Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the treatment of gases for the
removal of acid gases before release of the gases into the
atmosphere.
In the United States Patent No. 3,721l066 and United States
Patent No. 3,808,774, description is made of the use of a mineral
nahcolite as an absorbent and/or reactant for the removal of acid
gases from a gaseous stream passed into contact therewith. For
this purpose, the nahco].ite, in finely divided form, is deposited
to provide a highly pervious layer on the ingoing side of a filter
surface through which the gaseous system is drawn.
To form the layer of nahcolite on the ingoing side of the
filter surface, use can be made of procedures described in the
United States Pring patents No. 2,875,844, No. 2,875,847, and
No. 2,919,174, wherein the finely divided absorbent or reactant
particles are introduced for suspension into the gaseous stream
drawn through the filter medium whereby removal of gaseous
components is effected while the particulate material is in contact
with the gaseous stream during suspension and whereby the par-
ticulate material is carried by the gaseous stream for separation .
onto the ingoing side of the filter surface as the gaseous stream
. passes therethrough. This forms a layer of particulate material on
the ingoing side of the filter mediumO In this location, the
particulate material is in a position to be engaged by the
. through-going gaseous stream to effect removal of acid gases from -
the gaseous stream as it passes through the deposited layer.
In United States Patents No. 3,808,774 and No. 3,721,066,
.: description is made of the use of nepheline syenite as a reactant
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built up on the ingoing side of a filter surface for reaction to
remove acid gases from gaseous streams passing therethrough. As
described in the aforementioned patents, the activity of the
nepheline syenite, in the removal of acid gases, is increased by
wetting the nepheline syenite or by pre-exposure of the nepheline
syenite to moisture or high humidity. For this purpose, the
nepheline syenite is either wet before introduction to provide
the layer on the ingoing side of the filter surface or else
moisture is introduced into the gaseous stream in which the
nepheline syenite is suspended for building up the layer of
particulate material on the filter surface. In either event,
additional equipment is required to achieve the desired wetting
of the nepheline syenite, and until the desired amount of wetting
has been achieved for optimum efficiency, a considerable amount of
gas has been exhausted into the atmosphere which contains
undesirable amounts of acid gas.
Further, it has been found that the removal of acid gases
by either technique is not optimized until a layer of the desired
thickness of the particulate material has been built up on the
ingoing side of the filter surface and the particulate material in
the layer has been actuated for optimum acid gas removal. Thus,
penetration of the acid gases is highest when the filter surface
~` is ~eing brought back on-stream after cleaning and such penetration
diminishes as the layer is built up to the desired thickness and
defects in the filter layer are repaired and while the particulate
~ material in the layer is being treated to optimum removal
i~ efficiency.
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This invention relates to an improvement in the method for
reloading a filter surface for use in the removal of acid gases
from a gaseous stream during a normal filter cycle in which the
acid gases are removed by absorption or reaction during passage
of the gaseous stream through a layer of particulate material
built up on the ingoing side of a filter surface in which the
layer of particulate material is periodically removed from the
filter surface, the rebuilding of the layer of particulate material
on the ingoing side of the filter surface after the spent layer has
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` 10 been removed, comprising introducing the particulate treating
material into a gaseous stream for suspension of the treating
material therein, flowing the gaseous stream with the suspension
of treating material through the filter surface for separation of ~;
the particulate treating material onto the ingoing side of the
; filter surface until a layer of the desired thickness has been built
~ up on the ingoing side of the filter surface, recirculating filtered
~ gas during buildup of the layer, continuing the recirculation a~ter
the layer has been huilt up until the efficiency of the particulate
material for removal of acid gases has been optimized and then
: 20 discontinuing the recirculation of filtered gas.
~ This invention further relates to an apparatus for carrying
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" out the process of this invention comprising a filter housing
subdivided into a plurality of filter sections each of which has
an inlet plenum chamber into which the gases to be treated are
introduced and a clean gas plenum chamber which receives the gases
` after treatment, a plurality of filter elements within each section
. in which the ingoing sides of the filter elements communicate with
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the inlet plenum chamber and the outgoiny sides of the filter
elements communicate with the clean gas plenum chamber and means
for causing the gaseous stream to circulate through the sections
from the inlet plenum chamber, through the filter elements, to the
clean gas plenum chamber~ means for removing one section from the
normal filter flow for cleaning the filter elements and for
rebuilding the layer of particulate material on the filter elements
including for each section means for introducing the particulate
materia]. into the gas stream introduced into the inlet plenum
chamber whereby the particulate material is carried by the gas
stream to the ingoing side of the filter elements for separation
thereon to form a layer of the particulate material on the ingoing
side of the filter elements, a header common to the clean gas
plenum chambers of the plurality of filter sections, and means for
bleeding off a portion of the cleaned gas from the header for
recirculation to the filter section for pre-treatment of the
particulate material in the layer deposited on the ingoing side
of the filter elements to optimize acid gas removal.
It is a purpose of this invention to pro~ide a method
and apparatus for providing a layer of particulate absorbent
and/or reactant for the removal of acid gases from a gas
stream filtering therethrough, wherein the filtered gas is
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not released into the atmosphere until the desired mass and
integrity of the layer h~s been achieved and the particulate
~ material in the layer has been treated in a manner to tmprove
.: its efficiency for acid gas removal.
5 . These and other objects and advantages of this inven- -
tion will hereinafter appear and for purposes of illustration,
-~ but not of limitation, embodiments of the invention are s~o~m
in the accompanying drawings, in which:
Fig. 1 ~s a schematic flow diagram of a gas treating
system in which the interior of the fil~er tubes represent
the ingoing side of the filter surface and a shaker mechanism
~ is used to effect removal o~ the l~yer of particulate naterial ,
~ for replacement with a fresh increment;
: Fig. 2 is a cross-section of the filter tube, sh.owing
the layer of particulate material on tt~e ~ngoing side thereof
and
Fig. 3 is a fLow diagram illustrating a preferred
.;~ practice of this invention. :~
Briefly described, the invention comprises removal
; 20 of the filter surface from the normal filter stream for remo~ -~
. val of the filter cake, and then reloading the filLer surface
by introducing the particulate treating material for suspen-
. sion in the gaseous stream, and circulati~ng the gaseous stream
through the filter surface to build up t~e layer of particu-
late material on the ingoing side as the gaseous stream filters
therethrough until a layer of the desired thiclcness ~as been
built up on the filter surface, recirculating the filtered gas :
during buildup of the layer of particulate material and after
; the layer has been built up until the removal ef~iciency of
the particulate material has been optimized ~y pre-treatment
in which use is made of the recirculating gas stream.
The invention will first be described as applied to
,he use of nahcolite, as representative of minerals or other
particulate materials in which ac-tivation is increased when
heated to elevated temperature. It will be apparent that the
basic concept of this invention will have application also to
the pre-treatment of nepheline syenite and similar minerals or
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other particulates that are increased in activity by pre-
treatment to increase the temperature> moisture or other~7ise.
With nahcolite, utilization is made of the gas to be
cleaned, or cleaned gas, as the carrier in which the nahcolite
is suspended for transport to the filter surface ~Jhere the
particulate material separates out on the ingoing side to
form the layer as the gas filters therethrough. Such intro-
duction of particulate material is cGntinued until a layer of
the desired thickness has been built up on the filter surface
with the continuous recycle of the filter gas. ~ecycle of
filtered gas is continued after the introduction of particulate
material has been terminated to supply the additional heat for
; raising the nahcolite to operating temperature for optimum
; removal of acid gases. Thereafter, the filter section can ~e
returned to the normal filter cycle.
For this purpose, the hot gases issuing from the clean
gas plenum chamber of the gas treating unit are recirculated
~;~ with means for introducing the particulate material into the
recirculating gas stream whereby the particulate ma~erial is
conveyed for deposition to form the treated layer on the-in-
'i going side of the filter surface. When the particulate mater-
~l ial has been introduced in an amount to build u~-a layer of
i the desired thickness on the ingoing side of the filter sur-
: face, the introduction o particulate material is discontin-
ued while recirculation of the hot cleaned gas is continued
` until the layer of particulate ma~erial has been heated to
elevated temperature for optimum utilization in the removal
, of acid gases. Thereafter, recirculation oE cleaned gas is
i~ discontinued and the unit is returned on~stream to form a ` ;-
~ 30 part of the operating cycle for the processing of gases before
; exhaust into the atmospllere.
;, Referring now to the modification shown in Fig, 1,
; the numeral 10 indicates a gas treatment sectlon having a
bottom wall 12 in the form of a cell plate which separates
the section into an equalizing gas chamber 14 and a bag house
16. The equalizing chamber 14 comm~nicates directly with an
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inlet plenum ch~mber 18 having an inlet 20 through which the gas to
be treated is introduced into the section from a conduit 21.
A collecting hopper 22 communicates with the underside of
the equalizing chamber 14. An outlet opening 24 and closure 26
are provided at the bottom of the hopper for the removal of solids
collected in the hopper.
Each section of the plurality of sections making up the
assembly is provided wi-th a plurality of filter tubes 28 formed of
natural fibers, such as cotton and the like, and preferably of
synthetic fibers, such as Nylon(a trade mark for a polyamide
resin~, Dacron (a trade mark for a polyester resin), glass fibers
and the like high temperature resistant fibers, woven or non-woven
into a porous filter fabric. The upper ends of the ~ilter tubes
.......... 28 are closed with a loop for suspension by angle rods 32 from
shaker bars 34 which extend crosswise of the section. Means, such
as a motor 36 and eccentric 36' are operatively connected to the
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bars to impart a rocking mo~ement which causes the tubes to be
whipped in a manner to loosen any accumulated layer 38 of
;` particulate material on the ingoing side of the filter surface.
~: 20 For a more detailed description of a suitable device operating on
the shaker principle, reference can be made to United States Patent
` No. 2,879,863 and United States Patent No. 2,932,362. The lower
ends of the filter tubes 28 are anchored by rings or collars 40 to
~ the cell plate 12 in communication with openings 40 extending
- therethrough.
The portion of the bag house 16 outside of the filter
~ tube constitutes the clean gas plenum chamber 44 having an outlet
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opening 46 leading into conduit 48. The latter communicates
with an exhaust fan 50, in normal filter flow, for causing the
gas to be drawn into the section, through the filter tubes and
into the clean gas plenum chamber. It will be understood that
the exhaust fan or blower may be located other than in the
conduit 48, it being desirable to locate the blower for inducing
subatmospheric conditions within the clean air plenum chamber for
circulation of the gases in the desired direction through the gas
treating unit.
In Figure 1, illustration is made of a single treating
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section. It will be understood that the system is preferably
formed of two or more such sections, eacll of which is se~ar-
ately fed with the gas to be treated from a common header but
wit-h the clean gas plenum chanbers interconnected for exhaust
by a single unit. Thus one section can be cut off from the
normal flow of gases to be treated while the other sections
remain on stream.
In accordance with the practi.ce of this invention, a
bypass in the form of a conduit 52 communicates the outle~
conduit 48 with the inlet conduit 21, with the by~ass being
located beyond the blower. Blocking means, such as a damper
-54, is mounted for rocking movement about a pivot 56 between
open position, shown in solid lines in Fig. 1, and closed posi-
tion, shown ~n broken lines i~ Fig. 1. In the open position,
the damper 54 shuts off the bypass and leaves ~he condui~ 48
open for exhaust of the cleaned gas into the atmosphere. In
closed position, the passage to the atmos~here is blocked by
damper 54 while the bypass is open to enable the hot cleaned
` gases from the conduit 48 to pass :through the bypass and into
the conduit 21.
' A blocking means, in the form of a damper plate 58, ;~
; is also provided at the juncture of the bypass w~th th~ con-
duit 21 with means for actuation to block off the bypass when
in open position and to open the bypass and block off the con-
~ 25 duit 21 when in closed position.
: ~ A storage bin or hopper 60 containing nahcolite 62 -
in finely divided form is provided with an outlet 64 communi-
cating with the conduit 21 between the inlet 20 and the by-
pass 52. A valve means of conventional construction is pro-
; 30 vided at the outlet for controlling the flow of nahcolite from
the hopper into the conduit.
In a normal cycle of operation, the filter tubes 28
are lined internally with a removable layer 66 of nahcolite.
With the dam~ers 54 and 5g in open position, gas to
be treated is dra~7n through conduit 21, into the inlet plenum
chamber 18, through the equalizing cham~er 14 and into the
open ends of the filter tubes 28. ~s the gas is drawn through :~
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the filter tubes from the inside to the outside, acid gases
are extracted by the nahcolite and particulate matter, if any,
is filtered out so that cleaned gas passes through the filter
tubes into ~he clean gas plenum chamber from which it is drawn
by the blower 50 through the conduit 48 for release into the
atmosphere. The gases treated are usually the effluent gases
from a power plant or other exhaust from the burning of fossil
or gaseous fuel wherein the effluent gases are at a sufficiently
high temperature to maintain nahcolite at efficient operating
lQ temperature such as within the range of 180Q-550F.
~en the ability of the nahcolite to remove acid
gases from the gaseous stream passing into contact therewith
has become substantially exhausted, such as after 20-60 minutes
of operation, or when the pressure drop across the filter ele-
ment becomes excessive because of the buildup o~ the filter
cakeJ the section is relegated to a cleaning cycle in which
` the bags are shaken to loosen the layer of particulate material ~ `
on the ingoing side of the filter surface. The loosened parti-
culate material falls gravitationally into the hopper ~or
removal from the system.
During the cleaning cycle, gas flow is discontinued
by closure of damper 58 in the line 21 leading to the section
; to be cleaned, while dampers S~ remain open to permit the flow
of gas to be cleaned to each o~ the other sections.
Before the cleaned section îs returned on streamJ a
~- layer of nahcolite is reformed on the ingoing side of the fil-
ter tubes. In accordance wi.th the p-f actice of this invention,
this is accomplished by closing the damper 54 whereby clean
hot gas from the other sections is combined with the cleaned
gas recirculating in one section for passage through the by~ ;~
pass 52, the passage 21, and lnto theinlet 20 and cham~ers18
and 14 and then through the filter tubes. The gate valve 64
is opened for introduction o nahcolite which becomes suspended
in the gas stream passing through conduit 21 and from which
it is separated to reEorm the layer of nahcolite on the in-
golng side of the filter tubes as the gases filter there-
through. When a layer of the desired thickness has been built
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: up on the ingoing side of the filter tubes, the valve 64 is
closed while recirculation o the hot cleaned gases is con-
:`: tinued until the temperature of the nahcolite in ~he built
up layer has been raised to the desired ~emperatur~ for efi-
~ 5 cient and effective removal of acid gases, such as to a tem-
,~'' perature within the range of 180-550F.
Such additional heating by the recirculated hot
:` cleaned gas will often take 5-15 minutes after the layer has
'` been deposited thereby to provide for a reloading cycle of
~'~ 10 about 10-15 minutes in total. Thereafter the section can be
:~ returned on stream by opening the dampers 5~,and 58.
.," A multiple filter section of the ~ype preferred is
~: . illustrated in Fig. 3 wherein the filter elements are arranged
'~ ' in separate compartments A, B, C and D. Each c.ompartment has , '~
,'~ 15 its own damper 58a for controlling normal filter flow from -'
header 70 into the compartment and each compartment also'has
~ its own da,mper 58b for controlling flow of bypassed gas from
.,, header 82 which communicates with chamber 78 into which by-
.~ passed gas is circulated by bypass line 76. Nahcolite is
"'~, 20 introduced into chamber 78 from hopper ~0. The exhaust from , ~:
each of the compartments is combined-in header 48a for exhaust ~.
~ into the atmosphere by exhauster 50 or for recycle through ~y- ~`
,' pass 76, as heretofore described. In this instance, the
::' exhauster 90 in the bypass 76 draws off enough of the cleaned
-, 25 gas from the header 48a to handle one compartment. ';
~hen damper 52a is open, damper 58b to the same com-
.~ partment is closed to enable normal flow of gas to be cleaned ~'
to the compartment. I~hen damper 58a îs closed then damper 58b
~ to the same compartment is open.to shut off normal filter flow
,~ 30 and for enabling passage of bypass gas from the header 82 into ,.
the compartment. :
It will be apparent that the system described pro-
vides for reloading and heating of the nahcolite, withou.t the
: need for additional equipment or space and that deposition of
nahcolite to orm the operative layer is effected with clean
gas as it is generated during operation of the equipmen~. More
importantly, the heat used to raise the temperature of the
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nahcolite to a level for most efficient removal of acid gases
represents residual heat in the recirculating cleaned gas that
would otherwise be wasted into the atmosphere. In a four sec-
tion system, operating on a one hour cycle, it will be appar-
ent that three sections can be "on stream" while one section is
in the cleaning and regenerating cycle using the clean hot gases
- from the sec~ions that are on stream.
~hen use is made of nepheline syenite as the ~ar~icu~
late material, the same concepts can be employed or pre-treat-
ment of the particulate material to increase the moisture con-
~' tent. Thus the buildup of the layer of nepheline syenite on
the ingoing side of the filter surface can be achieved in the
same manner as described for nahcolite. ~lowever, instead of
merely recirculating the gases passing through the filter sur-
face, means are provided for introducing moisture into the
~ gas stream to increase the moisture content of the recircu-
'~! lated gases whereby the moisture content of the nepheline sye-
nite in the already deposited layer is also increased. I~hen
; the desired amount of moisture-content has been achieved for
optimum removal of acid gases by the nepheline syenite in the
, deposited layer, the recycle o clean gas can be discontinued
and the filter section returned to the normal filter cycle.
For this purpose, means would be provided for intro-
ducing moisture, as by spraying, into line 21. Such introduc- ;`
tion of moisture would be carried ou~ while ~he particulate
material is introduced for suspension into the gas stream to
be treated or recycled gas, and into the recycled gas after
the in~roduction of particulate ~aterial has been discontin-
ued.
Similarly, in the modification shown in Fig. 3, the
moisture would be introduced as by means of a spray ~6 into
the chamber 78 or else in lines 76 or ~2, during the intro-
duction of particulate material for suspension in the recycled
clean gas stream and af-terwards, until the moisture content
of the nepheLine syenite in the deposited layer has been
raised to the desired level. Thereafter the filter section
woula - e returned on stream.
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It will be understood that the concepts of this inven-
ion will have application to the pre-treatment of other mater-
'' 21s used in the removal of contaminated gases wherei.n the
re~oval efficiency of the material is increased by reaction
.,ith elements capable of being carried by recirculated gases
before release of the gases into the atmosphere. Such other
materials can be represented by absorbents such as activa~ed
carbon and/or reactants such as sodium aluminate or other
base materials as described in the aforementioned Pring patents.
1~ It will be understood that changes may be made in
the details of construction, arrangement and operation without
departin-g from the spirit of the invention, especially as
defined in the folloT~Jing claims.
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