreatment of the NFC with a high charge density cationic starch (degree of substitution 0.2) resulted in strong interactions with the colloidal silica, enhancing the dewatering rate and contributing to fine-particle retention. The medium charge cationic starch pretreatment led to effects suggesting a bridging mechanism of action, and subsequent colloidal silica had no significant effect on dewatering. Treatment of that system with a high level of colloidal silica (0.2%) resulted in lower retention. In general, the final colloidal silica treatments tended to decrease the level of flocculation in the suspensions, giving more uniform handsheets. Mechanisms, some of them related to the clustering and dispersion of cationic starch-treated NFC, were proposed to account for the observed effects.
Journal articles
Magazine articles
Development of converging-diverging multi-jet nozzles for molten smelt shattering in kraft recovery boilers, TAPPI Journal March 2021
ABSTRACT: The effective shattering of molten smelt is highly desired in recovery boiler systems. Ideally, shatter jet nozzle designs should: i) generate high shattering energy; ii) create a wide coverage; and iii) minimize steam consumption. This study proposes a novel converging-diverging multi-jet nozzle design to achieve these goals. A laboratory setup was established, and the nozzle performance was evaluated by generating jet pressure profiles from the measurement of a pitot tube array. The results show that the shatter jet strength is greater with a large throat diameter, high inlet pressure, and a short distance between the nozzle exit and impingement position. Increasing the number of orifices generates a wider jet coverage, and the distance between the orifices should be limited to avoid the formation of a low-pressure region between the orifices. The study also demonstrates that an optimized converging-diverging multi-jet nozzle significantly outperformed a conventional shatter jet nozzle by achieving higher energy and wider coverage while consuming less steam.
Journal articles
Magazine articles
Black liquor evaporator upgrades— life cycle cost analysis, TAPPI Journal March 2021
ABSTRACT: Black liquor evaporation is generally the most energy intensive unit operation in a pulp and paper manufacturing facility. The black liquor evaporators can represent a third or more of the total mill steam usage, followed by the paper machine and digester. Evaporator steam economy is defined as the unit mass of steam required to evaporate a unit mass of water from black liquor (i.e., lb/lb or kg/kg.) The economy is determined by the number of effects in an evaporator train and the system configuration. Older systems use four to six effects, most of which are the long tube vertical rising film type. Newer systems may be designed with seven or even eight effects using falling film and forced circulation crystallization technology for high product solids. The median age of all North American evaporator systems is 44 years. Roughly 25% of the current North American operating systems are 54 years or older. Older systems require more periodic maintenance and have a higher risk of unplanned downtime. Also, older systems have chronic issues with persistent liquor and vapor leaks, shell wall thinning, corrosion, and plugged tubes. Often these issues worsen to the point of requiring rebuild or replacement. When considering the age, technology, and lower efficiency of older systems, a major rebuild or new system may be warranted. The intent of this paper is to review the current state of black liquor evaporator systems in North America and present a basic method for determining whether a major rebuild or new installation is warrant-ed using total life cycle cost analysis (LCCA).
Journal articles
Magazine articles
Effects of phosphogypsum whiskers modification with calcium stearate and their impacts on properties of bleached softwood paper sheets, TAPPI Journal September 2021
ABSTRACT: By combining the structural properties and characteristics of phosphogypsum whiskers, a preliminary study on the modification of phosphogypsum whiskers and their application in papermaking was carried out. The effects of reaction temperature, reaction time, and reaction concentration on the solubility and retention of modified phosphogypsum whiskers and the effects of phosphogypsum whiskers on the physical properties of paper under different modified conditions were explored. The research results show that, after the phosphogypsum whiskers are modified with calcium stearate, a coating layer will be formed on the surface of the whiskers, which effectively reduces the solubility of the phosphogypsum whiskers. The best modification conditions are: the amount of calcium stearate relative to the absolute dry mass of the phosphogypsum whisker is 2.00%; the modification time is 30 min, and the modification temperature is 60°C. The use of modified phosphogypsum whiskers for paper filling will slightly reduce the whiteness, folding resistance, burst resistance, and tensile strength of the paper, but the tearing degree and retention of the filler will be increased to some extent.
Journal articles
Magazine articles
Furnishing autohydrolyzed poplar weakly alkaline P-RC APMP to make lightweight coated base paper, TAPPI Journal February 2022
ABSTRACT: This work investigated the effects of autohydrolysis pretreatment severity on poplar (Populus tomentosa Carr.) woodchips used to make a type of high-yield pulp (HYP) known as preconditioning followed by refiner chemical treatment, alkaline peroxide mechanical pulp (P-RC APMP). It also investigated the ratios for partially replacing sodium hydroxide (NaOH) with magnesium oxide (MgO) in the high-consistency (HC) retention stage of the P-RC APMP process on the obtained HYP’s properties. The results show that the pretreatment severity of autohydrolysis at combined hydrolysis factor (CHF) = 10.77 and the 50 wt% ratio for partially substituting NaOH with MgO were the optimum conditions for making light-weight coated (LWC) base paper. Compared to the conventional P-RC APMP, the optimized P-RC APMP had similar bulk and higher tensile, burst, and tear indices, as well as opacity, but a slightly lower ISO brightness. When the optimized P-RC APMP and commercial softwood bleached sulfate pulp (SBKP) were blended to make LWC base paper, the most favorable pulp furnish was comprised of 50% optimized P-RC APMP and 50% commercial SBKP. The obtained LWC base paper handsheet had better bulk, and its other properties could also meet the require-ments of LWC base paper.
Journal articles
Magazine articles
Calender barring review with experiences, TAPPI Journal July 2022
ABSTRACT: Excessive calender vibration affects all styles of calender stacks from single to multi-nip, all hard rolls, or a combination of hard and soft rolls. Calender vibration can be forced vibration or self-excited vibration. Forced vibration occurs at the first few harmonics of the calender roll rotational speeds and is caused by imbalance, misalignment, eccentricity, etc. Self-excited vibration, the focus of this paper, occurs at higher frequencies. Feedback paths for self-excited vibration must be understood in order to ameliorate the problem. This is presented in the context of the historical development of the theory of self-excited feedback mechanisms, followed by a survey of self-excited feedback mechanisms in various types of calender stacks. Methodology to determine which feed-back path is present and techniques to control or eliminate the resulting vibration follow. To obtain a flavor of the types of problems faced and practical remedial actions, a variety of experiences with barring issues are provided.
Journal articles
Magazine articles
Numerical investigation of the effect of ultrasound on paper drying, TAPPI Journal March 2022
ABSTRACT: The paper drying process is very energy inefficient. More than two-thirds of the total energy used in a paper machine is for drying paper. Novel drying technologies, such as ultrasound (US) drying, can be assessed numerically for developing next-generation drying technologies for the paper industry. This work numerically illustrates the impact on drying process energy efficiency of US transducers installed on a two-tiered dryer section of a paper machine. Piezoelectric transducers generate ultrasound waves, and liquid water mist can be ejected from the porous media. The drying rate of handsheet paper in the presence of direct-contact US is measured experimentally, and the resultant correlation is included in the theoretical model. The drying section of a paper machine is simulated by a theoretical drying model. In the model, three scenarios are considered. In the first scenario, the US modules are positioned in the dryer pockets, while in the second scenario, they are placed upstream of the drying section right after the press section. The third case is the combination of the first and second scenarios. The average moisture content and temperature during drying, enhancement of total mass flux leaving the paper by the US mechanism, total energy consumption, and thermal effect of heated US transducers are analyzed for all cases. Results show that the application of the US can decrease the total number of dryer drums for drying paper. This numerical study is based on the US correlation obtained with the US transducer direct-contact with the paper sample. Thus, future work should include US correlation based on a non-contact US transducer.
Journal articles
Magazine articles
Predicting strength characteristics of paper in real time using process parameters, TAPPI Journal March 2022
ABSTRACT: Online paper strength testing methods are currently unavailable, and papermakers have to wait for manufacture of a complete reel to assess quality. The current methodology is to test a very small sample of data (less than 0.005%) of the reel to confirm that the paper meets the specifications. This paper attempts to predict paper properties on a running paper machine so that papermakers can see the test values predicted in real time while changing various process parameters. This study was conducted at a recycled containerboard mill in Chicago using the multivariate analysis method. The program provided by Braincube was used to identify all parameters that affect strength characteristics. Nearly 1600 parameters were analyzed using a regression model to identify the major parameters that can help to predict sheet strength characteristics. The coefficients from the regression model were used with real-time data to predict sheet strength characteristics. Comparing the prediction with test results showed good correlation (95% in some cases). The process parameters identified related well to the papermaking process, thereby validating the model. If this method is used, it may be possible to predict various elastic moduli (E11, E12, E22, etc.) in the future as the next step, rather than the traditional single number “strength” tests used in the containerboard industry, such as ring crush test (RCT), corrugating medium test (CMT), and short-span compression strength test.
Journal articles
Magazine articles
The Shendye-Fleming OBA Index for paper and paperboard, TAPPI Journal March 2022
ABSTRACT: We are proposing a new one-dimensional scale to calculate the effects of optical brightening agents (OBA) on the bluish appearance of paper. This index is separate from brightness and whiteness indices.In the paper industry, one-dimensional scales are widely used for determining optical properties of paper and paperboard. Whiteness, tint, brightness, yellowness, and opacity are the most common optical properties of paper and paperboard. Most of the papers have a blue cast generated by addition of OBA or blue dyes. This blue cast is given because of the human perception that bluer is whiter, up to a certain limit. To quantify this effect, it is necessary to determine how much blue cast paper and paperboard have. As the printing industry follows the ISO 3664 Standard for viewing, which has a D50 light source, this also plays a very important role in showing a blue cast. Color perception is based on light source and light reflected from an object. The ultraviolet (UV) component in D50 interacts with OBA to provide a reflection in the blue region of the visible spectrum. Use of a UV blocking filter results in measurements without the effect of emission in the blue region. This difference is used in determining the OBA effect in the visible range of the paper. This equation is known as the Shendye-Fleming OBA Index.