Note: Descriptions are shown in the official language in which they were submitted.
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
METHOD AND APPARATUS FOR SCRUBBING GASES, USING MIXING VANES
Field of the Invention
This invention relates to a scrubber device for removal of particulate and
gaseous
impurities from exhaust gases produced by a combustion device, such as a
diesel or other
hydrocarbon fuelled engine. The exhaust gases are passed through a bath of
scrubbing
liquid containing and an inclined array of stationary mixing vanes which cause
turbulence
and the formation of finely dispersed bubbles, wherein the liquid/gas mixture
enhances
dissolution of impurity gases into the scrubbing liquid.
Background of the Invention
Exhaust gases are generated in many industrial and transportation
applications.
Environmental concerns as well as industrial consequences of release of
pollutants or
contaminants require their elimination or reduction. In recent times there has
been a
greater emphasis on the reduction of pollutants emitted in smoke plumes,
whether of
factories, electricity generating stations, vehicles or ships. Similarly them
has also been
an emphasis on the removal, or conversion, of toxic chemicals emitted from
industrial
processes, whether in the pulp and paper, plastics, or other industries. There
has also been
a desire to reduce the heat emitted by engine exhaust systems, whether for the
purpose
of achieviizg greater economies by trapping and re-using waste heat for
secondary and
~0 tertiary activities or for reducing the infra-red heat signature of an
engine intended for
military use. Further, a scrubber may, as one of its features, not only remove
undesired
elements, but may also reduce the noise of an exhaust flow.
There are many examples of specific instances when sembbing is desirable. For
example
it may be desired to remove gaseous and fine particulate matter contaminants,
odorous
compounds arid other undesirable elements from exhaust gases emanating from
combustion of fossil fuels, whether gas, ft~el oil, diesel oil and other
petroleum products.
The fuels aa~e commonly used in marine diesel engines and boilers, as well as
diesel
engines used for transportation and constrttcrion equipment. Sulfur dioxide is
a particular
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
component of many processes involving combustion, ranging from thermoelectric
generation, waste incineration, industrial processes,~and exhaust gases
ofprime movers,
including diesel engines. In some instances such as with forestry or mining
equipment,
use of a water scrubbing medium is also desired to discourage or eliminate
spark
emission.
In another field, it is desirable to scrub exhaust gases emanating from
industrial processes
such as chemical processes, heat transfer processes, food preparation,
agricultural
operations, mechanical parts clearing, paint spray operations and similar
processes.
Similarly, it may be desired to treat products of the combustion of solid,
liquid and
gaseous fuels such as biomass, coal, coal water slurry, coal and limestone
water slurry,
coal methanol slurry. Further still, scrubbing may be required for products of
combustion
from incineration systems for the thermal destruction of solid, liquid or
gaseous waste
products. These can include industrial and municipal wastes, biomedical
wastes,
hazardous and pathological solid and liquid wastes, and solids and liquids
contaminated
with toxic, hazardous, and pathological wastes, accidental hazardous and
dangerous
waste spills, and similar waste products. Further still, gas/water interaction
may be used
to clean and humidify exhaust gas for re-introduction of moist gas to the air
intake of a
combustion appliance for temperature control such as may be seen in a nitrogen
oxide
reduction scheme.
Scn~bbers ofvanous types are known. Removal of fine particles of dust, oxides
of sulfur
and nitrogen, odorous compounds, and similar contaminants from gas streams is
a
priority for environmental control abatement programs developed by regulatory
agencies
to minimize the impact of industrial processes on the natural environment by
reducing
acidification, ozone formation, nutrient generation and related adverse
effects. Devices
currently in use for removal of pollutants include cyclones, bag filters,
electrostatic
precipitators, and high energy scmbbers. Typically the input to output
efficiency of these
devices range from 85% to z 99.99%, with the high energy scn fibbers being the
most
efficient, and the cyclone and inertial. separators the least. Input to output
efficiency is
defined as the total concentration of particles of all size ranges in the
outlet gas stream
2
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
from the system as a percentage of the concentration in the total input to the
gas cleaning
unit. In many combustion appliances, such as a diesel engine for example, the
use of
exhaust scrubbers is~ restricted due to the low available back pressure,
necessitating a
large, costly and unreliable exhaust gas blower.
The type of unit for a specific application is determined by a number of
factors including
type of industrial process, type and size of particle released, temperature of
the gas
stream, process economics, land use adjacent to the site, and a number of
other factors.
High energy scrubbers using limestone and water slurry scrubbing solutions
have been
successfully used to scrub sulphur from the combustion gases produced when
burning
sulfur containing fuels, such as coal, heavy fuel oil, and so on.
A common method of scrubbing, for example, exhaust gases, is to spray a
scrubbing
medium, such as water, across the exhaust gas passage, or to force the exhaust
gases
through a continuously fed curtain of water, or along a channel with wetted
sides. These
technologies for scrubbing fine particles from gaseous streams have relied on
mechazucal
shear systems to produce large quantities of fine droplets of scrubbing
solution. In each
instance droplet surface axea is the controlling parameter determining the
efficiency of
the scrubber. To increase scrubber droplet surface area for a given water
mass, the
average droplet diameter must decrease. The energy required to decrease the
average
droplet size and thus increase the average droplet surface area increases
sharply. Thus the
efficiency of conventional scrubbers for fme particle removal is a function of
the energy
input as measured by the pressure loss across the scrubber. Typical high
efficiency
scrubbers (>99% efficiency) operate with pressure drops in the range of 45-60
inches of
water. Such units have high capital costs, and high energy and maintenance-
costs.
Prior Art
In contrast to the above conventional approach to scrubbing is the concept of
forcing j ets
or streams of gas into baths of liquid. U.S. Patent 4,300,924, to Coyle,
issued Nov. 17,
1981, describes a device for scrubbing diesel engine exhausts by driving the
exhaust
gases through a straight pipe into a tank of water, and allowing the exhaust
gases to
3
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
bubble through the water. The Coyle apparatus operates when the head of the
exhaust
gases is sufficient to force them out the plain cut end of the pipe.
US Patent 6,402,816 to Trivett et al., issued June 11, 2002, discloses a
scrubber device
having a header passage, a plurality of scrubber chambers and an exhaust
passage,
wherein the scrubber chambers direct exhaust gases downwardly into a liquid
bath where
the exhaust passes through a series of slots in the down pipe which impart
angular or
vortex motion in the bubbles as they rise. The gases are then passed through
the demister
and heat exchange pipes to remove scrubbing vapour before passing to the
exhaust
manifold.
Other scrubbers, such as that disclosed in US Patent 4,091,075 to Pessel,
issued l~Iay 23,
1978, utilize aqueous chemical baths to react with pollutant gases, such as
sulfur dioxide
contained in exhaust or flue gases.
Summary of the Invention
A scrubber for exhaust gases has an inlet from the source of gases, such as an
engine
system, connected through a series of nested counter-flow generally tubular
passages, to
an exhaust. Gases flowing from the inlet pipe continue in a counter-flow or
reverse
direction through a hot plenum. The hot plenum may have a convoluted or mufti-
lobed
surface or, for ease of construction may be cylindrical. A bath of scrubbing
liquid
encloses the exit end of the hot plenum, whereby the exhaust gases surge
through the
liquid bath and again reverse direction flow in a counter-flow direction
through a tubular
outlet plenum surrounding the convoluted hot plenum, whereafter the exhaust
gases exit
the scrubber. Optionally, wet sprays may also be included in the hot plenum to
introduce
scrubbing liquid to the exhaust gases prior to entry into the scrubbing bath.
Hot exhaust
gases have substantial buoyancy in water, and this buoyancy acts to drive the
gas
upwards through the bath of scrubbing liquid. If no further mixing or
diversions are
introduced, it has been noted that a large volume fraction of gas can pass
through a
system with little or no interaction with the scrubbing fluid. In the present
invention,
while passing through the liquid bath from the hot plenum, the exhaust gases
are
4
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
intercepted by a set of mixing vanes comprising an inclined array of flat,
partially
overlapping, stepped vanes which redirect the gases to flow between the vanes,
causing
turbulence in the exhaust gases. The vanes are sized and positioned so as to
pass only
a small fraction of the total exhaust gas flow through each slot, thereby
forcing the gas
to distribute and flow evenly between an array of mixing vanes.
As the mixing vanes are immersed in the liquid bath, the vanes cause
turbulence in the
mixhu a of exhaust gases and scrubbing liquid, causing the formation of highly
dispersed
fine bubbles, which enhance the solution of exhaust gas pollutants into the
scrubbing
liquid. The mixing vanes prevent the tendency of the gas buoyancy to keep the
two
gaseous and liquid media separate, as well as generating turbulent flow which
aids in
mixing, and thus material transfer from gas to water, vice-versa.
Particulate matter is also stripped from the exhaust gases in the scrubbing
liquid, and
collected at the base of the bath for removal. Scrubbing sprays can be
positioned in the
outlet plenum to dissipate the bubbles. Scrubbing sprays may also be placed in
the hot
inlet plenum to pre-quench the gas. The bath and sprays reduce the temperature
of the
exhaust gases. A further system of mist eliminator vanes are positioned across
the outlet
plenum to strip entrained scrubbing liquid from the exhaust gases wlvch then
pass
through the remainder ofthe outlet plenum adjacent to the inner wall which is
common
with the hot plenum. The heat of the inner wall vaporizes any remaining
liquids and
raises the temperature and dew point of the gases. This system is highly
effective in
reducing particulate matter, stripping sulphur and nitrogen components from
exhaust
gases, and reducing the heat signature thereof.
In one aspect of the gas scrubber of the present invention, exhaust gases are
scrubbed of
particulate and gaseous contaminants by means of a bubble generating device of
mixing
vanes which creates a large quantity of tiny bubbles of exhaust gas within the
liquid bath,
thereby significantly increasing the surface area and contact between the
exhaust gas and
the scrubbing liquid, and enhancing the dissolution of contaminant gases such
as SOX and
NOX into the scrubbing liquid.
5
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
In another aspect of the invention, scrubbing is achieved through bubble
generation with
minimized back pressure on the engine system. Baclc pressure may be as little
as two to
eight inches of water.
In a further aspect of the invention, concentric or otherwise nested hot
plenum and outlet
plenum have a common wall of convoluted cross section providing an increased
surface
area between the two passages permitting increased heat exchange during the
counter
flow passage of exhaust gases. A convoluted or star-shaped wall dividing the
hot plenum
from the exhaust plenum allows upstream exhaust gases to heat the wall and
transfer heat
to the downstream exhaust gases exiting the outlet plenum. This reduces the
degree of
relative humidity of the exhaust gases, raising the dew point and reducing the
incidence
of subsequent condensation in the system.
In another aspect of the invention, a liquid bath of scrubbing liquid closes
off the
reversing passageway between the hot plenum and the outlet plenum, wherein the
reversal of the gas flow direction initiates turbulence in the exhaust gases
prior to passage
through an array of mixing vanes.
These and other obj ects and features of the present invention will be
understood from the
following specification.
Brief Description of the Drawings
The principles, and the method of operation of the present inventive
apparatus, are
explained hereafter in the context of exemplary and non-limiting embodiments
of the
invention, with the aid of drawings in which:
Figure 1 is an isometric view of the scrubber embodying the present invention;
Figure 2 is a vertical cross-section of the scrubber taken along the line 2-2
of Figure 3;
Figure 3 is a horizontal cross-section taken along the line 3-3 of Figure 2;
Figure 4 is an enlarged view of the mixing zone and vanes illustrated in
Figures 2 and 3;
6
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
Figure 5 is a schematic view illustrating the gas flow through the liquid bath
and mixing
vanes of Figure 4.
Detailed Descr~tion of the Tnvention
The description which follows, and the embodiments described therein, are
provided by
way of illustration of examples of particular embodiments of the principals of
the present
invention. These examples are provided for the purpose of explanation, and not
of
limitation, of those principals and of the invention.
In the description which follows, like parts are marked throughout the
specification and
drawings with the same respective reference numerals.
Refernng to Figure 1, the scrubber device 1 generally may comprise a scrubber
body 2
having an inlet 3 for the introduction of exhaust gases and an outlet 4 from
which the
exhaust gases are discharged. Body 2 may be cylindrical or of other
appropriate shape.
A generally conical or V-shaped tanlc portion 5 forms a reservoir for a
scrubbing liquid.
Bath 5 contains a scrubbing liquid which, depending upon the nature ofthe
exhaust gases
and the application of the scrubber, may be a solvent for gas born
contaminants, and in
many applications may preferably be water. It has been found that in maritime
applications, sea water is an effective scrubbing solution. Both the scrubbing
liquid and
residue from the scrubbing operation maybe evacuated from scrubber 1 through
the drain
pipe 6. As may be seen in Figure 2, a secondary tank 7 may be positioned
around tank
5 to collect overflowing scrubbing liquid. A secondary outlet ~ may be used to
remove
excess liquid from tank 7. Not shown are ancillary piping for supply of
scrubbing liquid
to the scrubber device.
As may be seen in Figure 2, the internal components of the scrubber 1 are
illustrated in
vertical cross section. Exhaust gases, for example gases from the exhaust of
an internal
combustion engine, enter scr~.tbber 1 at inlet 3, in the direction indicated
by arrow G.
Exhaust gases typically contain both particulate matter (soot) and gaseous
impurities
resulting from combustion. Theparticulates maybe carbonaceous, orhydrocarbon,
while
7
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
the gas may include SOX and NOX and in particular may include SO2. The gases
are
conveyed through inlet passage 10 defined by wall 11. Passageway 10 may be
tubular,
having a length LI and a diameter D1. At the exit of passage 10, the exhaust
gases enter
a hot plenum 20 defined by cylindrical, convoluted or mufti-lobed side walls
21. As may
be seen from Figure 3, the side walls are preferably of a convoluted or star
shape to
increase the surface area of the plenum. There are eight star convolutions or
arms of
generally V-shape extending radially outwardly in the illustration of Figure
3, but
depending on the specif c application requirements and size there may be only
four arms,
or many more. A tubular (circular) hot plenum could be used as shown in
phantom as
2I', but with the consequent reduction of surface area. The V-shaped arms are
truncated
by end walls 21 a on each arm. Preferably, end wall 21 a is directly connected
to the outer
wall to the scrubber.
The passageway of hot plenum 20 is closed at its inlet end by an end wall 22
of
appropriate shape, (i.e. a star-shaped cross section, for the star plenum 21,
or a cone for
a circular plenum 21') thereby defining an upper chamber 23. Gases exiting
inlet 10 are
redirected by the end 22 of chamber 23 and flow in a counter-flow direction
(downwardly in Figure 2) along the passageway of hot plenum 20. Chamber 23 is
of
sufficient length to minimize back pressure on the exhaust supply resulting
from
redirection of the gas flow down plenum 20. The chamber also serves to reduce
resonance in the scrubber. Walls 21 of the hot star-shaped plenum terminate at
a
peripheral horizontal edge 24 within the periphery of scrubbing liquid tank 5.
An outlet plenum 30 surrounds the hot plenum 20 and is generally confined by
the
cylindrical outer wall of the scrubber. Outlet plenum 30 is defined by an
outer wall 31
and the star-shaped inner wall 21 of hot plenum 20, and therefore exhibits a
greater
surface area of wall 21. In the preferred embodiment of the scrubber design,
end walls
21a of hot plenum wall 21 may be sealed against wall 31, but alternatively,
they may
simply be braced intermittently against wall 31. If sealed, then a plurality
of passages
30a are defined for the outer plenum until joining into a single plenum
adjacent the exit
4. Conversely, if only intermittently braced, then the plurality of
passageways 30a are
8
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
in fact interconnected to create a single outer plenum with a convoluted inner
surface. In
a scrubber using a circular wall 21', outlet plenum 30 is annular. An
apertured distributor
plate (not shown) may be used at the base of plenum 30, to re-direct exhaust
gases
through a series of apertures into the annular outlet plenum 30. Plenum 30
directs the
exhaust gases in a direction counter-flow to that of hot plenum 20, and
conveys scrubbed
gases out through to exit 4.
As may be seen from Figures 2 and 3, the exhaust gases are directed through
inlet
passage 10, then counter flow through hot plenum 20 then again counter-flow
through
outlet plenum 30 to exit the scrubber at outlet 4.
The scrubbing liquid is contained in bath 5 and has a liquid level at rest,
WL, which
covers the horizontal peripheral lip 24 and the mixing vanes discussed
hereafter.
As may be seen from Figures 2, 3, and 4, at the somewhat triangular shaped
inlet end 33
of outlet plenum 30 (defined by peripheral lip 24 of the hot plenum wall 21
and outer wall
31), sets of mixing vanes 40 are interposed in the passage way to partially
obstruct the
passage of exhaust gases through the scrubbing liquid and into the outlet
plenum. As
may best be seen in Figure 4, with reference to Figure 3, mixing vanes 40
comprise a
series of several horizontal flat vanes partially overlapping one another and
spaced apart
to form an inclined or stepped array through which exhaust gases are passed.
The array
of vanes is inclined upwardly and outwardly to force gases to reverse
direction iu order
to pass inwardly through the spacing between the vanes. The array of vanes is
submerged below the liquid level in tank 5.
During operation of the scrubber, the pressure of the exhaust gases on the
surface of the
scrubbing liquid WL causes the liquid level to depress at the exit of hot
plenum 20 to a
level WL' thereby raising the liquid within triangular inlet 33 of passageways
30a of
outlet plenum 30 to level WL". The gases descending in hot plenum 10 then
reverse
direction and pass under peripheral lip 24 ofthe hot plenum and stream or
bubble through
the scrubbing liquid. The gases may even create a gas void under the array of
mixing
9
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
vaazes, as shown by the curved liquid level WL' in Figure 5. The exhaust gases
then turn
again to pass through the array of mixing vanes 40. The number of individual
vanes 41
of the mixing vane array 40 depends upon the size of the scrubber system but
generally
range from 12 to 15 vanes. Vanes 41 may typically be 3/4 inches wide in
horizontal
dimension, and one-eighth inch thick, with a spacing between vanes of one
eighth to
three quarters inch. Each vane is set baclc approximately 50% of its width
from the vane
below. The vanes cause redirection and acceleration of the gases, resulting in
turbulence
and formation of fine bubbles of exhaust gas within the scrubbing liquid. The
resulting
bubbles then proceed within mixing zone 42 of outlet plenum 30.
Particulate matter such as soot, of carbon or hydrocarbon composition, is
carried down
hot plenum passageway 20 and is absorbed in the scrubbing liquid, to slowly
descend
to the bottom of tank S. Radial baffles 43 within the tank aid in retaining a
degree of
quiescence to permit settlement on the particles. Soluble gases in the exhaust
stream,
such as SOX and NOX are dissolved in the scrubbing liquid, not only by merely
percolating through the liquid bath but principally at the liquid/gas
interface of the tiny
bubbles created during the turbulent, agitated flow of gases through the
mixing vanes. It
will be understood that the duration of time during which the gases are
immersed in
scrubbing liquid, or retained within the bubbles, effects the level of
dissolution of
pollutant gases.
In mixing zone 42 the bubbles of exhaust gas arise above the surface of the
scrubbing
liquid, where they coalesce and break up. Within passageway 30 or 30a, j ets
or nozzles
44 may be utilized to spray scrubbing liquid into the path of the exhaust
gases, further
2S causing coalescence and break up of the bubbles of gas, while also wetting
down the
walls 21 and 31 of passage way 30 for further contact exchange of gas
contaminants with
the scrubbing liquid. If desired, similax jets may be used in the lower
sections of plenum
20 to pre-wet and cool the hot exhaust gases.
Further along the passageway 30a are located a set of mist eliminator vanes
4S. These
vanes are designed to strip any remaining scrubbing liquid from the moisture
laden,
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
saturated stream of exhaust gases and entrained droplets. The array of mist
eliminator
vanes 45 is similar to and may be a mirror image of the array of mixing vanes
42. They
comprise a series of overlapping staggered flat vane members 46. Each vane 46
is
generally 3/4 inches wide, one-eighth inch thick and spaced at one-eighth to
3/4 inch
separation. The spacing between vanes 46 is sufficiently close to obtain good
contact
between the moisture laden gases and the vanes, but sufficiently separated to
avoid an
increased gas velocity which may strip deposited moisture from the vanes.
The liquid stripped from the gas stream by mist eliminators 45 drains down the
side walls
of passageway 30a and returns to the bath 5. Ridges on the passageway walls of
mixing
zone 42 may be used to direct the drainage direction, aiid even induce further
gas
exchange at the surface of the walls. The scrubbing liquid (i.e, water, etc.)
removed by
the mist eliminators and wall contact drips into the bottom of the tank, where
radial surge
or wave baffles inhibit agitation and allow settlement of particulate matter.
Such
particulate matter and excess treating liquid may be removed from the conical
bottom of
the tank. The liquid may then be cooled, treated and reintroduced into the
system.
Upon exiting the mist eliminator vanes, the exhaust gases have been cooled to
the
temperature of the scrubbing liquid of the bath 5. Typically, this will be in
the order of
40°C ifrecycled liquid is used. The exhaust gases are substantially
depleted of suspended
scrubbing liquid, but are generally I00% saturated. As may be seen from Figure
2 and
Figure 5, after the exhaust gases have been passed through mist eliminators
45, they
proceed through the balance ofpassages 30a, surrounded in greater part by wall
21 of hot
plenum 20. Wall 21 is hot from exposure to hot exhaust gases in the range of
250°-
450°C exiting into chamber 23 from inlet passage 10. It may be expected
that walls 21 of
the upper chamber 23 can be heated in the range of 250 to 300°C by the
incoming
exhaust gases.
After the exhaust gases have been cooled and scrubbed in the scrubbing liquid
and
mixing zone, and stripped of excess liquid in the mist eliminator vanes 45,
the exhaust
gas stream is reduced to a saturated gas without any significant entrained
liquid
11
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
component. The saturated exhaust gases are then re-heated radiantly as well as
by
conduction and convection from the heat transfer surface of common wall 21.
Depending
on gas flow rates and the length of the exposed wall portion 21 of the hot
plenum, the
gases will be re-heated at least 30°C and may be re-heated up to
200°C. As a result, the
moisture in the exhaust gases, when exiting the exhaust plenum, will be
normally. well
below the saturation point and typically at 75% saturation, thus eliminating
or
substantially reducing condensation of liquids on downstream piping, and
preventing/reducing visible fogging in the atmosphere. Consequently the
resulting gas
emission does not display a heat signatL~re or a visible moisture cloud, and
is substantially
reduced in both particulate and gaseous contaminants.
It will be understood that ideal flow rates of the exhaust gases are not
always maintained,
and occasional surges in flow rate will be experienced. The present invention
adjusts for
sudden increased flow rate by providing passage 47 extending between the bath
5 (below
edge 24) and the apex of the mixing vanes 40. Further, in the event that a
surge in gas
flow rate forces the scrubbing liquid through the mixing vanes 40 and into
mixing
chamber 42, the liquid may then overflow through an annular drain 48 located
at the
outer perimeter of the passage way 30a as indicated by arrow D. The net effect
is to
male the scrubber more reliable in varying flow situations, a common problem
for other
wet scrubber designs.
The present design operates with a minimal bacl pressure or head of one to six
inches of
water. The overall pressure cb-op of the system is less than six inches of
water, principally
from the hydrostatic pressure of the liquid bath level.
The scrubber is an effective means for removal of SOZ and particulate matter
resulting
from combustion of fuels, such as diesel fuel. Levels of ~0% particulate
removal and
95% SOz removal have been achieved by this apparatus and method.
It will also be apparent to one skilled in the art that a continuous flow and
exchange of
scrubbing liquid is required. Liquid may be introduced through the spray jets,
but
12
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
preferably is also introduced in a regular flow rate into bath 5 by a liquid
source, not
shown.
The exact exhaust gas parameters in any given situation will be determinative
of the size,
flow rate and temperatures used in a scrubber of the present invention. An
example of
one set of parameters using a star-shaped hot plenum, with the exhaust gases
of a one
megawatt engine (1500 horse power) are set out in the table below:
Example #1 - 1500 h.p. (1 Megawatt engine)
Inlet length L, 6'
diameter D~ 12"
Hot "Star Plenum" length LZ 9-12'
inner diameter 16"
DZ 44"
outer diameter
D3
Outlet Plenum length L3 11'-14'
diameter D3 44"
Inlet Temperature 200 - 490C
Mixing Chamber Temperature 40C
Outlet Temperature 70-200C
Gas Flow Rate 1-2kg/s
Liquid Re-circulationSeawater @ metric 20-30 Ton/hr
Rate Ton/hr
Bath Volume 1 cu m = 1 tonne
Mixing Number Size Separation Overlap
Vanes 15 3/4" w %2" 50%
1/4" t
13
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
A further example of scrubber parameters using a circular hot plenum, in a
7500 h.p.
engine is listed below.
Example #2 7500 h.p. (5.6 Megawatt engine)
Inlet length L1 6'
diameter Di 24"
Hot Plenum length LZ 12'
diameter D2 45"
Outlet Plenum length L3 I4'
diameter D3 60"
Inlet Temperature 480C
Mixing Chamber Temperature 40C
1 ~ Outlet Temperature 70 - 200 C
Gas Flow Rate 11 kg/sec
Liquid Re-Circulation Seawater@metric I20-130 Ton/hr
Rate Tonlllr
Bath Volume ~ 2 tons
15 ~ Mixing VanesNumber Size Separation Overlap
18 3/4" w 3/4" 50%
1/4" t.
The foregoing embodiments were operated with a back pressure head of 6 inches
of
water. The benefits of such minimized pressure head will be fully apparent to
persons
20 skilled in the art and is a dramatic improvement of other high efficiency
scrubbers which
employ pressture heads orders of magnitude larger.
hi operation, exhaust gases ranging from 200°C to 490°C which
include soot and reaction
gases such as sulphur dioxide and nitrogen oxide, are cooled to the
temperature of the
25 scrubbing Ii.quid bath, the partic7,zlate matter is stripped in the bath
and significant
percentages of sulphur dioxide are stt-ipped from the exhaust gas stream by
dissolution
in the scnzbbing liquid. Applicant leas found that in excess of 90% of sulphur
dioxide
may lie stripped from the exhaust.gas by this invention, and 20% of NOa may be
stripped.
14.
CA 02464269 2004-04-20
WO 03/045524 PCT/CA02/01846
Such high percentage of NOX removal is in part due to. the pH level of the
scrubbing
liquid caused by the dissolution of SOZ. Typically, in the example described
above, the
pH level is running in a range of 2-3, which is an excellent absorber of NOX.
Applicant has also found that up to 90% of the soot and 20% of the hydrocarbon
particulates are removed in the scrubbing liquid.
The foregoing description has been intended to indicate the nature of the
invention, its
operation and advantages, without being limited of size, shape, temperature or
operational rates. Variations from the description and example may be readily
understood by a person spilled in the art and incorporated without departing
from the
scope of this invention.
