WO2003090899A1

WO2003090899A1 - A method and an equipment for separating solids from a gas flow and the use of the same

Info

Publication number: WO2003090899A1
Application number: PCT/NO2003/000134
Authority: WO
Inventors: Morten Karlsen; Are DYRØY; Biplab K. Datta
Original assignee: Norsk Hydro Asa
Priority date: 2002-04-26
Filing date: 2003-04-23
Publication date: 2003-11-06
Also published as: NO20022016L; NO20022016D0; AU2003228151A1

Abstract

A method and an equipment for separating solids from a gas flow, in particular separation of a gas-solids mixture deriving from a process plant, such as a pneumatic transport system. The equipment has a main chamber with an inlet section for the mixture and a first outlet for removal of solids form the main chamber. The first outlet is arranged in the bottom part of the main chamber and the main chamber is further having a second outlet for removal of separated gas flow. An annular slit is arranged in the upper part of said main chamber. The second outlet is arranged above said slit. The equipment can advantageously be used in an electrolysis plant for the production of aluminium.

Description

A method and an equipment for separating solids from a gas flow and the use of same

The present invention relates to a method and an equipment for separating solids from a gas flow. In particular, the invention relates to separation of an air-solids mixture from a process plant, such as a pneumatic transport system, where the equipment is arranged at the end of a transportation line in the transport system as a termination unit.

Gas-solids separation technique has been a topic of discussion for a long time although several solutions are available in the market. However, the most commonly used solution has always been a cyclone separator. Unfortunately, due to its principle of operation, the cyclone separator will be subjected to severe wear, particularly at the wall in the entry section, whenever it has to separate even slightly abrasive material. This severe wear problem has been tackled by arranging an abrasion resistant lining at the inside wall of the cyclone. However, the lifespan of such abrasion resistant lining will be lirnited and furthermore such linings are expensive to replace. Therefore, in order to obtain reasonable maintenance intervals of the cyclones handling abrasive materials, there has been proposed better and even more expensive abrasion resistant lining materials.

In accordance with the equipment of the present invention, the use of expensive abrasion resistant linings will be superfluous. The problems related to abrasion will be avoided by the novel design of the separation equipment, because the handled material will not be allowed to act upon internal structural componentes in an abrasive manner similar to that of cyclones. One reason for this is that the material will be in contact with the internal structural components of the equipment at very low or zero velocities. In accordance with the present invention there is developed a method and an equipment that can separate solids from a gas-solids mixture such as an air-solids mixture in an efficient manner and that will be free from problems related to abrasion and wear.

In the following, the invention shall be further described by an example and figure where:

Fig. 1: discloses a schematic diagram of an embodiment of the equipment in accordance with the present invention.

As shown in Figure 1 the principal components of the equipment are:

•1 Inlet section

•2 Flow diverter

•3 One way valve

•4 Exhaust outlet by suction to filter

•5 Main chamber

•6 Conical hopper section

•7 Insert (if needed (material dependent))

•8 Outlet section

Principle of operation

The equipment can be applied as an unique replacement for a conventional air-solids cyclone separator arranged as a flow termination unit. The unit can be placed at the end of a pneumatic transportation system where it has to be maintained at substantially atmospheric pressure conditions during operation. Such transportation system may be arranged for transport of fluidisable materials such as alumina and/or fluoride, for instance in an electrolysis plant for production of aluminim. Other applications can be transport of other types of fluidisable products such as cement, flour etc.

One principle of the present invention is to provide a smooth outflow of fine fraction particles of the solids along with the air sucked out of the termination unit through the exhaust outlet 4 by suction to a filter (not shown). The exhaust outlet should be designed in accordance with capacity demands and critical outlet areas for the material to be handled. Coarser fractions will be separated from said outflow and can be removed through an separate outlet 8.

As can be seen from Figure 1, the air-solids mixture from a process plant, for instance at the end of a transportation line in a pneumatic transport system in an electroysis plant, enters a centrally arranged inlet section 1 of the termination unit. This section being of a T - shape allows some material to get deposited at the T, which immediately after initial inflow of material act as a protective layer for the pipe material. Thus, in case of handling of abrasive materials, the pipe wall material is subjected to very little erosion, if any.

After entering through the inlet section 1, that may have a cross-section of circular shape, six-sided shape, eight-sided shape or any other shape, the material falls under gravity into the main chamber 5 that may have a circular cross section and thus being of a cylindrical shape. However, the main chamber may have other cross-section geometries, and further being of an axis-symmetrical shape. The material gets deposited into the conical hopper section 6 below the main chamber. During the free fall of the material, it will be subjected to air current segregation and followingly fine particles will be suspended in the air. The gas flow inside the main chamber is upwardly directed in a coaxial flow path outside its central region where the inlet section is arranged. Said airborne suspended fine particles get sucked out of the chamber through the path in between the flow diverters 2. The flow diverters may be contstituted of one inner and one outer ring-shaped plate of a conical shape thus forming an annular slit or opening between said diverters. In the Figure, one inner ring is divergent towards the bottom of the main chamber, while one outer ring is convergent towards the bottom of said chamber. The inner ring extends beyond the outer ring, and towards the lowermost end of the inlet section. The outlet 4 is arranged in the annular space formed above said diverters.

The area of the slit can advantageously be equal to or somewhat smaller than the area of the exhaust outlet. Following this, the area of an air intake controlled by an one way vale 3, is designed to be equal to or somewhat larger than that of the two above mentioned areas.

The flow diverters 2, are further designed taking due consideration of the needed separation efficiency. At the flow diverters 2, the larger particles that may be suspended in the air flow will be separated from said flow. This because said larger particles have comparatively lower velocity than the air flow, and due to the change in flow direction they will further loose velocity and fall out of suspension of the flow. Followingly, said particles will settle towards the bottom of the main chamber 5. Advantageously, the flow diverters protrudes downwards from the upper part of the main chamber, and down to the level of the material inlet opening. The angle between each diverter and its respective part of the main chamber that it is affixed to, can be designed within a various range of angles, but should not be perpendicular to said respective part.

In this process, by control of the inlet and outlet air velocities it is possible to separate out the fine particles along with the escaping air while the coarser particles remain deposited inside the main chamber 5.

An one-way valve 3 is provided in an air intake of the equipment in order to maintain substantially atmospheric pressure inside the termination unit. In case of over-suction inside the main chamber 5, additional air will be sucked in from the surrounding atmosphere or from a storage silo in the system (not shown) and into the main chamber 5, thus securing that mainly atmospheric pressure conditions inside the main chamber 5 will be maintained when operating the equipment.

The conical hopper section 6 can be fitted with a suitable insert 7 in order to achieve a mass flow out of the main chamber 5 even by the application of a small angle with the horizontal for the conical hopper section 6. The insert may be formed as a double-conical element fixed centrally in the hopper section by appropriate means. The insert has the purpose of being a "static flow promoter" and its design should be decided upon physical properties of the material to be handled. According to this it is possible to save a lot of height for the conical section. This is particularly important in industrial situations and most needed when handling material that is not free flowing.

Principal advantages

• Almost no wear of the termination unit even when it is handling very erosive materials.

• Expected lifespan without maintenance is approximately 15 years.

• It can serve as an excellent alternative to the existing cyclone separators.

• It is able to separate out the fines along with the exit air while the coarser particles get deposited efficiently.

• Very simple construction.

• Operates with the same separation potential as cyclone, typical particle fraction to follow exhaust air is below 10 μm.

In basic all materials conveyed using pneumatic transport might be separated by the use of this unit. However, the unit is designed for highly erosive powders with high values of hardness.

It should be understood that in accordance with this novel principle of separation, the equipment can be modified in certain manners. For instance, the equipment may be provided with a plurality of outlets as well as air intakes (not shown).

Further the annular slit can be sectioned in several slit segments in its circumferential direction (not shown).

Claims

1. A method for separating solids from a gas flow, in particular separation of a gas-solids mixture deriving from a process plant, such as a pneumatic transport system, where the mixture is ducted into a main chamber of a separtion equipment and where solids are removed out of said main chamber through a first outlet arranged in the bottom thereof, the separated gas flow is removed out of said main chamber through a second outlet, characterised in that the gas is removed through an annular slit arranged in the upper part of said main chamber, where said second outlet is arranged above said slit.

2. A method in accordance with claim 1, characterised in that the gas-solids mixture flows into the main chamber through a centrally arranged inlet section that directs the flow of gas-solids from the top towards the bottom of the main chamber.

3. A method in accordance with claim 2, characterised in that solids in the gas-solids mixture falls out of suspension of the gas flow, and will followingly settle towards the bottom of the main chamber.

4. A method in accordance with claim 2, characterised in that the gas flow inside the main chamber is upwardly directed in a coaxial flow path outside its central region where the inlet section is arranged.

5. Equipment for separating solids from a gas flow, in particular separation of a gas-solids mixture deriving from a process plant, such as a pneumatic transport system, where the equipment has a main chamber with an inlet section for the mixture and. a first outlet for removal of solids from the main chamber, said first outlet is arranged in the bottom part of the main chamber, the main chamber further having a second outlet for removal of separated gas flow out of said main chamber, characterised in that an annular slit is arranged in the upper part of said main chamber, where said second outlet is arranged above said slit.

6. Equipment in accordance with claim 5, characterised in that the main chamber is cylindrical and that the slit is provided by the insertion of two conical rings, one inner ring and one outer ring, in the upper part of the chamber.

7. Equipment in accordance with claim 6, characterised in that the inner ring is divergent towards the bottom of the main chamber, and that the outer ring is convergent towards the bottom of said chamber.

8. Equipment in accordance with claim 7, characterised in that the inner ring extends beyond the outer ring.

9. Equipment in accordance with claim 8, characterised in that the inner ring extends towards the lowermost end of the inlet section.

10. Equipment in accordance with claim 5, characterised in that the main chamber is vented to its surroundings by means of a one way valve.

1. Use of equipment in accordance with claim 5-10 in an electrolysis plant for production of aluminium.