Kappa number variability at the continuous digester outlet is a major concern for pulp and paper mills. It is evident that the aforementioned variability is strongly linked to the feedstock wood properties, particularly lignin content. Online measurement of lignin content utilizing near-infrared spectroscopy at the inlet of the digester is paving the way for tighter control of the blow-line Kappa number. In this paper, an innovative approach of feedforwarding the lignin content to a model predictive controller was investigated with the help of modeling and simulation studies. For this purpose, a physics-based modeling library for continuous pulp digesters was developed and validated. Finally, model predictive control approaches with and without feedforwarding the lignin measurement were evaluated against current industrial control and proportional-integral-derivative (PID) schemes.

An Approach for Feedforward Model Predictive Control of Continuous Pulp Digesters

Due to the naturally varying feedstock, significant residence time, insufficient measurements and complex nature of the delignification process, producing pulp with consistent quality i.e. stable k ...

An Approach For Feedforward Model Predictive Control For Pulp and Paper Applications : Challenges And The Way Forward

RESUMO – O digestor continuo de celulose kraft e um reator pressurizado que tem a funcao de promover as reacoes de deslignificacao das fibras da madeira. Neste equipamento ocorre a dissolucao das cadeias de lignina, alem das indesejaveis reacoes de degradacao dos carboidratos. A qualidade da celulose produzida e medida pelo numero Kappa, que e uma referencia do teor de lignina residual e e o item mais importante para o controle das reacoes, sendo determinante para as etapas subsequentes do processo. Possui impactos significativos nos custos, meio ambiente e na qualidade da celulose final. Sua analise tem defasagem do tempo de retencao (~ 4 horas) quanto as principais variaveis de controle. Neste contexto, o objetivo deste trabalho foi obter um modelo de predicao do numero kappa, de forma antecipada ao resultado das analises de laboratorio. Foram tratados dados de processo obtidos durante dois meses de operacao, usando as principais variaveis de processo de um digestor continuo de celulose kraft de eucalipto, modelo kamyr. Na analise de regressao, foi utilizado o metodo dos minimos quadrados ordinarios, usando dados industriais para produzir modelos multi-input single-output. Apos ajuste do modelo aos dados observados, realizou-se a validacao com um novo conjunto de dados, obtendo erro percentual medio da ordem de 4 %, equivalente as incertezas do proprio metodo de medicao.

/pdf/predicao-do-numero-kappa-de-um-digestor-continuo-de-celulose-25ctgijaol.pdf

Predição do número kappa de um digestor contínuo de celulose kraft usando análise de regressão múltipla

In the pulp industry, digesters are used to disolve lignin in wood chips. The concentration of lignin is measured and is called the Kappa number. In this thesis, the question of whether an online K ...

/pdf/kappa-control-with-online-analyzer-using-samples-from-the-hrwbyznyu1.pdf

Kappa Control with Online Analyzer Using Samples from the Digester's Mid-phase

Various modeling approaches used for controlling a continuous digester are discussed: the Kappa control uses an approach based on modeling the reaction kinetics; an automatic grade change uses gain scheduling; and the level control uses an adaptive time series model. The strengths and weaknesses of each technique are discussed along with guidelines on model selection. The author's experience with each technique and implementation considerations are also covered.

Modeling and control of a continuous digester

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Modeling and control of a continuous digester