As shown in Figure 6.5, this scheme requires reflux/distillate and bottom-product/distillate ratio controls. A buffer tank in the top-product line is recommended.
As indicated earlier, reflux drum level control via boilup is difficult unless a lot of holdup is available. Overhead composition may be controlled by trimming the reflux/distillate ratio; base composition may be controlled by trimming the bottom-product/distillate ratio. Note that if either distillate or bottom product (or side product) is a demand flow, either reflux drum or base level control must manipulate feed rate.
Was this article helpful?