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Using bleaching stage models for benchmarking softwood ECF bleach plants, TAPPI Journal July 2022
ABSTRACT: Steady-state bleaching delignification and brightening models were used to gauge how well elemental chlorine-free (ECF) bleach plants were using chlorine dioxide to bleach 25-kappa softwood brownstocks. Case 1 examined the D0(EOP)D1 portion of Mill 1’s five-stage sequence that brightens the pulp to 86% ISO. Case 2 studied the D0(EO)D1 portion of Mill 2’s four-stage sequence, which brightens the pulp to 82% ISO, and Case 3 re-examined the same bleach plant several years after it made improvements around the extraction stage. The models highlighted days in the previously mentioned cases where high bleach usage occurred, presumably because of high brownstock and/or extraction washer carryover, and days where bleach usage was normal. In Case 2, the model esti-mated that 10 kg of the 44 kg chlorine dioxide/metric ton pulp consumed in bleaching was likely reacting with washer carryover sources; approximately two-thirds of this extra consumption was assumed to be reacting with extraction filtrate. Changes that Mill 2 made (Case 3) reduced the unproductive chlorine dioxide usage from 10 to 5 kg/metric ton pulp. When the delignification and brightening models were simultaneously solved, the models predicted somewhat different optimized distributions of chlorine dioxide to D0 and D1 vs. actual values used in bleach plants. However, the forecasted chlorine dioxide totals agreed with the actual values when washer carryover sources were considered. This study showed the bleaching models could be used as hypothetical benchmarks for softwood ECF bleach plants.
Journal articles
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On the usage of online fiber measurements for predicting bleached eucalyptus kraft pulp tensile index — an industrial case, TAPPI Journal July 2022
ABSTRACT: Cellulose pulp’s physical-mechanical properties are determined by laboratory tests obtained from prepared handsheets. However, this procedure is time intensive and presents a lead time until the results are available, hindering its utilization for monitoring and decision-making in a pulp mill. In this context, developing real-time solutions for physical-mechanical properties prediction is fundamental. This work applied a mathematical modeling approach to develop a soft sensor for tensile index monitoring. The mathematical model considers online morphology measurements obtained from the last bleaching stage outlet stream and important process variables for tensile index prediction. The results obtained are satisfactory compared to laboratory results, presenting a mean absolute percentual error of 2.5%, which agrees with the laboratory testing method’s reproducibility.
Journal articles
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Investigation of the Cellulose-Water Relationship by the Pressure Plate Method, TAPPI Journal July 2022
ABSTRACT: The swelling and water retention properties of pulp fibers are of basic importance in papermaking.
Journal articles
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Improving refining efficiency with deflocculation, TAPPI Journal May 2022
ABSTRACT: The ability to load a refiner requires the formation of a fiber mat between opposing refiner bars. One of the consequences of this is the formation of flocs that persist through the refiner grooves and exit the refiner. These flocs interfere with sheet strength, requiring additional energy to make up the strength deficit. In addition, flocs can initiate string formation, resulting in machine efficiency issues such as cross-machine profile deterioration and the downtime required to correct it. Novel refiner plate modifications have been shown to improve refining efficiency in otherwise identical refiner plates. Energy savings are typically around 15% of gross refining energy on the basis of the treated stock, although much higher reductions have also been seen. Addressing this previously underappreciated flaw in conventional refining enables greenhouse gas reduction and other benefits related to sheet strength and machine efficiency.
Journal articles
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Mechanical modification of softwood pulp fibers using a novel lightweight vertical bar plate, TAPPI Journal April 2021
ABSTRACT: Refiner plates made using sand casting have a draft angle, which results in a trapezoidal bar shape. These trapezoidal bar plates have a limited throughput compared to the vertical bar plates, and eventually the edges of the bars become dull, resulting in longer time to reach the target freeness and shorter service life. The new light-weight refiner plate with a bar insertion method into a plate base was developed by selecting an aluminium-based alloy as the plate base material and a stainless steel alloy with high wear resistance as the bar material. The light-weight plate with sharp bar edges was very effective in reducing refining energy by reaching the target freeness faster than the sand-cast bar plate. Finally, the lightweight sharp bar plate, which weighed only about half the weight of the cast bar plate, was expected to significantly contribute to easy replacement, improved paper quality, and larger throughput without excessive loss of fiber length.
Journal articles
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A case study review of wood ash land application programs in North America, TAPPI Journal February 2021
ABSTRACT: Several regulatory agencies and universities have published guidelines addressing the use of wood ash as liming material for agricultural land and as a soil amendment and fertilizer. This paper summarizes the experiences collected from several forest products facility-sponsored agricultural application programs across North America. These case studies are characterized in terms of the quality of the wood ash involved in the agricultural application, approval requirements, recommended management practices, agricultural benefits of wood ash, and challenges confronted by ash generators and farmers during storage, handling, and land application of wood ash.Reported benefits associated with land-applying wood ash include increasing the pH of acidic soils, improving soil quality, and increasing crop yields. Farmers apply wood ash on their land because in addition to its liming value, it has been shown to effectively fertilize the soil while maintaining soil pH at a level that is optimal for plant growth. Given the content of calcium, potassium, and magnesium that wood ash supplies to the soil, wood ash also improves soil tilth. Wood ash has also proven to be a cost-effective alternative to agricultural lime, especially in rural areas where access to commercial agricultural lime is limited. Some of the challenges identified in the review of case studies include lengthy application approvals in some jurisdictions; weather-related issues associated with delivery, storage, and application of wood ash; maintaining consistent ash quality; inaccurate assessment of required ash testing; potential increased equipment maintenance; and misconceptions on the part of some farmers and government agencies regarding the effect and efficacy of wood ash on soil quality and crop productivity.
Journal articles
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Continuous tannin extraction by use of screw reactor, TAPPI Journal February 2021
ABSTRACT: A pilot-size screw reactor (extraction unit) was used for tannin extraction of spruce. Yield of the same magnitude or better was obtained when comparing a screw reactor with batch reactors. A longer presoaking time in water seemed to be better than a short one for obtaining higher yield. A higher yield is obtained with lower dry-water ratio, which suggests that the internal diffusion in bark does not determine mass transfer as much as is the case without presoaking of bark. The higher dry-water ratio decreased the yield. The prior soaking of the bark also minimized the mechanical reactor feeding problems (clogging). The benefits of a screw reactor likely are that run time changes for different process conditions are flexible; it simplifies design and construction of an industrial unit for tannin production; and it saves space because of the need for fewer and smaller intermediate storage tanks.
Journal articles
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Addressing production bottlenecks and brownstock washer optimization via a membrane concentration system, TAPPI Journal July 2021
ABSTRACT: Advancements in membrane systems indicate that they will soon be robust enough to concentrate weak black liquor. To date, the economic impact of membrane systems on brownstock washing in kraft mills has not been studied and is necessary to understand the viability of these emerging systems and their best utilization.This study investigated the savings that a membrane system can generate related to brownstock washing. We found that evaporation costs are the primary barrier for mills seeking to increase wash water usage. Without these additional evaporation costs, we showed that our hypothetical 1000 tons/day bleached and brown pulp mills can achieve annual savings of over $1.0 MM when operating at higher dilution factors and fixed pulp production rate. We then investigated the impact of increasing pulp production on mills limited by their equipment. In washer-limited mill examples, we calculated that membrane systems can reduce the annual operating cost for a 7% production increase by 91%. Similarly, in evaporator-limited mill examples, membrane systems can reduce the annual operating cost for a 7% production increase by 86%. These results indicated that membrane systems make a production increase significantly more feasible for these equipment-limited mills.
Journal articles
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New learnings and strategies for meeting future recovery boiler particulate emission limits with existing electrostatic precipitators, TAPPI Journal June 2021
ABSTRACT: It is foreseeable that recovery boiler particulate emission limits in the United States and Canada will continue to get more stringent with time. Because of this, continued improvement of emission control equipment, as well as a better understanding of how operating parameters affect performance, are necessary. Although electrostatic precipitators (ESPs) are often viewed as a mature technology, many improvements in ESP technology continue to be developed. In recent years, academic efforts have improved the understanding of recovery boiler operating conditions on ESP performance. Additionally, advancements in materials, power supplies, and design continue to improve the efficiency and reliability of ESPs.This paper discusses how recovery boiler and electrostatic precipitator (ESP) operating factors affect ESP perfor-mance based on process simulations and practical experience, and how these learnings can be implemented to improve future operation of existing ESPs.
Journal articles
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Repulping of wet strength paper towel with potassium monopersulfate, TAPPI Journal September 2020
ABSTRACT: Potassium monopersulfate (KMPS) was used in repulping of polyamide-epichlorohydrin (PAE)-containing paper towel. The effectiveness of the repulping aid was compared with that of sodium hypochlorite. Addition of a 2.4% KMPS repulping aid achieved complete repulping of the paper towel, resulting in 88% screen yield and about 5% rejects. To reach a similar pulping result, two times the oxidative equivalent amount of sodium hypochlorite had to be used. Compared to the pulp fibers obtained from sodium hypochlorite repulping, those obtained from KMPS repulping had higher physical strength, longer fiber length, and lower fines content. This study demonstrated that KMPS was superior to sodium hypochlorite in repulping of PAE-containing paper towel in terms of effectiveness and pulp quality.