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Peracetate/singlet oxygen chemistry used in post-bleaching of kraft pulp as a practical oxidant for paper machines, TAPPI Journal May 2021
ABSTRACT: The use of a novel sodium peracetate/singlet oxygen chemistry for brightening bleached kraft pulp shows exciting potential for technical performance, supply logistics, safety, and cost reduction. Potential chemical carryover to the paper machine raises questions about whether peracetate will impact paper machine performance, such as metal corrosion, useful press felt life, and interference with existing biocide programs or paper machine chemistry. Sodium peracetate/singlet oxygen chemistry can be used in high-density storage chests for brightening/whitening and to increase color stability. Any oxidant used directly before the paper machine has the possibility of impacting paper machine operations. Traditional oxidants used in bleaching, such as chlorine dioxide and hydrogen peroxide, are known to cause corrosion on machinery metals and press felts. Hydrogen peroxide residuals can interfere with common biocide programs. Traditional oxidants used in biocide treatments themselves significantly degrade press felt life when the rule-of-thumb concentration thresholds are exceeded. Sodium peracetate is evaluated in this paper for its impact on nylon press felt fiber degradation, metal corrosion, and interference with typical biocide programs.Laboratory results indicate that sodium peracetate/singlet oxygen chemistry is less corrosive than chlorine, bromine, and hydrogen peroxide on press felt nylon fiber and can therefore be used at higher levels than those chemistries to increase brightness without increasing negative downstream impact. Sodium peracetate can also be used with current biocide programs without negative impacts such as consumptive degradation. Higher residuals of peracetate going to the paper machine may be useful as a biocide itself and can complement existing programs, allowing those programs to stay within their safe operating levels and thereby extend press felt useful life.
Journal articles
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Gas dispersion in the oxygen delignification process, TAPPI Journal May 2021
ABSTRACT: There has been very little knowledge about the state of gas dispersion in the oxygen delignification process, even though this has a major impact on the performance of the reactor. This paper presents a new continu-ous inline method for measuring oxygen bubble size distribution in the reactor, as well as results from studies con-ducted in softwood and hardwood lines. This new measurement worked well, and new information about oxygen bubble size, as well as how different reactor conditions affected the distribution, was obtained. For example:œ In the softwood line, the mean volume-weighted bubble size was about 0.1 mm, whereas in the hardwood line, this size was almost 10 times higher. For both lines, there was considerable variation in the measured bubble size over the long term.œ For both lines, an increase in mixer rotation speed caused a discernible decrease in the bubble size, and an increase in oxygen charge caused a discernible increase in the bubble size.œ In the softwood line, no coalescence of the bubbles in the reactor was observed, but in the hardwood line, some coalescence of the larger bubbles occurred.œ In the test conducted in the hardwood line, the use of brownstock washer defoamer caused a discernible increase in oxygen bubble size.œ In the hardwood line, reactor pressure had a noticeable effect on the amount of delignification, which indicated that improving mass transfer of oxygen (e.g., by decreasing the oxygen bubble size, in this case) should also have an increasing effect on the delignification.
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The role of gas dispersion in the oxygen delignification process, TAPPI Journal May 2021
ABSTRACT: Oxygen delignification is an essential part of the pulp production process. Delignification occurs with the aid of alkali and dissolved oxygen. Dissolved oxygen is obtained by dispersing oxygen gas into the pulp suspension by using efficient mixers. Little is known about the state of oxygen gas dispersion and its effect on oxygen delignification kinetics and efficiency. This paper will present the results for the effect of gas bubble size on the performance of oxygen delignification. The results are mainly based on detailed studies made in a Finnish hardwood mill where the oxygen bubble size distribution could be altered at the feed of the reactor. An essential aspect of these studies was the use of a new continuous inline gas bubble size measurement system to simultaneously determine the bubble size distribution at the feed and top of the reactor. Information about oxygen consumption in the reactor could also be obtained through the bubble size measurements. Accordingly, these studies quantify the effect of oxygen bubble size on the kappa reduction of the pulp. The effect of different chemical factors on the oxygen bubble size is also studied.Finally, the relationship between the gas bubble size and the liquid phase oxygen mass transfer coefficient (kLa) is presented. This connects the bubble size to the kappa reduction rate. Based on the presented modeling approach and the evaluation of practical factors that are not taken into account in the modeling, it was concluded that the volumetric average oxygen bubble size should preferably be smaller than 0.2 mm in practice.The information obtained with the new gas bubble size measurement system and the presented modeling approach give a very new basis for understanding, monitoring, adjusting, and designing oxygen delignification processes.
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The Future of Sustainability at Pulp and Paper Mills, Paper360º November/December 2021
The Future of Sustainability at Pulp and Paper Mills, Paper360º November/December 2021
Journal articles
Magazine articles
Application of ATR-IR measurements to predict the deinking efficiency of UV-cured inks, TAPPI Journal January 2022
ABSTRACT: In recent years, ultraviolet (UV)-curable ink has been developed and widely used in various printing applications. However, using UV-printed products (UV prints) in recovered paper recycling causes end-product dirt specks and quality issues. A new method was developed that can distinguish UV prints from other prints by means of attenuated total reflectance infrared (ATR-IR) spectroscopy. Application of this method could allow more efficient use of UV prints as raw materials for paper recycling.First, a mill trial was performed using UV prints alone as raw materials in a deinked pulp (DIP) process. Second, test prints were made with four types of UV inks: a conventional UV ink and three different highly-sensitive UV inks. Each print sample had four levels of four-color ink coverage patterns (100%, 75%, 50%, and 25%). Next, deinkability of all prints was evaluated by laboratory experiments. Finally, each print was measured using the ATR-IR method, and the relationship between the IR spectra and deinkability was investigated. Mill trial results showed that UV prints caused more than 20 times as many dirt specks as those printed with conventional oil-based ink. There were variations in recycling performance among UV prints taken from bales used for the mill trial. Lab tests clearly revealed that not all UV-printed products lead to dirt specks. In order to clarify the factors that affected deinkability of UV prints, the print samples were investigated by lab experiments. Key findings from lab experiments include: œ The number of dirt specks larger than 250 µm in diameter increased as the ink coverage increased. œ Higher ink coverage area showed stronger intensity of ATR-IR spectral bands associated with inks. These results indicate that deinkability of UV prints could be predicted by analysis of ATR-IR spectra. œ Finally, the method was applied for assessment of recovered paper from commercial printing presses. It was confirmed that this method made it possible to distinguish easily deinkable UV prints from other UV prints. Based on these findings, we concluded that the ATR-IR method is applicable for inspection of incoming recovered paper.
Journal articles
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Automating Process Cooling Can Eliminate ´Strainer Danger’, Paper360º January/February 2022
Automating Process Cooling Can Eliminate ´Strainer Danger’, Paper360º January/February 2022
Journal articles
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Machinery That Can Support Zero Landfill Goals, Paper360º January/February 2022
Machinery That Can Support Zero Landfill Goals, Paper360º January/February 2022
Journal articles
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Turning Pulper Rejects into Valuable Fuel, Paper360º January/February 2022
Turning Pulper Rejects into Valuable Fuel, Paper360º January/February 2022
Journal articles
Magazine articles
TAPPI Journal Summaries, Paper360º January/February 2022
TAPPI Journal Summaries, Paper360º January/February 2022
Journal articles
Magazine articles
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.