Process and device for continuous thermal hydrolysis

Abstract

Method for the continuous thermal hydrolysis of sludges containing organic matter, said method comprising the steps of: simultaneously injecting pressurized steam (100) into said sludges and mixing said sludges with said steam by means of a dynamic mixer-injector (4) so as to obtain a single-phase mixture, conveying said single-phase mixture towards a tube reactor (4) under pressure and bringing about the plug flow of this mixture into said reactor for a retention time that is sufficient and at a temperature that is sufficient to enable the thermal hydrolysis of the organic matter present in said sludges, cooling said single-phase mixture at its exit from said tube reactor to a temperature enabling the subsequent digestion of the hydrolyzed organic matter that it contains, depressurizing said cooled single-phase mixture.

Claims

1. A method for the continuous thermal hydrolysis of sludge containing organic matter, said method comprising the steps of: simultaneously injecting steam and the sludge into a dynamic mixer-injector having a chamber and rotating blades in the chamber; mixing the steam and sludge in the chamber of the dynamic mixer-injector to form a single-phase mixture by rotating the blades greater than 500 rpm in the chamber; conveying said single-phase mixture from the dynamic mixer-injector to a downstream tube reactor that is distinct from the dynamic mixer-injector; wherein conveying the single-phase mixture from the dynamic mixer-injector to the tube reactor includes conveying the single-phase mixture under pressure and moving the single-phase mixture in a plug flow fashion through the tube reactor; maintaining the temperature and retention time of the single-phase mixture in the reactor sufficient to thermally hydrolyze the organic matter present in the sludge; directing the single-phase mixture from the tube reactor; after exiting the tube reactor, cooling the single-phase mixture to a temperature that enables the subsequent digestion of the hydrolyzed organic matter in the single-phase mixture; and depressurizing the cooled single-phase mixture.

2. The method according to claim 1, characterized in that, at an exit from said dynamic mixer-injector, said single-phase mixture has a temperature of 100 C. to 200 C. and a pressure of 1 bar a to 25 bar a.

3. The method according to claim 2, characterized in that, at the exit from said dynamic mixer-injector, said single-phase mixture has a temperature of 150 C. to 170 C. and a pressure of 5 bar a to 20 bar a.

4. The method according to claim 1 characterized in that the steam used to make the single-phase mixture has a temperature of 100 C. to 220 C.

5. The method according to claim 1 characterized in that said retention time for said single-phase mixture in said tube reactor is from 10 minutes to 2 hours.

6. The method according to claim 1 characterized in that said single-phase mixture is cooled and diluted downstream from the tube reactor by addition of water or sludge.

7. The method according to claim 1 characterized in that the method further comprises preliminary steps including dewatering and homogenizing the sludge and producing a sludge having a dry solids content of 10% to 50% by weight.

8. The method of claim 1 wherein the speed of the rotating blades is modified according to the dry solids content of the sludge so that the single phase mixture can be made even when the dry solids content is high.

9. The method of claim 1 wherein the tube reactor includes a first vertical section and a second vertical section and wherein the first vertical section includes an inlet provided at the foot of the first vertical section and wherein the second vertical section includes an outlet provided at the foot of said second vertical section; and wherein the first and second vertical sections are interconnected by a curved section.

10. The method of claim 1 including adjusting the speed of the rotating blades according to the dry solids content of the sludge.

11. The method of claim 1 including rotating the blades in the chamber of the dynamic mixer-injector 1000-2000 rpm which mixes the steam and sludge to form a liquid single-phase mixture.

12. A method of thermal hydrolyzing sludge containing organic matter comprising: dewatering the sludge; pumping the sludge to a dynamic mixer-injector; moving the sludge through the dynamic mixer-injector having a chamber and rotating blades in the chamber; generating steam; injecting the steam into the dynamic mixer-injector; rotating the blades in the chamber of the dynamic mixer-injector greater than 500 rpm and contacting the sludge in the dynamic mixer-injector with the rotating blade and mixing the sludge with the steam to form a homogeneous single-phase mixture; transferring the single phase mixture to a thermal hydrolysis reactor located downstream from the dynamic mixer-injector and distinct from the dynamic mixer-injector; moving the single phase mixture through the thermal hydrolysis reactor in a plug flow fashion and maintaining the temperature and the retention time of the single phase mixture in the thermal hydrolysis reactor sufficient to hydrolyze the organic matter in the sludge; after thermally hydrolyzing the sludge, cooling the sludge by mixing dilution water with the sludge; after thermally hydrolyzing the sludge, directing the sludge through a heat exchanger and cooling the sludge; and directing the cooled thermal hydrolyzed sludge to a digester and digesting the sludge.

13. The method of claim 12 wherein after exiting the dynamic mixer-injector, the single phase mixture has a temperature of approximately 150 C. to approximately 170 C. and at a pressure of approximately 5 bar a to approximately 20 bar a; and wherein the retention time of the single phase mixture in the thermal hydrolysis reactor is approximately 10 minutes to approximately 2 hours; and wherein the temperature of the mixture in the thermal hydrolysis reactor is at least 100 C.

14. The method of claim 12 wherein there is provided a depressurizing unit disposed between the thermal hydrolysis reactor and a digester for causing a drop in the pressure of the single phase mixture prior to the single phase mixture being directed into the digester.

15. The method of claim 12 including mixing the sludge and steam in the dynamic mixer-injector sufficient to form a liquid and homogeneous single phase mixture that enables the single phase mixture to flow in a plug flow manner downstream of the dynamic mixer-injector.

16. The method of claim 12 including pumping the sludge continuously through the dynamic mixer-injector and continuously pumping the single phase mixture from the dynamic mixer-injector to and through the thermal hydrolysis reactor which constitutes a tube reactor.

17. The method of claim 12 including simultaneously pumping sludge into the dynamic mixer-injector and injecting steam into the dynamic mixer-injector.

18. The method of claim 12 wherein the blades only mix the sludge and steam and do not cause the sludge and steam to move through the dynamic mixer-injector.

19. The method of claim 12 wherein dewatering the sludge produces a dry solids content of over 20% by weight and the sludge with the dry solids content over 20% by weight is directed into the dynamic mixed-injector where steam is mixed with the sludge.

20. The method of claim 12 including adjusting the speed of the rotating blades according to the dry solids content of the sludge.

21. The method of claim 12 wherein the speed of the rotating blades is modified according to the dry solids content of the sludge.

Description

5. LIST OF FIGURES

(1) The invention as well as its different advantages will be understood more easily from the description of embodiments given with reference to the figures, of which:

(2) FIG. 1 is a schematic view of a device for the thermal hydrolysis of sludges according to the invention (surrounded by a line of dots and dashes) integrated into an installation including a digester provided downstream from this digester;

(3) FIG. 2 represents a form of thermal hydrolysis tube reactor that can be implemented in the present invention;

(4) FIG. 3 represents another form of a thermal hydrolysis tube reactor that can be implemented in the present invention;

(5) FIG. 4 represents yet another form of thermal hydrolysis tube reactor that can be implemented in the present invention;

(6) FIG. 5 is a graph showing, on the one hand, the development of the temperature within the tube reactor of a prior-art installation according to the patent documents WO2009/121873 that does not integrate a dynamic mixer-injector but in which steam and sludge are conveyed to the head of the reactor and, on the other hand, the development of the temperature within the tube reactor of an installation corresponding to the invention integrating a dynamic mixer-injector in which steam and sludge are mixed and then conveyed in the form of a homogeneous single-phase mixture to the head of the reactor.

6. DESCRIPTION OF EMBODIMENTS

(7) Referring to FIG. 1, a device according to the invention is described schematically. This device 1000 is integrated into an installation including a digester 9 that is not a part as such of the device according to the invention.

(8) Such an installation can be used to implement a method of lysis-digestion (LD) but it will be noted that it is also possible to integrate the method according to the invention into known prior-art configurations called digestion-lysis (DL) or digestion-lysis-digestion (DLD), given that in the configuration called DL a part of the sludge is hydrolyzed and then returned to the digester.

(9) Referring to FIG. 1, centrifuged sludges are conveyed by a pipe 1 to a hopper 2 provided with two worm screws enabling these sludges to be homogenized.

(10) These two worm screws also serve to cram a feeder pump 3 feeding sludges to the dynamic mixer-injector 4. The dewatered and homogenized sludges coming from the hopper 2 are thus pumped by means of the pump 3 into a pipe using means for leading these sludges into the dynamic mixer-injector 4. This dynamic mixer-injector 4 is also provided with means for injecting steam 100 generated by a steam generator not shown in FIG. 1. The mixer-injector comprises a cylindrical chamber provided with stirring means constituted by blades mounted on a rotation shaft moved by a rotor rotating at a speed of 1000 rpm to 2000 rpm, this speed being adjustable according to the dry solids content of the sludges. The retention time of the matter travelling continuously through the mixer-injector is short and, in practice, shorter than 10 min. The blades do not make the matter move forward in the chamber but only stir it vigorously.

(11) A wash water intake 200 is planned upstream to the dynamic mixer-injector 4. Through such water inflow means 200, the dynamic mixer-injector could be cleaned if need be.

(12) At the exit from the dynamic mixer, a pipe enables the single-phase mixture made within this mixer to be conveyed towards a thermal hydrolysis reactor 5.

(13) The treatment within this thermal hydrolysis reactor 5 is done at a temperature of 165 C. to 180 C., the interior of the reactor being maintained at a pressure of 8 bar a to 10 bar a (in this respect, it will be noted that lower or higher pressures could be implemented, depending especially on the dry solids content of the sludges).

(14) A water inlet 101 situated at the entry to the reactor 5 is provided to enable cleaning water to be led into the reactor during the cleaning phases that can be carried out when starting up the installation or during phases of maintenance of the installation.

(15) At the exit from the reactor 5, a drain 102 is, for its part, provided in order to remove non-condensable gases if any.

(16) The hydrolyzed sludges in the reactor 5 are then conveyed by a pipe to a heat exchanger 7. Before reaching this heat exchanger 7 cooling and dilution water is led into the hydrolyzed sludges by water injection means 201. If need be, this dilution could also be done after the exchanger 7.

(17) At the exit from the exchanger 7, the diluted sludges are conveyed to the digester 9. The depressurizing unit 8 which, by definition, causes a drop in pressure, is used to maintain the pressure prevailing in the thermal hydrolysis reactor 5. In the present example, this unit is constituted by a progressing cavity pump provided between the heat exchanger and the digester. In other embodiments, it could be constituted by a valve or any other unit used to carry out this function.

(18) At the exit from the device according to the invention, the thermally hydrolyzed sludges are sent to the digester 9 where they can be easily digested because they have undergone thermal hydrolysis.

(19) It is clearly specified that the representation in FIG. 1 of an installation integrating a device according to the invention is a schematic representation. In particular, the reactor 5 in which the thermal hydrolysis of the single-phase mixture of sludges and steam is carried out could have different shapes. Three of these shapes are given with reference to FIGS. 2, 3 and 4.

(20) As shown in FIG. 2, the reactor 5 has a vertical shape. The reactor is provided, in its lower part, with an intake of single-phase mixture of sludges heated with steam 501 and, in its upper part, with an outlet from the reactor 502. A drain 503 is provided to remove any non-condensable gases and means for measuring the pressure prevailing inside the reactor are also provided in its upper part.

(21) Referring to FIG. 3, the thermal hydrolysis reactor has a first vertical section provided at its base with an intake of single-phase mixture of sludges and steam 401, directly connected to a second vertical part provided at its foot with a discharge feature 402 for hydrolyzed sludges. A drain 403 is provided at the junction between these two vertical parts to remove the non-condensable gases if any. Means for measuring the pressure and the temperature in the reactor are also planned. It will be noted that, in this configuration, the second vertical section part is directly connected to the first vertical section without a horizontal section between the two.

(22) Referring to FIG. 4, the thermal hydrolysis reactor has a first vertical section provided at its head with an intake of single-phase mixture of sludges and steam 601, directly connected to a second vertical part provided at its foot with a discharge 602 of the hydrolyzed sludges. A drain 603 is provided at the junction between these two vertical parts to remove the non-condensable gases if any. Means for measuring the pressure and the temperature in the reactor are also planned. It will be noted that, in this configuration, the second vertical section part is directly connected to the first vertical section without a horizontal section between the two.

(23) FIG. 5 shows the progress in time of the temperature prevailing within the thermal hydrolysis reactor: on the one hand, in the invention, implementing a dynamic mixer-injector provided upstream to the thermal hydrolysis reactor and; on the other hand, in a similar installation according to the prior art in which no dynamic mixer-injector is used, the steam being injected at the foot of the reactor.

(24) Referring to this FIG. 5, it can be seen that, in the present invention, the temperature prevailing within the reactor gradually rises until it reaches and keeps the set-value temperature enabling the optimized thermal lysis of the hydrolysable organic compounds contained in the treated sludges.

(25) In the prior art, the temperature observed in the reactor is, at the outset, that of the injected steam. The temperature then undergoes major variations. This results from the fact that, in the technique according to this prior art, there is no systematic occurrence of an intimate mixing of steam with the sludges. On the contrary, the temperature fluctuations observed within the reactor result from the existence of polyphase flows within it. In the example described here, since the steam is injected at a speed (in practice above 5 m/s) far greater than that of the sludges (in practice below 3 m/s), it finds preferred passage through this sludge and does not intimately mix with this sludge, and does not efficiently yield its energy to the sludge.

(26) Quite to the contrary, through the use of a dynamic mixer-injector according to the invention upstream to the hydrolysis reactor, the mixture reaching this reactor is a perfectly liquid and homogenous single-phase mixture. It can therefore flow in a plug flow in this reactor. The set-value temperature is kept throughout the retention time in the reactor. The energy of the steam is therefore transferred in an optimized way to the sludges and the hydrolysis of the poorly biodegradable compounds can be done efficiently.

(27) It will also be noted that, through the invention, the theoretical quantity of energy to hydrolyze a given quantity of sludges corresponds more or less to the quantity effectively implemented to obtain this hydrolysis. In this respect, it will be noted that it is easy to compute the energy needed to increase the temperature of a fluid from a temperature A to a temperature B. In the framework of trials made by the Applicant, the computed theoretical flow rate of steam was 25 kilograms of steam at 13 bar a per hour, and the trials have shown that it was exactly this flow rate of steam that was effectively necessary to efficiently hydrolyze the sludges.

(28) In the prior-art installation, it was shown that the mixture between the sludge to be hydrolyzed and the steam was imperfect since the quantity of steam effectively injected to heat the sludge (15 kg/h) was smaller than the theoretically computed quantity (25 kg/h). A certain quantity of steam was therefore not condensed in the sludge. The presently described trials confirm the interest of the present invention.

(29) Finally, it will be noted that the invention enables the use of reactors having a volume 20% to 25% smaller than the volumes of the prior-art reactor.