Tank question: gas dissolved in solution adds to volume?

[Subystud]

Do gases dissolved in a liquid increase the volume of that liquid?

System:
The system considered in an 11,000 gallon tank. 10,000 gallons are liquid, 1,000 gallons are "headspace". Initially, the system is at neutral pressure. System is sealed and chemical is added (30 gal). System is regulated at 15 psig. Pressure generated is a function of reactions in the liquid phase. Negligible pressure rises due to addition of 30 gal. chemical. This is not a two-phase system. Gas is a NOx/CO2 mixture, liquid is an acidified wastewater sludge (pH = 2.0).

Assumptions:
- Ideal gas law applies
- Isothermal at 80F
- Henry's Law for gases dissolved in water applies without temperature compensation
- The balance component of gas is air (79% N2, 21%O2) - this overestimates the concentration of O2 because O2 reacts with NO.

Henry's law constants being used:

kH, O2 (mol/L) / atm 1.27E-03
kH, N2 (mol/L) / atm 6.30E-04
kH, CO2 (mol/L) / atm 3.46E-02
kH, CO (mol/L) / atm 2.00E-03
kH, NO (mol/L) / atm 1.80E-03
kH, NO2 (mol/L) / atm 2.43E-02
kH, N2O (mol/L) / atm 2.40E-02

Steady state gas phase concentrations:

Conc, CO2 ppmv 50,000
Conc, CO ppmv 658
Conc, NO ppmv 20,756
Conc, NO2 ppmv 8,813
Conc, N2O ppmv 493
Conc, N2 ppmv 726,231
Conc. O2 ppmv 193,049

In running the calculation, I get 246 SCF in gas and 163 SCF in liquid. Considering the pressure of the system, these comes to 123 ACF in gas and 81.5 ACF in liquid, which equates to 610 gal in the liquid phase.

IF the liquid level did rise 610 gal due to liquid phase reactions, then my new volume is 10,610 gal, with 390 gal of headspace. It would take some iteration, but approximately the system is now at 10,610 gal liq and 390 gal gas (the increase in liquid volume increases the volume of gas dissolved in solution, further adding to the liquid volume, but this is neglected).

Questions:
1. How valid is Henry's law assumption here? The liquid phase is not water - but sludge is often modeled as water. But what affect would a pH = 2 have on Henry's law?
2. Is my methodology correct for estimating the volume of gas in this system?

 

[bimr]

Yes, but the volume will not change appreciably because of the limited solubility.

 

[racookpe1978]

Physically, an "ordinary gas" above an ordinary liquid will be some 1/1000 less dense than the liquid.

So, if the gas dissolves into the liquid, there are 1000 liquid molecules originally, and 1001 after the gas dissolves into that volume. Thus, you would not expect much change in volume - though the difference could be measured. Perhaps.

On the other hand, acetylene "dissolves" into the gaps and spaces in the metal lattice in the acetylene tank, and the tank is considerably heavier when full than when empty. So, to the extreme, yes, the volume does go up as the gas molecules "push" their way in between the liquid molecules.

 

[chicopee]

It increase its volume and decreases its density. After all, an air lift pump works on that principle along with the rate of rise of the bubbles.