Powder separation method and powder separation device

Abstract

To provide a powder separation method and a powder separation device, capable of decreasing a manual workload and of easily separating powder from chlorine-containing gas.SOLUTION: The present invention provides a method of separating powder including an inorganic salt derived from a molten salt bath Bm in chlorine-containing gas Gc from the chlorine-containing gas Gc, generated by electrolysis using the molten salt bath Bm, the method comprising a collection process of collecting the powder present in the chlorine-containing gas Gc using a filter 2a by allowing the chlorine-containing gas Gc to flow through the filter 2a, a separation process of separating the powder collected by the filter 2a from the filter 2a, and a transportation process of transporting the powder separated from the filter 2a via a pipeline 3 using transportation gas Gt by feeding the transportation gas Gt with a dew point of -5°C or below into the pipeline 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for separating, from a chlorine-containing gas generated by electrolysis using a molten salt bath, a powder containing an inorganic salt derived from the molten salt bath in the chlorine-containing gas.

Background Art

[0002] In the production of metallic titanium by the Kroll process, magnesium chloride produced as a by-product may be decomposed into metallic magnesium and chlorine by electrolysis using a molten salt bath. In this case, metallic magnesium and chlorine can be used for the reduction of titanium tetrachloride and the chlorination of titanium ore, respectively.

[0003] Chlorine-containing gases generated by this type of electrolysis contain chlorides such as magnesium chloride and other inorganic salts derived from the components of the molten salt bath, which are, for example, evaporated and mixed in, and then become powders by being cooled or the like and are contained therein. In order to use the chlorine in the chlorine-containing gas for the above-mentioned applications and the like, it is necessary to separate the powder from the chlorine-containing gas.

[0004] Patent Document 1 states that, "In the electrolytic production of such metallic Mg, when chlorine gas is released from the bath surface of the molten bath salt 10 in the electrolysis chamber 21, droplets of chloride scatter upward. These droplets are sucked into the suction pipe 31 together with the chlorine gas and accumulate in the pipe as powders of chloride." (See paragraph 0007, FIG. 4). In this Patent Document 1, the object is to "provide a method and an apparatus for producing Mg by electrolysis that can effectively suppress the deposition of chloride in the suction pipe even in the case of a highly efficient electrolysis operation using bipolar electrodes", and "in an Mg electrolysis production method for producing metallic Mg by an electrolysis method using a molten bath salt containing MgCl 2 In the Mg electrolysis production method, when discharging and recovering the by-product gas mainly composed of chlorine gas generated during the electrolysis to the outside of the system, the by-product gas is forcibly cooled at the inlet portion of the discharge path thereof." and, "MgCl 2An electrolytic cell for producing metallic Mg by electrolysis using a molten bath salt containing [the relevant substance], an exhaust system for sucking and discharging the by-product gas mainly composed of chlorine gas generated in the electrolytic cell to the outside of the tank, and a gas cooler for forcibly cooling the by-product gas at the inlet portion of the exhaust system. The Mg electrolytic production apparatus is characterized by comprising these components.

[0005] Further, in Patent Document 2, it is described that "the chlorine gas generated in the molten salt electrolytic cell 1 is sucked out from the electrolytic cell 1 via the chlorine gas suction nozzle 21 and led to the bag filter 3 via the chlorine gas pipe 2. Since the chlorine gas generated in the molten salt electrolytic cell 1 rises from the electrolytic bath 11, the vapor of the electrolytic bath 11 is also transported into the chlorine gas pipe along with the chlorine gas." And there is a description that "the electrolytic bath vapor accompanying the chlorine gas is cooled and condensed and solidified to form fine powder while passing through the chlorine gas pipe 2. By leading the fine powder to the bag filter 3 together with the chlorine gas, the fine powder can be effectively captured and removed." (See paragraph 0027, 0028, and FIG. 3).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] When collecting the powder in the above chlorine-containing gas on a filter, it is conceivable to manually remove the above powder in a state where the powder is detached from the filter and the flow of the chlorine-containing gas to the filter is blocked.

[0008] On the one hand, since electrolysis using a molten salt bath can be carried out over a relatively long period of time, it is necessary to manually remove the powder periodically, increasing the workload. Further, even if the flow of the chlorine-containing gas is blocked, harmful chlorine in the chlorine-containing gas may remain around the filter, and in the case of manual removal of the powder, treatment of the chlorine is also required.

[0009] In neither Patent Document 1 nor Patent Document 2 has any consideration been given to how to remove the powder after it has been collected by the filter.

[0010] An object of the present invention is to provide a powder separation method and a powder separation device that can reduce the manual workload and facilitate the separation of powder from a chlorine-containing gas.

Means for Solving the Problems

[0011] The inventor considered that it is effective to use the flow of a liquid or a gas in a pipe to transport the powder collected by the filter from the chlorine-containing gas without manual labor. Here, when transporting the powder with a liquid such as water, due to the inorganic salts derived from the molten salt bath being contained in the powder, the inorganic salts may absorb the liquid and turn the powder into a muddy state, possibly blocking the inside of the pipe. There is also concern that chlorine, which is transported in trace amounts together with the powder, may come into contact with a liquid such as water to generate hydrochloric acid, corroding the pipe. On the other hand, it was found that if the gas is used for transportation as it is, the powder may turn into a muddy state due to the moisture in the gas, and in this case too, there is a risk of blocking the pipe. In contrast, the inventor obtained the finding that it is effective to use a dry gas as the transport gas for transporting the powder containing inorganic salts derived from the molten salt bath.

[0012] The powder separation method of the present invention is a method for separating powder containing inorganic salts derived from a molten salt bath from a chlorine-containing gas generated by electrolysis using a molten salt bath, the method comprising: a collecting step of passing the chlorine-containing gas through a filter and collecting the powder in the chlorine-containing gas on the filter; a desorbing step of desorbing the powder collected on the filter from the filter; and a transporting step of supplying a transport gas having a dew point temperature of -5°C or lower into a pipe and transporting the powder desorbed from the filter by the transport gas in the pipe.

[0013] Preferably, a storage step of storing the powder desorbed from the filter is further included between the desorbing step and the transporting step.

[0014] One or more on-off valves for restricting the passage of the chlorine-containing gas when closed are provided in the middle of the passage from the filter to the pipe, and it is preferable to close the on-off valve in the collecting step and open the on-off valve in the desorbing step.

[0015] In the transporting step, it is preferable to supply the transport gas from a gas supply port provided in the pipe.

[0016] In this case, it is preferable that a plurality of the gas supply ports are provided along the transport direction of the powder.

[0017] Also in this case, in the transporting step, it is preferable to supply the transport gas from the gas supply port obliquely inward in the transport direction of the powder with respect to the direction toward the center of the cross section of the pipe.

[0018] In the powder separation method of the present invention, it is preferable to separate powder containing magnesium chloride as the inorganic salt from the chlorine-containing gas generated by electrolysis of magnesium chloride.

[0019] The powder separation device of the present invention is a device for separating powder containing inorganic salts derived from a molten salt bath from a chlorine-containing gas generated by electrolysis using a molten salt bath, and includes a collection container having a filter for collecting the powder in the chlorine-containing gas by passing the chlorine-containing gas therethrough, a detachment device for detaching the powder collected by the filter from the filter, and a pipe connected to the collection container, through which the powder detached from the filter is sent and a transport gas having a dew point temperature of -5°C or lower is supplied to transport the powder.

[0020] It is preferable that one or more on-off valves that restrict the passage of the chlorine-containing gas when closed are provided in the middle of the passage from the collection container to the pipe.

[0021] The powder separation device of the present invention may include a storage container for storing the powder detached from the filter between the collection container and the pipe.

[0022] In this case, it is preferable that each of the passage between the collection container and the storage container and the passage between the storage container and the pipe has an on-off valve that restricts the passage of the chlorine-containing gas when closed.

[0023] The pipe preferably has a gas supply port used for supplying the transport gas into the pipe.

[0024] In this case, it is preferable that a plurality of the gas supply ports are provided along the powder transport direction.

[0025] Also in this case, it is preferable that the gas supply port is provided so as to supply the transport gas obliquely inward in the powder transport direction with respect to the direction toward the center of the cross section of the pipe.

[0026] The powder separation device of the present invention is preferably used for separating powder containing magnesium chloride as the inorganic salt from a chlorine-containing gas generated by electrolysis of magnesium chloride.

Advantages of the Invention

[0027] According to the powder separation method and powder separation device of the present invention, the amount of manual work can be reduced, and the separation of powder from chlorine-containing gas can be easily performed.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The powder separation method according to an embodiment of the present invention can be implemented, for example, by using a powder separation device 1 as shown in FIG. 1. As shown in FIG. 2, in this powder separation device 1, a chlorine-containing gas Gc is fed from a molten salt electrolytic cell 21 that performs electrolysis using a molten salt bath, and the molten salt electrolytic cell 21 is connected by an electrolytic cell connecting pipe 22. Note that FIGS. 1 and 2 schematically show the device or equipment, and the dimensions and shapes of each part are not limited to those shown in the drawings.

[0030] In the molten salt electrolytic cell 21, a molten salt containing an inorganic salt is stored inside to form a molten salt bath Bm, and by applying a voltage to an electrode including an anode and a cathode (not shown), electrolysis of the inorganic salt in the molten salt bath is performed. Examples of the inorganic salt contained in the molten salt bath Bm include chlorides, typically magnesium chloride (MgCl 2 ), sodium chloride (NaCl), calcium chloride (CaCl 2 ), potassium chloride (KCl), and the like. Note that the molten salt bath Bm further contains magnesium fluoride (MgF 2 ) or calcium fluoride (CaF2 ) may also include etc.

[0031] For example, when electrolyzing magnesium chloride using the molten salt electrolysis cell 21, by this electrolysis, in addition to metal magnesium (Mg) being generated at the cathode, chlorine (Cl 2 ) containing chlorine-containing gas Gc is generated at the anode. The chlorine-containing gas Gc is sent to the powder separator 1 through the electrolyzer connection pipe 22 in order to use the chlorine contained therein for chlorination of titanium ore, etc. Note that the metal magnesium generated by electrolysis can be used, for example, for the reduction of titanium tetrachloride. Also, although detailed description is omitted, chlorine-containing gas Gc containing chlorine may also be generated by electrolysis of sodium chloride, calcium chloride, potassium chloride, or zinc chloride. The chlorine concentration of the chlorine-containing gas Gc may be, for example, 90 vol% or more, typically 95 vol% or more, more typically 98 vol% or more. However, the present invention can be applied not only to the electrolysis examples mentioned here but also to any electrolysis that generates chlorine.

[0032] As illustrated in FIG. 1, the powder separator 1 into which the chlorine-containing gas Gc is fed includes a bottomed cylindrical collection container 2 having a filter 2a (such as a bag filter) through which the chlorine-containing gas Gc passes, a detachment device 2b for detaching the powder collected on the filter 2a from the filter 2a, and a pipe 3 connected to the collection container 2 for transporting the powder detached from the filter 2a with a transport gas Gt. In the powder separator 1 of this example, a storage container 4 for storing the powder detached from the filter 2a in the collection container 2 is provided between the collection container 2 and the pipe 3, but the storage container 4 may be omitted.

[0033] The chlorine-containing gas Gc sent from the electrolytic cell connecting pipe 22 flows into the collection container 2, for example, from the side, and passes through the filter 2a in the collection process, so that powder is collected on the filter 2a, and the purified gas Gp from which the powder is separated is obtained. In the illustrated collection container 2, a tank connecting pipe 32 connected to the chlorine tank 31 is connected to the upper side thereof (see FIG. 2), and the purified gas Gp flows out of the collection container 2 through the tank connecting pipe 32. When chlorine in the purified gas Gp is used for the chlorination of titanium ore, the collection container 2 may be connected to a titanium ore chlorination furnace. A valve 22a is provided in the middle of the electrolytic cell connecting pipe 22, and a valve 32a is provided in the middle of the tank connecting pipe 32. It is sufficient that at least one of the valve 22a and the valve 32a is provided, and either one can be omitted. Although not shown, a gas suction device may be installed on the chlorine tank 31 side.

[0034] During the collection process, the valve 22a of the electrolytic cell connecting pipe 22 and the valve 32a of the tank connecting pipe 32 are opened so that the chlorine-containing gas Gc flows from the molten salt electrolytic cell 21 to the powder separator 1. When only one of the valve 22a or the valve 32a is provided, the one is opened. On the other hand, in the collection process, one or more on-off valves provided in the middle of the passage from the filter 2a to the pipe 3, more specifically, in this embodiment, the on-off valve 5a provided in the passage 5 between the collection container 2 and the storage container 4 and the passage between the storage container 4 and the pipe 3 At least one, preferably both, of the on-off valves 6a provided in 6 can be closed. This is to suppress the inflow of the chlorine-containing gas Gc to the pipe 3 side. It is preferable that at least one of the on-off valve 5a and the on-off valve 6a can restrict the passage of gases such as the chlorine-containing gas Gc when closed.

[0035] Note that electromagnetic valves, ball valves, gate valves, or various other valves can be used for the above-described valve 22a, valve 32a, and the valve 42a described later, and the on-off valves 5a and 6a, and their materials are preferably PTFE (polytetrafluoroethylene) or ceramics from the viewpoint of corrosion resistance to chlorine.

[0036] The filter 2a is preferably excellent in corrosion resistance to chlorine, collection property of relatively fine particles, and heat resistance, and examples thereof include those made of PTFE (polytetrafluoroethylene), those made of ceramics, and the like.

[0037] The powder collected by the filter 2a is detached from the filter 2a using a detachment device 2b in the detachment step. In this embodiment, the detachment device 2b is a hammer or the like that strikes the collection container 2 from the outside and blows off the powder from the filter 2a by the impact. In addition to or instead of such a detachment device 2b, for example, although not shown, a detachment device that continuously or intermittently injects compressed gas onto the filter 2a to impact the filter 2a, a detachment device that vibrates the filter 2a, or a detachment device that directly strikes the filter 2a can also be provided.

[0038] In the separation process, in order to send the powder by dropping it from the collection container 2 to the storage container 4, etc., the on-off valve 5a provided in the middle of the passage 5 between the collection container 2 and the storage container 4 is opened. At this time, it is preferable to close the valve 22a provided in the middle of the electrolytic cell connecting pipe 22. Thereby, since the flow of the chlorine-containing gas Gc to the collection container 2 is blocked by the valve 22a, the inflow of the chlorine-containing gas Gc into the storage container 4 and the piping 3 on the downstream side thereof can be suppressed. When only the valve 32a is provided among the valve 22a and the valve 32a, the suction of the chlorine-containing gas Gc by the above-described gas suction device is blocked by closing the valve 32a. At this time, the flow of the chlorine-containing gas Gc to the collection container 2 side can be suppressed by flowing the chlorine-containing gas Gc not through the electrolytic cell connecting pipe 22 but through another line (not shown) connecting the molten salt electrolytic cell 21 and the tank connecting pipe 32 from the molten salt electrolytic cell 21. Alternatively, if there is no such another line, if the electrolysis in the molten salt electrolytic cell 21 is stopped, the chlorine-containing gas Gc will not be generated, and if the already generated chlorine-containing gas Gc is sucked by the gas suction device, the chlorine-containing gas Gc will not flow to the collection container 2 side. However, as will be described later, when sending the powder from the storage container 4 to the piping 3 by opening the on-off valve 6a, if the on-off valve 5a is closed, the inflow of the chlorine-containing gas Gc into the piping 3 and the corrosion of the piping 3 caused thereby can be suppressed. Therefore, it is not always necessary to close the valve 22a or the valve 32a as described above.

[0039] In the storage container 4, a storage process for storing the powder detached from the filter 2a is performed. By providing the storage container 4 between the collection container 2 and the piping 3, the timing of the powder transportation in the piping 3 can be adjusted, and the inflow of the chlorine-containing gas Gc into the piping 3 can be further suppressed. However, it is also possible to directly connect the collection container and the piping without providing the storage container 4. In this case, the powder may be stored in the lower part of the collection container.

[0040] The storage container 4 preferably has a tapered shape in which at least the downstream portion on the side of the pipe 3 narrows as it goes downstream so that the powder can be easily sent to the pipe 3 as in the illustrated embodiment. When the on-off valve 6a provided in the passage 6 between the storage container 4 and the pipe 3 is opened, the powder accumulated in the storage container 4 is sent to the pipe 3.

[0041] The powder detached from the filter 2a is stored in the storage container 4 as necessary and then sent to the pipe 3 by opening the on-off valve 6a. Then, the powder is transported in the pipe 3 by the supply of the transport gas Gt in the transport process. The transport gas Gt is supplied into the pipe 3 through the gas supply pipe 42 from a gas supply source 41 such as a tank-shaped one (see Fig. 2). In the transport process, the on-off valve 6a is closed, and the transport gas Gt flows along the transport direction of the powder (right direction in Fig. 1). The powder is guided by the flow of the transport gas Gt and transported in the pipe 3.

[0042] Here, it is important to use the transport gas Gt with a dew point temperature of -5°C or lower. Thereby, the powder can be prevented from becoming muddy due to the moisture in the transport gas Gt, and clogging of the pipe 3 can be suppressed. In other words, when the dew point temperature of the transport gas Gt exceeds -5°C, since the transport gas Gt is not sufficiently dry, the powder containing the hygroscopic inorganic salt becomes muddy and deposits due to the moisture, causing clogging in the pipe 3. Also, when using the transport gas Gt with a dew point temperature of -5°C or lower, there is an advantage that corrosion of the pipe due to hydrochloric acid (HCl) that can be generated by the reaction of chlorine that may be contained in a trace amount in the pipe 3 and the moisture in the transport gas Gt (Cl 2 +H 2 O→HClO+HCl) is suppressed.

[0043] From such a viewpoint, the lower the dew point temperature of the transport gas Gt, the more desirable it is, but typically it may be set to -40°C to -5°C.

[0044] As the transport gas Gt, air, nitrogen, argon, helium, or the like can be used. To adjust by lowering the dew point temperature of the transport gas Gt, for example, cooling, drying with an air dryer, or the like can be mentioned, but it is not limited to such methods.

[0045] The pipe 3 can be provided with a gas supply port 3a for supplying the transport gas Gt into the pipe 3. As in the illustrated embodiment, it is preferable to provide a plurality of gas supply ports 3a along the powder transport direction because smooth transport of the powder in the pipe 3 can be realized.

[0046] Further, the gas supply port 3a is preferably provided so that the transport gas Gt is supplied obliquely inward in the powder transport direction with respect to the direction (vertical direction in FIG. 1) toward the center of the cross section of the pipe 3 (the cross section perpendicular to the powder transport direction). Thereby, it becomes possible to transport the powder more smoothly in the transport direction in the pipe 3. In this example, the gas supply pipe 42 connected to the gas supply port 3a is provided in a direction inclined in the powder transport direction with respect to the direction in which its central axis faces the center of the cross section of the pipe, so that the transport gas Gt is supplied obliquely inward. The angle formed by the supply direction of the transport gas Gt at the gas supply port 3a and the direction toward the center of the cross section of the pipe is preferably 15° to 75°.

[0047] When a plurality of gas supply ports 3a are provided in the pipe 3, as shown in FIG. 2, the gas supply pipe 42 can be branched in the middle and connected to the plurality of gas supply ports 3a, and the transport gas Gt can be supplied from one gas supply source 41 to the plurality of gas supply ports 3a. Alternatively, a plurality of gas supply sources 41 may be used. A valve 42a may be provided in the middle of the gas supply pipe 42.

[0048] And also, when the pipe 3 is inclined with respect to the vertical direction or extends in the horizontal direction, the gas supply port 3a is preferably provided on the lower side in the vertical direction of the pipe 3 as shown. In this case, the powder accumulates on the lower side in the pipe due to its own weight, and the powder can be easily transported by floating it by the supply of the transport gas Gt from the lower gas supply port 3a.

[0049] The transport gas Gt may be continuously supplied from the gas supply port 3a, but if it is intermittently supplied, the amount of the transport gas Gt used can be reduced.

[0050] The pipe 3 can be connected to, for example, a powder storage tank 51 as shown in FIG. 2. The powder transported by the transport gas Gt in the pipe 3 reaches the powder storage tank 51 and is stored therein. The powder storage tank 51 may be provided with an exhaust port (not shown). When exhausting from the inside of the powder storage tank 51 through the exhaust port, the powder can be transported more efficiently by the transport gas Gt in the pipe 3.

[0051] In this way, the powder can be separated from the chlorine-containing gas Gc generated by electrolysis using the molten salt bath Bm, and the purified gas Gp from which the powder has been separated can be recovered. In the above-described embodiment, the powder can be easily transported by the transport gas Gt in the pipe 3 without manual operation, so the amount of work required for removing the powder can be reduced.

Example

[0052] Next, the powder separation method of the present invention was experimentally implemented and its effects were confirmed, and the description will be given below. However, the description here is for the purpose of mere exemplification and is not intended to be limited thereto.

[0053] (Example 1) Using the equipment as shown in FIGS. 1 and 2, the powder was separated from the chlorine-containing gas generated from the molten salt electrolysis cell. In the molten salt electrolysis cell, magnesium metal and chlorine were generated from magnesium chloride by electrolysis using a molten salt bath. The chlorine concentration of the chlorine-containing gas was about 99 vol%, and about 70 mass% of the powder in the chlorine-containing gas was magnesium chloride.

[0054] The pipes of the powder separation device were made of carbon steel, with an inner diameter of 250 mm and a length of 10 m. In the transportation process, a transportation gas with a dew point temperature of -5°C was intermittently supplied into the pipes to transport the powder inside the pipes. The supply direction of the transportation gas was inclined by 60° toward the powder transportation direction (horizontal direction) with respect to the direction (vertical direction) toward the center of the cross-section of the pipes.

[0055] As a result, it was possible to separate the powder from the chlorine-containing gas over a period of one month with substantially no manual labor required. During that period, no clogging of the pipes occurred.

[0056] (Example 2) The same procedure as in Example 1 was followed, except that the supply direction of the transportation gas was set to the vertical direction. As a result, the transportation amount of the powder per unit time decreased by 50% on a weight basis compared to the case of Example 1, but it was possible to separate the powder over a period of one month without any clogging of the pipes.

[0057] (Comparative Example 1) The same procedure as in Example 1 was followed, except that a transportation gas with a dew point temperature of 0°C was used. As a result, before one month had passed since the start of operation, the powder in the pipes became muddy and clogged. Work was required to eliminate the clogging. A screw with spiral flights provided on the outer peripheral surface of the rotating shaft was inserted into the pipes and rotationally driven, but the solidified powder could not be sufficiently removed. The clogging could finally be eliminated by removing the pipes and washing them with water.

[0058]

Table 1

[0059] From the above, it was found that according to this invention, the separation of powder from the chlorine-containing gas can be facilitated with a relatively small amount of work.

Explanation of Reference Numerals

[0060] 1 Powder separation device 2 Collection container 2a Filter 2b Detachment device 3 Pipe 3a Gas supply port 4 Storage container 5, 6 Passageway 5a, 6a On-off valve 21 Molten salt electrolytic cell 22 Electrolytic cell connecting pipe 22a Valve 31 Tank for chlorine 32 Tank connecting pipe 32a Valve 41 Gas supply source 42 Gas supply pipe 42a Valve 51 Powder storage tank Gc Chlorine-containing gas Gp Purified gas Gt Transport gas Bm Molten salt bath

Claims

**Claim 1** A method for separating a powder containing an inorganic salt derived from a molten salt bath from a chlorine-containing gas generated by electrolysis using a molten salt bath, comprising: a collecting step of passing the chlorine-containing gas through a filter and collecting the powder in the chlorine-containing gas on the filter; a desorbing step of desorbing the powder collected on the filter from the filter; a transporting step of supplying a transport gas having a dew point temperature of -5°C or lower into a pipe and transporting the powder desorbed from the filter by the transport gas in the pipe; wherein: in the transporting step, the transport gas is supplied from a gas supply port provided in the pipe; the powder separation method, wherein a plurality of the gas supply ports are provided along the powder transport direction. **Claim 2** The powder separation method according to claim 1, wherein in the transporting step, the transport gas is supplied from the gas supply port in a direction obliquely inward in the powder transport direction with respect to the direction toward the center of the cross section of the pipe. **Claim 3** A method for separating a powder containing an inorganic salt derived from a molten salt bath from a chlorine-containing gas generated by electrolysis using a molten salt bath, comprising: a collecting step of passing the chlorine-containing gas through a filter and collecting the powder in the chlorine-containing gas on the filter; a desorbing step of desorbing the powder collected on the filter from the filter; a transporting step of supplying a transport gas having a dew point temperature of -5°C or lower into a pipe and transporting the powder desorbed from the filter by the transport gas in the pipe; wherein: in the transporting step, the transport gas is supplied from a gas supply port provided in the pipe; the powder separation method, wherein in the transporting step, the transport gas is supplied from the gas supply port in a direction obliquely inward in the powder transport direction with respect to the direction toward the center of the cross section of the pipe. **Claim 4** The powder separation method according to any one of claims 1 to 3, further comprising a storing step of storing the powder desorbed from the filter between the desorbing step and the transporting step. **Claim 5** One or more on-off valves for restricting the passage of the chlorine-containing gas when closed are provided in the middle of the passage from the filter to the pipe; the powder separation method according to any one of claims 1 to 4, wherein the on-off valve is closed in the collecting step and opened in the desorbing step. **Claim 6** The powder separation method according to any one of claims 1 to 5, wherein a powder containing magnesium chloride as the inorganic salt is separated from a chlorine-containing gas generated by electrolysis of magnesium chloride.

7. An apparatus for separating a powder containing an inorganic salt derived from a molten salt bath from a chlorine-containing gas generated by electrolysis using a molten salt bath, comprising: a collection container having a filter for collecting the powder in the chlorine-containing gas by passing the chlorine-containing gas therethrough; a detachment device for detaching the powder collected on the filter from the filter; a pipe connected to the collection container, through which the powder detached from the filter is sent, and into which a transport gas having a dew point temperature of -5°C or lower is supplied to transport the powder; and the pipe has a gas supply port used for supplying the transport gas into the pipe; the powder separation device, wherein a plurality of the gas supply ports are provided along the powder transport direction.

8. The powder separation device according to claim 7, wherein the gas supply port is provided so as to supply the transport gas obliquely inward in the powder transport direction with respect to the direction toward the center of the cross section of the pipe.

9. An apparatus for separating a powder containing an inorganic salt derived from a molten salt bath from a chlorine-containing gas generated by electrolysis using a molten salt bath, comprising: a collection container having a filter for collecting the powder in the chlorine-containing gas by passing the chlorine-containing gas therethrough; a detachment device for detaching the powder collected on the filter from the filter; a pipe connected to the collection container, through which the powder detached from the filter is sent, and into which a transport gas having a dew point temperature of -5°C or lower is supplied to transport the powder; and the pipe has a gas supply port used for supplying the transport gas into the pipe; the powder separation device, wherein the gas supply port is provided so as to supply the transport gas obliquely inward in the powder transport direction with respect to the direction toward the center of the cross section of the pipe.

10. The powder separation device according to any one of claims 7 to 9, having one or more on-off valves that limit the passage of the chlorine-containing gas when closed, in the middle of the passage from the collection container to the pipe.

11. The powder separation device according to any one of claims 7 to 10, further comprising a storage container for storing the powder detached from the filter, between the collection container and the pipe.

12. The powder separation device according to claim 11, wherein each of the passage between the collection container and the storage container and the passage between the storage container and the pipe has an on-off valve that restricts the passage of the chlorine-containing gas when closed.

13. The powder separation device according to any one of claims 7 to 12, which is used for separating a powder containing magnesium chloride as the inorganic salt from a chlorine-containing gas generated by electrolysis of magnesium chloride.

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