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TEXT OF THE DESCRIPTION

Field of the invention

The present invention relates to a sterilizing apparatus, in particular for sterilizing post-consumer absorbent sanitary products

The term "absorbent sanitary products" generally refers to disposable absorbent products, such as diapers for babies, incontinence pads for adults, sanitary towels, absorbent tampons, absorbent bed linings, etc.

Description of the prior art

Absorbent sanitary products are generally composed of a variety of different materials, including sheets of plastic material, cellulose fluff, superabsorbent polymers, non-woven sheets, etc.

Absorbent sanitary products contain high-quality materials such as plastics and cellulose and it is, therefore, desirable to recover these materials for use in the market of recycled raw materials or for producing energy.

One of the difficulties encountered in recycling post-consumer absorbent sanitary products is that these products contain organic excretions and bacteria, and it is therefore necessary to carry out sterilization of the products before separating the materials. Another difficulty derives from the fact that the used absorbent sanitary products are usually thrown folded on themselves and closed in a packet form, with the outer plastic layer of the products forming an impermeable barrier. The outer waterproof layer prevents effective sterilization of the products.

The document WO 2010/065088 describes an autoclave for treating solid urban waste, which envisages the drying of the waste by steam. The apparatus described in the document WO 2010/065088 comprises a cylindrical rotating autoclave equipped with at least one door, which can be opened to allow access inside the autoclave, and sealed closed to allow pressurization of the autoclave, an inlet for contact steam that comes into direct contact with the waste contained within the autoclave, and a plurality of hollow metal bars with a rectangular cross-section fed with non-contact steam. This apparatus allows the sterilization of solid urban waste and the drying of the waste during autoclaving.

EP-A-2596810 - by the same applicant - describes a method for treating used absorbent sanitary products, which envisages: loading post-consumer absorbent sanitary products into a cylindrical rotating autoclave having an inner surface, and heating and pressurizing the autoclave at a sterilization temperature and at the same time rotating the autoclave about a longitudinal axis thereof. Autoclave heating provides a first temperature regime for the products contained in the autoclave and a second temperature regime, higher than the first temperature regime, for the inner surface of the autoclave.

The heat required for reaching the temperature for sterilizing the products contained in the autoclave comes mostly from the heat energy transferred through the inner wall of the autoclave. If the heat exchange between the wall of the autoclave and the absorbent sanitary products is not optimal, with the same thermal energy available, the transfer time of the thermal energy to the products is high, and consequently the time of the sterilization cycle of the products is high .

Object and summary of the invention The present invention aims to provide an apparatus for sterilizing post-consumer absorbent sanitary products that allows optimization of the transfer of thermal energy from the walls of the apparatus to the products.

According to the present invention, this object is achieved by an apparatus having the characteristics forming the subject of claim 1.

The claims form an integral part of the disclosure provided here in relation to the invention.

Brief description of the drawings

The present invention will now be described in detail with reference to the attached drawings, given purely by way of non-limiting example, wherein:

- Figure 1 is an axial cross-section of an apparatus according to the present invention,

Figure 2 is a diagram illustrating the steam supply to the apparatus of Figure 1, and

- Figures 3, 4 and 5 are details on an enlarged scale of the parts indicated by the arrows III, IV and V in Figure 1.

Detailed description

With reference to Figure 1, numeral 10 indicates an apparatus for sterilizing post-consumer absorbent sanitary products.

The apparatus comprises a container 12 rotatably supported about a longitudinal axis A by means of stationary supports 14, at least one of which is provided with actuating means that rotate the container 12 about the axis A. The longitudinal axis A of the container 12 is kept constantly fixed, preferably in a horizontal position.

The container 12 has an elongated shape along the longitudinal axis A, with an elongated cylindrical body 20 that extends between a first end 16 and a second end 18. The first end 16 is closed and has a generally hemispherical shape, and the second end 18 is provided with a loading/unloading opening 22, which is sealed closed by a removable door 24.

With reference in particular to Figures 2-5, the container 12 has a hollow wall 26 including an inner wall 28 and an outer wall 30, which enclose a hollow space 32. The hollow space 32 extends along the entire cylindrical body 20, from the first end 16 to the second end 18. Preferably, the hollow space also extends on the closed end 16. The inner wall 28 of the container 12 has an inner surface that delimits a treatment volume.

With reference in particular to Figures 2 and 3, the container 12 comprises a rotary joint 34 located at the first end 16 coaxial with the longitudinal axis A. The rotary joint 34 comprises a hub 36 fixed to the wall 26 of the container 12, having a hole 38 in communication with the inside of the container 12. The rotary joint 34 comprises two stationary rings 40, 42 arranged in sliding sealed contact with the central hub 36.

With reference to Figure 2, the stationary rings 40, 42 are connected, respectively, to a steam supply pipe 44 and to a condensate discharge pipe 46. An automatic condensate discharge device 47 is arranged on the condensate discharge pipe 46. In the central hub 36, a steam inlet chamber 48 and a condensate discharge chamber 50 are formed, in fluid connection with the respective stationary rings 40, 42. The steam inlet chamber 48 and the condensate discharge chamber 50 are connected to respective portions of the hollow space 32 through respective pipes 52, 54.

The hole 38 of the hub 36 is connected to a second steam supply pipe 56, which supplies pressurized steam inside the container 12 in direct contact with the products (contact steam) . The steam supply pipes 44, 56 are connected to a steam generator 58 by means of respective valves 60, 62. The hole 38 of the hub 36 is also connected to a vacuum pump 64 via a pipe 66 and a valve 68. The vacuum pump 64 extracts air from the container 12 prior to pressurization of the container 12 with the contact steam.

The container 12 has at least one hollow helical blade 70 fixed to the inner wall 28 of the container 12 and projecting inwardly of the container 12. The hollow helical blade 70 forms a screw with a pitch P (Figure 5) , coaxial with the longitudinal axis A and extending in the longitudinal direction A between the first end 16 and the second end 18 of the container 12. With reference to Figures 4 and 5, the hollow helical blade 70 has a helical cavity 72 which extends along the entire length of the hollow helical blade 70. The helical cavity 72 is delimited laterally by two first helical plates 74. A third helical plate 76 is fixed between the first two helical plates 74 and projects inwardly of the container 12 beyond the distal edges of the first two helical plates 74. The helical cavity 72 is delimited along its minor sides by an edge of the third helical plate 76 and by a part of the inner wall 28 of the container 12.

In the example illustrated in the Figures, the first two helical plates 74 are parallel to each other, so that the helical cavity 72 has a cross-section in the shape of a narrow rectangle. In other embodiments, the first two helical plates 74 could be inclined with respect to one another, so that the helical cavity 72 would have a triangular shape in cross-section.

With reference to Figure 5, the ratio between the height H of the hollow helical blade 70 and the radius R of the inner wall 28 of the container 12 is preferably equal to 0.2 ± 10%. The ratio between the height H' of the cavity 72 and the height H of the hollow helical blade 70 is preferably equal to 0.4 ± 10% .

With reference to Figures 3 and 4, the helical cavity 72 has an inlet opening 78 (Figure 3) located at the first end 16 of the container 12 and an outlet opening 80 (Figure 4) located at the second end 18 of the container 12. The inlet opening 78 and the outlet opening 80 are open on the hollow space 32. With reference to Figure 3, the portion of the hollow space 32 comprised between the outlet of the pipe 54 and the inlet opening 78 of the helical cavity 72 is closed by septa 82, so that the inlet opening 78 communicates directly with the steam inlet chamber 48 of the rotating connector 34 via a portion of the hollow space 32 and by means of the pipe 52. Alternatively, the outlet of the pipe 52 could be directly connected to the inlet opening 78 of the helical cavity 72 without a portion of closed hollow space between the outlet of the pipe 52 and the inlet opening 78.

The operation of the apparatus 10 is as follows. The container 12 is loaded with a load of post- consumer absorbent sanitary products coming from the recycling collection. Typically, absorbent sanitary products comprise an absorbent core of cellulose fibers and superabsorbent polymers. The absorbent core is usually enclosed between two sheets of plastic material joined together. Typically, the outer sheet (backsheet) is impermeable while the inner sheet (topsheet) is porous. The used absorbent sanitary products are usually folded so as to close the product in a packet form inside the waterproof outer sheet. Adhesive wings are usually provided to close the folded product. Organic excretions are thus enclosed within a sealed waterproof plastic sheet. The closed absorbent sanitary products are usually contained in plastic bags of the type normally used to contain household waste. The absorbent sanitary products are subjected to the sterilization treatment as they come from the collection .

The bags containing the absorbent sanitary products are loaded into the container 12 through the opening 22 after removing the door 24. During loading of the products, the container is rotated so that the helical blade 72 transports the products from the second end 18 towards the first end 16. When the container has been loaded with a predetermined amount of products (which can, for example, be measured with a load cell), the door 24 is closed and the vacuum pump 64 is activated to extract the air from the treatment volume. Then, the treatment volume is filled with pressurized contact steam fed through the hole 38 of the rotary joint 34.

At the same time, the wall 26 of the container 12 and the hollow helical blade 70 are heated by non- contact steam. The non-contact steam is fed from the chamber 48 of the rotary joint 34 to the inlet opening 78 of the hollow helical blade 70. Non-contact steam travels through the helical cavity 72 of the hollow helical blade 70. At the outlet 80 of the helical cavity 72, the non-contact steam fills the hollow space 32 of the wall 26. The condensed steam is expelled through the condensate discharge pipe 54 and the automatic condensate discharge device 47.

During the sterilization treatment, the container 12 is rotated about the axis A alternately in opposite directions. In this way, the products are continuously moved and are transported alternately in opposite directions inside the container 12. The non-contact steam inside the hollow helical blade 70 and the hollow space 26 creates hot spots that cause the bags and the outer plastic sheets of the absorbent sanitary products to break. These hot spots create localized fusion points that open holes in the plastic sheets and weaken the outer casings. The continuous movement of the products caused by the rotation of the container and of the helical blade 70 causes breakage of the outer casings and destructuring of the products. This allows a more effective drying and separation action of the materials .

The alternate transport of the products from the first end 16 to the second end 18 of the container 12, and vice versa, by means of the heated helical blade 70 provides effective contact of the products with the helical blade 70 and improves the transfer of heat to the products.

A particularly advantageous aspect of the present invention is that the non-contact steam first crosses the helical blade 70 and subsequently the hollow space 32 of the wall 26, so that the hollow helical blade 70 is hotter than the wall 26. Thus, the mass of products furthest from the wall 26, which receives less heat from the contact with the wall 26, receives more heat from the contact with the helical blade 70. This provides a more efficient and uniform heat transfer from the non-contact steam to the products.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments can be widely varied with respect to those described and illustrated, without thereby departing from the scope of the invention as defined by the claims that follow.