WASTE DRYING

Abstract

According to the present invention waste 7 is dried by applying the waste 7 to a floor 4 comprising several floor segments 34, 44, 46 and by conveying the waste 7 by a push floor mechanism in which only a part of the floor segments 34, 44, 46 is moved at a time in a direction of movement 8 or a counter direction 61. The energy for drying the waste 7 is provided by warm air 11 through openings 38 in the floor segments 34, 44, 46 from a pressure chamber 3 through the floor 4 into the waste 7 and through the waste 7.

Claims

1. A method for drying waste (7), comprising the steps of: applying waste (7) into a waste chamber (2) on an inlet end (6) of a floor (4) which comprises at least two floor segments (34, 44, 46), providing warm air (11) of a temperature of more than 70? C., preferably between 80? C. and 90? C., to a pressure chamber (3) beneath the floor (4), with a pressure being above the pressure in the waste chamber (2), so that the warm air (11) is passing through openings (38) in the floor (4) into the waste chamber (2) and through the waste (7); conveying the waste (7) in a direction of movement (8) from the inlet end (6) to an outlet end (12) of the floor (4) by moving individual floor segments (34, 44, 46) into the direction of movement (8) and in a counter direction (61) being opposite the direction of movement (8) for a predetermined amount, respectively; and conveying waste (7) having fallen from the outlet end (12) of the floor (4) out of the waste room (2).

2. A method according to claim 1, wherein the floor (4) is creating a floor pressure drop for the air passing the openings (38), wherein the waste (7) on the floor (4) creates a waste pressure drop for the air passing from the openings (38) through the waste (7), wherein the amount of waste (7) being applied to the floor (4) is controlled such that a ratio between the floor pressure drop and the waste pressure drop is at least 2.

3. A method according to claim 1, wherein off-gas (64) is sucked off from the waste chamber (2) above the waste (7).

4. A method according to claim 3, wherein the off-gas (64) is provided to at least one cyclone (10) to separate particles in the off-gas (64) from an exhaust air (65).

5. A method according to claim 4, wherein the off-gas (64) is sucked through at least two cyclones (10) connected in parallel to the waste chamber (2), each cyclone (10) being arranged at a different position in the direction of movement (8), whereas the temperature of the off-gas (64) flowing to each cyclone (10) is measured allowing to determine a temperature profile of the off-gas (64) in the direction of movement (8) and using this temperature profile to control at least one of the following variables: a) the temperature of the warm air (11) entering the pressure chamber (3); b) the volume flow of the warm air (11) entering the pressure chamber (3); and c) the movement speed of the waste (7) through the waste chamber (2).

6. A method according to claim 4, wherein the off-gas (64) or the exhaust air (65) is conveyed to a wet scrubbing unit (24).

7. A method according to claim 4, wherein the off-gas (64) or the exhaust air (65) is guided through a heat exchanger (68) for preheating fresh air (13) to be delivered to the pressure chamber (3) as warm air (11).

8. A method according to claim 4, wherein the warm air (11) is heated before entering the pressure chamber (3) by heat provided from a heat pump (31) in which latent heat of the off-gas (64) or the exhaust air (65) is used as a source of thermal energy.

9. A method according to claim 1, wherein the level of the waste (7) applied onto the floor (4) is controlled to be at a predetermined level.

10. A dryer (1) for drying waste (7), comprising a waste chamber (2) and a pressure chamber (3), said waste chamber (2) being separated from the pressure chamber (3) by a floor (4) for carrying the waste (7), wherein said floor (4) defines a plane (41) in which the floor (4) extends, an inlet (5) for applying waste (7) onto an inlet end (6) of the floor (4) and an outlet (9) for removing waste (7) from on outlet end (12) of the floor (4) defining a direction of movement (8) in the plane (41) from the inlet end (6) to the outlet end (12), wherein the floor (4) comprises at least two floor segments (34, 44, 46), each floor segment (34, 44, 46) being movable independent of at least one other floor segment (34, 44, 46) in the plane (41) in the direction of movement (8) and against the direction of movement (8), wherein the floor segments (34, 44, 46) comprise openings (38) connecting the pressure chamber (3) with the waste chamber (2), wherein the pressure chamber (3) is providable with air at a pressure being higher than the pressure in the waste chamber (2).

11. A dryer (1) according to claim 10, wherein the openings (38) are formed such that the air can pass the openings (38) from the pressure chamber (3) to the waste chamber (2) parallel to the plane (41).

12. A dryer (1) according to claim 10, wherein the openings (38) are formed by bulges (37) protruding from the plane (41).

13. A dryer (1) according to claim 10, further comprising at least two cyclones (10) connected in parallel to the waste chamber (2) by air outlets (17) and at least one exhaust air fan (16) arranged to suck the off-gas (64) in the waste chamber (2) through the cyclones (10), each air outlet (17) being arranged at a different position in the direction of movement (8), each air outlet (17) comprising a temperature sensor (18) for measuring the temperature of the air in the air outlet (17), said temperature sensors (18) being connected to a control device (66) for determining a temperature profile of the off-gas (64) in the waste chamber (2) in the direction of movement (8) and using this temperature profile to control at least one of the following components: A) a drying air heater (15) for controlling the temperature of the warm air entering the pressure chamber (3); B) a circulation fan (14) for controlling at least one of the following variables: the pressure in the pressure chamber (3) and the volume flow of the warm air (11) entering the pressure chamber (3); and C) a floor movement system (67) for controlling the movement speed of the waste (7) through the waste chamber (2).

14. A dryer (1) according to claim 10, further comprising an air preheater (20) comprising a heat exchanger for heat transfer between the off-gas of the waste chamber or exhaust air from at least one cyclone with fresh air to be provided to the pressure chamber.

15. A dryer (1) according to claim 10, further comprising a wet scrubbing unit (24) for cleaning the off-gas (64) of the waste chamber (2) or exhaust air (65) from at least one cyclone (10) and for transferring thermal energy from the off-gas (64) of the waste chamber (2) or exhaust air (65) from at least one cyclone (10) to the warm air (11).

Description

[0047] It should be noted that the individual features specified in the claims may be combined with one another in any desired technologically reasonable manner and form further embodiments of the invention. The specification, in particular taken together with the figures, explains the invention further and specifies particularly preferred embodiments of the invention. Particularly preferred variants of the invention and the technical field will now be explained in more detail with reference to the enclosed figures. It should be noted that the exemplary embodiment shown in the figures is not intended to restrict the invention. The figures are schematic and may not be to scale. The figures display:

[0048] FIG. 1 a schematic view of an example of a dryer for drying waste;

[0049] FIG. 2 a longitudinal section of the example of a dryer;

[0050] FIG. 3 a detail showing details of two floor segments of the example of a dryer;

[0051] FIG. 4 details of two parallel floor segments of a second example of a dryer;

[0052] FIG. 5 a top view of a part of a floor segment of the second example of a dryer;

[0053] FIG. 6 a section of a floor section of the second example of a dryer; and

[0054] FIG. 7 a top view of two floor sections of the second example of a dryer.

[0055] FIG. 1 shows an example of a dryer 1 for drying waste in a schematic view, FIG. 2 is a longitudinal section of this dryer 1. Both figures are discussed in the following in common (for sake of clarity only reference numerals are provided with in FIG. 1 and/or in FIG. 2). The waste comprises preferably municipal dry waste, industrial waste and/or biomass. The waste can be shredded and/or milled before being delivered into the dryer 1. In general, the waste is having a particle size distribution which is inhomogeneous and the composition of the waste is inhomogeneous as well. In particular, the waste comprises organic and/or inorganic compounds.

[0056] The dryer 1 comprises a waste chamber 2 and a pressure chamber 3 which are separated by a floor 4. The setup of the floor 4 will be described in more detail with respect to FIGS. 3 to 7. The dryer 1 has an inlet 5 defining an inlet end 6 of the floor 4. Through the inlet 5 waste 7 is applied onto the floor 4 as wet waste 69 and, thus, into the waste chamber 2. The waste 7 is moved through the waste chamber 2 in a direction of movement 8 from the inlet 5 to an outlet 9 of the waste chamber 2. The outlet 9 defines an outlet end 12 of the floor 4. A leveler 62 at the inlet 5 limits the height of the waste 7 on the floor 4. The leveler 62 is preferably a roll that presses the waste 7 to a defined height. At the outlet end 12 a dry waste feeder 63 is situated for conveying the waste 7 falling from the floor 4 at the outlet end 12 as dry waste 70 onwards, e.g. to a furnace for burning the dry waste 70 or the like. The dry waste feeder 63 is preferably a screw conveyor.

[0057] While moving the waste 7 through the waste chamber 2 the waste 7 is dried by providing warm air 11 having a temperature of about 80? C. to the pressure chamber 3 and driving the air through openings in the floor 4 into the waste chamber 2 and through the waste 7. The air is guided after having passed the waste 7 as an off-gas 64 through one of several cyclones 10 for particle or dust separation. The warm air 11 is provided by guiding fresh air 13 by use of a circulation fan 14 through a drying air heater 15.

[0058] After having passed the waste 7 the air enters the air room above the waste 7 in the waste chamber 2 as off-gas 64. The off-gas 64 is humid or moist and can contain particles from the waste 7 and/or chemical compounds carried along from the waste 7. By use of an exhaust air fan 16 the off-gas 64 is sucked from the waste chamber 2 through the cyclones 10. A plurality of cyclones 10 is arranged along the length of the waste chamber 2. Off-gas 64 from the waste chamber 2 is entering the cyclones 10 through air outlets 17 (only partially provided with reference numerals in FIG. 2 for reasons for sake of clarity). The length is limited by the inlet end 6 on the one end and by the outlet end 12 on the other end. Each air outlet 17 has a specific position in direction of movement 8, and, obviously, off-gas 64 from around the position of the air outlet 17 is passing through the respective outlet 17. The temperature of the off-gas 64 in the air outlets 17 is measured individually by temperature sensors 18. Thus, it is possible to define a temperature profile of the air in the waste chamber 2 in the direction of movement 8. The temperature sensors 18 are connected to a control device 66.

[0059] In the cyclones 10 particles are separated from the off-gas 64. Thus, an exhaust air 65 (only in part provided with reference numerals for the sake of clarity) is having a smaller particle load than the off-gas 64. The exhaust air 65 is collected in the exhaust air line 21.

[0060] At the inlet 5 the waste 7 that is deposited on the inlet end 6 of the floor 4 is wet waste 69, i.e. having a higher humidity of e.g. up to 40%, while the waste 7 that is leaving the floor 4 at the outlet end 12 is dry waste 70, i.e. having a lower humidity of e.g. 5% and less. Thermodynamically, the evaporation of water needs the enthalpy of evaporation to be introduced. Close to the inlet end 6 the humidity is high, therefore, the energy consumption necessary to evaporate the humidity is high. This leads to a large drop of the temperature of the air between the warm air 11 and the air in the air outlet 17 in this region of the dryer 1. Close to the outlet end 12 the waste 7 is already dryer, thus, less energy is necessary leading to a smaller temperature drop of the air between the warm air 11 and the air entering the respective air outlet 17. This temperature profile allows to control the dryer 1 in particular regarding the movement speed of the waste 7 through the waste chamber 2.

[0061] The movement of the waste 7 through the waste chamber 2 is the result of a walking floor principle implemented in the floor 4 as will be discussed in detail below. The floor 4 comprises several floor segments, which can be individually moved by a floor movement system 67, in this example a hydraulic floor movement system 19 which is controlled based on the temperature profile as mentioned above by the control device 66.

[0062] To increase the efficiency of the air heating an air preheater 20 with a heat exchanger 68 is positioned in the exhaust air line 21 in which the exhaust air 65 from the cyclones 10 is collected and sucked of by the exhaust air fan 16. The exhaust air fan 16 is controlled as well by the control device 66 being connected to the exhaust air fan 16. In the air preheater 20 the relatively warm exhaust air 65 is in heat exchange with the fresh air 13 to preheat the fresh air 13 before entering the drying air heater 15. Alternatively or additionally, via a recirculation line 22 at least a part of the exhaust air 65 can be guided from the exhaust air line 21 to the drying air heater 15. Therefore, a circulation of the drying air is possible. The flow through the recirculation line 22 can be controlled by a recirculation control valve 23 disposed in the recirculation line 22 being controlled by the control device 66.

[0063] The exhaust air is provided downstream of the exhaust air fan 16 to a wet scrubbing unit 24. In the wet scrubbing unit 24 possible contaminants in the exhaust air are scrubbed so that clean air 25 is taken from an upper dome 26 of the wet scrubbing unit 24. Simultaneously, the thermal energy content of the exhaust air is transferred in part to the washing solution, preferably water, being circulated by a scrubber pump 27 from a sump 28 of the wet scrubbing unit 24 through a scrubbing circulation line 29. While passing the circulation line 29 the washing solution passes a heat exchanger 30 being part of a heat pump 31. Here, an intermediary heat medium such as water is heated in the heat exchanger 30 by heat transfer from the washing solution and is then transferred via a pump 32 to the drying air heater 15 to heat the drying air provided as warm air 11 to the pressure chamber 3. Between the heat exchanger 30 and the drying air heater 15 the heat medium passes a heater coil 33 allowing in particular an easy start-up of the system and might provide further thermal energy to the heat medium if the situation in the drying air heater 15. Likewise, the heat medium downstream of the drying air heater 15 is passing the heater coil 33. It is possible to heat the intermediary heat medium by the heat pump 31 to the temperature of the warm air 11 when entering the pressure chamber 3 or above allowing to heat the warm air 11 accordingly. For example, the exhaust gas 65 when entering the wet scrubbing unit 24 is at a temperature of about 30? C. to 35? C. and the washing solution enters the wet scrubbing unit 24 with a temperature of 12? C. to 16? C. Due to i.a. the condensation enthalpy of the humidity in the exhaust air 65 which is transferred to the washing solution the temperature of the washing solution when leaving the wet scrubbing device 24 is about 25? C. to 30? C. which is used as a heat source in the heat pump 31.

[0064] By controlling the circulation fan 14 and the exhaust air fan 16 by the control device 66 preferably a situation is generated in which the pressure in the waste chamber 2 is identical to the ambient pressure around the dryer 1 while the pressure within the pressure chamber 3 is slightly above ambient forcing air from the pressure chamber 3 through the openings into the waste chamber 2.

[0065] The movement of the waste 7 through waste chamber 2 and the configuration of the floor 4 will be discussed in the following with respect to FIGS. 3 to 7. The floor 4 comprises several floor segments 34. Generally, it is sufficient to provide two floor segments 34. Nevertheless, in particular considering the weight of the floor segments 34 more than two floor segments 34 are preferred as by this the individual floor segment 34 is easier to move by the floor movement system 67 during the process of drying waste compared to a larger (preferably wider) floor segment 34. The floor segment 34 is usually build from materials that can carry the load of the waste 7 which is applied in use on top of the floor segment 34 and which can withstand the temperature of the warm air 11 conveyed into the pressure chamber 3. Preferably, the floor segments 34 are made from steel, in particular from stainless steel. As can be seen in particular in FIG. 3 each floor segment 34 is provided on a carrier 35, preferably made from steel, in particular from carbon steel. The carrier 35 and, consequently, the respective floor segment 34 can be moved in the direction of movement 8 and in the opposite direction 61. This is performed by the hydraulic floor movement system 19 as described above. In case of a floor segment 34 wearing off it can easily be separated from the respective carrier 35 and can be replaced. Preferably, each floor segment 34 spans the whole length of the waste chamber 2 as this facilitates the control of the movement of the floor segments 34 and, consequently, the waste 7 through the waste chamber 2.

[0066] As can be seen from FIG. 3 a seal 36 is provided between adjacent floor segments 34 to ensure that no air or only a small amount of air is leaking in between adjacent floor segments 34. Each seal 36 is fixed in this embodiment to one floor segment 34 and is moving with this floor segment 34. The seals 36 are preferably made from a thermoplastic material, in particular from polytetrafluorethylene (PTFE).

[0067] Each floor segment 34 comprises a plurality of bulges 37 only some of which are provided with a reference numeral in FIG. 3 for the sake of clarity. Each bulge 37 constitutes two openings 38. Each bulge 37 is manufactured by cutting two parallel lines in the direction of movement 8 into the floor segment 34 forming a strip and then shaping the strip into the final bulge 37 while elongating the strip. Thus, each opening 38 is delimited by a respective first edge 39 of a plane 41 of the floor segment 34 and a respective second edge 40 of the respective bulge 37.

[0068] The floor 4 defines a plane 41 which is spanned by the direction of movement 8 and a cross direction 42 of the floor 4. Therefore, the bulges 37 protrude from this plane 41. The openings 38 are formed in such a manner that air provide to the pressure chamber 3 is passing through the openings 38 parallel to the plane 41. The openings 38 are in this example oriented perpendicular to the plane 41. By the warm air 11 passing through the openings 38 a kind of an air cushion can be formed underneath the waste 7 on top of the floor 4 facilitating a homogeneous distribution of the warm air 11 over the entire waste 7. To further improve this a large number of openings 38 is preferred, in particular being spaced apart between 50 to 70 mm in the direction of movement 8 (measured between the centers of adjacent bulges 37) and about 45 to 65 mm in cross direction 42 (measured between the centers of adjacent bulges 37). Preferably, the bulges 37 are arranged in lines in the direction of movement 8, with adjacent lines being offset in direction of movement 8, preferably by half the distance between adjacent bulges 37 in the direction of movement 8. Preferably, the number of openings 38 and the area of the openings 38 is such that the total floor permeability is in the range of 7% to 7.5% resulting in a floor pressure drop being in the range of 70% to 80% of the total pressure drop of the floor 4 and the waste 7 on top of the floor 4. Preferably, the openings 38 are evenly distributed on the floor 4. The floor segments 34 can only move in the plane 41. It is not possible for the floor segments 34 e.g. to be raised out of the plane 41 by the floor movement system 67.

[0069] A second example of a dryer 1 having a different floor 4 is now described with respect to FIGS. 4 to 6. Here, only the differences of the second example shall be discussed while reference is made to the first example of the floor 4 described above for the sake of conciseness. In the second example the sealing mechanism between two adjacent floor segments 34 is different compared to the first example. Instead of a single seal 36 between two adjacent floor segments 34 as in the first example the sealing mechanism between two adjacent floor segments 34 relies on a first seal 43 attached two a first floor segment 44 and a second seal 45 attached to an adjacent second floor segment 46. The first seal 43 and the second seal 45 cooperatively generate the necessary sealing between the adjacent floor segments 44, 46. Both seals 43, 45 have a triangular cross section having a first oblique side 47 in the case of the first seal 43 and a second oblique side 48 in case of the second seal 45 which correspond to each other. This ensures the sealing effect while facilitating the relative movement between the adjacent floors segments 44, 46 in the direction of movement 8 and in the counter direction 61 as symbolized by the arrow 49 as the oblique sides 47, 48 act as gliding means as well.

[0070] Each carrier 35 of floor segment 34, 44, 46 has on a first side 50 (e.g. the left side seen in direction of movement 8) a first seal 43 and on an opposite second side 51 (e.g. the right side seen in direction of movement 8) a second seal 45. This allows an easy assembly of the floor 4 from respective floor segments 34. As in the first example the seals 43, 45 are preferably manufactured from a thermoplastic material, in particular PTFE.

[0071] Furthermore, FIG. 4 shows an example of how to move the floor segments 34, 44, 46. Each carrier 35 is mounted on a first rod 52 and a second rod 53 by mounting structures 54 attached to the inside of the carrier 34. By moving the first rod 52 and the second rod 53 in direction of the arrow 49 a movement of the respective floor segment 34 in direction of movement 8 and in the counter direction 61 can be generated. By rotating the rods 52, 53 an adjustment of the respective floor section 34 in a height direction 55 and a side direction 56 can be realized due to the crescent structure of the mounting structures 54 to create a floor 4 spanning the plane 41.

[0072] For the sake of clarity, the bulges 37 and the respective openings 38 are not depicted in FIG. 4. FIG. 5, disclosing a top view of one single floor segment 34 according to the second example, and FIG. 6, disclosing a section according to the line VI-VI in FIG. 5 disclose specifics of the bulges 37 and the openings 38. The bulges 37 are formed semi-circular from a strip of steel as described above. Each opening 38 has in this example a maximum diameter 57 in the direction of movement 8 and a maximum height 58 in the height direction 55. Preferably, to create a reasonable pressure drop for the warm air 11 flowing through the opening 38 is formed such that a ratio of the maximum height 58 to the maximum diameter 57 is in between 0.12 and 0.18.

[0073] Bulges 37 adjacent in the side direction 55 are placed having a side distance 59 between each other. Bulges 37 adjacent in the length direction 55 are placed having a length distance 60. Preferably, the bulges 37 are placed such on the floor segment 34 that a ratio of the side distance 59 to the length distance 60 being in the range of 0.75 to 0.9.

[0074] FIG. 7 depicts a top view on a first floor segment 44 and a second floor segment 46 according to the second example. Both the first floor segment 44 and the second floor segment 46 comprise a plurality of bulges 37 with respective openings 38 arranged in rows in the direction of movement 8. Each floor segment 44, 46 can be moved to a certain extend in the direction of movement 8 and in the counter direction 61. At least two, preferably more, floor segments 34, 44, 46 form the floor 4. It is preferred that groups of floor segments 34, 44, 46 are moved simultaneously, for example every other floor segment 34 being moved simultaneously (as an example a first, third, fifth and seventh floor segment 34 are moved simultaneously forming a first group, while the intermittent second, fourth, sixth and eight floor segments 34 are moved simultaneously independently from the first group forming a second group).

[0075] If a floor segment 34 moves in the direction of movement 8 the waste 7 being situated on this floor segment 34 is moved with the floor segment 34 as well in the direction of movement 8. Usually, the movement is a step like movement. I.e., the respective floor segment 34 is moved for a pre-determined amount (e.g. 10 cm [centimeters] or the like) in the direction of movement 8 creating a vacancy close to the inlet end 6 of the floor segment 34. Later on, the same floor segment 34 is moved for the same amount into the counter direction 61. Nevertheless, waste 7 has in the meantime been delivered through the inlet 5 onto the floor 2 so that the vacancy created is now filled and the leveler 62 (see FIG. 2) prevents a pile up of the waste 7. Therefore, the waste 7 at the outlet end 12 of the floor segment 34 drops from the floor segment 34, preferably into a dry waste feeder 63, e.g. a screw or belt conveyor.

[0076] According to the present invention waste 7 is dried by applying the waste 7 to a floor 4 comprising several floor segments 34, 44, 46 and by conveying the waste 7 by a push floor mechanism in which only a part of the floor segments 34, 44, 46 is moved at a time in a direction of movement 8 or a counter direction 61. The energy for drying the waste 7 is provided by warm air 11 through openings 38 in the floor segments 34, 44, 46 from a pressure chamber 3 through the floor 4 into the waste 7 and through the waste 7.

REFERENCE NUMERALS

[0077] 1 dryer [0078] 2 waste chamber [0079] 3 pressure chamber [0080] 4 floor [0081] 5 inlet [0082] 6 inlet end [0083] 7 waste [0084] 8 direction of movement [0085] 9 outlet [0086] 10 cyclone [0087] 11 warm air [0088] 12 outlet end [0089] 13 fresh air [0090] 14 circulation fan [0091] 15 drying air heater [0092] 16 exhaust air fan [0093] 17 air outlet [0094] 18 temperature sensor [0095] 19 hydraulic floor movement system [0096] 20 Air preheater [0097] 21 exhaust air line [0098] 22 recirculation line [0099] 23 recirculation control valve [0100] 24 wet scrubbing unit [0101] 25 clean air [0102] 26 upper dome [0103] 27 scrubber pump [0104] 28 sump [0105] 29 scrubbing circulation line [0106] 30 heat exchanger [0107] 31 heat pump [0108] 32 pump [0109] 33 heater coil [0110] 34 floor segment [0111] 35 carrier [0112] 36 seal [0113] 37 bulge [0114] 38 opening [0115] 39 first edge [0116] 40 second edge [0117] 41 plane [0118] 42 cross direction [0119] 43 first seal [0120] 44 first floor segment [0121] 45 second seal [0122] 46 second floor segment [0123] 47 first oblique side [0124] 48 second oblique side [0125] 49 arrow [0126] 50 first side [0127] 51 second side [0128] 52 first rod [0129] 53 second rod [0130] 54 mounting structure [0131] 55 height direction [0132] 56 length direction [0133] 57 maximum diameter [0134] 58 maximum height [0135] 59 side distance [0136] 60 length distance [0137] 61 counter direction [0138] 62 leveler [0139] 63 dry waste feeder [0140] 64 off-gas [0141] 65 exhaust air [0142] 66 control device [0143] 67 floor movement system [0144] 68 heat exchanger [0145] 69 wet waste [0146] 70 dried waste