calculating amount of 60# steam 1

[JGP08]

I need to calculate the amount of 60# steam I would have created in 7 hrs (time HX was down) with a water flow that gained about 30MMBTU/hr. now I know it should be a simple calculation with the energy and heat of vaporization. but not sure.

help!

 

[Latexman]

Sounds like homework to me.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[racookpe1978]

What was your nominal inlet conditions for the water that would have been heated?

(Energy out - energy in)/lbm water x amount of water/sec x nbr of seconds = energy gained in the HX

Now: From YOUR steam tables at 60 psig, what energy out do you think you were getting? Saturated, right?

 

[Latexman]

If it is homework, just let us know. We have a place homework questions can be asked.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[JGP08]

Racookpe1978,

the inlet conditions are

T = 80 F
P = 70 psig.

It is def saturated steam. but I guess i worded my question poorly, the steam is not being produced by the heat exchanger, it is created somewhere else in the process. however the purpose of the heat exchanger is raising the remperature to about 140 F. since the heat exchanger was down for cleaning this water wasnt heated up but it would've normally gained 30MMBTU/hr. now based on that how much 60# steam would I have created.

Thanks

 

[JGP08]

latexman,
No, is not homework but thanks for the info

 

[racookpe1978]

If your steam is being produced elsewhere (in a different heat exchanger) then in this heat exchanger, you need to use (Temp_water_out - Temp_water_in)x Cp_water = heat exchanged across the heat exchanger if no change of phase. At those low pressures and temperatures, it should be pretty simple.

When you know the energy of the hot water going into the second heat exchanger, and some estimate of its efficiency, then you get the steam energy out. Which will always be less than the orignal energy.

To get "value" of that steam, you need t

http://www.eng-tips.com/viewthread.cfm?qid=373730o

know the contract cost you are getting paid for the steam.

 

[JGP08]

racookpe1978,

Thank you so much for your help

 

[rotw]

as I see the system

total heat load (30MMBTU/hr) Q = sensible heat Qs + latent heat Ql

latent heat corresponds to the production of steam by vaporization; massflow balance is :
m1 (water kg/h at inlet) =m2 (kg/h steam) + m3 (water kg/h at outlet)

So heat balance should be: Q = m3 x Cp x (T_v - T_inlet) + m2 x h_v x Delta_W

Delta_W = change of vapour content ; I think this should be put to 1 but not sure
T_v = Temperature of vaporization at 60psig (steam tables).

Then basically knowing 'h_v, T_v, T_inlet' you are looking for m2 and m3 ; knowing the hours you can calculate back the amount of steam generated _ do you agree ?
This how I see the problem; I may have misunderstood the question; anyhow if someone can point out any flaw in this, thanks.
Sorry for using S.I units.

Therefore I think the question cant be answered without knowing the total flow of water at inlet ; the rated capacity of the heat exchanger that is down could be used















"If you want to acquire a knowledge or skill, read a book and practice the skill".

 

[waqasmanzoor]

JGP08

Dear, have you tried simulating the process in Aspen PLUS or Aspen HYSYS. Besides doing manual calculations (which you should do for better grasping of process engineering concepts), you can very easily (and swiftly) calculate the "LOST STEAM" by using the process simulators.

First simulate the process in normal operation and try to calculate the total steam produced in normal mode.

Then specify the duty of the HX in question as 0 MMBTU/H in the simulator, and again look at the total steam produced.

The difference between the two steam production rates would give you the "LOST STEAM PER HOUR".

MULTIPLY this "LOST STEAM PER HOUR" by 7 to get the steam lost in 7 hours.

If you share the process data then I can calculate this for you

Regards.

 

[waqasmanzoor]

By the way, 30 MMBTU/H seems to be a very big heat exchanger

How much is the water flow rate?