LU88336A1 - Device for fluidizing a pulverulent material - Google Patents

Description

FLUIDIZATION DEVICE D1ÜK POWDER MATERIAL

The present invention relates to a device for fluidizing a pulverulent material comprising a reservoir equipped with a primary fluidizing member which is connected to a supply of a primary fluidizing gas, a delivery tube for the fluidized pulverulent material, including one end plunges into the tank, this end comprising a capture member.

In order to facilitate the transport of the pulverulent materials through pipes, it is necessary to fluidize them, that is to say put the pulverulent materials in suspension in a flow of fluid. Generally, air or an inert gas, such as nitrogen, is used as the carrier fluid.

The powdery materials are generally introduced into a fluidization tank, into which a delivery tube is immersed, through which the fluidized powdery materials are discharged.

The -reservoir comprises a fluidization member through which a flow of a gas is injected into the reservoir. Near the fluidizing member, this gas suspends part of the pulverulent material. The powdery material thus fluidized then passes through a collecting member, generally a mouth constituting one end of the sending tube and is evacuated from the reservoir.

Most often, one or more refluidizations are carried out in the pneumatic transport circuit by injecting a gas into the sending tube during the journey. This is to avoid defluidization of the powdery materials in the delivery tube.

However, it has been found that even if a refluidization operation is carried out along the way, the evacuation pipes gradually become clogged by depositing the defluidized pulverulent material on the walls of the pipes.

The object of the present invention is to provide a device which makes it possible to increase the efficiency of the fluidization of pulverulent materials.

This objective is achieved by a device for fluidizing pulverulent materials comprising a reservoir equipped with a primary fluidizing member, which is connected to a supply of a primary fluidizing gas, a delivery tube for the pulverized fluidized material, including one end plunges into the reservoir, this end comprising a capture member essentially characterized by a secondary fluidization member located between the capture member and the delivery tube 32, connected to a supply of secondary fluidization gas.

By studying the defluidization phenomenon in more detail in the context of the present invention, it has been found that the defluidization takes place very close to the capture member of the sending tube. Refluidization en route could therefore not be effective because once the material is defluidized, it becomes very difficult to refluidize it inside a pipe by a simple injection of a carrier gas.

A main advantage of the proposed device is that the flow rate of primary fluidizing gas can be reduced compared to conventional systems. Indeed, according to the invention, a secondary fluidization member is used situated between a collection member and the end of the sending tube. Fluidization is therefore carried out in two stages. Secondary fluidization is extremely effective because all of the injected gas is used to fluidize the powder material. During the primary fluidization, only part of the injected gas contributes to the fluidization of the pulverulent material while the remainder of the gas only contributes to increasing the pressure inside the reservoir. The yield of the primary fluidization is therefore relatively low. To obtain a fluidization comparable to conventional systems, the total flow rate of fluidization gas can therefore be reduced significantly. On the other hand, when the same gas flow rate is used as in conventional systems, the fluidization obtained is far better.

Another advantage of the present invention is that the present device makes it possible to subject the pulverulent material to a secondary fluidization at the place where the material has the most tendency to defluidize. In this way, even pulverulent materials which are difficult to fluidize and to maintain in the fluidized state by conventional devices, can be easily fluidized without the risk of defluidization during the journey.

The secondary fluidization member preferably comprises a fluidization chamber supplied with the secondary fluidization gas, provided with at least one wall permeable to gas, through which the gas enters the flow of fluidized material.

This device makes it possible to increase the flow rate of the fluidization fluid at the critical location where the risk of defluidization is greatest. Indeed, very close to the mouth, the flow of fluidized materials undergoes a significant pressure drop and the risk that a defluidization takes place near the mouth is particularly high. If a secondary fluidizing gas flow, which keeps the particles in suspension, is passed through a permeable wall into the fluidized material flow at the critical location, the risk of defluidization is effectively eliminated.

According to another advantageous embodiment, the permeable wall is a porous plate. The porosity is preferably between 5 μια and 100 μια depending on the pulverulent material.

According to another preferred embodiment, the sending tube comprises one or more tertiary fluidization members located outside the tank. This tertiary fluidization may be necessary if the transport distances of the fluidized material are long.

According to yet another preferred embodiment, the delivery tube consists of an inner pipe and an outer coaxial pipe. Between the two pipes is arranged a space in which a secondary fluidizing gas, brought by a conduit, can circulate. The secondary fluidization member includes an inner tube made of a gas permeable material and an outer gas impermeable wall. The secondary fluidization member is connected to the sending tube by a peripheral bore which connects the inner tube to the inner pipe and the outer wall to the outer pipe of the sending tube. The peripheral bore allows the passage of the secondary fluidization gas from the space between the pipes in the secondary fluidization member.

Other particularities and advantages will emerge on reading the description of two advantageous embodiments presented below, by way of nonlimiting examples, with reference to the appended drawings in which: - Figure 1 shows schematically, in longitudinal section , a first advantageous embodiment, and - Figure 2 shows schematically, in longitudinal section, another advantageous embodiment.

In the first embodiment according to FIG. 1, there is seen a reservoir 10 of pulverulent materials equipped with a feed hopper 14. The reservoir 10 comprises, at its lower base, a member 16 for primary fluidization. This member 16 is equipped with a supply 20 of fluidizing gas connected to a chamber 24 · The upper part of the chamber 24 is closed by a porous plate 28 which is preferably made of sintered bronze, with a porosity of between 5 and 100 μπι. A fluidizing gas is brought, via the conduit 20, into the chamber 24. and diffuses through the plate 28 into the reservoir 10. Part of the pulverulent material, contained in the reservoir 10, is fluidized by the primary fluidizing gas.

A sending tube 32 plunges into the reservoir 10. One end of the tube 32 is equipped with a mouth and a secondary fluidization chamber 40 · The mouth 36 is located near the porous plate 28 so that that the fluidized material can be evacuated by the sending tube 32. The secondary fluidization chamber 40 is provided with a conduit 44 which connects it to a source of supply of secondary fluidization gas. The gas enters the chamber 40 and diffuses through a permeable wall 48 into the flow of fluidized material. This contribution of secondary fluidization gas to the flow of fluidized material makes it possible to avoid defluidization of the pulverulent material.

Figure 2 shows another advantageous embodiment of a device for fluidizing a pulverulent material.

A reservoir 10 comprises a lower base and an upper base, which is formed by a cover 52 provided with a conduit 56 for the supply of pulverulent material. A sending tube 32 enters the reservoir through the cover 52. The end of the tube 32, located in the reservoir 10, is formed by a mouth 36 and a secondary fluidization chamber 60. The sending tube 32 consists of an inner pipe 64 and an outer pipe 68 coaxial. Between the two pipes 64, 68 is arranged a space 72 in which a secondary fluidizing gas, supplied by a conduit 76, can circulate. The chamber 60 comprises an inner tube 80 made of a gas permeable material and an outer wall 84 impermeable to gas. The chamber 60. is connected to the sending tube 324 by a peripheral bore 88 which connects the inner tube 80 to the inner pipe 64 and the outer wall 84 to the outer pipe 68 of the sending tube. The peripheral bore 88 allows the passage of the secondary fluidizing gas from the space 72 comprised between the pipes 64, 68 in the chamber 60.

The lower base of the reservoir 10 comprises a primary fluidization chamber 24 equipped with a conduit 20 which is connected to a supply of primary fluidization gas. This gas enters the chamber 24 and diffuses through a porous plate 28 which constitutes the upper wall of the chamber 24, into the reservoir 10. The gas flow fluidizes part of the pulverulent material contained in said reservoir 10. The fluidized material passes through the mouth 36 in the secondary fluidization chamber 60. The secondary fluidization gas diffuses through the inner tube 80 of the chamber 60 in the material flow, fluidized and eliminates the risk that the material defluidizes at the start of its trajectory, after the mouth.

An advantage of this second embodiment is that only one passage should be provided for the sending tube 32 and the supply duct 44 for secondary fluidizing gas. Consequently, there is only need to seal a single passage point in the tank 10.

Claims (6)

1. Device for fluidizing a pulverulent material, comprising a primary fluidizing member (16) connected to a supply (20) of a primary fluidizing gas, a sending tube (32) for the fluidized pulverulent material, of which one end plunges into the reservoir (10), this end comprising a capture member (36) for the fluidized material characterized by a secondary fluidization member (40) located between the capture member and the delivery tube (32) , connected to a secondary fluidizing gas supply. 2. Device according to claim 1, characterized in that the secondary fluidization chamber (40.) comprises at least one wall permeable to the gas through which the secondary fluidization gas diffuses in the flow of the fluidized material. 3. Device according to claim 2 characterized in that the permeable wall is a porous plate (28). 4. Device according to claim 3 characterized in that the porosity of the permeable wall is between 5 μιη and 100 μτα. 5. Device according to any one of claims 1 to 4 characterized in that the sending tube (32) comprises one or more tertiary fluidization members located outside the tank (10). 6. Device according to any one of claims 1 to 5 characterized in that the sending tube (32) comprises an inner pipe (64) and an outer pipe (68) coaxial and a space (72) in which a secondary fluidizing gas supplied by a conduit (76) can circulate, in that the secondary fluidizing member (60) comprises an inner tube (80) made of a material permeable to gas, and an outer wall (84) coaxial impermeable to gas, and in that the fluidizing member (.60) is connected to the sending tube by a peripheral bore (88) which connects the inner tube (84) to the inner pipe (64) and the outer wall (84) to the outer pipe (68) of the sending tube (32) so as to allow the passage of the secondary fluidizing gas from the space (72) in the member (60).