An indutrial case is the desig and implementation of a feed -forward control system for a four -stage falling film evaporator with thermal vapour recompression .This control system contains a feed-forward compensation for the dry matter cotent of the feed to the evaporator (e.g.by measuring the density of milk using an in-line sensor), a feed-forward compensation for floe tp the evaporator and a feed-back control system using the measure desity (in-line sensor)of the concentrate ,The dry matter content of the steam supply to the ecaporator . In Figure 8 a schematic presentation of this feed-forward control system is given ,illustrating how a variation in input (dry matter content of the oncentrate) or set-point of the dry matter contnt of the concentrate will affect the steam supply to evaporator .Based on step-response measurement,the specific control algorithm is designed and implemented in the existing programmable logic controller(PLC) of the evaporator.

This new feed-forward control system has decreased the standard deviation in the dry matter content of the concentrate from 0.31%to 0.19%(m.m¹).Compared to a simple aontrol system ,It is now possible to increase the set-point of the dry matter content of the concentrate by at least 0.7%(m.m¹),reasulting in an annual energy saving of 10,000 Euros based on a nominal capacity of 30m³milk per hour .The capacity of the evaporator can now easily be adjust to the capacity of the spray dryer without large variations in dr matter content ,It is estimated that as a result of this ,the set-point for the moisture content of powder can also be increased by about 0.07%,which will reasult in an annual energy saving of 50,000 Euros.