CONVEYOR DISHWASHER AND METHOD FOR OPERATING A CONVEYOR DISHWASHER

Abstract

A conveyor dishwasher (2) having a final rinse zone (18) and at least one wash zone (12, 14, 16, 18) and also a conveyor apparatus for conveying washware through the treatment zones of the conveyor dishwasher (2), wherein the wash zone (12, 14, 16, 18) has an associated wash tank (32, 34, 36) in which at least a portion of the wash liquid which is sprayed in the at least one wash zone (12, 14, 16, 18) is collected. The conveyor dishwasher (2) includes a wastewater pump (61) for supplying wash liquid, which is produced as wastewater during operation of the conveyor dishwasher (2), as required to a heat exchanger device (60) in which at least a portion of the thermal energy of the supplied wash liquid is transferred to the final rinse liquid which is to be sprayed in the final rinse zone (18).

Claims

1. Conveyor dishwasher (2) having a final rinse zone (18) and at least one wash zone (12, 14, 16, 18) and also a conveyor apparatus for conveying washware through the treatment zones of the conveyor dishwasher (2), wherein the at least one wash zone (12, 14, 16, 18) has an associated wash tank (32, 34, 36) in which at least a portion of the wash liquid which is sprayed in the at least one wash zone (12, 14, 16, 18) is collected, characterized in that the conveyor dishwasher (2) has a wastewater pump (61) for supplying wash liquid, which is produced as wastewater during operation of the conveyor dishwasher (2), as required to a heat exchanger device (60) in which at least a portion of the thermal energy of the supplied wash liquid is transferred to the final rinse liquid which is to be sprayed in the final rinse zone (18), and in that the conveyor dishwasher (2) has a control device (50) which is designed to drive the wastewater pump (61) depending on a quantity of final rinse liquid which is currently required for final rinsing and/or a quantity of wastewater which is produced during operation of the conveyor dishwasher (2) and/or depending on a liquid level in the wash tank (32, 34, 36) and/or depending on a predefined event and/or depending on an operating cycle and/or operating state of the conveyor dishwasher (2).

2. Conveyor dishwasher (2) according to claim 1, wherein the control device (50) is designed to switch off the wastewater pump (61) automatically when the liquid level in the wash tank (32, 34, 36) falls below a predefined or predefinable first level, and to switch on the wastewater pump (61) automatically as soon as the liquid level in the wash tank (32, 34, 36) exceeds a predefined or predefinable second level, wherein the first level corresponds to the second level.

3. Conveyor dishwasher (2) according to claim 1, wherein the control device (50) is designed to initiate, as required, hot water treatment, which is independent of the heat exchanger device (60), of the final rinse liquid which is to be sprayed in the final rinse zone (18), specifically in particular when: i) the thermal energy which is transferred to the final rinse liquid, which is to be sprayed in the final rinse zone (18), in the heat exchanger device (60) is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature; and/or ii) no wash liquid is supplied to the heat exchanger device (60); and/or iii) the quantity of wash liquid which is supplied to the heat exchanger device (60) per unit time is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature.

4. Conveyor dishwasher (2) according to claim 1, wherein the conveyor dishwasher (2) has a boiler (9, 65) for heating, as required, the final rinse liquid which is to be sprayed in the final rinse zone (18), wherein the control device (50) is designed to activate the boiler (9, 65) when: i) the thermal energy which is transferred to the final rinse liquid, which is to be sprayed in the final rinse zone (18), in the heat exchanger device (60) is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature; and/or ii) no wash liquid is supplied to the heat exchanger device (60); and/or iii) the quantity of wash liquid which is supplied to the heat exchanger device (60) per unit time is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature.

5. Conveyor dishwasher (2) according to claim 4, wherein the boiler (9, 65) is designed to heat up the final rinse liquid which is to be sprayed in the final rinse zone (18) to a predefined or predefinable minimum temperature using electrical energy, steam, a heat pump, gas or hot water.

6. Conveyor dishwasher (2) according to claim 1, wherein an external boiler is provided, the conveyor dishwasher (2) forming or being able to form a flow connection with the said external boiler by means of a hot water connection (66), for supplying, as required, hot water as the final rinse liquid which is to be sprayed in the final rinse zone (18), wherein the control device (50) is designed to activate the hot water connection (66) when: i) the thermal energy which is transferred to the final rinse liquid, which is to be sprayed in the final rinse zone (18), in the heat exchanger device (60) is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature; and/or ii) no wash liquid is supplied to the heat exchanger device (60); and/or iii) the quantity of wash liquid which is supplied to the heat exchanger device (60) per unit time is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature.

7. Conveyor dishwasher (2) according to claim 1, wherein the conveyor dishwasher (2) has a wash system which is associated with the at least one wash zone (12, 14, 16, 18) and has at least one wash pump (33, 35, 45) and wash nozzles (26, 28, 30), wherein wash liquid from the wash tank (32, 34, 36) can be supplied to the wash nozzles (26, 28, 30) with the aid of the at least one wash pump (33, 35, 45), and wherein the wash liquid which is sprayed in the at least one wash zone (12, 14, 16, 18) by the wash nozzles (26, 28, 30) at least partially flows back into the wash tank (32, 34, 36) again due to gravity.

8. Conveyor dishwasher (2) according to claim 7, wherein the intake end of the wastewater pump (61) forms a direct flow connection with the wash tank (32, 34, 36).

9. Conveyor dishwasher (2) according to claim 7, wherein the conveyor dishwasher (2) has an auxiliary tank (67) which forms a flow connection with the wash tank (32, 34, 36) in particular by means of an overflow (68) or by means of a bypass line, wherein the intake end of the wastewater pump (61) forms a direct flow connection with the auxiliary tank (67).

10. Conveyor dishwasher (2) according to claim 9, wherein the wash tank (32, 34, 36) has a capacity of 20 to 200 litres, and the auxiliary tank (67) has a capacity of 10 to 50 litres.

11. Conveyor dishwasher (2) according to claim 1, wherein the conveyor dishwasher (2) further has a wastewater line (62) which forms or is able to form a flow connection with a wastewater system (63) and by means of which the wash liquid is discharged after the wash liquid has first passed the heat exchanger device (60).

12. Conveyor dishwasher (2) according to claim 1, wherein the heat exchanger device (60) has at least one counterflow heat exchanger.

13. Method for operating a conveyor dishwasher (2), in particular a conveyor dishwasher (2) according to claim 1, wherein at least a portion of the wash liquid which is produced as wastewater is at least temporarily supplied to a heat exchanger device (60) in which at least a portion of the thermal energy of the supplied wash liquid is transferred to the final rinse liquid which is to be sprayed in a final rinse zone (18) of the conveyor dishwasher (2).

14. Method according to claim 13, wherein the wash liquid is supplied as wastewater to a wastewater system (63) after passing the heat exchanger device (60).

15. Method according to claim 13, wherein the wash liquid is supplied to the heat exchanger device (60) cyclically and/or depending on a liquid level in the wash tank (32, 34, 36).

16. Method according to claim 13, wherein, when no wash liquid is supplied to the heat exchanger device (60) and/or when the thermal energy which is transferred to the quantity of final rinse liquid, which is to be sprayed in the final rinse zone (18), in the heat exchanger device (60) is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature, a boiler (9, 65) which operates independently of the heat exchanger device (60) is activated.

17. A conveyor dishwasher having a final rinse zone and at least one wash zone and a conveyor apparatus for conveying washware through treatment zones of the conveyor dishwasher, wherein the wash zone has an associated wash tank in which at least a portion of a wash liquid which is sprayed in the wash zone is collected, wherein the conveyor dishwasher includes a wastewater pump for supplying wash liquid, which is produced as wastewater during operation of the conveyor dishwasher, to a heat exchanger device in which at least a portion of the thermal energy of the supplied wash liquid is transferred to the final rinse liquid which is to be sprayed in the final rinse zone, and the conveyor dishwasher has a control device which is designed to drive the wastewater pump depending on (i) a quantity of final rinse liquid which is required for final rinsing and/or (ii) a quantity of wastewater which is produced during operation of the conveyor dishwasher and/or (iii) a liquid level in the wash tank (32, 34, 36) and/or (iv) occurrence of a predefined event and/or (v) an operating cycle and/or operating state of the conveyor dishwasher.

18. The conveyor dishwasher of claim 1, wherein the control device is designed to switch off the wastewater pump automatically when the liquid level in the wash tank falls below a predefined or predefinable first level, and to switch on the wastewater pump automatically as soon as the liquid level in the wash tank exceeds a predefined or predefinable second level.

19. The conveyor dishwasher of claim 2, wherein the control device is designed to initiate hot water treatment, which is independent of the heat exchanger device, of the final rinse liquid which is to be sprayed in the final rinse zone when: i) the thermal energy which is transferred to the final rinse liquid, which is to be sprayed in the final rinse zone, in the heat exchanger device is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature; and/or ii) no wash liquid is supplied to the heat exchanger device; and/or iii) the quantity of wash liquid which is supplied to the heat exchanger device per unit time is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 shows schematically a dishwasher which is designed in the form of a conveyor dishwasher, for the purpose of explaining the general construction and functioning;

[0040] FIG. 2 shows schematically a wash zone of an exemplary embodiment of the dishwasher according to the invention; and

[0041] FIG. 3 shows schematically a wash zone of a further exemplary embodiment of the conveyor dishwasher according to the invention.

DETAILED DESCRIPTION

[0042] FIG. 1 shows a conveyor dishwasher 2 having a conveyor apparatus 4 for conveying washware (not illustrated) in a direction 8 of conveying through the conveyor dishwasher 2. The conveyor dishwasher 2 has at least one wash zone, for example as illustrated in FIG. 1, a pre-wash zone 12 and a main wash zone 14 which is arranged after the pre-wash zone 12, as seen in the direction 8 of conveying.

[0043] As seen in the direction 8 of conveying, after the at least one wash zone 12, 14 there is arranged an post-wash zone 16, and after the post-wash zone 16 there is arranged at least one final rinse zone, for example as illustrated only a single final rinse zone 18. In the conveyor dishwasher 2 that is illustrated schematically in FIG. 1, adjoining the final rinse zone 18, as seen in the direction 8 of conveying the washware, is a drying zone 40. The respective zones 12, 14, 16, 18, 40 of the conveyor dishwasher 2 may be separated from one another by means of parting curtains 47.

[0044] In the embodiment which is illustrated schematically in FIG. 1, the entry tunnel 10 is also itself separated from the entry 11 by means of a parting curtain 47. By providing the parting curtains 47, overspray of wash liquid and final rinse liquid and the emergence of vapor from the conveyor dishwasher 2 are prevented.

[0045] Associated with the said treatment zones 12, 14, 16, 18 of the conveyor dishwasher 2 are spray nozzles 20, 22, 24, 26, 28, 30. These spray nozzles 20, 22, 24, 26, 28, 30 serve to spray liquid onto the washware as the latter is conveyed through the respective treatment zones 12, 14, 16, 18 by the conveyor apparatus 4. The individual spray systems of the treatment zones 12, 14, 16, 18 ensure that the washware to be treated is sprayed from both the upper side and the underside.

[0046] In the conveyor dishwasher 2 which is illustrated schematically in FIG. 1, however, the final rinse zone 18 has not only downwardly directed upper spray nozzles 20 and upwardly directed lower spray nozzles 22 but also transversely directed lateral spray nozzles 24 on each side of the conveyor apparatus 4. The use of lateral spray nozzles 24 makes it possible to spray the washware surfaces (dish surfaces) with final rinse liquid in targeted manner even in zones that are hidden behind other objects. Specifically when the conveyor system is fully loaded, that is to say when the dish carrier is loaded with plates side by side, the use of lateral spray nozzles 24 in the final rinse zone 18 is clearly advantageous, in respect of the final rinse result (effective rinsing of detergent residues off dish surfaces even in hidden zones), over systems in which only upper and lower spray nozzles 20, 22 and no transversely directed lateral spray nozzles 24 are provided in the final rinse zone 18.

[0047] Further associated with the post-wash zone 16, main wash zone 14 and pre-wash zone 12 are tanks (post-wash tank 32, main wash tank 34, pre-wash tank 36), for receiving sprayed liquid and/or for providing liquid for the spray nozzles 26, 28, 30 of the relevant treatment zones 14, 16, 18.

[0048] In the conveyor dishwasher 2 which is illustrated schematically in FIG. 1, final rinse liquid, which is composed of fresh water and metered-in rinse aid, is sprayed onto the washware (not illustrated) by means of the spray nozzles 20, 22, 24 of the final rinse zone 18, said spray nozzles 20, 22, 24 being arranged above and below and to the side of the conveyor apparatus 4. A portion of the sprayed final rinse liquid is conveyed, by means of a cascade system, from one treatment zone to another in the opposite direction to the direction 8 of conveying the washware. The remaining portion of the final rinse liquid which is sprayed in the final rinse zone 18 is fed directly into the pre-wash tank 36 which is associated with the pre-wash zone 12, by means of a valve V1 and a bypass line 38.

[0049] In the cascade system, the final rinse liquid which is sprayed by the final rinse nozzles 20, 22, 24 flows by gravity from the final rinse zone 18 into the post-wash tank 32, which is associated with the post-wash zone 16. The final rinse liquid which is sprayed in the final rinse zone 18 and which is collected by the post-wash tank 33 is then conveyed to the spray nozzles (post-wash nozzles 26) of the post-wash zone 16 with the aid of a post-wash pump 45. In the post-wash zone 16, wash liquid is rinsed off the washware. The liquid which is produced during this (post-wash liquid) flows by gravity into the main wash tank 34, which is associated with the main wash zone 14. Preferably, a drain element 39, for example a draining board or a baffle plate, is provided for this purpose and guides the post-wash liquid which is sprayed by the post-wash nozzles 26 into the main wash tank 34.

[0050] According to another embodiment, which is not shown in the drawings, the drain element 39 can be dispensed with if the main wash tank 34 extends below the post-wash nozzles 26 of the post-wash zone 16.

[0051] The liquid which is received by the main wash tank 34 of the main wash zone 14 is conventionally provided with a detergent and is sprayed onto the washware with the aid of a main wash pump 35 by means of the spray nozzles (main wash nozzles 28) of the main wash zone 14. The wash liquid which is sprayed by the main wash nozzles 28 flows by gravity back into the main wash tank 34.

[0052] The main wash tank 34 forms a fluid connection with the pre-wash tank 36, which is associated with the pre-wash zone 12, by means of an overflow line 37. The wash liquid which is sprayed in the main wash zone 14 reaches the pre-wash tank 36 by means of said overflow line 37 when a sufficient quantity of wash liquid is received in the main wash tank 34.

[0053] The liquid which is received in the pre-wash tank 36 of the pre-wash zone 12 is then sprayed onto the washware with the aid of a pre-wash pump 33 by means of the spray nozzles (pre-wash nozzles 30) of the pre-wash zone 12, in order to remove large pieces of dirt from the washware. The wash liquid which is sprayed by the pre-wash nozzles 30 flows by gravity back into the pre-wash tank 36.

[0054] The pre-wash tank 36 is provided with an overflow line 31 which, when a liquid level in the pre-wash tank 36 is exceeded, serves to supply the excess quantity of liquid to a heating device as wastewater. This aspect is described in detail below with reference to the illustrations in FIGS. 2 and 3.

[0055] As indicated above, the liquid which is sprayed in the main wash zone 14 and the pre-wash zone 12 preferably contains detergent, which is metered for example into the liquid which is received in the main wash tank 34 of the main wash zone 14 with the aid of a detergent metering device (not shown in the drawings).

[0056] As mentioned above, the drying zone 40 follows the final rinse zone 18, as seen in the direction 8 of conveying the washware. In the drying zone 40, the washware is dried by means of dry warm air in order to blow away or dry off moisture which is on the washware. In order to keep the humidity of the air in a range that is favorable to drying, it is conceivable for example to supply indoor air to the drying zone 40 from the outside, by means of an opening, for example the exit opening for the washware.

[0057] The warm moist air in the drying zone 40 is then removed from the drying zone 40, for example with the aid of a fan 41, by means of a further opening. In this context, it is advantageous if the outgoing air passes out of the drying zone 40 and through a device 42 for heat recovery in which for example a condenser may be provided. The device 42 for heat recovery serves to recover at least a portion of the thermal energy in the outgoing flow.

[0058] If, before the conveyor dishwasher 2 is first started up, the tanks which are associated with the wash zones 12, 14 and 16 (pre-wash tank 36, main wash tank 34, post-wash tank 32) are empty or only insufficiently filled, they must first be filled by means of a fresh water line 48 and/or by spraying final rinse liquid in the final rinse zone 18. The fresh water line 48 is connectable to a fresh water mains supply by means of a controllable valve V3. The quantity of wash liquid which is available in the main wash zone 14 and the pre-wash zone 12 may be monitored, with the aid of a level sensor that is provided in the main wash tank 34 and with the aid of a level sensor that is provided in the pre-wash tank 36 respectively, and signaled to a control device 50.

[0059] As illustrated in FIG. 1, a fresh water container 44 may be associated with the final rinse zone 18, for the interim storage of at least a portion of the fresh water which is provided for the final rinse. The fresh water container 44 is provided on one side with a fresh water connection, which is connectable by means of a controllable fresh water supply valve V2 to a fresh water mains supply, and on the other is connected to the intake side of a final rinse pump 43. It goes without saying, however, that it is also conceivable to dispense with a fresh water container 44 for the interim storage of at least a portion of the fresh water which is provided for the final rinse, and to connect the fresh water supply valve V2 directly to the intake side of the final rinse pump 43.

[0060] Nor is it absolutely necessary to provide a final rinse pump 43. Rather, it is possible for example also to use the pressure from the fresh water mains network in order to supply the fresh water which is to be sprayed in the final rinse zone 18, as final rinse liquid, to the final rinse nozzles 20, 22, 24.

[0061] In the case of the conveyor dishwasher 2 which is illustrated schematically in FIG. 1, by contrast, a final rinse pump 43 is used, whereof the delivery side is connected by means of a line system to a water heater 9 (boiler). In this context, the line system is designed such that the liquid which is conveyed by the final rinse pump 43 to the spray nozzles 20, 22, 24 of the final rinse zone 18 first passes through the device 42 for heat recovery, in which at least a portion of the thermal energy from the outgoing air that is removed from the conveyor dishwasher is used to heat the liquid which is supplied to the spray nozzles 20, 22, 24 of the final rinse zone 18.

[0062] As an alternative or in addition thereto, it is provided for the liquid which is to be conveyed by the final rinse pump 43 to the spray nozzles 20, 22, 24 of the final rinse zone 18 to pass through a heat exchanger device 60 in which at least a portion of the thermal energy of the wastewater which is produced during operation of the conveyor dishwasher 2 and which is to be removed is transferred to the final rinse liquid which is to be sprayed in the final rinse zone 18. The construction and functioning of this heat exchanger device 60 are described in more detail below with reference to the embodiments according to FIGS. 2 and 3.

[0063] Rinse aid is metered into the fresh water which is supplied to the final rinse pump 43, either directly from the fresh water supply valve V2 or from the fresh water container 44, with the aid of a rinse aid metering device which has a rinse aid pump 6. Preferably, the rinse aid metering device is arranged such that the metering of rinse aid into the fresh water is performed at a location in which the fresh water has not yet been heated. Tests in this context have shown that a markedly better and more even mixing of the rinse aid with the fresh water is produced if the rinse aid is metered into unheated fresh water.

[0064] To be more precise, rinse aid should preferably be metered into fresh water which is at a temperature of less than 40 C., preferably less than 30 C.

[0065] Consequently, in the embodiment of the conveyor dishwasher 2 which is illustrated schematically in FIG. 1, the metering of rinse aid takes place between the final rinse pump 43 and the water heater 9, or between the device 42 for heat recovery and the heat exchanger device 60. In FIG. 1, the control device 50 of the conveyor dishwasher 2 is indicated only schematically. In the control device 50, preferably a plurality of predefined or predefinable running programs are stored. To this end, the control device 50 has a corresponding storage device, preferably a random access memory (RAM). Each individual running program defines the process parameters which have been laid down for the treatment of the washware in the various treatment zones of the conveyor dishwasher 2, which in particular includes the temperature, in particular the minimum temperature, of the wash liquid which is to be sprayed in the pre-wash zone 12, the wash liquid which is to be sprayed in the main wash zone 14, the liquid which is to be sprayed in the post-wash zone 16 and/or the final rinse liquid which is to be sprayed in the final rinse zone 18.

[0066] To this end, it is preferred if a corresponding heating device 55, 56, 58 is arranged in the pre-wash tank 36 which is associated with the pre-wash zone 12, in the main wash tank 34 which is associated with the main wash zone 14 and/or in the post-wash tank 32 which is associated with the post-wash zone 16, in order to bring to temperature the liquid which is collected in the relevant tank 32, 34, 36 in accordance with the stipulation of a selected running program. The said heating devices 55, 56, 58 are drivable accordingly by the control device 50.

[0067] Further, a heating device 57 of the water heater 9 is drivable appropriately by the control device 50 in order as required to adjust the temperature, in particular the minimum temperature, of the final rinse liquid which is to be sprayed in the final rinse zone 18, in the event that the final rinse liquid which is to be sprayed has not yet been sufficiently brought to temperature after passing through the device 42 for heat recovery and/or after passing through the heat exchanger device 60.

[0068] A first exemplary embodiment of a heat exchanger device 60 which is downstream of the pre-wash zone 12 will be described in more detail below with reference to the illustration in FIG. 2.

[0069] To be more precise, FIG. 2 schematically illustrates in more detail a first exemplary embodiment of a wastewater energy recovery system which is used for example with the conveyor dishwasher 2 which is illustrated schematically in FIG. 1 and described above. In this exemplary embodiment of the wastewater energy recovery system, a wastewater pump 61 is used which may be driven appropriately by means of the above-mentioned control device 50. The intake side of the wastewater pump 61 forms a flow connection with a wash tank of a wash zone of the conveyor dishwasher 2.

[0070] In the text below, it is assumed that the intake side of the wastewater pump 61 is connected to the wash tank 36 of the first wash zone, as seen in the direction 8 of conveying the washware (for example the pre-wash zone 12).

[0071] The wastewater pump 61 serves to supply, as required, wash liquid which is produced as wastewater during operation of the conveyor dishwasher 2 to the heat exchanger device 60, in which at least a portion of the thermal energy of the supplied wash liquid is transferred to the final rinse liquid which is to be sprayed in the final rinse zone 18. Although it is not illustrated in FIG. 2, it goes without saying that it is conceivable for further wash zones to be connected between the final rinse zone 18 and the wash zone 12, such as the main wash zone 14 and post-wash zone 16 described with reference to the illustration in FIG. 1.

[0072] As can also be seen from the illustration in FIG. 2, there is associated with the wash zone 12 a corresponding wash system, part of which is a wash pump (in this case, for example, the pre-wash pump 33) by means of which the wash liquid collected in the wash tank 36 is supplied to corresponding wash nozzles (in this case, for example, the pre-wash nozzles 30). The wash liquid which is sprayed in the wash zone 12 by the wash nozzles 30 at least partially flows back into the wash tank 36 again due to gravity. In this regard, the wash system shown in FIG. 2 is designed as a recirculation system.

[0073] It should be emphasized in particular in this context thatas indicated schematically in FIG. 2the intake side of the wastewater pump 61 forms a direct flow connection with the wash tank 36. The delivery side of the wastewater pump 61, by contrast, is connected to a corresponding heat exchanger device 60 in order, as required, to supply wash liquid from the wash tank 36 to the heat exchanger device 60.

[0074] The heat exchanger device 60 is preferably designed as a counterflow heat exchanger in order to transfer, in a particularly efficient manner, at least a portion of the thermal energy of the wash liquid which is supplied to the heat exchanger device 60 to the fresh (cold) water which is to be sprayed in the final rinse zone 18 as final rinse liquid, and to heat this fresh water accordingly.

[0075] After it has passed through the heat exchanger device 60, the wash liquid is then supplied to a wastewater network 63 by means of a wastewater line 62.

[0076] As indicated schematically in FIG. 2, the wash tank 36 of the wash zone 12 is provided with a level sensor 64, by means of which the liquid level in the wash tank 36 is preferably detected continuously or at predefined times or in the case of predefined events.

[0077] According to the invention, the control device 50 is designed to drive the wastewater pump 61 depending on a quantity of wastewater which is actually currently produced during operation of the conveyor dishwasher 2. In other words, if during operation of the conveyor dishwasher 2 no wastewater which is to be removed from the conveyor dishwasher 2 or the wash tank 36 of the wash zone 12 is produced, the control device 50 switches off the wastewater pump 61, preferably automatically, such that no wash liquid is supplied to the heat exchanger device 60.

[0078] In particular in the case of the exemplary embodiment of the wastewater energy recovery system that is illustrated in FIG. 2, it is provided for the control device 50 of the conveyor dishwasher 2 to be designed to drive appropriately, that is to switch on or off, the wastewater pump 61 depending on a liquid level in the wash tank 36, which is detected with the aid of a level sensor 64.

[0079] Instead of driving the wastewater pump 61 in dependence on a liquid level which is detected in the wash tank 36, it goes without saying, however, that it is also conceivable for the control device 50 to be designed to drive the wastewater pump 61 appropriately, depending on a predefined event and/or depending on an operating cycle and/or operating state of the conveyor dishwasher 2. The essential point here is that the wastewater pump 61 is only driven and switched on if wash liquid which is to be removed from the conveyor dishwasher 2 as wastewater, and which can thus be used for energy recovery in the heat exchanger device 60, is actually produced during operation of the conveyor dishwasher 2.

[0080] In the embodiment of the wastewater energy recovery system according to the invention which is illustrated schematically in FIG. 2, it is in particular provided for the control device 50 to switch off the wastewater pump 61, preferably automatically, when the liquid level in the wash tank 36, which is detected with the aid of the level sensor 64, falls below a predefined or predefinable first level, wherein the wastewater pump 61 is switched on again, preferably automatically, as soon as the liquid level in the wash tank 36 exceeds a predefined or predefinable second level, wherein said second level preferably corresponds to the above-mentioned first level. The first and/or second level at which the wastewater pump 61 is switched on and off is preferably selected such that it is ensured that a sufficient quantity of wash liquid is always present in the wash tank 36 to be able to carry out the wash process in the wash zone 12 in the conventional way.

[0081] As also schematically illustrated in FIG. 2, the wastewater energy recovery system shown there is further provided with a hot water preparation apparatus 65 which is designed such that it is independent of the heat exchanger device 60. By means of said hot water preparation apparatus 65, hot water of the final rinse liquid which is to be sprayed in the final rinse zone 18 is prepared, in particular when the thermal energy which is transferred to the final rinse liquid, which is to be sprayed in the final rinse zone 18, in the heat exchanger device 60 is not sufficient to heat the final rinse liquid to a predefined or predefinable minimum temperature when no wash liquid is supplied to the heat exchanger device 60 and/or when the quantity of wash liquid which is supplied to the heat exchanger device 60 per unit time is not sufficient to heat the final rinse liquid which is to be sprayed in the final rinse zone 18 to the predefined or predefinable minimum temperature.

[0082] A situation of this kind occurs for example when the wash system is started up, specifically when the liquid level in the wash tank 36 falls below a defined level (first level) and thus a condition is present in which no wash liquid can be removed from the conveyor dishwasher 2 as wastewater and thus no energy can be recovered from the wastewater in the heat exchanger device 60.

[0083] In this case, the required energy for heating the fresh water which is to be sprayed in the final rinse zone 18 as final rinse liquid to the required final rinse temperature has to be provided with the aid of hot water preparation which is independent of the heat exchanger device 60.

[0084] For this purpose, in the wastewater energy recovery system according to the embodiment illustrated schematically in FIG. 2, a hot water preparation apparatus 65 that is internal to the dishwasher is used. This hot water preparation apparatus 65 may be used in addition to the water heater 9 shown in FIG. 1, or instead of the water heater 9 shown there. In either case, the hot water preparation apparatus 65 is designed to heat up the final rinse liquid which is to be sprayed in the final rinse zone to the predefined or predefinable minimum temperature for the final rinse liquid using electrical energy, steam, gas or hot water.

[0085] As also illustrated schematically in FIG. 2, as an alternative or in addition to the hot water preparation apparatus 65 that is internal to the dishwasher, the hot water preparation that is to be undertaken as required may be performed by means of an external hot water preparation apparatus (not explicitly illustrated in FIG. 2). It is conceivable in this context for example for the conveyor dishwasher 2 to form a flow connection or to be able to form a flow connection with an external hot water preparation apparatus, for example a centralized hot water supply provided in the building, by means of a hot water connection 66, in order as required to supply the conveyor dishwasher 2 with hot water which serves to be sprayed in the final rinse zone 18 as the final rinse liquid, or which serves to heat the final rinse liquid which is to be sprayed in the final rinse zone 18, for example by means of a heat exchanger or heat pump system.

[0086] Preferably, in this case the control device 50 is designed to activate the hot water connection 66 when the thermal energy which is transferred to the final rinse liquid, which is to be sprayed in the final rinse zone 18, in the heat exchanger device 60 is not sufficient to heat the final rinse liquid to the predefined or predefinable minimum temperature, when no wash liquid is supplied to the heat exchanger device 60, and/or when the quantity of wash liquid which is supplied to the heat exchanger device 60 per unit time is not sufficient to heat the final rinse liquid which is to be sprayed in the final rinse zone 18 to the predefined or predefinable minimum temperature.

[0087] A further exemplary embodiment of a wastewater energy recovery system will be described in more detail below with reference to the illustration in FIG. 3. The wastewater energy recovery system which is illustrated schematically in FIG. 3 is suitableas indeed is the wastewater energy recovery system shown in FIG. 2in particular for use in a wash zone, in particular the first wash zone, as seen in the direction of conveying the washware (pre-wash zone 12), in order to use the wash liquid that is produced as wastewater in this wash zone (pre-wash zone 12) for heat recovery.

[0088] Unlike the wastewater energy recovery system according to the schematic illustration in FIG. 2, however, in the case of the wastewater energy recovery system according to FIG. 3 it is provided for the intake side of the wastewater pump 61 not to form a direct flow connection with the wash tank 36 of the wash zone 12. Rather, in this case the intake side of the wastewater pump 61 forms or is able to form a flow connection with an auxiliary tank 67. This auxiliary tank 67 forms a flow connection with the wash tank 36 of the wash zone 12 by means of an overflow or similar bypass line, such that the wash liquid that is produced as wastewater in the wash zone 12 reaches the auxiliary tank 67 and is subject to interim storage there.

[0089] In this way, it is ensured that the wash liquid (wastewater) stored in the auxiliary tank 67 can no longer be recirculated in the wash zone 12, sinceas already explained in conjunction with the embodiment according to FIG. 2the intake side of the wash pump 33 of the wash system associated with the wash zone 12 is connected to the wash tank 36.

[0090] The wastewater which is subject to interim storage in the auxiliary tank 67 is supplied, as required, with the aid of the wastewater pump 61 to a heat exchanger device 60 which is preferably designed as a counterflow heat exchanger and serves to transfer at least a portion of the thermal energy of the wash liquid which is supplied as wastewater to the heat exchanger device 60 to the final rinse liquid which is to be sprayed in the final rinse zone 18.

[0091] By providing an auxiliary tank 67 of this kind, it is ensured in particular that even when the conveyor dishwasher 2 is started upthat is, in a condition in which no wastewater which is to be removed and can be used for heat recovery is produced during operation of the conveyor dishwasher 2the heat exchanger device 60 can always be provided with wastewater from the auxiliary tank 67.

[0092] Nonetheless, it is, however, also advantageous in the case of the wastewater energy recovery system according to FIG. 3 to provide hot water preparation which is independent of the heat exchanger device 60, for example in the form of a hot water preparation apparatus 65, wherein in this case too the hot water preparation apparatus 65 which is illustrated schematically in FIG. 3 may be designed to have the same construction as the water heater 9 shown in FIG. 1, or the hot water preparation apparatus 65 which is illustrated schematically in FIG. 3 may replace the water heater 9 shown in FIG. 1.

[0093] The hot water preparation apparatus 65 is activated by the control device 50 at least when the thermal energy which is transferred to the final rinse liquid, which is to be sprayed in the final rinse zone 18, in the heat exchanger device 60 is not sufficient to heat the final rinse liquid to the predefined or predefinable minimum temperature.

[0094] As also in the case of the wastewater energy recovery system illustrated schematically in FIG. 2, in the case of the embodiment illustrated schematically in FIG. 3 it is provided for the hot water preparation apparatus 65 to be designed in particular to heat up the final rinse liquid which is to be sprayed in the final rinse zone 18 to the predefined or predefinable minimum temperature using electrical energy, steam, gas or hot water.

[0095] In the case of the wastewater energy recovery system shown in FIG. 3, too, a wastewater line 62 is used to supply the wash liquid which is removed as wastewater from the conveyor dishwasher 2once it has passed through the heat exchanger device 60to a wastewater network 63.

[0096] The invention is not restricted to the embodiments illustrated in the drawings but results from an overall view of all the features and aspects disclosed herein.

[0097] In particular, the wastewater energy recovery system according to the invention is designed to supply wash liquid, continuously or cyclically, to the heat exchanger device 60 with the aid of the wastewater pump 61. In this context, the temperature of the wash liquid, depending on the machine type and the selected treatment program, is between 40 C. and 75 C. After flowing through the heat exchanger device 60, the wash liquid (wastewater) is cooled by approximately 20 C. to 30 C., to approximately 20 C. to 60 C.

[0098] The thermal energy is transferred to fresh water flowing in counterflow, with the result that said fresh water is heated by the same temperature difference as that by which the wastewater cools. Then, as required, the preheated fresh water is heated by a hot water preparation apparatus 65, such as a water heater 9, to the required process temperature of at least 65 C. or at least 80 C.

[0099] In particular, in this context it is also conceivable to provide, in the wash tank 36, the wash water supply line to the heat exchanger device 60, and/or the final rinse liquid outlet or the downstream line for the fresh water that is heated or pre-heated in the heat exchanger device 60, corresponding temperature sensors so that the control device 50 can activate the wastewater pump 61 and/or the hot water preparation apparatus 65 and/or the hot water connection 66 appropriately.