LPG vaporizer 1

[diensg2005]

Dear Sirs,

We are a company in Vietnam.
We plan to manufacture LPG vaporizer, but still not understand very well method for the calculation of vaporization of LPG. If you can help us, how to determine (step by step) the selection of length and dimension of pipe exchanger, the capacity of heater...etc.
By example, for a vaporizez:
- Capacity 200 kg/h
- Tube 1", SCH80
- Dimension of the water bath: 300 liter
- Ambiant temperature: 25 deg C
- LPG: 50% propane and 50% butane

Question:
- What is the length of the 1", SCH80 pipe?
- What is the capacity of the heater?

Thank you for your help.

Regards.

Tran Thanh Dien

 

[Homayun]

It's not that difficult. Calculate how much heat input (kJ/kg of LPG)(evaporation enthalpy) you need to vaporize your LPS. You can find this information in Perry. But I bet you could also find in in Google.

Then provide the same amount of enthalpy by your heating medium. If using hot water, you need to know the heat capacity and the Delta-T.

I have never designed a vaporizer, but I think it works like any other type of exchanger where the liquid is vaporised, like a reboiler or os.

I would bring the LPG to the shell side and allow the vapors leave via the top.

But I strongly advice to contact a certified Chemical Engineering company to design the LPG vaporiser.

Good luck

 

[UmeshMathur]

diensg2005:

In an unstirred water bath, you will have natural convection only outside the tubes. Convective heat transfer film coefficient correlations are available in the literature. Here is a good one:

Hewitt, Shires, and Bott: "Process Heat Transfer" (CRC Press, 1993). This book also shows a relevant solved example 2.15 on pages 116-117 (Chapter 2, "Mechanisms of Heat Transfer").

I would expect that the heat transfer resistance inside the tubes (vaporization of a light hydrocarbon mixture) will be negligible compared to the outside natural convection film resistance and the fouling resistance.

Doing the complete analysis will require some engineering expertise, as Homayun suggests. I assume you have staff with the requisite capability to do this yourself. Design methods are also available in the classic book:

D. Q. Kern: "Process Heat Transfer" (McGraw-Hill, 1950)

As you know, selecting the proper fouling coefficients is important for sizing the exchanger. Also, designing the control system to do the job properly on the vaporizing LPG side requires attention to many instrumentation and controller design issues.