1. An apparatus for use with a process controller, the apparatus comprising at least one processing device configured to implement: an equation editor configured to receive balance equations describing a chemical process to be controlled by the process controller using a model and to generate model information representing the balance equations; a model factory configured to receive the model information from the equation editor and generate an equation stack using the model information, the equation stack representing the balance equations; an equation evaluation engine configured to receive evaluation information from the process controller, evaluate at least one of the balance equations using the evaluation information and the equation stack, and provide an output of the evaluation; and a linearizer configured to (i) receive states and inputs of the model from the process controller, estimated parameters of the model, and equations evaluated for the states and inputs of the model from the equation evaluation engine, (ii) generate a linearized model by linearizing non-linear equations in the evaluated equations based on the states and inputs, the estimated parameters, and the output from the equation evaluation engine, and (iii) provide the linearized model to the process controller in order to control the process.