Process description for the C1 example simulation

A water-methanol feed enters the column at 1430 kmol/h with 29% methanol. The column includes 13 stages, a water-cooled total condenser and a steam-heated thermosiphon reboiler. The feed location is at stage 7. The target purity is 96% methanol in the distillate.

The overhead condenser completely condenses the column overhead by using cooling water on the tube side of a shell and tube heat exchanger. A vent valve on the reflux drum removes any non-condensables. A pump returns the reflux drum liquid as reflux and as produced liquid distillate.

The column includes a sump, which supplies the bottoms product and feeds a thermosiphon reboiler that uses condensable steam supplied to the shell side of a shell and tube heat exchanger. Natural circulation pushes the product flow through the thermosiphon reboiler, which partially vaporizes the product flow before it returns to the column.

The following table provides a summary of the design criteria for the simulation model.

Table 1: Design criteria

We design the control scheme according to the recommendations provided in Distillation Operation by Henry Kister1. We apply the following process control strategy:

• A flow controller controls the column feed flow.

• We control the pressure on the top tray of the column by manipulating the cooling water supply to the overhead condenser.

• We control the reflux drum level by manipulating the distillate product.

• We control the column sump level by manipulating the bottoms product.

• We control the temperature on stage 9 of the column by manipulating steam supply to the shell side of the reboiler.