6 replies to this topic

[nameless]

Dear all,

             As a part of my final year project i have been asked to design a agitated jackted vessel batch reactor with heat exchanger. Steam is passed continuously in the simple jacket to raise and maintain the temperature of the contents in the batch reactor and thereby facilitating the reaction to take place.The vapors (excess reactant and one of the products)evolved during the reaction are passed through heat exchangers and the condensate is sent back to the reactor(total reflux).The main purpose of the reflux is to maintain dilution in the reactor i.e contact b/w the reactants to ensure high conversion of the limiting reactant.Here is my question:will it suffice if calculate the required heat transfer area based on steam passed in the jacket and ignore the energy from the reflux since steam eventually makes up for the temperature drop in the reactor due to total reflux.

 

 

[aroon]

It seems your reaction is endothermic as you have to use steam to maintain temperature. At reaction temperature and pressure, part of the product and part excess reactant are getting evaporated so you are using total reflux. Based on this, your design should provide maximum heat required for the reaction to maintain temperature. There are following two things you must consider to calculate the duty required.

 

1. Highest endothermic heat of reaction (must be at initial stage due to high reaction rate in many cases).

2. To compensate heat lost from the system due to reflux condenser.

 

Addition of both these heat should be the maximum required heat for which your jacket should be design.

[nameless]

Thank you aroon,I have few questions:

 

since the reaction rate and enthalpy value of limiting reactant remain unavailable,is it okay if i calculate heat load of reactants.

Maximum heat required=Heat load+ enthalpy of reflux stream?

 

The reaction takes place under vacuum,the streams into the reactor are at atm. pressure.Is it fair to calculate heat load and thereby calculate max.heat?pls elucidate

Edited by nameless, 25 February 2014 - 11:39 PM.

[aroon]

Primary thing is, whenever you are designing a reactor, the reaction kinetics should be known first. Without this you can not even size the reactor. Then how you moved directly to the heating and maintaining temperature?

 

Heat load to the reactant will be useful during start-up only. There is no any relation of reactant heat load and maintaining reaction temperature, since it is batch reaction.

[nameless]

Using thumb rules and tonnage per year,non chemical engineers in this particular industry have already fixed volume of the reactor.I dont know how they managed to do it.Since it's a protected product rate equation of the reaction seems unavailable with the industry people,it's unavailable even on the journals.They want me to design the heat transfer area,Is there a way out?

 

p.s:i m trying to find the endothermic heat of reaction from literature

Edited by nameless, 26 February 2014 - 02:06 AM.

[aroon]

Not possible to calculate optimum area without proper data.

 

In such case, you may try to get practical lab test data for this reaction across the reflux condenser and steam consumption so that latent heat of steam condensation and sensible heat across the reflux condenser will give you necessary inputs.

[nameless]

Thank you aroon

 

Will the equation be something like this

 

(mass flow rate of steam*latent heat of steam)-(enthalpy of the reflux stream)

+Heat generated due to agitation=(U*A)/ln((T-t1)/(T-t2))

 

U-overall heat transfer cofficient 

A-Heat transfer area of the reactor

T-Jacket temperature

t1-intial temperature of the reactant mass

t2-final temperature of the reactant mass/product

Edited by nameless, 26 February 2014 - 08:44 AM.