Dynamic Behavior of a Thermally Coupled Distillation Column Implemented On a Reactor-Separation-Recycle System

Wednesday, October 19, 2011
Exhibit Hall B (Minneapolis Convention Center)
Daniel Mascote1, Nelly Ramírez1 and Arturo Jiménez2, (1)Departamento de Ingeniería Química, Alimentos y Ambiental, Universidad de las Américas Puebla, Cholula,Puebla, Mexico, (2)Departamento de Ingeniería Química, Instituto Tecnológico de Celaya, Celaya, Gto., Mexico

Nowadays, the installation and operation of systems with minimum energy and material consumption is a primary objective in the industrial environment; this goal can be achieved through the implementation of recycle streams to recover raw materials and the use of energy integration techniques to minimize the utilities requirements. However, It is well known that processes with recycle streams can present several control problems when the control structure is not properly selected, because of loops interactions and potential snowball effects.  Several researchers have analyzed the dynamic and control properties for reactor-separator-recycle systems using flash units and conventional distillation columns in the separation stage. This work presents the dynamic behavior of a thermally coupled distillation sequence implemented in RSR system. In particular, the implementation of the coupled system with side rectifier is considered. The analysis was conducted using the Aspen Dynamics process simulator and the dynamic responses of the thermally coupled system are compared to those generated by the use of a conventional distillation sequence. The plantwide control strategy was developed using the Luyben’s rule for the recycle streams, and the control configuration in the distillation columns was implemented taking into account the flow magnitude in the product streams; the L-B configuration was used for the thermally coupled arrangement, and the L-V configuration for the conventional sequence. A simplified process for ethylbenzene production was taken as a basis. The results obtained showed that selected control structure for the thermally coupled arrangement can ensure the process stability for inventory control against disturbances on feed streams in the RSR system. Despite that dynamic responses presented by this complex arrangement are not as smooth as those presented by the conventional scheme, it is shown that their implementation in a process with recycles streams can be feasible.

 


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