ABSTRACT
The split of feed stream into a distillate stream and bottoms stream can be referred to as the material balance split. Generally, the ratio of distillate/feed is about equal to the weight fraction of light components in the feed. One result of studying the material balance split can be to understand that the compositions and flow rates of both the distillate and bottoms streams interact with each other and cannot be independently controlled. Compositions of distillate and bottoms streams are directly linked by material balances. The flow rates of distillate and bottoms streams change as necessary to maintain the material balance and achieve the target compositions. The tray temperature gradient method requires only one steady-state simulation at design conditions, while the shift in material balance method requires two simulations with different product stream compositions. For vacuum towers, it is sometimes necessary to add pressure compensation to the most responsive temperature, so the control action is primarily for changes in composition.
