Revised steady-state model for chlorine dioxide brightening that considers extraction washer carryover effects

In an earlier investigation, a generalized model was developed to simulate the first chlorine dioxide (ClO2) brightening stage (D1). That stoichiometric model accurately predicts pulp brightness values for given bleach charges and vice versa for laboratory softwood pulps. The equation parameters are dependent on the kappa number and brightness of the extracted pulp. In this study, the earlier model was refined to include the negative effects of extraction carryover to simulate more realistically a mill’s D1 stage. Extracted pulps that contain washer carryover were found to brighten as if the pulp had a kappa number equal to the sum of the extracted kappa and the kappa value of extraction dissolved solids. If this higher kappa (i.e., apparent or wet kappa) is used in place of the extracted kappa with the D1 model, the equations suitably predicted the bleached brightness for a given bleach charge. The modified expressions were used to quantify the amount of carryover and to calculate carryover bleach consumption for a softwood D0(EOP)D1 fiber line. The mill’s washed pulps were found to have carryover levels of 1.4 kappa units, which was consuming 48% of the total D1 bleach charge. Additional analyses revealed that extraction carryover consumes 2.5-4.6 kg ClO2/ton pulp per kappa unit of carryover when bleaching a pulp to 78% to 84% ISO.

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Stoichiometric model of chlorine dioxide delignification of hardwood kraft pulps with oxidant-reinforced extraction effect,

TAPPI Journal ◽

10.32964/tj12.2.17 ◽

2013 ◽

Vol 12 (2) ◽

pp. 17-26 ◽

Cited By ~ 5

Author(s):

BRIAN N. BROGDON

Keyword(s):

Steady State ◽

Chlorine Dioxide ◽

Empirical Relationship ◽

Kappa Number ◽

Published Data ◽

Kraft Pulps ◽

Mathematical Transformation ◽

Stoichiometric Model ◽

Hardwood Species ◽

Steady State Model

A generalized, steady-state model for hardwoods is proposed for predicting bleaching delignification and/or chlorine dioxide (ClO2) consumption for sequences that use oxidant-reinforced extraction. Published data for various hardwood species and mixtures were analyzed to develop the model. The kappa number data from these studies were normalized to their respective pre-D0 kappa number, and the normalized kappa numbers were plotted against the bleach demand. This mathematical transformation allowed for various brownstocks and oxygen-delignified pulps with different kappa numbers to be modeled as a single curve based on an empirical relationship with fitted equation parameters. One of the two equation parameters could be expressed as simple functions of oxidant-reinforced extraction conditions (i.e., peroxide dosage). The model forecasts ClO2 usage reasonably well (±0.20% ClO2 on pulp) for conventional ClO2 delignification with extraction. Attempts to incorporate modified bleaching delignification processes that eliminate hexenuronic acids into the model were unsuccessful; data were insufficient to develop a relationship. This straightforward stoichiometric model contains relatively few fitted parameters to be determined. The model could be used with other steady-state brightening-stage models to predict bleach usage.

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Stoichiometric model of chlorine dioxide delignification of softwood kraft pulps with oxidant-reinforced extraction

TAPPI Journal ◽

10.32964/tj11.3.31 ◽

2012 ◽

Vol 11 (3) ◽

pp. 31-39 ◽

Cited By ~ 4

Author(s):

BRIAN N. BROGDON

Keyword(s):

Steady State ◽

Chlorine Dioxide ◽

Kappa Number ◽

Extraction Temperature ◽

Kraft Pulps ◽

Mathematical Transformation ◽

Stoichiometric Model ◽

Steady State Model ◽

Minimum Number ◽

Experimental Values

A generalized, steady-state model estimates bleaching delignification and/or chlorine dioxide consumption for sequences that employ oxidant-reinforced extraction. The model is based on Germgård’s stoichiometric expression for the D0E1 sequence, which relates chlorine dioxide uptake to post-extracted kappa number. Germgård’s integrated stoichiometric model was modified to normalize the extracted kappa number to the incoming kappa number. This mathematical transformation allows for various brownstocks and oxygen-delignified pulps with different kappa numbers to be modeled as a single curve whereby its shape is related to the stoichiometric parameter. From analyzing various softwood bleaching studies, it was determined that this stoichiometric parameter could be expressed as a simple function of oxidant-reinforced extraction conditions (e.g., extraction temperature and peroxide dosage). The generalized delignification model forecasts chlorine dioxide usage with small relative error from the experimental values, typically ±3% to ±10%. This model is relatively simple, with a minimum number of equation parameters to determined, and can be used with other steady-state brightening stage models to predict bleach usage.

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Extension of a steady-state chlorine dioxide brightening model for Z-ECF bleaching of softwood kraft pulps

TAPPI Journal ◽

10.32964/tj20.3.186 ◽

2021 ◽

Vol 20 (3) ◽

pp. 186-197

Author(s):

BRIAN N. BROGDON ◽

LUCIAN A. LUCIAN

Keyword(s):

Steady State ◽

Linear Relationship ◽

Chlorine Dioxide ◽

Current Model ◽

Kappa Number ◽

Kraft Pulps ◽

Current Investigation ◽

Elemental Chlorine ◽

Steady State Model ◽

Ecf Bleaching

Earlier studies developed a steady-state model to predict the brightness and/or bleach consumption during the chlorine dioxide brightening (D1) of softwood pulps produced by conventional elemental-chlorine-free (ECF) sequences. This model relates the chlorine dioxide consumed to the brightness gains predicated upon an asymptotic D1 brightness limit, an incoming D1 pulp brightness, and an equation parameter (β11). The current investigation examines the application of this model to ECF sequences that use ozone delignification (Z-ECF). Literature D1 data from various Z-ECF bleaching studies, which investigated OZ, OD0/Z, and OZ/D0 delignification, were fitted to the model. The β11 parameter was found to be linearly correlated to the entering kappa number. Interestingly, this linear relationship was found to be identical to the relationships observed when modeling the D1 stage for conventional ECF and chlorine-based bleach sequences. Subtle differences in D1 brightening response in the model among the various bleach sequences are reflected by incoming pulp brightness (at the same kappa number). The current model is used to illustrate how alterations to Z-ECF delignification affect D1 brightening and chlorine dioxide consumption.

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Improved steady-state models for chlorine dioxide delignification sequences that include washer carryover effects

TAPPI Journal ◽

10.32964/tj14.2.93 ◽

2015 ◽

Vol 14 (2) ◽

pp. 93-103 ◽

Cited By ~ 4

Author(s):

BRIAN N. BROGDON

Keyword(s):

Steady State ◽

Chlorine Dioxide ◽

Control Strategies ◽

Kappa Number ◽

Carryover Effects ◽

Advanced Process Control ◽

Elemental Chlorine ◽

Plant Data ◽

State Models ◽

Ecf Bleaching

In previous studies, generalized steady-state models were proposed to approximate the chlorine dioxide demand needed for the delignification of softwood and hardwood pulps, where the kappa number entering the bleach plant can fluctuate. However, these expressions neglect the effect of dissolved solids with the stock that originate from incomplete pulp washing. In this study, the original elemental chlorine-free (ECF) models are modified to include the effects of carryover from brownstock or post-oxygen washing. The stoichiometric bleach consumption from carryover, based on its composition, was calculated from various literature sources. The majority of the bleach demand (about 70%) results from the dissolved lignin contained in the brownstock carryover, with the remainder resulting from the inorganic sulfur constituents (e.g., sulfide and thiosulfate). When the effect of brownstock carryover was taken into account, the modified models accurately predicted the amount of chlorine dioxide consumed for a given delignification level (about ±0.1% chlorine dioxide) vs. actual bleach plant data. The improved models can be used to gauge the level of washer carryover entering the bleach plant if this parameter is not regularly monitored by the mill. Additionally, these modified expressions could be integrated into advanced process control strategies for ECF bleaching where the washer carryover or dissolved lignin entrainment is measured with online sensors.

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A steady state model describing the solubility of calcium oxalate in D(chlorine dioxide stage)-filtrates

Nordic Pulp & Paper Research Journal ◽

10.3183/npprj-2001-16-04-p389-395 ◽

2001 ◽

Vol 16 (4) ◽

pp. 389-395 ◽

Cited By ~ 3

Author(s):

Per Ulmgren ◽

Rune Rådeström

Keyword(s):

Steady State ◽

Calcium Oxalate ◽

Chlorine Dioxide ◽

State Model ◽

Steady State Model

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Generalized steady-state model for chlorine dioxide brightening of hardwood kraft pulps

TAPPI Journal ◽

10.32964/tj16.5.263 ◽

2017 ◽

Vol 16 (05) ◽

pp. 263-272

Author(s):

Brian Brogdon

Keyword(s):

Steady State ◽

Chlorine Dioxide ◽

Kinetic Studies ◽

Kraft Pulping ◽

State Model ◽

Kraft Pulps ◽

Steady State Model ◽

Plant Data ◽

Pulp Properties ◽

Hardwood Pulp

A generalized, steady-state model for the first chlorine dioxide brightening (D1) stage is proposed for North American hardwood kraft pulps. The model predicts the post-D1 brightness obtained for a given chlorine dioxide (ClO2) charge based on three equation parameters. Data from laboratory D1 studies were examined with the model to determine the relationships of the parameters to extracted pulp properties. The asymptotic D1 brightness limit at extremely high bleach charges was ~93% ISO for most hardwood pulps. This parameter can be calculated from the limiting light absorption coefficient of D1 kinetic studies (≈ 0.10 m2/kg) and the unbeaten light scattering coefficient of the pulp. A second parameter was linearly correlated to the extracted kappa number of the hardwood pulp. This relationship seems to be affected by the chosen kraft pulping process (e.g., liquor or dissolved solids profiling). The final parameter is the extracted pulp brightness. The hardwood D1 model forecasted the brightness values of laboratory pulps that differ from measured values of ±0.5 to ±0.6 points. Daily averages of bleach plant data for a southeastern U.S. hardwood fiber line were examined with the model. Predictions were generally 0.5 points higher than the measured mill brightness values. This observation implied that the D0(EOP) pulp contained a small amount of extraction washer carryover (~0.4 kappa units on pulp) that was consuming ~1.2 kg ClO2/ton pulp, which was not accounted for in the hardwood D1 model.

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