1. A simulation system for use in simulating the operation of a portion of an operating process plant communicatively coupled to the simulation system, the operating process plant including one or more process controllers communicatively coupled to one or more field devices processing physical materials to produce a product, the simulation system stored as instructions on a non-transitory computer-readable medium, the simulation system comprising: one or more simulation blocks configured to perform simulation of one or more pieces of equipment within the operating process plant, each simulation block including: a process model that models a portion of the operating process plant; and a simulation unit that uses the process model to simulate the operation of the portion of the operating process plant to produce a simulated output for an on-line process element associated with the portion of the operating process plant, the simulated output including one or more predicted future values for the on-line process element; and a control module communicatively coupled to the one or more simulation blocks and configured to control an online activity of the operating process plant using an actual value of the on-line process element; wherein at least one of the simulation blocks includes an input from the operating process plant configured to accept an indication, transmitted from the operating process plant, of the actual value of the on-line process element measured in a control loop of the operating process plant and corresponding to the simulated output for the on-line process element, wherein the actual value of the on-line process element and the simulated output for the on-line process element are compared to calculate a compensation factor to be applied to an output of the process model to produce a modified simulated output reflecting a non-modeled change in the operating process plant and wherein the control module is configured to automatically replace the actual value with the simulated output for the on-line process element when the actual value is known to be faulty or has a bad status, the simulated output being generated by the simulation system.