WO2008129119A1

WO2008129119A1 - Steam generator, method for operating a steam generator and a vessel of a steam generator

Info

Publication number: WO2008129119A1
Application number: PCT/FI2008/050185
Authority: WO
Inventors: Pertti Harvia
Original assignee: Pertti Harvia
Priority date: 2007-04-19
Filing date: 2008-04-14
Publication date: 2008-10-30
Also published as: EP2140199A1; WO2008129119A9; EP2140199A4

Abstract

The invention relates to a steam generator (10), which includes a cast-metal tank (11) equipped with connections (19', 20') and a cover (27), for the liquid to be vaporized, the cast part of which tank includes the bottom (24) and at least part of the side walls (23.1, 23.2) of the tank, and into the bottom (24) of which tank heating resistances (12.1, 12.2) for vaporizing the liquid, are cast. Heating resistances are cast additionally into the side walls of the tank, in such a way that they are arranged to extend into the area (A) of variation of the liquid surface (P1, P2) and the cover is arranged to form a side wall of the tank. In addition, the invention relates to a method for operating a steam generator and a vessel of a steam generator.

Description

Steam generator, method for operating a steam generator and a vessel of a steam generator

The present invention relates to a steam generator, which includes a tank of cast metal, equipped with a cover, for the liquid to be vaporized, the cast part of which tank includes the bottom and at least part of the side walls, and on the bottom of which tank there are cast heating resistances for vaporizing the liquid. In addition, the invention relates to a method for operating a steam generator and a vessel of a steam generator .

Various kinds of steam generators for steam-rooms and bathrooms intended for leisure use are known from the prior art. Liquid is vaporized in the tank of the generator and the steam thus formed is led to a normal-pressure steam-room. Vaporization takes place using electrical resistances belonging to the generator .

Known generators, however, suffer from several weaknesses. Various kinds of tube-resistance generators are known. These, however, have the drawbacks of noisiness and a tendency for the tube resistances to burn out. The tube resistances, which are in contact with the water being vaporized, collect a calcium layer on their surface, which tends to only thicken over time. As a result of this, the calcium layer forms an effective thermal insulator, which results in the resistances overheating and even burning out .

New liquid must be continuously fed to the generator to replace the liquid that has left as steam. There are also great difficulties associated with the reliable measurement of the amount of liquid in the generator at any time. One known method is to arrange elements, such as low-voltage rod electrodes, that measure that surface level in the tank. A change in the elec- trical conductivity of the rod indicates the surface level in the tank at the time. The rods too have a tendency to collect a calcium layer on their surface, which leads to uncertainty and disturbances in the measurement of the surface level.

Further, the addition of liquid to known generators creates a shock effect. This leads to the boiling of the liquid being stopped as if by a ^vwall', and it takes a little time before the boiling starts again. In addition, large bubbles collect in the tube resistances. When the tank is filled, cold water is led directly into the bubbling water already in the tank. That results in a sudden cessation of the bubbling and the 'collapse' of the surface of the liquid. The drop in surface level leads to the electrical surface-level guard 'losing' the sur- face level of the liquid. In addition, during filling the guard may not necessarily react with appropriate speed to the refilling, and overfilling of the tank may result. The feed of the liquid too may disturb the reliable operation of the surface-level guard.

There are weaknesses even in the arrangement of the overheating protection of known generators. In these, the overheating protection may be fitted directly to the resistances. A drop in the level of the liquid will result in the upper parts of the resistance being exposed, leading to their possible burning out.

Some references concerning the prior art are disclosed in UK patent GB 2 384 293 A and European patent application EP 0 807 428 A. A third generator according to the prior art is disclosed in an internet reference [I]. UK patent 642,858 discloses an electrically heated tank for heating and melting substances. However, such a tank with a removable cover is not suitable for steam-generator use, because it does not have, for example, means for measuring the surface level reliably. In addition, the resistances fitted in connection with the tank and the manner of arranging them in the tank do not permit efficient heat transfer to the tank structures.

A universal sensor element, in which there is a through opening for leading liquid into the generator and two blind holes for a low-power heating resistance and a temperature sensor, is known from PCT application publication WO - 2005/024300 A2. The amount of liquid in the tank at any time can be measured by the sensor for the temperature of the element, which is heated using a low-power resistance in the body. In addition, the liquid being led into the tank is preheated using the resistance in the body.

A steam generator, in which measurement of the amount of liquid in the tank from the temperature of the tank is applied, is known from EP patent application publication 1 221 570 A2. In this case too, a certain part of the tank is heated using a special resistance, which is essentially separate from the heating resistances evaporating the actual liquid.

The steam generators according to the prior art become complex, because in them the temperature of the measurement point, from which the amount of liquid in the tank is measured, is acted on by a special resistance fitted for this purpose to the tank structures, which requires its own electrical input and control and thus forms a construction complicating the implementation of the steam generator.

The present invention is intended to create an improved steam generator, a method for operating a steam generator, and further also a vessel for of a steam generator. The characteristic features of the steam generator according to the invention are stated in Claim 1 and those of the method in Claim 11. The characteristic features of the vessel of the steam generator are stated in Claim 17. Several important advantages are gained with the aid of the steam generator according to the invention. Firstly, the use of resistances cast into the bottom, which is at least partly of cast metal, and, in addition, also in the side walls of the tank, creates a heating effect directed to the liquid that is considerably widely distributed and thus the transfer of heat to the tank and to the liquid to be evaporated in it is particularly efficient. The boiling created by the generator is in all ways gentle and silent, compared to devices according to the prior art. The silence of the generator is an important advantage in terms of its operator comfort. According to one embodiment, the resistances cast into the side walls of the tank can extend into the zone of variation of the liquid level.

According to one embodiment, the surface level of the liquid can be, surprisingly, monitored by means of sensor means fitted outside the generator. Surprisingly, the sensor means can be arranged to measure the amount of liquid in the tank from above the liquid surface. The means can be formed of temperature sensors. By monitoring the temperature of the cast piece, i.e. the tank, the amount of liquid in the generator at any time can be determined with certainty and a possible lack of liquid avoided. The temperature of the tank, from which the amount of liquid is measured, is affected by the heating resistances integrated in the tank. This substantially simplifies the implementation of the generator and the control of its operation. According to one embodiment, there can be heat-transfer structures in the tank of the generator. According to one embodiment, the measurement of temperature, for example for measuring the surface level, can take place at the locations in the tank corresponding to the heat-transfer structures.

The generator and the surface-level measurement arranged in it are also more tolerant of calcification, which now cannot cause, for example, thermal transmission / surface-level measurement problems, as can happen in known generators. In addi- tion, except for the liquid and vapour connections, the tank can be essentially closed. This removes the need for various kinds of seals, for example, for the corresponding resistance and sensor feed-throughs . This brings, in turn, an obvious advantage in manufacturing technique.

The other features characteristic to the invention appear in the accompanying Claims while other advantages achieved by the invention are referred to more in the description portion.

The steam generator, method, and vessel of a steam generator according to the invention, which the embodiments described hereinafter in no way restrict, are examined in greater detail with reference to the accompanying drawings, in which

Figure 1 shows one example of the generator according to the invention, without the front wall, seen at an angle from in front,

Figure 2 shows a front view of the generator according to Figure 1,

Figure 3 shows the generator according to Figure 1, seen at angle from the rear,

Figure 4 shows a cross-sectional side view of the generator according to the invention, Figure 5 shows a flow diagram of an example of the method according to the invention, and

Figure 6 shows a cross-section of one example of the construction of a resistance cast into the generator, and

Figure 7 shows an example of a generator, in which the cover is formed by a second vessel.

Figures 1 - 4 show one example of a generator 10 according to the invention and its tank 11, seen from different directions. In the figures, the generator 10 is shown in the vertical position in which it is at the point of use. The steam generator 10 is intended mainly for the continuous creation of steam, for example, in steam saunas, steam rooms, and steam cabinets, being of a non-pressurized type, i.e. an ('open' ) type that operates mainly at normal pressure.

5 The steam generator 10 includes a tank 11, which is at least partly of cast metal and has a cover 27, equipped with connections 19', 20', for example, for a liquid substance, and heating resistances 12.1, 12.2 fitted in the tank 11 for evaporating the liquid that is led in. In addition, the steam generator

10 10 includes sensor means 21 for measuring the amount of liquid that is in the tank 11 at any time, and an overheating protection sensor, which can be external and thus in contact, for example, with the aluminium vessel 26. Thus the overheating protector has time to react if the level of the water suddenly

15 drops and the heating resistances 12.1, 12.2 will not have time to burn out .

The tank 11 is formed, for example, of an aluminium diecast vessel component 26, which is open at one side. Other materials 0 too, such as various metal alloys, may be considered. The open side can be equipped with holes 16 and a flange 28, equipped with a sealing groove / (silicon) gasket 17, to which a cover 27 (Figure 2) that tightly closes the vessel 26 and then forms the side wall of the tank 11, can be attached. The shape of the 5 cross-section of the tank 11 can narrow upwards and can have a slightly rounded construction. The narrowing is now achieved by a step, a ^vback part' 14. The height H of the tank 11 is greater than its width W. The ratio of these dimensions is effective in terms of both steam generation and also the arrangement of 0 the heating resistances 12.1, 12.2. The lower spaces, with a broader cross-section delimited by side walls 23.1, 23.2, can also be referred to as a boiling / vaporization chamber 11' and takes up most of the internal space of the tank 11. The height of the chamber 11 ' corresponds to most of the height of the 5 entire generator 10. Correspondingly, the upper space, which has a narrower cross-section than the lower vaporization cham- ber 11', can be referred to as a vaporization chamber or a steam separator 11*. The vaporization chamber 11 * also acts as an effective droplet eliminator.

The connections 19', 20' shown by way of example in Figure 1 can be, for example, in the cover 27 in such a way that they are in the area of the vapour chamber 11 ' . The connections can include at least one inlet connection 20' and at least one outlet connection 19 '. A pipe connected to the water mains network, by means of which water / other possible agents for vaporization is/are led to the generator 10, is attached to the inlet connection 20'. One possible example of other agents are scent-producing substances. Of course, there can also be a dedicated connection for scent-producing substances, or for other purposes. There can be a magnetic valve 22 in the water pipe, for controlling the flow of water being led into the tank 11 (Figure 3) .

A steam pipe 19 (with an internal diameter of 20 mm, for exam- pie) is connected to the outlet connection 19'. In Figure 4, the steam pipe 19 is in the upper part of the tank 11. The opposite end of it can be attached to the steam connection of the steam room, to which it is intended to lead the steam. The generator 10 can thus be installed outside the room where the steam is used, or even inside the room where the steam is used.

The heating resistances 12.1, 12.2 of the generator 10 are surprisingly, for example, entirely cast into the tank 11. Thus the tank resistances 12.1, 12.2 can be integrated in a diecast aluminium tank 11, for example, in its outermost side walls 23.1, 23.2 of cast metal that define the tank chamber 11' and additionally in the cast-metal bottom 24 of the tank 11. The generator 10 is then examined in its operating position. As can be seen from Figure 2, the heating resistances 12.1 integrated by casting in the protrusions 15.1, 15.2 in the casting of the opposite side walls 23.1, 23.2 extend at least partly into the area A of variation of the liquid surface P₁, P₂. In the area A, the variation of the liquid surface level changes in such a way that it drops through the evaporation of the liquid performed by the heating resistances 12.1, 12.2 and rises through the addition of liquid to the tank 11. Besides, or instead of casting the resistances 12.1, 12.2 into the jacket 23.1, 23.2, 24 of the tank 11, another way to arrange the resistances can be to arrange ribbed-plate shapes, into which a resistance can be cast (not shown), oriented facing into the tank 11, for example, inside the tank 11. Relating to this, aluminium is one example of a suitable material, which offers good thermal conductivity and thus also efficient heat transfer from the resistances 12.1, 12.2 cast into the base structures of the tank 11 (into the vessel component 26) to the liquid being vaporized. The surface thermal output of the resistances of the generator 10 (for example, about 10 W/cm²) is considerable compared to that of a traditional sauna stove (for example, about 3,2 W/cm²). By fitting the resistances 12.1 to the outer jacket 23.1, 23.2 of the evaporation chamber 11', the heat is very well distributed to the entire cast tank 11 and thus the temperature of the tank 11 correlates very well with the amount of water in it at any time. The use of cast-in resistances 12.1, 12.2 also achieves the advantage that now the heat created by the resistances 12.1, 12.2 can be stored better in the aluminium tank structures 26.

Pilot-stage tests of the generator have shown that cold water led into the tank 11 reduces the heat from 130 - 140⁰C to about 100⁰C. Thus, the boiling does not stop immediately, but instead becomes temporarily slightly less violent / subsides evenly / gently and then returns to its original level very quickly. The resistances 12.1, 12.2 themselves are practically unable to store heat, but now through their integration with the tank 11, the thermal storage capability of the generator 10 improves substantially. In the embodiment shown in the figures, there are three resistances, but their number / location / manner of connection can vary greatly. For the resistances 12.1, 12.2, there is a comb-like internal cast-material layer 15.1 - 15.3, which rises inwards from the basic jacket structure of the actual walls 23.1, 23.2, and bottom 24 of tank 11, on the side walls 23.1, 23.2 of the tank 11. Thus, the part of the casting 15.1 - 15.3 reserved for the resistances 12.1, 12.2 is three-dimensionally as if it were inside the liquid. The formations 15.1 - 15.3 can follow the path of the resistances 12.1, 12.2. Now each resistance 12.1, 12.2 can form in the tank 11 its own totality that winds (zig-zags) back and forwards like a comb, in which there is one resistance for each wall 23.1, 23.2, 24. It should be noted that in the embodiment shown in the figures there are visible resistances 12.1 and 12.2. The wall 23.1 is also equipped with its own resistance, which does not appear in Figures 1 - 4 due to the manner in which they are shown.

The resistances 12.1, 12.2 can also be connected in series. The dimensioning of the resistances 12.1, 12.2 can be selected appropriately, for example, according to the capacity of the tank 11. It is possible to use resistances of differing sizes. The ends of the resistances 12.1, 12.2 protrude from the rear part of the cast tank 11, in which there is the necessary equipment 18 for electrical connections. The spiral resistance wire 29 can start only from inside the casting 11, for example, at a distance of 5 - 10 mm from the outer surface of the casting 11, from which the ends of the resistances 12.1, 12.2 protrude from the casting 11. The control electronics of the resistances 12.1, 12.2 can be, as such, known (not shown).

In the embodiment shown, there is also a heat-transfer structure 13 in the upper part of the evaporation chamber 11 ' inside the tank 11. The surface-level guard totality 21, which mea- sures the surface level of the liquid in contact with the tank 11 at any time, is now surprisingly arranged in a heat-transfer connection with the structure 13. Stated more generally, the sensor means 21 can be fitted to the outer surface 14 of the tank 11, for example, at a location corresponding to the heat-transfer structure 13, thus being in the area of influence of the structure 13. In this case, the heat-transfer structure is formed of a ribbed construction 13 (in this case, seven ribs at a distance to each other) , which are also a permanent formation in the cast piece, in other words part of the casting. The row of ribs 13 is in the back formation 14 of the tank 11. In addition, the ribs 13 can be in the upper part 11' of the evaporation chamber II¹ the tank 11, above the resistances 12.1, 12.2.

The sensor means 21 are used to measure the amount of liquid in the tank 11 at any time, surprisingly from the temperature of the tank 11, particularly of its cast piece (vessel) 26, which the heating resistances 12.1, 12.2 mainly affect. The sensor means 21 are arranged to measure the amount of liquid in the tank 11, surprisingly from above the liquid level P₁, P₂ (Fig- ure 2) in the tank 11. Because the resistances 12.1 cast into the side walls, 23.1, 23.2 extend into the area A of variation of the liquid surface P₁, P₂, the part of the heating resistances 12.1 in the side walls 23.1, 23.2, by means of which the liquid in the tank 11 is heated, above the falling / fallen liquid surface then heat the tank structure 11 considerably because it then extends to the dry inner surface-area of the tank 11. The increase in the temperature of the tank 11 that this causes is used to indicate the surface level of the liquid, which can be detected using a sensor 21 above the liquid surface P₁, P₂.

Even more particularly, the temperature of the back part 14 of the vessel 26 rises when the surface level of the liquid in the tank 11 drops sufficiently as a result of evaporation. The sensor means 21 can be formed, for example, of one or more temperature sensors 21, which are connected to a measurement/control circuit 23. Their location is shown schematically in Figure 3. Now the sensors 21 in their entirety and, in addition the resistances 12.1 of the side walls 23.1, 23.2, or the formations 15.1, 15.3 arranged for them in the casting 11, are at least partly above the dropped water surface, in the area of the back part 14 of the tank. Also surprising in this case is the fact that the liquid surface level of the tank 11, i.e. the amount of liquid, can be measured from outside the tank 11, without contact relative to the liquid in the tank 11. The advantage of using external sensors 21 is that they do not deteriorate over time, as will happen due to the calcification of sensors inside the tank 11 in direct contact with the liquid.

In the embodiment shown, piping 20, more generally a liquid distribution element, is connected inside the tank 11 to the inlet connection 20'. Using this, it is possible to guide / direct the liquid flow led inside the tank 11 directly to the back part 14 and even more particularly to its heat-transfer structure 13. The cold water flow brought to the tank 11 through the inlet connection 20' immediately cools the back part 14 of the tank and the row of ribs 13. On the other hand, the possibly cool water will also preheat when it strikes the hot row of ribs 13. Thus, the effect of water introduced to the tank 11 on the boiling level is more controlled. The piping 20 can, according to one embodiment, be formed of a branched arrangement, so that the liquid can be sprayed more broadly onto the rib structure 13 than when only a single outlet is used. Thus the row of ribs 13 cools more evenly and rapidly over the entire area of the tank rear 14.

According to one embodiment, a separation element 25 (Figures 2 and 4) can also be arranged between the heat-transfer structure 13 and the tank component 11 ' equipped with the resistance means 12.1, 12.2. It can be formed, for example, of a planar piece, a separator plate. One task of the shield 25 is to eliminate the possible shock effect on the generator 10 of the liquid led into it from the connection 20' , and particularly on the boiling liquid associated with the resistances 12.1, 12.2 in its lower part 11'. Another task of the shield 25 is to isolate the boiling and bubbling liquid in the vaporization chamber 11' equipped with the resistances 12.1, 12.2 from splashing onto the row of ribs 13 , which might otherwise interfere with the surface-level measurement performed from the temperature of the tank 11. The separator plate 25 can be mainly in the area of the ribs 13, in which case it will not extend horizontally as far as the cover component 27 or to the rear wall of the tank 11 opposite to the cover component 27. In other words, despite the separator plate 25, the liquid can reach the vaporization chamber 11' and the generated steam can correspondingly reach the upper vaporization chamber 11* and then the steam connection 19 ' , through which it exits the generator 10.

Yet another advantage, for example, in a tank 11 cast from aluminium is that the calcium that enters the tank 11 along with the water and accumulates in it can even be detached from the aluminium tank 11. The different (greater) thermal expansion properties of aluminium compared to calcium mean that when the temperature drops possible calcium will detach in lumps from the internal surfaces of the tank 11. The lumps can be easily removed during servicing of the generator, for example, through the detachable cover 27. Because most of the internal surface of the vessel 26 now forms a heat-transfer surface, not even a local calcium layer on some point of the internal sur- face of the vessel 26 will cause problems. Heat can still be transferred efficiently to the liquid being vaporized from some other point in the vessel 26.

The resistances 12.1, 12.2 cast into the tank 11 can be, for example, as such, known industrial tube resistances integrated in the casting. One example of the cross-sectional diameter of such industrial Standard resistances can be 3 - 15 mm, such as 5 - 10 mm, for example 6 mm, 8 mm, or 8,5 mm. The material thickness of the comb-like cast formation 15.1 - 15.3, inside which the resistances 12.1, 12.2 are according to one embodi- ment, can be for example 7 - 20 mm ( a 2 - 6-mm cast layer between the resistance 12.1, 12.2 and the internal spaces of the tank 11) .

Figure 6 shows a cross-section of one example of the construc- tion of a resistance 12.1, 12.2. The construction of the resistance 12.1, 12.2 can be, for example, such that a spiral resistance wire 29, for example, is inside a resistance tube 30 or similar outer jacket. The wire 29 is surrounded by a filler agent 31 in a solid form acting as an insulator. The filler 31 can be, for example, magnesium oxide powder. The powder 31 is a poor thermal conductor, but nevertheless better than only air, for example.

One industrial way to manufacture such resistances 12.1, 12.2 is to fill a tube 30 of a diameter of, for example, 10 mm, with a resistance wire 29 and magnesium oxide 31. After filling, the tube 30 is plugged at both ends and is vibrated to compact the oxide powder 31 around the spiral wire 29. After vibration, the tube 30 can be milled to a diameter of 8,5 mm, for example. Other industrial methods of implementing resistances, which are not intended to be changed afterwards, or even to be partly removed from the casting 11, will also be obvious to one skilled in the art.

Even the same sensor totality that is used to measure the temperature of the tank 11, which indicates the surface level of the water, can act as an overheating sensor. On the other hand, the overheating sensor can also be a dedicated sensor, which is nevertheless in contact with, for example, the alu- minium jacket 26 of the tank 11. It should be understood that the figures show neither a possible protective jacket of the generator 10 nor other accessories that may belong to it (for example, an emptying pump, etc.) .

Figure 5 shows a flow chart of one rough example of an applica- tion of the sub-stages of the method according to the invention for operating a steam generator 10. In stage 500, the generator

10 is switched on. Stage 500 can include startup operations that are, as such known, for example prefilling the tank 11 with a safe amount of water according to a setting, if the tank has been emptied after its previous use.

As stage 501, liquid is vaporized using resistance means 12.1, 12.2 cast into the tank 11, which is at least partly of cast metal, and is led to the point of use of the steam, for exam- pie, a sauna, room, cabinet, or corresponding leisure room. The liquid is vaporized by resistances 12.1, 12.2, at least part of which extend into the area A of variation of the liquid surface P₁, P₂. These heating resistances 12.1 extending into the area A are in the side walls 23.1, 23.2 of the tank 11. A criterion value, on the basis of which the power supply to the resistances is regulated, is set for the heating. The temperature of the steam room is compared to the criterion value and on its basis the resistances 12.1, 12.2 of the generator 10 are controlled. In stage 502, the amount of liquid in the tank 11, i.e. the surface level at any time is measured from the temperature T of the tank 11, which is affected mainly by the heating resistances 12.1, 12.2 evaporating the liquid. The measurement is performed using a sensor 21 surprisingly above the liquid surface P₁, P₂ in the tank 11. On the basis of the temperature measurement, it is surprisingly possible to control the feed of liquid to the tank 11. In stage 503, a check is made as to whether the temperature T of the tank 11 exceeds the criterion value T_n^_x set for it. Exceeding the value indicates a drop in the water surface to below the minimum surface P₂ set for it (Figure 2) . If on the basis of the measurement it is seen that the temperature has been exceeded, as stage 504 a set additional amount of water is poured into the tank 11, when the surface level of the water will rise to the level P₁ (Figure 2) . In other words, adding liquid to the tank 11 is started when a criterion according to a setting is met, with reference to the temperature of the tank 11. As a result' of this, the temperature of the tank 11 drops slightly, but then starts once again to rise rapidly when the resistances 12.1, 12.2 perform the controlled heating of the added water. The generator 10 according to the invention is characterized by a rapid periodicity. This ensures that the generator 10 does not cool excessively and also that its operation is silent.

According to one embodiment, the liquid led into the tank 11 can, for its part, be used to cool the tank structures 13, 14. More particularly, it is possible to cool, for example, the structures through which the amount of liquid in the tank 11 is measured, for example, the ribbing 13 and/or the rear area 14 of the tank 11, which ribbing 13 is arranged on the inside of the tank 11. Of course, the amount of water to be fed can, on the other hand, also be controlled on the basis of the cooling of the row ribs 13, if this is possible. The heating process 501 continues as its own loop and the determining of the sur- face level 502 - 504 as its own loop.

As can be seen from Figure 7 , according to one embodiment the cover that tightly closes the side wall of the tank 11 can be formed, instead of a flat plate, also of a second tank 11.2. In that case, the tanks 11, 11.2 will be against each other on their open sides. The connection 19 can be used to lead the steam out and the connection 19 ' surprisingly to lead the liquid in. In that case, there can be an extension into the tank part 11.2, which distributes the liquid to the heat-transferring structures of both tanks, for example. By means of the embodiment, the liquid capacity of the generator can be easily doubled and, for instance, a 9 kW generator can be easily obtained. Of course, other ways of increasing the output of the generator 10 are also possible (increasing the number / size of the resistances) .

Though the invention is described above by describing the steam generator 10 as a totality, it is nevertheless obvious that the invention concerns equally the vessel 26 of cast metal, into the walls of which the resistances 12.1 - 12.3 are cast.

It must be understood that the above description and the related figures are only intended to illustrate the present invention. The invention is thus in no way restricted to only the embodiments disclosed or stated in the Claims, but many different variations and adaptations of the invention, which are possible within the scope on the inventive idea defined in the accompanying Claims, will be obvious to one skilled in the art.

REFERENCE:

[1] MrSteam: http: //www.mrsteam. com/support/steamhomeiom.pdf

Claims

1. Steam generator (10), which includes a cast-metal tank (11) equipped with connections (19', 20') and a cover (27), for the liquid to be vaporized, the cast part of which tank (11) includes the bottom (24) and at least part of the side walls (23.1, 23.2) of the tank (11), and into the bottom (24) of which tank (11) heating resistances (12.1, 12.2) for vaporizing the liquid, are cast, characterized in that - the heating resistances (12.1, 12.2) are cast additionally into the side walls (23.1, 23.2) of the tank (11), in such a way that they are arranged to extend into the area (A) of variation of the liquid surface (P₁ , P₂) and - the cover (27) is arranged to form a side wall of the tank (11) .

2. Steam generator (10) according to Claim 1, characterized in that the height (H) of the tank (11) is greater than its width (W) .

3. Steam generator (10) according to Claim 1 or 2 , characterized in that an evaporation chamber (H'), to which the said heating resistances (12.1, 12.2) are fitted, and a steam sepa- rator (H¹) are fitted to the tank (11).

4. Steam generator (10) according to any of Claims 1 - 3, characterized in that the steam generator (10) includes in addition sensor means (21) for measuring the amount of liquid in the tank (11) at any time, which sensor means (21) are arranged to measure the amount of liquid in the tank (11) from the temperature of the tank (11) , which is mainly affected by the heating resistances (12.1, 12.2) arranged to evaporate the liquid.

5. Steam generator (10) according to Claim 4, characterized in that the sensor means (21) are arranged to measure the amount of liquid in the tank (11), from above the liquid surface (P₁, P₂ ⁾-

6. Steam generator (10) according to any of Claims 1 - 5, characterized in that inside the tank (11) there is a heat-transfer structure (13) , at a point corresponding to which the sensor means (21) are arranged on the outer surface (14) of the tank (11) .

7. Steam generator (10) according to Claim 6, characterized in that the heat-transfer structure (13) is above the resistances (12.1, 12.2) in the tank (11).

8. Steam generator (10) according to Claim 6 or 7 , characterized in that the said connections include at least one inlet connection (19'), through which the liquid introduced to the tank (11) is arranged to be directed to the heat-transfer structure (13) .

9. Steam generator (10) according to any of Claims 6 - 8, characterized in that a separator element (25) is fitted to the tank (11), in order to at least partially separate from each other at least partly the heat-transfer structure (13) and the evaporation chamber (II¹) of the tank (11) equipped with resistance means (12.1, 12.2).

10. Steam generator (10) according to any of Claims 1 - 8, characterized in that the cover (27) is arranged to be formed by another tank (11.2) and which tanks (11, 11.2) are arranged against each other on their open sides.

11. Method for using a steam generator (10), in which

- in a tank (11), the bottom (24) of which and at least part of the side walls (23.1, 23.2) of which are of cast metal, a liquid is vaporized by means of heating resistances (12.1, 12.2) integrated in the cast metal,

- the amount of liquid in the tank (11) at any time is measured from the temperature of the tank (11) , and

- on the basis of the measurement additional liquid is led to the tank (11), characterized in that

- the amount of liquid in the tank (11) is measured from the temperature of the tank (11) , which is mainly affected by the heating resistances (12.1, 12.2) evaporating the liquid.

12. Method according to Claim 11, characterized in that the liquid led into the tank (11) is used to cool the tank structures (13, 14), from which the amount of liquid in the tank (11) is measured.

13. Method according to Claim 11 or 12, characterized in that the amount of liquid in the tank (11) is measured from above the liquid surface (P₁, P₂) .

14. Method according to any of Claims 11 - 13, characterized in that the liquid is vaporized by means of heating resistances (12.1, 12.2), at least part of which is arranged to extent into the area (A) of variation of the liquid surface (P₁, P₂) .

15. Method according to any of Claims 11 - 14, characterized in that the feed of the liquid into the tank (10) is controlled on the basis of the said temperature measurement.

16. Method according to Claim 15, characterized in that the feed of the liquid into the tank (11) is started when a criterion according to a setting, concerning the temperature of the tank (11) , is met.

17. Vessel (26) for a steam generator (10), the bottom (24) and at least part of the side walls (23.1, 23.2) of which vessel (26) are of cast metal, and which vessel (26) includes heating resistances (12.1, 12.2) for vaporizing the liquid, part of which is cast into the bottom (24) of the vessel (26) , characterized in that the heating resistances (12.1, 12.2) are cast, in addition, into the side walls (23.1, 23.2) of the vessel (26) , and the vessel (26) is open on one side.