Abstract:
The microturbine engine that is typically utilized to power an electrical generating system and/or boiler, chiller and the like includes a second boiler and a by-pass system for providing heated water at two different levels or where one of the boilers provides steam. The turbine exhaust is utilized as the heat transport medium and is directly connected to one of the boilers while the other is connected to the recuperator. The system can optionally provide cooling to the electrical and electronic components of the system by providing a water circuit for leading water into the electric and electronic components prior to feeding the boilers. The system is designed to assure that the delta heat difference between the medium being heated and the waste heat of the turbine is sufficient so that the heat exchange will be done efficiently.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to microturbines engines and more particularly to a system for generating hot water in a boiler and for selectively boosting the temperature of the medium for heat exchange relation by utilizing the turbine exhaust.  
         BACKGROUND OF THE INVENTION  
         [0002]    As one skilled in this art appreciates the microturbine has in the last few years become extremely useful for generating electricity. Typically, the microturbine comprises a compressor, combustor, turbine and a recuperator which serves to pre-heat the compressor discharge air prior to being injected into the combustor. The work produced by the turbine serves to rotate the armature of the electrical generator and an invertor converts the electrical current and controls its frequency. Details of the microturbine can be obtained by referring to co-pending patent application Ser. No. 09/934,640 filed on Aug. 22, 2001 by William R. Ryan entitled RECUPERATOR FOR USE WITH TURBINE/TURBO-ALTERNATOR, published and U.S. Pat. No. 6,314,717 granted to Teets et al on Nov. 13, 2001 entitled ELECTRICITY GENERATING SYSTEM HAVING AN ANNULAR COMBUSTOR both of which are commonly assigned to the assignee of this patent application, and both being incorporated by reference herein. Also, for more details of this invention reference should also be made to the microturbines manufactured by the assignee, Elliott Energy Systems, Inc., of Stuart, Fla. and, particularly of the types exemplified by Model Number TA-80.  
           [0003]    In certain residential or commercial applications the microturbine can also be utilized for powering a boiler for obtaining hot water or powering a chiller that can be used in a refrigeration absorption system. A simple system for obtaining these objectives is illustrated in FIG. 1 where a boiler is connected to the discharge of the recuperator. The temperature of the engine working medium discharging from the recuperator is typically over 500 degrees Fahrenheit and obviously, this temperature can be utilized wherever heat is needed, given that the heat can be transported efficiently and economically. The simple boiler application will be described hereinbelow in connection with the details of this invention.  
           [0004]    This invention contemplates that the microturbine system includes a microturbine engine, a recuperator, an electrical generator and a boiler as described in the immediate above paragraph. This invention augments the above-described simple microturbine/boiler system by incorporating a second boiler. The second boiler can be utilized for the purpose of obtaining hot water at a higher temperature that is available in the single boiler system or obtaining steam. In this system the second boiler is optionally preset so that both of the boilers are in continuously or alternatively is turned-off one of the boilers is rendered inoperative, i.e. all of the turbine exhaust flows into the recuperator and then to the first boiler and by-passes the second boiler. This invention also contemplates utilizing the water for cooling purposes of some of the systems components prior to the water flowing to the boiler.  
           [0005]    Another aspect of this invention is the use of the by-pass system to boost the temperature of the waste heat when used as a heat transport medium so as to assure that the delta temperature between this medium and the water is sufficient whereby efficient heat transfer will be effectuated. As one skilled in this technology appreciates, as the efficiency of the microturbine engine increases, the temperature of the exhaust being emitted from the turbine of the microturbine engine becomes reduced. Hence, given the need for a particular delta temperature in the indirect heat exchange relationship occurs, and the temperature of the engine working medium waste is not sufficient in the boiler, the amount of engine working medium waste can be throttled to provide the necessary delta to achieve efficient heat transfer.  
           [0006]    This invention should not be confused with the microturbine bypass system described and claimed in U.S. patent application contemporaneously filed by Gregory Brian Dettmer entitled MICROTURBINE DIRECT FIRED ABSORPTION CHILLER, and assigned to a common assignee. This system utilizes the recuperator exhaust heat to power a direct fired absorption chiller which would otherwise be unacceptable without the provisions of the Dettmer invention. In the Dettmer patent application, supra, the system includes a by-pass system for the recuperator, and is uniquely designed to provide a predetermined constant temperature for the direct fired absorption chiller. As mentioned above this by-pass system allows the use of a microturbine which was heretofore not practical since the available temperature for powering the chiller fluctuated.  
           [0007]    In the present invention, the purpose of the by-pass system for the recuperator is to flow the turbine exhaust into a heat exchanger or boiler and to divert the turbine exhaust when the heat exchanger is not in operation or is not required. To this end the turbine exhaust is directed directly into the recuperator rather than being directed into the heat exchanger. Obviously, when the temperatures of the working fluids that are in indirect heat exchange relation with each other are at or near parity, the ability to transfer heat is difficult and at best, inefficient. This system serves to increase the output temperature of the recuperator by utilizing the high temperature exhaust from the turbine. That is to say, that the higher temperature turbine exhaust fluid is utilized to boost the usable output temperature. Consequently, the available temperature of the fluid discharging from the recuperator is efficiently increased by virtue of this invention so that useable temperature required for heat transfer is attained.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of this invention is to provide for a microturbine engine that utilizes a recuperator and is designed to generate electricity and run a water boiler to include in the system a second boiler that serves to either obtain hot water that may be hotter than the water in the first boiler and/or steam.  
           [0009]    A feature of this invention is to mechanically adjust the flow of turbine exhaust into the second boiler by-passing that amount of flow entering the recuperator or alternatively, by-pass the second boiler so that all of the turbine exhaust flow enters the recuperator.  
           [0010]    A still further feature of this invention is to provide a control system that throttles the turbine exhaust to maintain the desired temperature in the first and second boiler.  
           [0011]    A still further feature of this invention is to provide a system having at least one boiler that utilizes the water from the water source to cool certain components of the microturbine system before entering the boiler for generating hot water.  
           [0012]    A still further feature of this invention is to provide for a microturbine as described a by-pass system that boost the temperature of the recuperator/boiler so as to efficiently transfer heat when the temperature of the heat exchange transport fluid is at or close to parity of the other fluid that is in heat exchange relationship. 
       
    
    
       [0013]    The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic illustrating the details of a microturbine system utilized for generating electricity and modified to power a boiler for generating hot water;  
         [0015]    [0015]FIG. 2 is a schematic illustrating the microturbine system depicted in FIG. 1 and including a second boiler and by-pass system made in accordance with this invention;  
         [0016]    [0016]FIG. 3 is a schematic illustration of the system depicted in FIG. 2 modified to provide a controller to maintain the desired heat transfer to both boilers and to assure that sufficient delta heat is maintained between the fluids in heat exchange relation; and  
         [0017]    [0017]FIG. 4 is a schematic illustration of another embodiment of this invention where the second boiler is mounted in tandem with the first boiler. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    While this invention pertains to a microturbine system powering an electrical generator it is to be understood that the microturbine can be utilized for other types of systems and hence, is not limited to an electrical generating system. The microturbine engine has become popular in the last several years and essentially is a jet engine that includes a turbine, compressor, combustor and recuperator. The microturbine is a miniaturized gas turbine engine that in recent years have been almost totally utilized for powering electrical generators. In certain configurations, the turbine and compressor are attached back-to-back on one end of a shaft that is common to the shaft connecting the armature of the electrical generator. Fuel and relatively hot pressurized air discharging from the compressor and pre-heated by the recuperator are fed to an annular combustor where they are combined and combusted to further heat and accelerate the engine&#39;s working medium for powering the turbine. The engine working medium is adiabatically expanded in the turbine for extracting energy which, in turn, is utilized for rotating the compressor and armature. The working medium after leaving the turbine is directed to the recuperator where it is placed in indirect heat exchange with the compressor discharge air prior to being admitted into the combustor. The turbine exhaust is ultimately discharged from the recuperator. As mentioned above further details of the microturbine reference should can be had by referring to co-pending patent application Ser. No. 09/934,640 filed on Aug. 22, 2001 by William R. Ryan, supra and U.S. Pat. No. 6,314,717 and the microturbines manufactured by the assignee, Elliott Energy Systems, Inc., of Stuart, Fla. and, particularly of the types exemplified by Model Number TA-80.  
         [0019]    Referring now to the FIG. 1, which is a microturbine system designed to generate electricity to which is added a boiler for generating hot water. The microturbine engine is generally illustrated by reference numeral  10  and includes a compressor  12  for compressing the air admitted therein which is preheated by being placed in indirect heat exchange with the turbine discharged gases in the reucperator  14 . The preheated compressor discharge air is combined with a fuel, which could either be a liquid or a gas, in the combustor  16  where it forms a gaseous engine working medium for powering the turbine  18 . The turbine  18  drives the compressor  12  and the turbine exhaust gases are routed to the recuperator  14  where it is placed in indirect heat exchange which serves to preheat the compressor discharge air. The power generated by the microturbine  10  serves to power the alternator  20  which through an inverter and associated electronic circuitry  22  produces the desired electrical output. This system just described is an illustration on how the microturbine/electrical generating system can simply be modified to take advantage of the energy of the high temperature turbine exhaust and obtain hot water by routing the exhaust through heat exchanger or boiler  24  which is indirect heat exchange with the water circuit  26 .  
         [0020]    According to this invention and as shown in FIG. 2, another boiler  28  is added to the microturbine system in order to obtain either water at a hotter temperature than is available at the boiler  24  or steam. For this modified system by-pass valve  30  is connected between the boiler  28  discharge and the discharge end of the turbine  18  (the same reference numerals are used to identify the same or similar elements depicted in all of the Figs.) so that opening valve  30  will dump turbine exhaust gases directly in the heat exchanger or boiler  28 . Hence, the waste heat from the turbine can be utilized directly in the heat exchanger  32  or directed into the recuperator  14  or a portion of the water heat from the turbine can be directed in the recuperator  14  while the remaining portion can be directed to boiler  28 . By-pass valve  30  may be either operated manually by adjusting handle  32  or automatically (see FIG. 3) by including a suitable temperature sensor  34 , a comparator or controller  36 , which could be digital or analog, and an actuator  38 . All of these elements are commercially available and a description thereof, for the sake of convenience and simplicity, is not included herein. Suffice it to say that the temperature sensor  34  measures the temperature of the waste heat and relays a signal to the controller  36 . The controller that has been set to a particular temperature schedule, measures the difference between the actual temperature measured by the temperature sensor  34  and a desired temperature. This output of the comparative signal is then relayed to actuator  38  that adjusts the by-pass valve to proportion the flow of waste heat to assure the proper temperature of the waste heat in the heat exchanger and hence maintain a difference in heat between the waste heat and the medium being heated so as to assure that the heat transfer efficiency is satisfactory.  
         [0021]    In this system, the microturbine not only powers the alternator for generating electricity, it is also functions to provide heat and cooling to the system components as is needed and as is compatible with the efficiency of the system. As disclosed herein, the fluid flow circuitry for both hot waste exhaust and water will be described immediately hereinbelow, it being understood that the water can be obtained from the public available water system or from storage containers or it may be from a process where water is cycled continuously. The water circuit flows from the inlet  40 , through line  42  and is divided by the divider valve  44  to flow in heat exchanges  46  and  48  for cooling the alternator and inverter  20  and electronic components  22 , respectively, and then flows through line  50  and combines with the divided flow in line  52  and directed into boiler  24 .The water in boiler  24  is in indirect heat exchange with the hot waste heat discharging from recuperator  14  An outlet valve  56  serves to tap hot water from boiler  24  as desired and the size of outlet valve is selected so that continuous water flow via line  58  is directed to the boiler  28 . Hot water or steam is tapped from boiler  28  vial line  60 . It is apparent from the foregoing that the water circuit not only cools the electrical and electronic equipment, but also allows tapping hot water from boiler  24  and hotter water or steam from boiler  28 .  
         [0022]    The heat is delivered to the boiler  24  via lines  62 ,  64  and  66 . The temperature of the waste heat in line  66  is predicated on the output of the recuperator  14 . Obviously, the main purpose of recuperator  14  is to pre-heat the compressor discharge air and the remaining energy in the waste heat fluid serves to power the boiler  24  and hence, the temperature of the water in the boiler  24  is determined by the outlet temperature of the recuperator  14  and the flow of the waste heat is continuous, and hence, since the residence time of the waste heat fluid in boiler  24  is limited and the amount of heat at the discharge end of the recuperator is limited, the boiler  24  is incapable of reaching temperature sufficient to obtain steam.  
         [0023]    The inclusion of the boiler  28  in accordance with this invention, augments the system by generating water that can be hotter than the water in boiler  24  or can be steam. The by-pass system serves to control the heat transfer in boiler  28 . For example, valve  30  can be fully opened and permit all of the turbine exhaust fluid to enter the boiler  28 . Since the residence time of the water remaining in the boiler  28  is determined by tapping the water in line  60 , the temperature of this water can easily reach the boiling temperature of 212° F. and become saturated to produce steam.  
         [0024]    It is apparent from the foregoing description that the water medium is in indirect heat exchange with the turbine discharge air as it flows through the recuperator  14 , the boilers  24  and  28  and since the by-pass valve can control the amount of heat transported to either or both boilers, the system can be designed to assure that the use of this energy is done efficiently. Hence, where the temperature difference between the medium being heated (water) and the waste heat is close to each other, the by-pass valve is utilized to assure that the delta temperature is sufficient to obtain effective heat transfer by boosting the boiler&#39;s working medium by adding turbine exhaust directly to the boiler  28 .  
         [0025]    [0025]FIG. 4 exemplifies another embodiment of this invention where the boilers are mounted in tandem or “piggy back” to lower the cost of the system and make it more efficient. In this embodiment, the function of boilers  24  and  28  are combined in the tandem boiler  70 . Both systems, i.e. the system depicted in FIG. 3 and the system depicted in FIG. 4 are identical to each other. The only difference is that the boiler  70  contains two water coils that are in indirect heat exchange with the turbine discharge air and the turbine discharge air after being spent in the recuperator  14 . For the sake of simplicity and convenience details of the description of this system is omitted and the description of FIG. 3 is incorporated herein by reference.  
         [0026]    What has been shown by this invention is a system for obtaining higher temperature water and/or steam by adding a second boiler and a by-pass valve for regulating the turbine waste heat that is in heat exchange relation with the water in the additional boiler. The system is designed to assure good heat transfer notwithstanding the fact that the efficiency of the microturbine engine is increasing. Hence, the turbine exhaust is utilized to the boost of the output temperature of the working fluid in the boiler to assure that the temperature difference between it and the water will provide efficient heat transfer.  
         [0027]    Although this invention has been shown and described with respect to detailed embodiments thereof, it will be appreciated and understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.