EP0298980A1

EP0298980A1 - Gas-gas heat exchanger

Info

Publication number: EP0298980A1
Application number: EP19870902037
Authority: EP
Inventors: Henry André MASSON
Original assignee: L'etat Belge Represente Par Le Secretaire General Des Services de la Programmation de la Politique Scientifique; Belge Etat
Current assignee: L'etat Belge Represente Par Le Secretaire General Des Services de la Programmation de la Politique Scientifique; Belge Etat
Priority date: 1986-03-12
Filing date: 1987-03-11
Publication date: 1989-01-18
Also published as: LU86352A1; WO1987005687A1; JPH01501767A

Abstract

Echangeur de chaleur du type gaz-gaz utilisant le principe des lits fluidisés interconnectés. Il consiste en un récipient tubulaire vertical cylindrique ou polygonal divisé verticalement et radialement en au moins quatre compartiments adjacents communiquant entre eux (1, 2, 3, 4), dont au moins deux compartiments adjacents forment une partie froide (1, 2) et comportant au moins une évacuation du gaz froid (7) et au moins deux compartiments adjacents forment une partie dite chaude et comportant au moins une évacuation du gaz chaud (8). Chaque compartiment contient un lit fluidisé qui comporte une matière solide mise en suspension par l'un des gaz chauds ou froids intervenant dans l'échange thermique. Dans le sens de circulation des solides fluidisés, un lit fluidisé à haute vitesse (1, 3) est suivi par un lit fluidisé à basse vitesse (2, 4) et celui-ci est suivi par un lit fluidisé à haute vitesse, un lit fluidisé à haute vitesse (1, 3) pouvant déborder par le haut dans le lit fluidisé à basse vitesse suivant (2, 4) et un lit fluidisé à basse vitesse (2, 4) communiquant par le bas (5, 6) avec le lit fluidisé à haute vitesse suivant (1, 3). Au moins un circuit de dérivation (15) à débit réglable (17) permet de recycler le gaz sortant dans la fluidisation d'un des lits fluidisés vers l'un des lits fluidisés.Gas-gas type heat exchanger using the principle of interconnected fluidized beds. It consists of a vertical cylindrical or polygonal tubular container 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 cold gas outlet (7) and at least two adjacent compartments form a so-called hot part and comprising at least one hot gas outlet (8). 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 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 speed fluidized bed, a bed fluidized at high speed (1, 3) being able to project from above into the following fluidized bed at low speed (2, 4) and a fluidized bed at low speed (2, 4) communicating from below (5, 6) with the next high speed fluidized bed (1, 3). At least one bypass circuit (15) with adjustable flow rate (17) makes it possible to recycle the gas leaving in the fluidization of one of the fluidized beds towards one of the fluidized beds.

Description

GAS-GAS HEAT EXCHANGER Subject of the invention.

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 which consume a lot of energy have led to a development of research in the field of heat recovery, in particular the heat contained in waste gases and fumes which are normally discharged into the ambient atmosphere.

In certain specific application cases, however, conventional heat exchangers cannot be used because of the high risks of corrosion of the installations, due to the aggressiveness of the gases. In addition, their conventional exchangers have particularly large dimensions in the case of high gas flow rates. In addition, it is common to find very rigid installations that are difficult to adjust with regard to optimal operating temperatures and flow rates. Summary of the state of the art The present invention is based in part on a number of known principles. Among these, the following should be mentioned in particular:

The high values of heat transfer coefficient between gas and solid within a fluidized layer or between a fluidized layer and an exchange surface are one of the remarkable characteristics of fluidized layers, which have led to significant industrial developments. like combustion in fluidized beds. • 'This property has thus been used to transfer calories from one fluidized bed to another, using an exchange bundle, where a heat transfer fluid or heat pipes circulate. This principle is illustrated for example in US-Λ-4 333 524 (LKI S et al.)

The basic physical principles make it possible to show that, for a given weight of solid, the pressure drop across a fluidized layer is maximum and constant in the fluidization regime, compared to the situation where the bed is not still fluidized or when it is already partially put into pneumatic transport.

This feature was used in US-A-4,441,435 (MIYAMOTO).

In combustion in a fluidized layer, it has been proposed to decouple the flow rate of the fluidizing gas from the quantity of oxygen introduced into the combustion chamber by mixing the air with recycled gases (GB-Λ-2,030,689 ( The Energy Equipment Co).

Fluidized beds behaving like liquids, it is known that they can overflow from one container to the other and put several beds in series and possibly connect the last to the first by making a circulating system. The motor is the difference in ventilation (and therefore density) of the successive beds.

Industrial applications of this principle exist from 1942 (Crac ing catalytiqu du petroleum).

By way of illustration, mention may be made of an application in granulation: US-A-3 241 520 (Wurster) and in fluidized combustion: FR-A-2 203 964 (Sprocket Properties).

For small-scale applications, more simplified and more compact configurations have been proposed, namely: for pyrolysis-combustion: LU-A-84 251 (Cockerill-Sambre) and US-A-4 414 001 (Xunii ) and for catalytic cracking: GB-A-1 562 571 (Melik-Akhnazarov et al.).

Gas-gas interchangeable fluidized bed heat exchangers have already been patented.

US Patent 4,257,478 (Stendahl) describes this idea. It suffers from the complete coupling between the gas flow and the solid flows circulating between the corr.parti.uents, which greatly limits the flexibility of the system. In addition, the gas is very poorly distributed through the fluidized layer leading to stagnant areas. Patent GE-Λ-2,074,302 (Exxon) also takes up this idea. The configuration is characterized by a complicated design of the gas distributor and a rough control of the material flow between the compartments. Aims of the present invention An object of the present invention aims to provide a gas-gas type heat exchanger which can find many applications in the heat exchange between two gases, at least one of which can 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. An additional aim of the present invention is to provide a heat exchanger which takes advantage of the principle of communicating fluidized beds.

Another object of the present invention consists in carrying out in a single simple and therefore economically attractive device, the coupled operations' heat exchange and pollution control of at least one az. Description of the characteristic elements of the invention

According to the present invention, the gas-gas type heat exchanger using the principle of interconnected fluidized beds is characterized in that it consists of a vertical cylindrical or polygonal tubular container divided vertically and radially with at least four adjacent compartments communicating with each other,

BAD ORIGIN of which at least two adjacent compartments form a so-called cold part and comprising at least one discharge of cold gas and at least two adjacent compartments form a so-called hot part and comprising at least one discharge of hot gas; in that each compartment contains a fluidized bed which comprises a solid material suspended by one of the hot or cold gases in¬ tervenant in the heat exchange; in that, in the direction of circulation of the fluidized solids, a fluidized bed at high speed is followed by a fluidized bed at low speed and this is followed by a fluidized bed at high speed, a fluidized bed at high speed being able to overflow from above 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 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 top of the system, the two levels are balanced by causing a circulation of the solid. According to a first advantageous embodiment of the present invention, the compartments 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 comprises two bypass circuits, a first of which recycles part of the hot gases leaving the bottom of the hot compartment at 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.

One can also provide a deriva¬ tion circuit which brings some of the incoming hot or cold gases 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 very simple in construction and therefore inexpensive.

The compact arrangement of the exchanger according to the present invention also promotes good thermal exchange between the hot gas and the cold gas, the exchange being able to be carried out, on the one hand, through partition walls of the hot part 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 appropriate solid materials such as for example sand and / or expanded clay, the particle size of which is judiciously determined to allow suitable fluidization at the speeds achieved in the apparatus.

It is easily understood that the gases are separated since the hot part is separated from the cold part by partitions which have only one opening at their lower part for the circulation of solid materials. With a view to further increasing the separation of the gases and with a view to preventing mixing thereof, through these openings, the injection of the fluidization gases can be arranged beyond said openings. It is also possible to use submerged more sophisticated communication orifices in which the flow of solid is regulated by a low flow of make-up gas (constituted by one of the two main gases or a third gas as the case may be). In this way, the decoupling between solid flow and main gas flows is improved; if the make-up gas is a third gas, the two main gas flows are completely avoided. This configuration can be very advantageous if one of the gases is toxic or

10 bothersome or if the mixture of the two gases can become explosive or generate toxic or harmful substances.

Preferably, the particular configuration is chosen so as to be able to gradually regulate the flow rate of transferred solid.

¹⁵ 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 recycling part of the gases has proven to be particularly advantageous as regards adjustment

20 end of operation in optimal conditions of the device. Such a bypass circuit makes it possible in particular, by adjusting the flow rate passing through it, to adjust the temperature level prevailing in the corresponding fluidized beds. According to a variant of the present invention, the

" ^D solids suspended in the flui¬ disation gases may at least partially consist of materials which can interact chemically or physically with the gases which hold them in suspension, with a view to cleaning them up, for example. solid materials

3 ° may consist of chemical reagents, active catalytic substances supported on suitable conventional support materials or chemical or physical absorbents, in particular pulverulent masses making it possible to fix these aerosols, droplets and

- ^' "fine particles possibly present in az to Brief description of the drawings

Other details for putting the invention into practice will appear on reading the description of particular embodiments shown in the appended figures, in which:

FIG. 1 is a schematic vertical section of the exchanger according to the invention,

FIG. 2 represents a schematic section of the device according to FIG. 1, at level A-A, and

FIG. 3 is a diagram of the exchanges of materials and of gas flows,

- Figures 4A to 4E of particular configurations of submerged communication orifices making it possible to appropriately regulate, in particular progressively, the flow of solid by a low flow of make-up gas.

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 2. If the partition 4 is lowered separating the two compartments so to allow an overflow, the two levels are balanced and cause a circulation of the solid according to the arrows.

A particularly preferred embodiment of the invention is shown in Figures 1 and 2. The exchanger com¬ carries 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 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 being heated by the hot gases, via outlet 7 when 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 by yielding part of its heat energy to the cold gas and leaves 1 "exchanger at 8. a bypass circuit 15 adjustable by means of a valve 17 makes it possible to recycle part of the hot gases at the bottom of one of the hot compartments 3 or 4, preferably compartment 3 carrying the fluidized bed at high speed This arrangement makes it possible to easily adjust the temperature level of the system. Circulation is ensured by a circulation fan 13.

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

To completely avoid the mixing of hot and cold gases, it is possible, in this particularly preferred mode of the invention, to fluidize the bottom 9 of the cold part

I, 2 and inject additional cold gas at a level

II located 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 manner for the hot compartments using the injector 12. To completely decouple the gas and circulating flow rates, it is possible to make communication orifices, of more complicated design, as illustrated in FIGS. 4Λ to 4Z. These arrangements are more complicated mechanically than the basic configuration but make it possible to completely avoid gas transfers from the hot part to the cold part and vice versa.

As is common practice, the device of the invention advantageously comprises a supply 13 of solid materials in the hot or cold part p r 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 annex fluidized bed.

Cn can also provide for a withdrawal of solid matter, possibly after chemical reaction, by the bottom ⁽ not shown). These can be sieved and re-injected into the hot part or the cold part 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. This type of configuration is well known and gives all the guarantees of reliability. Its construction is very easy, which constitutes an important advantage.

To further improve the operation of the installation, it may be advantageous to load in the fluidized bed ^• chemical reagents or lytically active cata- particles or chemical or physical absorbent. This makes it possible to combine with the heat exchange function, a chemical or physical reaction function such as depollution for example.

The regulation can be carried out in a practical manner as indicated in FIG. 2 while ensuring a large and regular circulation of the flow of solid materials.

The regulating device includes the measurement of differential pressure drops to control a motorized valve that 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 the figure 2).

According to FIG. 2, it is possible to regulate the flow of solids circulating between the hot part and the cold part by mounting a localized differential pressure sensor (20 and 2 Q ′) in at least one submerged orifice (5) in order to control by a motorized valve (24), the flows supplying at least one high-speed compartment (3). In FIG. 3, the gas flows are shown diagrammatically by continuous lines and by broken lines, the exchanges of material between a cold part 31 and a hot part 32. The main direction of circulation of the gases 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.

1 0 In FIGS. 4A to 4E, various configurations of the submerged orifices 5 ′ for communication are shown, which in particular in the case of FIGS. 4B, 4C, 4D and 4Ξ are configurations in J, L, U and in V allows¬ attempt to regulate the flow of solid transferred using a

1 5 low make-up gas flow. There is shown by an arrow bearing the mark 35, the distributor bearing the mark 37.

It will be noted that the device of the invention has 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.

^~ 5 Example

An application of the exchanger according to the invention is in the field of recovery of the heat energy contained in the waste gases from glass furnaces. Such a gas leaves the oven at 1400 ° C, passes through a

30 known regenerator which lowers the temperature to 472 ° C to send it to a chimney, the fresh air at 20 ° C being thus brought to 1045 ° C, before being injected into the oven. If you go downstream of the classic regenerator, a

J: exchanger according to the invention, the gas leaving the oven at 1400 ° C is brought to 535 ° C in the conventional regenerator and 302 ° C in the exchanger according to the invention before being evacuated in 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 classic 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 energy

1 0 calorific and using, as solid matter, 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

1 5 that it extends to the framework defined by the claims which also include a series of modifications such as for example the use of deflectors inclined with respect to vertical port, which are mounted on the partition walls, at l overflow location. Such a diposi-

-> f> tion significantly increases the flow rate.

Furthermore, it is possible to use all the conventional techniques within the reach of those skilled in the art with regard to the adjustment of the device. The addition of packing materials of adequate size makes it possible to "inflate" the fluidized bed without it being necessary to vary the speed of the fluidizing gas and acces¬ evening to serve as a support for chemical or physical reagent or chemical or physical absorbent which in this case has the advantage of remaining captive in one compartment, that is to say of not circulating like the rest of the fluidized flit from one compartment to the other. The present invention is characterized by its geometric simplicity, in particular by the fact that the dis¬

.o gas distributor is a distributor quite classi¬ that, as used for fluidized beds and that the section of the device remains constant with height, above said distributor.

Claims

CLAIMS. 1. Gas-gas type heat exchanger using the principle of interconnected fluidized beds, characterized in that it consists of a vertical cylindrical or polygonal tabular container 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 the cold gas (7) and

10 at least two adjacent compartments form a hot part (3, 4) and comprising at least one outlet for hot gas (8); 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 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 speed fluidized bed, a high speed fluidized bed (1, 3) can

20 overflowing 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 rate (17), - which makes it possible to recycle the gas leaving in the fluidization of one of the fluidized beds _> to 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 ,; 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

^ has two branch circuits, one of which recycles part of the hot gases leaving in the bottom of one of the hot compartments and the other recycles part of the cold gases leaving in the bottom of one of the 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 to 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 at high speed fluidized bed (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 supply of fluidizing gas takes place at a level higher than the level of the openings (5, 6) ensuring communication from below. 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 of fluidization, respectively, hot or cold (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 makes it possible to avoid having to vary the fluidization speed in the various compartments and, incidentally, makes it possible to use the materials packing as a support for a chemical reagent or a chemical or physical absorbent, particularly in the case of incompatibility with one of the two gaseous fluxes.

13. A method for recovering caorific 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 a cold gas is injected 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 method of claim 13 characterized in that one uses, as solid material, at least partially chemical reagents, catalytically active materials or chemical or physical absorbent masses which treat hot gases.

15. The method of claim 13 characterized in that one uses, as an immersed communication orifice, an orifice (51) of a configuration such that the flow of solid transferred is progressively adjustable.

16. Application of the method according to any one of claims 1 to 15 to pollution control.