Dynamic Behavior and Operational Aspects of Heat-Integrated Distillation Processes

摘要

Complex configurations of distillation columns have been shown to consume less energy than simple configurations. These complex configurations mainly result from two considerations: either a feed split, where the condensing vapor from the top of the high pressure column is used to heat the reboiler of the low pressure column, or the overheads from a high pressure column in a distillation train are used to reboil a column under lower pressure. Industrial experience shows that very often in these configurations there is still incentive for more energy reduction simply because of inefficient control. The energy integration increases the control loop coupling in the system, so that the operating strategy for the columns is no longer apparent. Therefore, the dynamic behavior and the opera-tional constraints of such systems become very important. The use of rigorous dynamic models of the processes is an essential instrument to pursue the goal of good and reliable process control. Such models allow the engineer to realistically simulate the process with the desired control system in place and to analyze the effects of equipment sizing, heat integration, and disturbances. Variable pairing proved to play an important role in the stability of the systems. Simple steady-state analysis is used to illustrate that effective control of energy-integrated distillation columns can be achieved by proper selection of manipulated variables and pairing them correctly with control variables. Hints will also be given, when multivariable predictive control schemes should be used.