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[reason991]

Hi, 

 

I'm thinking of getting a Shell and Tube heat exchanger. The goal is to vaporize a liquid recycle fluid (90% ammonia and 10% water) with heated geothermal brine solution through a heat exchanger, and feed the vaporized recycle fluid into steam turbine and generate power. 

 

I have the the following settings:

 

1.a Hot brine liquid entering inlet @180F and 100 psig

1.b Cold recycle gas mixture entering inlet @80~100F and 200~300 psig.

2. Hot liquid brine can have flowrate upto 20,000 bbl/day.

3. I have full control of the flowrate of the recycle liquid entering the heat exchanger. 

4. I do not know the exit temperature of both Shell side and the Tube side because I don't know what's possible.

5. The recycle fluid will have boiling T around 130F.

 

I want to raise the temperature of the recycle fluid as high as possible, but it will be restricted by the 180F temperature of the geothermal fluid. I don't care about the exit temperature of the geothermal fluid as long as I can heat up the recycle fluid as much as possible.

 

The readings I've done indicates that 10~15C approach temperature is feasible with good heat exchanger design, but this assumes that there's no phase change. But in my case, I need phase change. 

 

I probably want temperature cross because I want the recycle fluid T as high as possible. The software I have (Promax) has an ability to compute the "effective" approach temperature when there's a cross change, so I'm gonna go off of that. 

 

Question: What's a feasible approach temperature when hot liquid (stays as liquid) is used to vaporize a cold liquid into vapor? 

 

I'm trying to run process simulation scenarios, but I do not know what kind of approach temperature is realistic when vaporization is involved.

 

Thank you!

Edited by reason991, 29 July 2023 - 11:13 PM.

[Pilesar]

You did not supply the recycle flowrate, but if it is relatively small and the heating medium flow is large, then the temperature approach can be very small also. The heat transfer rate for boiling a liquid is different from the transfer rate of superheating a vapor. If it is important to have a high superheat, then you might consider separate heat exchanger designs for boiling and superheating. The exchanger designer ought to try many configurations to find an economical optimal solution. Determine how much value is in a degree of incremental superheat temperature and compare that to the cost to achieve that incremental temperature. "As high as possible" should not be the final temperature design criteria.