Patent Application
20070298356
The invention is described in greater detail below, partly in connection with embodiments of the invention shown in the appended drawings wherein:
The present invention concerns combustion in a heating furnace of a fuel with an oxidant, wherein the fuel and oxidant are supplied to a burner head. The burner head is secured in a furnace wall in a known fashion, so that the flame formed during combustion extends into the furnace interior.
Referring to the drawing, and particularly to
A burner head having three pairs of fuel and oxidant nozzles is shown in
According to the present invention, pairs of fuel nozzles and oxidant nozzles are provided, in contrast to the embodiment disclosed in the above-identified Swedish patent application, in which fuel is injected through one nozzle and the oxidant through a number of nozzles.
According to a preferred embodiment, the nozzles of the nozzle pairs shown and described herein are positioned along two mutually perpendicular diameters of the burner head, as shown in
Surprisingly, it was found that by injecting the same amount of fuel and oxidant through a number of pairs of fuel and oxidant nozzles, instead of using one fuel nozzle and a plurality of oxidant nozzles, the production of NOx is lowered even further. At the same time, local concentrations of heat and coolness within the furnace are reduced. A probable explanation is that the pairing of nozzles results in the formation of several zones with heavy turbulence, as compared to a burner head wherein fuel is injected through only one fuel nozzle.
According to a preferred embodiment, the burner head 1 includes an additional nozzle 7, a starting nozzle, wherein fuel and oxidant are discharged through respective individual and concentric channels 8, 9. Starting nozzle 7 is operated until the temperature within the furnace has reached the auto ignition temperature for the particular fuel and oxidant combination.
According to a preferred embodiment, the starting nozzle 7 is positioned at or near the center of the burner head 1.
A second combustion step, during which fuel and oxidant are injected through respective ones of the paired nozzles, can advantageously be initiated when the temperature within the furnace is above about 750° C.
According to a preferred embodiment, the discharge openings of nozzles 2, 3, and 4, 5, are outlets of laval or venturi nozzles.
The opening 22 is to allow supervision of the flame by means of the detection of ultraviolet light.
In
Thus, the burner disclosed permits two different modes of operation: on one hand as a normal oxyfuel burner, and on the other hand as a burner whose operation results in a flame with a substantially lower maximum temperature. The lower flame temperature is adapted to be below the temperature at which the production of NOx is limited by the reaction kinetics, which is about 1550° C.
The lower flame temperature is accomplished by the use of the mentioned positioning of the paired nozzles for fuel and for oxygen, whereby fuel and oxygen gas are combusted further away from the burner head as compared to what is the case for conventional oxyfuel combustion.
When carrying out the invention, a diffuse yet controlled combustion is achieved at process temperatures above the auto ignition temperature, substantially lowering the production of nitrous gases, mainly NO and NO2.
As a consequence, fuel and oxidant are mixed with flue gases of the furnace before the fuel and oxidant contact each other. In a way known per se, that results in a larger and cooler flame, in spite of the coefficient of utilization corresponding to combustion according to the prior art. Suitably, the nozzles can be directed straight ahead, that is, they do not need to be directed away from or toward each other. Instead, they can be angled toward or away from the longitudinal axis of the burner head.
According to a preferred embodiment, the oxidant is gaseous, and is an oxidant having an oxygen content of 85 vol % or above.
According to a principal feature of the invention, the oxidant is supplied to the burner at a pressure of at least 1 bar.
A normal pressure for normal applications is 4-5 bars.
The fuel is injected through normal nozzles at the available pressure.
A burner head according to the present invention is not larger than a known burner head for oxyfuel combustion. In a preferred embodiment, the burner head diameter is about 70 millimeters.
The compact structure provided by the present invention permits the invention to be applied to equipment already present at user premises. Also, the inventive structure can be positioned within a small, water-cooled protective jacket, for application at very high process temperatures.
According to the invention, the above-described advantages are achieved with any fuel, whether solid fuel, gaseous fuel, or liquid fuel. The apparatus according to the invention can replace existing combustion systems essentially without any reconstruction of the furnace equipment used in the process.
It is advantageous to choose as the fuel from among oil, propane, or natural gas.
Since the oxidant nozzles and the fuel nozzles can be directed straight ahead, a construction is achieved which is inexpensive, easy to maintain, and possible to apply to existing processes, and without any other measures other than exchanging the nozzle construction.
Several embodiments of the invention have been described herein. However, the design of the burner head can be varied, especially with respect to the number of pairs of fuel and oxidant nozzles.
Thus, the present invention should not be considered limited to the above-disclosed embodiments, but can be modified within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0601374-2 | Jun 2006 | SE | national |
