Distillation columns are complex gas-liquid two-phase systems. Many correlations and rules-of-thumb have been established to guide the design of distillation columns. However, industrial columns often still fail to reach their design goals because of limited knowledge about momentum-transfer, heat-transfer, and mass-transfer in different systems. Therefore, much effort has to be expended to develop different techniques to get information on the inside of troubled distillation columns.
Modern instruments can only reveal some phenomena inside troubled columns. To find more information on the very basic mechanisms which cause problem columns is still a great challenge. Developing modifications to an existing design or even providing a totally new design to solve a column’s operating problems is even more difficult. Often, data gathered in previous experiments and tests is useless. Conducting tests directly in a commercial column is impossible due to the high cost associated with the testing. Column simulators are a useful tool to fill this need. Column simulators are model-scale units that run on specific and well understood chemical systems. They are fitted with geometrically similar equipment to that in the problem column.
Over a long period, column simulators have been used for research and development by almost every vendor of distillation column hardware as well as many other companies in which distillation is an important part of their business. Many specific problems and areas of concern in tray and packing design can be investigated by simulators. Examples include:
The most important difference between a simulator and a distillation column is that a simulator has no reboiler and condenser. Therefore, there is little mass-transfer or heat-transfer in a simulator. Momentum-transfer is the main area of study with simulators. The design and operation of simulators is much simpler than that of real operating columns. Typically, the gas phase in simulators is air and the liquid can be water, oil or other liquids that satisfy environmental regulations.
Operation of simulators is much simpler than with real columns. The air driving force is provided by blowers without recirculation. The liquid circulates through the system, but there is no reflux. The temperature through the simulator is close to constant. Time to reach stable operation is short. Operating costs for a test series is much lower than with an operating column. If properly used, simulators can be very efficient and cost-effective tools for troubleshooting.
Typical problems that simulators can be used for include capacity limits, excessive pressure drops, entrainment, and vapor-liquid maldistribution. A simulator and case studies in its use are documented.
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