4 replies to this topic

[vntgpt]

Hi,

I am new to this forum, find it really helpful for young engineers to find out solutions for their problems. I too have a problem, so I decided to write here after trying to get the answer through internet and books.
1. I have three solvents, ethanol, acetonitrile and heptane and these will be recovered from reactors of capacity 5kL, 3kL and 2kL with surface area of 2.7 m2, 1.9 m2 and 1.46m2 and Boiling points are 78C, 82C and 98C respectively. I need to recover maximum possible solvents under reduced pressure conditions of 100 mmhg absolute. But my problem is I am not able to find any formula to calculate the maximum vaporization rate of these solvents or any other way. It would be very helpful for me if somebody can tell me the way to calculate the maximum vaporization rate? Note: Temperatures above boiling point under reduced pressure can be used to increase the rate of vaporization.

2. Secondly, I need to calculate the condenser heat transfer area which will completely condense the vapors to liquid. Chilled water is available at 10 deg C. For Calculation of condenser heat transfer area, we will consider, liquid volume being vaporized or the vapor volume of solvent being vaporised.

3. How and where we use heat of vaporization? Is it also being used for calculating condenser surface area?

Please give your expert comments so that I can solve this.

Thanks

Vineet

Edited by vntgpt, 13 January 2011 - 12:02 AM.

[saeed.s]

First off all, I suggest you calculate overal heat transfer of reactors and i think your reactor should be equipped with impeller, to do this , there are diffrent documents tha you can use and i think chapter 10 of chemical process equipment selection and design book is a good refrence.Also area of reactors and temperature difrence are known and you could calculate total duty of reactors.

In next step, you could calculate rate of evaporation based on total duty and lateant heat of slovents. You should consider( I assume it s a batch process) during evaporation, solvent level and area of reactor will be decrease then in beging of evaporation you have maximum evaporation rate.

with this total duty or evaporation rate, condenser calculation is easy.

[vntgpt]

Any idea how to use evaporation standards to calculate the evaporation rates of other solvents. Like diethyl ether and butyl acetate.

Emperical test work shows that the rate at which dry steam can be released from the surface of water is a function of pressure. A working approximation suggests: Maximum release rate without steam entrainment (kg/m² h) = 220 x pressure (bar a) The steam accumulator in Example 3.22.2 is operating at 10 bar g (11 bar a). The maximum release rate without steam entrainment will be: 220 x 11 bar a = 2 420 kg/m² h
And if steam is getting released from surface @ the rate of 220kg/m2h then rate of solvents like ethanol would be higher I think, with reference to evaporation standards.


Please help!!!


Vineet

First off all, I suggest you calculate overal heat transfer of reactors and i think your reactor should be equipped with impeller, to do this , there are diffrent documents tha you can use and i think chapter 10 of chemical process equipment selection and design book is a good refrence.Also area of reactors and temperature difrence are known and you could calculate total duty of reactors.

In next step, you could calculate rate of evaporation based on total duty and lateant heat of slovents. You should consider( I assume it s a batch process) during evaporation, solvent level and area of reactor will be decrease then in beging of evaporation you have maximum evaporation rate.

with this total duty or evaporation rate, condenser calculation is easy.

[breizh]

Let you try this resource :

http://www.chemsof.com/boil/boil.htm
Hope this helps

Breizh

[Mahesh@A&M]

I did similar calculations back in the past.Hope this might help you

Obtain VLE data or vapor pressure data for pure solvent at your reactor T&P conditions to determine percent flash. Once you know this value, do a mass balance using feed data to calculate vapor stream mass rate.

Solvent removal rate primarily depends on thermodynamics.

Use mass flow rate instead of volumetric rate to size solvent condenser. Make sure you keep impingment plate if necessary on solvent side.

Regards,
Mahesh A&M