AUTOMATIC REPLENISHMENT METHOD FOR THE TANK OF A STEAM GENERATOR AND DEVICE FOR CARRYING OUT THE METHOD

Abstract: By means of a temperature detector (10), the temperature is measured inside a cell box (3) which is in communication with the tank (1). When the level of liquid inside the cell box reaches a minimum level (LM), the temperature detector (10) is surrounded by steam, the temperature of which is higher with respect to the temperature of the liquid, and enables liquid supply by means (30) for feeding liquid to the cell box (3), thus replenishing the tank up to an operational level (LO), when the liquid enters the cell box, it cools the temperature detector which disables the liquid feeding means (30), cutting off inflow of cold liquid to the cell box (3).

Description: AUTOMATIC REPLENISHMENT METHOD FOR THE TANK OF A STEAM GENERATOR AND DEVICE FOR CARRYING OUT THE METHOD TECHNICAL FIELD The present invention relates to steam generator, in particular for housework, and concerns a method and device for carrying out automatically replenishment of the tanks of the steam generators during normal operation thereof . BACKGROUND ART It is known that, when working, pressure steam generators usually need intermittent supply of certain quantities of vaporisable liquid, that compensates the quantity of liquid taken as steam. This liquid can be water or solvent, such as trichloroethylene, in the case of for dry-cleaning machines . In known generators the liquid that is to be turned into steam is contained inside a tank that is filled up to a predetermined level through a filler or, in bigger models, through an inlet pipe connected with a container or the water system. Inside the tank there are also contained heat generating means, usually including an electric resistance set in direct contact with the liquid for heating thereof up to the temperature necessary to produce steam. The liquid level inside the tank is restored by a replenishment device. This replenishment device includes a float that is linked to a microswitch that is consequently operated as a consequence of the level change. The microswitch, in its turn, controls operation of an electric valve connected with a pipe for feeding liquid from an external source to the tank, thus allowing to restore the necessary level. Reaching of this level causes the microswitch opening, and, consequently, deactivation of the electric valve so that the liquid flow is cut off. Otherwise, there are level control devices formed by a couple of electronic detectors, designed to sense the presence of liquid at a minimum level and a maximum level. The steam generators of the above described examples feature some drawbacks, due, first of all, to the structure and position of the replenishment device. In fact, the float is situated inside the tank, and this results in making difficult any maintenance and possible substitution operations. Moreover, the float is subjected to calcareous encrustations due to the action of water and overheated steam. The same problems occur in the case, in which the level control device includes electronic detectors. This reduces their duration and increases considerably the necessity of periodic maintenance operations as well as power consumption. Moreover, the float indicating the differences in the liquid level needs a minimum quantity of water inside the tank, enough to allow it to be buoyant in every case. Therefore, it is necessary to heat and maintain at the evaporation temperature a quantity of liquid bigger than the quantity strictly needed for steam production. In this way, warming up time is rather long, and the power use is considerable. Furthermore, for float and microswitch best operation a certain gap between the minimum and maximum liquid level is necessary, and this on one hand increases the average liquid quantity to be maintained at the necessary temperature, thus further increasing power consumption, and on the other hand causes discontinuous steam production. DISCLOSURE OF THE INVENTION The object of the present invention is to propose a method for checking and restoring the liquid level in a steam generator that allows tc maintain a small quantity of vaporisable liquid inside the tank, thus reducing power consumption. A further object of the invention is to make a device that performs replenishment operation without any stop in steam production, that is almost in continuous way. Another object of the present invention is to propose a device that carries out the above mentioned method and is simple, easy to install and maintain, very reliable and long-lasting. The above mentioned objects are achieved by means of an automatic replenishment method for the tank of a steam generator with a series of replenishment cycles, in which after liquid is supplied to the tank until it reaches heating means activated for production of steam, each replenishment cycle includes: continuous temperature detection in a cell box situated outside the tank and set into communication therewith; allowing liquid supply to the tank, when liquid reaches a minimum level that causes raise of said temperature inside said cell box filled with steam, over a threshold temperature, by activation of liquid feeding means; cutting off liquid supply to the tank, when liquid reaches an operational level that causes drop of temperature inside the cell box (3) filled with the liquid, under the threshold temperature, by deactivation of the liquid feeding means . The device that carries out the method includes one cell box situated outside the tank and set into communication therewith so as to allow liquid and steam to flow therethrough. Temperature detector means, placed close to the cell box for detection of the temperature of liquid or steam contained therein, activate and deactivate liquid feeding means for restoring the liquid level inside the tank, respectively if said temperature is lower or higher than a threshold temperature. BRIEF DESCRIPTION OF THE DRAWINGS The characteristic features of the present The characteristic features of the present invention are pointed out in the following description with reference to the enclosed drawings, in which: - Fig. 1 shows a schematic perspective view of a steam generator equipped with the device being the subject of the present invention,- - Figs. 2a, 2b and 2c show schematic lateral views of the replenishment device, in subsequent working steps; - Fig. 3 shows a perspective view of a second embodiment of the replenishment device; - Figs. 4a and 4b show a third embodiment of the same device. BEST MODE OF CARRYING OUT THE INVENTION With reference to Figs. 1 and 2a, a tank 1, being a part of the boiler of a steam generator, that is designed to produce steam by heating the vaporisable liquid contained inside the tank. The liquid is heated by suitable heating means, not illustrated since they are known. In Fig. 1 this tank 1 has a parallelepiped shape, however, it is obvious that the tank, for the present invention, can assume any form as much convenient. Moreover, the method and the device being the subject of the present invention can be extended to other machines for steam production, such as solvent distillers used for dry-cleaning. In its upper part, the tank 1 features a supply inlet 5 and a steam outlet 6. The first is designed to receive, when the steam generator is started, a suitable quantity of liquid sufficient to reach an operational level LO inside the tank 1. In bigger steam generators the supply inlet 5 can be substituted for a feeding pipe connected, in a known way, with a container, or directly with the water system. The operational level LO tends to decrease as a consequence of the steam production and subsequent liquid consumption. In the beginning, the level can be very low, just enough to touch the above mentioned heating means. The steam, as it is produced, can flow out of the tank through the steam outlet 6, and reach the apparatus that needs steam for its operation. In the first embodiment, the replenishment device includes a cell box 3, situated outside the tank l in a lateral position with respect thereto. A lower part of the cell box 3, is connected with the same tank l via a lower duct 4a, in a region situated below the minimum liquid level LM. The upper part of the cell box 3 is also connected to the tank 1, but in a region over the operational level LO, via an upper duct 4b. Therefore, due to communicating vessels principle, the cell box 3 can contain steam, or liquid and steam, at a level that in every moment coincides with the level in the tank 1. A temperature detector 10 is connected with the cell box 3. The temperature detector 10 is preferably constituted by a bulb thermostat and is introduced laterally into the cell box 3 in a position approximately intermediate between the operational level LO and the minimum level LM. However, the indicator can be of any commonly known type, e.g. contact or pad thermostat. To the cell box 3, there are also connected means 30 that feed new liquid for restoring the level, from an external liquid source, usually from a suitable container or from the water system. The liquid feeding means 30 includes an electric valve 31, controlled by the temperature detector 10 in order to allow or prevent liquid inlet into the cell box 3 through a feeding pipe 33, via an opening 34 made in the same cell box 3. In the region of the opening 34, there is also provided a check valve 32, aimed at preventing the liquid from flowing back from the cell box 3 to the pipe 33. 6 7 PCMB96/00279 - 7 - The valve is of a known type and has been schematically shown in Figs. 1 and 3, as an example, with its rear extremity stretching out from the outside of the cell box 3 in direction opposite to the electric valve 31 extension. The electric valve 31 referred to in the present description can be also substituted, without invalidating the essence of the invention, for a pump of known type, likewise operated by the temperature detector 10, connected with a liquid container or directly with the water system. In a second embodiment (see Fig.3), beside what has already been described, the tank replenishment device features also timing means 7, including a push-button equipped with a manually operated timer, that opens the electric valve 31, or activates the pump, for a predetermined time, so as to allow a quantity of liquid enough to reach the operational level LO to go into the tank 1. The timing means 7 are usually used, instead of the supply inlet 5, for introduction of liquid into the tank 1 when the steam generator is started. Their position is schematically indicated in Fig. 3, as an example, in the region of the electric valve 31, but it is obvious that they can be placed in any other convenient position. According to a third embodiment of the device, as shown in Figs. 4a and 4b, a thermostat 10 is introduced directly in a recess 8 made in the side of the tank 1, in a position approximately intermediate between the operational level LO and the minimum level LM. A liquid feeding pipe 33 is also provided for supplying refilling liquid in a region near the recess 8, so that the liquid flow laps the same recess 8. 2607 PCMB96/00279 It is to be pointed out that, in the already mentioned figures, the minimum level LM and the difference between the operational level LO and minimum level LM have been deliberately emphasised for sake of clarity. In fact, it is convenient for the minimum level LM to be much lower while for the difference between the two above mentioned levels the best is to be less then the one illustrated. Operation of the steam generator needs a first start up step, during which a quantity of cold liquid sufficient for reaching the operational level LO is introduced into the tank 1 (Fig. 2a) . In the first embodiment of the liquid restoring device, the liquid is introduced manually, through the supply inlet 5; in the second embodiment the liquid is introduced as a consequence of timing means 7 activation (Fig. 3), and can be timed automatically or manually by an operator. In this situation, the heating means inside the tank 1 are not activated yet, therefore the temperature T inside the same tank and the cell box 3, in the region of the thermostat 10, is certainly lower with respect to a threshold temperature TS necessary for thermostat switching, and consequently for the electric valve 31 activation. At this point, the liquid has reached also the cell box 3 through the lower duct 4a, and is over the thermostat 10. Therefore, the above mentioned heating means, which bring the temperature of the liquid inside the tank 1 to a suitable level, are activated in known way so as to begin the production of steam, which is taken out, according to the needs, through the steam outlet 6. The liquid temperature remains substantially constant during the steam production step, and anyway lower with respect to the steam temperature, which can be higher than the threshold temperature TS. The temperature of the liquid in the cell box 3 is always lower with respect to the temperature of the liquid in the tank 1, because of the cell box form and location, as well as of limited thermal exchange with the same tank 1. Nevertheless, the temperature of the liquid in the cell box 3 is lower with respect to the threshold temperature TS that activates the thermostat 10, therefore the electric valve 31 is closed. As has been already stated, the working level LO tends to decrease due to the production and consumption of the steam. When the minimum level LM is reached, the thermostat 10 emerges and is surrounded by the steam. As has been already said, the steam temperature is higher than the liquid temperature and causes the heating of the same thermostat 10, thereby switching it. At this point, the thermostat causes opening of the electric valve 31 that allows the introduction of the cold liquid into the cell box 3, causing the raising of the level in the same cell box, and therefore, also in the tank 1, until the operational level LO is reached again. In this situation, the thermostat 10 is again dipped in the liquid and the temperature T around the same thermostat lowers below the threshold temperature TS. This allows the closure of the electric valve 31 and cut off of the liquid flow to the tank. Inasmuch as the liquid is introduced into the cell box 3 near the thermostat 10, which is directly in contact therewith, the temperature thereof lowers very quickly and the quantity of the liquid introduced into the tank 1 is small, as well as the difference between the operational level LO and the minimum level LM. As a consequence, drop of the temperature inside the tank 1 is limited and the steam production continues in a basically constant way. According to a variant of the proposed method, when the generator is started, only a small quantity of liquid, sufficient for it to touch the heating means without reaching the cell box 3 and the thermostat 10, is introduced into the tank 1. This allows the beginning of the steam production in a very short time. In this case, the thermostat 10 is initially touched by the steam, and the temperature T inside the cell box 3 quickly goes over the threshold temperature TS causing again liquid supply to the region of the thermostat and immediate cooling thereof, and, consequently, the liquid flow is cut off. This causes again a rapid heating of the cell box 3. A series of the above described liquid refilling cycles can gradually raise the operational level LO of the liquid which flows inside the cell box 3, until the thermostat 10 is dipped in the liquid. The replenishment cycles which take place afterwards are identical with the ones previously described, in which the thermostat 10 passes from the situation in which it is immersed in the liquid to the one in which it is touched by the steam. In the third embodiment of the replenishment device, as previously described, the working steps occur in analogous way. Difference consists in that, the cell box 3 is missing and the refill liquid is introduced into the tank 1 so as to touch the recess 8, so that the thermostat 10 detects the level difference directly inside the same tank. The advantages of the present invention derive mainly from the bigger gradualness of introduction of the refill liquid into the tank 1, that allows steam production to be more constant and controlled to a bigger extent. Furthermore, the access to the replenishment device is much easier and maintenance is simpler because all the working means of the same device are located outside the tank 1. Bulb or pad thermostat, or any other possible temperature detector, are more reliable with respect to the floating devices and the feelers used in the known art. Another advantage of the present replenishment method and device is that they permit to hold only a small quantity of liquid inside the tank 1 thus reducing warming up time and, at the same time, power consumption. It is understood that what above has been described as a mere, not limitative example, therefore all possible constructive variants are protected by the present technical solution, as described above and claimed in the following.

Claims: CLAIMS 1. Automatic replenishment method for the tank of a steam generator with a series of replenishment cycles, characterised in that after liquid is supplied to said tank (1) until it reaches heating means activated for production of steam, each replenishment cycle includes operation steps in which-. temperature (T) of a cell box (3) is continuously detected by temperature detector means (10) , said cell box (3) being situated outside said tank (1) and set into communication therewith; liquid supply to said tank (1) is allowed, when liquid reaches a minimum level (LM) that causes raise of said temperature (T) inside said cell box (3), filled with steam, over a threshold temperature (TS) , by activation of liquid feeding means (30) under control of said temperature detector means (10); liquid supply to said tank (1) is cut off, when liquid reaches an operational level (LO) that causes drop of said temperature (T) inside said cell box (3) , filled with liquid, under said threshold temperature (TS) , by deactivation of said liquid feeding means (30) under command of said temperature detector means (10) . 2. Method, according to claim 1, characterised in that, in at least some of said operation steps, said temperature detector means (10) detect situations in which alternatively liquid comes from said tank (1) to said cell box (3) thus causing consequent drop of temperature (T) below the threshold temperature (TS) , and then steam comes from said tank (1) to said cell box (3) , thus causing consequent raise of temperature (T) therein over the above mentioned threshold temperature (TS) . 3. Method, according to claim 1, characterised in that said liquid feeding means (30) introduce liquid into said cell box (3) in a region close to said temperature detector (10) , and in that this liquid flows from said cell box (3) into said tank (1) due to the communication between them. 4. Method, according to claim 1, characterised in that a step in which said steam generator is starting is carried out by manual activation of timing means (7) , aimed at operating said liquid feeding means (30) for a predetermined time sufficient to supply liquid into said tank (1) it reaches a level not higher than said operational level (LO) . 5. Automatic replenishment device for the tank of a steam generator including at least one tank (1) , for producing steam, by heating liquid contained therein, said device being characterised in that it includes: at least one cell box (3), situated outside said tank (1) and set into communication therewith so as to allow liquid and steam to flow therethrough; temperature detector means (10) , placed close to said cell box (3) and aimed at detecting temperature (T) of liquid or steam contained therein, and at activating and deactivating liquid feeding means (30) for restoring the liquid level inside the said tank (1) , respectively if said temperature (T) is lower or higher than a threshold temperature (TS) . 6. Device, according to claim 5, characterised in that said tank (1) and cell box (3) communicate via a lower duct (4a) connecting a lower part of said cell box (3) to said tank (1) in a region below said operational level (LO) , and via an upper duct (4b) connecting an upper part of said cell box (3) to said tank (1) in a region over said operational level (LO) . 7. Device, according to claim 5, characterised in that said temperature detector (10) includes a bulb thermostat. 8. Device, according to claim 5, characterised in that said temperature detector (10) includes a contact or pad thermostat. 9. Device, according to claim 5, characterised in that said liquid feeding means (30) include an electric valve (31) activated by said temperature detector (10) , a duct (33) for introduction, into said tank (1) , of liquid coming from an external source, and a single-acting check valve (32) . 10. Device, according to claim 5, characterised in that said liquid feeding means (30) include a pump (31) , activated by said temperature detector (10) , a duct (33) and a check valve (32) . 11. Device, according to claim 5, characterised in that said liquid feeding means (30) introduce restoring liquid into said cell box (3) in the region of said detector (10) . 12. Device, according to claim 5, characterised in that it includes also manually operated timing means (7) for activating said liquid feeding means (30) for a predetermined time . 13. Automatic replenishment device for the tank of a steam generator including at least one tank (1) , for producing steam, by heating liquid contained therein, said device being characterised in that it includes a temperature detector (10) , situated inside a recess (8) made in a side of said tank (1) , in an intermediate position between an operational level (LO) and a minimum level (LM) for said liquid, and in that it features also means (30) for feeding new liquid from an external source, controlled by said temperature detector (10) so as to introduce restoring liquid directly into said tank (1) , in the region of said temperature detector (10) .

Inventors: FIERRO ALFONSO, FIERRO, ALFONSO
Applicants: FIERRO ALFONSO, FUTURA STEAM S R L, FIERRO, ALFONSO, FUTURA STEAM S.R.L.
Application year: 1996
Main classification: F22B1
IPC codes: F22B1