Can use the liquid nitrogen for heat exchanger 2

[TPP393]

To all,

I want to design a heat exchanger (double pipe type) for cooling the off gas of propane and propylene mixture, if I use the liquid nitrogen in cold side, is it possible to excute this idea?

thanks!
TPP393

 

[gr2vessels]

TPP,
The question seems a bit vague.
Please first advise what do you intend to do with the liquid nitrogen flowing out of your exchanger? Then please advise what is the available flow of liquid nitrogen? Where is it going the excess heat put in that liquid nitrogen?
cheers,
gr2vessels

 

[TPP393]

Dear gr2vessels,

Thanks for your feedback. Below is the related information.

1. Hot flow inlet (gas mixture included propane and propylene) : 300kg/hr, Temp:50 degree C, P:17~18bar

2. Cold flow inlet (Liquid Nitrogen): 220kg/hr, Temp:-175 degree C, P:10~11bar

3. Want to design a heat exchanger if the liquid nitrogen can be applied on this idea.

4. when the liquid nitrogen changed to gas phase, we will receive gas volume into the nitrogen surge tank.

5. we hope to cooling the hot flow from 50 to 30~35 degree C, then we can receive all liquid hydrocarbon into receiver.

6. Suppose that liquid nitrogen will be changed to gas and the temp of outlet is around 5~10 degree C.

7. I drawn a simple PFD as attached for all you reference, please comment.

TPP

 

[BenThayer]

i doubt it will work for some of the following reasons:

the heat of vaporization of the nitrogen is not that great. compare the heat to be "removed" when condensing the propane vs. the heat to be "absorbed" when boiling the nitrogen.

the heat capacity of the nitrogen gas is not that great and you are more likely to have the exit temperature of the nitrogen to be much closer to the boiling point of the pressure downstream of your temperature control valve.

who is using the nitrogen and can they use it at the lower pressure (due to you expanding/cooling it across the temperature control valve)?

liquid nitrogen is an expensive refrigerant.

 

[epoisses]

It's a bit of a pity in engineering eyes to use -175 to cool from 50 to 30-35, isn't there any cooling water available to do it more cheaply? Or you might consider an air cooler if you're not located in the (sub)tropics.

 

[maddocks]

You're better off to consider propane refrigerant for this service. Excellent cooling properties, readily available, condenses at 110 Deg F and 200 psig with ambient air.. Liquid nitrogen would be hugely expensive and your stainless requirements and insulation costs would be massive. As well, with such a huge LMTD, the process control would be difficult.

 

[jamesbanda]

One point..

depends on the purpose of the cooling... continious or just a vent cooler for when other units are off line..I've seen comerical packages which use liquid nitrogen as backup vent condensers for when say a throx unit is off line...there not cheap but they can be effective to get to really cold temps..

it can be expensive if you have a gas nitrogen supply to site..

if you use liquid nitrogen to your site then its not that expensive as you have to heat up the n2 anyhow..

 

[dcasto]

It'll work, I'd flow control the N2 based on the proipane temp out. What you also need to know is what other gases besides C3 and C3= are in the mixture. If it 98% the C3's, then that butane tank won't hold the pressure at 35C as the pressure will be close to 14 atm, most C4 tanks are good for 5 to 10 atm