Question

In: Chemistry

We stated at the start of the course that any separation unit is generally more expensive if it has a higher separation factor. Carefully explain whether the correlation from Perry’s logically matches that statement for treating a given wastewater feed.

We stated at the start of the course that any separation unit is generally more expensive if it has a higher separation factor. Carefully explain whether the correlation from Perry’s logically matches that statement for treating a given wastewater feed.

Solutions

Expert Solution

Solution

Separation factors, recall, are defined so that 

                                 

where i and j are selected so that Sij > 1.

A given feed implies the physical properties are fixed, which implies the terminal settling velocity is constant (note: a misconception that some people have is the TSV changes with an increased tank diameter; we explicitly learned this is not the case, else we wouldn’t be able to scale up from lab tests to industrial scale). So if we are treating a given wastewater feed, by increasing the tank diameter we expect the following logic to hold:

• we will pay more for a larger diameter tank, (based on the correlation), so a

• larger tank diameter, implies

• larger tank area, implies

• slower horizontal velocity component for a given throughput Q, implying

• more time for solids to settle (i.e. a longer residence time), implying

• x_solid,under increases and x_solid,over decreases, implying

• S in the above equation gets larger and larger.

This sequence of logical events matches our expectation.


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