Effect of vapor liquid equilibrium on product quality and yield in oil shale pyrolysis

Separation of the products from the reacting organic matter is necessary to ensure product quality and reduce oil degradation to solid reside (coke) when considering conversion of oil shale to oil by in-situ processes. Many effects on yield and quality due to operational conditions may be explained by considering their role in volatilization. A five-reaction network with vapor-liquid equilibrium has been created in MATLAB to examine the effect of heating rate and pressure on volatilization. The model uses the Peng-Robinson equation of state, phase stability using the Gibbs tangent plane criterion, and Rachford-Rice flash calculations. Component compositions may be changed with automatically adjusting stoichiometry and species properties. A new feature is that dew and bubble point pressure calculations are performed at each calculation-step and plotted to show the phase behavior of the changing product composition with conversion. Product expulsion is represented as a mass fraction of generated vapor. The results indicate that for 10 degrees C/min and atmospheric pressure, 50% removal is enough to obtain a liquid yield that is 97% (977 mg/g TOC) of the maximum yield with 95% removal. The operational conditions with the lowest oil yield (127 mg/g TOC) are 0.001 degrees C/min and 500 psi with 5% vapor removed. Additionally, changing from high to low fractions of removed vapor move the maximum light oil yield from low pressure and low heating rate to high pressure and high heating rate.