Note: Descriptions are shown in the official language in which they were submitted.
~53~9
1 Fleld of the Invention
This invention relates to apparatus rfor and process
of purifying a waste gas stream primarily containing
minute pollutant liquid and solid particles. More
particularly, the process and apparatus are adapted to
remove pollutant particles as small as one micron or less
in an efficient manner.
Background of the Invention
Several approaches have been taken in the past to
remove contaminants from waste gas streams, which may
arise from various sources, where the contaminants may be ~ -
in vaporous or particulate form of liquid or solid -~
nature. A well known standard approach for removing
contaminants from a waste gas stream is to pass
countercurrently through the gas stream a scrubbing
solution. Such scrubbing solution may be sprayed
downwardly in a scrubbing tower where the gases move
upwardly through the tower. The tower may be of the
packed type having various forms of packing well known in
the art to enhance the gas liquid contact for removing
vaporous contaminants. Other approaches for removing
particulate contaminants involve spraying either
cocurrently or countercurrently to the air flow, a spray
which wets the particles and causes them to fall out under
the influence of gravity or the wetted particles may be
separated from the gas stream by using various types of
centrifugal treatments.
Canadian patent 352,850 and United States patents
2,195,707, 2,763,982, 3,651,622, 3,653,187 and 4,067,703
disclose various approaches to introducing a scrubbing
'~.
~5~ 9
1 spray into the gas stream and then separating the wetted
particulate cortaminants from the gas stream by passing
the treated gas stream through various types of
centrifugal separation devices which may be in the form of
centrifugal fans.
Alternate approaches involve the introduction of a
spray into the gas stream for purposes of wetting the
particles with the spray and removing the particles by
collecting them on the walls of the apparatus, or by
filtration. Such devices are disclosed in United States
patents 2,858,903, 2,935,375 and 3,016,979. There is,
however, no consideration given in this last approach to
using any foLm of device which would cause a vigorous
mixing of the fine spray of scrubbing solution into the
gas stream to enhance the wetting of the particulate
contaminants. In addition, one of these approaches, as
disclosed in United States patent 2,935,375, requires high
energy input in the use of a venturi which necessitates
considerable horsepower to drive the air compressor to
2~ accomp-ish removal. For example, a 200 horsepower motor
may be necessary so that the velocity of the stream of
gas, as it passes through the venturi, would be increased
from 3,000 feet per minute to about 18,000 feet per minute
at the point of constriction in the venturi in order to
achieve the desired atomi~ation of the introduced spray in
the gas stream.
Further difficulty encountered with the prior art
approaches is that none of them have produced an
economical energy efficient approach to removing very
minute particulate contaminants which may be as small as
;3~
1 one micron in size.
It is, therefore, an object of this invention to
provide an efficient removal of small minute particulate
liquid and/or solid contaminants from a waste gas stream.
Such object may be applied to the removal of contaminants
from a waste gas stream which is generated in a drying
oven for freshly printed materials.
Su__ary_of_the_Inve ion_
The process, according to the invention, purifies a
waste gas stream containing minute contaminate liquid and
solid particles as small as one micron or less. The
process comprises treating the gas stream with a fine
spray of scrubbing liquid by introducing into the gas -
stream the spray of a droplet size in the range of one
micron or less. The introduced scrubbing liquid is mixed
with the pollutent particles in a turbulent region without
appreciably increasing the pressure of the gaseous
stream. Such mixing enhances the conglomeration of
pollutant particles with scrubbing droplets to form larger
particles. The mixed gas stream is passed out of the
turbulent region and delivered to an area for removing the
enlarged conglomerated contaminant particles from the gas
stream to purify it.
Apparatus for purifying the waste gas stream
comprises a turbulence generator capable of generating
turbulence in the gas stream to a degree represented by
Reynolds number of in the range 1 x 10 or more without
appreciably increasing the pressure of the gas stream.
Means delivers the gas stream to an intake of the
turbulence generator and second means delivers the gas
1 stream away from a exnaust of the turbulence yenerator.
Means introduces into the gas a scrubbing spray of liquid
of droplet size in the range of one micron or less. The
spray means is located within the intake delivery means
and upstream of the turbulence generator. The exhaust
delivery means delivers the mixed gas stream and scrubbing
liguid which forms enlarged particles containing the
contaminants to means for removing the enlarged particles
from the gas stream to purify the waste gas stream.
Brief Description of the Drawings
________________________________
Preferred embodiments of the invention are
illustrated in drawings wherein:
Figure 1 is a block diagram schematically
illustrating the various steps in the process of the
invention;
Figure 2 is a perspective view of the apparatus
according to this invention in which the process is
carried out for separating contaminants from waste gases
derived from a printing ink drying oven;
Figure 3 is a perspective view of the turbulence
generator and filter device for removing fine particulate
contaminants;
Figure 4 is a section through a settling tank used
in the regeneration of the spent srubbing liquids; and
Figure 5 is a section through the turbulence
generator and preceding duct containing the tertiary
atomized spray device.
Detailed Description of the Preferred Embodime ts
Referring to Figure 1, the overall seguential steps
for treating waste gases are shown. The waste gases,
~S~3689
1 which contain pollutant vapours, and particles in the
liquid and/or solid state, are introduced to a treatment
and cooling zone 10. The waste gases are treated with a
primary spray of scrubbing liquid which is sprayed into
the waste gas stream. The primary spray, as shown, is
introduced to the treatment zone 10. The spray droplets
agglomerate with the pollutant particles to enlarge the
particles where the enlarged particles fall out of the
waste gas stream under the influence of gravity. In order
to cool the incoming waste gases which may be at elevated
temperatures, cooling air is introduced into the treatment ~-
zone and heat exchanged with the waste gases via a heat
exchanger, such that the waste gases as now primarily ~ -
treated and cooled emerged from the primary treatment zone
10. The waste gases are then passed to a secondary
treatment zone 12, wherein a secondary spray is introduced
into the waste gas stream to scrub further contaminants
from the waste gas stream. Depending upon the makeup of
the waste gases, usually after primary and secondary
treatments in zones 10 and 12, the gas stream contains
very fine particulate liquid and solid contaminants which
may be in the range of one micron or less.
To remove such finely divided contaminants in the
waste gas stream, which are of low concentration, the
waste gas stream is passed to a tertiary treatment zone
14. In this zone a very finely divided spray of scrubbing
liquid is introduced into the waste gas stream. Such spray
may be of droplet size in the range of one micron or less
to correspond with the size of the particulate
contaminants.
~i3~
1 The spray may be introduced into the waste gas stream in
either a cocurrent or countercurrent manner to cause a
contacting of the fine spray droplets with the minute
contaminants. It is preferred, however, that the spray be
introduced cocurrently. The waste gas stream is passed to
a turbulent region mixer 16, wherein a very high degree of
turbulence is induced in the waste gas stream by a
generator which has the capability, in combination with
related components, of not appreciably increasing the
pressure of the gas stream as it is passed through the
mixing region. In the mixing region, the very finely
divided scrubbing spray droplets are brought into contact
with the remaining contaminants to enlarge the contaminant
sizes. The waste gas stream is continuously removed from
the turbulent region and passed to a mist removal device
18. The removal device 18 removes essentially all of the
remaining enlarged particulate contaminants from the waste
gas stream to give the purified gas stream.
Referring to Figure 2, an apparatus is shown in
which the process, according to this invention, is carried
out. The waste gas stream is introduced into the
apparatus 20 via duct 22 in the direction of arrow 24.
The waste gases may be that removed from a drying oven for
printing inks and the like. Such waste gases are usually
at elevated temperatures as removed from the drying oven.
In addition, a fan or the like may be located before duct
- 2~ to withdraw the waste gases from the drying oven and
pass them under pressure through the treatment apparatus
20. Thus this fan acts as the prime mover of the waste
gases through the system. There may be a preliminary
1~.5~6~9
1 cooling of the waste gases in duct 24 before treatment in
the primary treatment and cooling zone. With reference to
Figure 1, the primary spray is directed into duct 22
having the enlarged treatment area 26 via spray nozzle
28. The nozzle is fed with pressurized scrubbing liquid
through line 30. As shown, the spray 32 from nozzle 28 is
directed in countercurrent relationship to the flow of
waste gases 24. The droplet size from nozzle 28 may be
relatively large compared to droplet spray in the tertiary
treatment zone, such droplet size in spray 32 may be in
the region of 50 to 100 microns. The primary treatment
zone effects a removal of the larger contaminants in the
waste gas stream, where the droplets, as they combine with
the particulate liquid and solid contaminants, cause such
contaminants to fall out of the air stream onto the base
of duct 22. Such contaminants, as entrained in the spent
scrubbing liquid as it settles out of the waste gas stream
onto the base of duct 22, are collected and removed ~rom
the duct via drain pipe 34.
The waste gas stream, after primary treatment spray,
is passed upwardly into a heat exchanger 36 which has an
inlet at 38 and is of the tube type heat exchanger having
an outlet at 40. Arrows 42 and 44 generally indicate the
passage of the waste gas stream through the heat exchanger
36. Fresh cool air is introduced into the heat exchanger
36 via centrifugal fan 46, where via ducting 48 is
directed to the inlet cowling 50 of the heat exchanger.
The air passes over the tubes 52 in the heat exchanger in
the direction of arrows 54 to cool the waste gases as they
pass through the tubes 52. The cooling air flows in the
~53~8~
1 direction o~ arrows 54 and pas~es ~p o~le~ ple~. 56
shown in dot within stack 58 and is removed from the
plenum 56 in the direction of arrow 58 via ducting 60.
The heated air may be recirculated to a plant for heating
purposes or exchanged in some other manner to derive
energy from the cooled waste gas stream.
In passing the waste gas stream downwardly into
ducting 62, the gases leave the primary treatment and
cooling zone and pass into the secondary treatment zone.
The waste gases, as they pass through ducting 62, turn
upwardly around elbow 64 into vertical ducting 66.
Located in the upper region of ducting 66 is a secondary
spray nozzle 63 which is fed with pressurized scrubbing
solution via line 70. The scrubbing solution is sprayed
downwardly as represented by spray 72 and thus
countercurrently of the flow of waste gases. The spray 72
may be of a droplet size similar to that from nozzle 28 in
the primary treatment zone, where removal of remaining
larqer contaminants and more of the vapours from the waste
gas stream is effected. The enlarged contaminant
particles, as wetted by the spray, fall out of the waste
gas stream down to the base of ducting 62. The spent
scrubbing liquid with contaminants is removed from the
ducting 62 via drain 74. The spent scrubbing liquids, as
gathered by drains 34 and 74 and as gathered from other
drains such as the drain from the base of the turbulence
generator shown in more detail in Figure 3, are delivered
to a common line 76 which passes all co'lected spent
scrubbing liquids to a settling tank which will be
described in more detail with respect to Figure 4.
1 In spraying the secondary treatment spray 72
downwardly and countercurrently, the spray, as it mixes
with the waste gas stream, works under the influence of
gravity to precipitate out of the waste gas stream the
larger particles, where the particle weight is sufficient
to overcome any buoying efect of the waste gas stream as
it flows upwardly in ducting 66. Ducting 66 via U-shaped
ducting 78 leads to horizontal duct work 80 which is
attached to the intake of the turbulence generator 82.
Referring to Figure 3, ducting 80, as leading into
the turbulence generator 82, is shown in more detail. The
turbulence generator 82 has a housing 84 which houses the
device for generating the turbulence in the treated waste
gas stream. According to a preferred embodiment, the
turbulence generator comprises a rotor bearingly mounted
at 86 in the housing and having a drive shaft 88 driven in
the direction of the arrow. The rotor 86 has projecting
therefrom a plurality of projections which, according to
this preferred embodiment, are in the form of spikes 90
extending from the rotor. The spikes 90 serve to generate
a high degree of turbulence in the waste gas stream. ThiS
is accomplished by rotating the rotor at very high speeds,
such as rpms in the ranges of 2,000 to 6,000 rpm for a
rotor having a diameter of approximately 36 inches. This
generates in the waste gas stream turbulence in the region
represented by Reynolds numbers in the range of of 1 x
to 1 x 10 . The turbulence generator 82 serves to
provide a highly turbulent mixing region for mixing the
tertiary spray introduced via line 92 into the waste gas
stream travelling in the direction of arrow 94.
1 The tertiary treatment spray has nozzle 9~ which, as
shown in Figure 5, introduces a fan type spray 98 into the
ducting 80. The nozzle 96 is of the type which introduces
the scrubbing solution in a very fine spray of droplet
sizes in the range of one micron or less. The gas stream
94 is moving preferably in the same direction as the
spray, thus the spray is introduced in a cocurrent manner,
as they move towards intake 100 of the turbulence
generator 82. The spikes 90 in contacting the gases exert
high sheer stresses on the waste gas stream to cause a
high degree of turbulence within the housing 84 of the
turbulence generator. This effects a high degree of
mixing of the finely disbursed scrubbing particles with
remaining contaminants to thereby effect a wetting and/or
absorption/adsorption of such contaminants. Some of the
contaminants, if the droplets are sufficiently enlarged,
may settle out on the housing 84 of the turbulence
generator and thus are removed from the turbulence
generator via drain 102 which~ as mentioned, may be tied
in with the drain lines of the other primary and secondary
treatment areas and transferred to the settling tanks via
line 76. In addition to these droplets which settle out
in the turbulence generator, large droplets which have not
settled out after the secondary spray have been found to
settle out also onto the housing 84.
The waste gases pass out of the turbulence
generating area in a continuous manner in the direction of
arrow 104. Referring to Figure 3, the waste gases, as
they contain the enlarged particulate contaminants, move
upwardly in ducting 106 into a filtration region 108,
, .
6~
1 which according to this preferred embodiment, contains a
compact arrangement of wire mesh 110 which serves to
remove essentially all of the remaining wetted contaminant
particles from the waste gas stream as the gas is passed
over the wire mesh in the direction of arrow 112. The gas
stream is sufficiently humidified with water vapour that
the liquid contaminant particles, which deposit on the
wire mesh do not appreciably evaporate into the now
purified gas stream. This is due to the vapour pressure
of the removed liquid droplets being less than the vapour
pressure of the water droplets in the humidified air.
Turning to Figure 2, the gases, as they pass through
the filtration system, pass out of the ~iltration device
via ducting 114 into stack 58 and are then exhausted to
atmosphere in the direction of arrow 116, as it passes
over the plenum 56 for the fresh air cooling medium. The
collected particulate droplets, as removed in the wire
mesh, may settle out in the base of filtration device 108
and are removed, therefrom, via drain 118 and may be
joined with the remaining spent scrubbing liquids and
returned to the settling tank via line 76.
The spent scrubbing liquids, as returned to settling
tank via line 76, are introduced into the settling tank
120, as shown in Figure 4, via an equalization chamber 122
having perforated lower region 124 to break up the
frothing action of the scrubbing solution as introduced in
the direction of arrow 126. The settling tank of Figure 4
is of sufficient length to achieve a settling out of the
contaminants. An upper scum layer is formed at 128 and
the heavier particulate contaminants separate out on the
~5~i8~
1 bottom of the settllng tank 120 in the region of 130.
This leaves an intermediate layer 132 of scrubbing liquid
which is withdrawn from the tank at 134 and passed back to
the various feed lines of the spray nozzles via lines
136. The scrubbing liquid, as separated out in the region
of 132, may contain some residuals of the liquid
contaminants. This has been found to be advantageous,
particularly in situations where the initial scrubbing
solution is water, so as to provide a common element in
attracting and wetting of the vaporous contaminants in
duct 22. Surfactants may be incorporated in the scrubbing
liquid to assist the wetting of the contaminant
particles. Thus, a scrubbing solution is generated after
initial use of the device which, in containing common
components to the particulate contaminants to ~e removed,
increases the efficiency of the scrubbing of the
contaminants from the waste gas stream.
The following is an example of the various
components used in the apparatus of Figure 2 for effecting
a high degree of removal of contaminants from the waste
gas stream. It is appreciated, of course, that this
example simply demonstrates a preferred mode in carrying
out the invention and is not to be constructed in any way
as limiting the scope of the c~aims. Waste gases from a
drying oven of a printing press are directed to the
apparatus of Figure 2 for purification. For every 1,000
cubic feet of waste gas treated, a total of 1.56 gallons
of scrubbing solution is introduced via the primary,
secondary and tertiary scrubbing group. Of this total
amount of scrubbing solution used, approximately .33
12
~5~36~39
1 gallons are introduced via the fine mist tertiary spray.
~he nozzles used for the primary and secondary sprays are
hydraulic nozzles which form droplet sizes in the range of
20 to 100 microns. An air atomizing nozzle is used to
provide the finely divided tertiary spray of approximately
1 micron or less. For the above conditions, ~5% to 95~
efficiencies in removal of contaminate particles from the
waste gas strem were realized.
Although preferred embodiments of the invention have
been described herein in detail, it will be understood by
those skilled in the art that variations may be made
thereto without departing from the spirit of the invention
or the scope of the appended claims.
3~
13
