Analysis of Azeotropic Distillation Sequences Start-up

SCENNA, NICOLAS JOSE; SONIA JUDITH BENZ; HUGO RODRÍGUEZ NESTOR; KLARIC, J. I.

Rio de Janeiro

Congreso; ENPROMER 2005:the 4th Mercosur Congress on Process Systems Engineering and the 2nd Mercosur Congress on Chemical Engineering; 2005

UNRJ

The optimal start-up of a two-distillation tower process involving multiple steady states is a very  complex task, since a rigorous dynamic optimization is necessary. Searching for optimal start-up strategies for tower sequences is far from trivial. Besides of the multiplicity of solutions, one of the complicating factors is the activation of the recycle stream, which severely constrains the possible start-up strategy. Furthermore, models, which can describe the structure and the process behavior during the start-up, are generally not available. For example, the impact of the start-up configuration considering structural variables like the different filling streams, ways of connecting columns (series or parallel), feed placements and ways of feeding columns (flow or batch), are significant parameters to be considered. Therefore, as the first approach to solve the problem, a comprehensive analysis of the process behavior is encouraged to look for suitable start-up procedures. Laroche et al. (1992) y Bekiaris et al. (1993) suggested that operability problems (start-up and control) could appear for the benzene-heptane-acetone (BHA) system. Scenna et al. (2003) obtained useful relationships and guidelines for starting up the stand-alone BHA homogeneous azeotropic column with multiplicity. However, if the entrainer recycle is not closed, the conclusions could be not definitive. Consequently, the distillation train consisting of the azeotropic column linked to the entrainer recovery column, which is connected to the first one by recycle streams will be studied as a case. In this study, the start-up policies space is explored taking into account operative costs reduction and operability criteria. This will be carried out by considering the product amount out of specifications that is wasted during the operation. Considering the system multiplicity, a PI temperature control will be used to assure getting the desired solution.