WO2010072980A1

WO2010072980A1 - Drying or dehydrating device

Info

Publication number: WO2010072980A1
Application number: PCT/FR2009/052677
Authority: WO
Inventors: Solène LE BRAS; Pascal Isambert; Jean-Marie Gaillard
Original assignee: Ceradry
Priority date: 2008-12-24
Filing date: 2009-12-23
Publication date: 2010-07-01
Also published as: FR2940416A1

Abstract

The invention relates to a drying or dehydrating device that comprises at least one substantially vertical wall (36) for limiting the thermal transfers between a so-called inside area, in which at least one product is put in contact with a gas maintained at an appropriate temperature for evaporating water, and the outside, said at least one wall (36) comprising at least one partition in the form of a plurality of plates (38) with spaces therebetween so as to enable the passage of hot and steam-saturated air present in the inside, and inclined so as to form an angle relative to the vertical, the lower ends (40) of said plates being offset towards the outside relative to the upper ends (42), characterised in that said plates (38) are arranged so that, for each plate, the lower end (40) is offset towards the bottom relative to the upper end (42) of the plate arranged immediately below in order to obtain a condensation phenomenon at said plates (38).

Description

DEVICE FOR DRYING OR DEHYDRATION

The present invention relates to a device for drying or dehydration.

According to DE-813,313, a dryer is known comprising plates on which the products to be dried rest. This type of dryer includes heavily perforated side walls, and especially not insulated, allowing air to flow from outside to inside and vice versa. The drying of the products results from this ventilation. To support the plates, the dryer includes inclined cleats which are spaced to allow air to circulate.

According to a more advanced embodiment, as illustrated in FIGS. 1 and 2, a drying or dehydrating device is in the form of an enclosure 10 or a tunnel delimited by a wall 12 for confining air warm in the environment close to the product 14 to dry or dehydrate place in the enclosure or tunnel.

Existing devices comprise means 16 for heating the air present in the enclosure or the tunnel or means for supplying hot air to the enclosure or tunnel, the hot air being heated outside said enclosure or said tunnel.

In contact with the product to be dried or dehydrated, the hot air is charged with water vapor. In addition, the existing devices comprise means 18 for extracting from the enclosure or the tunnel, hot air and saturated with water vapor, such as the device described in document CH-272.890. The latter includes a gas discharge system with movable shutters thanks to a single control adapted to occupy a first closed position that does not allow the passage of air during drying and an open and spaced position to cause the discharge of gases. In the open position, for each flap, the lower end is not shifted downward relative to the upper end of the flap located below to promote the passage of air to the outside. In a first variant, the hot air is rejected outside the enclosure or tunnel.

This solution has the merit of being simple is not satisfactory in terms of energy balance. To overcome this drawback, the existing devices may include a recirculation circuit 20 of hot air and saturated with water vapor to reinject this air back into the enclosure 10 or the tunnel. Prior to reinjection, the hot air saturated with water vapor passes through at least one condenser 22 in order to dry out. Even if this solution avoids the release of possible pollutants into the environment and slightly reduces energy consumption by recirculating hot air, this solution is not yet satisfactory in terms of energy balance. In this sense, it tends to improve the thermal insulation of the wall 12 to reduce heat losses (illustrated in Figure 2) to reduce the amount of energy to maintain the air at the appropriate temperature in the enclosure or the tunnel.

In the case of a poorly insulated wall 12, it may appear a phenomenon of condensation deemed parasitic due to the formation of water in the enclosure or tunnel at the inner surface 24. To counter this phenomenon, it tends to improve the thermal insulation of the wall which tends to reduce heat losses and / or to extract the air faster so that it is less loaded with water vapor which leads to to work with atmospheres whose hygrometry is quite low (<70%) which tends to increase the energy consumption and the appearance of defects on the products (deformations, cracks, ...).

Also, the present invention aims to overcome the disadvantages of the prior art by providing a drying device more efficient in terms of energy balance.

For this purpose, the subject of the invention is a drying or dewatering device comprising at least one substantially vertical wall making it possible to limit the heat transfer between a so-called inside zone in which at least one product is placed in contact with a maintained gas. at a suitable temperature for evaporation of water and outside, said at least one wall having at least one separation in the form of a plurality of plates spaced apart so as to allow the passage of hot air and saturated water vapor present therein, inclined to form an angle α with the vertical, the lower ends of said plates being offset outwardly relative to the upper ends, characterized in that said plates are arranged to so that for each plate the lower end is shifted downwards with respect to the upper end of the plate arranged just below to to obtain a phenomenon of condensation at said plates.

Other features and advantages will emerge from the following description of the invention, a description given by way of example only, with reference to the appended drawings in which:

FIG. 1 is a section of a drying chamber or tunnel according to the prior art,

FIG. 2 is a section illustrating in detail the wall of a drying chamber or tunnel according to the prior art,

FIG. 3 is a section of an enclosure or a tunnel according to the invention, FIG. 4 is a section of a wall of a drying or dewatering device according to the invention, and

- Figure 5 is a section illustrating in detail and schematically a wall of a drying device or dehydration according to the invention. In Figure 3, there is shown a drying device or dehydration in the form of an enclosure 30 enclosing a hot gas capable of being saturated with water vapor in contact with at least one product 32 to dry or dehydrate. However, the invention is not limited to this example, but may be suitable for all forms of devices regardless of the product to be dried, the area in which is placed or scrolls the product. Thus, the device according to the invention can be used by industries of mineral raw materials, for example for drying shaped terracotta products such as tiles or bricks, for drying wood, paper, products agri-food or pharmaceutical industry for dewatering, powdered products, organic materials or wet-formed parts.

Thus, the device according to the invention can be applied to climatic chambers, drying chambers, tunnel dryers, atomizers, etc. These various applications are given by way of example and are in no way limiting. Generally, the hot gas likely to saturate with water vapor is air. The device comprises means 34 for heating and / or maintaining the temperature of the gas so that the gas is at the appropriate temperature favoring the formation of water vapor. These means 34 for heating and / or maintaining temperature can be placed in the enclosure 30 or outside the enclosure, an air circuit then being provided between the enclosure and said means 34.

By way of example, the means 34 for heating and / or maintaining the temperature of the gas may be in the form of resistors, infrared lamps, burners or boilers. However, other technical solutions can be envisaged.

According to the invention, the device comprises at least one substantially vertical wall 36 for limiting thermal losses between the inside and the outside of the enclosure.

This wall 36 comprises at least one separation in the form of a plurality of plates 38 spaced apart so as to allow the passage of hot air saturated with water vapor present in the chamber, inclined to form a angle a with the vertical, the lower end 40 of the plates being shifted outwards with respect to the upper end 42.

For each plate, the lower end 40 is offset downwards with respect to the upper end 42 of the plate placed just below in order to obtain a phenomenon of condensation at the level of said plates and an evacuation of the condensed water towards the outside given the inclination of the plates. According to one embodiment, each plate is in the form of a rectangular blade whose large side is disposed substantially horizontal and constitutes the upper end 42 while the opposite large side corresponds to the lower end 40. The high ends 42 plates 38 are arranged in a same plane 44, substantially vertical, shown in dotted lines in FIGS. 4 and 5.

According to a first variant, the plates 38 can be fixed with a constant angle α and are called fins.

According to another variant, the plates 38 can be movable so as to adjust the value of the angle a and are called shutters. The difference in temperature between the inside and the outside of the separation formed by the plates 38 makes it possible to obtain the condensation of the water on the plates 38 which flow by gravity outside the enclosure, 44. This condensation on the plates 38 maintains the temperature of the plates at Dew temperatures of hot and humid air. Thus, the wall according to the invention makes it possible, on the one hand, to isolate the volume containing the hot and humid air, and on the other hand, to extract the water present in the hot and humid air in order to drying or dehydrating the product 32. According to one advantage of the invention, this type of wall provides a near perfect insulation, close to the adiabatic because the dew point temperature is very close to the dry temperature of the 'air. This almost perfect insulation makes it possible to maintain a high hygrometry during drying, close to the saturation curve, which results in fast drying while limiting the mechanical stresses involved during drying.

According to the prior art, drying devices comprise solid and insulated walls with materials such as rockwool or polyurethane foam that do not prevent condensation phenomena inside the dryer when looking for to reach a high degree of hygrometry. The system of the invention makes it possible to work at high relative humidity because the phenomenon of condensation on the shutters allows an insulation superior to any existing insulating material. The higher the degree of hygrometry, the greater the absolute humidity of the air. Thus, at a given temperature, the power of condensation and therefore of insulation will be all the more important because the latent heat of condensation is close to 2500 kj / kg of condensed water.

As illustrated in detail in FIG. 5, in contact with the film of condensed water present on the plates 38, the temperature rises sharply because the latent heat of condensation of the water insulates the wall significantly. This solution makes it possible to limit the heat losses (or the heat flow from the inside to the outside of the enclosure) which results in a reduction of the amount of energy necessary to heat or maintain the air at the same time. adequate temperature. Insofar as the place where the hot air and the water are separated forms the internal surface of the enclosure, this solution makes it possible to eliminate the pumps necessary to extract the hot air and saturated with water vapor of the enclosure and condensers for separating the water from the air provided in the devices of the prior art which results in a better energy balance.

This arrangement makes it possible to obtain the same temperature over the entire height of the zone occupied by the plates 38.

It is possible to modulate the heat flow through the wall by varying the thickness of the condensed water film on the plates 38 by adjusting the angle α and / or the length H of the plates (depending on the direction of flow some water).

In all cases, the distance E between two plates must be less than or equal to H.cos (a).

Preferably, the plates overlap for more than half their length.

To obtain a satisfactory result, the angle must vary from 1 to 60 °, H must vary from 50 to 200 mm, E must vary from 10 to 100 mm.

It is possible to quantify the heat flow through the wall according to the invention by defining the average exchange coefficient Ii: - h _q ³

With: pϋq: density of the liquid water in kg / m ³ . ρ _vap : density of steam water in kg / m ³ . g: weightlessness in kg / m ²

L _v : latent heat of vaporization in kj / kg. λ | _iq : thermal conductivity of water in W / mK V | _iq : dynamic viscosity of water in Pa.s.

T _sat : saturation temperature = dew temperature in K. T _p : temperature of the fins in K.

H _c : condensation height on the fin = H.cos (a) assuming that the fins overlap for half of their length.

The heat flux Φ passing through a surface wall Surf is calculated as follows:

In addition, the water flow rate is: Q = Φ / L _v

It is noted that the higher the condensation height on the fin H _c is and the lower the average exchange coefficient Ii.

For this purpose, the fins may comprise a suitable surface condition or any other element intended to increase the height of condensation on the fin H _c .

In the same way, the larger the difference (T _sat- T _p ), the lower the average exchange coefficient Ii.

For this purpose, it is possible to act on T _p for example by generating an air flow at the fins as will be explained later.

For example, for T _sat = 100 ⁰ C, T _p = 60 ⁰ C and H _c = 0.5 m ² , we obtain Ii = 5.178 W / m ² .K.

For a Surf surface = 0.5m ² , we obtain Φ = 103.7 kW and Q = 170.5 L / h.

Advantageously, the plates can be striated to reduce the height of condensation Hc. Advantageously, the wall according to the invention comprises a second separation in the form of an outer wall 46 sealed, not thermally insulated, for confining the air in the enclosure.

This outer wall 46 also makes it possible to limit the phenomena of convection with the outside which may be detrimental to the phenomenon of condensation on the plates.

Preferably, the convection coefficient in the zone between the wall formed by the plates and the outer wall 46 is close to 0 to prevent heat exchange between said zone and the enclosure 30. According to another variant, means 48 may be provided to generate a substantially horizontal flow and parallel to the wall so as to promote the condensation phenomena at the plates 38. According to a preferred embodiment, an air flow is generated by the introduction of the ambient air present outside the enclosure, between the separation formed by the plates 38 and the separation formed by the outer wall 46 through a ventilation system.

Alternatively, this air flow can be obtained by stirring the air present between the separation formed by the plates 38 and the separation formed by the outer wall 46. According to another embodiment, the device comprises means 50 for collecting the water flowing in the lower part between the separation formed by the plates 38 and the separation formed by the outer wall 46.

In the case of an enclosure, the horizontal walls may be insulated or not.

In the latter case, the horizontal walls may be slightly inclined so that the water which condenses therefrom flows by capillarity towards the substantially vertical walls according to the invention which collect the condensation water. According to one operating mode of the invention, it is possible to perform the drying in several phases, a first phase with a high hygrometry and at least one other subsequent phase with a lower hygrometry.

Claims

1. Drying or dewatering device comprising at least one substantially vertical wall (36) making it possible to limit the heat transfer between a so-called interior zone in which at least one product is placed in contact with a gas maintained at a suitable temperature allowing evaporation of the water and the outside, said at least one wall (36) having at least one separation in the form of a plurality of plates (38) spaced apart so as to allow the passage of hot air and saturated with water vapor present therein, inclined to form an angle α with the vertical, the lower ends (40) of said plates being offset outwardly with respect to the upper ends (42), characterized in that said plates (38) are arranged in such a way that for each plate the lower end (40) is offset downward with respect to the upper end (42) of the plate arranged just below the plate in order to obtain a condensation phenomenon at said plates (38).

2. Apparatus for drying or dehydration according to claim 1, characterized in that each plate (38) is in the form of a rectangular blade, a large side is disposed substantially horizontal and constitutes the upper end (42) then that the opposite large side corresponds to the lower end (40).

3. Drying or dewatering device according to claim 2, characterized in that the plates (38) are fixed with a constant angle α.

4. Drying or dewatering device according to claim 2, characterized in that the plates (38) are movable so as to adjust the value of the angle a.

5. Drying or dewatering device according to any one of the preceding claims, characterized in that the plates (38) form an angle α with the vertical and / or have a length H in the direction of flow of water adapted (s) to obtain the desired heat flow through the wall (36).

6. Apparatus for drying or dehydration according to any one of the preceding claims, characterized in that the plates (38) overlap on more than half of their length H.

7. Apparatus for drying or dewatering according to any one of the preceding claims, characterized in that said at least one wall (36) comprises a second separation in the form of a wall (46) sealed exterior.

8. Apparatus for drying or dewatering according to any one of the preceding claims, characterized in that it comprises means (48) for generating a flow promoting condensation phenomena at the plates (38).

9. Apparatus for drying or dewatering according to claim 7 and 8, characterized in that it comprises means for generating a flow of air at ambient temperature between the separation formed by the plates (38) and the separation formed by the outer wall (46).

10. Drying or dehydration device according to any one of the preceding claims, characterized in that it comprises means (50) for collecting the water flowing in the lower part of the wall (36).