The present invention generally relates to turbine systems and, more particularly, to power plant multi-staged turbine systems which have one or more bypassable bottom stages that are utilized or bypassed in response to temperature changes in the cooling sink of the power plant.
A typical turbine power plant utilizes a heat source, such as, for example, fuel combustion, to produce a vapor. The vapor enters the turbine portion of the system and expands as it travels through the turbine causing the turbine to rotate. This turbine in turn drives an electrical generator which produces electricity. As the vapor exits the turbine at a lower temperature and pressure, it enters a condenser wherein the vapor is cooled via heat transfer with a cooling medium until it condenses to a liquid. The condensed liquid is then pumped back to the heat source where it begins the cycle once again.
Although various heating, cooling and routing configurations can be utilized, the efficiency with which a turbine system produces work is largely a matter of the temperature difference between the hot inlet source as it enters the turbine and the cold cooling source used to condense the thermodynamic medium after it exits from the turbine. The theoretical Carnot efficiency of a heat engine is defined by the following equation: EQU Carnot efficiency=(1-T.sub.L /T.sub.H).times.100
Where
T.sub.L =the temperature of the cooling source in degrees Kelvin PA1 T.sub.H =the temperature of the hot source in degrees Kelvin
Although the maximum efficiency calculated by this equation is only theoretical, it does allow a useful comparison for determining the effect of a change in cooling source temperature. From this equation it is apparent that the greater the temperature differential between the hot and cold sources, the greater the efficiency of the system. Consequently, for a fixed high temperature input, a reduction in the temperature of the cooling source will increase the efficiency at which a turbine system will operate and thus increase its power output.
Turbine power plants typically utilize ambient air or water as their cooling medium. In certain geographic areas, the temperature of the cooling medium may fluctuate 50.degree. F. or more between the summer and winter. However, because the power plants must operate throughout the entire year, the designer cannot take full advantage of the colder cooling temperatures available at night or during the winter. Rather, the power plant must be designed so that it will operate even when the cooling medium is at its maximum summer temperature.
As can be seen in the aforementioned equation for determining Carnot efficiency, if the high temperature source remains at a constant temperature and the temperature of the cooling medium is reduced, the efficiency of the system will increase. Likewise, on the hottest summer day, the power plant's efficiency will be at a minimum, which must be taken into consideration in designing the power plant.
Another consideration is the inherent limit on the vacuum that can be developed by condensers used at steam power plants or the like. A typical condenser of this type can pull a vacuum of about 21/2 inches Hg. at a temperature of 108.7.degree. F. Even if it is desired to attempt to cool the condenser under optimum conditions, i.e., flowing river water at about 33.degree. F., it is still not possible to pull a vacuum lower than 21/2 inches Hg. because of the physical limitations of the equipment. As a result, the theoretical advantage available due to the colder condenser fluid source cannot be translated into an actual advantage for a condenser of a given size.
Thus, the potential exists for taking advantage of the increased operating efficiency which is available during the cooler time periods such as, for example, the winter months. Accordingly, it would be desirable to utilize a system or arrangement which would take full advantage of the highest efficiency available to the turbine system at all times.
The turbine system of the present invention takes advantage of the additional power available by utilizing additional turbine stages to extract additional work from the vapor at those times of the year when a lower cooling medium temperature is available. The present invention increases the overall efficiency and power output of a power plant by tracking the temperature of the cooling medium and increasing or decreasing the number of turbine stages through which the vapor passes in order to take maximum advantage of the available energy.
The turbine system of the present invention includes a multi-staged turbine with a high pressure turbine section and at least one lower pressure turbine section. Each of the turbine sections has an inlet opening for introducing a vaporized thermodynamic medium, such as, for example, a vaporized organic fluid, into the turbine section and a discharge opening for discharging the thermodynamic medium from the turbine section at a reduced temperature and pressure. The thermodynamic medium utilized in the turbine system should be selected to possess the most advantageous thermodynamic properties for the temperature regimen across which it must operate. Each of the turbine sections is mounted on a rotatable shaft. A linking conduit is provided for transporting the thermodynamic medium from the discharge opening of the high pressure turbine section to the inlet opening of the next lower pressure turbine section. A discharge conduit is provided at each turbine section for transporting the thermodynamic medium from the discharge opening of the respective pressure turbine sections to a mechanism for vapor liquification. A valve assembly may be used for selectively directing the thermodynamic medium through the linking and discharge conduits. The shafts of the lower pressure turbine stages may be provided with a clutch assembly for releasably interlocking the turbine section shafts so that the work done by the lower pressure turbine stages can be captured as electrical energy.
It is accordingly a general object of the present invention to provide an improved multi-stage turbine system.
Another object of this invention is to provide a multi-stage turbine system having at least one bypassable lower pressure turbine stage.
Another object of the present invention is to provide a power plant with a multi-stage turbine system having at least one bypassable lower pressure stage in which the lower pressure stage is bypassed in response to an increase in the cooling medium temperature of the power plant.
Another object of the present invention is to provide a turbine system designed to employ a circulating thermodynamic medium capable of being expanded to a saturation pressure at a readily attainable level at which condensation of the exhaust from the lowest stage can be effected at the lowest temperature made available by the lowest available ambient sink temperature.
Another object of the present invention is to provide a multi-stage turbine system with at least one bypassable lower pressure stage in which vapor, in response to a decrease in cooling medium temperature, is directed to the next lower pressure stage through which vapor was not previously passing.
Another object of the present invention is to provide a multi-stage turbine system having an overall increase in operating efficiency.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.