Sketch a control system diagram for a distillation column. The objectives of the control system are:

a. Reflux drum level is controlled by a cascade controller which manipulates the controller point of the distillate flow rate

b. Reflux flow rate back to the column is controlled by a ratio control scheme which manipulates specified reflux to distillate ratio

c. This specified reflux to distillate ratio can be changed by a composition controller at the distillate