Metodología para diseño, análisis y optimización termodinámica de columnas de destilación con intercambiadores de calor internos
Methodology for design, analysis and thermodynamic optimization of distillation columns with internal heat exchangers
D.F. Mendoza1* y C.A.M. Riascos2
1 Universidad Autónoma del Caribe, Departamento de Ingeniería Mecánica, Calle 90 No. 46-112, Barranquilla, Colombia. *Autor para la correspondencia. E-mail: diego.mendoza24@uac.edu.co Tel. (57) 5 357 59 44.
]]> 2 Universidad Nacional de Colombia, Bogotá D.C., Código Postal 111321 - Colombia.
Recibido 11 de Febrero de 2014
Aceptado 17 de Abril de 2015
Resumen
Se presenta una metodología para el diseño, análisis y optimización termodinámica de columnas de destilación con intercambiadores de calor internos. El método emplea la termodinámica irreversible y trayectorias de destilación reversibles para mapear, clasificar y evaluar las irreversibilidades del proceso, y una estrategia de optimización restringida multinivel para determinar la distribución de la carga de calor que minimiza la producción de entropía en la columna. La metodología propuesta es una extensión de trabajos anteriores (Mendoza y Riascos, 2010 y 2011), incluye el cálculo de trayectorias de destilación reversible como estrategia para establecer límites para las variables de diseño que se deben estimar durante la optimización, y para la eficiencia termodinámica alcanzable. La metodología se aplica al proceso de deshidratación de etanol por destilación extractiva empleando etilenglicol como agente de extracción, este sistema por la gran diferencia entre los puntos de ebullición de los componentes y la alta no idealidad representa un desafío interesante para el desarrollo de estrategias de diseño y optimización. Los resultados muestran que en las columnas de destilación con intercambiadores de calor secuenciales, optimizadas, la generación de entropía se reduce 14% (columna de recuperación de solvente) y 16% (columna extractiva) en comparación con su contraparte adiabática, también optimizada. Además, para el estudio de caso considerado, la metodología propuesta ha mostrado ser robusta, sin problemas de convergencia durante la optimización, permitiendo generar una propuesta para el diseño y operación óptimos de las columnas. Los resultados presentan buena concordancia con los obtenidos con el simulador Aspen PlusTM empleando el modelo radfrac.
Palabras clave: optimización, destilación extractiva, columnas diabáticas, generación de entropía, destilación reversible, termodinámica irreversible.
Abstract
]]> A methodology for design, analysis and thermodynamic optimization of distillation columns with internal heat exchangers is presented. The method employs irreversible thermodynamics and reversible distillation trajectories to map, classify and assess process irreversibilities, it employs a multilevel constrained optimization strategy to determine the heat load distribution that minimizes the entropy production in the column. The proposed methodology is an extension of previous works (Mendoza and Riascos, 2010 and 2011), it includes calculation of reversible distillation trajectories as strategy to define limits for design variables that must be estimated in the optimization, and for attainable thermodynamic efficiency. The ethanol dehydration process by extractive distillation using ethylene glycol as entrainer is used to illustrate the methodology, due to the difference between components boiling points and the high no ideality, this system is an interesting challenge for developing of design and optimization strategies. The results show that optimized distillation columns with sequential heat exchangers reduce the entropy generation 14% (solvent recovering column) and 16% (extractive column) compared with its optimized adiabatic ones. Furthermore, the proposed methodology showed to be robust, without convergence problems during the optimization, in that way, it allows to generate a suggestion for the optimal design and operation of the columns. The results show good concordance with the ones obtained with Aspen PlusTM employing radfrac model.Key words: optimization, extractive distillation, diabatic columns, entropy production, reversible distillation, irreversible thermodynamics.
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