JP7570941B2 - Heating system and heating method - Google Patents

Description

The present invention relates to a heating system and method for heating objects to be heated, such as waste lithium-ion batteries.

Lithium-ion batteries are composed of a positive electrode material made of aluminum foil coated with lithium, cobalt, nickel, etc., a negative electrode material made of copper foil coated with graphite, electrolyte, separator, etc. Lithium batteries therefore contain valuable materials such as lithium, cobalt, nickel, and copper. For this reason, recycling discarded lithium batteries and recovering these valuable materials is extremely beneficial for a country like Japan, which has few resources.

Waste lithium-ion batteries are difficult to process because they can ignite, cause electric shock, and generate hydrogen fluoride during recycling. For this reason, waste lithium-ion batteries are rendered harmless by heating and roasting, and then separated and recovered by heating, crushing or pulverizing, sieving, sorting, etc.

However, since the electrolyte contained in waste lithium-ion batteries is an organic solvent equivalent to kerosene, if the amount of waste to be processed increases, the aluminum contained in the waste lithium-ion batteries will melt and adhere to other materials due to the rise in temperature caused by the combustion of the electrolyte, which may make it difficult to recover valuable materials.

For example, Patent Document 1 discloses a technology for adjusting the heating temperature by injecting at least one type of gas from among nitrogen gas, carbon dioxide, and water vapor into the thermal incinerator and venting the inside of the thermal incinerator when the temperature exceeds a predetermined temperature of 450°C or higher and 525°C or lower.

JP 2018-159477 A

However, the technology described in Patent Document 1 requires the installation of new equipment such as piping to inject gas into the incinerator. In addition, when nitrogen gas or carbon dioxide is injected into the incinerator, the oxygen concentration around the furnace decreases, which may lead to oxygen deficiency.

The present invention aims to provide a heating system and a heating method that can suppress temperature rise without the need to install new equipment such as piping.

The heating system of the present invention is a heating system for heating a heated object which is a waste lithium-ion battery , and is characterized in that it comprises a heat treatment device that contains at least one of magnesium carbonate and dolomite together with the heated object, and a heating means that heats the heat treatment device so that the internal temperature of the heat treatment device is 400°C or higher and 550°C or lower.

According to the heating system of the present invention, when the internal temperature of the heat treatment device rises due to some factor and reaches approximately 600°C, at least one of the magnesium carbonate and dolomite undergoes a decarbonation reaction. The endothermic heat and carbon dioxide gas generated by this reaction suppress combustion within the heat treatment device, and the internal temperature of the heat treatment device can be reduced. This makes it possible to prevent the aluminum contained in the waste lithium-ion batteries from melting and adhering to other materials, thereby enabling the effective recovery of valuable resources.

This decarboxylation reaction automatically progresses when the internal temperature of the heat treatment device reaches approximately 600°C. Therefore, unlike the technology described in Patent Document 1, there is no need to install new equipment such as piping to introduce gas into the heat treatment device when the temperature reaches a certain level.

In the heating system of the present invention, it is also preferable to include a heat-resistant container that contains at least one of the magnesium carbonate and dolomite together with the object to be heated, has a heat-resistant temperature of at least 600°C or more, and has an insertion part that passes between the inside and the outside, and is contained inside the heat treatment device .

In this case, the object to be heated and at least one of the magnesium carbonate and dolomite are contained in the same heat-resistant container, making it possible to reduce the number of containers contained within the heat treatment device.

Furthermore, in the heating system of the present invention, the amount of the magnesium carbonate is preferably 1.2 kg or more per cubic ^meter of the volume of the internal space of the heat treatment device.

In this case, the volume of the carbon dioxide gas generated by the decarbonation reaction of magnesium carbonate is equal to or larger than the volume of the internal space of the heat treatment device, so that the carbon dioxide gas can fill the entire internal space of the heat treatment device, and the temperature rise is more reliably suppressed. In the case of dolomite, the amount is preferably 2.6 kg or more per 1 ^m3 of the internal space of the heat treatment device.

The heating method of the present invention is characterized in that at least one of magnesium carbonate and dolomite is contained inside a heat treatment device together with an object to be heated , which is a waste lithium-ion battery , and the object to be heated is heated by heating the inside of the heat treatment device to a temperature of 400°C or higher and 550°C or lower.

According to the heating method of the present invention, when the temperature of the space in which the heated object is heated rises due to some factor and reaches approximately 600°C, at least one of the magnesium carbonate and dolomite undergoes a decarbonation reaction. The endothermic heat and carbon dioxide gas generated by this reaction suppress combustion in the heat treatment device, and the temperature can be reduced. This suppresses the rise in temperature and prevents the aluminum contained in the waste lithium-ion batteries from melting and adhering to other materials, making it possible to effectively recover valuable resources.

This decarbonation reaction automatically progresses when the internal temperature of the space reaches approximately 600°C. Therefore, unlike the technology described in Patent Document 1, there is no need to install new equipment such as piping to introduce gas into the space when the temperature reaches a certain level.

FIG. 1 is a schematic cross-sectional view showing a heating system according to an embodiment of the present invention. 1 is a graph showing changes in the internal temperature of the electric furnaces in Test Examples 1 and 2 at high temperatures.

Heating system 100 according to an embodiment of the present invention will be described below with reference to FIG. 1. This heating system 100 is a device that heats an object to be heated. Note that FIG. 1 is a diagram for explaining this embodiment in a schematic manner, and the dimensions are exaggerated.

Here, we will explain the case where the heating system 100 is a system for rendering the waste lithium ion battery A, which is the heated object of the present invention, harmless by heating and roasting the waste lithium ion battery A.

The heating system 100 is a processing device for processing waste lithium-ion batteries A, for example, similar to that described in the above-mentioned Patent Document 1. Although not shown in detail, the heating system 100 includes a heat treatment furnace 10 and one or more heat-resistant containers 20 that are housed inside the heat treatment furnace 10 with the waste lithium-ion batteries A housed therein. Although not shown in the figure, the heating system 100 may also include a container transport device that loads and unloads the heat-resistant containers 20 into and from the heat treatment furnace 10.

The heat treatment furnace 10 is, for example, a substantially cylindrical vertical furnace with furnace walls 11 made of steel plates covered with fireproof material, and is heated by heating means 12 such as a gas burner. The heat treatment furnace 10 corresponds to the heat treatment device of the present invention. The internal temperature of the heat treatment furnace 10 is detected by a temperature sensor 13. In addition, although not shown, the heat treatment furnace 10 is also provided with a door that is used when inserting and removing the heat-resistant container 20 into the internal space.

The hearth 14 of the heat treatment furnace 10 may be made of a steel plate covered with a refractory material, similar to the furnace wall 11, and may be configured to be rotatable horizontally by a hearth rotation device (not shown).

The heat treatment furnace 10 contains multiple heat-resistant containers 20, which are placed on the hearth 14 with a gap between adjacent heat-resistant containers 20.

The shape of each heat-resistant container 20 is, for example, a box shape such as a rectangular parallelepiped, cube, cylinder, sphere, or oval sphere, and is not particularly limited. Here, the heat-resistant container 20 is cylindrical as a whole. The heat-resistant container 120 is made of stainless steel such as SUS304, and any material can be used as long as it has a heat-resistant temperature of at least 600°C, more preferably 650°C, and even more preferably 700°C.

The heat-resistant container 20 comprises a cylindrical body 21 with an open top, a top lid 22 that is removably attached to the top of the body 21, and an exhaust port 23 formed near the top of the top lid 22 or the body 21.

Furthermore, each heat-resistant container 20 is provided with a partition plate 24 in the middle in the height direction, which divides the internal space into upper and lower portions. Powder B made of at least one of magnesium carbonate (MgCO ₃ ) and dolomite (hereinafter referred to as magnesium carbonate powder) is contained in the space below the partition plate 24, and one or more waste lithium-ion batteries A are contained in the space above the partition plate 24. The waste lithium-ion batteries A may be contained in the heat-resistant container 20 in a stacked or overlapping manner.

The partition plate 24 has one or more through holes 25 formed vertically and having a diameter smaller than the particle size of the magnesium carbonate or other powder B. The particle size of the magnesium carbonate or other powder B is, for example, 3 mm to 10 mm.

When magnesium carbonate is heated to about 600° C., a decarbonation reaction proceeds while absorbing heat, as shown in the following reaction formula (1), and carbon dioxide gas is produced.
MgCO ₃ →MgO+CO ₂ -116.5kJ/mol... (1)

When dolomite is heated to approximately 600°C, the magnesium carbonate component undergoes an endothermic decarbonation reaction, as shown in reaction formula (1), producing carbon dioxide gas.

The amount of magnesium carbonate powder B contained in the heat-resistant container 20 is preferably 1.2 kg (about 14 mol) or more per ^m3 of the internal space of the heat treatment furnace 10 when the magnesium carbonate powder B is magnesium carbonate so that the carbon dioxide gas generated by the above reaction formula (1) fills the entire inside of the heat treatment furnace 10. Also, when the magnesium carbonate powder B is dolomite, the amount is preferably 2.6 kg (about 14 mol) or more per ^m3 of the internal space of the heat treatment furnace 10.

The heating system 100 further includes an exhaust mechanism 40 for exhausting the gas in the heat treatment furnace 10 to the outside. Here, the exhaust mechanism 40 is provided at the top of the heat treatment furnace 10 and includes an exhaust duct 41 that connects the inside and outside of the heat treatment furnace 10, and an exhaust fan 42 for exhausting the gas in the heat treatment furnace 10 to the outside via the exhaust duct 41. It is preferable that the suction port of the exhaust duct 41 is located slightly above the exhaust port 23 of the heat-resistant container 20.

The following describes a heating method according to an embodiment of the present invention using the heating system 100 described above.

First, as a preliminary treatment, the exhaust fan 42 is operated to perform a pre-purge, which exhausts residual gas from the heat treatment furnace 10 to the outside. After that, the inside of the heat treatment furnace 10 is heated by the heating means 12. The internal temperature of the heat treatment furnace 10 is increased while being monitored by the temperature sensor 13. The operation of the heating means 12 and the like is controlled so that the internal temperature is kept constant at a predetermined heating temperature between 400°C and 550°C, for example 600°C, so that the resin decomposes but the aluminum does not melt.

Next, in the heating system 100, the heat-resistant container 20 containing the waste lithium-ion batteries A and magnesium carbonate powder, etc. B is placed in a predetermined position in the heat treatment furnace 10 through the door.

Then, the operation of the heating means 12 and the like is controlled so that the internal temperature of the heat treatment furnace 10 is kept constant at the predetermined heating temperature, for example, 600°C. This heats the waste lithium-ion batteries A. Note that the exhaust of gas present in the internal space of the heat treatment furnace 10 by operating the exhaust fan 42 may be performed periodically or continuously as needed.

This heating creates a reducing atmosphere inside the heat-resistant container 20, and the plastics, such as the housings of the waste lithium-ion batteries A contained in the heat-resistant container 20, are carbonized by dry distillation into a carbonized mixture, separated from materials containing useful metals such as lithium, cobalt, nickel, and manganese. The electrolyte in the waste lithium-ion batteries A is volatilized, and together with gases generated by the thermal decomposition of flammable materials such as plastics, it is exhausted from the exhaust port 23 of the heat-resistant container 20 into the heat treatment furnace 10, and then exhausted to the outside by the exhaust mechanism 40.

When the internal temperature of the heat treatment furnace 10 rises for some reason to approximately 600°C, the magnesium carbonate or other powder B undergoes a decarboxylation reaction as shown in reaction formula (1) above. The endothermic heat and carbon dioxide gas generated by this reaction suppress combustion within the heat treatment furnace 10, lowering the internal temperature of the heat treatment furnace 10. This suppresses the temperature rise and prevents the aluminum contained in the waste lithium-ion batteries A from melting and adhering to other materials, making it possible to effectively recover valuable resources.

The above reaction will automatically proceed when the internal temperature reaches approximately 600°C if the heat-resistant container 20 containing powder B such as magnesium carbonate is placed in the heat treatment furnace 10. Therefore, unlike the technology described in Patent Document 1, there is no need to install new equipment such as piping to introduce gas into the heat treatment furnace 10 when the temperature reaches a predetermined level.

The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the object to be heated is a waste lithium-ion battery, but the object to be heated is not limited to this, and may be any object that is heated to a temperature of 400°C or higher and 550°C or lower. In addition, the heat treatment device of the present invention is not particularly limited, and a fluidized bed furnace, a tunnel furnace, a batch furnace such as a muffle, etc. can be suitably used.

(Test Example)
In a simulation of the above-mentioned heating system 100, a test was carried out to confirm whether or not the temperature rise is suppressed by simulating a temperature rise and storing magnesium carbonate or other powder B in the heat-resistant container 20. This will be described below.

In this test, a resin sheet was used instead of waste lithium-ion batteries A as the combustible material to generate a temperature rise. This resin sheet was made of fluororesin and had a rectangular shape with sides of 30 to 40 mm and a thickness of 0.5 to 2 mm. 40 g of the resin sheet was used in each test example.

Here, instead of the heat treatment furnace 10, an electric furnace F0-510 manufactured by Yamato Scientific Co., Ltd. equipped with an exhaust hood was used. This electric furnace had inner dimensions of 300 mm in width, 250 mm in depth, and 140 mm in height, and an internal volume of 10.5 L.

A cylindrical stainless steel tube with a lid was used to simulate the heat-resistant container 20. The stainless steel tube had an inner diameter of 70 mm, a height of 135 mm, and an internal volume of 0.52 L. A 3 mm through hole was formed in the upper part of the stainless steel tube.

The test was carried out as follows. First, a thermocouple was installed on top of the electric furnace. Then, the temperature of the electric furnace was raised until the internal temperature indicated by the thermocouple reached 600°C.

The stainless steel pipe containing the resin sheet and magnesium carbonate was placed inside an electric furnace with the internal temperature set to 600°C, and the door of the electric furnace was closed. The test conditions are summarized in Table 1. When the decarbonation reaction of 25 g of magnesium carbonate was completed, 21 L of carbon dioxide gas was generated, which is twice the internal volume of the electric furnace.

The heater of the electric furnace was turned off 30 seconds after the door of the electric furnace was closed. Temperature measurements were then continued until the internal temperature of the electric furnace fell below 400°C. The electric furnace was not forcibly ventilated.

As can be seen from Figure 2, which shows the change in the internal temperature of the electric furnace at high temperatures in Test Examples 1 and 2, Test Example 2, in which magnesium carbonate was contained in the stainless steel tube, shows that the maximum internal temperature of the electric furnace is suppressed compared to Test Example 1, in which magnesium carbonate was not contained. This confirms that containing magnesium carbonate is effective in suppressing temperature rise. Note that the elapsed time in Figure 2 is the time elapsed from the time the electric furnace door was closed.

10...heat treatment furnace (heat treatment apparatus), 11...furnace wall, 12...heating means, 13...temperature sensor, 14...furnace bed, 20...heat-resistant container, 21...main body, 22...top lid, 23...exhaust port, 24...partition plate, 25...through hole, 40...exhaust mechanism, 41...exhaust duct, 42...exhaust fan, 100...heating system, A...waste lithium ion battery (object to be heated), B...magnesium carbonate powder or the like (powder consisting of at least one of magnesium carbonate and dolomite).

Claims (4)

A heating system for heating a heated object which is a waste lithium-ion battery ,
A heat treatment device that accommodates at least one of magnesium carbonate and dolomite together with the object to be heated;
a heating unit for heating the heat treatment device so that an internal temperature of the heat treatment device is 400° C. or higher and 550° C. or lower. The heating system according to claim 1, further comprising a heat-resistant container that contains at least one of the magnesium carbonate and dolomite together with the object to be heated, has a heat-resistant temperature of at least 600°C or more, and has an insertion portion formed to connect the inside and the outside, and is contained inside the heat treatment device. 3. The heating system according to claim 1, wherein the amount of the magnesium carbonate is 1.2 kg or more per cubic ^meter of the volume of the inner space of the heat treatment device. A heating method comprising the steps of: housing at least one of magnesium carbonate and dolomite together with a heated object , which is a waste lithium-ion battery, inside a heat treatment device ; and heating the inside of the device to 400°C or higher and 550°C or lower, thereby heating the heated object.

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