US2780207A - Supercharged steam generating system - Google Patents

Description

Feb. 5, 1957 J. R. SHIELDS Filed May 5, 1953 n u m Nob/Niko umnsio m M m NH r. W5 ME I s L m w J w w w H1 EDUA- QOF d QmW United v States Patent SUPERCHARGED STEAM GENERATING SYSTEM James R. Shields, Penn Township, Allegheny County, Pa., assignor to Elliott Company, a corporation of Pennsylvania Application May 5, 1953, Serial No. 353,180

Claims. (Cl. 122--479) This invention relates to supercharged steam generating systems, and more particularly to one in which the supercharger is driven by hot combustion gases from the boiler and all of the useful power output is obtained from the steam side of the system.

A supercharged boiler is one that operates with combustion pressures in excess of normal atmospheric pressure, and it is distinguished from the normal forced or induced draft boiler by the fact that the pressure rise of the supercharger is used to increase the absolute gas pressures within the boiler and not primarily for overcoming frictional pressure losses. The combustion gases under pressure at the exit of the supercharged boiler are expanded through a turbine to provide the power necessary for driving the supercharging compressor. For steady state operating conditions near full load, a supercharged boiler system does not require variable inlet temperature control nor excess temperature protection of the superheater tubes. When, for reasons of efficiency and compactness, the design point operating temperatures of the boiler superheater and the gas turbine are selected for maximum unit heat absorption and just self-sustaining operation of the supercharger, no margin exists for rapid acceleration of load. Any acceleration is slow and causes the superheater tubes to be overheated.

It is among the objects of this invention to provide a supercharged boiler steam generating system operating at maximum design point temperatures, in which all of the useful power output is obtained from the steam side of the system, in which the load can be accelerated rapidly, and in which such acceleration takes place without overheating the superheater in the boiler.

In accordance with this invention a supercharged boiler is provided with an evaporator and a superheater which are connected in series by a steam-water separator drum outside or" the boiler. Feed water and the water from the drum are delivered to the evaporator. Associated with the boiler is a burner, to which fuel normally is supplied at a predetermined rate by adjustable means. A supercharger supplies compressed air to the boiler to supercharge it and to burn with the fuel at the burner in order to produce hot gases for generating steam in the evaporator and superheating it in the superheater. A conduit conducts hot combustion gases from the boiler to the supercharger to drive it. Another conduit conducts superheated steam from the superheater out of the boiler to operate a load, such as a steam turbine. There is a normally closed by-pass around the superheater for the hot gases, and means for opening the by-pass when the fuel supply to the burner is increased to rapidly accelerate the steam turbine. When the bypass is thus opened, the temperature of the combustion gases leaving the boiler will immediately be higher than normal to increase the speed of the supercharger, yet overheating of the superheater will be avoided because a smaller voltune of the hot gases will flow through the superheater.

The preferred embodiment of the invention is illus- 2,780,207 Patented Feb. 1957 trated in the accompanying drawings, in which the single figure is a schematic view of my system.

Referring to the drawing, a boiler 1 contains an evaporator 2 near one end and a superheater 3 near the other end. Each of these units may be constructed from a bundle of tubes in a conventional manner. Water is fed by a pump 4 through a pipe 5 to the evaporator, in which it is converted into steam by means of a burner 7 projecting into the boiler. The steam leaves the evaporator through a pipe 8 which is connected to the side of a steam and water separating drum 9 outside the boiler. The bottom of the drum is connected by a return pipe 11 to the inlet pipe 5 of the evaporator. The top of the drum is connected by a steam pipe 12 to one end of the superheater in order to conduct steam to it. The steam is superheated in the superheater and is conducted out of it and the boiler through a pipe 13 to a load, which may be a steam turbine 14 driving an electric generator 15 or any other equipment. The turbine may exhaust to a condenser (not shown) in the usual way for closed cycle return of feed water to pump 4.

Fuel, such as oil or gas, for the burner is delivered to it through a line 17 containing a throttle valve 18 that can be manually or automatically controlled. The air for combustion and for supercharging the boiler enters the boiler through the burner from a pipe 19 that is connected to a supercharger consisting of a rotary compressor 21 driven by a gas turbine 22. The turbine is driven by the hot combustion gases leaving the boiler through conduit 23 connecting it with the turbine inlet. The pressure inside the boiler usually is maintained greater than two atmospheres, four to eight atmospheres pressure being customary. The gases leaving the boiler, after they have passed through the superheater, have a temperature just high enough to produce self-sustaining operation of the supercharger. This temperature is usually of the order of 900 to 1,000 degrees F. at design full load. Consequently, all of the useful power output comes from steam pipe 13; the gas turbine has only enough power to drive the compressor. In cases where maximum cycle eificiency must be obtained a gas-to-water econ: omizer (not shown) can be used to recover heat from the gas turbine exhaust and transfer it to the feed water ahead of pump 4.

The system described thus far could be accelerated, but at a very definitely limited maximum rate, by opening wider the throttle valve 18 in the fuel line. However, since the supercharger cannot accelerate unless the tem: perature of the gas at the gas turbine inlet rises above the self-sustaining value, the air-fuel ratio would decrease and cause smoky poor combustion that cannot be tolerated. Regardless of this, the firing rate could not be accelerated suddenlywithout endangering the superheater by excessive metal temperatures, because of the inherent time lag for heat transfer between the gas and steam circuits. Hence, rapid acceleration in output of the conventional supercharged cycle is not possible, due to the fact that the necessity for higher than normal temperature to permit increased load on the supercharger is not compatible with safe superheater metal temperatures.

In accordance with this invention, 1 overcome this difiiculty by providing a gas by-pass across the superheater 3, either through it or around it. This by-pass 25 is closed by a valve or pivoteddamper 26 during normal operation, so that all of the hot gases inlthe boiler must pass through the superheater. However, when it is desired to accelerate the load and the throttle valve 18 in the fuel line is opened wider to do so, the damper likewise is opened so that hot gases can by-pass the; superheater to increase the gas turbine inlet temperature at once in order to increase the air flow to the burner 3 immediately. The resulting quickly increased gas temperature in the boiler rapidly accelerates the load, but at the same time the average gas temperature in the superheater is held where it was before acceleration or is actually reduced, because the mass gas flow through the superheater is reduced by the by-pass. Thus, overheating of the superheater is avoided.

The damper 26 is opened and closed automatically by a damper operator 27 operatively connected to it and preferably pneumatically controlled by a pneumatically operated fuel-air ratio controller 28 of any well known construction. Whenthe fuel rate is increased for load acceleration by opening the throttle valve, a fiow meter 29in thefuel line senses the increased fuel rate and sends a signalthrough a tube 31 to the controller. The con troller then transmits a signal through a tube 32 to the damper operator to open the damper sufficiently to bring the supercharger up to the new speed necessary for holding the fuel-air ratio constant at the increased fuel rate. A flow meter 33 in the air line and a speed governor 34 on the turbine are pneumatically connected to the fuel-air ratio controller to correct the'dampcr position when necessary, in order to prevent overshoot the new control point is reached.

it will be seen that in this system all of the useful power output is from the steam side. Consequently, the supercharger is self-sustaining only and is not a useful power generator. The system is designed so that the superheater by-pass is only opened during accelerating periods in order to provide a power boost for the supercharger and simultaneously protect the superheater. The gas turbine inlet temperature must increase over the normaldesign value for short periods when accelerating the load. Nevertheless, at such times the gas mass fiow through the superheater is reduced so that the superheater tube wall temperatures can be held within design limitations despite the increased firing rate to meet the acceleration demand.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A steam generating system comprising a supercharged boiler provided with an evaporator and a superheater, a separator drum connecting the evaporator and superheater in series, means for conducting feed water to the evaporator, a burner associated with the boiler, adjustable means for normally supplying fuel to the burner at a predetermined rate, a supercharger for supplying compressed air to the boiler to supercharge it and to burn with said fuel at the burner to produce hot gases for generating steam in the evaporator and superheating it in the superheater, a conduit for returning water from the drum to the evaporator, the boiler being provided with an outlet for said gases, the superheater and all of the evaporator being in the path of said gases as they flow to said outlet, a conduit for conducting hot gases from said outlet to the supercharger to drive it, means for conducting superheated steam from the superheater out of the boiler to operate a load, a normally closed by-pass across the superheater for said hot gases, and means for opening the by-pass when the fuel supply to the burner is increased to accelerate the load, whereby the temperature of the gases leaving the boiler will be higher than normal to increase the speed of the supercharger and overheating of the superheater will be avoided.

2. A steam generating system comprising a supercharged boiler provided with an evaporator and a superheater, a separator drum connecting the evaporator and superheater in series, means for conducting feedwater to the evaporator, a burner associated with the boiler, ad-

justable means for supplying fuel to the burner, a compressor for supplying compressed air to the boiler to supercharge it and to burnwith said fuel at the burner to produce hot gases for generating steam in the evaporator and superheating it in the superheater, a conduit for returning water from the drum to the evaporator, the boiler being provided with an outlet for said gases, the superheater and all of the evaporator being in the path of said gases as they flow to said outlet, a gas turbine driving the compressor, a conduit for conducting hot gases from the boiler outlet to the turbine to operate it, means for conducting superheated steam from the superheater out of the boiler to operate a load, said adjustable means normally being set to deliver enough fuel to operate the boiler for full load conditions, a normally closed bypass across the superheater for said hot gases, and means for opening the by-pass when said adjustable means is operated to increase the fuel supply to the burner to accelerate the load, whereby the temperature of the gases leaving the boiler will be higher than normal to increase the speed of the compressor and overheating of the superheater will be avoided.

3. A steam generating system comprising a supercharged boiler provided with an'evaporator and a superheater, a separator drum connecting the evaporator and superheater in series, means for conducting feed water to the evaporator, a burner associated with the boiler, means for normally supplying fuel to the burner at a predetermined rate, a supercharger for supplying compressed air to the boiler to supercharge it and to burn with said fuel at the burner to produce hot gases for generating steam in the evaporator and superheating it in the superheater, a conduit for returning water from the drum to the evaporator, the boiler being provided with an outlet for said gases, the superheater and all of the evaporator being in the path of said gases as they flow to said outlet, a conduit for conducting hot gases from said outlet to the supercharger to drive it, means for conducting superheated steam from the superheater out of the boiler to operate a load, a normally closed by-pass across the superheater for said hot gases, means for increasing the rate of fuel supply to the burner to accelerate the load, and means responsive to the increased fuel rate for opening said by-pass, whereby the temperature of the gases leaving the boiler will be higher than normal to increase the speed of the supercharger and overheating of the superheater will be avoided.

4. A steam generating system comprising a supercharged boiler provided with an evaporator and a superheater, a separator drum connecting the evaporator and superheater in series, means for conducting feed water to the evaporator, a burner associated with the boiler, means for normally supplying fuel to the burner at a predetermined rate, a supercharger for supplying compressed air to the boiler to supercharge it and to burn with said fuel at the burner to produce hot gases for generating steam in the evaporator and superheating it in the superheater, a conduit for returning water from the drum to the evaporator, the boiler being provided with an outlet for said gases, the superheater and all of the evaporator being in the path of said gases as they flow to said outlet, a conduit for conducting hot gases from said outlet to the supercharger to drive it, means for conducting superheated steam from the superheater out of'the boiler to operate a load, a by-pass across the superheater for said hot gases, a normally closed damper in the by-pass, means for increasing the rate of fuel supply to the burner to accelerate the load, means for opening said damper as the rate of fuel supply is increased, and means responsive to the speed of the supercharger for preventing overshoot of said acceleration.

S. A steam generating system comprising a supercharged boiler provided with an evaporator and a superheater, a separator drum connecting the evaporator and superheaterin series, meansforconducting feed water to the evaporator, a burner associated with the boiler, means for normally supplying fuel to the burner at a predetermined rate, a turbo-supercharger for supplying compressed air to the boiler to supercharge it and toburn with said fuel at the burner to produce hot gases for generating steam in the evaporator and superheating it in the superheater, a conduit for returning Water from the drum to the evaporator, the boiler being provided with an outlet for said gases, the superheater and all of the evaporator being in the path of said gases as they flow to said outlet, a conduit fior conducting hot gases from said outlet to the supercharger to drive it, means for conducting superheated steam from the superheater out of the boiler to operate a load, a by-pass across the superheater for said hot gases, a normally closed damper in the by-pass, a damper operator, a fuel-air ratio controller for operating the damper operator, means for increasing the rate of fuel supply to the burner to accelerate the load, a fuel flow meter responsive to the increased fuel rate for operating said controller to cause said operator to open the damper in order to speed up the supercharger, whereby more air will be delivered to the boiler to correspond with the increased fuel rate.

References Cited in the file of this patent UNITED STATES PATENTS 1,644,064 Langen Oct. 4, 1927 2,110,422 Norguet Mar. 8, 1938 2,112,391 Anxionnaz Mar. 29, 1938 2,641,233 Hemenway et a1. June 9, 1953

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