GB2350403A

GB2350403A - Device for producing energy by means of a turbo-machine

Info

Publication number: GB2350403A
Application number: GB0011544A
Authority: GB
Inventors: Jakob Keller
Original assignee: ABB Alstom Power Switzerland Ltd; Alstom Power Inc
Current assignee: General Electric Switzerland GmbH; Alstom Power Inc
Priority date: 1997-11-12
Filing date: 1998-11-03
Publication date: 2000-11-29
Anticipated expiration: 2018-11-03
Also published as: CA2320977A1; GB2350403B; CN1097150C; AU9618798A; NO20002183D0; GB2350403A9; EP0916826A1; WO1999024704A1; GB0011544D0; NO20002183L; CN1285894A; DE19881675T1

Abstract

The invention concerns a device for producing energy by means of a turbo-machine driven by a compressor device for isothermal compression of a compressible fluid preferably air, and which is directly supplied by the turbo-machine supply system, or after an intervening combustion chamber wherein the compressible fluid is lighted in the presence of a fuel The invention is characterised in that the compressor device is equipped with a spraying system for spraying a pressurised liquid in the intake zone of a nozzle system mounted downstream of said spray system such that in the intake zone an air-water mixture is formed and guided onto the nozzle system, and, downstream of said nozzle system, a chamber is arranged comprising at least two outlet conduits, an upper one and a lower one, and through the upper outlet conduit flows the compressed air which is sent into the turbo-machine via said supply system.

Description

1 97/174 Apparatus for the generation of energy by means of a fluid-flow

machine

Technical Field

The present invention relates to an apparatus for the generation of energy by means of a fluid-flow machine according to the preamble of claim 1.

Prior Art

Fluid-flow machines, of which, in the heat-engine category, the gas turbine constitutes a widespread energy- converting unit, are used for the generation of energy. Gas turbines are operated with the combustion gases of liquid or gaseous fuels. A typical gas-turbine construction has an air compressor, also called turbocompressor, which draws in fresh air, which is typically compressed to a pressure of 4 to 6 bar and is forced into a heat exchanger, in which it is preheated by still hot combustion gases flowing from the turbine. Finally, the preheated and compressed supply air passes together with fuels into a combustion chamber, in the course of which hot or combustion gases of at least 6000C are produced. These combustion gases flow at high velocity into the turbine and drive the latter, which is normally coupled to a generator for the generation of electricity.

Many attemps have been made to improve the operation of gas turbines with regard to their power density and their efficiency. The efficiency of a gas turbine depends in principle on the ratio of the energy input into the gas turbine to the energy converted by the gas turbine, which energy can be converted into electrical energy by means of a generator. It is thus necessary to reduce the proportion of energy which is theoretically made available to the gas turbine by the combustion gases but is not converted into electrical 2 97/174 energy. Since in conventional gas-turbine plants the air compressor is connected to the gas turbine by a common shaft and is driven by the turbine, this same proportion of energy, for example, which serves to drive the compressor stage is lost during the generation of electrical energy.

In addition to the improvement of the abovementioned aspects with regard to the power density and the efficiency of gas turbines, the thermal loading capacity of the individual components which are necessary for the operation of gas turbines is also increasingly important for the conception and design of such plants. Not least for reasons of competition, it is necessary to design gas-turbine plants in such a way that they are not too complicated and consequently not too costly, but on the other hand it is necessary to offer durable and high-quality products.

Thus, for example, conventional compressor stages in each case consist of a rotor and a stator, which are fitted with moving and guide blades and by means of which the air flowing through the compressor stage is heated by the compression from ambient temperature up to above 5000C. Such high temperatures put a considerable strain on the materials used in the compressor stage, and this has a lasting harmful effect on the service life of the individual components involved, so that complicated and extensive cooling measures have to be taken in order to increase the resistance of the materials in the compressor region to the high temperatures which occur.

Description of the invention

The object of the invention is to design an 35 apparatus for the generation of energy by means of a fluid-flow machine according to the preamble of claim 1 in such a way that the power density and the efficiency as well as the service life of the components of the 3 97/174 fluid-flow machine, in particular its thermally loaded components, are to be increased.

The solution to the object of the invention is specified in claim 1. Features advantageously developing the inventive idea are the subject matter of the subclaims.

According to the invention, an apparatus for the generation of energy by means of a fluid-flow machine, preferably a gas turbine, for the drive of which a compressor arrangement for compressing a compressible medium, preferably air, is provided, which medium, via a feed-line system, can be fed to the fluid-flow machine directly or after the interposition of a combustion chamber, in which the compressed medium can be ignited with the addition of fuel, is designed in such a way that the compressor arrangement provides at least one compressor stage in which the medium is compressed isothermally and which provides an atomizing device which atomizes a pressurized liquid in the inlet region of a nozzle arrangement, which is arranged downstream of the atomizing device in such a way that a water/air mixture flow directed toward the nozzle arrangement forms in the inlet region. A chamber is arranged downstream of the nozzle arrangement in the direction of flow, and this chamber has at least two outlet passages, a top outlet passage and a bottom outlet passage, through the top outlet passage of which the isothermally compressed air can be fed tothe fluid-flow machine via the feed-line system.

The idea underlying the invention is to convert air into a precompressed state in the course of an isothermal compression in which the air can be compressed to a comparably high degree, as is also possible in the case of conventional air-compressor stages, but without reaching high compression temperatures, so that this air, while avoiding a conventional air compressor and thus dispensing with the need to drive the air compressor by the gas 4 97/174 turbine, is directly available for the drive of the gas turbine.

Furthermore, it is possible to direct isothermally precompressed air to a conventional high-pressure precompressor stage, by means of which the air density is increased to a fixed desired value. In this way, the temperature of the highly compressed air, after passing the highcompression compressor unit, is reduced from normally 5550C to below 3000C. The low temperature level of the highly compressed air inside the compressor unit helps in particular to ensure that any components present in the compressor unit, such as, for. example, moving blades on the rotor and guide blades on the stator, are subjected to lower thermal loads, so that cooling measures can be completely or at least partly dispensed with, as a result of which the arrangement becomes simpler to maintain and becomes more cost-effective.

Finally, a gas turbine having the upstream isothermal compression according to the invention offers improved properties with regard to the utilization of the waste heat of the exhaust gases discharging from the gas turbine, especially since, as described above, the temperature level of the highly compressed air, after discharge from a high-pressure precompressor stage arranged downstream of the isothermal compression, is lower than in compressors of conventional gas-turbine plants, and therefore an improved heat transfer takes place between a heat exchanger in which the exhaust gases of the gas turbine are fed back (recuperator) and the highly compressed air.

Although a kinematic drive by means of the turbine is in turn required in order to arrange a high- compression compressor stage downstream of the isothermal compression, as a result of which the abovedescribed power loss of the gas turbine occurs, this proportion of energy is considerably reduced 97/174 compared with the exclusive precompression by means of conventional compressor stages. In addition, the lower temperatures of the highly compressed supply air, after discharge from the high- compression compressor stage, s contribute to an improved heat transfer at the recuperator, a factor which has a positive effect on the reduction of exhaust-gas emission values.

Especially in modern gas turbines having a high pressure ratio, the temperature of the air compressed by the compressor exceeds the temperature of the exhaust gas downstream of the turbine. For this reason alone, recuperation of the waste heat is not possible. In the isothermal compression according to the invention, however, the waste heat can mostly be recovered by means of recuperation.

The isothermal precompression of air according to the invention before entering a gas turbine or a highpressure compressor stage arranged upstream of the gas turbine is effected in an especially advantageous manner by utilizing the gravitation along a fall along which water falls through a high-pressure water line.

Provided at the bottom end of the high-pressure water line is an atomizing device which atomizes the pressurized water in the inlet region of a nozzle arrangement, which is arranged downstream of the atomizing device in such a way that a water/air mixture flow directed toward the nozzle arrangement forms in the inlet region. A high-pressure chamber is arranged downstream of the nozzle arrangement in the direction of flow, and the water/air mixture flows into this high-pressure chamber at high velocity on account of the nozzle effect. In the process, water and air separate, the air being isothermally compressed inside the high- pressure chamber on account of the damming effect inside the chamber. In addition, the highpressure chamber has at least two outlet passages, a top outlet passage and a bottom outlet passage, through the top outlet passage of which the isothermally 6 97/174 compressed air can be fed to the fluid-flow machine via the feed-line system.

The use of the combination according to the invention of isothermal precompression and an energy- generating fluid-flow machine, preferably a gas turbine, is especially suitable at orographically elevated water resources, such as, for example, mountain lakes, from which water can be taken for hydraulic compression.

The air isothermally precompressed in the high- pressure chamber is directly connected to the fluidflow machine via the corresponding feed-line system if the compression ratio of the air is sufficiently high. Otherwise, the outlet passage is connected to a high- pressure precompressor stage, by means of which the air can be precompressed to a desired value.

In order to also utilize the advantages of the isothermal compression even at locations where there are no natural falls predetermined by the orography, the water can also be directed at high flow velocities into the abovedescribed nozzle arrangement by means of rotary machines or by means of high-pressure-jet arrangements, so that in principle the isothermal compression can be achieved irrespective of orographical conditions. However, such solutions require an additional energy input, which, however, has to be taken into account in the overall efficiency during the operation of a gas turbine.

The compressor stage described is especially suitable at falls having heads of over 500 m.

The water arriving under high pressure at the end of the water line after passing through the fall is atomized by the atomizing device into very fine water droplets, the droplet diameter of which is typically 100 pm and smaller. The atomizing device is provided in the inlet region of the nozzle arrangement, which is preferably designed as a 2-phase Laval nozzle. Due to the water under very high pressure, flow velocities of 7 97/174 the individual water droplets of at least 100 m/s are achieved after passing the atomizing device, and these water droplets, on account of the orientation of the atomizing device and the design of the inlet region of the nozzle arrangement, move in the direction of the narrowing nozzle opening of the Laval nozzle.

A 2-phase Laval nozzle is distinguished by its special cross-sectional profile, which is selected in such a way that the relative difference in velocity between air and water always remains smaller than a certain value a, which is related to the energyconversion efficiency in the following way:

Air VWater -VO < VWa ter where v,,a,,: local water velocity VAir: local air velocity with e.g. c = 0.05 This efficiency requirement leads to a rapid 20 cross-sectional change in the case of small droplets and a short overall length of the Laval nozzle and to a slow cross-sectional change in the case of large droplets and a large overall length.

In detail, the sound velocity of the air/water mixture is given by:

JP a 4 QA1 FaPAir + a)PWater where: C: sound velocity of the mixture 8 97/174 p: static pressure a: volumetric fraction of the air p,,i,: density of the air p,,,,,e,: density of the water (1000 kg/m3) The air density and the pressure are linked with the temperature via an equation of state:

P=R,,2 7 m 2 PT S 2 K A ir where: T: temperature R: gas constant of the air In the 2-phase Laval nozzle, the water/air mixture is decelerated to a very low velocity. Here, it is of crucial importance that a 2-phase mixture of air and water, as a rule, has a very low sound velocity. At the entry to the Laval nozzle, the sound velocity is typically only about 23 m/s; on the other hand,the flow velocity of the mixture at this point is about 100-150 m/s. Here, therefore, the flow is within the high supersonic range. On account of the deceleration of the mixture in the Laval nozzle, the pressure greatly increases. The sound velocity also greatly increases with increasing pressure. on the other hand, the flow velocity drops to very small values. As in every Laval nozzle, Mach 1 is crossed at the narrowest cross section.

In addition to the described generation of water pressure by means of a fall, alternative pressure- generating techniques which direct water under high pressure specifically to an atomizing device may also be used. The build-up of the pressure of the water, irrespective of the way in which it is generated, should lead to fine atomization of the water by means 9 97/174 of an atomizing device and to a water/air volumetric ratio of about 0.05 to 0.1.

Typical overall lengths of Laval nozzles are about 15 m; however, if droplet sizes having a diameter of less than 100 gm are used, Laval nozzles having overall lengths of less than 15 m can also achieve very high efficiencies. As droplet diameters become larger, however, the minimum length of the Laval nozzle must increase if an efficiency loss is to be avoided.

Short description of the invention

The invention, without restricting the general inventive idea, is described below by way of example with reference to an exemplary embodiment and the drawing.

ways of embodying the invention, industrial applicability

In the single figure, the orographical system of a mountain B is utilized in order to utilize the water reservoir R, lying at a high level on the mountain, for driving a fluid-flow machine (not shown in the figure).

The water reservoir R is connected to a water line 1 of conventional design, through which the water plunges along a fall having a head of typically > 500 m. The water, accelerated by gravitation, passes at the end of the water line 1 through an atomizing device 2 into the inlet region E of a nozzle arrangement D. The atomizing device 2 has a nozzle outlet opening, by means of which the water under high pressure is atomized into very small water droplets. To form an air/water mixture, air-supply openings L, through which a sufficiently large amount of air can be supplied for forming a desired water/air mixture, are provided at the entry to the inlet region E. The nozzle arrangement D and the inlet region E of the nozzle arrangement D, which is 97/174 preferably designed as a two-phase Laval nozzle, are configured in such a way that the water/air mixture is directed toward the narrowing nozzle opening of the nozzle arrangement D at typically a water velocity of about 100 m/s and more. In the Laval nozzle, the mixture is decelerated to a low velocity and compressed in the process.

In the direction of flow, the Laval nozzle is connected to a pressure chamber 3, in which the water/air mixture discharging from the nozzle arrangement is regularly collected. Due to the high dynamic pressure forming in the pressurized chamber,. the air in the water/air mixture is isothermally compressed, the water at the same time being separated from the air inside the chamber. The separated water can be extracted from the chamber in a controlled manner via a bottom outlet opening 4. The air isothermally compressed inside the chamber passes via a second outlet opening 5 and a feed-line system (not shown in the figure) to the fluid-flow machine (likewise not shown in the figure) in order to accordingly drive the latter.

The technique of isothermal compression described above relates specifically to the production of water/air mixtures whose water/air ratios are between 30 and 40%. Such mixtures may be realized, for example, by utilizing falls having heads of > 500 m. For reasons of cost and also for reasons of efficiency, the water to be accelerated is directed downstream through normal water lines and is atomized in the desired manner by means of suitable atomizing devices.

97/174 List of designations 1 Water line 2 Atomizing device 3 High-pressure chamber 4 outlet opening for water outlet opening for air B Mountain D Nozzle arrangement E Inlet region L Air-supply openings R Water reservoir 12 97/174

Claims

Patent claims

1. An apparatus for the generation of energy by means of a fluid-flow machine, for the drive of which a compressor arrangement for isothermally compressing a compressible medium, preferably air, is provided, which medium, via a feed-line system, can be fed to the fluid-flow machine directly or after the interposition of a combustion chamber, in which the compressed medium can be ignited with the addition of fuel, characterized in that the compressor arrangement provides an atomizing device (2) which atomizes a pressurized liquid in the inlet region (E) of a nozzle arrangement (D), which is arranged downstream of the atomizing device (2) in such a way that a water/air mixture f low directed toward the nozzle arrangement (D) forms in the inlet region (E), in that a high- pressure chamber (3) is arranged downstream of the nozzle arrangement (D) in the direction of f low, and this high-pressure chamber (3) has at least two outlet passages, a top outlet passage (5) and a bottom outlet passage (4), through the top outlet passage (5) of which the compressed air can be fed to the fluid-flow machine via the feed-line system.

2. The apparatus as claimed in claim 1, characterized in that the nozzle arrangement (D) is a Laval nozzle.

3. The apparatus as claimed in claim 2, characterized in that the Laval nozzle is a 2-phase Laval nozzle.

4. The apparatus as claimed in one of claims 1 to 3, 30 characterized in that the liquid passes through a fall before entering the atomizing device (2).

5. The apparatus as claimed in claim 4, characterized in that the fall has a head of about 500 m and more.

6. The apparatus as claimed in one of claims 1 to 5, 35 characterized in that the liquid is water.

7. The apparatus as claimed in claim 6, characterized in that the atomizing device (2) atomizes the water 97/174 into water droplets which have a diameter of typically 100 gm and smaller.

8. The apparatus as claimed in claim 4, characterized in that the liquid has a flow velocity of about 100 m/s 5 before entering the atomizing device (2).

9. The apparatus as claimed in one of claims 1 to 8, characterized in that the inlet region (E) of a nozzle arrangement (D) provides at least one inflow opening f or air.

10. The apparatus as claimed in one of claims 1 to 9, characterized in that the water/air mixture flows into the high-pressure chamber (3) at high velocity and the water is separated from the air in the latter, the water discharging from the high-pressure chamber (3) through the bottom outlet opening.

11. The apparatus as claimed in one of claims 1 to 10, characterized in that the directed water/air mixture flow has a water/air volumetric ratio of between 0.05 and 0.1 before entering the nozzle arrangement (D).

12. The apparatus as claimed in one of claims 1 to 11, characterized in that the fluid-flow machine is a gas turbine.

13. The apparatus as claimed in claim 12, characterized in that the air isothermally compressed in the high-pressure chamber (3) can be f ed to a highcompression precompressor, which is connected to a combustion chamber, from which the hot gases produced in the combustion chamber can be fed to the gas turbine.

14. The apparatus as claimed in claim 12, characterized in that the isothermally compressed air can be passed directly into the combustion chamber.

15. The apparatus as claimed in claim 14, characterized in that the isothermally compressed air, before entering the combustion chamber, is thermally coupled to a heat exchanger, which is thermally fed by the waste heat of the exhaust gases of the gas turbine.