U.S. patent application number 09/972684 was filed with the patent office on 2002-08-29 for mobile granular bed filtration apparatus for hot gas conditioning.
This patent application is currently assigned to UNIVERSITE' DE SHERBROOKE. Invention is credited to Abatzoglou, Nicolas, Bureau, Jacques, Chornet, Esteban, Mincic, Aca.
Application Number | 20020116908 09/972684 |
Document ID | / |
Family ID | 25680886 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020116908 |
Kind Code |
A1 |
Abatzoglou, Nicolas ; et
al. |
August 29, 2002 |
MOBILE GRANULAR BED FILTRATION APPARATUS FOR HOT GAS
CONDITIONING
Abstract
Provided herein is a granular filtration apparatus for the
removal of particulate material from hot gas by contacting said hot
gas with granular filtration material. The apparatus being of the
type having a filtration chamber containing granular filtration
material and having a tapered lower portion comprising at least one
inlet tubing for feeding therein hot gases to be filtered and at
least one outlet tubing for drawing filtered hot gas. The main
feature of the present invention consists in a filtration unit
mounted in the filtration chamber above each inlet tubing. The
filtration unit comprising a first tubular member mounted above the
inlet tubing so as to prevent granular material from entering or
blocking said inlet tubing and a second tubular member having a
bottom and a top end and being mounted essentially in a co-axial
and spaced relationship above the first tubular member. During
operation, the granular filtration material is siphoned up and
fluidized by the hot gases as they travel up the second tubular
member, the granular filtration material enters the bottom end of
the second tubular member through the space between the first and
second tubular member, exits at the top end of the of the second
tubular member and falls outside the second tubular member and
towards the tapered lower portion of the filtration chamber to be
eventually recirculated and fluidized by the hot gases.
Inventors: |
Abatzoglou, Nicolas; (Rock
Forest, CA) ; Bureau, Jacques; (Sherbrooke, CA)
; Mincic, Aca; (Ascot, CA) ; Chornet, Esteban;
(Sherbrooke, CA) |
Correspondence
Address: |
DARBY & DARBY P.C.
805 Third Avenue
New York
NY
10022
US
|
Assignee: |
UNIVERSITE' DE SHERBROOKE
|
Family ID: |
25680886 |
Appl. No.: |
09/972684 |
Filed: |
October 5, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09972684 |
Oct 5, 2001 |
|
|
|
PCT/CA00/00389 |
Apr 7, 2000 |
|
|
|
Current U.S.
Class: |
55/474 |
Current CPC
Class: |
B01D 2273/20 20130101;
B01D 50/20 20220101; B01D 50/002 20130101; B01D 46/38 20130101 |
Class at
Publication: |
55/474 |
International
Class: |
B01D 046/32 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 1999 |
CA |
2,268,376 |
Sep 2, 1999 |
ES |
9901970 |
Claims
The embodiments in which exclusive rights are claimed are:
1. A granular filtration apparatus for the removal of particulate
material from hot gas by contacting said hot gas with granular
filtration material, said apparatus being of the type having a
filtration chamber containing granular filtration material and
having a tapered lower portion comprising at least one inlet for
feeding therein hot gases to be filtered and at least one outlet
for drawing filtered hot gas, said granular filtration apparatus
comprising a filtration unit mounted in the filtration chamber
above each inlet, said filtration unit comprising: a first tubular
member mounted above the inlet so as to prevent granular material
from entering or blocking said inlet; a second tubular member
having a bottom and a top end, said second tubular member being
mounted essentially in a co-axial and spaced relationship above
said first tubular member; whereby during operation, the granular
filtration material is siphoned up and fluidized by the hot gases
as they travel up the second tubular member, the granular
filtration material enters the bottom end of the second tubular
member through the space between the first and second tubular
member, exits at the top end of the second tubular member and falls
outside the second tubular member and towards the tapered lower
portion of the filtration chamber to be eventually recirculated and
fluidized by the hot gases.
2. The apparatus of claim 1 wherein said filtration unit comprises
a single hot gas inlet.
3. The apparatus of claims 1 or 2 wherein said hot gas inlet
comprises a gas distribution plate comprising a plurality of gas
distribution tuyeres.
4. The apparatus of any of claims 1 to 3 wherein said filtration
vessel is essentially cylindrical and said lower portion of said
vessel is conical and tapers to a single gas inlet.
5. The apparatus of claim 4 wherein said first and second tubular
members are cylindrical.
6. The apparatus of claim 5 wherein said first tubular member is
fastened to said gas distribution plate.
7. The apparatus of claim 6 wherein said second tubular member is
fastened by support rods to said filtration vessel.
8. The apparatus of any of the above claims wherein the pressure
drop through the filtration apparatus, measured between gas inlet
and outlet, is about 0.05 to about 0.20 atm.
9. The apparatus of any of the above claims wherein said chamber is
internally lined with a suitable insulating or refractory material
so as to withstand operating conditions at temperatures at least as
high as 600.degree. C.
10. The apparatus of claim 1 wherein said gas inlet comprises a gas
distribution plate fastened to the tapered lower portion of said
filtration chamber, said gas distribution plate comprising a
plurality of gas distribution tuyeres so as to prevent granular
material from entering or blocking said inlet said gas distribution
plate being encased in a tubular member open at its top end whereby
during operation, the granular filtration material is kept away
from said gas distribution plate and entrained and fluidized by the
hot gases.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the treatment of hot gases
from either combustion, gasification or pyrolysis processes. More
specifically, the invention relates to a granular bed filtration
apparatus for conditioning the above said gases.
[0003] 2. Description of the Prior Art
[0004] Classical power plants and incinerators produce electrical
power by generating steam with hot combustion gases in a boiler and
using the steam to drive steam turbines. Advanced high efficiency
power generation methods are based on gasification or pyrolysis of
appropriate feedstocks and use of the resulting synthetic gas
either in burners coupled with gas turbines or in internal
combustion engines. The gas turbines fed with hot combustion gases
are prone to rapid deterioration because of particulate and
corrosive particles contained in the combustion gases. Thus, it is
necessary to filter and otherwise condition the hot combustion
gases before their entry into the power turbines.
[0005] In a preliminary treatment, hot gases exiting a combustion
chamber are generally submitted to a cyclonic treatment to remove
particulate material larger than about 10 .mu.m. Smaller particles
remain in the gas stream and must also be removed to avoid
corrosion, pitting and other deterioration of the turbines. These
smaller particles are the target of specialized hot gas
filters.
[0006] A variety of hot gas filters are known. One branch of prior
art is concerned with fixed bed filters. In a fixed bed filter, hot
gases pass through a mass of filtering granules. These filters
require frequent cleaning and regeneration of the filtering media
as the filters quickly become plugged.
[0007] Another branch of prior art is concerned with mobile bed
filtering equipment where the filtering granules are constantly
moved. Movement is generally achieved by pneumatic recirculation
and gravitational cascade between baffles. This technique allows
better interception of small particulate matter and allows
filtering granule regeneration without interrupting the filtering
operation. For example, U.S. Pat. No. 4,017,278 proposes the use of
two concentric vertical cylindrical parts. The inner wall being
perforated to permit only the passage of the gas while the outer
wall is appropriately louvered to allow particles passing through
with the gas while maintaining granular filtering material trapped
in the annular space and in continuous movement downwards. The
granules leaving the filter from the bottom of the filter being
recycled back pneumatically after being cleaned in a cyclonic
collector. However, the recirculation of filtration particles
requires additional energy and instrumentation.
[0008] Yet another branch of prior art is concerned with fluid-bed
filters. In fluid-bed filters, the filtering material is kept
fluidized by the flow of hot gas. For example, U.S. Pat. No.
4,157,959 proposes a three-stage filtration method. In a first
stage a cylindrical fixed bed of granules is used to filter out
particles from an upward flowing gas stream; during this operation
a particles layer (cake) is built at the bottom of the fixed bed,
which is kept immobile by means of an adjustable rod/plate
combination. In a second stage, the plate is raised, allowing the
particle bed to be converted to a bubbling fluidized one. The
filtration continues up to maximum allowable pressure drop
occurring when the filter requires cleaning. In the last and third
step, the filtering granules are regenerated. The main drawback of
such technique is the requirement for moving parts and the downtime
associated with filtering granule regeneration.
[0009] Thus, despite advances in the art, there remains an
important need for an improved hot gas filtration system capable of
overcoming the drawbacks of the prior art.
[0010] One object of the present invention is to provide a hot gas
filtration apparatus which combines the benefits of a mobile
granular filtration bed and a fluidized bed.
[0011] A further object is to provide a hot gas filtration
apparatus capable of operating at elevated temperatures and
preferably without moving parts and without the requirement for
recirculating pumps.
SUMMARY OF THE INVENTION
[0012] The present invention provides a granular filtration
apparatus for the removal of particulate material from hot gas by
contacting said hot gas with granular filtration material. The
apparatus being of the type having a filtration chamber containing
granular filtration material and having a tapered lower portion
comprising at least one inlet tubing for feeding therein hot gases
to be filtered and at least one outlet tubing for drawing filtered
hot gas. The main features of the present invention consist of a
filtration unit mounted in the filtration chamber above each inlet
tubing. The filtration unit comprising a first tubular member
mounted above the inlet tubing so as to prevent granular material
from entering or blocking said inlet tubing and a second tubular
member having a bottom and a top end and being mounted essentially
in a co-axial and spaced relationship above the first tubular
member. During operation, the granular filtration material is
siphoned up and fluidized by the hot gases as they travel up the
second tubular member, the granular filtration material enters the
bottom end of the second tubular member through the space between
the first and second tubular member, exits at the top end of the
second tubular member and falls to the tapered lower portion of the
filtration chamber to be eventually recirculated and fluidized by
the hot gases.
[0013] The invention also provides a novel gas inlet distribution
plate fastened between the bottom tapered portion of the filtration
chamber. The distribution plate is provided with a plurality of gas
distribution tuyeres and is encased with the first tubular member
as described above.
[0014] Other features and further scope of applicability of the
present invention will become apparent from the detailed
description given hereinafter. It should be understood, however,
that this detailed description, while indicating preferred
embodiments of the invention, is given by way of illustration only,
since various changes and modifications within the spirit and scope
of the invention will become apparent to those skilled in the
art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of the filter of the present
invention;
[0016] FIG. 2 is a top view of the filter;
[0017] FIG. 3 is a side elevation view of the filter;
[0018] FIG. 4 is cut-away perspective view of the filter showing
internal components;
[0019] FIG. 5 is a magnified view of FIG. 4 showing in detail the
hot gas feed to the filter;
[0020] FIG. 6 is a cross-sectional, side elevation view of the
filter, in operation;
[0021] FIG. 7 is pictorial representation of the gas sampling train
used to evaluate the particle retention efficiency of the
filter.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Before describing the present invention in detail, it is to
be understood that the invention is not limited in its application
to the details of construction and parts illustrated in the
accompanying drawings and described herein. The invention is
capable of other embodiments and of being practiced in various
ways. It is also to be understood that the phraseology or
terminology used herein is for the purpose of description and not
limitation.
[0023] The present invention provides a novel hot gas filter for
recuperating particulate matter in hot gas prior to its use. The
filter of the present invention combines the operation of a
fluidized bed filter with a slowly moving granular bed filter.
Thus, in operation, the filtration bed of the filter of the present
invention is mobile, homogenized and its surface is being renewed
continuously.
[0024] Unlike other mobile granular bed filters, the filter of the
present invention has no internal or external mobile mechanical
parts. This feature is advantageous since it avoids mechanical
sealing and operation failures due to high temperatures and
frequently chemically aggressive environments.
[0025] Now referring to the drawings, more specifically to FIGS. 1,
2 and 3 the present invention comprises a cylindrical vessel 10
with a conical shape bottom 12. The vessel contains granular
filtering material. Advantageously, the granular filtering material
can be quartz, preferably 24 mesh size, or sand, preferably of high
sphericity and preferably also 24 mesh size. Of course, other
granular filtration material may also be used.
[0026] A hot gas inlet 14 is operatively connected to bottom 12. A
filtered gas outlet 16 is situated in the vertical wall of vessel
10. It is to be understood that the number of gas inlets and
outlets is a function of the size of the vessel. For vessels of
diameter less than 1 m, 1-2 inlets and outlets are sufficient while
for bigger vessels, up to 4 outlets are recommended.
[0027] During installation, vessel 10 is moved into position while
suspended on loop 18. Anchor plates 20 secure the vessel to a rigid
holding structure (not shown).
[0028] Spent particulate material can be removed through pipe 22.
This removal can be assisted by backflushing pipes 24 which are
connected to a compressed air or inert gas source.
[0029] Referring now to FIG. 4, there is shown a cross-sectional
view of the inside of vessel 10.
[0030] Inlet 14 is provided with a gas distribution plate 26
comprising a number of tuyeres 28 favoring equal gas distribution.
Gas entering vessel 10 through tuyeres 28 travels up a tube 30
having on open top. Directly above tube 30 is tube 32, open at both
ends. Tubes 30 and 32 are co-axial and of equal diameter.
Fluidization of particulate filtration material takes place in
tubes 30 and 32. The vertical spacing between tubes 30 and 32 will
depend on the filtering material used and it usually varies between
5-10 cm. Highly spherical materials require a small amount of
vertical spacing while easily bridging granules necessitates a
greater vertical spacing.
[0031] Tube 30 is fastened to gas distribution plate 26. Tube 32 is
fastened to the internal wall of vessel 10 by support rods 34.
[0032] Although the preferred shape of tubes 30 and 32 is that of a
cylinder, it is to be understood that the exact shape of tubes 30
and 32 can be varied at will so long as the general shape remains
tubular. For example, cylinders 30 and 32 could have elliptical,
triangular or square cross-sections.
[0033] The exact position of gas outlet 16 including its height
from the bottom of the vessel is a function of various parameters.
These parameters include: the total height of the central fluid-bed
tubes 30 and 32, the vertical position of the spacing between the
tubes 30 and 32, the nature and total height of the bed of
filtering material. The successful operation of the filter depends
on an appropriate balance between head pressure and pressure loss
across the bed. Advantageously, the pressure drop across the
fluidized bed will be about 0,05 to 0,20 atm.
[0034] Referring now to FIG. 6, in operation, hot gas will enter
through tuyeres 28, travel up tube 30 and continue up tube 32. This
will effectively siphon granular material up tube 32 and form a
fluidized bed therein. As gas exits the top of tube 32, it will
entrain the fluidized granular material which will fall down
towards the bottom 12 of vessel 10. This will create a constant
recirculation of granular filtration material in vessel 10. Gas
exiting from outlet 16 will have had contact with granular material
going up tube 32 and falling down around tube 32. It is to be
understood that the dimensions of cylinder 32 will need to be
sufficient to ensure appropriate contact time between the gas and
the filtering granules. The contact time will preferably be about 2
seconds.
[0035] It is to be noted that some of the granules resting in the
bottom 12 of vessel 10 serve as a support material for the
fluidized granules rather than directly participate in the
filtration.
[0036] Thus, the novel hot gas filter uses an "impact" rather than
`surface layer` mechanism to filter particles of size down to 1
micron or less with high efficiencies. The entrained fluidized-bed
column advantageously a) continuously renews the filtering media
and b) homogenizes the bulk of the filtering media;
[0037] The novel filter apparatus is advantageously equipped with
an appropriate system of tubes, valves and automation
instrumentation ensuring its continuous operation, regeneration
cycles, and back flushes if need be. It is to be understood that
tube diameters will be sufficiently large to avoid fouling and that
inclination angles will also be selected to provide proper
operation. The materials used for making the various parts of
filtration vessel 10 will be selected for their capacity to
withstand erosion and high temperature regimes. Advantageously,
portions of the filtration vessel exposed to high temperature will
be lined with suitable insulating and refractory material.
[0038] Finally, as previously mentioned, vessel 10 is provided with
various back flushing pipes 24 bringing in back flushing air or
inert gas pulses. Pipes 24 are connected to gas outlet 16, the top
of vessel 10 and upstream of gas inlet 12. The purpose of flushing
pipes 24 is to periodically clean the inlets and outlets, when
necessary. The frequency of these flushes is a function of the
amount and nature of the material filtered out of the gas. In the
worst cases one flush per day was found to be sufficient.
EXAMPLES
[0039] The apparatus of the present invention was tested on a pilot
plant scale. Reference is now made to FIG. 7. The tests relate to
the filtration of a producer gas to remove particles. The gas comes
from a bubbling fluid bed gasifier fed with residual polyethylene.
The hot gas received a pretreatment in a primary cyclone used to
remove the coarser particles. The gasifier is fed with 30 kg of
Polyethylene per hour and air at a stoichiometric ratio of 0,3. It
operates at a temperature of about 760.degree. C. and produces
about 120Nm3 of producer gas/h. A slip stream of this gas, equal to
about 10% of the main flow is diverted through the mobile fed
filter, using a HIBON.left brkt-bot. liquid ring
suction/compression gas pump.
[0040] The examples presented below illustrate four different
tests:
[0041] a) low sphericity fresh quartz as filtering media;
[0042] b) high sphericity fresh Ottawa sand as filtering media;
[0043] c) high sphericity regenerated Ottawa sand as filtering
media;
[0044] d) behavior of filter with time.
[0045] Pilot tests were conducted at temperatures between 400 and
550.degree. C. Higher temperatures (up to 850.degree. C.) are
possible.
[0046] The tests showed that with high sphericity sands each
operation-regeneration cycle was approximately 60 hours and
consequently preferable over low sphericity sands where the
operation-regeneration cycle was about 24 hours.
[0047] To evaluate the filtration capabilities and efficiency of
the filter, the producer gas was sampled upstream and downstream of
the filter. For this purpose two identical isokinetic sampling
trains depicted in FIG. 7 were used. These samplers allow for both
particles and condensable tar evaluation. The particles are
retained by a glass fiber filter operated at temperature above
400.degree. C. This precaution was taken in order to avoid
deposition of high molecular weight condensable tar which could be
measured as particles and thus biasing the sampling results. In
order to check the filtration efficiency as function of the
filtration time dual samples were taken.
[0048] Table 1 below summarizes the main parameters and results of
these experiments.
1TABLE 1 Tests with novel Granular Mobile Bed Filter Parameters
Units Test 1 Test 2 Test 3 Test 4 Tests Code NA-38 NA-47 NA-49
& 53 NA-49 & 53 Date 04/20/98 07/29/98 09/01/98 12/01/98
Duration (h) 13 55 52 52 Sampling time (h) 9 to 12 1 to 3 4 to 8
45-48 Sampling duration (h) 3 3 3.5 3 Temperature (.degree. C.) 510
430 420 420 Gas flowrate (Nm3/h) 18 10 10 15 Pressure drop range
(kPa) 6.8-24.5 5.1-23.8 8.2-26.9 8.2-26.9 Filtering media Fresh
Quartz Fresh Ottawa Regen. Regen. (24 mesh) Sand (24 mesh) Ottawa
sand Ottawa sand (24 mesh) (24 mesh) Particles load before (mg/Nm3)
2994 5412 2482 3945 Particles load after (mg/Nm3) 73 300 148 227
Particles removal (% w/w) 97.6 94.5 94.0 94.2 Efficiency
[0049]
2 Example of head pressure balance calculations Units PRESSURE LOSS
ACROSS THE QUASI FIXED BED Granular media data Initial porosity
(fixed bed) .epsilon. 0,39 Diameter Dp 7,00E-04 m 0,0276 in Nature
Quartz 24 mesh Density Ps 2459 kg/m3 Test conditions Temperature T
20 .degree. C. Pressure P 103800 Pa Gas flow rate (normal
conditions) Qn 2,000E + 01 Nm3/h Gas flow rate (actual conditions)
Qa 0,0060 m3/s Mass velocity G 123,0 lb/h*ft2 Gas data Viscosity
.mu. 1,80E-05 Pa.s Density pg 1,29E + 00 kg/m3 Solids density ps
2,46E + 03 kg/m3 Quasi fixed-bed data Diameter DF 0,23 M Length L
0,32 M Hypothesis 1 Gas velocity constant along the bed 2 Turbulent
flow across the bed 3 K2 .infin. 150 (Ergun equation) 4 K4 .infin.
1,75 (Ergun equation) 5 Sphericity (y) 0,67 Preliminary
Calculations Actual flow rate Qa 0,006 m3/s m/s s Gas Velocity V
0,136 Residence Time T 2,358 Pressure losses .DELTA.P 3,5 Kpa (near
three times than through the fixed bed) PRESSURE LOSS ACROSS THE
QUASI FIXED BED Granular media data Initial porosity (fixed bed)
.epsilon. 0,39 Diameter Dp 7,00E-04 m 0,0276 in Nature Quartz 24
mesh Density Ps 2459 kg/m3 Test conditions Temperature T 20
.degree. C. Pressure P 103800 Pa Gas flow rate (normal conditions)
Qn 2,00E + 01 Nm3/h Gas flow rate (actual conditions) Qa 0,0060
m3/s Mass velocity G 123,0 lb/h*ft2 Gas data Viscosity .mu.
1,80E-05 Pa.s Density pg 1,29E + 00 kg/m3 Solids density ps 2,46E +
03 kg/m3 Fluid Bed Data Diameter Dlf 0,0762 m Length Llf 0,4 m Mass
velocity at minimum fluidization Gmf 173,80 lb/h*ft2 Reynolds
number Nre 6,49 Friction factor Fm 4 Shape factor _s 0,67 Void
space factor at minimum Emf 0,39 fluidization Exponent N 1
Preliminary Calculations Actual flow rate Qa 0,0060 m3/s m/s s Gas
Velocity V 1,3 Residence Time T 0,306 Pressure losses calculation
Pressure losses .DELTA.P 1,1 KPa
[0050] Advantageously, the filter of the present invention will be
mounted in parallel with similar units. Hence, one filter may be
temporarily decommissioned for maintenance purposes without
interrupting the production of hot gas from the gasifier.
[0051] Although the invention has been described above with respect
with one specific form, it will be evident to a person skilled in
the art that it may be modified and refined in various ways. It is
therefore wished to have it understood that the present invention
should not be limited in scope, except by the terms of the
following claims.
* * * * *