Abstract:
A method and apparatus is provided for a system for maintaining hydrogen purity in an electrical power generator. The purity system includes: a generator, a hydrogen generator configured to provide hydrogen gas to the generator, a purity monitor for detecting the level of hydrogen purity in the generator and providing a signal when the purity drops below a predetermined threshold. The system automatically compensates for gas loss or contamination to maintain the desired level of efficiency in the electrical generator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 10/711,395 entitled “System for Maintaining Hydrogen Purity in Electrical Generators and Method Thereof” filed on Sep. 16, 2004 now U.S. Pat. No. 7,550,113, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF INVENTION 
     This disclosure relates generally to electrical generator systems and especially to electrical generators utilizing hydrogen gas to cool the generator. 
     BACKGROUND OF THE INVENTION 
     Modern electrical power plants often utilize turbine generators to produce electricity. During operation, these generators produce large amounts of heat which must be dissipated in order for the generators to operate at maximum efficiency. Traditionally, air was used as a cooling medium to help dissipate the heat. However, as generator capacity and size increased, hydrogen replaced air due to its high heat capacity and low density. Additionally, the use of hydrogen reduces the windage or friction losses over comparably sized air cooled units. 
     Due to the loss in efficiency from windage, it is desirable to maintain as high a purity level of the hydrogen in the generator. As shown in  FIG. 1 , as the windage loss increases due to impurities, the financial loss to the power plant correspondingly increases. For a 800 MW generator, an 8% decrease in the purity of the hydrogen in the generator increases the cost of producing electricity by almost $4000 per day. Accordingly, it is desirable to maintain as high a level of purity as possible. 
     While the generator is in operation, hydrogen is continuously lost due to leaks in seals. Traditionally, to maintain the appropriate level of pressure and purity in the generator, the power plant operator would purchase hydrogen gas in bulk from gas producers who delivered the gas in cylinders or by tanker truck. The operator would periodically check the purity level and add hydrogen from the hydrogen gas cylinders as needed. 
     As an alternative to using bulk purchased hydrogen gas, power plant operators have also used electrolysis gas generators which allow the operator to produce hydrogen gas on-site. The electrolysis generators use electricity to split water into hydrogen and oxygen gas. The use of electrolysis typically reduced the cost of using hydrogen and also reduced the security concerns of the power plants in having to receive and store large quantities of a flammable gas. Typically, however, the electrolysis generators which are economically viable for providing makeup gas for the electrical generator lacked the capacity to produce sufficient volumes of hydrogen to quickly purge or fill the electrical generator after it had been shut down for maintenance. Also, plant operators still relied on manual filling of the generators which did not allow for optimal efficiencies. 
     Accordingly, what is needed in the art is a system for maintaining high purity levels of hydrogen in an electrical power generator and for providing a means for utilizing an on-site hydrogen generator to produce sufficient hydrogen to purge or fill the electrical power generator. 
     SUMMARY OF THE INVENTION 
     A method and apparatus is provided for an a system for maintaining hydrogen purity in an electrical power generator. The purity system includes: a generator, a hydrogen generator configured to provide hydrogen gas to the generator, a purity monitor for detecting the level of hydrogen purity in the generator and providing a signal when the purity drops below a predetermined threshold. The system automatically compensates for gas loss or contamination to maintain the desired level of efficiency in the electrical generator. 
     The above discussed and other features will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings, which are meant to be exemplary and not limiting, and wherein like elements are numbered alike: 
         FIG. 1  is a graphical plot illustrating the windage losses as a function of hydrogen purity; 
         FIG. 2  is a schematic diagram illustrating the hydrogen purity system of the present invention; 
         FIG. 3  is a schematic diagram illustrating an alternate embodiment hydrogen purity system of the present invention; 
         FIG. 4  is a schematic diagram illustrating an alternate embodiment hydrogen purity system with excess hydrogen storage of the present invention; 
         FIG. 5  is a block flow diagram illustrating the method of operating the system of  FIG. 2 ; 
         FIG. 6  is a block flow diagram illustrating the method of operating the system of  FIG. 3 ; 
         FIG. 7  is a block flow diagram illustrating the method of operating the system of  FIG. 4 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     As the demand for power by consumers has increased, electrical power producers have increasingly turned to larger generators to fulfill the needs of society. As the size of the generators increased, it became increasingly more difficult to maintain the generator at an appropriate operating temperature to prevent damage to the generator components. Smaller generators relied on air cooling to dissipate heat from the generator rotor windings. To improve heat transfer, generator manufacturers began to utilize hydrogen gas as a transfer agent since the thermal conductivity of hydrogen is seven times that of air. 
     The switch to hydrogen also yielded side benefits by reducing the windage losses in the generator due to hydrogen&#39;s lower density. As shown in  FIG. 1 , the higher purity level of the hydrogen gas in the generator, the lower the windage losses. However, since the generator contains various components, such as seals, which must be lubricated, contaminants such as water and oil become mixed with the gas reducing the purity levels. To compensate for these contaminants, operators utilized purifying systems  22 , such as a heated regenerative dryer, which allowed removal of water from the generator without having to purge the generator of a costly gas. 
     In addition to contamination, operators must cope with hydrogen leaks which typically occur at the generators seals. As hydrogen escapes, the operator must add make-up hydrogen gas to the generator in order to maintain the heat transfer and low windage benefits. In a typical generator such as a GE Frame-7 generator, the loss of hydrogen and the amount of hydrogen can reach up to 20-40 cubic feet of hydrogen per hour. 
     An exemplary embodiment of the present invention is shown in  FIG. 2 . The generator system  10  includes a generator  12  which may be driven by any conventional means, such as a steam turbine (not shown). The generator  12  produces electricity which is transmitted to the utility grid  14 . The pressure inside the generator is monitored by a pressure monitor  16  and the purity of the hydrogen gas inside the generator is monitored by a monitor  18 . As will be described in more detail herein, the purity monitor may be of any suitable type capable, such as but not limited to a thermal conductivity analyzer or a vibrating element analyzer. 
     The generator  12  also includes a vent line  19  which connects to a solenoid valve  20 . The outlet of the valve  20  leads to a vent which allows the hydrogen gas to be properly dissipated into the atmosphere. As will be described in more detail herein, a communications link  17  connects the purity monitor  18  with the solenoid valve  20 . A hydrogen generator  24  provides hydrogen gas to the generator  12  through conduit  26 . Alternatively, a controller (not shown) in the generator  12  controls the solenoid valve  20  to vent the hydrogen gas. 
     In the preferred embodiment, the hydrogen generator will include a water-fed electrochemical cell which is capable of disassociating reactant water into hydrogen and oxygen gas. Suitable reactant water is deionized, distilled water, which is continuously supplied from a water source  28 . The electrochemical cell will preferably be of a polymer electrode membrane (PEM) type. The electrochemical cell may also be any other suitable electrochemical cell such as, but not limited to, alkaline, phosphoric acid, or solid oxide based cells. The hydrogen generator  24  may also be any non-electrochemical system capable of producing hydrogen gas such as, but not limited to, a steam methane, or natural gas reformation. 
     An output sensor  30  is incorporated into the hydrogen generator  24  to sense the differential pressure between the hydrogen generator  24  and the conduit  26 . The output sensor  30  may be a pressure transducer that converts gas pressure within the conduit  26  to a voltage or current level indicative of the gas pressure. Output sensor  30  may also be any other sensor suitable for sensing a qualitative or quantitative parameter of the gas and provide an electrical signal indicative of that parameter as an output. Such other sensors include, but are not limited to, a flow rate sensor, a mass flow sensor, and a differential pressure sensor. Optionally, a feedback signal  29  may be provided from the pressure monitor  16  to the hydrogen generator  24   
     Output sensor  30  interfaces with a controller (not shown) that is capable of converting the analog voltage or current level provided by the sensor  30  into a digital signal indicative of the sensed hydrogen pressure. The controller compares the sensed hydrogen pressure to a predetermined parameter for controlling the output of the hydrogen generator  24  as will be described in more detail herein. 
     An alternate embodiment of the electrical power generating system  10  is shown in  FIG. 3 . In this embodiment, the purity monitor  18  is electrically coupled to the electrolyzer  24  by line  32  to provide a control signal when the hydrogen gas purity level drops below a predetermined threshold. 
     Electrical power generators hold a large volume of hydrogen gas, typically at least 7,500 cubic feet. Consequently, at an event where the generator needs to be purged and filled with hydrogen gas, such as at startup, or after maintenance, the operator will need access to a large volume of hydrogen gas. Events such as startup or maintenance purging typically occur on an annual basis. Since a hydrogen generator capable of generating this volume of hydrogen in a short period of time would be greatly over-sized for daily operation. Accordingly, it is desirable to have a means for storing excess hydrogen gas generated by the hydrogen generator  24 . In the embodiment shown in  FIG. 4 , the hydrogen generator has a first conduit  26  and a valve  27  which provides hydrogen to the generator  12  as described herein above. The hydrogen generator  24  further includes a second conduit  34  and a valve  36  which fluidly couples the hydrogen generator to at least one storage tank  40 . The system  10  may also optionally include a solenoid valve  36  and a compressor  38  coupled to the conduit  34 . An optional pressure transducer  42  may be electrically coupled to the valve  36  to terminate filling of the tank  40  once a desired pressure level is reached. The compressor may be any suitable type, such as but not limited to a metal hydride compressor, an electrochemical compressor, or a mechanical compressor. The compressor  38  is shown external to the hydrogen generator  24  for exemplary purposes, preferably, the compressor may be integrated with the hydrogen generator  24 . A conduit  46  fluidly couples the tank  40  with the generator  12 . A valve  48  controls flow from the tank to the generator  12 . 
       FIGS. 5 ,  6 , and  7  are flow diagrams depicting the operation of the generating system  10 . These methods may be included and executed in the controller application code in one or more of the individual components of the system  10 , or may be embodied in a single central controller (not shown). These methods are embodied in computer instructions written to be executed by a microprocessor typically in the form of software. The software can be encoded in any language, including, but not limited to, assembly language, VHDL (Verilog Hardware Description Language), VHSIC HDL (Very High Speed IC Hardware Description Language), Fortran (formula translation), C, C++, Visual C++, Java, ALGOL (algorithmic language), BASIC (beginners all-purpose symbolic instruction code), visual BASIC, ActiveX, HTML (HyperText Markup Language), and any combination or derivative of at least one of the foregoing. Additionally, an operator can use an existing software application such as a spreadsheet or database and correlate various components enumerated in the algorithms. Furthermore, the software can be independent of other software or dependent upon other software, such as in the form of integrated software. 
     Referring to  FIGS. 2 and 5  an electrical power generating system control method  60  of  FIG. 5  will now be described. Method  60  starts at block  62  and proceeds to block  64 . At block  64 , the purity monitor  18  samples hydrogen from the generator  12  to determine a value H pure  indicative of the level of hydrogen purity in the sampled gas. Method  60  then proceeds to block  66 , where the purity level H pure  is compared with a desired level H pref . The parameter H pref  represents the purity level desired by the operator and allows the operator to balance efficiency requirements with hydrogen usage. Alternatively, the operator may choose to monitor the pressure level inside the generator  12  and purposes herein, the monitoring of pressure or purity may be used interchangeably. Typical values for H pref  are between 90% and 99% with a desired H pref  of 98%. A higher value of H pref  will typically result in greater hydrogen usage. Of the answer to query block  66  is negative, the method  60  returns to block  64  where the hydrogen gas is again sampled and measured. This loop continues generally until method  60  is externally terminated or paused, or until the query of block  66  is answered affirmatively. 
     If the answer to the query of block  66  is affirmative, either in the first instance or after one or more negative answers, the method  60  proceeds to block  68  where a control signal is passed from purity monitor  18  to the valve  20  causing the valve  20  to open. The opening of the valve  20  allows gas from the generator  12  to be vented to the atmosphere. 
     The method  60  then proceeds on to block  70  to produce hydrogen gas. Generally, the hydrogen generator  24  will detect the pressure drop at sensor  30  that results from the venting of the generator  12  which occurred in block  68 . Typically, upon detection of this drop in pressure below the desired pressure P des  the hydrogen generator  24  will initiate production of hydrogen gas which is transferred to the generator  12 . 
     The method  60  then continues on to block  72  where the gas from the generator  12  is sampled and the hydrogen purity measured. Method  60  then proceeds on to query block  74  where the H pure  is compared with a desired level H pref . If the query answers affirmative, the method  60  loops back to block  72  and continues to monitor the hydrogen purity H pure  in the generator  12 . This loop continues generally until method  60  is externally terminated or paused, or until the query of block  74  is answered negatively. 
     If the answer to the query in block  74  is negative, this is indicative that the purity level of the hydrogen gas in the generator has reached a level desired by the operator. The method  60  then proceeds on to block  76  where a control signal is passed from the purity monitor  18  to the valve  20 . The valve  20  closes and the venting of gas from the generator  12  stops. Method  60  then proceeds on to block  78  where hydrogen production ceases. In the preferred embodiment, when the valve  20  is closed, the pressure will rise in the generator. This pressure rise will be detected in the sensor  30 , and when the pressure in the generator reaches the desired pressure P des  the hydrogen generator  24  stops production of hydrogen gas. Typically, the desired pressure P des  is between 30 psi and 75 psi. Method  60  then continues back to block  64  to start the process again. It will be appreciated that method  60  is performed repetitively during the operation of the system  10 . 
     Referring to  FIGS. 3 and 6 , an alternate electrical power generation control method  80  of  FIG. 6  will now be described. After starting at block  82 , method  80  proceeds to block  84  where the hydrogen purity level the H pure  of the gas in the generator  12  is sampled measured. Method  80  then proceeds to query block  86  where the parameter H pure  is compared with the desired purity level H pref . If the query returns a negative response, the method  80  loops back to block  84  and the method continues until terminated or paused by the operator. 
     If the query block  86  returns an affirmative response, the method  80  continues on to block  88 . In block  90 , purity monitor  18  sends a control signal to the hydrogen generator  24  which causes the hydrogen generator  24  to initiate hydrogen production at a predetermined flow rate and pressure P des . Typically, the desired pressure P des  is between 30 psi and 75 psi, with a preferred pressure of 45 psi. In the preferred embodiment, the desired pressure P des  is greater than the relief pressure P relief  of valve  20 . 
     After hydrogen gas production is initiated, the method  80  continues on to query block  91  where P relief  and P gen  are introduced into the following query:
 
Is P gen &gt;P relief ?
 
     Here, the parameter P gen  represents the pressure inside the generator  12  and the parameter P relief  represents the pressure setting at which the valve  20  will open allowing the gas from the generator  12  to vent to the atmosphere. If the query in box  91  returns a negative, the method  80  loops back to box  90  and hydrogen continues to be generated and provided to the generator  12 . The method  80  continues until terminated or paused by the operator. 
     If the query in box  91  returns an affirmative response, indicating that the pressure inside the generator has reaches a value greater than the relief setting on the valve  20 , the method  80  continues on to box  92  and the valve  20  is opened. The method continues on to monitor the hydrogen purity level H pure  in box  93  and compare the measured level with the desired purity level in box  94  in a similar manner as has been described herein above. 
     Once the purity of the hydrogen gas in the generator achieves the desired purity level, the method  80  continues on to block  96  where the purity monitor  18  transmits a control signal to the hydrogen generator  24  causing the hydrogen generator to cease production of hydrogen gas. Once the hydrogen generator stops producing gas, the method  80  continues on to box  98  where the valve  20  will close once the pressure in the generator drops below the predetermined threshold. 
     Method  80  then continues back to block  84  to start the process again. It will be appreciated that method  80  is performed repetitively during the operation of the system  10 . 
     Referring to  FIGS. 4 and 7 , an alternate electrical power generation control method  100  of  FIG. 7  will now be described. After starting at block  102 , method  100  proceeds to block  104  where the hydrogen purity level the H pure  of the gas in the generator  12  is measured. Method  100  then proceeds to query block  106  where the parameter H pure  is compared with the desired purity level H pref . If the query block  106  returns an affirmative response, the method  100  proceeds to block  124  where the vent valve  20  is opened and gas from the generator  12  is vented to the atmosphere. The method  100  then proceeds generate hydrogen gas in block  126 . The purity level of the hydrogen gas in the generator  12  until query block  130  returns a negative response. The method  100  then proceeds to block  132  where the valve  20  is closed and the generation of hydrogen gas ceases in block  134 . If the query block  106  returns a negative response, the method  100  proceeds on to block  108  which opens the valve  36  allowing hydrogen gas to flow from the hydrogen generator  24  towards the tank  40 . The method  100  then optionally compresses the hydrogen gas in block  110  and proceeds to fill tank  40  in block  112 . 
     While the tank  40  is filling, the method  100  monitors the pressure P tank  in the tank  40 . The tank  40  will also have a maximum working pressure rating P max . Typically, the tank  40  will have a maximum pressure rating between 2000 psi and 10,000 psi, with a preferred rating of 2,400 psi. Method  100  proceeds to block  114  where P tank  and P max  are introduced into the following query:
 
IS P tank &lt;P max ?
 
     If the query block  114  responds affirmatively, the method  100  proceeds query box  118  where the hydrogen purity level is compared to the desired level. If the query block  118  returns an negative response, which would indicate that the generator required replenishment of pure hydrogen gas., the method  100  returns to block  112  in order to continue filling the tank with hydrogen. If the query in block  118  returns an affirmative response, the method  100  then proceeds on to block  120  where the valve  36  is closed and then onto block  122  where the vent valve  20  is opened and gas from the generator  12  is vented to the atmosphere. Method  100  then proceeds through blocks  126 - 134  to replenish the generator with hydrogen gas to the appropriate purity level in the same manner as was described herein above with respect to method  60  and blocks  72 - 78 . 
     It should be appreciated that the process steps in blocks  128 - 134  may also be accomplished using the alternate method described with respect method  80 . In addition, in applications where the hydrogen generator  24  is continuously producing gas for the generator  12 , it is within the contemplation of this invention that the hydrogen generator  24  provides hydrogen gas to both the tank  40  and the generator  12  simultaneously with preference being given to supplying the generator  12 . 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, may modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention.