Modelación digestor continuo planta Arauco L2.
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Date
2025
Journal Title
Journal ISSN
Volume Title
Publisher
Universidad de Concepción
Abstract
Esta memoria de título aborda el proceso de deslignificación Kraft de madera de pino radiata en el digestor continuo de planta Arauco L2 y el fenómeno de baja de número kappa de salida en condiciones de baja carga de astillas.
En este estudio se modela la cinética del proceso a lo largo del impregnador y digestor, utilizando modelos de reacciones en serie de deslignificación y degradación de carbohidratos, donde la ecuación que gobierna la velocidad de reacción cambia dependiendo de la cantidad de lignina presente en la madera o pulpa.
Para la modelación, el digestor e impregnador se dividen en secciones transversales y se modelan como reactores perfectamente agitados, en vez de un solo reactor de flujo pistón, así, un elemento continuo se trabaja como varios elementos finitos consecutivos. Para los cálculos se recurre al software WinGEMS para realizar balances de materia del proceso, y se recurre a MS Excel para realizar los cálculos de reacción en cada elemento finito. Durante la modelación existe recirculación de información entre estas dos herramientas.
Se utilizan datos operativos provenientes del funcionamiento del digestor durante dos periodos, un periodo de operación normal de un mes y un periodo de operación a baja carga de astillas con una duración de 36 horas. Las propiedades de los equipos de proceso y la estructura del proceso en si se obtienen de material proporcionado por Celulosa Arauco y Constitución.
De los resultados de la simulación se extrae que, de los modelos encontrados, el que mejor se ajusta al comportamiento del proceso de línea 2 es un ajuste de un modelo cinético presentado en material educativo interno de Celulosa Arauco. Con un error relativo de número kappa resultante de 13,4 %.
Se realiza un análisis de sensibilidad a este modelo, variando la temperatura del digestor. Se confirma que el modelo es estable y sigue la tendencia indicada por literatura, donde aumentos de temperatura resultan en un número kappa más bajo, y viceversa.
Se concluye que la baja en el número kappa a baja carga de astillas es producto del aumento del tiempo de residencia, dado que la baja se presenta aún en condiciones de mitigación del fenómeno, como el uso de reactivos más débiles.
Se extrae también que, si bien el modelo actual sigue la tendencia del proceso, este no es lo suficientemente exacto como para predecir de manera confiable los resultados de diferentes condiciones de operación.
This undergrad thesis tackles the kraft delignification process of radiata pine in the continuous digester vessel of Celulosa Arauco y Constitución, together with the decrease of kappa number during reduced wood chip feed. This study models the kinetics of the process along the impregnator and digester vessels, using in-series reaction models, where the equation that determines the reaction speed depends on the amount of lignin present in the wood or pulp. For modelling, the digester and impregnator are divided into longitudinal crosscuts and each one of said cuts is modeled as a perfectly stirred reactor, turning one continuous element into various consecutive finite ones. WinGEMS is used for mass balance calculations and process modelling, and MS Excel is used for reaction calculations in each finite element. There’s information feedback between these two tools. Two sets of operational data, sourced from the digester’s operation, is used for modelling. One set from normal operation spanning one month, and the other set from a reduced wood chip load period spanning 36 hours. Equipment properties and the process structure are sourced from documents supplied by Celulosa Arauco y Constitución. From the results it’s deduced that the best fitting model for the plant is an adjusted model found in internal training documents. With a relative error of 13,4% regarding the exit kappa number. A sensitivity analysis is carried out on this model, Varying digester temperature. It confirms that the model is stable and follows the tendency found in literature, where an increment in temperature results in lower kappa number, and vice versa. It is concluded that the decrease in kappa number in reduced wood chip load is caused by the increase in residence time, given that the decrease still happens despite mitigating conditions, like the use of weaker reactants. It is also concluded that, even though the model follows the tendency of the process, it is not exact enough to reliably predict the result of different operating conditions.
This undergrad thesis tackles the kraft delignification process of radiata pine in the continuous digester vessel of Celulosa Arauco y Constitución, together with the decrease of kappa number during reduced wood chip feed. This study models the kinetics of the process along the impregnator and digester vessels, using in-series reaction models, where the equation that determines the reaction speed depends on the amount of lignin present in the wood or pulp. For modelling, the digester and impregnator are divided into longitudinal crosscuts and each one of said cuts is modeled as a perfectly stirred reactor, turning one continuous element into various consecutive finite ones. WinGEMS is used for mass balance calculations and process modelling, and MS Excel is used for reaction calculations in each finite element. There’s information feedback between these two tools. Two sets of operational data, sourced from the digester’s operation, is used for modelling. One set from normal operation spanning one month, and the other set from a reduced wood chip load period spanning 36 hours. Equipment properties and the process structure are sourced from documents supplied by Celulosa Arauco y Constitución. From the results it’s deduced that the best fitting model for the plant is an adjusted model found in internal training documents. With a relative error of 13,4% regarding the exit kappa number. A sensitivity analysis is carried out on this model, Varying digester temperature. It confirms that the model is stable and follows the tendency found in literature, where an increment in temperature results in lower kappa number, and vice versa. It is concluded that the decrease in kappa number in reduced wood chip load is caused by the increase in residence time, given that the decrease still happens despite mitigating conditions, like the use of weaker reactants. It is also concluded that, even though the model follows the tendency of the process, it is not exact enough to reliably predict the result of different operating conditions.
Description
Tesis presentada para optar al título de Ingeniero/a Civil Químico/a.
Keywords
Deslignificación, Digestores, Lignina, Celulosa Arauco y Constitución (Chile). Planta Nueva Aldea Reglamentos