Patent Application
20100175679
The invention relates to a hot-air furnace module having a furnace chamber which is at least partially delimited by walls and with which there is associated an air-delivery device for producing an airstream and also a heat-transfer device for heating the airstream, and the invention also relates to a hot-air furnace which is formed from hot-air furnace modules.
A hot-air furnace, which is known from the market, for industrial applications, for example for the thermal oxidation of plastic fibres, has an air-delivery device which is designed as a blower and is intended to produce an airstream. The airstream is guided past a heat-transfer device, for example electrically operated heating bars or a heat-exchanger heated indirectly with thermal oil, and is heated. The heated airstream is then directed into a furnace chamber which is delimited by walls and in which the material which is to be thermally treated is located. The walls of the furnace chamber bring about a limitation of the cross-section through which the heated airstream is able to flow and thus ensure a concentrated introduction of heat into the material to be treated. The known hot-air furnace can be assembled, by the modular method of construction, from a plurality of hot-air furnace modules which may be prefabricated as subassemblies and which are connected to one another at the site at which the hot-air furnace is to be used. In certain cases, such as, in particular, in the manufacture of carbon fibres by oxidising plastic fibres, a uniform action on the material to be treated is of decisive importance, and this, in turn, presupposes precise, defined airflows. Basically, the fact is: the better the airflow distribution, the better the result.
The object of the invention consists in providing a hot-air furnace module, and also a hot-air furnace, which permit more effective and more precise thermal treatment of materials in the furnace chamber.
This object is achieved by means of a hot-air furnace module having the features in claim 1 and also by means of a hot-air furnace having the features in claim 19.
According to a first aspect of the invention, an incoming-air duct is provided which is constructed between the air-delivery device and the furnace chamber for directing the airstream delivered by the air-delivery device in one direction of flow, and which is provided with first and second throttling means which are arranged at a distance from one another in the direction of flow and are intended to even out the airstream before it flows through the furnace chamber (20). By means of the infeed duct between the air-delivery device and the furnace chamber, it is possible to obtain stabilisation of the airstream. A turbulent airstream flow which is present in the region of the air-delivery device becomes less turbulent with increasing remoteness from said device and with suitable configuration of the incoming-air duct. In order to achieve additional stabilisation of the airstream, at least two throttling means are provided, which lie one behind another at a distance in that cross-section of the incoming-air duct through which flow can take place, and are thus able, if configured in a suitable manner, to cause a significantly less turbulent flow to be present behind the particular throttling device than in front of it, in the direction of flow.
As a result of the series connection, according to the invention, of two throttling means, it is possible to achieve considerable stabilisation of the airflow. By means of an airflow with low turbulences, it is possible to achieve a particularly uniform transfer of heat to the material which is to be treated thermally in the furnace chamber. Greater temperature gradients, which could lead to unwanted, non-uniform thermal treatment of the material in the furnace chamber, are avoided.
Because of the low turbulences in the airflow within the furnace chamber, the excitation of vibrations in the material located in the furnace chamber is avoided, so that it is possible to thermally treat even delicate, in particular brittle, materials having a small cross-section, without the risk of breakage.
In a refinement of the invention, the second throttling means, which is associated with the incoming-air duct, is constructed as a wall of the furnace chamber. By this means, the second throttling means also acquires a delimiting function in addition to the stabilising function for the airstream. Said throttling means preferably spans the entire cross-section of the furnace chamber and thus completely replaces one of the walls, which are typically of flat design, of said furnace chamber. By configuring the throttling means with a surface area which corresponds to the cross-section of the furnace chamber, it is additionally possible to obtain a particularly homogeneous distribution of the airstream within said furnace chamber. This contributes considerably to the sought-after low-turbulence or turbulence-free airstream within the furnace chamber.
In one preferred form of embodiment, at least one throttling means is constructed as a wall which has clearances passing through it, in particular as a perforated metal sheet. Bores and/or slots may preferably be provided as the clearances. The clearances are arranged on the surface area with equal or unequal spacing and have uniform or varying geometries. A throttling means of this kind may be constructed, in particular, in the form of wire-mesh fabric consisting of a large number of wires arranged in a grid-like manner, or in the form of perforated metal sheet having a large number of bores.
It is expedient if the clearances in the throttling means, which throttling means are arranged at a distance from one another, are constructed in such a way that said throttling means have flow-resistances for the airstream which differ, at least in some cases. By this means it is possible to cause the airflow to initially be stabilised only partially at the first throttling means, without this resulting in the building-up of an excessively high flow-resistance which would have a negative effect on the air-volume stream which is delivered, as a whole, into the furnace chamber. In the second throttling means, which is connected downstream in a serial manner, the airstream, which has already been stabilised to a great extent by the first throttling means and the infeed duct, is additionally stabilised and then passes into the furnace chamber as a low-turbulence or turbulence-free or laminar airflow.
The first throttling means preferably has a lower flow-resistance than the second throttling means which is connected downstream in the direction of flow. The air-volume stream, which may optionally be highly turbulent, is first of all stabilised to a considerable extent by the first throttling means which has the lower flow-resistance. By means of the second throttling means, further stabilisation takes place before the air-volume stream passes into the furnace chamber. Under these circumstances, it is necessary, for a low-turbulence or turbulence-free air-volume stream, to accept a higher flow-resistance of the second throttling means in order to achieve the most complete stabilisation possible of said air-volume stream.
In one preferred form of embodiment, the first throttling means is constructed with a clear cross-section of between 20 and 30 percent of the surface area. Here, the “clear cross-section” denotes the relationship between surface areas of the clearances at the throttling means through which airstream is able to pass, and closed surface areas of the throttling means which constitute an obstacle to the airstream. In the case of a clear cross-section of at least 20 percent, therefore, referred to a total surface area of the throttling means, which may be designed, for example, as a rectangular sheet-metal panel, 20 percent of the surface area is perforated by clearances. Under these circumstances, said clearances may be evenly distributed with a fixed spacing and a fixed geometry. However, clearances in the edge regions of the throttling means may also have a different geometry and/or spacing from the clearances in the centre of the surface area of said throttling means.
In one preferred form of embodiment, the second throttling means is constructed with a clear cross-section of between 5 percent and 10 percent of the surface area. It is thereby possible to obtain intensive stabilisation of turbulences immediately before the airstream passes into the furnace chamber, so that a low-turbulence, and preferably a turbulence-free, laminar flow can develop within said furnace chamber.
In a further refinement of the invention, at least one of the throttling means is provided with air-directing means which are constructed as walls which are oriented orthogonally to a surface of said throttling means through which flow can take place. The dividing-up of the airstream into individual flows is thereby maintained, at least over a certain flow path, behind the clearances provided in the throttling means, referred to the direction of flow. Because of the walls on the throttling means, the individual flows do not mingle immediately behind the throttling means. On the contrary, the individual flows remain separate from one another, as a result of which it is possible to obtain advantageous stabilisation of the airflow. The walls of the air-directing means may have a height which is greater, by a multiple, than a thickness of the throttling means. The walls are preferably arranged in such a way that each airflow which passes out of the clearances in the throttling means is separated from an airflow from an adjacent clearance. The walls may, in particular, be manufactured from thin-walled sheet metal and may be welded to the throttling means.
In one preferred form of embodiment of the invention, a number of throttling means, which are provided, in particular, with air-directing means, are arranged immediately one behind another in the direction of flow, and form a throttling unit. By arranging a number of throttling means immediately one behind another, it is possible to provide a compact throttling unit which is able to bring about an advantageous stabilisation of the airflow. Under these circumstances, provision is preferably made for at least one of the throttling means which are arranged immediately one behind another to be provided with air-directing means.
In a further refinement of the invention, there may be provided a used-air duct which is connected downstream of the furnace chamber in the direction of flow and which is intended for at least partially feeding back to the air-delivery device the airstream which has been directed through the furnace chamber. It is thereby possible to obtain efficient utilisation of the kinetic energy and internal energy introduced into the airstream by the air-delivery device and heat-transfer device respectively. Under these circumstances, the airstream, which has already been heated and is in motion, flows through the furnace chamber and is fed to the air-delivery device again in a circular motion. It is thereby necessary, for a constant temperature in the furnace chamber, to replace the heat which has been radiated away through the walls of the furnace chamber and of the incoming-air and used-air ducts. In addition, it is necessary to heat up fresh air which has been fed in through the sluices, and to heat the plastic fibres to be oxidised, under which circumstances the water contained in the plastic fibres has to be evaporated at the beginning of the oxidation operation.
It is expedient if at least one throttling means for the airstream is provided in the used-air duct. A defined flow-resistance for the airstream after it has flowed through the furnace chamber is thereby ensured. This prevents the airstream dividing up, even in the furnace chamber, into two or more streams, which each flow away in the direction of least resistance, something which would give rise to unwanted disturbance of the airstream.
In one preferred form of embodiment, a first throttling means which is associated with the used-air duct is constructed as a wall of the furnace chamber. This ensures a constant flow-resistance over the entire cross-section of the furnace chamber, so that local flowing-away of the airstream fed into said furnace chamber can be at least substantially avoided.
It is expedient if the throttling means which are designed as walls of the furnace chamber are arranged in an opposed manner. This promotes a low-turbulence or laminar flow in the furnace chamber, since the airstream passing into said furnace chamber does not have to be rerouted until it passes out of the latter. That is to say, the vector of motion for an air particle which passes into the furnace chamber is substantially parallel to the vector of motion of said air particle on passing out of said furnace chamber.
In a further refinement of the invention, at least one separating device for decoupling airstreams in the furnace chamber is provided between the walls which are designed as throttling means. The separating device extends in the direction normal to the faces of the throttling means, which throttling means are arranged in an opposed manner, and is perforated only by narrow slots for passing through filament-directing bars and thus permits extensive separating-up of the furnace chamber into two regions which lie parallel and which are substantially independent in terms of fluidics. This is particularly advantageous if the material which is to be thermally treated is moved within the furnace chamber, for example for a continuous treatment process. By means of the separating device, it is possible, for example, for material to be conveyed through the furnace chamber in different directions without the airflows affecting one another.
In one preferred form of embodiment, the throttling means are arranged in the incoming-air duct and/or the used-air duct at an angle to one another, in particular an angle of 90 degrees. As a result of such rerouting of the airstream, it is possible to achieve a compact configuration of the hot-air furnace module, without having to accept considerable disturbance of the airstream. This also applies to the arrangement of the air-delivery device, the incoming-air duct and the walls designed as throttling means, which are oriented, in advantageous manner, in such a way that an airstream which is emitted by the air-delivery device is able to flow in a parallel direction but in counter-current to an airstream within the furnace chamber.
In one preferred form of embodiment, provision is made for the air-delivery device and the throttling means to be constructed in such a way that there can be developed, within the furnace chamber, a laminar airflow with a substantially uniform velocity distribution, in particular with a maximum velocity variation over the cross-section of the furnace chamber of +/−10 percent at a velocity of 1.5 m/s. It is thereby possible, for example, to carry out within the furnace chamber an oxidation process in which thin plastic fibres are oxidised by thermal oxidation to form carbon fibres, under which circumstances considerable embrittlement of the plastic fibres occurs. If a turbulent flow were present, the plastic fibres, which are typically conveyed through the furnace chamber at constant velocity, might be induced to vibrate and might break. With a laminar flow of the airstream within the furnace chamber, the risk of breakage of the plastic fibres is considerably reduced. In order to ensure particularly uniform thermal treatment of the material, the variation in the velocity of the airstream in all regions of the furnace chamber is limited to +/−10 percent. This ensures that the airstream flowing past the material does not cause any unevenly distributed introduction of energy into the material, such as might be the case in the event of different velocities within the airstream.
In a further refinement of the invention, there is provided, at least one wall region of the furnace chamber, a sluice device which is constructed for continuously feeding-in and/or conducting-away an endless material which is to be thermally treated in the furnace chamber. Said sluice device is configured in such a way that a material in the form of a strand or filament can be fed into or out of the furnace chamber. Under these circumstances, provision is made for it to be possible for fresh air to flow into the furnace chamber afterwards through the sluice devices. For this purpose, part of the quantity of air present in the furnace chamber is conducted away out of said furnace chamber by a used-air installation and is replaced by the fresh air that flows after it. The furnace chamber is thereby operated at a lower pressure, compared with the environment of the hot-air furnace, as a result of which it is possible to avoid uncontrolled flowing-away of air out of the hot-air furnace. This is of particular interest, since the used air may be laden with pollutants because of the oxidation processes taking place within the furnace chamber. The used-air installation is therefore equipped with one or more cleaning stages, in particular with a thermal used-gas aftertreatment installation, for the purpose of removing pollutants from the used air.
In one preferred form of embodiment, provision is made for the fresh air flowing in to be pre-heated in the region of the sluices, in particular in a heat-exchanging process with the used air sucked out. This permits particularly efficient operation of the hot-air furnace module.
According to another aspect of the invention, a hot-air furnace having hot-air furnace modules according to one of claims 1 to 18 is provided, in which hot-air furnace modules which are arranged in an adjacent manner in each case are oriented in a manner rotated by 180 degrees in relation to one another and are connected to one another in a communicating manner. The modular method of assembling the hot-air furnace makes it possible to obtain cost-effective series production of the individual parts from which the individual hot-air furnace modules are assembled. This arrangement of the hot-air furnace modules makes it possible to bring about an advantageous airstream, since the air-delivery devices which are arranged in an opposed manner prevent one-sided extraction of the airstream from the furnace chamber by suction.
In one form of embodiment of the hot-air furnace according to the invention, provision is made for said furnace to be assembled from six hot-air furnace modules and to have a length of the sides of 15 m×8.6 m×4.6 m. The hot-air furnace modules have a length of the sides of 2.5 m×8.6 m×4.6 m and can thus be transported without using a special heavy transporter.
In one preferred form of embodiment, the hot-air furnace modules delimit a common, uninterrupted furnace chamber. It is thereby possible, by arranging a number of hot-air furnace modules in a row, to erect a hot-air furnace with a furnace chamber of almost any desired length. In the abovementioned form of embodiment of the invention, provision is made for a length of 15 m for the furnace chamber and the height of the latter is 2 m, while the width is 4.7 m. Provided on the longitudinal sides of the furnace chamber at the ends in each case are sluice devices which permit continuous charging and discharging of material. Under these circumstances, the full length of 15 m is available to the material for the thermal treatment process.
It is expedient if the used-air ducts form a distributor chamber which is arranged downstream of the furnace chamber in the direction of flow and which is intended to provide a preferably equal distribution of airstreams from the furnace chamber to the air-delivery devices of the at least two adjacently arranged hot-air furnace modules. The common distributor chamber makes it possible to realise the splitting-up of the airstream flowing through the furnace chamber into at least two branches of the stream. These branches of the airstream are guided past the heat-transfer devices of the adjacently arranged hot-air furnace modules and are delivered into the respective incoming-air ducts and the common furnace chamber again by the respective air-delivery devices. As a result of this, it is possible to ensure that a uniform temperature prevails in the furnace chamber as a whole, even if the heat-transfer devices or the air-delivery devices have differing degrees of efficiency.
Other advantages and features of the invention emerge from the patent claims and also from the following description of preferred exemplified embodiments which are represented with the aid of the drawings. In said drawings:
A hot-air furnace 10 which is represented in
The furnace chamber 20, which is delimited by walls 16, 18, is of cubic configuration. Under these circumstances, vertically oriented walls 16 are of closed design, while horizontally oriented walls 18 are designed as perforated metal sheets having a large number of clearances 28 which are arranged in a regular manner and are provided with the same geometry. Because of the clearances 28, the horizontally oriented walls 18 allow an airstream to pass through. Under these circumstances, a flow-resistance to the airstream which is passing through is determined by the clear cross-section, that is to say by the ratio of the surface area of the clearances 28 to the total surface area of the wall 18 as a whole. In the case of the horizontally oriented walls 18, a clear cross-section of 10 percent is advantageously chosen, so that the clearances 28 take up only 1/10 of the total surface area of the wall 18.
Provided on the hot-air furnace modules 12 at the end face in each case is an air-delivery device which is designed as a blower 14 and which permits delivery of the air contained in the hot-air furnace module 12.
As is represented in greater detail in
The airstream then penetrates the cover, which is designed as a second throttling device 32, of the furnace chamber 20, which cover is designed as the second throttling means. Since the second throttling device 32 has a clear cross-section of about 10 percent, a uniform distribution of the molecules of air contained in the airstream comes about because of the damming-up of said airstream between the first and second throttling devices 30, 32, so that the same quantity of air is able to pass through the clearances 28 at all points on the second throttling device 32. The airstream has now penetrated into the furnace chamber 20 and flows in the vertical direction, in a laminar manner, from the second throttling device 32 towards a third throttling device 34 which is designed as the third throttling means. The furnace chamber 20 is subdivided, by a separating device 38 which is extended between the second and third throttling devices 32, 34, into a first furnace-chamber region 50 and a second furnace-chamber region 52. The separating device 38, which is interrupted by narrow slots for passing through filament-directing bars, prevents an unwanted interaction of the airflows between the first and second furnace-chamber regions 50, 52. This is of interest for the purpose of avoiding unwanted turbulences in the laminar airstream which result from the furnace-chamber regions 50, 52 affecting one another.
The throttling devices 30 to 34 described above, and also a fourth throttling device 36, may, in one preferred form of embodiment of the invention, be designed as throttling units 62, which are represented in the detail enlargement in
Indicated in outline in
On an underside, the furnace chamber 20 is delimited, as shown in
On the way to the blower 14, the airstream passes through a heat-transfer device 42, which is designed as a heat-exchanger which is heated indirectly with thermal oil and which heats the airstream to the target temperature which is desired for the furnace chamber 20. In the case of the present hot-air furnace module 10, it is possible, for example, to preset a target temperature in the furnace chamber 20 of 200 degrees to, in particular, 280 degrees Celsius.
As can be inferred from the equivalent circuit diagram shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 037 703.6 | Aug 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/006700 | 7/28/2007 | WO | 00 | 5/7/2009 |
