Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
DEVICE FOR ELIMINATION OF INCOMBUSTIBLE PARTICLES FROM GASES.
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Technical field
The present invention relates to a device for the elimination of particles
pr4~esent in
smoke and exhaust gases, in particular diesel engine exhaust gases and
particles
related to the combustion of wood fuel and ventilation air.
The object of the present invention is to obtain a device for
elimination/reduetion of the
amount of solid particles in smote and exhaust gases in order to thereby
reduce the
environmental risks, in particular for those being present in the
neighbourhood, i.e., are
present close to a major road having a high traffic load or are present in the
neighbourhood of frequent wood heating.
Background of the invention
Today wood heating exists to a large extent in the form of combustion of
chips, pellets
and larger blocks thanks to the fact that it is counted for as a renewable
energy source,
a bio fuel, as the carbon dioxide produced during combustion will return to
nature and
be assimilated by the growing plants.
At industrial wood heating there are considerable requirements on smoke gas
purification, which means very small emissions, but at small scale wood
heating the
combuston is very much done "by instinct°' and quite often an
incomplete combustion
will occur at nights as one reduces the admission of air in order to keep heat
as long as
possible. It is not pleasant to wake up in chilly or cool rooms and walk over
to the
heater on cool floors. Insufficient admission of combustion air will, however,
lead to
insufficient combustion, quite often a pyrolysis, and the production of carbon
monoxide
which is an extremely poisonous gas as it blocks the transport of oxygen in
the blood by
occupying the oxygen carrying sites in haemoglobin in the blood.
Small scale wood heating means emission of moisture in the form of steam
contained in
the wood (normally ~5% or more) but also emission of large amounts of
particles,
emissions of tar or more heavy hydrocarbons, such as polyaromathic compounds
(PAN),
NOX, hydrocarbons, such as methane, ethanol, benzene, and others, aldehydes,
such as
formaldehyde, as well as carbon monoxide and carbon dioxide. The correlation
between
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different substances in the exhaust of small scale wood heating is hard to
determine
due to the complex chemical reactions which occur at the combustion.
It is, however, clear that a moist fuel provides increasing emissions with the
excveption
~f f~~Bg, where moist wood gives 3 times higher amounts of CO, 5-10 times
higher
amounts of tar, 10 times higher amounts of light hydr~carbons and 30 times
higher
am~unts of Pf~H.
then it comes to the emission of carbon monoxide it is important that a
complete
combustion occurs, which means that at least stoichiometric amount of air (4.7
normal
cubic meters per kg dry wood) but in most cases a considerable excess, up to
100% to
obtain a complete combustion depending on incomplete in-mix of air and thereby
oxygen to the fire hearth.
In the mid 1980ties ceramic lined, in particular wood furnaces, were
introduced in
Sweden to obtain an improved combustion and improved assimilation of the
energy
content of the fuel. In spite of this, 60% of the emissions of PAH in Sweden
are
regarded as derived from wood heating and this is our foremost sole pollution
source.
Swedish authorities has invested SEK 30 millions to investigate the impact on
the health
by these emissions.
SE-C-513 391 discloses a device for complete cobustion of solid fuels and
comprises two
combustion chambers joined together, of which one is a combustion chamber for
drying
and gasification of the fuel and the second one is a final combustion chamber
for
combustion of the gasified fuel and whereby a ceramic filter is arranged as a
partition
wall between the chambers, which filter allows the gasified fuelt to pass
through but
blocks remaining solid substance to pass into the final combustion chamber and
whereby the combustion gas is forced to pass the ceramic filter whereby the
combustion
temperature is raised to a suitable combustion temperature. This device is
meant to
replace a conventional furnace.
N~-C-131,325 relates to a device for separating solid particles from a gas
stream by
direct the gas from a source to a mixing chamber where a mixture of steam and
atomized liquid droplets are introduced under such conditions that the liquid
droplets
are accelerated to a speed of at least 60 m/s over the inlet speed, whereby
solid
particles are caught by the liquid droplets, whereby a subpressure is obtained
in the
mixing chamber. The invention is thereby related to a ration between steam and
atomized droplets.
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US-A-6,019,819 relates to a device catching a condensate, which condensate
contains
oil and other hydrocarbons from food processing, such as French frying
potatoes.
S ~lO 99/56854 relates to a process for separating particles from a flow of
hot gas
whereby the relative humidity is primarily increased to almost saturation,
then gas and
particles are cooled adiabatically so that water condenses upon the particles
whereupon
the particle containing water is separated off.
EP-A-0 110 438 relates to a process and a device for purification of particle
containing
gas by means of condensation of water onto the particles in the gas and a
separation of
water droplets comprising particles.
However, there is a great demand for a completion of existing furnaces by
means of a
final combustion part to be able to reduce emissions of toxic gases and
compounds, as
we(( as there is a need for being able to eliminate particles on one hand from
small scale
wood heating, on the other hand from diesel engines, either mobile or
stationary.
Nothing in the prior art discussed above can provide this.
Summary of the present invention
The present invention relates to a device for the elimination of particles
from smoke and
exhaust gases and is characterized by
comprising a first chamber having an inlet for smoke or exhaust gas,
further comprising a heatable combustion zone,
comprising a second chamber having an inlet from said first chamber for said
gas, and
comprising an outlet for collection of particles.
In a preferred embodiment of the invention the device further comprises means
for
provide turbulence of said gas.
In a preferred embodiment of the invention the device further comprises means
for
adding atomized liquid, preferably water.
In a preferred embodiment of the invention the device further comprises an
outlet for
particle contain(ng condensate.
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In another preferred embodiment of the invention the device further comprises
a second
inlet into the first chamber for the addition of combustion aiding gas.
In a further preferred embodiment of the invention the device further
comprises a heat
exchanger arranged in the second chamber to heat ea~change between gas and
liquid.
In another preferred embodiment of the invention the device further comprises
a heat
exchanger arranged in the outlet of the second chamber for heat exchange
between gas
and gas.
Tn a another preferred embodiment of the invention the device further
comprises a
means for the addition of energy to said heatable combustion zone.
In a further preferred embodiment of the invention the device comprises a
means for
atomizing a liquid.
In another preferred embodiment of the invention the device comprises a means
for
transfer of liquid into vapour form.
In another preferred embodiment of the invention the device for separation of
a
condensate comprises a rotatable helical centrifuge.
In a further preferred embodiment of the invention the device comprises a gas
outlet
placed in the outlet of the second chamber, in which gas outlet there is an
evacuation
fan to obtain a subpressure in said first and second chambers for the driving
of said
helical centrifuge.
In a further preferred embodiment of the invention, in particular for the
purification of
diesel exhaust gases, the device comprises a tubular chamber having an inlet
part,
which chamber is provided with a gas permeable sock, which allows passage of a
substantially particle free gas to a second chamber,
that it comprises a brake plane arranged in the first chamber at the end
facing away
from the inlet part to catch particles and in connection to said brake plane
there is a
combustion zone arranged and
that it comprises an outlet for the elimination of collected, non-combusted
particles.
In a further preferred embodiment of the invention the device comprises a
temperature
influenced opening arranged in the inlet part to obtain a predetermined high
smoke gas
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flow in the first chamber to obtain a safe catch of the particles at the brake
plane of the
device.
Tn a further preferred embodiment of the invention the device catches and
makes the
5 particles subject to a combustion, said particles having a particle size
less than 1 Nm,
preferably less than 0,5 (am, more preferably less than ~,3 Nm, further more
preferably
less than 0,2 lam.
~etaited description of the present invention
The present invention will now be described in more detail with reference t~
the
accompanying drawing, however, without being restricted to this or the
embodiment
being related thereto, in which drawing
FTG. 1 shows a schematic cross-sectional view of a device according to the
invention,
FIG. 2 shows a graph over particle size versus the number of particles at wood
heating
in a pellet furnace,
FIG. 3 shows the particel size distribution after smoke gas purification in a
device
according to FIG. 1
FIG. 4 shows an electron microscopy image of a smoke gas particle prior to the
purification step,
FIG, 5 shows an electron microscopy image of an agglomerated particle obtained
after
passage of a smoke gas purification according to FIG. 1,
FIG. 6 shows a schematic embodiment of a device for catching and eliminating
particles
from a diesel engine,
FIG. 7 shows a second schematic embodiment of a device for catching and
eliminating
particles from a diesel engie,
FIG. 8 shows an embodiment of a device for catching and eliminating particles
from a
diesel engine according to FIG. 6,
FIG. 9 shows rate distribution in exhaust gases in a device according to FIG.
8, and
FIG. 10 shows a part device for the adjustment of gas flow speed in an exhaust
tube
from a diesel engine (not shown).
In the device according to FIG. 1 there is a first chamber 1 having an inlet 3
from a
combustion plant, such as a wood heating furnace (not shown). In connection to
the
inlet 3 there is an air inlet 4, as well, to obtain a forced addition of air.
In the first
chamber there is a fan 5, as well, to be able to perform a complete mixing of
incoming
air from the air inlet 4~ and smoke gas from the inlet 3.
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Above the first chamber 1, there is a second chamber 2 being arranged, which
is
connected to the first chamber 1 via a heatable combustion zone 6, which can
be a filter
containing an electrical heating, or be provided with heat from infra heaters
7 arranged
in the first chamber. Above the combustion zone 6 a fine mesh net 8 is
provided across
the cross-section of the section chamber 2. ~4bove this net 8 there is a water
inlet 9
arranged through which water and/or steam can be added to the formation of
cloud of
atomized water above the net 8. Tn the upper part of the second chamber 2
there is a
heat exchanger for heat exchange between hot gas and water, i.e., emittance of
heat to
water, being part of the water of a heating system of a house in a building
either as hot
tap water or as water carried heat to radiators.
The second chamber 2 is provided with a smoke gas outlet 17 being connected to
a
second heat exchanger 10 for heat exchange between gas and air. To the gas
part of
this heat exchanger 10 there is a condenser 11 being connected for deviation
of any
condensate from the gas.
In the condenser 11 there is suitably a helical centrifuge 16 being arranged.
In a smoke gas outlet 12 a fan 13 is arranged to draw gas/air through the
system of
first 1 and second 2 chambers. The second heat exchanger 10 is provided with
an inlet
14 and an outlet 15 for through going air.The outlet 15 can be connected to
the
ventilation system of a building while the inlet 14 suitably being connected
directly to a
fresh air inlet in a wall (not shown).
The system works in such a way that hot smoke gases, 850°C or more,
having their
contents of particles and volatile light and heavy hydrocarbons are introduced
into the
inlet 3 of the first chamber 1. There the smoke gases are mixed with incoming
air
through the air inlet 4 by means of the fan 5. The smoke gases so blended will
then
pass the combustion zone 6 in which, still combustible gases, including CO
(carbon
monoxide) are combusted to the formation of C~~, and water. The water is added
simultaneously through the water inlet 9 which can be connected to a water
line or to
the condenser 11, which water in close contact with the hot net 8 is vaporized
(atomized), whereby the aprticles and heavy gases are caught by the water and
are
carried further on past the first hea exchanger 9, where a heat exchange will
take place
against water. The, somewhat cooled smoke gases, 90-100°C, are then
transported to
the outlet of the second chamber and to the second heat exchanger 10 where a
further
cooling down will take place by means of heat exchange against air. Tn
particular in this
later part the water present in the smoke gases will condense and be collected
in the
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condenser 11 having its outlet 21 together with the particles which have been
carried by
the smoke gases from the primary combustion in the wood heating furnace, not
shown.
13y means of the fan 13 arranged in the smoke gas eachaust 12 the smoke gases
will be
drawn all the time through the two chamber and pass the two heat ea~changers.
This
subpressure will also allow the helical centrifuge 16 to s~;lf-rotate and
provides a longer
transportation way of the outgoing smoke gas to provide an increased
condensation of
ingoing water. The helical centrifuge is a helical screw provided in a tight
shaft, which
shaft is journalled in a bearing in a centrifuge housing via ceramic point
bearings. The
helm as such can be made of an inert material, such as stainless steel or
ceramics. Test
carried out show that the helical centrifuge will reach a rotational speed of
12-16000
rpm quite simple.
Outgoing air through the outlet 15 is normally about 10°C above
surrounding
temperature, i.e., normally about 30°C.
Tests carried out have shown a very good degree of particle separation. Thus a
device
according to the above has been run in connection with a pellet driven wood
heating
furnace (villa furnace).
The results are evident from the following table.
Table
Relates to Test 11, Test 2~~ Test 33,
KI.1154-1240 KI.1455-1529 KI.1540-1620
Amount of particles49 31 28
prior to cooling,
mg/m3 ntg
Amount of particles10 9 8
after cooling,
mg/m3 ntg
Separation degree80 71 71
%~)
pH 6,8 6,5 6,4
Suspending 65 63 45
Substances, mg/I
volume of 492 366 265-315
condensate, ml
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1) The determinations were carried out at normal wood heating. The effect
withdrawal
from the heating system was about 14.5 kW.
2) Determinations were carried out using an addition of water to the smoke
gases in
order to mimic wood heating using a fuel containing a higher moisture content
than
pellets.
3) Determinations were carri~:d ~ut as above with a further addition oaf water
to the
smoke gases.
4~) The difference between the percentage degree of separation and 100~/~ is
rust being
released from the metal in the equipment.
As evident from the table above a very high degree of particle elimination
will be
obtained.
As evident from FIG. 2 a substantial part of the particles present in the
smoke gases
from a pellet furnace a particle size of less than 1 Nm, whereby a very
substantial part
has a particle size less than 0,2 Nm, and in particular 0,1 Nm and less. Here
the
equipment cannot determine particles less than 0,04 pm.
As evident from FIG. 3 the particles, after combustion and agglomeration have
a
particle distribution exceeding 6 pm, which can be simple separated off. FIG.
4 shows a
non-agglomerated particle having a size of about 2 pm and FIG. 5 shows an
agglomerated particle having a size exceeding 1 mm. It is apparent that a
large particle
can be easily caught and eliminated.
FIG. 6 and FIG. 7 show schematic embodiments of a particle collecting and
eliminating
device in an exhaust tube at a diesel engine (not shown). The device comprises
a first
chamber 1 having an inlet part 3, a gas permeable sock 38, which allows
passage of
substantially particle-free gas to a second chamber 2. In the end of the first
chamber
facing away from the inlet part 3 there is a brake plane 39 being arranged in
the form of
a wall being placed perpendicular to the gas flow presenting the exhaust pipe.
In
connection with this wall 39 there is heatable combustion surface/zone 6
arranged. The
combustion zone is suitably heated by means of electricity obtained from a
generator of
an engine (not shown). Further, there is an outlet 41 being arranged in
connection to
the combustion zone 6 for continuous or intermittent of finally combusted
particles in
the combustion zone, which particles are suitably removed to a emptying
container (not
shown). Tn FIG. 6 the sock has the shape of a cone, while in FIG. 7 it takes
the shape of
a diametry plane. At the purification of diesel exhaust gases it shall be
noted that the
exhaust gases are pressed forward to the exhaust system using a fan (as
different from
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wood heating furnace example above, where a suction fan is placed on the
outgoing
side). By having a pressing fan the right velocities can be achieved in the
exhaust pipe
which will be further discussed below.
FIG. 8 shows a device wherein large particles are collected and/~r are
directly rem~ved
in a casing 4~3 which surrounds the combusti~n zone and where larger particles
can be
collected and/or be directly removed with the exhaust gases.
FIG. g shows the flow velocity around a device according to FTG. 8, whereby
zone A
relates to a velocity of about 20 m/s, while zone ~ denotes a velocity of
about 30 m/s.
In order to achieve that as many particles as possible reach the brake plane
39 the
velocity in the chamber 1 should be as high as possible, i.e., in this case
about 30 m/s.
FIG. 10 shows a device where the size of the opening around the apex of sock
38 can
vary with temperature. At idling the temperature of the exhaust gases are low,
as well
as the velocity, why the size of the opening should be small to increase the
velocity.
Having an increasing engine temperature and engine load the velocity of the
exhaust
gases increase why the size of the opening can increase. This can be carried
out by
means of a bimetal regulated opening device 42 surrounding the apex of the
sock 38.
The opening device should, in this case, be designed with a number of blade
parts
overlapping each other to facilitate a small opening around the sock. If a
device
according to FIG. 7 is used, the throttling will have another physical design
and can be
made of one or two sheets creating a slot shaped opening.
Foreliggande anordning kan ocksa anvandas for rening av luft, sasom
ventilationsluft,
varvid mikroskopiska partiklar, sasom allergener, bakterier och virus kan
elimineras.
The present invention can also be used for cleaning of air, such as
ventilation air,
whereby microscopic particles, such as allergens, bacteria and virus can be
eliminated.
