fig1 illustrates a state - of - the - art drying plant , where pre - dewatered sludge 1 is fed to a container 2 , from which it is fed via a feed screw 3 , which is driven by an adjustable motor 4 , is brought to a mixer 5 and goes from there through a further mixing and conveying screw 5 ′ for example , into the dryer 6 . as used herein , “ wet sludge ” encompasses liquid and dewatered sludge . besides the triple - pass drum dryer shown , it would also be possible to use a fluidised bed , belt , or disc dryer . the dried material is carried by the drying air supplied through a duct 7 to a separator 8 and then passed on through a rotary vane feeder 10 to a screw conveyor 11 . the fine solids particles that are left in the air after the pre - separator 8 are removed in a subsequent filter 9 and also fed to the screw conveyor 11 . the screw conveyor is designed as a cooling screw in order to maintain the temperatures allowed for storage in the carrier material silo 18 . the solids in the form of granulate are then fed through a lock 12 to a screening plant 13 , where oversized grains are brought to a crusher 14 and the granulate with the designated size is conveyed through a duct 15 to packing and transport equipment . as an option , part of the grain with the designated size can also be fed to the crusher . the material milled in the crusher 14 is mixed with the very fine solids from the screen 13 and then brought to a carrier material silo 18 by a screw conveyor 16 followed by a vertical bucket conveyor 17 . from here , the carrier material is fed to the mixer 5 through a carrier material feed screw 19 , which is driven by a speed - adjustable motor 20 . the energy for the drying process is generated according to fig1 using a burner 21 , which yields its heat to the circulating air in a heat exchanger 22 . some of the exhaust gas from the burner is returned to the burner though a duct 24 by means of a fan 23 or is brought through a duct 25 to the exhaust gas chimney stack 26 and then discharged into the atmosphere . the circulating air heated in the heat exchanger 22 is fed to the dryer 6 through the duct 27 . as an alternative , the exhaust gas from the burner can also be fed directly to the dryer 6 . the drying air is conveyed by a fan 28 located after the filter 9 . this also guarantees that there is a vacuum in that part of the air system where material is conveyed , thus no dust can be released into the atmosphere . after the fan 28 , the hot air charged with moisture is brought to a scrubber / condenser 29 , where cooling water is injected . after this , the air that has now been cooled and dried is brought through a duct 30 to the heat exchanger again and thus , is re - used . a partial air current is brought from the scrubber 29 through a duct 31 to the burner for incineration . fig2 now shows a system according to the invention , where the same elements are marked with the same references . in contrast to fig1 , this illustration shows a system where the exhaust gas from the burner is fed directly to the dryer , which can also use an indirect heating system ( with heat exchanger ). the liquid sludge 1 is also dried here in a dryer 6 after being mixed with sludge that has already been dried . the dried material is separated from the drying gas in a separator 8 . the illustration shows a storage section 32 of the separator 8 , where the dried , granulated material is stored . part of it is fed as final product through a discharge screw 33 to the rotary vane feeder 12 and then brought through duct 15 to the packing and transport devices . thanks to the special arrangement of the discharge screw 33 , whereby the effective flow rate of the final product can be modulated ( e . g ., by simple on / off or by variable rotation speed of the screw , as described above with respect to feed screw 19 with associated variable speed motor 20 ) the filling level in the container 32 is controlled . instead of being stored in a separate container , the dried material can also be stored directly in the separator 8 , where the discharge screw 33 then controls the filling level in the separator 8 . the dried material used as carrier is conveyed to a crusher 14 ′ and then directly to the mixer 5 by , for example , a tube chain conveyor 34 . in the mixer , it is mixed with fresh , liquid sludge from the liquid sludge silo 2 . in order to be able to re - circulate the dried material when the plant is shut down , an additional cooler 35 is provided here . as a result , there is no need here for the cooling screw ( 11 ), nor for the carrier material silo ( 18 ) with screw ( 19 ) and drive ( 20 ) required by the state - of - the - art system . by storing the material in the separator 8 or a directly adjoining container 32 , the material remains in the inert sector , i . e . in the enclosed system , with the drying gas , thus greatly reducing the risk of deflagration caused by dust , as well as the risk of fire .