2 replies to this topic

[waheedbhatti]

I am facing a problem of increasing iron content from 70 ppm to 100 ppm in benfield solution. We are dozing oxidizing agent(V2O5) to keep the protection layer intact. We have increase V+5 conc from 0.22 to 0.45%
remaining solution analysis are
eq carbonate: 29.5%
KHCO3 : 17.45
K2CO3 : 17.67
DEA :1.91
V+5 :0.45
V+4 :0.27
VT : 0.82
Fe :98 ppm
Any one have detail regarding this topic please share.
Regards

waheed bhatti

[tarafdar]

Dear Mr. Bhatti,

1.V₂O₅ is not an oxidizing agent.Vanadium(vanadium pentoxide or potassium meta venadate) is used to form the passivation layer which prevents corrosion.This layer may be disturbed by erosion (high fluid velocity,movement of tower internals etc.) or drying(peel off during shut down).

2.KNO₂ or air is added as oxidizing agent to convert V⁺⁴ to V⁺⁵ .(air is not recommended normally.You must be very careful during air-oxidation).

3.Your analysis shows same conc. for KHCO₃ & K₂CO₃.Is it from Absorber or Sripper outlet ?Or it is from Solution storage tank.For system monitoring you must take sample from process, not from the storage tank.If it is from the process then your carbonate & bicarbonate conc. should not be the same.

4.Your V_T is almost ok,though 1% is recommended.

5.Your V⁺⁵/V⁺⁴ is greater than 1,so you don't need to oxidize.

6.If your Fe content is steady for several days, then you don't have to worry.
Iron content less than 100ppm is o.k.
I have experience with 120ppm of Fe without any problem,but it was steady for long time.

7.Also check your soln. colour.Dark soln. means many impurities & it interferes with the analysis.You can remove colour by using your activated carbon filter, if you have.You must always use your mechanical side-stream filter to remove suspended iron & other suspended materials.Clean it time to time by observing the delta T.

8.Sometimes you may have sudden increase in Fe if you put some equipment in service which was not in service for several days(say the stand-by pump).It is not possible to passivate it seperately.Normally you must try to keep all stand-by equipments wet by establishing a small flow through them.

Regards.

[waheedbhatti]

Thanks a lot for your information. Have u any litertaure regarding this topic. moreover as V+4 converted to V+5 by KNO2 similarly V+5 is used to form megnatite which acts as passivation as per UOP. If u have any literature please send me.
thanks