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
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
RE: Softening plant capacity
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
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
For same resin volume, higher H/D ratio results in lower cost of the softner.