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The reflux drum level is controlled by the reflux drum level controller (LC12) by adjusting the top product draw. The tower bottom level is controlled by the tower bottom level controller (LC11) by adjusting the bottom product draw.

Level in the reflux accumulator and base of the column are typically controlled with the product flows. Again, there may be a cascade between level and flow or the level controllers may manipulate the control valves directly. This kind of strategy is simple to implement and works for most distillation processes.

Pressure is often considered the prime distillation control variable, as it affects temperature, condensation, vaporisation, compositions, volatilities and almost any process that takes place inside the column. Column pressure control is frequently integrated with the condenser control system.

Distillate Composition Control Determine Steady State Conditions. Report the design set point and controller bias ubias u b i a s value for the controller. Estimate Model. ... Obtain PID Parameters. ... Implement PID Controller. ... Set Point Changes. ... Disturbance Rejection. ... Distillation Simulation Code.

By and large, the main control objective in a distillation column operation is to maintain or keep the various process variables (i.e. controlled variables) at their desired set point, in the presence of various disturbances, by changing or manipulating the manipulated variables.

The main variables to be controlled in a distillation column are the following: Distillation column pressure, Reflux drum liquid level, column bottom liquid level, separation power base and Material balance split. The pressure in a distillation column has an overriding influence on the control of the process.

The design of a distillation column involves many parameters: product compositions, product flowrates, operating pressure, total number of trays, feed tray location, reflux ratio, reboiler heat input, condenser heat removal, column diameter, and column height.