Consider Example 13-1, where 40% ethanol (stream 1) is being blended with pure water (stream 2) to produce a product of 30% ethanol. Here we wish to use the RGA to help us develop the control structure (pair inputs and outputs).
We first develop the steady-state model, then linearize to find the process gain matrix, and finally calculate the RGA to decide on variable pairing. For simplicity we neglect density differences between the streams and components.
Neglecting density differences between the streams and components, the total blend product volumetric flow rate is equal the sum of the volumetric flow rates of the two feed streams,