NOVELTY - An extruder (13) has first holes (18', 19', 20') having a working or pelletization zone of length equal to the effective length necessary for the formation of pellets, once the feeding material has necessary humidity; and second holes (18'', 19'', 20'') having a length lower than effective length, from second holes exiting partially or fully dehydrated, but not thickened incoherent material.    USE - Used for a pelletization device (claimed), used in humid biomass production, or for the treatment of wastes and mud produced in municipal and industrial depuration systems, and in the packaging of food products, particularly animal foodstuffs.    ADVANTAGE - The extruder allows the feeding of raw material to the pelletization device having a humidity content higher than presently allowed (10-15 wt.%) to feed the raw material to the extruder. It allows reduction of the temperature reached within the extruder. It obtains the lowering of extrusion temperature and increased in productivity of the extruder.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a system for the pelletization of incoherent material comprising a pelletization device having the above extruder, in which downstream of the pelletization device is a sieve separating still incoherent material from pellets, a recirculation mechanism for the still incoherent material toward the pelletization device, and a mechanism to transfer the pellets material towards further working steps; and    (2) the production of pellets, by the extrusion system, comprising feeding material to be subjected to treatment to a pelletization device provided with the extruder; extruding the material through holes having different length; sieving the product exiting from the extruder, dividing the dehydrated but not thickened material from the pellets; recirculating the dehydrated material to preceding extrusion step; reintegrating the recirculation material with new material to be subjected to treatment; and sending the pellets obtained from the sieving step to following working steps.    DESCRIPTION OF DRAWING(S) - The invention shows the extruder applied to a pelletization device.    Extruder (13)    First holes (18', 19', 20')    Second holes (18'', 19'', 20'')