U.S. patent number 3,918,834 [Application Number 05/387,128] was granted by the patent office on 1975-11-11 for method of reducing the concentration of nitrogen oxides in a gaseous effluent from a thermal plant.
Invention is credited to Nikolai Alexandrovich Gurevich, Georgy Fedorovich Naidenov, Sergei Savatievich Nizhnik, Isaak Yakovlevich Sigal.
United States Patent |
3,918,834 |
Sigal , et al. |
November 11, 1975 |
Method of reducing the concentration of nitrogen oxides in a
gaseous effluent from a thermal plant
Abstract
A method of reducing the concentration of nitrogen oxides in a
gaseous effluent from a thermal plant fitted with burners,
consisting in the burning of the fuel in two stages under the
conditions of oxygen deficiency in a high-temperature zone, the
two-stage combustion being accomplished by redistributing the flows
of fuel and air inside the burners so that some air mixed with fuel
is introduced in a spiral flow at periphery of the passages through
the burners, and the rest of the air required for complete
combustion of the fuel being introduced in a straight-line flow
directed along the axis of the burners.
Inventors: |
Sigal; Isaak Yakovlevich (Kiev,
SU), Naidenov; Georgy Fedorovich (Kiev,
SU), Nizhnik; Sergei Savatievich (Kiev,
SU), Gurevich; Nikolai Alexandrovich (Kiev,
SU) |
Family
ID: |
23528577 |
Appl.
No.: |
05/387,128 |
Filed: |
August 9, 1973 |
Current U.S.
Class: |
431/10; 431/185;
431/187 |
Current CPC
Class: |
F23C
7/002 (20130101); F23B 5/00 (20130101); F23D
14/20 (20130101); F23B 2700/018 (20130101) |
Current International
Class: |
F23D
14/00 (20060101); F23C 7/00 (20060101); F23D
14/20 (20060101); F23B 007/00 () |
Field of
Search: |
;431/9,10,185,187
;239/403,405,406 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Anderson; William C.
Attorney, Agent or Firm: Waters, Schwartz & Nissen
Claims
What is claimed is:
1. A method of reducing the concentration of nitrogen oxides in a
gaseous effluent of the combustion in a thermal plant fitted with
burners having axial passages, the method comprising the steps of
burning a fuel in two stages within the same heat-receiving chamber
of the thermal plant, under the conditions of oxygen deficiency in
a high-temperature zone, the two-stage combustion being
accomplished by redistributing the flow of the fuel and air inside
the burners so that part of the air is introduced in a first,
spiral flow at the periphery of the passages of the burners, and
introducing the rest of the air, required for complete combustion
of the fuel, in a second, straight-line flow directed along the
axis of the burners, all of the fuel being introduced in a
peripheral zone surrounding the axial passages, together with the
first air flow, with which all fuel is intermixed, thereby causing
a cone-shaped flame to emerge from the peripheral zone,
constituting a first, high-temperature combustion stage, while the
second air flow contributes to a second, lower-temperature
combustion stage axially located with respect to but spaced at a
distance from the first stage.
2. The method as defined in claim 1, wherein the amount of air
allotted to the first, spiral flow is between 40 to 70 per cent of
the total air supply while the amount of air constituting the rest,
for the second, straight-line flow is 60 to 30 per cent of the
supply.
Description
The present invention relates to the protection of the atmosphere
by products of combustion of a natural fuel, predominantly a
gaseous one, and more specifically to a method of reducing the
concentration of nitrogen oxides in a gaseous effluent from a
thermal plant.
Known in the art is a method of reducing the concentration of
nitrogen oxides in flue gases of boilers by burning the fuel in two
stages. This method consists in that some of the air required for
burning the fuel is introduced through burners and the balance
required to obtain a complete combustion of the fuel is admitted
through special inlets (nozzles) outside the burners, the inlets
being arranged as a rule above the top row of burners.
It is known that nitrogen oxides are apt to form in a
high-temperature zone and that their concentration increases with
the amount of free oxygen present in the high-temperature zone. The
known method of burning fuel in two stages prevents the presence of
surplus oxygen in the high-temperature zone because the combustion
of the fuel at the first stage, which is the high-temperature one,
takes place under conditions with a deficiency in the oxidizer.
In the known method, which employs partial admission of air through
special inlets outside the burners, a number of disadvantages is
encountered such as:
THE NECESSITY IN ADDITIONAL BRANCHING OF WATER TUBES TO GIVE ROOM
FOR NOZZLES; THIS REDUCES THE AREA OF HEAT TRANSFER, INVOLVES EXTRA
COST AND IMPAIRS THE INTEGRITY OF THE BRICKWORK;
THE NECESSITY IN ADDITIONAL LINES WHICH MUST BE MADE AND INSTALLED
IN ORDER TO ADMIT AIR INTO THE NOZZLES;
DIFFICULTIES EXPERIENCED IN CONTROLLING THE REQUISITE RELATIONSHIP
BETWEEN THE RATES OF AIR FLOW TO THE BURNERS AND THE NOZZLES; THIS
MAKES THE PLANT DIFFICULT TO OPERATE; AND
INABILITY TO CONTROL THE TEMPERATURE OF THE FLAME FROM THE BURNERS
SO AS TO MAINTAIN THE TEMPERATURE SPECIFIED FOR SUPERHEATING THE
STEAM.
It is the object of the present invention to provide a method of
reducing the concentration of nitrogen oxides in the gaseous
effluent of thermal plants which eliminates the need for special
inlets (nozzles), the additional branching of water tubes, and
keeps intact the brickwork of the thermal plant while reducing the
concentration of the nitrogen oxides in gaseous effluent.
This object is attained in that a two-stage combustion of the fuel
is employed under the conditions of oxygen deficiency in a
high-temperature zone, the two-stage combustion being accomplished
by redistributing the flow of the fuel and the air inside the
burner or burners so that some air mixed with fuel is introduced in
a spiral flow at the periphery of a passage through the burner, and
the rest of the air, required for complete combustion of the fuel,
is introduced in a straight-line flow directed along the axis of
the burner.
The inventive method of reducing the concentration of nitrogen
oxides is accomplished by directly redistributing the fuel and air
flow directly so that the nitrogen oxide content of gaseous
effluent is reduced by 30 to 35% without installing special
nozzles, disturbing the brickwork of the thermal plant or branching
of water tubes. The method also allows to control the parameters of
the flame over a wide range, under variable conditions so, that the
fuel is utilized in a more effective way and thus a higher
operational reliability of the plant is achieved.
The disclosed method has been tested in a laboratory of the
Institute of Gas, Ukrainian Academy of Sciences, and in industrial
plants. The tests have proved the efficiency of the invention in
burning fuel in thermal plants of various designs.
The present invention will be best understood from the following
detailed description of a preferred, exemplary embodiment when read
in conjunction with the accompanying drawings, in which
FIG. 1 is a schematic longitudinal section of a burner for carrying
out the inventive method; and
FIG. 2 is an end view of FIG. 1 in the direction of arrow I.
The method of reducing the concentration of nitrogen oxides in the
gaseous effluent from a thermal plant equipped with burners
consists in a two-stage combustion of the fuel under the conditions
of oxygen deficiency in a high-temperature zone at the first stage.
The two-stage combustion is accomplished by redistributing the flow
of fuel and air inside the burners so that some of the air mixed
with the fuel is introduced in a spiral flow at the periphery of a
passage through the burner, and the rest of the air, required for
complete combustion of the fuel, is introduced in a straight-line
flow directed along the axis of the burner.
The method is performed with the aid of a burner comprising a
cylindrical part 1 (FIG. 1) and a tapered part 2. Welded to the
cylindrical part 1 there is an annular latter. The gas chamber 3
and the cylindrical part 1 are provided with holes 4 drilled
peripherally in preferably two rows so as to admit gaseous fuel
from the gas chamber 3 into the inner passage of the cylindrical
part 1 of. Welded to the cylindrical part 1 (FIGS. 1 and 2) of the
burner there is also a tangential branch 5 serving to admit some of
the air supply, the direction of flow being indicated by an arrow.
Disposed inside the burner, concentrically with its cylindrical
part 1 (FIG. 1), is a cylindrical tube 6 through which the rest of
the air, required for the complete combustion of the fuel at the
second stage of combustion, is introduced in a straight-line flow
along the axis of the burner.
The tapered part 2 of the burner forms a port in a brick-work 7 of
the thermal plant (not shown), the port widening towards a fire
chamber.
The inventive method of reducing the concentration of nitrogen
oxides in the gaseous effluent of the thermal plant is accomplished
as follows. Only part of the air required for the combustion of the
gaseous fuel is introduced through the tangential branch 5 (FIGS. 1
and 2). The flow of this air spirals around the periphery of the
passage through the cylindrical part 1 of the burner.
The gaseous fuel is introduced from the gas chamber 3 through the
holes 4 into the spiral flow of some of the air required for
combustion. The gaseous fuel mixes with the flow of air spiralling
around the periphery. The gas/air mixture (all the fuel and the
peripherally spiralling flow of air), being imparted a spiral
motion, spreads out into the periphery of the tapered part 2 of the
burner and thence to the periphery of the port where partial
combustion of the fuel takes place in a cone-shaped flame expanding
towards the fire chamber, this place being where a high-temperature
zone is formed at the first stage of combustion.
The axial space in the port (formed by the tapered part 2) is not
filled with the flame, and introduced into this space is the rest
of the air (roughly between 30 and 60% of the total amount required
for the complete combustion of the fuel), as it is issued from the
axial tube 6 in a straight-line flow. The sucking action of the
axial cocurrent flow of air causes the products of incomplete
combustion to move inwardly, towards the axis, at a point away from
the burner port, where the centrifugal force tending to separate
the peripheral flow from the axial one is low enough not to
counteract this sucking action.
This is why the rest of the fuel burns up in a straight-line axial
flow at a distance from the burner and the first, or
high-temperature, zone of combustion, and the second stage of
combustion is located at this distance .
* * * * *