Pressure-Driven Dynamic Simulation of Distillation Columns in Air Separation Units

Abstract

At the moment, the change in power generation from fossil energy sources to renewables poses several challenges to the energy system and major energy consumers such as cryogenic air separation plants. Due to a more volatile power generation and the lack of storage systems, the energy price fluctuates and power intensive processes need to adapt regarding their operational agility and flexibility. Currently, air separation units are designed for steady state operation at their optimal operating point with a minimum amount of load change procedures during their lifetime. Within this work, detailed dynamic models of all plant components are developed which are an important tool to get a deeper understanding of flexible plant operations. Based on this, the process design can be adapted to allow for a more flexible mode of operation. In addition, those models can be used to develop and optimise advanced load change control strategies, which are more agile and consume less equipment lifetime compared to the state-of-the-art load change procedures. Hence, air separation plants are able to perform more frequent load changes and participate in a fluctuating energy market. Furthermore, these tasks are particularly challenging for air separation units, since they are mainly characterised by a high degree of process integration, high demands on product purity and non-linear column responses during plant start-up. The “warm” start-up procedure is chosen as a representative scenario for any load change procedure, since it is the numerically most challenging simulation. “Warm” start-up means to initialise the model inventory at ambient conditions with zero flow. Based on this scenario, more technically relevant scenarios like the “cold” start-up after a plant shutdown as well as advanced control strategies can be investigated to allow a more flexible and agile operation.