Patent Application
20180313533
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 (NOx). The present invention is suitable for use with a large number of fuels.
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 NOx.
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 CO2 balance.
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.
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 NOx and 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.
Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:
In the embodiment of the invention illustrated by
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.
Several kinds of inert gases can be employed in this variant, for example nitrogen, carbon dioxide, or pressurized water vapor.
Analogously,
The embodiment of
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
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 NOR. 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| CH01728/15 | Nov 2015 | CH | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2016/057156 | 11/28/2016 | WO | 00 |
