EP1195203B1 - Device and method for electrostatically spraying liquids - Google Patents

Description

Technical application

The present invention relates to a device and a method for electrostatic atomization of a liquid medium, wherein the device comprises an electrically conductive nozzle body having an inner volume for receiving the liquid medium, at least one nozzle opening for the discharge of the liquid medium and a coaxial with a longitudinal axis of the nozzle body in Internal volume arranged high-voltage electrode, is charged with the flowing liquid medium immediately before exiting the nozzle opening electrostatically.

The device and the associated method are used in particular in turbomachines, such as gas or steam turbine plants, for injecting or injecting the liquid fuel.

State of the art

For the atomization of a liquid medium such as a liquid fuel pressure atomizers are often used in which the liquid medium under high pressure, the internal volume of a Nozzle body is supplied and atomized in the subsequent expansion through the nozzle opening into fine droplets. To assist this atomization, it is known to additionally electrostatically charge the liquid medium via a high-voltage electrode before it leaves the nozzle. This electrostatic charge causes a better and finer atomization due to the repulsive forces of the charges.

That's how it shows DE 41 06 564 A1 a device for the electrostatic atomization of liquids, in particular of fuel, which comprises a spray nozzle. The nozzle consists of an electrically conductive nozzle body, which is at ground potential and has a nozzle opening for the escape of a pressurized fluid volume. In the inner volume of the nozzle body, a nozzle opening is arranged coaxially opposite electrode, which is at a high voltage potential. The electrode has a conical tip, which is positioned directly at the outlet opening of the nozzle body tapered in the shape of a truncated cone. Due to the very high electric fields at this apex of the electrode, the liquid flowing past is charged electrostatically immediately before it leaves the nozzle opening. Due to this electrostatic charge, the liquid atomizes after exiting the nozzle opening to a very fine spray. A similar device is the DE 41 06 563 A1 refer to.

The U.S. 4,051,826 shows a device for fuel injection in a cylinder chamber a Combustion engine. The nozzle used in this case has a plurality of nozzle openings whose boundaries are formed as sharp edges. In this device, the housing is subjected to a high-voltage potential, so that prevail at the outlet openings very high electric fields, which also lead to an electrostatic charge of the exiting liquid. Due to a lack of high potential difference at these outlet openings, however, the size of the electrostatic charge is only small.

A method according to the preamble of claim 8 is known from US 5,234,170 known.

• regelsysteme erforderlich, so dass der Aufwand für die Bereitstellung eines derartigen Brennstoffsystems relativ hoch ist.

Especially in the preferred field of application of the present invention, the gas or steam turbine technology, the quality of the atomization of the liquid fuels used plays an essential role in the stability of the combustion, the efficiency and the pollutant emissions generated. In lean premixed gas turbine burners here are often multi-hole pressure nozzles are used to achieve a good distribution of the fuel in the combustion air.
In the case of such multi-hole pressure nozzles, as is the case with single-hole pressure nozzles, it is disadvantageous that the atomization quality depends on the pressure of the liquid medium or fuel oil to be atomized and thus on the oil throughput. In gas turbines with pressure nozzles, this circumstance has a particularly negative effect on the starting and part load behavior, since under these conditions the oil flow rates are low. This can be done by the FIG. 1 which shows the relative fuel mass flow (m_fuel) or fuel pressure (p_fuel) as a function of the gas turbine power. Especially at low pressure, the atomization quality of conventional pressure nozzles leaves something to be desired.
So far, in such gas turbine fuel systems, therefore, the fuel is usually supplied in different nozzle stages. A pilot stage covers the start and lower part load range. The other main stage is intended for the operation of the upper part load range and the full load. For both stages, however, separate fuel supply and

• control systems required, so that the cost of providing such a fuel system is relatively high.

Although electrostatic single-hole nozzles are known from the above-mentioned prior art, which lead to an increase in the atomization quality, however, these nozzle designs are not readily transferable to multi-hole nozzles. Thus, a corresponding electrode with conical tip would have to be provided for each nozzle opening, which is positioned exactly above the respective nozzle opening. However, this increases the effort in the production of the nozzles and leads to reliability problems due to the thermal distortion, especially in the very high temperatures occurring in combustion chambers of gas and steam turbines.
The construction of a multi-hole nozzle, on the other hand, indicated by the second mentioned publication results in reasonable high voltage values not to a satisfactory electrostatic charge of the liquid medium.

Description of the invention

The present invention is therefore based on the object to provide a device and a method for electrostatic atomization of a liquid medium, which in particular allow the use of a multi-hole pressure nozzle and to provide a sufficient Zerstäubungsqualität even when starting and at partial load of a turbomachine.

The object is achieved with the device and the method according to claims 1 and 8, respectively. Advantageous embodiments of the device and the associated method are the subject of the dependent claims.

The inventive device for atomizing a liquid medium consists of an electrically conductive nozzle body having an internal volume for receiving the liquid medium, at least one nozzle opening for the discharge of the liquid medium and a coaxial with a longitudinal axis of the nozzle body in the inner volume arranged high-voltage electrode. The high-voltage electrode is arranged such that it can charge electrostatic fluid flowing past it immediately before exiting from the nozzle opening or the nozzle openings upon application of a high voltage such that the atomization quality due to these electrostatic Charging is increased. Of course, for this purpose, the electrically conductive nozzle body is set to ground potential in order to generate a sufficient size of the electric field between the high voltage electrode and the nozzle body in the region of the nozzle opening. According to the invention, in the region of its greatest lateral extent, the high-voltage electrode has-in a plane substantially perpendicular to the longitudinal axis of the nozzle body-a circumferential sharp edge which runs at a small distance from the nozzle body in order to be able to effect the electrostatic charging of the flowing liquid medium. In this case, a sharp edge means in each case a sharp edge angle, ie an edge angle of less than 90 °. Of course, the sharp edge can also have a serrated profile with tips.
It goes without saying that this edge has to run in the immediate vicinity of the nozzle orifices in order to be able to bring about the desired electrostatic charging of the liquid medium immediately before it leaves the nozzle opening.

Preferably, the device is a multi-hole nozzle whose nozzle orifices are located in or near the plane in which the sharp edge of the high voltage electrode passes. It is also possible to provide a plurality of rows of nozzle openings, which are spaced apart in the longitudinal direction of the nozzle body, wherein then for each row a separate circumferential sharp edge is formed on the high voltage electrode.

Furthermore, a central outlet opening can be formed on the longitudinal axis of the nozzle body. Such a central nozzle opening is acted upon by an additional tip on the high voltage electrode in this area with an electric field, as is known from the prior art in single-hole nozzles.

Preferably, the nozzle body is rotationally symmetrical about its longitudinal axis and has a tapered, for example frustoconical, shape in the region of the nozzle openings. In a rotationally symmetrical configuration of the nozzle body or of the inner volume, the present high-voltage electrode is preferably formed approximately plate-shaped. Such a configuration is technically very easy to implement and is insensitive to thermal distortion.

During operation of the device, the liquid medium is supplied to the inner volume under pressure, the nozzle body is set to ground potential and the high voltage electrode is subjected to a high voltage, which causes an electrostatic charge of the liquid medium in a size, due to the additional electrostatic charge to a burst of the drop or the nozzle openings exiting drops leads.

In a method of operation of this sputtering apparatus, the high voltage electrode is pulsed at high voltage with a variable duty cycle (duration of high voltage / period). and / or, in particular embodiment, subjected to variable high voltage, wherein the sputtering quality is selectively influenced by changing the duty cycle of the high voltage. A targeted modulation of the high voltage and / or the sampling rate by a specific pulse rate is conceivable. Such an influence is particularly suitable for damping combustion instabilities during operation of a gas or steam turbine plant, the duty cycle being increased during startup or part load operation due to the lower fuel pressure and the duty ratio being lowered in the case of heavy partial load or full load operation. By this measure, an approximately constant atomization quality can be achieved throughout the operating range, since at high load operation, the high pressure already without electrostatic atomization leads to a high atomization quality, while at lower pressure in the start or low part load operation, the lower Druckzerstäubungsqualität increased by the additional electrostatic atomization becomes.

A change in the atomization in partial load operation can also be influenced by changing the high voltage, for example by increasing it from 10 kV to> 20 kV.

The present device and the associated method are therefore characterized by a simple construction, which allows in particular the principle of electrostatic atomization even with multi-hole pressure nozzles. The structure of the device with the circumferential sharp edge is much less susceptible to thermal distortion than a structure with separately provided for each nozzle opening cone tips.

Brief description of the drawings

Fig. 1

ein Beispiel für den relativen Brennstoff-Massenstrom und -druck in Abhängigkeit von der Leistung einer Gasturbine;

Fig. 2

schematisch den Aufbau einer ersten Ausführungsform der Vorrichtung;

Fig. 2a

schematisch den Aufbau einer zweiten Ausführungsform der Vorrichtung;

Fig. 3

schematisch eine Prinzipdarstellung des elektrostatischen Zerstäubens;

Fig. 4

Beispiele für die Wirkung des Einsatzes der vorliegenden Vorrichtung auf die Zerstäubungsqualität und

Fig. 5

Die Ansicht einer Hochspannungselektrode mit einem gezacktem Verlauf der scharfen Kante gemäss der Ansicht V-V der Figur 2.

The device will be briefly explained again below without limiting the general inventive idea in conjunction with the figures. Hereby show:

Fig. 1

an example of the relative fuel mass flow and pressure versus gas turbine power;

Fig. 2

schematically the structure of a first embodiment of the device;

Fig. 2a

schematically the structure of a second embodiment of the device;

Fig. 3

schematically a schematic diagram of the electrostatic sputtering;

Fig. 4

Examples of the effect of the use of the present device on the atomization quality and

Fig. 5

The view of a high voltage electrode with a serrated curve of the sharp edge according to the VV view of FIG. 2 ,

Ways to carry out the invention

Fig. 1 shows an example of the dependence of the fuel pressure in the operation of a gas turbine on the gas turbine power. It can be clearly seen in the figure that at low gas turbine power in starting or part-load operation, a significantly lower fuel pressure predominates than at higher gas turbine power or at full load operation. In the figure, the values for the relative fuel mass flow (m_fuel) and fuel pressure (p_fuel) are shown as a function of the gas turbine power. Due to the relationship shown, it can be seen that the pressure in the atomizer nozzle can assume very different values depending on the operating state of the gas turbine, so that the atomization quality of the pressure atomization does not turn out satisfactory at low gas turbine power.

Fig. 2 shows an example of a sputtering or atomizing nozzle according to the invention, with which the sputtering quality can be significantly increased, especially in the start or part load operation of a gas turbine. The figure shows the front region of the electrically conductive nozzle body 1, which encloses the inner volume 4 for receiving the liquid medium, for example a fuel oil or another non-conductive atomizing medium. The nozzle body is formed in the present example rotationally symmetrical about its longitudinal axis 1a. In the front area are nozzle openings 2 for the discharge of the liquid medium intended. The leaked electrostatically sprayed spray 5 is indicated schematically here. In the inner volume 4, a high-voltage electrode 3 is arranged to electrostatically charge the flowing liquid medium immediately before the exit from the nozzle openings 2. The high-voltage electrode 3 is plate-shaped and has a circumferential sharp edge 3a in the region of its greatest lateral extent. The plane in which this sharp edge 3 a extends essentially corresponds to the plane in which the nozzle openings 2 are arranged distributed on the nozzle body 1. In this case, a sharp edge 3 a is in any case an acute edge angle, ie an edge angle of less than 90 °. Like from the FIG. 5 it can be seen which the view according to the line VV of FIG. 2 Of course, the sharp edge 3a here can also have a serrated profile with tips.

It goes without saying that this edge 3 a must run in the immediate vicinity of the nozzle orifices 2 in order to be able to effect the desired electrostatic charging of the liquid medium immediately before it leaves the nozzle opening.

According to the Fig. 2a Furthermore, a central nozzle opening 2a can be formed on the longitudinal axis 1a of the nozzle body 1. Such a central nozzle opening 2a is acted upon by an additional tip 3b at the high voltage electrode 3 in this area with an electric field, as is known from the prior art in single-hole nozzles.

When a high voltage is applied to this high voltage electrode 3, an electric field having a particularly high field strength is formed at the sharp edge 3a. This high field strength allows the escape of electrons from the electrode and thus a charge of the oil, which flows around the electrode. Due to the proximity of the sharp edge 3a to the nozzle body 1, which is at ground potential, and the nozzle openings 2, the fuel oil is electrostatically charged immediately before exiting the nozzle openings, so that it can still maintain this electrostatic charge when exiting the nozzle substantially.
The distance of the sharp edge 3a from the nozzle body 1 must, of course, be selected as a function of the applied high voltage and the electrical properties of the liquid medium used so that no electrical breakdown to the nozzle body 1 takes place. On the other hand, this sharp edge 3a must be positioned as close as possible to the nozzle body 1 in order to achieve the desired size of the electric field. In general, when using such a multi-hole nozzle in burners of gas turbines, a high voltage U> 10 kV and a distance of the order of 1 mm between the sharp edge 3a and the nozzle body 1 are selected.

Fig. 3 shows the principle of action of the electrostatic charge in the electrostatic atomization. In the left part here a non-electrostatically charged droplet 6 is shown schematically, in which only the surface tension forces F _i act, holding the droplets together (by arrows indicated). Due to the gleichpolige charge of the oil when passing through the nozzle according to the invention act within the fluid elements mutually repelling electrostatic forces F _el . If these forces after exiting the nozzle are greater than the surface tension forces F _i holding the droplet together, the droplet bursts. The right side of the Fig. 3 In this case, the additionally acting electrostatic forces F _{el are shown} in an electrostatically charged droplet 7. The droplets 7 will burst until the charge forces within the droplet are smaller than the surface tension forces and the droplet is thus stable.

With the proposed technique it is possible to achieve sufficient Zerstäubungsgüten even at lower pressure in the nozzle. Thus, a decoupling of throughput of the liquid medium and atomization or atomization quality is possible.

In the method of operation of this sputtering apparatus, the high-voltage electrode 3 is subjected to a pulsed high voltage with variable duty cycle (duration of the high voltage / period) and / or, in a particular embodiment, with variable high voltage, wherein the sputtering quality is specifically influenced by changing the duty cycle of the high voltage. A targeted modulation of the high voltage and / or the sampling rate by a specific pulse rate is conceivable. Such influence is particularly useful for damping combustion instabilities in the operation of a gas or Steam turbine plant, wherein in the start or part load operation due to the lower fuel pressure increases the duty cycle and at higher part-load or full load operation, the duty ratio is lowered. By this measure, an approximately constant atomization quality can be achieved throughout the operating range, since at high load operation, the high pressure already without electrostatic atomization leads to a high atomization quality, while at lower pressure in the start or low part load operation, the lower Druckzerstäubungsqualität increased by the additional electrostatic atomization becomes.

A change in the atomization in partial load operation can also be influenced by changing the high voltage, for example by increasing it from 10 kV to> 20 kV.

Fig. 4 shows shadow shots on fuel nozzles with and without high voltage applied at different fuel flow rates. In all four representations can be seen in the upper part of the nozzle body, emerge from the four fuel jets through the outlet openings.
In the left part of the figure, the operation of the device without the application of a high voltage, that is shown as a conventional multi-hole pressure nozzle. While sufficient atomization can be seen with a high fuel flow rate of 3.95 l / min, corresponding to a pressure in the nozzle of 30 * 10 ⁵ Pa (30 bar) (lower part of the figure), with a lower fuel flow rate of only 1.32 l / min accordingly a pressure of 3.5 * 10 ⁵ Pa (3.5 bar) hardly achieve atomization of the fuel.
By applying the high-voltage electrode with a corresponding high voltage of 13.9 kV in the upper part and 16.9 kV in the lower part of the figure, a much better atomization can be achieved, as can be seen by comparison with the respective opposite figures with the same fuel flow. Especially with low fuel throughput can be achieved with the present device, a significant improvement in atomization quality, as in the FIG. 4 is recognizable.

The present device and the associated method are therefore characterized by a simple construction, which allows in particular the principle of electrostatic atomization even with multi-hole pressure nozzles. The construction of the device with the peripheral sharp edge 3a is much less susceptible to thermal distortion than a structure with separately provided for each nozzle opening cone tips.

LIST OF REFERENCE NUMBERS

1

nozzle body

1a

longitudinal axis

2

nozzle opening

2a

Nozzle opening, central

3

High-voltage electrode

3a

Sharp edge

3b

top

4

internal volume

5

Electrostatically atomized spray

6

Non-electrostatically charged drops

7

Electrostatically charged drop

Claims (12)

1. Apparatus for atomizing a liquid medium, comprising

   - an electrically conductive nozzle body (1), which has an internal volume (4) for admitting the liquid medium,

   - at least one nozzle opening (2) for the discharge of liquid medium, and

   - a high-voltage electrode (3) which is arranged coaxially with respect to a longitudinal axis (1a) of the nozzle body (1) in the internal volume (4) and, in the area of its greatest lateral extent, has a circumferential edge with an edge angle in order to electrostatically charge liquid medium flowing past it, immediately before emerging from the nozzle opening (2),

   characterized
   in that the edge angle is less than 90°, and the edge runs at a short distance from the nozzle body (1), in order to electrostatically charge the liquid medium flowing past it.
2. Apparatus according to Claim 1,
   characterized
   in that a plurality of nozzle openings (2) are provided for the liquid medium to emerge from.
3. Apparatus according to Claim 2,
   characterized
   in that the nozzle openings (2) are arranged distributed on one plane over the circumference of the nozzle body, in or in the vicinity of which plane the sharp edge (3a) of the high-voltage electrode (3) runs.
4. Apparatus according to Claim 3,
   characterized
   in that at least one further nozzle opening (2a) is arranged on the longitudinal axis (1a) of the nozzle body (1), with the high-voltage electrode (3) forming a point (3b) in this area.
5. Apparatus according to one of Claims 1 to 4,
   characterized
   in that the nozzle body (1) has a tapering shape in the area of the nozzle openings (2).
6. Apparatus according to one of Claims 1 to 5,
   characterized
   in that the high-voltage electrode (3) is essentially in the form of a plate.
7. Apparatus according to one of Claims 1 to 6,
   characterized
   in that the circumferential sharp edge (3a) of the high-voltage electrode (3) has a jagged profile with points.
8. Method for atomizing a liquid medium using an apparatus according to one of Claims 1 to 7, in which

   - the liquid medium is supplied to the internal volume (4) of the apparatus under pressure,

   - the nozzle body (1) is at earth potential, and

   - the high-voltage electrode (3) has a high voltage applied to it which results in the liquid medium being electrostatically charged to such an extent that this leads to bursting of droplets emerging from the nozzle opening or openings, because of the electrostatic charge,

   characterized in that
   the high-voltage electrode has a pulsed high voltage applied to it at a variable duty ratio, with the atomizing quality being influenced by varying the duty ratio of the high voltage.
9. Method according to Claim 8,
   characterized
   in that the high-voltage electrode (3) has a pulsed high voltage applied to it with a variable duty ratio and with a variable high voltage, with the atomizing quality being influenced by varying the duty ratio of the high voltage.
10. Method according to Claim 9,
    characterized
    in that the duty ratio is increased if the pressure of the liquid medium decreases, and is reduced if the pressure of the liquid medium is increased.
11. Method according to Claim 9 for atomizing liquid fuel in the combustion chamber of a gas turbine,
    characterized
    in that a higher duty ratio is set during starting or during partial-load operation of the gas turbine than when the gas turbine is being operated on full load.
12. Method according to Claim 8 for atomizing liquid fuel in the combustion chamber of a gas turbine,
    characterized
    in that the atomizing quality when the gas turbine is being operated on partial load is influenced by varying the high voltage.

Images