Note: Descriptions are shown in the official language in which they were submitted.
COMBUSTION PLANT AND METHOD FOR OPERATING A COMBUSTION
PLANT
[01] The invention relates to a combustion plant with a
flue gas outlet, which has nozzles on opposing sides of the
flue gas outlet, so as to meter a fluid into the flue gas.
In addition, the invention relates to a method for
operating a combustion plant, in which at least a portion
of the combustion air is added to the flue gas through
nozzles arranged on opposing sides of the flue gas outlet.
[02] In a combustion plant, it is known not just to vary
the primary air, but also to add the secondary air to the
flue gas through different nozzles. The addition of fluids
in the secondary combustion area serves to swirl the flue
gases, and is intended to produce a homogeneous mixing of
the flue gas and the secondary air added through the
nozzles. In practice, a strong swirling is achieved via
special nozzle formations, which leads to a mixing of the
added secondary air with the flue gas. For example, this is
described in DE 19 47 164 A, CN 102 620 285 A and US 2004/0
185 399 Al. The objective here is to keep the flue gas away
from the walls and optimally mix it in the center of the
flue gas outlet through suitably arranged nozzles and gas
flows adjusted thereto.
[03] The object of the invention is to further develop such
a combustion plant.
[04] This object is achieved with a generic combustion
plant, in which the nozzles are arranged and aligned in
such a way as to move the flue gas in the flue gas outlet
back and forth along a wavy line.
[05] The invention is based on the knowledge that the
nozzles can be used not just for swirling purposes, but can
also be arranged in such a way that the flue gas moves
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along a wavy line in the flue gas outlet. In other words, a
single flue gas particle is not guided in the flue gas
outlet coming from the furnace grate along a straight line
or spiral furnace grate. The particle is also not guided
through the flue gas accompanied by swirling so as to be
intensively mixed with secondary air.
[06] According to the invention, the flue gas particles
flow on a defined wavy line through the flue gas outlet. As
a result, essentially all particles have a longer retention
time in the flue gas outlet than would be possible given a
straight through-flow. While individual flue gas particles
have an especially long path inside of the flue gas outlet
when swirling, and other particles flow especially quickly
through the flue gas outlet, guiding the flue gas according
to the invention causes essentially all particles to
traverse a longer path in the flue gas outlet. This
increases the retention time of the particles in the flue
gas outlet, and all particles have a defined retention time
on a defined path. Guidance along the wavy line is
possible, since hot flue gases have a viscous consistency,
and can thus be guided on a path through the nozzles. This
results in a reproducible, uniform treatment of the flue
gas, and, in particular in edge areas of the flue gas
outlet, prevents flue gas particles from flowing in
straight strands along a relatively straight line through
the flue gas outlet, while other particles remain in the
flue gas outlet for a very long time due to swirling.
[07] According to the invention, the nozzles are not used
for swirling as in prior art, but rather are specifically
aligned in such a way that the flue gases flow along a wavy
line through the metered in fluid, thereby increasing the
retention time inside of the flue gas outlet.
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[08] In order to guide the flue gases along a wavy line,
pressure, volume flow and alignment along with nozzle
formation must be specially adjusted. Depending on the
geometric formation of the flue gas outlet, the nozzle
parameters can be set in simple tests in such a way as to
achieve a defined wavy line. This wavy line should have at
least three, and preferably even more than four, reversal
points.
[09] The added fluid can also be a liquid that as a rule
evaporates when entering into the flue gas outlet. It is
advantageous that a gas be added as the liquid. For
example, this gas can be air or steam.
[10] Known nozzles in flue gas outlets are arranged in the
flue gas outlet in such a way that the nozzle is aligned
perpendicular to the wall of the flue gas outlet in which
it is arranged.
[11] However, it is advantageous for
the solution
underlying the invention for the primary nozzle direction
of the two nozzles arranged on opposing sides of the flue
gas outlet to lie at an angle of at least 5 , preferably of
more than 10 , from a line connecting the nozzles.
[12] In particular if no other nozzle lies opposite the
nozzle, it is advantageous for the primary nozzle direction
of a nozzle to deviate from the shortest connection to the
opposing side of the flue gas outlet by at least 5 ,
preferably by more than 10 .
[13] In relation to a horizontal line, it is advantageous
for the primary nozzle direction of at least one nozzle to
deviate from a horizontal plane in the flue gas outlet by
at least 5 , preferably by more than 10 .
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[14] The invention is suitable in particular for combustion
plants which exhibit a furnace grate for combustion.
[15] It is here advantageous for the flue gas outlet of the
furnace grate to expand in the direction of flow of the
flue gas. A combustion plant in which the flue gas outlet
expands from the furnace grate in the direction of flue gas
flow is essential to the invention even independently of
the features of a combustion plant mentioned above.
[16] Expanding the flue gas outlet in this way leads to an
inverted nozzle, and hence slows down the flow in the flue
gas outlet. Either cumulatively or alternatively to moving
the flue gases along a wavy line, it is thus proposed that
the flow rate of the flue gases in the flue gas outlet be
decreased by expanding the flue gas outlet. A flue gas
outlet expansion is understood as a cross section of the
flue gas outlet that expands in the direction of flue gas
flow. The direction of flue gas flow given a wavy line is
here understood as the connection between reversal points
of the wave.
[17] In another embodiment of the combustion plant that is
also relevant to the invention even independently of the
aforementioned features, the flue gas outlet has a lower
and upper area, wherein the access from the furnace grate
to the flue gas outlet in the lower area is arranged offset
to the upper area.
[18] While the flue gases in the flue gas outlet
essentially flow toward the top and the retention time in
the flue gas outlet can be increased by moving the flue
gases along a wavy line and/or by expanding the flue gas
outlet, the retention time in the flue gas outlet can also
be increased while keeping the height of the flue gas
outlet unchanged by displacing the access from the furnace
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grate to the flue gas outlet to the remaining flue gas
outlet.
[19] A special embodiment provides that at least one nozzle
be arranged above the furnace grate in the direction of
flow of the flue gas before the flue gas outlet, so as to
inject fluid into the flue gas.
[20] The object underlying the invention is also achieved
with a generic method in which the combustion air is added
as primary combustion air and secondary combustion air or
as secondary combustion air during operation of the
incinerator at several varyingly different addition points.
While the addition of combustion air is usually optimized
and no longer changed during operation of the incinerator,
the invention proposes that the distribution of combustion
air to different addition points be varied during operation
of the incinerator.
[21] It is indeed known for combustion plants to vary the
primary air in the area of the furnace grate according to
an optical analysis of combustion on the grate transverse
to the conveying direction on the grate. What is new,
however, is varying the addition of air between the primary
and secondary combustion air and varying within different
addition points of the secondary air. It is here especially
advantageous for the combustion air ratio (X) to be held
constant during variation.
[22] The combustion air can be added distributed to the
nozzles and grate, or the distribution of partial volume
flows to these nozzles can be controllably varied.
[23] During operation of the incinerator, it is especially
advantageous that the combustion air be distributed to the
individual addition points optimized for NOR, CO and/or 02.
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This means that the distribution of volume flow for
addition to the individual nozzles and/or to the nozzles
and the grate is changed during operation of the
incinerator in order to optimize parameters like NOx, CO
and/or 02.
[24] Cumulatively or alternatively, it is provided that the
distribution of combustion air be split among the nozzles
in the flue gas outlet in such a way as to achieve a nearly
constant burnout per unit time. The gas and/or solid
burnout can here be optimized.
[25] The nozzles make it possible to vary the height of the
burnout plane inside of the flue gas outlet, and in
measurements to analyze the burnout as a function of height
in the flue gas outlet, and as a function thereof to vary
the fluid added via the nozzles in such a way, for example,
as to not drop below a specific burnout level in a specific
height of the flue gas outlet.
[26] An advantageous exemplary embodiment is shown on the
drawing, and will be explained in more detail below. Shown
on:
Figure 1 is a schematic view of the arrangement of fluid
addition points on a combustion plant, and
Figure 2 is a schematic view of a wavy line of flue gases
in a flue gas outlet.
[27] The combustion plant 1 shown on Figure 1 has a furnace
grate 2 and a flue gas outlet 3. The arrows 4 denote the
addition of primary air at the furnace grate 2, and the
arrows 5 to 9 denote the addition of secondary air via
nozzles. The nozzles 10 to 14 are only schematically
denoted. The nozzle 10 is here arranged above the furnace
grate 2, and the nozzles 11 and 12 are arranged on a side
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15 of the flue gas outlet 3, while the nozzles 13 and 14
are arranged on the opposing side 16 of the flue gas outlet
3.
[28] The dotted lines 17 to 21 denote the primary nozzle
direction of the nozzles 10 to 14.
[29] With respect to the primary nozzle direction 17, the
angle 22 shows the alignment relative to a line 23
connecting the nozzles 12 and 14. The angle 24 shows the
alignment of the primary nozzle direction 17 in relation to
the shortest connection 25 of the nozzle 14 to the opposing
side 15 of the flue gas outlet 3. Finally, the angle 26
shows the primary nozzle direction 17 of the nozzle 14 in
relation to a horizontal plane 27 in the flue gas outlet 3.
[30] The two opposing sides 15 and 16 of the flue gas
outlet 3 are at an angle 28 to each other, so that the flue
gas outlet 3 conically expands in the area between the
access 29 to the flue gas outlet 3 and a transition 30 to
perpendicular sides 31 and 32 of the flue gas outlet 3.
[31] This results in a lower area 33 of the flue gas outlet
3 between the access 29 from the furnace grate 2 to the
flue gas outlet 3 and the transition 30 from the area 33 of
the flue gas outlet 3 with the inclined sides 15, 16 to the
area 34 of the flue gas outlet with perpendicular walls 31
and 32, which is offset relative to this second area 34
between the perpendicular walls 31 and 32.
[32] The nozzle 10 with its primary nozzle direction 21 is
arranged on a wall 35 lying opposite the furnace grate 2,
and thus lies in an area 36 above the furnace grate 2 and
before the entry into the lower area 33.
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[33] During operation of the combustion plant 1, the
nozzles 10 to 14 generate a wavy line 37 of flue gas 38,
which arises on the furnace grate 2. Adding secondary
combustion air 39 to 43 as the gas to the flue gas 38
produces the wavy line 37 with its reversal points 44 to
48. The primary combustion air 49 is supplied to the
combustion plant 1 via the grate 2.
[34] This makes it possible to add the combustion air in
such a way that the flue gas 38 flows on the wavy line 37.
A preferred method additionally provides that either the
secondary combustion air 39 to 43 or the primary combustion
air 49 and the secondary combustion air 39 to 43 be added
distributed among the different addition points on the
grate 2 or on the nozzles 10 to 14 in varying quantities as
a volume flow or mass flow during operation of the
combustion plant. The combustion air ratio can here vary
during operation of the combustion plant. However, it is
advantageous for the combustion air ratio to be held
constant.
[35] Sensors 50, 51 and 52 for NOx, CO and/or 02 are
connected with a controller 53, so as to optimize the
distribution of combustion air comprised of primary
combustion air 49 and secondary combustion air 39 to 43 to
the individual addition points.
[36] The burnout can be determined from the measured values
ascertained with the sensors 50 to 52, making it possible
to adjust the distribution of combustion air to the nozzles
so that the burnout per unit time remains nearly constant.
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