Equipment for Continuous Distillation
The following is a brief discussions of the various equipment used in continuous distillation:
This is the main equipment where the separation process described above is carried out. In general, the distillation column is separated into 3 sections: rectifying (or enriching) section, stripping (or exhausting) section and feed (or flashing) section. At the rectifying section, the more volatile component is removed through contacting the rising vapour with the down-flowing liquid. At the stripping section, the down-flowing liquid is stripped of the more volatile component by the rising vapour.
The distillation can be equipped with trays or packings or both. See the Figure below.
This is a heat exchange equipment for condensing the hot vapour leaving the top of the distillation column. Either cooling water (e.g. using shell-and-tube heat exchanger) or air (using fin-fan condensers) can be used as the cooling medium. In either case, partial or total condensation may be achieved.
In the case of total condensation (as in the analysis above),
all the vapour is converted into liquid. For partial condensation, there remain
in the vapour state the most volatile components. The condensed liquid is partially
returned to the distillation column as reflux and partially withdrawn as distillate
product. Click here for more
This is a horizontal (usually) pressure vessel whereby the condensed vapour is collected.
Pumps can be used for returning the reflux liquid back to the distillation column, or for pumping out the bottoms product for storage, or for pumping the feed into the distillation column.
The purpose of the reboiler is to produce the vapour stream in the distillation column, called the reboiled vapour or the boil-up vapour. Reboilers can be both external or internal (stab-in). Steam reboilers or fired reboilers can be used. Fired reboilers typically uses fuel gas or fuel oil or combination of both. Click here for more information.
The heat exchanger is used for heat conservation: the hot bottoms stream is used to heat up the feed stream before it enters the distillation column. As a result the bottoms product is cooled and then rundown to storage. For better temperature control of the feed stream, a separate preheater or charge heater (both not shown in the above diagram) may be used. This is usually located downstream of the feed/bottom exchanger for final temperature adjustment. Steam may be used for the preheater, and fuel gas-fuel oil is used for the charge heater.
Charge Heater / Steam Preheater (not shown in Figure)
This can be a fuel gas/fuel oil-fired heater or steam-heated exchanger for final temperature control before the feed enters the column.
NOTE: Other distillation columns may have slightly different set-ups. The specific equipment used depends on the types of mixtures to be separated and the complexity of the operation. Some operations may have more than 1 feed inlet, as well as one or more sidedraws.
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