U.S. patent application number 10/540433 was filed with the patent office on 2006-10-26 for treatment of granular solids in a fluidized bed with microwaves.
This patent application is currently assigned to OUTOKUMPU OYJ. Invention is credited to Nikola Anastasijevic, Thorsten Gerdes, Michael Stroder, Monika Willert-Porada.
Application Number | 20060237300 10/540433 |
Document ID | / |
Family ID | 32477942 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060237300 |
Kind Code |
A1 |
Stroder; Michael ; et
al. |
October 26, 2006 |
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.degree. to 50.degree., in
particular 10.degree. to 20.degree., with respect to the principal
axis (11) of the fluidized-bed reactor (1, 1a).
Inventors: |
Stroder; Michael;
(Neu-Anspach, DE) ; Anastasijevic; Nikola;
(Altenstadt, DE) ; Gerdes; Thorsten; (Bayreuth,
DE) ; Willert-Porada; Monika; (Bayreuth, DE) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Assignee: |
OUTOKUMPU OYJ
Espoo
FI
|
Family ID: |
32477942 |
Appl. No.: |
10/540433 |
Filed: |
November 25, 2003 |
PCT Filed: |
November 25, 2003 |
PCT NO: |
PCT/EP03/13209 |
371 Date: |
May 15, 2006 |
Current U.S.
Class: |
204/157.15 ;
423/148; 423/47; 423/74 |
Current CPC
Class: |
B01J 2219/129 20130101;
B01J 8/36 20130101; C22B 11/02 20130101; B01J 8/1872 20130101; B01J
2208/00442 20130101; H05B 6/806 20130101; B01J 2208/00141 20130101;
B01J 8/388 20130101; F26B 3/08 20130101; F26B 3/343 20130101; C22B
5/14 20130101; C22B 1/10 20130101; B01J 8/42 20130101; F26B 3/084
20130101 |
Class at
Publication: |
204/157.15 ;
423/047; 423/074; 423/148 |
International
Class: |
C22B 15/00 20060101
C22B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2002 |
DE |
102 60 743.5 |
Claims
1. A method for thermal treating granular solids in a fluidized bed
which is located in a fluidized-bed reactor, comprising feeding
microwave radiation into the fluidized-bed reactor through at least
one wave guide, inclining microwaves by an irradiation angle of
10.degree. to 50.degree. with respect to a principal axis of the
fluidized-bed reactor.
2. The method as claimed in claim 1, further comprising feeding a
gas stream into the fluidized-bed reactor through the at least one
wave guide.
3. The method as claimed in claim 2, wherein the gas stream
introduced through the at least one wave guide contains gases which
react with the fluidized bed.
4. The method as claimed in claim 2 wherein the gas stream
introduced through the at least one wave guide is additionally
utilized for a fluidization of the fluidized bed.
5. The method as claimed in claim 2 wherein heat is additionally
supplied to the fluidized bed by the introduced gas stream.
6. The method as claimed in claim 2 wherein the fluidized bed is
cooled by the introduced gas stream.
7. The method as claimed in claim 2, wherein by of introducing the
gas stream into the at least one wave guide, solid deposits in the
at least one wave guide are avoided.
8. The method as claimed in claim 2, wherein the reactor comprises
at least two fluidized-bed reactors, which are separated from each
other by weirs or partitions such that solids can move as migrating
fluidized-bed from one fluidized-bed reactor into the adjacent
fluidized-bed reactor.
9. The method as claimed in claim 2, comprising combining a
microwave source with a secondary gassing of a ring conduit and
that the at least one wave guide is simultaneously used for
secondary gassing.
10. The method as claimed in claim 2, wherein the microwave
radiation has a frequency between 300 MHz and 30 GHz.
11. The method as claimed in claim 2, wherein the fluidized bed has
a temperature between 150.degree. C. and 1200.degree. C.
12. The method as claimed in claim 2, wherein the at least one wave
guide has a Particle-Froude-Number (Fr.sub.p) between 0.1 and
100.
13. A plant for thermal treating granular solids in a fluidized bed
as claimed in claim 1, comprising a fluidized-bed reactor, a
microwave source disposed outside the fluidized-bed reactor and a
wave guide for feeding the microwave radiation into the
fluidized-bed reactor, wherein the wave guide is inclined by an
angle of 10.degree. to 50.degree. with respect to a principal axis
of the fluidized-bed reactor.
14. The plant as claimed in claim 13, wherein the wave guide has a
rectangular or round cross-section, which is adjustable to the used
frequency of the microwave radiation.
15. The plant as claimed in claim 13, wherein the wave guide has a
length of 0.1 m to 10 m.
16. The method as claimed in claim 10, wherein the frequency is 435
MHz, 915 MHz, or 2.45 GHz.
17. The method as claimed in claim 12, wherein the
Particle-Froude-Number is between 2 and 30.
18. The plant as claimed in claim 13, wherein the angle is between
10.degree. and 20.degree..
Description
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.
[0023] In accordance with the invention, the gas velocities in the
wave guide are adjusted such that the Particle-Froude-Numbers in
the wave guide lie in the range between 0.1 and 100. The
Particle-Froude-Numbers are defined as follows: Fr p = u ( .rho. s
- .rho. f ) .rho. f * d p * g ##EQU1## with [0024] u=effective
velocity of the gas flow in m/s [0025] .rho..sub.s=density of the
solid particles or process gases penetrating into the wave guide in
kg/m.sup.3 [0026] .rho..sub.f=effective density of the purge gas in
the wave guide in kg/m.sup.3 [0027] d.sub.p=mean diameter in m of
the particles of the reactor inventory (or the particles formed)
during operation of the reactor [0028] g=gravitational constant in
m/s.sup.2.
[0029] To prevent solid particles or generated process gases from
the reactor from penetrating into the wave guide, gas serving as
purge gas flows through the wave guide. Solid particles can for
instance be dust particles present in the reactor or also the
treated solids. Process gases are obtained in the processes which
take place in the reactor. By specifying certain
Particle-Froude-Numbers, the density ratio of the entering solid
particles or process gases to the purge gas is considered in
accordance with the invention when adjusting the gas velocities,
which ratio, apart from the velocity of the purge gas stream, is
decisive for the question whether or not the purge gas stream can
entrain the entering particles. Substances can thereby be prevented
from penetrating into the wave guide. For most applications, a
Particle-Froude-Number between 2 and 30 is preferred.
[0030] The granular solids to be treated by the method in
accordance with the invention can for instance be ores and in
particular sulfidic ores, which are prepared e.g. for recovering
gold, copper or zinc. Furthermore, recycling substances, e.g.
zinc-containing processing oxide or waste substances, can be
subjected to the thermal treatment in the fluidized bed. If
sulfidic ores, such as e.g. auriferous arsenopyrite, are subjected
to the method, the sulfide is converted to oxide, and with a
suitable procedure there is preferably formed elementary sulfur and
only small amounts of SO.sub.2. The method of the invention
favorably loosens the structure of the ore, so that the subsequent
gold leaching leads to improved yields. The arsenic iron sulfide
(FeAsS) preferably formed by the thermal treatment can easily be
disposed of. Expediently, the solids to be treated at least partly
absorb the electromagnetic radiation used and thus heat the bed. It
was surprisingly found out that in particular material treated at
high field strengths can be leached more easily. Frequently, other
technical advantages can be realized as well, such as reduced
retention times or a decrease of the required process
temperatures.
[0031] In accordance with the invention, the solids can also be
passed through at least two succeeding fluidized-bed reactors, for
instance two turbulence chambers separated from each other by means
of weirs or partitions, in which the stationary fluidized beds are
disposed and into which electromagnetic waves are fed, which are
coming from wave guides. The solids can move as migrating
fluidized-bed from one fluidized-bed reactor into the adjacent
fluidized-bed reactor. One variant consists in that between two
turbulence chambers of the two adjacent fluidized-bed reactors an
intermediate chamber is disposed, which is connected with the
turbulence chambers and contains a fluidized bed of granular
solids, the intermediate chamber having no wave guide associated
thereto. Another variant of the method of the invention consists in
that for separating the two turbulence chambers a partition is
used, which has the opening in the bottom region.
[0032] Particularly advantageously, the operating conditions, in
particular temperature, composition of the fluidizing gas, energy
input and/or fluidization velocity, can be predetermined
differently for each of a plurality of fluidized-bed reactors. In
the case of one fluidized bed or a plurality of succeeding
fluidized beds, the solids thus can for instance first be passed
through a preheating chamber upstream of the first fluidized bed.
Furthermore, downstream of the last fluidized bed serving the
thermal treatment a cooling chamber can be provided for cooling the
solid product.
[0033] Furthermore, the present Invention relates to a plant in
particular for performing the above-described method for the
thermal treatment of granular solids in a fluidized bed. A plant in
accordance with the invention includes a fluidized-bed reactor, a
microwave source disposed outside the fluidized-bed reactor, and a
wave guide for feeding the microwave radiation into the
fluidized-bed reactor, the wave guide being inclined by an angle of
10.degree. to 500, in particular 10.degree. to 20.degree., with
respect to the principal axis of the fluidized-bed reactor.
[0034] Developments, advantages and possible applications of the
present invention can also be taken from the following description
of examples and from the drawing. All described and/or illustrated
features per se or in any combination belong to the subject-matter
of the invention, independent of their inclusion in the claims or
their back-reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 shows the thermal treatment of granular solids in a
stationary fluidized bed in a schematic representation;
[0036] FIG. 2 shows a method variant with a circulating fluidized
bed; and
[0037] FIGS. 3, 4, 5 show method variants with a plurality of
stationary fluidized beds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] FIG. 1 shows a plant for performing the method in accordance
with the invention for the thermal treatment of granular solids in
a stationary fluidized layer 3 which is also referred to as
fluidized bed.
[0039] The plant includes a fluidized-bed reactor 1, into which
granular solids to be treated are introduced through a conduit 2.
In a chamber, the solids form a stationary fluidized bed 3 which is
traversed by a fluidizing gas, e.g. air. For this purpose, the
fluidizing gas is passed from below through a gas distributor 4
into the fluidized bed 3. In the upper region of the fluidized-bed
reactor 1, an open wave guide 5, which leads to a microwave source
7, is connected to the chamber with the stationary fluidized bed 3.
The wave guide 5 is inclined by an angle .alpha. of 10.degree. to
20.degree. with respect to the vertical principal axis 11 of the
fluidized-bed reactor 1. The electromagnetic waves proceeding from
the microwave source 7 are passed through the wave guide 5 and fed
into the chamber of the fluidized-bed reactor 1. They at least
partly contribute to the heating of the fluidized bed 3.
Furthermore, purge gas, e.g. air or nitrogen, is laterally fed into
the wave guide 5 through a conduit 6, which purge gas flows on into
the fluidized-bed reactor and prevents the ingress of dust or
process gases from the chamber with the stationary fluidized bed 3
into the wave guide 5. In this way, the microwave source 7 is
protected against being damaged, and at the same time
microwave-absorbing soil deposits in the wave guide 5 are prevented
without the open wave guide 5 having to be closed by a
microwave-transparent window. By means of the angle of inclination,
reflections of the microwaves fed into the fluidized-bed reactor 1
are reduced considerably, so that the electromagnetic radiation can
better be absorbed by the solids and the efficiency of the plant
and of the method is increased.
[0040] If necessary for the process, the stationary fluidized bed 3
can additionally be heated by a heat exchanger 8 disposed in the
fluidized bed 3. Gases and vapors formed leave the chamber of the
fluidized-bed reactor 1 through a conduit 9 and are supplied to a
non-illustrated cooling and dedusting known per se. The treated
granular solids are withdrawn from the fluidized-bed reactor 1
through the discharge conduit 10.
[0041] In FIG. 2, the fluidized-bed reactor 1 constitutes a reactor
with a circulating fluidized bed (fluidized layer). The solids to
be treated are introduced into the fluidized-bed reactor 1 via
conduit 2 and entrained by fluidizing gas introduced into the
fluidized-bed reactor 1, whereby the circulating fluidized layer is
formed. The solids then are at least partly discharged from the
fluidized-bed reactor 1 along with the gas through a duct 18 and
introduced into a solids separator 12. The solids separated therein
are at least partly recirculated through a return conduit 13 into
the lower region of the circulating fluidized bed of the
fluidized-bed reactor 1. Part of the solids can also be discharged
through the discharge conduit 14. Coarse solids, which are
deposited at the bottom of the fluidized-bed reactor 1, can be
removed from the reactor 1 through an outlet conduit 15. The
fluidizing gas for forming the circulating fluidized bed, e.g. air,
is supplied to the fluidized-bed reactor 1 through a conduit 4a and
first gets into a distribution chamber 4b, before it flows into the
fluidized-bed reactor 1 through a grid 4c, entrains the introduced,
in particular fine-grained solids and forms a circulating fluidized
layer as fluidized bed.
[0042] A wave guide 5 connects a microwave source 7 with the
chamber of the fluidized-bed reactor 1, through which wave guide
microwaves are fed into the microwave reactor 1 for heating the
granular solids as in the plant in accordance with FIG. 1. In
addition, purge gas from a secondary gassing 6 flows through the
wave guide 5, in order to avoid the ingress of dirt as well as
deposits in the wave guide 5. The wave guide 5 is inclined by an
angle .alpha. of 10.degree. to 20.degree. with respect to the
principal axis 11 of the fluidized-bed reactor 1, in order to
minimize reflections of the irradiated microwaves at the solids and
in conjunction with the gas stream avoid dust deposits in the wave
guide 5. The microwave source 7 is disposed behind a bend of the
wave guide 5, in which the same is bent with respect to its
longitudinal axis by about the angle .alpha.. The secondary gassing
6 connected to a non-illustrated ring conduit substantially axially
meets the wave guide 5 in this bend.
[0043] In the present case as well, the inner region of the chamber
can again be provided with one or more heat exchangers for
additionally heating the granular solids, which was not represented
in FIG. 2 for a better clarity.
[0044] Dust-laden gas leaves the solids separator 12 through
conduit 9 and is first cooled in a waste heat boiler 16, before it
is passed through a dedusting 17. Separated dust can either be
removed from the process or be recirculated to the chamber of the
fluidized-bed reactor 1 through a non-illustrated conduit.
[0045] As shown in FIG. 3, two stationary fluidized-bed reactors 1
and 1a are arranged in series, an intermediate chamber 1c being
located between the chambers of the two reactors 1 and 1a. In all
three chambers, the solids form a stationary fluidized bed 3, 3a,
which is traversed by fluidizing gas. The fluidizing gas for each
chamber is supplied through a separate conduit 4a. The granular
solids to be treated enter the first fluidized-bed reactor 1
through conduit 2, and completely treated solids leave the second
fluidized-bed reactor 1a through the discharge conduit 10. From the
upper region of the chamber of the first reactor 1 a first wall 19
extends downwards. However, it does not extend down to the ground,
so that in the bottom region an opening 20 is left, through which
solids from the first fluidized bed 3 can get into the fluidized
bed 3a of the intermediate chamber 1c. The intermediate chamber 1c
extends up to a weir-like second wall 21, over which the solids
from the fluidized bed 3a of the intermediate chamber 1c are moved
into the chamber of the second fluidized-bed reactor 1a.
Corresponding to the plants as shown in FIGS. 1 and 2, wave guides
5 with purge air conduits 6 and microwave sources 7 are each
connected to the chambers of the two reactors 1 and 1a, which wave
guides are inclined by an angle .alpha. between 10.degree. and
20.degree. against the vertical principal axis 11. The principal
axes of the reactors 1 and 1a are each aligned vertically and
disposed in parallel, so that in the drawing merely one principal
axis is shown. The irradiation angle .alpha. in the first reactor 1
is different from the irradiation angle .alpha. in the second
reactor 1a. This is in particular expedient when for instance
microwaves of different frequencies are irradiated into the various
chambers. In accordance with the present invention it may of course
also be provided that the two irradiation angles .alpha. are equal
for both reactors 1, 1a. In the chambers of the reactors 1 and 1a
heat exchanging elements 8 may be arranged in addition.
[0046] The gas space 22 above the fluidized bed 3 of the first
fluidized-bed reactor 1 is separated from the gas space 23, which
belongs to the chamber of the second reactor 1a and the
intermediate chamber 1c, by the vertical wall 19. For the gas
spaces 22, 23 separate gas outlet conduits 9 and 9a exist. As a
result, different conditions can be maintained in the chambers of
the reactors 1 and 1a, in particular different temperatures can
exist or different fluidizing gases can be supplied through
separate gas supply conduits 4a. Furthermore, the two microwave
sources 7 can be designed differently and perform different
functions. In particular, microwaves of different frequency or
energy can be generated and be introduced through the wave guide
5.
[0047] As shown in FIG. 4, two stationary fluidized-bed reactors 1
and 1a without intermediate chamber are arranged directly
succeeding each other, a partition 19 being disposed between the
two. In the chambers of the two reactors 1, 1a the solids form a
stationary fluidized bed 3, 3a, which is fluidized by fluidizing
gas from a plurality of conduits 4a disposed one beside the other.
The granular solids to be treated are supplied to the first
fluidized-bed reactor 1 through conduit 2, and the treated solids
leave the fluidized-bed reactor 1a through the discharge conduit
10. From the upper region of the chamber of the first reactor 1, a
first wall 19 extends downwards, which does, however, not extend
down to the ground, so that in the bottom region an opening 20 is
left, through which solids from the first fluidized bed 3 can get
into the fluidized bed 3a of the second fluidized-bed reactor 1a.
Waveguides 5, which are connected to the microwave sources 7, each
extend to the two chambers of the reactors 1 and 1a. According to
the principle described already in the previous embodiments,
microwaves are fed into the two reactors 1, 1a through these open
wave guides, in order to heat the solids to be treated, which
absorb the microwave radiation, and reach the necessary process
temperatures. The wave guides 5 are again inclined by their
respective irradiation angles .alpha. between 10.degree. and
20.degree. against the principal axes 11 of the two reactors 1, 1a.
During the microwave irradiation, purge gas at the same time flows
into the wave guides 5 through purge air conduits 6, in order to
avoid deposits in said wave guides. In the chambers of the reactors
1 and 1a, heat exchanging elements 8 may be arranged in
addition.
[0048] The gas space 22 above the fluidized bed 3 of the first
fluidized-bed reactor 1 is separated from the gas space 23, which
belongs to the chamber of the second reactor 1a, by the vertical
wall 19. There exist separate gas discharge conduits 9 and 9a. As a
result, different conditions can be maintained in the various
reactor chambers 1 and 1a, in particular the temperatures or the
gas phase composition can be different. Different fluidizing gases
can also be supplied through the respective conduits 4a.
Furthermore, the two microwave sources 7 can be designed
differently and perform different functions.
[0049] In the arrangement as shown in FIG. 5, the solids to be
treated, which are supplied via conduit 2, first enter an
antechamber 31 and flow through a first intermediate chamber 32
into the first fluidized-bed reactor 1. The solids then are
discharged from the same to flow through a second intermediate
chamber 1c into the second fluidized-bed reactor 1a and finally
through the third intermediate chamber 33 into a cooling chamber
34, before the treated and cooled solids are withdrawn through the
discharge conduit 10. Wave guides 5 with associated non-illustrated
microwave sources each open into the chambers of the fluidized-bed
reactors 1 and 1a, in order to feed microwaves into the reactors 1
and 1a according to the above-described principle. Here as well,
the wave guides are inclined at an angle .alpha. of 10.degree. to
20.degree. with respect to the principal axis 11 of the
fluidized-bed reactors 1, 1a. All chambers include stationary
fluidized beds, to which fluidizing gas is supplied through
separate gas supply conduits 4a for each chamber. The exhaust gases
are discharged through corresponding conduits 9.
[0050] In the cooling chamber 34, the fluidized bed includes a
cooling means 35 for an indirect heat exchange, whose cooling
fluid, e.g. cooling water, is heated in the cooling means 35 and
then supplied through conduit 36 to the heat exchanger 37 in the
preheating chamber 31. There, the cooling fluid releases part of
its heat to the solids in the fluidized bed disposed there, whereby
a very economic utilization of heat is achieved.
[0051] To make the feeding of microwaves into a stationary or
circulating fluidized bed 3, 3a more efficient and also protect the
microwave source 7 against reflected microwave rays, the microwave
source 7 in accordance with the invention is disposed outside the
stationary or circulating fluidized bed 3, 3a and the fluidized-bed
reactors 1, 1a. The microwave radiation is fed into the
fluidized-bed reactor 1, 1a through at least one open wave guide 5,
the irradiation angle of the microwaves being inclined by an angle
of 10.degree. to 50.degree., preferably 10.degree. to 20.degree.,
with respect to the principal axis 11 of the respective
fluidized-bed reactor 1, 1a.
EXAMPLE
Calcination of Gold Ore in a Circulating Fluidized Bed
[0052] The following Table indicates typical method parameters for
a calcination of gold ore. For comparison, the data are indicated
with and without the inventive irradiation of the microwaves. The
microwave frequency is about 915 MHz in the indicated example.
TABLE-US-00001 without microwave with microwave Unit Inlet Outlet
Inlet Outlet Diameter of the CFB- mm 200 200 reactor of FIG. 2 kW 0
2 Installed microwave kg/h 150 195 performance Gold ore feed
.degree. C. 350 250 Primary air Nm.sup.3/h 30 30 kg/h 0.80 0.77 Oil
consumption: .degree. C. 525 425 Secondary air Nm.sup.3/h 24 24
kg/h 140 182 Melting loss Calcination gas, total Nm.sup.3/h 58 59
Flow rate .degree. C. 700 600 Temperature Composition, dry vol-%
18.7 23.3 CO.sub.2 vol-% 75.3 74.3 N.sub.2 vol-% 5.9 2.4 O.sub.2
ppV 220 134.1 SO.sub.2
[0053] Due to an increase in the flow rate by 30% with a reduced
oil consumption, the plant capacity can be increased particularly
with reduced emissions by using microwaves which are irradiated
under an angle of inclination of 15.degree..
LIST OF REFERENCE NUMERALS
[0054] 1,1a fluidized-bed reactor [0055] 1c intermediate chamber
[0056] 2 conduit [0057] 3,3a fluidized layer, fluidized bed [0058]
4 gas distributor [0059] 4a conduits [0060] 4b distribution chamber
[0061] 4c grid [0062] 5 wave guide [0063] 6 conduit, secondary
gassing [0064] 7 microwave source [0065] 8 heat exchanger [0066] 9
conduit, gas outlet conduit [0067] 10 discharge conduit [0068] 11
principal axis [0069] 12 solids separator [0070] 13 return conduit
[0071] 14 discharge conduit [0072] 15 outlet conduit [0073] 16
waste heat boiler [0074] 17 dedusting [0075] 18 duct [0076] 19
weir, partition [0077] 20 opening [0078] 21 weir, partition [0079]
31 antechamber [0080] 32 intermediate chamber [0081] 33
intermediate chamber [0082] 34 cooling chamber [0083] 35 cooling
means [0084] 36 conduit [0085] 37 heat exchanger
* * * * *