AU2252400A - Installation for thermolysis processing of waste with fumes that have a low freeoxygen content - Google Patents

Description

1 Installation for thermolytic treatment of waste with fumes having a low free oxygen content 5 The present invention relates to the thermolytic treatment of waste, such as for example industrial and/or urban waste. 10 There is already known, according to document EP-A-0 524 847, an installation for the treatment of industrial and/or urban waste, comprising in particular a thermolysis reactor which operates in a vertical mobile bed. More precisely, the waste is introduced into the top of the thermolysis reactor and passes by gravity into the more or less vertical reactor. 15 The hot gases are introduced at the base of the reactor, percolate in ascending flow through the bed of waste materials and progressively transfer their energy to the solids. These hot gases are, according to one embodiment of the installation (installation of figure 2 of the aforementioned document), essentially comprised of effluents resulting from a combustion of the thermolysis effluents in a fluidized 20 bed, the oxygen content of which is monitored. This monitoring of the oxygen content is effected by means of a control loop. The hot solids, essentially comprising coke and mineral materials, are discharged from the reactor via a line situated at the bottom of the latter. According to this document, some waste materials have a very 25 heterogeneous character, which causes significant fluctuations in the calorific power of the thermolysis gases. The combustion of such products with burners would thus lead to problems of flame stability. This is why a fluidized bed was chosen, as, thanks to its substantial thermal inertia, it permits a stable combustion of the thermolysis gases to be 30 assured, even when the calorific power of the gases to be burned falls appreciably. As has already been mentioned above, a portion of the fumes produced by the reactor operating in a fluidized bed is directed to the waste 2 thermolysis reactor, the other portion serving to pre-heat the combustion air. The quantity of combustion air introduced into the reactor operating in a fluidized bed is thus adjusted so as to permanently preserve a low oxygen content for the thermolysis gases, as has already been said. 5 According to this document, the oxygen content of the hot gases used for the thermolysis is less than 10%, preferably less than 4%, by volume. The present invention aims to improve this type of installation. It proposes, to this end, an installation for thermolytic treatment of waste which comprises: 10 - a chamber for thermolysis of the waste by direct contact with a hot gaseous fluid, - a line for introducing hot gaseous fluid into the chamber, - a line for extracting the gases present in the chamber, - a combustion chamber fluidically connected to the extraction line so as to 15 be able to burn the gases which have come from the thermolysis chamber and to the introduction line in order to supply it with combustion gases resulting from the combustion of the gases coming from the thermolysis chamber, characterized by 20 - a swirl burner mounted on the combustion chamber and connected to the extraction line in order to burn the gases which have come from the thermolysis chamber, - a post-combustion chamber, fluidically connected to the combustion chamber and suitable for subjecting a portion of the combustion gases 25 produced in the combustion chamber to a post-combustion, the other portion of these combustion gases being introduced into the introduction line, - a line supplying combustive oxygen pre-heated to a pre-determined temperature, for the burner, and 30 - means of regulating the quantity of oxygen supplied to the burner of the combustion chamber, in order to produce, at the exit from this combustion chamber, combustion gases which are practically devoid of free oxygen.

3 Thanks to such arrangements, it is possible to achieve optimum management of the oxygen content of the combustion gases sent to the thermolysis chamber. In particular, the swirl burner permits an optimum mixing and, therefore, an optimum combustion of the combustive oxygen with 5 combustible thermolysis gases diluted in a very large volume of inert combustion fumes coming from the previous treatment cycle. It is thus possible to best adjust, with the regulating means, the quantity of combustive oxygen supplied to this burner in order that the combustion gases intended to be reinjected into the thermolysis chamber are 10 practically devoid of free oxygen. Moreover, the post-combustion permits the completion of the oxygen-poor combustion which took place in the combustion chamber for the portion of combustion gas or fumes that was not reinjected into the thermolysis chamber. 15 There are thus available, at the exit from the post-combustion chamber, combustion gases or fumes the thermal energy of which can be put directly to use, without additional treatment. According to preferred arrangements, optionally combined: - a heat exchanger is placed on the introduction line in order to pre-heat the 20 combustive air up to a temperature of between 600 and 800*C; - the burner is also supplied with propane or natural gas; - the combustion gases entering the thermolysis chamber are kept at a temperature of between 450 0 C and 750*C, preferably around 650*C; - the thermolysis chamber is kept at a constant pressure of between 100 25 mbars and 1.2 bars; - the post-combustion chamber supplies a steam generator; - the solid residues coming from the thermolysis chamber are graded and the fraction of carbonated solid residues resulting therefrom is conducted to another combustion chamber in order to be burned there, this other 30 combustion chamber also supplying another steam generator; - the steam fractions which have come from each of the steam generators are globalized in order to be put to use in energy-generating form for the production of electricity.

4 These last provisions permit the on-site burning of all the combustible products arising from the waste, with a view to the production of steam and, therefore, of electricity. The thermolysis chamber can be of the horizontal type, in which the 5 products are borne by carriages moved through the thermolysis chamber by a mechanical assembly. In this case, means of fluidic connection, suitable for establishing a temporary fluidic link between the introduction line and a connection zone provided on the carriage and communicating with the reception zone for the solid products of the carriage, are provided. 10 According to another aspect, original in itself, the thermolysis chamber consists of a batch oven comprising: - an opening for the loading of waste, which can be closed tightly, - an opening for the discharge of solid thermolysis residues of the oven, which can be closed tightly; 15 - means of receiving a stationary batch of waste in the oven, - means of introducing recycled thermolysis gases, constituting the hot gases, into the oven and directly into the stationary batch in order to carry out a thermolysis by direct contact of the waste with these hot gases, and - means of exit for the thermolysis gases formed in the oven by thermolytic 20 treatment of the waste. Such an oven is of particular interest in that it permits treatment of bulky waste, such as tires. More particularly, such an oven solves the problem of the blockage of the systems for the introduction and extraction of products which exist in the case of ovens with vertical fluidized beds, such as are the subject of 25 document EP-A1-0 524 847 mentioned above, when the products are heterogeneous, i.e. of a non-constant grain size. For preference: - the reception means are mounted mobile between a position for receiving waste during the thermolytic treatment and a position for discharging the 30 solid thermolysis residues via the discharge opening; - the reception means are provided with means for passing hot gases to the stationary batch of waste; the introduction means introducing the hot gases under the reception means; 5 - cooling means are provided under the oven in order to cool the solid thermolysis residues. Other aims, characteristics and advantages of the invention emerge from the following description, given by way of non-limitative example, 5 with reference to the attached drawings, in which: - figure 1 is a schematic view of an installation according to a preferred embodiment of the invention; and - figure 2 is a schematic elevation view with longitudinal section of a batch charged thermolysis oven according to the invention. 10 Figure 1 illustrates a preferred embodiment of the installation according to the present invention. In this installation, the waste to be treated is conducted into a crusher 9 and then loaded into a carriage 11 by a conveyor system 10. The carriages 11 used in the installation of figure 1 can be for 15 example of the type of those which are described in international patent application WO-98/16594 and which permit an injection of hot gases directly into the batch of waste to be treated. The carriages 11 loaded with waste are then conducted, one by one, into a thermolysis chamber or oven 12 equipped, to this end, with a tight 20 entry door 13. tight entry door 13. In order to prevent the entry of oxygen into the thermolysis oven 12 during the transfer from a carriage inside the latter, the carriage 11 can be conducted to the oven 12 by a loader (not represented) in which the carriage 11 25 has been placed under inert atmosphere. During the transfer of the carriage 11 into the oven 12, means for establishing a tight connection between the oven 12 and the loader, such as a bellows, are deployed, in order to effect a transfer of the carriage 11 to the oven 12 under an inert atmosphere. The installation comprises a line 14 for introducing the hot gaseous 30 fluid into the thermolysis oven 12. As will be described in more detail below, this hot gaseous fluid consisting of combustion gases resulting from the combustion of thermolysis gases extracted previously from the thermolysis oven 12.

6 This introduction line has several branches 14a-14i, each ending in means of fluidic connection (for example a telescopic bellows, not represented in figure 1) in order to establish a temporary fluidic connection between the introduction line 14 and a connection zone provided on each of the carriages 11 5 and communicating with a zone for receiving waste of these carriages 11. As has already been said, this permits the injection of the hot gaseous fluid directly into the batch of waste in order to effect the thermolysis. The hot gaseous fluid (combustion gases, also called "fumes" below) is injected at a temperature of between 4500C and 7500C, preferably at a 10 temperature of the order of 650 0 C into the thermolysis oven 12 which is kept at a constant pressure of between 100 mbars and 1.2 bars. Thus, the waste is firstly dehydrated then raised to its thermolysis temperature as each carriage 11 advances into the thermolysis oven 12 and is connected to the successive branches 14a-14i of the introduction line 14. 15 After treatment, each carriage 11 loaded with solid residues is recovered, under an inert atmosphere, for example by means of the aforementioned loader, at the site of a tight exit door 15 of the oven 12. The treatment of these solid residues will also be described in more detail below. 20 The thermolysis gases formed in the oven 12 are extracted from the latter by an extraction line 16 having several branches 16a-16i. This extraction is carried out by pumping means placed on the extraction line 16. These means have not been represented on figure 1 and can, for example, consist of a surpressor. 25 The introduction line 14 and extraction line 16 are, preferably, heat insulated, in order, firstly, to bring the high temperature thermolysis gases in a combustion chamber described below and, secondly, to keep at high temperature the hot gaseous fluid to be introduced into the thermolysis oven 12. The thermolysis gases which have come from the thermolysis oven 30 12 are conducted by the extraction line 16 to a dust separator 17. After being rid of their dust, the thermolysis gases are conducted to a burner 18 of a combustion chamber 19, by a line 20.

7 This burner 18 is a swirl burner of the type marketed by the company BLOOM. The burner 18 also has an inlet 21 for propane or natural gas permitting in particular the supply of a back-up, the provision of a support or pilot 5 flame, and the starting-up of the thermolysis process. A line 22 supplying combustive oxygen is also connected to this burner 18. The combustive oxygen can be pure oxygen or have come from air or indeed oxygen-enriched air. Before being injected into the burner 18, this combustive oxygen is 10 pre-heated to a temperature of between 600 and 8000C. To this end, the supply line 22 passes into two heat exchangers 23, 24 before serving a post-combustion chamber 25 then the burner 18. More precisely, this line 22 supplying combustive oxygen is connected, firstly, to a back-up burner 26 of the post-combustion chamber 25 15 and to a furnace 27 of this chamber 25, which is connected to an exit 28 from the combustion chamber 19. In this respect, it is to be noted that, in other embodiments, a fume transfer line can separate the furnace 27 and, therefore, the post-combustion chamber 25, from the exit 28 of the combustion chamber 19. 20 The burner 26 is also equipped with an inlet 29 for propane or natural gas, which can be connected to the same source as the inlet 21 of the burner 18. Means of regulating the quantity of oxygen supplied to the burner 18 of the combustion chamber 19 are also provided in order to produce, at the 25 exit from this combustion chamber 19, combustion gases which are practically devoid of free oxygen (oxygen content preferably below 0.5%). These means of regulation also serve, in the case of the present preferred embodiment, to manage the quantity of oxygen supplied to the post-combustion chamber 25. There may be for example an oxygen meter 30 placed on the 30 introduction line 14, at the exit from the combustion chamber 19, and connected to a system of servo-control cocks, shown schematically at 31 and placed on the line 22 supplying combustive oxygen. The link between the oxygen meter 30 and d the system of servo-control cocks 31 has not been shown on figure 1, for the sake of clarity. A portion of the combustion gases or fumes of the combustion chamber 19 thus leaves the latter via this line 14 which is equipped, to this end, 5 with a pumping group 32. The other portion of the fumes, not used for a recycling into the thermolysis oven 12, is sent into the post-combustion chamber 25, in order to complete their combustion before they are put to use as described below. The fumes from the combustion chamber 19 and from the post 10 combustion chamber 25 pass respectively through the exchangers 23 and 24 in order to pre-heat the combustive air up to a temperature of between 600 and ... . . one of its ends to an oxygen source 33, followed by a pumping group 34, passes through the exchangers 23 and 24 before serving the burners 18 and 26. As a variant, these two exchangers 23, 24 can of course be 15 replaced by a single, double-circuit exchanger, or indeed just one, single-circuit, exchanger can be used. As the purpose of the installation of figure 1 is the on-site treatment of all the thermolysis products, the fumes leaving the post-combustion chamber 25 are conducted by a line 35, which passes through the exchanger 24, to a 20 steam generator 36, for example of the double-circulation boiler type supplied with water (37). In the present case, the steam that is produced supplies the turbogenerator unit 38 for the production of electricity. The condensation water produced by this unit is evacuated via the line 39. As a variant, hot water can of 25 course be produced with the fumes that have come from the post-combustion chamber 25, instead of producing electricity. The cooled fumes are extracted from the generator 36 via a line 40 equipped with a pumping group 41, and sent into a bag filter 42 in order to separate the solid particles from them before these fumes are discharged into 30 the atmosphere via a stack 43. The pumping group 41, comprising for example an extraction fan, also controls the separation between the fumes intended for the oven 12 and 9 those intended for the post-combustion chamber 25, the flow rate being governed by the pressure in the oven 12. A safety procedure, involving in particular the pumping groups or fans 32 and 41, also allows the passage of oxygen from the post-combustion 5 chamber 25 to the combustion chamber 19 to be prevented. Each carriage 11 loaded with solid thermolysis residues is conducted by the aforementioned loader to a cooling unit 44, also equipped to prevent free oxygen from entering this loader. equipped to prevent free oxygen from entering this loader. 10 Once in the unit 44, this carriage 11 is emptied onto a conveyor which passes the solid residues into a pool 45 in order to cool them. These residues are subsequently subjected to a washing process at 46, and are then screened at 47. The screen has, here, a hole diameter equal to 8 mm. The particles, having passed through the screen, are then subjected to 15 an attrition stage at 48, and are then screened anew by means of a screen 49 having, this time, a hole diameter equal to 0.8 mm. The carbonated fraction is separated, by means of this screening, from the inorganic fraction. The carbonated fraction is then subjected to a drainage step at 50 before being conducted, for storage, into a silo 51. The inorganic fraction is 20 subjected to a grading stage at 52. Following this grading, minerals (53), magnetic materials (54) and non-magnetic materials (55) are recovered. During the grading, the metals are also subjected to a compacting stage. The particles which have been retained at 47 by the screen are conducted to a flotation tank 56. 25 The densest materials (metals . . .) are recovered at the bottom of the basin and sent to 52 for separation. The least dense materials (carbonated fractions) are recovered at the top of the basin 56 and conducted into a crusher 57 where they are reduced to a size of less than 0.8 mm. These carbonated particles are subsequently subjected to drainage 30 at 50, then sent into the silo 51. The silo 51 supplies a dense fluidized-bed oven 58 intended to burn the carbonated fraction or charcoal stored in the silo 51.

10 The fumes produced in this oven 58 pass through a steam generator 59 supplied with water (60). The steam fraction leaving this generator 59 is conducted, with that leaving the generator 36, to the turbogenerator unit 38. The fumes produced in the oven 58 also pass through an 5 economizer 61 which pre-heats combustive oxygen intended for the oven 58. This combustive oxygen is conducted to the oven 58 via a line 62 connected to a source 63 of pure oxygen, pure air or oxygen-enriched air and equipped with a pumping group 64. The fumes leaving the economizer 61 are conducted via a line 65, 10 equipped with a pumping group 66, to the bag filter 42. The ashes recovered at the bottom of the oven 58 are collected and evacuated at 67, while the ashes collected at the top of the oven 58 are recycled into the latter via a line 68. One end of this line 68 is, moreover, also connected to the bottom 15 of the bag filter 42. The remaining evacuation residues leaving from the bottom of the bag filter 42 are evacuated at 69. According to the variant of figure 2, the thermolysis chamber consists of a batch-charged thermolysis oven 112. 20 This oven 112 is vertical and closed tightly at its upper and lower ends, during the thermolytic treatment, by panels 170,171 mobile in translation in a horizontal plane. Panel 170 permits the closure of the loading opening of the oven 112, more or less transverse to the longitudinal axis of this same oven 112, while 25 panel 171 is intended to close the discharge opening of this oven 112, which also extends more or less transverse to the aforementioned axis. The discharge opening opens out into a buried pool 172 for the recovery of the solid thermolysis residues. In order to receive a stationary batch of waste to be treated non 30 continuously, a fixed tank 173 is mounted in the oven 112, between the panels 170 and 171. This tank 173 is fitted with a base consisting of a grille in two parts 174. Each of the two parts of the grille 174 is mobile in pivoting between a 11 horizontal position in which they are an extension of each other in order to receive a batch of waste and a position apart from each other and for discharge via the discharge opening, after the removal of the plate 171. A side inlet 175 for recycled thermolysis gases opens out into the 5 oven 112 under the grille 174. This inlet is connected to the introduction line 14 of the installation of figure 1, when the oven 112 replaces the horizontal oven 12 of figure 1. Thus, the recycled thermolysis gases enter the batch of waste after passing through the grille 174 in order to carry out a thermolysis by direct contact of hot gases with a stationary batch of waste to be treated. 10 The thermolysis gases formed in the oven 112 are extracted from the latter via a side outlet 176 connected, in the case where the oven 112 is used as part of the installation of figure 1, to the extraction line 16. The oven 112 is supplied with waste by gravity by means of a loader 177 which is mobile horizontally above this oven 112. 15 To this end, a tank 178, similar to the tank 173, is installed in the loader 177. It will be seen in this respect that the lower end of the loader 177 is not closed. According to a variant of this version, the loader can be replaced by a loader supplying the oven via a side opening, by means of a rolling belt. 20 Such a loader can also be mounted mobile in translation in order to serve an array of thermolysis ovens. A side injection of hot gases into the batch can also be envisaged. It is also possible to provide for a lateral discharge of the residues by means of a sheet for receiving waste which is mounted mobile in tilting. 25 It goes without saying that the above description has been provided only by way of a non-limitative example and that numerous variants can be proposed by the person skilled in the art without exceeding the scope of the invention.

Claims (13)

1. Installation for thermolytic treatment of waste comprising: - a chamber (12) for thermolysis of the waste by direct contact with a hot 5 gaseous fluid, - a line (14) for introducing hot gaseous fluid into the chamber, - a line (16) for extracting the gases present in the chamber, - a combustion chamber (19) fluidically connected to the extraction line (16) so as to be able to burn gases which have come from the thermolysis 10 chamber (12) and to the introduction line (14) in order to supply it with combustion gases resulting from the combustion of the gases coming from the thermolysis chamber (12), characterized by - a swirl burner (18) mounted on the combustion chamber (19) and 15 connected to the extraction line (16) in order to burn the gases which have come from the thermolysis chamber (12), - a post-combustion chamber (25) fluidically connected to the combustion chamber (19) and suitable for subjecting a portion of the combustion gases produced in the combustion chamber (19) to a post-combustion, the other 20 portion of these combustion gases being introduced into the introduction line (14), - a line (22) supplying combustive oxygen pre-heated to a pre-determined temperature, for the burner (18), and - means of regulating the quantity of oxygen supplied to the burner (18) of 25 the combustion chamber (19), in order to produce, at the exit from this combustion chamber (19), combustion gases which are practically devoid of free oxygen.

2. Installation according to claim 1, characterized in that the thermolysis chamber consists of a batch furnace comprising: 30 - an opening for the loading of waste, which can be closed tightly, - an opening for the discharge of the solid thermolysis residues, which can be closed tightly; - means (174) of receiving a stationary batch of waste in the oven, 13 - means (175) of introducing recycled thermolysis gases, constituting the hot gases, into the oven, directly into the stationary batch in order to carry out a thermolysis by direct contact of the waste with these hot gases, and - means (176) of exit for the thermolysis gases formed in the oven by 5 thermolytic treatment of the waste.

3. Installation according to any one of the previous claims, characterized in that a heat exchanger (23, 24) is placed on the introduction line (14) in order to pre-heat the combustive air up to a temperature of between 600 and 800*C. 10

4. Installation according to any one of the previous claims, characterized in that the burner (18) is also supplied with propane or natural gas.

5. Installation according to any one of the previous claims, characterized in that the combustion gases entering the thermolysis chamber are kept at a temperature of between 450"C and 750*C, preferably about 650"C. 15

6. Installation according to any one of the previous claims, characterized in that the thermolysis chamber is kept at a constant pressure of between 100 mbars and 1.2 bars.

7. Installation according to any one of the previous claims, characterized in that the post-combustion chamber (25) supplies a steam 20 generator (36).

8. Installation according to any one of the previous claims, characterized in that the solid residues coming from the thermolysis chamber are graded and the fraction of carbonated solid residues resulting therefrom is conducted to another combustion chamber (58) in order to be burned there, this 25 other combustion chamber (58) also supplying another steam generator (59).

9. Installation according to claims 7 and 8, characterized in that the steam fractions which have come out of each of the steam generators (36, 59) are globalized in order to be used in energy-generating form for the production of electricity. 30

10. Installation according to claim 1, characterized in that the thermolysis chamber (12) is of the horizontal type, in which the waste is borne by carriages (11) moved across the chamber by a mechanical assembly. 14

11. Installation according to claim 2, characterized in that the reception means (174) are mounted mobile between a position for receiving the waste during the thermolytic treatment and a position for discharging the solid thermolysis residues via the discharge opening. 5

12. Installation according to claim 2 or 11, characterized in that the reception means are provided with means for passing hot gases to the stationary batch of waste, the introduction means introducing the hot gases under the reception means.

13. Installation according to any one of claims 2, 11 and 12, 10 characterized in that cooling means are provided under the oven in order to cool the solid thermolysis residues.