Thermodynamic Data to Support High-Temperature Syngas Quench Design: Vapor-Liquid Equilibrium Calculations
Allan H. Harvey
procedure has been developed, based on a dilute-solution model of the liquid phase and the rigorous virial expansion for the vapor phase, for modeling the vapor-liquid equilibrium between water and a synthesis gas consisting primarily of H2, CO, and CO2. Calculations of the vapor-liquid equilibrium have been performed at temperatures and pressures typical for a quench step in an IGCC power plant. The uncertainty in the calculated vapor-phase mole fraction of water is less than 0.01, and is primarily due to the omission of higher-order terms in the virial expansion. Other thermodynamic calculation methods were examined and compared to the more rigorous calculations. The ideal-gas assumption for the vapor phase seriously underestimates (by about 0.09 mole fraction at typical conditions) the water content of the equilibrium vapor. The Peng-Robinson equation performs much better, producing vapor-phase mole fractions of water that differ from the more rigorous results by amounts similar to the uncertainty in the virial approach.