LU86352A1 - GAS-GAS HEAT EXCHANGER - Google Patents

Description

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\ V / GAS-GAS HEAT EXCHANGER.

The present invention relates to a heat exchanger between two gases, which in particular makes it possible to limit a mixture of the gases to be treated.

The constantly increasing prices of fuels used in industrial processes, such as in particular the manufacture of glass and in other operations consuming large amounts of energy have led to a development of research in the field of heat recovery, in particular of the heat contained in waste gases and fumes which are normally discharged into the ambient atmosphere.

In certain specific application cases, conventional heat exchangers cannot however be used because of the high risks of corrosion of the installations, due to the aggressiveness of the gases. Furthermore, conventional exchangers have particularly large dimensions in the case of high gas flow rates. In addition, it is common to find very rigid and difficult to adjust installations with regard to optimal operating temperatures and flow rates.

An object of the present invention is to provide a gas-gas type heat exchanger which can find numerous applications in the heat exchange between two gases, at least one of which may be corrosive.

Another object of the present invention is to provide a gas-gas type heat exchanger which limits the mixing of the two gases which are subjected to heat exchange.

Another object of the present invention is to provide an easily adjustable heat exchanger with regard to operating temperatures and flow rates, under optimal conditions.

Another object of the present invention is to provide a heat exchanger of the aforementioned type of very simple and robust construction.

A complementary object of the present invention 1 2 aims to provide a heat exchanger which takes advantage of. principle of communicating fluidized beds.

According to the present invention, the gas-gas type exchanger using the principle of interconnected fluidized intercon-5 beds is characterized in that it consists of a vertical cylindrical or polygonal tubular container divided vertically and radially into at least four adjacent compartments communicating between them, of which at least two adjacent compartments form a so-called cold part and comprising at least one outlet for cold gas and at least two adjacent compartments form a so-called hot part and comprising at least one outlet for hot gas; in that each compartment contains a fluidized bed which comprises a solid material suspended by one of the hot or cold gases involved in the heat exchange; in that, in the direction of flow of the fluidized solids, a high speed fluidized bed is followed by a low speed fluidized bed and this is followed by a high speed fluidized bed, a high speed fluidized bed being capable of overflow from the top into the next low speed fluidized bed and a low speed fluidized bed communicating from below with the next high speed fluidized bed; and in that it comprises at least one bypass circuit with adjustable flow rate which makes it possible to recycle the gas leaving in the fluidization of one of the fluidized beds, towards at least one of the fluidized beds.

It is known in fact that the expansion of a fluidized layer increases with the speed of fluidization and that, on the other hand, the pressure drop in a fluidized layer 30 balances the weight of solid per unit of section. Consequently, if a fluidized communicating vessel is produced, with different gas speeds in the two branches, the equilibrium heights will be different. Therefore, by providing an overflow at the upper part 35 of the system, the two levels are balanced, causing a circulation of the solid.

According to a first advantageous embodiment of the present invention, the compartments i 3 all have an identical section. Alternatively, a smaller section can be provided for the low-speed fluidized bed compartments.

Preferably, the device of the invention 5 comprises two bypass circuits, a first of which recycles part of the hot gases leaving the bottom of the hot compartment with a high-speed fluidized bed or in the hot compartment with a low-speed fluidized bed and the second recycles part of the cold gases leaving the bottom of the cold compartment with a high-speed fluidized bed or in the cold compartment with a low-speed fluidized bed.

It is also possible to provide a bypass circuit which brings part of the hot or cold incoming gases 15 to the outlet.

It can easily be seen that the exchanger according to the present invention has a particularly compact construction and simple installation. It suffices to provide corrosion-resistant materials for the constituent elements such as the external wall of the reactor and the partition walls. These elements are of very simple construction and, therefore, inexpensive.

The compact arrangement of the exchanger according to the present invention also promotes good heat exchange between the hot gas and the cold gas, the exchange being able to take place, on the one hand, through partitions separating the part hot and the cold part and, on the other hand, using the solid matter kept in suspension by the gases, which circulate from one part to the other, passing from a so-called hot part to a so-called cold part.

We therefore choose suitable solid materials such as for example sand and / or expanded clay-35 sée, the particle size is judiciously determined to allow proper fluidization at the speeds achieved in the device.

It is easily understood that the gases are separated t 4 since the hot part is separated from the cold part by partitions which only have an opening at their lower part for the circulation of solid materials. In order to further increase the separation of the gases 5 and in order to prevent mixing of these, through these openings, the injection of the fluidization gases can be arranged beyond said openings.

It should be noted that in the application of the device according to the invention to the heat exchange between two gases, the use of at least one bypass circuit for the recycling of part of the gases has proven to be particularly advantageous with regard to the fine adjustment of the operation in optimal conditions of the device. Such a bypass circuit makes it possible in particular, by adjusting the flow rate which passes through it, to regulate the temperature level prevailing in the corresponding fluidized beds.

According to a variant of the present invention, the solids suspended in the fluidizing gases can at least partially consist of,,. s, chemically or. physically materials that can interact / with the gases that keep them in suspension, in order to clean them up, for example. Thus, the solid materials can consist of chemical reagents, catalytically active substances supported on suitable conventional support materials or chemical or physical absorbents, in particular pulverulent masses making it possible to fix aerosols, droplets and fines. particles possibly present in the gases to be treated.

30 Other details will appear on reading the description of a particular embodiment represented in the appended figures, in which: - Figure 1 is a schematic vertical section of = the exchanger according to the invention, 35 - 2 shows a schematic section of the device according to Figure 1, at level AA, and - Figure 3 is a diagram of the exchange of materials and gas flows.

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The principle of the invention will be described below. If the fluidization speed of compartment 1 is higher than that applied to compartment 2, the equilibrium level of the bed will be higher than that of compartment 5. If the partition 4 separating the two compartments is lowered so as to allow an overflow, the two levels balance and cause a circulation of the solid according to the arrows.

A particularly preferred embodiment of the invention 10 is represented in FIGS. 1 and 2. The exchanger comprises four compartments 1, 2, 3, 4, two of which (1, 2) form the cold part and the other two (3, 4) the hot part. Within each part, the compartments are brought to different fluidization speeds which cause the following circulation: the solid particles pass from compartment 1 to compartment 2 by overflow because the fluidization speed of 1 is greater than that of 2 ; the solid particles pass from compartment 2 to 3 through the bottom 5, from 3 to 4 by 20 overflow since the fluidization speed of 3 is greater than that of 4 and from 4 to 1 through the bottom 6.

The cold gas leaves the exchanger, after having been heated by the hot gases, via outlet 7 while it has been supplied with 9 to fluidize the solid materials. The hot gas supplied at 10 to suspend the solid matter passes through the compartments 3 and 4, yielding part of its heat energy to the cold gas and leaves the exchanger at 8. A bypass circuit 15 adjustable by means of a valve 17 allows to recycle part of the hot gases at the bottom of one of the hot compartments 3 or 4, preferably compartment 3 comprising the high-speed fluidized bed. This arrangement allows the temperature level of the system to be easily adjusted. Circulation is ensured by a circulation fan 18.

The cold gas is discharged through line 7 and the hot fluidizing gas through line 8 which allows them to be separated.

î 6 • To completely avoid the mixing of hot and cold gases, it is possible, according to this particularly preferred mode of the invention, to fluidize the bottom 9 of the cold part 1, 2 and inject additional cold gas at a level 5 11 located at above the communication orifices 5, 6.

In this case, the section of the device must increase with the height of the device. One can proceed in a similar way for the hot compartments using the injector 12.

As is common practice, the device of the invention advantageously comprises a supply 13 of the solid materials in the hot or cold part by a hopper and a worm. It is understood that the supply can be done by any means known per se, for example by a butterfly valve or an annexed fluidized bed.

It is also possible to provide for withdrawal of solid materials, possibly after chemical reaction, from the bottom (not shown). These can be screened and reinjected into the hot part or the cold part in order to play the role of thermal flywheel.

The device of the present invention may also include a cyclone system (not shown in the figures) or any other system for filtering gases at high temperature to purify the gas and recycle the fine dust carried away.

Gas distributors are those commonly used in simple fluidized beds, such as, for example, perforated plates, bell plates, perforated tubes, etc.

In order to further improve the operation of the installation, it may be advantageous to load chemical reagents or catalytically active particles or chemical or physical absorbents into the fluidized bed. This makes it possible to combine with the heat exchange function, a chemical or physical reaction function such as pollution control for example.

Regulation can be done in a way

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7 practical as shown in Figure 2 while ensuring a large and regular flow of solids flow.

The regulating device includes the measurement of differential pressure drops to control a motorized valve which can be mounted on the conduit 11 and / or the conduit 12 (only the embodiment of a motorized valve on the circuit 12 is shown in Figure 2).

According to FIG. 2, it is possible to regulate the flow of 10 solids circulating between the hot part and the cold part by mounting a localized differential pressure sensor (20 and 20 ′) in at least one submerged orifice (5) in order to code by a motorized valve (24), the flows supplying at least one high-speed compartment 15 (3).

In FIG. 3, the gas circulation is schematically indicated by continuous lines and by the exchange of material with broken lines, / between a cold part 31 and a hot part 32. The main direction of gas flow 20 is marked by a simple arrow and the possible gas bypass circuits are indicated by a double arrow. The various control valves 24 that can be mounted in the bypass circuit are also shown.

It will be noted that the device of the invention benefits from greater compactness and better heat transfer; heat transfer takes place through the circulation of solid particles and through the partition wall between the hot and cold parts. The invention will be described below by way of illustrative example of a particular practical application.

Example

One application of the exchanger according to the invention is in the field of recovering the heat energy contained in the waste gases from glass furnaces. Such a gas leaves the oven at 1400 ° C., passes through a known regenerator which lowers the temperature to 472 ° C. to send it into a chimney, the fresh air at 20 ° C. being thus brought to 1045 ° C., before being injected into the oven. If mounted downstream of the conventional regenerator, an exchanger according to the invention, the gas leaving the oven at 1400 ° C is brought to 535 ° C in the conventional regenerator and to 302 ° C in the exchanger according to invention before being vented into a chimney. Ambient air at 20 ° C is heated to 251 ° C in the exchanger according to the invention and brought to 1161 ° C in the conventional regenerator. This results in a significant improvement in the energy balance of the installation. The bed plays the role of mass making it possible to fix or capture the aerosols, the droplets and the very fine particles present in the gas.

In the case of a hot gas containing hydrochloric acid and originating, for example, from the incineration of waste, said gas can be treated in the exchanger according to the invention by recovering part of its heat energy and using , as a solid material, inter alia, slaked lime, which chemically neutralizes the acid gas before discharging it into the atmosphere.

It is obvious that the present invention is not limited to the embodiments described but that it extends to the scope defined by the claims which also include a series of modifications such as for example the use of inclined deflectors with respect to the vertical, which are mounted on the partition walls, at the point of overflow. Such an arrangement makes it possible to significantly increase the flow rate. Furthermore, it is possible to use all the conventional techniques within the reach of those skilled in the art as regards the adjustment of the device. The addition of adequately sized packing materials makes it possible to "inflate" the fluidized bed without it being necessary to vary the speed of the fluidizing gas and incidentally can serve as a support for chemical or physical reagent or absorbent chemical or physical which in this case has the advantage of remaining captive in a *> 9 compartment, that is to say of not circulating like the rest of the fluidized bed from one compartment to the other.

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Claims (14)

1. Gas-gas type heat exchanger using the principle of interconnected fluidized beds, characterized in that it consists of a vertical cylindrical or polygonal tubular container 5 divided vertically and radially into at least four adjacent compartments communicating with each other (1, 2, 3, 4), of which at least two adjacent compartments form a cold part (1, 2) and comprising at least one outlet for cold gas (7) and 1q at least two adjacent compartments form a hot part (3, 4) and comprising at least one outlet for the hot gas (8) j in that each compartment contains a fluidized bed which comprises a solid material suspended by one of the hot or cold gases involved in .j, - the heat exchange; in that, in the direction of circulation of the fluidized solids, a high speed fluidized bed (1, 3) is followed by a low speed fluidized bed (2, 4) and this is followed by a high fluidized bed speed, a high-speed fluidized bed (1, 3) which can overflow from above into the next low-speed fluidized bed (2, 4) and a low-speed fluidized bed (2, 4) communicating from below (5, 6) with the following high-speed fluidized bed (1, 3); and in that it comprises at least one bypass circuit (15) with adjustable flow (17) -, ς which makes it possible to recycle the gas leaving in the fluidization of one of the fluidized beds; towards one of the fluidized beds. 2. Heat exchanger according to claim 1 characterized in that all the compartments (1, 2, 3, 4) have an identical section. 3 (-j 3. Heat exchanger according to claim 1 characterized in that the low speed fluidized bed compartments (2, 4) have a smaller section. 4. Heat exchanger according to any one of the preceding claims, characterized in that it comprises two bypass circuits, one of which recycles part of the hot gases leaving in the bottom of one of the hot compartments and the other recycles a part of the cold gases leaving at the bottom of one of the * and 11 cold compartments. 5. Heat exchanger according to any one of the preceding claims, characterized in that it comprises at least one bypass circuit which brings part of the incoming hot or cold gases towards the outlet. 6. Heat exchanger according to any one of the preceding claims, characterized in that the bypass circuit recycles part of the hot gases leaving the bottom of the hot compartment with a high-speed fluidized bed 10. (3). 7. Heat exchanger according to any one of the preceding claims, characterized in that the solid material suspended by the hot and cold gases is sand or expanded clay. 8. Heat exchanger according to any one of the preceding claims, characterized in that the solid material suspended by the hot and cold gases contains chemical reagents, catalytically active materials, or chemical or physical absorbents. 9. Heat exchanger according to any one of the preceding claims, characterized in that part of the fluidizing gas supply takes place at a level higher than the level of the openings (5, 6) ensuring communication by the bottom of adjacent compartments. 10. Heat exchanger according to any one of the preceding claims, characterized in that the partition walls allowing an overflow from the top have deflectors inclined relative to the vertical. 11. Heat exchanger characterized in that a valve (24) controlled by the pressure difference between the high speed compartment and the low speed compartment of the same hot or cold part is mounted in the gas injection pipe. fluidization, hot or cold, respectively (11,12). 12. Heat exchanger according to any one of the preceding claims, characterized in that packing materials are used to inflate the fluidized bed, which avoids having to vary the fluidization speed in the various compartments. and incidentally allows the packing materials to be used as a support for a chemical reagent or a chemical or physical absorbent. 13. Method for recovering the heat energy from hot gases, characterized in that the hot gas is injected into the hot part of the device according to the preceding claims with a view to fluidizing a solid material therein and in that injects a cold gas into the cold part of the device according to any one of the preceding claims with a view to fluidizing the solid material which circulates from one compartment to the other. 14. The process as claimed in claim 13, characterized in that chemical reagents, catalytically active materials or chemical or physical absorbent masses which treat hot gases are used as solid material at least partially. 25 30 35 V