US2225311A - Gas turbine system - Google Patents

Description

Dec. 17, 1940. A. LYSHOLM GAS TURBINE SYSTEM Filed Dec. 11, 1937 INV NTOR.

KW ATTORNEY.

Patented Dec. 17, 1940 UNITED STATES 2,225,311 GAS TURBINE SYSTEM\ Alf Lylholm, Stockholm, Sweden, assignor to Aktiebolaget Milo, Stockholm, Sweden, a corporation of Sweden Application December 11, 1937, Serial No. 179,23 In Germany December 15, 1936 Claims.

The present invention relates to gas turbine systems of the continuous combustion type and has particular reference to systems of this character in which the motive fluid is formed by the 5 combustion of gas generated in a gas producer. Still more particularly, the invention relates to systems of the above character in which the gas for the motive fluid is formed in a gas producer utilizing solid fuel for the production of the gas.

In continuous combustion gas turbine systems, it is well known that the thermal efficiency of the system can be increased by expanding the motive fluid in a plurality of turbine stages and reheating partially expanded motive fluid between stages. The extent to which the thermal efficiency can be increased is increased by increasing the number of times the motive fluid is reheated between pressure stages, but practical considerations limit to a relatively low value the number of times the motive fluid can be reheated.

In order to obtain such increased thermal efficiency, it has already been proposed to reheat motive fluid between expansion stages in continuous gas turbine systems and such reheating has heretofore been carried out in numerous different ways, all of which ways, however, have certain disadvantages, particularly if the motive fluid must be produced from solid fuel.

The general object of the present invention is the provision of the novel method and means for carrying the method into effect whereby intermediate or stage reheating may be effected in a system of the character under consideration with minimum loss, and to provide such method and means which will enable such system to be advantageously operated, with interstage reheating, with motive fluid formed with gas produced from solid fuel.

The manner in which the above general object and other objects of the invention are attained, together with the advantages to be derived from use of the invention, may best be understood from a consideration of the ensuing portion of this specification in which a suitable form of apparatus for carrying the invention into effect will be described by way of example.

In the drawing forming a part of this specian electric generator, and it an air compressor.

In the embodiment illustrated, turbines HI and I2 are of the axial flow type, compressor I8 is of the rotary screw type, and the turbines, compressor and generator are mounted on a common 5 shaft indicated generally at ll so as to rotate at the same speed. It will be understood that in so far as the present invention is concerned, other types of turbine and compressor apparatus may be employed and it will further be understood that the turbine, compressor and generator units need not necessarily be coupled together in the manner shown in the illustrated embodiment.

The high pressure turbine Ill receives hot gaseous motive fluid from a combustion chamber 2|! and exhausts motive fluid at intermediate pressure .to a reheating combustion chamber 22. From this latter chamber the reheated motive fluid at intermediate pressure is delivered to the inlet of the low pressure turbine l2 which exhausts low pressure gases through the conduit 24 to a regenerator 26, from which the gases are finally discharged through the outlet conduit 28.

The means for producing gas to be used as a constituent of the motive fluid comprises, in the embodiment shown, a gas producer indicated generally at 30 having a combustion chamber 32 to which solid fuel, indicated at 34, is admitted through a feed hopper 36 controlled by valve 38.

The fuel is supported on a grate 40 which may be of any suitable character, and air necessary to support the combustion necessary to produce the gas from the fuel is admitted to the gas producer through conduit 42 leading from the discharge end of comprmsor l8. Conduit 42 passes through regenerator 26 so that the compressed air is preheated before being admitted to the gas producer. The quantity of air admitted to the gas producer, which determines the quantity of gas generated for formation of motive fluid, is controlled by valve 44, the action of which will hereinafter be more fully described. A branch conduit 46 supplies compressed air to the combustion chamber 20 for burning the gas from the producer admitted to this chamber to form the high pressure motive fluid admitted to turbine [0. This, production of the initial supply of motive fluid will hereinafter be referred to as primary combustion.

Gas produced in the producer 30 is delivered through conduit 48 and branch conduits 50 and 52, branch 50 supplying gas to the combustion chamber 20 and branch 52 supplying gas to the reheating chamber 22.

A valve 54 is provided in branch 52 for controlling the admission 01 gas to the reheating chamber, this valve being actuated by a thermostat 56 responsive to the temperature of the gases exhausted from the low pressure turbine and operating to close valve 54 it the temperature of these exhaust gases exceeds a predetermined value.

The system illustrated is controlled by means of a governor indicated diagrammatically at 58 and connected with valve 44 by means of suitable linkage, which in the embodiment illustrated is diagrammatically indicated by lever 60, motion transmitting rods 62, 64, and 88, and bell cranks l8 and 10, so that upon increase in load on the system, valve 44 is opened to increase the amount or air admitted to the gas producer II. It will be understood, 01 course, that the system may be either a variable speed system or a constant speed system and that the governing means may be of any known speed or load responsive type, of which there are many and which need not be described herein for an understanding of the present invention.

In the control system illustrated, the motion transmitting rod 62 is connected by means 0! bell crank 12, rod 14, and lever 18 to a by-pass valve 18 which controls a by-pass conduit for venting the compressor ii at an intermediate place to reduce the quantity of air compressed at a given speed of operation of the compressor. From the drawing it will be evident that the connection between the governor and the by-pass valve 18 is such that upon decrease in load on the system, valve 18 will be opened.

The operation of the system illustrated will now be described, it being assumed for the purpose or this description that the system is designed to operate at substantially constant speed.

Air from compressor I6 is delivered under the control of valve 44 to the gas producer and the rich gas formed in the producer is supplied to the combustion chamber 20 and the reheating chamber 22. Through the branch conduit 48,

compressed air is supplied to combustion chain ber 20, the amount of air supplied to the combustion chamber being in excess of the quantity required to burn the gas supplied to this chamber from the gas producer, so that the motive fluid supplied to turbine i0 consists of combustion gases containing a substantial quantity of excess air.

This motive fluid containing excess air is exhausted by turbine ill to the reheating chamber 22 in which chamber additional rich gas from the gas producer is burned with the excess air to reheat the motive fiuid supplied to the low pressure turbine l2. This will hereinafter be referred to as secondary combustion and advantageously the motive fluid is heated by this secondary combustion to a temperature approximately the same as that of the motive fluid admitted to the high pressure turbine.

It is characteristic of turbines exhausting to constant back pressure that if the turbine is supplied with motive fluid at substantially constant temperature, the exhaust gas temperature rises if the load on the turbine decreases. If the load decreases to a comparatively low load value, this rise in exhaust temperature may reach dangerous proportions and for this reason the thermostatically controlled valve 54 is provided in the embodiment illustrated so that in case the load on the system drops to such low value as to produce dangerously high exhaust gas temperatures, valve 54 will be closed to the extent necessary to reduce the reheating eflect and the temperature of the gases admitted to the low pressure turbine, to a degree such that the exhaust gases therefrom are not permitted to rise beyond a maximum temperature which is safe for continued operation of the turbine.

It with the system operating as above described the load drops, valve 44 will be moved toward closed position and the quantity of air admitted to the gas producer reduced to correspondingly reduce the amount of gas available for burning in the combustion chambers. It will be appreciated that within the scope oi the invention other specific means may be employed to reduce the quantity of air admitted to the producer when the load on the system drops.

In continuous combustion gas turbine systems, free flow of the gaseous media under all conditions 01' load is desirable from the standpoint of efficiency, since throttling oi the compressed air or o! the motive fluid introduces losses which it naturally is desirable to avoid. In the system just described, the throttling losses are negligible because of the fact that in the system described, the quantity of air admitted to the gas producer, which quantity must be throttled at part load, constitutes only a very small fraction of the total amount of air comlpressed. Even at full load the amount 01' air supplied to the gas producer is relatively very small, being only suflicient to support the incomplete combustion necessary to produce the rich fuel gas formed in the producer.

It is further to be noted that in the system described, the throttling losses involved in eiiecting the reheating oi the motive fluid are substantially negligible since all of the air necessary for the combustion in the reheating chamber is in the form of excess air in the exhaust gases from the high pressure turbine and the only throttling required is that 01' the rich iuel-gas supplied to the reheating chamber. The quantity of this gas is relatively very small as compared with the quantity of air required for its complete combustion. It will thus be evident that in the system described, the total amount of throttling required during any normal operation of the system is relatively very little in relation to the total quantity of fluids flowing through the system.

In the embodiment illustrated, the screw compressor shown is of the positive displacement type, such, for example, as the kind shown in United States Letters Patent 2,111,568 granted to me March 22, 1938, and the quantity of air compressed is substantially proportional to the speed of operation of the compressor. If it be assumed that the system is of the constant speed type, a compressor of this kind would supply sufficient compressed air for full load operation even at partial loads and this would, among other disadvantageous results, involve useless work of compression which would reduce the efiiciency of the system. Consequently, for a constant speed system, a compressor of this character should be provided with means to reduce the amount of air compressed as the load on the system drops. In the present embodiment this means has been indicated diagrammatically by the by-pass passage 80 and control valve 16 which, under the influence of the governor means, operates to bypass a part of the air from the compressor at an aaeasn intermediate point before compression is commenced, when the load on the system drops and the quantity of gas produced for the motive fluid is reduced.

While for purposes of illustrating the present invention, certain specific means of control for applied to gas turbine systems having diiferent forms and arrangements of turbines, and with difierent arrangements for generator and/or compressor drive in relation to the turbines employed. For clarity of illustration, the high andlow pressure turbines have been shown separately but it will be appreciated that reheating may be effected between the different pressure sections or stages of a single turbine unit and as herein employed the term turbine is to be understood as applicable to turbine sections or stages between which reheating may be eflected.

It is also to be understood that the invention is not limited to the specific arrangement hereinbefore described by way of illustration, but is to be considered as embracing all forms of apparatus and methods of operation thereof falling within the scope of the appended claims.

What I claim is:

1. The method of operating a gas turbine system of the'continuous combustion type having a plurality of expansion stages, by the aid of a solid fuel gas generator which includes the steps of compressing air in the system, supplying a portion of the compressed air to said generator to produce incombustibly rich fuel gas therein at high pressure, burning a portion oi said gas with a second portion of the compressed air to produce high temperature motive fluid containing substantial quantities of excess air, expanding the motive fluid to an intermediate pressure in a part of the turbine system, reheating the intermediate pressure motive fluid by burning therewith at such intermediate pressure a second portion of said gas, expanding the reheated motiv'e fluid in another part of the turbine system, and controlling the quantity of motive fluid producedinthesystembyvaryinginaccordance with variations in the load on the system the quantity of the portion of the compressed air supplied to said generator.

2. In the operation of a gas turbine system of the continuous combustion type in which motive fluid is formed by primary combustion at relatively hi h initial pressure and is reheated between expansion stages by secondary combustion at relatively lower pressure with air compressed in the system, that improvement which includes producing incombustibly rich fuel gas at a single source by incomplet; combustion with a-portion of the compressed air at said initial pressuremupplyingsaidgasattheinitialpresmre and at the lower pressure from said single source for said primary and secondary combustion; respectively and decreasing the proportion of the fuel gas supplied for secondary combustion at said lower pressure as compared with the proportion supplied at said initial pressure for primary combustion when the load on the system drops below a predetermined value.

3. In the operation of a gas turbine system of the continuous combustion type in which motive fluid is formed by primary combustion at relatively high initial pressure and is reheated between expansion stages by secondary combustion at lower pressure with air compressed in the system, that improvement which includes producing incombustibly rich fuel gas at a single source by incomplete combustion with solid fuel of a portion of the compressed air at said initial pressure, supplying said gas at said initial pressure and at said lower pressure from said single source for primary and secondary combustion respectively, governing the system by varying the portion of the compressed air at said initial pressure utilized for said incomplete combustion with solid fuel in accordance with variations in the load on the system, and reducing the proportion of said gas utilized at lower pressure for secondary combustion when the load on the system drops below a predetermined value.

4. In a gas turbine system of the continuous combustion type, a plurality of turbine stages serially arranged with respect to flow of motive fluid therethrough, a primary combustion chamber for forming motive fluid, a secondary combustion chamber for reheating motive fluid exhausted from one of said stages and supplied to another of said stages, a solid fuel burning gas producer, compressor means driven by a turbine constituting a part of the system, means for supplying a portion of the air from said compressor means to said gas producer, means for supplying gas from said producer to said primary and secondary combustion chambers at relatively high and relatively low pressures, respectively, means for supplying compressed air in excess quantity to said primary combustion chamber and means for varying the quantity of compressed air supplied to said gas producer in accordance with variations in load on the system.

5. In a gas turbine system of the continuous combustion type, a plurality of turbine stages serially arranged with respect to flow of motive fluid therethrough, a primary combustion chamber for forming motive fluid, a secondary combustion chamber for reheating motive fluid exhausted from one of said turbines and supplied to another of said turbines, a solid fuel burning gas producer, compressor means driven by a turbine constituting a part of the system, means. for supplying a portion of the air from said compressor means to said as: producer. means for supplying gas from said producer to said primary and secondary combustion chambers at relatively high and relatively low pressures, respectively, means for supplying compressed air in excess quantity to said primary combustion chamber, means for varying the quantity or compressed air supplied to said gas producer in accordance with variations in load on the system. and means for reducing the quantity of gas supplied to said secondary combustion chamber when the load on the system drops below a predetermined value.

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