ARRANGEMENT FOR THE OUTLET NOZZLE OF A SUBMERGED PLASMA TORCH DEDICATED TO WASTE TREATMENT

Abstract

An injection and cooling system configured to equip a plasma torch, a plasma torch equipped with the system, an installation for treatment of a liquid solution including such a plasma torch, and a method for treatment of a liquid solution by injection into a plasma generated by such a plasma torch submerged in a different liquid solution.

Claims

1. Injection and cooling system, intended to equip a plasma torch, having a cavity intended to contain plasma and combustion gas and comprising: a first injection device devised to inject, into said cavity, a liquid solution to be treated hereinafter referred to as solution S.sub.1, a second injection device arranged against said first injection device and devised to inject, into said cavity, an oxidant gas, a cooling device devised to cool the gas(es) contained in said cavity, said system comprising a third injection device inserted between said second injection device and said cooling device and devised to inject, into said cavity, a liquid solution different to the liquid solution to be treated hereinafter referred to as solution S.sub.3 and said four devices being hollow, coaxially aligned and defining said cavity, said system successively comprising said first injection device, said second injection device, said third injection device and said cooling device, said devices being placed on top of one another.

2. Injection and cooling system according to claim 1, characterised in that said first injection device comprises at least one first channel leading to said cavity and devised to convey said solution S.sub.1 therein.

3. Injection and cooling system according to claim 1 or 2, characterised in that said second injection device comprises at least one second channel leading to said cavity and devised to convey said oxidant gas therein.

4. Injection and cooling system according to any one of claims 1 to 3, characterised in that said third injection device comprises at least one third channel leading to said cavity and devised to convey said solution S.sub.3 therein.

5. Injection and cooling system according to any one of claims 1 to 4, characterised in that said cooling device comprises at least one sheath cooled by internal water circulation.

6. Plasma torch equipped with an injection and cooling system according to any one of claims 1 to 5.

7. Installation for the treatment of a liquid solution S.sub.1 comprising: a plasma torch equipped with an injection and cooling system according to any one of claims 1 to 5; a container of liquid solution S.sub.1; first means devised to convey the liquid solution S.sub.1 from said container of liquid solution S.sub.1 to the first injection device of said injection and cooling system; a container of oxidant gas; second means devised to convey the oxidant gas from said container of oxidant gas to the second injection device of said injection and cooling system; a container of liquid solution S.sub.3; and third means devised to convey the liquid solution S.sub.3 from said container of liquid solution S.sub.3 to the third injection device of said injection and cooling system.

8. Treatment installation according to claim 7, characterised in that said container of liquid solution S.sub.3 is a reactor containing a solution S.sub.2 different to the liquid solution S.sub.1 to be treated.

9. Treatment installation according to claim 7, characterised in that said installation further has a reactor containing a solution S.sub.2 different to the liquid solution S.sub.1.

10. Treatment installation according to any one of claims 7 to 9, characterised in that said installation further comprises a device generating ultraviolet radiation.

11. Treatment installation according to any one of claims 7 to 10, characterised in that said installation further comprises at least one or a plurality of additional elements chosen from the group consisting of (i) means devised to apply an electrical current or a given potential to the plasma torch and more particularly to the electrodes forming this plasma torch, (ii) means devised to supply the plasma torch with a plasma-forming gas and optionally a secondary gas, (iii) a condenser, (iv) an air filter, (v) a device for cooling the solution S.sub.2, (vi) a device for filtering the solution S.sub.2, (vii) means devised to control and adjust the pH of the solution S.sub.2 and (viii) means devised to add an acid or a base to the solution S.sub.2.

12. Method for the treatment of a solution S.sub.1 comprising a step consisting of injecting said solution S.sub.1 into a plasma generated using a plasma torch as defined in claim 6 and submerged in a solution S.sub.2 different from said solution S.sub.1.

13. Method according to claim 12, characterised in that it comprises steps consisting of: a) generating a plasma from a plasma torch equipped with an injection and cooling system according to any one of claims 1 to 5; c) introducing an oxidant gas in the vicinity of the plasma via the second injection device of said injection and cooling system; d) introducing the solution S.sub.3 in the vicinity of the plasma via the third injection device of said injection and cooling system; and e) introducing the solution S.sub.1 into the plasma submerged in this way via the first injection device of said injection and cooling system.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0112] FIG. 1 is a general and schematic view of a waste treatment device according to the international application WO 2011/064361 and according to the present invention with, as an insert, the schematic representation of the injection and cooling system according to the present invention.

[0113] FIG. 2 is a more detailed view of a blown arc plasma torch suitable for being used in a device for the treatment of liquid waste according to the present invention.

[0114] FIG. 3 relates to the first injection device of the injection and cooling system according to the present invention. FIG. 3A is a longitudinal sectional partial schematic view of the first injection device of the injection and cooling system arranged on the plasma torch. FIG. 3B is a perspective partial schematic view of the first injection device of the injection and cooling system.

[0115] FIG. 4 relates to the second injection device of the injection and cooling system according to the present invention. FIG. 4A is a longitudinal sectional partial schematic view of the first and second injection devices of the injection and cooling system arranged on the plasma torch. FIG. 4B is a perspective partial schematic view of the second injection device of the injection and cooling system.

[0116] FIG. 5 relates to the third injection device of the injection and cooling system according to the present invention. FIG. 5A is a longitudinal sectional partial schematic view of the first, second and third injection devices of the injection and cooling system arranged on the plasma torch. FIG. 5B is a perspective partial schematic view of the third injection device of the injection and cooling system.

[0117] FIG. 6 relates to the cooling device of the injection and cooling system according to the present invention. FIG. 6A is a longitudinal sectional partial schematic view of the first, second and third injection devices and the cooling device of the injection and cooling system arranged on the plasma torch. FIG. 6B is a perspective partial schematic view of the cooling device of the injection and cooling system.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

I. Device

[0118] Hereinafter, the terms axial and radial are defined with respect to the axis of the plasma torch AA.

[0119] FIG. 1 illustrates in the right-hand section thereof the operating principle of the method as described in the international application WO 2011/064361 [5] and as implemented in the present invention.

[0120] FIG. 1 illustrates the description provided hereinafter. The present invention is based on the use of a blown arc plasma 1 submerged in a reactor of cylindrical shape and having a volume of 50 L, filled with water 2. The liquid product to be treated 3 such as a mixture of tributyl phosphate (TBP) and dodecane is introduced into the plasma via the first injection device of the injection and cooling system according to the invention. Once in the plasma, the liquid is instantaneously brought to a very high temperature of the order of 2000 C. in the presence of oxygen, resulting in the total destruction of the organic matter.

[0121] FIG. 2 represents the plasma torch used. It consists of a conventional plasma torch wherein a refractory metal cathode 10 particularly made of tungsten, of conical shape, protected by an argon stream generates an electric arc to an anode 11. The anode 11 is presented in the form of a copper sheath 10 cm in length and 10 mm in diameter. This arc is blown by an argon and oxygen stream. The plasma torch used has a device 12 for cooling by internal water circulation the diaphragm and the anode.

[0122] FIGS. 3A and 3B represent the first injection device 13 of the injection and cooling system according to the invention. This first device is placed at the outlet of the plasma torch and particularly in the vicinity of the anode 11. More particularly, this first device is presented in the form of a cooled metal part made of Inconel measuring 26 mm in height, cylindrical with a circular cross-section and having a central recess 14 of cylindrical shape with a circular cross-section. This central recess 14 forms part of the cavity of the injection and cooling system. This first device has an attachment flange 15 projecting radially outwards having at least one orifice 16 for the passage of a tie rod. Advantageously, the attachment flange has four orifices 16 for the passage of tie rods. This first device 13 has a circulation chamber 17 of the liquid to be treated, at least one intake channel 18 of the liquid to be treated leading to said circulation chamber 17 and at least one injection channel 19 of the liquid to be treated connected to said circulation chamber 17 and leading to the central recess 14 i.e. in the cavity of the injection and cooling system. The intake channel 18 of the liquid to be treated leads via at least one orifice 20 to the side wall of the first injection device 13. The injection channel 19 is oriented towards to the outlet orifice of the plasma 21. The liquid to be treated is injected at a rate of a few centimetres per second, this rate varying according to an adjustable flow rate between 0 and 4 litres per hour.

[0123] FIGS. 4A and 4B represent the second injection device 22 of the injection and cooling system according to the invention. This second device 22 is placed on and in contact with the first injection device 13. More particularly, this second device 22 is presented in the form of a metal part made of Inconel, measuring 22 mm in height, cylindrical with a circular cross-section and having a central recess 23. The walls defining the central recess 23 have an internal radial surface of tapered shape. In fact, this second device 22 acts as a divergent at the nozzle outlet. This second device 22 has an oxidant gas circulation chamber 24, at least one oxidant gas intake channel 25 leading to said circulation chamber 24 and at least one oxidant gas injection channel 26 connected to said circulation chamber 24 and leading to the central recess 23 i.e. in the cavity of the injection and cooling system. The oxidant gas intake channel 25 leads via at least one orifice 27 to the side wall of the second injection device 22. The injection channel 26 of a few mm in diameter is oriented towards the third injection device 28. The second injection device has at least one orifice 29 for the passage of a tie rod. Advantageously, it has four orifices 29 for the passage of tie rods.

[0124] FIGS. 5A and 5B represent the third injection device 28 of the injection and cooling system according to the invention. This third device 28 is placed on and in contact with the second injection device 22. More particularly, this third device 28 is presented in the form of a metal part made of stainless steel, measuring 22 mm in height, cylindrical with a circular cross-section and having a central recess 30 of cylindrical shape with a circular cross-section and having a central recess 30. The walls defining the central recess 30 have an internal radial surface of tapered shape. This third device 28 has a circulation chamber 31 of the solution S.sub.3 as defined above and particularly water, at least one intake channel 32 of the solution S.sub.3 and particularly water leading to said circulation chamber 31 and at least one injection channel 33 of the solution S.sub.3 and particularly water connected to said circulation chamber 31 and leading to the central recess 30 i.e. in the cavity of the injection and cooling system. The intake channel 32 of the solution S.sub.3 and particularly water leads via at least one orifice 34 to the side wall of the third injection device 28. The injection channel 33 is oriented towards the cooling device 35. The third injection device has at least one orifice 36 for the passage of a tie rod. Advantageously, it has four orifices 36 for the passage of tie rods.

[0125] FIGS. 6A and 6B represent the cooling device 35 of the injection and cooling system according to the invention. This cooling device 35 is presented in the form of a metal part made of stainless steel, measuring 107 mm in height, having the shape of a shaft (or sheath or nozzle) and having a central recess in the form of a shaft (or sheath or nozzle) wherein the internal walls define a cylindrical central recess 37 having a circular cross-section. In the wall thereof, the cooling device 35 has a channel 38 or a plurality of channels for circulating a coolant such as water. This cooling device 35 has an attachment flange 39 projecting radially outwards having at least one orifice 40 for the passage of a tie rod. Advantageously, the attachment flange has four orifices 40 for the passage of tie rods.

[0126] The injection and cooling system according to the invention has at least one tie rod or bolt which jointly provides the attachment and fastening of the devices 13, 22, 28 and 35 to one another and with the plasma torch. These tie rods pass through the orifices 16, 27, 34 and 40.

[0127] The treatment method using a blown arc plasma 1 obtained from a plasma torch equipped with an injection and cooling system submerged in a reactor filled with an aqueous solution 2. This aqueous solution may further contain in solubilised form metal ions and hydrogen peroxide in order to carry out a Fenton reaction maintained by the UV radiation from the plasma torch.

[0128] After instantaneous gasification and decomposition in the argon-oxygen plasma plume, the residual or partially oxidised organic compounds are subjected to a second oxygen stream introduced via the second injection device 22 of the injection and cooling system according to the invention.

[0129] The combustion gases are then quenched with water so that they reach a temperature level suitable for establishing the chemical equilibriums compatible with emission requirements. The addition of water which may also be the aqueous solution of the reactor is carried out by means of the third injection device 28 of the injection and cooling system according to the invention.

[0130] The gases then pass though the cooling device 35 of the injection and cooling system according to the invention wherein they finish cooling and adopt the final composition thereof before entering the core of the aqueous solution wherein they are instantaneously quenched.

[0131] During bubbling, the gases are purified of the dust thereof and neutralisable chemical species such as HCl, HF, SOx, NOx, P.sub.2O.sub.5, etc. They then pass through a condenser 4 which also acts as a demister and are discharged outside. According to purification level sought, the gases may be subjected to ultra-high-efficiency filtration 7 to prevent any particle emissions.

[0132] The aqueous solution of the reactor may contain ions suitable for catalysing the optimisation of the degradation of residual compounds at very low levels. For example, ferrous ions Fe.sup.2+ associated with the presence of hydrogen peroxide may be added so as to catalyse the formation of OH radicals ensuring the destruction of residual organic matter. The Fe.sup.3+/Fe.sup.2+ transition may then be performed by the UV radiation from the arc plasma.

[0133] The operation of the plasma torch and the combustion of the organic matter cause overheating of the aqueous solution situated in the reactor. In order to reduce the saturating vapour pressure, the water is cooled in a loop via an exchanger 6. The temperature thereof is maintained at a level limiting the vapour pressure at the reactor surface. The cooling circuit is equipped upstream from the exchanger 6 with a filter 5 retrieving the solids from the precipitation of the minerals present in the effluents to be treated. This filtration-cooling loop extracts the solution into the lower part of the reactor and reintroduces same into the upper part thereof.

[0134] During the treatment, the reactor solution may become acidic or basic according to the circumstances. Online monitoring of the pH 8 enables continuous adjustment of the value thereof by adding an acid of a based according to the circumstances 9. This adjustment should, if applicable, account for the chemical requirements imposed by the use of the Fenton reaction.

II. Operation and Performances

[0135] The experimental development phases used to design the enhancements described in the present invention clearly illustrate the various enhancement steps.

[0136] The tests were conducted on a solution to be treated comprising a mixture of tributyl phosphate (TBP) and dodecane, this mixture having the dual specificity of having a high NCV (10 kW.Math.h.Math.L.sup.1). This solution was injected into the plasma at a feed rate of 3 L.Math.h.sup.1.

[0137] The plasma torch operates at a flow rate of 30 NL.Math.min.sup.1 of argon and 180 NL.Math.min.sup.1 of oxygen in the arrangement represented in FIG. 1.

[0138] The measurements made on the composition of the solution show destruction rates greater than 99.5%. The positioning of the various stages at the plasma torch outlet modifies the gas emission composition substantially. The CO and CO.sub.2 contents, representative of the level of oxidation of the gas mixture, were monitored in the following four scenarios:

Untreated Injection into Plasma Flame:

[0139] CO composition at outlet: 12%

[0140] CO.sub.2 composition at outlet: 4%

Injection into Plasma Flame Followed by Re-Enrichment with O.sub.2 (40 NL.Math.Min.sup.1):

[0141] CO composition at outlet: 9%

[0142] CO.sub.2 composition at outlet: 6%

[0143] Note herein that adding oxygen provides superior oxidation but also partial cooling of the gas enabling a thermal shift of the CO/CO.sub.2 equilibrium.

Injection into Plasma Flame Followed by Re-Enrichment with O.sub.2 (40 NL.Math.Min.sup.1) and Cooling in Nozzle:

[0144] CO composition at outlet: 8%

[0145] CO.sub.2 composition at outlet: 9%

[0146] The cooling provided by the outlet nozzle is not sufficient as the CO level is still well above emission standards.

Injection into Plasma Flame Followed by Re-Enrichment with O.sub.2 (40 NL.Math.Min.sup.1), Addition of Cooling Water (0.3 L.Math.Min.sup.1) and Cooling in Nozzle:

[0147] CO composition at outlet: 0.2%

[0148] CO.sub.2 composition at outlet: 8%

[0149] This last test demonstrates the effectiveness of the technological enhancements applied.

REFERENCES

[0150] [1] Patent application EP 0,469,737 (Tioxide Group Services Limited) Destruction process published on 5 Feb. 1992. [0151] [2] Alekseev N. V., Samokhin A. V., Belivtsev A. N. and Zhavoronkova V. I., (2000) Thermal-Plasma Jet Oxidation of Phenol in Aqueous Solutions, High Energy Chemistry, Vol. 34, No 6, pp. 389-393. [0152] [3] Fortin L., Soucy G., Kasireddy V., Bernier J.-L., Boulos M. I (1999) The Use of Thermal Plasma for Wastewater Treatment, 14th International Symposium on Plasma ChemistryISPC'14, Prague (Czech Republic), pp. 2387-2392. [0153] [4] International application WO 97/22556 (Alcan International Limited) Thermal Plasma Reactor and Wastewater Treatment Method published on 26 Jun. 1997. [0154] [5] International application WO 2011/064361 (CEA) Method and device for the treatment of waste through injection into an immersed plasma published on 3 Jun. 2011.