Prime-mover dynamo plants – Fluid-current motors
Reexamination Certificate
1999-09-27
2001-05-01
Enad, Elvin (Department: 2834)
Prime-mover dynamo plants
Fluid-current motors
C290S00100C, C290S00100C, C290S00100C
Reexamination Certificate
active
06225706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for the isothermal compression of a compressible medium, preferably air, for the operation of a turbomachine which is intended to generate energy and in which a pressurized liquid, preferably water, is atomized by means of an atomization device and, together with the air, forms a liquid-air mixture which, in order to be compressed, is introduced into a nozzle arrangement in which most of the kinetic energy of the liquid-air mixture is converted into compression energy as a result of the pressure of the air increasing. The invention furthermore describes an atomization device and a nozzle arrangement.
2. Discussion of Background
To produce energy, it is proposed, in U.S. Pat. No. 4,797,563, to supply a gas turbine with isothermally precompressed air which is accelerated along a descending gradient, which is designed as a horizontal chute, as a liquid-air mixture, by means of the force of gravity and is compressed in a pressure chamber which adjoins the bottom end of the chute, where the air is separated from the liquid again. The air which has been compressed in this way is then fed to the combustion chamber of a gas turbine, within which the highly compressed air which is at a low temperature level is mixed with fuel and ignited. The principal advantages of the isothermal compression are, firstly, the fact that there is no need for conventional compressor stages which are driven by the gas turbine and consequently impair the efficiency of the overall gas-turbine plant, and secondly the fact that the precompressed air, which is at a relatively low temperature, is able to impose considerably lower thermal loads on the components of the plant which come into thermal contact with this air, with the result that the requirements imposed in the individual components of the plant can be reduced.
The principle of isothermal compression, which is known per se and is described in the abovementioned U.S. Pat. No. 4,797,563, is an interesting possibility which appears to point the way forward for providing air to gas turbine plants in precompressed form, and consequently it is desirable to optimize this technology. In particular, the efficiency of compressor arrangements of this nature is to be increased, in order in this way to improve the overall efficiency of energy-producing plants, and in this case, in particular, gas-turbine plants.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to refine a method for the isothermal compression of a compressible medium, preferably air, for the operation of a turbomachine which is intended to generate energy and in which a pressurized liquid, preferably water, is atomized by means of an atomization device and, together with the air, forms a liquid-air mixture which, in order to be compressed, is introduced into a nozzle arrangement in which most of the kinetic energy of the liquid-air mixture is converted into compression energy as a result of the pressure of the air increasing, in such a manner that, on the one hand, the compression efficiency is to be increased, the intention being that the plant components which are required for this purpose are to be produced in as inexpensive and compact a manner as possible, i.e. in the smallest possible structural form. Moreover, the plant components which are required to carry out the desired method, in particular the atomization device which is required to produce a liquid-air mixture and the nozzle arrangement which is provided for compression, are to be modified with a view to the desired optimization of the compression efficiency.
Working on the basis of a large number of experiments carried out in the run-up to the invention, the invention is based on the principle that, by suitably setting the droplet size or bubble size and velocity of the liquid-air mixture, it is possible to have a decisive influence on the compression efficiency which can be achieved with a compressor arrangement, for example with a Laval nozzle.
According to the invention, a method is refined in such a manner that the liquid-air mixture is introduced into the nozzle arrangement at a velocity which is greater than the speed of sound, and within the nozzle arrangement it is decelerated from the trans-sonic range into the subsonic range and, at the same time, a desired pressure increase takes place. The atomization of the liquid before it enters the nozzle arrangement takes place inside the atomization device, in such a manner that liquid droplets with a diameter of approx. 200 &mgr;m and less are formed within the liquid-air mixture. It has been recognized that, in order to form the liquid-air mixture which is as homogenous as possible, the liquid stream which is to be atomized has to be fed to the atomization device at high pressure, so that the exit speed of the liquid leaving the atomization device is approximately 100 to 200 m/sec. As the pressure increases and/or the percentage of liquid by volume increases, the cloud of droplets changes into a liquid containing bubbles. Since the relative velocity of the two phases is considerably reduced after this transition, owing to the increased resistance to relative movement, the fineness of the mixture is particularly important only in the initial phase of the cloud of droplets.
According to the invention, it has been recognized that liquid atomization using the abovementioned high exit velocities and a liquid-droplet formation with droplet diameters which are as small as possible, result in the formation of a liquid-air mixture which, when it passes through a Laval nozzle, undergoes considerably better compression than is the case for liquid-air mixtures with lower flow velocities and greater droplet diameters, according to the prior art known hitherto. It is thus possible, depending on the quality and efficiency of the atomization operation, to have a decisive influence on the length of the Laval nozzle which is required for the compression. Put simply, it is possible to state that the more homogenous a liquid-air mixture, comprising liquid droplets with diameters which are as small as possible, and the greater the flow velocity of the mixture, the shorter it is possible for the length of the Laval nozzle to become. Thus a large number of flow investigations have shown that the deceleration action of the liquid-air mixture which enters the Laval nozzle is at its height in the first half of the total length of the Laval nozzle, provided that the liquid-air mixture moves past the Laval nozzle at a high speed, with a droplet distribution which is as homogenous as possible and with droplets with a very small diameter. Working on this basis, it is possible to reduce the structural size of Laval nozzles considerably.
In order to increase the atomization produced by the atomizer device, i.e. reduce the diameter of the liquid droplets and to set the droplet distribution to be as homogenous as possible within the liquid-air mixture which forms, it is particularly advantageous if the high-pressure liquid which is fed to the atomizer device is at a temperature which, under the pressure conditions prevailing during the atomization operation, lies just above the evaporation temperature of the liquid. This ensures that, in addition to the atomization effect which is produced by the atomization device, the liquid droplets, after they have passed through the atomizer nozzle, are additionally subjected to an evaporation process, which contributes to reducing the diameter of the droplets further. Briefly exceeding the boiling point leads to particularly small droplets. However, it is very much dependent on the overall process of the power plant whether it is possible, from a thermodynamic viewpoint, to select such an atomization temperature.
A further possibility of optimizing the atomization operation is to admix a second liquid with the liquid which is to be atomized before it passes through the atomizer device. In this case, the second liquid is to be admixed to the liquid to be atomized und
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Enad Elvin
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