Patent Publication Number: US-2010115912-A1

Title: Parallel turbine arrangement and method

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to gas turbines. More particularly, the subject matter relates to a parallel gas turbine arrangement. 
     A typical gas turbine drives a generator that provides power to an electrical power grid. The rotational speed of the turbine is locked to a frequency of the grid. This grid frequency remains relatively constant, which in the United States is 60 hertz. During overloading conditions of the grid, however, the grid frequency begins to drop. The drop is sensed by control systems at power plants, which quickly increase power generation and supply to the grid to reduce further drops in grid frequency. During such frequency drops, however, turbines connected to the grid, decrease rotational speed and stay in sync with the grid frequency. This reduction in rotational speed of the turbine slows down a compressor that is rotationally driven by the turbine and consequently reduces airflow through the turbine. This reduced airflow through the turbine reduces efficiency and power generation by the turbine at times when it is greatly needed. 
     As a result of these principles, the art is always receptive to turbine arrangements with increased output, flexibility and efficiency. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a parallel turbine arrangement includes a compressor and a first turbine in operable communication with the compressor, and a second turbine in operable communication with the compressor. 
     According to another aspect of the invention, a method for increasing operational flexibility of a power plant includes compressing fluid into a compressed fluid flow, dividing the compressed fluid flow into a first stream and a second stream, feeding a first turbine with the first stream and feeding a second turbine with the second stream. 
     According to yet another aspect of the invention, a parallel turbine arrangement includes a compressor having a compressor discharge flow divided into a plurality of streams, and each of the plurality of streams is in operable communication with a separate turbine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  depicts a schematic view of a parallel turbine arrangement disclosed herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A detailed description of the hereinafter described embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figure. 
     Referring to  FIG. 1 , an embodiment of a parallel turbine arrangement  100  is illustrated. The turbine arrangement  100  includes a single compressor  110  that feeds air to two separate turbines  120 ,  130 . Having the two separate turbines  120 ,  130  operate with a single compressor  110  allows one of the turbines, turbine  120 , to be in rotational sync with the compressor  110  and the other turbine  130 , rotating a generator  300 , to be in rotational sync with the frequency of a power grid  140 . This allows the rotation of the compressor  110  and the frequency of the power grid  140  to be completely independent of one another. This decoupling of the compressor  110  from the power grid  140  allows compressor  110  and turbine  120  to operate nearer to their peak rotational efficiency regardless of conditions, such as, the frequency of the power grid  140 , the ambient temperature and the density of a compressor intake fluid  150 , for example. 
     Operating the two turbines  120 ,  130  with the single compressor  110  includes ducting and proportioning fluid from the compressor  110  to each of the two turbines  120 ,  130 . The ducting and proportioning of compressed fluid flow  160  includes dividing the compressed fluid flow  160  into a plurality of streams  170 ,  180 , running through a corresponding plurality of ducts  190 . In the embodiment shown in  FIG. 1 , a first stream  170  feeds a first combustor  210  that in turn feeds a first turbine  120 . Similarly, a second stream  180  feeds a second combustor  220  that in turn feeds a second turbine  130 . The invention is not limited to a two turbine arrangement, however, and may include any number of parallel turbines. Additionally, the streams  170 ,  180  may have generally equal volume flow rates, or substantially different volume flow rates. It is to be understood that the volume flow rates of the streams  170 ,  180  may be tailored for specific applications without departing from the scope of the invention. 
     At least one proportioning device  230  provides an operator with the flexibility of tailoring the volume flow rate of the compressed fluid flow  160  into each of the turbines  120 ,  130 . The proportioning device  230  divides the fluid flow  160  between the two ducts  190 . The proportioning device  230  may be a valve, baffle, louver or any other mechanism for regulating volume flow rate of the compressed fluid flow  160 . The parallel turbine arrangement  100  may also include any number of the proportioning devices  230  to regulate the compressed fluid flow  160  into the corresponding ducts  190 . 
     In the embodiment herein described, the first turbine  120  is in rotational sync with the compressor  110  and provides the compressor  110  with power. Thus, the first turbine  120  is also referred to herein as a compressor turbine  120 . The compressor turbine  120  is fed by the first stream  170  also referred to herein as the compressor turbine stream  170 . It is to be understood, however, that the compressor turbine  120  may additionally be configured to provide power to devices other than the compressor  110 . Further, the second turbine  130  is turning the generator  300  in rotational sync with the power grid  140  and provides the power grid  140  with power. Thus, the second turbine  130 , also referred to herein as an output turbine  130 , is fed by the second stream  180 , also referred to as the output turbine stream  180 . The power grid  140  includes a system for distributing electricity to consumers. However, it should be understood that the output turbine  130  might be configured to provide power to any other output source or device other than the generator  300 /power grid  140  or in addition to the generator  300 /power grid  140 . 
     The foregoing adjustability of the compressor turbine stream  170  and the output turbine stream  180 , among other things, allows an operator to independently configure the speed and power generation of each of the turbines  120 ,  130 . The rotational speed of the output turbine  130  and generator  300  is fixable to a grid frequency of the power grid  140 . The grid frequency is the frequency at which alternating current electricity is transmitted from a power plant to a user via the power grid  140 . The power grid  140  determines the grid frequency and each power plant needs to supply power to the grid at that frequency. Embodiments disclosed herein allow the rotational speed of the compressor turbine  120  to be configured independently of the grid frequency. This decoupling allows the rotational speed of the compressor  110  and the overall power output of the parallel turbine arrangement  100  to be configured independently of the grid frequency of the power grid  140 . As such, the rotational speed of the compressor  110  may be increased or decreased independently of any relationship to the grid frequency. This decoupling further allows an operator to produce constant or even increased power output from the parallel turbine arrangement  100  even during times when the grid frequency drops. This also allows for greater overall operational flexibility and efficiency of the parallel turbine arrangement  100 . 
     Additional operational efficiencies can be gained through porting of exhaust from the two turbines  120 ,  130  to a heat recovery steam generator  240 . The heat recovery steam generator  240  recovers heat from a combusted output stream  250  to generate steam  260  to drive a steam turbine (not shown). This combination of the parallel turbine arrangement  100  with the heat recovery steam generator  240  is referred to as a combined cycle power plant. In one embodiment, at least one of the output streams  250  includes a bypass valve  270  that is configured to allow the combusted output stream  250  to bypass the heat recovery steam generator  240 . The bypass opening  270  may be a valve, baffle, louver, door or any other mechanism for regulating volume flow rate of the output stream  250 . 
     In another embodiment, at least two of the turbines  120 ,  130  use common parts. For example, the two turbines  120 ,  130  may use a common combustor swozzle, transition piece, compressor discharge can, turbine bucket, or any other component. Using the same components enables cost savings driven by volume production. Additionally, the turbines  120 ,  130  may be smaller in size and thereby subjected to less operating stress than a corresponding single turbine system having the same overall power output. Centrifugal stresses on the turbine buckets (not shown) are one such load that is reduced by embodiments of the present invention. 
     Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” and their derivatives are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first” and “second” are used to distinguish elements and are not used to denote a particular order. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.