WO1992011796A1

WO1992011796A1 - Process for washing crockery in large plants

Info

Publication number: WO1992011796A1
Application number: PCT/EP1991/002488
Authority: WO
Inventors: Siegmund Krauss
Original assignee: Deutsche Lufthansa Aktiengesellschaft
Priority date: 1991-01-05
Filing date: 1991-12-21
Publication date: 1992-07-23
Also published as: DE59103136D1; EP0565551B1; EP0565551A1; DE4100164C1

Abstract

When being washed in large plants, the crockery (1) first passes through a pre-rinsing region (4) to which only tenside-free, preferably heated fresh water is supplied. The waste water from this region (4) passes via an oil and fat separating station (14) to a drain (15). The washing water is supplied to the subsequent washing regions (5-8) in a counterflow cascade. The waste water containing tensides from the detergent circulation region (5) at the end of the cascade is discharged directly into the drain (15). Thus the operation of the oil and fat separating station (14) is not hampered by the formation of emulsions by tensides, and the tenside-containing waste water from the subsequent washing regions (5-8) contains so little oil and fat that it can be discharged into the drain (15), by-passing the oil and fat separating station (14).

Description

Process for washing dishes in large plants

The invention relates to a method for washing dining utensils in large systems in several successive process steps, the dining utensils passing through several washing zones, in which the supplied washing water, partially mixed with surfactants, is passed in cascade-like fashion in the opposite direction to the respective previous washing zone as washing water is, and wherein only tenside-free fresh water is supplied in a pre-clearing zone.

In order to wash the relatively large amounts of crockery accumulating in cafeterias and similar facilities, dishwashers designed for example as a belt machine are used, through which the dishes to be washed are conveyed on a conveyor belt. The tableware passes through several rinsing zones, for example a pre-clearing zone, a cleaner circulation zone, a washing zone, a pump rinsing zone and a fresh water rinsing zone. Depending on the type of machine and the special requirements, fewer wash zones can be provided. In each rinsing zone, the rinsing water is collected in a lower collecting basin and fed in cascade fashion in the opposite direction to the movement of the dishes in the rinsing zone in each case as rinsing water. In a known device (CH-PS-340 322), which works according to the method described above, fresh water is only supplied in the last rinsing zone and in the pre-clearing zone, in all other rinsing zones the rinsing water contains the surfactants required for the cleaning process, which Remove fat and other solid components.

The flushing water discharged is contaminated with the surfactants used and has such a high oil and fat content that direct discharge into the sewage pipe is not permitted. The known method primarily serves to save energy.

Since limit values for the oil and fat content (generally "heavy lipophilic substances") are specified for the wastewater, in most cases a very complex aftertreatment is required with the conventional processes. Known oil and fat separators can separate wastewater from undissolved oil and fat; those amounts of oil and fat which, in the present process, are dissolved in the wastewater by the action of the surfactants taken up, cannot be separated off in oil and fat separators; they would pollute the sewage.

In another known method (WO 83/01187), heated fresh water is supplied only to the last rinsing zone; the rinse water supplied to the pre-clearing zone is used in a heat exchanger for preheating the fresh water. Here too, the focus is on saving energy. The wastewater discharged contains both surfactants and large amounts of oil and fat and can therefore only be fed into the wastewater pipe after extensive post-treatment.

The object of the invention is therefore to provide a method of the type mentioned, with which without elaborate post-treatment processes, a considerable reduction in the content of heavy lipophilic substances, in particular oils and fats, in the wastewater of large-scale dishwashers can be achieved.

This object is achieved in that the wastewater withdrawn from the upstream pre-clearing zone is passed to an oil and fat separation stage and the wastewater withdrawn from the flushing zone located at the end of the cascade is fed directly to the wastewater line.

Since the vast majority of the oil and fat adhering to the tableware is rinsed off in the pre-clearing zone without surfactants or other detergent additives and thus largely without the formation of emulsions, an almost complete separation of oil and fat is possible in the oil and fat separator downstream of this pre-clearing zone, so that the waste water of this stage fed to the waste water pipe is only very slightly contaminated with oils or fats; the exposure to these substances is far below the permissible limit.

In the other rinsing zones, the process steps are carried out in the conventional manner with cascade-shaped wastewater management, but the addition of surfactants or other detergent additives can be considerably reduced compared to the conventional method, because the rinsing water used in the pre-clearing zone - if necessary after heating - is one more effective removal of oil and grease residues.

The surfactant-containing wastewater discharged from these further rinsing zones, operated with cascade-type wastewater guidance, is so slightly contaminated with oils or fats that it does not have to be passed through an oil and grease separator, but can be fed directly into the wastewater line. This will achieved that the oil and fat separator used does not have to process any surfactant-containing wastewater, so that the emulsion formation is limited only to the natural emulsifiers contained in the food residues and is therefore very low.

Advantageous embodiments of the invention are the subject of dependent claims.

The invention also relates to a method according to the preamble of the independent patent claim 4. This method is carried out in large, single-stage dishwashing machines in which the introduced dinnerware is subjected to several rinsing process steps in succession.

To solve the same problem of the invention, it is proposed according to claim 4 that only the wastewater obtained in the pre-clearing process step is fed to an oil and fat separation stage, and that the wastewater obtained in the subsequent rinsing process steps is disposed of directly without going through the oil and fat separation stage.

According to the previously described process, it is also achieved here that the wastewater supplied to the oil and fat separation stage does not contain any surfactants as emulsifiers, so that the greatest possible oil and fat separation is made possible, while the wastewater contaminated with surfactants in the subsequent process steps is so low with oils and fats are contaminated that they can be disposed of directly in the sewage pipe bypassing the oil and grease separation stage.

Here, too, advantageous embodiments of the method are the subject of further subclaims. The invention is explained in more detail below using exemplary embodiments which are illustrated in the drawing. It shows:

Fig. 1 shows a simplified flow diagram of the process flow in a dishwasher designed as a belt machine and

Fig. 2 is a simplified representation of a single-stage dishwasher.

In the automatic belt conveyor shown schematically in FIG. 1, the dinnerware 1 to be washed is located as washware on a conveyor belt 2, which moves in the direction of arrow 3 through the automatic belt machine. The dinnerware 1 passes through a pre-clearing zone 4, a cleaner circulation zone 5, a washing zone 6, a pump rinsing zone 7 and a fresh water rinsing zone 8. The zones 5-7 are made up of upper and lower nozzle bars 9 and 10, respectively the tableware 1 sprayed washing water each collected and collected in a sump 11, sucked in via a pump 12 and then sprayed again through the washing system and the dishes. The previous rinsing zone - with the exception of the pre-clearing zone 4 - is regenerated with the overflow water of the subsequent zone. The overflow is step-shaped, so that a return cannot take place. The amount of regeneration water results from the incoming rinse-fresh water.

Fresh water heated to 40-80 ° C or higher is supplied in the pre-clearing zone 4, which contains no additives of surfactants or other detergent additives. The largely oil and fat-containing food residues are removed from the tableware 1 by the temperature and flow effects of the supplied rinsing water and reach the drip pan 11 of the pre-clearing zone 4 Solids can be separated by solid and sludge separators (not shown). The waste water is fed to a heat exchanger 13 and there heats the fresh water supplied to the pre-clearing zone 4. The heat exchanger 13 forms a cooling stage; additionally or instead, a separate cooling stage (not shown) can also be provided. On the one hand, this reduces the heat requirement of the system; on the other hand, the wastewater discharged from the pre-clearing zone 4 is cooled, whereby the separation of oil and fat in the subsequent oil and fat separator 14 is facilitated and improved, so that 90 to 99% of all oil and fat substances are separated. From there, the wastewater enters a wastewater line 15 which leads to a wastewater system.

In order to increase the efficiency of the pre-clearing zone 4, the fresh water should be fed in as hot as possible. For this purpose, a fresh water heating device (not shown) is provided for the pre-clearing zone 4. Instead, it is also possible to do without heating the fresh water.

The fresh water supplied to the pre-clearing zone 4 can - as shown - be sprayed directly over the items to be washed or it can be supplied to the pre-clearing zone 4 by means of a circulation process and then sprayed onto the items to be washed.

A cascading process water flow is carried out in the subsequent rinsing zones 5-8. Fresh water heated to about 40 to 80 ° C. is supplied via a fresh water line 16 in the fresh water rinse zone 8, with which the dinnerware 1 is rinsed clean before it leaves the system. The process water from the fresh water rinse zone 8 reaches the pump rinse zone 7 via a line 8a, with a line 17 Detergent and other rinse aids may be added.

The process water passes from the pump rinsing zone 7 via line 7a into the upstream washing zone 6 in order to be used there as rinsing water.

The process water from the washing zone 6 passes through a line 6a as rinsing water into the upstream cleaner circulation zone 5 in order to carry out the first rinsing process there. The wastewater coming out of this cleaner circulation zone 5, but containing only a little oil or fat, is fed via a line 5a at the end of the cascade to the wastewater line 15 behind the oil and fat separation stage 14.

Fig. 2 shows a highly simplified representation of a single-stage dishwasher used in a large system. In it, the dinnerware 1 is subjected to several successive rinsing process steps, with rinse water from the upper and lower nozzle bars 9 'and 10' being sprayed onto the dinnerware 1 in the manner already described. The waste water is drawn off from a collecting trough 11 'by means of a pump 12'.

In a first pre-clearing process step, only hot fresh water with a temperature of about 40-80 ° C. is supplied for pre-clearing via a pump 18. The waste water of this first process step, which is loaded with solids and in particular oil and fat but is free of washing and cleaning additives, in particular surfactants, is fed to the waste water line 15 via the pump 12 'and a multi-way valve 19 via an oil and fat separator 14'. In this process step up to 99% of the fats and oils are removed. In the subsequent rinsing process steps, the multi-way valve 19 is switched so that the wastewater drawn off from the collecting trough 11 'is fed directly to the wastewater line 15, bypassing the oil and fat separation stage 14'. In these following the pre-clearing process step

Flushing process steps are carried out with rinsing water mixed with surfactants and possibly other washing additives and, if necessary, circulated by means of a circulation pump. In a final rinsing step, a fresh water rinse is carried out. The resulting wastewater containing surfactants does not pollute the oil and fat separation stage 14 ', but instead reaches the waste water system directly via the waste water line 15.

Even with the method carried out according to FIG. 2, the load values for oils and greases can be reduced below the permissible limit values of the discharge conditions of the municipal or other waste water systems if the pre-clearing operation is carried out appropriately. As in the previously described method, the consumption of environmentally harmful washing additives, in particular surfactants, is considerably reduced without the fresh water consumption being significantly increased compared to conventional methods.

Claims

Process for washing dinnerware in large plants

1.Procedure for washing dining utensils in large plants in a number of successive process steps, the dining utensils passing through several washing zones in which the supplied washing water, partially mixed with surfactants, is passed in cascade-like fashion in the opposite direction to the respective previous washing zone as washing water, and whereby only surfactant-free fresh water is fed into a pre-clearing zone (4), characterized in that the wastewater drawn off from the preceding pre-clearing zone (4) has an oil and fat separation stage (14) and the wastewater drawn off from the rinsing zone (5) located at the end of the cascade is fed directly to the sewage pipe (15).

2. The method according to claim 2, characterized in that the drawn off from the preclearing zone (4) via a sewage Küh ^"stage the oil and Fettabscheidestufe (14) is supplied.

3. The method according to claim 2, characterized in that the cooling stage has a heat exchanger (13).

4. A process for washing dishes in large plants in several successive process steps, with the supplied wash water being mixed with surfactants in at least some process steps and with only surfactant-free, heated fresh water being added in a pre-clearing process step, characterized in that only the pre-clearing water Process step wastewater is supplied to an oil and fat separation stage (14 ') and that the wastewater obtained in the subsequent rinsing process steps is immediately disposed of without passing through the oil and fat separation stage (14').

5. The method according to claim 4, characterized in that the waste water obtained in the pre-clearing process step is cooled.

6. The method according to claim 5, characterized in that the waste water obtained in the pre-clearing process step is cooled in a heat exchanger.