Note: Descriptions are shown in the official language in which they were submitted.
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Equipment and method for enhancing combustion and heat transfer
in a boiler by using sound.
The invention concerns equipment and a method for enhancing the combustion
event and heat transfer in a heating boiler.
The invention relates to combustion taking place in power plants, heating
furnaces,
heating boilers and other such combustion spaces and to enhancement of such
combustion. In the following, the name of heating boiler will be used for
these
application objects of the invention.
Combustion is a complex event, which depends on several different factors,
such as
the particle size of the fuel, the combustion temperature and the structure of
the
heating boiler. The fuel used in the combustion event becomes oxidized,
whereby
heat will result. At typical combustion temperatures, combustion of hot solid
matter
depends on the speed at which oxygen is diffused into the surface of the
matter. As
the combustion proceeds, the particle size and particle mass are reduced. When
burning carbon, the combustion results in carbon monoxide, which in the
continued
combustion will become carbon dioxide.
It is a known method to enhance the combustion event by causing turbulence to
occur in the combustion space to enhance movement of the matter and heat
transfer
in the combustion. However, in known solutions problems still occur in the
completion of combustion taking place in power plants, heating furnaces and
heating boilers and other such installations. It is difficult to make
turbulence
generators, such as agitators; to reach high temperatures, which are typically
in a
range of 600-1000°C. In particular, problems occur in the combustion of
non-
volatile carbon particles.
Enhancing of combustion is also associated with cleaning of the heat transfer
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surfaces of the heating boiler to remove ash particles and unburnt carbon
particles
from them. Acoustic cleaning is a known cleaning method, wherein sound sources
are placed in the heat transfer parts of the heating boiler and sound is
produced
periodically at intervals of about 2-15 minutes for a few seconds each time.
Acoustic
cleaning equipment is known e.g. from publications WO-82/01328 and WO-
82/03803.
The purpose of the invention is to bring about equipment and a method for
enhancing the combustion event in such a way that the combustion is more
complete
and emissions are reduced.
Another purpose of the invention is to bring about equipment of a new kind,
wherein a sound source based on a pulse burner is used as the sound source.
The equipment according to the invention for enhancing the combustion event
and
heat transfer in a heating boiler is mainly characterised in that the space
above the
major combustion zone in the combustion space of the heating boiler is
equipped
with sound sources to generate an acoustic field in order to enhance the
combustion
event and to achieve a more complete combustion, and that the sound sources
are
placed in such a way that the acoustic pressure patterns generated by the
sound
sources meet at angles of 20-90° sideways and/or vertically.
The method according to the invention for its part is characterised in that in
a space
above the major combustion zone in the combustion space of the heating boiler
a
rotating acoustic field is generated by sound sources, which are located on
various
sides and/or at different elevations of the heating boiler.
In the arrangement according to the invention, the combustion event is
enhanced in
such a way in a heating boiler that an acoustic field is applied to a space
above the
actual major combustion zone. Matter volatilisiilg at this location has
already burnt
out for the most part, but some carbon still remains in the form of small
particles,
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which have not yet burnt. The acoustic field is preferably continuous and it
is
generated by suitable sound sources, one or more, which are placed in the
combustion space of the heating boiler. The sound source is preferably a sound
source based on a pulse burner. By the arrangement according to the invention,
the
combustion event is enhanced in such a way that more heat is obtained from the
fuel
used and less combustion residue will result. At the same time, a cleaner
combustion
is also achieved, wluch means that harmful emissions are reduced.
By using the sound source according to the invention, which is based on a
pulse
burner, that problem is solved, which is associated with pneumatically
operated
sound sources in that due to the higher pressure existing inside the
combustion space
dust or other impurities will drift from the combustion space into the sound
source.
No such problem occurs in the sound source based on a pulse burner.
In the following, the invention will be described with reference to the
figures shown
in the appended drawing, but the intention is not to limit the invention only
to the
embodiments shown in the figures.
Figure 1 shows a heating boiler and the location therein of the equipment
according
to the invention.
Figure 2 shows an example of the acoustic field according to the invention.
Figure 3A shows the sound source according to the invention.
Figure 3B shows a valve in the sound source according to the invention.
Figure 3C is a cross-sectional view of the sound source according to the
invention.
Figure 3D is another cross-sectional view of the sound source according to the
invention.
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Figure 1 is a schematic view of a heating boiler, wherein the method according
to
the invention for enhancing the combustion event is applied. Sound sources S
are
located in combustion space 11 of heating boiler 10. The place of location of
sound
sources S is a space above the major combustion zone before cooling of the
combustion gases. The sound sources used are preferably such sound horns known
in acoustic cleaning, which produce a sound volume of 130-170 dB at a
frequency
of 20-1000 Hz. The sound source used may also be pneumatically operated
continuous sirens or the sound source according to the invention shoran in
Figures
3A-D, which is based on a pulse burner. Due to the good penetration depth, the
acoustic frequency range chosen is preferably used explicitly in order to
enhance the
combustion event. The power and frequency of the sound sources S may be
controlled within the chosen range according to the type and size of boiler
and the
locations of sound sources S. The sound volume is chosen so that the acoustic
pressure level generated by sound sources S is preferably no less than 130 dB
at the
place where acoustic pressure patterns meet, where the temperature ~in the
combustion space 11 is typically over 800°C. Sotmd sources S are placed
in
combustion space 11 in such a way that the acoustic pressure patterns which
they
generate will meet at angles of 20-90° sideways and/or vertically.
In an advantageous embodiment of the invention, sound sources S are placed at
different elevations in the heating boiler 10, and when moving upwards in the
combustion space 11 the frequency of the sound source S is increased as the
diameter and mass of solid particles diminish further ahead in combustion
space 11.
Hereby the desired effect enhancing the combustion event will remain at an
optimum.
In another advantageous embodiment of the invention, sound sources S are
placed in
such a way in heating boiler 10 that the resulting acoustic field is rotating.
Figure 2
illustrates such a rotating acoustic field, which is generated by locating in
the
combustion space 11 of a heating boiler, which as regards its diameter is of a
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rectangular shape, four sound sources S, which are used to generate the
acoustic
pressure direction pattern shown in Figure 2. A rotating acoustic field of a
corresponding kind can also be generated in a heatiilg boiler of some other
shape.
The number and locations of sound sources S may be different from those shown
in
5 tlus example, when generating a rotating acoustic field.
In an advantageous embodiment of the invention a part of the secondary and/or
tertiary air needed in the combustion event is supplied through the sound
sources S
placed in heating boiler 10. This supplied air at the same time functions as
cooling
air for sound sources S.
Figure 3A shows a sound source SP according to the invention, which is based
on a
pulse burner. Figure 3B shows an example of the structure of a valve V of
sound
source SP, Figure 3C is a cross-sectional view of sound source SP along line A-
A'
indicated in Figure 3A and Figure 3D is a cross-sectional view of sound source
SP
along line B-B' indicated in Figure 3A.
The sound source used is a pulse burner, which preferably operates with the
combustion reaction between a gaseous or gasified fuel and air and functions
on the
"pulse jet" principle known as such. In such an embodiment the sound source SP
includes an antechamber SPi, into which air under pressure is supplied through
assembly Li, a combustion chamber SPz, iizto which a gaseous inflammable
matter
is supplied through assembly Lz, and a sound horn SP3. Between antechamber SP1
and combustion chamber SPz there is a valve/set of valves V, whose structure
is
shown by the cross-sectional view in Figure 3B. In addition, sound source SP
includes one or more igniters I located in combustion chamber SPz. Combustion
chamber SPz is surrounded by cooling devices C including cooling fins ci,. .
.,cn. Into
cooling devices C a cooling medium, preferably cooling air or water, is
conducted
by way of assembly L3.
After the combustion event, the pressure of combustion chamber SPz is released
into
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the space to be cleaned, that is, into combustion space 11.
The igniting device/devices I used are preferably spark plugs or a hot shoe
functioning as a constantly glowing igniting component.
The pulse burner operating as sound source SP preferably uses hydrocarbon gas
and
air in starting. In addition, in one embodiment of the invention a gasified
gas is used,
which is taken from that part of the combustion space, where no secondary or
tertiary air has yet been introduced.
The sound source according to the invention forms a continuous acoustic
pressure
pulse, with which a continuous quick pulse-like acoustic pressure can be
driven into
the combustion space of the boiler.
The invention may be applied in all types of power plants, heating furnaces,
heating
boilers and other such installations. The sound sources used are sound horns
known
in acoustic cleaung, but also sound sources of other lcinds may be used.
The following is a presentation of the claims, but the invention is not
intended to be
limited only to the different embodiments presented in the claims.
