Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
13371~1
The invention relates to a method and an
apparatus for reducing the CO content of waste gases
produced in incinerators, especially incinerators for
domestic and special garbage, where this garbage is
incinerated, for example, in a rotary kiln and the
waste gases are sent through a boiler downstream of
the furnace.
Waste gases produced in garbage incin-
erators, and also those derived from coal fired power
plant boilers, contain, among other th1ngs, carbon
monoxide, the amount of which should be kept as small
as possible. The requirement for TA air is that it
should be a pure gas containing less than lOOmg/m of
carbon monoxide.
In the case of garbage incinerators, for
example, the garbage is charged into a rotary kiln,
operating in parallel flow where it is incinerated.
These kilns end up in waste heat boilers in
which the slag is removed from the bottom while the
waste gases or flue gases flow through the first
boiler flue almost perpendicularly from bottom to
top. After a deflection there follows a further heat
exchange in a convection part. The waste heat boiler
is followed by a waste gas cleaning processing for
dehalogenizing, desulphurizing and dust removal.
The oxygen content of the boiler amounts to
about 10% and the fule gas~-temperatures in the lower
part of the first boiler flue usually exceed 800C.
The oxygen originates with the rotary kiln process
and with the so-called secondary air supply.
Since this prerequisite per se should
produce satisfactory burn out of -the CO in the waste
gas, it is assumed tha-t jets form in the waste gas
and that the mixing of waste gases and atmospheric
oxygen is inadequate. ~
~'
1337161
Now it is an object of the invention to
reduce the CO content of the waste gases of
incinerators.
According to the invention, this is
accomplished by thoroughly mixing the waste gases in
the lower part of the waste heat boiler downstream of
the furnace, and for this purpose the combustion
gases are injected into the boiler through burners,
for example high velocity burners.
The combustion gases are, preferably
injected into the boiler at right angles with respect
to the direction of flow of the waste gases,
preferably at a velocity of about 100 m/s or more.
It is desirable to inject the combustion
gases into the boiler in several different planes or
levels and from opposite sides of the boiler.
A suitable apparatus for the implementation
of this method comprises a plurality of burners, e.g.
high velocity burners, which are incorporated into
the first boiler flue, and which are preferably
arranged immediately above the outlet from the rotary
kiln into the boiler, the combustion gas outlet
nozzles being directed towards the interior of the
boiler.
The burners are preferably built into two
opposite walls of the boiler and are directed towards
each other, while being arranged in several vertical
planes one above the other.
The combustion gas outlet nozzles of the
burners run substantially horizontally.
The burners facing each other in the two
walls of the boiler are preferably adjustable in
height in relation to each other, the burners built
into one wall of the boiler being alternately
adjustable in height in relation -to each other.
13371 61
According to another embodiment of the
invention, additional burners may be provided in the
boiler above these burners, the said additional
burners being arranged horizontally with respect to
the burners first mentioned and being staggered in
relation thereto by half the distance between the
centres thereof.
A preferred embodiment of the invention is
described hereinafter in conjunction with the drawing
attached hereto, wherein:
Fig. 1 illustrates diagrammatically the end
of a rotary kiln projecting into the first boiler
flue of a waste heat boiler; and
Fig. 2 is a cross-section taken along line
II-II of Fig. 1.
The temperatures in the first radiation
flue of the boiler, immediately above the end of the
rotary kiln, are about 1000 - 1500C, about
750 - 850C in the middle of the flue, and about
600 - 700C at the upper end in the area of
deflection of the flue. These temperatures fluctuate,
depending upon the composition of the garbage, the
method of operating the furnace, and the degree of
contamination of the boiler, as cause for example by
fly-ash and/or other solid or liquid deposits
produced by the combustion reaction within the
boiler, for instance by residues of incomplete
combustion within the boiler.
However, in view of these temperatures,
mechanical circulation devices seem undesirable,
especially for reasons of operating safety.
According to the invention, therefore, flue
gases are thoroughly mixed with the aid of burners,
more particularly high velocity burners.
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1 3371 61
High velocity burners are to be understood
to mean burners in which combustion takes place in a
combustion chamber provided in the burner, the
combustion gases flowing into the boiler or boiler
flue at speeds of 100 m/s or more.
The waste gases or flue gases flowing
through the boiler are drawn in and are thoroughly
mixed by the high outlet pulses of the combustion
gases emerging from the burners, in order to achieve
a reaction which is as complete as possible between
CO and 2
Fig. 1 illustrates diagrammatically the end
of a rotary kiln 10 projecting into the first
radiation flue or boiler flue 14 of a boiler marked
generally 12. Between the outer periphery of rotary
kiln 10, and the opening in boiler flue 14, there is
an annular gap between 10 and 40 mm wide, for
example, through which so called secondary air enters
boiler 12. However, this gap is not shown in Fig. 1.
Waste gases from rotary kiln 10 flow
vertically in boiler flue 14 from bottom to top.
According to the invention they are thoroughly mixed
in the flue with each other and with secondary air.
Above the inlet end of rotary kiln 10, in
boiler flue 14, preferably directly above, there are
provided burners 16, 18, 20, 22, 24, 26, more
particularly so called high velocity burners. These
burners are mounted and installed in opposed side
walls 36, 38 of boiler flue 14.
In the example illustrated, three burners
are built into each side wall in boiler flue 14,
namely burners 16, 18, 20 in side wall 38 and burners
22, 24, 26 in side wall 36.
Burners 16, 18, 20 thus face burners 22,
24, 26 and the jets of combustion gas emerging from
nozzles 30 are direc,ed towards one another.
1 337 1 6 1
In the vertical direction, individual
burners are adjustable in height in relation to each
other. For example, burners 16, 18, 20 may lie in
one plane while burners 22, 24, 26 may lie in another
higher plane.
It has also been found desirable for the
burners installed in one of walls 36 or 38 to be
adjustable in height in relation to each other, as
shown in Fig. 1.
Thus burners 16 and 20, installed in wall
38, lie in a horizontal plane extending through
burners 16 and 20, but burner 18 lies in a higher
plane. The same applied to burners 22, 24, 26
mounted in wall 36 of boiler flue 14. In this case,
as shown in Fig. 1, burners 22 and 26 lie in the
upper plane whereas burner 24, built into wall 36
between burners 22 and 26, is arranged in a lower
plane.
Both the vertical and horizontal cross-
section of the burners can be selected as a function
of the radiation cone 32 of the combus-tion gases
emerging from burner nozzles 30.
Measurements have shown that the angle of
this cone 32 amounts to about 20.
It is desirable for the horizontal distance
between the burners to be such that radiation cones
32 meet and in-tersect approximately at the central
plane 40 of the boiler flue 14.
The same applies to the vertical distance A
between the two groups of burners.
The centre line of burner nozzles 30 (and
thus the centre line of radiation cones 32)
preferably extends horizontally and at right angles
to side wall 36 or 38. It must be emphasized however
that this need not be the case, i.e. the centre lines
of the burner nozzles or radiation cones centre lines
1 337 1 6 1
may also be upwardly or downwardly inclined at an
acute angle with respect to the horizontal. They may
also form with relevant side wall 36 or 38 an angle
other than 90. (The term horizontal relates to the
fact that boiler flue 14 is arranged vertically and
that the waste gases from rotary kiln 10 flow
vertically from bottom to top).
With this arrangement of burners 16 - 26,
the horizontal and vertical spacing of which
corresponds to the diameter of the jet 1n the middle
of the boiler flue 14, very thorough mixing of the
waste gases flowing in boiler flue 14 from bottom to
top is already obtained, since this arrangement
already covers a very large part of the cross-
sectional area of the boiler flue. The alternate
displacement of individual burners causes frequent
deflection of the waste gases ascending in the boiler
flue, thus intensifying the mixing and reaction. The
burners are preferably arranged as close as possible,
i.e. immediately above the outlet from rotary kiln
10, thus ensuring that secondary air is drawn up from
the burner jets at the highest possible temperature
and that the longest possible time is provided for
the oxygen to react with the carbon monoxide.
In addition, more burners 28 may be
provided above burners 16 - 26, e.g. two burners in
each of two further planes and which are constructed
in the same way as burners 16 - 26. However, burners
28 are preferably arranged horizontally in relation
to burners 22, 18, 26 and are staggered by half the
distances between the centres thereof.
With these additional burners 28 it is
possible to mix jets of waste gas not yet covered by
the lower groups of burners, thus still further
improving the reaction between CO and 2
1 337 1 6 1
The burners themselves, which are available
on the market, may be operated with propane gas, for
example.
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