Refrigeration – Air compressor – cooler and expander type
Reexamination Certificate
1999-09-27
2001-09-11
Doerrler, William (Department: 3744)
Refrigeration
Air compressor, cooler and expander type
Reexamination Certificate
active
06286333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the field of fluid mechanics. It relates to a method of generating a third gas flow of medium pressure and medium temperature, which can be particularly employed as cooling air for a gas turbine, from a first gas flow of high pressure and high temperature.
The invention also relates to an appliance for carrying out the method.
2. Discussion of Background
A particular difficulty associated with the cooling of gas turbines consists in the fact that only a limited number of pressure stages are available on the compressor for the supply of secondary air. Because of this limitation, it frequently happens that cooling air is made available at a very high pressure and that high losses occur before the cooling air reaches a desired pressure level, which may be very much lower than the pressure level at which it is made available. In this case, a further problem consists in the fact that the temperature of the cooling air is very high because simply reducing the pressure does not reduce the stagnation temperature of the cooling air.
A particularly critical situation arises in the case of the low supply pressure level of a compressor when the inlet guide vanes of the compressor are substantially closed. In this case, the low supply pressure, which would be approximately 2 bar with the inlet guide vanes fully open, can fall below the ambient pressure. As a consequence of this, the lowest permissible supply pressure for supplying the bearings with sealing air and the last turbine disk with cooling air would be up to 5 bar, although a positive pressure of 200 mbar would be sufficient.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel method and appliance by means of which the cooling air, or a gas flow in general, can be lowered with good efficiency from a comparatively high initial pressure and a comparatively high initial temperature to a more suitable lower level of pressure and temperature.
The object is achieved by the totality of the features of claim
1
and of claim
4
. The core of the invention consists in lowering the pressure and the temperature of the inlet-end gas flow in several steps by combination with a further gas flow, of lower pressure and lower temperature, in a favorable manner—in terms of energy—in a cascade of energy exchangers.
There is a plurality of different types of energy exchangers which can be employed in such a cascade, including turbochargers, pressure-wave machines, Ranque-Hilsch tubes or simple jet injectors. In each case, a gas flow at high pressure and a gas flow at low pressure are combined in such individual energy exchangers to provide a resultant gas flow with a medium pressure. A first preferred embodiment of the method according to the invention is therefore one wherein, from a first mass flow with a first pressure and a first temperature and a second mass flow with a second pressure and a second temperature, which are smaller than the first pressure and the first temperature, a resultant third mass flow with a third pressure and a third temperature is generated in each of the energy exchangers, which third pressure and third temperature lie between the first and the second pressures and the first and second temperatures, wherein the respective third mass flow of the second and all further energy exchangers is divided into two partial flows, wherein the first partial flow is used as the first mass flow of the following energy exchanger within the cascade, wherein the second partial flow is used as the second mass flow of the preceding energy exchanger within the cascade, wherein the first gas flow is fed into the first energy exchanger as the first mass flow, wherein the second gas flow is fed into the last energy exchanger as the second mass flow, and wherein the first partial flow of the last energy exchanger is extracted from the cascade as the resultant gas flow.
The differences between the various types of energy exchangers are essentially associated with the different fields of application, with different complexity and different effectiveness. The simplest class of energy exchangers are the so-called direct fluid/fluid energy exchangers, which include the jet injector and the Ranque-Hilsch tube. In accordance with a second preferred embodiment of the method, therefore, it is possible to achieve high effectiveness in a particularly simple manner if the energy exchangers are configured as jet injectors, i.e. if in each of the energy exchangers of the cascade, the first and the second mass flows are respectively injected as a jet into a mixing space and are there mixed with one another to form the third mass flow.
The appliance for carrying out the method according to the invention is one wherein a plurality of energy exchangers are connected in series in a cascade, wherein each of the energy exchangers has two inlet openings and one outlet opening, wherein the outlet opening of one energy exchanger is respectively connected to the first inlet opening of the following energy exchanger, wherein means are present which respectively feed back a partial flow from the outlet opening of an energy exchanger to its second inlet opening, wherein the first inlet opening of the first energy exchanger is provided as the high-pressure inlet for feeding in the first gas flow, wherein the second inlet opening of the last energy exchanger is provided as the low-pressure inlet for feeding in the second gas flow, and wherein the outlet opening from the last energy exchanger is provided as the medium-pressure outlet for extracting the third gas flow.
An embodiment of the appliance according to the invention which is preferred because of its simplicity is one wherein each of the energy exchangers is configured as a jet injector and each has a mixing space through which the gases flow, wherein two nozzle-shaped inlets, which form the two inlet openings of the energy exchanger, are provided upstream of the mixing space, and wherein an outlet, which forms the outlet opening of the energy exchanger, is arranged downstream of the mixing space.
A very compact construction for the complete cascade can be achieved by an arrangement wherein the injector cascade is made up of a plurality of semicircular tube segments, which are stepped in diameter, which are alternately and concentrically arranged on both sides of a central plane and whose open sides are oriented relative to the central plane in such a way that the tube segments engage with one another and that mixing ducts, which are connected to one another in the manner of a cascade, are respectively formed between two sequential tube segments on the same side of the central plane.
Further embodiments follow from the dependent claims.
REFERENCES:
patent: 5311749 (1994-05-01), McAuliffe et al.
patent: 5461882 (1995-10-01), Zywiak
patent: 6070418 (2000-06-01), Crabtree et al.
Hagström Gustav
Keller Georg
Keller Jakob
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Doerrler William
Drake Malik
Keller Georg
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