Publication: Desarrollo de una nueva herramienta para la validación de datos de equilibrios de fases. Su efecto en la simulación de procesos
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2018-09-10
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Universidad Complutense de Madrid
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Abstract
El trabajo realizado que conforma esta investigación, recogida en la presente memoria, es una nueva propuesta para evaluar la calidad de los datos obtenidos en situaciones de equilibrio de fases. Está basada en la resolución rigurosa de la ecuación de Gibbs-Duhem, dando lugar a dos formas independientes de comprobación denominadas forma-integral y forma-diferencial.La temática se abordó con un estudio exhaustivo de antecedentes, con un análisis crítico de los principales procedimientos propuestos en la literatura. Se concluye que los métodos actuales,algunos de los cuales no se formulan con la rigurosidad termodinámica necesaria, no ofrecen una garantía sobre la calidad de los datos, dando lugar, en muchos casos, a valoraciones contradictorias. Para evaluar la naturaleza de los valores de equilibrio entre fases (líquido vapor,líquido-líquido-vapor, líquido-líquido y sólido-líquido), se generan unos parámetros específicos que permiten una valoración global del conjunto, y también de manera individual,punto-a-punto. Se establecen límites numéricos para dichos parámetros y para los diferentes casos de equilibrio. Se generan previamente unos sistemas “hipotéticos” en los que se inducen errores conocidos de las diferentes variables que caracterizan los equilibrios. Establecida la metodología, esta se aplica a una base de datos generada para este trabajo, utilizando más de quinientos sistemas, con el fin de verificar su consistencia termodinámica, dependiendo de los casos de equilibrio de fases, realizando una comparativa de los resultados obtenidos con el nuevo método y otros que se consideraron usuales en esta temática.El método propuesto resulta riguroso, garantizando que los datos validados puedan ser empleados en cálculos posteriores, principalmente en el diseño de unidades de proceso. Con su aplicación puede evitarse la utilización de varios de los métodos clásicos, algunos de los cuales producen resultados incoherentes, a pesar de calificar de “consistente” un sistema. Una recomendación importante de la metodología propuesta se refiere a la modelización, ya que los resultados finales dependen de la adecuada elección del modelo y del procedimiento decorrelación de datos. En la memoria se presentan ejemplos valorando la repercusión del modelo y del procedimiento en el diseño final de una operación de destilación.
The work carried out that forms this investigation, collected in the present document, is a new proposed method to evaluate the quality of experimental data of phase equilibria. This method is based on the rigorous solution of the Gibbs-Duhem equation, resulting in two independent forms to validate the data: the integral-form and the differential-form. The initial approach to this problem is developed by a critical analysis of the most used consistency tests in the literature. The main conclusion of this study is that the available methods do not offer enough guaranty about the quality of the data, producing incoherent values in some cases, especially when some of these methods are not formulated with enough thermodynamic rigor. In order to evaluate the data related to phase equilibria (vapor-liquid, liquid-liquid-vapor, liquid-liquid and solid-liquid) a set of specific parameters are generated, which allow both, a global and a point-to-point verification. Numerical bounds are established to these parameters, depending of the type of phase equilibria. Several “hypothetical” systems are previously generated with known errors in the value of the variable characterizing the phase equilibria. Once the method is correctly established, it is applied to a database created specifically for this work to evaluate the thermodynamically consistency of each included system. It comprises more than five hundred systems of different type of phase equilibria. When it is available, others consistency tests detailed in the literature have been used to make a comparison with the new method. The proposed method is rigorous, granting that data are suitable to be used in other calculations, mainly those related with the design of process units. This new test avoids the use of any other consistency method, which produce incoherent results, even when they considered a system “consistent”. An important recommendation from the proposed method is related with the modelling of the experimental info, because the results depend on the selected model and the performance of a correct parameter fitting. In this dissertation, some examples of the effect of the model on the design process of a distillation column are presented.
The work carried out that forms this investigation, collected in the present document, is a new proposed method to evaluate the quality of experimental data of phase equilibria. This method is based on the rigorous solution of the Gibbs-Duhem equation, resulting in two independent forms to validate the data: the integral-form and the differential-form. The initial approach to this problem is developed by a critical analysis of the most used consistency tests in the literature. The main conclusion of this study is that the available methods do not offer enough guaranty about the quality of the data, producing incoherent values in some cases, especially when some of these methods are not formulated with enough thermodynamic rigor. In order to evaluate the data related to phase equilibria (vapor-liquid, liquid-liquid-vapor, liquid-liquid and solid-liquid) a set of specific parameters are generated, which allow both, a global and a point-to-point verification. Numerical bounds are established to these parameters, depending of the type of phase equilibria. Several “hypothetical” systems are previously generated with known errors in the value of the variable characterizing the phase equilibria. Once the method is correctly established, it is applied to a database created specifically for this work to evaluate the thermodynamically consistency of each included system. It comprises more than five hundred systems of different type of phase equilibria. When it is available, others consistency tests detailed in the literature have been used to make a comparison with the new method. The proposed method is rigorous, granting that data are suitable to be used in other calculations, mainly those related with the design of process units. This new test avoids the use of any other consistency method, which produce incoherent results, even when they considered a system “consistent”. An important recommendation from the proposed method is related with the modelling of the experimental info, because the results depend on the selected model and the performance of a correct parameter fitting. In this dissertation, some examples of the effect of the model on the design process of a distillation column are presented.
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Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Ingeniería Química, leída el 07/07/2017. Tesis formato europeo (compendio de artículos)