U.S. patent application number 11/810422 was filed with the patent office on 2008-12-04 for apparatus and method for top removal of granular material from a fluidized bed deposition reactor.
Invention is credited to Stephen Michael Lord.
Application Number | 20080299015 11/810422 |
Document ID | / |
Family ID | 40088456 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080299015 |
Kind Code |
A1 |
Lord; Stephen Michael |
December 4, 2008 |
Apparatus and method for top removal of granular material from a
fluidized bed deposition reactor
Abstract
Removal of the product from the top of the reactor enables a
decreased disengaging height and provides a passive means of
controlling the bed level despite deposition increasing the weight
and height of the bed. The savings from reducing the disengaging
height allow use of a taller fluidized bed in a shorter overall
reactor length and thus provides increased production with reduced
reactor cost. The separation of the gas inlet from the product
outlet allows the gas inlet area to be cooler than the product
outlet. The separation of the product grinding, caused by the inlet
gas, from the product outlet reduces the loss of seed in the
product and produces a more uniform product. Removing the hot
product and the hot gas at the same place allows energy recovery
from both in a single step.
Inventors: |
Lord; Stephen Michael;
(Encinitas, CA) |
Correspondence
Address: |
STEPHEN MICHAEL LORD
109 PEPPERTREE LANE
ENCINITAS
CA
92024
US
|
Family ID: |
40088456 |
Appl. No.: |
11/810422 |
Filed: |
June 4, 2007 |
Current U.S.
Class: |
422/145 |
Current CPC
Class: |
F27B 15/09 20130101;
B01J 2208/00761 20130101; B01J 2208/0061 20130101; B01J 8/0055
20130101; B01J 8/1809 20130101; B07B 9/00 20130101; B01J 8/0025
20130101; B01J 8/1836 20130101; F27D 17/008 20130101 |
Class at
Publication: |
422/145 |
International
Class: |
F27B 15/09 20060101
F27B015/09 |
Claims
1. An apparatus and method of operation for top removal of granular
material from a fluidized bed deposition reactor comprising: a
container of a set height with at least one gas inlet at or near
the bottom and at least one gas and solids outlet at or near the
top, a bed of granular particles of variable height which is
fluidized and deposited on by a gas flow, a gas/granular product
separator means and a method of operation where the height of the
bed of granular particles is allowed to increase until it reaches a
stable height.
2. An apparatus for recovering heat while separating the granular
product comprising: one or more product separator means and one or
more heat recovery means.
3. An apparatus of claim 1 where at least one means for granular
product removal is also provided at the bottom.
4. An apparatus of claim 2 where at least one of the heat recovery
means is primarily by radiation to a heat recovery boiler.
5. An apparatus of claim 2 where more than one separator means are
used to provide more than one product streams of different average
particle size.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
DESCRIPTION OF ATTACHED APPENDIX
[0003] Not Applicable
BACKGROUND OF THE INVENTION
[0004] This invention relates generally to the field of deposition
reactors and more specifically to an apparatus and method for top
removal of granular material from a fluidized bed deposition
reactor.
[0005] Fluidized bed reactors have a long tradition in the chemical
industry where the bed usually consists of a finely divided
valuable catalyst which makes it necessary to design the reactors
to prevent catalyst losses. Thus was developed the practice of
requiring a large disengaging height above the bed surface and of
using cyclones to capture the fine dust and return it to the bed. A
concept called total disengaging height, or TDH, was developed to
estimate the height where all the particles that would settle out
by gravity had settled out. Internal cyclones were provided at this
height to capture the finer dust and return it to the bed. Whenever
the catalyst was removed it was removed from the bottom by gravity.
Other reactors called dilute phase or transport reactors entrained
all the solids up through the reactor and out the top, but these
reactors did not have a recognizable bed. When these gas-solids
reactor concepts were applied to the design of deposition reactors
where gases are introduced to make the bed particles grow, the
dilute phase reactor had the major problem that it produced mainly
a fine dust which was undesirable. Thus the majority of deposition
reactors have been fluidized beds and so the basic design of
fluidized beds with a large disengaging height and bottom solids
outlet has been used. The idea of internal cyclones has seldom been
used because of the deposition on the outside of the cyclones and
the problems of reintroducing particles without plugging the
cyclone outlets. Since some fine dust is always made, most
deposition reactors have external cyclones or filters to trap the
dust and prevent damage to the equipment used to recover the
effluent gases. Thus the historic approach has been to have removal
of the product from the bottom, provide a large disengaging height
to minimize product loss, and use external dust removal. The
primary use for deposition reactors is in high purity silicon
deposition and Lord in U.S. Pat. No. 6,451,277 in FIG. 1b describes
a bed heating method which removes beads from near the top of the
bed and then heats them and returns them to the bed. It is notable
that the product, 3, is still removed from the bottom. In the above
patent this bed heating method is rejected in favor of a preferred
option where the beads are removed by gravity from the bottom then
reheated and returned to the bed in a pulsed mode. Lord in U.S.
Pat. No. 6,827,786 provides a detailed description of a multistage
deposition reactor which takes advantage of increased bed height to
produce additional silicon by use of additional gas injection
points along the side of the reactor. In this design the seed
generation by grinding is spread out along the reactor because of
the extra nozzles and some deposition occurs further from the
inlet, but most of the grinding and deposition occurs in the bottom
where the solid product is removed. Lord discusses, Col3 line 25,
the "De Beers" paper which showed the need for some residence time
and temperature to fully crystallize the product and dehydrogenate
the beads. He does this in the pulsed bead heater at high
temperature and with short residence time. Lord and his many
references do not discuss energy recovery from the effluent gas
although Lord in U.S. Pat. No. 5,798,137 and 6,451,277 discusses
the use of the heat from the outgoing product to heat the incoming
gas.
[0006] The primary deficiency of the prior technology is staying
with the inherited fluid bed design of a bottom outlet and large
disengaging space and accepting the inherent conflicting demands
caused by introducing the cold deposition gas, which also provides
the bulk of the seed generation by grinding, at the same location
as the hot product was removed. Lord in various patents attempts to
deal with the heat and seed generation problem by spreading out the
gas injection, but sufficient gas to fully fluidize the bed must be
injected at the bottom, so there is a limit to what can be
accomplished in this manner. Inevitably the bottom temperature must
be maintained above 800.degree. C. to provide the needed
crystallization, and some seeds are lost to the product which is in
turn contaminated with broken "seed beads." The combination of high
temperature and high deposition gas concentration leads to rapid
reactions, increased wall deposits and increased risk of
agglomeration and plugging.
[0007] This multistage design approach also leads to tall reactors
and there are cost and manufacturability issues in producing the
high purity liners for such reactors which restrict the number of
stages and hence production capacity of a given diameter reactor.
It is also necessary to measure the bed level and take corrective
action by removing some of the bed as the bed grows by opening
valves and changing purge flows to allow the right amount of beads
to leave the bed. Errors or stuck valves can lead to situations
where the bed is too high or too low. Both of these conditions are
undesirable upsets.
BRIEF SUMMARY OF THE INVENTION
[0008] The primary object of the invention is to provide a shorter
reactor with greater production.
[0009] Another object of the invention is to provide a passive
method of level control.
[0010] Another object of the invention is to provide a better
quality product.
[0011] A further object of the invention is to reduce the need for
high temperature at the bottom of the reactor.
[0012] Yet another object of the invention is to reduce the risk of
plugging.
[0013] Still yet another object of the invention is to reduce the
thickness of wall deposits.
[0014] Another object of the invention is to reduce the pressure in
the product removal system.
[0015] Another object of the invention is to recover energy.
[0016] Other objects and advantages of the present invention will
become apparent from the following descriptions, taken in
connection with the accompanying drawings, wherein, by way of
illustration and example, an embodiment of the present invention is
disclosed.
[0017] In accordance with a preferred embodiment of the invention,
there is disclosed an apparatus and method for top removal of
granular material from a fluidized bed deposition reactor
comprising: removal of the product from the top of the reactor
together with the effluent gas, separation of the granular product
from the effluent gas, simultaneous recovery of heat from the
product and the gas and optional further dust and heat
recovery.
[0018] The technical benefits of this design are passive level
control, decreased disengaging height, taller fluidized bed in a
shorter reactor, separation of gas inlet from product outlet,
separation of product grinding from product outlet and energy
recovery which in turn lead to lower capital and operating cost, a
better quality product and greater throughput for a given reactor
diameter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The drawings constitute a part of this specification and
include exemplary embodiments of the invention, which may be
embodied in various forms. It is to be understood that in some
instances various aspects of the invention may be shown exaggerated
or enlarged to facilitate an understanding of the invention.
[0020] FIG. 1 is a schematic diagram illustrating the operation of
a fluidized bed deposition reactor of the prior art with bottom
removal and a large disengaging space.
[0021] FIG. 2a is the same diagram modified to show the benefits of
the invention.
[0022] FIG. 2b is a detailed schematic of the top of the reactor
showing the granular particle removal mechanism.
[0023] FIG. 3 is a schematic of a product separator with integrated
heat recovery.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Detailed descriptions of the preferred embodiments are
provided herein. It is to be understood, however, that the present
invention may be embodied in various forms. Therefore, specific
details disclosed herein are not to be interpreted as limiting, but
rather as a basis for the claims and as a representative basis for
teaching one skilled in the art to employ the present invention in
virtually any appropriately detailed system, structure or
manner.
[0025] Turning first to FIG. 1 there is shown a schematic of a
typical fluidized bed deposition reactor comprising a containment
vessel or liner, 111, of a height, 144, a gas introduction means,
112, an optional gas distribution means, 113, a bottom product
removal means, 114, a bed heating means, 115, a gas/dust mixture
exit, 116, a connecting means, 127, a dust/gas separation means,
117, a dust removal means, 118, and a gas exit, 119. The
containment vessel, 111, surrounds a bed of granules, 120,
fluidized by gas bubbles, 121, and having an average top level,
122, above which product granules, 123, thrown up above the bed
describe arcs as they rise from random impact within the bed then
fall under gravity in a reduced disengaging space, 124, while the
small entrained dust particles, 125, continue up and leave with the
effluent gas, 126, through the gas/dust mixture exit, 116, through
the connecting means, 127, then enter the dust/gas separation
means, 117, where most of the dust, 125, is removed from the gas,
126, and then ultimately leaves the system via the dust removal
means, 118, while the gas, 126, and residual dust leaves via an
exit, 119. The differential pressure meter, 128, measures the
difference in pressure between the bottom product removal means,
114, and the gas exit, 119. This measurement indicates the level,
122, of the bed of granules, 120. The bottom removal means, 114, is
used to control the top level, 122, to maintain the disengaging
space, 124, so that the product granules, 123, are returned to the
bed of granules, 120, and are thus removed by the bottom product
removal means, 114. This is a very general schematic and the patent
literature is full of the various methods and machines that have
been proposed to fulfill these requirements. It is possible to have
more than one gas entry and to avoid the gas distribution
mechanism; the heating means can be of many different kinds, and
the dust removal can be done by a cyclone as shown, by a filter or
by another gas cleaning device.
[0026] In accordance with the present invention, FIG. 2a shows a
schematic similar to FIG. 1 but modified to remove the granular
product from the top via a gas/granular separator means, 230,
inserted before the effluent gas enters the gas/dust separation
means, 217. A further modification is the removal of the
differential pressure transmitter, 128, shown in FIG. 1, which is
not required for bed level control. The invention thus comprises a
containment vessel or liner, 211, of a height, 244, a gas
introduction means, 212, an optional gas distribution means, 213,
an optional bottom product removal means, 214, a bed heating means,
215, a gas/dust/granular mixture exit, 216, a first connecting
means, 241, a gas/granular separator means, 230, with a granular
removal means, 231, an optional heat recovery means, 242, a further
connecting means, 229, a gas/dust separation means, 217, a further
optional heat recovery means, 243, a dust removal means, 218, and a
gas exit, 219. The containment vessel, 211, surrounds a bed of
granules, 220, fluidized by gas bubbles, 221, and slugs, 240, and
having an average top level, 222, above which some granules, 223,
thrown up above the bed describe arcs as they rise from random
impact within the bed then fall under gravity in a reduced
disengaging space, 224, while some granules, 236, and the small
entrained dust particles, 225, continue up and leave with the
effluent gas, 233, through the gas/dust/granular mixture exit, 216,
the connecting means, 241, and into the gas/granular separator
means, 230, where the granules are removed via the granular removal
means, 231. The remaining gas and dust leave through the gas/dust
top exit tube, 229, then enter the gas/dust separation means, 217,
where most of the dust, 225, is removed from the gas, 233, and
ultimately leaves the system via the dust removal means, 218, while
the gas, 233, and residual dust leaves via an exit, 219.
[0027] To accomplish the removal of large granules the average top
level, 222, is very close to the gas/dust/granular mixture exit,
216, and consequently some of the product granules, 236, thrown up
above the bed do not describe arcs as they rise then fall under
gravity in the disengaging space, 224, but continue with the
entrained dust, 225, out the gas/dust/granular mixture exit, 216.
Since the average bed level, 222, is closer to the exit, 216, the
bed level, 222, can be taller and/or the overall height, 244, can
be shorter compared to the prior art as shown in FIG. 1.
[0028] Turning to FIG. 2b there is shown in detail the various
mechanisms which cause the product granules, 236, to be carried out
the gas exit, 216. The basic mechanism is the random ejection of
product granules, 236, from the top of the bed, 222, and the
pneumatic conveying of these granules out the gas/dust/granular
exit, 216. In addition the bed level oscillates up and down due to
the formation of gas slugs, 240, which lift sections of the bed up
to the high level, 232, until they break through and the bed level
recedes to the low level, 234. It is also possible for the bed to
reach extra high levels, 235, where the bed is above the exit
briefly. The exit tube, 241, can be attached to the exit, 216, at
90.degree. as shown or sloped above or below the horizontal. The
angle chosen can be determined by the application of standard
pneumatic conveying calculations using the gas velocity in the exit
tube, 241.
[0029] Turning now to FIG. 3 there is shown a more detailed
schematic of a product separator, 330, with an integrated heat
recovery system, 301, suitable for high temperature and high purity
applications. The gas/dust/granular mixture, 333, enters the
product separator, 330, through an inlet, 357, which goes through
the heat recovery system, 301, via a penetration, 358; the gas and
dust, 356, then separate to the top and exit via the exit tube,
329, while the granules, 336, separate to the bottom exit, 331,
where it is fluidized by a purge stream, 359, and withdrawn as
needed.
[0030] The heat recovery system, 301, is comprised of a heat
transfer fluid, 360, contained in a container, 351, which is shaped
to capture heat, 350, from the wall of the product separator and
has an inlet, 354, and an outlet, 355, for the heat transfer fluid,
360. The container can use various heat transfer fluids such as
water or hot oil. It is usually advantageous for the container to
be a pressure vessel to permit heat recovery at higher
temperatures. The heat may be transferred from the wall to the
container by radiation, conduction or convection and well-known
heat transfer techniques can be used to enhance the heat transfer
from the gas and solids to the wall. Similarly, well-known
gas-solids removal techniques, such as cyclones or filters, can be
used to enhance the gas-solids separation.
[0031] In a particularly advantageous design, the heat is
transferred by radiation from the hot surface of the product
separator to a pressurized container which has water, 352, coming
in through the inlet, 354, and steam, 353, leaving through the
exit, 355.
[0032] An example using FIG. 2 would be as follows. The diameter of
the container is 300 mm, the overall height of the liner, 244, is 7
meters, the average bed level, 222, is 6 meters, the high level is
about 6.6 meters and the low level is about 5.4 meters. The gas
superficial velocity at the top of the container is 4.7 ft/s (1.4
m/s). The average particle size of the granules is 1 mm and the
terminal velocity is 21.8 ft/s (6.56 m/s). The particle terminal
velocity is thus about 4 times the superficial gas velocity. This
means that in order to carry the granules out of the reactor, the
local velocity in areas just above the bed must have local surges
where it is 4 times higher than average. Velocity surges of this
magnitude occur close to the top of the bed at about 20 cm above
the bed. The slug, 240, has a maximum length of about 1.2 meter,
and so the periodic growth and bursting of the slug provides the
variation in height of 1.2 meters between low and high level. As
the slug bursts, it also accelerates the granular particles which
are. then entrained out of the reactor. Thus the granular removal
varies with the pulsing of the slugs, 240
[0033] In comparison, for FIG. 1 under similar operating conditions
with an average bed level, 122, of 6 meters, the overall height
would be 10 meters in order to allow for the disengaging space
normally required under the prior art.
[0034] The granules and gas at the bottom of the reactor are at
700.degree. C., then are heated up and leave the reactor as stream,
233, via exit, 216, at a temperature of 800.degree. C. They enter
the cyclonic product separator, 230, through a tangential inlet
which forces the gas and solids to the wall of the vessel to
improve gas to wall heat transfer. The diameter of the cyclone is
10 inches (250 mm) and the length is 6 ft (1.8 m). This is longer
than needed for solely the solids removal in order to provide
sufficient surface area for heat transfer. The gas and granules
both leave at 600.degree. C. The dust/gas separator, 217, is of a
similar size but only removes about half the heat because of the
reduction in the temperature difference. The gas and dust then
leave the dust/gas separator at 500.degree. C. Both heat recovery
systems recover the heat as 150 psig steam, which is a standard
utility useful in the facility for a variety of purposes and thus
always in demand.
[0035] While the invention has been described in connection with a
preferred embodiment, it is not intended to limit the scope of the
invention to the particular form set forth, but on the contrary, it
is intended to cover such alternatives, modifications, and
equivalents as may be included within the spirit and scope of the
invention as defined by the appended claims.
* * * * *