Increased pulp yield by prolonged impregnation in softwood kraft pulping

Tavast, Daniel; Brännvall, Elisabet

doi:10.3183/npprj-2017-32-01-p014-020

Cited by 13 publications

(9 citation statements)

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“…Therefore, it was impossible to distinguish between the effects of EA and temperature. In the study by Tavast and Brännvall (2017), part of the spent impregnation liquor was removed prior to adjusting the average alkali concentration to the same level at the beginning of the cooking stage. Another difference to the present study was that the calculations to obtain a certain EA concentration were made under the only consideration of the EA in the free liquor and the assumption that also the bound liquor has the same concentration.…”

Section: Resultsmentioning

confidence: 99%

“…A specific impregnation stage operating at a lower temperature than the subsequent cooking also suppresses the reject formation (Tikka and Kovasin 1990;Tikka et al 1993). The same is true for a prolonged impregnation time (Tolonen et al 2010;Tavast and Brännvall 2017), but this approach decreases productivity and thus the high pressure approach is preferred (Malkov et al 2002). Chip thickness reduction can also be a remedy, as thickness is the most critical dimension in impregnation (Akhtaruzzaman and Virkola 1979).…”

Section: Introductionmentioning

confidence: 99%

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Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose

Brännvall

2018

Holzforschung

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Pulp yield can be improved by a more homogeneous delignification of the chips, achieved by improved impregnation prior to the cooking stage. Complete and efficient impregnation is obtained by increasing the diffusion rate by means of an impregnation liquor with a high initial effective alkali concentration (HIEAC). In the present study, the effect of HIEAC in the impregnation was evaluated and compared to a reference impregnation procedure and a prolonged impregnation. After the various impregnation scenarios, the alkali concentration was always adjusted to the same level in the beginning of the cooking stage. Impregnation with a HIEAC resulted in yield improvements by 1–1.5% units, due to a higher cellulose yield and possibly also to higher yield of glucomannan. The HIEAC with an even alkali distribution within the chips prior to the cooking stage resulted in a more uniform delignification carbohydrate degradation. Yield increase obtained by uniform delignification is due to both decreased shives content as well as less secondary peeling.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose

Brännvall

2018

Holzforschung

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“…Although pulping processes differ in sensitivity to uneven distribution of chemicals during impregnation and uneven temperatures (Rydholm 1965), all fibers in the wood need to get their share of the chemicals and the heat during the cooking process. Therefore, many recent studies have addressed the impregnation of wood chips in kraft pulping, the most common chemical pulping method (Malkov et al 2002;Malkov et al 2003;Wedin et al 2010;Brännvall and Bäckström 2016;Tavast and Brännvall 2017;Brännvall and Reimann 2018). Poor wood chip quality can result in more shives in the pulp, or even in digester shutdown.…”

Section: Introductionmentioning

confidence: 99%

New drum-chipping technology for a more uniform size distribution of wood chips

2020

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Wood chips from a novel type of drum chipper were compared to wood chips from a conventional disc chipper in an evaluation based on demonstration-scale and industrial-scale machinery. The evaluation was performed as the wood chippers were used as production machines in a kraft pulp mill using softwood. The average bulk density of the wood chips from the disc chipper and the drum chipper was similar and within the range of 138–140 kg/m3. The size distribution of the wood chips was investigated using a conventional screening method, and by using an automatized image-analysis system based on laser scanning. The average length was set to be the same, but the wood chips from the drum chipper had a more uniform length. The average thickness was similar, but the drum chipper generated slightly more thinner wood chips. Compared to the disc chipper and using the screening method, the drum chipper generated a similar fraction of oversized and overthick wood chips, 51% more large accept chips, 11% more total accept chips, and 74% less pin chips and fines. Image analysis resulted in similar data. The results indicate that drum chippers warrant further attention as an alternative to conventional industrial-scale disc chippers.

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“…40 (Brännvall and Bäckström 2016). A higher alkali consumption during the impregnation stage is assumed to lead to less alkali consumed in the cooking stage, as previously shown (Andrews et al 1983, Tolonen et al 2010, Tavast and Brännvall 2017, Brännvall and Bäckström 2016.…”

Section: Assessment Of High Alkali Impregnation (Hai) By Mill Simulatmentioning

confidence: 78%

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

Brännvall

Kulander

2019

Nordic Pulp &Amp; Paper Research Journal

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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.

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Increased pulp yield by prolonged impregnation in softwood kraft pulping

Cited by 13 publications

References 0 publications

Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose

Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose

New drum-chipping technology for a more uniform size distribution of wood chips

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

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