METHOD FOR INTRODUCING A TREATMENT MEDIUM INTO THE WASTE GAS FLOW IN COMBUSTION PROCESSES

METHODE D'INTRODUCTION D'UN MEDIUM DE TRAITEMENT A L'ECOULEMENT DES GAZ DE COMBUSTION AU COURS DE PROCESSUS DE COMBUSTION

English Abstract

The method for introducing a treatment medium into the waste
gas flow in combustion processes provides that a carrier medium
is mixed with a treatment medium, wherein these media are brought
to a pressure level necessary for atomization in a one-component
nozzle prior to mixing. The quantitative proportion of treatment
medium to carrier medium, which is adjustable as desired, is
adjusted as a function of the NOx gas concentration in the
treated gas flow or as a function of the gas quantity. It is
substantial in this method that a plurality of atomizing nozzles
are arranged in different planes, and that the flame development
in the furnace is monitored by means of flame detectors. When
the flame front reaches the lowest nozzle plane, the supply of
treatment medium to these nozzles is blocked and the nozzles
located above the latter, in which there is not yet a flame, are
regulated with respect to the throughput of treatment medium as a
function of the NOx gas concentration or the waste gas quantity.
As soon as the flame front forms again in the area of the lowest
nozzles, treatment medium is again admitted to these atomizing
nozzles. Carrier medium can also be admitted to the lower
atomizing nozzles without treatment medium in order to cool the
nozzles when the carrier medium is water.

French Abstract

La méthode pour introduire un agent de traitement dans un flux de gaz de combustion prévoit le mélange d'un agent véhiculeur avec l'agent de traitement, et ces agents sont amenés au niveau de pression nécessaire à la pulvérisation dans un gicleur monobloc avant d'être mélangés. La proportion d'agent de traitement mélangé à l'agent véhiculeur, qu'on peut régler à la valeur souhaitée, est choisie en fonction de la concentration de gaz NOx dans le flux de gaz traité ou en fonction de la quantité de gaz. Il est essentiel dans la présente méthode qu'une pluralité de gicleurs-pulvérisateurs soient disposés sur différents plans et que le développement de la flamme dans le foyer soit contrôlé au moyen de détecteurs de flamme. Quand le front de flamme atteint le plan des gicleurs les plus bas, l'alimentation en agent de traitement de ces gicleurs est bloquée et les gicleurs au-dessus, dans lesquels il n'y a pas encore de flamme, sont réglés en tenant compte du débit d'alimentation en agent de traitement en fonction de la concentration de gaz NOx ou de la quantité de gaz de combustion. Dès que le front de flamme se reforme dans la zone des gicleurs les plus bas, ceux-ci sont à nouveau alimentés en agent de traitement. Les gicleurs-pulvérisateurs les plus bas peuvent aussi être alimentés en agent véhiculeur sans agent de traitement dans le but de refroidir les gicleurs lorsqu'on utilise de l'eau comme agent véhiculeur.

Claims

Claims
1. Method for the introduction of a treatment medium in the form
of chemicals into the waste gas flow in combustion processes by
means of a carrier medium through an atomizing nozzle for
reducing the nitric oxide concentrations, wherein the
introduction into the furnace is effected in at least two plane
lying one on top of the other, in which atomizing nozzles are
arranged, treatment medium being admitted to the latter
alternately or jointly, as desired, characterized in that the
switching from one nozzle plane to the next nozzle plane is
effected as a function of the presence of a flame in the area of
the respective nozzle plane.
2. Method according to claim 1, characterized in that all nozzle
planes are acted upon in the absence of a flame, and in that, in
the presence of a flame in one or more nozzle planes, the
respective nozzle plane is completely cut off from the supply of
treatment medium and the remaining nozzle planes are acted upon
corresponding to the determined requirement of treatment medium.
3. Method according to claim 1 or 2, characterized in that flame
detectors, particularly optical pyrometers, thermographic
cameras, video cameras, photocells, etc., are used for monitoring
the flame.

Description

2 ~
~S~5~ FOR INTRO~CIN~ A ~P~NT ~DI~ INTO T~ T~ ~AB ~0
IN ~ O~ ~kO~ ~R
The invention is directed to a method for in~ ucing a
treatment medium in the form of chemicals into the waste ga~ ~low
in combu~tion proc~s~es by means of a carrier ~edium through an
atomizing nozzle for reducing the nitric oxide co~c~ntration,
wherein i~,~LGd~ction into the furnace is effected in at least two
planes lying one above the other, in which atomizing nozzles are
arranged, the treatment medium being admitted to the latter
alternately or jointly, as desired.
The il.~Lo~ e~ chemical~ for reducing the nitric oxide
content in the waste gases are generally ~ -n; ~ ~ ~al ammoniac,
urea or calci~m cyanamide, which can be mixed under certain
circumst~n~e~C with different hydrocarbon compound~ as so-called
reinforcing chemic~ls. The reactions taking place be~ween these
chemical~ and nitric o~ s in the flue gas flow are reduction
reactions in which the nitrogen monoxide present in the flue gas
is re~llce~ to pure nitrogen. These reactions require relatively
high ambient temperatures in order for the reaction to run
optimally and quickly. How~ver, these temperatures are between
750~C and 1,100~C, dep~ on the chemicals or on the chemical
~ixture. It is generally true for these chemicals, within

83~
certain limit~, that higher temperature~ al~o ensure more
effective reaction conditions. For thi~ reason, in the known
method, the treatment media are introduced in a plurality of
planes by means of akomizing nozzles, wherein treatment medium is
admitted to the individual planes correspondinq to the respective
favorable temperature conditions. Thermoelements which determine
the temperature distribution and automatically effect a switching
between the individual nozzle planes are used for this purpose.
In spite of thi6 expenditure, the process does not always
proceed in a satisfactory manner. Increase~ in the ovexall level
of nitric oxides in the flue ga~ have even been deter i ne~, which
can be traced back to ~ destruction by means of combustion of the
in~.o~cPd che~icals when the latter contain nitrogen.
~ he object of the present invention i to provide a method
in which a reliable reduction of the nitric oxide concentration
in the flue gas is ensured.
This object is met, according to the invention, proçee~in~
from the method ~entioned in the beg; nn; ng, in that the switching
from one nozzle plane to the next nozzle plane is e~fected as a
function of the presPnGe of a flame in the area of the respective
noz~le plane.
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This suggestion for a solution i~ based on the realization
that the introduced chemicals are always destroyed when they come
into contact with a flame. The present invention accordingly no
longer bases the regulating process on a deteL ;ne~ temperature
profile, as was previously the case, but rather solely on the
presence or absence of a ~lame.
In a preferred emb~diment of the method, according to the
invention, all nozzle planes are acted upon in the absence o~ a
flame and when a flame is present in one or more of the nozzle
planes, this nozzle plane is completely cut off from ~he supply
of treatment media and the ~- a;n;n~ nozzle planes are acted upon
corres~on~inq to the determined required treatment medium. In
c~nn~ction with a sensitive monitoring o~ the flame in the
~_ hv-~tion chamber by m~ans of flame detectors, particularly
optical ~ ers, thermographic cameras, video ca~er~s,
photocells, etc., the guantity o~ treatment medium n~ces~Ary for
adjusting a desired nitric oxide content in the ~lue gas can be
in~Lo~ced reg~rdless of the height of the respective flame front
within the co~bustion chArh~r. The aforementioned ~lame
detectors work very quickly, so that a switching from one nozzle
plane to the next nozzle plane can be e~ected very quickly and
destruction caused by chemical splitting of the introduced
chemicals is prevented.

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The invention is described in more detail in the following
by means of the drawings.
Fig. 1 shows a s~h~- ~tic view of the apparatus for introducing
the trea~ment medium; and
Fig. 2 shows a cchematic view of the process flow chart in
connection with the regulating system.
The schematic flow chart for the carrier medium and the
treatment medium can be seen from Fig. 1. According to the
latter, a reservoir container for the che~ical which is to be
intro~ce~ into the furnace and is found in this container, e.g.
in powder for~ designated by 1. The chemical arrives in a
container 3 via a lock 2, water for dissolving the chemical being
intro~o~e~ int~ the container 3 via a valve 4. The prepared
solution or suspen~ion is kept in constant circulating movement
by ~eans of an agitat3r 5 in order to prevent separation. A
level ~onitoring system which ensures the supply of chemicals
from the reservoir 1 when falling ~elow the minimum level is
designated by 6. A floater 7 monitors the liquid status in the
container 3 and influences the valve 4 for the supply of water
into the container 3. The treatment medium is supplied to a
plurality of atomizing no~zles 10 via a line 8 by means of a pump
9, which atomizing nozzles 10 are arranged in the wall 11 of a
furnace 12 so as to be distributed in a plurality of planes. A

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check valve 14 is provided in the pressure line 13 leading ~rom
the pump 9 to the atomizing nozzles 10 in ~rder to prevent the
return flow of carrier medium into the container 3. The carrier
medium, which is water in the present example, is guided by means
of pumps 15 via valves 16 to a pressure line 17 which leads to
the atomizing nozzles 10. A check valve 18 and a pressuxe
~ ring point 19 are provided inside the pressure line.
Another pressure measuring point 20 monitors the pressure in the
atomizing nozzles 10. A flame detector 21 is provided in the
vicinity of the atomizing nozzles 10 of the lower row o~ nozzle~
and blocks a valve 22 in the pressure feed line 13 for the
treatment medium via a regulating system, not shown in this
drawing, when a flame is pressnt in the area of the lower
atomizing nozzle 10. If this i~ not desired, the carrier medium
can also be blocked or throttled by means of a valve 23 when t~e
operating conditions in the furnace allow. A certain supply of
carrier medium can certainly ba desired in order to cool the
atomizing nozzle cven if the treatment medium is blocked.
The regulating system, which helps to regulate the
introduction of the treatment medium generally and, over and
above this, as a function of the flame development in the
furnace, is now expl~in~ by means of Fig. 2. The same reference
numbers are used insofar as parts which were already described in
Fig. 1 are concerned. Treatment medium and carrier medium are
supplied to the atomi~ing nozzles 10, which open into the furnace

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12, by means of pumps 9 and 15. The boiler, to which feed water
is supplied via a line 25, is designated in its entirety by 24.
The steam tapping line is designated by 26, whereas the flue gas
exhaust is sy~bolized by reference number 27.
The delivery quantity of treatment medium, i.e. the chemical
which is provided for introduction into the furnace 12, i5
adjusted by meanC of a regulating system 2B. The regulating i8
effected as a ~unction of the NOx concentration in the flue gas
of the flue gas eXhaust 27, wherein the measurement of this gas
concentration is effected at a location in which flue gas whi~h
has already been treated, i.e. flue gas mixed with the.treatment
medium, is located. This signal is supplied to the regulating
system 28 via ~he line 29. The value which, when exceede~,
causes treatment medium to be supplied to the furnace for
~reating ~he flue gas is adjusted by means of a reference value
tran~mitter 30 ~or the reference value of the N~x content. The
supply of treatment medium is thus regulated a~ a function of the
difference between the a~tual NOX content supplied via the l me
29 and the v~lue predeter~ined by the reference value transmittsr
30. Further, the regulating system 28 can regulate the supplied
quantity of treatment ~edium or additionally as a function of the
flue gas volume flow, wherein this value is measured in the flue
gas exhaust 27 and the correspon~;ng signal is supplied to the
regulating system 28 by means of the line 31.

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This measurement value, which concerns the vol~me ~low of
the f lue gas, is also directed via a line 31 to another
regulating system 32 which is provided for adju~ting the
atomization pressure. A reference value transmitter 33 for the
atomization pressure predetermines a fixed value adapted to the
nozzle configuration, or the atomization pressure can be adjusted
as a function of the flue gas volume flow or the evaporator load.
The meas~c ~t value concerning the flue gas volume flow is
supplied via line 31, while the mea~ nt value c-onc~rning the
evaporator load is supplied via line 34. A ~ignal line which
supplies the actual pre~;1i ng atomization pressure to the
regulating system 32 is designated by 35.
A flame detector 21 is provided below the lower atomizing
nozzle 10 closer to ~he furnace and directs a signal, via a line
36, to a regulating system 37 when a flame occurs in this area,
which regulating ~ystem 37 transmits a corre~pon~;~g oontrol
command, via a ~on~ol line 38, to the valve 22 which monitors
the feed of treatment medium to the atomizing nozzle of the lower
nozzle plane.
When no flame i5 determined by the detector 21, both the
carrier medium and the treatment medium are supplied to the
atomizing nozzles in all planes by means of the pumps 15 and 9,
respectively, wherein the quantity of the supplied treatment
medium is adjusted by means of the regulating systPm 28 as a
...,. ~ . .
.. ... .

2~2~3~
function of the N~x content or ,as a function of ~he waste ga~
volume flow. As soon as the detector 21 dete~ ;~es a flame in
the area of the lower no~zle plane, the valve 22 is closed in
order to pLeVe~l~ a decomposition of the introduced chemical, and
treatment medi~m i~ admitted only to the upper row o~ atomizin~
nozzles lOr wherein the upper row of nozzles is supplied with
more treatment medium after the exclusion of the lower row to the
extent that nothing has changed with respect to the ~lue gas
co~cPntration up ~o that point. For the rest, treatment mediu~
i8 admitted to these no~zles of the upper row via the regulating
syste~ 28 corre~pQn~; n~ to the required treat~ent medium.
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Representative Drawing