3 replies to this topic

[ankitg009]

Hey All,

 

I am a recent graduate(Chemical Engineer) and i have been given a task of designing vessels. The data available to me is the volumetric flow rate along with pressure ,temperature and thermodynamic properties.

 

 I want to know the basis on which retention time or residence time is estimated. What are the parameters which should be kept in mind before estimating the same.

 

Thanks in advance.

[StefanCh]

Dear ankitg009,

 

Residence time equals the volume of the reactor divided by the volumetric flow rate. Meters cubed divided by meters cubed per second yields second. In other words the yield is the residence time of the product.

 

Before estimating the product you should be aware of of the volume, flow rate, temperature, pressure and all the data you were given.

 

Good luck and I hope I helped.

[MTumack]

I would say typically if you are designing a vessel you shouldn't be estimating the residence time, you should be using the required residence time within the scope of your vessels required operating time to design the actual size of the vessel with respect to the physical volume of fluids needing to be stored in your vessel at any given time.

 

As far as I am concerned, estimating the residence time of a vessel is kind of an academic pursuit (or perhaps a retrofitting, i suppose) in that if you need 5 minutes, you design for 5 minutes worth of volume flow rate, then adjust so your actual vessel  can actually operate with respect to weirs, level guages / switches (probably want at least 12" between each phase if we are talking about a float type level switch), dumps, etc.

[ankitg009]

Dear MTumack

 

What you mean to say is that, choosing residence time is entirely upto us. We can choose 5 min or 10 min, depending upon our gut feeling.??

 

Aren' t there some industrial standards which should be followed in this case.?

 

Some  of the refrences i have got says that the hold up time (LLL to NLL) should be 5 min and surge up time (NLL to HLL) should be 5 min, which would simply mean that the overall residence time for a vessel will be around 15-20 min.

 

Please provide clarity on this.

 

And i really dint understand what you meant by this.

"then adjust so your actual vessel  can actually operate with respect to weirs, level gauges / switches (probably want at least 12" between each phase if we are talking about a float type level switch), dumps, etc."

Edited by ankitg009, 27 March 2015 - 04:18 AM.