Continuous-flow dryer comprising an exhaust air recirculation device

Abstract

A continuous-flow dryer for drying a material by hot air is provided with a first and a second section, through which the material flows successively in a transport direction. It includes a fresh air supply device, 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 and exhaust air are led, for transferring waste heat of the exhaust air into the fresh air. With the exhaust air recirculation device a first part of the exhaust air is removed from the first section and recirculated directly into the first section. Furthermore, a second part of the exhaust air is removed from the first section, led through the heat exchanger, and recirculated as supply air into the first section. The fresh air supply device supplies fresh air as supply air into the second section.

Claims

1. A continuous-flow dryer (10) having two sections for drying a material (14) with hot air (24), comprising: a fresh air supply device (28) for supplying fresh air (26) as supply air (32) into one of the two sections (20); an exhaust air recirculation device (38) for removing exhaust air (34) from a further of the two sections (22) and for recirculating a portion of the exhaust air as recirculated supply air (42) into the further of the two sections through a recirculation line (40); 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); a line (50) which branches off the recirculation line (40) and through which a further portion of the exhaust air (34) is led to the heat exchanger (54); and a removal device (68, 70) for removing another portion of the exhaust air (34) from the continuous-flow dryer (10).

2. The continuous-flow dryer according to claim 1, wherein the removal device (68, 70) is arranged, in flow direction of the exhaust air (34), after the heat exchanger (54).

3. The continuous-flow dryer according to claim 1, wherein a device (38, 46, 52, 64, 70) for controlling an amount of removed exhaust air (34) in relation to an amount of recirculated exhaust air (34) is provided.

4. The continuous-flow dryer according to claim 1, wherein the material (14) is passed successively in a transport direction (18) from the one of the two sections to the further of the two sections, the second section.

5. The continuous-flow dryer according to claim 1, wherein the material (14) is passed successively in a transport direction (18) from the further of the two sections to the one of the two sections.

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 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 recirculated supply air (42).

8. The continuous-flow dryer according to claim 1, wherein the heat exchanger (54) is dimensioned such that water condenses out on it from the exhaust air (34).

9. The continuous-flow dryer according to claim 1, wherein the exhaust air recirculation device (38) is provided with a suction device for sucking out exhaust air (34).

10. A method for operating a continuous-flow dryer (10) for drying a material (14) with hot air (24), comprising: supplying fresh air (26) as supply air (32) into one of two sections of the continuous-flow dryer (10); removing exhaust air (34) from a further of the two sections; feeing a portion of the exhaust air as recirculated supply air (42) back into the further of the two sections; feeding a further portion of the exhaust air to a heat exchanger (54); transferring, by the heat exchanger (54), waste heat (58) from the further portion of the exhaust air (34) into the fresh air (26); and removing a balance of the exhaust air (34) from the continuous-flow dryer (10).

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 in the first section 20 into 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 20 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 20 as exhaust air 34 by means of an exhaust air outlet 36 with a fan. This exhaust air 34 thus constitutes outgoing air.

(9) The material 14 then passes from the first section 20 into the second section 22. In the second section 22, 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 22 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 22. 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 22 is thus largely recirculated directly as supply air 42 into the section 22 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 has a separating surface 56 at which, on one side, the branched-off exhaust air 34 is led out of the first section 22 as heat-supplying air and, on the other side, the fresh air 26 is led along as heat-discharging air. At the separating surface 56, heat therefore changes from the exhaust air 34 as waste heat 58 to the fresh air 26. At the same time, water 60 condenses out of the exhaust air 34 at the separating surface 56 with the cooling of the exhaust air 34.

(14) A recirculation line 62 leads the air, thus cooled and condensed out, as supply air 42 back into the second section 22. For this purpose, a sucking fan 64 to be separately regulated can be arranged in the recirculation line 62. The recirculation line 62 leads at a junction 66, in the flow direction after the branch 48, into the recirculation line 40.

(15) In the flow direction shortly after the fan 64, a line 68 leading outwards into the surroundings of the continuous-flow dryer 10 branches off with a flap 70 arranged therein. This line 68 serves, with the associated flap 70, to discharge cooled exhaust air 34 from the recirculation line 62 into the surroundings.

(16) With such a discharge of a part of the exhaust air 34 into the surroundings of the continuous-flow dryer 10, a slight negative pressure arises in the section 22. To equalise this negative pressure, air from the surroundings of the continuous-flow dryer 10 is forced into the first section 22 from outside. At the same time, no air and thus also no dust can escape to the outside from the section 22. In this case, the material 14 to be dried in the section 22 is already comparatively dry and therefore particularly prone to dust formation. The supply of air from outside into the section 22 therefore prevents a dusting of the surroundings of the continuous-flow dryer 10.

(17) The fresh air 26 is led by means of a supply line 72 through the heat exchanger 54 and, as explained above, through the heater 30 into the first section 20. In so doing, the amount of supply air 32 thus supplied is controlled by means of a flap 74 which is arranged in the supply line 72 before the heat exchanger 54.

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

LIST OF REFERENCE SYMBOLS

(19) 10 continuous-flow dryer

(20) 12 housing

(21) 14 material

(22) 16 belt

(23) 18 transport direction

(24) 20 section

(25) 22 section

(26) 24 hot air

(27) 26 fresh air

(28) 28 fresh air supply device

(29) 30 heater

(30) 32 supply air

(31) 34 exhaust air

(32) 36 exhaust air outlet

(33) 38 exhaust air recirculation device

(34) 40 recirculation line

(35) 42 supply air

(36) 44 heater

(37) 46 flap

(38) 48 branch

(39) 50 line

(40) 52 fan

(41) 54 heat exchanger

(42) 56 separating surface

(43) 58 waste heat

(44) 60 water

(45) 62 recirculation line

(46) 64 fan

(47) 66 junction

(48) 68 line

(49) 70 flap

(50) 72 supply line

(51) 74 flap

(52) 76 control