US2907170A - Combined gas turbine and steam generator - Google Patents

Description

Oct. 6, 1959 o. E. F. zADNlK COMBINED GAS TURBINE AND STEAM GENERATOR 4Filed. Dec. 12, 1952 -IIL a uobtuuzwv Prof rro ERNST F/EpR/CH Zep/wit Bf a' @j COMBINED GAS TURBINE AND STEAM GENERATOR Otto Ernst Friedrich Zadnik, Newcastle-upon-Tyne, England, assignor to C. A. Parsons & Company Limited, NeWcastle-upon-Tyne, England Application December 12, 1952, Serial No. 325,523A

2 Claims. (Cl. 60-39.14)

This invention relates to gas turbine plantsusing` the exhaust heat cycle, where use is made of the heat content of the` exhaust gases of the gas turbine in a steam generator. The exhaust heat cycle in this particular ,case consists of a compressor driven by aturbine, and a separatework turbinethe exhaust of which passes through a combustion chamber and thence through a heat exchanger. The turbine which drives the compressor is hereinafter referred to as the compressor turbine.and the arrangement of compressor and compressorl turbine as the compressor set.

In particular the invention relates to gas turbine plants using. the exhaust heat cycle applied in locomotives though the invention is not limited to use in locomotives.

The term fgas turbine is usually applied to plants in which the working uid is air, or air and the products of combustion or like gaseous working medium. In our case, however, we introduce steam which is another form of gaseous medium included in the present invention.

It is commonly known that in gas turbine driven locomotives the heat content of the exhaust gases can be utilized by means of a steam generator, which provides steam for train heating.

It follows that if such steam were always available it could also be used for driving a steam turbine and steam operated auxiliary apparatus. This applies to the driving of the compressor turbine.

Unfortunately, however, by the nature of locomotive service the amount of exhaust heat varies considerably from idling to full load, with the result thatl it cannot be relied upon to give a satisfactory steam lgenerator output when the normal cycle is used.

Even train heating, which may be based on the average steam supply, is not satisfactory with the steam generator alone, and hitherto it has been necessary to have a second steam generator with separate and independent ring, mostly of oil, or to provide the steam generator with an additional burner.

This burner has to be tted with an automatic control which means complicating the plant and providing a source of possible trouble.

There is the further inherent diliculty in thataccording to the thermodynamics of the gas turbine for a given output, the exhaust temperature falls when the ambient temperature at the compressor inlet falls. Thus in winter for example when ambient temperatures are lower than in the summer the exhaust temperature for the same output would be correspondingly lower with the result that less exhaust heat is available for the steam generator when it is most needed.

The object of the invention is to provide a gas turbine plant operating on the exhaust heat cycle as defined above, use being made of the heat content of the exhaust gases of the gas turbine in a steam generator with improved heat availability for steam generation, that is to say that suicient exhaust heat can be made available for the steam generator at all times.

The invention consists in a gas turbine plant using 2,967,17 Patented Oct-v 6, 41.959

an exhaust heat cycle comprising `a compressor driveny by a turbineY and a separate work turbine, the exhaust of which passes through a combustion `chamber and thence through a heat exchanger and use being made in a steam generator of theheat content of the exhaust gases from the Yaforesaid heat exchanger, incorporating an arrangement of ducts and metering devices, which makes a full steam supply available at reduced load, by tapping hot air from the work turbine exhaust or any point of the cycle between the compressor and the work turbine exhaust and mixing said hot'air with the air entering, the compressor or tapping air from a stage of thercompress'or and leading it directly into the combustion chamber or by tapping hot air between the compressor turbineand the ,work turbine and leading it directly intov the combusption chamber, the tapped quantities being controlled and adjusted by the aforesaid metering devices.

'Ihe drawing consists of a single ligure showingin schematiczform1 a gas turbine plant embodyingv the invention ina preferred form.

The inlet of the compressor 1 has a throttlevalve 2 forcontrolling the inlet of the air to theV compressor. The rst stage or primary stages of the compressor are indicated at 3 while the second stage or stages are indicatedat 4. A shaft 5 connects the compressor with a compressor turbine 6. The working medium, in this case air leaves the compressor turbine and yenters chamber 7 from which it enters work turbine 8a, said work turbine being mechanically independent of the compressor turbine 6. The air on leaving the work turbine enters exhaust duct 48b from which it enters combustion chamber 9 into which is injected fuel through injector 10. After c ombustion in the combustion chamber the combustion products enter heat exchanger 11 where they give up their heat content to the compressed air on its way from the compressor to the compressor turbine 6.

On leavingthe heat exchanger 11 the combustion products` enter chamber 12 from whichl they enter a steam generator 13. A duct 14 is arranged in communication Withichamber 12, through valve 1,6 which allows, when open, for thev bypassing of the steam generator by allowing part or all of the combustion products to pass out to atmosphere.

The exhaust of the combustion products to atmo-sphere from the steam generator 13 is controlled .by valve 17 in duct 15. Valves 16 and17y arev controlled by Pressure control device 1S which prevents the pressure in the steam` generator 13 from rising above a predetermined maximum.

The feed water is led tothe steam generator through pipe19 and after conversion to steam leaves thel generaf tor through duct 20. Valved pipes 21 permit the bleed,- ing of this steam for driving the various auxiliaries where necessary.

Duct 20 is also in communication with a steam turbine 22 which drives an electric motor-generator 23 through clutch 25 and also blower 24. The |generator 23 charges batteries 27 through a switch box 26.

The arrangement may comprise auxiliary equipment including a starter, a switch box and a diesel'set comprising diesel engine and generator indicated by numerals 28,y 29, 30, 31 and 31 respectively.

A duct 32 allows air to be bled from the first stages of the compressor direct to the combustion chamber, this flow being controlled by metering device 33.

Also in communication with duct 32 is a duct 34 which permits the air passing through chamber '7 to be led into duct 32 and thence to the combustion chamber thus bypassing the Awork turbine 8a. This-flow is controlled by metering device 35.

Hot airrleaving the work turbine exhaust mayhalso be led to the inlet of the compressor via duct 36,' 'this flow being controlled by metering device 37. The amount of this air which enters the compressor inlet at a point downstream of throttle valve 2 is controlled by metering device 38.

This hot air from the work turbine exhaust may also be led by means of a continuation of duct 36 to filters 40, which iilter the air entering the compartment 41 on its way to compressor 1, for the purpose of preventing ice formation on the filters. The amount of hot exhaust air entering the filters is controlled by metering device 39.

A duct 42 connects chamber 7 with duct 36 thus increasing the pressure in the duct and reducing the volume of the air flowing through it enabling the size of duct 37 to be kept within reasonable limits, this ow being controlled by metering device 43.

The pressure in duct 36 may be further increased by tapping air from the compressor outlet through duct 44 under the control of metering device 45.

For starting purposes air from blower 24 may be led through duct 46 to the inlet of compressor downstream of throttle valve 2, the latter being closed, this flow being controlled by metering device 47.

Provision is also made for leading steam into the air circuit to act as a working medium supplementing the air. This is achieved by leading steam from duct 20 to a point just downstream of the compressor outlet prior to entry into the heat exchanger 11. This ow of steam is controlled by valve 49 in duct 48` The various parts are connected as shown in the diagram.

In operation the preparation of the plant before starting the gas turbine consists of:

(1) Starting the electrically driven blower 24 with the throttle 2 closed and the valve 47 open. A ow of air then passes through the compressor, then around the outside of the tubes in the heat exchanger, through the turbines and combustion chamber, then through the inside of the tubes of the heat exchanger and thence to the steam generator, that is, the path of the air How with the engines at full load.

(2) The valves 33 and 35 may be opened in order to increase the air flow through the combustion chamber for quicker heating up.

(3) The fuel is injected at 10 and the burners lighted. The fuel air/ratio is adjusted in such a way that the combustion gases have the desired temperature. After a lapse of some time, iirst the heat exchanger is heated up to full temperature, and then the steam generator some time later. Since there is also an air iiow along the path of the main ilow through the heat exchanger and the turbines, the whole plant will be heated up approximately to such temperatures as obtain when running under service conditions.

To make starting of the compressor set easy the temperature of the heat exchanger must be raised enough. With the exhaust heat cycle, the burners are lighted before starting. If the blower is able to provide a certain air flow, the compressor set should begin to run without any alteration when a certain tube temperature 'of the heat exchanger is reached. There is no power take off from the compressor shaft except for a tachometer or governor, the bearings are warmed up and since valve 3S is open, the pressure drop is more concentrated on theco'mpressor turbine.

The electric motor 23 driving the blower 24 may have a second and higher speed range, to be used :for starting.

With the compressor started the throttle 2 is opened; the blower 24 may be shut down and the plant be ready for self sustained running, idling or with load.

When an auxiliary diesel set or a large capacity battery is available the unit can be heated up and started by a starter motor, as shown in the drawing by dotted lines. The throttle 2 would be open. The opening of the valves 33 and 35 would provide a quicker heating up and a self sustained running at lower speed, Therefore even when starting is effected by a starter motor, the compressor itself doing the work of the blower 24, the invention offers the advantage of using the iirst stages of the compressor for an increased air supply to the combustion chamber and of using valve 3S for an easier start.

After the start the engine is kept idling Ifor some time with the locomotive stationary. The invention provides means to supply suiiicient exhaust heat for full steam production under idling conditions. Keeping valve 33 open means an additional amount of air passes through the combustion chamber where it is heated up and contributes to the raising of the amount and temperature of the Agas entering the steam generator. Since the tubes of the heat exchanger are now at full temperature, the compressor set tends to accelerate. In order to keep its speed at idling speed, the valves 37, 43 and 45 may be opened as necessary.

Valve 37 provides a back How of hot air into the compressor, raising the whole temperature level of the cycle according .to the raised inlet temperature. If the tube temperature is kept constant such raising of the inlet temperature would reduce the power available. With the inlet temperature equal to the exhaust temperature, no thermal power production could take place. With all valves 33, 35, 43 and 45 closed, and 37 open the temperature of the exhaust gases would be -raised and the temperature dilerence available for steam generation would be greater. Opening of valve 33 increases the amount of air passing through the combustion chamber thus allowing the combustion of more fuel and an increase inthe amount of exhaust heat available. Opening of valve 35 eases the starting and also aiects the amount of exhaust heat available under idling conditions. Opening of valve 43 provides hot air with higher pressure than 37 so allowing for smaller ducts; Opening of valve 45 provides the greatest back flow of air but reduces at the same time the eiciency of the compressor set. As shown in the drawing the air under pressure from valves 43 and 45 can be used as injector jets in duct 36.

The flow in duct 36 may also be accelerated by use of the inlet throttle 2.

The combined use of one or all of the valves 33, 35, 37, 43, 45 and the throttle 2 provides a means for increasing both the amount and temperature of the gases passing through the steam generator at idling speed and for adjusting the idling speed according to the requirements of the locomotive service.

In actual service the power needed varies ina wide range between idling and full load according to the speed and the tractive effort. At part loads the inlet temperature of the compressor may be raised by feeding hot air through duct 36 to the compressor inlet, which gives an increased steam production because of the raised exhaust temperature. The ilow in duct 36 can be accelerated by the jets controlled by valves 43 and 45 or by the throttle 2. Opening valves 33 and 35 allows for a further increase of the exhaust heat available. The use of valve 37 for the extraction of hot air only has practically no elect on the thermal efficiency of the cycle and it should therefore be used rst.

The less hot air fed back into the compressor inlet, the greater is the output of the turbines. Although in general the invention comprehends the interfering with the mass ow in the cycle and the heat ilow through the combustion chamber at a certain output the exhaust heat should. be suicient for the required steam production and no interference with the main ow of the cycle would be necessary.

The invention is of particular advantage in overcoming the difficulties encountered under arctic conditions. As already mentioned the temperature of the exhaust gases is lowest, when the inlet temperature of the compressor is lowest and the steam production will then be lowest when it is most needed. The feeding back of hot air raises it to normal level or above. If the compressor and the reduced density of the air results in a reduction of the output, Practically full output can be restored by feeding steam into the air leaving the compressor before entering the heat exchanger through pipe 48 and controlled by the valve 49.

Since, according to the invention, steam is always available, the auxiliaries of the locomotives can be steam operated, fed by the pipes 21, Thus steam can be bled through pipes 21 to the inlet of the heat exchanger which means that a mixture of air and steam can be used to drive the compressor turbine if desired.

The electric motor-generator 23, which drives the blower by one clutch 25, can be constructed so that it can also work` las a generator driven by a steam turbine 22 using the other clutch 25.

I claim:

1. A gas turbine plant using an exhaust heat cycle and comprising a compressor, a compressor turbine driving the compressor, a work turbine mechanically independent of the compressor turbine, means connecting the compressor turbine and work turbine aerodynamically in series, a combustion chamber, a heat exchanger, means leading the exhaust ofthe work turbine to the combustion chamber and therefrom to the heat exchanger for preheating air leaving the compressor, means conducting the said air from the compressor through the said heat exchanger to the compressor turbine, a steam generator, and means for conducting the exhaust gases from the said Work turbine after passing through the said heat exchanger thereto for generating steam, and ducts and metering devices for tapping hot air from a point of the cycle between the compressor inlet and the work turbine exhaust and mixing said hot air with the air entering the compressor and, in addition, ducts and metering devices for tapping' air from a point between a stage of the compressor and the work turbine and leading this air directly to the combustion chamber, the tapped quantities being controlled and adjusted by the aforesaid metering devices, and having in addition supplementary means for the purpose of heating up the turbines, the combustion' chamber, the heat exchanger and steam generator, the said supplementary means comprising a blower driven independently of the turbines and piping connecting the said blower to the compressor inlet and to the combustion chamber whereby the air iiow from the blower is divided into two streams, one stream passing through the compressor, the heat exchanger and the turbines on its way to the combustion chamber, the other stream by-passing these and going to the combustion chamber direct; these two streams joining before entering the combustion, chamber, being heated therein and then passing on as one stream through the heat exchanger and steam generator.

2, A gas turbine plant according to Claim 1, in which the blower is connected for starting the compressor set by blowing air through the hot heat exchanger into the compressor turbine and in which hot air is tapped from the chamber between the compressor turbine and the work turbine and led direct to the combustion chamber.

` References Cited in the file of this patent UNITED STATES PATENTS 2,130,310 Neumann Sept. 13, 1938 2,312,995 Anxionnaz Mar. 2, 1943 2,404,748 Salzmann July 23, 1946 2,404,938 Armacost et al July 30, 1946 2,414,170 Salzmann Ian. 14, 1947 2,434,950 Nettel Jan. 27, 1948 2,482,791 Nettel Sept. 27, 1949 2,539,255 Karrer Jan. 23, 1951 2,608,822 Pavlecka Sept. 2, 1952 2,653,447 Heller Sept. 29, 1953 FOREIGN PATENTS 960,332 France Oct. 24, 1949

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