Patent Grant
8266909
This invention relates generally to power plants. More specifically, this invention relates to a method and apparatus for preventing contaminants from becoming entrained with the working fluid within a steam power plant.
Steam turbine power generation plants utilize the energy present in a working medium at high pressure to turn a turbine, which, in turn, turns a generator, generating electrical energy. The working fluid must be free of particulate debris in order to prevent blockages within the system. The chemistry of the working fluid must also be closely monitored and controlled to eliminate harmful soluble contaminants which, if present in the working fluid, may deposit on internal components, possibly damaging those components over time.
During operation of the steam turbine power generation plant the particulate debris may be continually removed from the working fluid via filters etc, and the chemistry of the working fluid may be continually kept within tolerance using continuous treatment techniques such as condensate polishing. However, during periods when the power plant is not operating, such as prior to its first use, or during a scheduled shut down, these contaminants may not be continually removed from the working fluid. If a power plant were to be started-up without regard to a possible build up of these contaminants, the contaminants could overwhelm the continuous treatment techniques in place within the power plant, and cause damage to the components of the power plant.
Techniques for eliminating any built up debris have been developed. One of the simpler methods includes simply generating steam using existing working fluid and possibly adding new, chemically appropriate fluid to the working fluid, exhausting that steam to the atmosphere until the level of particulate debris reaches acceptable limits, and then using that steam to flush the rest of the system until the steam and condensate reach acceptable limits for particulate and chemical contaminants. At that point the working fluid is acceptable for use and the power plant can be brought online. However, this type of purging method may take up to several days, and consume hundreds of thousands of gallons of high quality working fluid.
Some power generation plants are peaking, or ready-reserve power plants, which produce power only during peak demand periods. This requires steam turbine power plants that can come online quickly, as demand changes. Thus, fast start-up times are imperative for such a system. Peaking steam turbine power generation plants, such as the Flex-Plant™ 10 power generation plant, may employ a condenser where the operating pressure in the condenser is above ambient pressure. Conventional methods for treatment of working fluids, such as condensate polishing, may enable a sufficiently fast start-up time in conventional power plants, but in a positive pressure condenser power plant, the associated high temperature of the condensate renders the usual polishing process ineffective. Thus, in order to permit the use of condensate polishing, the condensate must be cooled, which reduces operating efficiency. Consequently, other methods of treating the condensate have been developed.
Positive pressure condenser power plants may inject pressure maintaining fluid, for example nitrogen, or other suitable gas, into the condenser to help maintain positive pressure in the condenser during shutdown, to prevent the entry into the system of contaminant containing atmospheric air during shutdown. A positive pressure condenser system is disclosed in U.S. patent application Ser. No. 12/366,763, filed Feb. 6, 2009, entitled CONDENSER SYSTEM, by James C. Bellows, the entire disclosure of which is incorporated herein by reference. Positive pressure condenser power plants may also use a pressure maintaining fluid, such as a nitrogen blanket, to fill the interior areas of the condenser (Air Cooled Heat Exchanger: “ACHE”), the high pressure boiler, and the main steam system, during periods of shutdown, in order to prevent contaminant containing atmospheric air from entering these components, and subsequently becoming entrained with the working fluid contained in the interior regions of those components. However, the interior of the steam turbine itself and steam exhaust duct between the steam turbine and condenser may not be blanketed with this pressure maintaining fluid so that, for instance, humans may enter and perform required maintenance. Instead, contaminant containing atmospheric air may be left in these interior areas, and an air dryer is used to help minimize moisture and corrosion.
The invention is explained in the following description in view of the drawings that show:
The present inventors have recognized that when certain steam turbine power plants are started-up, such as those that include large steam turbine exhaust ducts, or those with positive pressure condensers, contaminate introducing fluid (“contaminated fluid”), usually air, present in the interior areas of the power plant which were not blanketed with a pressure maintaining fluid, may become entrained with the other fluid present in the other components of the power plant. The other fluid may include the working fluid for generating power, the pressure maintaining fluid, for example, nitrogen, argon, helium, or neon gas, etc., or a combination of the working fluid and the pressure maintaining fluid. The entrainment of this contaminated fluid with the working fluid at start-up may add a significant amount of contaminants to the uncontaminated fluid at the precise time when efficient and fast removal of these contaminants is critical to enable fast start-up of the plant. For example, if air becomes entrained with the working fluid, the CO2 present in the air will form carbonic acid within the power plant. The inventors have thus recognized the importance of preventing this contaminated fluid from becoming entrained with the uncontaminated fluid at start-up.
The inventors have developed an innovative, yet simple way to prevent this contaminated fluid from becoming entrained with the uncontaminated fluid. The inventors have added a vent and a vent valve to the steam turbine exhaust duct for selective and innovative venting of contaminated fluid. When it is desired to purge contaminated fluid from the interior areas of the steam turbine plant, for example upon start-up, the vent valve is opened for a period, and remains open as the steam is introduced into the steam turbine. Typically the period the vent valve is open is several seconds. The initial steam entering the turbine forces contaminated fluid out the vent. This purging continues until enough contaminated fluid is removed from the interior areas to reduce or eliminate contaminated fluid entrainment concerns. At this point the steam turbine isolation valve is opened and then the vent valve is closed, thus redirecting the steam to the condenser, permitting the completion of the remaining procedures for bringing the power plant online. In an embodiment, the vent valve may be on the order of a six inch valve, and an eighteen inch steam turbine isolation valve bypass is used to facilitate operation of the steam turbine isolation valve. As such, a steam turbine isolation valve bypass valve is opened before closing the vent valve, which permits the steam turbine isolation valve to open, after which the vent valve and steam turbine isolation valve bypass valve are closed. The inventors recognize that some, sacrificial uncontaminated fluid will be lost from the system during this purging, however the total volume lost is minimal. However, this invention reduces the need for chemical treatment of the working fluid during start-up, which is of paramount importance.
Further, the inventors recognize that this purging method could be used at times other than start-up of the power plant, when it becomes necessary to purge any contaminated fluid and/or working fluid as needed. The inventors have also recognized that this system and method of removing contaminated fluid is not limited to positive pressure condenser power plants, but can be applied to any steam power plant where there is a desire to remove contaminated fluid from the power plant, or a desire to prevent contaminated fluid from coming in contact with uncontaminated fluid.
Referring to
Thus, with this simple, yet innovative modification to a steam turbine power plant, the inventors have created a way to decrease the amount of treatment the working fluid in a positive pressure steam power plant may require at start up. This reduction in treatment may correspond to a reduction in start-up time for these steam power plants, and reduced start up time is of paramount importance to the success of these systems. The inventors have done this by adding simple, inexpensive components, which may be controlled by existing controllers.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
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