REGULATION SYSTEM FOR DOUBLE-SHAFT GAS TURBINES

Abstract: A regulating system for regulating a double-shaft gas turbine, wherein simultaneously: the fuel feed electrovalve is governed by a signal proportional to the difference beetween the number of revolutions per minute of the power turbine and a reference value; the movable nozzles of the power turbine are governed by a signal either proportional to the difference between the number of revolutions per minute of the compressor and a reference value, or proportional to the difference between the temperature of the exhaust gases and a relevant reference value; and the movable stator-blades of the compressor are governed by a signal proportional to the ratio between the revolutions per minute of the compressor to the square root of the ratio of the absolute ambient temperature to an absolute reference or design temperature.

Description: The present invention relates to a regulation system which makes it possible a double-shaft gas turbine with a high cycle compression ratio to be accomplished, which is endowed with a wide power regulation range inside which high efficiencies are maintained, also independently from ambient temperature. From the prior state of the art, several types of systems for double-shaft gas turbines regulating are known, one of which is initially based on the regulation of fuel injection and of the orientation of the movable nozzles of the power turbine until the minimum revolution speed at which the compressor normally operates, is reached; and subsequently, for a further reduction of power fed by the gas turbine, the orientation is controlled of one row only of movable stator-blades, with the number of revolutions per minute, i.e., the revolution speed, of said compressor being kept constant. The above said regulation system makes it possible the efficiency of the gas turbine to be maintained substantially constant within a wide range of variation of the power of the same turbine. Said system is however efficient only when it is applied to gas turbines having medium values of compression ratio, i.e., values of the order of 7 ÷ 8, and which are inherently more elastic from the view point of the preservation of efficiency with varying loads (power). In the field of the high compression ratios, of the order of 14 ÷ 15, and therefore with higher cycle efficiencies, on the contrary an intrinsic limitation exists in the range of variation of power inside which said high efficiencies are accomplished , because the efficiency, which is maximum at design point, decreases, when the operating conditions become different from said design point, faster than it would do in case of gas turbines with lower compression ratios. Another approach tendered by the prior art, which, however, is directed to ameliorating the adverse effects of cyclic load applications, rather than to improving the efficiency of a turbine, can be found in US-A-4 299 088, in which air flow is governed to control the output of the gas turbine while fuel flow in controlled to hold the firing or exhaust temperatures substantially constant. Still another prior art disclosure is US-A-4 539 810 which discloses a control apparatus comprising an acceleration condition detecting mechanism intended to control, as a function of the acceleration, the speed for opening variable nozzles in the inlet portion of a power turbine and/or variable inlet guide vanes installed in the inlet portion of a compressor of the engine. The purpose of the present invention is precisely to obviate the drawback outlined above, and, therefore, to provide a regulating system for a two-shaft gas turbine, which makes it possible to obtain a higher efficiency by means of higher compression ratios, the efficiency drop being simultaneously minimized within a wide range of power variations, and independently of the ambient temperature. Therefore, according to the prior art (see US-A-4 299 088), there is provided a regulating system to maintain a constant high efficiency for a double-shaft turbine having a high-compression-ratio compressor provided with a plurality of rows of movable stator blades with a power turbine equipped with movable nozzles (18), a, combustion chamber to which fuel is delivered through a regulating electrovalve and designed for a specific design ambient temperature, which comprises: a) a sensor for detecting the number of revolutions per min of said power turbine and for generating a first signal representative of the number of revolutions per min of said power turbine; b) a comparator unit for accepting said first signal and producing a first output signal when said first signal is compared to a first reference value; c) a means for accepting said first output signal for varying said regulating electrovalve; d) a sensor for detecting the number of revolutions per min of the shaft of said high-compression ratio compressor and for generating a second signal representative of the number of revolutions per min of said high-compression-ratio compressor shaft; (e) a comparator for accepting said second signal and for producing a second output signal when said second signal is compared to a second reference signal; f) a means for accepting said second output signal for governing said movable nozzles of said power turbine; whereby according to the invention, there is provided the further features: g) a sensor for detecting the ambient temperature as a third reference value and a compensating unit connected to said sensor for generating a third output signal when said second signal is compensated by said compensating unit, and h) a means for accepting said third output signal for governing said movable stator-blades of said high -compression-ratio compressor In another version, there is provided from the prior art (see US-A-4 299 088) a regulating system to maintain a constant high efficiency for a double-shaft turbine having a high-compression-ratio compressor provided with a plurality of rows of movable stator blades with a power turbine equipped with movable nozzles a combustion chamber to which fuel is delivered through a regulating electrovalve, and designed for a specific design ambient temperature, which comprises: a) a sensor for detecting the number of revolutions per min of said power turbine and for generating a first signal representative of the number of revolutions per min of said power turbine; b) a comparator unit for accepting said first signal and producing a first output signal when said first signal is compared to a first reference value; c) a means for accepting said first output signal for varying said regulating electrovalve; d) a sensor for detecting the temperature of the exhaust gases of said power turbine and for generating a second signal representative of the temperature of the exhaust gases of said power turbine; e) a comparator for accepting said second signal and for producing a second output signal when said second signal in compared to a second reference value; f) a means for accepting said second output signal for governing said movable nozzles of said power turbine; whereby according to the invention, there is provided the further features: g) a sensor for detecting the number of revolutions per min of the shaft of said high-compression-ratio compressor and for generating a third signal representative of the number of revolutions per min of the shaft of said high-compression-ratio compressor; h) a sensor for detecting the ambient temperature as a third reference value and a compensating unit connected to said sensor for generating a third output signal when said third signal is compensated by said compensating unit and i) a means for accepting said third output signal for governing said movable stator-blades of said high-compression-ratio compressor. More particularly, by causing the orientation of the movable stator blades of the compressor to be varied concurrently with the fuel injection and the orientation of the movable nozzles of the power turbine as a linear function of the RPM of the compressor shaft, continuously corrected on the basis of the ambient temperature, the eficiency of the turbine is improved. Still more particularly, the RPM of the compressor shaft is detected and compensated for relative to the ambient temperature, on the basis of the formula: wherein: N c is the RPM of the compressor shaft, corrected as a function, of the absolute (°K) ambient temperature; N is the measured RPM of the compressor shaft; T is the absolute (°K) ambient temperature, and Tr is an absolute (°K) reference or design ambient temperature. The invention is now better explained by referring to the hereto attached drawing, which depicts a preferred form of practical embodiment, given for only illustrative and non-limitative purposes, because technical and structural variants may be supplied at any time, without departing from the purview of the present invention. In said drawing, the figure shows a diagram of the regulating system for a double-shaft gas turbine, having a high compression ratio, according to the invention. Referring to said figure, by the reference numeral 1 the compressor of a double-shaft gas turbine is indicated, with the two shafts of the turbine being respectively indicated by the reference numerals 2 and 3, which compressor compresses air intaken through the filter 4, and delivers it into the combustion chamber 5, to which also the fuel comes, through the regulating electrovalve 6. The flue gases expand first inside the turbine 7, which drives the compressor 1 through said shaft 2, and subsequently inside the power turbine 8, which drives an operating machine, or a generator 9, and are then discharged to atmosphere through the exhaust 10. The revolution speed, or number of revolutions per minute of the shaft 3 of the power turbine 8 detected by the sensor 11 is compared inside the comparator unit 12 to a reference or set value, 13, and the output 12' from the comparator unit 12 is used in order to drive the fuel electrovalve 6. Simultaneouly to the above, the number of revolutions per minute N of the shaft 2 of the compressor 1, detected by the sensor 14, or the temperature of the gases at exhaust 10, detected by the sensor 15, are compared to set values inside the comparator unit 16, which governs, by means of its output 17, the movable nozzles 18 of the power turbine 8. Finally, the number of revolutions per minute N detected by the said sensor 14 is also input, together with the value of the ambient temperature T detected by means of the sensor 19, to a unit 20 which performs the compensation of said number of revolutions per minute N relatively to said temperature, in order to obtain a signal equal to the corrected number of revolutions per minute by means of which the movable stator-blades 21 of compressor 1 are governed.

Claims: A regulating system to maintain a constant high efficiency far a double-shaft turbine having a high-compression-ratio compressor (1) provided with a plurality of rows of movable stator blades (21), with a power turbine (8) equipped with movable nozzles (18), a combustion chamber (5) to which fuel is delivered through a regulating electrovalve (6), and designed for a specific design ambient temperature, comprising: a) a sensor (11) for detecting the number of revolutions per min of said power turbine (8) and for generating a first signal representative of the number of revolutions per min of said power turbine (8); b) a comparator unit (12) for accepting said first signal and producing a first output signal (12') when said first signal is compared to a first reference value (13); c) a means for accepting said first output signal (12') for varying said regulating electrovalve (6); d) a sensor (14) for detecting the number of revolutions per min of the shaft (2) of said high-compression-ratio compressor (1) and for generating a second signal representative of the number of revolutions per min of said high-compression-ratio compressor shaft (2); (e) a comparator (16) for accepting said second signal and for producing a second output signal (17) when said second signal is compared to a second reference signal; f) a means for accepting said second output signal (17) for governing said movable nozzles (18) of said power turbine (8); and characterised by : g) a sensor (19) for detecting the ambient temperature as a third reference value and a compensating unit (20) connected to said sensor (19) for generating a third output signal when said second signal is compensated by said compensating unit (20), and h) a means for accepting said third output signal for governing said movable stator-blades ((21) of said high-compression-ratio compressor (1). A regulating system according to Claim 1, wherein said third output signal is said second signal divided by the square root of the ratio of said ambient temperature to said design ambient temperature. A regulating system to maintain a constant high efficiency for a double-shaft turbine having a high-compression-ratio compressor (1) provided with a plurality of rows of movable stator blades (21), with a power turbine (8) equipped with movable nozzles (18), a combustion chamber (5) to which fuel is delivered through a regulating electrovalve (6), and designed for a specific design ambient temperature, comprising: a) a sensor (11) for detecting the number of, revolutions per min of said power turbine (8) and for generating a first signal representative of the number of revolutions per min of said power turbine (8); b) a comparator unit (12) for accepting said first signal and producing a first output signal (12') when said first signal is compared to a first reference value (13); c) a means for accepting said first output signal (12') for varying said regulating electrovalve (6); d) a sensor (15) for detecting the temperature of the exhaust gases of said power turbine (8) and for geerating a second signal representative of the temperature of the exhaust gases of said power turbine; e) a comparator (16) for accepting said second signal and for producing a second output signal when said second signal in compared to a second reference value; f) a means for accepting said second output signal for governing said movable nozzles (18) of said power turbine (8); and characterised by : g) a sensor for detecting the number of revolutions per min of the shaft (2) of said high-compression-ratio compressor (1) and for generating a third signal representative of the number of revolutions per min of the shaft (2) of said high-compression-ratio compressor (1); h) a sensor (19) for detecting the ambient temperature as a third reference value and a compensating unit (20) connected to said sensor (19) for generating a third output signal when said third signal is compensated by said compensating unit (20), and i ) a means for accepting said third output signal for governing said movable stator-blades (21) of said high -compression-ratio compressor (1). A regulating system according to Claim 3, wherein said third output signal is said second signal divided by the square root of the ratio of said ambient temperature to said design ambient temperature.

Inventors: BENVENUTI, ERIO, INNOCENTI, BRUNO
Applicants: NUOVOPIGNONE INDUSTRIE MECCANICHE E FONDERIA S.P.A.
Application year: 1988
Main classification: F02C9
IPC codes: F01D17, F02C9, F02C7