Patent Number: 051376814
Section: summary

BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates to an improvement in steam power plants for the generation of electricity, and in particular to reducing feed water requirements and condenser complexity by mechanically compressing power turbine exhaust steam to be recycled to the turbine. 2. Description of the Prior Art Although there are many variations of controls and operating elements in steam power plants, the basic elements include a thermal steam source, steam turbines, generators, and one or more condensers to reclaim the turbine exhaust as hot feed water. Various pressure controls and the recycling of dry turbine exhaust steam to super heater tubes are well known variations to the basic power plant to control operating conditions and increase thermal efficiency. Re-compression of turbine exhaust steam by mechanical means to be recycled to the power turbine has not been previously been included in such systems, as the mechanical energy used in compression cannot be entirely extracted as work energy by the turbine, resulting in a net energy loss. However, particularily with nuclear fueled power plants, the large quantities of cooling water and boiler feed water required are, in many locations, more critical limitations than thermal efficiency. Consequently, in such locations it may be advantageous to sacrifice optimum thermal efficiency in order to reduce water requirements. An objective of the present invention is to reduce feed water requirements in the steam loop, and by so doing, also reduce the size and complexity of the condensers. Although mechanically compressed turbine exhaust steam has not previously been used for this purpose, it has been known to mechanically compress steam engine exhaust for auxiliary purposes, such as described in U.S. Pat. No. 1,066,348 to G. T. Voorhees, which describes mechanically compressed exhaust steam utilized for auxiliary heating systems, such as moisture absorption generators. Similarly, U.S. Pat. No. 4,239,603 describes the use of a turbo compressor heat engine to re-pressure a portion of the process vapor from a steam ejection vacuum cooling or drying system, thereby reducing the fuel costs associated with condensing the vapor and regenerating the steam in a boiler. Gas turbine power plants typically extract a portion of turbine power to compress the inlet air prior to combustion, as the work extracted for compression is more than recouped by the increased combustion efficiency. It is also known in gas turbine technology, particularly turbo-prop and turbofan aircraft engines, to use a coaxial dual shaft for the turbine-compressor drive linkage, to accommodate different rotating speeds for the high and low pressure extraction/compression stages. It is an objective of this invention to utilize a dual shaft compresser-turbine in a steam power plant to re-compress the turbine exhaust steam, and to recycle it to the turbine inlet in order to reduce the amount of condensation and steam generation required in the system cycle, thereby sacrificing some thermal efficiency in order to decrease feed water requirements and condenser size and complexity. SUMMARY OF THE INVENTION In the apparatus of the present invention, a steam power plant includes dual shaft turbine-compressor as the power extraction turbine. The turbine exhaust steam is passed through a dryer and then introduced to the compressor section, where its pressure is raised by mechanical compression, and then is mixed with fresh steam by jet ejectors. The mixed steam is thereafter routed to the turbine inlet. In the method of generating electricity by the present invention, dry high pressure steam is generated by a thermal source, is mixed with re-compressed turbine exhaust steam by jet ejectors, and the mixed steam is input to the turbine section of a coaxial dual shaft turbine-compressor. Thermal energy is extracted from the mixed steam by the turbine section and converted into mechanical energy. A portion of the mechanical energy is used to drive an electrical generator and the remaining mechanical energy is used to re-compress turbine exhaust steam. The turbine exhaust steam is passed through a dryer to eliminate moisture, and the dried exhaust steam is routed to the compressor section. The compressor mechanically raises steam pressure, and such re-compressed steam is routed to the jet ejectors to be mixed with fresh steam.