CONTINUOUS FLOW DRYER HAVING AT LEAST TWO SECTIONS

Abstract

The invention relates to a continuous flow dryer (10) for drying a material (14) by means of hot air (24), comprising a first and a second section (20, 22), which in a transport direction (18) are successively passed through by the material (14), and which in terms of flow are separated to a great extent. The invention is characterized in that a fresh air supply device (28) for supplying fresh air (26) as first infeed air (32) into the first section (20) is provided, an exhaust air recirculation device (44) for removing exhaust air (40) from the second section (22) and for recirculating exhaust air (40) as second infeed air (42) back into the second section (22) is provided. Furthermore, a heat exchanger (58) is provided, through which the fresh air (26) on the one hand and the exhaust air (40) on the other hand are guided, for transferring waste heat (62) of the exhaust air (40) into the fresh air (26).

Claims

1-10. (canceled)

11. A continuous flow dryer for drying a material by means of hot air, comprising: a first section and a second section through which the material passes successively in a transport direction, the first section and the second section being largely separated in terms of air flow; a fresh air supply device for supplying fresh air as first supply air into the first section; an exhaust air recirculating device for discharging exhaust air from the second section and for recirculating exhaust air as second supply air back into the second section; and a heat exchanger through which the fresh air and the exhaust air are led, the heat exchanger being configured to conduct waste heat from the exhaust air into the fresh air.

12. The continuous flow dryer according to claim 11, wherein the heat exchanger is dimensioned such that water condenses out on it from the exhaust air.

13. The continuous flow dryer according to claim 11, further comprising a first heater for heating the first supply air before it is supplied into the first section.

14. The continuous flow dryer according to claim 11, further comprising a second heater for heating the second supply air before it is recirculated into the second section.

15. The continuous flow dryer according to claim 11, wherein the exhaust air recirculating device is provided with a recirculating line, for direct recirculating of exhaust air from the second section as recirculating air back into the second section.

16. The continuous flow dryer according to claim 11, wherein at least two regions are provided in the second section and wherein the exhaust air of the two regions is guided together through the heat exchanger.

17. The continuous flow dryer according to claim 11, further comprising an exhaust air sensor by means of which a moisture in the exhaust air can be determined.

18. The continuous flow dryer according to claim 11, wherein two belts are provided for transporting the material through the continuous flow dryer.

19. The continuous flow dryer according to claim 18, wherein the two belts include a first belt assigned to the first section and a second belt assigned to the second section.

20. The continuous flow dryer according claim 11, wherein the transport direction is directed from the second section to the first section.

21. A method for operating a through-flow dryer for drying a material by means of hot air, the through-flow dryer having a first section and a second section through which the material passes successively in a transporting direction, the first section and the second section being largely separated in terms of air flow, comprising: supplying fresh air as first supply air into the first section; discharging exhaust air from the second section; recirculating exhaust air as second supply air back into the second section; and conducting exhaust heat from the exhaust air into the fresh air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] An exemplary embodiment of the solution according to the invention is explained in greater detail with reference to the following drawings:

[0033] FIG. 1 shows a highly simplified longitudinal section of a through-flow dryer according to the prior art.

[0034] FIG. 2 shows a highly simplified longitudinal section of a through-flow dryer according to the invention.

[0035] FIG. 3 shows a highly simplified longitudinal section of a through-flow dryer according to the invention, which is equipped with a regulating device.

[0036] FIG. 4 shows a highly simplified longitudinal section of a through-flow dryer according to the invention, which is according to the prior art.

[0037] FIG. 5 shows a highly simplified longitudinal section of a through-flow dryer according to the invention.

[0038] FIG. 6 shows a highly simplified longitudinal section of a further through-flow dryer according to the invention, which is according to the prior art, having three regions.

[0039] FIG. 7 shows a through-flow dryer according to FIG. 6, which is equipped with a regulating device.

DETAILED DESCRIPTION

[0040] FIGS. 1 to 3 each show a through-flow dryer 10 in the form of a belt dryer. The through-flow dryer 10 has a housing 12, through which firstly moist or wet material 14 is to be transported through by means of a belt 16 in a transport direction 18. The material 14 passes through during the transporting a first section 20 and a second section 22. The two sections 20 and 22 subdivide the housing 12 spatially. Inside the housing 12 there is situated furthermore hot air 24 which removes moisture from the material 14 (not shown) to be dried. With the removal of moisture from the material 14 the material becomes dryer, it is dried.

[0041] FIGS. 2 and 3 illustrate how in the exemplary embodiments there the hot air 24 is produced. For this fresh air flows from outside the housing 12, conveyed by a fresh air supply device 28, into the housing 12. The fresh air in this case flows through a first heater 30. The first heater 30 heats the fresh air 26 on its way through the heater 30. With the heating of the fresh air 26 the relative air moisture decreases, the fresh air 26 becomes dryer.

[0042] This fresh air 26 after heating is referred to as first supply air 32. The first supply air 32 flows into the first sector 20 and flows around there the individual particles of the material 14 or flows through the layer of the material 14 on the belt 16. On this flowing-around of the particles of the material 14 the first supply air 32 takes up moisture from the material 14. The relative air moisture of the first supply air 32 takes up moisture from the material 14. The relative air moisture of the first supply air 32 increases, the first supply air 32 becomes dryer. The moistened supply air 32 is subsequently removed from the first section 20 as first exhaust air 34 from the housing 12 into its surroundings. This exhaust air thus constitutes outgoing air.

[0043] After the first section 20 the material flows through the second section 22. This second section is for its part subdivided into two regions 36, 38. The two regions 36, 38 are connected in series and separated largely from one another in terms of air flow. Alternatively to the exemplary embodiments shown, the second section 22 can also be subdivided into more than two regions 36, 38, in particular three, four or five regions.

[0044] At both regions 36, 38 in each case a second exhaust air 40 is led out and in each case a second supply air 42 is supplied. The second supply air 40 is led back into the respective region by means of an exhaust air recirculation device 44 partly directly as second supply air 42 into the respective region. Before the supplying of the second supply air 42 into the respective region 36, 38, in each case a second heater 46 is provided. The second heater 46 heats the second supply air 42, whereby the relative moisture of the second supply air 42 falls.

[0045] The exhaust air recirculation device 44 comprises a recirculation line 48, through which likewise the exhaust air 40 flows. This recirculation line 48 has a branch 50 and a supply 52. At the branching 50 a part of the exhaust air is branched off and by means of a line is led into a collecting line 56. The collecting line 56, in FIG. 3, or the line 54, in FIG. 2, comprises preferably a regulated or controlled fan 57. The collecting line 56 collects the exhaust air 40 branched off from the first and second region 36, 38 and leads this exhaust air to a heat exchanger 58. The heat exchanger 58 is arranged in front of the first heater 30 in the fresh air supply device 28.

[0046] The exhaust air 40 flows through the heat exchanger 58 and at the same time the fresh air 26 flows through this heat exchanger 58. The exhaust air 40 and the fresh air 26 are thus separated from one another by means of a separating surface 60 shown symbolically in FIGS. 2 and 3. Via this separating surface 60 the exhaust air 40 and the fresh air 26 exchange heat and thermal energy. Since the exhaust air 40 is generally warmer than the fresh air 26, the fresh air is normally heated by means of the heat from the exhaust air 40. The heat of the exhaust air 40 given off is here referred to as waste heat 62. The giving off of the heat 62 has the result that the exhaust air 40 cools. How much waste heat 62 the exhaust air 40 gives off on passing through the heat exchanger 58 depends on the area and the heat permeability or the heat transition coefficient of the material.

[0047] The area and the heat permeability of the separating surface 60 are chosen in the exemplary embodiments of FIGS. 2 and 3 such that the exhaust air 40 flowing through is at the same time dehumidified. This means that at the separating surface 60 the exhaust air 40 is cooled to such an extent that there a relative air moisture of 100% (in words: one hundred per cent) prevails. At the separating surface 60 water 64 or moisture then separates out from the exhaust air 40. With the separating-out of water 64 at the separating surface 60, the water 64 is withdrawn from the exhaust air 40, the exhaust air 40 becomes dryer.

[0048] The water 64 flows off as water from the heat exchanger 58 and the dryer, cooler exhaust air 40 is led by means of a supply line 66 to the second section 22.

[0049] At the second section 22 the supply line 66 separates into two lines 68. The supply line 66, shown in FIG. 3, or the line 68, shown in FIG. 2 can advantageously comprise a fan 69. This fan 69 is in this exemplary embodiment able to be regulated with regard to its speed and act as sucking. The lines 68 connect in a flowing line the supply line 66 with the supply line 52 of the respective region 36, 38. The exhaust air 40 is thus fed into the recirculation line 48 by means of the supply line 52. Within the recirculation line 48 there forms at the supply line 52 a mixture of supplied dehumidified, colder exhaust air 40 and moist warm exhaust air 40 from the recirculation from the respective region 36, 38. This mixture of the exhaust air 40 flows through the second heater 46 as second supply air 42 into the respective regions 36, 38 of the second section 22.

[0050] In order to regulate the air flows of the exhaust air 40 and of the supply air 42 in the respective lines, the through-flow dryer 10 comprises according to FIG. 3 a regulating device 70. The regulating device 70 is operatively coupled with a plurality of exhaust air sensors 72 and to a plurality of supply-air sensors 74.

[0051] The individual exhaust air sensor 72 measures in the exhaust air 40 from the second section 22 in each case region 36, 38 the relative air moisture. Depending on the relative air moisture of the exhaust air 40 the regulating device 70 then regulates the separation of the exhaust air 40 in the region of 90 to 100% (in words: ninety to one hundred per cent), in particular 95 to 100% (in words ninety-five to one hundred per cent), exhaust air 40 is led increased to the heat exchanger 58 and the heat exchanger at the heat exchanger dehumidified.

[0052] The only supply air sensor 74 measures in the supply air 42 to the respective region 36, 38 of the second section 22 the relative air moisture in the flow direction after the supply 52 and before the second heater 46. Depending on the relative air moisture of the supply air 42, the regulating device 70 regulates the admixing of the exhaust air 40 at the supply 52.

[0053] In an alternative exemplary embodiment, not illustrated, the exhaust air sensor 72 and the supply air sensor 74 can additionally measure the temperature prevailing there.

[0054] FIGS. 4 to 7 show in each case a through-flow dryer 110 in the form of a belt dryer. The through-flow dryer 110 comprises a housing 112, through which firstly moist or wet material 114 is to be transported by means of a transport belt 116 in a transporting direction 118. The material 114 passes through, on this transport, successively firstly a first section 120 and then a second section 122, which subdivide the housing 112 spatially. In each of the sections 120, 122, hot air is situated inside the housing 112. The respective hot air 124 of the individual sections 120, 122 is largely separated in terms of air flow. The hot air 124 withdraws in each of the sections the moisture 120, 122 from the material 114 or liquid 126 transported therein, in particular water. The removal of liquid 126 from the material 114 dehumidifies the material 114. The material 114 becomes dryer or is dried.

[0055] The exemplary embodiments in FIGS. 5 to 7 show the air guidance according to the invention of the hot air 124 in the sections 120 and 122. The hot air 124 for the second section 122 is generated in an air supply device 128 by means of a heat exchanger 130 and a heater 132. The heat exchanger 130 and the heater 132 in this case heat fresh air 134 from the surroundings and lead it into the second section 122. From the second section an exhaust air recirculation device 136 leads back used fresh air 134 as exhaust air 138 from the second section 122 into the first section 120 as supply air 140 for the first section 120. This supply air 140 is in the first section 120 further moistened by the material 114 present therein and then by means of an exhaust air recirculation device 142 is led out of the first section 120 and discharged as outgoing air 144 to the surroundings of the through-flow dryer 110.

[0056] In order that a heat energy 146 contained in the outgoing air 144 is not discharged unused into the surroundings, the exhaust air 138 is conveyed to the heat exchanger 130 of the air supply device 128 by means of the exhaust air recirculation device 142. The exhaust air 138 becomes outgoing air after flowing through the heat exchanger 144.

[0057] The heat exchanger 130 of the air supply device 128 thus at the same time has the exhaust air 38 and the fresh air 134 flowing through it. The exhaust air 138 and the fresh air 134 are in this case in terms of flow separated by means of an exchange surface 148 and separating surface. This exchange surface 148 transmits the heat energy 146 of the exhaust air 138 to the fresh air 134. In order to heat the fresh air 134 further, in the flow direction of the fresh air 134 after the heat exchanger 130 the heater is arranged, before the fresh air 134 then flows into the second section 122. In the second section 122 the fresh air 134 flows around and through the material 114 and the transport belt 116 of the transport device 118. On flowing around the material 114 the fresh air 134 takes up the liquid 126 contained in the material 114. The fresh air 134 is enriched with water or becomes more moist.

[0058] From the second section 122 the fresh air 134 flows out by means of the exhaust air recirculation device 136 as exhaust air 138. The exhaust air recirculation device 136 comprises a fan 150 and a heater 152. The fan 150 sucks the exhaust air 138 out of the second section 122 and leads it through the heater 152 into the first section 120. The heater 152 heats the exhaust air 138 in doing so. With the heating the relative air moisture of the first exhaust air 138 falls, it is thus processed or more receptive. The first exhaust air 138 becomes thereby supply air 140.

[0059] The supply air 140 flows through in FIG. 5 the first section 120 and in doing so takes up likewise liquid. By means of the exhaust air recirculation device 142 which comprises a fan 150, the exhaust air 138 is then discharged to the surroundings from the first section 122 after flowing through the heat exchanger 130 as outgoing air 144.

[0060] FIG. 6 and FIG. 7 show an exemplary embodiment of a through-flow dryer 110, in which the first section is subdivided into a first region 154, a second region 156 and a third region 158.

[0061] The second and third region 156, 158 are intermediate members between the second section 122 and the first region 154. The regions 154, 156, 158 form a series circuit. In both regions 156, 158 supply air 140 is supplied by the region following in the transport direction 118 by means of a respective recirculation device 136. The supply air 140 flows through the respective region 156, 158. After flowing through, this used supply air 140 is recirculated as exhaust air 138 by means of a recirculation device 136 in the transport direction 118 in the respectively preceding regions 154, 156. These exhaust air recirculation devices 136 also comprise in each case a fan 150 and a heater 152. The fan 150 transports also here the exhaust air 38 further and the heater heats this.

[0062] As shown in FIG. 7, the air supply device 128 and the exhaust air recirculation device 136 is designed with in each case one supply air sensor 160, which is provided downstream in front of the respective heaters 132 and 152. The supply air sensors 160 and the heaters 132 and 152 are operatively coupled to a regulating device 162, for example a customary programmable logic controller (PLC). In addition, the regulating device 162 is operatively coupled to the heaters 132, 152 and additionally or alternatively to the fans 150. The regulating device 162 regulates thus, by means of which signals determined by the supply air sensors 160 the respective heaters 132 and 152. Depending on the embodiment of the regulating device 162, additionally or alternatively the respective fans 150 are regulated.

LIST OF REFERENCE SYMBOLS

[0063] 10 through-flow dryer [0064] 12 housing [0065] 14 material [0066] 16 belt [0067] 18 transport direction [0068] 20 section [0069] 22 section [0070] 24 hot air [0071] 26 fresh air [0072] 28 fresh-air supply device [0073] 30 heater [0074] 32 supply air [0075] 34 exhaust air [0076] 36 region [0077] 38 region [0078] 40 exhaust air [0079] 42 supply air [0080] 44 exhaust air recirculation device [0081] 46 heater [0082] 48 recirculation device [0083] 50 branch [0084] 52 supply [0085] 54 line [0086] 56 collecting line [0087] 57 fan [0088] 58 heat exchanger [0089] 60 separating surface [0090] 62 waste heat [0091] 64 water [0092] 66 supply line [0093] 68 line [0094] 69 fan [0095] 70 regulating device [0096] 72 exhaust air sensor [0097] 74 supply air sensor [0098] 110 through-flow dryer [0099] 112 housing [0100] 114 material [0101] 116 transport belt [0102] 118 transport direction [0103] 120 first section [0104] 122 second section [0105] 124 hot air [0106] 126 liquid [0107] 128 air supply device [0108] 130 heat exchanger [0109] 132 heater [0110] 134 fresh air [0111] 136 exhaust air recirculation device [0112] 138 exhaust air [0113] 140 supply air [0114] 142 exhaust air recirculation device [0115] 144 outgoing air [0116] 146 thermal energy [0117] 148 exchange surface [0118] 150 fan [0119] 152 heater [0120] 154 region [0121] 156 region [0122] 158 region [0123] 160 supply air sensor [0124] 162 regulating device