4 replies to this topic

[Ranga v]

Oleum unit effluent having sulphate conc of 5000 ppm is treated in NF unit for sulphate removal.Reject from NF having conc15000 ppm ,pH neutral 7.5 which is further treated in single effect Evaporator. Condensate from vaporiser observed to convert acidic pH less than 4.0.What may be cause & mitigation

[breizh]

Hi,

you may have liquid saturated (sulfate) carried over with the vapor. Check whether the mist eliminator is in good condition (not damaged, not partially plugged).

Check also whether the feed rate of the evaporator is adequate .

 

Breizh

[Ranga v]

Thanks Feed flow is normal.Current the evaporator is operating under negative pressure -0.775 kg/cm2g based on which what should be the temperature of Evaporator feed with sulphate conc 15000 Ppm.

[breizh]

Hi,

To support your query:

Calculate or measure the boiling point of the solution at atmospheric pressure and use the chart provided to get the Boiling point at the given pressure.

 

To calculate the boiling point of the solution, use this relationship: BP = BP solvent(water) +boiling point elevation (delta T)

 

Boiling point elevation: delta T =i*Kb*m

with Kb (water)=0.52 C.Kg.mol-1 ,

m =molality of the solution  mol Na2So4 / kg  water,

i= van't hoff factor= 3 or total mol dissociates (2 Na+ and 1 So42-)

 

intermediate calculation :

Molecular weight Na2SO4  142 g/mol 

15000 ppm weight = 1.5 % or 15 g Na2 SO4 /1000 g solution  equivalent  to 15 gNa2SO4 per 985 g H2O  thus molality 

m= 15/142/.985 = 0.1072 mol/kg water

 

delta T = 0.52*3*.0.1072 =0.167 C or BP solution = 100+0.167= 100.167 C # 100.2 C close to BP water at atmospheric pressure

 

 

Use a steam table or the chart given to calculate the BP of the solution at your pressure.

 

Pressure unit to be converted in absolute pressure .

Pabs =0.24 bar or 180 torr (mm Hg)

 

T ebul should be close to 64 C

 

Note: If the concentration is about sulfate only (SO4 2-), the calculation will be a little different but the methodology the same and the results slightly different (higher delta T).

 

Good luck

Breizh

Attached Files

•  BPnomogr.pdf   52.72KB   2 downloads

[Ranga v]

Thanks