Method and installation for drying a damp web

Abstract

An installation for drying a web of non-woven material includes a fan (6), a heating oven (3), an outlet pipe (C2) which puts the outlet of the oven (3) in communication with the intake of the fan (6), a branch pipe (C3) branching from the inlet pipe (C1) upstream of the heat source (4) putting the pipe (C1) in communication with the inlet of a drying device (10, 11), a pipe (C4) for the extraction of air from the drying device (10, 11) and a humidity level probe (13) mounted in the extraction pipe (C4).

Claims

1. Installation for drying a web of non-woven material characterised in that it comprises: a fan (6), a heating oven (3) with an inlet and an outlet, an inlet pipe (C1) which puts the discharge of the fan (6) in communication with the inlet of the oven (3) and sends discharged air to the inlet of the oven, a heat source (4) arranged such that the air discharged into the inlet pipe (C1) is heated, an outlet pipe (C2) which puts the outlet of the oven (3) in communication with the intake of the fan (6), a branch pipe (C3), branching off from the inlet pipe (C1) upstream of the heat source (4), putting the inlet pipe (C1) in communication with the inlet of a drying device (10, 11), a transport means (2) which moves a web in the drying device (10, 11) and in the oven (3), the drying device (10, 11) being upstream of the oven (3) in the direction of movement of the web, an extraction pipe (C4) for the air of the drying device (10, 11), a probe (13) for the humidity level mounted in the extraction pipe (C4) for measuring the level of humidity in the air evacuated from the drying device (10, 11), the probe (13) being connected to a control unit which compares the relative humidity to a guide level and which, if the relative humidity is greater than the guide level: raises the temperature of the heat source (4) and/or increases the flow of air in the inlet pipe (C1) and/or increases the flow of air in the branch pipe (C3).

2. Installation according to claim 1, characterised by a branch fan (8) mounted in the branch pipe (C3).

3. Installation according to claim 1, characterised by a flap (9) for controlling the flow of air in the branch pipe (C3).

4. Installation according to claim 1, characterised by an extraction fan mounted in the extraction pipe (C4).

5. Installation according claim 4 wherein the extraction fan is mounted in the extraction pipe (C4) just downstream of the direction of the passage of air of the drying device (10, 11).

6. Installation according to claim 1, characterised by a flowmeter (18) mounted in the extraction pipe (C4), by a flowmeter (17) mounted in the branch pipe (C3) and by a control unit (UC) connected by signal technology to flowmeters (17) and (18) and controlling the flow in the extraction pipe (C4) such that it is greater than the flow in the branch pipe (C3).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings given solely by way of example:

(2) FIG. 1 is a diagram illustrating the prior art,

(3) FIG. 2 is a circulation diagram illustrating the invention, and

(4) FIG. 3 is diagram similar to FIG. 2 illustrating a variant.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

(5) In FIG. 2, the web to be dried 1 circulates around a drum 2 (or on a conveyor).

(6) Hot air is injected under pressure through an inlet pipe C1 into the hood 3 by means of a fan V1 6 (referred to as the main fan) and a heat source 4 which reheats the air. Said heat source 4 can be for example a gas burner or a heat exchanger (using oil, air, water or electricity).

(7) Said hot air then traverses the damp web and the drum 2 (or the web of the conveyor) by this method, the water contained in the web is evaporated as the web advances over the drum 2 (or on the conveyor). The air which has traversed the web is cooled and charged with humidity. It is them sucked via an extraction pipe C2 to the inside of the drum 2 by the fan V1 6, then reheated again by the heat source 4 and reinjected into the circuit and so on.

(8) The heat source 4 can be placed upstream or downstream of the fan V1 6. Preferably, it is placed downstream as described in the figure in the case of an exchanger and upstream in the case of a gas burner.

(9) The motor of the fan V1 6 is driven by a frequency converter 14.

(10) The temperature of the hot air injected into the hood 3 is controlled by the action of the heat source 4.

(11) A portion of the cooled and humid air is evacuated out of the circuit so as not to concentrate the humidity in the circulation circuit. Therefore, a portion of cooled and humid air is evacuated through the branch pipe C3 by means of the pressure generated at the output by the fan V1 (6) if it is sufficient or by means of an additional branch fan V2 (8).

(12) The branch pipe C3 can be connected upstream of V1.

(13) Flaps 9 can be installed in the branch pipe C3 in order to be able to control the amount of extracted flow.

(14) If there is a branch fan V2 (8), the motor of this fan can be driven by a frequency converter. If there are control flaps 9, said drive by converter is not necessary.

(15) To address this deficit of air in the circuit, reserve air from the production hall or outside the building is suctioned upstream of the fan V1 6 via the reserve pipe 7.

(16) The cooled and humid air evacuated by the branch pipe C3 is then injected into a diffusion box 10 which diffuses the air above a drying vacuum box 11 arranged upstream of the oven 3 on which the web to be dried circulates.

(17) Said drying vacuum box 11 can be arranged either in a conveyor (support web=conveyor web), or in a cylinder (support web=nickel cylinder, perforated metal sheet, metal web).

(18) The air is suctioned into the drying box 11 by a final extraction fan V3 12. Preferably, said fan 12 is positioned closest to the drying box 11.

(19) A probe for measuring relative humidity 13 is installed in the drying box 11 or downstream of the drying box 11. Preferably, it is installed just upstream of the fan 12 in an extraction pipe C4.

(20) Said probe 13 measures the relative humidity of the air in the drying box 11 or downstream of the drying box. Preferably, the measurement is performed just upstream of the final extraction fan 12.

(21) The relative humidity measured in the drying box 11 or downstream of the drying box 11 (preferably just upstream of the final extraction fan 12) is controlled at a level of less than 100% by influencing the drying temperature of the oven and/or the rotational speed of the main fan V1 6 of the oven and/or the rotational speed of the branch fan V2 8 of the oven and/or the position of the control flaps 9.

(22) The signal of relative humidity is sent via a line L1 to a control unit UR which compares the signal with a guide level and sends control signals as a result to the fan 6 via line L2, to the heat source 4 via line L3, to the flap 9 via line L4 and/or to the fan 8 (to its converter 15) via line L5.

(23) In another manner of implementing the invention (cf. FIG. 3), it is possible to add the following elements to the configuration described in FIG. 2:

(24) The motor of the fan V3 12 is driven by a frequency converter 16.

(25) A flowmeter 17 measures the flow extracted by the oven in the branch pipe C3. Said flowmeter can be installed in front of or after the branch fan V2 8.

(26) A flowmeter 18 measures the flow of air suctioned by the drying suction box 11. Said flowmeter can be installed in front of or after the final extraction fan V3 12.

(27) The air extracted by the oven can contain combustion gases (NOx, CO) which can be dangerous for operators working on the production line. To ensure that the system functions correctly it is imperative that 100% of the flow blown in by the diffusion box is suctioned off by the drying box, otherwise polluted air will be diffused into the production room.

(28) To satisfy this requirement a control system makes it possible to control the amount of flow suctioned by the drying box (measured by the flowmeter 18) as a function of the flow in the branch pipe (measured by the flowmeter 17) by means of lines L6, L7 and L8.

(29) It is calculated for example Q extraction=K*Q branch, with K>1.

(30) Preferred value: K=1.1

EXAMPLES

(31) Example of production without the system according to the invention (corresponds to the configuration described for FIG. 2):

(32) A web of 45 gsm 50% Viscose 50% PET to 220 m/min is produced with a machine width of 3500 mm.

(33) 4 injectors are used for bonding the web at pressures of 50-80-120-120 bars with strips of type 2J14-2J14-2J14-1J7 Strip 2J14=2 rows, diameter of the holes=120 m, centre-to-centre of holes=1.4 mm

(34) Strip 1J7=1 row, diameter of the holes=120 m, centre-to-centre of holes=0.7 mm

(35) The wet web then passes onto a dewatering conveyor by vacuum provided with: 1 low vacuum dewatering box: slot width=10 mm, vacuum=100 mbar 1 high vacuum dewatering box: slot width=8 mm, vacuum=400 mbar

(36) The web of the conveyor has a permeability of about 800 cfm.

(37) The drying box (11), fed from above by the diffusion box (10), is integrated into said conveyor, downstream of the 2 dewatering boxes. Said drying box has a slot width of 600 mm.

(38) Just upstream of said drying box (after the 2 dewatering boxes), the wetting level of the web is 120% (=120 g water for 100 g dry web).

(39) When the web has passed underneath the drying box it is then transported up to the oven to be completely dried.

(40) The oven which is used for drying said web is provided with a branch fan V2 8 and a main fan V1 6. The motors of these 2 fans are controlled by frequency converter.

(41) The heat source 4 is a gas burner.

(42) The branch piping of said oven is connected to the diffusion box 10.

(43) In order to obtain a dry web at the outlet of the oven, the following guide levels were applied in the oven:

(44) T level air in the hood 3: 120 C.

(45) % V1=70%

(46) % V2=85%.

(47) The temperature and the humidity of the air extracted by the branch piping are increased:

(48) T C.=82 C. HR=20% (70 g water/kg dry air)

(49) The temperature and the humidity of air in the drying box 11 are measured:

(50) T C.=43 C. HR=100%

(51) The presence of droplets of water is noted in said drying box.

(52) The air in the drying box has therefore reached saturation.

(53) Just after the drying box 11 (ahead of the oven) the web is measured as having a wetting level of 130%.

(54) This value is greater than the value measured just upstream of the drying box (120%).

(55) The web has therefore been rewetted by the current of air arriving from the branched casing of the oven.

(56) The system of the diffusion box+drying box has not therefore been able to lower the wetting level of the web prior to the oven and does not provide a satisfactory result.

(57) In these conditions, the oven uses a total of 2410 Kw, divided into: 2320 Kw gas 90 Kw electricity. Example of the same requirement of production with the system according to the invention (corresponds to the configuration described in FIG. 3 or 4): the speed of the branch fan V2 is regulated to obtain the relative humidity desired upstream of the final extraction fan V3.

(58) A web of 45 gsm 50% viscose 50% PET to 220 m/min is produced with a machine width of 3500 mm.

(59) 4 injectors are used for bonding the web, at pressures of 50-80-120-120 bar with strips of the type 2J14-2J14-2J14-1J7

(60) Strip 2J14=2 rows, diameter of the holes 120 m, centre-to-centre of holes=1.4 mm

(61) Strip 1J7=1 row, diameter of the holes=120 m, centre-to-centre of holes=0.7 mm

(62) The wet web can then passes onto a dewatering conveyor by vacuum provided with: 1 low vacuum dewatering box: slot width=10 mm, vacuum=100 mbar 1 high vacuum dewatering box: slot width=8 mm, vacuum=400 mbar

(63) The web of the conveyor has a permeability of about 800 cfm.

(64) The drying box 11, fed from above by the diffusion box 10, is integrated into this conveyor downstream of the 2 dewatering boxes. Said drying box has a slot width of 600 mm.

(65) Just upstream of this drying box (after the 2 dewatering boxes) the wetting level of the web is 120% (=120 g water for 100 g dry web).

(66) When the web has passed underneath the drying box it is then transported up to the oven to be completely dried.

(67) The oven which is used for drying said web is provided with a branch fan V2 8 and a main fan V1 6. The motors of these 2 fans are controlled by a frequency converter.

(68) The source of heat 4 is a gas burner.

(69) The branch piping of said oven is connected to the diffusion box 10.

(70) The drying box 11 is connected to a fan V3 12. Just upstream of said fan a probe 13 is installed which measures the relative humidity of the air current.

(71) The speed of the branch fan V2 is controlled to obtain the desired relative humidity upstream of the final extraction fan V3.

(72) A guide level of 95% is set for said relative humidity.

(73) In order to obtain a dry web at the outlet of the oven, the following guide levels were applied in the oven:

(74) T guide level air in the hood 3: 120 C.

(75) % V1=55%

(76) The control stabilised the value of the speed of rotation of the fan V2 at 95%.

(77) The temperature and relative air humidity extracted by the branch piping are increased:

(78) T C.=95 C. HR=10% (57 g water/kg dry air)

(79) The temperature and the humidity of the air in the drying box 11 are measured:

(80) T C.=47 C. HR=95% (69 g water/kg dry air)

(81) The air traversing the web on the drying box recovered 6957=12 g water/kg air. This quantity corresponds to the amount of water which was extracted from the web by evaporation on said drying box.

(82) The wetting level of the web is checked just after the drying box: the measurement is 101%.

(83) This value is therefore much lower than the value measured just upstream of the drying box (120%).

(84) The web has therefore been partially dried this time by the current of air from the branch casing of the oven!!

(85) The air was not condensed in the diffusion box.

(86) In these conditions, the oven uses a total of 1860 Kw, divided into: 1805 Kw gas 55 Kw electricity Example of the same requirement of production with the system according to the invention (corresponds to the configuration described for FIG. 3 or 4): the temperature of the air injected into the hood is controlled to obtain the desired relative humidity upstream of the final extraction fan V3.

(87) A web 45 of gsm 50% Viscose 50% PET to 220 m/min is produced on a machine width of 3500 mm.

(88) 4 injectors are used or bonding the web, at pressures of 50-80-120-120 bar with strip types 2J14-2J14-2J14-1J7

(89) Strip 2J14=2 rows, diameter of the holes=120 m, centre-to-centre of holes=1.4 mm

(90) Strip 1J7=1 row, diameter of the holes=120 m, centre-to-centre of holes=0.7 mm

(91) The wet web then passes onto a dewatering conveyor by vacuum provided with: 1 low vacuum dewatering box: slot width=10 mm, vacuum=100 mbar 1 high vacuum dewatering box: slot width=8 mm, vacuum=400 mbar

(92) The web of the conveyor has a permeability of about 800 cfm.

(93) The drying box 11, fed from above by the diffusion box 10, is integrated into said conveyor downstream of the 2 dewatering boxes. Said drying box has slot width of 600 mm.

(94) Just upstream of said drying box (after the 2 dewatering boxes), the wetting level of the web is 120% (=120 g water for 100 g dry web).

(95) When the web has passed underneath the drying box it is then transported up to the oven to be completely dried.

(96) The oven which used for drying said web is provided with a branch fan V2 8 and a main fan V1 6. The motors of these 2 fans are controlled by frequency converter.

(97) The heat source 4 is a gas burner.

(98) The branch piping of said oven is connected to the diffusion box 10.

(99) The drying box 11 is connected to a fan V3 12. Just upstream of said fan a probe 13 is installed which measures the relative humidity of the air current.

(100) The temperature of the air injected into the hood is controlled to obtain the desired relative humidity upstream of the final extraction fan V3.

(101) A guide level of 95% is set for said relative humidity.

(102) In order to obtain a dry web at the exit of the oven, the following guide levels were applied in the oven

(103) % V1=50%

(104) % V2=85%

(105) The control stabilised the temperature of the air injected into the hood at 130 C.

(106) The temperature and the relative air humidity extracted by the branch piping are increased:

(107) T C.=99 C. HR=10% (67 g water/kg dry air)

(108) The temperature and the humidity of the air in the drying box 11 are measured:

(109) T C.=51 C. HR=95% (82 g water/kg dry air)

(110) The air traversing the web on the drying box recovered 8267=15 g water/kg air. This quantity corresponds to the amount of water which was extracted from the web by evaporation on said drying box.

(111) The wetting level of the web is checked just after the drying box: the measurement is 105%.

(112) This value is therefore much lower than the value measured just upstream of the drying box (120%).

(113) This time the web has therefore been partially dried by the current of air from the branch casing of the oven!!

(114) The air was not condensed in the diffusion box.

(115) In these conditions the oven uses a total of 1935 Kw, divided into: 1897 Kw gas 38 Kw electricity.