WO2008077437A1

WO2008077437A1 - Dosing apparatus for dosing a solid detergent composition being conductive in solution

Info

Publication number: WO2008077437A1
Application number: PCT/EP2006/070149
Authority: WO
Inventors: Carola Stingl; Gerold Carlhoff; Heribert Lohwieser; Andreas Ruppert
Original assignee: Ecolab Inc.
Priority date: 2006-12-22
Filing date: 2006-12-22
Publication date: 2008-07-03

Abstract

A dosing apparatus for dosing a soluble but solid composition^) and a corresponding method for dosing is provided, the dosing apparatus comprises at least one box or a box for keeping the solid composition, a solution reservoir(3) for keeping the composition solution(4), at least one spray means (5) for bringing the composition solution into contact with the solid composition being in the box such that an amount of the solid composition dissolves and the thus resulting solution flows into the solution reservoir, a supply line (6) comprising a liquid connection (7) for supplying a liquid, preferably water, to the solution reservoir (3), a discharge line (8), comprising a discharge for discharging the composition solution, a spray line (10) for feeding the spray means with composition solution coming from the solution reservoir, a circulation line coming from the solution reservoir and ending in the solution reservoir for circulating composition solution, means, preferably two level gauges (12, 13), for measuring the filling height in the solution reservoir, measuring means <14)for measuring the conductivity of the composition solution, at least one motorised feed pump (15) for moving the composition solution.

Description

DOSING APPARATUS FOR DOSING A SOLID DETERGENT COMPOSITION

BEING CONDUCTIVE IN SOLUTION

Description

TECHNICAL FIELD

[0001] The present invention relates to a dosing apparatus for dosing a soluble but solid composition, the composition being conductive in solution, and a method for dosing a soluble but solid composition using said dosing apparatus.

BACKGROUND ART

[0002] A solid composition concentrate which can be brought into solution, for example, for cleaning purposes in a washing machine or the like has, compared to corresponding liquid compositions concentrates, the advantage that normally the concentration of the active components is much higher than the concentration of said active components in a corresponding liquid composition, since the amount of solvent is reduced or the solvent can even be avoided at all. This has the advantage that the solid composition, i.e. a solid detergent composition, saves volume and weight with respect to storage and transportation capacities.

[0003] However, such solid compositions need to be brought into solution in order to use them, for example, in a cleaning process. Devices and methods for the generation of liquid detergent concentrates from solid detergent compositions are well known in the state of the art.

[0004] The US 2002/01472124 A1 , for example, describes a device for generating a liquid detergent concentrate from a solid detergent, wherein the device includes a solid detergent reservoir for holding a solid detergent, a stock solution reservoir for holding a stock solution, and a hot-water heater for controlling the temperature of water used to generate the stock solution from the solid detergent. The device further provides a nuzzle for directing hot water against the exposed surface of a block of a solid detergent and the thus generated stock solutions are collected in a reservoir. According to the US 2002/0147124 A1 the concentration of the stock solution can be maintained at a relatively constant level for a given solid detergent composition by controlling the distance between the nuzzle and the exposed surface of the block detergent, the area of the exposed surface, the temperature of the water flow, the pressure of the water flow against the exposed su r- face, the duration of application of the water flow against the exposed surface, the volume of the capsule and the opening sizes provided by a certain support member. By controlling these parameters to specific values it is believed according to the US 2002/0147124 A1 that the concentration of the stock solution will remain relatively constant for a particular solid detergent composition.

[0005] The US patent 5,137,694 discloses a cleaning system and dispenser which feature a reservoir for retaining a liquid detergent solution, a chamber for retaining a solid dissolvable detergent, a measurement device for measuring the concentration of detergent in the liquid detergent solution, and a flow control device for circulating the liquid detergent solution from the reservoir into contact with the solid detergent so as to dissolve a portion of the solid detergent and increase the concentration of detergent in the liquid detergent solution. In order to achieve a liquid detergent solution having a pre-determined concentration the dispenser according to US 5,173,694 provides a circulation of the liquid detergent solution which is dependent on a response signal from the concentration measuring device so that the concentration of the detergent in the liquid detergent solution does not fall below a pre-determined minimum. Said dispenser also includes a measurement device for measuring the volume of solution in the reservoir and for adding fresh water to the reservoir when the volume of solution is below the predetermined minimum. The dispenser also includes a flow control apparatus for dispensing a solution from the reservoir to the use point. [0006] However, even if the cleaning system and dispenser according to US

5,137,694 provides certain features in order to automatically obtain and maintain a constant aqueous detergent solution, there remain a few draw-backs if the dispenser is to be used in applications where the concentration of the dissolved solid composition is more critical, as for example in medical applications, such as cleaning of medical devices.

[0007] Therefore, there is a need for a dosing device, which is capable for automatically dissolving the soluble but solid composition in such a manner that a solution can be provided by said dosing device which has a constant level of a pre-determined concentration of an active component.

[0008] Hence it is the object of the present invention to provide an improved dosing device for dosing a soluble but solid composition with respect to the automatic maintenance of a pre-determined concentration of active compounds of the composition. A further object of the present invention is to provide a dosing device which fulfils the requirements of applications in the medical field. A further object of the present invention is to provide a method for dosing a soluble but solid composition which comprises the use of the dosing device according to the present invention.

DESCRIPTION OF THE INVENTION

[0009] The present invention solves the above-mentioned problem by means of a dosing apparatus for dosing a soluble but solid composition having the features of claim 1 and by means of a method for dosing a soluble but solid composition having the features of claim 11. Preferred embodiments of said dosing apparatus and said method are the subject matter of further dependent claims.

[0010] "Solid composition" in the sense of the present application means any composition not being liquid or fluent but having a firm or solid constitution, - A -

including, for example, powders or formed blocks of the composition in any kind of shapes, preferably with little or no hollow spaces within the block. Also included are pastes or gels having a viscosity of above 20000 mPas.

[0011] In a general aspect of the invention the dosing apparatus for dosing a soluble but solid composition comprises at least one box or a box for keeping the solid composition, a solution reservoir for keeping the composition solution, at least one spray means for bringing the composition solution into contact with the solid composition being in the box such that an amount of the solid composition dissolves and the thus resulting solution flows into the solution reservoir, a supply line comprising a liquid connection for supplying a liquid, preferably water, to the solution reservoir, a discharge line, comprising a discharge for discharging the composition solution, a spray line for feeding the spray means with composition solution coming from the solution reservoir, a circulation line coming from the solution reservoir and ending in the solution reservoir for circulating composition solu- tion, means, preferably two level gauges, for measuring the filling height in the solution reservoir, measuring means for measuring the conductivity of the composition solution, at least one motorised feed pump for moving the composition solution through the discharge line, the spray line and/or the circulation line, and an electronic control unit for controlling the operation of the dosing apparatus. The solid composition which is brought into solution by the dosing apparatus is a composition being conductive in solution.

[0012] The above described dosing apparatus allows to provide and maintain a solution having a pre-determined concentration of a soluble but solid composition. The dosing apparatus according to the present invention has a few ad- vantages over similar devices according to the state of the art. For example, one advantage is that the solid composition kept in the box can be brought into solution using the solution which already contains the dissolved composition thereby avoiding the necessity of using fresh water as it is necessary with most of the dosing devices according to the state of the art. Using the composition solution for dis- solving the solid composition allows it to obtain a more concentrated composition solution than if only using a pure liquid, i.e. fresh water, to dissolve the solid composition.

[0013] Another advantage of the dosing apparatus according to the invention is that the concentration of the composition solution can be exactly determined by measuring the conductivity of the composition solution other than controlling the concentration by means of, for example, the temperature, the pressure and/or the duration of the application of a water flow against the exposed surface of a solid composition as is it necessary in similar devices according to the state of the art.

[0014] A further important advantage of the present dosing apparatus is that the composition solution kept in the solution reservoir can be circulated through the circulation line thereby providing a balanced concentration of the compounds throughout the composition solution.

[0015] In a further aspect of the invention the supply line of the dosing apparatus comprises a flow control element, e.g. a solenoid valve, and optionally a flow regulator and/or a backflow preventer. The flow control element is connected to the electronic control unit which controls the operation of the flow control element which regulates, for example, the amount of water or other liquids which are supplied to the solution reservoir. The liquid connection of the supply line is in a preferred embodiment of the invention a fresh water connection.

[0016] In another preferred embodiment of the invention the discharge line of the dosing apparatus further comprises a flow control element, e.g. a solenoid valve, and, optionally, a non-return valve. The flow control element of the discharge line is preferably also connected to the electronic control unit which controls the operation of said flow control element, thereby regulating, for example, the amount of composition solution which is provided at the discharge, i.e. at the use point. The discharge line, the supply line as well as the spray line, preferably comprise flow control elements which are correspondingly connected with and controlled by the electronic control unit.

[0017] In a particularly preferred embodiment of the invention the measuring means for measuring the conductivity of the composition solution is comprised within the circulation line. The placement of the measuring means within the circulation line has the advantage that the measuring means are in contact with the feed of the composition solution rather than with the stagnant solution. This avoids erroneous measurements which may occur due to local concentration differences in the stagnant composition solution kept in the solution reservoir. Furthermore, since the measuring means is in contact with the electronic control unit it is possible to calculate continuously a mean value of the conductivity of the composition solution going through the circulation line. The thus obtained mean value of conductivity is considered to represent more exactly the actual concentration of the composition solution compared to a conductivity value measured only at a local place within the solution reservoir.

[0018] Furthermore, in a preferred embodiment of the dosing the measuring means are placed in the circulation line in such a manner that during work of the dosing apparatus the measuring means can never be out of contact with the composition solution. This means that the measuring means are placed in a height which is below the lowest possible filling height of the composition solution in the solution reservoir.

[0019] In a further aspect of the invention the dosing apparatus further comprises a drain line comprising a drain connection and optionally a drain tap. The drain tap is preferably not connected to the electronic control unit but can be oper- ated manually. The drain line may be useful if the dosing apparatus needs to be cleaned, serviced or repaired and the remaining composition solution needs to be removed from the dosing apparatus without being dependent on electricity or a correct operating of the dosing apparatus. [0020] In a further particularly preferred embodiment of the invention the spray line, the circulation line and/or the drain line of the dosing apparatus is/are connected to the discharge line via one or more branches. This allows it to construct the dosing apparatus in a space-saving manner because certain feeding lines share parts of the feeding lines with each other. Another advantage of such a construction is that it is possible to have only one motorised feed pump for moving composition solution to the discharge line, the spray line and the circulation line instead of the need of having a motorised feed pump for each of said feed lines. In case none of the discharge line, the spray line and/or the circulation line should have its own motorised feed pump there is a need to provide additional flow control elements within the respective feed lines in order to allow a correct operation of the dosing apparatus. In case the dosing apparatus is constructed according to this preferred embodiment the flow control element and the one or more motorised feed pumps have to be controlled by the electronic control unit which is connected to said flow control elements and the motorised feed pump or pumps.

[0021] In a further aspect of the invention the box of the dosing apparatus comprises a lid with a magnet. In this embodiment the dosing apparatus further comprises a magnetic switch being under control of the electronic control unit. These construction features are security features which allow it, for instance, to stop the operation of the dosing apparatus by switching off the feed pumps and/or closing the flow control elements in case the lid of the box is not properly closed, provided the electronic control unit is adequately programmed.

[0022] In another aspect of the invention the box of the dosing apparatus is suited to keep a capsule filled with the solid composition in such way that the spray means can spray the composition solution against the exposed surface of the solid composition and the resulting - more concentrated - solution can flow back into the solution reservoir. To facilitate the handling of the solid composition it is preferred that this solid composition is kept in a storable and transportable capsule, the capsule preferably having a removable lid so that the solid composition can easily be transferred to the dosing apparatus by merely removing the lid and placing the capsule upside down within the box. However, this requires of course that the solid composition within the capsule has a consistence which prevents the solid composition from falling out of the capsule. Therefore, the solid composition within the capsule, e.g. in form of a powder or a paste, is preferably in a pressed or in a form having such a high viscosity that the composition cannot flow out of the capsule.

[0023] In a further embodiment the solid composition is not in a capsule but in the form of a massive block being wrapped with or packed in any kind of foil, e.g. polymer or metal foil, or paper. In these embodiments the block of the solid composition has to be unwrapped or unpacked before it is placed within the box of the dosing apparatus.

[0024] In a further aspect of the invention means can be provided within the box, for example a switch, which registers whether a solid compositions capsule is placed within the box or not. In case there is no solid composition capsule placed within said box the electronic control unit could be programmed in such way that the operating of the dosing apparatus is prevented.

[0025] The present invention further provides a method for dosing a solid but soluble composition. Said method comprises the steps of: a) placing the solid composition or the capsule containing the solid composition into the box of the above-described dosing apparatus, b) adding a pre-determined amount of liquid via the supply line to the solution reservoir, c) spraying the liquid taken from the solution reservoir by means of the spray line onto the solid composition so that an amount of the solid composition dissolves and the thus resulting solution flows back into the solution reservoir, the spraying is performed for a pre-determined time or until a pre-determined concentration of composition solution in the solution reservoir is reached, d) continuously or discontinuously circulating the composition solution through the circulation line, thereby measuring the conductivity of the composition solution with the measuring means, and e) discharging at least a portion of the composition solution via the discharge line to a use point. [0026] In a preferred embodiment of the method according to the invention the amount of the liquid added via the supply line to the solution reservoir is controlled by the upper level gauge. This level gauge is connected with the electronic control unit. The step of adding liquid via the supply line to the solution reservoir is either necessary when beginning with the operation of the dosing apparatus and no solution is within the solution reservoir or in case that during operation of the dosing apparatus a certain amount of the composition solution is removed from the dosing apparatus, i.e. discharged at the use point. Therefore, the method according to the present invention may also comprise the step that after discharging the solved composition via the discharge line or the drain line, the solution reservoir is re-filled with liquid via the supply line.

[0027] In one aspect of the method according to the invention the moment of re-filling and the amount of re-filled liquid is controlled by two level gauges, i.e. an upper and a lower level gauge. For example, in a typical embodiment of the invention 1 -10 litres, preferably 2-6 litres, more preferably 3-5 litres, e.g. 4 litres of composition solution are discharged at the use point, thereby the filling height of the solution within the solution reservoir reaches the lower level gauge. The level gauge sends this information to the electronic control unit which internally regulates the adding of new liquid via the supply line to the solution reservoir by, for example, opening the corresponding flow control element. In a typical operation procedure said flow control element is being closed by the electronic control unit when the filling height of the composition solution within the solution reservoir reaches the upper level gauge. In order to then increase the concentration of the composition within the composition solution the electronic control unit typically makes the spray means work while at the same time the option of discharging the composition solution via the discharge line is temporarily suspended until the predetermined concentration of the composition solution is reached again.

[0028] In accordance to a preferred embodiment of the method according to the invention the step of circulating the composition solution is performed periodi- cally for a certain time in the case that the spray line and the discharge line are kept closed. The circulation than make sure that the concentration of the composition solution is kept uniformly. In a typical embodiment the circulation is performed every 10 to 30 minutes for a duration of 3 to 10 minutes in the case that the spray line and the discharge line are not in use.

[0029] In another embodiment of the method of the present invention also more than one motorised feed pumps can be comprised within the dosing apparatus so that the steps of moving the respective liquids through the supply line, the spray line, the discharge line, the drain line and/or the circulation line is performed by more than one motorised feed pump, e.g. one motorised feed pump for each one of the above mentioned feed lines.

[0030] As apparent from the above the method for dosing the soluble but solid composition, is preferably performed in such a way that the added amount of liquid via the supply line, the time for spraying the liquid via the spray line onto the solid composition, the time of circulating the composition solution through the cir- culation line, the amount of discharged composition solution via the discharge line, the work of the two level gauges, the work of the measuring means and/or the work of the one or more motorised feed pumps are controlled by the electronic control unit. This allows an automated procedure for dosing the soluble but solid composition, wherein the person performing the method, for example, merely needs to decide which concentration the composition solution he wants to draw from the discharge should have.

[0031] In a certain aspect of the invention, the solid composition which is used together with the above described dosing apparatus or the corresponding method comprises a surfactant, selected form the group comprising non-ionic, anionic and amphoteric surfactants or mixtures thereof. Preferred surfactants are non-ionic surfactants. [0032] The solid composition used within the present invention may further comprise one or more basic compounds selected from the group comprising hydroxides, amines, ammonia, alkalimetals, oxides, silikates and the like.

[0033] In an alternative embodiment of the invention the solid composition comprises one or more acids selected from the group comprising inorganic and/or organic acids or mixtures thereof. Examples of such acids are citric acid, phosphoric acid, phosphonous acid, lactic acid and peracetic acid.

[0034] In a further embodiment of the invention the solid composition further comprises a complexing agent, such as a polyacrylic acid, nitrilotriacetat, methyl- glycine diacetic acid (MGDA) and/or phosphates.

[0035] Further compounds of the solid composition used within the present invention may comprise corrosion inhibitors, such as sodium silicate, defoaming agents such as silicon defoamer, paraffin wax defoamer and/or hexylenglycol, and/or further agents like disinfecting agent, preservatives, enzymes and/or bleaching agents.

[0036] In a further embodiment of the invention the solid composition may also comprise water in order to regulate the viscosity of the composition which typically is of interest for the consistency of the solid composition, which may be filled into a capsule or, in another embodiment may not be filled in a capsule. In a particularly preferred embodiment of the invention the consistency of the solid composition, if kept in a capsule, is such that on the one side the capsule can be put upside down into the box of the dosing apparatus and that on the other side the dissolution of the solid composition is performed in an appropriate time and manner when liquid is sprayed with the spray means onto the surface of the solid composition placed in the capsule. [0037] In a typical embodiment of the invention the solid composition comprises a) 15 to 25 wt.-% of a silicate, preferably sodium silicate SiO2/NaO2 1 :1 , b) 1 to 5 wt.-% of an alkali hydroxide, preferably sodium hydroxide, c) 1 to 5 wt.-% of a polyacrylic acid, d) up to 1 wt.-5 of a non-ionic surfactant, e) up to 1 wt.-% of a defoaming agent, preferably silicon/paraffin wax, f) 30 to 50 wt.-% of nitrolotriace- tate or methylglycine diacetic acid, and g) 100 wt.-% of water.

[0038] The solid composition to be used within the present invention preferably has a conductivity in solution of 30 to 300 mS/cm at 20 ⁰C if the composition solution has a concentration of 15 to 40 wt.-% in water, e.g. 20 wt.-% in water. In a more preferred embodiments of the invention the above defined conductivity is 40 to 200 mS/cm, 50 to 150 mS/cm, 60 to 100 mS/cm, and most preferred 70 to 90 mS/cm.

[0039] In a further preferred embodiment of the invention the rate of dissolving of the solid composition in water is 200 g/l at 20 ⁰C under stirring within up to 40 minutes, preferably within up to 30 minutes, more preferred within up to 20 minutes and most preferred within up to 10 minutes. The rate of dissolving is determined as follows: 20 g of solid composition was given into a beaker filled with 100 ml of tab water (20 ⁰C). The solution was stirred with a magnetic stirrer at approx. 800 rpm. The time was documented when the solid composition was dis- solved completely.

DESCRIPTION OF THE FIGURES

[0040] Figure 1 shows schematically the dosing apparatus according to the present invention.

[0041] Fig. 2 shows a perspective view of one actual embodiment of the dosing apparatus of the present invention. [0042] The dosing apparatus shown in Fig. 1 is a preferred embodiment of the present invention. Fig. 1 indicates a mounting plate 32 on which most of the devices of the dosing system are mounted. Within the dosing system a supply line 6 is leading from a liquid connection 7 to an infeed point 33 located at or in the solution reservoir 3. The liquid feed, preferably water, is controlled by a flow control element 17 which is electronically controlled to an electronic control unit 16. The supply line 6 further comprises a backflow preventer 19 and a flow regulator 18. The backflow preventer 19 prevents any flow of liquid backwards from the solution reservoir 3 towards the liquid connection 7. This is safety mechanism nec- essary to keep any composition solution out of the original liquid supply. Further, within the dosing system a box 2 is indicated keeping a capsule 31 containing a solid composition 1. The box 2 has an opening closable with a lid 28, the lid having a magnet 29. Further, a magnetic switch 30 is under control of the electronic control unit 16. The box 2 has a further opening at its bottom and a colander 36. The colander 36 is to prevent the solid composition 1 or other objects from falling into the solution reservoir 3. Furthermore a line 8/10/11 is leading to a first branch 26. The line 8/10/11 comprises a motorised feed pump 15. The pump 15 is electrically connected to the electronic control unit 16. The line 8/10/11 is coming from a sump 35 of the solution reservoir 3 so that a total drain of the solution reservoir 3 is pos- sible if necessary. From the first branch 26 a drain line 23 leads to a drain connection 24 while the drain line 23 further comprises a drain tap 25. The drain line 23 is normally closed but can be opened for service purposes or the like when all the solution has to be drained off without being dependent on electricity or correctly operating dosing apparatus. From the first branch 26 a line is leading to a second branch 27 from which a discharge line 8 is leading to a discharge 9. The discharge line 8 further comprises a flow control element 20 and a non -return valve 21. The flow control element 20 is electronically connected to the electronic control unit 16 and controls the amount of solution which can be discharged via the discharge line 8. The non-return valve 21 is to prevent backflow of discharged solution from the discharge 9 into the discharge line 8. Further, a circulation line 11 is leading from the second branch 27 to a circulation outlet 34 which is located within the solution reservoir 3. The circulation line 11 further comprises a measuring means 14 which is electrically connected to the electronic control unit 16. The measuring means 14 is to measure the conductivity of the composition solution circulating through the circulation line 11 and is to provide the electronic control unit 16 with the measured data so that the electronic control unit 16 can control the operation of the dosing apparatus. Further, a spray line 10 is leading from the second branch 27 to a spray means 5 which is located in the box 2 above the colander 36. The spray line 10 comprises a flow control element 22 which is electronically connected to the electronic control unit 16. The flow control element 22 controls the solution feed within the spray line 10 and, consequently, the operation of the spray means 5. Finally, the dosing apparatus in Fig. 1 comprises an upper level gauge 12 and a lower level gauge 13 which are located at the solution reservoir 3 and which are both electrically connected to the electronic control unit 16. The level gauges 12 and 13 are intended to provide the electronic control unit 16 with information about the filling height of the composition solution 4 within the solution reservoir 3 so that the electronic control unit 16 can control the operation of, for example, the flow control element 17 of the supply line 6 and of the flow control element 20 of the discharge line 8.

LIST OF REFERENCE SIGNS

(1) solid composition

(2) box

(3) solution reservoir

(4) composition solution

(5) spray means

(6) supply line

(7) liquid connection

(8) discharge line

(9) discharge

(10) spray line

(11 ) circulation line

(12) upper level gauge (13) lower level gauge

(14) measuring means

(15) motorized feed pump

(16) electronic control unit (17) flow control element of the supply line

(18) flow regulator

(19) backflow preventer

(20) flow control element of the discharge line

(21 ) non-return valve (22) flow control element of the spray line

(23) drain line

(24) drain connection

(25) drain tap

(26) first branch (27) second branch

(28) lid of the box

(29) magnet of the lid

(30) magnetic switch

(31 ) capsule for the solid composition (32) mounting plate

(33) infeed point

(34) circulation outlet

(35) sump of the solution reservoir

(36) colander of the box

Claims

1. Dosing apparatus for dosing a soluble but solid composition (1 ), the composition being conductive in solution, comprising: a) at least one box (2) for keeping the solid composition (1 ), 5 b) a solution reservoir (3) for keeping the composition solution (4), c) at least one spray means (5) for bringing the composition solution (4) into contact with the solid composition (1 ) being in the box (2) such that an amount of the solid composition (1 ) dissolves and the thus resulting solution flows into the solution reservoir (3), io d) a supply line (6) comprising a liquid connection (7) for supplying a liquid, preferably water, to the solution reservoir (3), e) a discharge line (8) comprising a discharge (9) for discharging the composition solution (4), f) a spray line (10) for feeding the spray means (5) with the composition so- i5 lution (4) coming from the solution reservoir (3), g) a circulation line (11 ) coming from the solution reservoir (3) and ending in the solution reservoir (3) for circulating the composition solution (4), h) means, preferably at least two level gauges (12, 13), for measuring the filling height in the solution reservoir (3), 20 i) measuring means (14) for measuring the conductivity of the composition solution (4), j) at least one motorized feed pump (15) for moving the composition solution (4) through the discharge line (8), the spray line (10) and/or the circulation line (11 ), and

25 k) an electronic control unit (16) for controlling the operation of the dosing apparatus.

2. The dosing apparatus according to claim 1 , wherein the supply line (6) further comprises a flow control element (17) and, optionally, a flow regulator (18)

30 and/or a backflow preventer (19).

3. The dosing apparatus according to any of the preceding claims, wherein the discharge line (8) further comprises a flow control element (20) and, optionally, a non-return valve (21 ).

4. The dosing apparatus according to any of the preceding claims, wherein the spray line (10) further comprises a flow control element (22).

5. The dosing apparatus according to any of the preceding claims, wherein the measuring means (14) for measuring the conductivity is comprised within the circulation line (11 ).

6. The dosing apparatus according to any of the preceding claims, wherein the dosing apparatus further comprises an drain line (23) comprising an drain connection (24) and, optionally, an drain tap (25).

7. The dosing apparatus according to any of the preceding claims, wherein the spray line (10), the circulation line (11 ) and/or the drain line (23) is/are connected to the discharge line (8) via one or more branches (26, 27).

8. The dosing apparatus according to claim 7, wherein the dosing apparatus comprises the flow control elements (20, 22) and only one motorized feed pump (15) for moving the composition solution (4) through the discharge line (8), the spray line (10) and the circulation line (11), wherein the feed direction is controlled by the electronic control unit (16) and the flow control elements (20, 22).

9. The dosing apparatus according to any of the preceding claims, wherein the box (2) comprises a lid (28) with a magnet (29) and the dosing apparatus further comprises a magnetic switch (30) being under control of the electronic control unit (16).

10. The dosing apparatus according to any of the preceding claims, wherein the box (2) is capable for keeping a capsule (31 ) containing the solid composition (1) in that way that the spray means (5) is capable for bringing the composition solution (4) into contact with the solid composition (1 ) and that the result- ing solution can flow into the solution reservoir (3).

11. A method for dosing a soluble but solid composition (1 ), comprising the steps of: a) placing the solid composition (1 ) or the capsule (31 ) containing the solid composition (1 ) into the box (2) of the dosing apparatus according to any of the claims 1 to 10, b) adding a pre-determined amount of liquid via the supply line (6) to the solution reservoir (3), c) spraying the liquid taken from the solution reservoir (3) via the spray line (10) onto the solid composition (1 ) such that an amount of the solid composition (1) dissolves and the thus resulting solution flows back into the solution reservoir (3), the spraying is performed for a pre-determined time or until a pre-determined concentration of the composition solution (4) in the solution reservoir (3) is reached, d) continuously or discontinuously circulating the composition solution (4) via the circulation line (11), thereby measuring the conductivity of the composition solution (4) with the measuring means (14), and e) discharging at least a portion of the composition solution (4) via the discharge line (8) to a use point.

12. The method according to claim 11 , wherein the amount of liquid added via the supply line (6) to the solution reservoir (3) is controlled by the upper level gauge (12).

13. The method according to claim 11 or 12, wherein after discharging of at least a portion of the composition solution (4) via the discharge line (8) or the drain line (23) the solution reservoir (3) is refilled with liquid via the supply line (6).

14. The method according to claim 13, wherein the moment of refilling and the amount of refilled liquid is controlled by the two level gauges (12, 13).

15. The method according to any of the claims 11 to 14, wherein one or more motorized feed pumps (15) move the respective liquids through the supply line (6), the spray line (10), the discharge line (8), the drain line (23) and/or the circulation line (11 ).

16. The method according to any of the claims 11 to 15, wherein the added amount of liquid via the supply line (6), the time for spraying the liquid via the spray line (10) onto the solid composition (1 ), the time of circulating the composition solution (4) through the circulation line (11 ), the amount of discharged composition solution (4) via the discharge line (8), the work of the two level gauges (12, 13), the work of the measuring means (14) and/or the work of the one or more motorized feed pumps (15) are controlled by the electronic control unit (16).

17. The dosing apparatus or the method for dosing according to any of the pre- ceding claims, wherein the solid composition (1 ), being conductive in solution, comprises a surfactant selected from the group comprising non-ionic, anionic and amphoteric surfactants or mixtures thereof.

18. The dosing apparatus or the method for dosing according to claim 17, wherein the solid composition (1 ) further comprises a basic compound selected from the group comprising hydroxides, amins, ammonia, basic metal oxides and the like.

19. The dosing apparatus or the method for dosing according to claim 17, wherein the solid composition (1 ) further comprises an acid selected from the group comprising inorganic and organic acids or mixtures thereof.

20. The dosing apparatus or the method for dosing according to any of the preceding claims, wherein the solid composition (1 ) further comprises a com- plexing agent, such as polyacrylic acids and/or nitrilotriacetat.

21. The dosing apparatus or the method for dosing according to any of the preceding claims, wherein the solid composition (1 ) further comprises a corrosion inhibitor, such as sodium silicate.

22. The dosing apparatus or the method for dosing according to any of the pre- ceding claims, wherein the solid composition (1 ) further comprises a defoam- ing agent, such as silicone and/or paraffin.

23. The dosing apparatus or the method for dosing according to any of the preceding claims, wherein the solid composition (1 ) further comprises water.

24. The dosing apparatus or the method for dosing according to any of the claims 1 to 16, wherein the solid composition (1 ) comprises: a) 15 to 25 wt. -% of a silicate, preferably sodium silicate Siθ2/Naθ2 1 :1 , b) 1 to 5 wt.-% of an alkali hydroxide, preferably sodium hydroxide, c) 1 to 5 wt.-% of a polyacrylic acid, d) up to 1 wt.-% of a non-ionic surfactant, e) up to 1 wt.-% of a defoaming agent, preferably silicone/paraffin, f) 30 to 50 wt. -% of a nitrilotriacetat or methylglycine diacetic acid, and g) add to 100 wt.-% of water.

25. The dosing apparatus or the method for dosing according to any of the preceding claims, wherein the conductivity of the composition solution (4) is 30 to 300 mS/cm at 20 ⁰C if the composition solution (4) has a concentration of 15 to 40 wt. -% in water.

26. The dosing apparatus or the method for dosing according to claim 25, wherein the conductivity is 40 to 200 mS/cm, preferably 50 to 150 mS/cm, more preferably 60 to 100 mS/cm, and most preferably 70 to 90 mS/cm.

27. The dosing apparatus or the method for dosing according to any of the claims 1 to 24, wherein the rate of dissolving of a massive block of the solid composition (1 ) in water is 200g/l at 20 ⁰C under stirring within up to 40 minutes, preferably within up to 30 minutes, and most preferably within up to 20 minutes.

28. The dosing apparatus or the method for dosing according to any of the claims 1 to 24, wherein the rate of dissolving of a massive block of the solid composition (1 ) in water is 200g/l at 20 ⁰C under stirring within up to 40 minutes, preferably within up to 30 minutes, most preferably within up to 20 minutes, and the conductivity of the composition solution (4) is 40 to 200 mS/cm, preferably 50 to 150 mS/cm, more preferably 60 to 100 mS/cm, and most preferably 70 to 90 mS/cm at 20 ⁰C if the composition solution (4) has a concentration of 20 wt. -% in water.