Simulation of Condensation in Biogas containing Ammonia


  • Lars Erik Øi
  • Terje Bråthen
  • Jon Hovland



CO2, methane, water, biogas, phase envelope, Aspen HYSYS, Aspen Plus


Condensation in raw biogas during compression is a problem because the CO2 and water in the liquid phase is very corrosive. Raw biogas typically contains 60 mol-% methane, 40 mol-% CO2, is saturated with water and may contain contaminants as ammonia (NH3). In case of NH3, it is of interest whether it has influence on the dew point (condensation) temperature. The aim of this work is to calculate the dew point under different conditions using different equilibrium models. Phase envelopes showing the two-phase area are also calculated. For dry mixtures of methane and CO2 with up to 1 mol-% NH3 (a high value for biogas), the different models gave similar results. When the NH3 increased from 0 to 1 mol-%, the dew point temperature increased with approximately 3 K. When water was included, the amount of calculated NH3 dissolved in water varied considerably with the model. The electrolyte based models Sour PR, Sour SRK and Electrolyte NRTL did not calculate reasonable dew point temperatures, but the dissolved amounts of NH3 and CO2 were more reasonable using the electrolyte models compared to using PR or SRK. For biogas simulation including NH3, a simple equation of state as PR or SRK can be recommended to determine the dew point. If accurate composition of the condensed liquid is to be calculated, an electrolyte based model like Sour PR, Sour SRK or the Electrolyte NRTL is recommended.


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.

N. E. Ahmad, M. Mel and N. Sinaga. Design of Liquefaction Process of Biogas using Aspen HYSYS Simulation. Journal of Advanced Research in Biofuel and Bioenergy, 2:10-15, 2018.

API (American Petroleum Institute). A New Correlation of NH3, CO2 and H2S Volatility Data from Aqueous Sour Water Systems. EPA report 600/2-80-067, 1980.

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.

G. P. Ayers. Solubility of ammonia in water in the presence of atmospheric CO2. Tellus, 37B:35-40, 1985.

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.

T. Bråthen, L. E. Øi and J. Hovland. Simulation of Dew Points in Raw Biogas Using PR and SRK Equations of State. In Linköping Electronic Conference Proceedings SIMS 60, pp. 31-36, 2019. doi: 10.3384/ecp20170112.

T. Bråthen, L. E. Øi and J. Hovland. Simulation of condensation in Raw Biogas containing H2S. In Linköping Electronic Conference Proceedings SIMS 61, pp. 300-305, 2020.

V. Gudjonsdottir and C. I. Ferreira. Comparison of Models for Calculation of the Thermodynamic Properties of NH3-CO2-H2O Mixture. International Refrigeration and Air Conditioning Conference. Paper 1641 (2016).

J. Hovland. Compression of raw biogas – A feasibility study. Tel-Tek report 2217020-1, 2017. Available on

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

H. Jilvero, K. J. Jens, F. Normann, K. Andersson, M. Halstensen, D. Eimer and F. Johnsson. Equilibrium measurements of the NH3-CO2-H2O system – measurements and evaluation of vapor-liquid equilibrium data at low temperatures. Fluid Phase Equilibria, 385:237-247, 2015.

O. Kunz and W. Wagner. The GERG-2008 Wide-Range Equation of State for Natural Gases and Other Mixtures: An Expansion of GERG-2004. J. Chem. Eng. Data, 57:3032-3091, 2012.

F. Kurz, B. Rumpf and G. Maurer. Vapor-liquid-solid equilibria in the system NH3-CO2-H2O from around 310 to 470 K: New experimental data and modeling. Fluid Phase Equilibria, 104:261-275, 1995.

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 Phase. Energies, 10(2034):1-11, 2017. Doi:10.3390/en10122034.

J. Li, L. Wei and X. Li. Modeling of CO2-CH4-H2S-brine based on cubic EOS and fugacity-activity approach and their comparisons. Energy Procedia, 63:3598-3607, 2014.

J. Longhi. Phase equilibria in the system CO2-H2O I: New equilibrium relations at low temperatures. Geochimica et Cosmochimica Acta, 69(3): 529-539, 2005.

B. Nabgan, T.A.T. Abdullah, W. Nabgan, A. Ahmad, I. Saeh and K. Moghadamian. Process Simulation for Removing Impurities From Wastewater Using Sour Water 2-Strippers system via Aspen Hysys. Chem. Prod. Process Model, 11(4):315-321, 2016.

T. Neumann, M. Tho, I. H. Bell, E. Lemmon and R. Span. Fundamental Thermodynamic Models for Mixtures Containing Ammonia. Fluid Phase Equilibria, 511:112496, 2020.

D. Peng and D. B. Robinson. A New Two-Constant Equation of State. Industrial & Engineering Chemistry Fundamentals, 15(1):59-646, 1976.

L. Pellegrini. Biogas to liquefied biomethane via cryogenic upgrading technologies. Renewable Energy, 124:75-83, 2018.

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

H. Que and C.C. Chen. Thermodynamic Modeling of the NH3-CO2-H2O system with Electrolyte NRTL Model. Ind. Eng. Chem. Res., 50(19):11406-11421, 2011.

S. Skogestad. Experience in Norsk Hydro with cubic equations of state. Fluid Phase Equilibria, 67:179-188 1983.

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

L F. Sotoft, M. B. Pryds, A. K. Nielsen and B. Norddahl. Process Simulation of Ammonia Recovery from Biogas Digestate by Air Stripping with Reduced Chemical Consumption, 37:2465-2470, 2015.

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.

Y. Tan, W. Nookuea, H. Li, E. Thorin and J. Yan. Cryogenic technology for biogas upgrading combined with carbon capture – a review of systems and property impacts. Energy Procedia, 142:3741-3746, 2017.

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.

Z. Ziabakhsh-Ganji and H. Kooi. An Equation of State for thermodynamic equilibrium of gas mixtures and brines to allow simulation of the effects of impurities in subsurface CO2 storage. International Journal of Greenhouse Gas Control, 11(Supplement):S21-S34, 2012.

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

L. E. Øi. Removal of CO2 from exhaust gas. PhD Thesis, Telemark University College, Porsgrunn. (TUC 3: 2012)