Details Matter when Designing Hot Vapor Bypass Systems

Pressure control is the most important parameter that is used in distillation optimization. Engineers realize that there are three important parameters in distillation optimization: temperature, pressure, and composition. When two of these are controlled, the other parameter is fixed. When pressure and temperature are controlled and/or optimized, the composition is known. Effective column pressure control is critical to controlling product quality targets.

Hot Vapor Bypass systems have been used extensively in the industry. There have been several good papers recently regarding trouble areas of the industry’s design methodology. This paper will illustrate a severe instability that occurred within Valero.

This case study will illustrate that even when a design configuration has been installed many times; it can be the source of problems, unexpected consequences, and even possibly result in unit shutdowns. In this case study severe disturbances resulted. This design has been used many times in industry. Design practitioners should consider this experience and abandon this type of design that are prone to operating instabilities. Good designs are those that avoids failure even when it is operating outside of its intended operation range.