An indicator-based problem reduction scheme for coupled reactive transport models

A number of effective models have been developed for simulating chemical transport in porous media; however, when a reactive chemical problem comprises multiple species within a substantial domain for a long period of time, the computational cost can become prohibitively expensive. This issue is addressed here by proposing a new numerical procedure to reduce the number of transport equations to be solved. This new problem reduction scheme (PRS) uses a predictor-corrector approach, which ‘predicts’ the transport of a set of non-indicator species using results from a set of indicator species before ‘correcting’ the non-indicator concentrations using a mass balance error measure. The full chemical transport model is described along with an experimental validation. The PRS scheme is then presented together with an investigation, based on a 16 species reactive advective-diffusion problem, which determines the range of applicability of different orders of PRS. The results of a further study are presented in which a set of PRS simulations are compared with those from full model predictions. The application of the scheme to the intermediate-sized problems considered in the present study showed reductions of up to 82 % in CPU time with good levels of accuracy maintained