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Batch Distillation With Distillate Drawn Off

HYSYS can perform unsteady-state (dynamic) model when properly instructed to do so. Before we begin the set up of the process we need to establish the total reflux case operating conditions. The initial charge of liquid will be heated and evaporation begins. The column will be run until it reaches the desired condition (in our case a desired amount of distillate concentration). Then distillate will be drawn off.  

Operating Conditions

We will illustrate this approach in the form of a study case. Once the reboiler starts providing heat, we would like to reflux the distillation column until we obtain a concentration of 80% ethanol by providing 120,000 BTU/hr to the reboiler, and then we will draw distillate off at the top. HYSYS will tell us the profile of the batch distillation model and how long it will take to do so. We will use the same tower with 24 plates. The feed stream will be fed to the reboiler and will be 0 lb/hr since we do not have any feed but just an initial charge. We will assume that 200 lb of a mixture of 50% ethanol and isopropanol are initially charged to the reboiler. (Note that in the example that follows we will assume the total capacity of the reboiler to be 400 lb for simplicity. Therefore the tank will be half full).

Fixed Distillate Draw Rate

The batch distillation with distillate being drawn off is the same as the total reflux ratio case but the only difference will to open the distillate valve at 100 percent in the FIC-100 controller. To do so, when entering data in the controller, put 100 in the OP box before starting the simulation as shown below:

Programmed Distillate Draw Rate

See the Programmed Distillate Draw Rate case (not yet developed)