Patent Description:
In general, pulp is dried in a pulp dryer by air flotation drying, which uses hot air blows or the like. The dryer comprises at least one, usually several circulation fans that supply heated air to the drying devices. Circulation fans are usually arranged on top of each other to form so-called fan towers. Fan towers are arranged adjacent to the drying section of the pulp dryer. The fans are installed in the fan tower so that their suction openings are confined to the front and back sides of the fan tower, seen in the direction of the web movement.

The dryer further comprises heating devices, which heat the air before it enters as drying air into the drying section. Heating devices, such as heat exchangers or steam radiators, are arranged in front of the suction openings of the fans, i.e. on the front and back sides of the fan towers. The air is transferred to the fan through the heating device, from the entry side of the heating device to its exit side. In front of the heating devices, i.e. on their entry side, is usually arranged a filter net or the like to prevent dust and debris, such as shredded pulp, paper, fibres or the like from entering into the heating device and further into the fan. Dust and other debris remain attached to the filter net, i.e. the filter surface, which thus has to be cleaned every now and then.

Traditionally cleaning of the filter nets of the pulp dryer's heating devices, such as steam radiators, takes place manually with a dust suction apparatus, which resembles nozzle head and hose of a giant vacuum cleaner and which is connected to a central vacuum system of the pulp dryer. The cleaning takes place at least a few times per week, in practice often every day. The person operating the dust suction apparatus must, at least partly, enter the restricted space between the adjacent fan towers, where the temperature is high, even over <NUM>, and where the air humidity is high. The nozzle of the dust suction apparatus is moved manually on the surface of the net filter to be cleaned. The work is hard, very unpleasant and unergonomic.

Due to the reasons stated above, it is difficult to perform the dust suction with sufficient care, and it is also not always done often enough. Hot steam and condensate pipes also constitute an occupational safety risk for operators working in the restricted space between fan towers. Inadequate dust suction causes an increase of pressure loss and a reduction in the amount of air in the recirculation fans. This may lead in the dryer section to an impaired drying efficiency and to runnability problems, whereby the production of the pulp dryer decreases.

Various automatic or semiautomatic cleaning devices have been proposed, e.g. in <CIT>. An automatic cleaning system is disclosed in <CIT>, where a suction nozzle and a blower nozzle are arranged on opposite sides of the filter net. However, there is still a need to improve the cleaning of the filter nets in pulp dryers as well as the function of the automatic or semiautomatic cleaning devices.

An object of the present invention is to reduce or even eliminate the above-mentioned problems appearing in the prior art.

An object of the present invention is to provide a solution, with which the cleaning of the filter nets of the fan towers in a pulp dryer is easy and quick.

Another object of the present invention is to provide a stationary cleaning unit and arrangement, which provide reliable and effective cleaning operation even in demanding pulp dryer conditions and which are easy to fit even in restricted space between the fan towers.

In order to realise the above-mentioned objects, the invention is characterised by what is presented in the characterising parts of the enclosed independent claims.

The embodiments and advantages mentioned in this text relate, when applicable, to the cleaning unit, the cleaning arrangement and the fan tower according to the invention, even though they are not always specifically mentioned.

A typical stationary cleaning unit according to the present invention for a cleaning arrangement in a fan tower of a pulp dryer, comprises.

A typical cleaning arrangement according to the present invention for pulp dryer's fan tower comprises.

wherein the arrangement comprises at least two stationary cleaning units according to the present invention comprising a filter net channel formed between a suction device and a replacement air device, arranged in the vicinity of the first and the second spool, wherein the filter net is arranged to be transported through the filter net channels of the stationary cleaning units.

A typical fan tower of a pulp dryer according to the present invention comprises.

A typical pulp dryer according to the present invention comprises at least one fan tower according to the invention.

Now it has been surprisingly found that the function and efficiency of a stationary cleaning unit comprising a suction device and a replacement air device can be significantly improved by arranging at least one sealing element in connection with the suction device at the entry or exit opening and by arranging the replacement air device to blow replacement air towards the exit opening. In this manner it is possible to successfully control the conditions at the suction area as well as to ensure the smooth operation of the cleaning unit. Unexpected efficiency in removal of dust and debris from the filter net surface has been observed as the replacement air blow towards the exit opening of the filter net channel effectively ejects the dust, debris and the like from the filter net surface and transfers it towards the suction opening without creating harmful turbulence at the suction area. Furthermore, the directing of the replacement air blow towards the exit opening provides steady transfer of the filter net through the filter net channel and past the suction device and replacement air device. The problems encountered with prior art devices where the blow was targeted directly to the suction, where decreased or completely solved and the cleaning results were unpredictably improved. The sealing of the suction area with sealing elements located at entry and/or exit opening and the directed replacement air blow make it also possible to increase the amount of air that is removed by the suction device from the suction area.

The stationary cleaning unit according to the present invention comprises a suction device and a replacement air device that are arranged on a distance from each other to form filter net channel with an entry opening and an exit opening. The distance between the suction opening of the suction device and the replacement air device, i.e. the width of the filter net channel, may be less than <NUM>, preferably less than <NUM>, for example in a range of <NUM> - <NUM>, preferably <NUM> - <NUM> or <NUM> - <NUM>. The filter net is arranged to be transported through the filter net channel, supported at least by the suction from the suction device and air blow(s) from the replacement air device. The filter net is cleaned from dust and/or other debris during its transport through the filter net channel. This means that the suction device is arranged on the first side of the filter net and the replacement air device is arranged on the second side of the filter net, opposite to the suction device. The suction opening and the blowing means are arranged to face each other. The replacement air device is arranged to blow air through the filter net during the filter net's transport through the filter net channel. In this manner formation of a local underpressure on the second side of the filter net can be avoided, the filter net's transport is stabilized, and at the same time the cleaning action of the filter net surface can be enhanced as the air blows effectively loosen and carry dust away from the filter net. The short distance between the suction device and the replacement air device provides improved suction efficiency and effective dust and debris removal, while minimising the space needed for the cleaning unit.

The suction device of the cleaning unit is arranged to remove air, dust and debris from the suction area on a first side of the filter net, when the filter net is moving or transported through the filter net channel past the suction device. The suction device is preferably arranged to extend over the whole width of the filter net to be cleaned, i.e. the suction device preferably has a width which corresponds to the width of the filter net. The suction device of the cleaning unit has a suction opening for removal of air, dust, debris and the like from a suction area. The suction area is here understood as the area on the filter net surface onto which the suction opening exerts a suction impact. The suction area extends, at the maximum, from the entry opening to the exit opening of the filter net channel. The height of the suction area may be < <NUM>, for example <NUM> - <NUM>, seen in direction of movement of the filter. The height of the suction opening, and thus the height of the suction area, may be adjustable, e.g. by using adjustment means such as adjustment screws or the like. The width of the suction opening preferably corresponds to the width of the filter net. The suction opening of the suction device preferably extends from a first end of the suction device to a second end of the suction device and over the whole width of the filter net.

The suction opening of the suction device is arranged at a suitable distance from the filter net to ensure the formation of an effective suction area on the filter net surface. The distance between the suction opening and the filter net surface may be, for example, less than <NUM>, preferably less than <NUM>, for example <NUM> - <NUM>.

The suction device may comprise a hollow body, where dust, debris and the like are transferred from the filter net surface through the suction opening. The suction opening is at a first end of a suction channel, which extends from the suction opening and leads the dust, debris and the like away from the filter net surface, preferably to the hollow body of the suction device. The suction channel has a cross-sectional area which may be formed as uniformly decreasing from the suction opening towards the hollow body. In general, the suction channel is free from steps, waists, cavities or other disruptions, which might cause flow turbulence and/or collection of dust/debris.

According to one preferable embodiment the suction device comprises a hollow body and a suction channel with a suction opening, wherein the suction channel is connected to the lower part of the hollow body, which preferably has a circular cross section. The hollow body may be in form of a pipe, tube or the like. The lower part is here understood as the part of the hollow body which is underneath an imaginary horizontal line drawn through the geometric centre of the hollow body. When the suction channel is connected to the lower part of the hollow body, the air which is removed from the suction area is brought into a circular motion which improves the ejection of this dust and/or debris laden air through the hollow body.

The suction device of the cleaning unit may preferably be arranged in connection with a central suction system or vacuum system of the pulp dryer. For example, the suction device may comprise a conduit leading to a quick release connection, which is arranged accessible from the service platform. The relatively short conduit leading from the hollow body of the suction device to the quick release connection is also easy to keep clean, e.g. by sweeping. When the filter net is to be cleaned, the hose of the central suction or vacuum system of the pulp dryer is connected to the quick release connection of the suction device.

The stationary cleaning unit comprises further a replacement air device, which comprises blowing means arranged to provide replacement air towards the exit opening of the filter net channel. It has been surprisingly found out that correctly directed blow of replacement air, i.e. towards the exit opening, is much more effective in removing dust and debris from the net while minimizing the risk for disturbances in filter net transfer. According to one embodiment of the invention the blowing means of the replacement air device comprise at least one blow opening. For example, the replacement air device may comprise a blow slot or a plurality of blow openings, such as blow holes or blow nozzles or blow nozzle groups, arranged in a row. Blow opening(s) may have a diameter or slot width in the range of <NUM> - <NUM>, preferably <NUM> - <NUM>, especially for feeding of pressurized air. Preferably, the replacement air device has a width which corresponds to the width of the filter net and/or to the width of the suction device. The width of the blowing means preferably corresponds to the width of the filter net and/or the width of the suction opening. The blowing means of the replacement air device preferably extends from a first end of the replacement air device to a second end of the replacement air device and over the whole width of the filter net. For example, the replacement air device may comprise an elongated blow slot extending preferably from the first end of the replacement air device to the second end of the device.

The replacement air device may be arranged in connection with a system providing pressurized air. For example, the blow nozzles or blow slot may be arranged in connection with the system providing pressurized air in the pulp mill. According to one preferable embodiment replacement air device may be a blow-off pipe, arranged to be fed with pressurised air, and comprising at least one horizontal row of blow openings or an elongated blow slot.

The distance between the replacement air device and the filter net to be cleaned may be less than <NUM>, preferably <NUM> - <NUM>.

According to one preferable embodiment the blowing means of the replacement air device may be arranged to blow replacement air towards the exit opening of the filter net channel in an angle of <NUM> - <NUM>°, preferably <NUM> - <NUM>°, measured from a horizontal imaginary reference line. The blow angle of the blowing means may be arranged adjustable, which means that the blow angle can be adjusted in order to obtain optimal operational stability and maximal dust/debris removal from the filter net surface. The correct positioning of the blowing means of the replacement air device may also improve the function of the sealing element arranged on the exit opening of the filter net channel and decrease the collection of dust and/or debris to the exit opening. In this manner the risk for blocking of the exit opening is decreased or even completely avoided.

According to one embodiment the blowing means of the replacement air device comprises blow nozzles or blow nozzle groups, where the blow direction of the nozzles may be adjustable also in a width direction of the filter net channel, i.e. in width direction of the filter net. This means that the of blow direction of the blowing means may be arranged adjustable towards the edges of the filter net or towards the horizontal central line of the filter net. In this manner the replacement air device can provide optimal replacement air supply in different operational conditions.

The replacement air device may comprise a support surface, arranged next to the blowing means in the blow direction of the blowing means. The support surface defines the filter net channel at its exit opening and provides support for the filter net, especially when a mechanical sealing element is arranged in connection with the suction device at the exit opening. The support surface may be appropriately formed to assist the blowing of the replacement air through the filter net at the desired blow angle. According to one embodiment of the invention the support surface may be curved surface. According to one embodiment the support surface may form an angle of <NUM> - <NUM>°, preferably <NUM> - <NUM>°, and enhance the blowing of replacement air by forcibly directing the blow(s) through the filter net transported through the filter net channel. The support surface may also function as a seal on the second side of the filter net at the exit opening of the filter net channel.

The stationary cleaning unit comprises at least one sealing element in connection with the suction device at the entry opening and/or at the exit opening of the filter net channel. A first sealing element may be arranged at the entry opening of the filter net channel, on the first side of the filter net, in connection with the suction device. The position of the first sealing element may be adjustable in relation to the replacement air device. This means that the width of the filter net channel at the entry opening can be optimised such that the entry of air to the suction area and the risk for dust/debris accumulation at the entry opening is minimised. The functioning of the cleaning unit is improved when the position of the first sealing element can be adjusted. The first sealing element may be a labyrinth sealing element, or it may contain parts, which are formed as labyrinth sealing element. Alternatively, the first sealing element may be a rotatable roll-like rounded border or rim that can be optionally supported against the filter net.

Preferably, the first sealing element may have a guide surface arranged to form a gap seal at the entry opening of the filter net channel, i.e. the first sealing element may form a mechanical seal that blocks the entry of air with the filter net surface to the suction area. The guide surface of the first sealing element may be tapering towards the entry opening. At the same time the gap seal allows dust and/or debris on the filter net surface to enter the suction area.

A second sealing element may be arranged at the exit opening of the filter net channel of the cleaning unit, in connection with the suction device, wherein the sealing element comprises a brush-like sealing member. The second sealing element, such as brush-like sealing member, may be arranged into a contact with the first side of the filter net for delimiting the suction area. The brush-like sealing member may comprise bristles that can be made of soft metal, such as brass. The second sealing element, especially when comprising brush-like sealing member, provides not only effective sealing of the suction area, but it also improves the cleaning effect when it is in slight contact with the filter net surface as the filter net is reeled past it. The second sealing element loosen dust and debris from the filter net surface that can then be removed by the suction device. The second sealing element is arranged to face the support surface of the replacement air device, which is on the second side of the filter net. The second sealing element and the support surface are thus opposite each other, forming the exit opening of the filter net channel.

According to one preferable embodiment the stationary cleaning unit comprises a support surface arranged next to the blowing means in the blow direction of the blowing means and a second sealing element at the exit opening of the filter net channel in connection with the suction device, arranged into a contact with the first side of the filter net. It has unexpectedly shown that the close arrangement of the replacement air blowing, appropriately formed support surface and the second sealing element at the exit opening of the filter net channel provides an improved cleaning efficiency and stabile function of the cleaning unit. According to one embodiment the blowing means of the replacement air device, support surface and second sealing element are arranged within <NUM> or less, preferably within <NUM> or less, from each other in height direction of the filter channel, i.e. travel direction of the filter net.

A further sealing element may be arranged at the entry opening of the filter net channel in the connection with the replacement air device, approximately against the first sealing element, but on the second side of the filter net.

The stationary cleaning unit may alternatively or in addition comprise a further blowing means arranged in connection with the suction device to blow towards the exit opening of the filter net channel and for providing sealing of the exit opening. The further blowing means may structurally be identical to the blowing means of the replacement air device. The further blowing means for sealing the exit opening may comprise at least one blow slot or a plurality of blow openings arranged in a row.

It is also possible to arrange additional blowing means in connection with the suction device at the entry opening of the filter net channel to blow towards the suction area.

The cleaning arrangement according to the present invention comprises in addition to the stationary cleaning units a first rotatable spool and a second rotatable spool, which are parallel with each other and arranged on a distance from each other. The distance between the spools may be freely determined, depending on the dimensions of the heating devices and fan towers. Typically, the cleaning arrangement is arranged to protect or cover a plurality of superposed heating devices. For example, one arrangement may be arranged to cover <NUM> - <NUM>, preferably <NUM> - <NUM>, heating devices. The distance between the first spool and the second spool may be, for example, <NUM> - <NUM>, preferably <NUM> - <NUM>.

The first and second rotatable spools comprise an axis and flanges at the ends of the axis. The spools are made of metal, preferably steel. Preferably the length of the spool axis corresponds to the width of the filter net used in the arrangement.

The stationary cleaning units are arranged in fixed positions in the vicinity of the first and the second spools. In this manner the surface of that part of the filter net, which is reeled or wound around the spool, becomes clean. The stationary cleaning units do not comprise moving parts that are easily damaged or require extensive maintenance. This increases the overall robustness of the cleaning units and the cleaning arrangement. The stationary cleaning units are relatively small in size and compact, which means that they can easily fitted even as retrofit in the restricted spaces between the adjacent fan towers in the existing pulp dryers. Furthermore, the compactness of the cleaning units, which is due to close arrangement of the suction device and the replacement air device, among others, minimises the disturbances in air flows around the stationary cleaning unit.

The filter net has a length, which is at least two times the distance between the first and second rotatable spools. According to one embodiment of the invention the length of the filter net is at least two times the distance between the first and second rotatable spools, but less than <NUM> times the distance. This means that a part of the filter net covers the heating device(s) in a conventional manner, while another part of the net is wound or coiled around the first and/or second spool. During the normal operation at least half of the filter net is coiled or wound around first and/or second spool, while the rest of the filter net is tensioned between the spools and forms a flat even filter net surface. The length of the filter net reeled around the spool is at least the same as the length of the filter net tensioned between the spools, or longer. The filter net has a first end, which is permanently attached to the first spool and a second end, which is permanently attached to the second spool. The end of the filter net may be attached to the axis of the spool, for example by using elongated attachment strip.

The filter net may be any net that is suitable for the purpose and withstands the hot and humid environment of the pulp dryer. According to one preferable embodiment the filter net is made of stainless steel. The filter net may be a woven filter net with e.g. <NUM>. <NUM> apertures. The filter net has a first side facing the space between the fan towers and a second side facing the heating device.

According to the invention the filter net in a pulp dryer can be effectively and easily cleaned by using a cleaning arrangement comprising where the filter net is reeled from spool to spool and simultaneously, during reeling, the surface of the filter net is cleaned with a stationary cleaning unit comprising at least a suction device. The filter net is reeled back-and-forth between the spools, while the cleaning units are immovable, arranged in fixed positions. In operation, the first part of the filter net is filtering the dust and debris, while the clean second part of the filter net is coiled around one of the spools. When the first part of the filter net is to be cleaned, the first part of the filter net is reeled around the other spool and simultaneously cleaned by the cleaning unit before it is reeled around the spool. At the same time the clean second part of the filter net is unreeled from the other spool to cover the heating devices and to filter dust and debris. When the second part of the filter net becomes fouled, the cleaning operation is repeated by reeling the second part around the spool and unreeling the clean first part. The cleaning arrangement thus provides a mechanically simple and reliable construction, which however is able to achieve remarkably good cleaning results. Furthermore, the cleaning arrangement is easy to scale to different sizes, which makes it suitable for use in various pulp dryers around the world. The cleaning arrangement is also easy to use, and it improves working conditions of the operators and increases their motivation to perform the cleaning actions.

According to one preferable embodiment the filter net is tensioned with tension rolls arranged in the vicinity of the first and second spools, as well as the suction device and/or replacement air device. The tension rolls may be arranged dealigned from the general filter net plane, on the same side of the net as the suction device, i.e. the first side. The tension rolls and/or support surfaces tension the filter net around from the suction device and prevent its fluttering. Furthermore, the support surface may provide support for the sealing elements, which may press the filter net towards the support surface.

Typically, a fan tower of a pulp dryer comprises at least one fan, preferably several superposed fans, typically <NUM> - <NUM>, more typically <NUM> - <NUM> superposed fans. The fans are arranged to remove moist air from a drying section of the pulp dryer and to blow heated air into the drying section of the pulp dryer. The drying section of the pulp dryer comprises a plurality of horizontal drying decks, where pulp web is dried by hot air blows generated by drying devices. The fans supply heated air to the drying devices, and therefore at least one heating device, such as a heat exchanger, a steam radiator or the like, is arranged on the suction side of said fan for heating the air entering the fan. The heating device has a first side which faces the fan and a second opposite side facing away from the fan. The cleaning arrangement according to the invention is arranged on the second side of the heating device, i.e. on the side that faces away from the fan. The cleaning arrangement is arranged to protect the heating device and to filter the air to be heated before it is led to the heating device.

The cleaning arrangement further comprises power transfer means arranged in connection with the first and second spool for operating them rotatably. By rotating the first and second spool it is possible to reel the filter net around the first or second spool and simultaneously free the net from the other spool, as desired. According to one preferable embodiment the power transfer means may comprise a number of sprockets and a chain, which are arranged to rotate the first and second spool. A sprocket or cog may be arranged in the end of the spool, where it may form or replace the flange at one end of the spool axis. The chain is arranged to pass around the sprockets and to rotate the spools. The power transmission means may be operable with machine power, e.g. cordless driver, or with human power. Preferably the power transmission means are manually operable, for example by a crank or rotatable wheel. The power transmission means may also be operable with a pedal, if desired. When the power transmission means are operable with human power or with e.g. cordless driver, the cleaning arrangement contains less electrical parts and it is easy to service and maintain, even in demanding conditions. Furthermore, the construction and use of such cleaning arrangement is inexpensive and simple. The devices needed for operation, such as crank or rotatable wheel, are preferably arranged accessible from a service platform, so that the operator does not need to enter the cramped space between two adjacent fan towers.

The cleaning arrangement may comprise a mechanical limiter, which is arranged in connection with the first and second spool to prevent excess reeling. The mechanical limiter stops the rotation of the spool when the filter net has been completely reeled away from the spool. The mechanical limiter may be arranged or attached to the spool or the mechanical limiter may be arranged or attached to the suitable location on the chain of the power transmission means in order to restrainingly interact with the spool and to prevent its rotation.

The cleaning arrangement may comprise side supports, which comprise side sealing elements in contact with the first side of the filter net. The side supports, as well as the side sealing elements extend preferably from the first spool to the second spool. The side supports may be made of metal. e.g. steel, stainless steel or aluminium profile. The arrangement is preferably attached to the fan tower structures by the side supports. The side sealing elements may be similar to the sealing elements of the cleaning unit. For example, the side sealing elements they may be brush-like sealing members made of soft metal. The side sealing elements are in contact with the first side of the filter net and they are arranged to push the filter net tightly towards the net-like support structure arranged on the second side of the filter net. The side sealing elements are preferably arranged deflecting towards the central line of the filter net in its length direction.

According to one embodiment of the invention the cleaning arrangement comprises a support net structure, arranged on the second side of the filter net. The support net has coarser mesh size than the filter net itself, and it is intended to support the filter net and ensure that the filter net remains flat and tensioned between the spools. The support net structure is attached to the side supports.

The cleaning arrangement may further comprise a cleaning indicator system, which comprises at least one pressure sensor arranged on the second side of the filter net. When the underpressure on the second side of the filter net exceeds a pre-determined limit value, the cleaning indicator system is arranged to provide an alarm, which indicates the cleaning need of the filter net. The alarm may be a visual alarm, e.g. flashing light arranged on the location of the filter net needing cleaning. Alternatively, or in addition, the cleaning indicator system may be in functional contact with one of the control systems of the pulp dryer, and the alarm is provided in an operating room of the pulp dryer. In this way the cleaning arrangement may provide real-time information of the cleaning need of the filter nets, which reduces unnecessary or wrongly situated cleaning.

The following schematical non-limiting drawings further demonstrates certain aspects of the present invention. The invention may be better understood by reference to the drawings in combination with the detailed description of the embodiments presented herein.

<FIG> shows a fan tower <NUM> according to one embodiment of the invention. Fan tower <NUM> comprises a plurality of fans <NUM> as well as a heating device <NUM> arranged on the suction side of the fans <NUM>. An arrangement <NUM> according to the present invention is arranged on the side of the heating device <NUM> which faces away from the fan <NUM>. The arrangement <NUM> comprises a first rotatable spool <NUM> and a second rotatable spool <NUM>', which are parallel with each other. Immovable stationary cleaning units <NUM> are arranged in the close vicinity of the first and the second spools <NUM>, <NUM>'. Side supports <NUM> (only one is shown in <FIG>) connect the first and second spools <NUM>, <NUM>'. The filter net (not shown) is partly tensioned between the spools <NUM>, <NUM>' and partly wound around one of the spools.

<FIG> shows an embodiment of the power transmission means of an arrangement <NUM> according to the present invention. The power transmission means comprises a main sprocket <NUM> attached to the end of the spool <NUM> as well as a chain <NUM> that are arranged to rotate the spool <NUM>. The power transmission means may further comprise a plurality of additional sprockets <NUM>, which help to tension the chain <NUM> running around them. The chain <NUM> runs around a crank sprocket <NUM>, which can be rotated by rotating a crank <NUM>. The movement of the crank <NUM> is transferred to the main sprocket <NUM> at the end of the spool <NUM> by using a simple mechanical power transmission means comprising the chain <NUM> and a necessary number of additional sprockets <NUM>.

<FIG> shows an embodiment of a stationary cleaning unit <NUM> according to the present invention. A filter net <NUM> is attached to a spool <NUM>. The filter net <NUM> is tensioned with a tension roll <NUM> arranged in the vicinity of the spool <NUM>. The location, such as distance from the spool <NUM>, of the tension roll is adjustable for proper tensioning of the filter net <NUM>, as indicated by black double-headed arrow. A stationary cleaning unit <NUM> is arranged in the close vicinity of the spool <NUM>. The cleaning unit <NUM> comprises a suction device <NUM>, which comprises a hollow body <NUM>, a suction opening <NUM>, and a suction channel <NUM>. The cleaning unit <NUM> comprises also a replacement air device <NUM>, which comprises a blowing means <NUM>. A filter net channel is formed between the suction device <NUM> and the replacement air device <NUM> and the filter net <NUM> is arranged to be transported through the filter net channel while the suction device <NUM> is removing debris and dust from a suction area A on a first side of the filter net <NUM>. The suction area A extends from the entry opening A' of the filter net channel to the exit opening A" of the filter net channel. In <FIG> the suction area A is delimited by a first sealing element <NUM> which is arranged at the entry opening A' of the filter net channel. The distance of the first sealing element <NUM> from the filter net <NUM> is adjustable as indicated by the double-headed arrow. The suction area A is further delimited by a second sealing element <NUM>' arranged at the exit opening A" of the filter net channel. The second sealing element <NUM>' comprises brush-like sealing member <NUM>, which is arranged in a slight contact with the first side of the filter net <NUM>. The distance and height location of the second sealing element <NUM>' is adjustable as indicted by the double-headed arrows.

The blowing means <NUM> are arranged to blow through the filter net <NUM> towards the exit opening A" of the filter net channel. The blow angle of the blowing means <NUM> is adjustable, as indicated by the black double-headed arrow. The blowing means <NUM> can be rotated around its longitudinal axis in order to provide the desired blow angle towards the exit opening A". A support surface <NUM> is arranged next to the blowing means <NUM> in the blow direction of the blowing means. The support surface <NUM> provides support for the filter net <NUM>, effectively directs the blown replacement air through the filter net and improves the cleaning of the surface of the filter net <NUM>. A further sealing element <NUM> is seen at the entry opening A' of the filter net channel, attached to the replacement air device <NUM>.

It is seen from <FIG> that the cleaning unit <NUM> is relatively small and compact, which means that it does not disturb the air flows, indicated with white arrows, which are flowing around it in the spaces between the adjacent fan towers. Furthermore, the smooth and uniform design of the suction channel <NUM> and the connection of the suction channel <NUM> to the lower part of the hollow body <NUM> ensure the effective and turbulence-free air flow within the suction channel <NUM>, as indicated with the white arrows.

In <FIG> a dashed line shows an alternative form of the suction channel <NUM>.

<FIG> shows an another embodiment of a stationary cleaning unit according to the present invention. The reference numbering corresponds to the reference numbering of <FIG>, i.e. the same parts have the same reference number. It is seen from <FIG> that the first sealing element <NUM> is formed as a labyrinth seal. The support surface <NUM>, arranged next to the blowing means <NUM>, is curved.

The stationary cleaning unit <NUM> in <FIG> comprise a further blowing means <NUM> arranged in connection with the suction device <NUM> at the exit opening A" of the filter net channel.

<FIG> shows another embodiment of the arrangement <NUM> of the present invention. The arrangement <NUM> comprises a first rotatable spool <NUM> and a second rotatable spool <NUM>', which are parallel with each other. Immovable cleaning units <NUM> are arranged in the close vicinity of the first and the second spools <NUM>, <NUM>'. Side supports <NUM> connect the first and second spools <NUM>, <NUM>' and the filter net <NUM> is tensioned between the spools <NUM>, <NUM>'. The steam inlet and condensate connections <NUM> of the heating device are also visible in <FIG>.

Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.

Claim 1:
A stationary cleaning unit (<NUM>) for a cleaning arrangement (<NUM>) in a fan tower (<NUM>) of a pulp dryer, the cleaning unit (<NUM>) comprising
- a suction device (<NUM>) having a suction opening (<NUM>) for removal of air and dust from a suction area (A),
- a replacement air device (<NUM>), which comprises blowing means (<NUM>) arranged to provide replacement air to the suction area (A),
wherein the suction device (<NUM>) and the replacement air device (<NUM>) are arranged on a distance from each other to form filter net channel with an entry opening (A') and an exit opening (A"),
characterised in that
at least one sealing element (<NUM>, <NUM>') is arranged in connection with the suction device (<NUM>) at the entry opening (A') or at the exit opening (A") of the filter net channel, and that the blowing means (<NUM>) are arranged to blow replacement air towards the exit opening (A") of the filter net channel.