SI9111971A - Device for separating material in fluidic trough and for perception obturation - Google Patents

Abstract

The invention deals with the process and preparation for handling with a powdery substance in a liquid trough which allows it to detect and prevent clogging of porous walls for liquefaction of non-product products liquefied and mixed with dust. Exists in by dividing the porous wall into two parts: the first is is located under the supply pipe and is mounted on horizontal level below it for the second part that is placed under the balancing tube, where each of these parts is powered by two independent ones spaces and measured liquefaction in each of these two spaces. This difference grows in dependency from the clogging of the porous wall placed below supply pipe, and allows the walls to be clogged when the difference exceeds a certain predicted value. Invention is used for transmission in a liquid sump for everything the following products: alumina, lime, cement, metal plastic powders and powders, food grade products, etc.

Description

ALUMINUM ΡΕΟΊΙΝΕΥ

Preparation for separation of substances in a liquid bed and for detecting clogging

1. Technical field of the invention

The present invention relates to all a device for treating a powdery substance in the state of a liquid bed according to its distributions based on its dimension or its tolerance or the physical treatment of the separation of foreign bodies to which it is mixed.

It is known to transfer, from one point to another, powdery liquids in the liquid state. The material is said to be liquefied when in powder form and when its granulometry and cohesion are such that the blown air, even at low speed, causes decohesion of particles from each other and a reduction of internal friction forces, thus creating a suspension behaves as a homogeneous fluid. Such materials are e.g. alumina, cements and gypsum, lime, fly ash, calcium fluoride, rubber and plastic fillers, catalysts, powdered graphite, sulfates and phosphates, metal powders, powder plastic materials, foodstuffs such as starch, milk powder, flour ip

2. State of the art

The prior art may be described by those patent files filed by the applicant and to which the subject matter of the invention of the patent application may be used.

French Patent Document FR 2 575 734, entitled "Liquid-Controlled Liquid Distributable Dispenser," describes a device that allows regulating the flow of liquid-liable substance in the case of alumina.

The French patent FR 2 575 680, entitled Liquid sump preparation for the continuous separation of two mixed solid phases, describes a device which enables, in a product consisting of liquefied fine particles, pieces of agglomerated particles which are unsuitable for liquefaction.

The Franconian Patent File FR 2 391 136 entitled The procedure for self-regulating pneumatic transport describes a process and a device for the automatic control of flow in a fluid bed transport system without the need for mechanical organs.

The device which is the subject of the invention may, as mentioned, be used in any of the devices and processes indicated.

The apparatus described in French patent file FR 2 575 734 comprises (Fig. 1):

- an alumina-filled collecting tank 1 connected to the caisson 2 by means of a feed tube 3 emanating from the side of the caisson 7A (on the left in the figure)

- a caisson 2 comprising:

at its lower part 2B a porous wall 4 for liquefaction and a supply pipe 5 for liquefied gas, which is at a constant pressure and which is adjustable;

on its upper portion 2A at the end 7B which is opposite to that of the feed pipe, balancing tube and degassing tube;

on the side of the end 7B belonging to the balancing tube and immediately above the porous wall 4, the outlet mouth 8 for the liquefied dusty substance.

In the absence of liquefaction gas, the dusty material accumulated in the tank 1 is lowered into the caisson to form a slope 10 which, with the porous liquid wall, depends on the nature and physical state of the powdery substance.

However, when a liquefied gas is supplied, with the mouth 8 closed, down the pipe 5 and the means 12 to regulate the flow through the porous wall 4, the dusty substance begins to liquefy; it quickly fills the top of the caisson and then rises slightly in the balancing tube to a certain height h (Fig. 2), which depends on the pressure P _f for the liquefaction and on the medium density of the powder in the balancing tube 6. The calculation shows and experience confirms that for dusty substances, when the system is in equilibrium, and for the mouth diameter 8, the flow of the substance changes uniformly depending on the gas pressure for the liquefaction, which provides a comfortable means of regulating this flow.

3. Clarification of the problem

In fact, the liquefaction pressure P is balanced by the hydrostatic pressure due to the height h of the fluid bed in the equilibration tube, which is increased to reduce the pressure in the porous wall. The unique relationship between the pressure P for liquefaction and the flow of matter, therefore, assumes that the pressure drop in the porous wall does not change, that is, that the wall does not clog.

This, however, is a case of perfectly suitable substances and proper granulometry, that it is a single liquefied phase. However, when the substance to be distributed forms two solid phases, one of which tends to decant under liquefaction conditions, this phase decanting on the porous wall increases the pressure drop through that wall. With a constant liquefaction pressure, the height of the liquefied substance in the balancing tube is reduced and hence the flow through the mouth 8.

This problem arises mainly in two cases:

- in the case of fresh aluminum oxide, comprising heavy particles of non-combustible masonry, called clots, which have been mixed with alumina when calcined;

- in a system for supplying aluminum electrolysis tubs, where aluminum is recycled which was used to trap the fluorine vapors emitted from the tubs. This alumina, which is full of trapped products, tends to form compact agglomerates, called clots deposited on the porous wall in this area.

It is an object of the invention to propose an agent which continuously follows the degree of clogging of the porous wall so that it can be drawn in at an appropriate time to clear it.

4. The solution to the problem

The solution provided by the inventors for this problem is shown in FIG. 3 to 5.

It is useful to remember first the different sizes that regulate liquefaction.

The fluid pressure P _f is equal to:

P = P + d.h, f c 'where it is

- P _c pressure drop through porous wall

- d is the specific mass of the liquid powder in the liquid state

- h is the height of the powder in the regulating tube.

On the other hand, P _c = kv, where

- k is the pressure drop coefficient in the porous wall

- into the velocity of air through the porous wall.

Under normal industrial conditions for these systems, the flow rate of the liquefied air is, in fact, always sufficiently weak that the flow regime is laminar, and therefore that the pressure losses through the porous wall are proportional to the velocity.

The inventors first discovered that the clots, due to their inability to liquefy, are deposited on a portion of the porous wall directly or adjacent to the feed tube 3.

Based on this finding, they have imagined a device which is presented in vertical section in FIG. 3.

We find a collecting tank 13 that is connected to the caisson 14 by means of a feed tube 15, a balance tube 16, and an outlet mouth 17 for a dusty substance. The caisson, whose horizontal cross-section is generally rectangular, is in vertical section from two parts to the left and to the right in the figure:

On the left side of the picture, that is, on the side of the feed tube, there is a liquid chamber 18 and a porous wall 19 at a level lower than that of the liquid chamber 20 and a porous wall 21 of the caisson wall, which is positioned to the right of the picture next to the pipe balancing and at the outlet mouth 17. The two liquefaction chambers 18 and 20 are fed by a common tube 22 that divides into two arms 23 and 24.

At the start of operation, when the liquefaction gas is introduced, the pressures are balanced as follows:

The liquefaction pressure in the left part of the figure is P _n and is equal to the sum of two terms: a pressure drop in the porous wall proportional to the velocity of the liquefaction gas and a barimetric pressure of the fluid bed in the balance tube proportional to the height of this column h /.

P _f i - P _cl + d-hp where P is the pressure drop through the porous wall and d is the apparent density of the fluid bed.

Also, the fluid pressure Ρ _β in the right part of the image is the same:

Ρβ - ^ c2 ⁺ ^ '^ 2 ·

Therefore, differential pressure will be observed

P _n - Ρ _β - d. ^ - h ^ + P _cl -P _c2 .

So P _cl = k _rVl and P _c2 = k ^ v,.

The porous walls 19 and 21 are identical as long as they remain suitable and without clots, and then k _} = k ₂ .

In contrast, the faster the clots are deposited on wall 19, the pressure drop in that wall increases and follows:

^P cl = ( ^k l + Κ> - ^ν ν where k _x is the pressure drop coefficient that changes and increases with porous wall contamination 19.

Finally, the following applies:

^Ρ η - ^ρ β = d-Chfh ^ + C ^ + k) .v ₁ -k ₂ .v ₂ .

Finally, the difference hj - h ₂ uniquely depends on the height difference between the porous walls of the two parts of the caisson, ie the geometry of the preparation.

The apparent density d is also constant and depends only on the liquefied product.

The coefficients kj and k ^ depend only on the characteristics of the porous walls. The coefficient k * increases from zero with porous wall contamination 19.

In contrast, the velocities v ₂ and v ₂ depend on the conditions of the liquefaction air supply. If Ρ _{θ is indicated by the pressure in the pipes at the level just before the split that feeds the porous walls 19 and 21, the value of v can be obtained by solving the system of equations:

^P n = ( ^k i ^{+ k} x) - ^v i + ^d - ^h i where P is the pressure drop in the tubes supplying the caisson 18.

P is proportional to the square of the prektok, that is, to the square of the velocity of air coming through the surface S _{2 of the} porous wall 19:

P », = A (v,) ² .

The coefficient A depends on the geometric characteristics of the pipe and is proportional to the surface Sj of the porous wall, but is constant in a given device.

Solving the system leads to a second order equation that allows it to be calculated in.

Finally, you get:

(k, + k,) + ((k _{I +} k _x ) ² 8

2Α

It can also be calculated in by solving the system:

^P f2 ^ 2 ' ^V 2 ^' ^ 2 ^P f2 =

P -P fO ct2 ct2 = Bv wherein B, like A, is a proportionality coefficient that depends only on the pipe geometry and on the surface S _{2 of the} porous wall 21.

Finally, it is established:

-k, + (l ^ ² - 4.B (dh ₂ - Ρ _{θ )) ^1/2 v ₂ = ----------------------- ------------------------------------- 2.A

It is interesting to note:

a) How does the pressure difference Ρ _η -Ρ _β vary as a function of k _{x the} degree of wall contamination 19

b) how the velocity in ₁ through the wall 19 varies depending on the pollution levels of that wall.

When we insert the values for v and v ₂ into the expression for P _Q -P, written above, it is found that the pressure difference P _n -P is the sum of three terms:

- constant d (h ₁ - h ₂ ), which depends on the geometry of the device for the difference in height h ₁ - h ₂ .

- Article (^ + ^) ν _ρ which depends on:

- of a certain number of constants that are related to the construction of the device,

- from pressure P for adjustment

- from the coefficient to _{x of the} degree of contamination of the porous wall 19 on which the clots are decanted

- Article k ₂ .v ₂ , which depends on the constants associated with the construction of the device and on the pressure P for adjustment.

The analysis of the function P _fl -P _G = f (k _x ) shows that it increases as k _x increases. The pressure difference therefore increases as the wall becomes contaminated.

b) Analysis of the function Vj = g (k _x ) shows that this function tends toward 0 as k _x increases and tends to infinity. So the equations written above apply only if v is much greater than the value in _mf , which is the minimum liquidization rate for the substance under consideration.

Thus, by continuously measuring and possibly recording the pressure difference Ρ _η -Ρ _β, you can:

- we follow the development of porous wall pollution in the area of clot decantation

- automatic or manual cleaning of the device is initiated, determining the predicted value for Ρ _η -Ρ _β corresponding to a speed close to but greater than the minimum liquefaction speed under which the device cannot operate.

5. Examples

Example 1

The system for supplying the aluminum electrolysis tubs was designed according to the principle of the invention.

The left portion, which is located below the feed tube, has a length measured in terms of the plane of FIG. 3, about 26 cm wide and about 20 cm wide. The right part of the box has a length of about 16 cm and a width of 20 cm. The porous wall in the right part is placed 10 cm above the porous wall in the left part.

At the start of operation, when the porous walls are not clogged, the following parameters are recorded:

- liquefaction pressure P = 650 mm water column (6375 Pa)

- liquefaction pressure Ρ _β - 600 mm water column (5884 Pa)

- the height of the fluid in the balance column is 58 cm.

With an outlet diameter of 19 mm, an alumina flow of about 25,000 g / min is obtained.

The difference in liquefaction pressures, initially about 50 mm of water column (490 Pa), gradually increases during operation; it is continuously recorded and when it reaches the value of about 90 mm of water column (883 Pa), the preparation is stopped and the porous wall is cleaned.

This example is given only in illustration; it is clear that the dimensioning of porous surfaces, the difference between porous surfaces on the left and on the right, the difference in heights between these surfaces depends on the nature of the product being supplied, its content of clots, the flow to be provided and the time between two consecutive cleanings.

Example 2

The object of the present invention has been used in the preparation protected in the French patent file FR 2 575 680. This use is presented in FIG. 4.

It permits the separation of a liquefied powder from a non-liquefied substance which is mixed with it. The fence 25, which is suspended by elastic means not represented, consists of two lower caissons 26 and 27, which are supplied with liquefied gas by means of two arms 28 and 29, which emanate from a common tube 30 and from a common upper caisson. 31. Both caissons are separated by a porous wall of two parts 32 and 33, the caisson 26 and the porous wall 32 being placed lower than the caisson 27 and the porous wall 33 when the material is fed. The upper caisson comprises:

- supplying 34 mixtures of non-liquefied material and non-liquid material,

- overflow 35 to remove the liquefied phase,

- a sieve system 36 for removal of a non-liquid solid phase decanted on a portion of a porous wall,

- liquefaction gas hose 37,

- a vibration system which gives a porous wall alternating motion having an arrow direction 38.

During operation, the particles of the non-liquefied substance are deposited on the porous wall 30, causing an increase in the pressure difference Ρ _η -Ρ _β . When this difference reaches the predetermined value, the system for vibrating and opening the sieves 36 is automatically triggered, resulting in clogging of the porous wall. As soon as the pressure difference returns to its initial level, the vibration stops and the sieves close.

Example 3

The object of the present invention has been applied to a process to be protected in patent file FR 2 391 136. This use is presented in FIG. 5. A number of features that have already been described in the preceding examples can be found in this figure. Liquid enclosure with a lower caisson and with a porous wall of two vertically spaced sections, a conduit for a dusty product. The apparatus further comprises a gas inlet pipe 39 at elevated pressure, the mouth of which is above the porous wall in the form of an injector 40, and a pipe 41 intended for pneumatic transport and provided with a mouth 42 positioned vertically with respect to the injector. It is also explained in the patent file FR 2 391 136 that this system enables automatic control of the flow of dusty matter. While the operation may be disturbed by the presence of a non-liquid material, it allows the system to be added at two levels of the porous wall and control the pressure differences of the liquid to detect the degree of clogging of the porous wall and to clean up that wall in a timely manner.

Claims (5)

PATENT APPLICATIONS 1. A device for handling a dusty substance in a liquid bed mixed with non-liquid products which is equipped with a clogging system comprising: a) Dust collecting agent 13, b) a liquefaction agent comprising a caisson 14 of two parts: an upper portion which is connected at one end to the collecting means by a feed pipe 15 and the opposite end by a balancing tube 16, the lower gas supply portion being liquefaction separated from the upper part by means of a porous wall 19, 21, c) a means for removing the dusty substance which is located in the upper part of the caisson at the end opposite the inlet tube, characterized in that the porous wall is divided into two parts: the first part (19), which is located below the inlet tube; and is located in the adjacent area at a horizontal level lower than that of the second portion (21), which is located below the balancing tube and in the adjacent area, with the lower part of the coffer also divided into two independent spaces (18 and 20) below each of the parts of the porous wall and supplied with liquefied gas through the same tube (22), which is divided into two arms (23 and 24), and the apparatus is provided with measuring means and means for recording the time of difference of pressure that governs each of the two independent volumes. 2. Flow-controlled dispensing device for detecting clogging of a liquefied powder material according to claim 1, characterized in that the liquefied product removal means consists of an outlet mouth (17) for the powdered substance, which is placed directly above the porous wall adjacent to the balancing tube. 3. Apparatus for handling powdered liquefied matter and separating it from a non-liquefied and miscible substance according to claim 1, characterized in that it is provided with a vibrating system capable of conveying a porous wall alternating motion, with a system of sieves that allow the removal of a solid phase which has not been liquefied and decanted at the bottom of the porous wall, and provides a means for removing the liquefied product consisting of a diaper that is mounted on the upper part of the caisson opposite the feed pipe. 4. A device for transferring a powdered substance in a controlled flow and in detecting liquefied clogging according to claim 1, characterized in that the liquid product removal agent consists of: a) high pressure gas inlet pipes (39) ending with an injector (40) in the upper part of the caisson above the porous wall opposite the inlet pipe b) a vertical transfer tube (41) fitted at its lower end with a mouth (42) positioned vertically and above the injector. 5. A clogging method using a device according to any one of claims 1 to 4, characterized in that the pressure difference between the two independent slots of the lower part of the caisson is constantly monitored and that a porous wall is cleaned when that pressure difference exceeds a predetermined estimated value.