SE520713C2 - Device, method and system for drying biological waste - Google Patents

Description

35 . . , . ,. 520 715 2 The aim of the wastewater treatment plants is to be able to handle the biological fraction with the existing transport and handling systems that exist today.

There is also an effort from society to, within the framework of the cycle adaptation of various activities, recycle and reuse the energy and nutritional values as well as valuable minerals found in biological waste and return them to the cycle in the form of, for example, sludge to the fields or as raw material in animal feed production.

One method to get around the problems described above is microwave drying of the waste. There are currently a number of different devices of this type. However, these have a number of problems. For example, there is a risk of fire due to the risk of overheating when irradiating the waste with high-energy microwaves. In addition, unpleasant odors can be formed and unwanted substances, such as mold spores, can be spread in connection with the drying of the waste, and these can spread throughout the premises and it is also difficult to achieve effective drying.

Purpose of the invention The purpose of the invention is thus to provide a device and a method for drying biological waste consisting of, for example, fruit, vegetables, meat and fish, with which the above-mentioned problems with the known technology are eliminated. A further purpose of the invention is to provide a device and a method/system for drying the waste and thereby making it storage-stable so that existing transport and handling systems can be used without extra investments. A further purpose of the invention is to provide a method for handling biological waste that is economically and in terms of handling advantageous, at the same time as set societal goals in terms of circular thinking can be achieved. 10 15 20 25 30 35 520 713 gig. 3 Summary of the invention The above-mentioned objects are achieved according to the invention with a device characterized in that the device comprises a closed circuit, which passes through said chamber, through which the air is arranged to circulate. This means that any malodorous gases formed in the drying chamber do not diffuse into the surrounding air, but remain in the closed system, which means that the device can be placed, for example, in a grocery store without the risk of bad odors or the spread of bacteria.

A dehumidification unit is further suitably arranged in the closed circuit, for the purpose of dehumidifying the air that exits the chamber. The air in the closed system is thereby dehumidified and can thus be recirculated into the chamber for new moisture absorption. The air can thus be reused and does not need to be replaced in the closed system. A closed container is suitably tightly connected to said dehumidification unit, for receiving and storing the discharged liquid. This means that the discharged liquid does not come into direct contact with the surrounding air, and thus does not emit any bad odor, bacteria or the like to the surroundings.

Furthermore, a heating unit is suitably arranged in said circuit, for the purpose of heating the gas, before it enters the chamber, in order to obtain a more efficient liquid uptake. This in turn allows the waste in the chamber to be heated to a suitable temperature.

Preferably, a stirring means is arranged in the chamber for stirring the waste. This allows for more even heating and drying of the waste, which avoids the formation of hot zones in the waste, thereby reducing the risk of overheating.

Furthermore, a sensor is suitably arranged in the closed circuit, before the dehumidification unit in the flow direction, whereby the sensor is connected to a control unit, for controlling the radiation effect in relation to the moisture content in the air stream in said position, in order to obtain an equilibrium between the moisture generated during the irradiation and the moisture that the air stream is able to transport away.

The device can thus be optimized in such a way that exactly as much moisture is generated in the chamber as the air in the closed circuit is able to transport away. Furthermore, the irradiation with, for example, microwaves can be interrupted at a suitable time. Furthermore, the above-mentioned objectives are achieved with a method as a function of the sensor output signal. for drying biological waste, comprising the steps of placing the waste in a tightly closed chamber, blowing hot air into the chamber to heat the waste, irradiating the waste in the chamber preferably with microwaves, to dry the waste, removing released moisture from the chamber with an outgoing air stream and recirculating the air via a closed circuit to blow the air back into the chamber. This method results in drying the waste, at the same time as the moisture that is generated is removed from the chamber. Thanks to the closed circuit, malodorous and contaminated gases are further prevented from spreading to the surroundings.

The method also suitably comprises the step of transporting the outgoing air stream via the closed circuit to a dehumidification unit for cooling and dehumidifying the air, and then to a heating unit for obtaining warm air, and then blowing the warm air into the chamber again, whereby the air is circulated in the closed circuit. The heating of the air before the chamber means that the air has an increased tendency to remove moisture, which increases the efficiency of the device. Furthermore, the air is dehumidified in the dehumidification unit in a conventional manner, and can thus be recirculated to the chamber for absorbing further moisture.

The discharged liquid formed in the dehumidification unit is preferably conveyed via a closed system to a closed storage chamber. This means that the liquid does not come into direct contact with the surrounding air, and thus does not emit any bad odors or bacteria into the environment.

Furthermore, the step of irradiating the waste in the chamber with preferably microwaves for drying the waste also includes irradiating the waste with a uniform radiation effect, until the moisture content in the outgoing air stream drops below a predetermined value.

This results in rapid and efficient drying, until the waste has reached a predetermined degree of dryness. Suitably, the step of irradiating the waste in the chamber with preferably microwaves for drying the waste also includes, after said uniform irradiation, lowering the radiation power stepwise/continuously and, under a certain power, pulsing the radiation source to a predetermined moisture content in the outgoing air stream, and then ceasing the irradiation. This pulsing allows the waste to cool between the pulses, which contributes to an effective final drying to obtain a high degree of dryness of the waste. Furthermore, the step of irradiating the waste in the chamber with preferably microwaves for drying the waste also includes initially gradually increasing the radiation power, while monitoring the temperature in the chamber, so that it does not exceed a predetermined value. This provides a gentle temperature gradient at the beginning of the heating process.

Finally, the above-mentioned objects are achieved with a system for processing and drying biological waste, the system comprising a device of the type described above.

Preferably, the system also includes a distribution device for finely distributing the waste before drying, which contributes to a more even drying result. Furthermore, the system also suitably includes an extraction device for extracting dried waste from the chamber in the drying device to a storage unit. Furthermore, a packaging device, whereby the dried waste is transported to this for direct packaging in bags or the like, can also be included in the system. This results in a fully automatic 10 15 20 25 30 35 520 713 6 method for handling biological waste, in the vicinity of the place where the waste arises.

Brief description of the drawings The invention will hereinafter be further described by way of example with reference to the accompanying drawings.

Fig. 1 is a schematic view of a device according to the invention.

Fig. 2 is a perspective view of a drying device according to an embodiment of the invention.

Fig. 3 is a schematic view of a system comprising a drying device according to the invention.

Description of preferred embodiments The drying device 1 according to Figs. 1 and 2 comprises a cylindrical drying chamber 2, which is made of a microwave-permeable material, for example plastic. The drying chamber 2 is surrounded, except at its top, by a microwave-shielding metal casing (not shown). Two air nozzles open into the bottom of the chamber 2 and three microwave applicators/guides 17 open into the side wall of the metal casing, which are connected to microwave-generating magnetrons 14 which are cooled by a cooling fan 15. Together, these form a microwave unit 13. The microwave applicators are evenly distributed in the height direction of the chamber. The air nozzles 5 blow out air at an angle, preferably about 30°, relative to the horizontal plane at mutually different angles, to form a cyclic rotation of the air. This results in a large contact surface between waste and air. In this case, the nozzles consist of plates covering the orifices, and which have oblique (about 30°) through openings. Furthermore, a stirring member 4 is arranged in the chamber, which comprises a centrally rotatably mounted arm. This stirring member is connected to a motor, and can be rotated in the chamber at a speed of, for example, 10-20 revolutions per minute. The chamber is open upwards, but is closed by a lid 3, which also comprises a metal plate, to complete the shielding metal casing. Together, this plate, together with the above-mentioned metal casing, completely surrounds the drying chamber 2, when the lid is closed, to provide complete shielding. At the top of the chamber there is an opening 6, covered with a perforated plate 7 around the upper part of the drying chamber, through which opening 6 the air exits. From this top opening 6 a channel 16 extends, which leads to a condenser 9. The channel 16 then leads via a fan 8 to an electric heating battery 12 and then finally opens into the air nozzle 5 described above to form a closed circuit. The condenser 9 is further tightly connected to a container 10 for condensate. This container can be emptied via a valve 11. Furthermore, a number of sensors S1, S2 are provided in the device. These can be located at a number of different positions in the device, but in the case shown, a first humidity sensor S1 is arranged before the condenser for the purpose of checking the humidity content in the outgoing air flow. at the chamber. Furthermore, a second sensor is located before the nozzles for measuring the air temperature in the chamber.

The sensors are connected to a control unit 18. Together, the above-described units form a closed loop, or circulation system, in which the air can be circulated without coming into contact with the surrounding atmosphere during drying. As an example, the air in the system during drying may have a circulation rate of about 100 n?/h.

When drying biological waste, e.g. fruit residues, fish, vegetables and meat, the waste is placed in the chamber 2, after which the lid 3 is closed and the chamber 2 is sealed. Preferably, the waste has been finely divided into pieces of even size before being placed in the chamber 1. This can be done by means of a distribution device I which is placed in connection with the drying device. This is shown schematically in Fig. 3. The distribution device also comprises an integrated sorting table for sorting the waste. Optionally, a distribution device for this purpose can be arranged in the chamber. The fan 16 is then started, and air thereby begins to circulate in the system. In connection with this, the electric heating battery 12 is started, which heats the air to a selected temperature, whereby the air later gives off this heat to the waste in the chamber. The air is heated by the battery to a temperature of between about 50°-150°C, preferably between 75°-100°C, suitably about 80°C.

The heating of the air leads to an increase in the air's ability to absorb moisture. Thanks to the injection of hot air, the waste in the chamber is thus heated. When the waste has reached a set temperature, the magnetrons 14 are started at a relatively low power, which is increased gradually as the evaporation of moisture from the waste increases. The magnetron power is then kept at a constant level until the moisture sensor S1 located before the condenser 9 indicates that the moisture content in the outgoing air is decreasing, after which the magnetron power is gradually reduced until it falls below a certain value, during which the magnetrons 14 are pulsed for 10-20 seconds per minute until the moisture content in the air stream reaches a preset value. The microwave radiation is then interrupted, while the fan 8 is allowed to remain on for a further period of time, in order to achieve a post-drying of the waste. During the entire drying period, the above-mentioned sensors S1, S2 monitor the moisture content and temperature in the various parts of the system, respectively, in order to control the magnetron irradiation and the electric heating and thus optimize the drying process, while avoiding overheating of the system and the formation of liquid in the chamber. Optimally, the air removes precisely all the moisture generated during microwave drying of the waste. If too much moisture is removed, the waste risks overheating, with a risk of fire as a result. The device can therefore also, as an extra safety measure, be provided with means for fire protection. If too little moisture is removed, liquid forms in the drying chamber 2, which leads to a poorer drying result and greater time consumption. The moist air that is formed in the chamber is sucked out through the perforated plate 7 and out into the duct and on to the condenser. In the condenser 9 the air is dehumidified in a conventional manner. Before the condenser the air can have a relative humidity of 20-100%. When the air is cooled in the condenser the relative humidity rises to 100% and water is precipitated. The condensate is transported to the above-described condensate container 11 for storage. After the condenser the air is transported further to the electric heating battery where the air is heated again and the relative humidity drops to 15-25%, before being blown back into the drying chamber.

The units described above are arranged in a closed system, which means that no odor or the like is at risk of escaping, which makes the device suitable for use in, for example, grocery stores and restaurants.

The waste product from the above-described device is the bioflakes, so-called bioflakes. Thanks to the drying process, unlike pressing, for example, the entire nutritional value that was in the waste remains. This means that the bioflakes can be used as an additive in, for example, animal feed. Furthermore, the bioflakes can be used as an additive in, for example, composting, digestion or incineration. Thus, the biological waste is transformed from garbage into a useful product. Another advantage of drying is that the volume and weight of the waste are significantly reduced. In the case of animal waste, the volume after drying is about 50% of the original and in the case of vegetable waste, the volume is about 10-20% of the original. The weight reductions in each case are of a corresponding magnitude. The maximum moisture content is 10% in both cases. This also leads to reduced transport costs.

The waste is sanitized by heating to at least 75°C for at least 1 hour, whereby pathogenic bacteria are killed. The bioflakes are thus stable at room temperature for at least six months, and are essentially odorless. This dried waste can be stored in a normal room. The waste can be conveniently stored directly in containers that are adapted for transport. A suction device is conveniently used to empty the chamber of dried waste into a storage container before new waste for drying can be filled into the chamber. Thanks to the fact that the dried waste is both stable in storage and essentially odorless and sanitized, the dried waste can also be collected by the same vehicle that delivers, for example, food, which results in a changed and cheaper waste management. Furthermore, a conventional packaging machine can be arranged in connection with the drying device, for direct packaging of the bioflakes in bags or the like.

It is understood that a number of modifications of the above-described embodiment of the invention are possible within the scope of the invention, as defined by the following patent claims. For example, the above-mentioned fan can be located in different positions in the system, since its sole purpose is to circulate the air in the closed circuit. Furthermore, the sensor placement can vary, and the sensors can be, for example, temperature or humidity meters, depending on the design of the control box. It is also described above that the air flow from the air nozzles has an angle relative to the horizontal plane of about 30°. This angle can of course be varied with respect to the geometry of the chamber, etc. The embodiment described above also has air nozzles for blowing air into the bottom of the chamber, and air outlets at the top of the chamber. These nozzles and outlets can be located at different locations in the chamber, but are suitably, as in the above example, arranged on opposite sides of the chamber, to provide an air flow through essentially the entire chamber. The radiation sources described in the exemplary embodiments are microwave sources, more specifically magnetrons, but it is also possible to use radiation sources in certain other wavelength ranges, for example in the infrared radiation range. The use of a condenser as a dehumidifying unit is also described above, but this condenser can be replaced by a compressor, for example. Furthermore, a number of alternatives and possible modifications are described in the above description.

Claims (17)

u) UI 520 713 l2 PATENT CLAIMS Device for drying biological waste, in particular food waste, the device comprising a chamber (2) for receiving the waste and at least one radiation generating source (14), preferably a microwave generating source, which is arranged for irradiating and drying the waste in said chamber (2), characterized in that the device comprises a closed circuit (2, 16), which passes through said chamber (2), through which air is arranged to circulate, in such a way that at least one nozzle is arranged in said chamber, through which hot air, for heating said waste, is intended to be introduced. Device according to claim 1, characterized in that a dehumidification unit (9) is arranged in said circuit (2, 16), for the purpose of dehumidifying the air exiting the chamber (2). Device according to claim 2, characterized in that a closed container (10) is tightly connected to said dehumidification unit (9), for receiving and storing dispensed liquid. Device according to claim 1, 2 or 3, characterized in that a heating unit (12) is arranged in said circuit, for the purpose of heating the air, before it enters the chamber (2). Device according to one of the preceding claims, characterized in that a stirring means (5), for stirring the waste, is arranged in the chamber (2). Device according to claim 2 or 3, characterized in that at least one sensor (S1) is arranged in the closed circuit, before the dehumidification unit (9) in the flow direction, the sensor (S1) being connected to a control unit ( 18), for controlling the microwave power in relation to the moisture content of the air stream in said position. A process for drying biological waste, comprising the steps of: 10 15 20 25 30 Q! U '| 520 713 13 place the waste in a tight-fitting chamber, blow hot air (A) into the chamber to heat the waste, irradiate the waste in the chamber preferably with microwaves, to dry the waste, remove excess moisture from the chamber with an outlet (B) , via a closed circuit (2, 16) air flow and recirculate the air to re-blow the air into the chamber. A method according to claim 7, also comprising the step of: transporting the output (16) and then to an air stream (B) via the closed circuit (2, 16) to a dehumidification unit for cooling and dehumidifying the air, 12), and then a heating unit for obtaining hot air, in the chamber, the air 16). also including blowing again the hot air (A) is circulated in the closed circuit (2, A method according to claim 8, comprising: passing the discharged liquid formed in the dehumidification unit (9) to a closed storage chamber (10) via a closed system. A method according to any one of claims 7-9, wherein the step of irradiating the waste in the chamber (2) with preferably microwaves for drying the waste further comprises the step of: irradiating the waste with an even radiating effect, until the moisture content in the the outgoing air flow (B) falls below a predetermined value. The method of claim 10, wherein the step of irradiating the waste in the chamber (2) with preferably microwaves for drying the waste further comprises the step of: after said even irradiation gradually lowering the radiation effect and, during a certain effect, pulsing the radiation source during 10-20 sec per minute until the moisture content of the air stream 10 15 20 25 30 520 713 14 reaches a preset value, and then stop irradiating. A method according to claim 10 or 11, wherein the step of irradiating the waste in the chamber (2) with preferably microwaves for drying the waste further comprises the step of: initially gradually increasing the radiating power, while monitoring the temperature of the exhaust air flow from the chamber (2), value. so that this does not exceed one predetermined Systems for processing and drying biological waste, in particular food waste, characterized in that the system comprises a drying device (II) of the type defined in any one of claims 1-6. k ä n n e t e c k n a t av (I), atomization of the biological waste before drying. The system of claim 13, further comprising a distribution device for System according to claim 13 or 14, characterized in that it also comprises an extraction device (III), from the chamber in the drying device for extraction of dried biological waste (II) system to a storage unit. System according to claim 14 or 15, characterized in that said devices are integrated in a unit. 17. A system according to any one of claims 13-16, characterized in that it also comprises a packaging device (IV), wherein the dried waste is transported to it for direct packaging in bags or the like (V).