(570c) Development of the Start-up Procedure for a Thermally Coupled Distillation Columns System through Dynamic Simulation

The operation of a continuous column distillation is periodically interrupted in order to perform maintenance procedures. The maintenance process aims to create conditions for equipment, facilities and services to function properly. After the maintenance, it is required perform the start-up operation. The start-up procedure of a distillation column can take several hours to days to reach the steady state. The longer the time required for the column operation reaches the steady state, the greater the amount of off-spec products and higher power consumption which reduces the yield of the process and increases the cost of the operation. The start-up operation of a chemical process is one of the most complicated processes observed in industrial practice because consists of simultaneous changes in several variables besides presenting problems operability, control, and simulation. To be able to develop a suitable start-up procedure is necessary to know and understand the dynamic behavior of a distillation column during the start-up operation. The dynamic behavior of a distillation column during the start-up operation is highly complex. This dynamic behavior is observed for a period of time that goes from the initial state of start-up to a pseudo-steady state, which is obtained when the defined composition of a product is observed. The complication of the start-up operation becomes larger for a thermally coupled distillation columns system. The thermally coupled distillation columns system is the interconnection of two distillation columns by two streams, one in the vapor phase and another in the liquid phase, which results in reduced power consumption of the process. The system studied is two thermally coupled columns where one is an extraction column used to separate the ethanol-water azeotropic mixture with ethylene glycol as solvent. The work aims to study the dynamic behavior of a thermally coupled distillation columns system during the start-up operation and based on this study propose a procedure suitable to start-up the system. Dynamic simulation and the start-up procedure were developed in Aspen Tech software. From the model developed in Aspen Tech was possible to analyze the dynamic behavior of the start-up operation of thermally coupled distillation columns system and propose an appropriate procedure satisfactorily.