Title: Apparatus and method for composting.

The invention relates to a composting device comprising a composting tank rotatable about an at least fictitious axis of rotation. The invention also relates to a method for composting with the aid of such a composting tank. Composting is an accelerated form of the natural decaying process, which essentially amounts to microorganisms causing decay being well fed and provided for. To that end, sufficient nutrients such as nitrogen, carbon, air, water and the like must be present. Heat is formed during the process, resulting in heating of the product and release of gaseous products such as carbon dioxide and water vapour. Due to heating and the development of specific moulds, the undesired bacteria and seeds of weeds present in the waste are killed. This is important when, for instance, faeces and animal waste are also processed.

Traditionally, composting takes place by heaping up organic rest materials. With this so-called open air composting, a spontaneous microbiological activity, and worms, insects and the like cause decay of the organic material and a strong rise in temperature in the waste heaps. The waste has to be turned regularly for new supply of oxygen (aerating). The process takes up three to six months, while an important part of the nutrient value (minerals) of the matter is lost.

With a different manner of composting, use is made of a rotating composting drum for processing various sorts of organic rest materials into useful fertilizer. Composting can then be effected in a considerably shorter period of time than with open air composting. During the drum composting, minerals are bound to organic matter so that they no longer flush out and are released, initiated by the plant (through excretion of sugars by the plant). Pasteurization and drying can ensure the absence of harmful microorganisms.

Such, a composting drum, which has a cylinder shell rotatable about its central axis, is known from practice. The cylinder shell is open at both its end walls. At a small distance, detachable walls are placed in alignment with these open ends, before the ends, transverse to the central axis of the drum. These detachable walls do not rotate along with the cylinder shell, they are stationary walls. There is an opening in the top of each of the detachable walls. The opening in one detachable wall is for filling the drum with the material to be composted, and for natural aeration. Via the opening in the other detachable wall, forced deaeration takes place with the aid of a fan. A drawback of the known device is that the aeration and deaeration from the end walls of the drum is less effective for an adequate air exchange for the benefit of all the material present to be composted in the, generally, long drum. The fact is that the fan also draws in ambient air, via the crack at the deaeration side, into the drum. Then, this ambient air is prematurely discharged with the deaeration flow. Further, via the crack at the aeration side, the air having flowed into the drum with the aeration flow leaks away prematurely, i.e., before this air has reached the material to be composted situated farther down the drum. It is further inconvenient that material present in the composting drum leaks away, during use, through the cracks between the detachable walls and the cylindrical shell, and through the openings in the detachable walls. The thus formed leakage flows of material from the drum are to be returned into the drum.

An object of the invention is to effect a more effective aeration with a rotatable composting tank. To that end, according to the invention, a composting device comprising a composting tank rotatable about an at least fictitious axis of rotation is characterized in that a first air duct for air exchange between the interior and the exterior of the composting tank extends through a first wall part of the composting tank into the interior of the composting tank, which first wall part is situated at a first side of the composting tank, intersecting

the axis of rotation. According to the invention, a method for composting material containing organic matter, wherein the material is rotated in a rotatable composting tank about an at least fictitious axis of rotation of the composting tank is characterized in that during rotation of the material, air is exchanged between the interior and the exterior of the composting tank via a first air duct which extends through a first wall part of the composting tank into the interior of the composting tank, which first wall part is located at a first side of the composting tank, intersecting the axis of rotation.

The first air duct can be designed for operatively aerating or deaerating the composting tank. Aeration and/or deaeration can take place in a natural manner, but also in a forced manner, by means of, for instance, one or more fans and/or compressors. As the first air duct extends into the interior of the composting tank, the first air duct services the material situated further down the tank. Further, in case of aeration, introduced air is prevented from leaking away prematurely and, in case of deaeration, ambient air is prevented from being drawn in at the deaeration side. As the first wall part is situated at first side of the composting tank, intersecting the axis of rotation, the location where the first air duct extends through the first wall part of the composting tank can be in the direct proximity of the axis of rotation. Owing to this location, directly at the axis of rotation, the first air duct can be held in an effective position for aeration when the composting tank is rotated. The first air duct for instance can extend along the axis of rotation. But the first air duct can also be at a suitable angle to the axis of rotation, for instance by bearing mounting the first wall part and/or the first air duct relative to a wall part of the composting tank rotating along with the composting tank.

Specific embodiments of the invention are laid down in the subclaims.

In the following, the invention is further elucidated with reference to the schematic Figures in the accompanying drawing.

I ¹ Ig. 1 schematically shows, in side view, a longitudinal cross section of an example of an embodiment of a composting device according to the invention; and

Fig. 2 schematically shows, in side view, a longitudinal cross section of an example of a different embodiment of a compositing device according to the invention.

Presently, reference is first made to Fig. 1. Fig. 1 shows a composting device 1 comprising a composting tank 2 rotating about a fictitious axis of rotation 3. The respective rotation is indicated with reference numeral 4.

In the example, the composting tank 2 is cylindrical. Due to this shape, in the following, the composting tank 2 is also indicated as composting drum 2 or, shorter still, drum 2. This does not mean that a composting tank according to the invention cannot have various other forms with, for instance, an angular instead of a circular cross-section or with, for instance, an elliptic instead of an angular cross-section.

In the example, the axis of rotation is not a physical but a fictitious axis of rotation, i.e. the mathematical central axis of the drum 2. Rotation of the drum 3 can be effected through, for instance, gear drive along the circular outer circumference of the drum 2. However, rotation about a physical axis of rotation about which the drum rotates is also possible.

Depending on the use, the drum rotates, as a rule, at a relatively low rotational speed. The rotational speed for instance for drums with a length of 10 meters and a diameter of 2 meters, up to drums with a length of 25 metes and a diameter of 5 meters is for many uses in the order of 1 to 3 revolutions per minute.

In the example, the drum 2 has a drum shell 6 which is provided with two flaps 5 which are located, in the situation shown, at the top of the drum. When these flaps 5 are open, the drum can be filled with material 7 to be composted, for instance via the filling spouts 8 of the composting device 1.

The drum can also be emptied via these flaps, with the drum for instance in a position such that the flaps are located at the bottom of the drum so that the content of the drum can be discharged via the conveyor belt 9 of the composting device 1 situated under the drum. A drum can have different numbers and different types of flaps.

The drum 2 has a first side 10 that intersects the axis of rotation 3. In the example shown, the first side is an end wall of the drum 2. In case the form of the composting tank is other than cylindrical, the first side can also be formed differently, or intersect the axis of rotation in a different manner, for instance, the first side can intersect the axis of rotation obliquely. At the first side 10, a first wall part 11 of the drum is located. Through this first wall part

11 extends a first air duct 12 into the interior of the drum 2. The first air duct

12 serves for air exchange between the interior and the exterior of the drum 2. In the example shown, the first air duct 12 serves for aeration of the drum 2. The associated direction of the airflow is indicated with arrows A. The aeration can be forced by means of, for instance, a fan 14.

During rotation of the drum 2, the first wall part 11 and the first air duct 12 do not rotate along with the drum. The first air duct 12 is thus held in a position effective for aeration during rotation of the drum. Preferably, the first wall part 11 and/or the first air duct 12 are/is bearing-mounted in the remaining part of the end wall at the first side 10 of the drum. The Figure shows such a bearing 15. Bearing-mounting is simple and effective and prevents material 7 from leaking from the drum.

The composting process depends on the amount of material to be composted. A larger amount of material yields a better composting. It further applies that the more the drum is filled with material, the more economical the drum can be utilized. However, an air chamber needs to be present in that the material to be composted can adequately take up oxygen and release water vapour and carbon. It is therefore important to achieve an optimal degree of filling with an optimal air exchange. A good air exchange is achieved if the

first air duct terminates in the interior of the composting tank above the level to which the composting tank has been filled with the material. The fact is that in that case, the air duct terminates more or less freely in the air chamber.

When a composting drum is filled with the material 7 for approximately 50% of the maximum internal height of the drum, upon rotation of the drum, it mixes the material 7 together well, and the air chamber in the drum is sufficiently large for an adequate air exchange. In that case, it is advantageous when the location where the first air duct 12 terminates in the interior of the drum, is at a height in the upper 50% of the internal height range of the drum. In the case of aeration, efficient mixing of material introduced into the rotation drum and the material 7 takes place and, in the case of deaeration, released gases are efficiently discharged.

It has appeared that as a rule, the drum is used more efficiently when it is filled for more than 50% with the material 7. A particularly efficient process is obtained when the drum is filled for approximately 80% of the maximum internal height of the drum. In the latter case, it is advantageous when the location where the first air duct 12 terminates in the interior of the drum is at a height in the upper 20% of the internal height range of the drum. In the case of aeration, efficient mixing of air introduced into the rotation drum and the material 7 takes place, and, in the case of deaeration, released gases are discharged efficiently.

In use, material 7 may end up in the first air duct 12 at the location where the first air duct 12 terminates in the interior of the drum. That is why it is advantageous when a conveyor screw is located in the interior of the first air duct, which conveys the material having ended up in the first air duct back into the drum, i.e., in the direction of the arrow B in Fig. 1. In the Figure, a first conveyor screw 16 is shown which is placed in the first air duct with its axial direction parallel to the longitudinal direction of the first air duct 12. A drive 17 drives the conveyor screw in the desired direction of rotation.

V

Various types of conveyor screws can be used. The screw can for instance have a screw axis having one or more helicoidally oriented, elongated propeller blades thereon. Also, several shorter propeller blades instead of helicoidally oriented, elongated propeller blades can be provided on the screw axis. Further, conveyor screws with helicoidally elongated propeller blades can also be designed without screw axis. It is important that the presence of the conveyor screw in the interior of the first air duct does not prevent the airflow through the air duct. This can be realized by using, for instance, a screw diameter which is smaller than the internal diameter of the air duct. A screw diameter of approximately two thirds of the internal diameter of the air duct is, for instance, suitable for effectively returning material to the drum without hindering the airflow.

At the other end wall 20 of the drum 2, a second air duct 22 for air exchange between the interior and the exterior of the drum extends through a second wall part 21 into the interior of the drum. This is realized in a similar manner as with the first air duct 12. In the example of Fig. 1, the second air duct 22 is designed for operatively deaerating the drum. This can be natural deaeration, but also forced deaeration, with the aid of, for instance, a fan 24. The associated direction of the deaeration flow is indicated with arrows C. The second wall part 21 is bearing mounted in a similar manner as the first wall part 11, by means of the bearing 25. For returning material having ended up in the second air duct, in the direction of the arrow D, the second air duct is provided with a conveyor screw 26 with drive 27.

This combination of the first and second air ducts, while one is designed for aeration and the other for deaeration, provides a particularly effective and controllable air exchange, so that composting in the drum is possible within a very short period of time, even less than 24 hours. With the aid of the air exchange, also, for instance, the temperature in the drum can be monitored for the purpose of, for instance, pasteurization. With pasteurization, a high temperature is utilized for a specific period of time, for instance a

temperature of 70 degrees Centigrade for one hour, or a temperature of 60 degrees Centigrade for ten hours.

Reference is now made to the exemplary embodiment shown in Fig. 2. Here is shown a composting drum 102 of a type similar to the drum 2 of Fig. 1. At the end wall 120, the drum 102 has a second deaeration duct 122 of the same type as the second air duct 22 on the side 20 of the drum 2. A difference between the examples of Figs. 1 and 2 is that the drum 102 has a different first air duct 112 for aerating the drum 102. The first air duct 112 extends through a first wall part 111 of the drum into the interior of the drum, while the first wall part 111 is located at a first end wall 110 of the drum, intersecting the axis of rotation. The walls of the first air duct 112 located in the interior of the drum are perforated for the passage of air from the interior of the first air duct to the interior of the drum. The respective perforations are indicated with reference numeral 128. In the example, a fan 114 effects forced aeration in the direction of the arrows E in Fig. 2.

In this manner, the mass of the material 107 is effectively provided from the interior with fresh air, while gases to be discharged which accumulate in the top of the drum are effectively discharged via the air duct 122. In the example, the air duct 112 is a cylindrical tube situated coaxially in the drum. In the drum is located a helicoidally oriented, elongated blade 130 which is connected to the cylinder shell 106 via holders 129. The blade 130 runs closely around the air duct. Upon rotation of the drum, the blade 130 enables a continuous cleaning of the outer circumference of the first duct 112 so that a good air passage through the perforations 128 remains guaranteed.

In the above-mentioned examples, during rotation, the composting tanks remains closed for supply and discharge of material. This means that the process is carried out batch-wise in the sense that prior to rotation of the composting tank, an empty composting tank is first filled with material to a desired level of filling, and that after rotation, the tank is completely emptied.

In this manner, the process can be carried out in a short period of time and a high-grade fertilizer is obtained. It is noted that such advantages are also achieved if the closing mentioned during rotation of the composting tank is utilized in combination with other manners of aeration/deaeration. The technique described by means of the above-mentioned examples provides a particularly intensive and rapid manner of composting, while the nutrient value is effectively retained in that it is bound to the organic matter during composting.

It is noted that the above-mentioned examples of embodiments of the invention are not limitative and that within the range of the accompanying claims, various alternatives are possible. For instance, on one side of the composting tank, intersecting the axis of rotation, more than one of such air ducts can be utilized. On such a side, for instance both an air duct for aeration and an air duct for deaeration can be used. Such and comparable alternatives are understood to fall within the framework of the invention as defined in the accompanying clams.