Abstract:
A system including a vessel including a heat source and a flue; a turbine; a condenser; a fluid conduit circuit disposed between the vessel, the turbine and the condenser; and a diverter coupled to the flue to direct a portion of an exhaust from the flue to contact with a cooling medium for the condenser water. A method including diverting a portion of exhaust from a flue of a vessel; modifying the pH of a cooling medium for a condenser with the portion of exhaust; and condensing heated fluid from the vessel with the pH modified cooling medium.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     This invention was developed under Contract DE-AC04-94AL85000 between Sandia Corporation and the U.S. Department of Energy. The U.S. Government has certain rights in this invention. 
    
    
     FIELD 
     Power plant operation. 
     BACKGROUND 
     A fossil fuel power plant is a system that burns fossil fuel such as coal, natural gas or petroleum to produce electricity. Most power plant systems convert fossil fuel energy to mechanical or electric energy by burning fuel (coal, natural gas or petroleum) in a vessel (e.g., a boiler) and circulating a working fluid such as water through the boiler. In the case of water as the working fluid, the fuel converts the water to high temperature and pressure steam and the steam in turn is used to do work in the form of rotating a turbine shaft. The steam does work as it expands through the turbine. The rotation of the shaft is then converted to electrical energy from a generator. From the turbine, the working fluid is transferred to a condenser where it is condensed by, for example, a heat exchange process. The working fluid (condensate) is then cycled back into the heating vessel. 
     The main purposes of the condenser are to condense the working fluid (e.g., steam) from the turbine for reuse in the cycle and to maximize turbine efficiency by maintaining proper vacuum. One type of condenser used in power plant systems is a shell and tube heat exchanger. As heat exchangers, these condensers convert the working fluid (e.g., steam) from a gaseous to liquid state by a cooling medium (e.g., water) at atmospheric pressure or below atmospheric pressure. The working fluid (e.g., steam) from the turbine flows on the shell side of the condenser, while the cooling medium flows in the tube side. Most of the heat liberated due to condensation of the working fluid is carried away by the cooling medium (e.g., water). The condensed working fluid (condensate) is collected in the bottom of the condenser (in a hot well) and then pumped back to the heating vessel (e.g., boiler) to repeat the cycle. 
     A large volume of cooling medium (e.g., water) must be circulated through the tubes of the condenser to absorb the heat from the working fluid (e.g., steam). As the steam cools and condenses, the temperature of the cooling water rises. The waste heat generated at the condenser is released to the atmosphere through a cooling tower associated with the condenser. 
     Water-based cooling systems fall in either once-through or closed-loop designs. Once-through cooling systems withdraw a large volume of water from river, lake, estuary or ocean. The water is pumped through a condenser in a single pass and returned to the same or nearby water body. 
     Closed-loop cooling systems receive their cooling water from a cooling tower and basin, cooling pond or cooling lake that is typically associated with a river, lake, estuary or ocean as a water source. Because evaporation in plant cooling towers removes cooling water from the evaporated system, regular additions of “make-up” cooling water are needed from the source. Make-up volumes are much lower than daily once-through volumes and may range from hundreds of thousands to millions of gallons per day. 
     Recently, to meet cooling water demands, particularly in closed-cycle cooling systems, the power plant industry has looked to reclaimed water as an additional source. Reclaimed water includes domestic and industrial wastewaters, such as water from oil and gas wells, mine pool waters, produced water from carbon dioxide storage in saline formations, and ash pond basins. 
     Corrosion and the build up of scale in a condenser caused by the cooling medium (e.g., water) is a concern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic embodiment of a power plant system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic of an embodiment of a power plant system. System  100  includes vessel or boiler  120  containing heat source  122 . Fuel source  110  is connected to vessel  120  to provide fuel to the vessel. In one embodiment the fuel source is natural gas or coal. Extending through vessel  120  is fluid conduit circuit  130 . In one embodiment, fluid conduit circuit  130  provides purified water to vessel  120 . The purified water is converted to steam inside vessel  120  by combustion of fuel from fuel source  110 . Fluid conduit circuit  130  transports the steam from vessel  120  to turbine  140 . 
     From turbine  140 , fluid conduit circuit  130  connects to condenser  160 . In condenser  160 , the steam within fluid conduit circuit  130  is condensed for reuse. One way steam is condensed is through a heat exchange or similar process in which the steam is cooled by a cooling medium, such as cooling water.  FIG. 1  shows condenser  160  having fluid conduit circuit  130  extending therein. Also extending into condenser  160  is cooling conduit circuit  172 . Cooling conduit circuit  172  contains a cooling medium such as water. 
     In one embodiment, condenser  160  includes a heat exchanger with, for example, a number of tube sheets. Steam from fluid conduit circuit  130  is introduced to a shell side of the heat exchanger with the cooling fluid supplied to the tube or bore side (through the tube sheets). The cooling fluid condenses the steam to a condensate that may be returned to vessel  120  via pump  131 . 
     In one embodiment, the cooling medium that is introduced into condenser  160  and is used to cool/condense the working fluid in fluid conduit circuit  130  is supplied from cooling tower  170  through cooling conduit circuit  172 . From condenser  160 , the cooling fluid is returned to cooling tower  170 . In one embodiment, the cooling fluid is water, such as fresh water, salt water or reclaimed water. Some of the water that is introduced to condenser  160  is lost to evaporation from cooling tower  170  and the remaining water is recycled for reuse in cooling fluid conduit circuit  130 . Make-up water supplied to cooling tower  170  from a water source make up for the water lost to evaporation indicated as cooling medium source  175 . 
     Referring to vessel  120  (e.g., boiler), the vessel includes flue  125 . Flue  125  is in communication with an interior of vessel  120  and is used to disperse combustion gases generated by combusting the fuel from fuel source  110  (e.g., natural gas, coal, etc.). In one embodiment, a portion of the exhaust from flue  125  is diverted by way of a diverter  178  in flue  125 . Diverter  178  is, for example, a damper that directs a portion of the exhaust into conduit  180 . Conduit  180  is, for example, a tube or other shaped duct having interior dimension(s) to allow a volume of exhaust (gas) therethrough. Conduit  180  is directed into cooling medium source  175  that supplies cooling medium to condenser  160 . As noted above, water as a cooling medium, whether fresh, salt or reclaimed or some combination thereof may form calcium carbonate and/or silica scale when mixed with or in contact with components (e.g., metal components) of condenser  160  (e.g., tube sheets). Scale tends to be produced when the water is at a pH greater than 7.0 (e.g., pH of 8-9). One way to reduce the formation of scale in cooling tower  170  and condenser  160  is to lower the pH. In the case of a combustion source for vessel  120  that is natural gas, an exhaust through flue  125  contains carbon dioxide (CO 2 ) and possibly other substances such as nitrogen, oxides of nitrogen. Carbon dioxide can function as a weak acid when combined with water. By diverting a portion of exhaust from flue  125  into the cooling medium source (e.g., water) to condenser  160 , the pH of the cooling medium that enters condenser  160  may be decreased. Corrosion and silica scale can also be inhibited by raising the pH of water above a pH of 8-9. In the case of a coal-fired power plant, the exhaust through a combustion flue (e.g., flue  125 ) contains coal ash. Coal ash is commonly a mixture oxide of metals (e.g., calcium silicate) that tends to be basic when mixed with water. By exposing a cooling medium source (e.g., water) to coal ash, the pH of the cooling medium that enters condenser  160  may be increased. 
       FIG. 1  shows conduit  180  extending from flue  125  to cooling medium source  175  to mix with a cooling medium (e.g., water) in cooling medium source  175  prior to the cooling medium entering cooling tower  170  as, for example, make-up water. Conduit  180  supplies exhaust from flue  125  into cooling medium source  175 . In one embodiment, where cooling medium source  175  stores water in a reservoir, exhaust from flue  125  may be supplied by terminating conduit  180  in cooling medium source  175 . Representatively, conduit  180  may be an aluminum tube having an end disposed in cooling medium source  175  such as below a minimum level requirement for a reservoir. In this manner, the exhaust can mix with water in cooling medium source  175 . 
       FIG. 1  also shows optional filter  174  connected to conduit  180  at a position proximal to cooling medium source  175 . Filter  174  may be used to trap particulates or other unwanted gas components in the exhaust diverted from flue  125  before the exhaust is mixed with cooling medium in cooling medium source  175 . To trap particulates, filter  174  contains, for example, a cordierite, silicon carbide, or ceramic fiber filter core. 
     In another embodiment (shown in dashed lines marked B), conduit  180  in system  100  may supply exhaust from flue  125  into reverse osmosis filtration unit  173 . Osmosis filtration unit  173  may be used to remove salts (e.g., dissolved salts) that might otherwise cause scaling of cooling tower  170 .  FIG. 1  shows reverse osmosis filtration unit  173  disposed between cooling medium source  175  and cooling tower  170  to treat water supplied to cooling tower  170 . In another embodiment, water in cooling tower  170  may be connected to reverse osmosis filtration unit  173  so that the water receives continuous filtration. In either embodiment, conduit  180  brings exhaust from flue  125 , optionally through filter  174 , and into reverse osmosis filtration unit  173  so that the exhaust mixes with water in the filtration unit. 
     In another embodiment (shown in dashed lines marked C), conduit  180  in system  100  may supply exhaust from flue  125  into cooling tower  170  to be mixed with the cooling medium (e.g., water) present in cooling conduit circuit  172 . In an example of a cooling tower used to cool a cooling medium of water, heated water from condenser  160  is directed to cooling tower  170 . In cooling tower, the heated water is exposed to an air draft to cool the water. The cooled water is then collected in a collection basin for use in cooling conduit circuit  172 . In an embodiment where exhaust from flue  125  is supplied to cooling tower  170 , conduit  180  may extend from flue  125  into a collection basin in cooling tower  170  where it can be mixed with water present in the system. 
     In another embodiment, conduit  180  in system  100  may supply exhaust from flue  125  into multiple locations. For example, exhaust from flue  125  may be diverted into cooling medium source  175  and into cooling tower  170  (path marked C) and/or into reverse osmosis filtration unit  173  (path marked B). In another embodiment, exhaust from flue  125  can be diverted to one or more of these locations at different times in an electricity producing process. For instance, in a natural gas-fired power plant using water as a cooling medium, exhaust from flue  125  might initially be introduced at cooling medium source  175 . If during processing, a pH of water in cooling tower  170  is found to be a pH 8 or greater, the exhaust could be directed to the cooling tower (path marked C). In another embodiment, exhaust from flue  125  is introduced at any commercially and mechanically feasible location where it can mix with a cooling medium for condenser  160  and modify a property of the cooling medium (e.g., change the pH of the cooling medium). 
     In one embodiment, a system of diverting a portion of the exhaust from a power plant flue may include an automated sample processing system.  FIG. 1  shows control computer  200  in communication with the various system components to provide a centralized user interface for controlling the components in a power plant operation process. It shall be appreciated that control computer  200  and the various system components may be configured to communicate through hardwires or wirelessly, for example, the system may utilize data lines which may be conventional conductors or fiber optic. 
     Control computer  200  may also communicate with one or more local databases  210  so that data or protocols may be transferred to or from local database(s)  210 . For example, local database  210  may store one or a plurality of operation protocols that are designed to be performed by the components of system  100 . Furthermore, control computer  200  may use local database(s)  210  for storage of information received from components of system  100 , such as reports and/or status information. 
     Representatively, as described above, vessel  120  is used, in one embodiment, to produce high pressure steam suitable for rotating turbine  140  and generating electricity  150 . In producing the steam in vessel  120 , exhaust is generated at flue  125  and a portion of that exhaust is diverted through diverter  178  to be mixed with cooling medium for condenser  160 . In one embodiment, the volume of exhaust may be monitored and/or controlled by control computer  200 . For example, a processing protocol delivered to control computer  200  includes instructions for generating steam in vessel  120 . These instructions are provided in a machine-readable form to be executed by control computer  200 . Accordingly, control computer  200  executes the instructions to meter the components into vessel  120  (e.g., fuel from fuel source  110 , water for circuit  130 ). Such metering is controlled and monitored by control computer  200  by, for example, opening/controlling a valve to deliver fuel from fuel source  110  and powering/controlling a pump in circuit  130 . Similarly, in one embodiment, control computer  200  executes instructions to control a flow of cooling medium into condenser  160  and into cooling tower  170  (e.g., from cooling medium source  175 ). 
     Based on the fuel consumption and steam production in vessel  120 , control computer can determine the volume of exhaust produced at an exit of flue  125 . Control computer  200  can then control diverter  178  to divert a portion of that volume into conduit  180  to mix with the cooling medium (e.g., water). Where the cooling medium is water, in one embodiment, a pH of cooling medium source  174  is measured at regular intervals with pH monitor  179  during processing of electricity. Control computer  200  regulates the volume of exhaust that is diverted through conduit  180  based on a pH reading at cooling medium source  175 . In a natural gas-fired power plant, for example, the exhaust from flue may be used to lower the pH of water to inhibit scale and/or corrosion. Representatively, if a reading of pH of water at cooling medium source  175  is pH 8, control computer  200  may execute program instructions to open diverter  178  to divert a greater volume of exhaust from flue  125  into cooling medium source  175 . If a reading of pH of water at cooling medium source  175  is pH 6, control computer may be programmed to maintain a position of diverter  178  so that the pH stays approximately pH 6 or execute program instructions to close diverter  178  to raise the pH slightly. In one embodiment, control computer  200  may contain programmed instructions allowing for a range of acceptable pH readings (e.g., pH 6.5-7.5 for natural gas-fired power plant). Obtaining feedback from cooling medium source  175  allows program instructions in control computer  200  to be executed to seek to stay within the acceptable range and inhibit scale in condenser  160  and cooling tower  170 , by seeking to achieve, in one embodiment, an optimal pH of water in cooling medium source  175 . It is appreciated that control computer  200  may be used to control and monitor additional components of system  100  that may or may not have to do with cooling medium source  175 . 
     In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. The particular embodiments described are not provided to limit the invention but to illustrate it. The scope of the invention is not to be determined by the specific examples provided above but only by the claims below. In other instances, well-known structures, devices, and operations have been shown in block diagram form or without detail in order to avoid obscuring the understanding of the description. Where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated in the FIGURE to indicate corresponding or analogous elements, which may optionally have similar characteristics. 
     It should also be appreciated that reference throughout this specification to “one embodiment”, “an embodiment”, “one or more embodiments”, or “different embodiments”, for example, means that a particular feature may be included in the practice of the invention. Similarly, it should be appreciated that in the description, various features are sometimes grouped together in a single embodiment, FIGURE, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of the invention.