Patent Application
20080299506
This application claims the priority to DE Patent Application Serial No. 10 2007 025 051.9-13, entitled “Metallurgical gas burner,” filed May 29, 2007. The specification of the above-identified application is incorporated herewith by reference.
The present invention relates to a steam generator gas burner for burning gases of low calorific value, which comprises a core air tube, a gas tube arranged coaxially around the core air tube to form a gas flow cross section, in particular an annular gas flow cross section, and at least one further tube element arranged coaxially around the gas tube to form a secondary air flow cross section, in particular an annular secondary air flow cross section, wherein first swirlers being arranged in the gas flow cross section.
When forming gas firing systems for steam generators, gas burners which burn gases of low calorific value are also used. Such gases of low calorific value are made available in particular in the vicinity of metallurgical plants as what are known as metallurgical gases. They may take the form of top gas, blast furnace gas, converter gas, coke-oven gas or similar process-residue-gases.
For burning these gases, it is known from practice to provide customary gas burners with an additional ring cross section, through which the gas of low calorific value is fed to the burner mouth and the burner flame.
In the case of gas firing systems, pressure vibrations may occur in the region of the combustion chamber and lead to damage to the lining of the steel structure. Pressure vibrations occur where there is a source of excitation, a resonant cavity and a connection via pipelines. The occurrence of pressure vibrations in the firing system is a consequence of the technical properties of the overall installation in terms of flow, heat and combustion as well as the acoustic properties. The basis for pressure vibrations is a regenerative cycle in which the supply lines of the resonant system, the burner, the coupling element and the flame including the combustion chamber are the source of excitation and intensification. The pressure vibrations are attributable to a sudden increase in volume after the ignition of the combustible fuel-air mixture. If the combustion produces sufficiently strong pulses with a frequency close to the natural frequency of the combustion chamber, a resonance vibration is created, causing the additional loading. With increasing output of the steam generator, and consequently the burner, and with increasing caloric value of the fuel gas greater levels of sound energy are transferred to the combustion chamber walls. Since maximum values of the energy conversion per unit of space and time, consequently also great fluctuations, occur specifically in flames that are short, and consequently hot, in contrast a smooth combustion control is successful in avoiding excitation of resonance vibration as a result of delayed reaction.
From practice a steam generator gas burner of the generic type is known that has swirlers arranged in the gas flow cross section of the gas of low calorific value. With the aid of these swirlers, on the one hand the mixing between gas of low calorific value and combustion air is influenced, but on the other hand so too is the gas outlet velocity, thereby ensuring a stably burning combustion.
Often, however, gases produced in metallurgical plants are mixed there and are then fed to the steam generator gas burner as metallurgical gas of low calorific value. In the case of such mixing of a number of metallurgical gases the properties of the fuel, in particular the calorific value of the combustion gas fed to the steam generator gas burner, change, depending on the mixing ratio of the various gases. The varying properties of the fuel have an influence on the formation of the flame and can then in turn lead to combustion chamber vibrations being caused by the combustion. With increasing ignition intensity, which occurs for example when there is a higher calorific value of the combustible gas, the excitation energy increases. Under certain boundary conditions, a resonance vibration of the flue gas column may then occur in the combustion chamber.
The present invention relates to adapting a steam generator gas burner to varying properties of the combustible gas, in particular a fluctuating calorific value, while taking into consideration the respective ignition intensity.
The steam generator gas burner according to an exemplary embodiment of the present invention includes first swirlers which are adjustably arranged.
Because of the fact that the first swirlers are adjustably arranged within the gas flow cross section, it is possible, if appropriate, to influence the degree of swirling of the flowing combustion gas of low calorific value produced by the first swirlers for adjustment of the tangential velocity component of the gas, and consequently the degree of swirling of the combustible gas flow, even during the operation of a steam generator gas burner. The first swirlers have the effect that the combustible gas flow, initially flowing in the longitudinally axial direction of the gas burner, experiences a deflection in the tangential direction, which imparts a swirl pulse, known as the combustible gas swirl, to the combustible gas flow flowing again in the longitudinally axial direction after leaving the first swirlers. By adjusting the combustible gas swirl, i.e. varying the amount and the degree/inclination of the deflection of the combustible gas flow from its original longitudinally axial direction of flow into a tangential direction of deflection, influence can be brought to bear on the mixing taking place in the mouth region of the burner of the combusible gas of low calorific value with the primary or core air added in the core air tube and the secondary air added radially outside. Depending on the respectively applicable properties of the combustible gas, in particular the respective calorific value of the combustible gas, the first swirlers are set and if applicable adjusted during operation in such a way that optimum burning and flame formation take place, avoiding the occurrence of furnace chamber vibrations. The degree of swirling to be achieved by the position of the first swirlers can in this case both be set, and made to suit the quality of gas to be burned, in a one-off event when the steam generator gas burner is put into operation and be permanently and/or continuously controlled and adapted in accordance with the properties of the combustible material and the combustible gas flow during the operation of the steam generator gas burner.
In a particularly favourable way, the first swirlers can be arranged adjustably in the gas flow cross section in such a way that the first swirlers are formed as swirl blades extending in the radial direction of the core air tube. As a result, the first swirlers in the form of blades protrude from the outer side of the core air tube into the gas flow cross section, and can therefore be rotatably formed, in particular about the longitudinal axis. Rotation about the longitudinal axis then allows a greater or smaller cross-sectional area of the respective swirl blades, depending on the rotational position, to oppose the direction of flow of the combustible gas flow, and consequently set the combustible gas flow into a different degree of swirling, acting as a flow obstacle and a flow diverting area. For this purpose, the invention provides in a refinement that the first swirlers are rotatably arranged respectively about their longitudinal axis, extending in the radial direction of the core air tube, on the outside of the core air tube.
It is expedient furthermore if the first swirlers are arranged upstream of the mouth regions of the core air tube and the gas tube into the furnace chamber, which the invention likewise provides. As a result, an evening out of the combustible gas flow provided with a swirling pulse is achieved before it reaches the mouth region in the burner. In particular, this is expedient whenever the secondary air is provided with a corresponding degree of swirl. According to a development of the invention, it is then also of advantage in this respect if the first swirlers are arranged at a position situated further upstream with respect to second swirlers arranged in the secondary air flow cross section.
Altogether, the arrangement of first swirlers in the gas flow cross section, but also the arrangement of second swirlers in the secondary air flow cross section have the effect of allowing delayed mixing of the combustible gas and the combustion air to be achieved in the outlet region of the steam generator gas burner to the furnace chamber, with the aid of which the ignition can be positioned optimally in each case.
To assist the delayed mixing of the combustible gas and the combustion air further, the invention is distinguished in a development by a flow directing ring, which is arranged in the mouth region at the end face of the gas tube and has first flow areas, deflecting gas flowing in the gas flow cross section in the direction towards the burner longitudinal axis, and second flow areas, deflecting air flowing in the secondary air flow cross section in the direction away from the burner longitudinal axis. As a result, the secondary air flow is deflected outwards and the combustion gas flow is deflected inwards, and consequently the meeting of the two gases is delayed.
It is of advantage here if the flow directing ring is arranged axially adjustably on the gas tube, which the invention provides in a refinement.
A favourable design of the flow directing ring can be realized if the flow directing ring has holes, especially an area of the flow directing ring that covers the gas flow cross section of the gas tube is formed as a perforated plate.
Advantageous materials for producing the flow directing ring are heat-resistant sheet metal, ceramic material or cast metal, in particular centrifugally cast metal, the invention finally further providing in an advantageous refinement that the flow directing ring is cooled and/or is provided with a ceramic coating.
FIGURE shows a steam generator gas burner according to an exemplary embodiment of the present invention.
FIGURE shows in a schematic and partially sectional side view and cross-sectional representation a steam generator gas burner denoted overall by 1, which is designed in the form of what is known as an annular burner. The burner has a core air tube 2, which is arranged in the centre of the steam generator gas burner 1, coaxially around the longitudinal axis 3 of the latter. Combustion air is supplied as core air through the core air tube 2 to the mouth side of the steam generator gas burner 1 that is facing a furnace chamber 4 of a steam generator. Formed around the outside of the core air tube 2, at least in the further end region of the steam generator gas burner 1 on the mouth side, is an annular gas flow cross section 5. This gas flow cross section 5 is delimited on the outside by a gas tube 6, which is arranged coaxially around the core air tube 2. Formed around the gas tube 6 is a further flow region as an annular secondary air flow cross section 7, which is enclosed and delimited on the outside by a tube element 8. A combustible or combustion gas of low calorific value, known as a metallurgical gas, which can occur at various production locations in a metallurgical plant, is supplied through the gas flow cross section 5 to the mouth region of the steam generator gas burner 1. The metallurgical gas may be a mixture of various gases such as blast-furnace top gas, coke-oven gas or the like. Secondary combustion air, known as secondary air, is fed through the secondary air flow cross section 7 to the mouth region of the steam generator gas burner 1. In the gas flow cross section 5 first swirlers 9 and in the secondary air flow cross section 7 second swirlers 10 are arranged. The first and second swirlers 9, 10 are arranged as swirler rings on the respective tube, the core air tube 2 in the case of the first swirlers 9 and the gas tube 6 in the case of the second swirlers 10, and extend through the respective flow cross section 5, 7 to the next tube, the gas tube 6 in the case of the first swirlers 9 and the tube element 8 in the case of the second swirlers 10.
The first swirlers 9 take the form of swirl blades and form a ring of blades. The respective longitudinal axis of each of the individual first swirlers 9 of the ring of blades is positioned such that it is radially directed at the longitudinal axis 3. Each individual swirl blade 9 is rotatably about this longitudinal axis, and consequently adjustable in its relative position in the gas flow cross section 5. Both the first swirlers 9 and the second swirlers 10 are arranged upstream of the mouth opening of the steam generator gas burner 1 towards the furnace chamber 4 within the respective flow cross section 5, 7, the first swirlers 9 being positioned further upstream than the second swirlers 10 with respect to the mouth opening of the steam generator gas burner 1.
A flow directing ring 11 is arranged in the mouth opening of the gas tube 6. It is arranged and/or fastened on the inner side of the gas tube 6 such that it is adjustable axially in the direction of the longitudinal axis 3. The flow directing ring 11 has flow elements 12, which have first flow areas 12a, interacting with the gas flow cross section 5, and second flow areas 12b, interacting with the secondary air flow cross section 7. The first flow areas 12a are designed here in such a way that gas flowing in the gas flow cross section 5 is deflected in the direction towards the burner longitudinal axis 3 and the second flow areas 12b are designed here in such a way that air flowing in the secondary air flow cross section 7 is deflected in the direction away from the burner longitudinal axis 3. The flow directing ring 11 is in this case also formed in such a way that its annular end face 13 merely covers the outlet side of the gas flow cross section 5 on the mouth side, and this area is provided in the form of a perforated plate. Only the second flow areas 12b reach on the outside slightly into the continuation of the secondary air flow cross section 7 into the furnace chamber 4. The flow directing ring 11 consists of a metallic cast material, in particular centrifugally cast material, but may also be produced from a ceramic material or a heat-resistant sheet metal. Furthermore, the flow directing ring 11 may be cooled and/or provided with a ceramic coating.
As known from customary gas burners, arranged inside the core air tube 2 are gas lances 14a, 14b, with which it is also additionally possible if desired to feed gas of high calorific value, for example natural gas, to the mouth of the steam generator gas burner, for burning as supplementary combustible gas. Furthermore, an oil or gas ignition burner 15 is arranged in the centre of the burner along the longitudinal axis 3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102007025051.9-13 | May 2007 | DE | national |
