Intensity of Refining
The traditional way of characterizing the process of refining was through net Specific Refining Energy (SRE), calculated as the useful energy imparted to the stock after allowing for the no load energy needed to run the refiner. This is still commonly used today; the units are kWh/tonne or kWs/kg or hpdays/tonne.
[ 1 kWh/tonne = 3.6GWs/kg = 17.9 hpday/ton ]
Several theories of refining have been developed over the years in an effort to better understand the process by which energy is applied to the actual fibre and to better control the process. Some of these theories focus on the work being done by the refiner itself, while others consider what happens at the level of the individual fibres. An example of the former approach is the Specific Edge Load (SEL). This idea of refining intensity was introduced by Wultsch & Flucher (1)and developed further by Brecht and Siewert(2). The idea is to apply the SRE term (calculated as above) to the number of bar crossings within the refiner. The result is expressed in Ws/m or J/m. A refinement of the SEL approach, Specific Surface Load (SSL), was suggested by Lumiainen in 1990(3). This approach considers not just the length of the bar edges, but also the area of the bars, its units are Ws/m2 or J/m2.