SLUDGE TREATMENT DEVICE AND METHOD
The invention relates to a device and method for the treatment of sludge with a powder additive, in a co-rotating twin-screw extruder having a length/diameter ratio of less than 20 and comprising a control means allowing the feed flow of powder additive to be adjusted according to the sludge feed flow.
1 . A device for the treatment of sludge with a powder additive, said device comprising:
a sleeve enclosing two co-rotating screws, said screws of said sleeve consisting of two or three successive zones: the first zone ensuring the mixture of the sludge and powder additive; the second zone ensuring the conveyance of the mixture of sludge and powder additive; the third zone located upstream of the first zone, ensuring the conveyance of the sludge from the sludge feed inlet to the first zone;
a sludge feed inlet emerging upstream of the first zone or third zone, if any;
a powder additive feed inlet emerging at the first zone or third zone, if any;
an outlet for the mixture of sludge and powder additive downstream of the second zone;
a control means allowing the powder additive feed flow to be adjusted according to the sludge feed flow;
said device having a length/diameter ratio of less than 20.
2 . A device according to claim 1 , characterized in that the powder additive feed inlet comprises a volumetric metering device.
3 . A device according to claim 2 , characterized in that the volumetric metering device is a volumetric metering device with co-rotating twin screws.
4 . A device according to claim 3 , characterized in that the ends of the co-rotating twin screws of the volumetric metering device are located at least 0.5 cm away from the co-rotating twin screws of the device.
5 . A method for the treatment of sludge by extrusion characterized in that it comprises the following steps:
introduction of sludge into a co-rotating twin-screw extruder;
introduction of a powder additive in the extruder downstream of the sludge inlet;
mixing the sludge and powder additive in the extruder;
recovery of the sludge and powder additive mixture at the outlet of the extruder;
in which the powder additive feed flow is adjusted according to the sludge feed flow and in which the dwell time of the sludge in the extruder is less than 1 minute.
6 . A method according to claim 5 , characterized in that the treatment of the sludge by extrusion is performed
using a device comprising:
a sleeve enclosing two co-rotating screws, said screws of said sleeve consisting of two or three successive zones: the first zone ensuring the mixture of the sludge and powder additive; the second zone ensuring the conveyance of the mixture of sludge and powder additive; the third zone located upstream of the first zone, ensuring the conveyance of the sludge from the sludge feed inlet to the first zone;
a sludge feed inlet emerging upstream of the first zone or third zone, if any;
a powder additive feed inlet emerging at the first zone or third zone, if any;
an outlet for the mixture of sludge and powder additive downstream of the second zone;
a control means allowing the powder additive feed flow to be adjusted according to the sludge feed flow;
said device having a length/diameter ratio of less than 20.
7 . A method according to claim 5 , characterized in that the flow of sludge treated is greater than 500 kg/hour.
8 . A method according to claim 5 , characterized in that the sludge is defiocculated before being introduced into the extruder.
9 . A method according to claim 5 , characterized in that the powder additive is lime.
10 . A method according to claim 9 , characterized in that the ratio between the mass of lime and the total mass of lime and sludge introduced into the sleeve is less than 35%.
11 . A method according to claim 5 , characterized in that the powder additive is dry sludge.
12 . A method according to claim 5 , characterized in that the scanned image of the sludge exiting the extruder has a variance of the grey level of the topographic surface of less than 20%.
13 . A method according to claim 6 , characterized in that the flow of sludge treated is greater than 500 kg/hour.
14 . A method according to claim 13 , characterized in that the sludge is deflocculated before being introduced into the extruder.
15 . A method according to claim 14 , characterized in that the powder additive is lime.
16 . A method according to claim 15 , characterized in that the ratio between the mass of lime and the total mass of lime and sludge introduced into the sleeve is less than 35%.
17 . A method according to claim 16 , characterized in that the powder additive is dry sludge.
18 . A method according to claim 17 , characterized in that the scanned image of the sludge exiting the extruder has a variance of the grey level of the topographic surface of less than 20%.