Patent Description:
Consumption of water and energy represents, by far, the largest costs associated with owning and operating a tunnel-type dishwasher. Reduction of water and energy consumption is also highly desirable from the perspective of protecting the environment. <CIT> discloses a tunnel-type dishwasher aiming to reduce the consumption of water and energy. Another document, <CIT>, suggests performing an initial pre-heating of the incoming fresh water in a heat exchanger arranged in the pre-rinse section of a dishwasher. However, there is a need for even further reducing the consumption of tunnel-type dishwashers.

It is an object of the present invention to solve, or at least mitigate, parts or all of the above-mentioned problems. To this end, there is provided a tunnel-type dishwasher as defined in claim <NUM>, the dishwasher comprising a water supply line for receiving clean water to be used in the dishwasher; a wash item entrance for receiving a feed of wash items to be washed by the dishwasher; a wash item exit for discharging said wash items when they have been washed by the dishwasher; a rinsing section upstream, with respect to a feed direction of said wash items, of the wash item exit; a main washing section upstream, with respect to said feed direction, of the rinsing section; a pre-washing section upstream, with respect to said feed direction, of the main washing section, the pre-washing section comprising a pre-washing sprayer for spraying a pre-washing liquid onto the wash items, a pre-washing liquid tank for pre-washing liquid that is to be sprayed from the pre-washing sprayer, and a pre-washing liquid inlet configured to receive liquid that has been used in the main washing and/or rinsing section(s); and a pre-washing liquid cooler for cooling the pre-washing liquid of the pre-washing liquid tank. The pre-washing liquid cooler allows reducing the water consumption of the dishwasher, since the need for moderately tempered, relatively clean water to the pre-washing section is reduced, which allows reducing the supply of clean water to e.g. the rinsing section. By way of example, according to <CIT>, cold tap water, or a bypass flow of moderately tempered rinse liquid, is supplied to the pre-washing section, thereby diluting the pre-washing liquid with liquid having a lower temperature. By using a pre-washing liquid cooler in the pre-washing liquid tank, the liquid supply to the pre-washing section can be reduced, and can, to an increased extent, rely on the flow of higher tempered liquid from the sections downstream, with respect to the feed direction of the wash items, of the pre-washing section. The flowrate of any bypass flow from the rinsing section to the pre-washing section does not need to be set to meet any cooling need of the pre-washing section, but can instead, for example, be adjusted to correspond to the need for clean final rinse liquid in the rinsing section, minus the need for regeneration of dishwashing liquid in the main washing section. A transporter may be configured to move the wash items in the feed direction from the wash item entrance, via the pre-washing, main washing, and rinsing sections to the wash item exit.

The cooler is configured as a pre-washing liquid heat exchanger arranged for exchanging heat between the clean water in the water supply line and the pre-washing liquid of the pre-washing liquid tank. Thereby, the heat removed from the pre-washing liquid is recycled for heating clean water to be used, e.g., for final rinse in the rinsing section. This reduces the energy consumption of the dishwasher. Typically, the pre-washing liquid tank may be provided with a spent liquid outlet connected to a drain. A lower temperature of the liquid sent to the drain generally means less energy consumed by the dishwasher.

The tunnel-type dishwasher further comprises a gas discharge flow heat exchanger connected to the water supply line upstream, with regard to a flow direction of the water in the water supply line, of the pre-washing liquid heat exchanger, and configured to exchange heat between the supply water and a discharge flow of air and steam from the dishwasher. The gas discharge flow heat exchanger allows recovering heat from the discharge flow of air and steam, which reduces the energy consumption of the dishwasher as well as the emission of heat and steam to the working environment outside the dishwasher.

According to an embodiment, said gas discharge flow heat exchanger may be arranged so as to receive said discharge flow of air and steam from the pre-washing section. Compared to receiving the discharge flow from other sections of the dishwasher, the lower temperature of the pre-washing section allows reducing the discharge flow rate, as well as results in a lower temperature of the discharge flow at the gas discharge outlet of said gas discharge flow heat exchanger. This may result in a significant improvement of the work environment around the dishwasher. Moreover, the lower flow rate and temperature of the discharge flow substantially reduces the cooling power needed to bring down the temperature of the discharge flow to a temperature suitable for discharge into the work environment. In combination with the pre-washing liquid heat exchanger downstream, with respect to the flow direction of the water in the water supply line, of the gas discharge flow heat exchanger, this synergistically results in that, for a given supply water flow rate, more cooling power of the supply water is saved for use in the pre-washing liquid heat exchanger.

According to an embodiment, the tunnel-type dishwasher may further comprise a fan configured to actively move said discharge flow of air and steam. The fan may be configured to generate a maximum discharge flow of less than <NUM><NUM>/h; according to further embodiments, it may be configured to generate a maximum discharge flow of less than <NUM><NUM>/h, or of less than <NUM><NUM>/h. According to tests, a discharge flow of less than <NUM><NUM>/h may be sufficient for maintaining an underpressure inside the dishwasher.

According to an embodiment, the pre-washing liquid cooler may be configured as a tube heat exchanger arranged inside the pre-washing liquid tank. Such an arrangement is particularly efficient for exchanging heat with the pre-washing liquid. Moreover, it is insensitive to clogging and relatively easy to clean.

According to another aspect of the invention, parts or all of the above mentioned problems are solved, or at least mitigated, by a method of dishwashing a feed of wash items as defined in claim <NUM>, the method comprising moving said wash items in a forward direction through a pre-washing section, a main washing section, and a rinsing section; moving a flow of liquid in a backward direction through the rinsing section, the main washing section, and the pre-washing section; and cooling said liquid in the pre-washing section. The liquid may be cooled by heat conduction, for example by conducting heat to a cooler. Such a cooler may be configured as a heat exchanger. The cooler may be in direct contact with the liquid.

Said liquid is cooled in a pre-washing liquid tank of the pre-washing section by exchanging heat with supply water to be supplied to the rinsing section. The heat is exchanged between said liquid and said supply water via a heat exchanger. The pre-washing liquid tank is for liquid to be sprayed from a pre-washing sprayer of the pre-washing section onto the wash-items.

The method further comprises moving a flow of air and steam along said backward direction through the rinsing section, the main washing section, and the pre-washing section; and discharging said flow of air and steam via an outlet arranged in said pre-washing section.

According to an embodiment, the method may further comprise cooling said flow of air and steam by exchanging heat with supply water to be supplied to the rinsing section.

The above, as well as additional objects, features and advantages of the present invention will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:.

Tunnel-type dishwashers are often used in e.g. restaurants, hotels, hospitals, etc., which generate a large amount of items to be washed. Typically, the items to be washed pass through the different sections of the tunnel-type dishwasher sequentially. A tunnel-type dishwasher may, by way of example, be of rack conveyor type, i.e. comprising a conveyor for moving dishwashing racks or baskets through the dishwasher, or of flight type, i.e. comprising a conveyor provided with support structures for holding the wash item individually, without the need for a rack.

<FIG> illustrates a tunnel-type dishwasher <NUM> of flight type. The dishwasher <NUM> comprises a pre-washing section <NUM>, a main washing section <NUM>, a rinsing section <NUM>, and a drying section <NUM>. In the illustrated embodiment, the pre-washing section is divided into a recirculation pre-washing section 12a and a bypass pre-washing section 12b. The main washing section <NUM> comprises two consecutive sub-sections 14a, 14b. The rinsing section <NUM> comprises a rinsing entry zone 16a, a recirculation rinsing zone 16b, and a non-recirculation, final rinsing zone 16c. Items to be washed, such as trays, tableware, cooking utensils or similar, are placed directly onto an endless conveyor belt <NUM>, which acts as a transporter and moves the items along a wash item feed direction <NUM> through a wash item entrance <NUM>, via the consecutive sections <NUM>, <NUM>, <NUM>, <NUM>, to the wash item exit <NUM> of the dishwasher <NUM>. Curtains <NUM> are provided at the entrance <NUM>, between the sections 12a, 12b, <NUM>, <NUM>, <NUM>, and at the exit <NUM>, to avoid splashing and excessive heat transfer between sections and outside the dishwasher <NUM>. Potable tap water is supplied to the dishwasher <NUM> via a water supply line <NUM>, and is sprayed onto the wash items in the final rinsing zone 16c. A decanting arrangement allows liquid entering the final rinsing zone 16c to flow against the feed direction <NUM> of the wash items, via a recirculation rinsing liquid tank <NUM> arranged in the rinsing section <NUM>; respective dishwashing liquid tanks 34a-b in the main washing sub-sections 14a-b; and a pre-washing liquid tank <NUM> arranged in the pre-washing section <NUM>. Spent liquid leaves the dishwasher <NUM> via an outlet <NUM>, which is connected to a drain (not shown).

<FIG> illustrate the dishwasher in greater magnification and, for clarity, with only one main washing section <NUM>. Following the path of the water supply line <NUM>, the supply water first passes through a gas discharge flow heat exchanger <NUM> configured to exchange heat between the supply water and a discharge flow of air and steam from the pre-washing section <NUM>. A typical temperature of the supply water when entering the gas discharge flow heat exchanger <NUM> may be between <NUM> and <NUM>, and the gas discharge flow heat exchanger <NUM> may typically heat the supply water to a temperature of between <NUM> and <NUM>. The supply water is then passed on to a pre-washing liquid heat exchanger <NUM> arranged in the pre-washing liquid recirculation tank <NUM>. In the pre-washing liquid heat exchanger <NUM>, which is configured as a meandering tube for the supply water inside the pre-washing liquid tank <NUM>, the supply water receives heat from the pre-washing liquid, and simultaneously cools the pre-washing liquid in the pre-washing liquid tank <NUM>. A typical temperature of the supply water when leaving the pre-washing liquid heat exchanger <NUM> may be between <NUM> and <NUM>, which may be only slightly lower than the typical temperature of the pre-washing liquid in the pre-washing liquid recirculation tank <NUM>. Typical temperatures of the pre-washing liquid in the pre-washing liquid recirculation tank <NUM> may be between <NUM> and <NUM> in order to avoid denaturing the protein content of any food residues on the wash items during pre-washing. Now with reference to <FIG>, the water supply line <NUM> is connected to a booster heater arrangement <NUM>, downstream of the pre-washing liquid heat exchanger <NUM>, for heating the supply water to a temperature of about <NUM>, which temperature is suitable for spraying onto the wash items in the final rinsing zone 16c in order for the wash items to quickly dry once they leave the rinsing section <NUM>. The booster heater arrangement <NUM> comprises two electrical heaters 42a, 42b arranged in series. Finally, the water supply line <NUM> delivers the clean, hot water to a final rinse sprayer <NUM> in the final rinsing zone 16c, where it is used as final rinse liquid. Any rinsing agents may also be added to the water in the booster heater arrangement <NUM>, or elsewhere in the rinsing section <NUM>. Final rinse liquid that has been sprayed from the final rinse sprayer <NUM> is collected in the recirculation rinsing liquid tank <NUM>, which stores rinsing liquid that is to be re-used. A rinsing liquid pump <NUM> pumps rinsing liquid from the recirculation rinsing liquid tank <NUM> into a rinsing liquid line <NUM>, which is connected to a recirculation rinsing sprayer <NUM>. Rinsing liquid sprayed from the recirculation rinsing sprayer <NUM> is once again collected in the recirculation rinsing liquid tank <NUM>. Due to the recirculation, the rinsing liquid spends some time in the recirculation rinsing zone 16b, and cools off over time. Therefore, the rinsing liquid in the recirculation rinsing liquid tank <NUM> holds a lower temperature than the final rinse liquid sprayed from the final rinse sprayer <NUM>. Excessive rinsing liquid in the recirculation rinsing liquid tank <NUM> is allowed to overflow, via a decanting passage <NUM>, into the dishwashing liquid tank <NUM>, which brings us back to <FIG>. In the dishwashing liquid tank <NUM>, dishwashing chemicals, such as detergent, may be added to prepare the rinsing liquid to be used as dishwashing liquid.

A main washing pump <NUM> pumps dishwashing liquid from the dishwashing liquid tank <NUM> to a dishwashing sprayer <NUM>, and dishwashing liquid sprayed from the dishwashing sprayer <NUM> is collected in the dishwashing liquid tank <NUM>. The dishwashing liquid in the dishwashing liquid tank <NUM> is typically held at a temperature of about <NUM> - <NUM>, to efficiently remove the fat content of any food residues on the wash items. This temperature is maintained partly due to the decanting flow of the somewhat hotter rinsing liquid from the rinsing section <NUM>, and partly by means of a dishwashing liquid heater <NUM>. Excessive dishwashing liquid in the dishwashing liquid tank <NUM> is allowed to overflow, via a decanting passage <NUM>, into the pre-washing liquid tank <NUM> for use as pre-washing liquid.

A pre-wash pump <NUM> pumps pre-washing liquid from the pre-washing liquid tank <NUM> to a pre-washing sprayer <NUM>, and pre-washing liquid sprayed from the pre-washing sprayer <NUM> is collected in the pre-washing liquid tank <NUM>. Excessive pre-washing liquid in the pre-washing liquid tank <NUM> is allowed to overflow into the outlet <NUM>.

Again with reference to <FIG>, the rinsing liquid line <NUM> branches off to a rinsing section entry sprayer <NUM>, which is arranged in the rinsing entry zone 16a of the rinsing section <NUM>. Rinsing liquid sprayed from the rinsing section entry sprayer 16a is collected in the dishwashing liquid tank <NUM> (<FIG>). The rinsing liquid line <NUM> also branches off to a bypass line <NUM>, which is configured to transport a bypass flow of rinsing liquid to the pre-washing section <NUM>, bringing us once again to <FIG>. In the illustrated embodiment, the rinsing liquid bypass flow is sprayed from a bypass sprayer <NUM> arranged in the bypass pre-washing section 12b, and thereafter collected in the pre-washing liquid tank <NUM>. Alternatively, the bypass flow may, for example, be allowed to flow directly into the pre-washing liquid tank <NUM>. The flow rate of the bypass flow can be adjusted to bypass the excess rinsing liquid, if any, that is not needed for regenerating the dishwashing liquid in the main washing section <NUM>; alternatively, the bypass flow may be completely dispensed with. Thanks to the pre-washing liquid heat exchanger <NUM>, the bypass flow is not needed for cooling the pre-washing liquid in the pre-washing section <NUM>. Hence, the final rinsing liquid flow rate may be reduced to just barely satisfy the need for final rinse of the wash items, or the need for regenerating the dishwashing liquid, whichever is the greatest.

Due to the sprayers and the elevated temperatures involved, the dishwasher <NUM>, and particularly the rinsing section <NUM>, generates substantial amounts of hot air and steam. The dishwasher <NUM> is configured to generate a flow of this air and steam in a flow direction opposite to the feed direction <NUM> of the wash items, and to draw the air and steam into the gas discharge flow heat exchanger <NUM> via an outlet <NUM> in the pre-washing section <NUM>. Thereby, the lower temperature of the pre-washing section <NUM> will condense a portion of the steam, and reduce the gas volume, prior to discharge. The air and steam is actively drawn out of the pre-washing section <NUM> and through the gas discharge flow heat exchanger <NUM> by means of a fan <NUM>, and discharged from a gas discharge outlet <NUM>. Thanks to the low pre-washing section temperature enabled by the pre-washing liquid heat exchanger <NUM>, the air holds a relatively low temperature, and holds a relatively limited steam content, already when entering the gas discharge flow heat exchanger <NUM>. Due to the lower volume occupied by the relatively cool and dry air and steam mixture, the flow rate through the gas discharge flow heat exchanger <NUM> is relatively low, and thanks to the relatively low flow rate, a high heat exchanging efficiency in the gas discharge flow heat exchanger <NUM> may relatively easily be obtained. Thereby, a discharge flow rate as low as about <NUM><NUM>/h may be sufficient for maintaining an underpressure in the dishwasher <NUM>, and the air discharged from the gas discharge outlet <NUM> may have a temperature as low as <NUM>.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claim 1:
A tunnel-type dishwasher comprising
a water supply line (<NUM>) for receiving clean water to be used in the dishwasher (<NUM>);
a wash item entrance (<NUM>) for receiving a feed of wash items to be washed by the dishwasher (<NUM>);
a wash item exit (<NUM>) for discharging said wash items when they have been washed by the dishwasher (<NUM>);
a rinsing section (<NUM>) upstream, with respect to a feed direction (<NUM>) of said wash items, of the wash item exit (<NUM>);
a main washing section (<NUM>) upstream, with respect to said feed direction (<NUM>), of the rinsing section (<NUM>);
a pre-washing section (<NUM>) upstream, with respect to said feed direction (<NUM>), of the main washing section (<NUM>), the pre-washing section (<NUM>) comprising a pre-washing sprayer (<NUM>) for spraying a pre-washing liquid onto the wash items, a pre-washing liquid tank (<NUM>) for pre-washing liquid that is to be sprayed from the pre-washing sprayer (<NUM>), and a pre-washing liquid inlet (<NUM>, <NUM>) configured to receive liquid that has been used in the main washing and/or rinsing section(s) (<NUM>, <NUM>); and $
a gas discharge flow heat exchanger (<NUM>);
characterised in that the tunnel-type dishwasher comprises further
a pre-washing liquid cooler (<NUM>) for cooling the pre-washing liquid of the pre-washing liquid tank (<NUM>), wherein the pre-washing liquid cooler (<NUM>) is configured as a pre-washing liquid heat exchanger arranged for exchanging heat between the clean water in the water supply line (<NUM>) and the pre-washing liquid of the pre-washing liquid tank (<NUM>); and wherein
the agas discharge flow heat exchanger (<NUM>) is connected to the water supply line (<NUM>) upstream, with regard to a flow direction of the water in the water supply line (<NUM>), of the pre-washing liquid heat exchanger (<NUM>), and configured to exchange heat between the supply water and a discharge flow of air and steam from the dishwasher (<NUM>).