Oven for dismantling photovoltaic modules and method for emergency shutdown of a pyrolysis sequence

Abstract

The invention relates to a furnace (1) for recycling photovoltaic modules (100), comprising a pyrolysis chamber (2), a post-combustion chamber (3), a first (411) and a second (412) distribution circuits for a fuel gas and an oxidizing gas, connected to the chamber (2), a third distribution circuit (6) for neutral gas configured to inject said gas into the chamber (2), a fourth distribution circuit (7) for water configured to inject water into the chamber (2), a temperature sensor (32) for measuring a temperature called the outlet temperature of the chamber (3), a pressure sensor (29) for measuring a pressure called the internal pressure of the chamber (2), and a controller (C) configured to control the injection of neutral gas by the third distribution circuit (6) as a function of the outlet temperature, and to control the injection of water by the fourth distribution circuit (7) as a function of the internal pressure.Figure to be published with the abbreviation: Figure 2.

Description

Title of the invention: Oven for dismantling photovoltaic modules and method for emergency shutdown of a pyrolysis sequence. FIELD OF THE 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 the materials from which they are made. The furnace allows for the safe implementation of pyrolysis sequences because 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 ([Fig. 1]). 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 to dismantle the photovoltaic module 100 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, included in the sandwich of functional layers (photovoltaic module), are formed of organic compounds, which can be decomposed by pyrolysis or burned by combustion, thereby inducing the separation of the layers into mineral materials of the sandwich.

[0005] In general, a pyrolysis process comprises four main phases: - a preheating phase of the chamber up to approximately 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 the pyrolysis of polymers are highly flammable and release a large 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 in 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 incidental 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 intended to house a batch of photovoltaic modules, and isolated from the outside by a sealed door,

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

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

[0013] - a third neutral gas distribution circuit, fluidly connected to the enclosure pyrolysis, and configured to inject said neutral gas into a portion 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 enclosure of pyrolysis, 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, disposed in the distal region of the post chamber combustion, to measure a temperature called the outlet temperature,

[0016] - a pressure sensor, disposed in the pyrolysis chamber, to measure a pressure, also called internal pressure

[0017] - a controller configured to control the injection of neutral gas by the third distribution circuit based on outlet temperature, and to control water injection by the fourth distribution circuit based on 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 part called the 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 / 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 an emergency shutdown method for 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 a 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 within the range [atmospheric pressure + 40 Pa; atmospheric pressure + 50 Pa]; • an opening and a closing of the third distribution circuit, in step b), are activated 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 a closing of the fourth distribution circuit, in step c), are activated respectively when the internal pressure is less than a minimum threshold pressure and when the internal pressure is greater than 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 closure of the third distribution circuit and / or the closure 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] [Fig-1] Fig.1 presents an exploded view of a photovoltaic panel;

[0026] [Fig.2] Fig.2 presents an oven according to the present invention;

[0027] [Fig.3] Fig.3 shows an example of actuation of the third circuit of neutral gas distribution from the furnace, in an emergency shutdown method according to the invention;

[0028] [Fig.4] Fig.4 presents an example of actuation of the fourth water distribution circuit of the furnace, in an emergency stop method according to the invention.

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

[0030] The present invention relates to a furnace for recycling 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 2 schematically presents an oven 1 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] The oven 1 includes a pyrolysis chamber 2 intended to house the batch of photovoltaic modules 100. The 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, disposed 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 the one hand, to the pyrolysis chamber 2, at a proximal region 3a of the post-combustion chamber 3, and on the other hand, to a gas vent 9, at a distal region 3b of the post-combustion chamber 3. The vent 9 is also connected to a combustion gas treatment unit (for example, 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] Commercial combustible gases include, for example, natural gas or liquefied petroleum gas (LPG). A gas containing oxygen is, for example, air.

[0038] It should be noted that pyrolysis is an anaerobic process during which organic matter (polymers, fats, etc.) is evaporated by the action of heat. Therefore, in such a process, it is critical to limit the oxygen content in chamber 2 to prevent the combustion of polymers. 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 legislation) in order to ensure complete combustion of the gases before their release.

[0039] The oven according to the invention includes a neutral gas distribution circuit, referred to as the third distribution circuit 6, fluidly connected to the pyrolysis chamber 2. It is configured to inject said neutral gas (for example nitrogen) into a part of the pyrolysis chamber 2 located away from 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 back 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 could 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 for efficiently, and rapidly if necessary, evacuating these gases from the pyrolysis chamber 2 to the post-combustion chamber 3.

[0041] In the embodiment illustrated in [Fig. 2], the boundary zone between the pyrolysis chamber 2 and the post-combustion chamber 3 is located in the upper part 2a of the chamber 2, and the part of the chamber distant from the boundary zone extends below the batch of photovoltaic modules 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 the 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 post-combustion 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 batch of photovoltaic modules 100.

[0042] Advantageously, the third distribution circuit 6 is capable of injecting the neutral gas into the pyrolysis chamber 2 at a flow rate between 0 and 500 Nm³ / h (norm cubic meters per hour). The pyrolysis chamber 2 can, for example, have a volume of approximately 20 m³ to 50 m³.

[0043] The oven also includes a water distribution circuit, referred to as the fourth distribution circuit 7, fluidically 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 over all 100 photovoltaic modules. They advantageously allow the water to be injected in the form of a mist of millimeter-sized droplets (spray), in order 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 further 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 – referred to as the outlet temperature Ts – of the afterburner gases. The pressure sensor 29 is located in the pyrolysis chamber 2, to measure a pressure referred to as the 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 exhaust 9, which fan is connected to the pressure sensor 29 to ensure regulation.

[0046] Finally, the oven 1 according to the invention includes a controller C configured to control the injection of neutral gas by the third distribution circuit 6 as a function of the outlet temperature Ts, 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 the enclosure 2 can induce a sudden rise in temperature (risk of fire) and / or pressure (risk of explosion in the 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 method, also the subject of the present invention, in the event of an incident situation.

[0049] The emergency shutdown process 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 the opening of the third distribution circuit 6 to inject the neutral gas, so as to push the pyrolysis gases towards the post-combustion chamber 3, and prevent them from participating in a runaway combustion in the pyrolysis chamber 2. It is also provided, in this step b), for the reduction of the injection flow rate or the closure of the third distribution circuit 6 as soon as the outlet temperature Ts is greater than a maximum threshold temperature Tseuii_MAX.

[0051] Preferably, the maximum threshold temperature Tseuii_MAX is between 900°C and 1000°C, more 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 Tseuii Max is defined to prevent the afterburner chamber 3 from reaching a critical temperature Tcritique, which could damage the oven and the installation. The Tcritique temperature is a thermal resistance temperature value for the pyrolysis system, determined by the oven manufacturer in the design.

[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 Ts is below a minimum threshold temperature Tseuii_M1N and when the outlet temperature Ts is above the maximum threshold temperature TseuU_max. For example, the actuating of the opening and closing of the third distribution circuit 6 can result in a succession of pulses, as illustrated in [Fig. 3]. The opening duration t0 of the third distribution circuit 6 can be between 1 s and 5 s.

[0054] The closing time tf of the third distribution circuit 6 can be between 10s and 30s.

[0055] Preferably, the minimum threshold temperature Tseuii_M1N is between 860°C and 890°C, or even more 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 by the third distribution circuit 6 can thus be controlled to the outlet temperature Ts of the post-combustion chamber 3, so that the latter remains above the minimum threshold temperature Tseuii MiN and that it never reaches the critical temperature Tcritique.

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

[0058] The third step c) of the emergency shutdown procedure corresponds to the opening of the fourth distribution circuit 7 to inject water, so as to cool the photovoltaic modules 100 and more generally the interior of the enclosure 2. The injection of water, which will immediately vaporize, induces an increase in the internal pressure within the enclosure 2. It is intended that the fourth circuit of distribution 7 is either closed or its injection flow rate is reduced, as soon as the internal pressure P reaches a maximum threshold pressure PseuiiMAx-

[0059] Preferably, the maximum threshold pressure Pseuii max is chosen between the following limits: [atmospheric pressure plus 40 Pa] and [atmospheric pressure plus 50 Pa],

[0060] The maximum threshold pressure Pseuii Max is defined so as to prevent the pyrolysis chamber 2 from reaching a critical pressure P^tique, beyond which an explosion or free escape (to safeguard the installation) is likely to occur. The critical pressure PcritiqUe 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 Pseuii min and when the internal pressure P is greater than the maximum threshold pressure Pseuii max. By way of example, the actuating of the opening and closing of the fourth distribution circuit 7 can be achieved through a succession of pulses, as illustrated in [Fig. 4]. The opening time t'o of the fourth distribution circuit 7 can be between 1 s and 5 s. Its closing time t'f can be between 10 s and 30 s.

[0062] Preferably, the minimum threshold pressure Pseuii 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 by 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 PCTitique, but remains above the minimum threshold pressure Pseuii min, that is to say allowing an injection of water for the rapid cooling of the enclosure 2.

[0064] Although the example given was of an injection with a slotted profile, other injection profiles could be implemented, in particular with a gradual opening and / or closing of circuit 7 (modulation of the flow rate 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 shutdown procedure according to the invention are managed automatically by the controller C in case 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

Demands

1. Oven (1) for recycling photovoltaic modules (100), configured for batch processing and comprising: - a pyrolysis chamber (2) for holding 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 a gas containing oxygen, fluidly connected to the pyrolysis chamber (2), - a third distribution circuit (6) for an inert gas, fluidly connected to the pyrolysis chamber (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 (Ts), - a pressure sensor (29), disposed in the pyrolysis chamber (2), for measuring a pressure referred to as the 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 (Ts),and to control the injection of water through the fourth distribution circuit (7) according to the internal pressure (P).

2. Oven (1) for recycling photovoltaic modules (100) according to the preceding claim, 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).

3. Oven (1) for recycling photovoltaic modules (100) according to any one of the preceding claims, wherein the third distribution circuit (6) is configured to inject the neutral gas into the pyrolysis chamber (2) with a flow rate between 0 and 500 Nm³ / h

4. 11. Oven (1) for recycling photovoltaic modules (100) 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.

5. A method for the emergency shutdown of a furnace (1) for recycling photovoltaic modules (100) according to any one of the preceding claims, the method 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 (Ts) is above a minimum threshold temperature (Tseuii MiN) and remains below a critical temperature (Tcritique), c) modulating the injection rate of water by the fourth distribution circuit (7) so that the internal pressure (P) is above a minimum threshold pressure (Pseuii miin) and remains below a critical pressure (PcritiqUe).

6. Emergency shutdown method according to the preceding claim, wherein the maximum threshold temperature (Tseuii_MAX) is between 900°C and 1000°C.

7. Emergency shutdown method according to one of the two preceding claims, wherein the maximum threshold pressure (Pseuii max) is within the range [atmospheric pressure + 40 Pa; atmospheric pressure + 50 Pa].

8. An emergency shutdown method according to any one of the three preceding claims, wherein an opening and a closing of the third distribution circuit (6), in step b), are actuated respectively when the outlet temperature (Ts) is below a minimum threshold temperature (Tseuii.M1N) and when the outlet temperature (Ts) is above the maximum threshold temperature (TseuirMAX).

9. )■ Emergency shutdown method according to the preceding claim, wherein the minimum threshold temperature (Tseuii MiN) is between 860°C and 890°C.

10. An emergency shutdown method according to any one of the five preceding claims, wherein an 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 (Pseuii min) and when the internal pressure (P) is greater than the maximum threshold pressure (Pseuii max)-

11. Emergency stop method according to any one of the six 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.

12. Emergency shutdown method according to any one of the seven 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.

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