| Summary: | 碩士 === 中原大學 === 化學工程學系 === 87 === In this research, the process characteristics and optimal control schemes of a heterogeneous azeotropic distillation are investigated by the dynamic simulation of distillation with three components: isopropyl alcohol, water and cyclohexane. Some of special characteristics in the azeotropic distillation process found in this research match those in the past literature, such as multiple steady-state, parameter sensitivity, hysteresis phenomenon and critical reflux flow rate.
In most distillation process, temperature measurements instead of product concentration are used to infer to product quality. In this study, the temperature-based control scheme is also selected. According to temperature profiles in the azeotropic distillation column, two types of systems can be distinguished: high and low reflux flow rates. Both types represent the conversion of the system between organic and water phases. The control scheme under the high reflux flow rate would get effectiveness of separation. Besides, there are three advantages of the operating process at critical reflux: higher flow-rate of products, lower entrainer loss of cyclohexane and lower cost of energy. For the above reasons, the dynamic characteristics of operating at critical reflux flow rate should be studied before developing the control strategy.
Among the temperature profiles, two-break points exist at high reflux flow rate and only one-break point at low reflux flow rate. In the open loop simulation, the change of heat duty will cause the transformation of temperature profile in column, however the change of reflux will not. Therefore, the reboiler is used to control the minor-break point temperature region and reflux to control the major-break point temperature region. In these two-control loops, it is economical to operate processes near high critical reflux flow rate, but system interaction will happen. In this study, the proposed partial decoupling scheme would demonstrate its effectiveness via the simulation results.
|
|---|
