Simulation of Dew Points in Raw Biogas Using PR and SRK Equations of State

Terje Bråthen
Department of and Process, Energy and Environmental Technology, University of South-Eastern Norway, Norway

Lars Erik Øi
Department of and Process, Energy and Environmental Technology, University of South-Eastern Norway, Norway

Jon Hovland
SINTEF Tel-Tek, SINTEF Industry, Porsgrunn, Norway

Ladda ner artikelhttps://doi.org/10.3384/ecp20170112

Ingår i: Proceedings of The 60th SIMS Conference on Simulation and Modelling SIMS 2019, August 12-16, Västerås, Sweden

Linköping Electronic Conference Proceedings 170:17, s. 112-117

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Publicerad: 2020-01-24

ISBN: 978-91-7929-897-5

ISSN: 1650-3686 (tryckt), 1650-3740 (online)


Biogas contains mainly methane, but raw biogas can contain large amounts of CO2 and is normally saturated with water. Condensation, especially during compression, may lead to operational problems. The aim of this work is to calculate the dew point (condensation limit) under different conditions with different models in the simulation programs Aspen HYSYS and Aspen Plus. Binary coefficients for water and CO2 in these models will be fitted to experimental data from the literature. Traditionally, gas mixtures of methane, CO2 and water are calculated with standard models like Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK). For dry biogas (mixtures with only methane and CO2) all the models give similar results. For a biogas mixture with 60 mol-% methane and 40 mol-% CO2 with 0.1 mol-% added water, the models using binary coefficients fitted for binary mixtures (especially for CO2 and water), gave reasonable results up to about 70 bar, with deviations in the calculated dew point up to 8 K. The binary coefficient for water and CO2 was fitted to experimental data from the literature for a mixture with a CH4 to CO2 molar ratio of 30/70, 50/50 and 70/30. The fitted kij values for the PR model were 0.65, 0.21 and 0.17, respectively. For the SRK model, the kij values were slightly higher. At pressures below 70 bar and temperatures below 40 °C, the uncertainty for calculated dew-points in mixtures with 30 to 100 % CH4 was reduced to less than 4 K.


CO<sub>2</sub>, methane, water, biogas, phase envelope, Aspen HYSYS, Aspen Plus


A. Aasen, M. Hammer, G. Skaugen, J. P. Jakobsen, and Ø. Wilhelmsen. Thermodynamic models to accurately describe the PVTxy-behaviour of water/carbon dioxide mixtures,  Fluid Phase Equilibria,  442:125-139, 2017.

S. Z. S. Al Ghafri, E. Forte, G. C. Maitland, J.J. Rodriguez-Henriquez, and J. P. M. Trusler. Experimental and Modeling Study of the Phase Behaviour of (Methane + CO2 + Water) Mixtures.  Journal of Physical Chemistry, 118:14462-14478, 2014.

A. Austegard, E. Solbraa, G. de Koeijer, and M. J. Mølnvik.  Thermodynamic models for calculating mutual solubilities in H2O-CO2-CH4 mixtures. Trans IChemE, Part A, Chem. Eng. Res. Des., 84(A9):781-7946, 2006.

Y. Bi, T. Yang and K. Guo. Determination of the upper quadruple phase equilibrium region for carbon dioxide and methane mixed gas hydrates.  Journal of Petroleum Science and Engineering, 101:62-67, 2013.

A. Chapoy, R. Burgass, A. Terrigeol, and C. Coquelet. Water Content of CH4 rich Mixtures: Measurements and Modeling using the Cubic-Plus-Association Equation of State. Journal of Natural Gas Engineering, 1(13):85-97, 2016.

A. Dhima, J. de Hemptinne and J. Jose. Solubility of Hydrocarbons and CO Mixtures in Water under High Pressure. Ind. Eng. Chem. Res., 38:3144-3169, 1999.

J. Hovland. Compression of raw biogas – A feasibility study. Tel-Tek report 2217020-1, 2017. Available on https://www.biogas2020.se/wp-content/uploads/2017/06/2217020-1compressionrawbiogas.pdf

M. J. Huron and J. Vidal. New mixing rules in simple equations of state for representing vapour-liquid equilibria of strongly non-ideal mixtures. Fluid Phase Equilibria, 3:255-271, 1979.

C. Jarne, S. T. Blanco, M. A. Gallardo, E. Rauzi, S. Otin, and I. Valesco. Dew Points of Ternary Methane (or Ethane) + Carcon Dioxide + Water Mixtures: Measurements and Correlation. Energy & Fuels, 18:396-404, 2004.

L. N. Legoix, L. Ruffine, J. P. Donval, and M. Haeckel. Phase Equilibria of the CH4-CO2 Binary and the CH4-CO2-H2O Ternary Mixtures in the Presence of a CO2-Rich Liquid hase. Energies, 10(2034):1-11, 2017. Doi:10.3390/en10122034.

J. Longhi. Phase equilibria in the system CO2-H2O I: New equilibrium relations at low temperatures. Geochimica et Cosmochimica Acta, 69, No. 3: 529-539, 2005.

D. Peng and D. B. Robinson. A New Two-Constant Equation of State. Ind. Eng. Chem. Fundam., 15(1):59-646, 1976.

R. Privat and J. N. Jaubert, Predicting the Phase Equilibria of Carbon Dioxide Containing Mixtures Involved in CCS Processes Using the PPR78 Model. InTech, 2014. Available on http://dx.doi.org/10.5772/57058.

J. Qin, R. J. Rosenbauer, and Z. Duan. Experimental Measurements of Vapor-Liquid Equilibria of the H2O + CO2 + CH4 Ternary System. Journal of Chemical Engineering Data, 53:1246-1249, 2008.

G. Soave. Equilibrium constants from a modified RedlichKwong equation of state. Chemical Engineering Science, 27:1197-1203, 1972. 

K. Y. Song and R. Kobayashi. The water content of a CO2-rich gas mixture containing 5.31 mol% methane along three-phase and super-critical conditions. Journal of Chemical Engineering Data, 35(3):320-322, 1990.

N. Spycher, K. Pruess, and J. Ennis-King. CO2-H2O mixtures in the geological sequestration of CO2. I. Assessment and calculation of mutual solubilities from 12 to 100 ºC and up to 600 bar. Geochimica et Cosmochimica Acta, 67 (16):3015-3031, 2003.

R. Stryjek and J. H. Vera. PRSV – An Improved Peng-Robinson Equation of State with New Mixing Rules for Strongly Nonideal Mixtures. The Canadian Journal of Chemical Engineering, 64:334-340, 1986.

C. H. Twu, D. Bluck, J. R. Cunningham, and J. E. Coon. A Cubic Equation of State with a New Alpha Function and a New Mixing Rule. Fluid Phase Equilibria, 69:33-50, 1991.

L. E. Øi and J. Hovland. Simulation of Condensation in Compressed Raw Biogas Using Aspen HYSYS. In Linköping Electronic Conference Proceedings SIMS 59, pages 31-36, 2018. doi: 10.3384/ecp1815331

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