Dynamic simulation with an equation based flowsheeting system

The ASCENT-II dynamic simulation system is described. Differential equations, integral equations and retarded equations are treated by universal mathematical units which can be used to form the unit modules. The equation solving method employed permits the degrees of freedom in a flowsheet to be changed almost arbitrarily, allowing simulation and design to be done simultaneously. Decision variables specified as trajectories are handled cleanly and neatly. The tear variable concepts is introduced in order to reduce computation time in the numerical integration of differential-algebraic systems. A method is developed to treat the integration step-size as a variable to be calculated such that the integration error criteria is automatically satisfied at each step of numerical integration. The spline collocation method is studied within the context of flowsheeting and is found to be a suitable global approximation method.