FR2960056A1 - METHOD AND DEVICE FOR DESTRUCTION OF PYROTECHNIC COMPOUNDS - Google Patents

Abstract

The present invention relates to a method and a device for destroying at least one pyrotechnic compound, comprising the heat treatment of a feedstock consisting essentially of the said at least one pyrotechnic compound or an aqueous slurry containing the at least one pyrotechnic compound or in an aqueous solution containing said at least one pyrotechnic compound, said sludge or aqueous solution being capable of containing in addition organic matter. Said method comprises: - the constitution of a mixture by adding to said charge of a powder material in an amount suitable for ensuring the inerting of said at least one pyrotechnic compound present, considered in the dry state; said pulverulent material having a melting or decomposition temperature higher than the maximum temperature for carrying out said process, and - the heat treatment in an oven of said mixture, at a temperature sufficiently high to lead to the destruction of said at least one pyrotechnic compound .

Description

The present invention relates to a method for destroying pyrotechnic compounds. It also relates to a device suitable for implementing said method. Said method and device are particularly useful in soil remediation contexts containing pyrotechnic compounds. They are particularly suitable for treating soils polluted with nitrocellulose. The production sites for pyrotechnic compounds have often been exploited for several decades or even more than one hundred years, and the methods for treating rejects, rejects or surplus pyrotechnic compounds have not always respected, for example the past, the current environmental standards. One method used in the past has been to get rid of pyrotechnic compounds by dumping them into basins (artificial or natural) in order to inert these compounds in the presence of water. Over the years and especially during the First World War, large quantities of pyrotechnic compounds (up to 10,000 tons per site), including nitrocellulose and military powder for small caliber weapons, have been rejected and preserved. in basin, underwater, mixed with various materials (sand, clay, organic materials, etc.). Today, industrial soil remediation policies require the decontamination of these basins. The present invention falls within this framework and proposes an original method for destroying pyrotechnic compounds. The proposed method makes it possible to overcome the pyrotechnic dangers associated with such operations. It can thus be implemented without danger within a pyrotechnic site or in an urban environment. Methods of destroying pyrotechnic compounds, "pure" or contained in an aqueous slurry or aqueous solution, have already been described. "Pure" pyrotechnic compounds are usually destroyed by open burning. This method generates atmospheric pollution and pyrotechnic and / or fire hazards. One method of destroying pyrotechnic compounds contained in an aqueous slurry or an aqueous solution is to compost them in an oxygenated medium so as to degrade them biologically.

To the slurry or aqueous solution containing the pyrotechnic compound (s), manure, vegetable substances, water and wood chips are added. Windrows are aerated by turning them over. The large quantities of compost to be treated (it takes about 10 m3 of material added to 1 m of mud or aqueous solution) induce heavy handling operations and require large storage. A further difficulty of this method is to maintain, throughout the degradation process, a sufficient moisture of the compost to ensure the inerting of the pyrotechnic compound (s) within it. Another method relies on the thermal degradation of the pyrotechnic compound (s) contained in a sludge or aqueous solution. Typically, common pyrotechnic compounds (RDX, HMX, nitrocellulose, etc.) begin to thermally decompose between 180 ° C and 350 ° C. In the presence of water, said compounds are inerted. During the heat treatment, said water evaporates before the decomposition process of the pyrotechnic compound (s) begins. A variation of this method is to suck the sludge, dry it and then process it in an oven. This variant of course has the disadvantage of presenting a pyrotechnic hazard, since the material is no longer inert with water from the beginning of the treatment. According to another variant, the sludge or aqueous solutions containing the pyrotechnic compound (s) are directly introduced into the furnace. In this case too, the product placed in the oven first begins to dry before the decomposition of the pyrotechnic compound begins. It therefore presents a pyrotechnic danger during treatment. Those skilled in the art are therefore always in search of a method for destroying pyrotechnic compounds contained in aqueous sludges or solutions, which is economical, environmentally friendly and without pyrotechnic danger, which process can also ideally be opens for the destruction of "pure" pyrotechnic compounds. To avoid any pyrotechnic hazard, the material entering the process (material to be treated) and the material handled during the process (material being processed) must not be classified as a pyrotechnic product. Such a classification can be determined by pyrotechnic sensitivity tests, well known to those skilled in the art, which can vary from one country to another according to local regulations. Such classification is generally determined by means of tests that meet UN standards for the classification of substances for carriage. According to the latter standards, a material designated as inert in the rest of the document is outside the UN class 1 (corresponding to pyrotechnic products). The method of the invention makes it possible to thermally destroy at least one pyrotechnic compound, "pure" or contained in an aqueous solution or an aqueous sludge (which may both contain organic materials), by raising the temperature in an oven, without generating pyrotechnic danger. For this purpose, a pulverulent material having a melting or decomposition temperature higher than that of the furnace, and thus also greater than the decomposition temperature (the highest) of the pyrotechnic compound (s), is added to the (x) said "pyrotechnic" compound (s) "pure (s)" or contained (s) in an aqueous sludge or an aqueous solution, before its (their) introduction in the oven, and in sufficient quantity to ensure the inerting of the (said) pyrotechnic compound (s) considered dry.

According to its first object, the present invention therefore relates to a method of destroying at least one pyrotechnic compound comprising the heat treatment of a feedstock consisting essentially of said at least one pyrotechnic compound ("pure") or an aqueous slurry containing said at least one pyrotechnic compound or an aqueous solution containing said at least one pyrotechnic compound, said sludge or aqueous solution being capable of containing further organic matter. Typically, said method comprises: - constituting a mixture by adding to said feedstock a powder material in an amount suitable to ensure the inerting of said at least one pyrotechnic compound present, considered in the dry state; said pulverulent material having a melting or decomposition temperature above the maximum temperature for carrying out said process, and - the heat treatment in an oven of said mixture at a temperature sufficiently high to lead to the destruction of said at least one compound pyrotechnic.

When the pyrotechnic compound (s) (to be destroyed) is (are) contained in a sludge or an aqueous solution, said mud or heat-treated aqueous solution begins to dry up, before starting the decomposition of the said pyrotechnic compound (s), hence the pyrotechnic danger mentioned above The addition, in an effective amount, of the powdery material to the charge (pyrotechnic compound (s) "pure (s) "or contained in a sludge or aqueous solution) ensures the inerting of said" pure "pyrotechnic compound (s)" or after drying (when (s) ) is (are) initially contained in a sludge or aqueous solution), throughout the process, until the complete destruction of said pyrotechnic compound (s) .This process therefore presents no danger The mixture - pyrotechnic charge added with the said powdery material - thus behaves like an inert product for the duration of the process. of the invention. It is understood that the mixture in question is a sufficiently homogeneous mixture, preferably as uniform as possible, so that the inerting sought is ensured (in all its mass). The (minimal) quantity of powdery material to be added to said charge to be inerted (by inerting said at least one pyrotechnic compound present therein) obviously depends on the quantity of pyrotechnic compound (s) present in said charge. and pyrotechnic sensitivity properties of the at least one pyrotechnic compound in question. This (minimal) quantity to be added is determined using laboratory tests, well known to those skilled in the art, for measuring the amount of inert material to be added to at least one pyrotechnic compound to ensure its inerting. Typically, the amount of pulverulent material added is such that its mass represents at least 85% of the sum of the masses of said at least one dry pyrotechnic compound and said added powdery material. The mass of pulverulent material added is generally from 90% to 99% of said sum of masses. When the pyrotechnic compound (s) is (are) contained in a sludge or aqueous solution, the mass of pulverulent material added, determined from the content of pyrotechnic compound (s) in the mud or the aqueous solution, typically represents between 50% and 95% of the total mass introduced into the oven. Thus, generally, the method of the invention comprises (in addition to the two successive mixing and heat treatment steps set out above), prior to the addition of the pulverulent material (prior to said first mixing step): measuring the mass ratio of the at least one pyrotechnic compound in the charge, advantageously measured by thermogravimetry.

It should be noted that such a measurement could be carried out well in advance of said process or that it may be non-mandatory in certain contexts, particularly if it is known that the rate of pyrotechnic compound (s) to be destroyed is very low. and / or that safety is assured every time by using a large quantity, certainly in (large) excess, of powdery material. However, it should be understood that, in order to optimize the implementation of the process, in particular with a view to minimizing the volume of mixture to be heat treated, it is advantageous to know the minimum effective quantity of powder material to be added (for reasons safety, to add in a reasonable excess).

In the same way, the process of the invention generally comprises (in addition to the two successive stages of mixing and heat treatment mentioned above), with reference to the subsequent heat treatment, a preliminary step of measuring the decomposition temperature of said at least one pyrotechnic compound to be destroyed present in the charge. This measurement is advantageously also carried out by thermogravimetry. Nor is it obligatory in certain contexts, for example when the compound or mixture of compounds to be destroyed is perfectly identified (i.e. when its decomposition temperature is already known).

According to an advantageous variant, by thermogravimetry, one determines both the mass ratio of the at least one pyrotechnic compound to be destroyed within the charge and the decomposition temperature of said at least one compound. In the context of variants of the implementation of the process of the invention, at the end of the heat treatment (at the furnace outlet), provision is made for: the measurement, advantageously by thermogravimetry, of the (residual) mass ratio of said at least one pyrotechnic compound, and / or, advantageously, and - the recovery of the products (of the treated feedstock) for recycling into the process or disposal. Note that, in the event that the residual rate is (almost) zero, its "measure" may consist of a simple control, and that, in the event that the residual rate is certainly zero, its measurement is superfluous. In the event that the feedstock to be treated contains several pyrotechnic compounds, the oven temperature is obviously adequate for the destruction of the compound having the highest decomposition temperature. The powder material used obviously has a sufficiently small particle size to be able to ensure an intimate mixture with the at least one "pure" pyrotechnic compound or contained in a sludge or an aqueous solution. The median diameter (the particle size) of said pulverulent material is generally between 0.01 and 5 mm, advantageously between 0.06 and 2 mm. Said powder material is chosen from inorganic and organic materials or mixtures thereof. Minerals are particularly preferred. It is advantageously sand (conventionally composed mainly of quartz, granite and mineral salts). The preferred organic material is sawdust. Said powder material is therefore preferably sand or sawdust. It consists very advantageously of sand. Any other organic or inorganic material may be used, provided, of course, that its melting or decomposition temperature is greater than the maximum process temperature (at the maximum operating temperature of the oven during said process ), and therefore also greater than the decomposition temperature of said at least one pyrotechnic compound (to be destroyed). The process of the invention is particularly suitable for the destruction of nitrocellulose (T-decomposition 180 ° C) and military powders for small caliber weapons. However, it is suitable for the destruction of other pyrotechnic compounds, such as in particular RDX, HMX, CL2O, nitroglycerin and solid propellant fragments. More generally, it is suitable for the destruction of any pyrotechnic compound and mixture of pyrotechnic compounds, insofar as a pulverulent material, capable of ensuring inerting and having an adequate melting temperature or decomposition, exists. The method of the invention can be implemented continuously or sequentially. According to a first variant, more particularly adapted when the said pyrotechnic compound (s) is (are) contained in a mud or an aqueous solution containing organic materials, the heat treatment of the process of the invention is implemented under aerobic conditions. This first variant may also be suitable for "pure" pyrotechnic compounds, but in this case, the second variant described below is preferred. In the context of this first variant (hereinafter described in a context of treating sludges or solutions with organic materials), the furnace is brought to a temperature sufficient to ensure the destruction by combustion of the at least one pyrotechnic compound and said material. organic (included in the aqueous slurry or in the aqueous solution) contained in the mixture introduced into the oven. The heating of the oven is adjusted so that the temperature of the products at the outlet of the oven is between 250 and 450 ° C. This imposes a temperature in the furnace certainly high enough (up to 1000 ° C locally) to lead to the destruction of said at least pyrotechnic compound and said organic material. Given this high temperature in the oven (much higher temperature (at least 100 ° C, generally at least 200 ° C) at the decomposition temperature of the pyrotechnic compound (s) present (s)), the powder material suitable for carrying out the process according to this variant is a mineral material, advantageously sand. The combustion destruction of said at least one pyrotechnic compound and said organic material at this elevated temperature produces gases and particles. The powder material can indeed break mechanically in the oven. Fine dust of said powder material can therefore also be produced. These emissions make it necessary to associate the oven with ventilation connected to an evacuation outlet extended by a chimney (chimney often incompatible with an urbanized environment) equipped with particulate filters and a post-combustion gas treatment device. At the end of the process, the soiled pulverulent material is recovered by residues, carbonized combustion products, not evacuated, originating from the organic material and by mineral elements coming from the sludge or the aqueous solution. Said soiled powdery material can be recycled in the process or repelled according to its state. According to a second, advantageous variant, the heat treatment of the process of the invention is carried out under anaerobic condition at a lower temperature. The oven is brought to the decomposition temperature of the at least one pyrotechnic compound to be destroyed, typically between 180 ° C and 350 ° C for common pyrotechnic compounds, or at a temperature similar to slightly higher (up to + 50 ° C maximum ) at said decomposition temperature. Given the lower temperature of the furnace compared to the previous variant, the powder material can be chosen not only from mineral materials but also from mixtures of organic and inorganic materials and from organic materials. Under these conditions, only said at least one pyrotechnic compound is destroyed and at the end of the process the pulverulent material and the undecomposed dry organic matter are recovered, if said material was present in the sludge or aqueous starting solution. After separation, said powdery material is recycled or scrapped according to its state and said dry or rehydrated organic material can be disposed of or redeposited at the place of sampling. The advantage of this variant is that it does not generate large quantities of gas and particulate emissions, and therefore does not require an emission processing device associated with the furnace. Ventilation connected to an exhaust vent only with activated carbon filters and particulate filters is required to trap products (eg volatile organic compounds and / or dust) that may be emitted at ambient temperature. "low" oven operation (less than 500 ° C, usually less than 400 ° C). According to its second object, the invention relates to a device suitable for implementing the method of the invention, as described above. This device comprises a mixer, for example of the concrete mixer type, for mixing (effectively) the charge to be treated with said powder material and an oven. In order to prevent the product introduced into the oven from settling by gravity and / or to prevent the formation of a dried mud shell which makes a thermal barrier limiting the degradation of the pyrotechnic material, it is recommended to use a rotary kiln or circulation of material. Ventilation makes it possible to suck up and evacuate, through an outlet of the oven, the gases and particles emitted by the heat treatment. The device of the invention is advantageously equipped with an original measurement means: a macro thermobalance, in particular of the type described in the reference "Thermal analysis of energy crops, Part I. The applicability of a macro-thermobalance for biomass studies ", Khalil RA et al., Journal of Analytical and Applied Pyrolysis, 2008, vol. 81, No. 1, pp. 52-59, using the method of determination by thermogravimetry known to those skilled in the art and in particular allowing rapid measurement (in 15 to 30 s), on representative sample masses (500 g per analysis), the level of compound (s) pyrotechnic (s) content (s) in a slurry or aqueous solution and thus to determine the amount of powder material to be added. This measuring instrument is adapted to the temporal sequence of the process, unlike the usual laboratory methods (for example chromatography) requiring several hours of analysis. The principle consists in heating the sample arranged in thin layers on several trays so as to determine by weighing, at 100'C, the amount of water evaporated, then at a higher temperature, at the decomposition temperature of the at least one compound pyrotechnic, the amount of said at least one decomposed pyrotechnic compound. This analysis is advantageously also carried out at the furnace outlet so as to ensure that the pyrotechnic compound has been destroyed. At the furnace outlet, it is also possible to ensure the absence of a pyrotechnic compound by performing a simple colorimetric test using colored indicators, reacting to the presence of chemical bonds characteristic of the pyrotechnic compound (s) ( s) Wanted. The measurement of the rate of pyrotechnic compound (s), at the entrance and exit of the furnace, is generally essential to control, pyrotechnically process safety.

According to the variant of implementation of the process (see above), the outlet of the oven can be provided simply with activated carbon filters and particles (low temperature implementation variant) or extended by a chimney equipped with particulate filters and a means of gas afterburning (variant implementation at high temperature). It is now proposed to illustrate the present invention by an example. Said example relates to the implementation of the method of the invention according to its first variant (in aerobic condition, "at high temperature"), for the destruction of nitrocellulose (pyrotechnic compound of class 1) contained in a pool of a industrial pyrotechnic site operated for over a hundred years. The mass of nitrocellulose contained in said basin is about 8000 t.

The products recovered in said basin consist of sludge (based on sand, pebbles) aqueous or aqueous solutions that may contain organic material, mainly of plant origin. The concentration of nitrocellulose in said recovered and dried products ranges from 100% (the product recovered is then composed of nitrocellulose fibers soaked in water) to 0% depending on the location of the sample. It may happen that the recovered products do not contain, locally, nitrocellulose. The mud is drawn from the basin by a mechanical shovel and then scoured (we remove the large stones, branches ...) and deposited on a concrete slab. After natural spinning, the residual water content is at least 70%. A representative sample (sludge) with a mass of 500 g is analyzed by means of a macro thermobalance to determine the level of nitrocellulose contained in its volume. It is to be treated according to the invention. The amount of powder material to be added to said sample, so as to ensure the inerta e of the charge in the oven, can then be determined. The powder material added is fine sand, washed. The median diameter of the particles of said sand of about 1 mm. The amount (mass) of sand added represents 90% of the sum of the dry nitrocellulose and sand masses, the target inerta is thus ensured), hence the importance of a rapid and reliable measurement of the nitrocellulose content. . The mixing process between the mud containing the nitrocellulose and the sand is discontinuous: it is done in a concrete mixer (600 Kg per batch (batch)), as is used in the plants where the cement is prepared. The oven used is a rotary kiln. The quantity of material introduced per hour in the oven is 3 to 3.5 tons. The residence time in the oven is about 20 minutes. The oven is cleaned periodically. The time intervals between each cleaning of the furnace are variable (of the order of the month generally, but this is more frequent when the treated sludge contains clay (the clay when drying is a crust on the walls of the oven). The furnace is thermally powered by a gas burner and its power is modulated so that at the outlet of said furnace the temperature of the sand and carbonized organic material residues is from 250 ° C. to 450 ° C. destruction of the nitrocellulose The temperature in the oven can then rise locally up to 1000 ° C. A high-flow fan (5000 m3 / h) ensures, via a venting mouth, the extraction in a chimney of the products. Gaseous and particulate combustion produced by the combustion of the organic material (sludge) and the pyrotechnic compound The mechanical effect caused by the rotation of the furnace can also lead to the breaking of sand particles. ie they can also be carried away by the extraction means. Particle filters and a gas afterburning means, arranged at the outlet of the extraction device, limit the discharges into the atmosphere. The products after such (first) treatment consist, at the outlet of the oven, of sand containing from 3 to 5% of carbonized organic material. The sand took on a black color Ir had a dirty white color originally). It does not contain any pollutant. A measurement of the (residual) rate of pyrotechnic compound (nitrocellulose) is carried out (by means of the macro thermobalance) on the products after treatment, in order to ensure the smooth running of the process and its efficiency.

Post-treatment products can be reused in the process. The sand is replaced periodically (typically after a few days of implementation of the process), when it contains too much carbonized organic matter dust or that its particle size has decreased too much mechanically in the oven. The non-recycled sand in the process is stored on site and discharged into the sludge basin containing nitrocellulose.

Claims (14)

REVENDICATIONS1. A method of destroying at least one pyrotechnic compound, comprising the heat treatment of a feedstock consisting essentially of said at least one pyrotechnic compound or an aqueous slurry containing said at least one pyrotechnic compound or an aqueous solution containing said at least one pyrotechnic compound, said sludge or aqueous solution being capable of containing in addition organic matter, characterized in that it comprises: - the constitution of a mixture by adding to said charge of a powder material in an amount suitable to ensure the inerting said at least one pyrotechnic compound present, considered in the dry state; said pulverulent material having a melting or decomposition temperature higher than the maximum temperature for carrying out said process, and - the heat treatment in an oven of said mixture at a temperature sufficiently high to lead to the destruction of said at least one pyrotechnic compound . 2. Method according to claim 1, characterized in that it comprises, in addition, prior to the addition of said powder material: - measuring the mass ratio of said at least one pyrotechnic compound within said charge and / or advantageously and that of the decomposition temperature of said at least one pyrotechnic compound; the said measurement (s) being advantageously carried out by thermogravimetry. 3. Method according to claim 1 or 2, characterized in that it further comprises, after said heat treatment: the measurement, advantageously by thermogravimetry, of the mass ratio of said at least one pyrotechnic compound within the treated load; and / or, advantageously, and - the recovery of said treated feed, for recycling into the process or landfilling. 4. Method according to any one of claims 1 to 3, characterized in that the amount of said added powder material is such that its mass is at least 85% of the sum of the masses of said at least one dry pyrotechnic compound and said powder material added. 5. Method according to any one of claims 1 to 4, characterized in that said powder material has a particle size of 0.01 mm to 5 mm, preferably between 0.06 and 2 mm. 10 6. Method according to any one of claims 1 to 5, characterized in that said powder material is selected from organic materials, inorganic and mixtures thereof, preferably from mineral materials. 15 7. Method according to any one of claims 1 to 6, characterized in that said powder material is sand or sawdust. 8. A method according to any one of claims 1 to 7, characterized in that said at least one pyrotechnic compound is nitrocellulose, a military powder for small caliber weapons, RDX, HMX, 0_20, nitroglycerine, fragmented solid propellant. 9. Method according to any one of claims 1 to 8, characterized in that it is implemented continuously or sequentially. 10. Method according to any one of claims 1 to 9, characterized in that said heat treatment is carried out under aerobic conditions at a temperature much higher than the decomposition temperature of said at least one pyrotechnic compound. 11. Process according to claim 1, characterized in that said heat treatment is carried out anaerobically at a temperature equal to or slightly greater than the decomposition temperature of said at least one pyrotechnic compound. 12. Device suitable for implementing the method according to any one of claims 1 to 11, characterized in that it comprises a mixer, preferably a concrete mixer type, a furnace, preferably rotating or circulating material, and suction ventilation of the gases and volatile particles produced in the furnace associated with a discharge outlet of said furnace; as well as advantageously a thermogravimetric analysis means consisting of a macro thermobalance. 10 13. Device according to claim 12, characterized in that said discharge mouth is extended by a chimney provided with particle filters and a gas afterburner means. 14. Device according to claim 12, characterized in that said outlet mouth is provided with active carbon filters and particles.