Continuous-flow dryer comprising a heat exchanger

Abstract

A continuous-flow dryer for drying a material by means of hot air is provided with a fresh air supply device for supplying fresh air as supply air, an exhaust air recirculation device for removing exhaust air and for recirculating exhaust air as supply air, and a heat exchanger, through which fresh air on the one hand and exhaust air on the other hand are led, for transferring waste heat of the exhaust air into the fresh air. According to the invention, the removed exhaust air is supplied at the bottom into the heat exchanger.

Claims

1. A continuous-flow dryer (10) for drying a material by means of hot air, comprising a fresh air supply device (28) for supplying fresh air (26) as supply air (32), an exhaust air recirculation device (38) for removing exhaust air (34) and for recirculating exhaust air as recirculated supply air (42), and a heat exchanger (54), through which fresh air (26) on the one hand and exhaust air (34) on the other hand are led, for transferring waste heat of the exhaust air (34) into the fresh air (26), the heat exchanger (54) having a first portion (56) through which the exhaust air (34) flows upwardly and a second portion (58) through which the exhaust air (34) flows downwardly, the exhaust air being diverted in a U-shape between the first portion (56) and the second portion (58), and a separating surface (60) arranged in the first portion (56) between the fresh air (26) and the exhaust air (34), the separating surface being configured to allow water (64) which condenses out of the exhaust air (34) to flow along the separating surface (60), wherein the exhaust air (34) is supplied at a bottom of the first portion into the heat exchanger (54).

2. The continuous-flow dryer according to claim 1, wherein the exhaust air (34) is removed at a bottom of the second portion from the heat exchanger (54).

3. The continuous-flow dryer according to claim 1, wherein the exhaust air (34) first flows through the first portion (56) and subsequently through the second portion (58), whereas the fresh air (26) first flows through the second portion (58) and subsequently through the first portion (56).

4. The continuous-flow dryer according to claim 1, wherein a first and a second section are provided, through which the material (14) is passed successively in a transport direction (18), the fresh air supply device (28) being designed for supplying the fresh air (26) as the supply air into the first section, and the exhaust air recirculation device (38) for removing the exhaust air (34) from the second section and for recirculating it as the recirculated supply air back into the second section.

5. The continuous-flow dryer according to claim 1, wherein a first and a second section (20, 22) are provided, through which the material (14) is passed successively in a transport direction (18), the fresh air supply device (28) being designed for supplying the fresh air (26) as the supply air (32) into the second section (22), and the exhaust air recirculation device (38) being designed for removing the exhaust air (34) from the first section (20) and for recirculating it as the recirculated supply air (42) back into the first section (20).

6. The continuous-flow dryer according to claim 1, wherein a heater (30) is provided, by means of which the fresh air (26) is to be heated up before being supplied as the supply air (32).

7. The continuous-flow dryer according to claim 1, wherein a heater (44) is provided, by means of which the exhaust air (34) led through the heat exchanger (54) is to be heated up before being supplied as the recirculated supply air (42).

8. A method for operating a continuous-flow dryer (10) for drying a material (14) by hot air (24), comprising: supplying fresh air (26) as supply air (32); removing exhaust air (34) and recirculating the exhaust air (34) as recirculated supply air (42); leading the fresh air (26) and the exhaust air (34) through a heat exchanger (54), for transferring waste heat of the exhaust air (34) into the fresh air (26); and supplying the exhaust air (34) at a bottom into the heat exchanger (54), wherein leading the exhaust air (34) through the heat exchanger comprises leading the exhaust air upwardly through a first portion (56) of the heat exchanger (54), diverting the exhaust air in a U-shape from the first portion (56) of the heat exchanger (54) to a second portion (58) of the heat exchanger, leading the exhaust air downwardly through the second portion (58) of the heat exchanger, and allowing water to condense on a separating surface (60) arranged in the first portion (56) between the fresh air (26) and the exhaust air (34) and to flow along the separating surface (60).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the solution according to the invention is explained in more detail below with the aid of the appended schematic drawings, in which:

(2) FIG. 1 shows a highly simplified longitudinal section of a continuous-flow dryer according to the prior art and

(3) FIG. 2 shows a highly simplified longitudinal section of a continuous-flow dryer according to the invention.

DETAILED DESCRIPTION

(4) In FIGS. 1 and 2 there is each shown a continuous-flow dryer 10 in the form of a belt dryer. The continuous-flow dryer 10 has a housing 12, through which the initially moist or wet material 14 is to be transported by means of a belt 16 in a transport direction 18 through the continuous-flow dryer 10.

(5) During transport, the material 14 passes firstly through a first section 20 and after that a second section 22. The two sections 20 and 22 divide the housing 12 spatially. In the transport direction they are largely separated from one another in terms of air flow, if necessary, by means of one dividing wall or a plurality of dividing walls. The sections 20 and 22 can also for their part be further subdivided into subsections.

(6) Within the housing 12 there is hot air 24 which withdraws moisture (not shown) from the material 14 to be dried. With the withdrawing of moisture from the material 14, the material 14 becomes drier, it is dried.

(7) FIG. 2 illustrates how such a material 14 is dried by means of hot air in the continuous-flow dryer 10, according to the invention, there. For drying, fresh air 26 flows from outside the housing 12, conveyed by a fresh air supply device 28, into the housing 12. The fresh air 26 flows through a first heater 30 which heats the fresh air 26 on its way through the heater 30. With the heating of the fresh air 26, the relative air moisture of the fresh air 26 decreases, the fresh air 26 becomes drier.

(8) This fresh air 26, after the heating, is referred to as the supply air 32. The supply air 32 flows into the section 22 and there flows around the individual particles of the material 14 or it flows through the layer of the material 14 on the belt 16. On this flowing around the particles of the material 14, the supply air 32 takes up moisture from the material 14. The relative air moisture of the supply air 32 increases, the supply air 32 becomes more moist. The moistened supply air 32 is subsequently discharged from the housing 12 into surroundings thereof from the section 22 as exhaust air 34 by means of an exhaust air outlet 36 with a fan. This exhaust air 34 thus constitutes outgoing air.

(9) Before the material 14 reaches the second section 22, it passes through the first section 20. In the section 20, exhaust air 34 is discharged at the bottom. This exhaust air 34 is led by means of an exhaust air recirculation device 38, which comprises in particular a fan, to a recirculation line 40. Through the recirculation line 40, this exhaust air 34 is largely recirculated again into the section 20 as supply air 42.

(10) A flap 46 can be connected to the recirculation line 40, through which flap a part of the exhaust air 34 can be discharged directly into the surroundings of the continuous-flow dryer 10.

(11) At the outlet of the recirculation line 40 there is arranged a heater 44, by means of which the recirculated exhaust air 34 can be heated up before its re-entry as supply air 42 into the section 20. The heater 44 may be, but does not necessarily have to be, provided. Alternatively, the heater 44 can also have a comparatively small heat capacity. The exhaust air 34 from the section 20 is thus largely recirculated directly as supply air 42 into the section 20 by means of the exhaust air recirculation device 38.

(12) The recirculation line 40 further has a branch 48, to which a line 50 is connected. At the branch 48, a part of the exhaust air 34 is branched off from the recirculation line 40 and led out by means of the line 50. For this purpose, a sucking fan 52 to be separately regulated can be arranged in the line 50. The line 50 leads the branched-off exhaust air to a heat exchanger 54, and through it.

(13) The heat exchanger 54 comprises two portions 56 and 58 which as such each constitute an independent heat exchanger and through which are to flow separately heat-supplying air and heat-discharging air.

(14) The two portions 56 and 58 of the heat exchanger 54 each have a separating surface 60 at which, on one side, the branched-off exhaust air 34 is led out of the first section 20 as heat-supplying air and, on the other side, the fresh air 26 is led along as heat-discharging air. At each of the separating surfaces 60, heat therefore changes from the exhaust air 34 as waste heat 62 to the fresh air 26. At the same time, water 64 condenses out of the exhaust air 34 at the separating surface 60 with the cooling of the exhaust air 34.

(15) The portion 56 forms the part, designated here as first portion, of the heat exchanger 54. At it the discharged exhaust air 34 is supplied by means of the line 50 downwards, in particular also at the bottom side from below. The exhaust air 34 then rises on flowing through the portion 56 from below upwards. At the same time the exhaust air 34 cools down at the associated separating surface 60 and the water 64 condensing there flows off along the separating surface 60 downwards. In so doing, this water 64 entrains dust particles from the exhaust air 34 with it, which would otherwise be deposited on the separating surface 60.

(16) The exhaust air 34 flows upwards, in particular also at the top side upwards, out of the portion 56, is then diverted in a U-shape and then flows upwards, in particular also at the top side from above, into the portion 58 designated here as second portion 58. In the second portion 58 a condensation of water 64 does not necessarily occur. It is therefore more advantageous if the exhaust air 34 flows downwards and thus entrains at the same time those dust particles with it, which are contained in the exhaust air 34. These dust particles are thus discharged, together with the exhaust air 34, from the heat exchanger 54, without the latter being dirtied or sooted.

(17) Subsequently, the exhaust air 34 then flows downwards, in particular also at the bottom side from below, out of the second portion 58 and flows off through a recirculation line 66. The recirculation line 66 leads the air, thus cooled and condensed out, as supply air 42 back into the first section 20. For this purpose, a sucking fan 68 to be separately regulated can be arranged in the recirculation line 66. The recirculation line 66 leads at a junction 70, in the flow direction after the branch 48, into the recirculation line 40.

(18) In the flow direction shortly after the fan 68, a line 72 leading outwards into the surroundings of the continuous-flow dryer 10 branches off with a flap 74 arranged therein. This line 72 serves, with the associated flap 74, to discharge cooled exhaust air 34 from the recirculation line 66 into the surroundings. With such a discharge of a part of the exhaust air into the surroundings of the continuous-flow dryer 10, a slight negative pressure arises in the section 20. To equalize this negative pressure, air from the surroundings of the continuous-flow dryer 10 is forced into the first section 20 from outside. At the same time, no air and thus also no dust can escape to the outside from the section 20. This supply of air from outside into the section 20 therefore prevents a dusting of the surroundings of the continuous-flow dryer 10.

(19) The fresh air 26 is led by means of a supply line 76 through the heat exchanger 54 and, as explained above, through the heater 30 into the second section 22. In so doing, the amount of supply air 32 thus supplied is controlled by means of a flap 78 which is arranged in the supply line 76 before the heat exchanger 54.

(20) The fresh air 26 flows into the second portion 58 of the heat exchanger 54 firstly laterally, at the right side with respect to FIG. 2, at the associated side face of the heat exchanger 54. There, in the second portion 58 the exhaust air 34 is already comparatively highly cooled. The exhaust air 34 can, however, still transmit heat to the likewise comparatively cold fresh air 26.

(21) The fresh air 26 thereafter flows out of the second portion 58 of the heat exchanger 54 at the opposite side face and passes over laterally into its first portion 56. In the first portion 56 the exhaust air 34 flowing through there is comparatively hot and can likewise advantageously emit further heat to the fresh air 26 already preheated in the second portion 58.

(22) The fresh air 26 thus heated then flows out of the first portion 56 laterally at the left side with respect to FIG. 2 and is transported by means of the supply line 76 further to the heater 30.

(23) The flaps and fans mentioned are controlled, and in particular regulated, altogether by means of a control 80, with various measuring devices and sensors (not shown) coupled to the control 76 being able to be provided.

LIST OF REFERENCE SYMBOLS

(24) 10 continuous-flow dryer

(25) 12 housing

(26) 14 material

(27) 16 belt

(28) 18 transport direction

(29) 20 section

(30) 22 section

(31) 24 hot air

(32) 26 fresh air

(33) 28 fresh air supply device

(34) 30 heater

(35) 32 supply air

(36) 34 exhaust air

(37) 36 exhaust air outlet

(38) 38 exhaust air recirculation device

(39) 40 recirculation line

(40) 42 supply air

(41) 44 heater

(42) 46 flap

(43) 48 branch

(44) 50 line

(45) 52 fan

(46) 54 heat exchanger

(47) 56 portion of the heat exchanger

(48) 58 portion of the heat exchanger

(49) 60 separating surface

(50) 62 waste heat

(51) 64 water

(52) 66 recirculation line

(53) 68 fan

(54) 70 junction

(55) 72 line

(56) 74 flap

(57) 76 supply line

(58) 78 flap

(59) 80 control