Distillation tower configurations

Equipment Constraints These are the physical constraints for individual pieces of eqiiipment within a unit. Examples of these are flooding and weeping limits in distillation towers, specific pump curves, neat exchanger areas and configurations, and reactor volume limits. Equipment constraints may be imposed when the operation of two pieces of equipment within the unit work together to maintain safety, efficiency, or quahty. An example of this is the temperature constraint imposed on reactors beyond which heat removal is less than heat generation, leading to the potential of a runaway. While this temperature could be interpreted as a process constraint, it is due to the equipment limitations that the temperature is set. 

Fluctuating reboiler duty will have the same effect on a distillation tower as pumping the gas pedal on a car (that is, unpleasant changes in acceleration). A typical thermosiphon reboiler configuration is shown in Figure 18-12. The density difference between the liquid-filled reboiler inlet line and the vapor-liquid mixture in the outlet line drives the process-side fluid through the reboiler. 

Figure 4.89 shows the unit and stream configuration for the main fractionator in Aspen HYSYS. To build the main fractionator, we follow the same procedure as a cmde distillation tower described in Chapter 2 ... 

Distillation columns The simulator column models include not just the column itself, but also the reboiler, condenser, overhead receiver drum, and reflux pump (but not bottoms pump). ICARUS has 10 possible configurations to which a column can be mapped. Alternatively, the column can be mapped to a packed or trayed tower, and the ancillary items can be created as separate Icarus project components. 

Specialised units are used to simulate complex fractionation processes in petroleum refining. Typical configuration consists of a main column with pump-around and side strippers (Fig. 3.14). Among applications, we may cite pre-flash tower, crude atmospheric distillation, or Fluid Catalytic Cracking (FCC) main fractionator. 

Figure 10.43 Two-effect distillation (a) tower and heat exchanger configuration (b) T-Q diagram.

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