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### Topic: Separation of dissolved gas  (Read 1788 times)

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##### Separation of dissolved gas
« on: March 12, 2016, 05:08:43 AM »
Hi,

Hydrocarbons with carbon dioxide are coming out of my reactor. At the stream pressure, using the antoine equation i've found that carbon dioxide is above its boiling point whereas the hydrocarbons are not. I am making the assumption that some of the carbon dioxide will be dissolved in the liquid stream , in which case I have to remove it.

I know how to perform standard gas liquid separation , (flash, distilation , etc) but I don't think it should undergo phase equilibrium separation, since carbon dioxide is already gas.

I think I have to use a knock-out drum, but the equations i've found only correlate the maximum vapour velocity to the separator empirical constant (Kv) and the densities of the liquid and gas phases. How does this take into consideration the dissolved vapour? I am supposed to assume that the liquid density includes the dissolved component?

Vv=Kv ((ρL-ρV)/ρV)^0.5

Also how does this take into account the residence time in the separator, the degree of separation achieved and the actual size of the separator? Is there something I am missing?Should I be performing a flash calculation instead?

Thanks

#### curiouscat

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##### Re: Separation of dissolved gas
« Reply #1 on: March 15, 2016, 11:16:09 PM »
What you are missing is the solubility data for CO2 in your hydrocarbon.

Something may be above its BP but yet may not exert its full Vap Pr because it has a high solubility in another fluid.

Look for activity coefficients.

The knock out drum equations are all *sizing* equations. But first you need a thermodynamic eq. to predict the best equilibrium separation achievable. Good sizing can only ensure you approach equilibrium as closely as you can.

#### PN

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##### Re: Separation of dissolved gas
« Reply #2 on: April 05, 2016, 12:04:43 PM »
sorry, could you tell us what type of your reactor?

as far as i know main function of knock out drum in the industry is to remove carry-over liquid from gas with certain droplet diameter, not to remove dissolved gas from liquid

-PN-