Flash Vessel Sizing Methods

[anj3]

thread124-125547:
From the Brown-Souders equation one can determine the flash vessel diameter and height. However, when I apply it to my HTF data(flashing HTF) :

vapor stream: .03 kg/s
density of liquid: 52.8 lb/ft3
vapor density: .325 lb/ft3
K value= .2 for a system without a wire mesh

I attain a radius with a value of 1.9 inches which is too small and inconsistent with known vessel sizes. Are there other methods to size a flash vessel? Are there models that might apply specifically for certain heat transfer fluids(HTF), such as therminol in this case?

Thank you so much for your help!

 

[chemebabak]

anj3,

Souders-Brown is Vmax = (k) ?((?L - ?V) / ?V] )

According to your values V max is 2.54 ft/s
Vmax = 0.2*?((52.8 - 0.325) / 0.325) = 2.54 ft/s

volumetric flow rate = vapor mass flow rate / ?V
Vol = 0.03 kg/s * 2.2 lb/kg / 0.325 lb/ft3 = 0.2 ft3/s

Area = Vol flow / Vmax
Area = 0.2 ft3/s / 2.54 ft/s = 0.08 ft2

MINIMUM vessel diameter = ?(Area / (? / 4))
D = ?(0.08 ft2 / 0.785) = 0.32 ft = 3.8 in

Therefore your vessel must be at least 3.8 inches.

That being said, what kind of process has such a low flow of only 0.03 kg/s?

 

[anj3]

Such a low flow rate is used for a the HTF recycling in a solar plant heat exchanger system.
Is it possible to have such a small flash vessel? Are there other methods to calculate the diameter and height for a flash vessel that will apply for the use of therminol?

Thank you again!

 

[chemebabak]

For such a small vessel you do not even need a vessel. You can design a 6", schedule 80 vertical pipe. The bottom of the pipe can be fitted with a sight glass and valve to manually drain the precipitated fluid. You could also get fancy and automate the process.

By the way, 6" schedule 80 pipe has in inside diameter of 5.761 inches. ASME, Section VIII, Division 1 requires that any vessel larger than 6" ID have an ASME stamp. This requires a safety valve and it would increase your cost.

See sketch:

http://files.engineering.com/getfil...9719-7bb790585eb6&file=6_in_Sch_80_vessel.pdf

 

[anj3]

Does that method apply when the liquid stream is waste and the vapor stream will be connected to a condenser to condense the vapor back to liquid and be recirculated in the system?

 

[sdtobin]

Always work smarter, not harder. Check out eaton for vapor liquid separators, and I bet your process requirments are orders of magnitude smaller than their smallest units. Check out the link as follows:

http://www.eaton.com/Filtration/USA/Products/SeparatorProducts/index.htm

 

[Boghi1990]

Hi,

I have to size a flash tank. There are 20 drain lines running into the flash tank. Flash Tank is connected to a surface condenser (Pressure in the condenser is 0.736 psia)through a 6" vent line and a 3 " drain line. Hot condensate flows through these drains from different sources. Upstream operating pressures and temperatures range from 1813 to 110 psia and 10650 F to 693F.

I do not have the mass flow rates for these drain lines, so I have to estimate/calculate those flow rates in order to size the flash vessel. The hot condensate will flash before the it reaches the flash tank, so down the drain line there will be a two phase flow.

Does anyone know of a methodoly on how to estimate the flow rates for each of these drain lines?

Knowing the mass flow rates, what method should be followed to size the flash tank? (Diameter, Height, inlet pipe into the tank)?

Regards,

One Point

 

[786392]

Dear Hello/Good Afternoon,

Kindly raise your query as a fresh/separate post

Best Regards
Qalander(Chem)

 

[mfelzien]

Boghi1990 (Mechanical)

Are you sizing a flash vessel that is already in service? Are you sure on those temperatures... OUCH. Melting point of carbon steel is about 2800 deg F.

There really is no good way to answer your question. You might assume that the lines leaving your flash tank were sized for reasonable flow velocities and get a range of the flows. (Say 30ft/s). Knowing the density and pipe diameter you can find the mass flow into the condenser.

There are several ways to find your diameter and length (iterative solution). If you look in Brannans book you will see an example. But, you’re going to need to know your composition and flow rates to size a flash vessel.

Look further upstream to find flow information and perform an overall mass balance on the system to see if that will help your problem.