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The Impact of Dissolved Matter on Fiberline Processes
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). BTG Instruments.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The impact of dissolved matter on the performance of four fiberline process stages was investigated: oxygen delignification, hot acid treatment, chlorine dioxide bleaching, and hydrogen peroxide reinforced alkaline extraction. In particular the impact on delignification due to dissolved lignin was studied.

The impact of unoxidized and oxidized dissolved matter on lignin and carbohydrate degradation was investigated in a laboratory oxygen delignification stage. It was concluded that the delignification was decreased by the presence of unoxidized dissolved matter but increased in the case of oxidized dissolved matter. Both types of dissolved matter comparably increased the carbohydrate degradation. Thus, the presence of unoxidized dissolved matter impaired the selectivity. In the case of oxidized dissolved matter, the selec­tiv­ity was affected in the same way as when using a higher sodium hydroxide charge.

The presence of dissolved matter reduced the efficiency of a laboratory hot acid stage, and subsequently further affected the chemical demand in a following chlorine dioxide stage. In a laboratory chlorine dioxide stage, the presence of dissolved matter reduced the delignifica­tion. The additional chemical demand required to compensate for this reduc­tion was proportional to the content of dissolved matter. Moreover, the total chemical demand was found proportional to the total kappa number of the pulp, that is the sum of the fiber and filtrate kappa numbers. Finally, the presence of dissolved matter in a laboratory hydrogen peroxide reinforced alkaline extrac­tion stage reduced both the delignification and the brightness.

Furthermore, mill studies showed that the content of dissolved lignin varied significantly, and often more than the fiber-bound lignin, in a bleaching stage. For chlorine dioxide stages, it was proposed that the chemical consumption could be reduced by controlling the chemical charge based on the sum of the fiber-bound lignin and the dissolved lignin.

Abstract [en]

Pulp mills employ different control strategies to decrease the consumption of raw materials while still maintaining high product quality. To operate a kraft pulp mill in an efficient manner, it is essential to identify the key process parameters. Residual lignin is one of the most important parameters in chemical pulping and most mills base their process control on measurements of the lignin content, analyzed as kappa number. However, they typically only determine the content of the fiber-bound lignin while the dissolved lignin in the pulp slurry is merely seen as a disturbance.

Dissolved matter, especially dissolved lignin, consumes bleaching chemicals, and any variability of the dissolved lignin content will lead to non-optimal chemical charges and subsequently higher production cost. By measuring the dissolved lignin content as well as the fiber-bound lignin content, pulp mills can however apply chemicals based on the actual total bleach load. The impact of dissolved matter was investigated in four different process stages and it was concluded that both the content and the type of dissolved matter affected the performance of the stages. Furthermore, increasing the chemical charges in the process stages could only partly compensate for the negative impact of the dissolved matter.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2018. , p. 104
Series
Karlstad University Studies, ISSN 1403-8099 ; 2018:29
Keywords [en]
Bleach plant control, Carbonate, Carryover, Chlorine dioxide bleaching, COD, Dissolved lignin, Dissolved matter, Fiberline control, Filtrate, Hexenuronic acid, Hydrogen peroxide bleaching, Kappa number, Oxygen delignification, Wash loss
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-67511ISBN: 978-91-7063-862-6 (print)ISBN: 978-91-7063-957-9 (electronic)OAI: oai:DiVA.org:kau-67511DiVA, id: diva2:1229678
Public defence
2018-09-06, Nyquistsalen, 9C203, Karlstads universitet, Karlstad, 13:00 (Swedish)
Opponent
Supervisors
Funder
Knowledge Foundation
Note

Finansiär är även BTG Instruments. 

Artikel 4, 5 och 6 ingick som manuskript i avhandlingen, nu publicerade. 

Available from: 2018-08-17 Created: 2018-07-02 Last updated: 2019-12-13Bibliographically approved
List of papers
1. A new sensor and a novel control concept for optimized fiber line operation
Open this publication in new window or tab >>A new sensor and a novel control concept for optimized fiber line operation
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2014 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 13, no 10, p. 39-45Article in journal (Refereed) Published
Abstract [en]

Kraft and sulfite pulp mills use several consecutive process stages for pulp production. However, usually only one key pulp parameter is used for process control and that is the lignin content in the fibers, typically expressed as the kappa number. Even so, to improve process efficiency, more variables need to be monitored. To do that, a new sensor was developed, the dissolved lignin transmitter (DLT), along with a new control concept. The DLT measures the dissolved lignin content in the pulp slurry using a unique principle based on optical measurements. The device can measure the dissolved lignin inline at low consistency and at medium consistency. The sensor has two major applications: 1) improving the efficiency in washing stages and 2) optimizing chemical charges. Results from several mill trials have shown that the contribution from dissolved lignin in the filtrate portion of the pulp is up to 30% of the total bleach load, i.e., fiber and filtrate kappa number combined into the bleach plant. Hence, chemical savings can be achieved taking this component into account compared to only measuring the washed fiber kappa number. Application: The results of this study can help mills understand how to better control the pulping stages, which might lead to significant economic savings and better pollution control.

Place, publisher, year, edition, pages
TECH ASSOC PULP PAPER IND INC, 2014
National Category
Chemical Sciences
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-41498 (URN)000343916600007 ()
Available from: 2016-04-25 Created: 2016-04-11 Last updated: 2020-05-20Bibliographically approved
2. Impact of dissolved lignin in oxygen delignification and chlorine dioxide stages
Open this publication in new window or tab >>Impact of dissolved lignin in oxygen delignification and chlorine dioxide stages
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2016 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 15, no 3, p. 167-174Article in journal (Refereed) Published
Abstract [en]

While carryover of dissolved lignin between stages in the pulp mill fiber line is a well-known problem, it is still typically seen only as a minor disturbance factor or bias in the control of oxygen (O-2) delignification and bleaching stages. The present study, however, reveals that it plays a larger role than anticipated, and that it should be properly analyzed in order to correctly control the process stages. This is especially important for the O-2 and D-0 stages as the lignin content is still high in these positions. The results of the study show that dissolved lignin carried over between stages may have a significant impact on the bleaching chemical consumption and, indirectly, on the pulp quality. Mill investigations have shown very large variations in the dissolved lignin content in the pulp before the oxygen delignification stage and before the D-0 stage that have significantly influenced the bleaching chemical demand and, subsequently, the degree of delignification. In order to develop a better understanding of the mechanisms of the dissolved lignin's reactions, laboratory O-2 and D-0 experiments with controlled levels of dissolved lignin were conducted. It was anticipated that a better feedforward control could be achieved using an online dissolved lignin measurement, and results from mill trials are presented. Chlorine dioxide laboratory experiments using different levels of carryover (i.e., different dissolved lignin contents) were conducted. It was concluded that the filtrate kappa number provides a relevant measure of the bleach demand due to the dissolved lignin and that, subsequently, the combined fiber and filtrate kappa number provides an appropriate measure for optimum feedforward control of the stages. Mill results support these findings, which show that the chemical consumption is reduced significantly using the total kappa number. The post-D or post-DE kappa number feedback control can most probably be eliminated by using this technology.

National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-42029 (URN)000373923900004 ()
Conference
Conference on Pulping, Engineering, Environmental, Recycling, Sustainability (PEERS), OCT 25-28, 2015, Atlanta, GA
Available from: 2016-05-13 Created: 2016-05-13 Last updated: 2018-07-02Bibliographically approved
3. Impact of dissolved matter in the oxygen delignification stage
Open this publication in new window or tab >>Impact of dissolved matter in the oxygen delignification stage
2017 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 16, no 5, p. 275-284Article in journal (Refereed) Published
Abstract [en]

The presence of dissolved matter in the pulp suspension in an oxygen (O-2) delignification stage, consisting mainly of dissolved lignin, is normally considered to negatively affect the delignification rate due to the competing reactions between the fiber bound lignin and the lignin dissolved in the filtrate. Recirculated oxidized filtrate from the post-O-2 washing is usually considered to be less harmful to the delignification efficiency than unoxidized dissolved matter originating from the cooking stage. To develop a better understanding of the mechanisms of the dissolved matter's reactions and impact on the O-2 stage performance, laboratory oxygen delignification experiments with varying levels of unoxidized and oxidized dissolved matter were conducted. The results showed that unoxidized dissolved matter had a negative impact on the delignification in the O-2 stage, whereas oxidized dissolved matter actually had a positive effect. The delignification efficiency of the laboratory experiments thus depends on both the amount of dissolved matter and its origin. The pulp viscosity decreased with increasing dissolved matter content irrespective of its origin but at higher COD levels; however, the viscosity drop was larger for the unoxidized dissolved matter. In terms of selectivity, the oxidized filtrate had a similar impact as additional NaOH charge. Both types of filtrates consumed hydroxide and the final pH decreased with increasing dissolved matter content. The final pH was significantly lower in the unoxidized filtrate experiments at higher COD levels, indicating a high reactivity between the unoxidized dissolved matter and the oxygen in the reactor. Based on the results, further understanding is achieved about the relation between pre-O-2 washing performance and process configuration in an actual mill case, as well as the impact of dissolved matter on delignification. The importance of efficient removal of harmful unoxidized dissolved matter is verified, but the results also suggest that the oxidized dissolved matter that is recirculated from post-O-2 washing actually has a significant positive impact on the delignification and is not just a potential problem in case of carryover to the bleach plant. Subsequently, pulp washing efficiency is critical both pre- and post-O-2.

Place, publisher, year, edition, pages
TAPPI Press, 2017
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-65647 (URN)000403367800004 ()
Available from: 2018-01-17 Created: 2018-01-17 Last updated: 2018-07-05Bibliographically approved
4. Oxygen delignification: Laboratory evaluation of the impact of dissolved organic matter, sodium car­bonate and sodium thiosulfate
Open this publication in new window or tab >>Oxygen delignification: Laboratory evaluation of the impact of dissolved organic matter, sodium car­bonate and sodium thiosulfate
2019 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 7, p. 645-652Article in journal (Refereed) Published
Abstract [en]

Dissolved matter (DM) in the oxygen delignification (O2Del) stage affects the lignin and carbohydrate degradation. To understand this topic better, laboratory O2Del experiments were conducted with controlled addition of either unoxidized dissolved matter (UnoxDM) originating from the cooking stage or oxidized dissolved matter (OxDM) recycled from the post-O2Del washing. The presence of UnoxDM decreased the delignification, while the presence of OxDM showed the opposite effect, both compared to a well-washed pulp and at the same alkali charge level. However, both types of DM had a negative impact on the carbohydrate degradation. The distribution between these DMs will affect the resulting lignin degradation, because the filtrate accompanying the fibers into the O2Del stage is a mixture of UnoxDM and OxDM. It is proposed that the positive impact on the delignification by OxDM is due to the high carbonate ion concentration in the filtrate. Further, the high content of thiosulfate ions in the UnoxDM was one of the reasons for the lower delignification in its presence.

Place, publisher, year, edition, pages
Walter de Gruyter, 2019
Keywords
carbonate, carryover, COD; dissolved lignin, dissolved organic matter, filtrate, oxidized dissolved matter, oxygen delignification, thiosulfate, unoxidized dissolved matter
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-67509 (URN)10.1515/hf-2018-0179 (DOI)
Note

Artikeln ingick som manuskript i Wilkes doktorsavhandling The Impact of Dissolved Matter on Fiberline Processes.

Available from: 2018-06-30 Created: 2018-06-30 Last updated: 2019-09-12Bibliographically approved
5. Impact of dissolved organic matter in DO-and ADO-stages in bleaching of birch kraft pulp
Open this publication in new window or tab >>Impact of dissolved organic matter in DO-and ADO-stages in bleaching of birch kraft pulp
2019 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 34, no 4, p. 433-441Article in journal (Refereed) Published
Abstract [en]

To be able to charge a correct amount of chlorine dioxide in the D-0-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 O-2-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.

Place, publisher, year, edition, pages
Walter de Gruyter, 2019
Keywords
acid treatment; carryover; chlorine dioxide bleaching; HexA; kappa number
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-67506 (URN)10.1515/npprj-2018-0047 (DOI)000497995600004 ()
Note

Denna artikel var publicerad som manuskript i Wilkes doktorsavhandling The Impact of Dissolved Matter on Fiberline Processes (2018)

Available from: 2018-06-08 Created: 2018-06-08 Last updated: 2019-12-13Bibliographically approved
6. Impact of dissolved organic matter in hydrogen peroxide reinforced alkaline extraction stages
Open this publication in new window or tab >>Impact of dissolved organic matter in hydrogen peroxide reinforced alkaline extraction stages
2019 (English)In: Appita journal, ISSN 1038-6807, Vol. 72, no 1, p. 4-14Article in journal (Refereed) Published
Abstract [en]

It has been demonstrated in previous studies that carryover of dissolved organic matter to a following bleaching stage has a significant impact on the reactions in oxygen delignification and chlorine dioxide stages. Since hydrogen peroxide is commonly used in the bleach plant in various positions, the present study was conducted to investigate the impact of dissolved matter on the performance of a hydrogen peroxide reinforced alkaline extraction stage. The results of a study using an OD(EP) bleaching sequence showed that chlorine dioxide filtrates have a negative impact on delignification and brightening. In the case studied, the kappa number after the laboratory (EP)-stage was up to 26% higher and the brightness was up to 10% ISO lower when carryover of dissolved matter from a chlorine dioxide stage was present. Compensating for these reductions by increasing the sodium hydroxide charge improved the brightness significantly less than the delignification.

Place, publisher, year, edition, pages
Appita, 2019
Keywords
Bleaching; bleach plant control; carryover; chlorine dioxide; dissolved lignin; dissolved matter; filtrate; hydrogen peroxide; kappa number; washing
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-67510 (URN)
Note

Artikeln ingick som manuskript i Wilkes doktorsavhandling The Impact of Dissolved Matter on Fiberline Processes.

Available from: 2018-06-30 Created: 2018-06-30 Last updated: 2019-11-25Bibliographically approved

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