| Treatment of granular solids in a fluidized bed with microwaves -> Monitor Keywords |
|
|
  Treatment of granular solids in a fluidized bed with microwavesUSPTO Application #: 20060237300Title: Treatment of granular solids in a fluidized bed with microwaves Abstract: This invention relates to a method for the thermal treatment of granular solids in a fluidized bed (3, 3a) which is located in a fluidized-bed reactor (1, 1a), wherein microwave radiation is fed into the fluidized-bed reactor (1, 1a) through at least one wave guide (5), and to a corresponding plant. To improve the efficiency of the microwave irradiation, the irradiation angle of the microwaves is inclined by an angle of 10° to 50°, in particular 10° to 20°, with respect to the principal axis (11) of the fluidized-bed reactor (1, 1a). (end of abstract) Agent: Morgan & Finnegan, L.L.P. - New York, NY, US Inventors: Michael Stroder, Nikola Anastasijevic, Thorsten Gerdes, Monika Willert-Porada USPTO Applicaton #: 20060237300 - Class: 204157150 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Non-distilling Bottoms Treatment, Processes Of Treating Materials By Wave Energy The Patent Description & Claims data below is from USPTO Patent Application 20060237300. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This invention relates to a method for the thermal treatment of granular solids in a fluidized bed which is located in a fluidized-bed reactor, wherein microwave radiation is fed into the fluidized-bed reactor through at least one wave guide, and to a corresponding plant. [0002] There are several possibilities for coupling a microwave source to fluidized-bed reactors. These include for instance an open wave guide, a slot antenna, a coupling loop, a diaphragm, a coaxial antenna filled with gas or another dielectric, or a wave guide occluded with a microwave-transparent substance (window). The type of decoupling the microwaves from the feed conduit can be effected in different ways. [0003] Theoretically, microwave energy can be transported in wave guides free of loss. The wave guide cross-section is obtained as a logical development of an electric oscillating circuit comprising coil and capacitor towards very high frequencies. Theoretically, such oscillating circuit can likewise be operated free of loss. In the case of a substantial increase of the resonance frequency, the coil of an electric oscillating circuit becomes half a winding, which corresponds to the one side of the wave guide cross-section. The capacitor becomes a plate capacitor, which likewise corresponds to two sides of the wave guide cross-section. In reality, an oscillating circuit loses energy due to the ohmic resistance in coil and capacitor. The wave guide loses energy due to the ohmic resistance in the wave guide wall. [0004] Energy can be branched off from an electric oscillating circuit by coupling a second oscillating circuit thereto, which withdraws energy from the first one. Similarly, by flanging a second wave guide to a first wave guide energy can be decoupled from the same (wave guide transition). When the first wave guide is shut off behind the coupling point by a shorting plunger, the entire energy can even be diverted to the second wave guide. [0005] The microwave energy in a wave guide is enclosed by the electrically conductive walls. In the walls, wall currents are flowing, and in the wave guide cross-section an electromagnetic field exists, whose field strength can be several 10 KV per meter. When an electrically conductive antenna rod is put into the wave guide, the same can directly dissipate the potential difference of the electromagnetic field and with a suitable shape also emit the same again at its end (antenna or probe decoupling). An antenna rod which enters the wave guide through an opening and contacts the wave guide wall at another point can still directly receive wall currents and likewise emit the same at its end. When the wave guide is shut off by a shorting plunger behind the antenna coupling, the entire energy can be diverted from the wave guide into the antenna in this case as well. [0006] When the field lines of the wall currents in wave guides are interrupted by slots, microwave energy emerges from the wave guide through these slots (slot decoupling), as the energy cannot flow on in the wall. The wall currents in a rectangular wave guide flow parallel to the center line on the middle of the broad side of the wave guide, and transverse to the center line on the middle of the narrow side of the wave guide. Transverse slots in the broad side and longitudinal slots in the narrow side therefore decouple microwave radiation from wave guides. [0007] Microwave radiation can be conducted in electrically conductive hollow sections of all kinds of geometries, as long as their dimensions do not fall below certain minimum values. The exact calculation of the resonance conditions involves rather complex mathematics, as the Maxwell equations (unsteady, nonlinear differential equations) must ultimately be solved with the corresponding marginal conditions. In the case of a rectangular or round wave guide cross-section, however, the equations can be simplified to such an extent that they can be solved analytically and problems as regards the design of wave guides become clearer and are easier to solve. Therefore, and due to the relatively easy production, only rectangular wave guides or round wave guides are used industrially, which are also preferably used in accordance with the invention. The chiefly used rectangular wave guides are standardized in the Anglo-Saxon literature. [0008] These standard dimensions were adopted in Germany, which is why odd dimensions appear in part. In general, all industrial microwave sources of the frequency 2.45 GHz are equipped with a rectangular wave guide of the type R26, which has a cross-section of 43.times.86 mm. In wave guides, different oscillation states exist: In the transversal electric mode (TE mode), the electric field component lies transverse to the wave guide direction and the magnetic component lies in wave guide direction. In the transversal magnetic mode (TM mode), the magnetic field component lies transverse to the wave guide direction and the electric component lies in wave guide direction. Both oscillation states can appear in all directions in space with different mode numbers (e.g. TE-1-1, TM-2-0). [0009] A method for the thermal treatment of granular solids is known from U.S. Pat. No. 5,972,302, wherein sulfidic ore is subjected to an oxidation supported by microwaves. This method is chiefly concerned with the calcination of pyrite in a fluidized bed, wherein the microwaves introduced into the fluidized bed promote the formation of hematite and elementary sulfur and suppress the formation of SO.sub.2. There is employed a stationary fluidized bed which Is directly irradiated by the microwave source disposed directly above the same. The microwave source or the entrance point of the microwaves necessarily gets in contact with the gases, vapors and dusts ascending from the fluidized bed. [0010] EP 0 403 820 B1 describes a method for drying substances in a fluidized bed, wherein the microwave source is disposed outside the fluidized bed and the microwaves are introduced into the fluidized bed by means of a wave guide. There are frequently reflections of microwave radiation at the solids to be heated, whereby the efficiency is reduced and the microwave source is possibly damaged. In the case of open microwave wave guides, there are also dust deposits in the wave guide, which absorb part of the microwave radiation and can damage the microwave source. This can be avoided by microwave-transparent windows, which occlude the wave guide between the reactor and the microwave source. In this case, however, deposits on the window lead to an impairment of the microwave radiation. DESCRIPTION OF THE INVENTION [0011] It is therefore the object underlying the invention to make the feeding of microwaves into a stationary or circulating fluidized bed more efficient and protect the microwave source in a better way. [0012] In accordance with the invention, this object is substantially solved in a method as mentioned above in that the irradiation angle of the microwaves is inclined by an angle of 10.degree. to 50.degree., particularly preferably, however, between 10.degree. and 20.degree., with respect to the principal axis of the fluidized-bed reactor. In accordance with the invention, the irradiation angle .alpha. can also be variably adjustable. [0013] Electromagnetic waves are transverse waves, i.e. have a polarizing direction, the direction of the electric field strength being parallel to the transmitter dipole, the direction of the magnetic excitation vertical thereto. To introduce as much microwave energy as possible into the substances to be excited, the degree of reflection must be minimized. The degree of reflection is known to depend on the angle of incidence, the refractive index of the substance to be excited, and on the polarizing direction. As the substances to be excited in the fluidized bed are ores, recycling substances or waste substances, which either unevenly lie on a grid in the fluidized bed or circulate with introduced gas in the reactor space, there is no distinct surface on which the microwave rays impinge. When introducing microwaves from a plurality of microwave sources, the reflected microwaves form standing waves of multiple modes in the reactor space. These modes are also obtained in the case of microwaves from only one microwave source, as the microwaves are reflected at the wall of the reactor in various directions. These microwaves reinforce each other by increasing the amplitude in some regions, and cancel each other again in other regions. This produces a multitude of standing waves. It was surprisingly found out that in particular with an irradiation angle of the microwaves of 10 to 20 degrees with respect to the principal axis of the reactor the smallest reflection and thus the highest efficiency can be achieved. By principal axis of the reactor there is in particular meant the vertical axis of symmetry. The reflection onto the microwave source also is smallest at the same time. For protection, the microwave source also is disposed outside the stationary or circulating fluidized bed, the microwave radiation being fed into the fluidized-bed reactor through at least one wave guide. [0014] In a particular preferred embodiment, a gas stream is additionally fed into the fluidized-bed reactor through the wave guide, which gas stream is also used for microwave irradiation. Coupling the microwave radiation and at the same time the secondary stream under an angle of 10.degree. up to in particular 20.degree. into the fluidized-bed reactor turned out to be particularly favorable, as in this angular range the returning microwave performance is minimal on the one hand and on the other hand no dust deposits are observed in the wave guide. Hence, the heating efficiency and the operational safety are highest in this range. In dependence on the properties of the fluidized bed, however, irradiation angles between 200 and 50.degree. may be expedient in terms of apparatus. By means of the additional continuous gas stream from the wave guide it is reliably avoided that dust or process gases enter the wave guide, spread up to the microwave source and damage the same or form solid deposits in the wave guide. In accordance with the invention, microwave-transparent windows in the wave guide for shielding the microwave source, as they are commonly used in the prior art, can therefore be omitted. The same involve the problem that deposits of dust or other solids on the window can impair and partly absorb the microwave radiation. Therefore, the open wave guides in accordance with the invention are particularly advantageous. [0015] An improvement of the method is achieved when the gas stream introduced through the wave guide contains gases which react with the fluidized bed and in the case of a circulating fluidized-bed reactor can even be utilized for an additional fluidization of the fluidized bed. Thus, part of the gas which so far has been introduced into the fluidized bed through other supply conduits is used for dedusting the wave guide. As a result, providing neutral purge gas can also be omitted. [0016] Another improvement is obtained in accordance with the invention when the gas stream introduced through the wave guide has a temperature difference with respect to the gases and solids present in the fluidized-bed reactor. In this way, additional heat can specifically be introduced into the fluidized bed or the fluidized bed can be cooled, depending on the desired effect. [0017] The thermal treatment can not only be effected in a stationary, but also in a circulating fluidized bed, wherein the solids circulate continuously between a fluidized-bed reactor, a solids separator connected with the upper region of the fluidized-bed reactor and a return conduit connecting the solids separator with the lower region of the fluidized-bed reactor. Usually, the amount of solids circulating per hour is at least three times the amount of solids present in the fluidized-bed reactor. [0018] Another advantage is obtained in that solid deposits in the wave guide are avoided by the continuous gas stream through the wave guide. These solid deposits change the cross-section of the wave guide in an undesired way and absorb part of the microwave energy which was designed for the solids in the fluidized bed. Due to the absorption of energy in the wave guide, the same is heated very much, whereby the material is subject to a strong thermal wear. In addition, solid deposits in the wave guide effect undesired feedbacks to the microwave source. [0019] In the case of a circulating fluidized bed an improvement of the previous method is obtained when the microwave source is combined with the secondary gassing of the ring conduit. The microwave radiation is introduced into the reactor under the preferred irradiation angle, and at the same time the wave guide is used for secondary gassing. [0020] Suitable microwave sources, i.e. sources for the electromagnetic waves, include e.g. a magnetron or a klystron. Furthermore, high-frequency generators with corresponding coils or power transistors can be used. The frequencies of the electromagnetic waves proceeding from the microwave source usually lie in the range from 300 MHz to 30 GHz. Preferably, the ISM frequencies 435 MHz, 915 MHz and 2.45 GHz are used. Expediently, the optimum frequencies are determined for each application in a trial operation. [0021] In accordance with the invention, the wave guide wholly or largely consists of electrically conductive material, e.g. copper. The length of the wave guide lies in the range from 0.1 to 10 m. The wave guide may be straight or curved. There are preferably used sections of round or rectangular cross-section, the dimensions being in particular adjusted to the frequency used. [0022] The temperatures in the fluidized bed lie for instance in the range from 150 to 1200.degree. C., and it may be recommended to introduce additional heat into the fluidized bed, e.g. through indirect heat exchange. For temperature measurement in the fluidized bed, insulated sensing elements, radiation pyrometers or fiber-optic sensors can be used. Continue reading... Full patent description for Treatment of granular solids in a fluidized bed with microwaves Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Treatment of granular solids in a fluidized bed with microwaves patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Treatment of granular solids in a fluidized bed with microwaves or other areas of interest. ### Previous Patent Application: Method for recovering solvents Next Patent Application: Apparatus for producing nanocarbon, method for producing nanocarbon and method for collecting nanocarbon Industry Class: Chemistry: electrical and wave energy ### FreshPatents.com Support Thank you for viewing the Treatment of granular solids in a fluidized bed with microwaves patent info. IP-related news and info Results in 0.98739 seconds Other interesting Feshpatents.com categories: Computers: Graphics , I/O , Processors , Dyn. Storage , Static Storage , Printers |
||
