An approach to the design of process experiments is presented for the
situation where there is a large number of potentially adjustable proc
ess variables, and where these variables are coupled due to process op
erating constraints. Some variations of the partial least squares (PLS
) algorithm called 'selective PLS' are introduced. These algorithms al
low one to combine information in past process data with current knowl
edge of the process, and thereby to separate the variables into a smal
l number of orthogonal groups that form the basis for experimental des
igns and process optimization. The concepts are illustrated using data
from an industrial mineral flotation circuit used to concentrate valu
able minerals from an ore.