EP1195203A2 - Device and method for electrostatically spraying liquids - Google Patents

Abstract

The vaporizer has an electrically conductive jet body (1) having an internal volume (4) for reception of the fluid medium and at least one jet opening (2), cooperating with a HV electrode (3) positioned coaxial to the longitudinal axis of the jet body within the internal volume. The HV electrode has a sharp edge (3a) at its widest part, positioned adjacent the jet opening, for electrostatic charging of the fluid flowing through the latter. An Independent claim for a vaporization method for a fluid medium is also included.

Description

Technical application area

The present invention relates to a device as well as a method of electrostatic Atomization of a liquid medium, the Device an electrically conductive nozzle body with an internal volume to hold the liquid Medium, at least one nozzle opening for the outlet of the liquid medium as well as a coaxial to one Longitudinal axis of the nozzle body arranged in the inner volume Has high voltage electrode, with the flowing past liquid medium immediately before the outlet electrostatically charged from the nozzle opening becomes.

The device and the associated method are used particularly in turbomachinery, such as gas or Steam turbine systems, for injection or Injection of the liquid fuel used.

State of the art

For the atomization of a liquid medium such as for example, a liquid fuel are common Pressure atomizers used, in which the liquid Medium under high pressure the internal volume of a Nozzle body is fed and in the subsequent Expansion through the nozzle opening into fine drops atomized. It is to support this atomization known, the liquid medium via a high voltage electrode before additionally emerging from the nozzle charge electrostatically. This electrostatic Due to the repulsive forces, charging causes the Loads a better and finer atomization.

DE 41 06 564 A1 shows a device for electrostatic atomization of liquids, especially of fuel, which is an atomizer nozzle includes. The nozzle consists of an electrically conductive Nozzle body that is at ground potential and a nozzle opening for exiting one under pressure has standing liquid volume. In the interior volume of the nozzle body is one of the nozzle openings coaxially opposite electrode arranged on the a high voltage potential. The electrode points a cone tip that is directly at the outlet opening of the frustoconical nozzle body is positioned. Due to the very high electrical Fields at this cone tip of the electrode becomes the flowing fluid immediately before the Leaving the nozzle opening electrostatically charged. Because of this electrostatic charge atomizes the liquid after exiting the Nozzle opening to a very fine spray. A Similar device is to DE 41 06 563 A1 remove.

US 4,051,826 shows a device for Fuel injection into a cylinder space Combustion engine. The nozzle used here has several nozzle openings, the limits of which are formed as sharp edges. At this Device is the housing with a high voltage potential pressurized so that at the outlet openings very high electric fields prevail that also to an electrostatic charge of the escaping liquid. Because of a missing high potential difference at these outlet openings is the size of the electrostatic charge however only slightly.

Especially in the preferred field of application present invention, gas or steam turbine technology, plays the quality of the atomization of the liquid fuels used an essential Role for the stability of the combustion, the efficiency as well as the pollutant emissions generated. at lean premixed gas turbine burners come here Frequently multi-hole pressure nozzles are used to ensure a good one Distribution of the fuel in the combustion air too to reach.

With such multi-hole pressure nozzles - as with single-hole pressure nozzles - disadvantageous from that the atomization quality from the pressure of the atomizer liquid medium or fuel oil and thus the oil throughput is dependent. Works in gas turbines with pressure nozzles this fact has a particularly negative impact on the start and part-load behavior because under these conditions the oil flow rates are low. This can be seen from FIG. 1 can be recognized, the relative fuel mass flow (m_brennstoff) or fuel pressure (p_brennstoff) depending on the gas turbine power shows. Especially at low pressure, the Atomization quality of conventional pressure nozzles wish left.

So far, such gas turbine fuel systems therefore usually the fuel in fed to different nozzle levels. A pilot stage covers the start and lower part load range. The Another main stage is for the operation of the upper one Partial load range and full load are provided. For however, both stages are separate fuel supply and control systems required, so the effort for the Provision of such a fuel system is relatively high.

Although from the above-mentioned prior art electrostatic single-hole nozzles known to lead to a Lead to increase atomization quality, however these nozzle designs do not readily arise Multi-hole nozzles transferable. So for every nozzle opening a corresponding electrode with a conical Tip are provided that are just above each Nozzle opening is positioned. However, this increases the Effort in the manufacture of the nozzles and leads straight in the combustion chambers of gas and steam turbines occurring very high temperatures to reliability problems due to the thermal distortion.

The other, by the second named Published construction of a Multi-hole nozzle leads to acceptable high voltage values not a satisfactory electrostatic Charging the liquid medium.

Description of the invention

The present invention is therefore based on the object based, an apparatus and a method for electrostatic atomization of a liquid medium to provide, in particular the use of a Allow multi-hole pressure nozzle and sufficient Atomization quality even when starting and at partial load are able to deliver a turbomachine.

The task is done with the device as well Method solved according to claims 1 and 8, respectively. Advantageous embodiments of the device and the associated method are the subject of the dependent claims.

The atomizing device according to the invention A liquid medium consists of an electrical one conductive nozzle body that has an internal volume for Has recording of the liquid medium, at least a nozzle opening for the outlet of the liquid Medium and one coaxial to a longitudinal axis of the Nozzle body arranged in the internal volume high-voltage electrode. The high voltage electrode is arranged so that it flows past liquid Medium immediately before exiting the nozzle opening or the nozzle openings when creating one High voltage can electrostatically charge that the atomization quality due to this electrostatic Charge is increased. Of course the electrically conductive nozzle body is used for this Ground potential placed to a sufficient size of the electric field between high voltage electrode and To produce nozzle body in the area of the nozzle opening. According to the high-voltage electrode in Area of their greatest lateral extent - in one Plane substantially perpendicular to the longitudinal axis of the Nozzle body - a peripheral sharp edge on that runs at a short distance from the nozzle body to the electrostatic charging of the flowing by to be able to effect liquid medium. Under one sharp edge is always a sharp one Edge angle, i.e. an edge angle of less than 90 ° to understand. The sharp edge can of course also a jagged course with tips exhibit.

It goes without saying that this edge in immediate vicinity of the nozzle orifice must run to the desired electrostatic Immediate charging of the liquid medium effect before exiting the nozzle opening can.

It is preferably the device a multi-hole nozzle, the nozzle openings in or are located near the plane in which the sharp Edge of the high voltage electrode runs. Here is it is also possible to have multiple rows of nozzle openings to be provided in the longitudinal direction of the nozzle body are spaced from each other, then for each row a separate all-round sharp edge on the high-voltage electrode is trained.

Furthermore, a central outlet opening can be opened the longitudinal axis of the nozzle body. A such a central nozzle opening is through a additional tip on the high voltage electrode in applied an electrical field to this area, like this from the prior art Single hole nozzles are known.

The nozzle body is preferably rotationally symmetrical formed around its longitudinal axis and points a tapered, for example frustoconical, Form in the area of the nozzle openings. at a rotationally symmetrical design of the The nozzle body or the inner volume is the present one High voltage electrode preferably approximately plate-shaped educated. Such a configuration leaves is and is technically very easy to implement insensitive to thermal distortion.

When operating the device according to the invention the liquid medium becomes the internal volume under pressure supplied, the nozzle body is connected to ground potential and the high voltage electrode with a high voltage charged with an electrostatic charge on the liquid medium in a size caused by the additional electrostatic charge to one Bursting out of or the nozzle openings escaping drops leads.

In a special embodiment of the operating method this atomizing device is the High voltage electrode with a pulsed high voltage with variable duty cycle (duration of high voltage / Period) and / or variable high voltage acted upon, the atomization quality by Change the duty cycle of the high voltage is influenced in a targeted manner. Also targeted modulation the high voltage and / or the duty cycle by a certain pulse rate is conceivable. Such Influence is particularly useful for damping Combustion instabilities when operating a gas or Steam turbine system on, in the start or part load operation due to the lower fuel pressure Duty cycle increased and with stronger partial load or Full load operation the duty cycle is reduced. Through this measure, an approximately constant Atomization quality throughout the entire operating area can be achieved because in full load operation the high pressure even without electrostatic atomization leads to a high atomization quality, while at lower pressure in start-up or low part-load operation the lower pressure atomization quality the additional electrostatic atomization increases becomes.

A change in atomization in part-load operation can also by changing the high voltage be influenced, for example by this of 10 kV is increased to> 20kV.

The present device and the associated one Processes are therefore characterized by a simple Construction, which in particular the principle of electrostatic atomization even with multi-hole pressure nozzles allows. The construction of the device with the surrounding sharp edge is much less sensitive against thermal distortion as 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 erfindungsgemäßen Vorrichtung;

Fig. 2a

schematisch den Aufbau einer zweiten Ausführungsform der erfindungsgemäßen 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 according to the invention is briefly explained again below without restricting the general inventive concept in conjunction with the figures. Here show:

Fig. 1

an example of the relative fuel mass flow and pressure depending on the performance of a gas turbine;

Fig. 2

schematically the structure of a first embodiment of the device according to the invention;

Fig. 2a

schematically the structure of a second embodiment of the device according to the invention;

Fig. 3

schematically shows a schematic diagram of electrostatic atomization;

Fig. 4

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

Fig. 5

The view of a high-voltage electrode with a jagged course of the sharp edge according to the view VV of Figure 2.

Ways of Carrying Out the Invention

Fig. 1 shows an example of the dependence of Fuel pressure when operating a gas turbine from the Gas turbine power. In the figure is clearly too recognize that at low gas turbine power in Start or part load operation a much lower Fuel pressure prevails than with higher gas turbine output or at full load. In the figure are the values for the relative fuel mass flow (m_brennstoff) and fuel pressure (p_brennstoff) depending on the gas turbine power shown. Because of the illustrated It can be seen that the pressure in the Atomizer nozzle depending on the operating state of the gas turbine can take very different values, so the Atomization quality of the pressure atomization just at lower gas turbine performance unsatisfactory fails.

Fig. 2 shows an example of an inventive Atomizing device or atomizing nozzle, with the atomization quality just in the start or Part load operation of a gas turbine can be significantly increased can. The figure shows the front area of the electrical conductive nozzle body 1, the internal volume 4 for receiving the liquid medium, for example a fuel oil or another non-conductive Atomizing medium, encloses. The nozzle body is in the present example rotationally symmetrical about its Longitudinal axis 1a formed. Are in the front area Nozzle openings 2 for the exit of the liquid medium intended. The leaked electrostatically atomized Spray 5 is indicated schematically here. In the interior volume 4, a high-voltage electrode 3 is arranged, around the flowing liquid medium immediately in front the discharge from the nozzle openings 2 electrostatically charge. The high voltage electrode 3 is plate-shaped trained and exhibits in the area of their largest lateral extent a circumferential sharp edge 3a on. The plane in which this sharp edge 3a runs corresponds essentially to the level at which the Nozzle openings 2 are distributed on the nozzle body 1 are. Below a sharp edge 3a is in always an acute edge angle, i.e. on Understand edge angles of less than 90 °. How from 5 can be seen, which the view according to represents the line V-V of Figure 2, the sharp Edge 3a of course also one have a jagged course with tips.

It goes without saying that this edge 3a in the immediate vicinity of the nozzle opening (s) 2 must run to the desired electrostatic Immediate charging of the liquid medium effect before exiting the nozzle opening can.

According to FIG. 2a, a central can continue Nozzle opening 2a on the longitudinal axis 1a of the nozzle body 1 be formed. Such a central Nozzle opening 2a is covered by an additional tip 3b on the high-voltage electrode 3 in this area an electric field, as this emerges from the State of the art in single-hole nozzles is known.

A high voltage is applied to this high-voltage electrode 3 created, so forms on the sharp edge 3a an electric field with a particularly high field strength out. This high field strength enables leakage of Electrons from the electrode and thus a charge of the oil that flows around the electrode. Through the Proximity of the sharp edge 3a to the nozzle body 1 that is on Ground potential is, and the nozzle openings 2 will Fuel oil immediately before it exits the nozzle openings electrostatically charged so it's this electrostatic charge when exiting the nozzle can essentially still be maintained.

The distance of the sharp edge 3a from the nozzle body 1 must depend on the high voltage applied and the electrical properties of the used liquid medium can of course be chosen so that there is no electrical breakdown to the nozzle body 1 takes place. On the other hand, this must be sharp Edge 3a positioned as close as possible to the nozzle body 1 be the desired size of the electric field to be able to achieve. Usually when used of such a multi-hole nozzle in gas turbine burners a high voltage U> 10 kV and a distance in on the order of 1 mm between the sharp edge 3a and the nozzle body 1 can be selected.

Fig. 3 shows the principle of action of electrostatic charging in electrostatic atomization. In the left part, a non-electrostatically charged drop 6 is shown schematically, in which only the surface tension forces F _i act that hold the drop together (indicated by arrows). Due to the same-pole charging of the oil as it passes through the nozzle according to the invention, mutually repelling electrostatic forces F _el act within the fluid elements. If these forces are greater than the surface tension forces F _i , which hold the drop together, after exiting the nozzle, the drop bursts. The right side of FIG. 3 shows the additionally acting electrostatic forces F _el in an electrostatically charged drop 7. The drops 7 will burst until the charge forces within the drop are smaller than the surface tension forces and the drop is thus stable.

The proposed technology also works sufficient atomization quality at lower pressure in the nozzle to reach. Decoupling from Throughput of the liquid medium and atomization or Atomization quality possible.

In a special embodiment of the operating method this atomizing device is the High voltage electrode 3 with a pulsed High voltage with variable duty cycle (duration of the High voltage / period) and / or more variable High voltage applied, the atomization quality by changing the duty cycle of the High voltage is targeted. Also one targeted modulation of the high voltage and / or Duty cycle through a certain pulse frequency is conceivable. Such influence is particularly useful to dampen combustion instabilities in Operation of a gas or steam turbine system, wherein in start or part load operation due to the lower Fuel pressure increases the duty cycle and at stronger duty cycle or full load operation the duty cycle is lowered. This measure can an almost constant atomization quality during of the entire operating area can be reached, because in Full load operation the high pressure without electrostatic Atomization to a high atomization quality leads while at lower pressure in the start or lower part-load operation the lower pressure atomization quality through the additional electrostatic Atomization is increased.

A change in atomization in part-load operation can also by changing the high voltage be influenced, for example by this of 10 kV is increased to> 20kV.

Fig. 4 shows shadow recordings on the invention Fuel nozzles with and without high voltage with different fuel throughput. In All four representations are in the upper area Recognize nozzle body from which four fuel jets exit through the outlet openings.

The left part of the figure shows the operation of the device without the application of high voltage, ie as a conventional multi-hole pressure nozzle. While with a high fuel throughput of 3.95 l / min corresponding to a pressure in the nozzle of 30 * 10 ⁵ Pa (30 bar) sufficient atomization can be seen (lower part of the figure), with a lower fuel throughput of only 1.32 l / min corresponding to a pressure of 3.5 * 10 ⁵ Pa (3.5 bar) hardly any atomization of the fuel can be achieved.

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 can be a significantly better atomization achieve as by comparing each with the opposite figures with the same fuel throughput can be seen. Especially with little Fuel throughput can be with the present Device a significant improvement in the atomization quality achieve as in Figure 4 is recognizable.

The present device and the associated one Processes are therefore characterized by a simple Construction, which in particular the principle of electrostatic atomization even with multi-hole pressure nozzles allows. The construction of the device with the peripheral sharp edge 3a is much less sensitive against thermal distortion as 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 drop

7

Electrostatically charged drop

Claims (12)

Device for atomizing a liquid medium, consisting of an electrically conductive nozzle body (1) which has an internal volume (4) for holding the liquid medium, at least one nozzle opening (2) for the exit of the liquid medium, and a high-voltage electrode (3) arranged coaxially to a longitudinal axis (1a) of the nozzle body (1) in the inner volume (4), in order to electrostatically charge liquid medium flowing past immediately before it emerges from the nozzle opening (2), characterized in that the high-voltage electrode (3) has a circumferential sharp edge (3a) in the area of its greatest lateral extent, which runs at a short distance from the nozzle body (1) in order to effect the electrostatic charging of the flowing liquid medium. Device according to claim 1,
characterized in that several nozzle openings (2) are provided for the exit of the liquid medium. Device according to claim 2,
characterized in that the nozzle openings (2) are arranged in a plane distributed over the circumference of the nozzle body, in or near which the sharp edge (3a) of the high-voltage electrode (3) extends. Device 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), the high-voltage electrode (3) forming a tip (3b) in this area. Device according to one of claims 1 to 4,
characterized in that the nozzle body (1) has a tapering shape in the region of the nozzle openings (2). Device according to one of claims 1 to 5,
characterized in that the high-voltage electrode (3) is substantially plate-shaped. Device according to one of claims 1 to 6,
characterized in that the peripheral sharp edge (3a) of the high-voltage electrode (3) has a jagged course with tips. A method of atomizing a liquid medium using an apparatus according to any one of claims 1 to 7, in which the liquid medium is fed to the inner volume (4) of the device under pressure, the nozzle body (1) is connected to ground potential and the high-voltage electrode (3) is subjected to a high voltage which causes an electrostatic charging of the liquid medium in a size which leads to the bursting of drops emerging from the nozzle or openings due to the electrostatic charging. A method according to claim 8,
characterized in that a pulsed high voltage with a variable pulse duty factor and / or variable high voltage is applied to the high voltage electrode (3), the atomization quality being influenced by changing the pulse duty factor of the high voltage. Method according to claim 9,
characterized in that when the pressure of the liquid medium is reduced the pulse duty factor is increased and when the pressure of the liquid medium is increased it is reduced. Method according to claim 9 for atomizing liquid fuel in the combustion chamber of a gas turbine,
characterized in that a higher duty cycle is set when starting or in partial load operation of the gas turbine than in full load operation of the gas turbine. Method according to claim 8 for atomizing liquid fuel in the combustion chamber of a gas turbine,
characterized in that the atomization quality in part-load operation of the gas turbine is influenced by changing the high voltage.

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