4 replies to this topic

[sdahidi]

Dear All,

Could you please advice how I can get a curve/table for the tube metal temperature along the tube length for Shell & Tube Heat Exchanger using ChemCad. I build the rating model for Air Preheater installed within boiler package we have and with ChemCad sucessfully obtained tube & shell side temperatures at different zones, the simulation calculated also the mean metal temperature along the whole tube length.

Appreciate any help in this regard, i need to check the metal temperature along the tube length to check if it is enough above the dew point temperature of sulfuric acid to avoid corrosion.

Thanks in advance for your assistance.

Regards,
Sami

[Zauberberg]

The first place to check for metal temperature is cold-end of an exchanger.

If this is a BWF-Flue Gas exchanger, you can safely assume that the cold-end metal temperature is equal to the BFW inlet temperature. In other words, the tube metal at the inlet of BFW to the exchanger will be at the same temperature as Boiler Feed Water, and this is due to the fact that the resistance for heat transfer between liquid and metal is fairly small. Therefore if you want to eliminate cold-end corrosion, you have to ensure that BFW inlet temperature is about 5-10C higher than the calculated acid gas (sulfuric acid) dew point temperature.

Also read more at: http://v_ganapathy.t...m/corrosion.pdf

[Zauberberg]

For calculating tube metal temperatures, refer to the following pages from "Process Heat Transfer" by D.Q.Kern.

Attached Files

•  Tube-Metal Temperature.pdf   274.36KB   63 downloads

[jcazenave]

I know it is not exactly your question, but if you are interested by the detailed tube temperature, why not use an rigorous shell & Tube modelisation tools like HTFS - Aspen EDR or HTRI ? These should be able to answer your question. This is of course if your company has access to one of them

[Zauberberg]

I know it is not exactly your question, but if you are interested by the detailed tube temperature, why not use an rigorous shell & Tube modelisation tools like HTFS - Aspen EDR or HTRI ? These should be able to answer your question. This is of course if your company has access to one of them

Good point - but there's no need for rigorous modeling in this particular application. The fact is that the flue gas will definitely reach BFW inlet temperature (and experience localized condensation if the temperature is below Acid dew point).

Modeling would be interesting for gas-to-gas exchanger application, however a fairly good results can be obtained by Kern's method as well.