Dew Points of Hot Gases from Coal-Gasification Processes. Final Report

摘要

Effluent gases from coal-gasification processes often contain high-molecular-weight hydrocarbons (tars) which, upon condensation, may foul heat exchangers needed to recover sensible heat. Efficient design of heat exchangers and separation equipment for the removal of tars requires information about the phase-equilibrium behavior of these systems. A computer program has been written to predict dew points and condensation-versus-temperature behavior of gasifier effluents containing coal tars. Predictions have been tested using experimentally determined dew points for methane/water/Lurgi coal-tar fraction mixtures. The comparisons are generally good. Calculation of tar properties is based on a tar-characterization procedure where vacuum distillation, at high reflux, is used to produce narrow-boiling fractions. Each fraction is treated as a pseudo component; its properties are based on the vapor-pressure datum obtained during fractionation, on the results of elemental analysis, and on the proton NMR spectrum of the fraction. Calculation of vapor-phase properties are based on the virial equation of state with second coefficients calculated using the square-well potential. Calculation of liquid-phase properties are based on Henry's constants for the light gases and on standard-state fugacities (vapor pressures) for the tar fractions. To establish and verify our vapor-pressure correlation (SWAP), measurements were made of vapor pressures for seven heavy hydrocarbons; four heavy, nitrogen-containing hydrocarbons derivatives; and four sulfur-containing hydrocarbon derivatives. If water is present, it is assumed to condense as a pure liquid. (ERA citation 07:045516)