We can conclude that drying on a drum dryer takes place as a boiling phenomenon
mechanism; consequently, an infrared temperature sensor can be used as a local
moisture sensor for the dried product (Xf. This measurement works with a thin film, without contact, is precise and quite cheap compared to other methods. It can
be used to detect moisture unevenness and location of wet zones in real time, and
eventually to detect anomalies such as absence of product on the dryer.
The feasibility of unevenness correction of Xf has been demonstrated, using a
complementary heating source, i.e. an inductive heater. It increases the drum dryer
productivity, by avoiding over-drying which is the conventional way to overcome
unevenness in industry. Of course for adequate control, the power of the additional
local heating should be related to the moisture unevenness and to the drum size. It
should be taken into account that the controlled electrical power is partially used for
increasing the moisture evaporation rate.
The next step is to include the above sensor and actuator in a control loop in
order to adjust the local additional power to the objective in moisture content. In
fact, the industrial control can combine several actuators - steam pressure @v),
rotation speed (Vrc) and local induction heating (Pind) - with specific dynamics and
nonlinear response, which is a more complex strategy. This will be the subject of
part 2 of this paper.