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Online monitoring of the size distribution of lime nodules in a full-scale operated lime kiln using an in-situ laser triangulation camera, TAPPI Journal June 2024
ABSTRACT: To maximize efficiency of the recausticizing process in a pulp mill, producing a reburned lime with high and consistent reactivity is process critical. Prior investigations have demonstrated a correlation between the reactivity of lime and its nodule size, as well as the dusting behavior of the kiln. Therefore, monitoring the nodule size produced in the lime kiln could be a promising indirect method to measure the performance of the lime kiln. The objective of this investigation was to evaluate the utility of a laser triangulation camera for online monitoring of nodule size distribution for the lime kiln. A series of full-scale trials were performed in a lime kiln of a kraft pulp mill in which a camera was installed at the exit conveyor to analyze the lime discharging from the kiln. The nodule size distribution was analyzed for correlation with the lime temperature, flue gas temperature, and rotational speed of the kiln. The monitoring demonstrated temporal stability, and the results showed that the lime temperature had the most significant effect on the nodule size. The rotational speed of the lime kiln and the flue gas temperature showed limited effect on nodule size, but they had significant impact on the specific energy demand. The overall conclusion of the study is that the camera methodology effectively correlates lime temperature with nodule size distribution, and it advocates for the methods of implementation in automating lime temperature control, facilitating the production of consistently reactive lime at a lower specific energy consumption.
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Life cycle carbon analysis of packaging products containing nonwood residues: A case study on linerboard and corrugating medium, TAPPI Journal March 2024
ABSTRACT: Circularity is creating momentum toward utilizing waste feedstock in a myriad of applications. The paper industry is not an exception to this trend, and packaging products made from agricultural or agro-industrial residues are receiving more attention now than ever. Additionally, negative consumer perceptions of tree felling are accelerating the acceptance of these fibers. Nevertheless, adopting these residues raises the issue of whether they constitute a better alternative to fight climate change than wood. Answering this question is imperative to ensure that pledges to reduce carbon footprints across the industry are fulfilled. This paper aims to estimate the carbon footprint of corrugating medium and linerboard containing wheat straw and sugarcane bagasse pulp compared to analogous wood-based materials. The goal was also to understand how methodological decisions to allocate emissions to nonwood residues can affect the results. This study includes a life cycle carbon analysis spanning from cradle to grave, which comprises stages for residue production, pulping, paper-making, waste management, and corresponding transportation. For the proposed case study, the results suggest that straw- and bagasse-based medium and linerboard can present a higher carbon footprint than products made from virgin and recycled wood fibers. The main driver is the production of nonwood chemimechanical pulp. In addition, the lower capacity of nonwood residues to be recycled increases the overall impact. Finally, decisions around emissions allocation highly influence the results. This study helps mitigate part of the uncertainty around the environmental sustainability of corrugating medium and linerboard made from the selected nonwood residues.
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Life cycle carbon analysis of packaging products containing purposely grown nonwood fibers: A case study on the use of switchgrass pulp for linerboard and corrugating medium, TAPPI Journal March 2024
ABSTRACT: Sustainability is driving innovation in the pulp and paper industry to produce goods with lower carbon footprints. Although most of the efforts are currently focused on increasing energy efficiency or switching to renewable fuels, the attention toward alternative feedstocks has increased in recent years. Claims of nonwood fibers requiring lower use of chemicals and energy than wood fibers, along with negative consumer perceptions of tree felling, are helping purposely grown nonwoods to gain market share. The potential nonwood fiber environmental superiority over virgin or recycled wood fibers remains controversial and is often driven more by emotion and public perception rather than facts. This paper estimates the carbon footprint of corrugating medium and linerboard containing switchgrass pulp compared to analogous wood-based materials. The study includes a life cycle carbon analysis spanning from cradle to gate, which comprises stages for fiber production, pulping, papermaking, and corresponding transportation. Carbon footprints for virgin linerboard, recycled linerboard, virgin medium, and recycled medium were estimated at around 510, 620, 460, and 670 kg carbon dioxide equivalent per metric ton (kg CO2eq/t), respectively. Replacing 30% of the virgin or recycled material with switchgrass pulp translated into carbon footprint increases of around 60%, 45%, 62%, and 38%, respectively. Thus, for the proposed case study, the results suggest that switchgrass-based medium and linerboard can present a higher carbon footprint than products made from virgin and recycled wood fibers. The main driver is the production of nonwood mechanical pulp.This study was designed to mitigate part of the uncertainty around the environmental sustainability of medium and linerboard made from the selected purposely grown nonwood fibers.
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Factors affecting phosphorus uptake/dissolution during slaking and causticizing, TAPPI Journal March 2024
ABSTRACT: Hydroxide is regenerated in the recovery cycle of kraft pulp mills by the addition of lime (CaO) to green liquor. Phosphate in green liquor can react with the lime during slaking/causticizing. Total titratable alkali (TTA), sulfidity, the concentration of phosphate in the green liquor, temperature, and the liming ratio were all variables explored in this work to determine their influence on phosphorus uptake and dissolution. Experiments were also run in which the lime was slaked before being added to the green liquor to separate reactions with phosphate during slaking and reactions that occur during causticizing. Both reburnt lime and technical grade CaO were used. The experiment results indicate that phosphorus primarily reacts with slaked lime (Ca(OH)2), and that the final concentration of phosphate in the white liquor at the end of slaking and causticizing is nearly independent of the initial concentration of phosphorus and only mildly dependent on the carbonate concentration in the green liquor. There do appear to be differences in the rate at which phosphate reacts with reburnt lime and technical grade CaO, though the reason for this was not determined.
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Utilization of Areca leaf residues for sustainable production of greyboard, TAPPI Journal May 2024
ABSTRACT: This study primarily focused on the production of greyboard using waste materials from small scale industries, and specifically using Areca leaf waste fibers as a sustainable and environmentally friendly resource. Areca leaf waste fibers were employed as the primary raw material for greyboard manufacturing. The resulting greyboard exhibited commendable properties, including a tear index of 7.53 mN·m2/g, tensile index of 18.34·N·m/g (i.e., breaking length of 1870 m), burst factor of 9.24 (gf/cm2)/(g/m2) and stiffness factor of 33.1. This greyboard was created through a series of steps, including hydrothermal treatment of the material at 155°C and mechanical pulping refinement. The produced greyboard met the specifications outlined in the Indian Standard 2617 (1967) for greyboard. The key objective of this work was to leverage agricultural waste resources to develop a chemical-free greyboard, resulting in reduced waste disposal in open fields and a decrease in chemical usage within the greyboard manufacturing industry. Various characterization techniques, including field emission scanning electron microscopy (FE-SEM), attenuated total reflection•Fourier transform infrared (ATR-FTIR) analysis, and X-ray diffraction (XRD), were used to assess the fiber quality, including aspects such as functional groups, morphology, and crystallinity for the materials used in the manufacturing process.
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Using bleaching stage models for benchmarking hardwood ECF bleach plants, TAPPI Journal October 2023
ABSTRACT: Steady-state models estimated the performance of the D0(EOP)D1 bleach sequence at two mixed hardwood bleach plants in the southern United States. At Mill 1, the full sequence’s chlorine dioxide charge that brightens the pulp to ~84% ISO was monitored for two weeks. Mill 2 considered the partial sequence that brightens the pulp to ~86% ISO for nearly four weeks. Elevated levels of chlorine dioxide were linked to increased washer carryover in brownstock and extraction areas. For Mills 1 and 2, an extra 0.24% and 0.33% chlorine dioxide was consumed in the D0 stage. This extra bleach demand was equivalent to an additional 4.8 and 5.5 kappa load to the brownstock, respectively. Some differences were observed for the D1 stage. Mill 1 had extraction carryover that averaged 1.1 units higher than was measured, contributing to use of an extra 0.22% of chlorine dioxide. Mill 2 had extraction carryover that averaged between 0 and 0.7 kappa units and consumed up to 0.13% more chlorine dioxide. Another data set from Mill 2 showed high brownstock and extraction carryover, leading to ~0.90% more total chlorine dioxide usage to brighten to 84% ISO. Overall, this investigation illustrated that the models could be employed as benchmarks.
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Cross-flow separation characteristics and piloting of graphene oxide nanofiltration membrane sheets and tubes for kraft black liquor concentration, TAPPI Journal September 2023
ABSTRACT: Dewatering of weak black liquor (WBL) in the kraft cycle by evaporation is highly energy intensive. Membranes are an attractive alternative for energy-efficient dewatering, but existing commercial polymeric or ceramic membranes are either degraded in BL or have high capital costs. Our recent works have demonstrated the engineering of graphene oxide (GO) nanofiltration membranes, their stability and promising performance in BL conditions, and preliminary scale-up into sheets and tubes. Here, we describe in detail the separation characteristics of GO membrane sheets and tubes under real BL conditions and crossflow operation. Recycle-mode piloting of a GO tubular membrane showed average “production flux” of 16 L/m2/h (LMH) and high rejections of lignin (98.3%), total solids (66%), and total organic carbon (83%), with no signs of irreversible fouling identified. A corresponding GO sheet membrane produced an average flux of ~25 LMH and maintained high lignin rejection of ~97% during a slipstream pilot at a kraft mill site using WBL with ~16 wt% total solids (TS). Finally, we piloted a Dow/DuPont XUS1808 polyamide composite reverse osmosis (RO) membrane for last-mile processing of the GO nanofiltration membrane permeate. The RO membrane showed a steady state flux of 19 LMH at 65 bar and produced ~0.02 wt% TS water product, which is highly suitable for reuse in pulp washing operations in the kraft process. The results have strong positive implications for the industrial application of GO membranes in BL concentration and other related applications.
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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.