COMPOSTING PLANT

BACKGROUND OF THE INVENTION

[0001] The invention relates to a composting plant according to the preamble of claim 1 , and particularly to a composting plant comprising one or more containers comprising a first end and a second end, conveyor means provided at the first end of the container for feeding material to be composted to the containers as well as discharge means provided at the second end of the container for conveying the composted material out of the container.

[0002] According to prior art, composting is carried out as clamp composting, tunnel composting or as various applications thereof. In clamp composting, the material to be composted is collected outdoors in heaps on a concrete base or a corresponding flat base. The heaps may come in many different shapes and sizes, and they are mechanically turned at regular intervals in order to produce sufficient aeration. Tunnel composting differs from clamp composting mainly in that tunnel composting takes place indoors in a tunnel- like building. In the prior art composting procedures, in practice the material to be composted is transferred, mixed and aerated using a bucket loader and/or a loosening tool developed for the purpose and/or a fixed aeration pipe system.

[0003] A problem with the above-described prior art composting arrangements is that aeration and mixing of the material to be composted cannot be performed in a similar manner on all particles contained in a compost. Neither can any additional aeration possibly to be performed on the material be carried out in a controlled and accurate manner ubiquitously in a heap. This results in formation of airless pockets in the heaps in which the composting process stops and may even change into an anaerobic biogas process. This, in turn, results in large differences in local temperatures in the mass being composted, since unlike areas in aerobic state, areas in anaerobic state do not produce, but consume, heat. Such a non-uniform temperature, in turn, means that the process temperature cannot ubiquitously rise to a level required by a hygienic end product, and the pathogen contents of the end result remain too high in terms of official requirements. Furthermore, such a non-uniform process according to conventional composting methods also influences the fact that the end product of composting contains organic substance, which further continues uncontrolled decomposition and emits odorous gases to the environment.

BRIEF DESCRIPTION OF THE INVENTION

[0004] An object of the invention is thus to provide a composting plant according to the preamble of claim 1 so as to solve the aforementioned problems. The object of the invention is achieved by a composting plant which is characterized in that the container is a drum container to be rotated around its substantially horizontal longitudinal axis by rotating means.

[0005] Preferred embodiments of the invention are disclosed in the dependent claims.

[0006] The idea underlying the invention is that for a composting process, at least one container, preferably a drum-like container, is provided into which the material to be composted is fed by conveyor means. The material to be composted may be mixed with a support substance to enhance the composting process in the container. This support material is mixed with the material to be composted by mixing means, preferably prior to feeding the material to be composted to the container by means of e.g. mixing means integrated in the conveyor means. The operation of the composting plant is based on the fact that the drum container is made rotatable around its substantially horizontal longitudinal axis. This enables the composting process to be controlled by this rotating of the drum container such that transfer, mixing, lifting, turning, and aeration of the mass to be composted as well as other possible functions are optionally combined with this rotating of the drum container. According to the invention, the drum container is not rotated continuously but periodically. The rotating may take place by rotating the drum container by a part of one turn, half a turn or one complete turn at a time. Preferably, however, the drum container is rotated by 2 to 5 complete turns per day. The inside of the drum container is provided with wings, surface contours or other corresponding guide means to guide the movement of the material to be composted inside the drum container e.g. by mixing, transferring and lifting the material to be composted. These guide means may be fixed, movable or rotatable in relation to a wall of the container, so that their movement may be connected with the rotation of the container.

[0007] Each container is further provided with aeration means for feeding air to a container in order to enhance the composting process of the material to be composted. Furthermore, each container is provided with discharge means for discharging composted material out of the container. The composting plant as described above operates as a continuous process and

the composting process taking place therein may be guided in a controlled manner according to the requirements of the material being composted at a particular time.

[0008] The composting plant according to the invention provides a controlled process which takes place at a high and uniform temperature and which is considerably faster than the conventional composting processes. Clamp composting requires a total processing time, including after-ripening, of about 12 months, tunnel composting about 9 to 12 months, whereas the composting plant according to the invention requires only 2 to 4 months. In addition, the composting apparatus according to the invention provides a uniform and controlled process which may utilize a high and uniform process temperature to ensure a hygienic and high-quality end product. The composting plant according to the invention operates as an automated process whose operating costs are low. Furthermore, it is possible to recover heat generated by the process and at the same time prevent odorous emissions as well.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is now described in closer detail in connection with preferred embodiments and with reference to the accompanying drawings, in which:

[0010] Figure 1 is a schematic side view showing a composting plant according to the present invention; and

[0011] Figure 2 is an end view showing the composting plant of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

[0012] In the following, the invention is described in connection with one embodiment of a composting plant according to the invention.

[0013] An embodiment of the composting plant according to the present invention comprises one or more containers 2. In this embodiment according to Figure 1 , the composting plant comprises one container 2, which is a cylindrical drum container arranged in a horizontal plane such that the longitudinal axis of the cylinder is substantially horizontal. In the present context, substantially horizontal means a horizontal position as well as a position at an angle of not more than about 20 degrees with respect to the horizontal. In such a case, the cylindrical containers 2 comprise a first and a second end 4, 6 as well as a housing extending between the ends. However, it is to be noted that

the container 2 may also have another shape or it may also be in another position. The volume of the container 2 may be 5 m ³ to 300 m ³ , preferably 50 m ³ to 125 m ³ . Containers 2 larger or smaller than this are also possible. The composting plant may thus comprise one or more containers 2 as described above that may differ in size and properties, in accordance with different materials to be composted. In order to achieve an optimal composting result, the dimensions of the drum container 2 are to be selected such that the passing through time for the material to be composted does not allow the material to be composted to dry too much or too little in the drum container. Too much or too little drying results in diminished process control and an impaired end product.

[0014] In this embodiment, conveyor means 8 are connected to the first end 4 of the container 2 for conveying the material to be composted to the container 2. The conveyor means 8 may be e.g. a screw conveyor, belt conveyor or another conveyor appropriate for such a use. In this embodiment, the conveyor means 8 are preferably provided in the first end 4 of the cylindrical container 2, wherefrom the conveyor means 8 feed the material to be composted to the container 2. Prior to being conveyed to the container 2 by the conveyor means 8, the material to be composted may be pre-processed by pre-processing means, such as grinding means for breaking up the material to be composted.

[0015] The material to be composted may be mixed with a support substance, such as peat, straw, sawdust or the like, or a chemical mixing agent in order to enhance the composting process and to produce an appropriate mixture material. The dry content of the mixture material being produced is typically 10 to 30%. The support substance may be fed by the mixing means directly to the container 4 in to the material to be composted contained therein or, preferably, the support substance is mixed with the material to be composted by means of the mixing means prior to feeding the material to be composted to the container 2, in which case a finished mixture material is fed to the container 2. The mixing means may be separate means or they may be integrated in the conveyor means 8, in which case the procedures of mixing and conveying the material to be composted to the container 2 take place simultaneously.

[0016] According to the present invention, the drum container 2 is made rotatable around its substantially horizontal longitudinal axis 12. When such a cylindrical, substantially horizontally lying drum container 2 is used, ro-

tating thus takes place around this horizontal longitudinal axis of the cylinder. The drum container 2 is thus installed in a frame of the composting plant such that it is able to rotate. The container 2 is rotated by rotating means 14 which, in the embodiment according to Figure 2, comprise hydraulic rotating means, and a hydraulic fist in particular. The housing of the drum container 2 is provided with stop parts or teeth 16, against which the hydraulic fist impacts or is pushed, rotating the container. The rotating means 14 further comprise stopping means which prevent the drum container from rotating backwards on the rotating means 14 after rotating. These rotating means 14 and their operation are arranged such that the drum container is rotated by only a part of a turn, half a turn or one complete turn at a time. The hydraulic fist as well as the stop parts 16 provided in the housing of the drum container are situated between the ends of the container, preferably centrally at a similar distance from the first and the second end 4, 6. Alternatively, the rotating means 14 may also be located at another place. The rotation of the container 2 is automated and it may be adjusted according to the material being composted at a time. In a normal case, the container is rotated 2 to 5 complete turns per day.

[0017] The inside of the drum container 2 is provided with guide means (not shown) for guiding the mass contained in the container by rotating the drum container 2. These guide means are arranged such that they enable the material to be composted contained in the drum container 2 to be mixed and/or lifted upwards and/or pushed forward in the container 2 towards the other end thereof. The guide means are wings provided inside the container 2 and/or surface contours provided on the inner surface of the container or other corresponding guide elements that are capable of performing the aforementioned tasks in connection with the rotation of the drum container 2. These guide means may comprise e.g. surface contours or separate wings provided in an inner wall of the container 2 or a screw-like structure provided inside the container which extends substantially between the ends of the container 2. At least some of these guide means are fixed, movable or rotatable with respect to the wall of the drum container 2. The movement and/or rotation of the guide means is preferably connected or engaged with the rotation of the drum container 2, so they do not have to be rotated separately.

[0018] Depending on the properties of the material to be composted or the mixture material, the composting process is enhanced in the container 2 by feeding air to the container 2 from the first and/or second end 4, 6 of the

container 2 by the aeration means. Alternatively or additionally, aeration may be carried out by feeding air to the container 2 through the housing of the container, using e.g. aerator pipes. According to the invention, aeration may be carried out by any suitable means which further enable the aeration process to be adjusted as well. The mixing and aeration of the material to be composted in the container 2 ensure that the material to be composted becomes processed ubiquitously, which results in as good and uniform-quality composted product as possible. Mixing and aeration as well as the support substance used enable the temperature of the composting process, and thus the quality and composting speed of the end product, to be adjusted. This adjustment enables a controlled, controllable and stable composting process.

[0019] During the process, the temperature in the container 2 is preferably at least 55°C, but it may rise up to 70 ⁰ C. A majority of the heat generated in the process binds itself to the air fed to the container 2 by the aeration means. The aeration air is further fed out of the container 2 by the aeration means and recovered, so by using heat recovery means, it is possible to recover heat from this discharge air for recycling. Furthermore, odours and possible detrimental gases which are generated during the process and which bind themselves to the discharge air can be removed using an air purification apparatus after heat recovery. For instance, a biofilter, ozonizer or a corresponding purification apparatus may be used as the air purification apparatus. Thus, no odorous gases or similar detrimental gases are emitted to the environment. After purification, the discharge air may be removed out of the composting plant. Odorous gases may be purified also without heat recovery.

[0020] The composting plant according to the invention further comprises discharge means 10 for conveying the already composted material out of the container 2 and further to a discharge conveyor which transfers the composted material to a desired post storage or intermediate storage or another place. In the present embodiment, the discharge means 6 are provided at the second end 6 of the container 12, opposite the conveyor means 8. Any suitable means may be used as the discharge means 10 for discharging the already composted material out of the container 2. In an embodiment, the mixing means may be used also as the discharge means for transferring the composted material out of the container. However, the second end 6 of the container 2 may also be provided with separate discharge wings for discharging the composted material.

[0021] A preferable passing through time for the material to be composted is at least seven days, and typically the passing through time is 10 to 12 days. The end product then produced by the composting plant is extremely hygienic and high-quality compost, earth-improving material or the like. Such a compost is free e.g. of salmonella and listeria, and it does not cause disadvantageous leakages or odours to the environment. Furthermore, the compost thus achieved does not attract harmful animals, such as rats, mice, birds or flies.

[0022] The composting plant according to the present invention is intended for local composting in particular. Such a composting plant may also be placed in a movable structure, such as a freight container, so that it may be transported to a desired place for use.

[0023] It is apparent to a person skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the above-described examples but may vary within the scope of the claims.