3 replies to this topic

[sarah21]

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Edited by sarah21, 11 March 2011 - 05:33 PM.

[pavanayi]

Sarah,
Light key component is the one we want to avoid being present in the bottom
Heavy key component is the one we want to avoid being present in the top

But since distillation (or for that matter any separation) is not 100% efficient, we always have small fractions of light key in the bottom and small amounts of heavy key in the top (This is assuming a one feed, one top product and one bottom product column configuration)

components lighter than light key end up in the top distillate stream
components heavier than the heavy key end up in the bottom stream
components which are in between light and heavy key spread themselves between top and bottom streams.

In your case, you have designated ethylbenzene as the heavy key, and assumed whole of it (100%) recovered to the top stream.
Either
redefine your light and heavy keys or
redefine your recovery values.

I am amused by your flow rates though. Is that correct? Is 0.0014331 kg/hr 81% of bottom flow?

Edited by pavanayi, 10 March 2011 - 11:03 AM.

[sarah21]

Thanks for your reply and observation.
I do believe my HK and LK components are fine, i think you are right i will have to redefine my recovery values. The objective is to to produce 100 tonnes of styrene a year so i know the residue flow is very low but these values are correct as far as i know (lecturer has checked them too). 0.0014331 kg/hr is the total residual flow and 81% of that is tar and 19 % is styrene.

Edited by sarah21, 10 March 2011 - 12:27 PM.

[pavanayi]

Sarah,
something else is also not looking right to me here.
You have calculated the relative volatilities based on heavy key (ethyl benzene) as your reference component. (relative volatility: 1)
You then state that Styrene is the light key, and gave relative volatility 0.767( <1)? I would expect a value > 1 for a more volatile component than your reference component.
Please recheck.