Why the steam lowers the pH in the process of expansion in turbine equipment? 1

[Espcex92]

Why the steam lowers the pH in the process of expansion in turbine equipment? Could someone show me some literature that best explains this phenomenon?

 

[electricpete]

I never heard anything about expansion affecting ph.

There may be volatile additives which maintain basic condensate/feed system ph and are carried through the entire loop - boiler to condensate and feed and back to boiler.

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(2B)+(2B)' ?

 

[hacksaw]

there are no measurements for steam pH so assuming for the moment you are describing some point in the condensate return system, just where are you taking the condensate sample and what is the sample temperature.

you also need to be specific regarding the the boiler pressure and the sort of water treatment program you have in place.

 

[Espcex92]

Where, I worked the last year, after being expanded in the turbine condensing, the superheated steam's condensate generates a pH of about 3 and to be reused in the process needs to have its pH adjusted to about 8. This is done with the use of amine (usually morpholine). I would like to understand what explains this decrease in pH of the condensate in the expansion of the steam in the turbine.

 

[chicopee]

May be carbonic acid as a guess.

 

[macmet]

Is it possible you're seeing the pH change across the boiler and not the steam turbine?

If so, you could precipitate components of the feedwater when the water boils, which could be seen as deposit on the surface of the boiler tubes.

 

[btrueblood]

Is the condensate being used to scrub the exhaust? Dunno how else you'd get enough exposure to CO2 (which wouldn't explain a pH of 3) or other acid compounds (NOx, SOx).

 

[IRstuff]

In a sterile environment, steam should be quite pure:

http://pro-analitika.hu/characteristics_of_deionized_water.pdf

That said, typical condensation systems are not exactly designed to produce pure water, and may contain biologicals as well as inorganic contaminants. A pH of 3, which is pretty acidic, would suggest a fairly substantial contamination with ions.

TTFN
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[EdStainless]

Or it could be an artifact of the measurement.
Most pH probes are better thermometers than they are selective ion measuring tools.
The temperature compensation setting on the meter does not compensate for what is happening in the sample or probe, only the meter.
Between temp errors and the volatilizing of the amine I can see a downward shift.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Espcex92]

I don't know what's happening exactly, but the reduction of the pH in expansion of the turbine is a fact! No doubt about it!Perhaps a physical-chemical phenomenon? Perhaps an imbalance of ions H+ caused by the expansion of the steam turbine?
Contamination with ions or error read's interpretation of the pH probes? I'm not sure about that! Actually, I don't believe that! I still believe on phenomenon physical-chemical.

 

[IRstuff]

Steam is steam; there's nothing physically you can do to pure water to change its pH

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[25362]

Chicopee's assumption is apparently correct. Carbon dioxide is a normal by-product of the breakdown of boiler water alkalinity, and occurs in most boilers to varying degrees.
A link on this subject:

http://www.gewater.com/handbook/boiler_water_systems/ch_19_Condensate.jsp

 

[IRstuff]

Sure, but the equilibrium pH of carbonic acid is not particularly close to pH=3

http://ion.chem.usu.edu/~sbialkow/Classes/3600/Overheads/Carbonate/CO2.html

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[Espcex92]

IRstuff,

Do you already heard about: Kp = equilibrium constant in terms of partial pressure and its relationship with Kc = equilibrium constant in terms of concentration? { Kp = Kc.(RT)^n} ... Then, I think it can explain what I'm telling!

 

[btrueblood]

I like Ed's explanation best. Esp, were you checking the pH of a near-room temperature sample?

 

[25362]

To IRstuff,

It appears (from the net) that at 20^oC, equilibrium shows:

for 0.056 mol CO₂/L ==> pH = 3.81,
a value decreasing with higher CO₂ concentrations.

These pH levels, and lower, are found in drinks such as Coke, Sprite, Pepsi, Dr Pepper, 7 Up, RC Cola, etc.

 

[25362]

Let's not forget the mentioned link speaks about atmospheric CO₂, with a concentration quite different from that expected in the water of a turbine condenser.

 

[hacksaw]

fantastic response given the incomplete description of the problem actually being encountered, pretty soon we can add solar neutrinos and global warming!

 

[chicopee]

Any aspect not discussed is if the boiler had undergone an acid treatment prior to the test?

 

[MortenA]

@25362, true but at atm conditions you dont get 0.56 mol CO2/l. Softdrinks have low pH due to eg citric and other acids acid being added.