Abstract:
Various embodiments of a fuel-control system and associated methods for regulating the administration of a fuel to a fuel consuming device are disclosed. In one aspect, the fuel consuming device is a gas turbine receiving fuel through a feeder conduit from first and second sources of gas. According to one method, natural gas fuel is delivered from said first and second sources into said surge tank via first and second conduits, each conduit having pressure-control valves and sensors. The natural gas is delivered to the turbine from the surge tank via a feeder conduit. Pressure measurements are taken by the sensors for the first and second conduits, which are sent to a controller. The controller is then used to manipulate the valves to supply the turbine with fuel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a division of and claims priority to U.S. patent application Ser. No. 11/225,987, filed Sep. 14, 2005. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   None. 
   BACKGROUND OF THE INVENTION 
   Conventional power systems for telecommunications facilities have used AC which is purchased from a commercial utility. Because of blackouts and other disturbances in the commercial power grid, some facilities use a diesel generator to back up the commercial AC. When the AC power goes dead, the diesel generator is activated. It takes a while for the generator to come online, however. In the interim, an array of batteries will bridge the downtime. If the diesel generator fails, e.g., runs out of fuel, the batteries will drain to power the facility until they run out. 
   Gas turbines have been widely used by utility companies to generate electrical power. Many are adapted such that they operate on natural gas. Such turbines are normally included in an arrangement which ensures that the natural gas fuel is delivered at a steady pressure. This prevents erratic electrical production. 
   SUMMARY OF THE INVENTION 
   Embodiments of the present invention relate to a fuel-control system and associated methods for regulating the administration of a fuel to a fuel consuming device. In one aspect, the fuel consuming device is a gas turbine receiving fuel through a feeder conduit from first and second sources of gas. According to one method, natural gas fuel is delivered from the first and second fuel sources into a surge tank via first and second conduits, each conduit having pressure-control valves and sensors. The natural gas is delivered to the turbine from the surge tank via a feeder conduit. Pressure measurements are taken by the sensors for the first and second conduits, which are sent to a controller. The controller is then used to manipulate the valves to supply the turbine with fuel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is described in detail below with reference to the attached drawing figures, wherein: 
       FIG. 1  is a schematic diagram showing the power system of the present invention. 
       FIG. 2  depicts the fuel-control system of the present invention. 
       FIG. 3  shows the several components of the invention which are contained in a control cabinet. 
       FIG. 4  is a flow diagram showing the processes of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The system disclosed herein uses a gas turbine generator as the primary source of power to sustain DC power to a DC bus which is electrically connected to a base transceiver station (BTS). The turbine normally operates on natural gas from a utility pipeline, but if the utility source is unavailable (e.g., a backhoe ruptures a pipeline) or the pressure has dropped below what is necessary to drive the turbine, the system can call on a backup source of natural gas which is stored in tanks. The turbine is able to run on only utility natural gas, partial utility and partial stored natural gas, or only stored natural gas thanks to a valve arrangement using pressure-controlled valves and a surge tank. The pressure-controlled valves are controlled using a controller. The controller may be some kind of computing device, e.g., a programmable logic controller (PLC) or a microprocessor. A PLC is used in the preferred embodiment. This arrangement makes for smooth transitioning between utility and stored natural gas sources. 
   Lithium Metal Polymer batteries (LMPs) are connected into the DC bus. The LMPs are always online. When the electrical output of the turbine generator dips, the LMPs will cover the dip so that the BTS does not experience any temporary power drop. When the turbine is inactive, the LMPs drain to back up the BTS. 
   Should the LMPs completely lose their charge to the point that the BTS power requirements are not met, the system includes a low-power fuel cell which is used to back up the PLC only. When the fuel cell is brought online, the PLC circuit is isolated from the DC bus by throwing a breaker. Because it is backed up with the fuel cell, the PLC remains functional and is able to continue to control the valves even though the DC bus is dead. It also enables the PLC to continue to transmit alarm messages so that interested parties are able to monitor what is happening at the site. 
     FIGS. 1-4  help in understanding the disclosed embodiment. Referring first to  FIG. 1 , a schematic diagram  100  shows the many components of a power system which relies primarily on a microturbine generator  104  which is backed up by one or more LMP batteries  106 . This backup arrangement is used to ensure that DC power is maintained to the power-distribution unit (not shown) for a BTS  102 . The BTS is the radio-hardware portion of a cellular base station. It is involved in the transmission and receiving of voice and data. Power distribution units comprise the electrical equipment for making the necessary connections into the telecommunication-cell-site equipment. 
   Microturbine generator  104  produces AC. BTS  102  consumes DC, not AC. Thus, the AC received from microturbine generator  104  must be converted. To do this, system  100  includes one or more rectifiers  134 . Rectifiers  134  convert AC to DC. The particular rectifiers used in the present invention are switch mode rectifiers (SMRs). SMRs are advantageous for use here because they are highly efficient, small, and relatively light weight. 
   The DC output from the rectifiers  134  is electrically connected into a DC bus  130 . The DC input to BTS  102  is also connected to bus  130 . Thus, BTS  102  is able to receive its primary source of power from turbine  104 . 
   If the turbine fails for some reason, e.g., for lack of fuel, the LMPs  106  will immediately pick up the load because they are also connected into bus  130 . This connection also causes them to be charged when the turbine is functional. The LMPs used in the preferred embodiment of the invention are 48-volt, 63-amp-hour batteries manufactured by Avestor, Inc. (Model No. SE 48S63), but the scope of the invention is not to be limited to any particular battery, manufacturer, or amp-hour/voltage level used. Other kinds of batteries could be used instead and still fall within the scope of the present invention. Three batteries are used in the present embodiment. 
     FIG. 1  also discloses a control system  108  which includes a controller  110  which is, in the preferred embodiment, some form of computing device. Controller  110  serves numerous purposes. First, it is used to send alarm information to an outside monitoring administrator when certain conditions are sensed. Sensors at different points will transmit alarm messages if certain events occur. For example, pressure sensors will indicate disruption in availability of utility natural gas, stored natural gas, and stored hydrogen (which is used to fuel a PLC backup fuel cell). A pressure sensor will also be used to sense disruption in the feeder line to the turbine. Other alarms will be transmitted in the event of electrical irregularities. Properly located voltage sensors will indicate voltage drops at the turbine, LMP, and fuel-cell outputs. These alarms will be transmitted to an interested party. This enables remote monitoring by an administrator not at the site. 
   Second, controller  110  regulates the delivery of natural gas to turbine  104  and enables the automated administration of utility versus stored sources with preference given to natural gas from the utility. This is done using a valve arrangement which is responsive to measurements taken by a plurality of pressure sensors. 
   Third, the controller is adapted to open and shut a breaker  140  to isolate the control system from the DC bus upon the occurrence of certain conditions as will be discussed in more detail later. 
   PLCs like the one used in the preferred embodiment as controller  110  will be known to those skilled in the art as devices which are widely used for industrial control applications. They employ the hardware architecture of a computer but also include a relay control subsystem. A PLC uses these components to automatically respond to sensed conditions in the power system. Though a PLC is used in the preferred embodiment, another kind of device, such as microprocessor arrangements could be used instead, and other computing devices could also be used and still fall within the scope of the present invention. 
   Controller  110  is supported by an independent backup system. The backup system includes a fuel cell  112  which is driven using gaseous hydrogen fuel from a hydrogen tank  114 . 
   Fuel cells are electrochemical-energy-conversion devices. They utilize hydrogen and oxygen. Proton exchange membranes (or other equivalent devices) in the fuel cell cause the electron from hydrogen to be removed temporarily. Later, this hydrogen electron is returned when the hydrogen is combined with the oxygen to produce water. This creates electricity. The reaction is entirely noncombustive and generates DC electrical power. Because the only by-products of this reaction are heat, water, and electricity, a fuel cell is friendly to the environment. In addition, a fuel cell is capable of providing electrical power for as long as hydrogen fuel is supplied to the unit. It does not discharge over time like a battery. 
   In the preferred embodiment disclosed in  FIG. 1 , fuel cell  112  includes a plurality of PEMs. Though fuel cell  112  used in the preferred embodiment uses PEMs, other fuel-cell technologies exist which might be used instead and still fall within the scope of the present invention. One example of a PEM-type fuel cell which is suitable for use with the present invention is a 500 W modular, cartridge-based, proton exchange membrane power module manufactured by ReliOn, Inc. of Spokane, Wash. 
   In the  FIG. 1  arrangement, fuel cell  112  receives hydrogen fuel via a tube  118  which runs from a pressurized hydrogen tank  114 . The flow rate of hydrogen is controlled using an automated pressure-control valve  116  which is disposed in tube  118  between the tank and fuel cell. If the stored hydrogen is released from the tank  114  by opening valve  116 , it is consumed by fuel cell  112  to generate DC power. This DC power is introduced into line  120  so that it is able to be consumed by the controller  110 . Because a PLC uses AC power, the DC output of fuel cell  112  must be converted. This is done by a power inverter  122  which is located between controller  110  and line  120 . 
   The entire control system  108  with its independent backup arrangement comprising fuel cell  112  is able to be electronically isolated from DC bus  130  using a breaker  140  which is adapted (using controller  110 ) to open up when voltage in the DC bus reaches a predetermined minimum voltage. 
     FIG. 2  shows a fuel-control side  200  of the invention. The fuel controls are housed in a cabinet  202  which is located on a platform  210 . Platform  210  may be a concrete slab or some other supporting surface. 
   A primary source of fuel is natural gas which is delivered in an underground pipeline  204 . A secondary source of natural gas is maintained in a plurality of natural gas tanks  206 . These tanks maintain natural gas at high pressures and are all incorporated into a header  208 . Header  208  serves as a manifold which causes the pressure from each of the tanks to be equalized. 
   A plurality of automated pressure-control valves (which in the preferred embodiment are explosion proof valves) are incorporated into the system so that both (i) the underground primary utility source of natural gas from pipe  204  and (ii) stored source  206  can be used as fuel for the microturbine  104  either alternatively or at the same time. Explosion proof valves are widely used in industry for controlling the flow of natural gas and other explosive gases. A primary pressure-control valve  212  regulates the flow in a pipe  220  which receives natural gas from underground pipeline  204 . A secondary pressure-control valve  214  regulates the flow of gas in a pipe  222  which receives stored natural gas from header  208 . A third pressure-control valve  216  is disposed in a pipe  226  and regulates the flow of natural gas to microturbine  104  through underground turbine feeder pipe  224 . Though explosion proof valves have been selected for use in the preferred embodiment, other kinds of flow-control valves, e.g., globe valves, could be used as well and still fall within the scope of the present invention. 
   Interposed between all three valves ( 212 ,  214 , and  216 ) at a T-junction between pipes  220 ,  222 , and  226  is a surge tank. A surge tank is a vessel which includes a chamber which receives gas from one or more feeder pipes and is used to absorb pressure irregularities. Here it is used to minimize any disruptive effect caused by the automated adjustments of valves  212  and  214 . Otherwise manipulation of these valves might cause pressure irregularities in pipe  226  which could not be accommodated by turbine  104 . Turbines require the delivery of fuel on or about some specific pressure. For example, the turbine in the preferred embodiment requires natural gas at 15 lbs. of pressure. Others require 7 lbs. or some other constant pressure. Surge tank  218  along with pressure-control valve  216  maintain steady natural gas pressures in turbine feeder pipe  224  to ensure proper operation of the turbine. 
   Valves  212 ,  214 , and  216  are all electronically controlled via electrical connections which are symbolically represented by dotted lines  230 ,  232 , and  234  respectively in the figure. Each electrical connection exists between the controller  110  (not visible in  FIG. 2  because it is contained in cabinet  202 ) and a respective valve. The manner of electrical connection and programming required for control purposes are all within the skill of one skilled in the art. Connections  230 ,  232 , and  234  enable each of the pressure-control valves to be individually controlled to regulate the flow rates and pressures in pipes  220 ,  222 , and  226 . 
   The overall objective is to, using pressure-control valves  212 ,  214 ,  216 , and surge tank  218 , optionally and in variable amounts, use the two natural gas sources while at the same time regulating the pressure in turbine feeder pipe  224  so that it is maintained at or close to the ideal level, e.g., 15 lbs. of pressure. Valves  212  and  214  function to select how much of each natural gas source (e.g., utility in pipe  204  or stored gas in tanks  206 ) is being consumed. Valve  216  is used to maintain a steady pressure level in turbine feeder pipe  224  so that the turbine operates properly. 
     FIG. 3  shows the contents of control cabinet  202 . Cabinet  202  includes from top to bottom, SMRs  134 , inverter  122 , and controller  110 . Included below are, from left to right, the LMPs  106 , fuel cell  112 , and hydrogen tank  114 . Some details have been omitted for simplicity sake, e.g., some components as well as precise connection arrangements between all the devices. 
   A power-management flow chart  400  of  FIG. 4  shows both the operational aspects of system  100  as well as different contingency plans intended to handle natural gas availability problems. The entire power management method is managed by a process which is programmed into controller  110 . The  FIG. 4  process assumes that valve  214  is initially closed but that valves  212  and  216  are opened up (at least partially). 
   In a first step  402  of the process, an inquiry is made as to whether natural gas is available from the utility pipeline. This question is answered by measuring the pressure in pipe  204  at valve  212  using a pressure sensor  213 . Information from this sensor  213  is received by controller  110  through line of communications  232 . Using controller  110 , a determination is made as to whether this pressure is above a predetermined minimum value. The minimum value is set at or slightly above what is known as the minimum pressure required to drive the turbine. If the measured pressure is above this minimum, the process moves on to a step  404 . 
   In step  404 , the surge tank will be supplied with natural gas via pipe  204  only. To do so, pressure-control valve  212  is caused by the controller (through line of communications  232 ) to deliver natural gas at a pressure that is at or slightly above that required by the turbine (e.g., 15 lbs.). Valve  214  remains completely closed while this is occurring. 
   After that, in step  405 , controller  110  ensures that breaker  140  is in closed position (if it is not already in that position). This is necessary so that the controller receives power from the DC bus  130 . 
   Next, in a step  406 , the turbine generator consumes natural gas and generates AC power. The AC power is then converted to DC power by the SMRs  134 . The DC power output from the SMRs  134  is introduced into DC bus  130  which maintains power to BTS  102 . While this occurs, LMPs  106  will charge in a step  408  because they are connected into the DC bus. It is important that the LMPs  106  remain charged so that they are available for backup and bridging purposes if needed. 
   If in inquiry step  402  the pressure measured in pipe  204  at valve  212  (using a pressure sensor  213 ) is detected to be below the predetermined minimum pressure required to drive the turbine, the process moves on to a second inquiry step  410 . 
   In step  410 , an inquiry is made as to whether stored natural gas is available that, either alone or in combination with natural gas available from the utility, is sufficient to drive the turbine. The controller determines the availability of stored natural gas in tanks  206  by taking readings (through line of communications  232 ) from a pressure sensor  215  in pipe  222  at valve  214 . When these readings are received by controller  110 , they are considered in combination with simultaneous pressure readings from pipe  204  regarding the availability of utility natural gas and a determination is made by the controller as to whether the total natural gas available will be sufficient to meet the predetermined minimum value required to meet the fuel requirements of the turbine. If enough stored natural gas is available, the process moves on to a step  412 . 
   In step  412  the necessary contribution of natural gas from the storage tanks  206  is introduced into surge tank  218 . The controller accomplishes this by opening up valve  214  to the extent necessary to meet the fuel requirements of the turbine  104  based on all the available information. When this occurs, the stored natural gas mixes in surge tank  218  with whatever utility natural gas is available (possibly none) and then, in step  406 , causes the turbine to consume the natural gas from the two sources and drive a generator. The AC power produced is then converted to DC and introduced into DC bus  130  to maintain power to the BTS. 
   Regardless of the mode of fuel consumption in step  406 : (i) utility natural gas only, (ii) stored natural gas only, or (iii) a combined supply from both sources simultaneously, the process will continually check in a step  414  to determine whether the total natural gas available is sufficient to drive the turbine  104  and thus, meet the BTS requirements for DC power consumption. This is done by measuring the pressure at valve  216  in pipe  226  using a pressure sensor  217 . The reading from this sensor  217  will be received by the controller via connection  234 . The controller will compare this reading to a predetermined (and stored) value which represents the minimum pressure required to effectively drive turbine  104 . If the measured value is above the minimum, the process will continuously loop between turbine consumption step  406  and checking step  414  and the turbine will remain continuously operational. If, however, the supply of natural gas from both available sources is not enough to power the turbine, the answer at step  414  will be no. This will occur when: (i) there is a temporary dip in the power because of some fuel pressure irregularity, mechanical, or other momentary failure; or (ii) the turbine is completely nonfunctional because there is no longer enough fuel to drive it. In either case, the process will move on to a step  416 . 
   In step  416 , an inquiry is made as to whether the LMPs have enough charge to maintain the BTS  102 . This is determinable by measuring the voltage in DC bus  130  using a voltage sensor (not shown). The controller will be programmed to recognize the minimum voltage which is indicative of what will satisfy the minimum power required to support the BTS power requirements. If voltage is sensed at a level above the minimum, the LMPs  106  will drain in a step  418 . For temporary dips in power, the LMPs will act to bridge, causing the momentary dip to have no effect on the actual power available to the DC bus  130 . For substantial/longer losses in power, the LMPs will act as a backup power source. Both scenarios are handled by the  FIG. 4  process. 
   After step  418 , the process will continually loop back to step  402  and then back through steps  410  and  416 . This causes the process to continually monitor whether natural gas has become available from either of sources  204  or  206 . If so, the turbine will be returned to service. If not, the LMPs  106  will continue to drain. 
   After a considerable amount of time without natural gas, the constant dependence on battery power will cause the charge in the batteries to become depleted. The controller  110  is programmed to recognize when voltage in the DC bus  130  drops to the point at which the BTS  102  is unable to function properly. When this occurs, the process causes breaker  140  to be thrown in a step  420 . This opens up the circuit, causing control system  108  including controller  110  and fuel cell  112  to be electrically isolated from the DC bus  130 . 
   At the same time breaker  140  is thrown, the controller also causes pressure-control valve  116  to open up. This causes hydrogen to be delivered from tank  114  to be consumed by the fuel cell to maintain power to the controller  110  in a step  422 . Thus, although power has been lost to the BTS  102 , control system  108  will remain functional because of the DC power produced by the hydrogen-powered fuel cell. 
   After step  422 , the process loops back to step  402 . This creates a continuous loop which will cause the controller  110  to continually monitor whether natural gas has become available from either utility source  204  or storage tanks  206 . If so, the turbine will come back online and the process (pursuant to steps  402 ,  404 ,  405 , and  406  or steps  410 ,  412 ,  405 , and  406 ) will cause the system to revert back to AC production and recharge the LMPs (in step  408 ). But if natural gas is still not available, the fuel cell will continue to operate in step  424  in order to keep the controller  110  powered. 
   It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, all matter shown in the accompanying drawings or described hereinabove is to be interpreted as illustrative and not limiting. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description.