Plantwide inventories of main components and impurities in a complex plant are sharply affected by interactions between recycles which, in general, are not desirable. However, this paper demonstrates how the interactions between some recycle loops may be exploited to create feasible plantwide control structures that are impossible to achieve simultaneously with stand-alone units. Thus, flowsheet architecture, equipment design and control system design must be interrelated. Simultaneous design is necessary for items involved in plantwide control structures. The paper presents a simulation based methodology for evaluating the effect of recycle interactions on dynamics and plantwide control of complex plants. Steady-state and dynamic simulations are combined with controllability analysis, both in steady state and in dynamic mode. A case study handling the removal of impurities in a plant with nested loops illustrates the approach. The controllability of two flowsheet alternatives is evaluated. The steady-state analysis is confirmed at low frequencies. Possible difficulties may occur at higher frequencies, where the period of disturbances and the time constants of the distillation columns are of the same order of magnitude. The relative direction of disturbances plays a significant role. Closed loop simulation validates the main trends of the controllability analysis, showing in the same time the difficulty in managing a perfect multivariable control of the material balance.