Process description for the CC2 example simulation

The Cumene production process, described by Turton1 for a capacity of 100,000 tons per year, consists of the feed section, a cooled tubular reactor at elevated pressure, and two distillation columns at atmospheric pressure. We combine fresh liquid feeds of propylene (FeedC3) and benzene (FeedBenzene) with recycled, unreacted benzene (RecycleBenz). The combined feed is then vaporized (V800), preheated (FE801 and H801), and fed into the gas-phase reactor (R802). We remove the exothermic reaction heat (HSR802) on the reactor’s shell side to generate high-pressure steam (V804). We cool the hot reactor effluent against the reactor feed (FE801) and then feed it to the first column (T801), which produces a distillate stream of benzene (S12) that we recycle back into the feed section (RecycleBenz). The second column (T802) separates the desired cumene product from p-diisopropylbenzene, the product of the undesired side reaction.

We apply the following control strategy, suggested by Luyben for this process:

Feed section

• Control the flow of the fresh propylene feed.

• Regulate the fresh benzene feed by controlling the ratio of the mass rates of fresh propylene and total benzene (fresh and recycled benzene rates).

• Control the level in the vaporizer by manipulating the heat input.

Reactor section

• Control the reactor section’s pressure by manipulating the letdown valve opening.

• Control the reactor inlet temperature by manipulating the hot-side utility valve in the feed heater.

• Control the reactor temperature by manipulating the high-pressure steam valve on the shell side. We model the shell side by using a Drum that represents a boiler.

• Controller the level in the boiler by manipulating the inlet value for the boiler feed water.

Purge

• Control the pressure in the flash tank by manipulating the vent valve, thus regulating the purge gas outlet.

Separation section

The two distillation columns have almost identical controls:

• Control the Stage 1 temperature of the benzene column by manipulating the reflux valve.

• Control the ratio of the feed to the reflux rates of the cumene column by manipulating the reflux valve.

• Control the condenser levels by manipulating the distillate valves, thus regulating the distillate draws.

• Control the condenser pressures by manipulating the cooling water valves.

• Control a stage temperature in each column by manipulating the steam supply for the reboilers. For the benzene column, control the temperature for Stage 11. For the cumene column, control the temperature for Stage 16.

• Control the sump levels by manipulating the outlet valves for the bottom products, thus regulating the bottom product draws.