I am carrying out biochemical methane potential tests in one litre reactors on organic waste streams and I am looking to convert the measured gas volumes into normal volumes i.e. at STP. Is the ideal gas equation (see below) the most suitable equation for this and if so what is the best way to measure the ambient pressure within the reactors (note using 1L duran bottles with two port caps as reactors). Can the temperature of the gas in the displacement bottle be assumed as room temperature?
Ideal gas equation:
Vo=(V.P.To)/(Po.T)
Where:
Vo=normal volume
V=measured volume
P=ambient pressure
To=normal temp
Po=normal pressure
T=ambient temperature of gas in displacement jar
The ideal gas equation is the right one. You can measure ambient pressure with specific instruments. Even if gas temperature can be slightly different, you can use ambient temperature.
This approach is incomplete. Your equation does not consider the effect of water vapor, which makes up about 5.5% of biogas volume at 35 C and 16% at 55 C. See the paper by Brian Richards et al. below for more details and equations. Or check out the stdVol() function in the biogas package (see link below). The function uses the following three equations (copied from the help file):
"First, the contribution of water vapor is removed and volume is corrected to the standard pressure:
vd = vm*(pm - pw)/ps
where vd = dry volume at standard pressure ps, vm = measured
volume at pressure pm, and pw = vapor pressure of water (all
pressures in Pa). Water vapor pressure pw is calculated from the
Antoine equation:
pw = rh*10^(11.20963 - 2354.731/(T + 7.559)))
where rh = relative humidity (‘rh’ above) and T = measurement
temperature (K, converted from ‘temp’ argument). In the second
step, the volume is adjusted for temperature.
vs = vd*Ts/T
where vs = standardised volume and Ts = standardisation
temperature (K, converted from ‘temp.std’ argument)."
With either these equations, those in the paper, or using the function itself you can calculate the effect of error in temperature or pressure. Ambient air pressure is measured at weather stations, but in general does not differ from 1 atm (101 kPa) by much.
https://cran.r-project.org/web/packages/biogas/index.html
Article Methods for kinetic analysis of methane fermentation in high...
The biogas normalization to standard P and T can be done according to:
VDI 4630, 2006. Fermentation of organic materials, Characterisation of Substrate,Sampling, Collection of Material Data, Fermentation Tests, VDI Gesellschaft Energietechnik.
DINUCCIO, E., BALSARI, P., GIOELLI, F. y MENARDO, S. 2010. Evaluation of the biogas productivity potential of some Italian agro-industrial biomasses. Bioresource Technology, vol. 101, no. 10, pp. 3780-3783. ISSN 09608524. DOI 10.1016/j.biortech.2009.12.113.
They porpouse an ecuation that also count the water vapour pressure.
Thanks for these posts - I am in this problem wth a data set right now and the papers linked here are invaluable!
- Badges
- Science topic
- Similar topics
- Instrumentation Engineering
- Instruments