Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2002-03-22
2003-07-29
Lazarus, Ira S. (Department: 1746)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S638000, C034S641000, C034S643000
Reexamination Certificate
active
06598315
ABSTRACT:
The object of the present invention is a nozzle arrangement in an airborne web-drying apparatus and a method for improving the heat transfer in airborne web-drying, the apparatus and the method being defined in the preambles of the independent claims presented below.
Then the object of the invention is typically a nozzle arrangement which comprises at least one overpressure nozzle extending transversely of the web and having on both sides of the nozzle, i.e. on the entrance and exit sides of the nozzle, a nozzle slot extending across the web, in which case the nozzle slots on the opposite sides of the nozzle comprise one nozzle slot extending across the web or a row of successive nozzle orifices. The nozzle slots are arranged to blow drying air jets obliquely against each other, or they are arranged to blow drying air jets, which are guided against each other with the aid of curved Coanda-surfaces. The arrangement further comprises at least one direct impingement nozzle extending across the web, in which case a plurality of nozzle slots or nozzle orifices are formed in this direct impingement nozzle for blowing drying air mainly perpendicularly against the web. Advantageously the nozzle orifices or slots of the direct impingement nozzle are arranged in one or more rows, or otherwise evenly distributed on the supporting surface of the direct impingement nozzle.
A plurality of overpressure nozzles or direct impingement nozzles are typically arranged in an alternating succession on both sides of the web. Thereby an overpressure nozzle and a direct impingement nozzle are arranged opposite each other, as shown e.g. in the international patent publication WO 95/14199. In the solution presented in the WO-publication the space between each overpressure nozzle and the adjacent direct impingement nozzle forms a discharge passage for the wet discharge air. The discharge passages are ineffective regions regarding the drying of the web.
The aim is to continuously improve the effect of the airborne web-drying for instance in order to be able to make the drying faster and/or to reduce the size of the dryer. One economical means to improve the effect of airborne web-drying is to increase the nozzle temperature. However, it is not possible to increase the nozzle temperature in some applications, or the desired effect can not be obtained with this single measure.
The object of the present invention is to provide an improved nozzle arrangement and a method which are able to increase the effect of airborne web-drying.
A particular object is to provide a nozzle arrangement which is easy to realise in airborne web-drying apparatuses of different types.
A further object is to provide an improved nozzle arrangement and method which do not require substantial extra space for the airborne web-drying apparatus.
In order to reach the above-mentioned objects the nozzle arrangement and method according to the invention in airborne web-drying are characterised in what is defined in the characterising parts of the independent claims presented below.
The solution according to the invention uses nozzle assemblies which in the same structure combine at least one overpressure nozzle and at least one direct impingement nozzle. The assembly of overpressure nozzle and direct impingement nozzle is advantageously mounted in a common frame structure and in a common nozzle box. The nozzle assembly comprises typically an overpressure nozzle and a direct impingement nozzle arranged on both sides of the overpressure nozzle, i.e. on its entrance and exit sides. Thus no conventional discharge passage for wet air is formed between the overpressure nozzle and the direct impingement nozzles in the nozzle assembly. Compared to conventional solutions a larger part of the area of the dryer can in this way be utilised in the actual drying process. The discharge passages for the wet air are arranged between the different nozzle assemblies. Each passage discharges drying air blown by both the overpressure nozzle and the direct impingement nozzle. The direct impingement nozzles are arranged in relation to the web, so that they do not hinder air from being discharged from the overpressure nozzle. The web will further facilitate the air discharge from the direct impingement nozzle region in the travel direction of the web.
In another typical solution according to the invention a direct impingement nozzle is arranged on the entrance or exit side in the travel direction of the web of the over pressure nozzle and directly attached to the overpressure nozzle, so that an assembly comprising an overpressure nozzle and one direct impingement nozzle is formed.
The distance between the nozzle slots of the overpressure nozzle and the first nozzle orifice row closest to the overpressure nozzle is advantageously >30 mm but <100 mm, typically 40 to 60 mm.
In conventional airborne web-drying solutions there is a relatively wide discharge air passage between each successive nozzle pair. Then the actual nozzles cover only less than half of the total area. In this case there will be a poor heat transfer in the region of the discharge air passage, as no air jets are directed at the web in this region. In the solution according to the invention the drying utilises also a part of the empty space left between the individual nozzles in conventional dryers. The direct impingement arranged in connection with the overpressure nozzle enables an increased total amount of drying air to be directed at the web, i.e. in this region the heat-transfer coefficient can be increased and the heat transfer can be made more efficient. In measurements it was found that a considerably increased heat transfer can be achieved with the solution according to the invention. The heat transfer can be made more efficient with the solution according to the invention, also when the temperature of the drying air must kept very low, such as for instance in the drying of “thermal coatings”.
Each nozzle assembly according to the invention has typically nozzle orifices in one or two direct impingement nozzle sections, the nozzle orifices occupy an area having a total length of 20 to 250 mm in the travel direction of the web, typically >50 mm, most typically >100 mm, or covering 10 to 60% of the length of the nozzle distribution. A direct impingement nozzle can of course also have only one row of nozzles or nozzle orifices, in which case the area is very small.
The nozzle orifices of the direct impingement nozzle parts have typically a diameter of 2 to 10 mm, most typically about 5 mm, and the nozzles are arranged at a distance from each other which is 10 to 50 mm, typically 20 to 30 mm, both in the web cross direction and in the web travel direction. The nozzle orifices are typically arranged in rows in the cross direction of the web. There are typically 2 to 7 successive rows of nozzle orifices in the travel direction of the web. Advantageously the nozzle orifices in different rows are overlapping, so that the total coverage of the orifices is as large as possible. The nozzle orifices can also be arranged evenly on the supporting surface of the nozzle in other ways. An airborne web-drying apparatus contains typically several successive nozzle assemblies on both sides of the web to be dried.
In steam-heated dryers the heat source forms an upper limit for the temperature. Also in this case the drying can be made more effective with the solution according to the invention. An effective nozzle can increase the drying effect also in gas-heated dryers.
On the other hand the solution according to the invention can also be used in small spaces, particularly in short spaces, in order to maximise the drying effect.
The gap between two successive assemblies according to the invention forms a discharge passage for wet discharge air. The nozzle assemblies are disposed on different sides of the web to be dried, advantageously in such a manner that there is always a part of a nozzle assembly, preferably an overpressure nozzle part, on the other side of the web opposite to a discharge passage
Heikkilä Pertti
Solin Richard
Lathrop & Clark LLP
Lazarus Ira S.
Metso Paper Inc.
O'Malley Kathryn S.
LandOfFree
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