ES2634028B1 - Gas turbine with two stages of compression and intermediate cooling by means of a refrigerating machine - Google Patents

Abstract

Gas turbine with two compression stages and intermediate cooling by means of a refrigerating machine. # The present invention is therefore based on a gas turbine with two compression stages. Between these two stages a heat exchanger is inserted, constituted by the evaporator of a refrigerating machine mechanically operated by the turbine itself, prior to the use of a speed reduction box, in order to lower the temperature of the working fluid of the turbine in its transition to the second compression stage, thereby achieving the desired fluid pressure, at the outlet of the second compressor, doing a smaller job than it should have been done to bring that working fluid up to that same pressure in a single stage without cooling. This results in greater efficiency of the gas turbine itself.

Description

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DESCRIPTION

Gas turbine with two stages of compression and intermediate cooling by means of a refrigerating machine.

The present invention relates to a gas turbine that follows the Brayton thermodynamic cycle. It makes use of a two-stage compression, the working fluid being cooled to temperatures even lower than those of the first compressor's own admission, in the transition between the first and the second stage. This is achieved through the use of a refrigerating machine, driven by the axis of the turbine itself, responsible for absorbing part of the heat generated in the first stage of compression, achieving significantly higher yields than those obtained without this method, and even greater than those obtained through the use of the already known air-air air-liquid exchangers or other systems that will be mentioned later.

The fact that the compressors are unable to perform reversible adiabatic processes, since they perform their work in a finite time, prevents them from acting as isentropic systems, so that as the working fluid is compressed, it gains temperature in a way greater than it would if the process were reversible.

This thermal gain is what motivates the need to divide the compression of the working fluid of the turbines in several stages, in order to lower its temperature between them, managing to need less work to achieve the desired final pressure than if it were used A single compression without refrigeration.

Technical sector

The present invention is framed in the sector of the technique belonging to the aerospace industry and energy production, that is, the two sectors where gas turbines are mostly used.

Background to the invention

Various systems used to achieve a cooling of the working fluid between the different compression stages of the gas turbines are known. There are those that use surface exchangers that produce a heat transfer between the pressurized fluid in the preceding stages and some refrigerant fluid, be it atmospheric air, water, etc. Its objective is to try to bring the temperature of the pressurized fluid closer to the temperature it had prior to its compression, keeping its pressure constant, in order to reduce the work necessary to increase its pressure again in the later stages.

Various types of devices are also known to try to extract the heat present in the working fluid. Some of these methods would be the evaporative coolers, which are based on a wet filter through which the working fluid is run, in our case air, in order for this to give heat to the liquid water to achieve a change of state.

It is also known the use of fog systems, which are based on the same principle as evaporative coolers, with the exception that they make use of water sprayers that spray it on the working fluid.

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Likewise, wet compression systems by mechanical cooling base their operating principle on the injection of atomized water directly to the turbine's working fluid flow, achieving temperatures as low as desired, with the proviso that energy consumption usually makes this economically unfeasible system, as well as your space needs.

However, the thermal extraction capacity of these methods has been shown to be considerably improved, given that in the best case they only manage to lower the temperature of the working fluid of the turbine a few tens of degrees, so it has been devised a new method, whose characteristics are the object of the present invention.

Description of the invention

The gas turbine is of the type that consists of a compression system divided into several stages, theoretically adiabatic compression (according to the Brayton cycle) being applied to the working fluid, atmospheric air in this case.

However, and with the aim of increasing the efficiency of the cycle, by reducing the work that is necessary to perform in the second stage to compress the working fluid to the desired pressure, it has been decided to necessarily reduce its temperature at the exit of the first stage until a temperature even lower than it had before undergoing any transformation.

For the realization of this work, and that makes sense from a thermodynamic and therefore economic point of view, the use of a refrigeration cycle has been devised, the compressor that animates it being mechanically driven by the turbine shaft itself, prior adaptation of its speed in a gear train.

Making use of the evaporator of the refrigerating machine as an exchanger built in a material with a high index of thermal conductivity (between the working fluid of the turbine and the cooling fluid) and insulated as much as possible from the outside, in order to avoid The surrounding heat absorption, we can cool the air to the desired temperature.

Knowing that the efficiency of the refrigerating machine depends on the ratio between the heat absorbed and the difference between the heat ceded by the machine and the absorbed, we can deduce that the smaller the difference between the heat absorbed and the ceded, the greater the efficiency of the machine, being able to easily exceed the unit.

This is where the role of the refrigerating machine condenser becomes especially important. This must have a great capacity for heat transfer, both by construction and by situation, to achieve the above in the previous paragraph, since the higher the efficiency of the machine, the less work the compressor has to do (already that this is powered by the turbine itself), leading to a greater performance of the gas turbine, since this depends on the work done by the turbine, the one absorbed by the different compressors, by the compressor of the refrigerating machine and the heat needed to make it work.

Brief description of the drawings

For better understanding of what is described herein, some drawings are attached in which, only by way of example, a practical case of the turbine is shown.

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FIG. 1, schematically shows the operation of the system. The interaction between the refrigerating machine and the gas turbine can be observed, the latter being the one that produces the work necessary to operate the refrigerating machine and the first one that absorbs part of the heat generated in the compression process of the working fluid of the turbine in its first compression stage.

Enumeration of parts:

- (1): Axial compressor

- (2): Axial compressor

- (3): Axial turbine

- (4): Conductions for the working fluid of the gas turbine, represented by a solid line with arrows

- (5): Combustion chamber

- (6): Speed reduction box

- (7): Refrigerator machine compressor

- (8): Conduits for the working fluid of the refrigerating machine, represented by a solid line with arrows

- (9): Refrigerator machine condenser

- (10): Coolant reservoir

- (11): Refrigeration machine expansion valve

- (12): Refrigerator / heat exchanger evaporator

- (13): Turbine shaft, represented by a dashed line

- (a, [...], k): Points with different thermodynamic status of the respective working fluids

FIG. 2 and FIG. 3 show respectively the thermodynamic cycle followed by the refrigerating machine and the turbine. Both cycles are represented by two Pressure-Volume diagrams. It should be noted that they have been represented as two reversible cycles, so that the actual operation of both machines will be substantially different from what is embodied here. However, given the impossibility of representing irreversible cycles, it has been decided to include these two modeling, with a purely explanatory spirit.

The cycles have been represented by points, named from (a) to (k), which correspond to the thermodynamic state of the working fluid of each of the machines at the different points thereof. This designation can also be seen in FIG. 1, referring to the state in which the working fluid is located according to the position it occupies with respect to the system.

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Enumeration of points of FIG. 2 and FIG. 3:

- (a, [...], k): Points with different thermodynamic status of the respective working fluids

Description of a preferred embodiment

In accordance with FIG. 1 we can observe how the turbine consists of a first compressor (1), a secondary compressor (2), a heat exchanger, which acts as an evaporator of the refrigerating machine (12), indirect surface contact and cross flow ( The compressed fluid in the first compressor (1) of the gas turbine gives heat to the refrigerant fluid of the refrigerating machine when it is in phase change, from liquid to gas), a combustion chamber (5) where it rises the temperature of the working fluid of the turbine and with it its enthalpy and finally the turbine (3), the working fluid flowing between the different parts that constitute the system through its own ducts (4) and rotating the entire compressor assembly ( 1 and 2) and turbine (3) in solidarity thanks to an axis (13).

The refrigerating machine consists of a compressor (7), which raises the pressure of the working fluid, in this case cooling fluid, when it is completely in the gas phase, running it through lines or pipes (8). The compressor (7) is mechanically driven by the turbine, transforming the speed of rotation of its axis (13) into a more suitable for the operation of the refrigerating machine by using a gearbox (6).

The refrigerant fluid travels from the compressor (7) to the condenser (9), being there where it gives heat to the outside, with the consequent change of gas phase to liquid. The liquefied gas is collected in a tank (10), then traveling along the mentioned lines (8) to an expansion valve (11), where its pressure decreases sharply, leading to the phase change that will occur later in the evaporator (12 ). This takes the heat necessary to change the refrigerant fluid of the compressed working fluid in the first stage of compression to the turbine (1). Once the refrigerant fluid leaves the evaporator (12) it travels back to the compressor (7), where it will reprint the work necessary to complete the thermodynamic cycle again.

In accordance with FIG. 3 it is possible to observe the works to which the working fluid is subjected to as it passes through the turbine in a supposedly reversible cycle. The cycle begins at (a) where the fluid accesses the system, as can also be seen in FIG. 1 (there may or may not be diffusers at the inlet of the turbine, which slow down the air flow by increasing its pressure, depending on the application of the turbine) and undergoes a first transformation, it is adiabaticly compressed by the first compressor (1) until it reaches a (b). In the section between (b) and (c) the working fluid is cooled isobarically yielding a heat Q2 ’in the heat exchanger (12). From (c) to (d) the working fluid is again compressed adiabatically, this time by the second compressor of the gas turbine (2) traveling at all times through the said conduits (4). Between (d) and (e) the working fluid absorbs a heat Q1 in the combustion chamber (5), usually in the form of fuel burning. Finally, in the section between (e) and (f) the working fluid undergoes an adiabatic expansion in the turbine (3) until its initial pressure is recovered (Pa = Pf). It is worth mentioning that this expansion, the one between (e) and (f) is the only one in the cycle that produces work instead of consuming it. It should be noted that it is not taken into account if a nozzle could exist after the working fluid has left the turbine, it will depend on the application to which the use of the turbine is intended.

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In accordance with FIG. 2 we can observe a modeling (to reversible works) of the refrigerating machine described here. The cycle begins in (h) where after its exit from the evaporator (12), which acts as an exchanger in the gas turbine, the cooling fluid is in a gaseous state and occupying its maximum possible volume (its density is the minimum that you will have throughout the cycle). Between (h) and (i) the fluid, now in a necessarily gaseous state, to avoid damage to the compressor (7), passes through the compressor (7) where it undergoes an adiabatic compression which therefore leads to an increase in its temperature . Between (i) and (k) the fluid gives a heat Q1 in the condenser, in an isothermal manner, also returning to a liquid state, this being in turn collected in a tank (10). As it passes through the expansion valve (11), the fluid undergoes an abrupt decrease in its pressure, which is reflected in the interval between (k) and (g) as an adiabatic expansion. Finally, the refrigerant fluid passes through the evaporator of the refrigerating machine (12) where, acting as an exchanger in the gas turbine, it collects the heat transferred by the turbine's working fluid, Q2 ', and changes completely from liquid to gaseous phase , which is reflected in the diagram as an isothermal expansion between (g) and (h).

As you can see, the system is shown in its most elementary, basic state. It can be considerably improved by the relevant addition of the typical improvements of both the refrigeration cycle and the gas turbine cycle, such as overheating in the latter, for example. However, it has been decided to omit all possible improvements, reducing the system to its most primary state, in order to simplify the drafting and understanding of the present invention. The description of a hypothetical parallel association of several stages in compression and refrigeration machines has also been overlooked, due to the redundancy that this entails.

It is evident that the present invention would have a wide range of application, both in the aerospace and energy production industries, being able, in the latter case, to complement the combined cycle or cogeneration plants in their search for the highest possible efficiency . For its part, in the aerospace industry would have great application when creating more efficient engines, with lower consumption and emissions of harmful gases directly into the atmosphere. It would in turn increase the service autonomy of the aforementioned aircraft, reducing the cost of transporting goods or passengers.

Claims (15)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 1. Gas turbine with at least two compression stages and at least one intermediate cooling stage, comprising a first axial compressor (1) and a second axial compressor (2), driven by the axis (13) of an axial turbine (3), characterized in that the intermediate cooling stage is carried out by means of a refrigerating machine arranged between both axial compressors (1, 2), wherein the refrigerating machine comprises at least one compressor (7), at least one gearbox (6 ), at least one condenser (9), at least one expansion valve (11), and at least one evaporator (12), see where the working fluid of the refrigerating machine passes through the compressor (7), said compressor ( 7) is actuated by the gearbox (6) also actuated by the axis (13) of the axial turbine (3), said compressor (7) is connected to the condenser (9) at whose outlet the expansion valve ( 11) after which the evaporator (12) of the refrigerating machine is arranged, the c This exchanges heat with the gas turbine fluid between both axial compressors (1, 2). 2. A gas turbine according to claim 1, characterized in that between the condenser (9) and the expansion valve (11) it comprises at least one reservoir (10) of the cooling fluid. 3. Gas turbine according to claim 1, characterized in that at least one of the axial compressors (1, 2) applies an adiabatic compression of the working fluid according to the Brayton cycle. 4. Gas turbine according to claim 3, characterized in that the working fluid is atmospheric air. 5. Gas turbine according to claim 1, characterized in that the compressor (7) of the refrigerating machine is mechanically driven by the axis of the axial turbine (3), after adjusting its speed by means of a gearbox (6). 6. Gas turbine according to claim 5, characterized in that the gearbox (6) is a gear train. 7. Gas turbine according to claim 5, characterized in that the evaporator (12) is an indirect surface contact and cross flow heat exchanger. 8. Gas turbine according to claim 1, characterized in that it comprises a combustion chamber (5) between the second axial compressor (2) and the axial turbine (3) where the temperature of the working fluid is raised. 9. Gas turbine according to claim 1, characterized in that the assembly of the first and second axial compressor (1, 2) and the axial turbine (3) rotate in solidarity thanks to an axis (13). 10. Gas turbine according to claim 1, characterized in that it comprises at least one diffuser at the inlet that slows down the workflow by increasing its pressure. 11. Gas turbine according to claim 1, characterized in that it comprises at least one nozzle at the outlet. 12. Gas turbine according to claim 1, characterized in that it comprises several compression stages and refrigerating machines, associated in parallel. 5 10 fifteen twenty 25 30 13. Method of operation of a gas turbine according to claims 1 or 2, with at least two axial compressors (1, 2) driven by the shaft (13) of an axial turbine (3), characterized in that it comprises a refrigerating machine closed cycle with the stages of: i) increase the pressure of a refrigerant fluid by a compressor (7), operated by a gearbox (6) driven by the shaft (13); ii) liquefy the cooling fluid in a condenser (9) that gives heat to the outside; iii) arranging the refrigerant fluid in a tank (10) whose outlet comprises an expansion valve (11) for reducing the working fluid pressure; iv) evaporate the cooling fluid in an evaporator (12), capturing the heat of the turbine fluid (3) between the two compressors (1 and 2). 14. Method of operation of a gas turbine according to claim 13 wherein: i) the refrigerant fluid travels through pipes (8) from the compressor (7) to the condenser (9), where heat is transferred to the outside until a change from gas phase to liquid occurs; ii) the liquefied refrigerant fluid is collected in a tank (10), traveling through said conduits (8) to an expansion valve (11), where its pressure decreases sharply, leading to the change of subsequent phase in the evaporator (12 ). 15. Method of operation of a gas turbine according to claim 14 wherein: - the refrigerant fluid, as it passes through the expansion valve (11), undergoes an abrupt decrease in its pressure according to an adiabatic expansion.