10 replies to this topic

[GoleGole]

Hello Community, I have been stuck on a problem in my internship. I ave been assigned the work of "Energy balance for A indirect heating jackted reactor" and find the theorotical amount of steam consumed. The way the system works is fairly easy for a overview. Basially instead of just shooting in steam inside the jacket, water is heated instead which is then recirculated through the reactor jackets and the heat exchanger used.

 

This is important in my industry as the reaction is highly exothermic and if extra exothermicity occurs, the return water valve opens and water flows out of the recirculation loop (steam heat exchanger and jacket) and cold water is added artially or complely circulated inside the jacket to maintain a given setpoint.

 

DATA Available:-

Mass of the Reactants

Cp of the reactant

Water inelt temps inside te jacket

Water outlet temps from the jacket

Steam Properties(Everything except the flowrate)

Amount if Water Circulated/ Recirculated 

 

In short, will the energy balance be as simple as equating ML(Steam) = MCpdt (Reactants) to estimate the value? Thank You!

[latexman]

Your words confused me.  Why is the water heated if the process is so exothermic?  That does not make sense to me.  Perhaps I misunderstand.

 

A well labelled and dimensioned drawing/sketch is worth 1,000 words.  Please attach a PFD or P&ID.

[Pilesar]

Your Q=MCpdT might give the approximate theoretical duty required. The jacket heat will not all go into the reactor wall. There is an outside of the jacket which will get hot and transfer heat also. If the reactants react during the heating, then consider the heat of reaction also and the Cp of the products.The hot water and steam will have heat losses in the exterior piping. Include the affects of phase change if present. I think you will find that the steam consumption will be more than predicted just by considering the reactor contents.

  I have designed similar process arrangements in the past for batch catalyst preparation. An important parameter is the heat transfer coefficient in the equation Q=UAdT. Jacket heat transfer can be very low. Water in the jacket will not transfer heat as well as steam. The walls of the reactor vessel are thick and resist the heat transfer. 

[breizh]

Hi,

The most efficient way to produce hot water is to use pick heater (sort of valve), I used similar equipment to produce resins in batch reactors.

edit:

https://www.pickheaters.com/

You may want to contact them.

Good luck

Breizh

Attached Files

•  Producing Hot Water by Direct Steam Injection.pdf   243.36KB   82 downloads

[GoleGole]

Hey! Thank You. I'll surely go through the same and contact them. 

Hi,

The most efficient way to produce hot water is to use pick heater (sort of valve), I used similar equipment to produce resins in batch reactors.

You may want to contact them.

Good luck

Breizh

[GoleGole]

Yes exactly, I tried to use the method where I used the formula Q=UAdt. However I was not able to process results reotely close to the actual value.Turns out I was not able to make out the value of U for producing proper results.

Is there anyway, you can tell me the methodolgy that might need to be followed. I can get all the data that might be needed. Thank You!

Your Q=MCpdT might give the approximate theoretical duty required. The jacket heat will not all go into the reactor wall. There is an outside of the jacket which will get hot and transfer heat also. If the reactants react during the heating, then consider the heat of reaction also and the Cp of the products.The hot water and steam will have heat losses in the exterior piping. Include the affects of phase change if present. I think you will find that the steam consumption will be more than predicted just by considering the reactor contents.

  I have designed similar process arrangements in the past for batch catalyst preparation. An important parameter is the heat transfer coefficient in the equation Q=UAdT. Jacket heat transfer can be very low. Water in the jacket will not transfer heat as well as steam. The walls of the reactor vessel are thick and resist the heat transfer. 

[Pilesar]

Collect data. Put data into spreadsheet by time. Use the two equations to start calculating. Fill in data gaps where needed. Find redundant methods to calculate unknowns. Reconcile data to help the redundant calcs match each other. Explain mismatches where possible.

Calculate total enthalpy for the cold side at the each time point (a simulator helps here.) Differences in enthalpy equal heat change.

The U will be constant. The A will be constant. In a batch process, the dT will not be constant since the cold side will heat up. So the rate of heat transfer will change also. If your water flow is constant, then the water outlet temperature will get warmer as the internals heat.

When the answers using redundant methods are not close, then reconsider assumptions. If a batch process, then perform calcs for several batches to check method.

This may be a good time to reread your heat transfer textbook.

[latexman]

 

This may be a good time to reread your heat transfer textbook.

 

 

And, study Pick Heaters (steam injection).  There is good info. there.

[GoleGole]

Thank you so much! I'll try this out today itself and update the results here.

 

Collect data. Put data into spreadsheet by time. Use the two equations to start calculating. Fill in data gaps where needed. Find redundant methods to calculate unknowns. Reconcile data to help the redundant calcs match each other. Explain mismatches where possible.

Calculate total enthalpy for the cold side at the each time point (a simulator helps here.) Differences in enthalpy equal heat change.

The U will be constant. The A will be constant. In a batch process, the dT will not be constant since the cold side will heat up. So the rate of heat transfer will change also. If your water flow is constant, then the water outlet temperature will get warmer as the internals heat.

When the answers using redundant methods are not close, then reconsider assumptions. If a batch process, then perform calcs for several batches to check method.

This may be a good time to reread your heat transfer textbook.

 

[breizh]

Hi,

If you want to stick to your model, get a copy of Process Heat transfer by Kern, chapter 18.

 

This book is the reference in Heat transfer.

 

Note: You will find similar results in Perry's chemical engineers' handbook, same with excel sheets attached.

Breizh

Attached Files

•  process_calcs.xls   347KB   85 downloads
•  batchheatingcooling.xls   159.5KB   75 downloads

[GoleGole]

Thank You! Will go through Kerns and update the progress here. 

Hi,

If you want to stick to your model, get a copy of Process Heat transfer by Kern, chapter 18.

 

This book is the reference in Heat transfer.

 

Note: You will find similar results in Perry's chemical engineers' handbook, same with excel sheets attached.

Breizh