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High Pressure System Boiler Water Chemical Dosing Calculations (Coal F

trisodium phosphate neutral amine carbohydrazide blowdown residual phosphate power plant coal high pressure boiler

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#1 S.win

S.win

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Posted 24 November 2016 - 10:17 AM

Hello,

 

Good day everyone.

 

Recently working in a coal fired power plant industry (HP system). I just want to ask if there are calculations for dosing the right amount of chemicals such as TRISODIUM PHOSPHATE, NEUTRAL AMINE, and CARBOHYDRAZIDE with respect to the parameters (temperature, pressure, flow, pH, conductivity, load, etc) monitored in the boiler. 

 

Just would like to have an idea in which I could calculate the right chemical dosings and later plot the actual performance such as residual phosphate, residual carbohydrazide and the like with respect to the monitored parameters so that I could come up with a trend.

 

In the power plant where I am currently working now does not have any calculations for dosing the right amount of chemicals but rather depend on estimations only. Well, estimations would be okay for basis of the adjustments but would also like to know the calculations for dosing the right amount so that I could relate also the estimations on the chemical adjustments with respect to the calculated values. 

 

Hoping for your positive response.

 

Thank you in advance.



#2 -G-

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Posted 24 November 2016 - 11:13 AM

Hi there,
 
I work in a CHP plant which produces HP (130 bar) and MP (15bar) steam. Our amine dosing pump is controlled by feed water flow rate, we then make sure that the feed/boiler water pH is in the correct range. We only dose phosphate to our MP drum.
 
We had this from a recent water chemistry audit....

For feedwater dosing, a target pH of 9.4-9.6 should be set (with either ammonia or proprietary amine dosing). This is equivalent to a Specific Conductivity of 7-11 μS/cm. Amine dosing should then be controlled to Specific Conductivity as this is generally a more reliable measurement than pH in high purity waters.

For the boiler waters, chemical targets are more difficult to establish as they depend on knowing the concentrations of alkalising chemicals to be achieved and determining the equivalent pH and Specific Conductivity ranges. For the Medium Pressure drum, a combination of phosphate, caustic, ethanolamine, methoxypropylamine and organic acids from amine decomposition could be present, so this is not straightforward. For FAC control in the Medium Pressure boiler water, chemical conditioning with tri-sodium phosphate to achieve a target concentration of 3-6 mg/l as PO4 would normally be recommended, which corresponds to a boiler water pH of 9.5-9.8 and a Specific Conductivity of 15-30 μS/cm. However, these targets may not be appropriate for the current chemical blends.

For the High Pressure boiler water, a pH target of 9.2-9.5 would be more appropriate.


In the past we have always gone by pH, if it goes out of range we manually adjust to get the desired pH, but according to this specific conductivity is best used to control amine dosing.

Hope this helps.


Edited by -G-, 24 November 2016 - 11:17 AM.


#3 breizh

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Posted 24 November 2016 - 08:54 PM

Hi ,

 

https://www.gewater....dbook/index.jsp

 

Take a look at this handbook .

 

you should consider to talk to the Chemicals supplier for your boiler house , they are supposed to help you and provide technical assistance .

 

Breizh



#4 S.win

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Posted 28 November 2016 - 09:39 PM

Thank you all for your feedback. i will try to understand more of it. 

 

To -G-: in the power plant where i'm working, they're also basing their adjustments on the conductivity readings (both specific & cationic) especially the amine dosing and phosphate with additional residual phosphate reading. However i'm still looking for a guide as to the theoretical calculation of all chemical dosing system and later relate it to the adjustment done by basing only on the conductivity.

 

To breizh: thank you for the provided link. I've partly read it and i do hope i can find some useful infos which i can apply here in the operation and control of chemical dosing system.






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