FR2780235A1 - Destruction of toxic waste in plasma jet - Google Patents

Abstract

The method involves injecting waste, in fluid form, into the center of a plasma jet against the flow.- DETAILED DESCRIPTION - Fluid (F) to be treated is forced under pressure, at supersonic speed, through a nozzle (3) located on the axis (4) of a plasma jet (2) and directed towards the discharge orifice of a plasma torch (1). The torch produces a symmetrical, concentrated flow with extremely high central temperatures, over 4000 degrees C, in view of which the injecting nozzle is cooled by water circulation. During injection the fluid is vaporized as fine droplets, maximizing the surface area available for heat transfer. Typically, the equipment forms part of a treatment plant for the destruction of chemical warfare weapons, other means being provided for reducing solid wastes. The fluid/plasma mass ratio, in the range 0.1-1, and type of plasma gas are chosen to suit the type of waste, as is the distance (d) of the nozzle from the originating torch, which ranges from 10 to 50 cm with torch powers between 200 and 700 kW. In the complete plant, fluid and solid materials are produced from the weapons material in a detonation chamber. Fluids undergo the plasma process and the solids are heated to recover metals, producing also gases which are further treated to extract pollutants in condensate form

Description

PROCESS FOR INJECTING A FLUID INTO A PLASMA JET

  TO BE TREATED AND APPLIED IN PARTICULAR TO THE DESTRUCTION OF

TOXIC WASTE

  The present invention relates to the treatment of fluids, in particular fluids containing toxic waste, by decomposition by injection into

  a jet of arc plasma from a plasma torch.

  More specifically, the invention relates to the injection into a blown arc plasma of liquid or gaseous products for the purpose of destruction, thanks to the high enthalpy and temperature of the plasma, of the gas or

toxic liquids.

  The aim of the present invention is to propose a new method of injecting fluids into the plasma jet at the outlet of the torch, in

  optimal enthalpy, flow and temperature conditions.

  To this end, the invention relates to a process for injecting a fluid to be treated into a plasma jet from a torch, in particular of the blown arc plasma type, characterized in that it consists in injecting said fluid in the axis, inside and against the current of the dart of the plasma jet, at the outlet of the torch, said injection being preferably carried out in supersonic regime and with a ratio of the mass flow of said fluid of the order of 0.1 to 1 times that of plasma. In the case of injection of a liquid, this will advantageously be injected in vaporized form in fine droplets, so as to increase the

  plasma exchange surfaces.

  The means for injecting fluids into the plasma dart, under such conditions, will, taking into account the temperatures present, which may reach or exceed 4000 C in the dart, suitable cooling means, in particular a circulation of fluid such as of water. The subject of the invention is also an application, inter alia, of the above injection method, to the destruction of toxic waste, in particular fluids originating from chemical weapons, within the framework of the

  destruction or neutralization of these weapons.

  To this end, the invention relates to an application of said method characterized in that it consists in injecting at the outlet of a plasma torch with a blown arc in the dart of the plasma jet, in the axis and against the current of the latter, the fluids from the separation in an ammunition detonation chamber containing toxic substances and to treat the gaseous effluents from said injection by brutal cooling, the nature of the plasma gas, as well as the separation conditions in said chamber detonation and cooling of said gaseous effluents being determined so as to minimize the gas flows by favoring the generation of products

  condensable, such as soot, salt, particulate deposits.

  Other characteristics and advantages will emerge from the description which

  will follow modes of implementation of the method of the invention, description

  given by way of example only and with reference to the appended drawings in which: - Figure 1 is a diagram illustrating the injection principle of the invention - Figure 2 is a diagram illustrating an application of the method of the invention to the treatment of toxic products in connection with the destruction of chemical weapons; FIG. 3 illustrates a first variant of the method of FIG. 2, and

  - Figure 4 illustrates a second variant.

  In FIG. 1, the nose of a blown arc plasma torch, preferably of the tubular or axisymmetric type, is shown diagrammatically at 1 in order to obtain a plasma jet at the torch outlet, the dart 2 of which is the more axisymmetric and more concentrated possible, to obtain in the heart of the dart the highest possible temperature. Specifically, in the heart of the sting, in accordance with the invention, is injected by appropriate means symbolized in 3, in the axis 4 of the sting 2 and at

  counter-current, a fluid F to be treated.

  Said injection, symbolized at I in FIG. 1, is preferably carried out at a speed of ejection of the supersonic fluid F and with a ratio of the mass flow rates of the fluid and the plasma gas of the plasma respectively.

torch 1, of the order of 0.1 to 1.

  The distance d between the nose of the torch 1 and the injection means 3 depends of course on the type and the power of the torch; it is around 10 to 50 cm for a torch in the power range of 200 kW

at 700 KW.

  The fluid F, when in the liquid state, is preferably vaporized in the dart 2 in fine droplets so as to increase the exchange surfaces

with plasma.

  The nature of the plasma gas as well as the ratio of the mass flow rates of injected fluid / plasma gas are adapted to the nature of the

  constituents of the fluid F to be treated.

  The injection means 3 will of course be continuously cooled during the injection, for example using a circulation of a fluid such as water, taking into account the temperature level reached in the sting 2 and which can

exceed 4,000 C.

  The conjunction of the very high enthalpy (thermodynamic energy) of the plasma and the chosen injection mode, creating maximum turbulence, results in synergistic effects causing intimate and total contact between the molecules to be "cracked" and the plasma. and endothermic chemical reactions, thus ensuring optimal molecular dissociation and

  much stronger reaction kinetics.

  The injection process according to the invention is susceptible of numerous applications. We will now describe one with reference to Figures 2 to 4, and which

  generally targets the destruction of chemical weapons.

  The objective is the destruction of toxic waste constituted by ammunition, composed of approximately 80% of metal, 17% of toxic elements and

  pyrotechnics and 3% inert materials.

  The first stage of the destruction process is a separation of the solid, liquid, gaseous phases of the ammunition using the

  operation of its pyrotechnic charge.

  For this purpose, a detonation chamber 5 is used. Its principle is

well known.

  One or more munitions are detonated there, in particular by

  thermal rise of ammunition.

  The products from the detonation chamber 5 are separated into fluids 6 and solid debris 7. The first (6) are injected into the dart 2 of a plasma torch 1 with a blown arc, in accordance with the process of

figure 1.

  In this type of application, the ratio of fluid mass flow rates

  injected / plasma gas will preferably be close to 1.

  The solid debris 7 is introduced into an oven 8 in which is

  mounted torch 1, the metal parts being melted in a bath 9.

  The gaseous effluents 10 from the furnace 8 are treated in a heat exchanger 1 1 o there is an abrupt cooling of the effluents to obtain maximum condensation in solid form (soot, salts, deposits

  particulate matter) of polluting substances.

  To favor such condensation as much as possible, the following parameters will be acted on, depending of course on the nature of the munitions condensation temperature, quantity of oxygen leaving the furnace 8 for cooling. Generally, we will look for, in the

  wherever possible, the lowest possible oxygen level.

  The oxygen present in the gaseous effluents 10 can come from the molecules of the products decomposed in the chamber 5, from the atmosphere of the latter and from the plasma gas of the torch 1, insofar as this gas

is air.

  At the level of the munitions to be treated, it is possible to combine various ammunitions to be treated in the same chamber 5 in order to keep an average oxygen level

as low as possible.

  To reduce oxygen, it is advantageously possible to use as plasma gas, as well as for the atmosphere internal to the detonation chamber 5,

  a neutral gas, for example nitrogen.

  In addition, the detonation chamber can be optionally put

under depression.

  For example, the gaseous effluents 10 will be subjected to a

  brutal cooling bringing the gases to room temperature.

  Cooling can take place in a single step or

  stepped according to specific objectives.

  Preferably, the heat exchanger 11 will be a device

  not introducing any additional quantity of gas stream to be treated.

  The treatment in 11, under the conditions explained above, is likely to favor combinations of oxygen giving non-toxic products or in the form of water or carbon dioxide and to avoid combinations of oxygen in the form NOx-SOx, in the form of dioxins or

  furans and in the form of carbon monoxide.

  If necessary, a punctual injection of water vapor can be made, to provide in a practical form a supplement of oxygen / hydrogen necessary for example to avoid the formation of CO, at a certain stage of the

  treatment or to promote the appearance of such a desired molecule.

  Advantageously, the management of the effluents 10 will take into account, in a step symbolized at 12 in FIG. 2, the separation of the soot, salts and particles according to their nature, for example by a suitable centrifugal device, the incorporation into the molten bath 9 of the furnace 8 of the maximum possible of carbon soot and arsenic particles, the treatment of major residual pollutants NOx-SOx and minor, by the process best suited among the

  industrial solutions: wet, semi-wet, dry routes.

  Said management will also take into account the neutralization and / or recovery treatments of the acids present, mainly based on chlorine, fluorine, bromine, phosphorus and sulfur, as well as the

  ex situ recovery of the remaining quantities of arsenic in the form AS203.

  As a variant of the process of FIG. 2 and for reasons of convenience of operating management, the melting part of the solid elements (7) can be

  dissociated from the destruction of fluids part (6).

  In this case, illustrated by FIGS. 3 and 4, the single plasma furnace 8 may advantageously be replaced by a reactor 13 equipped with a plasma torch 1 for the treatment of fluids 6 and by a separate melting furnace

solids 7.

  This could be for example (FIG. 3) an inductive heating oven i15 14, which has the advantage of less thermally stressing the refractories without adding anything to the gas balance. The gaseous effluents 15 from the oven 14

  are treated in 1 1 as the gaseous effluents 10 from the reactor 1 3.

  The separate oven can also be (FIG. 4) a fluidized bed oven 16

  whose purpose will be to clean the metal parts and no longer to melt them.

  The thermal mixing, at a temperature of the order of 1200 ° C., of the sand bed 17 of the furnace 16 is advantageously carried out by the outlet effluents

  of reactor 13, which adds nothing to the gas balance.

  The gaseous effluents 18 from the oven 16 are treated in 1 1 like the

effluents 10 of Figures 2 and 3.

  In the devices of FIGS. 3 and 4, the injection of the fluids into the sting 2 of the plasma of the torch 1 is carried out according to the same process as in the

Figure 2 device.

  In the devices of FIGS. 2 to 4, solid by-products, such as fly ash, originating from stage 12, may advantageously be added, in the context of the management of the by-products of the smoke treatments. solids 7 before their introduction into the

oven (8, 14, 16).

  Finally, the invention is obviously not limited to the embodiments shown and described above but on the contrary covers all of them.

  variants, in particular as regards the nature of the fluids and solids to be treated and the constraints imposed on gaseous and solid effluents from the 5 stages of treatment of said fluids and solids.

Claims (13)

  1. Method for injecting a fluid (F) to be treated into a plasma jet from a torch (1), in particular of the blown arc plasma type, characterized in that   that it consists in injecting said fluid (F) in the axis (4), inside and against   current of the dart (2) of the plasma jet, at the outlet of the torch, said injection (I) being preferably carried out in supersonic regime and with a ratio of   mass flow of said fluid of the order of 0.1 to 1 times that of plasma.   2. Method according to claim 1, characterized in that the fluid   in liquid form is injected in vaporized form in fine droplets.   3. Application of the method according to claim 1 or 2, to the destruction of toxic waste in particular of fluids from chemical weapons, characterized in that it consists in injecting at the outlet of a plasma torch with a blown arc (1) into the dart (2) of the plasma jet, in the axis and against the current, the fluids (6) coming from the separation in a detonation chamber (5) of munitions containing toxic substances and to treat the effluents gaseous (10) resulting from said injection by brutal cooling (11), the nature of the plasma gas, as well as the conditions of separation in said detonation chamber (5) and of cooling of said gaseous effluents (10) being determined so as to minimize gas flows by favoring the generation of condensable products, such as soot, salts, deposits particulate.   4. Application according to claim 3, characterized in that the cooling is carried out so as to bring the gases to the temperature   in one or more steps.   5. Application according to claim 3 or 4, characterized in that the   plasma gas is a neutral gas, especially nitrogen.   6. Application according to one of claims 3 to 5, characterized in that   that the atmosphere in the detonation chamber (5) is formed of a gas neutral, especially nitrogen.   7. Application according to one of claims 3 to 5, characterized in that   that the detonation chamber (5) is placed under vacuum.   8. Application according to one of claims 3 to 7, characterized in that   that the solid part (7) coming from the detonation chamber (5) is melted in an oven (8) incorporating the plasma torch (1).   9. Application according to one of claims 3 to 7, characterized in that   that the fluids part (6) coming from the detonation chamber (5) is treated in a reactor (13) incorporating the plasma torch (1), and the solids part (7)   is treated in a separate oven (14, 16).   10. Application according to claim 9, characterized in that the separate oven is an induction oven (14), the gaseous effluents (15) from the latter being treated jointly with the gaseous effluents (10) from the   fluid treatment reactor (1 3) (6).   1. Application according to claim 9, characterized in that the separate oven is a fluidized bed oven (16), the gaseous effluents (18) from this   the latter being treated by an abrupt cooling according to claim 4.   12. Application according to claim 11, characterized in that the fluidized bed oven (16) comprises a sand bed (17) stirred by the effluents   gaseous (10) from said reactor (13) for processing fluids (6).   13. Application according to one of claims 3 to 12, characterized in   what is done in one of the stages of treatment a punctual injection   water vapor for additional oxygen / hydrogen supply.