Air Cooled Steam Condenser design 1

[Aerox]

I would like to design an air cooled condenser to condense saturated steam. It is to be used in a food processing plant.
My understanding of this process is still a little poor after a fair amount of reading. I have tried to keep the problem basic for now. I will possibly introduce my actual masses and calculations for further help but initially I'd like to make sure that my thoughts are correct.

The saturated steam has come from an upstream evaporator and is saturated @ 0.2 bars (absolute). The saturation temperature is 60 degrees C at this pressure.
Condensation will occur inside single pass tube bundles.

To my understanding, we assume condensation will occur at this constant temperature and produce saturated liquid water. When the water has condensed, will it still be @ 0.2 bars and 60 degrees (ignoring pressure drop)? There would be some pressure drop but it would still be close to these, right?

The energy (Q) required to condense the steam is equal to the mass of steam*(-heat of vaporisation).
I would also like to cool the water condensate to 25 degrees C. Can the condenser do this by say increasing mass flow of air or should it be cooled in a separate process? The extra energy required would be mass*Cp*dT. (I think I'd have to use the Cp of water at 0.2 bar or whatever the resulting pressure is? 4.185 according to engineeringtooblbox.com)

When the water has been cooled, it will be recirculated to join a pipeline where the water pressure is 1 bar. If the condensate is at a lower pressure does it need to be increased before joining and how could this be best achieved? Could a pump fix this?

After this my next steps are to decide on the dimensions and number of tubes, number of fins, calculate required air flow and fan sizing.

Would appreciate some help. Any amendments to my thoughts are welcome.

 

[srfish]

I am guessing that your design air temperature is approximately 38 C. In an air cooler you will only be able to cool the liquid condensate to approximately 43 C.

 

[EdStainless]

There are people that design and build these for a living.
Go to them.
They will offer performance guarantees.
And don't forget your vacuum extraction system. You need it to remove non-condensable gases.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

An elevated shell and tube HX with this steam on the shellside and coolant on the tubeside could do this job. This HX would have both condensing and subcooling functions performed within the same shell.

HX would have to be elevated at 9-10m or more to allow for the 10m barometric leg plus the drop across a LCV that maintains level in the HX - the flooded section of the tube bundle does the subcooling duty. While the upper section does the condensing service. With this external barometric leg, you would have enpugh pressure at the bottom to get this subcooled water into this 1bar line (presume you mean 1.0bar abs).

This scheme is typical of overheads condensors in columns where both condensing and subcooling functions are performed in the one shell. Take a look at these for the control scheme required. A dPIC and dPCV is required to bypass some hot steam at 60degC directly into the HX shell to prevent pressure in the shell from collapsing further than 0.2bar abs.

The coolant has to be at 20degC or so to get this steam down to 25degC at the exit of the HX - you wont get this with air as coolant, unless this dairy plant is some where in the Arctic ? If you've got excess steam at 100psig or so, you could get some chilled water at 120degC made from plant cooling water with a steam jet condensor ? This chilled water unit may be a vendor supplied package.

 

[georgeverghese]

Unless there is existing space at an elevated platform at approx +10m or higher for this HX, you may find the cost for elevating this HX prohibitive in comparison to a pump option. If you go for the pump, then the LCV for maintaining adequate subcooling would be shifted to d/s of the pump. As suggested earlier, you'll need steam powered ejectors on the shellside of this HX to get rid of non condensibles. The other ejector for the steam jet coolng unit would be in the vendor's supply scope.