Pyrolysis method for breaking down photovoltaic modules

Abstract

The invention relates to a pyrolysis method for breaking down photovoltaic modules, said method comprising different thermal phases and taking place in a pyrolysis enclosure having an internal atmosphere that is isolated from the outside, the thermal phases being as follows: - a pyrolysis phase, referred to as the first phase, during which polymers included in the photovoltaic modules are decomposed into pyrolysis gases, said gases passing from the pyrolysis enclosure to a post-combustion chamber in order to be incinerated therein; - an oxidation phase, referred to as the second phase, after the first phase, for oxidising the carbonaceous residues generated during the pyrolysis phase. According to the method of the invention, a temperature sensor measures a temperature in the post-combustion chamber, referred to as the central temperature, and a carbon monoxide sensor measures the carbon monoxide concentration in the pyrolysis enclosure. The second phase is not initiated until at least one of the following two conditions is met: - condition one: the difference between the central temperature and a target temperature is below a predefined threshold temperature difference; - condition two: the carbon monoxide concentration in the pyrolysis enclosure is below a predefined threshold concentration.

Description

Pyrolysis process for dismantling photovoltaic modules FIELD OF INVENTION

[0001] The present invention relates to the field of photovoltaic module recycling. It relates in particular to a pyrolysis process, implemented in a batch-operated pyrolysis furnace, particularly suitable for the thermal dismantling of photovoltaic modules for the purpose of recycling the materials from which they are made. 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. Therefore, the composition of the gaseous atmosphere within the furnace is critical and must be very carefully controlled, particularly to ensure a safe transition from the pyrolysis to the oxidation phase. SUBJECT OF THE INVENTION

[0007] The present invention proposes an automated and safe pyrolysis process, particularly suitable for the thermal dismantling of photovoltaic modules for the efficient recycling of the materials from which they are formed. BRIEF DESCRIPTION OF THE INVENTION

[0008] The invention relates to a pyrolysis process for dismantling photovoltaic modules, comprising different thermal phases and operating in a pyrolysis chamber having an internal atmosphere isolated from the outside, the thermal phases being as follows:

[0009] - a pyrolysis phase, called the first phase, during which polymers included in the photovoltaic modules are decomposed into pyrolysis gas, said gases passing from the pyrolysis chamber to a post-combustion chamber to be incinerated;

[0010] - an oxidation phase, called the second phase, following the first phase, to oxidize carbonaceous residues generated during the pyrolysis phase. According to the process of the invention, a temperature sensor measures a temperature in the afterburner chamber, called the core temperature, and a carbon monoxide sensor measures the carbon monoxide concentration in the pyrolysis chamber. The second phase is not initiated until at least one of the following two conditions is met:

[0011] - First condition: the difference between the core temperature and a setpoint temperature is less than a predefined threshold temperature difference.

[0012] - second condition: the concentration of carbon monoxide in the pyrolysis chamber is less than a predefined threshold concentration.

[0013] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: the setpoint temperature is greater than or equal to 850°C, preferably between 850°C and 1200°C, or between 850°C and 1000°C; the threshold temperature difference is between 1°C and 5°C; the difference between the core temperature and the setpoint temperature must be less than the predefined threshold temperature difference for a measurement period of between 10s and 5min, preferably between 20s and 1min, before considering the first condition satisfied; the threshold concentration is less than or equal to 5%, or even less than or equal to 2%; the carbon monoxide concentration must be less than the predefined threshold concentration for a measurement period of between 10s and 5min, preferably between 20s and 1min, before considering the second condition satisfied;The carbon monoxide sensor is placed in an extreme area of ​​the pyrolysis chamber, near the fluidic link between the pyrolysis chamber and the afterburner chamber; the pyrolysis process includes, before engaging the second phase, an injection of neutral gas into the pyrolysis chamber, and as long as at least one of the first and second conditions is not satisfied with this injection of neutral gas, the second phase is not engaged; if at least one of the first and second conditions is satisfied for a neutral gas flow rate equal to a predetermined maximum flow rate, the second phase may be engaged; the second phase is engaged automatically if the first and second conditions are satisfied, for a neutral gas flow rate equal to a predetermined maximum flow rate; the injection of neutral gas is made at an increasing flow rate up to a predetermined maximum flow rate; the predetermined maximum flow rate is less than or equal to 600 Nm; 3 / h, preferably between 50 Nm 3 / h and 300 Nm 3 / h; the pyrolysis process includes a cooling phase, called the third phase, which follows the second phase, and the third phase is not started until at least one of the first and second conditions is met; the pyrolysis process includes, before starting the third phase, an injection of neutral gas into the pyrolysis chamber, and as long as at least one of the first and second conditions is not met with this injection of neutral gas, the third phase is not started; the third phase is started automatically if the first and second conditions are met, for a flow rate of neutral gas equal to a predetermined maximum flow rate. BRIEF DESCRIPTION OF THE FIGURES

[0014] 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:

[0015] This presents an exploded view of a photovoltaic panel;

[0016] This presents a batch processing pyrolysis oven, in which a pyrolysis process according to the present invention can be implemented;

[0017] Presents a thermal cycle graph of a pyrolysis process according to the invention;

[0018] This presents a graph representing temperatures (measured and setpoint) in the pyrolysis chamber and in the post-combustion chamber of a furnace, and a carbon monoxide level in the pyrolysis chamber, during a pyrolysis process according to the invention.

[0019] The figures are schematic representations which, for the sake of readability, are not necessarily to scale. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention relates to a pyrolysis process for dismantling photovoltaic modules 100. Such a process is preferred to a combustion process in 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).

[0021] The pyrolysis process takes place in a pyrolysis chamber whose internal atmosphere is isolated from the outside. 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 within the chamber to prevent the combustion of polymers. The gases produced during pyrolysis are organic, toxic, and combustible. Typically, an afterburner is used to treat these gases by burning them at high temperatures to ensure their complete combustion.

[0022] The process according to the invention can be implemented in a pyrolysis furnace 1, adapted for batch processing, as illustrated in the figure. It comprises a pyrolysis chamber 2, isolated from the outside by a sealed door 25. The pyrolysis chamber 2 is fluidly connected to an afterburner chamber 3. Heating means are available for heating the pyrolysis chamber 2 and the afterburner chamber 3. Preferably, at least one burner 41 is arranged in the lower part of the pyrolysis chamber 2, and at least two burners 42, 43 are provided in the afterburner chamber 3. They are supplied by a commercial fuel gas supply, for example natural gas or liquefied petroleum gas (LPG), and by an oxygen-containing oxidizing gas supply, for example air. The 100 photovoltaic modules are held in a support 500, which is introduced into the enclosure 2 to apply the pyrolysis process to said modules 100.

[0023] Before mounting them on the 500 support, it is advantageous to break the glass layer 120 of the 100 photovoltaic modules. Because this layer is made of tempered glass, it fractures into small, non-cutting pieces a few millimeters in size upon impact. However, due to the presence of polymer layers, each 100 module retains its intact shape, typically a rectangle measuring 1 to several meters. 2 , and can be easily placed on support 500. This pre-fracturing of the glass layer 120 allows the recovery, at the end of pyrolysis treatment, of fragments of mineral materials (glass, semiconductor, metals), which are easier to sort and handle than large-dimension layers.

[0024] The pyrolysis process, as mentioned in the introduction, comprises different thermal phases. An example of a temperature cycle for this process is shown in.

[0025] A preliminary preheating phase of enclosure 2 starts after the photovoltaic modules 100 are loaded into said enclosure and after the door 25 of the furnace 1 is closed. This phase brings enclosure 2 from an initial temperature typically between 150°C and 300°C, up to a temperature of around 400°C to 450°C; the internal atmosphere of enclosure 2 is reducing, mainly consisting of the combustion gases from the burner 41.

[0026] This is followed by a pyrolysis phase, known as the first phase, during which polymers (polymer layers 131, 132, 133), included in the photovoltaic modules 100, are decomposed into flammable gases, called pyrolysis gases. These gases pass from the pyrolysis chamber 2 to the afterburner chamber 3 to be incinerated. The pyrolysis phase takes place in the pyrolysis chamber 2, which is heated to a temperature T enceintebetween 300°C and 800°C, preferably between 400°C and 600°C. The injection of oxidant (air) at the burner 41 is such that the internal atmosphere of enclosure 2 contains less than 4%, or even 2%, of oxygen; the internal atmosphere of enclosure 2, during pyrolysis, is not imposed but endured, as it results from the decomposition of polymers; it mainly comprises combustion gases and pyrolysis gases (including carbon monoxide).

[0027] During pyrolysis, a layered dislocation of module 100, linked to the decomposition of the polymer layers, occurs. Since the glass layer 120 has been previously broken, glass fragments fall into the support 500, and the cell layer (silicon and contact) also breaks into pieces due to its fall into / onto the support 500.

[0028] The post-combustion chamber 3 is subjected to a temperature above 850°C (in accordance with waste incineration legislation) to ensure complete combustion of the pyrolysis gases; the residual gases are then evacuated (evacuation 9) to a combustion gas treatment unit (e.g. scrubber), after which the fluid can be released into the atmosphere.

[0029] The process then includes an oxidation phase, known as the second phase, to oxidize carbonaceous residues generated during the pyrolysis phase. The temperature range is typically [500°C – 800°C], and the internal atmosphere of chamber 2 can contain between 5% and 20% oxygen, preferably between 5% and 10%.

[0030] Finally, following the second phase, a cooling phase, known as the third phase, is carried out to lower the temperature of the mineral fragments resulting from pyrolysis, in order to remove them from chamber 2 of the furnace. This third phase is preferably carried out under a neutral atmosphere (typically nitrogen) for safety reasons, and lowers the temperature of chamber 2 to approximately 300°C or less.

[0031] It is particularly critical to move from the first phase to the second phase. Indeed, the addition of oxygen to enclosure 2 for the oxidation phase must take place when there is no more pyrolysis gas left (or very little remains), to avoid inducing combustion in pyrolysis enclosure 2, which would release a huge amount of energy and could therefore cause a sudden rise in temperature (risk of fire) and / or pressure (explosion in enclosure 2).

[0032] The pyrolysis process according to the invention provides that a temperature sensor 31 measures a temperature of the afterburner chamber 3, referred to as the central temperature T c , and that a carbon monoxide sensor 26 measures the carbon monoxide concentration in the pyrolysis chamber 2.

[0033] The temperature sensor 31 is advantageously positioned centrally in the afterburner chamber 3, so as to translate the temperature (central temperature T c ) at the heart of chamber 3. The carbon monoxide sensor 26 is, for its part, preferentially located in an extreme area of ​​the pyrolysis chamber 2, near the fluidic link between the pyrolysis chamber 2 and the post-combustion chamber 3, as illustrated on the.

[0034] According to the invention, the second phase is not initiated until at least one of the following two conditions is met.

[0035] The first condition relates to the central temperature T c of the afterburner chamber 3.

[0036] According to the first condition, the difference between the central temperature T c and a setpoint temperature TC ch.p-c must be less than a predefined threshold temperature difference ΔT seuil The setpoint temperature TC ch.p-c must be equal to or greater than 850°C, preferably between 850°C and 1200°C, or between 850°C and 1000°C. The threshold temperature difference ΔT seuil is preferably between 1°C and 10°C, and even more preferably between 1°C and 5°C.

[0037] The fact that the central temperature T c does not differ by more than 1°C at 10°C (or by more than 1°C at 5°C) from the setpoint temperature TC ch.p-c This reflects a decrease in the arrival of pyrolysis gases. As can be seen on the graph, the central temperature T cis very close to the setpoint temperature TC ch.p-c in a first sequence P1 of the pyrolysis phase; in a second sequence P2, large differences ΔT are observed between the central temperature T c of the afterburner chamber 3 and the setpoint temperature TC ch.p-c , related to the arrival of pyrolysis gas (from the decomposition of polymer layers in pyrolysis chamber 2) in said chamber 3.

[0038] Preferably, the difference between the central temperature T c and the setpoint temperature TC ch.p-c must be less than the predefined threshold temperature difference ΔT seuil for a measurement period of between 10s and 5min, preferably between 20s and 1min, before considering the first condition satisfied.

[0039] The second condition relates to the carbon monoxide content: the carbon monoxide concentration C COin pyrolysis chamber 2 must be less than a predefined threshold concentration C seuil .

[0040] Advantageously, the threshold concentration C seuil is less than or equal to 5% (by volume of CO in the atmosphere of chamber 2), preferably less than or equal to 3%, or even less than or equal to 2%. The low concentration of carbon monoxide reflects a decrease in the arrival of pyrolysis gases, which are usually laden with CO.

[0041] Preferably, the concentration of carbon monoxide C CO must be lower than the predefined threshold concentration C seuil for a measurement period of between 10s and 5min, preferably between 20s and 1min, before considering the second condition satisfied.

[0042] To ensure a safe transition from the first phase to the second phase, the process according to the invention may require that the second phase not be initiated until the two aforementioned conditions are met. As mentioned previously, the two conditions are advantageously considered met if the difference between the central temperature T c and the setpoint temperature TC ch.p-c is less than the predefined threshold temperature difference ΔT seuil for a measurement period of between 10 seconds and 5 minutes, preferably between 20 seconds and 1 minute, and if the carbon monoxide concentration C CO is lower than the predefined threshold concentration C seuil for a measurement duration of between 10s and 5min, preferably between 20s and 1min. Potential fluctuations in temperature and / or CO concentration are thus taken into account and the transition from the first phase to the second phase is made more secure.

[0043] Another variant of the process can be implemented to further secure the transition from the pyrolysis phase to the oxidation phase. When at least one of the first and second conditions is met, and before initiating the second phase, the pyrolysis process can also include the injection of a neutral gas into the pyrolysis chamber 2. This injection acts as a piston to force as much pyrolysis gas as possible towards the afterburner chamber 3. A neutral gas is defined as an inert gas, such as nitrogen or argon. This neutral gas injection is advantageously carried out via an injection system 6, which may include a plurality of nozzles, located in a proximal area of ​​the chamber 2, opposite the extremity area near the junction with the afterburner chamber 3.

[0044] With this injection of neutral gas, pyrolysis gases residing in the pyrolysis chamber 2 can be pushed towards the afterburner chamber 3, thus inducing an increase in the carbon monoxide concentration in the extreme zone of the chamber 2, as well as an increase in combustion in the afterburner chamber 3 (with heat release) and therefore an increase in the core temperature T c Thus, with the neutral gas injection activated, as long as at least one of the first and second conditions is not met, the second phase is not initiated.

[0045] The piston effect of neutral gas injection can depend on the applied gas flow rate. Advantageously, the condition(s) must be met for a neutral gas flow rate equal to a predetermined maximum flow rate. The maximum flow rate is preferably less than or equal to 600 Nm³ / s 3 / h (norm cubic meter per hour), preferably between 50 and 300 Nm 3 / h. Pyrolysis chamber 2 typically has a volume of approximately 20 m³ 3 at 50 m 3 .

[0046] Preferably, the neutral gas is injected at an increasing flow rate up to the predetermined maximum flow rate. It is also advantageous for the neutral gas to have a high temperature (above 300°C, or even above 400°C) at the time of injection, to limit its impact on the temperature of chamber 2.

[0047] According to the invention, the second phase can thus be engaged: if the first condition, the second condition or both conditions are satisfied at the end of the pyrolysis phase, and after injection of neutral gas.

[0048] It is easy to trigger the second phase automatically, based on the information returned by the temperature sensors 31 and carbon monoxide concentration 26 and by the neutral gas injection system 6, to a controller, and based on a decision algorithm.

[0049] Advantageously, to ensure a high level of safety, the second phase is automatically engaged if the first and second conditions are met, for a neutral gas flow equal to the predetermined maximum flow.

[0050] Note that the injection of neutral gas can also be started before an (instantaneous) measurement indicates that one or both of the conditions are met. Such an injection can be triggered during the pyrolysis phase, or even at the very beginning of the pyrolysis phase.

[0051] As mentioned previously, the pyrolysis process according to the invention includes a cooling phase (third phase), which follows the second phase. The transition from the second phase (oxidation phase) to the third phase is also critical because incomplete oxidation will leave highly reactive carbon residues in the pyrolysis chamber 2, and the release of air during the unloading of the support 500 with the dislocated modules, at a high temperature (typically around 300°C), can lead to spontaneous ignition of the carbon residues.

[0052] Thus, according to the pyrolysis process of the invention, the third phase is advantageously not initiated until at least one of the first and second conditions is satisfied.

[0053] The pyrolysis process may also include, when at least one of the first and second conditions is met, and before initiating the third phase, an injection of neutral gas into the pyrolysis chamber 2; as long as at least one of the first and second conditions is not met with this injection of neutral gas, the third phase is not initiated. Advantageously, the condition(s) must be met for a neutral gas flow rate equal to the predetermined maximum flow rate. The injection of neutral gas is typically carried out at an increasing flow rate up to the maximum flow rate.

[0054] The automation of the transition from the second to the third phase can be easily implemented. Preferably, to maximize safety, the cooling phase is initiated automatically if the first and second conditions are met, for a neutral gas flow rate equal to the predetermined maximum flow rate.

[0055] 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

A pyrolysis process for dismantling photovoltaic modules (100), comprising different thermal phases and operating in a pyrolysis chamber (2) having an internal atmosphere insulated from the outside: - a pyrolysis phase, referred to as the first phase, during which polymers included in the photovoltaic modules (100) are decomposed into pyrolysis gases, said gases passing from the pyrolysis chamber (2) to a post-combustion chamber (3) to be incinerated; - an oxidation phase, referred to as the second phase, following the first phase, to oxidize carbonaceous residues generated during the pyrolysis phase; wherein: - a temperature sensor (31) measures a temperature in the post-combustion chamber (3), referred to as the core temperature (T c), and a carbon monoxide sensor (26) measures the carbon monoxide concentration in the pyrolysis chamber (2); - the second phase is not initiated until the following two conditions are met for a measurement period of between 10 s and 5 min: > first condition: the difference between the core temperature (T c ) and a setpoint temperature (TC ch.p-c ), greater than or equal to 850°C, is less than a threshold temperature difference (ΔT seuil ) predefined, between 1°C and 5°C, > second condition: the concentration of carbon monoxide (C co ) in the pyrolysis chamber (2) is less than a threshold concentration (C seuil ) predefined, less than or equal to 5% by volume. A pyrolysis process according to the preceding claim, wherein the setpoint temperature (TC ch.p-c ) is between 850°C and 1200°C. A pyrolysis process according to any one of the preceding claims, wherein the difference between the core temperature (T c ) and the setpoint temperature (TC ch.p-c ) must be less than the threshold temperature difference (ΔT seuil ) predefined for a measurement duration of between 20s and 1min, before considering the first condition satisfied. A pyrolysis process according to any one of the preceding claims, wherein the threshold concentration (C seuil ) is less than or equal to 2%. A pyrolysis process according to any one of the preceding claims, wherein the concentration of carbon monoxide (C co ) must be lower than the threshold concentration (C seuil ) predefined for a measurement duration of between 20s and 1min, before considering the second condition satisfied. Pyrolysis method according to any one of the preceding claims, wherein the carbon monoxide sensor (26) is placed in an extreme area of ​​the pyrolysis chamber (2), near the fluidic link between the pyrolysis chamber (2) and the post-combustion chamber (3). A pyrolysis process according to any one of the preceding claims, comprising, before engaging the second phase, an injection of neutral gas into the pyrolysis chamber (2), and in which, as long as the first and second conditions are not satisfied, for a measurement period of between 10s and 5min, with this injection of neutral gas, the second phase is not engaged. Pyrolysis process according to the preceding claim, wherein the second phase is automatically engaged if the first and second conditions are met, for a neutral gas flow rate equal to a predetermined maximum flow rate. A pyrolysis process according to one of the two preceding claims, wherein the injection of neutral gas is made at an increasing flow rate up to a predetermined maximum flow rate. A pyrolysis process according to the preceding claim, wherein the predetermined maximum flow rate is less than or equal to 600 Nm 3 / h, preferably between 50 Nm 3 / h and 300 Nm 3 / h. A pyrolysis process according to one of the four preceding claims, wherein the neutral gas has a temperature greater than 300°C, or even greater than 400°C, at the time of its injection. A pyrolysis process according to any one of the preceding claims, comprising a cooling phase, referred to as the third phase, which follows the second phase, and in which the third phase is not initiated until at least one of the first and second conditions is met. Pyrolysis process according to the preceding claim, comprising, before engaging the third phase, an injection of neutral gas into the pyrolysis chamber (2), and in which, as long as at least one of the first and second conditions is not satisfied with this injection of neutral gas, the third phase is not engaged. Pyrolysis process according to the preceding claim, wherein the third phase is automatically engaged if the first and second conditions are met, for a neutral gas flow rate equal to a predetermined maximum flow rate.

Images