METHOD FOR DEWATERING SLUDGE ASSISTED BY A FLOCCULATING REAGENT AND FACILITY FOR IMPLEMENTING SUCH A METHOD

Abstract

Method for dewatering sludge assisted by flocculating reagent, said method comprising an injection of flocculating reagent into the sludge and a step for dewatering said sludge, characterized in that it comprises a preliminary step for mixing (4) said sludge so as to destructure it and reduce its viscosity. Installation for implementing this method.

Claims

1-18. (canceled)

19. Method for dewatering sludges assisted by flocculating reagent, said method comprising an injection of flocculating reagent into the sludge and a step for dewatering said sludge, characterized in that it comprises a preliminary step prior to said step of dewatering, for mixing said sludge so as to destructure it and reduce its viscosity.

20. Method according to claim 19, characterized in that said preliminary step for mixing said sludge comprises the introduction of this sludge into a mixer comprising a cylindrical chamber provided with blades mounted rotationally on a shaft rotating at a speed of rotation of 500 rpm to 4000 rpm.

21. Method according to claim 19, characterized in that said speed of rotation ranges from 1000 rpm to 2000 rpm.

22. Method according to claim 19, characterized in that said step of dewatering is a step of centrifugation implemented with at least one centrifuge.

23. Method according to claim 19, characterized in that said step for injecting flocculating reagent is done by injecting said flocculating reagent during or upstream to said preliminary step.

24. Method according to claim 19, characterized in that the method comprises the injection of hot water and/or live steam or flash steam and/or condensates during or upstream to said preliminary step for pre-heating said sludge.

25. Method according to claim 19, characterized in that the method comprises an injection of dilution water into said sludge during or upstream to said preliminary step.

26. Method according claim 19, characterized in that the method comprises oxygenating said sludge during or upstream to said preliminary step.

27. Method according to claim 19, characterized in that the method comprises an injection of coagulant reagent into said sludge during or upstream to said preliminary step.

28. A method of dewatering sludge that destructures the sludge and reduces the viscosity of the sludge upstream of dewatering, the method comprising: injecting a flocculating reagent into the sludge; after injecting the flocculating reagent into the sludge, directing the sludge into a cylindrical mixer having a plurality of blades mounted on a shaft; prior to the sludge being directed into the mixer, injecting water or steam into the sludge; prior to the sludge being directed into the mixer, oxygenating the sludge by injecting compressed air into the sludge; wherein the sludge in the cylindrical mixer is conditioned by the addition of the flocculating reagent, water or steam and the compressed air; mixing the conditioned sludge in the cylindrical mixer by rotating the blades in the cylindrical mixer approximately 500-4000 rpm and in the process destructuring the sludge and reducing the viscosity of the sludge in the process; and after mixing the sludge in the cylindrical mixer, directing the sludge to a dewatering device and dewatering the sludge.

29. The method of claim 28 wherein prior to directing the conditioned sludge to the cylindrical mixer, directing the conditioned sludge to a collector and thereafter directing the conditioned sludge from the collector to the cylindrical mixer; and wherein there is a degasser operatively interconnected between the cylindrical mixer and the dewatering device, and wherein the method includes directing the sludge from the cylindrical mixer to the degasser and degassing the sludge in the degasser and thereafter directing the sludge from the degasser to the dewatering device.

30. A dewatering system for dewatering sludge comprising: a sludge inlet configured to receive sludge and direct the sludge into the dewatering system; a flocculating reagent injection site forming a part of the dewatering system and configured to receive a flocculating reagent and to inject the flocculating reagent into the sludge; a cylindrical dynamic mixer located downstream of said sludge inlet and said flocculating reagent injection site for receiving sludge and configured to destructure the sludge and reduce the viscosity of the sludge; the cylindrical dynamic mixer including a shaft and a plurality of blades mounted on the shaft and wherein the blades are configured to rotate and engage the sludge; upstream of the cylindrical dynamic mixer, the system includes a water or steam inlet for receiving water or steam and configured to mix the water or steam with the sludge prior to the sludge reaching the cylindrical dynamic mixer; upstream of the cylindrical dynamic mixer, the system includes a compressed air inlet for recovering compressed air and configured to inject the pressed air into the system where it is mixed with the sludge prior to the sludge reaching the cylindrical dynamic mixer; a dewatering device located downstream of the cylindrical dynamic mixer and configured to dewater the sludge after the sludge has been mixed and destructured in the cylindrical dynamic mixer; and a degasser operatively interconnected between the cylindrical dynamic mixer and the dewatering device for receiving sludge from the cylindrical dynamic mixer and wherein the degasser is configured to degas the sludge prior to the sludge being directed to the dewatering device.

Description

LIST OF FIGURES

[0046] The invention, as well as its different advantages will be understood more easily from the following description of an embodiment, given purely by way of a non-exhaustive illustration and with reference to the figures, of which:

[0047] FIG. 1 is a schematic representation of a plant according to the present invention;

[0048] FIG. 2 is a graph indicating consumption values for flocculating reagent (polymer) during the implementation of the plant according to FIG. 1 using the method according to the invention on the one hand and a classic prior art method on the other hand.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0049] Plant

[0050] Referring to FIG. 1, the plant comprises a sludge-dewatering apparatus constituted by a centrifuge (Andritz®, model D2L). This centrifuge is connected to sludge-feed means 2 and polymer-injecting means 3.

[0051] In accordance with the present invention the plant also has a mixer 4 provided upstream to said dewatering apparatus provided with means for the injection of compressed air 5,d e, water-feed means 6, and means 6a for injecting ferrous chloride.

[0052] The sludge-feed means 2, the polymer-injection means 3, the compressed air injection means 5 and the water-feed means are connected by pipes, respectively 12, 13, 15, 16 to a collector 7. Valves 22, 23, 25, 26 enable the distribution, respectively, of the sludge, polymer, compressed air and water within it. The pipe 15 for feeding compressed air to the collector 7 is equipped with a flowmeter 55.

[0053] The sludge-feed means 2, the polymer-injection means 3, and the water-feed means are connected by pipes, respectively 32, 33, 36 to the centrifuge 1. Valves 42, 43, 46 enable the distribution, respectively, of the sludge, polymer and water directly to its spout.

[0054] The pipes 16 and 56 for conveying water respectively to the collector 7 and to the centrifuge are each equipped with a flowmeter 56.

[0055] The compressed-air injection means 5 for their part are connected by a pipe 35 to a degassing chamber 8, equipped with a vent 8a, a valve 45 enabling the distribution of this compressed air to this vent. This degassing chamber is connected to the spout of the centrifuge 1 by a pipe 9.

[0056] In accordance with the present invention, the mixer 4 comprises a cylindrical chamber 4a equipped with a rotating shaft 4b on which there are mounted blades 4c. The rotating shaft is moved by a motor (not shown in FIG. 1) which enables the blades to be driven at a high rotating speed of 500 rpm to 4000 rpm.

[0057] The mixer 4 receives sludge, polymer, ferrous chloride, water and compressed air coming from the collector 7 via a common pipe. The mixed sludge is conveyed towards the degassing chamber 8 by a pipe 11.

[0058] The plant described here enables water, polymer and compressed air to be conveyed to the collector 7 and/or towards the centrifuge.

[0059] Method

[0060] The plant described here has been implemented to dewater the mixed sludge digested according to the prior art on the one hand and according to the invention on the other hand. This sludge has an initial dry solid content of 28%.

[0061] In the context of these experiments, the centrifuge has always been used at its maximum capacity (2000 G).

[0062] In a first experimental phase, the valves 22, 23, 25, 26, 45, 46 were closed and only the valves 42 and 43 were opened so as to direct the sludge and the polymer coming from the feeding means 2 and 3 for these constituents directly to the spout of the centrifuge 1, without travelling through the mixer according to the prior art.

[0063] In a second experimental phase according to the invention, the valves 23, 25, 26, 45, 46 were kept closed. The valve 22 was opened to authorize the distribution of the sludge in the mixer 4 via the collector 7 and the valve 42 was closed. The valve 43 was kept open to continue to convey the polymer to the spout of the centrifuge 1.

[0064] In a third experimental phase, the valves 25, 26, 35, 46 was kept closed. The valve 22 was kept open, the valve 43 was closed and the valve 23 was opened to permit, according to the invention, the conveyance of the sludge and polymer to the mixer 4.

[0065] During each of these three experimental phases, the polymer was used in three different doses, i.e. 5 kg/TDM (tonnes of dry matter), 7.5 kg/TDM et 11 kg/TDM. The mixer was used for the second and third experimental phases with a blade speed of 2000 rpm enabling the sludge to be destructured before it was conveyed to the centrifuge 1 via the degassing chamber 8.

[0066] Since the sludge does not need it, no ferrous chloride was added.

[0067] The results of dry solid content values for the sludge at exit from the centrifuge 1 are summarized in the graph shown in FIG. 3.

[0068] These results show that, with the same polymer dose, it is possible through the invention to obtain a dry solid content for the sludge that is far better with the invention, especially when the injection of polymer is done in the collector provided upstream to the dynamic mixer.

[0069] Thus, for a polymer dose of 11.3 kilograms per tonne of dry matter (TDM), through the invention, a dry matter content for sludge of 32%, and even more than 33% was obtained by injecting polymer upstream to the dynamic mixer, whereas the dry matter content obtained in the prior art was only 28.5%. This was obtained without any addition of ferrous chloride and compressed air because the sludge does not need it. A comparable dry matter content of 29% was obtained by implementing polymer at a rate of only 5 kg/TDM, giving savings of nearly 50% in quantity of polymer.