Indirect Fired Heater Design

[jeap]

Hi All!

I'm just trying to verify the actual capacity of a indirect fired heater API 12K type. API 12K only gives a general guidance based on "standard capacities" from 100M to 1.5 MM btu/h


After following a laboriuos method to find heat transfer coefficients at the fire tube side, and calculate heat transfer for a specific service I found that I don't know what are the main restrictions in the hyraulic design of the fire tube, for instance flue gas speed through it in order to mantain a natural draft of air, or something else. Please I need some advice on that restrictions.

Thanks in advance

PD I've read
thread794-24190 where some British standard where mentioned.

 

[monaco8774]

Used to design these but its been a while, from memory Indirect fired heaters usually if its a fired tube (U-type) the heat transfer is based on a heat flux of around 10,000 btu/ft2 total from tube to indirect medium (assuming typical water) Then heat transfer on the heated fluid in the bundle on top is based usually on turbulent convective heat transfer on the inside (Nu=0.023.Re^0.8.Pr^0.33)and natural convection on outside of tubes, of course condution through the tube.
Also you need to calculate minimum draught for the stack to get stoichiometric + 10 extra air through the stack.

You get a good reference on Kern's book on heat transfer but wife stacked it away in the loft years ago.

 

[KernOily]

"You get a good reference on Kern's book on heat transfer but wife stacked it away in the loft years ago."

Ummm, would you have her dig it out and then sell it to me? ;-) Pete

 

[SindelA]

Capacity of Indirect Heaters are relative.

First you must know the Inlet Temperature, Pressure, and flow rates of Gas, Oil, and Water. Note the water is more critical.

Second you must know the coil split, like 4 passes upstream and 6 passes downstream.

Third you must know the desired outlet pressure and you can usually assume 70F for the temperature.

From this you can calculate the JT effect and thus know the capacity of the Indirect Heater. Also keep in mind, after the media leaves the choke you want this temperature to be +5 Deg above the hydrate formation line at pressure.

Most of the time you can just figure 35 to 40 Degrees F.

I got tired of doing this manual and wrote a spreadsheet program to make these calculations. Takes about 5 minutes, lol.



Regards,

Allen
Sindel & Associates

http://www.consulting.awsindel.org

 

[raidkhalaf]

Hi, I am looking for the mechanical details of indirect water bath heater, and I'll be very grateful if someone tell me how to get them.

 

[dcasto]

The old Smith Industries use to publish a book about them. Might be one in a library somewhere, I'll sell mine on ebay when I retire, I love it.