Operating temperature of Hydrotreating and Hydrocracking units, is between the range of design Start of Run and End of Run temperatures.
Start of Run (SOR) means the minimum design temperature when the catalyst is fresh or newly commissioned.
End of Run (EOR) means the maximum design temperature when the catalyst has been exhausted and has completed its life. End of run (EOR) is the point when the catalyst cannot meet one or more required product properties at typical throughput.
Soon after the commissioning, the average temperature (normally called as WABT i.e. Weight Average Temperature) of the diesel hydrotreating or hydrocracker unit should be at design start of run. But normally the average temperature remains below the SOR due to high activity of the catalyst, lower Sulfur in the feed or less severe feed than the design.
Further, when we operate below the SOR temperature then it should be avoided to go below the minimum design temperature due to Hydro-Demetallationn (or metals removal from the feed, Organometallics are converted to their respective metal sulfides).