Patent Application
20060127292
The invention is concerned with a device and a method for destroying ozone in gases including an integrated heat exchanger.
Starting-point for the invention was a problem that exists in the semi-conductor industry, where ozone is used to thoroughly clean so-called wafers. In this process, the wafers which have been brought into a chamber are flushed with water and, and high concentrations of ozone are separately introduced into the chamber. Due to its high concentration, the ozone that is not converted in the course of the cleaning process has to be completely destroyed for safety reasons. To this end, it was common state of the art to pass the ozone escaping from the wafer chamber over aluminum oxide and destroy it by means of UV radiation in the range of 254 nm and exposure to a temperature of approximately 70° C. However, if a dose of 0.1% hydrofluoric acid is additionally introduced into the wafer chamber for cleaning purposes, a proportion of which also being discharged from the wafer chamber and thus conducted over aluminum oxide, the latter will instantly react with the hydrofluoric acid and will become useless.
Another method known to remove residual ozone consists in its thermal destruction at temperatures >350° C., a process which is distinguished by a high consumption of energy. In order to minimize this high energy consumption, state of the art already suggested to connect a heat exchanger in series upstream or downstream, in order to heat up the gas. In the course of this process, the cold gas led into the device is then pre-heated with the hot, ozone-free gas discharged from the device. Thus, the full energy requirement in the form of heat energy no longer has to be brought in, instead, only the respective heat losses need to be compensated. According to the state of the art it is customary in this method to employ shell-and-tube exchangers which are distinguished by a coaxial arrangement of the tubes or a so-called revolver construction. However, in this case it is disadvantageous that such a tubular flow is characterized by a relatively high pressure drop and accordingly requires a large structural volume.
In order to destroy ozone in an aircraft environmental control system, US-A-2003/0202916 proposes a catalytic converter, with a staggered arrangement of rib-shaped elements which possess an impregnation consisting of the catalyst applied and anodized layers on one side of their surface. The anodized layers serve as a carrier for the catalyst, providing an additional surface for an improved distribution of the catalyst. After leaving the converter, the airflow thus cleared of ozone is conducted over a heat exchanger, the construction of which not being mentioned in further detail.
From DE-A-199 02 109, the use of recuperative heat exchangers has become known to be applicable in the thermal decomposition of N2O in gases containing N2O. Temperatures of from 800 to 1,200° C. are required for this thermal decomposition. The heat exchanger possesses solid-bed bulk material composed of inert particles, e.g. Al2O rings which are heated up to the required working temperature.
The heat exchanger is thus reaction chamber and heat exchanger in one. The converted gas is then cooled down by means of heat exchange, while the heat carrying elements and the new gas to be converted anew are heated up.
In addition, a method for a very specialized application has become known with DE-T-600 07 811, to prevent clogging in a plate heat exchanger developed for heating and cooling of a gas containing deposit-forming components. This gas is released in the process of producing (meth)acrylic acid or (meth)acrylic acid esters. The plate exchanger is modified in such a way that its flow-through width is exactly defined and its inlet possesses a gas dispersion plate.
It is an aspect of the present invention to provide a device and a method for destroying ozone, allowing for the destruction of ozone in a most simple and economic way, and in particular to employ a heat exchanger that shows a minimum necessary pressure drop, and that can be installed as space-saving as possible.
This problem was solved by a device for destroying ozone in gases, including a heat exchanger composed of two parts which are separated from each other and related to each other by heat contact, and a reaction chamber for ozone destruction, which is preceded by a collecting chamber for the gas containing ozone, and/or a distribution chamber for the essentially ozone-free gas which is arranged downstream, whereby the one part has an inlet for the ozone-containing gas to be heated and leads to the reaction chamber, while the other part leads from the reaction chamber to an outlet for the gas which is essentially free of ozone and to be cooled down, thereby reversing the flow direction, both parts being formed by plates lying close to each other and each defining a plane, with the part allocated to the ozone-containing gas constituting the preheating plane, and the part allocated to the essentially ozone-free gas constituting the recooling plane, each part comprising at least one plane, and the preheating plane(s) and recooling plane(s) to be arranged in such a manner that they have heat contact.
In accordance with a preferred embodiment, the part into which the gas containing ozone flows and the part in which the cooled, essentially ozone-free gas leaves the heat exchanger are flowed through relative to each other in such a manner that the directions of the gases flowing in and out cross over.
Thus, according to invention, a recuperative heat exchanger is made available which is designed as a plate heat exchanger. This arrangement makes it possible to preheat the ozone-containing gas with the essentially ozone-free gas, which is concomitantly cooled down, almost without incurring any pressure losses. Due to the reversal of the flow direction of the gas which is essentially free of ozone and flows out of the heat exchanger relative to the inflowing gas containing ozone, both parts of the heat exchanger are flowed through, in principle, relative to each other, in a counterflow. Preferably, the flow directions of the inflowing, ozone-containing gas to be heated up cross over the essentially ozone-free gas to be cooled down on its way to the outlet. This assures a maximum temperature difference and thus a maximum of possible heat exchange, particularly since the preheating and recooling planes effecting the heat exchange are situated in close (heat) contact with one another, while an optimum of compactness concerning the construction of the device is provided.
In this regard, the success of the device according to the present invention is not necessarily limited to a combination of a reversed flow direction and the over-crossing arrangement of the flow directions. Depending on the given requirement profile, the result may prove sufficient, even if an over-crossing arrangement of the flow directions is not provided.
In case the inflowing gas comprises organic substances possessing chemical double bonds in addition to ozone, the temperature of the preheating plane will mostly be sufficient to crack the organic double bonds contained therein.
The device according to the invention is structurally designed so that a collecting chamber for the ozone-containing gas precedes the reaction chamber, and/or a distribution chamber for the essentially ozone-free gas is set downstream of the reaction chamber. This is particularly efficient if the one part which holds the ozone-containing gas to be heated up, and/or the other part, in which the essentially ozone-free gas to be cooled down is led to the outlet, are composed of several preheating or recooling planes, respectively. The collecting chamber for the ozone-containing gas will then serve to combine the gases from all planes, and the distribution chamber will serve to conduct the essentially ozone-free gas into the respective recooling planes.
According to the invention it is possible that there is at least one more recooling plane in the heat exchanger than in the preheating planes. This is suitable because the inflowing ozone-containing gas is subject to compression as a result of the heating.
The reaction chamber of the device according to the invention comprises at least one heating element, with which the gas containing ozone is brought to a temperature required for the destruction of the ozone. In all, the device according to the invention works very economically, since the amount of heat energy supplied by the heating element equals the temperature difference of the gaseous flows at the inlet and the outlet of the heat exchanger, provided there is a good insulation.
The collecting chamber and the distribution chamber are, according to another embodiment of the device of the present invention, arranged in such a manner that the distribution chamber lies opposite to the at least one preheating plane, and the collecting chamber to the at least one recooling plane. Simple constructional measures thus achieve that the flow directions of the inflowing, ozone-containing gas to be heated and the essentially ozone-free, outflowing gas cross over at the site of the preheating plane(s) and the recooling plane(s).
The problem as mentioned at the beginning is also solved by a method for destroying ozone in gases, in which the gas containing ozone flows through an inlet to a first part of a heat exchanger and is led through a collecting chamber to a reaction chamber for ozone destruction, in which the gas is heated by at least one heating element up to a temperature at which ozone is destroyed, from where the hot gas then passes a distribution chamber and is led, essentially free of ozone, into another part of the heat exchanger, while the flow direction of the gas is reversed, and to a gas outlet, whereby the inflowing and outflowing gas flows through plates forming at least one plane in inflowing as well as in outflowing direction, respectively, at least one plane in inflowing direction constituting the preheating plane, and at least one plane in outflowing direction constituting the recooling plane, so that the outflowing gas of the recooling plane(s) heats up the inflowing gas of the preheating plane(s) by means of heat contact of the planes relative to each other, the outflowing gas of the recooling plane being cooled concomitantly.
The preheating plane(s) are arranged in close contact to the recooling plane(s), thus permitting an efficient heat exchange.
By applying the method according to the present invention, the gas is led into a collecting chamber once it has flowed through the plane(s) belonging to the first part and then into the reaction chamber. As already stated further above with regard to the device of the present invention, this is particularly reasonable, when more than one preheating planes exist, in order to permit combining of the gas in the collecting chamber and conducting it from there into the reaction chamber.
Accordingly, the gas leaving the reaction chamber is conducted into a distribution chamber, from where it is led towards the inflowing gas to the outlet. The distribution chamber takes over distributing the purified, essentially ozone-free gas to the various recooling planes. In this regard, it is highly preferred that there shall be at least one more recooling plane than preheating planes, due to the compression of the gas subsequent to its heating in the preheating plane.
In accordance with another embodiment of the method of the present invention, it is possible that the flow directions of the inflowing gas containing ozone and the outflowing, essentially ozone-free gas cross over.
The method according to the present invention can be successfully applied to both dry and humid, water-containing gases.
In order to accomplish the thermal destruction of ozone, the gas is heated in the reaction chamber up to at least 300° C., preferably up to 350° C., and most preferably up to temperatures above 350° C.
The device for destroying ozone in gases according to the present invention and the corresponding method are preferably applied in systems, for which the semi-conductor industry demands a complete destruction of the high ozone concentrations used for cleaning of wafers. For this purpose the device of the present invention is also particularly advantageous, because, owing to its construction as a plate heat exchanger with integrated reaction chamber, and thus integrated electrical heating appliance, it represents an extremely compact device, not demanding much space, as demanded by semi-conductor industry.
In the following, the invention is explained in further detail on the basis of an exemplary embodiment.
a is a schematic representation of the device according to the present invention including a heat-exchanger and a reaction chamber integrated in one shell.
b is a schematic representation of the heat-exchanger plates in relation to their preheating and recooling planes, and
c is a schematic representation of the heat-exchanger plates in relation to their preheating and recooling planes in a perspective rotated by an angle of 90°.
Reference is made to
Both parts are formed by plates 9 arranged closely next to each other, so that there is a close heat contact between the inflowing gas and the gas flowing to outlet 7 to assure a good transfer of heat, and each of the said parts defines at least one plate plane. The heat-exchanger 1 shown in
The ozone-containing gas is conducted from the one preheating plane 11 as shown to a collecting chamber 15 which essentially has the purpose to combine the ozone-containing gas from the various preheating planes 11 and to lead it into the reaction chamber 3. In the embodiment, the reaction chamber 3 comprises two heating elements 19, 21, through which the ozone-containing gas is heated up to more than 350° C. The temperature is controlled by a thermoelectric element, which is not shown in the
The reaction chamber 3 is not the only site where destruction of ozone takes place in the device according to the present invention. Because of the temperature profile existing in the preheating plane 11 of the heat-exchanger 1, ozone will already be destroyed there as well. The preheating plane 11 essentially contributes to the reaction enthalpy. Owing to the preheating capacity of the heat-exchanger 1 in the pre-treatment plane 11, it must be assumed that the temperature inside the collecting chamber 15 will already amount to approximately 300° C. This temperature is sufficient to destroy a considerable amount of the ozone. However, the essentially complete destruction of ozone is only accomplished in the reaction chamber 3.
The hot, essentially ozone-free gas is conducted from the reaction chamber 3 into the distribution chamber 23 which serves the purpose of leading the gas to the various recooling planes 13. Since the recooling plane(s) 13 stand in close contact with the plate, or plates, in such a manner that the plates of the respective stages immediately adjoin, the ozone-free gas flowing from the distribution chamber 23 towards the outlet 7 under reversal of the flow direction is now brought into a quasi countercurrent contact with the gas that flows from the preheating plane 11 or preheating planes 11 towards the collecting chamber 15. The collecting chamber 15 is configured that it lies opposite to the outlet 7, whereas the distribution chamber 23 accordingly lies opposite to the inlet 5. This accomplishes, by simple construction and at the same time efficaciously, that the flow directions of the inflowing and outflowing gases cross over. This produces a highest possible exchange of heat. Through this heat exchange the ozone-free gas flowing from the reaction chamber 3 over to the distribution chamber 23 towards the outlet 7 is cooled down to just about the same temperature of the gas that contains the ozone and flows into the preheating plane 5 through inlet 5, while the gas containing ozone is concomitantly heated up in the process.
In
The arrangement of the preheating and recooling planes 11, 13 in form of closely adjoining plates 9 of the heat-exchanger 1, intended to guarantee close heat contact, is shown in
Exemplary construction data applying to the recuperative heat-exchanger according to the present invention are presented in the following Table 1.
Additional Table 2 indicates the temperatures of the gas, its respective ozone concentrations, and the pressure drop, each measured at inlet 5 and outlet 7. The temperature inside the reaction chamber 3 amounted to approximately 380° C.
As shown in Table 2, heat-exchanger 1 displays a high rate of heat recovery, while the ozone in the gas is completely destroyed and the pressure difference is low. Thus, the very high heat recovery values can also be achieved under very economical conditions.
The recuperative heat-exchanger 1 employed according to invention is hence distinguished by an extraordinary heat transfer which is 3 to 5 times better than when shell-and-tube exchangers are used. In addition, depending on the design, the spatial requirement of the recuperative heat-exchanger 1 is up to 90% less compared to a shell-and tube exchanger. Transport and installation of the device is therefore easy to accomplish.
It is therefore a matter of self-understanding that the device according to the present invention representing a combination of plate heat-exchanger 1 and reaction chamber 3, equipped with electrical heating element(s) 19, 21, may be used just as well in any other applications in which ozone needs to be thermally destroyed, in particular, when ozone occurs in high concentrations in dry or humid gases. For example, waste water purification or bleaching of paper may be mentioned in this regard, since extremely high ozone concentrations are also applied here.
In general, the specific advantage of the invented device and the invented method is that very high ozone concentrations can be destroyed economically, and that this is possible in a complete manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102004051945.5 | Oct 2004 | DE | national |
