Patent Application
20140127116
The invention relates to reactors for chemical processes such as fluidized bed reactors. More particularly, the invention relates to a gas distribution arrangement, a device for handling a chemical reaction comprising such a gas distribution arrangement and a method of providing a chemical reaction chamber with a gas.
In some chemical reactions it is of interest to let a gas enter a chemical reaction chamber via a distribution plate, where the function of the distribution plate is to ensure a uniform supply of the gas to the chemical reaction chamber.
One type of chemical reaction chamber where the use of such a distribution plate is needed is the Fluidized Bed Reactor. Fluidized Bed Reactors are for instance described by W. O. Fildvedt et al in “Development of fluidized bed reactors for silicon production”, Solar Energy Materials and Solar Cells, Volume 94, Issue 12, December 2010.
Here a gas is transported to the chamber from a gas inlet area, often denoted Windbox, via a distribution plate.
One known distribution plate is described in U.S. Pat. No. 3,889,631.
In certain chemical reactions encouraged in Fluidized Bed Reactors (FBR), the chamber is held at a high temperature while the gas inlet area has a lower temperature. As the gas enters the high-temperature chamber of the FBR, the gas will decompose and be deposited. This type of chemical process is attractive to use when for instance producing polysilicon from silanes in gas form.
However, it is important in this case that this decomposition does not take place until the gas reaches the chamber, because the gas may start to decompose within the distribution plate and clog it, which will negatively influence the chemical process. This may be solved through cooling the distribution plate. However, if this is done heat may be lost from the chamber through the distribution plate.
There is therefore a need for improvement in relation to distribution plates.
The invention is therefore directed towards solving at least some of the above mentioned problems associated with distribution plates.
One object of the invention is thus to solve one or more of the above mentioned problems.
This object is according to a first aspect of the invention achieved through a gas distribution arrangement comprising distribution plate for separating a chemical reaction chamber from a gas inlet area and having a first side arranged to face the chemical reaction chamber and a second side arranged to face the gas inlet area, the distribution plate comprising a set of throughholes stretching between the first and the second side, wherein:
the first side of the plate comprises a first material surrounding the holes and having a first thermal conductivity, and the plate also comprises a second material forming a base structure also surrounding the holes and having a second thermal conductivity.
In a preferred embodiment of the present invention the gas distribution arrangement is for the production of silicon and more preferably for the production of polysilicon from silanes and/or chlorosilanes in gas form.
Preferably, the gas distribution arrangement is for a fluidizing bed reactor in a chemical reaction chamber.
It should be appreciated that embodiments and aspects of the invention are suitable or adaptable for other types of chemical reaction chambers and/or fluidizing bed reactors.
This object is according to a second aspect of the invention achieved through a device for handling a chemical reaction comprising:
a chemical reaction chamber,
a gas inlet area, and
a distribution plate for separating the chemical reaction chamber from the gas inlet area, where the distribution plate is a distribution plate as defined in the first aspect of the invention.
This object is according to a third aspect of the invention achieved through a method of providing a chemical reaction chamber with a gas comprising the steps of:
providing the gas G at a first temperature T1 in a gas inlet area,
heating the reaction chamber to a second temperature T2,
preventing heat of the reaction chamber from reaching the gas inlet area using a first side of a distribution plate, which first side is made of a first material having a first thermal conductivity, and
transporting the gas from the gas inlet area through holes in the distribution plate to the reaction chamber, while cooling the holes using a base structure of the distribution plate, which base structure is of a second material having a second thermal conductivity and also surrounds the holes.
The invention according to these aspects has a number of advantages. The invention avoids clogging of the distribution plate. It also improves the ability of the chemical reaction chamber to retain a desired temperature, which reduces the energy consumption of the chemical reaction chamber. Another advantage of the invention is that the net heat transport through the distribution plate is reduced. A further advantage is that a high temperature gradient is sustained over the distribution plate thereby enabling more advantageous process parameters.
The dependent claims are concerned with advantageous variations of the invention.
It should be appreciated that one or more of the invention embodiments and aspects may also comprise one, or a combination of, the elements described herein with reference to the drawings.
It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
The invention will now be described in more detail in relation to the enclosed drawings, in which:
In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices and methods are omitted so as not to obscure the description of the invention with unnecessary detail.
The invention is generally directed towards improvements of distribution plates used in chemical reaction chambers such as in Fluidized Bed Reactors.
A device for handling a chemical reaction is schematically shown in
In the device 10 there is a reactor chamber 14, which is separated from a gas inlet area 12 through a distribution plate 16. A heater 13 is attached to the chamber 14 in order to provide heat to it. The distribution plate 16 is here a part of the wall of the chamber and in this example furthermore the bottom of the chamber 14. It should however be realised that it may as an example also be a part of the side wall of the chamber. The plate has furthermore a first side 20, which faces the chamber 14 and a second side 18 that faces the gas inlet area 12. In this first embodiment there is also one distribution plate. It should be realized that it is possible to use more than one such plate. The plate is here furthermore shown as being planar. It should be realized that it is not limited to being planar but may have any suitable shape. It may for instance be curved or bent. The shape of the distribution plate may furthermore be adapted to the intended shape of the reactor chamber 14.
The plate is perforated, which means that a gas G can come from the gas inlet area 12 and enter the chamber 14 via the distribution plate 16, where the distribution plate 16 here has the function to distribute the gas evenly in the chamber 14. The plate 16 is furthermore thermally connected to a heat diverting element, here in the form of a heat sink 17. In one variation of the invention the heat sink and distribution plate together make up a gas distribution arrangement of the invention. In other variations only the distribution plate makes up such a gas distribution arrangement. The heat sink may here be further cooled by a cooling media, typically a cooling fluid, which may be circulated in a loop. A cooling fluid may be a liquid like water or a gas such as air.
In some embodiments of the invention the distance between the holes is about seventeen times higher than the diameter. The hole density may also be higher than 500 holes/m2, with advantage higher than 1000 holes/m2, advantageously higher than 3000 holes/m2 and in some embodiments about 3500 holes/m2. In the figure a line B-B through the centre of the plate is also shown
As can be seen the first side 20 is comprised or is made of a first material 24, which material surrounds the holes and has a first thermal conductivity. The first material may surround the holes in a direction that is perpendicular to the length direction of the holes. Here also the holes 22 are shown. The first material 24 is a substantially non-compressible fibrous material which is machinable, such as packed ceramic fibre insulation. These holes 22 have walls that are at least partly made up of a third material, which material has a third thermal conductivity. In the figure also the second side 18 of the plate 16 is shown. The second side comprises or is made of a second material 28 surrounding the holes and having a second thermal conductivity. Also the second material may surround the holes in a direction that is perpendicular to the length direction of the holes. In this first embodiment of the invention the distribution plate 16 is formed through a base plate or base section on which insulation is placed, where the insulation is made of the first material 24 and the base plate or base structure of the second material 28. Furthermore in this first embodiment the second and third materials are the same material and therefore the second and third thermal conductivities are the same. The walls of the holes are therefore, in this first embodiment wholly provided through the base plate. This means that the walls of the holes are obtained through protrusions that stretch out from the base plate through the insulation towards the first side 20. The second and third materials here have a higher thermal conductivity than the first material and for instance more than 100 times higher. The material of the walls and base plate are in this example a metal, which in the first embodiment is aluminium. It should however be realized that other materials may be used, such as for instance steel, copper or even graphite. It is an advantage if the material chosen has properties which make it resistant to any reaction with the gas coming into contact with the material. For example, when chlorosilanes are used, corrosion-resisting alloys such as Inconel® may be preferred to aluminum.
Each hole thus has at least one wall. In case the holes have a circular or elliptical cross-section each hole will only have one wall. However, if the walls have square or rectangular cross-section, then they will have four walls and if they have triangular cross-section they will have three walls.
The parts of the holes that stretch through the insulation 24 are here formed as tubes having an inner surface with an inner diameter and an outer surface with an outer diameter. Furthermore a first section of this tube at a first end of the tube facing the first side 20 has an outer surface with an increasing outer diameter from a first to a second outer diameter in the direction from the first side 20 towards the base plate 28. The outer diameter thus increases from a first outer diameter that is essentially equal to the inner diameter of the tube to a second larger diameter. In this embodiment the tube wall made up of the inner and outer surfaces has a linearly increasing wall thickness in the first section, which makes the holes have a conical shape facing the chamber, i.e. in the opposite direction.
This means that at the first side 20 the holes are surrounded by insulation 24 right up till the inner diameter. It should here be realized that as an alternative it is possible that the tubes have the same outer diameter all the way to the base plate 28.
The base plate may be cooled, for instance using the previously mentioned heat sink.
A chemical reaction in the reactor for which the distribution plate can be employed may require a high temperature difference between the chamber and the gas inlet area during transport to the chamber. In for instance silicon production, where silanes like monosilane or trichlorosilane are used as gas, the temperature in the chamber may need to be above 700° C., for instance around 710° C. or 800° C., while the temperature in the gas inlet area typically is below 420° C. and with advantage slightly lower, such as a temperature in the range of 250° C. to 400° C. and more preferably 300° C. to 350° C. The reason for this is that at 420° C. silane starts to decompose, while good crystal structures are obtained at 710° C. This means that the latter temperature is present at the first side 20 of the distribution plate 16, while the former is present at the second side 18.
This also means that if nothing is done, the throughholes will exhibit a gradual increase in temperature from the second 18 to the first side 20. However, this also means that parts of the holes will have the temperature at which the gas decomposes. The result is that material, and in this example silicon, will be deposited on the walls of the holes. This will lead to the holes becoming clogged, which will result in the chemical process becoming less and less effective. This also means that it may be necessary to replace distribution plates frequently.
This problem of clogging is thus serious and needs to be addressed. At the same time it is important that the heat of the chamber is not lost via the distribution plate, which leads to an unnecessarily high energy consumption.
These and other problems are according to the invention addressed through keeping the temperature of the holes as close to the temperature of the gas inlet area as possible. This is combined with keeping the temperature at the first side of the plate, the side facing the chamber, at the chamber temperature.
This is according to the invention solved through the first side of the distribution plate comprising a first material surrounding the holes and having a first thermal conductivity for retaining the chamber temperature combined with using the second material of the base plate having a second thermal conductivity cool the holes of the distribution plate.
The thermal conductivity of the second material is with advantage higher than the thermal conductivity of the first material.
The thermal conductivity of the second material is with advantage at least 100 times higher, with advantage 1000 times higher and according to the first embodiment about 3000 times higher than the thermal conductivity of the first material. Here the first material, i.e. the insulation, may have a thermal conductivity of 0.08 W/m-K while aluminium may have a thermal conductivity of 237 W/m-K.
The heat that is transferred to the holes will be led away from the walls to the base plate and into the optional heat sink, which will prevent clogging.
Through the use of insulating material, the temperature of the chamber will be held high also adjacent to the first side of the distribution plate, which ensures a good chemical reaction. As small amounts of heat from the chamber is transferred to the holes, it is also clear that the energy losses are small, even in the case that a heat sink is connected to the distribution plate, which furthermore leads to an economical operation of the device with optimal heat and energy savings. In this way the energy consumption of the chemical reaction chamber is reduced. Another advantage of the invention is that the net heat transport through the distribution plate is reduced. Yet another advantage is that a high temperature gradient is sustained over the distribution plate thereby enabling more advantageous process parameters. The construction of the distribution plate is also robust.
Here the conical shape of the holes has the further advantage of reducing the amount of heat transferred into the holes from the chamber even further.
It is possible to vary the design of the holes in several ways in order to improve the ability to keep the whole temperature down and lower the heat dissipation from the chamber even further.
The wall of the hole is here in the bottom made up of the second material 28 of the base plate, which as one example is aluminium. However the part that protrudes through the insulation 24, which in this embodiment is a tube only including the first section 29, is made of another material, which is here anisotropic graphite. Here the whole part of the tube stretching up through the insulation is made of this other material, the third material 26. The outer diameter Do of the outer surface in this section 29 is here furthermore increasing in the direction from the chamber to the base plate. It is increased from the first outer diameter that is equal to the inner diameter D1 to the second outer diameter. The outer surface having the outer diameter Do is here curved and the radius of this outer surface may more particularly increase essentially exponentially or logarithmically.
Furthermore in this second embodiment the part of the hole wall that is provided with this third material is anisotropic and has a higher thermal conductivity along the length of the hole than radially away from the hole. This means that the first section 29 is anisotropic. In this second embodiment this higher thermal conductivity furthermore follows the curvature of the outer diameter Do.
This has the advantage of even further reducing the heat transfer from the reaction chamber to the hole while maximizing cooling of the whole throughhole surface thanks to favored heat exchange with the heat sink. Operating parameters will be set such as to keep gas temperature close to the inner wall lower than the decomposition temperature at the outlet of the through-hole.
A second variation of the hole according to a third embodiment of the invention is shown in
A third hole variation according to a fourth embodiment is shown in
The thermal conductivity along the hole may be at least four times higher than the thermal conductivity radially away from the hole, preferably at least 20 and with advantage at least 100 times higher. As an example it may be approximately 120 times higher.
It should here be realised that the fourth embodiment may be varied in that the first and second sections of the third material may have the same shape and thermal conductivity direction as the first section of the third material in the second embodiment.
An example of one way of operating the device will now be described with reference being made to
In the method, the gas is provided at a first temperature T1 in a gas inlet area, step 32, which temperature may be 200° C. The reaction chamber is also heated to a second temperature T2, step 34, which second temperature is here a temperature of 600° C. However, it shall be appreciated by those skilled in the art that operation parameters will depend on the process considered and the gas used. For example, when using Chlorosilanes, temperatures will be generally higher.
In order to keep the heat from dissipating, the heat of the reaction chamber is furthermore stopped from reaching the gas inlet area using the first side of the distribution plate, step 36, i.e. using the first material having the first thermal conductivity. This first side may here have a third temperature T3. The gas is also transported from the gas inlet area through the holes in the distribution plate to the reaction chamber, step 38, and this transporting is made while cooling the holes using the base structure of the distribution plate. This cooling of the walls will lead to the gas being transported through the holes also being cooled.
Through this way of operating, the heat in the chamber is to a high degree retained in the chamber, here at the temperature where silane decomposes and the heat of the chamber is stopped from escaping through the distribution plate by the use of the insulation, which is beneficial for the energy consumption of the device. At the same time cooling of the hole walls ensures that clogging is avoided.
In a further embodiment of the above method there is an additional method step whereby the gas is heated in the inlet area 12 and/or is heated prior to entering the inlet area 22.
The gas in the holes would normally receive heat from the upper part of the distribution plate, i.e. from the part of the plate that is closest to the reaction chamber. This heat is removed by the cooling provided through the invention. The gas will also receive heat directly from the reaction chamber. This heat transfer can be influenced by the speed which the gas is passed through the distribution plate. The heating can thus also be regulated through the velocity of the gas.
The example of a chemical process that was given above was the production of silicon. The invention is naturally not limited to this field but may be used for other types of processes, such as for instance oil and gas production processes.
A hole wall or base structure being described as anisotropic may be obtained in different ways. It is for instance possible that the material used as a wall or base structure is as such thermally anisotropic. However it is also possible to obtain anisotropy through assembly of different isotropic layers of material, where the interfaces between the layers cause the anisotropy.
There are thus several ways in which the anisotropic walls can be obtained. It is for instance possible to provide the walls based on using highly anisotropic flexible materials, shaping them according to the desired function and binding them together with a high temperature binder. This is for instance described at http://www.techapps.com/thermal-straps.html. As an example it is possible to bake highly conductive graphite strings in a sintered material such as silicon nitride, silicon carbide or other suitable material. As an alternative it is possible to produce a synthetic custom carbon design directly (premature technology), which is described at http://www.asbury.com/images/pdf/SyntheticGraphitePartI .pdf. This may be done by a number of methods. The whole or parts of a hole wall may be produced from a synthetic graphite material produced from high temperature treatment of carbon particles of different properties.
There is yet a further way in which the invention may be provided, which is shown in
A number of tests have been performed on the distribution plate described in the first embodiment.
In one experiment a cooling media was passed through the heat sink. In this example, the inlet temperature of the cooling media was 10° C. while the outlet temperature was 44° C. This setup resulted in a temperature of 278° C. at the first side of the plate in the chamber while the temperature at the second side of the plate was about 35° C. A considerable temperature difference was thus observed. A further test of the plate was done with water at boiling temperature. The water inlet was reduced to a bare minimum such that the whole heat sink reservoir reached boiling. At the outlet of the heat sink there was provided a 1.5 m high vertical section which overflowed when the water level got too high. This setup yielded a close to constant temperature around the heat sink and the extracted heat was removed as evaporation energy. By using this setup the second side of the distribution plate would hold a constant temperature T1 of about 78° C. while the temperature T3 at the first side reached 423 C. Further into the chamber an even higher temperature T2 of 650° C. was obtained.
The results of the last test are shown in a graph in
With reference to
The layer 50 is a substantially planar structure and is located adjacent the first side 20. However, it should be appreciated that the layer 50 may be another shape which substantially matches the shape or contour of the first side 20. The layer 50 has a typical thickness of 2 mm or lower. Preferably the layer 50 is located using mechanical clamping means around the outer circumference of the layer 50 and/or the layer 50 is attached to the first side 20 using a suitable adhesive. In an alternative variation the layer 50 is a silicate, such as a silicon dioxide, silicon carbide, silicon nitride or similar type of material, which is formed onto the first surface by a suitable process.
The layer 50 is formed with a series of holes 52 which align with the throughholes 22 of the distribution plate. The layer 50 is preferably made from a material which will substantially withstand the abrasive action of the fluidizing bed. A preferred material for the layer 50 is silicon, but other suitable materials may be used. The purpose of the layer 50 is to provide a protective layer over the first side 20 in order to protect the first material 24 and help prevent any material contaminants coming from the first material 24 into the reaction chamber 14.
In this further embodiment of the device, the inlet area 12 is provided with means (not shown in
While the invention has been described in connection with what is presently considered to be most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1150423-0 | May 2011 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/058775 | 5/11/2012 | WO | 00 | 1/17/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61484818 | May 2011 | US |
