Process air heater design

[abutt116]

Somebody could guide me about process air heater design complete calculations. Exchanger is shell and tube and heating is with 200 psi steam. Inlet temperature of air is 70F and required outlet is about 200F.

Thanks.

 

[epoisses]

Abutt, nobody can give a sensible answer to this because of missing data. Please let us know the specific problem you are struggling with.

 

[abutt116]

Our existing process air heater is shell and tube, 16 feet in length, 195 tubes, 1.5" OD, 16" air inlet and 16" air outlet. Air is in the tubes. 200 psi steam is on the shell side. Air flow is about 6000 scfm at 5 psi to the heater.
This exchanger is about 30 years old and now giving problems.
We have one used air heater (shell and tube exchnger) available at our plant. It has 560 tubes, 3/4" OD, 11 feet in length, 12" air inlet and 12" air outlet. Can i use this exchanger for the above mentioned service without any problem (pressure drop etc.)
I can see that heat transfer will be more in the exchanger having more tubes but i am worried about the pressure drop due to 12" inlet and outlet(existing heater has 16") and more number of tubes.

Help will be appreciated.

Thanks.

 

[epoisses]

You'd have to run a HX simulation to see where you'd end up exactly. But you may want to do the easiest checks first: are material, DT and DP compatible?

BTW, what are the "problems" you are referring to, pressure drop?

 

[srfish]

Running through some of our simple software shows no problem. This is based on an air density of 0.0895 #/cu ft and an air flow of 27,000 lb/hr. The tube pressure drop including end losses is 0.46 psi. Then using 108 sq inches for the 12'' nozzles and a conservative 1.5 velocity heads gives 0.18 psi for the nozzles.

The estimated overall heat transfer rate was 15.8, thus showing no problem on the heat transfer