Measurement techniques that with sufficiently high resolution describe the fibre distribution in refining zones.
Development of sensor technologies, mathematical models and control strategies are crucial for the accomplishment of improved energy efficiency in refining processes. Sensors installed inside the refining zone have the potential of revealing previously hidden process information. Such information can be used for studies of dynamic process phenomena and the results can be incorporated into mathematical models. Thereafter, new refining control strategies can be formulated and the goal of improved energy efficiency will be within reach.
Consequently, considering new sensor technologies is the first step and for the application in question the area offers true challenges. Refining is known to be a complex, multivariable, time-varying process that is subjected to a lot of disturbances and the environment in the refining zone is indeed hostile. In addition to these motivating challenges, the results obtained from measurement projects have the thrilling potential of reforming the knowledge of the process fundamentals.
The purpose of this project is to develop measurement techniques that with sufficiently high resolution describe the fiber distribution in refining zones. The project is carried out at Chalmers under supervising by experienced researchers at Chalmers Industriteknik (CIT) and in cooperation with a supervising group including representatives from the participating companies.
A pre-study was performed with the purpose to investigate whether small lasers and photo sensors can be used to obtain information about the fiber distribution inside refining zones. Pulp samples were subjected to light of different wavelengths and an interval of constant transmittance was identified.
The results also show that as the density of the pulp sample increases, the intensity of the transmitted light decreases. Thereby it is reasonable that assume that, at a well chosen wavelength, the light extinction can be used as a measure of the pulp density.
The configuration of the measurement equipment is illustrated in the figure below. Each sensor should include fibers for illumination as well as detection. The light is injected on the stator side. It passes the refiner gap and is reflected on the rotor side. It passes through the refiner gap again and then the remaining light is detected on the stator side. The fact that the light passes the gap twice implies that a high power light source is needed. However, with a light source that can meet the demands, it will be possible to study process variations in the rotational direction. Result from such measurement would allow investigation of the commonly considered assumption that the refining process is rotationally symmetric.
By the installation of sensors at different radial positions, as illustrated in the figure, the relative pulp distribution can be studied. Furthermore, as a complement to the light extinction measurements, sensors for pressure measurements are considered. The combination of these sensor technologies is believed to give interesting insight into how the pulp material is distributed inside the refining zone.