Process tomography is a sensing technique that can be used to measure distributed flows inside pipes. As a result, it is suitable for use as the sensor in a feedback control system for regulating the concentration of a substance in a fluid flow along the pipe. This paper describes such a control system and starts by developing a model based on the convection-diffusion equation, which describes the diffusion of a substance within the fluid flow, and then develops a state space description of the system. The state space model is used as the basis of a state feedback design. Estimates of the states are obtained from an observer that uses the measurements obtained by the tomographic sensor. A simulation of a feedback system based upon proportional plus integral control is presented.