EP1496333B1 - Method and device for destroying solid propellant motors - Google Patents

Abstract

The method involves cutting a scrapped solid propellant engine into sections, and withdrawing sections that do not contain propellant. The sections containing propellant are cooled at a very low temperature by immersing it in a cryogenic liquid. The propellant is fragmented and separated from the envelope of each section. The sections of empty envelope are collected for deactivating residues. An independent claim is also included for an installation for the destruction of a solid propellant engine.

Description

The present invention is in the field of solid propellant engines. It relates more particularly to the destruction of reformed engines including engines that have reached the limit of operational use and are removed from service.

A solid propellant engine essentially comprises a hollow cylindrical envelope inside which is placed at least one block of solid propellant, to simplify we will say thereafter a block of propellant. One end of the envelope is closed by a dome and the opposite end by a nozzle; the dome and the nozzle will be considered as part of the envelope.

The engines considered here are engines for which the solid propellant block has been secured to the envelope and can not be removed simply from the envelope. It is essentially engine called "molded-glued" for which the block of propellant is molded and glued during the manufacture of the engine in the envelope suitably prepared for this purpose. We will assimilate to this type of engine those for which the propellant block, prepared elsewhere, is introduced and wedged irreversibly in the envelope, this setting being wanted or accidental. We will retain the term glued molded motor to refer to the motors treated in this invention.

The destruction of an engine consists in first putting it in a state such that it can not perform its propulsion function and then in a second time to separate the envelope and the propellant to treat them separately, given that only the propellant presents a pyrotechnic risk that requires precautions and special conditions in its treatment for the disposal or recycling of certain elements.

The problem of destruction specifically addressed here is that of the destruction of a very large number of engines, typically several thousand; you have to be able to process dozens of engines a day.

The process and the destruction facility must be able to operate at a very high speed: it is therefore requested a process with simple and fast steps and a rustic installation.

In addition, the process and the installation must be safe. An incident on a motor or part of a motor during a process step must remain limited or be limited to that part of the engine and to the location of the installation where it takes place. The incident should not spread to the entire facility and become catastrophic given the large number of engines necessarily present at the destruction site.

The state of the art describes several engine destruction methods but under conditions, we will see during the analysis of these processes, which do not correspond to the problem.

US Patent 5,220,107 describes the fragmentation of a bare propellant block, that is to say not glued inside the casing of an engine, by cooling at very low temperature of the propellant block and using a grinder or a press to break it up.

US Pat. No. 5,025,632 describes the extraction of propellant from a molded-glued motor with a central channel using at least one jet of cryogenic liquid. This method of destruction derived from the "water knife", is very long and does not meet the need for a large pace of work. Moreover, it is potentially dangerous because one works on a whole engine.

US Pat. No. 5,552,093 describes the extraction of the propellant from a molded-on engine which has been cooled by immersion in liquid nitrogen: the block is broken up by shocks applied in particular to the propellant block. The application of shocks on even cooled propellant remains potentially dangerous and this danger is increased by the fact that one operates, again, on a whole engine. In addition for relatively long engines it is not excluded that fragments get stuck in the envelope and require additional manipulations to extract them from the envelope.

• trouer l'enveloppe et en extraire une partie du propergol
• découper un tronçon du moteur
• pulvériser le propergol exposé avec une solution caustique par une buse télescopique afin d'en extraire le propergol
• découper le tronçon suivant et pulvériser à nouveau
• répéter l'étape de découpage/pulvérisation jusqu'à l'extrémité de l'enveloppe du moteur, et
• récupérer des tronçons d'enveloppe vides et du propergol fragmenté.

US6245958 is a basis for claims 1 and 11 and discloses a method and an apparatus for destroying molded and solid solid propellant engines consisting essentially of a propellant block and an envelope, comprising the steps of:

• pierce the envelope and extract some of the propellant
• cut a section of the engine
• spray the exposed propellant with a caustic solution through a telescopic nozzle to extract the propellant
• cut the next section and spray again
• repeat the cutting / spraying step to the end of the motor casing, and
• retrieve empty envelope sections and fragmented propellant.

The present invention aims to solve the difficulties that are not taken into account by these various methods when it is necessary to design a destruction process at a very high rate and this without unreasonably increasing the parallel operating facilities to destroy a large number of engines.

• le moteur est découpé en tronçons perpendiculairement à l'axe du moteur,
• les tronçons ne contenant pas de propergol sont retirés de la suite de la séquence,
• les tronçons contenant du propergol sont refroidis à une température très inférieure au domaine de température de transition vitreuse du liant du propergol,
• le propergol est séparé de l'enveloppe de chaque tronçon, le tronçon est ainsi vidé du propergol qu'il contenait,
• les tronçons d'enveloppe vides sont récupérés pour une étape complémentaire de désactivation des éventuels résidus de propergol,
• le propergol fragmenté est récupéré pour un traitement ultérieur.

The method of destroying a solid propellant engine according to the invention comprises the following steps:

• the engine is cut into sections perpendicular to the axis of the engine,
• sections not containing propellant are removed from the rest of the sequence,
• the sections containing propellant are cooled to a temperature much lower than the glass transition temperature range of the propellant binder,
• the propellant is separated from the envelope of each section, the section is thus emptied of the propellant that it contained,
• the empty envelope sections are recovered for a complementary step of deactivating any propellant residues,
• the fragmented propellant is recovered for further processing.

The present method therefore relates to solid propellant engines for which the propellant block is integral with the casing; the engines that enter this process do not include an ignition device: it is removed and removed from the engine in a preparatory operation before delivery of the engines to the destruction site. The motor casing is either all-metal or composite material. The propellant block has a central channel that extends over its entire length or only a part: in the latter case the portion of the side opposite the nozzle has no channel. The propellant block can be possibly full over its entire length, that is to say does not have a central channel.

• des tronçons sans propergol : en général il y a un seul tronçon de ce type par moteur, ce tronçon porte tout ou partie de la tuyère, il ne contient pas de matériau pyrotechnique, ce type de tronçon est retiré de la présente séquence,
• des tronçons avec du propergol : la portion découpée du bloc est restée collée à la portion découpée de l'enveloppe, ce type de tronçon va suivre les autres étapes du procédé. Au moins une des extrémités du tronçon est grande ouverte : c'est-à-dire que le diamètre de l'ouverture est sensiblement égal au calibre du moteur.

The sections cut in the engine are of two types:

• sections without propellant: generally there is only one section of this type by motor, this section carries all or part of the nozzle, it does not contain pyrotechnic material, this type of section is removed from the present sequence,
• sections with propellant: the cut portion of the block remained glued to the cut portion of the envelope, this type of section will follow the other steps of the process. At least one of the ends of the section is wide open: that is to say that the diameter of the opening is substantially equal to the size of the engine.

Advantageously, the sections containing propellant have a length ratio "1" of the section on outer diameter "d" of the section less than or equal to 2.5, (1 / d ≤ 2.5).

All known methods for cutting motors in sections are usable. However, given the need for a high rate and also safety requirements it will be advantageous to use methods using at least one jet of high pressure liquid with possibly adding suitable abrasive products.

Preferably, to increase the efficiency of the operation, the method uses several jets arranged in parallel and prepositioned with respect to the motor to cut the different sections in a single operation.

Preferentially, to increase safety, to be cut the engine is immersed in the same liquid as that used for the jets; most commonly the liquid used is water.

The liquid and the shell and propellant chips resulting from the cutting operations are regularly removed for suitable treatments.

The sections containing propellant are, using appropriate handling means, transported and immersed in a bath of a neutral cryogenic liquid vis-a-vis the stub components; generally the cryogenic liquid used is liquid nitrogen.

The immersion of the sections lasts long enough for the cooling of the envelope and propellant is quite important and that the differential contractions of the envelope and the propellant create tensions cracking and cracking the propellant and also the detachment of the envelope.

Typically the target end temperature for the engine section is at least 20 ° C lower than the glass transition temperature range of the propellant binder. Advantageously, a temperature of between about -100 ° C. and about -80 ° C. is targeted for the propellant and the casing.

Then the sufficiently cooled sections are directed to a station to extract the propellant, weakened by the cold. The propellant is extracted by imposing slight deformations on the envelope: these deformations remain in the elastic domain of deformation of the envelope at this temperature. The propellant breaks into rather large fragments, typically about the size of a closed fist.

The section was arranged vertical axis and the propellant fragments fall by gravity and are recovered either on a conveyor belt or in a receptacle containing water to render the propellant fragments inert. The engine section having a relatively small length relative to its diameter, 1 / d ≤ 2.5, the propellant fragments do not get stuck in the envelope.

In a first variant, the cooled engine section, vertical axis and opening of larger diameter directed downwards, is disposed between a stop and a cylinder head. The cylinder axis is horizontal and perpendicular to the axis of the engine section. The displacement of the cylinder head is calculated so that the deformation of the envelope remains in the field of elastic deformation of the envelope.

According to another variant, the cooled engine section is driven between two rolls rolling mill, these rollers are appropriately spaced to impose, again, a deformation which remains in the field of elastic deformation of the envelope. The rollers slightly drive and deform the engine section from the bottom of said section to its upper part which facilitates the extraction of propellant fragments by gravity.

The empty envelope section optionally includes some residual traces of small thickness of propellant remained glued at certain points of the interior of the envelope. The empty section is retrieved for a subsequent step of deactivating such residues.

Advantageously, this deactivation is done in a closed chamber which includes burners whose flames burn the traces of propellant. The fumes are folded down and washed with water, so no gaseous effluents are released into the atmosphere. Wash waters are collected for treatment and decontamination according to known methods.

Preferably, when the oxidizing charge of the propellant is soluble in a liquid, the deactivation of any propellant residues adhering to the interior of the casing is done by soaking the empty casing section in said liquid. When the oxidizing charge is dissolved in the liquid, there remains on the inner wall of the casing only matrix flakes consisting of binder and combustible load without pyrotechnic danger. The kinetics of diffusion of the oxidizing charge and of its dissolution in the liquid is advantageously accelerated by heating the liquid. The liquid containing the oxidizing charge in solution is recovered for further processing by known methods. Frequently the oxidizing charge is ammonium perchlorate and the liquid used to dissolve it is water.

Having many engines to destroy, it may seem paradoxical to multiply the objects to be treated by cutting the engine into sections.

From a safety point of view, sections without propellant that do not present a pyrotechnic risk are removed from the sequence of operations. A section containing propellant is relatively short and will not be propulsive in case of accidental ignition: it will not have disordered and untimely movements that can spread the incident to an entire station. However, precautions must be taken with regard to thermal effects.

• les tronçons sont refroidis plus rapidement qu'un moteur entier : masse plus faible, surface d'échange thermique avec le liquide cryogénique plus importante,
• les tronçons étant court les fragments tombent par gravité et ne présentent pas de risque de coincement existant sur un moteur complet,
• la désactivation des résidus de propergol faite sur des tronçons d'enveloppe vides est plus facile que celle faite sur l'enveloppe complète d'un moteur et cela quel que soit le procédé adopté.

From an efficiency point of view, this division into sections contributes to that of the following steps of the process:

• the sections are cooled faster than an entire engine: lower mass, heat exchange surface with the larger cryogenic liquid,
• the sections being short the fragments fall by gravity and do not present any risk of jamming existing on a complete engine,
• the deactivation of the propellant residues made on empty sections of the casing is easier than that made on the complete casing of an engine, whatever the method adopted.

The fragments of propellants obtained after the elastic deformation of the envelope are generally quite large: a few centimeters, about the size of a closed fist. To move to the next stage of treatment of the propellant, it is necessary to proceed to a finer grinding of said fragments so as to obtain grains of propellant, grains whose dimensions are of the order of at most one centimeter and preferably a few millimeters.

This grinding can be done in different ways but preferably using knife mills and advantageously the grinding is done under water spray.

The next step of treatment of the propellant, thus granulated, is the dissolution of the oxidizing charge in a suitable liquid, for example water when the oxidizing charge is perchlorate.

Preferably to accelerate the kinetics of dissolution it is done in a perfectly stirred and thermoregulated reactor.

The liquid which contains the oxidizing charge in solution is separated from the solid residue; the latter comprises the binder and the possible combustible charge, it does not present a pyrotechnic risk. The solid residue is either directly landfilled in a landfill or upgraded to extract the metal fuel charge after known and conventional treatments for industrial waste.

The liquid is either treated by biodegradation processes such as that described in patent FR 2 788 055 or its corresponding US Pat. No. 6,328,891 for degrading the oxidizing charge, or treated to enhance said oxidizing charge and recrystallize it by known methods.

Below the invention is explained in more detail with the aid of figures representing an installation for carrying out the method.

Figure 1 schematically shows an installation for carrying out the method.

Figure 2 is a basic plan of a propellant fragmentation plant after cooling the section.

Figure 1 shows schematically the succession of different positions for the implementation of the method. Figure 1a) in plan, Figure 1b) in profile.

The engines are brought to a storage workshop, identified for the traceability of the operation and are placed one by one on a conveyor and are introduced, one by one, by a first airlock in the installation.

At the cutting station 1 the engine is immersed in a tank containing water and positioned on a bench rotating relative to a ramp of several jets high pressure suitably arranged: the engine is cut into sections. The high-pressure ramps are made with standard equipment such as DIGITAL CONTROL, feeding high-pressure jets, about 300 MPa with two pumps. In general, there is a section which contains no propellant but a large part of the nozzle, this section containing no pyrotechnic product is removed from the sequence.

The other sections 10 of the engine are hooked to another conveyor and pass, through an airlock, to the cooling station 2 by immersion in the cryogenic liquid: this station essentially comprises a bath of great length in which are immersed several suitably spaced sections; the sections move as the process progresses and thus stay in the liquid for a long time, which favors their cooling down to temperatures of about -100 ° C.

By another airlock the sections are directed, one by one, to the fragmentation station 3 of the propellant stuck in the envelope section. An example of an installation is described in more detail in FIG.

At this station the suitably oriented section is deformed by compression of the envelope: the propellant, weakened, cracked and cracked by cooling is fragmented. The fragments are recovered for further processing.

The empty propellant casing sections are directed to a residue deactivation station 6. The deactivation of the sections is, in this example, made by immersing said sections in a tank containing water.

The propellant fragments are directed to a fine grinding station 4 using knife mills with water spray. High-performance standard devices, with some security adaptations, can process up to 1000kg / hour of propellant.

The grains obtained after fine grinding are introduced to the dissolution station 5 in a large volume reactor, said reactor is perfectly stirred and thermoregulated to increase the kinetics of dissolution of the oxidizing charge in water.

In this diagram are not shown in detail all the different means of manipulation, nor the opening and closing devices of the airlock of the installation, nor the easements of each workstation.

FIG. 2 schematically represents views a) of profile and b) in plan of an apparatus 11 for extracting the propellant from a section 10 of cooled engine.

The apparatus essentially comprises a rectangular frame 13, anchored on four legs with a stop 14 on one side of the frame and a hydropneumatic jack 15 fixed on the opposite side; the cylinder is arranged horizontally.

The motor section 10 to be treated is hooked, vertical axis to a handling means shown schematically by reference 12. Said handling means brings the motor section 10 between the stop 14 and the cylinder rod 16.

The cylinder rod 16 is supported on the envelope of the engine section about one-third of its height from the bottom of the section. The displacement of the jack rod 16 is determined to impose a deformation to the envelope which remains in the elastic domain of the deformations thereof and to break up the cold propellant and separate it from the envelope.

A receptacle 17, containing water to render inert the propellant fragments which fall by simple effect of gravity is placed under the engine section; said receptacle 17 is only shown in Figure 2a).

This device is placed in a suitable room with entry and exit locks and all servitudes necessary for remote operation.

Claims (12)

1. Process for destroying a solid-propellant rocket motor, the said cast-bonded motor essentially consisting of a block of propellant and a casing, which process is characterized in that it comprises the following steps :

   - the motor is cut up into sections (10) perpendicular to the axis of the motor ;

   - the sections (10) not containing propellant are withdrawn from the rest of the sequence ;

   - the sections (10) containing propellant are cooled to a temperature very much below the glass transition temperature range of the propellant binder ;

   - the propellant is fragmented and separated from the casing of each section (10), i.e. the section (10) is thus emptied of the propellant that it contained ;

   - the empty casing sections (10) are recovered for a supplementary step of deactivating the residues ; and

   - the fragmented propellant is recovered for subsequent treatment.
2. Process for destroying a solid-propellant rocket motor according to claim 1, characterized in that the sections (10) containing propellant have a length/outside diameter ratio of less than or equal to 2.5.
3. Process for destroying a solid-propellant rocket motor according to claim 1 or 2, characterized in that the motor is cut up by at least one high-pressure liquid jet.
4. Process for destroying a solid-propellant rocket motor according to claim 3, characterized in that, for cutting up the motor, the latter is immersed in a tank containing the same liquid as that used for supplying a spray rail delivering several jets that are prepositioned relative to the motor.
5. Process for destroying a solid-propellant rocket motor according to any one of claims 1 to 4, characterized in that the sections (10) containing propellant are cooled by immersion in a cryogenic liquid.
6. Process for destroying a solid-propellant rocket motor according to claim 5, characterized in that the cryogenic liquid is liquid nitrogen.
7. Process for destroying a solid-propellant rocket motor according to claim 5 or 6, characterized in that the section (10) is cooled to a temperature between about -100°C and about -80°C.
8. Process for destroying a solid-propellant rocket motor according to any one of claims 1 to 7, characterized in that the casing of each cooled section (10) is subjected to elastic deformation stresses in order to fragment the propellant, the fragments of which are collected in a receptacle.
9. Process for destroying a solid-propellant rocket motor according to any one of claims 1 to 8, characterized in that each empty section (10) is deactivated by burning off the traces of propellant residues, with recovery and scrubbing of the flue gases.
10. Process for destroying a solid-propellant rocket motor according to any one of claims 1 to 8, characterized in that each empty section (10) is deactivated by immersing the section (10) in a liquid that dissolves the oxidizing charge.
11. Plant for the destruction of a solid-propellant rocket motor, the said motor essentially consisting of a block of propellant bonded to a casing, characterized in that it comprises :

    - a station for preparing the motors, which communicates via an airlock with

    - a station (1) for cutting the said motor into sections (10);

    - a station (2) for cooling the sections containing propellant ;

    - at least one propellant fragmentation station (3), with recovery of the properlant fragments and of the empty casing sections (10); and

    - a station (6) for deactivating the propellant residues on the empty casing sections (10).
12. Plant for the destruction of a solid-propellant rocket motor according to claim 11, characterized in that it comprises :

    - a station (4) for fine milling of the propellant fragments ; and

    - a station (5) for dissolving the oxidizing charge of the finely milled propellant.

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