Method and device for processing liquid organic waste material

Abstract

The invention relates to a method for processing liquid organic waste material, particularly slurry or sludge. This method comprises the following steps of: a) feeding a quantity of liquid waste material to a first space, b) distributing the liquid waste material over a moving surface in the first space and heating the first space with the liquid waste material therein, c) extracting primary vapour created by partial evaporation of the liquid waste material from the first space, d) compressing the extracted primary vapour in mechanical manner, e) transferring at least a part of the waste material dried out by evaporation from the first space to a second space, f) feeding the compressed primary vapour to the second space and bringing it into heat-exchanging contact with the dried-out waste material, g) feeding primary vapour condensed by the heat-exchanging contact from the second back to the first space, and f) discharging waste material dried by the heat-exchanging contact from the second space. The invention also relates to a device for performing this method.

Description

[0001] Method and device for processing liquid organic waste material

[0002] The invention relates to a method for processing liquid organic waste material, particularly slurry or sludge.

[0003] Slurry is currently causing severe problems in areas with intensive livestock farming. This is because slurry is a mixture of manure and urine, which combination produces ammonia, a compound of nitrogen and hydrogen (NH3). When ammonia is released in gas form from for instance animal accommodations or from fertilized agricultural land due to evaporation, it is spread by the wind. Finally, the ammonia find its way onto and into the soil again as nitrogen deposition, either through precipitation or through direct absorption from the air. Nitrogen deposition makes the soil rich in nutrients, which is a problem in nature areas. Flora which conversely thrives on nutrient-poor soil, and fauna associated therewith, will disappear there, causing a decrease in biodiversity.

[0004] Because manure production is directly associated with the number of animals being held, proposed solutions are based on (considerably) decreasing cattle numbers. A decrease in cattle numbers is however met with much resistance from livestock farmers, and seems unlikely to be achieved on a voluntary basis.

[0005] Described in US 5 810 975 A is a device for extracting a solid residue from a watery slurry. This is a device which is provided with a single vertical hollow shaft with horizontally rotating discs over which the slurry is distributed. The slurry is dried in a single revolution of the discs.

[0006] US 2021 / 094842 Al describes a processing system for separating liquids and solids from a slurry. This is also a device with a single hollow shaft, although the shaft has a horizontal orientation and the rotating discs a vertical orientation.

[0007] The invention has for its object to provide a technical solution to the problem of ammonia emission from slurry. The invention provides for this purpose a method comprising the steps of: a) feeding a quantity of liquid waste material to a first space, b) distributing the liquid waste material over a moving surface in the first space and heating the first space with the liquid waste material therein, c) extracting primary vapour created by partial evaporation of the liquid waste material from the first space, d) compressing the extracted primary vapour in mechanical manner, e) transferring at least a part of the waste material dried out by evaporation from the first space to a second space, f) feeding the compressed primary vapour to the second space and bringing it into heatexchanging contact with the dried-out waste material, g) feeding primary vapour condensed by the heat-exchanging contact from the second back to the first space, and f) discharging waste material dried by the heat-exchanging contact from the second space.

[0008] Processing the liquid organic waste material in this way enables recovery therefrom of a dry, thick fraction, which can be used as natural fertilizer. Because the liquid waste material is distributed over a moving surface, the evaporation is particularly effective. The mechanical compression of the vapour, which still contains latent heat, results in a high efficiency, as does the use of the compressed vapour for the drying in the second space. The process of bringing the vapour still containing latent heat to a higher pressure and temperature by mechanical compression is known as mechanical vapour recompression (MVR). The use of the condensed vapour, which still contains heat, for the drying in the first space also increases the efficiency of the method. A highly efficient method is thus achieved. Also contributing to this is the fact that the method is performed in two spaces, since optimal conditions for drying the liquid waste material or the already partially dried-out waste material can then be created in each space.

[0009] Step a) of the method can otherwise be repeated, optionally more than once, in order to maintain the quantity of liquid waste material in the first space when moisture evaporates therefrom during steps b) and c).

[0010] It is preferred for the waste material in the first and second space to be heated to a temperature above 70°C in order to obtain a sanitized product that meets legal requirements for export. In this respect it can also be important for the waste material to remain in the first and second space at this high temperature for a total of at least an hour before being discharged. For this purpose the temperature of the compressed primary vapour which is brought into heatexchanging contact with the partially dried-out waste material in the second space can be in the order of 105-130°C, for instance about 110°C.

[0011] The waste material is preferably exposed to a temperature of at least 70°C for a longer time, for instance at least 2 hours, at least 3 hours, at least 4 hours, at least 5 hours, at least 6 hours, at least 7 hours, at least 8 hours, at least 9 hours or at least 10 hours. On the other hand, the residence time in the first and second space must not be too long, this in order to obtain a method with sufficient processing capacity.

[0012] In an embodiment of the method the liquid waste material can be distributed over a rotating surface in step b). A rotating surface is a compact form of a moving surface. In addition, the rotating movement of the surface results in a self-cleaning action, eliminating the need to perform time-consuming CIP (Clean In Place) procedures. The rotating surface can comprise one or more single, solid discs.

[0013] In another embodiment of the method the compressed primary vapour can be brought into heat-exchanging contact with the dried-out waste material in a rotating movement in step f). Such a rotating movement can be realized in a compact space. The compressed primary vapour can be introduced into one or more disc-shaped chambers or hollow discs rotating in the dried-out waste material.

[0014] In yet another embodiment secondary vapour created in step f) by further drying of the waste material can be extracted from the second space, be compressed in mechanical manner, be fed back to the second space and be brought into heat-exchanging contact with the dried-out waste material. The residual heat in the secondary vapour can thus be used advantageously, this further increasing the efficiency of the method.

[0015] In an embodiment of the method the primary and / or secondary vapour can be washed with liquid prior to being respectively fed or fed back to the second space. Volatile components from the vapour can be captured hereby.

[0016] Volatile waste from the vapour can here be crystallized and separated during washing. In the case of slurry the crystallized volatile components can comprise ammonia. The crystallized ammonia can in turn be used as artificial fertilizer, making the method largely circular.

[0017] In an embodiment of the method the liquid waste material can be heated in the first space by heat-exchanging contact with a heating liquid. Owing to the high heat capacity of liquids, it is possible to suffice with a relatively small quantity of heating liquid to heat the liquid waste material. The heating liquid preferably has a temperature which lies relatively close to boiling point, for instance in the order of 75-95°C, particularly about 90°C.

[0018] In another embodiment the second space can also be heated by heat-exchanging contact with a heating liquid. This can be the same or a different heating liquid, which is brought to and kept at a similar temperature.

[0019] In yet another embodiment of the method a pressure lower than atmospheric pressure can prevail in the first space and / or in the second space during drying of the waste material. This enhances evaporation and makes it possible to work at lower temperatures.

[0020] It is further possible in an embodiment that dry air is supplied to the second space prior to step h) and, after heat-exchanging contact with the dried-out waste material, is extracted together with tertiary vapour resulting therefrom, is compressed in mechanical manner, is fed back to the second space and is brought into heat-exchanging contact with the dried-out waste material. By supplying extra dry air the waste material can dried out still further and a relatively high dry substance content (DS) of for instance DS > 90% can be achieved.

[0021] Finally, in an embodiment at least a part of the vapour condensed by the heat-exchanging content can be drained, cooled and discharged after it leaves the second space. The moisture released from the liquid organic waste material during drying is thus finally permanently removed.

[0022] The invention also relates to a device for processing liquid organic waste material, particularly slurry or sludge. According to the invention, such a processing device comprises: - a first space with a feed for liquid waste material,

[0023] - a surface arranged movably in the first space,

[0024] - first drive means connected to the movable surface,

[0025] - first heating means for heating the first space,

[0026] - first extractor means connected to the first space for the purpose of extracting vapour therefrom,

[0027] - a mechanical compressor connected to the extractor means,

[0028] - a second space connected to the first space,

[0029] - second heating means for heating the second space, which second heating means comprise a heat exchanger arranged in the second space and connected to the mechanical compressor, and

[0030] - a return conduit connecting the heat exchanger to the first heating means.

[0031] This combination of components makes the processing device particularly suitable for performing the above described method. The first and second heating means can be configured to heat each of the first and the second space to a temperature of at least 70°C. The first space can otherwise comprise a number of separate compartments, wherein a part of the liquid waste material can in each case be transferred from a compartment to a subsequent compartment after some time, as it dries out further. The at least partially emptied compartment can here then be (re)filled with fresh waste material.

[0032] The movable surface can here be arranged rotatably in the first space.

[0033] When the rotatable surface comprises a number of discs arranged on a shaft parallel and with intermediate space, the contact surface with the liquid waste material is increased while a compact device is still obtained. The discs are preferably solid or single discs providing a relatively high evaporation capacity.

[0034] When the shaft is oriented substantially horizontally and the discs are oriented substantially vertically, the discs rotate partially through the liquid waste material and partially through an empty space above the liquid surface, where the material carried along on the discs is then dried. The filling height of the liquid waste material in the first space then determines the part of a revolution of the discs over which the carried-along material comes into contact with the atmosphere in the first space and moisture can evaporate therefrom.

[0035] The feed can here be arranged in a bottom of the first space lying under the shaft and the discs. The first space can thus be filled with liquid waste material to a desired level in simple manner.

[0036] In order to achieve a uniform heating of the liquid waste material the first heating means can comprise a number of heating members placed between every two discs. In an embodiment these heating members can comprise radiators through which a heating liquid can flow. Liquid radiators are efficient heat exchangers.

[0037] In another embodiment the first drive means can comprise a motor connected to the shaft. A compact drive is realized in this way.

[0038] In yet another embodiment the heat exchanger can be arranged rotatably in the second space and can be connected to the second drive means. The rotating movement of the compressed primary vapour through the dried-out waste material can thus be brought about in structurally simple manner.

[0039] The heat exchanger can here comprise a number of disc-shaped chambers arranged on a hollow shaft parallel and with intermediate space. The contact surface with the waste material to be dried is thus also increased in the second space, while a compact device is in this case also obtained. The disc-shaped chambers, also referred to as hollow discs, provide for a good heat transfer between the compressed primary vapour and the already partially dried-out waste material. And just as the discs in the first space, the disc-shaped chambers also provide for a self-cleaning action of the device.

[0040] In a further embodiment of this device the hollow shaft can be oriented substantially horizontally, and the disc-shaped chambers can be oriented substantially vertically. The discshaped chambers here also rotate partially through the waste material and partially through an empty space above the surface of the waste material, and the material carried along on the discshaped chambers can be dried in this empty space. The filling height of the waste material in the second space here also determines the part of a revolution of the discs over which the carried-along material comes into contact with the atmosphere in the second space so that moisture can evaporate.

[0041] The second space can also be divided into a number of compartments, in which the waste material is dried increasingly further. The waste material can then be displaced in one or more steps from a feed side of the second space to a discharge side thereof, wherein the compartments are alternately (re)filled and wholly or partially emptied.

[0042] The hollow shaft can be parallel to the shaft in the first space, and the first and second space can be placed adjacently of each other, whereby a compact device is obtained.

[0043] The second drive means can here comprise a motor connected to the hollow shaft, whereby a compact drive is also realized for the second space.

[0044] In an embodiment the processing device can further be provided with second extractor means connected to the second space for the purpose of extracting vapour therefrom, which second extractor means are connected to a mechanical compressor. The vapour from the second space, which still contains a considerable amount of residual heat, can hereby be reused, this further increasing the efficiency of the processing device. In an embodiment the device can further be provided with a gas washer connected to the first space and / or the second space for the purpose of capturing volatile waste.

[0045] The device can also be provided here with a crystal separator connected to the gas washer, whereby the volatile waste can be discharged from the gas washer after crystallization.

[0046] In yet another embodiment the second heating means can further comprise a jacket which surrounds the second space at least partially and through which a heating liquid can flow. With the combination of a heating jacket on the outer side and a rotating heat exchanger in the second space the waste material is dried in efficient manner. It is once again possible to suffice here with a relatively small quantity of heating liquid.

[0047] When the jacket is in liquid connection with the radiators, the heating liquid can be used in both the first and the second space, this minimizing heat losses.

[0048] The first space and the second space of the processing device can otherwise be formed in a joint housing. This simplifies the construction.

[0049] In an embodiment of the processing device the extractor means can further be configured to generate a pressure lower than atmospheric pressure in the first space and / or in the second space, whereby evaporation can take place at lower temperatures.

[0050] The device can also be provided with means for supplying dry air to the second space, whereby the waste material can reach a high dry substance content (DS) when it leaves the processing device.

[0051] Finally, in an embodiment the device is provided with means, placed downstream of the heat exchanger, for draining, cooling and discharging vapour condensed in the heat exchanger. With these draining, cooling and discharging means, which can comprise a cooling tower, the moisture extracted from the liquid organic waste material during drying is permanently removed from the device, as long as this moisture is not needed as heating liquid.

[0052] The invention will now be elucidated on the basis of two embodiments, wherein reference is made to the accompanying drawing in which corresponding components are designated with reference numerals increased in each case by 100, and in which:

[0053] Fig. 1 is a schematic representation of the processing device according to the invention,

[0054] Fig. 2 is a perspective view of an embodiment of the processing device, wherein a side wall and the upper side have been omitted,

[0055] Fig. 3 is a view corresponding with Fig. 2, wherein a part of the rotatable surface in the first space is shown in section,

[0056] Fig. 4 is a view corresponding with Fig. 2, which is shown in section along a plane through the shafts in the first and second space,

[0057] Fig. 5 is a view corresponding with Fig. 4, wherein a part of the rotatable surface in the first space is further shown in section, Fig. 6 is a cross-section through the view of Fig. 2,

[0058] Fig. 7 is a perspective view of the processing device of Fig. 2-6 from a different angle, wherein a different side wall and the upper side have been omitted,

[0059] Fig. 8 is a view corresponding with Fig. 7, wherein a part of the rotatable heat exchanger in the second space is shown in section,

[0060] Fig. 9 is a view corresponding with Fig. 2 of another embodiment of the processing device, wherein a side wall and the upper side are shown transparently,

[0061] Fig. 10 is a view corresponding with Fig. 6 of this embodiment, wherein the upper side has once again been omitted,

[0062] Fig. 11 is a view corresponding with Fig. 6 of this alternative embodiment, and

[0063] Fig. 12 is a schematic representation of the method according to the invention.

[0064] A device 1 for processing liquid organic waste material A, particularly slurry or sludge, comprises a first space 2 and a second space 3 (figure 1). The first space 2 is provided with a feed 4 for the liquid waste material A. The processing device 1 further comprises first heating means 5 for heating the first space 2, and first extractor means 6 connected to first space 2 for the purpose of extracting primary vapour V 1 therefrom. A discharge 22 of first space 2 is connected via a conduit 7 to a feed 23 of the second space 3. Processing device 1 further comprises means 8 for transferring waste material from the first space 2 to the second space 3, for instance in the form of a pump. Second space 3 further comprises a discharge 24 through which dried waste material DS can be discharged from processing device 1. Processing device 1 additionally comprises second heating means 9 for heating the second space 3, and second extractor means 10 connected to second space 3 for the purpose of extracting secondary vapour V2 therefrom.

[0065] In the shown embodiment the first heating means 5 comprise a first heat exchanger through which a heating liquid L flows. In the shown embodiment this heat exchanger is connected to the second heating means 9, these likewise comprising a heat exchanger through which heating liquid L flows. The first and second heating means 5, 9 are in this embodiment incorporated in a closed circuit 11, whereby the heating liquid is guided from second space 3 along a heating unit 12, for instance a biogas-fired heating boiler. This heating unit 12 serves particularly to bring the processing device 1 to temperature when it is started up. Once the processing process is running, sufficient heat is generated by the mechanical vapour recompression (MVR) to keep the heating liquid at the required temperature. It is even possible to envisage dispensing with the use of a heating unit altogether. The first and second heating means 5, 9 are configured to heat each of the first and the second space 2, 3 to a temperature above 70°C. Such a temperature is necessary to allow the dried waste material DS to be utilized as natural fertilizer after processing.

[0066] The first extractor means 6 are here connected via a conduit 16 to a mechanical compressor 13. Primary vapour VI, which was extracted from first space 2 and still contains latent heat, is hereby brought to a higher pressure and higher temperature as part of an MVR process. Arranged in second space 3 is a second heat exchanger 14 which forms part of the second heating means 9 and which is connected to the mechanical compressor 13. This second heat exchanger 14 is further connected via a return conduit 15, with a condensate / vapour mixer 72 and a liquid pump 73 therein, to the circuit 11 of the first heating means 5.

[0067] The second extractor means 10 are also connected via a conduit 17 to a mechanical compressor, in the shown embodiment the same mechanical compressor 13 which is also used to compress the primary vapour from first space 2. Secondary vapour, which was extracted from second space 3 and still contains latent heat, is hereby brought to a higher pressure and higher temperature, likewise as part of the MVR process.

[0068] The first and second extractor means 6, 10 can be configured to generate a pressure lower than atmospheric pressure, so a partial vacuum, in the first space 2 and / or in the second space 3. For this purpose the first and second extractor means 6, 10 can each comprise a vacuum pump 65, 66. Reducing the pressure in the space 2, 3 in which the waste material is accommodated enhances the evaporation and thereby speeds up the drying process.

[0069] In the shown embodiment a gas washer 18 is arranged between the first and second extractor means 6, 10 on one side and the mechanical compressor 13 on the other. A crystal separator 19 is incorporated with gas washer 18 in a closed circuit 20. The crystal separator 19 has a discharge 21 for discharged crystals. Such a gas washer 18 can be useful when slurry, in which ammonia is present, is for instance processed in the device 1. However, when device 1 is used to process bio-sludge, from which the ammonia has already been removed, the gas washer can be dispensed with or be bypassed by means of a bypass conduit (not shown here). The optional character of the gas washer 18 is represented with broken lines 61.

[0070] Instead of a single, joint gas washer and a single, joint mechanical compressor for purifying of and recompressing in an MVR process of both the primary vapour V 1 from first space 2 and the secondary vapour V2 from second space 3, a separate gas washer and crystal separator could otherwise also be provided for each of the extractor means 6, 10.

[0071] In the shown embodiment the processing device 1 is further also provided with means 25 for supplying dry air to second space 3, for instance in the form of an opening closable by a controllable valve. When a lower pressure prevails in second space 3 than in the surrounding atmosphere, ambient air is drawn in as soon as the valve is opened.

[0072] Finally, in the shown embodiment the device 1 is provided with means 74, placed downstream of heat exchanger 14, for draining, cooling and discharging vapour condensed in heat exchanger 14. These draining, cooling and discharging means 74 comprise here a drain conduit 75 which is connected to return conduit 15 and which leads to a condensate feed 80 at the top of cooling tower 76. Arranged between drain conduit 75 and return conduit 15 is a controllable valve (not shown here), which determines which part of the condensed vapour will be fed back from heat exchanger 14 for use as heating liquid and which part will be discharged permanently from device 1.

[0073] In cooling tower 76 the condensed vapour is cooled by heat-exchanging contact with ambient air, which is drawn in through an air supply 77 and blown out through an air discharge 78. The cooled condensate C leaves cooling tower 76 through a liquid discharge 79. The pressure needed to lift the condensed vapour to the condensate feed 80 at the top of cooling tower 76 determines the liquid pressure in device 1 to be generated by mechanical compressor 13. In other words, the height of cooling tower 76 determines the compression ratio of the mechanical compressor 13 and thereby also the temperature increase AT experienced by the vapour during the mechanical compression. In practice it is for instance possible to opt for a lift height to the condensate feed 80 in the order of 5 metres, this creating an overpressure of 0.5 bar.

[0074] Means are otherwise arranged in first space 2 for enhancing the evaporation of liquid from the liquid waste material A. These evaporation-enhancing means comprise here a movable surface 26 over which the waste material A can be spread out, and first drive means 27 connected to the movable surface 26.

[0075] In the shown embodiment the movable surface 26 is arranged rotatably in first space 2. The rotatable surface 26 comprises here a number of vertically oriented solid or single discs 28 which are arranged on a horizontal shaft 29 parallel and with intermediate space (Fig. 2, 3). Outer ends 30 of shaft 29 are received rotatably in bearings 31 (Fig. 4, 5), which in turn are mounted on a housing 32 which bounds the first space 2. The first drive means 27 comprise here a motor 71 connected to shaft 29, for instance an electric motor. Rotatingly driving the discs 28 moves them in each case through a bath of liquid waste material A present in the first space 2, wherein part of the waste material A is carried along and comes into contact above the bath with the drying atmosphere in first space 2.

[0076] In the shown embodiment the housing 32 is elongate and is formed by two long side walls 33, two short end walls 34, a bottom 35 and a cover (not shown here). The feed 4 for the liquid waste material A is in this case arranged in bottom 35. In this embodiment housing 32 is supported by four legs 36 at the corners. At the position of bearings 31 the housing, which can be manufactured from sheet material, is strengthened by two transverse beams 37 and two longitudinal beams 38 connected thereto. Housing 32 is provided with strengthening profiles 67, 68 along its lower edge as well.

[0077] In the shown embodiment the first space 2 is otherwise divided into a number of compartments which are mutually separated by intermediate walls 64 and which each have their own feed 4 in the bottom 35. Via these openings in bottom 35 the liquid waste material A can in each case be fed to one of the compartments, and also be discharged therefrom again when a determined degree of drying has been achieved. The waste material is thus guided through first space 2 in steps until it has dried out sufficiently to be transferred from the final compartment to second space 3.

[0078] The first heating means 5 comprise here a number of heating members 39 which are placed between every two discs 28 (Fig. 3, 5). These heating members 39 here comprise radiators through which heating liquid L flows, as stated. An intermediate space between adjacent discs 28 which is slightly greater than a thickness of a radiator 39 has been opted for here. Because each disc 28 thus rotates between two radiators 39, an optimal heat transfer is achieved from the heating liquid L to the liquid waste material A, which is set into motion by the rotating disc 28 and is partially carried along on the surface thereof. Radiators 39 are each connected on one side to an inlet manifold 40, whereby the heating liquid L is distributed over the different radiators 39. The other side of each radiator 39 is connected to an outlet manifold 41 in which the heating liquid L is collected again before being guided on to second space 3.

[0079] The heat exchanger 14 which forms part of the second heating means 9 is here likewise arranged rotatably in second space 3. The rotatable second heat exchanger 14 is connected to second drive means 42. In the shown embodiment this second heat exchanger 14 comprises a number of vertically oriented disc-shaped chambers 43. These chambers 43 are arranged on a horizontally oriented hollow shaft 44 parallel and with intermediate space. The hollow shaft 44 is here parallel to the shaft 29 in first space 2. Outer ends 45 of this hollow shaft 44 are once again received rotatably in bearings 46, which in turn are once again mounted on a housing 47 which also bounds the second space 3 (Fig. 4, 5). The second drive means 42 likewise comprise here a motor 48 connected to hollow shaft 44, for instance an electric motor.

[0080] In this embodiment the hollow shaft 44 extends through motor 48 and is provided with a connector 49 whereby hollow shaft 44 can be connected to a conduit from the mechanical compressor 13. Each disc-shaped chamber 43 is connected to the interior of shaft 44 via a number of openings 59 offset in peripheral direction. The vapour VI from first space 2, which has been brought to a higher pressure and temperature by mechanical compressor 13, can thus spread over the disc-shaped chambers 43 of second heat exchanger 14.

[0081] By rotatingly driving the disc-shaped chambers 43 they are also moved through a bath of, by now, already somewhat pre-dried waste material A present in second space 3. The bath of waste material is here initially set into motion, also owing to the presence of scraping elements 62, placed at an angle, on a peripheral surface 63 of each chamber 43 (Fig. 6-8), allowing the heat transfer to take place more uniformly. In addition, part of the already pre-dried waste material A adheres to the surface of the disc-shaped chamber 43 and is carried along thereby and, above the bath, brought into contact with the drying atmosphere in second space 3. The second housing 47 is here also elongate. This housing 47 is once again formed by two long side walls 50, two short end walls 51, a bottom 52 and a cover (not shown here either). In this embodiment the disc-shaped chambers 43 have a smaller diameter than the discs 28, and second space 3 is smaller than first space 2. Bottom 52 of second housing 47 therefore does not form part of the boundary of second space 3, but an inner bottom 53 is provided. In this embodiment the inner bottom 53 follows the shape of the disc-shaped chambers 43 and supports on bottom 52 via supports 54. The second housing 47 is once again supported by four legs 55 at the corners, is once again strengthened at the position of bearings 46 by two transverse beams 56 and two longitudinal beams 57 connected thereto, and is provided along its lower edge with strengthening profiles 69, 70.

[0082] Inner bottom 53 and bottom 52 define together with side walls 50 and end walls 51 a space 58 which surrounds a part of the second space 3 in the manner of a jacket. A heating liquid flows through this jacket space 58, which forms part of the second heating means 9. In the shown embodiment the jacket space 58 is in liquid connection with the first heating means 5, and together with radiators 39 and inlet and outlet manifolds 40, 41 forms the closed circuit 11 in which the heating liquid L circulates. The outlet manifold 41 here even forms one whole with the jacket space 58. As can be seen in Fig. 1, an outlet side of the second heat exchanger 14, so of the hollow shaft 44 with the disc-shaped chambers 43 thereon, is likewise connected to this closed circuit. The physical connections between the different parts of circuit 11, so conduits, connectors and valves, are however not shown in Fig. 2-8.

[0083] In the shown embodiment the first housing 32 and the second housing 47 are connected to each other by a structure 60 arranged therebetween to form a joint housing. As stated, each housing 32, 47 is closed on the upper side by a cover (not shown). Arranged in these covers are the first and second extractor means 6, 10, for instance in the form of openings closable by valves, to which suction conduits are connected.

[0084] The mechanical compressor 13, gas washer 18 and crystal separator 19 connected to the first and second extractor means 6, 10, as well as vacuum pumps 65, 66 which may be present are arranged outside the housings 32, 47. This also applies to the conduits and pumps through which the liquid waste material A is supplied, is transferred from first space 2 to second phase 3, and is discharged from second space 3. The heating unit 12, which is optionally incorporated in the closed circuit 11 and whereby the heating liquid L is initially brought to temperature, is located outside the housings 32, 47 and is not shown in detail. This also applies to the drain conduit 75 and cooling tower 76.

[0085] In an alternative embodiment of processing device 101, of which only those components will be described that differ from the first embodiment, both the shaft 129 with the solid discs 128 and the hollow shaft 144 with the disc-shaped chambers 143 parallel thereto are modular (Fig. 10, 11). Each shaft 129, 144 comprises here four mutually coupled shaft modules 129A-D, 144A-D, respectively. The solid discs 128 and the disc-shaped chambers 143 are here arranged in groups on a corresponding shaft module 129 A-D, 144A-D, respectively. In the shown embodiment 18 solid discs 128 are arranged on each shaft module 129 A-D, while each hollow shaft module 144A-D carries in this embodiment four disc-shaped chambers 143. The modular construction limits loads on the shafts 129, 144 as well as bending associated therewith, so that a strong and rigid construction is obtained.

[0086] In this embodiment the first space 102 is divided into two compartments which are separated from each other by an intermediate wall (not shown here), and which each have 36 solid discs 128 and 36 heating members 139 in the form of radiators (Fig. 10). The second space 103 is here also divided into compartments, in the shown embodiment four compartments 181. These compartments are separated from each other by intermediate walls 182, the height of which is chosen such that an optimal filling height is maintained in each compartment. When the amount of waste material in one of the compartments 181 is such that the optimal filling height is exceeded, the excess of waste material will fall over the intermediate wall 182 into the adjacent compartment 181. The height of intermediate walls 182 decreases from the feed side to the discharge side of second space 103 so that the waste material is displaced from the feed side to the discharge side during drying.

[0087] This displacement is set into action and maintained by transferring partially dried-out waste material from first space 102 to second space 103. The waste material is urged toward a subsequent compartment 181 by means of the scraping elements 162 which are placed at an angle and are arranged along a periphery 163 of each disc-shaped chamber 143. A closable discharge opening 124 is formed in the bottom of the final compartment 181.

[0088] In this embodiment the hollow shaft 144 and the disc-shaped chambers 143 have a different construction than in the first embodiment. Each disc-shaped chamber 143 has here a triangular section, as seen from shaft 144 toward the inner wall 153 of second space 103. As stated, each shaft segment 144A-D carries here four disc-shaped chambers 143 which are in turn connected via openings 159 to the interior of the hollow shaft 144. The inner hollow shaft segments 144B and 144C are attached with their ends to a hollow intermediate shaft 183, which is mounted in an intermediate bearing 184 carried by the corresponding intermediate wall 182. The outer hollow shaft segments 144 A and 144D are each attached with an end to a hollow intermediate shaft 183 and are attached with their other outer end to a hollow end shaft 185, which is received rotatably in a bearing 146, this in turn being mounted on housing 147. Each hollow end shaft 185 protrudes with a part having openings 159 through the outer disc-shaped chamber 143 and is attached to a perforated intermediate wall 186. Further shown in this embodiment is the joint upper side 187 of the housings 132, 147 of first and second space 102, 103, while motors 148 and 171 are here shown in a slightly different arrangement than in the first embodiment.

[0089] In the two above described processing device 1, 101 liquid organic waste material such as slurry or sludge can thus be processed using the method 200 according to the invention (Fig. 12). A quantity of the liquid waste material is here first fed to the first space 2, 102 (step 201). In first space 2, 102 the liquid waste material can then be distributed over the moving, particularly rotating surface 26, 126, while first space 2, 102 with the liquid waste material therein is simultaneously heated by heat-exchanging contact with the heating liquid L (step 202). The primary vapour VI created by partial evaporation of the liquid waste material A is extracted from first space 2, 102 (step 203) and brought to a higher pressure (and thereby higher temperature) in the mechanical compressor 13 (step 204).

[0090] The degree of evaporation in first space 2, 102 can be set by adjusting the temperature in the space and the filling height of the liquid waste material. The filling height determines the parts of the revolution of discs 28, 128 over which the material carried along therewith comes into contact with the atmosphere in first space 2, 102 and moisture can evaporate therefrom. If the filling height is chosen correctly, a quantity of moisture of 5-6 l / (m2-h) can evaporate on the solid discs 28, 128 at a temperature of 70°C and an underpressure in the first space 2, 102. In order to maintain the filling height, fresh liquid waste material can be fed to first space 2, 102 periodically, for instance every 5 minutes. When first space 2, 102 consists of a plurality of compartments, it is possible at the same time as fresh material being fed to the first compartment for a quantity of liquid waste material to be transferred from the first to the second compartment, this in order also to maintain the filling height there. If there are more than two compartments, this operation can of course be repeated. By feeding liquid waste material in relatively small and frequent steps not only the filling height, but also the temperature in the first space remains substantially constant. It is only in the first compartment that the temperature can temporarily drop a few degrees.

[0091] When the waste material has dried out to a determined extent by evaporation, for instance to a dry substance content in the order of about 30%, it can be transferred partially or wholly from the first space 2, 102 to the second space 3, 103 (step 205). It is here also important to set the filling height of the waste material in second space 3, 103 such that optimal conditions for an efficient evaporation are achieved. At the same time, the compressed primary vapour is fed to the rotating heat exchanger 14, 114 in second space 3, 103 and so brought into heat-exchanging contact with the dried-out waste material (step 206). This causes even more vapour to evaporate from the already partially dried-out waste material. If the filling height is chosen correctly, a quantity of moisture of 1-2 l / (m2-h) can evaporate on the hollow discs 43, 143 at a temperature of 70°C and an underpressure in the second space 3, 103. When moisture evaporates from the partially dried-out waste material, the compressed vapour condenses and the thus formed condensation, optionally mixed with vapour, is then fed back from second space 3, 103 to first space 2, 102, particularly to the first heating means 5, 105 located in first space 2, 102 (step 207).

[0092] The waste material in second space 3, 103 is heated not only by the compressed vapour, but also by heat-exchanging contact with the heating liquid L which circulates between the first and second space 2, 102, 3, 103. Dry air can optionally also be supplied to the second space in order to dry out the waste material still further, for instance to a dry substance content of 90% or more (step 208). When the waste material has finally dried sufficiently due to the heat-exchanging contact, it can be discharged from second space 3, 103 (step 209).

[0093] The residence time of the waste material in processing device 1, 101 is determined by the moisture content of the liquid waste material being fed, the desired dry substance content of the waste material after it leaves the device, the temperature and (under )pressure in the device and the setting of the degree of filling or filling height. In order to be classified as a sanitized product that meets legal requirements for export, the waste material must have been treated at temperatures above 70°C for a determined amount of time. It is therefore not very useful to dimension the method and device for a minimal throughput time. When the liquid waste material to be treated is slurry with a dry substance content of about 10%, and a dry substance content of 45-50% is desired at the end of the treatment, the throughput time in the processing device can be 4 to 6 hours in practice. This is enough time to be able to categorize the final product as export-worthy sanitized product.

[0094] When the waste material is dried further in second space 3, secondary vapour V2 is created, which is extracted (step 210), brought to higher pressure (and temperature) by the mechanical compressor 13, and can then used again to dry the waste material. Both this secondary vapour V2 and the primary vapour VI from first space 2 can optionally be washed in a gas washer (step 211) prior to the mechanical compression, whereby volatile ammonia is removed from the vapour and is bonded in the form of crystals. These crystals can be recovered from the gas washer.

[0095] The final result of the method is that the slurry is processed into a dry fraction with a very high dry substance content (in the order of as much as 90% and higher), crystals containing ammonia, and water (vapour). The dry fraction can be used directly as natural fertilizer, while the ammonia crystals can be used directly as artificial fertilizer. The water vapour can be cooled following condensation and subsequently be discharged, since it contains no contaminants. The total amount of liquid organic waste material is thus reused, without nitrogen being released in the process. Because the vapour which is created during drying, and which still contains latent heat, is reused to heat the waste material after mechanical recompression, the described manner of processing requires only a small amount of energy. And because drying is performed in two steps, these taking place in two separate spaces, which are specially adapted to the moisture content of the liquid waste material or the already partially dried-out waste material, both the efficiency and the opacity of the processing are increased. The mechanical recompression of the vapour extracted from the two spaces can hereby also take place under optimal conditions. The method can furthermore be performed in a relatively simple, compact and robust device, which requires a relatively modest investment and has a low energy consumption, and which can be maintained and cleaned in simple manner.

[0096] Although the invention has been elucidated above on the basis of an embodiment, it will be apparent that it is not limited thereto and can be varied in many ways within the scope of the following claims.

Claims

Claims1. Method for processing liquid organic waste material, particularly slurry or sludge, comprising the steps of: a) feeding a quantity of liquid waste material to a first space, b) distributing the liquid waste material over a moving surface in the first space and heating the first space with the liquid waste material therein, c) extracting primary vapour created by partial evaporation of the liquid waste material from the first space, d) compressing the extracted primary vapour in mechanical manner, e) transferring at least a part of the waste material dried out by evaporation from the first space to a second space, f) feeding the compressed primary vapour to the second space and bringing it into heatexchanging contact with the dried-out waste material, g) feeding primary vapour condensed by the heat-exchanging contact from the second back to the first space, and f) discharging waste material dried by the heat-exchanging contact from the second space.

2. Method according to claim 1 , wherein the liquid waste material is distributed over a rotating surface in step b).

3. Method according to claim 1 or 2, wherein the compressed primary vapour is brought into heatexchanging contact with the dried-out waste material in a rotating movement in step f).

4. Method according to any one of the foregoing claims, wherein secondary vapour created in step f) by further drying of the waste material is extracted from the second space, is compressed in mechanical manner, is fed back to the second space and is brought into heat-exchanging contact with the dried-out waste material.

5. Method according to any one of the foregoing claims, wherein the primary and / or secondary vapour is washed with liquid prior to being respectively fed or fed back to the second space.

6. Method according to claim 5, wherein volatile waste from the vapour is crystallized and separated during washing.

7. Method according to any one of the foregoing claims, wherein the liquid waste material is heated in the first space by heat-exchanging contact with a heating liquid.

8. Method according to any one of the foregoing claims, wherein the second space is heated by heat-exchanging contact with a heating liquid.

9. Method according to any one of the foregoing claims, wherein a pressure lower than atmospheric pressure prevails in the first space and / or in the second space during drying of the waste material.

10. Method according to any one of the foregoing claims, wherein dry air is supplied to the second space prior to step h) and, after heat-exchanging contact with the dried-out waste material, is extracted together with tertiary vapour resulting therefrom, is compressed in mechanical manner, is fed back to the second space and is brought into heat-exchanging contact with the dried-out waste material.

11. Method according to any one of the foregoing claims, wherein at least a part of the vapour condensed by the heat-exchanging content is drained, cooled and discharged after it leaves the second space.

12. Device for processing liquid organic waste material, particularly slurry or sludge, comprising:- a first space with a feed for liquid waste material,- a surface arranged movably in the first space,- first drive means connected to the movable surface,- first heating means for heating the first space,- first extractor means connected to the first space for the purpose of extracting vapour therefrom,- a mechanical compressor connected to the extractor means,- a second space connected to the first space,- second heating means for heating the second space, which second heating means comprise a heat exchanger arranged in the second space and connected to the mechanical compressor, and- a return conduit connecting the heat exchanger to the first heating means.

13. Device according to claim 12, wherein the surface is arranged rotatably in the first space.

14. Device according to claim 13, wherein the rotatable surface comprises a number of discs arranged on a shaft parallel and with intermediate space.

15. Device according to claim 14, wherein the shaft is oriented substantially horizontally and the discs are oriented substantially vertically.

16. Device according to claim 15, wherein the feed is arranged in a bottom of the first space lying under the shaft and the discs.

17. Device according to any one of the claims 14-16, wherein the first heating means comprise a number of heating members placed between every two discs.

18. Device according to claim 17, wherein the heating members comprise radiators through which a heating liquid can flow.

19. Device according to any one of the claims 14-18, wherein the first drive means comprise a motor connected to the shaft.

20. Device according to any one of the claims 12-19, wherein the heat exchanger is arranged rotatably in the second space and is connected to second drive means.

21. Device according to claim 20, wherein the heat exchanger comprises a number of disc-shaped chambers arranged on a hollow shaft parallel and with intermediate space.

22. Device according to claim 21, wherein the hollow shaft is oriented substantially horizontally and the disc-shaped chambers are oriented substantially vertically.

23. Device according to any one of the claims 20-22, wherein the second drive means comprise a motor connected to the hollow shaft.

24. Device according to any one of the claims 12-23, further provided with second extractor means connected to the second space for the purpose of extracting vapour therefrom, which second extractor means are connected to a mechanical compressor.

25. Device according to any one of the claims 12-24, further provided with a gas washer connected to the first space and / or the second space.

26. Device according to claim 25, further provided with a crystal separator connected to the gas washer.

27. Device according to any one of the claims 12-26, wherein the second heating means further comprise a jacket which surrounds the second space at least partially and through which a heating liquid can flow.

28. Device according to claims 18 and 27, wherein the jacket is in liquid connection with the radiators.

29. Device according to any one of the claims 12-28, wherein the first space and the second space are formed in a joint housing.

30. Device according to any one of the claims 12-29, wherein the extractor means are further configured to generate a pressure lower than atmospheric pressure in the first space and / or in the second space.

31. Device according to any one of the claims 12-30, further provided with means for supplying dry air to the second space.

32. Device according to any one of the claims 12-31, further provided with means, placed downstream of the heat exchanger, for draining, cooling and discharging vapour condensed in the heat exchanger.

33. Device according to claim 32, wherein the draining, cooling and discharging means comprise a cooling tower.

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