The viscosities of unbleached alkaline pulps. IV. The effect of alkali

Fleming, B. I.; Kubes, G. J.

doi:10.1080/02773818508085189

Cited by 3 publications

(6 citation statements)

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“…When there is no concentration gradient within the chips, hydroxide or EA concentration during cooking becomes a function of cooking time and initial alkali charge, a set of conditions that were studied by Fleming and Kubes (1985). When there is a concentration gradient within the chips, this modified factor, G([OH']), has to be calculated numerically, and accumulated for progressive increments across the wood chips.…”

Section: Theorymentioning

confidence: 99%

“…If we include the effect of [OH -], eq 2 becomes When there is no concentration gradient within the chips, the hydroxide or EA (effective alkali) concentration during cooking becomes a function of cooking time, initial alkali charge, and the liquor-to-wood mass ratio, a set of conditions that were studied by Fleming and Kubes. 4 When there is a concentration gradient within the chips, this modified factor, G([OH -]), has to be calculated numerically, and for increasing time across the wood chips. When the time scale, ∆t, is small enough, G x ([OH -]) can be calculated as where [OH -] x,t is the hydroxide concentration for a given position at a given time, G T the relative rate factor ()exp((E/R)(1/373 -1/T))) at the digester temperature at a given time, and ∆t a small time interval during which temperature and [OH -] can be treated as constant.…”

Section: Letmentioning

confidence: 99%

“…Therefore, the term “a” in eq 6 is not constant either. If we include the effect of [OH - ], eq 2 becomes When there is no concentration gradient within the chips, the hydroxide or EA (effective alkali) concentration during cooking becomes a function of cooking time, initial alkali charge, and the liquor-to-wood mass ratio, a set of conditions that were studied by Fleming and Kubes . When there is a concentration gradient within the chips, this modified factor, G ([OH - ]), has to be calculated numerically, and for increasing time across the wood chips.…”

Section: Theorymentioning

confidence: 99%

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Nonuniformity of Carbohydrate Degradation during Kraft Pulping−Measurement and Modeling Using a Modified G-Factor

Li¹,

Moeser²,

Roen³

2000

Ind. Eng. Chem. Res.

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is an independent graduate school, research organization, and information center for science and technology mainly concerned with manufacture and uses of pulp, paper, paperboard, and other forest products and byproducts.Established in 1929, the Institute provides research and information services to the wood, fiber, and allied industries in a unique partnership between education and business. The Institute is supported by 52 North American companies.The purpose of the Institute is fulfilled through four missions, which are:• to provide a multidisciplinary education to students who advance the science and technology of the industry and who rise into leadership positions within the industry;• to conduct and foster research that creates knowledge to satisfy the technological needs of the industry;• to serve as a key gl;obal resource for the acquisition, assessment, and dissemination of industry information, providing critically important information to decision-makers at all levels of the industry; and • to aggressively seek out technological opportunities and facilitate the transfer and implementation of those technologies in collaboration with industry partners. ACCREDITATION The Institute of Paper Science and Technology is accredited by the Commission on Colleges of the Southern Association of Colleges and Schools to award the Master of Science and Doctor of Philosophy degrees. NOTICE AND DISCLAIMERThe Institute of Paper Science and Technology (IPST) has provided a high standard of professional service and has put forth its best efforts within the time and funds available for this project. The information and conclusions are advisory and are intended only for internal use by any company who may receive this report. Each company must decide for itself the best approach to solving any problems it may have and how, or whether, this reported information should be considered in its approach.IPST does not recommend particular products, procedures, materials, or service. These are included only in the interest of completeness within a laboratory context and budgetary constraint. Actual products, procedures, materials, and services used may differ and are peculiar to the operations of each company.In no event shall IPST or its employees and agents have any obligation or liability for damages including, but not limited to, consequential damages arising out of or in connection with any company's use of or inability to use the reported information. IPST provides no warranty or guaranty of results.The Institute of Paper Science and Technology assures equal opportunity to all qualified persons without regard to race, color, religion, sex, national origin, age, disability, marital status, or Vietnam era veterans status in the admission to, participation in, treatment of, or emptoyment in the programs and activities which the Institute operates.

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Section: Theorymentioning

confidence: 99%

Section: Letmentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

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Nonuniformity of Carbohydrate Degradation during Kraft Pulping−Measurement and Modeling Using a Modified G-Factor

Li¹,

Moeser²,

Roen³

2000

Ind. Eng. Chem. Res.

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“…The need to correct for the effect of pulp yield in predicting viscosity will also be discussed. Fleming et al (1983Fleming et al ( , 1985) developed a kinetic model for pulp viscosity. The rate of change of viscosity is represented by:…”

Section: Prediction Of Pulp Viscositymentioning

confidence: 99%

“…As seen from Equation (13), it is necessary to know the variation of [OM with time to predict viscosity. Since this information is not always available, Kubes and his co-workers (Fleming et al, 1983;Fleming and Kubes, 1985) developed a regression equation that calculates final pulp viscosity using the G-factor and residual alkalinity at the end of the cook.…”

Section: Prediction Of Pulp Viscositymentioning

confidence: 99%

A contribution to the modeling of kraft pulping

Agarwal

Gustafson

1997

Can J Chem Eng

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This paper presents a mathematical model for pulping that considers the effect of alkali diffusion and chemical reaction. An approximation for 3-dimensional diffusion in wood chips is tested against pulping data. A method for predicting pulp viscosity is also presented. The model simulates the effect of key pulping variables on pulp kappa number, viscosity, yield, residual alkalinity and pulping uniformity. Experimental data from a number of sources are successfully predicted by the model.On presente dans cet article un modele mathematique pour la mise en pite qui prend en consideration l'effet de la diffusion des alcalins et de la reaction chimique. Une approximation de la diffusion tridimensionnelle dans des copeaux de bois est testee par rapport a des donnees de mise en pite. Une methode de prediction de la viscosite de la pite est egalement presentee. le modele simule I'effet de variables cles de mise en pite sur le Kapa de la pite, la viscositt, le rendement, I'alcalinite residuelle et l'uniformite du traitement. Des donnees experimentales de differentes sources sont predites avec succ&s par le modele. Keywords: pulping model, difhsion, pulp uniformity, pulp viscosity, simulation.iffusion of alkali from pulping liquor into the wood D chips plays an important role in kraft pulping. The overall pulping rate is determined by the rates of reaction and diffusion. It has been shown that the lignin content of cooked chips varies across chip thickness (Gullichsen et al., 1992). Lignin content for cooked chips is highest at the chip center and lowest at the surface. For chips less than 2 mm thick, pulping is uniform. For thicker chips, alkali consumption rate exceeds the rate of diffusion at pulping temperature. The apparent reaction rate is diffusion-limited. Diffusion limitation leads to nonuniform pulping. The final pulp contains fibers with a nonuniform distribution of kappa number (kappa number is proportional to % lignin in pulp). Layered pulping of 2 to 10 mm thick chips has shown that 2 mm chips produce pulp of kappa 15 while 10 mm chips give kappa 70. The large change in kappa with thickness is mainly due to the role of alkali diffusion. Pulping nonuniformity increases the average kappa of pulp and eventually leads to high screening rejects. Clearly, it is necessary to consider the effect of difision in order to quantitatively predict haft pulping performance. This paper presents a comprehensive model for pulping that considers the combined effect of chemical reaction and alkali diffusion. Some improvements are made to an earlier reaction-diffusion based model by Gustafson et al. (1983). A modified treatment for diffusion is used in this work. A method for predicting pulp viscosity is also presented. Model prediction for four different quantities -kappa, yield, viscosity and residual alkali are compared with experimental data from three sources. Some of the data shown here is reproduced from an earlier paper (Agarwal et al., 1994) to make a more complete presentation of model capabilities. Diffusion in wood...

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Chemical Pulping Processe: Sections 4.2.8–4.3.6.5

Sixta¹

2006

Handbook of Pulp

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The viscosities of unbleached alkaline pulps. IV. The effect of alkali

Cited by 3 publications

References 1 publication

Nonuniformity of Carbohydrate Degradation during Kraft Pulping−Measurement and Modeling Using a Modified G-Factor

Nonuniformity of Carbohydrate Degradation during Kraft Pulping−Measurement and Modeling Using a Modified G-Factor

A contribution to the modeling of kraft pulping

Chemical Pulping Processe: Sections 4.2.8–4.3.6.5

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