Investigation of strategies for executing sequential modular simulations

Abstract

Alternative strategies for solving constrained and unconstrained steady state flowsheet problems using a sequential modular simulation system are studied. Test results obtained using six flowsheet problems of varying degree of nonlinearity indicate that the direct application of Broyden's method and of a successive linearization approach are closely competitive. Use of the identify matrix to initialize Broyden's method and a simple step size control strategy proved preferable to perturbation based approximations. Diagonal approximations are desirable in initializing the constraint equation contributions to the composite Jacobian. Simple separator/stoichiometric reaction linear models also were found to be preferable to more elaborate perturbation based linearized models. Because of the overheads associated with solving the linearized flowsheet model, the linearization strategy appears worthwile primarily for CPU time intensive simulations. All tests in this study were performed using the LSP flowsheeting system. The linearized subproblems were solved using the LINBAL package.