EP2038598A2 - Hot gas generator and drying or dehydratiion installation employing such a generator - Google Patents

Abstract

The subject of the invention is a hot gas generator (8), particularly for a dehydration or drying unit, the generator comprising a burner or hearth (9) and being characterized in that it comprises at least one exchange circuit (10) comprising at least one pipe through which the gas to be heated flows, the pipe comprising a cool gas inlet end (11) and a hot gas discharge outlet (12), the pipe having a surface for heat exchange between the combustion gases generated by the burner or hearth (9) and the gas to be heated which flows through the pipe, the pipe also providing a physical barrier between the heated gases and the combustion gases generated by the burner or hearth. Application to producing a drying or dehydration installation.

Description

HOT GAS GENERATOR AND DRYING OR DEHYDRATION INSTALLATION USING SUCH A GENERATOR

The technical field of the invention is that of hot gas generators, including generators for equipping the dewatering or drying units of materials.

It is known (for example from EP0049677) to produce a wood waste drying unit comprising a drying means fed by the combustion gases supplied by a boiler.

This device uses the combustion gases directly. But these include residues that impregnate in a more or less strong way the dried material and limit the subsequent uses of this material.

It is thus not possible to implement such a drying unit to dehydrate edible materials and to be subsequently consumed (for example by animals). Even for the drying or the dehydration of ligneous materials, the residues of combustion impregnate the wood which affects its external aspect. The residues of combustion can subsequently exude out of the wood leading to pollutions of the houses. The combustion residues can also hinder the further processing of the wood (for example for furniture) by modifying the mechanical characteristics of the latter.

The invention aims to provide a hot gas generator to overcome such drawbacks. The generator according to the invention thus makes it possible to generate a stream of hot gas whose chemical characteristics can be completely controlled.

Moreover, the generator according to the invention also makes it possible to control the temperature of the gas generated while ensuring the recovery of the thermal energy of the burner or the hearth with excellent efficiency.

The generator according to the invention can implement burners or foci of various technologies using all types of fuels. It ensures in all cases the generation of a hot and clean gas does not disrupt the drying process or dehydration.

Thus, the subject of the invention is a hot gas generator, in particular for a dehydration or drying unit, a generator comprising a burner or a hearth and characterized in that it comprises at least one exchange circuit comprising at least one tubing in which circulates the gas to be heated, tubing having a fresh gas inlet end and a hot gas discharge outlet, tubing having a heat exchange surface between the combustion gases generated by the burner or furnace and the gas to be heated circulating in the tubing, the tubing also ensuring a physical separation between the heated gases and the combustion gases generated by the burner or hearth.

The pipe or pipes of the exchange circuits will preferably be oriented so that the flow of heated gas flows in the tubing in a direction opposite to that of the flow of combustion gases from the burner or hearth.

The hot gas generator may comprise means for regulating the speed of the hot gases leaving the various pipes. Each exchange circuit may furthermore comprise an outlet collecting channel and at least one intake channel, the outlet manifold and the inlet channel being connected to each other by means of tubes that are substantially parallel to each other. other. The intake channels and the outlet manifold may be substantially annular.

The hot gas generator may comprise at least one set of tubes having a corrugated profile.

It may also include a hot gas collecting duct, conduit which will be connected to the outlet manifold by tubes. It may also include a fresh gas supply duct which will be connected to the various intake channels by tubes.

According to a particular embodiment, the means for regulating the speed of the hot gases will be constituted by valves interposed between the fresh gas supply duct and each tube connecting this duct to the different intake ducts.

The intake channels will be advantageously compartmentalized in different sectors, each sector being connected to a single valve.

The hot gas generator may comprise at least two exchange circuits, each exchange circuit being disposed in a chamber through which the combustion gases circulate.

The two chambers may be concentric, the passage of the combustion gases from one chamber to the other being effected at a first end of a first chamber, the flow direction of the combustion gases being in the second chamber the opposite of the one in the first room.

The fresh gas supply duct may be arranged coaxially with the first chamber and inside a flue gas discharge chimney. The burner or fireplace may also be disposed at a second end of the first chamber.

The hot gas generator may comprise a third chamber surrounding the second chamber, the third chamber which will contain tubings connecting the exchange circuit of the second chamber to the fresh gas supply duct.

The invention also relates to a dehydration or drying installation using such a hot gas generator.

This dehydration or drying plant may be such that the fresh gas supply duct to the hot gas generator will be connected to a hot air recovery circuit that will be extracted from an enclosure receiving the material or materials to be dehydrated . The hot air recovery circuit may incorporate at least one condenser to dehydrate the air.

The dehydration or drying plant may include an activation circuit of the burner or fireplace using a portion of the hot air from the condenser.

It may also comprise a mixer disposed upstream of the chamber and for mixing the hot air from the generator with a fresh air portion out of the condenser.

The invention will be better understood on reading the following description of various embodiments, a description given with reference to the accompanying drawings and in which: FIG. 1 is a diagrammatic representation of an installation for drying organic material a hot gas generator according to the invention,

FIG. 2 is an external perspective view of the generator according to one embodiment of the invention; FIG. 3 is another external perspective view of the generator, the vessel envelope being partially cut off,

FIG. 4 is another external perspective view of the generator cut along a longitudinal plane; FIG. 5 is a longitudinal sectional view of the generator assembly;

FIG. 6 is a view similar to FIG. 5, but in which some of the tubes have been removed to show more precisely the main circuits and the directions of circulation of the fluids,

FIG. 7a is an enlarged sectional view of one of the valves used in the generator according to the invention,

FIG. 7b is an exploded perspective view of this valve; FIG. 8 shows a dehydration plant implementing the generator according to the invention.

Figure 1 shows an installation 1 for drying organic material 2. The materials 2 (for example agricultural waste or breadmaking) are arranged in a furnace 3. The materials may be carried by a drive means (not shown) such as a treadmill or a worm. This drive means will allow the loading and unloading of the oven 3.

The oven 3 is connected to a cyclone 4 which is intended to ensure the separation of solids from the gas stream flowing in the oven 3. The dried or dehydrated solids are removed periodically or continuously (according to the method) by the conduits 5 and 6.

The drying is ensured by a hot gas stream G which circulates in the oven 3 and which is led by a pipe 7 which leaves a hot gas generator 8.

The generator 8 is shown schematically in the form of an exchanger. It comprises a burner or a hearth 9 (for example a gas burner or a furnace fed by biomass) and an exchange circuit 10 comprising at least one pipe in which the gas to be heated circulates. The hot gas is here air.

The tubing of the exchange circuit 10 has a fresh air inlet end 11 and a hot air discharge outlet 12. The intake end 11 is connected to a condenser 13 which receives via the pipe 15 the hot air leaving the upper part of the cyclone 4. This condenser is cooled by fresh air circulating in an exchange circuit and entering this circuit through the inlet pipe 14. The condenser 13 ensures dehydration hot air flowing in the pipe 15 and preheating the previously dehydrated ambient air and conducted through the pipe 14.

The preheated air is led to the intake end 11 of the exchange circuit 10 via a duct 22.

The liquid water (H20) is recovered at the bottom 16 of the condenser 13. An accelerator (such as a pump or extractor) 17 is disposed at a stack 19 exhaust gas and accelerates and regulates the flow of hot air G flowing in the oven 3.

Furthermore, some of the residual hot air is also used to activate the burner or the firebox 9. This hot air is led to the burner via the pipe 20 on which an accelerator 18 is installed.

The combustion gases from the burner or the hearth 9 are discharged through a chimney 21.

According to the invention the tubing of the exchange circuit 10 has a surface to ensure a good heat exchange between the combustion gases generated by the burner or the hearth 9 and the gas to be heated (here air) brought by the conduit 22.

The tubing of the exchange circuit 10 makes it possible moreover to ensure a physical separation between the heated gases and the combustion gases generated by the burner 9.

Thus the flow G of hot gas is perfectly clean and does not degrade the quality of the organic material 2.

Figures 2 to 5 show an embodiment of a hot gas generator according to the invention.

FIG. 2 shows an external view of this generator 8. It can be seen that it comprises a substantially cylindrical tank 23. This tank will be arranged vertically (as shown in the figure) in the case of a biomass fireplace and it will be arranged horizontally in the case of a liquid or gaseous fuel burner. The lower part of the tank carries the burner or the hearth 9, the upper part carries the chimney 21 for evacuation of the combustion gases from the burner or the hearth 9. This gas supply duct 22 is also seen in this figure. fresh. This duct radially crosses the chimney 21 and (as is more particularly visible in Figures 3 to 5) it has an end which is disposed coaxially with the vessel 23 and inside the chimney 21 for discharging the combustion gases.

Finally, FIG. 2 shows the pipe 7 which discharges the hot gases out of the generator 8. The internal structure of the generator 8 is more particularly visible in FIGS. 3 to 5.

The tank 23 of the generator surrounds a number of tubings which are organized in different exchange circuits.

The generator shown here has two concentric exchange circuits.

Each exchange circuit is arranged in a specific chamber through which the combustion gases from the burner flow.

The generator thus comprises a first cylindrical chamber 24 surrounding the axis of the generator and which is delimited by a first cylindrical partition 26 carried by a support 27 integral with the bottom of the tank 23 (FIG. 5). The generator 8 also comprises a second annular chamber 25, surrounding the first chamber 24 and which is delimited on the one hand by the first partition 26 and on the other by a second partition 28, concentric with the first partition 26. The second partition 28 is secured to a plate 29 which is fixed at an upper end of the tank 23 and on which is fixed a housing 30 carrying the chimney 21.

As is more particularly visible in FIG. 6, the combustion gases C originating from the burner or the hearth 9 firstly pass through the first chamber 24 in the direction indicated by the arrows C (vertically from bottom to top, ie from the burner or fireplace 9 to the chimney 21). The gases are stopped by the upper partition plate 29 and then flow into the second chamber 25 in the reverse direction, vertically and from top to bottom.

Finally, the combustion gases are stopped by the bottom of the tank 23 and they go up through a third chamber 31 delimited by the tank 23 and the second partition 28 to join the chimney 21 through holes 32 made in the plate 29. (Figure 6). Thus the flow direction of the combustion gases in the second chamber 25 is the opposite of that it has in the first chamber 24.

The flow direction of the combustion gases in the third chamber 31 is also the opposite of that which it has in the second chamber 25.

It is also noted in the figures that the fresh gas is supplied to the generator at the duct 22 which is arranged coaxially with the various chambers 24, 25, 31 and inside the chimney 21 for evacuating the combustion gases.

The fresh gas is introduced into the generator 8 in a direction D which is the opposite of that of the flow C of the combustion gases from the burner or the hearth. This opposite direction is respected in the first chamber 24. It is also respected in the second chamber 25 (as well as in the third chamber 31).

Indeed the fresh gases are brought from the conduit 22 into the exchanger which is arranged in the second chamber 25 by pipes 33 which conduct the fresh gases at the bottom of the second chamber 25.

These fresh gases back in the second chamber in a direction opposite to that of the combustion gases in the latter. This particular orientation of the direction of the flow of gas to be heated in a direction opposite to that of the combustion gases makes it possible to improve the efficiency of the heat exchange at each exchange circuit.

According to the invention, each exchange circuit arranged in a chamber is designed to optimize heat transfer.

Each exchange circuit thus comprises a single outlet collection channel for the hot gases and several intake channels. The outlet manifold and the inlet channels are connected to each other by pipes substantially parallel to each other.

As can be seen in FIGS. 5 and 6, the first exchange circuit (located in the first chamber 24) therefore comprises an annular outlet manifold 34.1 which is arranged in the vicinity of the burner or the hearth 9.

The first exchange circuit also has four intake channels 35a1, 35b1, 35c1 and 35d1 (FIG. 6). These channels are all annular except the channel 35al which is in fact a box disposed substantially at the axis of the generator.

The diameters of the channels 35b1, 35c1 and 35d1 are also different from each other.

The outlet manifold 34.1 and the inlet channels 35a1, 35b1, 35c1 and 35d1 are connected to each other by manifolds 36 substantially parallel to each other.

For clarity of the figure, only the median tubes 36 connecting the channel 35al and the manifold 34.1 are visible in Figure 6. The other pipes connecting the channels 35bl, 35cl, 35dl to the manifold 34.1 are visible in Figures 4 and 5.

The division of the exchange circuit from several intake channels optimizes the introduction of tubing 26 in the volume of the chamber considered. This greatly increases the heat exchange surface between the combustion gases and the gas pipes to be heated. This improves the efficiency of the generator and also its ability to generate a large volume of hot gas. As is more particularly visible in Figures 4 and 5, some pipes 36 are straight and other pipes have a corrugated profile.

This corrugated profile also allows to increase the heat exchange surface. The hot gas generator according to the invention also comprises a toroidal conduit 37 for collecting the hot gases supplied by the different exchange circuits.

The duct 37 carries the pipe 7 for discharging the hot gases generated by the generator. The duct 37 is connected by tubings (38.1, 38.2) to the outlet manifolds (34.1, 34.2) of the different exchange circuits. Thus the manifold 34.1 of the first exchange circuit is connected to the conduit 37 by tubing 38.1 rectangular section. See in particular Figures 4 and 5.

The second exchange circuit (that which is arranged in the second chamber 25) has a structure similar to that of the first exchange circuit.

It comprises an annular outlet manifold 34.2 which is arranged in the vicinity of the plate 29.

This second exchange circuit comprises four intake channels 35a2, 35b2, 35c2 and 35d2. These channels are all annular and disposed at the lower end of the second chamber 25.

As already mentioned, the fresh gas is fed from the duct 22 to the various intake ducts 35a2, 35b2, 35c2, 35d2 by tubing 33 with a rectangular section (see FIG. 3).

Tubing 36 with a straight or corrugated profile connects the inlet channels and the outlet manifold 34.2.

The latter is itself connected to the duct 37 for discharging hot gases by tubing 38.2 with a rectangular section. See in particular Figures 3, 5 and 6.

The combination of two heat exchange circuits makes it possible to improve the efficiency of the generator. Indeed, calories provided by the combustion gases can be sampled at each of the exchange circuits.

Furthermore the passage of the pipes 33 in the third chamber 31 ensures a preheating of the fresh gas upstream of the second chamber and still uses a portion of the available calories. The generator according to the invention therefore provides in a relatively compact volume an excellent thermal efficiency.

Specifically it is possible to achieve with two exchange circuits a generator 8 generating a flow having a speed between 5.0 m / s and 8.0 m / s of hot gas having a temperature of about 600 ⁰ C .

The skilled person will easily size the generator according to the desired characteristics (temperature and flow). The different shapes and lengths for the pipes 36 (within the same exchange circuit and between the different exchange circuits) lead to different head losses at each tubing. In order to ensure a homogeneous hot gas generation flow, means will be provided for regulating the speed of the hot gases leaving the various pipes.

These means are for example constituted by valves which will be interposed between the duct 22 for supplying fresh gas and each tube which connects this duct to the various inlet channels 35 (35a1,..., 35d1... 35a2,. .., 35d2).

These means are not shown in detail in Figures 3 to 6. They are arranged at the different flanges marked 39 (Figures 5 and 6). Moreover, in order to allow control of the gas velocity at each group of pipes, the inlet channels 35 will be compartmentalized in different sectors, each sector being connected to a single valve. There will be no disruption of the gas flow coming out of each valve. This avoids flow returns from an intake channel to a valve and the flow is regularized.

The subdivision of the channels 35 will be simply achieved by providing sheet partitions dividing the annular channel considered in different sectors. Figures 7a and 7b show the structure of such a valve 40 of flow control.

It comprises a plunger 41 having a conical end 42 which is intended to cooperate with a complementary bearing surface of a support 43. The support 43 is screwed to a base 44. A spring 45 is dimensioned solely to withstand the weight of the plunger 41. last is therefore supported on its range in the rest position of the valve (as shown in Figure 7a).

The direction of passage of the fresh gas is represented by the arrows D.

The fresh gas from the conduit 22 enters the valve 40 through the orifice 46. It pushes the plunger 41 against the action of the spring 45. The fresh gas passes into the chamber 47 and spring downstream through the bore 48 to go to the inlet channel 35 considered.

It can be seen that the gas passage section will vary as a function of the axial position of the plunger 41. An increase in the pressure of the hot gas downstream will therefore push the plunger upwards and reduce the fresh gas inlet pressure.

The valve thus makes it possible to regulate the hot gas pressure and thus regulates the speed of the air in the various pipes. Depending on the pressure drop characteristics of the pipes 36 considered characteristics of the valve will of course be different.

The different valves will be dimensioned according to the desired result, which is to obtain the same hot gas outlet velocity for all the pipes at the exhaust duct 37.

The skilled person will easily size these different valves according to the characteristics of the generator that he realizes. The hot gas generator according to the invention can be implemented in different installations.

Figure 8 thus shows a dehydration plant, for example for timber.

This installation 1 comprises a closed enclosure 50 inside which are disposed the elements 58 of timber to be dried, placed for example on a carriage.

The generator 8 supplies hot air through its gas evacuation pipe 7 and receives fresh air through its conduit 22. The pipe 7 is connected to the enclosure 50 via a pipe 52.

After circulation in the enclosure 50, the hot air is discharged through an outlet pipe 53 which is connected to a condenser 13. This condenser is cooled by fresh outside air circulating in an exchange circuit and entering this circuit through the inlet manifold 14. The condenser 13 makes it possible to ensure the dehydration of the hot air flowing in the pipe 53.

The air thus dehydrated is fed to the intake duct 22 of the generator 8 via the pipe 59. The liquid water (H20) is recovered at the bottom 16 of the condenser 13. An accelerator (such as a pump) 17 allows accelerate and regulate the flow of hot air G flowing in the enclosure 50 and in the generator 8.

Thus the duct bringing the fresh air 22 to the generator 8 is connected to a hot air recovery circuit which is extracted from the enclosure 50 receiving the materials to be dehydrated.

Part of the hot air recovered in the condenser 13 is used to activate the burner or the hearth 9, via the duct 57. This duct is connected to the duct 22 by means of a three-way valve 51 whose function is to enable the extraction of a quantity of preheated air to supplement the losses possibly caused by leaks. Another three-way valve 54 is interposed between an upstream portion (duct 57), a downstream portion 60 (towards the burner) and an exhaust 61. It allows the regulation of the preheated air flow necessary for the activation of the burner or the home

9. The final surplus being directed by the exhaust 61 to the outside or another application via the valve 54. This closed circuit operation ensures a preheating of the fresh air and thus improves the efficiency of the

1 installation.

Furthermore, a mixer 55 is disposed at the inlet of the enclosure 50. It is possible at this mixer to dose the hot air from the generator 8 with a portion of the fresh air leaving the condenser 13 by means of a shutter 56.

It is thus possible to regulate the dehydration temperature relatively accurately. It will thus be possible to produce an installation operating continuously with an air at 120 ^° C. ensuring rapid drying of the timber.

Of course, it is possible to realize drying facilities for different materials, for example for cereals.

Claims

1. Generator (8) of hot gas, especially for a unit (1) for dehydration or drying, generator comprising a burner or a hearth (9) and characterized in that it comprises at least one exchange circuit (10). ) comprising at least one tubular in which the gas to be heated circulates, tubing having a fresh gas inlet end (11) and a hot gas discharge outlet (12), tubing having a heat exchange surface between them. combustion gases generated by the burner or the hearth (9) and the gas to be heated circulating in the pipe, the pipe also ensuring a physical separation between the heated gases and the combustion gases generated by the burner or the hearth (9) . 2. Hot gas generator according to claim 1, characterized in that the or the pipes (36) of the exchange circuits are oriented so that the flow (D) of heated gas flows in the tubing in a reverse direction of that of the flow (C) of the combustion gases from the burner or furnace (9). 3. Hot gas generator according to one of claims 1 or 2, characterized in that it comprises means (40) for regulating the speed of hot gases leaving the various pipes (36). 4. Hot gas generator according to one of claims 1 to 3, characterized in that each exchange circuit comprises an outlet collector channel (34.1, 34.2) and at least one inlet channel (35al, ... 35dl, 35a2, ... 35d2), the outlet manifold and the inlet channel being connected to each other by pipes (36) substantially parallel to each other. 5. hot gas generator according to claim 4, characterized in that the inlet channels (35al ..., 35dl, 35a2 ..., 35d2) and the outlet manifold (34.1, 34.2) are substantially annular. 6. Hot gas generator according to one of claims 4 or 5, characterized in that it comprises at least one set of tubes (36) having a corrugated profile. 7. hot gas generator according to one of claims 4 to 6, characterized in that it comprises a conduit (37) for collecting hot gases, which conduit is connected to the outlet manifold (34.1, 34.2) by tubes ( 38.1, 38.2). 8. Hot gas generator according to one of claims 4 to 7, characterized in that it comprises a conduit (22) for supplying fresh gas which is connected to the different inlet channels (35al ..., 35dl, 35a2 ..., 35d2) by tubes (33). 9. Hot gas generator according to claim 8, characterized in that the means for regulating the speed of hot gases are constituted by valves (40) interposed between the fresh gas supply duct (22) and each tube ( 33) connecting this conduit to the different inlet channels (35al ... 35dl, 35a2 ... 35d2). 10. Hot gas generator according to claim 9, characterized in that the inlet channels (35al ... 35dl, 35a2 ... 35d2) are divided into different sectors, each sector being connected to a single valve (40). . 11. hot gas generator according to one of claims 1 to 10, characterized in that it comprises at least two exchange circuits, each exchange circuit being arranged in a chamber (24, 25) through which circulate the combustion gas (C). 12. Hot gas generator according to claim 11, characterized in that the two chambers (24, 25) are concentric, the passage of combustion gases from one chamber to the other being effected at a first end. a first chamber, the flow direction of the combustion gases being in the second chamber the opposite of that in the first chamber. 13. Hot gas generator according to one of claims 8 and 12, characterized in that the duct (22) for supplying fresh gas is arranged coaxially with the first chamber (24) and inside a chimney (21). ) for the evacuation of combustion gases. 14. Hot gas generator according to claim 12 or 13, characterized in that the burner or hearth (9) is arranged at a second end of the first chamber (24). 15. Hot gas generator according to claims 8 and 12 to 14, characterized in that it comprises a third chamber (31) surrounding the second chamber (25), third chamber which contains tubings (33) connecting the circuit of exchange of the second chamber to the supply duct of fresh gas. 16. Installation (1) dehydration or drying, especially for woody materials, characterized in that it comprises at least one hot gas generator (8) according to one of the preceding claims. Dehydrating or drying plant according to claim 16, characterized in that the fresh gas supply duct (22) to the hot gas generator (8) is connected to a hot air recovery circuit which is extracted from an enclosure (3, 50) receiving the material or materials to be dehydrated. 18. dehydration or drying plant according to claim 17, characterized in that the hot air recovery circuit incorporates at least one condenser (13) ensuring the dehydration of the air. 19. Dehydration or drying plant according to one of claims 16 to 18, characterized in that it comprises an activation circuit of the burner or hearth (9) using a portion of the hot air from the condenser (13). 20. Dehydration or drying plant according to one of claims 17 to 19, characterized in that it comprises a mixer (55) disposed upstream of the chamber (50) and for mixing the hot air from the generator ( 8) with a portion of fresh air leaving the condenser (13).