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bicarbonates, which in the combined form, do not exist as gases. At any given pH value,
the amounts of bicarbonate, versus free carbon dioxide present, form an equilibrium.
When any two of the three mentioned parameters are known, (namely pH, quantity of
bicarbonate, quantity of free carbon dioxide), the third may be calculated.
The fact that severe corrosion occurs in oxygen-free condensate return piping
substantiates that carbon dioxide is corrosive it is also an accelerating factor in dissolved
oxygen corrosion.
2.0 PHYSICAL LAWS
The laws associated with gas removal are presented here to better understand the
principles of deaeration and degasification. These apply not to only deaerator, but to all
forms of mechanical gas removal.
2.1 Boyle’s Law
The pressure of gas is inversely proportional to its volume when the quantity and
temperature remains constant.
2.2 Dalton’s Law
The total pressure of a mixture of gases is equal to the sum of the pressures which each
gas would exert if it occupied the same volume as the mixture. The total pressure of a
gas mixture is the sum of partial pressures of the individual components (PT = P1 + P2 +
P3 . .). For example: in a mixture of 75% oxygen and 25% carbon dioxide at 100 psi total
pressure, the partial pressure of oxygen would be 75 psi and carbon dioxide 25 psi.
2.3 Henry’s Law
The quantity of gas dissolved in a liquid is directly proportional to the pressure of gas
upon the liquid, at any given liquid temperature. This applies to the individual
components of a gaseous mixture as well as a single gas. The concentration of each
component, therefore, is proportional to its own partial pressure, and not the total
pressure: for example, if a quantity of a gas is dissolved in a volume of liquid at 50 psi
pressure, twice as much will be dissolved if the pressure is double.
2.4 Summary
The solubility of a gas in a liquid decreases as the temperature of the liquid increases.
When the liquid reaches its saturation temperature, all uncombined gases are
theoretically insoluble, and may be removed.
Certain gases (carbon dioxide, hydrogen sulfide, and ammonia) particularly react and
combine with ions in the liquid. To effect their more complete removal, adjustment in
pH may be necessary. It is clear that a gas can be removed from water by reducing the
partial pressure of that gas in the surrounding atmosphere, regardless of the total
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