Method for the emergency stoppage of a pyrolysis sequence in a furnace for breaking down photovoltaic modules

Abstract

The invention relates to a furnace (1) for recycling photovoltaic modules (100), said furnace comprising a pyrolysis enclosure (2), a post-combustion chamber (3), a first circuit (411) and a second circuit (412) for distributing a combustible gas and an oxidizing gas, which circuits are connected to the enclosure (2), a third, neutral gas distribution circuit (6) designed to inject said gas into the enclosure (2), a fourth, water distribution circuit (7) designed to inject the water into the enclosure (2), a temperature sensor (32) for measuring what is referred to as the outlet temperature of the chamber (3), a pressure sensor (29) for measuring a pressure referred to as the internal pressure of the enclosure (2), and a controller (C) designed to control the injection of neutral gas by the third distribution circuit (6) on the basis of the outlet temperature and to control the injection of water by the fourth distribution circuit (7) on the basis of the internal pressure.

Description

EMERGENCY STOPPING PROCEDURE FOR A PYROLYSIS SEQUENCE IN AN OVEN FOR THE DISMANTLING OF PHOTOVOLTAIC MODULES FIELD OF INVENTION

[0001] The present invention relates to the field of photovoltaic module recycling. It relates in particular to a batch pyrolysis furnace, especially suited for the thermal dismantling of photovoltaic modules for the purpose of recycling their constituent materials. The furnace allows for the safe execution of pyrolysis sequences, as a safety system and an emergency shutdown procedure are defined in case of an incident. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Given the exponential increase in photovoltaic panels produced and installed, their recycling becomes essential to recover and valorize the precious materials that compose them (metals, glass, silicon...).

[0003] In a recycling process, the metal frame 110 (“frame”) of the end-of-life photovoltaic panels 200 and the junction box 150 are first separated from the photovoltaic module 100, which is a sandwich of functional layers, generally including a stack of glass 120, polymer layers 131, 132, 133 and photovoltaic cells 140 with semiconductor and metal contacts (). The polymer layers may include, in particular, ethylene vinyl acetate (EVA), polyethylene terephthalate (PET), polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF).

[0004] It is then known that the photovoltaic module 100 can be dismantled either by a mechanical process or by thermal treatment based on a pyrolysis and / or combustion process. Tunnel furnaces (continuous processing, combustion process) or batch furnaces (batch processing, pyrolysis or combustion process) can be used. The polymer layers 131, 132, 133, contained within the sandwich of functional layers (photovoltaic module), are formed of organic compounds, which can be decomposed by pyrolysis or burned by combustion, thus separating the layers into mineral materials of the sandwich.

[0005] In general, a pyrolysis process comprises four main phases: a preheating phase of the enclosure up to about 300°C, a pyrolysis phase, between 300°C and 500°C, under an oxygen-poor or oxygen-free atmosphere, during which the polymers are decomposed and pyrolysis gases are generated, an oxidation phase, between 450°C and 600°C, under an oxidizing atmosphere (air), during which the carbon residues potentially formed during pyrolysis are decomposed, a cooling phase, down to a temperature allowing the removal of mineral materials from the dismantling of the modules.

[0006] The gases produced by polymer pyrolysis are highly flammable and release a significant amount of energy during combustion. Injecting air into the pyrolysis chamber under suboptimal conditions, particularly between the pyrolysis and oxidation phases, can lead to an uncontrolled oxidation reaction and result in a sudden rise in temperature (risk of fire) and / or pressure (risk of explosion within the pyrolysis chamber).

[0007] In incident mode, it is therefore required to have a safety system and an emergency shutdown procedure to safeguard the integrity of the furnace and ensure the safety of its environment (human, material, atmospheric emissions). SUBJECT OF THE INVENTION

[0008] The present invention proposes a pyrolysis oven particularly suitable for the thermal dismantling of photovoltaic modules and safe in that it includes a safety system allowing an emergency shutdown procedure to be applied in incident situations. BRIEF DESCRIPTION OF THE INVENTION

[0009] The invention relates to an oven for recycling photovoltaic modules, configured for batch processing and comprising:

[0010] - a pyrolysis chamber designed to house a batch of photovoltaic modules, and isolated from the outside by a sealed door,

[0011] - a post-combustion chamber fluidically connected, on the one hand, to the pyrolysis chamber, at a proximal region of the post-combustion chamber, and on the other hand, to a gas vent, at a distal region of the post-combustion chamber,

[0012] - a first distribution circuit for a combustible gas and a second distribution circuit for a gas containing oxygen, fluidly connected to the pyrolysis chamber,

[0013] - a third neutral gas distribution circuit, fluidly connected to the pyrolysis chamber, and configured to inject said neutral gas into a part of the pyrolysis chamber located away from a boundary zone between the pyrolysis chamber and the post-combustion chamber,

[0014] - a fourth water distribution circuit, fluidically connected to the pyrolysis chamber, and configured to inject water into a part of the pyrolysis chamber extending above the batch of photovoltaic modules, known as the upper part,

[0015] - a temperature sensor, located in the distal region of the afterburner chamber, to measure a temperature known as the outlet temperature,

[0016] - a pressure sensor, placed inside the pyrolysis chamber, to measure a pressure known as internal pressure,

[0017] - a controller configured to control the injection of neutral gas through the third distribution circuit according to the outlet temperature, and to control the injection of water through the fourth distribution circuit according to the internal pressure.

[0018] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: the boundary zone between the pyrolysis chamber and the afterburner chamber is located in the upper part of the pyrolysis chamber; the part of the pyrolysis chamber distant from the boundary zone extends below the batch of photovoltaic modules and corresponds to a so-called lower part; the third distribution circuit is configured to inject the neutral gas into the pyrolysis chamber with a flow rate between 0 and 500 Nm³ 3 / h; the fourth distribution circuit is configured to inject water into the pyrolysis chamber with a flow rate between 0 and 50 liters / h.

[0019] The invention also relates to a method for emergency shutdown of a furnace for recycling photovoltaic modules as described above, the method comprising the following steps:

[0020] a) the closure of the first and second distribution circuits, to prevent any entry of combustible gas or gas containing oxygen into the pyrolysis chamber,

[0021] b) the modulation of the neutral gas injection flow rate by the third distribution circuit so that the outlet temperature is above a minimum threshold temperature and remains below a critical temperature,

[0022] c) the modulation of a water injection flow rate by the fourth distribution circuit so that the internal pressure is greater than a minimum threshold pressure and remains less than a critical pressure.

[0023] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: the maximum threshold temperature is between 900°C and 1000°C; the maximum threshold pressure is in the range [atmospheric pressure + 40 Pa; atmospheric pressure + 50 Pa]; an opening and closing of the third distribution circuit, in step b), are actuated respectively when the outlet temperature is below a minimum threshold temperature and when the outlet temperature is above the maximum threshold temperature; the minimum threshold temperature is between 860°C and 890°C; an opening and closing of the fourth distribution circuit, in step c), are actuated respectively when the internal pressure is below a minimum threshold pressure and when the internal pressure is above the maximum threshold pressure;The opening of the third distribution circuit and / or the opening of the fourth distribution circuit takes place for a duration of between 1s and 5s; the closing of the third distribution circuit and / or the closing of the fourth distribution circuit takes place for a duration of between 10s and 30s. BRIEF DESCRIPTION OF THE FIGURES

[0024] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0025] This presents an exploded view of a photovoltaic panel;

[0026] This presents an oven conforming to the present invention;

[0027] This presents an example of actuation of the third neutral gas distribution circuit of the furnace, in an emergency shutdown method according to the invention;

[0028] This presents an example of actuation of the fourth water distribution circuit of the furnace, in an emergency shutdown method according to the invention.

[0029] The figures are schematic representations which, for the sake of readability, are not necessarily to scale. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention relates to a furnace for the recycling of photovoltaic modules 100, for the thermal dismantling of the modules 100, with a view to recovering the mineral materials of which they are formed, a pyrolysis process is preferred to a combustion process during which the risk of degradation of the materials to be recycled is high, because the temperature during combustion is not controlled (possible melting of metals).

[0031] The oven according to the invention allows a pyrolysis process to be carried out safely because it includes various elements enabling it to implement a very effective emergency stop process to deal with incidental situations related in particular to overheating in the pyrolysis chamber, by unwanted combustion.

[0032] Figure 1 schematically presents an oven according to the invention. It is configured to perform batch processing, and not continuous processing like tunnel ovens. A batch consists of a set of photovoltaic modules 100, held in one or more supports 500, which will be introduced into the oven 1 for processing, and then removed from said oven.

[0033] Oven 1 includes a pyrolysis chamber 2 intended to house the batch of photovoltaic modules 100. Chamber 2 is isolated from the outside by a sealed door 25.

[0034] The furnace 1 includes a commercial fuel gas distribution circuit, referred to as the first distribution circuit 411, and a gas containing oxygen (oxidizer) distribution circuit, referred to as the second distribution circuit 412, both fluidly connected to the enclosure 2. These first 411 and second 412 distribution circuits supply at least one burner 41, located in the enclosure 2, which corresponds to the heating means of the pyrolysis enclosure 2.

[0035] The furnace 1 also includes a post-combustion chamber 3 fluidically connected on one side to the pyrolysis chamber 2, at a proximal region 3a (inlet) of the post-combustion chamber 3, and on the other side to a gas vent 9, at a distal region 3b (outlet) of the post-combustion chamber 3. The vent 9 is also connected to a combustion gas treatment unit (e.g. scrubber), after which the fluid can be released into the atmosphere.

[0036] Heating means are available to heat the post-combustion chamber 3. Preferably, at least two burners 42,43 are provided in the post-combustion chamber 3, supplied by fuel gas distribution circuits G1 and oxidizer G2.

[0037] Examples of commercial combustible gases include natural gas and liquefied petroleum gas (LPG). An example of a gas containing oxygen is air.

[0038] It is important to remember that pyrolysis is an anaerobic process during which organic matter (polymers, fats, etc.) is evaporated by heat. Therefore, it is critical in such a process to limit the oxygen content in chamber 2 (typically less than 5% oxygen by volume) to prevent the polymers from burning. The gases produced during pyrolysis are organic, toxic, and combustible. The afterburner chamber 3 is used to treat these gases by burning them at a high temperature (>850°C according to current regulations) to ensure complete combustion before they are released.

[0039] The furnace according to the invention comprises a neutral gas distribution circuit, referred to as the third distribution circuit 6, fluidically connected to the pyrolysis chamber 2. By neutral gas, we mean an inert gas, non-reactive with the other gases present in the pyrolysis chamber 2, and not capable of fueling the combustion of the gases in the pyrolysis chamber 2, such as nitrogen or argon. It is configured to inject said neutral gas into a portion of the pyrolysis chamber 2 located at a boundary zone between the chamber 2 and the post-combustion chamber 3.Indeed, the injection of the neutral gas aims to provide a piston effect (relative overpressure of the pyrolysis chamber 2 with respect to the post-combustion chamber 3), the role of which is to push the pyrolysis gases (highly flammable) contained in the chamber 2 towards the post-combustion chamber 3, in incidental situations where these gases cause an uncontrolled combustion phenomenon in the chamber 2, which can lead to a fire or an explosive overpressure.

[0040] It should be noted that a vacuum is generally created in the furnace 1 by means of a fan placed downstream of the exhaust 9. This suction mainly compensates for the overpressure generated by the combustion of the commercial fuel gas by the heating means in the pyrolysis chamber 2. Although the pyrolysis gases are carried by this flow, this fan does not constitute an active system allowing for the efficient, and rapid if necessary, evacuation of these gases from the pyrolysis chamber 2 to the post-combustion chamber 3.

[0041] In the embodiment illustrated in the figure, the boundary zone between the pyrolysis chamber 2 and the afterburner chamber 3 is located in the upper part 2a of chamber 2, and the part of the chamber distant from the boundary zone extends below the photovoltaic module array 100 and corresponds to a so-called lower part 2b. In such a configuration, it is clear that the injection of neutral gas in the lower part 2b of chamber 2 will generally push the pyrolysis gases towards the upper part 2a, in particular towards the boundary zone and the proximal region 3a of the afterburner chamber 3. Of course, other locations for the third distribution circuit 6 could be considered, and other furnace designs could propose different arrangements of the boundary zone, the door 25, and the photovoltaic module array 100.

[0042] Advantageously, the third distribution circuit 6 is capable of injecting the neutral gas into the pyrolysis chamber 2 with a flow rate between 0 and 500 Nm 3 / h (norm cubic meter per hour). Pyrolysis chamber 2 can, for example, have a volume on the order of 20 m³ 3 at 50 m 3 .

[0043] The oven also includes a water distribution circuit, called the fourth distribution circuit 7, fluidly connected to the pyrolysis chamber 2. It is configured to inject water into the upper part 2a of the chamber 2 extending above the batch of photovoltaic modules 100. Preferably, injection nozzles are distributed uniformly above all the photovoltaic modules 100. They advantageously allow the water to be injected in the form of a mist of millimeter-sized droplets (spray), so as to maximize the exchange surface and therefore the cooling capacity.

[0044] Advantageously, the fourth distribution circuit 7 is capable of injecting water into the pyrolysis chamber with a flow rate between 0 and 50 liters / h, preferably between 0 and 20 liters / h.

[0045] The furnace also includes a temperature sensor 32 and a pressure sensor 29. The temperature sensor 32 is located in the distal region 3b of the afterburner chamber 3, to measure the temperature – known as the outlet temperature T s - gases at the post-combustion outlet. The pressure sensor 29 is located in the pyrolysis chamber 2, to measure a pressure called internal pressure P. In standard operation, this internal pressure P is regulated around a nominal value (lower than atmospheric pressure) by the fan located downstream of the extraction 9, which fan is connected to the pressure sensor 29 to ensure regulation.

[0046] Finally, the furnace 1 according to the invention includes a controller C configured to control the injection of neutral gas through the third distribution circuit 6 as a function of the outlet temperature T s , and to control the injection of water by the fourth distribution circuit 7 as a function of the internal pressure P.

[0047] As mentioned in the introduction, during a pyrolysis process, the transition from the pyrolysis phase to the oxidation phase is critical, and an uncontrolled introduction (or one linked to a one-off failure) of oxygen into enclosure 2 can induce a sudden rise in temperature, for example on the order of 10K / min (risk of fire), and / or a sudden rise in pressure, for example on the order of 10Pa / s (risk of explosion in enclosure 2 or risk of release of toxic gases into the atmosphere due to the triggering of a free exhaust to prevent an explosion).

[0048] The characteristics of the oven 1 allow the implementation of an emergency shutdown procedure, also the subject of the present invention, in the event of an incident situation.

[0049] The emergency shutdown procedure includes a first step a) which aims to prevent any entry of commercial combustible gas or gas containing oxygen into the pyrolysis enclosure 2: it therefore consists of closing the first 411 and the second 412 distribution circuit, via safety systems, preferably redundant.

[0050] The second step b) corresponds to opening the third distribution circuit 6 to inject the neutral gas, so as to push the pyrolysis gases back towards the afterburner chamber 3, and prevent them from contributing to a runaway combustion in the pyrolysis chamber 2. Furthermore, in this step b), the injection flow rate is reduced or the third distribution circuit 6 is closed as soon as the outlet temperature Ts exceeds a maximum threshold temperature T seuil-MAX .

[0051] Preferably, the maximum threshold temperature T seuil-MAX is between 900°C and 1000°C, preferably between 900°C and 950°C, or even between 900°C and 920°C, or even between 900°C and 910°C.

[0052] The maximum threshold temperature T seuil-MAX is defined in such a way as to prevent the afterburner chamber 3 from rising to a critical temperature T critique, which could damage the oven and the installation. The temperature T critique is a thermal resistance temperature data of the pyrolysis installation attached to the oven design by its manufacturer.

[0053] According to an advantageous embodiment, the opening and closing of the third distribution circuit 6, in step b), are actuated respectively when the outlet temperature T s is below a minimum threshold temperature T seuil-MIN and when the outlet temperature T s is above the maximum threshold temperature T seuil-MAX For example, the actuation of the opening and closing of the third distribution circuit 6 can result in a succession of pulses, as illustrated in the figure. The opening duration t O the third distribution circuit 6 can be between 1s and 5s.

[0054] The duration of the closure t fthe third distribution circuit 6 can be between 10s and 30s.

[0055] Preferably, the minimum threshold temperature T seuil-MIN is between 860°C and 890°C, preferably between 860°C and 880°C, or even between 860°C and 870°C. Note that this minimum threshold temperature is defined in relation to the regulatory temperature imposed by waste treatment legislation (850°C); if this legislation were to change, the minimum and maximum threshold temperatures could be shifted, typically by the corresponding temperature difference.

[0056] The injection of neutral gas via the third distribution circuit 6 can thus be controlled by the outlet temperature T s of the afterburner chamber 3, so that the latter remains above the minimum threshold temperature T seuil-MIN and that it never reaches the critical temperature T critique .

[0057] Although the example given was of an injection with a slotted profile, other injection profiles could be implemented, including with a gradual opening and / or closing (flow modulation between 0% and 100%) of circuit 6.

[0058] The third step (c) of the emergency shutdown procedure involves opening the fourth distribution circuit 7 to inject water, thereby cooling the photovoltaic modules 100 and, more generally, the interior of enclosure 2. The water injection, which will immediately vaporize, induces an increase in internal pressure within enclosure 2. The fourth distribution circuit 7 is expected to be closed, or its injection rate reduced, as soon as the internal pressure P reaches a maximum threshold pressure P seuil-MAX .

[0059] Preferably, the maximum threshold pressure P seuil-MAXis chosen between the following limits: [atmospheric pressure plus 40 Pa] and [atmospheric pressure plus 50 Pa].

[0060] The maximum threshold pressure P seuil-MAX is defined in such a way as to prevent the pyrolysis chamber 2 from reaching a critical pressure P critique Beyond which an explosion or a free escape (to safeguard the installation) is likely to occur. The critical pressure P critique is associated with the maximum pressure resistance of the installation as designed by its manufacturer.

[0061] According to an advantageous embodiment, the opening and closing of the fourth distribution circuit 7, in step c), are actuated respectively when the internal pressure P is less than a minimum threshold pressure P seuil-MIN and when the internal pressure P is greater than the maximum threshold pressure P seuil-MAXFor example, the opening and closing of the fourth distribution circuit 7 can be achieved through a succession of pulses, as illustrated in the figure. The opening duration t' O of the fourth distribution circuit 7 can be between 1s and 5s. Its closing time t' f can be between 10s and 30s.

[0062] Preferably, the minimum threshold pressure P seuil-MIN is chosen between the following limits: [atmospheric pressure minus 100 Pa] and [atmospheric pressure], preferably around [atmospheric pressure minus 50 Pa].

[0063] The injection of water through the fourth distribution circuit 7 can thus be controlled by the internal pressure P of the enclosure 2, so that said pressure P never reaches the critical pressure P critique , but remaining above the minimum threshold pressure P seuil-MIN, that is to say by allowing water injection for the rapid cooling of enclosure 2.

[0064] Although the example given was of an injection with a slotted profile, other injection profiles could be implemented, including with a gradual opening and / or closing of circuit 7 (flow modulation between 0% and 100%).

[0065] Steps b) and c) can be carried out in parallel (preferred) or in staggered order.

[0066] Advantageously, steps a), b) and c) of the emergency stop method according to the invention are managed automatically by the controller C in the event of an incident situation, which can be detected for example by an abnormal increase in temperature in the pyrolysis chamber 2.

[0067] Of course, the invention is not limited to the embodiments and examples described, and alternative embodiments can be made without departing from the scope of the invention.

Claims

Emergency shutdown method for a furnace (1) for recycling photovoltaic modules (100), the furnace (1) being configured for batch processing and comprising: - a pyrolysis chamber (2) intended to hold a batch of photovoltaic modules (100), and isolated from the outside by a sealed door (25), - an afterburner chamber (3) fluidly connected on one side to the pyrolysis chamber (2), at a proximal region (3a) of the afterburner chamber (3), and on the other side to a gas vent (9), at a distal region (3b) of the afterburner chamber (3), - a first distribution circuit (411) for a combustible gas and a second distribution circuit (412) for an oxygen-containing gas, fluidly connected to the pyrolysis chamber (2), - a third distribution circuit (6) for an inert gas, fluidly connected to the chamber pyrolysis (2),and configured to inject said neutral gas into a part (2b) of the pyrolysis chamber (2) located at a distance from a boundary zone between the pyrolysis chamber (2) and the post-combustion chamber (3), - a fourth water distribution circuit (7), fluidly connected to the pyrolysis chamber (2), and configured to inject water into a part (2a) of the pyrolysis chamber (2) extending above the batch of photovoltaic modules (100), referred to as the upper part (2a), - a temperature sensor (32), disposed in the distal region (3b) of the post-combustion chamber (3), for measuring a temperature referred to as the outlet temperature (T, s - a pressure sensor (29), located in the pyrolysis chamber (2), to measure a pressure called internal pressure (P), - a controller (C) configured to control the injection of neutral gas by the third distribution circuit (6) as a function of the outlet temperature (T s), and to control the injection of water by the fourth distribution circuit (7) as a function of the internal pressure (P); the emergency shutdown procedure comprising the following steps: a) closing the first (411) and second (412) distribution circuits to prevent any entry of combustible gas or oxygen-containing gas into the pyrolysis chamber (2), b) modulating the injection rate of neutral gas by the third distribution circuit (6) so that the outlet temperature (T s ) is greater than a minimum threshold temperature (T seuil-MIN and remains below a critical temperature (T critique ),c) the modulation of a water injection flow rate by the fourth distribution circuit (7) so that the internal pressure (P) is greater than a minimum threshold pressure (P seuil-MIIN ) and remains below a critical pressure (P critique ). Emergency shutdown method according to the preceding claim, wherein the maximum threshold temperature (T seuil-MAX ) is between 900°C and 1000°C. An emergency shutdown method according to any one of the preceding claims, wherein the maximum threshold pressure (P seuil-MAX ) is within the range [atmospheric pressure + 40 Pa; atmospheric pressure + 50 Pa]. An emergency shutdown method according to any one of the preceding claims, wherein an opening and a closing of the third distribution circuit (6), in step b), are actuated respectively when the outlet temperature (T s ) is below a minimum threshold temperature (T seuil-MIN ) and when the outlet temperature (T s ) is greater than the maximum threshold temperature (T seuil-MAX ). Emergency shutdown method according to the preceding claim, wherein the minimum threshold temperature (T seuil-MIN ) is between 860°C and 890°C. An emergency shutdown method according to any one of the preceding claims, wherein an opening and a closing of the fourth distribution circuit (7), in step c), are actuated respectively when the internal pressure (P) is less than a minimum threshold pressure (P seuil-MIN ) and when the internal pressure (P) is greater than the maximum threshold pressure (P seuil-MAX ). Emergency stop method according to any one of the preceding claims, wherein the opening of the third distribution circuit (6) and / or the opening of the fourth distribution circuit (7) takes place for a duration of between 1s and 5s. Emergency shutdown method according to any one of the preceding claims, wherein the closure of the third distribution circuit (6) and / or the closure of the fourth distribution circuit (7) takes place for a period of between 10s and 30s. Emergency shutdown method according to any one of the preceding claims, wherein: - the boundary zone between the pyrolysis chamber (2) and the post-combustion chamber (3) is located in the upper part (2a) of the pyrolysis chamber (2), and - the part of the pyrolysis chamber (2) distant from the boundary zone extends below the batch of photovoltaic modules (100) and corresponds to a part called the lower part (2b). An emergency shutdown method according to any one of the preceding claims, wherein the third distribution circuit (6) is configured to inject neutral gas into the pyrolysis chamber (2) with a flow rate between 0 and 500 Nm 3 / h. Emergency shutdown method according to any one of the preceding claims, wherein the fourth distribution circuit (7) is configured to inject water into the pyrolysis chamber (2) with a flow rate between 0 and 50 liters / h.

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