The effect of operating pressure on distillation column throughput

Abstract

In retrofit design, design engineers often want to increase the throughput of an existing distillation column. Among the operating parameters, pressure is very important. Some researchers state that increasing pressure can increase the throughput. Others claim that decreasing pressure can increase the throughput. This paper investigates the effect of operating pressure on the throughput of an existing distillation column. Operating pressure has a very complex influence on distillation performance. It affects relative volatility between the components, molar vapour flow rates, flooding limitations and vapour density. Taking account of all these factors, it is shown that the effect of changing the operating pressure is strongly related to the operating pressure itself. When the operating pressure is less than about 3 bar, increasing pressure can increase the throughput of the existing column; when pressure is greater than about 7 bar, decreasing pressure can increase the throughput; and when pressure is in an intermediate range, pressure changes have little influence on the throughput. However, one might specify the operating pressure for other reasons, such as to promote heat integration, meet equipment constraints, etc. This paper provides a clear and quantitative picture of the influence of pressure on the throughput of an existing distillation column. The understanding of these effects is very important for both retrofit design and grass-roots design.