US20180313533A1

US20180313533A1 - Burner

Info

Publication number: US20180313533A1
Application number: US15/779,394
Authority: US
Inventors: André VAN DER VEKEN
Original assignee: Fireforce Technology Sarl
Current assignee: Fireforce Technology Sarl
Priority date: 2015-11-26
Filing date: 2016-11-28
Publication date: 2018-11-01
Also published as: WO2017090012A1; CH711812A1; EP3380788B1; CN108884997A; EP3380788A1

Abstract

The invention relates to a burner for gaseous, fluid or powdery fuels, into which three components are introduced: a fuel (40); an oxidizing gas (10), for example air; and an inert gas (20), for example gases produced by combustion, nitrogen or water vapor. Two components, for example, air and inert gas, are mixed together and propelled by at least one injection stage (95) arranged at different positions in relation to the movement of the fuel.

Description

TECHNICAL FIELD

The present invention relates to a burner for gaseous or gasifiable fuels. According to an important aspect, the burner of the invention allows the combustion at moderate temperature, without visible flame, and is characterized by a particularly low emission rate, in particular as regards the CO, solid particles, and oxides of nitrogen (NO_x). The present invention is suitable for use with a large number of fuels.

STATE OF THE ART

Several variants of burners are known in the art, making it possible to use any kind of fuel. Flame burners cause a localized high temperature, which results in the formation of unwanted pollutants, such as NO_x.
Flameless burners are also known which combine good energy efficiency with low emissions. In these burners, also known as FLOX® burners, a portion of the flue gas is recycled in the combustion zone. In this way, the mixture is depleted and a diffuse combustion is obtained whose temperature is more uniform than in conventional devices. These advantages, however, require proper adjustment of the combustion parameters. In these burners, the fuel and the oxidizing gas are injected at the same time and at the same place into the combustion chamber so that an optimal and homogeneous concentration of these components is ideally obtained. If optimal conditions are not achieved, imbalances may occur which result in imperfect combustion.
In order to achieve the optimum combustion conditions, the more efficient known burners are complex constructions, requiring precise manufacture with a large number of parts assembled with close tolerances. This obviously has a detrimental effect on the cost of the product and sometimes also on its reliability.
The burner of the invention can be adapted to use a large number of combustible substances, for example combustible gas, flammable liquids, solids, or also gases and volatile products resulting from a pyrolysis reaction. In this latter application, the burner of the invention is particularly efficient and can be advantageously coupled to a pyrolysis furnace to produce charcoal and energy from wood or plant products. When charcoal is used for soil improvement or sequestered in any way, these facilities can produce renewable energy with a positive CO₂balance.
Document EP2184538 discloses a FLOX burner with recirculation of flue gas.
Document EP2669575 discloses a burner in which the oxidant flow is periodically varied. However, this document does not describe stepped injectors with respect to fuel movement. Similarly, EP1486729 discloses a burner with air and water injectors arranged laterally, but without recycling of flue gas. Moreover, this burner is optimized for the thermal degradation of PCBs, and operates at very high temperatures. DE19619919, DE19613777, DE102004034211, EP0413104 and U.S. Pat. No. 6,155,818 describe other solutions of interest as technological background.

BRIEF SUMMARY OF THE INVENTION

One aim of the present invention is to provide a burner free from the limitations of known devices.
Another aim of the invention is to provide a burner that allows clean combustion, that is energy efficient, and that is accompanied by a low level of NO_xand CO emissions.
According to the invention, these aims are achieved in particular by means of a burner with recirculation of inert gas or combustion gas in the combustion zone, and staged injection, defined by the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

FIG. 1 schematically illustrates a burner according to one aspect of the invention associated with a fuel source. FIG. 1a illustrates the enlarged detail ‘A’ therefrom.

FIGS. 2, 3, 4 and 5 illustrate variants of the burner of the invention.

EXAMPLE(S) OF EMBODIMENT OF THE INVENTION

In the embodiment of the invention illustrated by FIGS. 1 and 1 a, the combustion chamber 70 is a vertical cylindrical body 70 which may be made of steel, or any other suitable material. Of course, the invention could be implemented by combustion chambers of different shape and/or orientation: these characteristics are not essential for the invention.
In the illustrated example, a fuel gas 40 is produced by a pyrolysis furnace 45 in which wood, or a similar material, is converted into charcoal with the production of combustible gases and vapors. The fuels, produced and preheated by the pyrolysis, enter through a lower opening and move upwardly by natural convection, pass through the combustion zone 77 in which they are converted into burnt product 60, and exit through the upper opening.
The present device has been specifically designed for burning pyrolysis products, and has provided very satisfactory results in this application, being capable of high energy efficiency with low emissions. However, the invention may be adapted to burn any fuel, be it gaseous, volatile, an atomized liquid, or a sprayed solid substance. The movement of the fuel can be by natural convention, as is the case in this example, or be pushed by a blower, for example.
The duct 80 serves to introduce combustion air into the combustion volume 77, which is essential for combustion. In the illustrated example, it descends into the combustion zone while remaining in the peripheral position. This is not an indispensable feature of the invention. The duct 80 could indeed be in a central position, or also external to the combustion chamber 77. The air 10 is drawn by a fan 13 or by any other appropriate means creating a pressure difference. The invention also includes variants in which the combustion air is drawn into the combustion chamber by a depression created downstream, for example by a natural convection or forced convection chimney.
The main part of the oxidizing gas 10 is not discharged directly into the combustion zone. The duct 80 is surrounded, at least partially, by a conduit 90 of inert gas 20, in this case a flue gas taken downstream of the combustion zone 77, therefore a gas with zero oxidizing capacity, or at least greatly reduced oxidizing capacity, compared with that of the oxidizing gas 10. The oxidant 10 is mixed with the inert gas 20 by the injectors 35, and the mixture 30 is injected through the nozzles 95 into the combustion zone 77. The speed of ejection of the air 10 by the injectors 35 generates, by the Venturi effect, a depression which draws the inert gas 20 to descend into the pipe 90.
Importantly, the injection of the burnt air/gas mixture 30 is multi-stage, arranged one after the other in the combustion zone, relative to the movement (vertical in this example) of the fuel, so that a vertical combustion profile is established. In addition, the speed of the pulsed air causes a powerful transverse mixing. Technical tests have shown that this device makes it possible to obtain an optimal and low-emission combustion of gases 40. Furthermore, adjusting it is excessively simple because it is reduced to the choice of the speed of the fan 13. This parameter is, moreover, not very critical, and the tests performed have shown that wide variations in ventilation velocity have a very limited effect on the operation of the burner of the invention, which is therefore particularly suitable for simple installations and does not require sharp monitoring.
The construction of the burner is also particularly simple and does not require precision machining and fitting. It is worth mentioning that the geometry of the injectors 35 could be much more refined than what is shown, as evidenced by the large number of Venturi injectors known in the art. The illustrated structure, however, has provided quite satisfactory results and has the advantage of simple and inexpensive construction.
Optionally, a direct injection of air 15 into the combustion chamber can be provided upstream of the injectors 95 and higher in the combustion zone. This injection makes it possible to burn any combustible products that would not have been entirely consumed in the combustion zone 77.
FIG. 2 shows a variant of the burner of the invention wherein the inert gas conduit is disposed within the oxidizing gas pipe. In this variant, the inert gas is pressurized, for example by a pump or a fan, not shown, and mixes with the oxidizing gas (e.g. air) in the injectors 35 which are placed on the side wall of the conduit 90 opposite the nozzles 95 of the air duct 80. This variant has the same advantages as that of FIG. 1 with regard to the quality of the combustion, with the difference that the inert gas is taken from outside and that it is the driving fluid of the injectors 35, so that the air 10 (oxidant) is sucked by the Venturi effect.
Several kinds of inert gases can be employed in this variant, for example nitrogen, carbon dioxide, or pressurized water vapor. FIG. 2 illustrates in particular a particularly advantageous variant in which the inert gas 20 is pressurized water vapor produced by a steam generator 22 (illustrated here very schematically), preferably heated by the burner itself.
FIG. 3 refers to another variant of the invention in which the driving fluid is a pressurized inert gas which draws air (combustion gas) by the Venturi effect. The difference with the examples presented above is that the mixture of air and inert gas is not at the level of the stages 95, but in a Venturi unit 35 placed higher. Although the figure shows a single unit 35, it is quite clear that without exceeding the scope of the invention, a plurality of units 35 may be upstream of the injection stages 95.
Analogously, FIG. 4 shows a variant in which the oxidizing fluid 10 is pulsed air which also serves as a driving fluid in a Venturi unit 35 placed upstream of the injection stages 95, in which the air is mixed with a inert gas 20 produced from combustion. Also in this case, a single injector is shown to simplify the drawing, but the invention may include several.
The embodiment of FIG. 5 comprises two injection groups 101 and 102, positioned at different heights in the combustion chamber. In the illustrated example, the injection groups 101 and 102 are positioned peripherally and opposite each other, but this is not an essential feature. The injection groups 101 and 102 are supplied with combustion gas by two blowers 13, 130, as illustrated, or by a single common blower, or by natural aspiration, as mentioned above.
In the first injection group 101, the inert gas conduit 90 rises to the upper regions of the combustion zone, for example above the injection nozzles 195 of the second injection group, or substantially to the same height of said nozzles, so as to suck inert gas at maximum temperature.
The second injection group has the function, among others, to mitigate the combustion temperature in the upper regions of the burner. For this purpose, the external pipe 120 is not connected with the hot flue gases, but with a source of cold and inert gas, for example water vapor, or the combustion gas, but cooled. In the example illustrated, the external pipe is in communication with the combustion gases downstream of a heat exchanger 160. It is also possible to combine the two types of gas, either to recycle combustion gases, cooled or not, into the external pipe, and to inject vaporized or nebulized water into it.
The burner of FIG. 5 makes it possible to obtain an optimal vertical temperature profile and favorable to a complete and clean combustion. The first injection group 101 recycles into the combustion zone very hot gases, taken near the hottest point of the chamber, which allows complete combustion, and also makes it possible to consume low-volatility fuels, for example fuel oil.
Experience has shown, however, that a burner with a single injector group can reach, at the top, temperatures that are too high and harmful to the materials, and giving rise to the production of NO_R. This disadvantage is overcome by the second injector group 102, which recycles in the combustion zone gases at a lower temperature than those recycled by the first group. For example, the first injector group could recycle flue gases having a temperature of 800° C., and the second group 102 could recycle still flue gases, cooled to 200-300° C.
The invention presented is not limited to the examples described with the aid of the figures. In particular, it also includes variants in which a mixture comprising a combustible gas and an inert or oxidizing gas is injected in a staged fashion in the claimed manner. In other embodiments, the conduits 80 and 90, which are shown here as coaxial, could be simply parallel, with passages in correspondence of the injection stages, without one completely surrounding the other. These conduits are furthermore not necessarily straight, as shown. Other variations are possible, and the invention includes all those having the features defined by the appended claims.

REFERENCE NUMBERS USED IN THE FIGURES

10 Influx of oxidizing gas
13 Fan
15 Direct injection of oxidizing gas
20 Influx of inert gas or flue gas
22 Steam generator
30 Gas mixture
35 Injector/mixer
40 Influx of fuel
45 Fuel source, e.g. pyrolysis oven
60 Evacuation of combustion products
70 Wall, combustion chamber
77 Combustion zone
80 Oxidizing gas conduit
85 Conduit of depleted mixture
90 Inert gas conduit
95 Injection nozzles
101 First injection group
102 Second injection group
120 Cold gas
130 Source of inert gas
140 Mixed gas mixture
160 Heat exchanger
195 Injection nozzles of the second group

Claims

1. A burner comprising a combustion zone into which three components are introduced by a first injection group:

i. a fuel;

ii. an oxidizing gas, for example air;

iii. an inert gas, for example gases from combustion, nitrogen, or water vapor;

wherein:

two components are mixed together and the resulting mixture is injected and pulsed at a plurality of stages into the third component in the combustion zone, and in that the fuel is in motion and traverses the combustion zone, while the oxidizing gas and the inert gas are mixed together by one or more injectors, so that the mixture thus obtained is drawn into the combustion zone at a plurality of injection stages arranged at different positions relative to the movement of the fuel.

2. The burner of claim 1, wherein said fuel comprises one or more of: hydrocarbon gas, mineral oil, solid fuel.

3. The burner of claim 1, wherein said fuel comprises gaseous and/or volatile products emitted by a pyrolysis furnace.

4. The burner claim 1, wherein said mixture of two components and the injection of the mixture into the third component takes place in an injector based on the Venturi effect.

5. The burner of claim 1, wherein said oxidizing gas is air and said inert gas is a part of the flue gases from the combustion, the air being introduced under overpressure into a conduit of the oxidizing gas provided with a plurality of injectors, wherein the conduit for the oxidizing gas is surrounded at least partially by an inert gas conduit, equipped with injection stages opposite the injectors.

6. The burner of claim 1, in which said oxidizing gas is air and said inert gas is pressurized water vapor or a pressurized inert gas introduced into an inert gas conduit provided with a plurality of injectors surrounded at least partially by a conduit for the oxidizing gas, equipped with injection stages opposite the injectors.

7. The burner of claim 1, wherein said oxidizing gas is air and said inert gas is pressurized water vapor or a pressurized inert gas introduced into an inert gas conduit provided with a plurality of injectors surrounded at least partially by a conduit for the oxidizing gas, equipped with injection stages opposite the injectors.

8. The burner of claim 1, comprising one or several orifices for the injection of combustion gas downstream of the combustion zone.

9. The burner of claim 1, wherein said inert gas is water vapor produced by a steam generator.

10. The burner of claim 1, wherein said inert gas is a part of the flue gases from combustion in the combustion zone, and said oxidizing gas is air drawn by a fan.

11. The burner of claim 1, comprising a second injection unit, connected to a source of colder inert gas of the inert gas recycled by the first injector.

12. The burner of claim 11, wherein the first injection group injects an inert gas consisting of a part of the combustion flue gases taken from the upper region of the combustion chamber, substantially at the same level, or higher, than the second injection group.