×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Softening plant capacity

Softening plant capacity

Softening plant capacity

(OP)
What should be the capacity of a softening plant( in litres/hr) for a 3 MW boiler @1000 Kpa.All condensate is being returned back to the boiler.Any guidelines/ basis for working out the make up rate?

RE: Softening plant capacity

I will try to do some calculation in the absence of clear data.

The basic assumption is that the boiler feed water (including the returned condensate) is at atmospheric pressure and at 100C. The enthalpy difference of saturated steam at 11 bara and feed water at 1 bara is 2363.14 kJ/kg. If your boiler capacity is 3 MW, then the steam output rate is (3000 kJ/s)/(2363.14 kJ/kg) = 1.26 kg/s or 4570 kg/hr.

Presuming 100% condensate is returned back and the feed water tank is at atmospheric pressure, you need to count the amount of flashing. Enthalpy of liquid at 11 bara is 781 kJ/kg and enthalpy of liquid at 1 bara is 417.5 kJ/kg. The difference is the driving force for flashing of condensate into steam. The enthalpy of steam at 1 bara is 2674.95 kJ/kg. So, the flash steam is (781-417.5)*100/(2674.95-417.5)  = 16%

The loss of condensate, therefore, is 4570*16/100 = 731kg/hr or 731 L/hr. This is the minimum makeup flowrate required for the above assumptions.

Now check for the actual feed water tank pressures and then assume some steam leakage and get actual condensate flowdata if you have metering on the line.

RE: Softening plant capacity

(OP)
Thanks Quark for a good explanation!Do we need to add blow down rate to this figure? If yes what would be an acceptable figure?Thanks again.

RE: Softening plant capacity

Yes, you must add blowdown rate to the above figure (infact, I forgot about it). The rate of blowdown may vary from 4 to 8% and can be anything if the water quality is bad.

Theoretically, you can calculate it by input water TDS and maximum permissible TDS limit in the boiler drum. ABMA recommends 3500 ppm for a boiler of 10 barg pressure (actually for the pressure range 51-300 psig). Suppose, if your feed water quality is 250 ppm TDS then the blowdown rate is 250/(3500-250) = 7.69%. This procedure assumes that dissolved solids are absent in the steam and are fully accumulated in the boiler drum.

RE: Softening plant capacity

Dear,
As most usually 100% condensate return is not manageable,thus a  safety factor of around 4%~6% be considered for this part.

Further to cater for possible problems with water quality an overall 30%~33% plus capacity should serve as Min. benchmark.

Hope this helps

Best Regards
Qalander(Chem)

RE: Softening plant capacity

I think, other uncertainities can be mitigated by capacity of the day tank and Softner OBR. Per hour output is dependant upon the superficial velocity (and thus vessel diameter) and OBR is dependant upon the volume. You can study various softner sizes vis-a-vis the day tank volume and can come to an optimal solution.

For same resin volume, higher H/D ratio results in lower cost of the softner.

 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources