Abstract:
A method of controlling a gas booster comprises computing in an engine control unit a reference discharge pressure for the gas booster. In the engine control unit, an actual discharge pressure of the gas booster and the reference discharge pressure are compared. The engine control unit generates a correcting signal derived from the step of comparing. The engine control unit sends the correcting signal to an inlet valve in flow communication with the gas booster. The inlet valve is adjusted in response to the correcting signal. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to ascertain quickly the subject matter of the technical disclosure. The abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to gas boosters and, more particularly, to and apparatus and integrated method of modulating a gas booster based upon feedback control of an effective suction flow area of the gas booster. 
     Gas boosters are used to compress and thereby boost the pressure of the fuel gas that is eventually fed to a turbine engine. Commonly, a metering or control valve is intermediate the gas booster and turbine. The metering valve regulates the amount of fuel into the turbine. Thus, when the turbine is accelerated or decelerated, the metering valve is correspondingly opened or closed. 
     Previous designs have used a pressure transducer to monitor pressure downstream of the gas booster in order to regulate the metering valve downstream of the gas booster. For example, U.S. Pat. No. 4,087,961 discloses a boost compressor, a pressure regulator downstream of the boost compressor, and a pressure transducer and metering valve downstream of the pressure regulator. A speed governor utilizes the inlet pressure from the pressure regulator and a discharge pressure from the turbine to open or close the metering valve. In turn, the rate of fuel flow into the turbine is controlled. 
     U.S. Pat. No. 5,305,597 also regulates gas flow at a point downstream of a gas booster and upstream of a turbine. A pressure regulator maintains a constant differential pressure across a metering valve. A mass flow meter is downstream of the metering valve. The metering valve, resolver, and mass flow meter cooperate with an electronic control circuit to generate a feedback signal indicative of the mass fuel flow. 
     In an effort to reduce the costs associated with using a gas booster, U.S. Pat. No. 4,922,710 attempts to lower the power requirements for the gas booster. A complex series of metering valves downstream of the gas booster minimize pressure drops prior to the turbine. 
     However, the above past designs do not address fuel control upstream of or at the gas booster. Moreover, the foregoing past designs do not endeavor to provide booster suction control. Yet, gas boosters need an efficient means of compression. The power consumed by the compression process is a function of the fuel delivery rate and the pressure ratio. Therefore, the discharge pressure, or the booster&#39;s ability to deliver fuel at a desired discharge pressure is a primary factor in efficiency. The booster discharge pressure must be high enough to overcome the pressure drops required to meter fuel to satisfy the system needs. Yet, fuel delivered at pressures excessively beyond the system requirements translates into energy wasted. 
     As can be seen, there is a need for an apparatus and method of regulating the gas delivered to a gas booster. Another need is for an apparatus and method of fuel control upstream of or at the gas booster to provide booster suction control. A further need is for an apparatus and method that improves the efficiency of a gas booster by employing a feedback signal to regulate the delivery of gas to the booster. 
     In addressing the above needs, the present invention provides in one aspect a method of controlling a gas booster, comprising computing in an engine control unit a reference discharge pressure for the gas booster; comparing in the engine control unit an actual discharge pressure of the gas booster and the reference discharge pressure; generating from the engine control unit a correcting signal derived from the step of comparing; sending from the engine control unit the correcting signal to an inlet valve in flow communication with the gas booster; and adjusting the inlet valve in response to the correcting signal. 
     In another aspect of the present invention, an apparatus for controlling a gas booster that is used to raise commonly low site pressures of 0.25 to 15 psig to a pressure usable by a turbine engine fuel delivery system comprises a first signal loop having an engine control unit and a receiver of the gas booster, with the said engine control unit being responsive to an actual discharge pressure signal from the receiver; and a second signal loop having the engine control unit and an effective suction flow area of the gas booster, with the effective suction flow area being responsive to a correcting signal from the engine control unit. 
    
    
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a control system for controlling a gas booster according to an embodiment of the present invention; and 
     FIG. 2 is a schematic diagram of two feedback loops that are a part of the control system shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 schematically depicts a control system  10  for controlling or modulating the output pressure of a gas booster  15 . In general, and unlike past designs that control pressure downstream of the gas booster, the present invention achieves modulation and control at a point upstream of or at the gas booster  15 , as further described below. One feedback signal loop  22 , and optionally a second feedback signal loop  23 , enable the modulation. 
     More specifically, the control system  10  includes an engine control unit (ECU)  11  that may comprise a turbine engine control unit when used in the application of a turbine engine fuel delivery system. The engine control unit  11  includes a central processing unit of any well-known design that can compute and compare various parameters. 
     The ECU  11  can compute a reference discharge pressure that is based on parameters such as ambient pressure, ambient temperature, load condition, inlet valve gas pressure, and recuperator gas temperature. “Ambient pressure” identified in FIG. 1 as P atm  refers to the pressure surrounding the system  10  which may typically vary between about 10.1 to 14.7 psia, while “ambient temperature” denoted as T atm  refers to the temperature surrounding the system  10  and may typically vary between about −20 to 120° F. “Load condition” denoted as W f  refers to the fuel flow rate from the system  10  to a control valve (not shown) upstream of a turbine (not shown). The flow rate may oftentimes range between 5 and 60 lbm/hr of natural gas. “Inlet valve gas pressure” refers to the pressure entering an effective suction flow area  13  upstream of or at the gas booster  15 , as further described below. Such pressure may typically vary between 0.25 to 15 psig. Recuperator gas temperature denoted as T 5  refers to the gas exit temperature from a recuperator (not shown) that may be utilized in conjunction with a turbine, as well known in the art. 
     With some or all of the above parameters, as well as others, the ECU  11  may compute the reference discharge pressure. Accordingly, the particular reference discharge pressure represents an optimum discharge pressure that may vary depending upon the desired application and preferences of the user. As such, the particular calculation used to compute the reference discharge pressure may vary. 
     Upon computing the reference discharge pressure, the ECU  11  is able to compare the reference discharge pressure to an actual discharge pressure signal  19  derived from the gas booster  15 , as described below. Upon the ECU  11  making such comparison, a correcting signal  12  may be generated by the ECU  11  and sent into the first signal loop  22  (FIG.  2 ). 
     The first signal loop  22  comprises the ECU  11 , an effective suction flow area  13 , the gas booster  15 , a receiver  17  of the gas booster  15 , a transducer  18 , a first summing junction  20 , and optionally a second summing junction  21  which is part of the second signal loop  23  described below. In FIG. 1, the effective suction flow area  13  is shown as being upstream of the gas booster  15 . However, the suction flow area  13  may alternatively be disposed at or be a part of the gas booster  15 . In any event, the effective suction flow area  13  controls the effective gas flow into the gas booster  15 . Accordingly, the effective suction flow area  13  may comprise an inlet valve and, more specifically, an electro-pneumatic valve. Irrespective of the specific means used, the effective suction flow area  13  receives the correcting signal  12 . In response, the effective suction flow area  13  is adjusted by increasing or decreasing the flow through the area  13 . 
     Upon the effective suction flow area  13  being adjusted, an effective amount of a gas  25  is flowed from a gas source (not shown), such as a facility or site supply, through the flow area  13 , and to the gas booster  15 . The gas booster  15  can be of any well-known design and may be motor-driven. Preferably, however, the gas booster  15  is of a positive displacement type. From the gas booster  15 , the gas  25  is flowed to a check valve  16  that is of any well-known design that can maintain high pressure in the receiver  17 . From the check valve  16 , the pressurized gas flows to the receiver  17  that is also of any well-known design that can direct the gas  25  to both the control valve and transducer  18  mentioned above. 
     The receiver  17  transmits pressure to the transducer  18  that converts the pressure into the actual discharge pressure signal  19  mentioned above and denoted P out  in FIGS. 1 and 2. The actual discharge pressure signal  19  is then sent to first summing junction or logic  20 . The first summing junction  20  compares the actual discharge pressure signal  19  to a reference or target discharge pressure signal  24  that is generated by ECU  11  according to the above calculations. The first junction  20  generates and sends a first comparison signal  26  directly to the ECU  11  or indirectly to the ECU  11  via a second summing junction or logic  21  when the optional second signal loop  23  is utilized. When the second signal loop  23  is utilized, the second junction  21  compares the first comparison signal  26  to a position signal  27  from a transformer  14 , further described below. The second junction  21  then generates and sends a second comparison signal  28  to the ECU  11 . Thereby, the actual discharge pressure signal is effectively received by the ECU  11  for comparison with the computed reference discharge pressure described above. 
     In the embodiment where the second signal loop  23  is not utilized, the ECU  11  may generate the correcting signal  12  in the absence of data indicating the actual suction flow area  13 . Instead, the ECU  11  sends the correcting signal  12  based on previously programmed characteristics of the effective suction flow area or valve  13 . That is, the effective suction flow area  13  as a function of valve command is known and recognized by the ECU  11 . Where the second signal loop  23  mentioned above is utilized, the actual suction flow area  13  is monitored and controlled by the second feedback loop  23 . 
     The second loop  23  comprises the ECU  11 , the effective suction flow area  13 , a transformer  14 , and the second summing junction  21 . From the ECU  11 , the correcting signal  12  is transmitted to the effective suction flow area  13  and then to the transformer  14 . The transformer  14  serves to transform a position of the effective suction flow area  13  that adjusts flow rate, such as a radial or linear position, to the position signal  27  identified above. Accordingly, the transformer can be of various designs, such as radial variable differential transformer, linear variable differential transformer, or even proximity probes. The transformer  14  provides the position signal  27  to the second junction  21  which then compares such signal  27  to the first comparison signal  26 , as described above. 
     By virtue of the first feedback signal loop  22 , and optionally the second feedback signal loop  23 , the ECU  11  may continuously compare the actual discharge pressure from the gas booster  15  to a target discharge pressure, and the effective suction flow area  13  may be continuously modulated for optimum gas delivery to the booster  15 . In other words, power is saved by limiting the suction flow when the system  10  requirements permit limited suction flow. Where the gas booster  15  is a constant volumetric device, as an example, power consumption is a function of two factors—pressure ratio across the booster system and throughput flow rate. Pressure ratio, a well-defined booster parameter, is the ratio (in absolute units) of the discharge pressure to the suction pressure. Thus, if a compressor that provides the compressed gas to the booster  15  only compresses the amount of gas needed to maintain the desired discharge pressure, the throughput flow rate is reduced. In turn, power savings results. 
     More specifically, the first feedback signal loop  22  and optionally the second feedback signal loop  23  allow the receiver  17  to be unloaded or pre-loaded to an optimized pressure in anticipation of load changes. In other words, if the turbine is undergoing a part load and it is anticipated that the load will be increased, the pressure to the receiver  17  can be increased. Likewise, if the turbine is undergoing a large load and it is anticipated that the load will be reduced, the pressure to the receiver  17  can be reduced. 
     As an example, if the load condition is determined to be low (such as 10-15 kW for a 75 kW turbine engine), then the fuel flow rate is also low (such as 20-25 lbm/hr of natural gas). Subsequently, the turbine engine can “set up” for an ascending load change that arrives at the maximum load of 75 kW. To “set up,” the ECU  11  would command the effective suction flow area  13  to increase its opening, allowing the gas booster discharge pressure to climb to a desired pressure (such as to 120 psig). Once the desired pressure is reached, the ECU  11  would command the flow area  13  to close. The result would be “pre-loading” the gas booster receiver  17  in anticipation of the ascending load change. When the ascending load change occurs, the receiver  17  is sufficiently preloaded to satisfy the fuel demand. 
     Conversely, if the load condition is determined to be high (such as 75 kW for a 75 kW turbine engine), then the fuel flow rate is also high (such as 40-45 lbm/hr of natural gas). Subsequently, the turbine engine can trim the gas booster discharge pressure for the prevailing conditions. The ECU  11  would command the effective suction flow area  13  to close, trimming the gas booster receiver  17  to a discharge pressure no higher than required to sustain the fuel flow demand (such as about 75 psig). The result is “unloading” of the gas booster  15  for energy savings. In other words, only the minimum amount of energy required to deliver the fuel is put into compressing the gas. If a descending load change occurs which does not require higher pressure, the receiver  17  can readily match the fuel demand. 
     For those skilled in the art, it can be seen that the present invention provides an apparatus and method of regulating the gas delivered to a gas booster. Also provided is an apparatus and method of fuel control upstream of or at the gas booster to provide booster suction control. The apparatus and method of the present invention improves the efficiency of a gas booster by employing a feedback signal to regulate the delivery of gas to the booster. 
     In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. In addition, benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.