EP0451066B1 - Cooking steam generator with drain device - Google Patents

Abstract

The steam generator according to the invention is characterised by the presence of an intermediate duct (17) which admits the drain water into the lowest central part of the enclosure (1) of the generator and is connected to a vane pump (19), the output (20) of which delivers into an output duct (21) which rises to an upper elbow (28) and then descends to a drain duct (22). Heating tubes (8, 9, 10) bring about the evaporation of the water which they contain and the steam escapes into a horizontal upper duct (6) and then into a steam conduction duct (4). The generator finds application in particular in food cooking ovens. <IMAGE>

Description

The present invention relates to devices for producing water vapor from liquid water, the water vapor can be used in particular in food cooking appliances.

Numerous steam generators are already known, which generally comprise a generator enclosure suitable for containing water, means for bringing water into the enclosure, a steam conduction pipe for bringing the steam in a use enclosure, and means for heating the water contained in the generator enclosure to bring the water to a boil and produce steam.

Thus, the document EP-A-0 323 939 describes such a steam generator comprising a lower horizontal pipe, an upper horizontal pipe, the two lower and upper horizontal pipes being connected by one or more parallel vertical heating tubes and by a return tube also vertical, a bypass of the return tube being provided with water level detection means. A lateral lower orifice, closable by a valve, allows the water contained in the generator to drain to empty the generator at the end of use.

The applicants have noted, on such a steam generator, a tendency to localized heating, causing for example the excessive heating of one of the heating tubes while the other tubes operate correctly at appropriate temperatures.

It has become apparent that the heating problems do not occur at the start of operation, but only occur after a sufficient period of operation.

An in-depth examination of this problem has shown that localized heating can be suppressed by ensuring proper removal of the tart debris which tends to accumulate in the lower part of the steam generator.

Thus, the problem proposed by the present invention is to eliminate, in a simple, automatic and inexpensive manner, the excessive differential heating appearing on the heating elements of the steam generators after a period of operation.

The solution must allow sufficient removal of the scale appearing in the lower part of the steam generator.

A first solution is suggested in document EP-A-317 444, which describes a steam generator in which the heating means are of a particular nature, using porous bodies. The porous heating body is immersed in an enclosure containing water and bounded by a lower wall provided with an evacuation orifice in a lower evacuation pipe closed by a valve. The document suggests removing the scale particles by opening the lower valve for the flow of water, and simultaneously supplying rinsing water through an upper pipe. Such a cleaning process requires an additional volume of rinsing water, and means for supplying and controlling the flow of rinsing water, which significantly increases the cost of the installation. In addition, such a structure, with water supply in the upper part of the enclosure, will be difficult to apply to a steam generator in which the heating means are vertical tubes, since it would then be necessary to introduce the rinsing water into each tubes separately.

Another solution is proposed in documents DE-U-8 901 904 and EP-A-383 327 (state of the art within the meaning of Article 54 (3) EPC). In these documents, the heating means are introduced into an enclosure filled with water up to an intermediate level. A suction and discharge pump circulates discharge water in an intermediate pipe arranged between the pump and the bottom wall of the generator enclosure. These documents recommend placing the water evacuation orifice in the lower wall of the enclosure in the vicinity of the side wall of the enclosure, and positioning in a diametrically opposite situation a nozzle for injecting rinsing water. . The combination of the pump and the rinsing nozzle produces a strong current of fluid in the tank, ensuring its cleaning. This structure is also complex and expensive, since it requires not only an additional flow of rinse water, but also means for supplying rinse water, control of rinse water flow, and a pump. 'evacuation. In addition, this solution would not be suitable for cleaning steam generators in which the heating means are vertical tubes: the means described do not make it possible to produce a flow of fluid inside the tubes, since the current product is perpendicular to the axis of the heating tubes.

• une canalisation intermédiaire débouchant par sa première extrémité dans un orifice de la paroi inférieure de l'enceinte de générateur de vapeur d'eau, la canalisation intermédiaire étant horizontale ou descendante jusqu'à sa seconde extrémité,
• une pompe à aspiration et refoulement, dont l'entrée est raccordée à la seconde extrémité de canalisation intermédiaire, et dont la sortie refoule dans une canalisation de sortie prolongée par une canalisation de vidange,
• l'orifice de paroi inférieure d'enceinte est disposé en zone centrale de ladite paroi,
• ledit orifice constitue la portion de paroi inférieure la plus basse, ladite paroi inférieure formant une surface régulière plane ou descendante vers ledit orifice.

Thus, the invention makes it possible to solve this problem in a simple and economical manner by providing a generator having the characteristics of claim 1, that is to say comprising:

• an intermediate pipe opening at its first end into an orifice in the lower wall of the steam generator enclosure, the intermediate pipe being horizontal or down to its second end,
• a suction and discharge pump, the inlet of which is connected to the second end of the intermediate pipe, and the outlet of which discharges into an outlet pipe extended by a drain pipe,
• the lower enclosure wall orifice is disposed in the central zone of said wall,
• said orifice constitutes the lowest lower wall portion, said lower wall forming a regular flat or descending surface towards said orifice.

This combination of characteristics causes a rapid swirling of water within the generator enclosure during emptying. The entrainment of scale particles is considerably improved, producing an evacuation which becomes sufficient to solve the problem of the invention, without requiring an external supply of rinsing water.

The pump is advantageously a rotary vane pump, rotating around an axis parallel to the second end of the intermediate pipe, and discharging into an outlet pipe orifice disposed radially on the periphery of the rotation area of the pallets. The rotary vanes are driven by an asynchronous electric motor. Such a type of pump is well suited for use in the present invention, because it has a very high robustness and is not sensitive to the risks of blockage. Scale particles cannot block the pump and degrade it.

Preferably, the outlet pipe is ascending from the pump to an upper bend, and then descending to the drain pipe. By this arrangement, a water passage is left permanently from the enclosure of the steam generator to the drain pipe, the pump not preventing the passage of water but simply ensuring its drive when it is rotating. As a result, the device avoids the appearance of overpressures inside the steam generator, any overpressure causing the flow of water in the direction of the drain pipe. The device is also very reliable, since nothing can prevent the evacuation of the water contained in the enclosure of the steam generator. This solution also has an economic advantage, because it is of a particularly low cost, not requiring the use of solenoid valves.

The evacuation structure according to the invention can be applied to types of steam generator in which the heating means are immersion resistors inserted simply in the enclosure containing the water. However, the invention is particularly advantageous when it is applied to a steam generator in which the heating means are vertical heating tubes connecting a transverse lower pipe and a transverse upper pipe, with a return pipe also vertical. , the heating tubes being provided with an electrical resistance wound in a helix and in contact with the external face of their wall. Indeed, according to such a structure, the tartar naturally tends to form in the heating tubes and, as a result of temperature variations, the tartar tends to detach from the walls and to fall in the form of powder in the lower pipe. The scale is then completely removed by the removal means according to the invention.

• la figure 1 est une vue schématique illustrant l'implantation des moyens de l'invention pour réaliser un générateur de vapeur d'eau adapté par exemple à un four pour la cuisson alimentaire ;
• la figure 2 est une vue schématique en perspective d'un autre mode de réalisation du dispositif selon l'invention ;
• la figure 3 est une vue de côté en coupe d'une enceinte de générateur de vapeur d'eau pouvant être utilisée selon l'invention ; et
• la figure 4 est une vue schématique en coupe partielle en perspective d'une pompe à palettes rotatives utilisable dans le générateur selon la présente invention.

Other objects, characteristics and advantages of the present invention will emerge from the following description of particular embodiments, given in relation to the attached figures, among which:

• Figure 1 is a schematic view illustrating the layout of the means of the invention for producing a steam generator adapted for example to an oven for cooking food;
• Figure 2 is a schematic perspective view of another embodiment of the device according to the invention;
• Figure 3 is a sectional side view of a steam generator enclosure that can be used according to the invention; and
• FIG. 4 is a schematic view in partial section in perspective of a rotary vane pump usable in the generator according to the present invention.

As shown in Figures 1 and 2, a steam generator according to the present invention comprises a generator enclosure 1 suitable for containing water. A water supply pipe 2, provided with a solenoid valve 3, allows the supply of water in the lower part of the enclosure 1 of the generator. A steam conduction pipe 4 makes it possible to recover the steam in the upper part of the enclosure 1 to bring it into a use enclosure schematically represented 5, for example the enclosure of an oven for food cooking.

In the embodiment shown, the enclosure 1 comprises an upper horizontal pipe 6, a lower horizontal pipe 7, both connected by at least one vertical heating tube, for example three tubes 8, 9 and 10 respectively, and by a tube vertical return 11. The heating tubes 8, 9 and 10 are hollow tubes, for example metal, carrying helical electrical resistors such as the resistor 12 of the tube 8 in contact with the outer face of each tube.

As shown in section in FIG. 3, the heating tubes are connected to the upper and lower pipes by flexible connectors such as the connector 120 which has only been shown in FIG. 3.

The return tube 11 is provided with a parallel bypass 13 which comprises means for measuring the water level A. For example, the measuring means comprise a resistive probe 14, the lower end of which is at an intermediate level A desired water, and which provides an electrical signal of presence or absence of water at level A. The electrical signal is sent to an electrical treatment device, not shown in the figures, making it possible to control valve 3 to admit water until reaching level A in which the water comes into contact with the probe 14, and cut off the water supply as long as the probe 14 indicates the contact of water on the probe.

Electrical resistors such as resistor 12 are designed to heat the walls of tubes 8, 9 and 10 and bring the water they contain to a boil. The water vapor escapes from the top and enters the upper horizontal pipe 6, then escapes through the steam conduction pipe 4 into the enclosure 5. The complete operation of this type of generator is described in document EP-A-0 323 939.

According to the invention, the lower wall 15 of the lower horizontal pipe 7 is generally flat and horizontal and comprises an orifice 16, formed in its central part as shown in FIG. 3. The orifice 16 is connected to the first end of an intermediate pipe 17, the second end 18 of which is connected to the inlet of a pump 19. The intermediate pipe 17 is horizontal or descending from its first end adjacent to the lower pipe 7 to its second end 18 adjacent to the pump 19. Thus, the pump 19 is located at a level lower than the level of the lower pipe 7 of the generator.

The pump 19 is a suction and discharge pump, the outlet 20 of which discharges into an outlet pipe 21 extended by a drain pipe 22.

The pump 19 is a rotary vane pump, for example as shown schematically in Figure 4 in perspective and in partial section. The intermediate pipe 17 opens into a pump enclosure 23 through an axial orifice 24. The pump comprises rotary vanes such as the pallet 25, rotatably mounted on a drive shaft 26 coaxial with the orifice 24 and the adjacent part of the pipe intermediate 17. The outlet orifice 27 of the pump is disposed radially in the upper part of the enclosure wall 23, as shown in FIG. 4. The rotation of the vanes 25 causes the water to flow back into the outlet pipe 21 .

In FIGS. 1 and 2, the outlet pipe 21 comprises an ascending part from the outlet 20 of the pump 19 to an upper bend 28, and a downward part from the upper bend 28 to the drain pipe 22.

We mark the level B of the upper bend 28 relative to the base plane 29 of the device, as shown in FIGS. 1 and 2. We also mark the level A that the surface of the surface makes, relative to the same base plane 29 water contained in the enclosure 1 by the regulation of the solenoid valve 3 and the probe 14 associated with the electrical treatment device. The level C, relative to the same base plane 29, of the vapor conduction pipe 4 is also identified, or at least the maximum level that this pipe 4 has between the pipe upper 6 and the steam chamber 5.

According to a first embodiment shown in FIG. 1, the steam generator is of the type of fluent steam generator at atmospheric pressure. The water level regulation means maintain inside the enclosure 1 a level close to the level A and substantially constant. It is then advantageous to provide a level B of the upper bend 28 of the outlet pipe 21 which is higher than the level A of the water in the enclosure, but lower than the level C of the steam conductive pipe 4. This produces a double security of the water level: assuming that the water intake solenoid valve 3 remains open despite the level A of the water in enclosure 1 being exceeded, the water can then flow freely through the outlet pipe 21 as far as the drain pipe 22, the vane pump 19 not opposing the circulation of water even when it is not rotating. The maximum level of water then exceeds level A, but should not exceed level B of the upper bend 28 of outlet pipe 21. As a result, the water is not likely to flow through the conduction pipe of steam 4 in the oven use enclosure 5.

By providing a level B of the upper bend 28 of the outlet pipe 21 only slightly higher than the level A of normal regulation of the water level in the enclosure 1, there is a double security for adjusting the water level in the enclosure. 1, if the level B is lower than the level of the upper pipe 6 of the enclosure 1. In fact, assuming a malfunction of the valve 3 which would remain in the open state, the water in the enclosure 1 should not exceed the level B of the upper bend 28, that is to say should remain below the level of the upper pipe 6 of the enclosure 1. In this state, the steam generator can still function properly, and produce steam which is separated from the water in the upper pipe 6 and is evacuated by the steam conduction pipe 4.

In the embodiment shown in FIG. 2, a solenoid valve 30 is interposed in the intermediate pipe 17, and is associated with control means for controlling its closing during the production of steam in the steam generator, and for command its opening during the emptying phase. Others parts of the device are identical to those of the embodiment of FIG. 1. In this case, the level B of the upper elbow 28 can be chosen to be greater, equal or less than the level A of normal regulation of the water in the enclosure 1 It is however preferable to keep an upper bend 28, which avoids the return of liquid which may come from the drain pipe 22.

This embodiment comprising a solenoid valve 30 may also be suitable in the case where the steam generator must produce steam under pressure higher than atmospheric pressure.

In normal operation, the device of the present invention is such that the water level is kept substantially constant and at the intermediate height A in the enclosure 1. The electrical resistors such as the resistor 12 are supplied by an external source d electrical energy, and they heat the tubes 8, 9 and 10 and the water they contain. This water vaporizes and the steam escapes through the upper pipe 6 and the steam conduction pipe 4 into the enclosure 5 for using steam. The evaporation of the water lowers the water level in the enclosure 1, and when the level becomes lower than the level A, the probe 14 emits an electrical signal causing the opening of the solenoid valve 3 and the introduction of water in the lower horizontal pipe 7. When the normal level A is again reached, the probe 14 produces another electrical signal causing the closing of the solenoid valve 3. The device is thus kept in operation as long as one wishes produce steam.

After normal operation, for example at the end of each day, the user orders the start of a draining step, during which the electrical resistors 12 are no longer supplied, the solenoid valve 3 remains closed, and the pump 19 is supplied with electrical energy to cause rotation of the rotary vanes 25. In the embodiments comprising a solenoid valve 30 in the intermediate pipe 17, the solenoid valve 30 must then be open to allow the passage of water in the pipe 17. The pump 19 causes the rapid vortex suction of the water contained in the enclosure 1 and its ejection in the drain pipe 22. After total ejection, the rotation of the pump 19 is stopped, it is closed if necessary, the solenoid valve 30, and the device is ready to admit water again and produce steam.

In the event of overpressures in the steam generator or in the enclosure 5 of an oven, in the embodiment of FIG. 1 not comprising a solenoid valve 30, the overpressure causes the water to flow back through the intermediate pipe 17, via the outlet pipe 21 and the drain pipe 22, thus limiting the overpressure in the enclosure 5 and in the enclosure 1.

Claims (6)

1. Steam generator comprising :

   - a generator enclosure (1) adapted for containing water, means (2, 3) for feeding water into the enclosure (1), a steam conduction duct (4) for feeding the steam produced into a user enclosure (5), means (12) for heating the water contained in the generator enclosure (1) for bringing the water to boiling point and producing steam,

   - a suction and delivery pump (19) whose output (20) discharges into an outlet duct (21) extended by a discharge duct (22),
   characterized in that :

   - an intermediate duct (17) opens at its first end into the lower wall (15) of the steam generator enclosure (1), the intermediate duct (17) being horizontal or descending to its second end (18),

   - the first end of the intermediate duct (17) opens into an orifice (16) disposed in a central zone of the lower wall (15) of the generator enclosure (1),

   - the orifice (16) forms the lowest lower wall portion (15), said lower wall (15) forming a regular flat surface or a surface descending towards said orifice (16),

   - the input of the suction and delivery pump (19) is connected to the second end (18) of the intermediate duct (17).
2. Steam generator as claimed in claim 1, characterized in that the pump (19) is a rotary vane pump (25).
3. Steam generator as claimed in claims 1 or 2, characterized in that the outlet duct (21) rises from the pump (19) as far as an upper bend (28) and then descends from the upper bend (28) to the emptying duct (22).
4. Steam generator as claimed in any of claims 1 to 3, characterized in that :

   - the steam generator is provided with water level regulation means (14, 3) maintaining a substantially constant water level (A) inside the generator enclosure (1),

   - an electrovalve (30) is inserted in the intermediate duct (17), with means for controlling closure of the electrovalve (30) during the production of steam and means for controlling opening of the electrovalve (30) during emptying.
5. Steam generator as claimed in any of claims 1 to 4, characterized in that :

   - the enclosure (1) comprises a horizontal upper duct (6) and a horizontal lower duct (7), said upper (6) and lower (7) ducts being connected together by at least one vertical heating tube (8) and by a vertical return tube (11),

   - the heating means (12) comprise a helically wound electric resistance in contact with the external face of the heating tube (8),

   - the flow orifice (16) is formed in the lower wall of the horizontal lower duct (7).
6. Oven for cooking food, characterized in that it comprises a steam generator and emptying means such as claimed in any of claims 1 to 5.

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