US3097486A - Combined gas and steam power cycle - Google Patents

Description

July 16, 1963 R. c. ROE 3,09

COMBINED GAS AND STEAM POWER CYCLE Filed Feb. 9, 1961 G's/surname HIE COMPEESSOE INVHVTOR. PAL PH C Pas.

BY MMMW-W ATTORNEK).

United States Patent 3,097,486 COMBINED GAS AND STEAM POWER CYCLE Ralph C. Roe, Tenatly, N.J., assignor to Burns and Roe, Inc, New York, N.Y., a corporation of New Jersey Fiied Feb. 9, 1961, Ser. No. 88,037 2 Ciaims. (Cl. ell-49.18)

This invention relates to power plants, and more particularly, to such plants comprising a combined gas and steam cycle for power generation.

Recent technological advances have made it practical to combine gas turbine cycles with steam cycles, such combined systems providing certain advantages including increased station output for the same steam flow by virtue of the fact that the gas turbine produces power as well as the steam turbine and, further, the overall station efficiency is improved by the combined cycle and a reduction is thereby achieved in the total cost per net kilowatt-hour as compared to the conventional steam-turbine cycle.

Those persons skilled in the art will readily appreciate that gas turbine systems involving combustion of fuel in the turbines to drive same have the disadvantage that the hot dust laden combustion gases erode, corrode and destroy the various turbine parts. Additionally, these sys tems have only a narrow application since the fuel must be as acceptable as possible to the turbine. Accordingly, it has been proposed to provide hot air turbine systems in which air is compressed and heated out of contact with products of combustion and then delivered to a gas turbine for driving same so that any fuel can be used in the furnace. In such systems, a small portion of the turbine exhaust has been utilized to support combustion of fuel used to heat the air. However, in systems of this type, problems have arisen concerning control of the rate of combustion and consequent heating of the compressed air as the power demand on the turbine varies. Additionally, the problem of maintaining the air heater at a reasonable temperature to assure its structural integrity has caused considerable difliculty.

I have contributed by my invention, a novel combined gas and steam power cycle which eliminates the foregoing problems through a construction that is emcient and yet relatively simple. The present concept is based upon an awareness that a relatively great amount of fuel is burned to generate steam thus requiring a great amount of combustion supporting air, and that boiler output is desirably a function of the power demand on the system.

In essence, my combined cycle has a steam generator or boiler including a furnace, a steam operated turbine connected to receive steam from the generator, an air heater disposed in heat transfer relation to the same furnace, compressor means supplying air under pressure to the heater, and gas operated turbine means connected to receive heated compressed air from the heater.

As a particular feature of my invention, I provide means for delivering the entire exhaust from the gas turbine to the furnace to support the combustion of fuel therein, this exhaust constituting the sole supply of combustion air for the furnace. This feature of the invention, in combination with speed or air flow control means sensing the power demands on the plant and regulating the compressor output, and thus the turbine speed or air control accordingly, effectively controls the rate of fuel combustion in the furnace. Thus, it will be appreciated that the higher the demands on the system, the hotter the furnace automatically will be, and conversely, the lower the demands on the system, the smaller the rate of flow of air that will pass through the turbine and to the furnace to support combustion, thereby reducing the heat output. In accordance with this feature of the invention, a minimum of excess air is utilized for combustion thus assuring the most efficient conversion of fuel "ice into heat energy and the maintenance of maximum furnace temperatures for a given quantity of fuel consumed.

As has already been stated, the air heater is disposed in heat transfer relation to the furnace. Actually, the air heater may comprise a unit having a large surface area positioned in the radiant heat section of the steam generator. Thus, as the load demand on the system varies, and the compressor output is regulated by the speed control or air control means, the rate of flow of air through the air heater is also regulated, wherefore as the furnace becomes hotter, a greater quantity of air is automatically passed through the radiant air heater to maintain this unit cool enough to assure structural integrity.

As another feature of my invention, means are provided for tapping a portion of the compressed air before it enters the heater, and this tapped air is introduced into the heater at a zone intermediate its inlet and outlet. In this way, the temperature of the air leaving the heater may be controlled. Damper means may be provided in the bypass to regulate the flow of air bypassing the initial portion of the heater. In some instances, it may be desirable to bypass a portion of the compressed air around the heater altogether and deliver the same to the inlet side of the gas turbine along with the heated air.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

A specific embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawing, forming a part of the specification, wherein the single FIGURE is a diagrammatic illustration of a combined system according to the present invention.

Referring now to the drawing, there is shown a steam generator or boiler 10 including a furnace 11 of conventional construction. Steam is delivered through a steam line 12. from the generator '10 to the input side :of a steam turbo-generator 14, for example, to drive same.

The combined system of the present invention also includes an air compressor 15 which compresses atmospheric air and delivers it through a line 16 to an air heater 17 positioned in the steam generator 10. The heater illustrated includes a divided header 19, land the compressed air is admitted to the heater through its upper or inlet side, as shown. The heated compressed air is discharged from the heater through the other side of the header and is delivered through line 20 to a gas driven turbine-generator 21, for example, which utilize-s part of its output to drive the compressor 15. As shown in the drawing, a line 22 conducts the total air exhaust from the turbine-generator 21 to the furnace 11 where this air constitutes the entire supply of air utilized to support combustion.

Actually, the air heater 17 comprises in its preferred form, a series of steel tubes which are positioned in the radiant heat section of the steam generator. The tubes may be provided in two sections, the first connecting the inlet side of the header 19 with a secondary header 24, and the second section connecting the secondary header with the outlet side of the header 19. Thus, the compressed air passes through the first section of heater tubes thence through the secondary header to the second section, and finally to the outlet side of the header 19.

In order to maintain the operating temperature of the air driving the gas turbine 21 constant at all loads, I provide a bypass line 25 which is tapped into compressed air line 16 and connects with the secondary header 24-, as shown. This bypass line 25 is equipped with a damper 26 which may be controlled by a regulator (not shown) of conventional design and responsive to temperature variations in the air leaving the heater 17. The line 25 may, if desired, bypass the heater 17 altogether and connect directly to the line 20, for some applications. In any case, it is important to understand that the bypass is elfective to feed cooler air to the air in line 20 at rates to maintain the air temperature constant to the turbine 21 at all load conditions.

In operation, the steam generator makes steam in the usual way for delivery through steam line 12 to the steam turbo-generator 14. At the same time, the compressor '15 compresses atmospheric air which is conducted through compressed air line 16 to the header 19 and the radiant airheater 17. The air, thus compressed and heated is conveyed via line 20 to the gas turbine 21 for its operation. While expanding through the turbine, the air of course gives up a considerable portion of its heat, but upon being exhausted from the turbine will have a temperature of several hundred degrees Fahrenheit, and approximately 900 F., in a typical case. All of this exhaust air is conveyed through line 22 to the furnace 11 where it is admitted as the sole supply of combustion air.

It will be appreciated by those skilled in the art that the heat input and hence the temperature in the furnace will be controlled by the usual combustion control 30, which may be of the Bailey meter type, for example which includes the usual steam tap 31, and steam and air orifices 32 and 34, all connected to the control meter 35 whereby the air and fuel flow to the furnace are controlled. The combustion control may respond to steam pressure or to the demands for steam of the steam turbine as controlled by the steam turbine governor. Additionally, the furnace will be called upon to supply the heat required to operate the gas turbine system by heating the :air from the gas turbine compressor to temperatures suitable for operation of the gas turbine. Accordingly, and because of the coordination of the system which is the subject of my invention, as the power demand drops, the required air for combustion is decreased and hence the compressor output is reduced, the flow of air through the air heater and to the gas turbine is thereby reduced and the gas turbine exhaust, or furnace combustion air, is also reduced. Since less combustion supporting air flows to the furnace, the furnace heat input and temperature are reduced, but the requirement for heating the air for the gas turbine is similarly decreased, and therefore it is possible to maintain the air temperature from the heater substantially constant. Conversely, as more power is demanded, governor 27 opens its throttle to the steam turbine, the combustion control demands more air, which in turn, acting either through the governor or the air control of the compressor, supplies more air to the heater and to the gas turbine and thence will supply from the gas turbine exhaust more air to the furnace. The boiler in turn will supply more steam to the steam turbine. In this way the air requirements for combustion are coordinated with the air flow through the compressor, the air flow and the heat input in the heater, and the output of the gas turbine, the exhaust of which supplies the total cornbustion air. Regardless of whether the load increases or decreases, the furnace heat input and temperature will respond to the heat requirements of the air heater and all will react according to the load demands on the combined steam and gas turbine system while the fuel is burned with 4 maximum thermal efficiency by virtue of the utilization in the furnace of a minimum of excess combustion air.

It is also important to realize that by reason of the present contribution, as the power demand is increased, and the furnace temperature rises, the rate of flow of air through the air heater 17 is also increased, thus maintaining the heater tubes sufiiciently cool to prevent their destruction.

As has already been stated, a bypass is provided between the compressed air line 16 and the secondary header 24 of the air heater. By this means, the temperature of air to the gas turbine is maintained substantially constant at all load conditions. Actually, the mass flow of air through the heater is directly proportional to the total heat release in the furnace so that when the demands on the steam boiler decrease, mass flow through the heater decreases and the heat release in the furnace decreases. Conversely, when the demands on the steam generator increase, the mass flow on the heater increases and the total heat release of the furnace increases. The result is that by this economic combination, the heater is largely selfregulating but to take care of any possible lack of precise regulation, the bypass regulates the mass flow through a portion of the heater in order to obtain extremely close regulation of temperature at a substantially constant level. As the temperature of the air leaving the heater changes, the flow of bypassed air is reduced or increased by damper 26.

From the foregoing description, it will be seen that I contribute by my invention, a combined steam and gas power cycle with fool-proof furnace temperature control means for both the steam and gas sides of the cycle, which control means are automatically responsive to the power demands made on the system. It will also be seen that the air is heated in a radiant air heater in the steam boiler, the heater being self-regulating to' the extent that the rate of air flow through the heater increases at higher furnace temperatures during periods of high power demands, wherefore the heater tubes cannot overheat.

I believe that the construction and operation of my novel combined steam and gas power system will now be understood and that the advantages of my invention will be fully appreciated by those persons skilled in the art.

I now claim:

1. In a power plant of the class described, a combination gas and steam cycle comprising, a steam generator including a single furnace, a steam operated turbine connected to receive steam from said generator, an air heater disposed in the radiant zone of said furnace, means supplying air under pressure to said radiant heater, gas operated turbine means connected to receive heated compressed air from said heater, means delivering the entire exhaust from said gas turbine to said furnace to support combustion of fuel therein, said gas turbine exhaust constituting the sole supply of combustion air in said furnace, and control means sensing variations in the demand on said power plant and regulating the flow of air under pressure to said heater and thus also to said furnace to vary the thermal output of said heater and steam generator in direct relation to variations in power requirements, the air flow through said heater thus being at all times automatically proportional to the heat generated to maintain the integrity of said heater.

2. In a power plant of the class described, a combination gas and steam cycle comprising, a steam generator including a single furnace, a steam operated turbine connected to receive steam from said generator, an air heater disposed in the radiant zone of said furnace, means supplying air under pressure to said radiant heater, gas operated turbine means connected to receive heated compressed air from said heater, means delivering the entire exhaust from said gas turbine to said furnace to support combustion of fuel therein, said gas turbine exhaust constituting the sole supply of combustion air in said furnace, a bypass for conducting a portion of the air under pressure to said heater at a point intermediate its inlet and References Cited in the file of this patent outlet sides, a damper in said "bypass controlling the flow of compressed air therethrough, and control means sens- UNITED STATES PATENTS ing variations in the demand on said power plant and regulating the flow of air under pressure to said heater 5 Eggs; g

and thus also to said furnace to vary the thermal output of said heater and steam generator in direct relation to FOREIGN PATENTS variations in power requirements, the air flow through said heater thus being at all times automatically proportional 487,433 Canada Oct. 21, 1952 to the heat generated to maintain the integrity of said 10 1,038,643 France May 13, 1953 578,628 Great Britain July 5, 1946 heater.

Claims (1)

1. 2. IN A POWER PLANT OF THE CLASS DESCRIBED, A COMBINATION GAS AND STEAM CYCLE COMPRISING, A STREAM GENERATOR INCLUDING A SINGLE FURNACE, A STEAM OPERATED TURBINE CONNECTED TO RECEIVE STEAM FROM SAID GENERATOR, AN AIR HEATER DISPOSED IN THE RADIANT ZONE OF SAID FURNACE, MEANS SUPPLYING AIR UNDER PRESSURE TO SAID RADIANT HEATER, GAS OPERATED TURBINE MEANS CONNECTED TO RECEIVE HEATED COMPRESSED AIR FROM SAID HEATER, MEANS DELIVERING THE ENTIRE EXHAUST FROM SAID GAS TURBINE TO SAID FURNACE TO SUPPORT COMBUSTION OF FUEL THEREIN, SAID GAS TURBINE EXHAUST CONSTITUTING THE SOLE SUPPLY OF COMBUSTION AIR IN SAID FURNACE A BYPASS FOR CONDUCTING A PORTION OF THE AIR UNDER PRESSURE TO SAID HEATER AT A POINT INTERMEDIATE ITS INLET AND

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