In this entry we will learn how to determine the number of stages from a very popular diagram used in distillation field, McCabe-Thiele diagram. It is actually pretty easy and direct if one knows how to use it.
First of all we have to know what it means by minimum number of stages. It is actually another way of saying that we have an infinite amount of reflux ratio. We know that the slope of the operating line for a rectifying section is equal to v/v+1, this means the slope will be one in case of having a very high reflux ratio. The operating line will simply follow the y=x line in the diagram.
Secondly we need to mark all those important points such distillate composition, feed composition and bottom composition. Feed composition is however not needed in this case. Feed has no influence on the minimum number of stages if we have an infinite reflux ratio.
The next step is to draw stages in the diagram. It is worth mentioning that the order to start drawing the stage does not matter. We can either start stepping off from distillate or from bottom. The result remains the same and will not change at all.
Hence for this example we need minimum 3 stages without considering the tray efficiency. Normally we need more than 3 if we take the tray efficiency into account.
First of all we have to know what it means by minimum number of stages. It is actually another way of saying that we have an infinite amount of reflux ratio. We know that the slope of the operating line for a rectifying section is equal to v/v+1, this means the slope will be one in case of having a very high reflux ratio. The operating line will simply follow the y=x line in the diagram.
Secondly we need to mark all those important points such distillate composition, feed composition and bottom composition. Feed composition is however not needed in this case. Feed has no influence on the minimum number of stages if we have an infinite reflux ratio.
Hence for this example we need minimum 3 stages without considering the tray efficiency. Normally we need more than 3 if we take the tray efficiency into account.
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