Method for Sterilizing and Pasteurizing Container Packed Products

My invention relates to a method for sterilizing or pasteurizing container-packed products such as plastic bags (pouches) while using a conveyor with box-shaped carriers, jointly covering a path in a space, provided with nozzles for supplying a liquid heated to the desired temperature. Such a method is known, for bottles, from the French Pat. No. 619,254. This publication relates to a so-called beer pasteurizer in which the product to be treated needs only be exposed to a temperature below 100.degree., so that a treatment space can be used which freely communicates with the ambient atmosphere.

Though in the method known from said French Patent, measures are taken for intensifying the heat transfer by using nozzles for spraying a liquid heated to the desired temperature, this liquid will, however, on dripping down along the carriers soon suffer from a fall in temperature, so that in the lower region of the apparatus a rather poor heat transfer will occur. This means that for a final pasteurization or sterilization a longer stay in the treatment space will be necessary.

It should be noted that from the British Pat. No. 983,316 a method is known for sterilizing or pasteurizing products packed in containers, while a closed treatment space is utilized with a certain overpressure. This overpressure allows a temperature of over 100.degree. and constitutes an additional counter pressure, in order to prevent undesired bulging of containers consisting of slack material. In this known method, however, no box-shaped carriers but cylindrical carriers are used whereby only a limited type of container can be treated viz. a glass container or can which can be slid into the cylinders in a row (a so-called "stick") for following the treatment path. This known method is therefore improper for treating containers consisting of plastic pouches or bags.

My invention aims to combine the advantages of the two aforementioned methods while avoiding the disadvantages and simultaneously improving the heat transfer.

My invention aims in one aspect to allow a thermal treatment at a temperature which is over 100.degree.C, while according to another aspect, the invention aims to provide a method which allows to treat the contents of plastic pouches which are only difficultly accessible to the heating medium when a plurality of pouches or bags is in a carrier. These objects are attained according to my invention by the combination of an overpressure in the treatment space and a continuous washing of the containers with liquid which is fed to the carriers through the nozzles in a quantity of liquid flowing from each carrier.

Due to these features such a change of the liquid quantity continuously available in each carrier, is obtained that the pouches bearing on each other (but floating slightly owing to the liquid) are efficiently washed, so that products and containers which can only be treated difficultly can be efficiently sterilized or pasteurized.

By adding slightly more liquid than that which flows off from the carriers, there is a continuous immersion of the containers to be sterilized. As an additional advantage of this constant immersion, reference is made to the apparent loss in weight of contents of the containers, so that a lesser load is applied to the wall of the containers. This is particularly of importance at higher temperatures in containers of a synthetic material.

My invention further relates to an apparatus for performing the aforementioned method, comprising a housing provided with an endless conveyor with perforated box-shaped carriers for the containers to be treated, the conveyor following a closed path which extends at least partially within the housing, nozzles for liquid being arranged within the housing, as is known from the aforementioned British Pat. Specification No. 983,316.

In order to adapt this apparatus to the method according to the invention, means are provided for introducing at least into the upper part of the housing compressed gas, while the downwardly directed nozzles are at least arranged along the greater part of the conveyor path. Due to these features operations can be performed at a certain overpressure in order to prevent the containers from undesired bulging, while it is furthermore ensured that independent of the position of the carriers within the housing, a nozzle will always introduce a water jet at the desired temperature into each carrier for permanently replacing the heating liquid available in the carrier.

FIG. 1 is a vertical section through a schematically represented apparatus;

FIG. 2 is, on a larger scale, a perspective view of an individual carrier and some spraying members;

FIG. 3A to 3D are modifications of a possible arrangement according to a horizontal section on line III--III in FIG. 1;

FIG. 3E is a modification for a carrier.

As is shown in FIG. 1 the apparatus consists of a treatment space 1, a feed column 2 and a discharge column 3, surrounded by parts of a housing 4. Within this housing an endless conveyor 5 is travelling along a looped path in the space. A loading- and a discharge station 6, 7 (schematically represented) are arranged in the left-hand part of the housing 4. The construction of this apparatus essential sofar in this connection, does not differ fundamentally from the apparatuses, as for example described in the British Pat. No. 983,316, the U.S. Pat. Nos. 3,181,689, 3,163,284, 3,211,275, 3,315,787 and 3,379,115.

The conveyor 5 consists in the described embodiment of two chains 8 (see FIG. 2) between which equidistantly spaced carriers 9 are disposed. These box-shaped carriers serve to accomodate articles like container-packed products and particularly plastic pouches containing milk or any other, eventually pharmaceutical, liquid. Each carrier 9 has a rectangular shape and is provided both in side walls and bottom with perforations 10. Nozzles 11 (see FIG. 2 and 3) are disposed within the treatment space 1 for spraying liquid. These nozzles are connected to conduits 12. The housing 4 is further provided with means 13 via which a compressed gas e.g. air can be introduced into the upper part of the housing.

The nozzles 11 are downwardly directed in order to introduce the liquid jet into the passing carriers 9. The space between two adjacent nozzles 11 is about equal to the smallest dimension of the carriers 9, so that liquid is almost continuously supplied to these carriers on following the path through space 1. The liquid is regularly distributed on the surface of the carriers via the conduits 12 and the nozzles 11. This liquid which for a great part is coming from a receptacle 14 at the lower end of the apparatus, is heated to the desired sterilizing or pasteurizing temperature and passed via a pump (not shown) to the various conduits 12.

In FIGS. 3A to 3D various modifications are shown for the arrangement of the conduits 12 and the nozzles 11. FIG. 3E shows that it is also possible to feed the liquid to an individual compartment 15 of the carrier 9, whereupon this liquid flows, via apertures in the intermediate wall 16, to the containers in the carrier 9.

The arrangement of nozzles 11 along the entire path of the conveyor 5 aims to replace continuously the liquid in the carriers 9, which liquid is, at the temperature desired, to achieve thereby as fast as possible the sterilization or pasteurization of the products in the containers. The liquid jets issuing from the nozzles 11 are tuned in such a manner to the perforations 10 of the carriers 9, that a situation of equilibrium arises in which the carriers 9 remain filled with liquid which is continuously replaced. This is an important improvement with respect to the system according to the aforementioned British Pat. No. 983,316., since in that system the liquid from the upper end of the treatment space will drip down along the carriers which is attendant with a gradual fall in temperature. The required intensity of the heat transfer which is especially desired when pouches of synthetic material are used, is considerably promoted by the system according to my invention.