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

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

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

(OP)
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?

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

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.

=====================================
(2B)+(2B)' ?

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

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.

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

(OP)
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.

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

May be carbonic acid as a guess.

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

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.

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

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).

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

In a sterile environment, steam should be quite pure: http://pro-analitika.hu/characteristics_of_deioniz...

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.

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

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

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

(OP)
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.

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

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_syste...

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

(OP)
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!

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

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

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

To IRstuff,

It appears (from the net) that at 20oC, 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. smile2

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

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.

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



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

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

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

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

@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.

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

If you are using organic oxygen scavengers or organic amines then they ultimately breakdown into CO2 , which forms carbonic acid in the pre-condensate film on the condenser tubes.

The chemicals added in the DA have to end up somewhere- what goes in must go out. As the feedwater enters the steam drum some chemicals remain in the boiler water and are blown down to the flash tank via the continuous blowdown line. The high iron content of the boiler water acts as a catalyst to breakdown some of the chemicals The fraction that passes into the steam phase are sometimes thermally cracked in the superheater ( espescially in duct fired HRSG's) and CO2 and hydrocarbons are the end result.

Once the steam finalyy arrives at the condenser , there occurs another split of chemicals- some passes to the precondensate ddroplets , and some chemical amines escape with the noncondensibles to the SJAE or vacuum pump vent. The CO2 forms carbonic acid, and the pH at teh interface between setam and pre-condensate has a lower pH - this leads to FAC of the ACC CS tubes. See papers by Barry Dooley on this issue.

"Whom the gods would destroy, they first make mad "

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

MortenA

I never insinuated that the pH level of carbonated drinks is due to CO2. BTW, a variety of acids are used beside citric.
BTW you dropped a cero.

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

I worked in a plant where we used weak acid cation dealkalizers ahead of the water softeners, for boiler make-up.

Naturally occurring bicarbonate alkalinity in boiler make-up water breaks down into CO2 under boiler conditions. This CO2 is carried out of the boiler harmlessly - until the steam condenses. The CO2 dissolves in the condensate, resulting in a pH of about the same as soda pop.

The requirement for dealkalizers, and whether they are installed before or after the softeners is totally dependent upon local water conditions.

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