Temperature control for extractive dividing-wall column with an adjustable vapor split: Methylal/methanol azeotrope separation

In our previous work, the extractive dividing-wall column (EDWC) was proved to be a promising energy-saving method for methylal/methanol azeotrope separation because it offered about an 8.3% energy saving over the corresponding conventional extractive distillation columns. We also have explored two effective composition control structures for the stabilization of the EDWC previously. However, the composition control needs online composition analyzers which are usually expensive, require high maintenance, and introduce large lags. Therefore, it is highly desirable to avoid the use of composition analyzers to economically gain this energy-saving potential. In this work, the use of temperature control instead of composition control for the EDWC process is investigated to overcome the above drawbacks. Several control structures are developed on the basis of singular value decomposition (SVD) analysis. Two temperature control structures with an adjustable vapor split are proposed first. Dynamic simulations show that the structure can handle feed disturbances effectively, except for 20% changes in methanol or water concentrations. Then, a differential temperature control is further developed. Dynamic simulations demonstrate that this structure reduces the offsets in methanol product purities. Moreover, several group comparisons of dynamic responses are demonstrated to confirm the feasibility and superiority of temperature control for stabilizing the EDWC process.