Use of explosive as abrasive in water jet cutting

Abstract

The present invention relates to a method for waterjet cutting of ammunition, wherein ammunition is cut with a water jet, wherein the water used for cutting is subjected to cleaning after cutting, wherein the cleaning process includes at least one first separation process, wherein particles larger than 2.6 mm are separated in the first separation process, and wherein the water is at least partially returned to the waterjet cutting process after cleaning.

Description

[0001] The invention relates to a method for cutting up munitions (ammunition) by means of water jet cutting, wherein the explosive itself is used as an abrasive.

[0002] Explosive ordnance, particularly from the Second World War, continues to pose a threat to shipping and the environment. Therefore, these items should be cleared for environmental reasons and in line with the EU's maritime security strategy. Decommissioning directly at sea makes sense for a variety of reasons, as otherwise the ordnance would be legally imported, potentially creating significant bureaucratic and technical hurdles. Disposal on land could also result in very high logistical costs. Until now, such ordnance has been neutralized individually by specialists. However, in order to mitigate this threat potential within a limited timeframe and before the ordnance completely rusts away, new concepts are needed, particularly floating platforms for decommissioning and disposal of explosive ordnance at sea.

[0003] One of the fundamental problems with explosive ordnance disposal is that every step carries the risk of unintended ordnance being dislodged. In addition to the primary impact, there is also the risk that the pressure wave generated by the initial explosion could detonate further ordnance.

[0004] A mobile defusing chamber is known from DE 10 2020 212 443 A1.

[0005] From DE 10 2015 115 822 A1 a method and a device for separating particles of a certain size from a suspension is known.

[0006] From DE 10 2016 115 468 A1 a method and a device for the disposal of underwater munitions are known.

[0007] US 7 225 716 B1 discloses a method for removing the detonator from explosive projectiles using liquid jet technology.

[0008] DE 43 03 868 A1 discloses a method and a system for separating and recovering abrasives in water jet applications.

[0009] The recirculation of moist abrasives during waterjet cutting is known from US 2018 / 0161958 A1.

[0010] It is currently assumed that water jet cutting in such a defusing chamber is a very good way to break up the munitions.

[0011] The challenge, however, is that the explosives must not be detonated during waterjet cutting, and they must be safely removed from the water used for cutting at the end of the process to prevent uncontrolled release into the environment. During separation, it is important to avoid recombining larger and therefore critical quantities of explosives, which would create a renewed risk of unintentional detonation.

[0012] The object of the invention is to provide a cutting method for the safe fragmentation of munitions.

[0013] This object is achieved by the method having the features specified in claim 1. Advantageous further developments emerge from the subclaims, the following description, and the drawing.

[0014] The inventive method for waterjet cutting ammunition serves to reduce munitions, in particular old, recovered munitions, to such an extent that they can be safely fed into an incinerator. For this purpose, ammunition is cut with a waterjet. Ammunition is generally defined as containing explosives and is ejected from a weapon. For the purposes of the invention, however, ammunition also includes bombs, mines, and grenades, provided they contain explosives. Ammunition includes both deployed ammunition, for example, dropped bombs or laid mines that arrived there as duds, for example. For the purposes of the invention, however, ammunition also includes, in particular, dumped ammunition, i.e. ammunition that has not been used but has simply been dumped into the sea for disposal.In contrast to duds, for example, these may not be detonated, and therefore not be considered live ammunition in the true sense of the word. The ammunition contains an explosive, which can be intended either as an active agent or as a propellant for the deployment of the ammunition. The ammunition contains a portion of explosive that is also separated or washed out during water jet cutting and removed with the water jet cutting process. The ammunition may also have a solid casing or projectile, which is typically made of metal, but can also be made of another material. The ammunition may also comprise other components. Explosives within the meaning of the invention includes explosives and explosively hazardous substances, in particular initiators, propellants and gunpowder, such as black powder and gunpowder or propellant powder, ignition agents and pyrotechnic products.In contrast to, for example, a metal saw blade or a laser cutting process, the risk with waterjet cutting is easier to calculate. However, waterjet cutting also presents challenges. During waterjet cutting, particles of the explosive are carried along with the water. During waterjet cutting, particles of explosives form in the cutting water. Of course, this explosive cannot simply be released into the environment. There is also the risk that during further processing, for example during cleaning activities, or elsewhere, the explosives will settle, for example as sediment, and thus reach a critical total quantity. If uncontrolled, this can also become a hazard. This can quickly result in large quantities of water, which would require a lot of energy if disposed of directly.On the other hand, it has been found that these explosive particles can also be used as an abrasive and can therefore remain in the water. After cutting, the water used for cutting is fed to a suitable wastewater treatment plant for cleaning. This cleaning process comprises at least an initial separation process. In the first separation process, particles that exceed a critical size are separated. A critical size is considered to be a size above which energetic conversion is possible at the high energies occurring in the water jet process, i.e. ignition and thus an unwanted release of energy can occur. The exact size depends on the explosive and can therefore vary depending on the explosive used in the munitions to be cut up.Instead of the critical size, the critical mass is often used, but for separation, the size is better suited than the mass to defining a separation limit. According to the invention, the actual critical mass is not important here, as this depends on the explosive and, above all, on its condition. However, since the exact explosive is often not known during clearance and, above all, the exact condition is also not known, a conservative assumption is made that a conventional explosive of optimal quality is used, so that the explosive present in the ammunition due to poor storage and aging is in any case less reactive, i.e. has a theoretically higher critical mass. Therefore, the inventive aiming for a critical size is sensible, which describes a size at which an optimal explosive could experience energetic conversion.Without this precise knowledge, the general upper limit has been determined to be the separation of particles larger than 2.8 mm, and preferably larger than 2.6 mm. After cleaning, at least some of the purified water is returned to the waterjet cutting process along with the remaining particles. It has been found that the explosive particles can be used as an abrasive in waterjet cutting. Adjusting the cutting parameters may be appropriate due to the abrasive. However, explosive particles that are too large themselves pose a danger, as they are subjected to so much energy in the waterjet cutting process that uncontrolled decomposition can occur. This, in turn, could even lead to the remaining explosives present in the munitions being detonated or to damage the waterjet equipment.However, it has been shown that it is sufficient to separate the fraction of particles larger than 2.6 mm, as all particles smaller than this are sufficiently small to eliminate this risk. The smaller particles, however, remain in the water and thus act directly as an abrasive. It may be harmless that the separation of the fraction of particles larger than 2.6 mm also separates some smaller particles, as long as the majority of the smaller particles remain in the water. Therefore, the separation process does not need to be very precise in terms of selectivity.

[0015] In this context, particle size refers, for example, to the diameter. The diameter is the most useful parameter, especially for spherical particles.

[0016] In a further embodiment of the invention, particles of metallic or other materials are separated during wastewater treatment, and predominantly only the explosive particles of the appropriate particle size are allowed to pass through. Metal particles can be easily removed from the process water magnetically or via another suitable separation process, particularly due to the high density of metal particles, for example, in a hydrocyclone.

[0017] In a further embodiment of the invention, particles larger than 1 mm are separated in the first separation process. This increases safety, for example if the munitions contain an unknown explosive with a potentially higher hazard potential. To further increase this safety, the limit of particles that are separated can be lowered further. A separation size of up to 100 µm is useful as a lower limit for separation. This means that all particles larger than the selected upper limit for the remaining particles are separated. Further separation would only leave particles that are too small, making them no longer effective as a blasting agent. Preferably, even smaller particles are not completely separated, as otherwise the effect as an abrasive would be too greatly weakened.

[0018] In a further embodiment of the invention, waterjet cutting is carried out at a pressure of less than 3600 bar. Limiting the pressure also limits the energy applied at specific points. At higher pressures, the explosives in the munitions can be ignited by the mechanically applied energy. Therefore, limiting the pressure to less than 3600 bar is considered sufficient safety. Thus, particles of at least 100 µm remain in the water as an abrasive.

[0019] In a further embodiment of the invention, the first separation process is a continuous separation process. Preferably, the first separation process is carried out using a hydrocyclone. Continuous separation processes have the advantage that only limited enrichment, for example as sludge, occurs. While, for example, in simple filtration a filter cake forms on a filter sheet and thus more and more material accumulates, potentially exceeding a critical mass, in a continuous separation process the solid matter, which in this case comprises the most dangerous particles of explosives with a size of more than 2.6 mm, is also continuously removed, i.e., it is not first enriched. The continuous separation process thus serves to increase the safety of water purification.

[0020] In a further embodiment of the invention, a second separation process is carried out after the first separation process. In the second separation process, particles larger than 10 µm, preferably larger than 50 µm, are separated. This results in a fraction of, for example, 2.6 mm to 10 µm, preferably 2.6 mm to 50 µm. This fraction is small enough that the particles do not pose a risk, but on the other hand, the particles are large enough to be used as an abrasive. The separation enables targeted and metered addition to the waterjet cutting process. Therefore, the particles separated in the second separation process are preferably at least partially returned to the waterjet cutting process. Separation and targeted addition also prevents excessive enrichment.

[0021] In a further embodiment of the invention, a partial stream of water is removed from the circuit after the first separation process, which also includes removal after an optional second separation process. Since this partial stream still contains very small amounts of explosives, it is purified by ultrafiltration. Since only residual amounts are required here, an accumulation in the filter cake is acceptable, but the filter cake must not become too large, and the filter must be replaced or cleaned accordingly frequently.

[0022] In a further embodiment, the particles extracted from the water are fed to a combustion device. In particular, the feed can be discontinuous, meaning that they are only fed to combustion when a certain amount of particles accumulates or after a predetermined time interval.

[0023] In a further embodiment of the invention, the water between the separation process and the re-feed for waterjet cutting is at least partially analyzed by means of a sensor for the particle size remaining in the water. The sensor can be based on a known principle, for example scattered light analysis. It can be provided that the sensor records the detected number or diameter of the particles and forwards it to a control device. Should the number or diameter of the particles exceed the predetermined maximum value, the control device can switch off the waterjet cutting device or switch the water supply. This prevents damage to the waterjet cutting device in the event of a malfunction of the separation device.

[0024] It can also be provided that the sensor or another sensor detects the number of particles and the water jet cutting device supplies additional cutting particles depending on the measured particles, so that a sufficient number of cutting agents is always supplied to the water jet cutting device.

[0025] In a further embodiment of the invention, the method is carried out on board a floating decommissioning platform. A reliable circulation process, for example, for the cutting water, as well as the safety of the floating decommissioning platform itself, are particularly important on a floating decommissioning platform. Therefore, the application of the method according to the invention is particularly advantageous on a decommissioning platform.

[0026] The method according to the invention is explained in more detail below using an embodiment shown in the drawing. Fig. 1 Example device for carrying out the method

[0027] In Fig. 1 A decommissioning platform 10 is shown, which is intended to exemplify the method according to the invention. A piece of explosive ordnance 30 is, for example, recovered from the seabed and brought onto the decommissioning platform 10 and into a defusing chamber 20. In the defusing chamber 20, the piece of explosive ordnance 30 is divided into pieces of explosive ordnance using a waterjet cutting device 50. These pieces of explosive ordnance 90 are then transferred to an incineration device 40 and incinerated there.

[0028] The water from the waterjet cutting process is fed from the defusing chamber via the cutting wastewater line 80 to a first separation device 61, preferably a hydrocyclone. In the first separation device 61, all particles larger than 1 mm are separated. Selecting 1 mm ensures that all particles larger than 2.6 mm are reliably separated. The separated particles are also fed to the combustion device 40 as coarse explosive particles 91. Since the first separation device 61 is a hydrocyclone, the material flow of the coarse explosive particles 91 is a sludge. This reliably prevents excessive enrichment and compaction of the explosive before combustion.

[0029] The water coming from the first separation device 61 can either be fed directly back to the water jet cutting device 50 via a direct cutting water return 81, or fed to an optional second separation device 62 via a first water transfer 82. In the second separation device 62, particles larger than 10 µm are separated, resulting in a medium fraction between 10 µm and 1 mm. The medium explosive particles 92 are fed to a dosing device 70, which adds the explosive particles of the medium fraction in a metered manner to the water supplied to the water jet cutting device 50. Any excess of the medium fraction can also be burned in the combustion device 40.

[0030] The water from the second separation device 62 can be fed either via the cutting water return 83 to the dosing device 70 or via a second water transfer 84 to a third separation device 63. The third separation device 63 is, for example, an ultrafiltration system and serves to remove all explosive residues as completely as possible. This allows the water from the third separation device 63 to be safely discharged via a water discharge 85. The fine explosive particles 93 are also transferred to the combustion device 40 along with the filter cake from the third separation device 63. Care must be taken to ensure that the total size of the filter cake does not exceed a critical size. Reference symbol

[0031] 10Demolition platform 20Defussion chamber 30Explosive ordnance 40Incineration device 50Water jet cutting device 61First separation device 62Second separation device 63Third separation device 70Dosing device 80Cutting wastewater line 81Direct cutting water return 82First water transfer 83Cutting water return 84Second water transfer 85Water discharge 90Explosive ordnance parts 91Coarse explosive particles 92Medium explosive particles 93Fine explosive particles

Claims

1. A method for water jet cutting of ammunition, wherein ammunition is cut with a water jet, wherein particles of explosive are formed in the water during water jet cutting, wherein the water used for cutting is passed to a cleaning process after cutting, wherein the cleaning process comprises at least a first separation process, wherein particles which exceed a critical size are separated in the first separation process, wherein the cleaned water with the remaining particles is at least partially fed back to the water jet cutting process.

2. Method according to claim 1, characterized in that Particles with a size of more than 2.8 mm, preferably more than 2.6 mm, are separated, wherein the water is at least partially fed back to the water jet cutting after cleaning.

3. Method according to one of the preceding claims, characterized in thatIn the first separation process, particles with a size of more than 1 mm are separated.

4. Method according to one of the preceding claims, characterized in that waterjet cutting is carried out at a pressure of less than 3600 bar.

5. Method according to one of the preceding claims, characterized in that the first separation process is a continuous separation process.

6. Method according to claim 5, characterized in that the first separation process is carried out using a hydrocyclone.

7. Method according to one of the preceding claims, characterized in that after the first separation process, a second separation process is carried out, whereby particles with a size of more than 10 µm are separated in the second separation process.

8. Method according to claim 7, characterized in that In the second separation process, particles with a size of more than 50 µm are separated.

9. Method according to one of claims 7 to 8, characterized in thatthe particles separated in the second separation process are at least partially fed back into the water jet cutting process.

10. Method according to one of the preceding claims, characterized in that a partial stream of water is removed from the circuit after the first separation process, whereby the partial stream is cleaned by ultrafiltration.

11. Method according to one of the preceding claims, characterized in that the procedure is carried out on board a delaboration platform (10).

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