Condensate Flash Tank

[alquimista]

Hello everybody,

This is my very first post since I have discorvered this very useful website. I am currently working in a Spanish refinery and I am process engineering, just fresh from university. In my section of the plant, we have a HDS unit, Phatalic and Maleic Anyhride units, among with a solvent one.

I have been asked to calculate the right size (diameter, lenght) for a condensate flash vessel where the condensate at around 12 kg/cm2 is flashed to a pressure of around 2,5 kg/cm2 so the steam is introduced back in the low pressure steam network.

I have been trying to get information with no success. Do you know if there is some standarized procedure to calculate it?

The actual flash tank is vertical and it has a heavy corrosion problem after 35 years on stream. The unit has also been revamped and more equipment is discharging condensate to it, so in adition to corrosion the tank has become small for the required service.

This is only a very preliminary calculation. With the dimensions, material and thickness I will get a cost estimate that we will present to our management for the budget approval for 2007.

Thanks a lot
Best regards

 

[25362]

Visite el thread794-105012 con especial atencion a lo que Milton Beychok dijo.

Good luck.

 

[alquimista]

25362,

Thanks a lot for your answer. It was my first topic and I had not discovered the search tool.
Tomorrow at work I will perform a prelimanary calculation with all the information I have gotten reading the topics.

Thanks again

 

[elguero]

Look up properties of saturated steam and saturated water in a steam table. (The Chemical Engineers Handbook has an abbreviated version.) Assume the flash is isenthalpic (constant enthalpy), therefore, HL(12) = HL(2.5)+HV(2.5), where HL is liquid enthalpy and HV is vapor enthalpy. This will require trial and error. Start at a temperature 5 degC lower, then go to your next guess. Shouldn't take more than about four or five trials. Que le vaya bien.

 

[davsy]

If you need a bit of further information you could look at the Spirax Sarco website. They have some fairly good learning modules and one of them is on Flash steam

http://www.spiraxsarco.com/learn/block.asp?id=14

you can also get a price from them for a suitable Flash vessel. They are represented in Spain

 

[elguero]

I neglected to mention that the value of vapor amount you estimate from the isenthalpic calculation can be used as a basis for determining the diameter of the vessel. A flow of 0.1 ft/sec (3 cm/sec) is reasonable. Make sure your vessel has a tangential feed and an axial discharge. Make it so that the discharge nozzle enters the vessel, like a cyclone separator. Con eso, no falta mas para contar.