Note: Descriptions are shown in the official language in which they were submitted.
WO 2006/113176 CA 02604908 2007-10-15PCT/US2006/013074
Method And Apparatus for Treating Lime Slurry for Grit Removal
Background of the Invention
Lime has been found to have many uses. Such uses have included the treatment
of sewage sludge to remove pathogens, lime stabilization of waste water,
pasteurization
of sludge and many other treatment processes.
Examples of such processes involving use of lime include U.S. patents
5,013,458;
5,186,840; 5,405,536; 5,554,279 and 5,681,481.
In many uses, lime in the form of calcium oxide (CaO) is mixed with water
(H20)
to form calcium hydroxide (Ca0H2). The chemical reaction which occurs during
such
mixing, gives off heat in the form of an exothermic reaction, and when done
with excess
water is commonly referred to as "lime slaking", a process which is
accomplished in a
device known as a lime slaker. The resulting mixture of lime (Ca0112) and
water is
known as a lime slurry. Lime slurries are known to have some unique
properties, one of
which is its inherent ability to form scale on surfaces which come into
contact with the
lime slurry. The formation of scale, or "scaling" can render the various
delivery systems,
such as pipes, troughs, conduits, etc. unusable over time due to the build-up
of scale.
Alternatively, such scale build-up can require frequent cleaning and descaling
of the
equipment that is used to handle lime slurries. Cleaning and descaling
operations can be
considerably labor intensive.
Lime.slurries also contain a certain amount of inert material that is commonly
referred to as grit. Grit results because the calcium oxide, generally in the
form of
quicklime (CaO) contains a certain amount of material other than CaO.
Typically, lime
contains approximately 90%-95% CaO, and 5%-10% inert material, or grit.
The presence of grit in a lime slurry can cause numerous problems, including
grit
build-up in downstream process chambers or vessels, grit acting to plug or
clog nozzles
and orifices through which the slurry passes, and abrasions caused to
treatment
equipment and slurry delivery equipment such as pumps, pipes, valves, etc.
because of
the abrasive nature of grit particles.
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Various techniques have been attempted for separation of unwanted grit that is
contained within a lime slurry.
For example, U.S. patent 4,482,528 describes some of the problems that are
encountered when trying to separate unwanted grit from a lime slurry. For
example,
using a gravity classifier to separate grit from a lime slurry when
discharging from a lime
slaker, is described as being unable to effectively remove particles smaller
than 100 mesh
(140 microns).
The gravity separation of grit, directly after the slaking of lime in a lime
slaking
device can be problematic, in that the amount and size of the grit removed
will vary as
the rate of discharge from the lime slaker varies. At high discharge rates
from the slaker,
the slurry will have less retention time in the grit separation chamber, which
can be
insufficient for the smaller grit particles to settle, such that the grit
particles can be
conveyed through the separation chamber and into the finished lime slurry,
resulting in
inconsistent and highly variable amounts of grit removal.
U.S. patent 4,482,528 attempts to improve upon gravity separation of grit by
the
use of a cyclone followed by at least one gravity classifier device. The
cyclone operates
centrifugally, and removes grit and lime, which discharges from the cyclone
into a
gravity classifier, wherein dilution water is added in order to allow the grit
to settle in the
classifier.
Summary of Invention
The present invention provides a method and apparatus for removing unwanted
grit from a lime slurry while allowing some grit to remain, without requiring
multiple
steps of cyclone separation plus gravity separation, and without requiring the
use of
dilution water in the process and therefore without introducing variations in
slurry
concentration to the resultant final slurry output.
Accordingly, it is a primary object of this invention to provide a novel
method
and apparatus for removing grit particles from a watery lime slurry during the
process of
delivering slurry from a slurry tank, whereby the slurry is substantially
continuously
delivered from the slurry tank to a grit separator, with a portion of the
slurry being
extracted for discharge, while the rest of the slurry is recirculated to the
slurry tank after
separation of some of the grit from the slurry.
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It is a further object of this invention to accomplish the above object,
wherein the
separation of grit occurs in a gravity-operative grit classifier.
It is another object of this invention to accomplish the above objects,
wherein the
slurry that is extracted is done on a controlled basis.
It is a further object of this invention to accomplish the above objects,
wherein the
recirculation of slurry involves the serial flow of slurry from the slurry
tank to the grit
separation point, followed by a recirculation of the remaining slurry to the
slurry tank.
It is another object of this invention, wherein grit is separated from a
watery lime
slurry, by the substantially continuous delivery of slurry to a grit
separation point, and
wherein the rest of the slurry is recirculated to the slurry tank, and wherein
a parallel flow
of slurry from the slurry tank provides for substantially continuous
delivering of slurry.
Other objects and advantages of the present invention will be readily apparent
upon a reading of the following brief descriptions of the drawing figures, the
detailed
descriptions of the preferred embodiments, and the appended claims.
Brief Description of The Drawing Figures
Fig. 1 is a flow diagram illustrating delivery of lime to a slurry tank from a
lime
slaker, followed by the delivery of slurry from a slurry tank to an extraction
site for some
of the slurry, while the rest of the slurry is delivered to a separation
device for separating
some of the grit from the slurry, with the slurry then being recirculated to
the slurry tank,
wherein the flow of slurry from the slurry tank to the point of grit
separation, followed by
the recirculation of slurry from the grit separation point to the slurry tank,
is serial.
Fig. 2 is an illustration of a flow diagram, similar to that of Fig. 1, but
wherein the
withdrawal of slurry from the slurry tank to the point of grit separation and
return to the
slurry tank is in a parallel flow arrangement to the extraction of slurry from
the system.
Fig. 3 is an enlarged detail view of the extraction of slurry from a delivery
conduit, in a vertical upward direction.
Fig. 4 is a detail view of the extraction of slurry from a slurry conduit, in
a
vertical upward direction, in which the cross-sectional size of the vertical
upward conduit
has at least a portion that is of greater cross-sectional size.
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Fig. 5 is a detail view showing the extraction of slurry from the slurry
discharge
line via a vertical downward direction, for gravity extraction of grit along
with the
extraction of slurry.
Fig. 6 is an illustration of a flow diagram of an alternative embodiment,
somewhat
similar to that of Fig. 2, but wherein the slurry is pumped from the slurry
tank through a
suction line, to discharge, through a stilling well.
Fig. 7 is an enlarged, detailed view of the illustration of a portion of Fig.
6,
showing a liquid level for the slurry in the tank, and wherein grit is
illustrated as being
separated out of the slurry in the slurry tank, and wherein slurry is
discharged from the
stilling well of Fig. 6, with Fig. 7 also illustrating in phantom an
alternative placement for
the stilling well that is outside the slurry tank, as distinguished from the
stilling well
shown inside the slurry tank in the full line illustration of Fig. 7.
Fig. 8 is an illustration similar to that of Fig. 7, but wherein the diameter
of the
stilling well is greater than that of the stilling well illustrated in Fig. 7,
illustrating an
increased cross-sectional area for the stilling well for controlling the rise
rate of the slurry
in the stilling well prior to entering the suction line, so that grit that is
subjected to
turbulence in the slurry tank in the embodiment of Fig. 8, and wherein the
flow velocity
of slurry through the stilling well in Fig. 8 would be reduced from that of a
stilling well
of lesser cross-section as illustrated in Fig. 7, whereby increased residence
time of slurry
in the stilling well takes place in the embodiment of Fig. 8, relative to the
residence time
of slurry in the bottom of the stilling well of Fig. 7.
Fig. 9 is a vertical view of an alternative embodiment of a stilling well that
is
adjustable in cross-section.
Fig. 10 is an end view of the stilling well of Fig. 9, taken along the line X-
x of
Fig. 9.
Detailed Descriptions of The Preferred Embodiments
Referring now to the drawings in detail, reference is first made to Fig. 1, in
which
a serial slurry treatment system is generally designated by the numeral 10, as
including a
lime slaker 11, which may have a agitation device such as a mixer 12 therein,
for
delivering slaked lime via conduit 13, to a slurry tank 14. The lime slaker 11
may be of
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any desired type, such as the type disclosed in U.S. patent 2,904,401; U.S.
patent
5,368,731; U.S. patent 4,261,953; U.S. patent 4,482,528, or of any other
desired type.
The watery lime slurry is thus delivered from the slurry tank 14, which may
have
one or more mixers 15 therein, to be delivered via a delivery line, conduit,
or pipe 16, by
means of a pump, to a delivery line 18, then to a grit classifier 23 via
delivery lines 20, 21
and 22, as shown in Fig. 1. During the delivery of lime slurry as described
above, to the
grit classifier 23, some of the lime slurry may be extracted via extraction
line 24, in a
controlled manner, with the control being provided via flowmeter 25 and
control valve
26, to discharge via line 27, which may lead to the point of application of
the lime slurry.
The grit removal or separation device 23 includes a tank 30, having a liquid
level
31 therein, with a sloped auger 32, the lower end of which is immersed with
the liquid
level 31, and which operates to engage grit particles and convey them up the
sloped
surface 33, to a point of discharge 34, as shown.
The grit separation device 23 may be provided with a movable wall 35,
controlled
by a suitable electric or pneumatic actuator 36, for leftward and rightward
movement, as
shown, between the full line position 35 as shown, and a phantom line position
37, as
shown, in order to vary the cross-sectional surface area, which will cause an
automatic,
continuous or intermittent variation in the volume of liquid 31 retained
within the grit
classifier 23.
The upper edge of grit classifier wall 38 provides a means for overflow of
lime
slurry from the grit classifier 23, via line 40, recirculating back into the
slurry tank 14, as
shown.
The pump 17 is selected in size, to provide a desired velocity through the
conduit,
pipe or delivery line 18, 20, 21, so that particles of lime and grit do not
settle within such
delivery line, pipe or conduit. The selected velocity of flow through the
lines 18, 20, 21
also provides a scouring action from entrained grit which helps keep the same
from
clogging due to build-up of scale within the same.
It will thus be seen that the grit classifier 23, while acting via gravity
removal of
grit, allows a small quantity of grit to remain in the slurry to assist the
scouring action of
the slurry with some grit in it, for preventing build-up of lime scale within
the system.
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It will also be understood that the electric or pneumatic activator drive 36
for
varying placement of the wall 35 can be operated continuously or
automatically, as may
be desired.
It will be seen, that in accordance with this invention, it is not necessary
to add
any dilution water to the lime slurry, such that the percentage of lime
relative to water
remains substantially constant.
It will also be apparent by the use of the flovvmeter 25 and valve 26, the
amount
of lime being feed to discharge, such as the point of application, can be
carefully
controlled.
Referring to Fig. 2, the parallel loop system will now be described, with
similar
components to those illustrated in Fig. 1 operating in the same manner as such
components are described above with respect to Fig. 1. The lime slaker 111 is
may be
provided with one or more agitation devices such as a mixer 112, for
delivering slaked
lime via conduit or delivery line 113 to the lime slurry tank 114. The lime
slurry tank
114 is provided with one or more mixers 115 therein, suitable motor driven, as
are those
for the embodiment of Fig. 1, whereby some of the discharge from the slurry
tank 114 is
delivered via line 116, being pumped in the direction shown via pump 117, to
delivery
lines, conduits, pipes or the like 118 and 120, to delivery line 122, into the
gravity
separation classifier 123, to form a liquid level 131 therein in the volume
130 thereof,
such that grit can separate via gravity therein, for discharge via auger 132
up slope 133,
to grit discharge location 134, as shown.
The recirculation of the slurry from grit classifier tank 123, over end wall
138,
back to the slurry tank 114, via conduit or delivery line 140, is similar to
that described
above with respect to Fig. 1. Similarly, the automatic, continuous or
intermittent
variation in volume of liquid level 131 in separation classifier 123, by
movement of the
wall 135 from the full line position shown, to the phantom line position 137
shown, via
wall drive mechanism 136, is similar to that set forth above with respect to
Fig. 1.
Parallel to the flow from slurry tank 114 via pump 117 and conduit 118, 120,
121
and 122, is the flow via line 216 from the tank 114, as will now be described.
The pump 217 pumps the watery lime slurry from tank 114, via conduits or
delivery lines 218, 220, 221 and 240, back into the tank 114. During the
course of such
=
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recirculation, extraction can occur via line 124, controlled by flowmeter 125
and valve
126, to the point of application via line 127.
With reference now to Fig. 3, it will be seen that the extraction of lime
slurry from
line 21 of Fig. 1 can be vertically upwardly, via extraction line 19, where it
may be
desired to minimize the extraction of grit particles. Such may be desirable
for purposes
as air pollution control, wherein upwardly from extraction line 19 (not
shown), the lime
slurry is sprayed through a nozzle into the air to be treated. In such
situations, it can be
desirable to avoid the tendency of grit particles to clog nozzles, and thus
the extraction
location 19 may be upwardly, as shown. Similarly, with respect to the
embodiment of
Fig. 2, the extraction can occur upwardly, via phantom extraction line 119.
With respect
to a vertical upward extraction, from the system shown in Fig. 2, such
extraction can
occur from line 221, via phantom line 119, similar to the extraction shown in
Fig. 3 that
is vertically upwardly, via line 19, from horizontal line 21.
With respect to Fig. 4, from line 21, such extraction can likewise be
vertically
upwardly via line 19, but with line 19 having a predetermined cross-sectional
diameter
that varies from a lower end 19a thereof, to an upper end 19b thereof, with
such cross-
sectional size at the upper-most end further reducing the tendency for grit
particles to
travel upward via line 19, with the embodiment of Fig. 4 sufficing to slow the
rate of rise
of fluid therein, because of the upwardly increasing diameter, for the virtual
illumination
of any grit particles from passing upwardly via line 19. The extraction can
then proceed
via line 224, through flowmeter 225, through control valve 226 and via
extraction line
227, to the point of application. It will be understood that the flowmefer 225
and valve
226 operate similarly to the operation of the flowmeter 25 and valve 26
illustrated in Fig.
1.
With reference now to Fig. 5, it will be seen that the line 18 shown in Fig.
1, is
illustrated in cross-section, as having a lime slurry, with grit therein, and
that the
discharge line shown in phantom at 29 in Fig. 1, is illustrated in Fig. 5, to
illustrate an
alternative withdrawal or extraction of lime slurry from the bottom of
recirculation line
18, or alternatively via phantom extraction line 229 illustrated in Fig. 2,
such that grit
particles can be drawn off via extraction line 324 through flowmeter 325 and
valve 326,
via extraction discharge line 327, to the point of application. Such may be
desirable
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where one may desire to scour scale build-up downstream of extraction lines
29, 229, as
shown in Fig. 5.
It will also be apparent that the valves 26, 126, 226 and 326 can be
controlled to
be open partially, or fully; in the later case, should one desire to allow a
flush of high
velocity lime slurry to pass therethrough to the point of application, for
providing a
cleaning action.
With reference now to Fig. 6, it will be seen that various components of a
slurry
treatment system are indicated, having numerals that identify them by numerals
that are
similar in many cases to the numerals used in identification of components in
Fig. 1,
except that comparable numerals in the case of the system of Fig. 6 are of the
300 series,
as distinguished from comparable elements in the system of Fig. 1, that are
identified by
numerals in the tens. Thus, the system 310 of Fig. 6 is generally designated
as
distinguished from the numeral 10 which designates.the slurry treatment system
of Fig. 1.
Similarly in Fig. 6, the lime slaker is identified by the numeral 311, having
a mixer 312
therein for delivering slaked lime via conduit 313 to a slurry tank 314 having
a mixer 315
therein such that slurry is delivered via a conduit 316 by means of a pump 317
via lines
318, 320 and 321, and back through delivery line 322 to a tank 330 having a
liquid level
331 therein, with a sloped auger 332 in the tank 330, which operates to engage
grit particles
and convey them up a sloped surface 333 to a point of discharge 334 as shown.
The grit separation device 323 may be provided with a movable wall 335
controlled by a suitable actuator 336 for leftward and rightward movement, as
shown,
between the full line position 335 therefor and a phantom line position 337,
as shown, in
order to vary the cross-sectional surface area for causing an automatic,
continuous or
intermittent variation in the volume of liquid 331 retained within the grit
classifier 323.
Similarly, the upper edge of the grit classifier 338 provides a means for
overflow of lime
slurry from the grit classifier 323 via line 340, recirculating back into the
slurry tank 314,
as shown.
The pump 317 is likewise selected in size to provide a desired velocity via
the
lines 316, 318, 320. A discharge line is shown in phantom at 329, as an
option, to
illustrate an alternative withdrawal or extraction of lime slurry from the
bottom of
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recirculation line 318 in the event that one may desire to scour scale build-
up downstream
of extraction line 329.
Also, optionally, if desired, an extraction can occur similar to that via line
24 as
shown in Fig. 5, through a flow-meter similar to that 25 of Fig. 1 and control
valve similar
to that 26 of Fig. 1, if desired.
In the embodiment of Fig. 6, slurry can be withdrawn via line 351, which
operates
from suction provided through line 352 from suction pump 353 to a discharge
line 354.
The suction line 351 is located in a preferably round cross-sectional, pipe-
like stilling
well 350, the bottom of which extends lower into the liquid level "L" of
slurry in the tank
314 than the bottom of suction line 351.
With specific reference to the enlarged detail view of a portion of the
illustration
of Fig. 6, that is present in Fig. 7, it will be seen that the stilling well
350 has a cross-
sectional area determined by a diameter D1, which is selected to have a
predetermined
flow velocity responsive to the suction drawn via pump 353 such that there is
a sufficient
residence time for slurry entering the bottom of the stilling well 350, at
level H1, to allow
for gravity separation of grit "G" from the slurry in the tank 314, prior to a
portion of that
slurry entering the suction line 351, the mouth of which is at level 112
within the stilling
well 350. Thus, between the suction created via pump 353 and the cross-
sectional area of
the stilling well 350, the rise rate of slurry in the stilling well is
controlled such that a
desirable percentage of, or all grit particles do not reach the lower end of
the suction line
351. This is because the velocity of flow from the stilling well is determined
by the rate
of flow divided by the cross-sectional area of the stilling well 350.
It will be understood, by reference to the phantom illustration at the right
side of
Fig. 7, that the stilling well could be located outside the slurry tank 314,
as is the phantom
illustrated stilling well 450 of Fig. 7, connected thereto via a connection
line 453, which
allows slurry from inside the tank 314 to enter the bottom of the stilling
well 450, prior to
rising to the point of entry 112 at a predetermined level within the stilling
well 450, to
enter the suction line 451 and to be withdrawn therefrom via phantom suction
line 452,
similar to that of line 352 of the full line illustration of Fig. 7, as the
same is drawn via a
suction pump (not illustrated) for the phantom stilling well illustrated at
the right end of
Fig. 7.
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Referring now to Fig. 8, it will be seen that a slurry tank 514 is provided
similar
to that of the slurry tank 314 of Fig. 7, and wherein agitation is provided
via an impeller
in the tank 514, for agitation of a slurry disposed therein at level "L", and
having a
conduit 516 for slurry. However, with
respect to Fig. 8, it will be seen that the preferably round cross-sectional,
pipe-like stilling
well 550 is shown having a larger cross-sectional area as indicated by a
larger diameter
D2 therefor, whereby liquid entering the stilling well 550, being subjected to
a suction
provided by the suction pump 553 for delivery to a discharge line 552, 554
will create a
reduced flow velocity for the system of Fig. 8, relative to that for the
system of Fig. 7, at
the lower end of the stilling well 550. Thus, liquid entering the bottom of
suction line
551 at height H2 after passing into the stilling well via its bottom at level
111, will have
an even greater residence time at the bottom of the stilling well 550, than
the residence
time of liquid entering the bottom of the stilling well 350 of Fig. 7, with
the reduced flow
that creates such residence time giving a greater amount of time for grit "G"
to settle out
of the slurry in the tank 514.
In both of the embodiments of Figs. 7 and 8 it will be seen that lime slakers
311,
511, respectively can provide lime to the slurry tanks 314, 515, respectively,
via their
respective delivery lines 313, 513.
Also, it will be noted that in Figs. 9 and 10 a means 612 is optionally
provided for
adjusting the cross-sectional area of the stilling well in the form (for
example only) of a
pneumatic or other drive means, for altering the cross-sectional area of the
stilling well
650, by movement of one or more walls thereof as shown at the upper end of the
stilling
well 650, so that the flattened walls 653, 654 thereof can slide relative to
each other
between the full line and phantom line illustrations therefor, outside the
slurry withdrawal
line 651.
It will be apparent from the foregoing that various modifications may be
provided, in the details of construction of an apparatus in accordance with
this invention,
as well as in the use and operation thereof, all within the spirit and scope
of the invention
as defined in the appended claims. It will further be understood that where
features of
this invention are recited in the "means plus function" terminology, it is
intended that
they embrace all means capable of providing such function in addition to the
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representative embodiments described and illustrated, unless otherwise
specifically
limited herein.
