2 replies to this topic

[wamit]

Dear all,

I have been given a task to provide a preliminary steam drum size (diameter and tangent length).
The only parameters i have is 43.5 Barg @ 258 Deg C , 14000 kg/hr saturated steam is to be produced , using the heat from the flue gases of the fired heaters.

The BFW flow is 19.4 m3/hr.The vessel residence time is 10 min.

I would apprecaite if some one could guide me through the calculations


With warm Regards,
Amit

[JEBradley]

I think you maybe need to go away to get a bit more information.

I think there's still a lot you can do with the figures though:

You know you're generating saturated steam at 43.5 bar. Check your steam tables to find the enthalpy change of vaporisation - I got 1685 kJ/kg. If you multiply this by the production rate of 14000 kg/h you should get about 23 600 000 kJ/h or 6.55 MW (Pretty high!!)

What temperature does the water start at? Ive neglected all sensible heat because it will be small compared to the latent heat - but find this out anyway.

I dont know what BFW is???? but i guessed it's maybe the flue gases????

I did a couple of extra calcs. - these are all just estimates because i dont have the info but it might give you an idea.

Using Q=UAΔT Lets say U=200 Wm^-1K^-1 which should be easily achievable; Q is 6.55x10⁶ A=? and ΔT is unknown but lets say the gas is about 600 so call the ΔT=300K

Re-arranging and solving, A turns out to be about 100m²

This seems to be a lot to me so start asking yourself some questions - is the steam production really that high? What is the heat transfer arrangement - I have no idea, could be flue gases running through the drum as an internal coil or maybe the gases pass directly over it??? A well designed heat exchanger could potentially reduce the size 10-fold.

Im confused by the residence time - if thats referring to the 19.4m³ /h then the volume is only 3.2m³ - actually this sounds normal now (but not for the amount of heat that needs transferring).

[wamit]

Dear Sir,
Thank you For all the inputs.
With reference to the above inputs given .
Yes the steam make is 14000 kg/hr.
The BFW is at 158 Deg C which gets heated in the economiser section of the heater (Stack)to 258.1 Deg C.

The residence time is 10 min of rth vessel.

With warm Regards,

Amit