Ozone-enhanced bleaching of softwood kraft pulp

TAPPI Journal ◽  
2010 ◽  
Vol 9 (8) ◽  
pp. 16-23 ◽  
Author(s):  
JEAN-CHRISTOPHE HOSTACHY
Keyword(s):  
Capital Investment ◽  
Kraft Pulp ◽  
Operating Cost ◽  
Pulp Mill ◽  
Economic Benefits ◽  
Variable Cost ◽  
Pulp Mills ◽  
Pulp Bleaching ◽  
Softwood Kraft Pulp ◽  
Hardwood Pulp

By using ozone in their bleaching processes, many hardwood pulp mills in various parts of the world have improved product quality and their environmental and process performance, and reduced operating costs to increase competitiveness. The challenge for softwood pulp is to rethink the use of ozone according to their specific requirements. This paper summarizes results obtained using ozone bleaching on softwood (Pinus radiata) kraft pulp, for which the brightening ability of limited ozone dosages can enhance the economic benefits without impairing pulp quality. This work evaluated the chemical justification to use ozone at the end of the bleaching sequence and the effect on pulp quality, and considered the practical consequences of this new option. Special attention was given to the economic and technical aspects, including investment cost, variable cost, and process implementation. Ozone was shown to be the ideal complement of chlorine dioxide for final pulp bleaching. Both chemicals can easily be combined at the end of the bleaching sequence. Taking into account pulp mill capacity, capital investment, and total operating cost, the financial savings were calculated to be in the range of EUR 5 million (USD 6 million) per year, with a payback period of about 1.5 years.

Fate of phosphorus in the recovery cycle of the kraft pulping process

TAPPI Journal ◽  
2020 ◽  
Vol 19 (3) ◽  
pp. 139-148
Author(s):  
MARYAM SADEGH MOUSAVI ◽  
NIKOLAI DEMARTINI
Keyword(s):  
Kraft Pulp ◽  
Pulp Mill ◽  
Field Studies ◽  
Kraft Pulping ◽  
Pulp Mills ◽  
Recovery Cycle ◽  
Green Liquor ◽  
Green Liquor Dregs ◽  
Kraft Pulp Mills ◽  
Negative Effect

The accumulation of nonprocess elements in the recovery cycle is a common problem for kraft pulp mills trying to reduce their water closure or to utilize biofuels in their lime kiln. Nonprocess elements such as magne-sium (Mg), manganese (Mn), silicon (Si), aluminum (Al), and phosphorus (P) enter the recovery cycle via wood, make-up chemicals, lime rock, biofuels, and process water. The main purge point for these elements is green liquor dregs and lime mud. If not purged, these elements can cause operational problems for the mill. Phosphorus reacts with calcium oxide (CaO) in the lime during slaking; as a result, part of the lime is unavailable for slaking reactions. The first part of this project, through laboratory work, identified rhenanite (NaCa(PO4)) as the form of P in the lime cycle and showed the negative effect of P on the availability of the lime. The second part of this project involved field studies and performing a mass balance for P at a Canadian kraft pulp mill.

scholarly journals Consequences in a softwood kraft pulp mill of initial high alkali concentration in the impregnation stage

2019 ◽  
Vol 34 (1) ◽  
pp. 28-35 ◽  
Author(s):  
Elisabet Brännvall ◽  
Ida Kulander
Keyword(s):  
Kraft Pulp ◽  
Pulp Mill ◽  
Alkali Concentration ◽  
Pulp Yield ◽  
Kraft Pulp Mill ◽  
White Liquor ◽  
High Initial Concentration ◽  
Softwood Kraft Pulp ◽  
High Alkali ◽  
Energy Balances

Abstract Impregnation with high initial concentration is fast and efficient, leading to a homogeneous delignification in the subsequent cook, resulting in improved screened pulp yield. To obtain high initial alkali concentration, the white liquor flow needs to be significantly increased. The moisture content of the wood chips and the alkali concentration of the white liquor limit the initial alkali concentration of the impregnation liquor that can be reached. It is therefore of interest to evaluate the possibility to implement high alkali impregnation (HAI) industrially and the consequences this would have on the mill system. The effect of HAI on mass and energy balances in a kraft pulp mill has been studied using mill model simulations. The sensitivity to disturbances in important parameters for process control has been compared to impregnation scenarios used industrially. It was shown that high initial alkali concentration can be achieved on industrial scale by increased white liquor flow. HAI has a positive effect on recovery flows and reduces the need for make-up chemicals. The HAI concept is less sensitive to variations in process parameters, such as chip moisture and white liquor concentration, thus diminishing the risk of alkali depletion in chip cores.

scholarly journals Method for analysis of ClO2 and Cl2 air emissions from pulp mill

2019 ◽  
Vol 34 (1) ◽  
pp. 19-27
Author(s):  
Kimona Häggström ◽  
Magnus Gunnarsson ◽  
Katarina Bremert-Jirholm ◽  
Nina Simic
Keyword(s):  
Chlorine Dioxide ◽  
Analytical Method ◽  
Kraft Pulp ◽  
Pulp Mill ◽  
Air Emissions ◽  
Pulp Mills ◽  
Limit Of Quantification ◽  
Regulatory Standards ◽  
Low Concentrations ◽  
Kraft Pulp Mills

Abstract Chlorine dioxide is commonly used as a bleaching agent in kraft pulp mills. Scrubbers are required to remove any remaining ClO2 from the plant tail gases. To control the air emissions of chlorine compounds, chlorine dioxide and chlorine contents must be monitored to ensure that the strict regulatory standards are met. However, the currently used analytical method is not suitable for detection of low concentrations of chlorine and chlorine dioxide. A new method for measuring chlorine dioxide and chlorine emissions was developed, which ensures compliance with the stringent requirements imposed by the authorities. The two species could be measured separately with a limit of quantification of 3 ppm. The method was robust and easy to use in the pulp mill environment and it was validated both in the laboratory and the field. The specificity of the method was demonstrated, Cl2 analysis was not sensitive to the presence of ClO2 and vice versa. The uncertainty (±2×RSD) of the analytical method in the field was estimated from duplicate measurements performed in the range of 3–500 ppm for ClO2 and 3–300 ppm for Cl2, and was found to be ±20 % and ±10 %, respectively. Possible interferences in the analytical method are also discussed.

Some Toxic Constituents of Chlorination-Stage Effluents from Bleached Kraft Pulp Mills

1981 ◽  
Vol 38 (7) ◽  
pp. 739-743 ◽  
Author(s):  
A. B. McKague
Keyword(s):  
Gas Chromatography ◽  
Rainbow Trout ◽  
Kraft Pulp ◽  
Pulp Mill ◽  
Salmo Gairdneri ◽  
Pulp Mills ◽  
Juvenile Rainbow Trout ◽  
Bleached Kraft Pulp ◽  
Toxic Materials ◽  
Kraft Pulp Mills

Constituents responsible for the toxicity of a sample of bleached kraft chlorination-stage effluent to juvenile rainbow trout (Salmo gairdneri) were investigated. Tetrachlorocatechol, 3,4,5-trichlorocatechol, and 2,6-dichlorohydroquinone were identified and evidence was obtained for the presence of other chlorodihydroxybenzenes in toxic acidic fractions of the sample. Concentrations of 0.46 mg/L 3,4,5-trichloro- and 0.74 mg/L tetrachloro-catechol were estimated in the sample by analytical gas chromatography. Toxic materials in the nonacidic fraction were not identified although the nontoxic dichloromethyl methyl sulfone was isolated.Key words: chlorination-stage effluent, toxicity, pulp mill, chlorocatechols, chlorodihydroxybenzenes

The Effects of the Order of Chemical Addition on the Peroxide Bleaching of an Oxygen-Delignified Softwood Kraft Pulp

Holzforschung ◽  
2000 ◽  
Vol 54 (3) ◽  
pp. 279-286 ◽  
Author(s):  
Luc Lapierre ◽  
Richard Berry ◽  
Jean Bouchard
Keyword(s):  
Sodium Hydroxide ◽  
Kraft Pulp ◽  
Complex Form ◽  
Optimum Concentration ◽  
Operating Conditions ◽  
Pulp Bleaching ◽  
Peroxide Bleaching ◽  
Softwood Kraft Pulp ◽  
Marginal Improvement

Summary In pulp bleaching, while the peroxide-stage chemical charges and the physical operating conditions have been optimized, little attention has been given to the order in which these chemicals are added. We assessed the effects of chemicals, individually and combined, and the effects of the order of addition of these chemicals on peroxide bleaching performance in an acid-treated pulp and in a chelated pulp. We found that adding magnesium to an acid-treated pulp is essential for good peroxide bleaching, while adding magnesium to a chelated pulp provides only a marginal improvement in most additions. But adding magnesium and sodium hydroxide, or sodium hydroxide and magnesium sequentially into a bleaching solution before adding the solution into pulp, causes inefficient peroxide bleaching. This is particularly the case with a chelated pulp. This inefficiency can be avoided if a chelant is added between the additions of magnesium and sodium hydroxide. Magnesium is substantially more effective when in a complex form with either the pulp or a chelant, and the optimum concentration of magnesium for use in peroxide bleaching can be determined by following the peroxide residual.

scholarly journals A 30-Year Study of Impacts, Recovery, and Development of Critical Effect Sizes for Endocrine Disruption in White Sucker (Catostomus commersonii) Exposed to Bleached-Kraft Pulp Mill Effluent at Jackfish Bay, Ontario, Canada

2021 ◽  
Vol 12 ◽  
Author(s):  
Erin J. Ussery ◽  
Mark E. McMaster ◽  
Mark R. Servos ◽  
David H. Miller ◽  
Kelly R. Munkittrick
Keyword(s):  
Endocrine Disruption ◽  
Kraft Pulp ◽  
Pulp Mill ◽  
Early Years ◽  
Sex Steroid ◽  
White Sucker ◽  
Fish Health ◽  
Pulp Bleaching ◽  
Kraft Pulp Mill ◽  
Bleached Kraft Pulp

Jackfish Bay is an isolated bay on the north shore of Lake Superior, Canada that has received effluent from a large bleached-kraft pulp mill since the 1940s. Studies conducted in the late 1980s found evidence of reductions in sex steroid hormone levels in multiple fish species living in the Bay, and increased growth, condition and relative liver weights, with a reduction in internal fat storage, reduced gonadal sizes, delayed sexual maturation, and altered levels of circulating sex steroid hormones in white sucker (Catostomus commersonii). These early studies provided some of the first pieces of evidence of endocrine disruption in wild animals. Studies on white sucker have continued at Jackfish Bay, monitoring fish health after the installation of secondary waste treatment (1989), changes in the pulp bleaching process (1990s), during facility maintenance shutdowns and during a series of facility closures associated with changing ownership (2000s), and were carried through to 2019 resulting in a 30-year study of fish health impacts, endocrine disruption, chemical exposure, and ecosystem recovery. The objective of the present study was to summarize and understand more than 75 physiological, endocrine, chemical and whole organism endpoints that have been studied providing important context for the complexity of endocrine responses, species differences, and challenges with extrapolation. Differences in body size, liver size, gonad size and condition persist, although changes in liver and gonad indices are much smaller than in the early years. Population modeling of the initial reproductive alterations predicted a 30% reduction in the population size, however with improvements over the last couple of decades those population impacts improved considerably. Reflection on these 30 years of detailed studies, on environmental conditions, physiological, and whole organism endpoints, gives insight into the complexity of endocrine responses to environmental change and mitigation.

Impact of dissolved organic matter in D0- and AD0-stages in bleaching of birch kraft pulp

2019 ◽  
Vol 34 (4) ◽  
pp. 433-441
Author(s):  
Caroline Wilke ◽  
Niclas Andersson ◽  
Ulf Germgård
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Kraft Pulp ◽  
Pulp Mill ◽  
Good Control ◽  
Process Conditions ◽  
Dissolved Matter ◽  
Softwood Kraft Pulp ◽  
Polluting Emissions ◽  
Birch Kraft Pulp

Abstract To be able to charge a correct amount of chlorine dioxide in the D0-stage, a pulp mill needs good control of the bleaching process and good sensors to keep the variability of the bleaching result on an acceptable level. It is also important to include the bleaching agent demand from the dissolved matter in the pulp slurry. If this is done correctly, over- or undercharging of bleaching agents can be reduced, which lead to lower bleaching chemical cost, lower polluting emissions and higher pulp quality. Our previous research has shown that the dissolved organic carryover from the O2-stage varies significantly when bleaching softwood kraft pulp. The present study investigated the corresponding impact in the case of bleaching of birch pulp. Different mill configurations and process conditions have been simulated in laboratory trials, including proceeding A-stage treatment, different degrees of washing before and between the stages, and a comparison of the effects of recycled and non-recycled wash filtrates. The results have confirmed the significant impact of the dissolved organic matter, and the knowledge which have been generated can be used to understand how measurement and control concepts can be developed to improve the pulp quality control and to decrease production cost.

Optimization of elemental chlorine-free bleaching for a softwood kraft pulp – part 1: impact of oxidative extraction on chlorine dioxide stoichiometry

TAPPI Journal ◽  
2010 ◽  
Vol 9 (8) ◽  
pp. 27-35 ◽  
Author(s):  
BRIAN N. BROGDON
Keyword(s):  
Decision Making ◽  
Chlorine Dioxide ◽  
Kraft Pulp ◽  
Alkaline Extraction ◽  
Pulp Bleaching ◽  
Elemental Chlorine ◽  
Kraft Pulp Bleaching ◽  
Softwood Kraft Pulp ◽  
Chemical Usage ◽  
Minimize Costs

The present investigation meticulously analyzes how oxidative alkaline extraction can be augmented through process changes, and how these augmentations can be leveraged to optimize chlorine dioxide usage with elemental chlorine-free (ECF) sequences for a conventional softwood kraft pulp. Bleaching data from Basta and co-workers (1992 TAPPI Pulping Conference) are re-examined and re-interpreted in this study. We determined that ~60% to 65% of the overall ClO2 charge should be applied in the D0-stage. Peroxide addition to an (EOP) can replace 0.6 to 2.5 Kg. ClO2 per Kg H2O2. Boosting the (EO) temperature to 80°C is equivalent to a 70°C (EOP) with 0.25% to 0.30% H2O2,whereas a 90°C (EO) is equivalent to 0.50% – 0.75% H2O2 in a 70°C (EOP). The stoichiometric bleaching data from this study can guide decision-making for lowering chemical usage and minimize costs to reach target brightness levels with three- and five-stage sequences.

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