McAvoy, Thomas J.Wang, Y.The relative disturbance gain (RDG) is a recently introduced index that can be used to assess control loop operability. It is applied to the problem of controlling composition at both ends of heat integrated towers. Using the RDG the ability of the towers to respond to set point changes, feed flow, feed composition and heat input upsets is assessed. A general approach to calculating the RDG is given.en-USTechnical Report