EP1800062B1 - Burner for combustion of a low-calorific fuel gas and method for operating a burner - Google Patents

Abstract

The invention relates to a burner (1), for the combustion of a low-calorific fuel gas (SG), with an air channel (2), running along a burner axis (12), for the introduction of combustion air (10) and a fuel gas channel (26), embodied for a high volumetric flow of low-calorific fuel gas (SG), whereby the fuel gas channel (26) and the air channel (2) open out into a mixing region (27). According to the invention, a low-nitrogen oxide synthesis gas operation of the burner (1) may be achieved, whereby a swirl element (4) is arranged in the air channel (2) for the generation of turbulent combustion air (10). The swirling element is provided in an opening region (28) directly adjacent to the flow of the mixing region (27). The invention further relates to a method of operation of a synthesis gas burner (1), whereby, directly before the mixing of the synthesis gas (SG) with the combustion air (10), the level of turbulence of the mass air flow is significantly increased on the microscopic level and a temporally and spatially homogenous mixing of the synthesis gas/air mixture is achieved.

Description

The invention relates to a burner for the combustion of a low-calorie combustible gas, with an air duct extending along a burner axis for the supply of combustion air and with a fuel gas channel, which is designed for a high volume flow on low calorific fuel gas, wherein the fuel gas channel and the air duct open in a mixing area ,

The invention further relates to a method for operating a burner in which a fossil fuel gasified and gasified fossil fuel fed as a low calorific synthesis gas to the burner, mixed with combustion air to a synthesis gas-air mixture and is burned in a combustion chamber.

The EP 0956475 B1 shows a burner for high calorific fuels, such as natural gas or oil which has a largely homogeneous mixture of high calorific fuels and combustion air. For this purpose, a swirling element is introduced within the air supply annular channel in such a way that the inlet of the high-calorie fuel is arranged downstream of the swirling element within the air channel. The fuel is introduced to achieve a homogeneous mixing by means of a plurality of inlet channels which are arranged in the swirl vanes within the air supply channel. This mixture is then introduced into the combustion chamber for combustion.

In view of the global efforts to reduce the pollutant emissions of combustion plants, especially in gas turbines, burners and operating methods for burners have been developed in recent years, which have particularly low emissions of nitrogen oxides (NO _x ). It will It is often emphasized that such burners can be operated not only with one fuel, but possibly with different fuels, for example oil, natural gas and / or coal gas, either selectively or even in combination, in order to increase supply reliability and flexibility in operation. Such burners are for example in the EP 0 276 696 B1 described.

Compared to the classical gas turbine fuels natural gas and petroleum, which consist essentially of hydrocarbon compounds, the combustible constituents of synthesis gases are essentially carbon monoxide and hydrogen. Depending on the gasification process and overall plant concept, the calorific value of the synthesis gas is about 5 to 10 times smaller compared to the calorific value of natural gas. Main constituents in addition to carbon monoxide and hydrogen are inert components such as nitrogen and / or water vapor and possibly also carbon dioxide. Due to the low calorific value consequently high volume flows of fuel gas must be supplied through the burner of the combustion chamber. As a result, for the combustion of low calorific fuels - e.g. Synthesis gas - a separate fuel gas channel, which is designed for a high volume flow of low calorific fuel gas, must be provided.

For the selective operation of a gas and steam turbine plant with a synthesis gas from a gasification or a secondary or substitute fuel, the burner must be designed in the combustion chamber associated with the gas turbine as a two- or multi-fuel burner, both with the synthesis gas and with the second fuel, eg natural gas or heating oil can be applied as needed. The respective fuel is supplied via a specially constructed fuel passage in the burner of the combustion zone.

In the EP 1 277 920 A1 a method for operating a burner of a gas turbine and a power plant with integrated coal gasification is shown. In the method of operating the burner, a fossil fuel is gasified and gaseous fossil fuel is fed as synthesis gas to the burner associated with the gas turbine for combustion. In this case, the synthesis gas is divided into a first partial flow and a second partial flow and the partial flows are fed to the burner for combustion separately. By this mode of operation with two synthesis gas substreams a stepped synthesis gas operation is possible, which is adapted to the load of the gas turbine.

In addition to the stoichiometric combustion temperature of the synthesis gas, the quality of mixing between synthesis gas and combustion air at the flame front is an important influencing variable for avoiding temperature peaks and thus for minimizing the formation of thermal nitrogen oxides. A spatially good mixture of combustion air and synthesis gas is particularly difficult due to the high volume flows of required synthesis gas and the correspondingly large spatial extent of the mixing area. On the other hand, the lowest possible production of nitrogen oxides, for reasons of environmental protection and corresponding legal guidelines for pollutant emissions, is an essential requirement for combustion, in particular for combustion in the gas turbine plant of a power plant. The formation of nitrogen oxides increases exponentially rapidly with the combustion flame temperature. An inhomogeneous mixture of fuel and air results in a certain distribution of the flame temperatures in the combustion region. The maximum temperature of such a distribution determined by the said exponential relationship of nitrogen oxide formation and flame temperature significantly the amount of undesirable nitrogen oxides formed.

Based on this problem, the object of the invention is a burner for the combustion of low calorific fuel gases, in particular synthesis gases, indicate that leads to a lower nitrogen oxide formation. Another object of the invention is to provide a method of operating a burner in which a low calorie fuel gas is burned.

The solution of the problem, which is directed to a burner, is carried out according to the invention by a burner for combustion of a low calorific fuel gas, with an extending along a burner axis air duct for the supply of combustion air and a fuel gas channel, which is designed for a high volume flow of low calorific fuel gas wherein the fuel gas channel and the air channel open into a mixing region, wherein the air channel has an orifice region directly fluidically adjacent to the mixing region, wherein in the mouth region, a swirling element is provided for generating turbulent combustion air and wherein upstream of the swirling element swirl blades are arranged in the air channel ,

The invention is based on the consideration that in the known burners for combustion of low-calorie combustion gases, the nitrogen oxide formation is too high due to insufficient mixing of the low calorific fuel gas with the combustion air in the mixing area in view of future pollutant limits. By incorporating a swirling element into the air duct, the degree of turbulence of the air mass flow is increased even before the combustion air is mixed with the low-calorie combustion gas. The invention has recognized that it is particularly important in this context to carry out a turbulence gradient increase only in the microscopic range, ie large eddy bales with pronounced trailing regions and in particular with upstream flow components must be avoided, otherwise there is a risk of a flashback in the burner itself. In order to enable a particularly stable burner operation, the air duct in this case has an orifice region which is arranged directly adjacent to the mixing region in terms of flow, wherein the swirling element is arranged in the mouth area. It has been found that the arrangement of the swirling element in the immediate vicinity of the mixing region in the mouth region leads to a particularly effective formation of air vortex, so that the generated turbulences propagate to the adjoining mixing region largely trouble-free in the microscopic range. As a result, both a spatial and a temporally largely homogeneous mixture of low calorific fuel gas and combustion air and thus a reduced nitrogen production is achieved. Surprisingly, it has been found that the exact positioning of the swirling element in the air duct is particularly critical for the mixing result in the mixing area.

A significant advantage of the invention is that a particularly good mixture of combustion air and fuel gas is achieved by the microturbulent flow of combustion air, at the same time caused by the swirling pressure loss is low. It is achieved by the mixture of low-calorie fuel gas and turbulence-prone combustion air in the mixing region, a significantly improved spatial homogeneity of the fuel gas-air mixture in the mixing region. The microturbulences ensure a particularly intimate mixing while avoiding a flashback.

Another advantage of the invention is the arrangement of the swirling element in the immediate vicinity of the mixing area in the mouth region. This leads to a particularly effective turbulence. In order to achieve a good mixing result as far as possible further installations in the wake region of the swirling element should be avoided.

In a preferred embodiment, the swirling element is designed so that the producible turbulent flow of the Combustion air at Verwirbelungselement has substantially no areas of back-flowing combustion air. In this way, a safe operation of the burner is ensured in the combustion of low-calorie fuel gas and in particular the risk of a flashback in the burner itself prevented.

Preferably, the air channel is formed as an annular channel which surrounds the fuel gas channel concentrically.

1. a) Einen ersten Begrenzungsring mit einer Symmetrieachse,
2. b) einen zweiten größeren Begrenzungsring, dessen Mittelpunkt auf der Symmetrieachse liegt,
3. c) eine Verbindungsfläche, die durch die beiden Begrenzungsringe aufgespannt ist, und
4. d) entlang auf der Verbindungsfläche liegender Kreise, deren jeweiliger Mittelpunkt auf der Symmetrieachse liegt, eine Vielzahl von flächigen Auslenkelementen, die jeweils gegen eine normale der Verbindungsfläche geneigt sind.

In order to achieve the most effective turbulence increase in the microscopic range for the burner, special requirements are placed on the structural design and arrangement of the swirling element. According to a particularly preferred embodiment of the invention, the swirling element hereby comprises:

1. a) a first boundary ring with an axis of symmetry,
2. b) a second larger limiting ring whose center lies on the axis of symmetry,
3. c) a connecting surface, which is spanned by the two boundary rings, and
4. d) along lying on the connecting surface circles whose respective center lies on the axis of symmetry, a plurality of planar deflection elements, which are each inclined to a normal of the connecting surface.

The swirling element is particularly suitable for use in an annular air duct. There are at least two, preferably three circles provided.

In an investigation of the temporal variation of the mixing ratio in experiments has been shown that locally occurring temporal variations in the mixing ratio between the low calorific fuel gas and the combustion air are very low due to the above-described structural design of the swirling element. At the same time, there is only a slight pressure loss connected to the so-designed swirling element, so that the efficiency of the burner remains almost unaffected.

Preferred dimensions, the connecting surface is less than half of the area enclosed by the larger boundary ring circular area in the swirling element. Further preferably, the diameter of the larger boundary ring is less than about 1 m, in particular 50 to 80 cm. Thus, the swirl element is for use in small flow channels, such as e.g. in the air duct of the burner, suitable.

In a further preferred embodiment, the deflection elements associated with a circle are equally spaced from one another. This achieves a uniform turbulence over the entire connecting surface and thus brings about a particularly homogeneous mixing of the low-calorie combustible gas, in particular of the synthesis gas, with the combustion air in the mixing region.

It is further preferred that each deflection element tapers from the connection surface to a tear-off edge for generating vertebrae. Preferably, it has approximately trapezoidal or triangular shape. By this embodiment, a particularly intense turbulence is achieved.

Preferred dimensions of the associated at a respective circle deflecting elements are inclined in the same direction. Preferably arranged on adjacent circles deflecting elements are inclined in opposite directions. This arrangement of the deflection causes a homogenization over larger areas of the air flow takes place in addition to the local good mixing by the turbulence. This is particularly important to turbulence at the microscopic area at the confluence of the low calorific fuel gas and the combustion air in the mixing area with a view to obtaining a homogeneous synthesis gas combustion air mixture in burner operation.

In a particularly preferred embodiment, the burner is designed such that swirl vanes are arranged in the air duct upstream of the swirling element. This ensures that the combustion air in the air duct is already pre-impounded by means of a swirl blade, before the swirling combustion air flow through the swirling element experiences a turbulence increase in the microscopic range downstream of the swirling element. Furthermore, it is thereby achieved that a swirling element with the above-described advantageous effects on the homogeneity of the mixture of low-calorie combustion gas and combustion air in the mixing region can also be used in conjunction with swirl vanes, which ultimately have a favorable effect on the stability of the combustion of the low-calorie combustible gas. In this case, at least one of the swirl blades can be formed as a hollow blade, from which, if required, a high-calorie fuel, in particular natural gas, can be introduced into the air duct. By means of this additional embodiment, it is possible to use a uniform injection of high-calorie fuel, for example in a natural gas operation of the burner, from a swirl blade designed as a hollow blade with a further homogenizing effect on the fuel / air mixture in combination with the above-mentioned advantages.

The burner can be designed as a premix or hybrid burner for use in gas turbine systems, with an air supply channel, in particular an annular channel, which encloses at least three further, in particular concentric to the air supply channel arranged annular channels for supplying fluidic media, two of these channels for supplying a Serving pilot burner and wherein the pilot burner, a pilot flame to maintain combustion is generated.

The object directed to a method according to the invention is achieved by a method for operating a burner in which a fossil fuel gasified and gasified fossil fuel fed as a low calorific synthesis gas to the burner, and the combustion air mixed into a synthesis gas-air mixture and in a combustion chamber is burned, and immediately before the mixture of the synthesis gas with the combustion air, the degree of turbulence of the air mass flow is increased. Preferably, microturbulences are generated.

The advantages of the method for operating a burner result from the above-described advantages of the burner according to the invention for the combustion of a low-calorie combustible gas, in particular a synthesis gas.

In a preferred embodiment of the method, this is used in the operation of a burner of a gas turbine.

Further preferred is an application of the method in the operation of a power plant with integrated gasification of a fossil fuel to a synthesis gas, in particular coal gas.

FIG 1

eine Kraftwerksanlage mit integrierter Vergasungseinrichtung,

FIG 2

einen Längsschnitt durch einen Brenner gemäß der Erfindung,

FIG 3

ein Verwirbelungselement in Draufsicht, und

FIG 4

ein Verwirbelungselement in Seitenansicht.

In the following the invention will be explained in more detail with reference to an embodiment. It show schematically and not to scale

FIG. 1

a power plant with integrated gasification device,

FIG. 2

a longitudinal section through a burner according to the invention,

FIG. 3

a swirl element in plan view, and

FIG. 4

a swirl element in side view.

Like reference numerals have the same meaning in the figures.

The power plant 24 according to FIG. 1 comprises a gas turbine plant 25 with a gas turbine installation 25 upstream of a gasification device 23 for a fossil fuel B. The gas turbine plant 25 comprises a compressor 14, a combustion chamber 16 and a combustion chamber 16 downstream turbine 18. The compressor 14 and the turbine 18 are connected via a common rotor shaft 15 coupled together. Downstream of the turbine 18, an electric generator 19 is coupled via a generator shaft 22 to the turbine. The combustion chamber 16 comprises a combustion chamber 17 and a burner 1 projecting into the combustion chamber 17 for combustion of a low-calorie combustible gas SG, which is obtained from the gasification device 23 by gasification of the fossil fuel B.

During operation of the gas turbine 18, air 10 is sucked into the compressor 14 and is highly compressed there. The compressed air 10 is then supplied as combustion air 10 to the burner 1 and mixed with the low-calorie fuel gas SG. The resulting fuel gas-air mixture is burned in the combustion chamber 17, with very hot combustion gases. The hot combustion gases are fed to the turbine 18 where they relax to perform work and put both the compressor-side rotor shaft 15 and the generator shaft 22 in rotation. In this way, electric power is generated, which the generator 19 emits for distribution in an electrical network. Downstream of the turbine 18, the partially cooled and expanded combustion gases are discharged as exhaust 20. These exhaust gases 20 are polluting, in particular nitrogen oxides are present in the exhaust gas, which form at the high combustion temperatures in the combustion chamber 17.

Increased nitrogen oxide emission also occurs when the fuel gas / air mixture is not mixed sufficiently homogeneously or experiences a temporal or spatial change in the mixture field. This generally leads to an unfavorable mixture of the low-calorie combustible gas SG with the combustion air 10 and to a considerable increase in the nitrogen oxide formation rate in the combustion process.

Here, the invention provides a remedy in which it proposes a solution that significantly improves the quality of mixing between the synthesis gas SG and the combustion air 10 at the flame front, thus ensuring a low-emission synthesis gas operation of the burner 1, wherein temperature peaks are avoided and thus a Lowering of the thermal nitrogen oxide formation compared to conventional synthesis gas burners is achieved.

To illustrate the concept of the invention shows FIG. 2 a burner 1 for combustion of the low calorie combustible gas SG according to the invention. The burner 1 is approximately rotationally symmetrical with respect to an axis 12. A pilot burner 9 directed along the axis 12 with a fuel supply channel 8 is concentrically surrounded by an air supply annular channel 7. The fuel supply channel 8 is designed for fuels with high calorific value, such as for exposure to natural gas or fuel oil.

The fuel gas channel 26 is designed for a high volume flow of low-calorie fuel gas SG. The fuel gas channel 26 is viewed downstream in the flow direction of the fuel gas SG partially concentrically enclosed by an air supply annular channel 2. In the air supply annular channel 2 is a - schematically illustrated - ring of swirl vanes 5 installed, one of these swirl blades 5 may be formed as a hollow blade 5a , The swirl blade 5 may, if necessary, an inlet formed by openings for a fuel supply of a have high calorific fuel. Downstream of the swirl vane ring 5 is a - shown schematically - swirling element 4 is installed in the air duct 2. The fuel gas channel 26 and the air channel 2 each open into a common mixing region 27, where the low-calorie fuel gas SG is mixed intensively with the combustion air 10. The turbulence element 4 in the air duct 2 provides for the generation of turbulent combustion air 10, so that a good mixing result in the mixing region 27 and thus a low-emission synthesis gas operation of the burner 1 is achieved. It is particularly advantageous for the result of the mixture if - as in FIG. 2 shown - the air duct 2 has an orifice region 28 directly fluidically adjacent to the mixing region 27, wherein the swirling element 4 is arranged in the mouth region. The swirling element 4 is designed such that the producible turbulent flow of the combustion air 10 at the swirling element 4 has substantially no regions of combustion air 10 flowing back. This ensures that no flammable combustible gas-air mixture to the swirling element 4 can flow back appreciably and thus no combustion at the swirling element 4 is stabilized, which could have a damage of the swirling element result. A permanent operation of the burner 1 with synthesis gas SG with low nitrogen oxide formation is thus achieved.

The burner 1 can be operated via the pilot burner 9 as a diffusion burner, wherein a high-calorie fuel is used. Alternatively, it can also be used as a premix burner; ie a high calorific fuel and combustion air 10 are first mixed and then fed to the combustion. In that case, the pilot burner 9 serves to maintain a pilot flame which stabilizes combustion during premix burner operation with a possibly varying fuel-air ratio.

In a synthesis gas operation of the burner 1, the low-calorie synthesis gas SG with the combustion air 10 is first transferred downstream into the mixing region 27 where it is intimately mixed and burned in a combustion zone, not shown.

As already explained, it has hitherto been difficult because of the large volume flows of low-calorie combustible gas SG and thus the geometric extent of the mixing region 27 to ensure a temporally and spatially homogeneous mixture with regard to low-NOx combustion. With the burner 1 of the invention, a particularly homogeneous mixture of combustion air 10 and fuel gas SG is achieved. This is achieved by the swirling element 4 in the air duct, that the combustion air 10 is transferred immediately upstream of the mixing region 27 in a turbulent flow. This depends on a turbulence gradient increase in the microscopic range, ie large vortex paths with pronounced trailing regions and in particular upstream flow components must be avoided, since otherwise there would be the risk of a flashback in the burner 1 itself. This requirement has a direct influence on the structural design of the swirling element 4. A possible particularly advantageous design is in FIG. 3 shown in a plan view of a swirling element 4. The swirling element 4 does not necessarily have to occupy the entire channel height of the air channel 2.

With the in FIG. 3 shown Verwirbelungselement 4 a spatially and temporally particularly homogeneous mixture of combustion air 10 and synthesis gas SG is achieved. At the same time caused by the swirling element 4 pressure loss is very low, whereby the efficiency of the synthesis gas burner 1 is hardly affected.

The following is the FIG. 3 , which shows a plan view of a turbulence element 4 and the FIG. 4 that one with the same reference numerals provided turbulator 4 in a side view, are discussed in more detail:

From an inner boundary ring 52 lead distributed over the ring circumference a plurality of webs 54 to an outer boundary ring 53. The center of the outer boundary ring 53 lies on the axis of symmetry 59 of the inner boundary ring 52 and the webs 54 are directed normal to the inner boundary ring 52. The connecting surface 56 represents the lateral surface of a truncated cone between the inner delimiting ring 52 and the outer delimiting ring 53. Arranged on each web 54 are trapezoidal plane deflection elements 51 pointing in the interior of the truncated cone. The wide side 51 a of each deflecting element 51 is connected to a web 54. The deflection elements are arranged at equal distances from each other along three concentric circles 55a, 55b, 55c, which are concentric with the axis of symmetry 59. The deflection elements 51 are inclined relative to a normal one of the connection axis 56, the deflection elements 51 being inclined in the same direction along a circle 55a, 55b, 55c from one circle 55a, 55b, 55c to an adjacent circle 55a, 55b, 55c.

A flow through the turbulence element 4 with combustion air 10, normal to the connection surface 56 into the interior of the truncated cone, results in the formation of vertebrae 57 on the narrow sides 51b of the deflection elements 51. Thus, the combustion air 10 is impressed on a microturbulence, which continues into the mixing region 27 inside. The volumetric flows of low calorific fuel gas SG and turbulent combustion air 10 out of the air duct 2 which are introduced into the mixing region 27 are mixed particularly intensively and homogeneously by these microturbulences in the combustion air 10. The inclination of the deflection elements 51 characterizes the main flow of the combustion air 10 in addition to secondary flows 58, which in addition to the local good mixing due to the turbulence, a homogenization of the fuel gas-air mixture over the entire cross-sectional area of the mixing region 27 (see FIG. 2 ), favor. This embodiment of the swirling element 4, which only influences the air flow in the air duct 2 during the synthesis gas operation, has the consequence that the pressure loss caused by the turbulence is particularly low.

The burner 1 of the invention is therefore particularly suitable for operation in a power plant 24 with integrated gasification of a fossil fuel to a synthesis gas SG, for example coal gas. The burner 1 is arranged in a combustion chamber 16 of a gas turbine plant 25.

Claims (8)

1. Burner (1) for the combustion of a low-calorie fuel gas (SG), with an air duct (2), extending along a burner axis (12) for the supply of combustion air (10) and with a fuel-gas duct (26) which is designed for a high volume flow of low-calorie fuel gas (SG), the fuel-gas duct (26) and the air duct (2) issuing into a mixing region (27), characterized in that the air duct (2) has a region of issue (28) directly adjacently to the mixing region (27) in terms of flow, a turbulence element (4) for the generation of turbulent combustion air (10) being provided in the region of issue, and swirl blades (5) being arranged in the air duct (2) upstream of the turbulence element (4).
2. Burner (1) according to Claim 1, characterized in that the air duct (2) is designed as an annular duct which surrounds the fuel-gas duct (26) concentrically.
3. Burner (1) according to one of the preceding claims, characterized in that the turbulence element (4) has

   a) a first boundary ring (52) with an axis of symmetry (59),

   b) a second, larger boundary ring (53), the centre point of which lies on the axis of symmetry (59),

   c) a connecting surface (56) which is spanned by the two boundary rings (52, 53), and

   d) along circles (55a, 55b, 55c) which lie on the connecting surface (56) and the respective centre point of which lies on the axis of symmetry (59), a multiplicity of sheet-like deflection elements (51) which are in each case inclined with respect to a normal of the connecting surface (56).
4. Burner (1) according to Claim 3, characterized in that the connecting surface (56) of the turbulence element (4) amounts to less than half of the circular surface surrounded by the larger boundary ring (53).
5. Burner (1) according to Claim 3 or 4, characterized in that the deflection elements (51) of the turbulence element (4) which are assigned to a circle (55a, 55b, 55c) are at an equal distance from one another.
6. Burner (1) according to Claim 3, 4 or 5, characterized in that each deflection element (51) of the turbulence element (4) tapers from the connecting surface (56) towards a breakaway edge (51b) for the generation of vortices, the said deflection element having, in particular, an approximately trapezoidal or triangular shape.
7. Burner (1) according to one of Claims 4 to 7, characterized in that the deflection elements (51) of the turbulence element (4) which are assigned to a circle (55a, 55b, 55c) are inclined codirectionally.
8. Burner (1) according to Claim 8, characterized in that deflection elements (51) arranged on mutually adjacent circles (55a, 55b, 55c) of the turbulence element (51) are inclined contradirectionally.

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