Abstract:
A control method and mechanization is disclosed to bleed compressor air in order to control the gas turbine of a turbo heater. Compressed air may selectively bleed with a control value in order to increase or decrease the efficiency of the gas turbine unit. Additionally, the control system enables the bleed air system allows to re-circulate compressed air to mix with the combustion air and provide a pre-heat thereof. The control system further enables re-direction of the combustion feed stream into the exhaust gas stream to promote complete combustion of the unburned fuel and combustion by-products in a catalytic converter downstream of the gas turbine to provide a breathable exhaust gas from the turbo heater.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/092,005, filed on Dec. 15, 2014. The entire disclosure of the above application is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to engine control of a micro gas turbine engine, and more particularly relates to a control method to bleed turbine compressor air for controlling the exhaust gas temperature of a micro gas turbine heater. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0004]    Gas turbine engines are typically used in work-generating applications in the form of a rotating drive shaft, and engine control is generally optimized for maximum shaft work per unit of fuel. In these applications bleed air is commonly used with the objective to power accessories or control cycle parameters such as surge. In all of these cases, it is recognized that the bleed air reduces the thermal efficiency of the gas turbine in terms of shaft work per unit fuel. This efficiency loss is typically addressed by using a “bleed-less” engine technology. 
         [0005]    Recent efforts have shown that gas turbine engines can be useful in heat generation applications. In particular, a small gas turbine engine has proven to be relatively trouble-free and extremely efficient such that it makes an excellent heater. Such a heater application is different from the conventional work-generating applications in that the efficiency objective is heat output rather than shaft work. As such varying the bleed air to control heat output certainly changes the energy balance of the system but results in no loss of efficiency since any shaft work loss is turned into useful heat. 
         [0006]    Accordingly, it is desirable to provide a method to bleed turbine compressor air for controlling the exhaust gas temperature of a gas turbine heater. In addition, it is desirable to a control algorithm for bleeding turbine compressor air to control the exhaust gas temperature of a gas turbine heater. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       SUMMARY 
       [0007]    In accordance with the present disclosure, a heater module includes an internal combustion micro turbine with no external or exposed flame, and burning of the fuel is configured to be contained entirely within the combustion walls. The heater module is capable of converting over 90% of any suitable fuel (e.g. an ultra-low sulfur Diesel fuel) to usable heat. During operation the diesel fuel is vaporized rather than burned as a liquid, before it enters the combustion chamber. A control algorithm and mechanization of the heater module enable precise control of the exhaust gas temperature through turbine compressor air bleeding. As a result, combustion is continuously sustained which is highly efficient and extremely clean. Output from the micro turbine produces clean exhaust. An after-treatment device in the form of a catalytic converter reduces the emission in the exhaust such that clean, breathable air is output from the heater module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. Thus, the selected embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0009]      FIG. 1  is a schematic illustration of an embodiment of the gas turbine heater showing a mechanization for bleeding turbine compressor into the bypass stream of the gas turbine heater; 
           [0010]      FIG. 2  is a schematic illustration of an embodiment of the gas turbine heater showing a mechanization for bleeding turbine compressor into the compressor intake for pre-heating the turbine inlet air; and 
           [0011]      FIG. 3  is a schematic illustration of an embodiment of the gas turbine heater showing mechanization for bleeding turbine compressor into the turbine exhaust stream of the gas turbine heater. 
       
    
    
       [0012]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0013]    The present disclosure provides a method and control system for varying the bleed air from the turbine compressor to control heat output. The bleed air can be reintroduced or recirculated at various locations within the turbo heater without any result in loss of efficiency since the heat associated with the bleed air is recovered within the system. Example embodiments will now be described more fully with reference to the accompanying drawings. There is no intention to be limited by any principle presented in the preceding background or the following detailed description. Like reference numbers will be used to indicate the same or similar components in various embodiments. 
         [0014]    Turbo heater  10  is a diesel fueled self-contained and self-sustaining heating system for supplying heated air in remote locations. Turbo heater  10  may also be equipped with a generator set (not shown) driven by the shaft assembly for providing electrical power. The turbo heater includes a micro turbine  12  designed to supply the majority of its energy as heat in the form of exhaust gases, and a minor amount as shaft power used to rotate the turbine compressor and drive an auxiliary fan  26 . The configuration of turbo heater  10  provides an economical construction which is especially designed for reduced manufacturing costs. The internal aerodynamics, such as the turbine and compressor wheels, uses well-developed technology. In this regard, a peak cycle temperature of about 1500° F. is preferred to allow the use of economical materials for the high temperature components. 
         [0015]    With reference now to  FIGS. 1-3 , a turbo heater  10  includes a micro turbine engine  12  and one or more heat exchange elements  14 ,  28  which are supported with in a housing  16 . Gas turbine engine  12  draws ambient combustion air (A C ) through a compressor  18 , receives fuel, preferably an ultra-low sulfur Diesel fuel, from a fuel system (not shown) to form an air-fuel mixture which is drawn into the a combustor  20 . In the combustor  20  the air fuel mixture is burned in a combustor  20  to form an exhaust gas which exits the combustor  20  and expands the through a turbine  22 . As such, gas turbine engine  12  provides a source of heat, as well as a source of rotary power. The rotating components of the gas turbine engine  12 , namely compressor  18  and turbine  22 , are mounted on a high-speed shaft assembly  24 . The shaft assembly  24  may also be coupled through a reduction gear assembly or gearbox (not shown) to a fan  26 . The fan  26  functions to draw intake air (A I ) which includes combustion air (A C ) well as bypass air (A B ) into the housing  16 . As schematically shown in the figures, the compressor  18  and the turbine  22  are mounted on a common shaft assembly  24 . One skilled in the art should, however, recognize that the shaft assembly of gas turbine engine  12  may include multiple, separate shafts. Likewise, the fan  26  is illustrated as an axial fan, but may take any form which functions to draw intake air into the turbo heater housing. 
         [0016]    A heat exchange element  14  is used to recover the resulting heat in the exhaust gases and transfer the resulting heat to it to heated air (A E ) exhausted from the turbo heater  10 . The heat exchange element  14  preferably includes a suitable catalytic converter  28  which reduces the carbon monoxide and other exhaust emissions in the exhaust gases (E T ) to discharge essentially breathable heated air (A E ) from the turbo heater  10 . 
         [0017]    The turbo heater  10  is provided with an engine controller  30  which is operably coupled to the gas turbine engine  12 . The turbo heater  10  further includes an engine speed sensor  32  for measuring the engine speed. In one embodiment, the engine speed sensor may be a tachometer measuring the rotational speed of the shaft assembly  24 . The turbo heater  10  also includes a temperature sensor  34  configured to measure a temperature at that location and send a signal representative of the measured value to the engine controller  30 . In one embodiment, the temperature sensor is a thermocouple arranged at the discharge of the turbine  22 . While the control algorithm of the present disclosure is illustrated and described as using the turbine exhaust temperature, one skilled in the art will appreciate that use a temperature measurement at any turbine location. Further details concerning the components and configuration of the turbo heater  10  in general, as well as the engine controller  30  are described in U.S. Pat. No. 6,073,857, U.S. Pat. No. 6,161,768, U.S. Pat. No. 6,679,433 and U.S. Pat. No. 8,327,644, the disclosures of which are expressly incorporated by reference herein. 
         [0018]    With continued reference to  FIG. 1 , the turbo heater  10  includes a bleed air circuit  40  having a bleed air control valve  42  in fluid communication with the feed line  44  from the compressor  18  to the combustor  20 . The bleed air control valve  42  is operable to re-direct air from the feed line  44  to a vent line  46  which dumps air from the compressor  18  into the bypass stream flowing between the turbine  12  and the housing  16 . In this configuration, the bleed air is vented into the by-pass stream (A B ) such that the heat associated with the bleed air is recovered in the heater exhaust. In this configuration, the bleed air is vented to the by-pass stream when heat generation from the gas turbine is required. While the bleed air control valve  42  is shown in the teed line  44  from the compressor  18  to the combustor  20 , one skilled in the art will appreciate that the bleed air control value  42  may re-direct bleed air from the compressor  18  at any location where the pressure differential in the vent line  46  provides air flow rate of bleed air into the by-pass stream (A B ). 
         [0019]    With reference to  FIG. 2 , turbo heater  10  is substantially similar to that shown in  FIG. 1 , but includes a bleed air circuit  40 ′ in fluid communication with the feed line  44  from the compressor  18  to the combustor  20 . The bleed air control valve  42 ′ is operable to bleed air from the feed line  44  to a recirculation line  46 ′ which re-directs bleed air into the inlet of the compressor  18 . In this configuration, the bleed air is re-circulated into the compressor intake to provide an intake air pre-heat when the ambient temperatures are extremely low. Additional sensors, such as temperature sensor  34 . 1  in the compressor  18  and/or temperature sensor  34 . 2  at the inlet of the gas turbine  12 , are configured to measure a temperature at those locations and send a signal representative of the measured value to the engine controller  30 . Again, one skilled in the art will appreciate that the bleed air control value  42 ′ may re-direct bleed air from the compressor  18  at any location where the pressure differential in the recirculation line  46 ′ provides sufficient air flow rate of bleed air into the compressor inlet (A C ). 
         [0020]    With reference to  FIG. 3 , the turbo heater  10 , and in particular micro turbine  12  includes a bleed air circuit  40 ″ in fluid communication with the feed line  44  between the compressor  18  and the combustor  20 . The bleed air control valve  42 ″ is operable to re-direct air from the feed line  44  through the by-pass line  46 ″ into the turbine exhaust stream (E T ). In this configuration, the bleed air is passed through the catalytic convertor  28  for enriching oxygen/air content in the exhaust stream (E T ) for promoting the catalytic reaction and recovering heat in the heat exchange element  14 . An additional sensor  34 . 3 , such as a temperature sensor and/or an exhaust gas sensor, is configured to measure a temperature or exhaust gas quality at that location and send a signal representative of the measured value to the engine controller  30 . Again, one skilled in the art will appreciate that the bleed air control value  42 ″ may re-direct bleed air from the compressor  18  at any location where the pressure differential in the by-pass line  46 ″ provides sufficient air flow rate of bleed air into the exhaust stream (E T ). 
         [0021]    Various embodiments of the turbo heater  10 , and in particular the sensors  34 ,  34 . 1 ,  34 . 2 ,  34 . 3  and the bleed air circuit  40 ,  40 ′,  40 ″ are described above and illustrated in  FIGS. 1-3 . One skilled in the art will appreciate that a gas turbine  12  will likely include multiple sensors for use in the operation and control of the turbo heater  10 . Likewise, the gas turbine  12  may have a bleed air configuration circuit which includes one or more bleed air circuits  40 ,  40 ′,  40 ″ as described above. As such, a multiple directional control valve or multiple control valves may be used to re-direct bleed air into the by-pass stream (A B ) or the turbine exhaust stream (E T ) or to re-circulate bleed air into the compressor inlet (A C ). 
         [0022]    As noted above, the turbo heater  10  includes an engine controller  30  in communication with various sensors and control devices (e.g., valves) associated with the turbo heater  10 . The engine controller  30  may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the turbo heater  10 . The engine controller  30  may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus is configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the engine controller  30 . 
         [0023]    A program stored in the memory system is on a computer readable medium or machine readable medium known in the art, and which should be understood to be a computer program code residing on a non-transitory carrier. In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like. 
         [0024]    Instead of an engine controller  30 , the turbo heater  10  may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle. The engine controller  30  is generally configured to carry out many different tasks, including those set forth in the control algorithm detailed below. 
         [0025]    The control algorithm executed on the engine controller  30  may take into account various operating states of the turbo heater  10  with the objective to optimize heat generation from the turbo heater  10 . For example, a call for heat command requires additional heat generation from the gas turbine  12 . The call for heat may result from a user input to increase the heat output from the turbo heater  10  or from the engine controller  30  to maintain the desired operating temperature of the gas turbine  12 . Under this condition, the engine controller  30  will query (or recall from memory) the current speed of the shaft from the speed sensor  32  and the current temperature of the turbine exhaust from sensor  34 . Based on these operating conditions, the engine controller  30  will adjust the bleed air control valve  42  to affect the call for heat. For example, when a call for more heat is received and the turbine  12  is operating at a relatively low engine speed, the bleed air control valve  42  is adjusted to open and re-direct a portion of the compressor air off of the feed line  44 , which will cause the gas turbine to speed up and generate more heat. Conversely, when a call for less heat is received, the bleed air control valve  42  will close down causing the gas turbine  12  to run cooler and slower. A full range of value setting are exercised on the basis of the engine speed and turbine exhaust gas temperatures to optimize the heat generation and fuel efficiency of the turbo heater  10 . In this regard, the control algorithm provides means for controlling the outlet temperature of the turbine exhaust by varying the bleed air from the compressor. 
         [0026]    The control algorithm executed on the engine controller  30  may take into account the temperature of the combustion air stream (A C ). For example, the temperature of the combustion air may be too cold for proper combustion, during start-up or in extremely cold operating conditions, such that a pre-heat of the combustion air is beneficial. Under this condition, the engine controller will query will query (or recall from memory) the current inlet temperature of the combustion air. Based on this measurement, the engine controller  30  will adjust the bleed air control valve  42 ′ to a recirculate the heated feed stream so as to provide a pre-heat charge for the combustion air. Specifically, the air in feed line  44  which has been heated by virtue of the work imparted by the compressor  18  is recirculated to and mixed with the combustion air stream (A C ) to increase its temperature. 
         [0027]    The control algorithm executed on the engine controller  30  may also take into account the temperature or emission quality of the exhaust gas stream (E T ) to ensure complete combustion of the air-fuel mixture in the gas turbine  12  and the combustion by-products in the catalytic converter  28 . For example, the exhaust gas quality (e.g., oxygen content, CO content, NOx content) of the exhaust gas stream (E T ) may not meet the proper levels for providing a breathable air, such that additional after-treatment of the exhaust gas stream is necessary. Under this condition, the engine controller  30  will query (or recall from memory) the current temperature and/or gas quality of the exhaust gas stream. Based on this measurement, the engine controller  30  will adjust the bleed air control valve  42 ″ to increase the air flow to the catalytic converter  28 . Specifically, the air in feed line  44  is re-directed into the exhaust gas stream to enrich the oxygen content so that complete combustion of any unburned fuel and combustion by-products can be occur in the catalytic converter  228 . 
         [0028]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.