WO2011144862A2

WO2011144862A2 - Method and device for heat exchanger fouling removal

Info

Publication number: WO2011144862A2
Application number: PCT/FR2011/051116
Authority: WO
Inventors: El Hani Bouhabila; Thierry Malard
Original assignee: Solios Environnement
Priority date: 2010-05-21
Filing date: 2011-05-18
Publication date: 2011-11-24
Also published as: FR2960289A3; FR2960289B3; WO2011144862A3

Abstract

The invention relates to a method for removing fouling from a heat exchanger (2) used to cool a gas loaded with dust and pollutants and originating from fused-salt electrolysis cells during aluminium production, in which the gas can travel through a flow circuit (1) comprising at least one heat exchanger (2) capable of cooling said gas (3) and distribution members (6, 7, 8) capable of moving inside the pipe (1). The invention is characterised in that it comprises a step in which the distribution members (6, 7, 8) are moved between a first position (6a, 7a, 8a) in which the gas (3) travels through the heat exchanger (2) in a first flow direction (S1) and a second position (6b, 7b, 8b) in which the gas (3) travels through the heat exchanger (2) in a second opposite flow direction (S2).

Description

METHOD AND DEVICE FOR DISENGAGING

HEAT EXCHANGER.

The present invention relates to the de-encreasing heat exchanger, and more particularly to the de-encreasing heat exchanger used for cooling the electrolysis cell gases during the production of aluminum. The heat exchangers used for cooling gas charged with dust and gaseous components that can condense on the walls of the exchanger and form a solid deposit, become dirty during operation. Since the solid deposits obtained generally have a low thermal conductivity, their accumulation on the tubes of the exchangers leads to a decrease in their thermal efficiency.

In the remainder of this document, we will designate by the generic term "pollutants" the gaseous components that can condense on the walls of the exchanger and form with the dust a solid deposit. We will also use the term "gas" to designate the hot gases to be cooled, whether it is a single gas or a mixture of gases.

For this type of application, the hot gas charged with dust and pollutants circulates outside and perpendicularly to the tubes in which circulates a cool heat transfer fluid. The hot gas thereby cools by heat transfer to the cold heat transfer fluid which heats up. During this operation, a deposit of particles is formed on the outer surface of the tubes. The thickness and consistency of this deposit depends on the operating conditions and the nature of the pollutants. To limit the formation of deposition of dust and pollutants on the outer surface of the exchanger tubes, there is commonly set up a filter upstream of the exchanger.

This filter has the role of capturing the majority of the dust upstream of the heat exchanger thus limiting its fouling. A continuous measurement of the pressure drop of this trap makes it possible to inform about its level of fouling and the need for its replacement or its cleaning. It may consist of a grid or a set of sieves and must be easily removable. Sometimes two filters are placed in parallel on two separate circuits alternately supplying the exchanger. Isolating members placed upstream and downstream of the filters make it possible to disassemble a filter arranged in one circuit and to clean it while retaining normal operation in the other circuit.

For the cooling of gases from igneous electrolysis cells during aluminum production, this solution is not satisfactory because the clogging of the filter is fast and requires frequent intervention of maintenance personnel. The proposed invention makes it possible to unclog the exchangers without these disadvantages.

It consists mainly of a process of de-fouling heat exchangers used for cooling gas charged with dust and pollutants, especially from igneous electrolysis cells during the manufacture of aluminum; said gas being adapted to pass through a flow circuit comprising at least one heat exchanger adapted to cool said gas, and distribution members adapted to move in said duct, comprising a step of moving said dispensing members between a first position wherein said gas passes through the heat exchanger in a first direction of circulation, and a second position wherein said gas passes through the heat exchanger in a second direction of flow opposite to the first direction of flow.

In a variant, the displacement step is repeated periodically.

In a variant, the flow circuit comprises a primary circuit for passing said gas, a secondary circuit for passing said gas; said secondary circuit comprising a circuit portion common to the primary circuit; said heat exchanger being disposed in said circuit portion characterized in that said first position is an open position of a portion of the primary circuit and closure of a portion of the secondary circuit, and said second position is a position opening a portion of the secondary circuit and closing a portion of the primary circuit.

The operating time in each direction of circulation of the gas to be cooled is substantially identical so as to avoid the preferential accumulation of deposition on one of the half-faces of the tubes.

The delay between two reversals of the flow direction of the gas to be cooled is adapted according to the clogging speed of the exchanger. It can for example be performed once every 3 to 10 days. And it can be done automatically or manually.

Part of the particles torn off the accumulated deposits on the tubes of the heat exchanger is carried away by the hot gas. It is then captured by the gas purification unit that is usually found downstream on aluminum manufacturing facilities. Heavier particles may also fall under the heat exchanger where they are collected in a hopper.

This method also has the advantage of not requiring the intervention of maintenance personnel at each de-fouling operation. This is necessary only to evacuate the solid deposits collected at the bottom of the hopper when it is full.

The invention also consists in a device for de-fouling a heat exchanger used for cooling gas charged with dust and pollutants, especially from igneous electrolysis cells during the manufacture of aluminum, said device comprising at least one exchanger heat source adapted to cool said gas, further comprising distribution members adapted to move between a first position in which said gas passes through the heat exchanger in a first direction of circulation and a second position in which said gas passes through the heat exchanger in a second direction of traffic opposite to the first direction of circulation.

In a variant, the device comprises:

a primary circuit for passing said gas, a secondary circuit for passing said gas; said secondary circuit comprising a circuit portion of the primary circuit; said heat exchanger being disposed in said circuit portion. Alternatively, the device comprises a control unit adapted to control the periodic movement of said dispensing members.

The invention consists, apart from the arrangements described above, in a certain number of other arrangements which will be more explicitly discussed below with regard to exemplary embodiments, described with reference to the appended drawings, but which do not are in no way limiting. On these drawings:

- Fig. l represents a schematic view of a de-fouling device according to the state of the art with a filter upstream of the exchanger,

- Fig. 2 is a schematic view of the section of a tube of a heat exchanger showing an example of solid deposition,

- Fig. 3 is a schematic view of an exemplary embodiment of the invention.

The term "heat exchanger" is used in the singular in the present description to designate one or more heat exchangers. These heat exchangers comprise one or more tubes or channels for circulating a heat transfer fluid.

Referring to FIG. 1 of the drawings, we can see, schematically represented, a tubular heat exchanger 2 placed in a hot gas flow circuit 1 flowing in the direction represented by the arrow 4. Upstream of the heat exchanger 2, a filter 16 can trap the dust carried by the hot gas. In this figure, solely by way of example, the flow of a cold heat transfer fluid inside the heat exchanger is shown against the current relative to the hot gas 3. Referring to FIG. 2 of the drawings, schematically shown, a tube 5 of the heat exchanger 2. The hot gas 3 flows outside the tubes in the direction shown by the arrow 4. The cold heat transfer fluid 6 circulates inside the tubes. The tubes 5 have an ellipsoidal shape to limit the solid deposition 7 of dust and pollutants on the outer face of the tubes.

Referring to FIG. 3 of the drawings, it is possible to see, schematically represented, an example of a de-inking device 9 according to the invention. This device 9 comprises a hot gas flow circuit 1 charged with dust and pollutants flowing in the direction represented by the arrow 4. This hot gas comes, for example, from the electrolytic cell of an aluminum manufacturing device. .

The device 9 according to the invention comprises a primary circuit in which the hot gas circulates when it passes through the exchanger 2 in a first flow direction SI, and a secondary circuit 1b in which the hot gas circulates. when it passes through the exchanger 2 in a second flow direction S2, opposite to the first direction of flow SI. The heat exchanger 2 is placed in a circuit portion 10 common to the two circuits 1a and 1b.

In this embodiment, the orientation of the hot gas to the primary circuit or to the secondary circuit lb is ensured by the combination of distribution members 6, 7 and 8.

These dispensing members 6, 7, 8 comprise for example pivoting flaps, rotary valves or guillotines. These distribution members 6, 8, and 9 are moved between a position 6a, 7a, 8a for opening the primary circuit and for closing the secondary circuit 1b to circulate the gas 3 in the primary circuit 1a through the exchanger of heat 2 in the first direction of circulation SI; and a position 6b, 7b, 8b of opening of the secondary circuit 1b and closing of the primary circuit 1a to circulate the gas 3 in the secondary circuit 1b and through the heat exchanger 2 in the second direction of circulation S2 , opposed to the first sense.

The unclogging device 9 according to the invention further comprises a control unit 20 able to control the displacement of said dispensing members 7, 8, 9. Advantageously, the distribution members 7, 8, 9 are moved periodically.

Claims

1. A method of removing heat exchanger (2) used for cooling gas (3) charged with dust and pollutants, especially from igneous electrolysis cells during the manufacture of aluminum; said gas being adapted to pass through a flow circuit (1) comprising at least one heat exchanger

(2) adapted to cool said gas (3), and distribution members (6, 7, 8) adapted to move in said conduit (1),

characterized in that it comprises a step of moving said dispensing members (6, 7, 8) between a first position (6a, 7a, 8a) in which said gas (3) passes through the heat exchanger (2) in a first direction of circulation (SI), and a second position (6b, 7b, 8b) in which said gas (3) passes through the heat exchanger (2) in a second direction of circulation (S2) opposite to the first direction of circulation (SI).

2. Method according to claim 1, characterized in that the displacement step is repeated periodically.

The method of claim 1 or 2, wherein the flow circuit

(1) comprises a primary circuit (1a) for passing said gas (3), a secondary circuit (1b) for passing said gas (3); said secondary circuit (1b) including a circuit portion (10) common to the primary circuit (1a); said heat exchanger (2) being disposed in said circuit portion (10) characterized in that said first position (6a, 7a, 8a) is an open position of the primary circuit (1a) and closing of a portion of the secondary circuit (lb), and said second position (6b, 7b, 8b) is an open position of the secondary circuit (1b) and of closing a portion of the primary circuit (1a).

4. Apparatus (9) for removing heat exchanger (2) used for cooling gas (3) charged with dust and pollutants, especially from igneous electrolysis cells during the manufacture of aluminum, said device ( 9) comprising at least one heat exchanger (2) adapted to cool said gas (3),

characterized in that it further comprises distribution members (6, 7, 8) adapted to move between a first position (6a, 7a, 8a) in which said gas

(3) passes through the heat exchanger (2) in a first direction of circulation (SI) and a second position (6b, 7b, 8b) in which said gas (3) passes through the heat exchanger. heat (2) in a second direction of circulation (S2) opposite the first direction of circulation (SI).

5. Device (9) according to claim 4, characterized in that it comprises:

a primary circuit (1a) for passing said gas (3),

a secondary circuit (1b) for passing said gas (3); said secondary circuit (1b) including a circuit portion (10) of the primary circuit (1b); said heat exchanger being disposed in said circuit portion (10).

6. Device (9) according to claim 4 or 5, characterized in that it comprises a control unit (20) adapted to control the periodic movement of said dispensing members (7, 8, 9).