4 replies to this topic

[Sridhar P]

Require the calculation for Hydrazine dosing in Boilers based on O2 content.

Similarly for amine dosing in boiler based on PH.

Can anyone help on the same.

Thanks and Regards,
P.Sridhar

[breizh]

Hi ,
Attached a link from ARKEMA about O2 scavenger :
http://www.arkema-in...ure/pdf/346.pdf

It should support your query.
Breizh

[kkala]

Require the calculation for Hydrazine dosing in Boilers based on O2 content.
Similarly for amine dosing in boiler based on PH.

1. Reaction of hydrazine NH2NH2+O2-->2H2O+N2 indicates dosing of 1 gr NH2NH2 / gr O2. In practice 1.5 to 2.0 gr NH2NH2 / gr O2 is applied, probably because hydrazine protects metal from corrosion by converting Fe2O3 to Fe3O4. Injection is into deaerator (or close to it).
2. Neutralizing amines (morpholine DR=0.3, diethylaminoethanol DR=1.7, dimethylpropylamine DR=1.7, cyclohexylamine DR=4.0, even ammonia DR=10.0) keep boiler water pH constant (8 to 10). Dosing depends on bicarbonate alkalinity in BFW and the stability of amine bicarbonate according to Betz; but nowadays these can be practically 0, since there are no carbonates / bicarbonates downstream deaerator in a modern boiler.
So I assume (without practical experience) that one can accept a rather low concentration in liquid, able to create the pH required, performing buffer solution calculations (dissociation of weak bases in water). Resulting dosing have to be multiplied by (1+DR), where DR=distribution factor, to account for the amine passing from water into steam.

The reference used for (2) (Betz, Handbook of Industrial Water Conditioning, 7th ed, 1976) does not give more precise info on amine dosing, and DR does not seem quite clear; probably some other (or modern) references are more detailed.
Same reference is used for (1), results seem precise in this case. Hydrazine injection into BFW (boiler feed water) of 7 mg O2/l was recently specified for residual content of 0.2-0.6 mg/l in boiler drums, but hydrazine was replaced by carbohydrazide due to its toxicity.

Edited by kkala, 03 May 2010 - 01:27 AM.

[ankur2061]

Sridhar,

Send me your mail ID. I can send you a oxygen scavenger dosing spreadsheet based on various oxygen scavenger chemicals.

Regards,
Ankur.

[ankur2061]

Sridhar,

Send me your mail ID. I can send you a oxygen scavenger dosing spreadsheet based on various oxygen scavenger chemicals.

Regards,
Ankur.

Dear All,

Attached spreadsheet for "Hydrazine" dosing for BFW.

Regards,
Ankur.

Attached Files

•  Oxygen_Scavenger.xls   21KB   506 downloads