Abstract:
A battery powered ignition and control system for a gas burner includes circuits for controlling a pilot burner, a main burner, a flame sensor and an igniter. Mechanically latched valves, which require power only to switch between and open and closed state are used to control the pilot and main gas. The circuitry spends a majority of time in a powered down state and draws power only when required to interrogate the state of the flame and to perform an ignition sequence as required, as periodically dictated by a watchdog system. The latching valves are electrically pulsed to change state and thus draw very low average power when called upon. Lithium batteries provide system power for a long duration.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority of U.S. provisional application Ser. No. 60/525,881, filed Dec. 1, 2003, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     Embodiments of the invention relate to gas burner controls for gas heaters and the like, and in particular to a new and novel way to power and control said burner such that the system draws very low average electrical power. 
     BACKGROUND OF THE INVENTION 
     A specialized type of heater apparatus is conventionally used for heating natural gas pipelines. The requirement for such heaters arises as a result of the possibility for condensation of water and hydrocarbon vapors, entrained in the natural gas, which can produce hydrates and resulting problems therefrom. The problem is conventionally avoided by heating the pipeline gas through the use of the specialized pipeline heater. 
     The need for pipeline heaters typically arises in locations along the pipeline or at well sites that are remote and often without an electrical supply available to operate conventional heaters. Typical types of such heaters include direct or indirect fired heaters, most often for heating a heat-transferring substance such as glycol, by a gas burner. The gas burner is ignited by a pilot light, the pilot light being a smaller gas burning flame. 
     Conventional heaters in use today often comprise manually operated pilot flame ignition systems without safety features for providing reliable re-lighting of an extinguished pilot flame. The heaters also include thermally operated main burner shut-off features. Therefore, the burners presently used are not reliable for avoiding condensation in the pipeline, and do not have the much needed safety features for detecting and reacting to burner pilot flame failure. Further, the burners presently used have continual pilot flames, regardless of infrequent burner use, resulting in wasted fuel due to unnecessary pilot burn time. 
     Burner controls and spark igniter devices are known and available for heaters used in other industries where the availability of power is not an issue. However, in industries where power is not readily available, such as in the case of pipelines, control and ignition remains an issue. 
     In order for electrically ignited gas burners to operate as stand-alone units without the need for connection to line voltage, attempts have been made to use electrical storage batteries for use as the power supply to the ignition circuits. Examples of such systems are taught in U.S. Pat. Nos. 3,174,534 and 3,174,535 to Weber and in U.S. Pat. No. 4,131,413 to Ryno. The Weber patents teach applying the battery power through an oscillation circuit across a transformer which supplies power to a spark gap. The battery is recharged after ignition by a thermopile charger, which receives energy from the flame. The Ryno patent similarly uses a battery supply which is recharged by a thermopile. Another concept available in the industry is to use solar energy to recharge the batteries. 
     While the introduction of rechargeable batteries, recharged by thermopiles or solar, is significant because gas burners are relatively maintenance-free over a lifetime of 15 years or more, the recharging circuit and rechargeable battery greatly increases the cost and complexity of the system. In addition, rechargeable batteries have a life expectancy of only three to five years and typically have performance issues in cold temperature operation and storage. 
     SUMMARY OF THE INVENTION 
     In accordance with embodiments of the present invention, a control system is taught which minimizes a requirement for energy consumption by implementing a timer or watchdog system into a control system which requires minimal power to periodically interrogate a state of a device being controlled. When the control system senses an operational state, it returns to sleep. When the control system senses a non-operational state, it momentarily utilizes energy to trigger one or more latches to change state, causing the device to be made operational and then returns to sleep. Additionally, should the device not be made operational as a result of the activation of the latch, further sensing of a non-operational state would cause the system to be shut down by momentarily energizing the latch. 
     In a burner implementation, the state of gas valves can be altered with the momentary energizing of latching valves based on sensing flame states, such as the operational presence of a flame or the non-operational absence of a flame. The watchdog timer is an extremely low powered alarm clock-like timer circuit which, at periodic intervals, interrogates the flame sensor regarding the presence or absence of flame. 
     More particularly, in one embodiment, a long-life energy source such as a lithium battery is utilized as the power source to switch the latching valves. To minimize the current drain from the battery, all of the circuits including the control valves remain un-energized except for the brief time required to change the state of the latching valves. As the current drain from the battery is required only to change the state of the latching valves and is not required to maintain the latch once it has been switched, the battery life is extended resulting in less frequent replacement or recharging. 
     In the burner control implementation, the control system of an embodiment of the invention utilizes conventional components of a burner control and ignition system and valve control systems including a main burner valve for providing gas to the main burner and a pilot valve for providing gas to the pilot burner. Further, a flame sensor and a flame sensor circuit provide a flame signal. Ignition electrodes and an ignition circuit drive the electrodes to produce a spark during lighting of the pilot burner. A first switching circuit is used for controlling the ignition circuit and the main burner. 
     Small latching valves, typically being mechanical devices including alternating magnetically latched states which consume only minute amounts of energy to switch from open to closed states, are used to control larger pneumatically-powered valves for the main burner gas. If the flame is detected, the circuit immediately powers off. If flame is not detected, the circuit reacts accordingly to disable all gas flow and then powers off or alternatively, the circuit may try to relight the flame. In any case, power is only on for sub-second durations. As a safety feature in the event that the flame fails to ignite after a predetermined amount of time or during normal operation, the control system disables the gas flow to the burner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of an alternate embodiment of a burner control system of the present invention having a main gas valve controlled by a main latching valve and a pilot flame latching valve for providing gas directly to a pilot flame; 
         FIG. 2  is a schematic illustrating operation of components according to  FIG. 1  of the burner control system in normal operation, shown in solid lines, and in the event of loss of flame, as shown in dashed lines; and 
         FIG. 3  is a schematic of a controller and power circuits according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the invention utilize at least one latch which is operable between an open state and a closed state and which utilizes minimal power to switch between states and virtually no power therebetween. Further, power is not required to maintain the latch in either state once switched. Minimum power usage is achieved by a timer which actuates a sequence of events to determine the operation or state of an apparatus at period intervals. When the apparatus is detected to be in a first state, the latch is maintained in the open state, without the need to apply power to maintain it in that state. If the apparatus is determined to be in a second state, the latch is switched to the closed state. Each time the latch or latches are switched only a momentary application of power operable only for switching between states is required, thus power is conserved. 
     Having reference to  FIG. 1 , a burner control system  10  embodiment is shown. The system  1  comprises a controller  11  which incorporates a watchdog system or timer (not shown), a main burner valve  13  to provide a flow of gas from a main gas supply  12  to the main burner  14 . Typically, the main gas supply  12  also feeds the pilot burner  15 . A flame sensor  16  continuously monitors the pilot burner  15  for the presence of a flame and may monitor the main burner  14 . An igniter  17 , typically a high voltage igniter, is positioned adjacent the pilot burner  15  for igniting the pilot burner  15 . 
     Actuation energy, typically a pressurized gas flow such as from the main gas supply  12  or alternatively instrument air, is provided to pneumatically operate the main burner valve  13 , and optionally, additional pneumatic valves, such as an emergency shutdown (ESD) valve  18 , connected upstream of the main burner valve  13 . 
     Actuation of the main burner valve  13  is controlled by a magnetic latching valve  20 . Typically, the main burner valve  13  is a slave valve to the latching valve  20  as the latching valve  20  may not have enough gas flow capacity therethrough. Further, the flow of gas to the pilot burner  15  is controlled by a latching valve  21 . Latching valves  20 , 21  are controlled by a pulse of electrical energy from a controller  11 . When a pulse of electrical energy is applied to either of the latching valves  20 , 21 , the state changes from open state to closed state or from a closed state to open state depending on the polarity of the pulse. In the open state, actuation energy is directed from the latching valve  20  and applied to the corresponding gas valve. 
     When the main gas latching valve  20  is in the open state, it permits the main gas supply  12  pressure, or alternatively instrument air, to be applied to the actuation bellows of the main gas valve  13 , thus pneumatically opening the main gas valve  13  which flows gas from the main gas supply  12  to a main burner  14  and enables the combustion process to provide heat. 
     When the pilot flame latching valve  21  is in the open state, it allows gas from the main gas supply  12  to be directed to the pilot burner  15  to provide a source of ignition gas, which when ignited produces a flame for igniting the main burner  14 . 
     Having reference to  FIGS. 1 and 2 , a watchdog timer circuit  110 , at periodic, timed intervals, enters an active phase and signals the controller  11  to interrogate the pilot burner  15 , using the flame sensor  16 , for the presence of a flame. If the flame sensor  16  senses a first state, the presence of a flame, the controller  11  subsequently turns the power off and the system  1  remains dormant until the next timed interval and the watchdog timer circuit  100  enters an inactive phase. If the flame sensor  16  senses a second state, the absence of a flame, the controller  11  initiates an ignition sequence to relight the pilot burner  15 . 
     In the ignition sequence, the latching valves  20 ,  21  are initially and momentarily powered to the closed state to stop the flow of gas thereto. After a predetermined interval to permit the dispersion or purging of any gas present in the system, the latching valves  20 ,  21  are momentarily powered to switch to the open state to permit gas to flow thereto and the igniter  17  is powered to ignite the pilot burner  15  and ultimately the main burner  14 . The flame sensor  16  monitors the pilot burner  15  for the presence of flame and if the ignition was successful and a flame is detected the controller  11  shuts the power off and becomes dormant until the next interval. If however, the ignition was not successful and no flame is detected the ignition sequence will be repeated. Preferably, the ignition sequence will be attempted 3 times and if unsuccessful each time, the latching valves  20 , 21  will be momentarily powered to the closed state to shut off the flow of gas thereto and an alarm will be sent via an alarm relay  22 . 
     In another embodiment, as required by pertinent regulations, at least one pneumatic ESD valve  18  is powered by an ESD latching valve  23 . The ESD latching valve  23  is powered to the open state to permit the flow of gas to the main burner valve  13 . In the event that the controller  11  receives a signal S that the system must be shutdown, the ESD latching valve  23  is momentarily powered to the closed state to close the at least one pneumatic ESD valve  18  and the flow of gas from the main gas supply  12  is stopped, regardless the state of the main burner valve  13 . 
     Further, a temperature sensor  30 , preferably a 1000 ohm resistance-temperature detector (RTD), is provided to monitor the process temperature. If the temperature is above a setpoint range, the controller  11  momentarily powers the main burner latching valve  20  to shut off the main burner valve  13  until such time as the temperature returns to the setpoint range. 
     Further, a high pressure switch  31  and a low pressure switch  32  monitor the pressure in the main gas supply  12  and should the pressures rise or fall from a preset range of pressures, resulting in either of the switches  31  being switched on, an alarm is sent via the alarm relay  22   
       FIG. 3  illustrates a simplified schematic of an embodiment of the control system  1 . A microcomputer  100 , including program memory, RAM, port controls, analog to digital converters, and other support circuitry, controls the system  1  operations. The pilot flame latching valve  21  is opened by the microcomputer  100  pulsing line  101  low which causes an H-bridge to drive a current pulse through the pilot latching valve&#39;s coil  61  in the opening direction. The pilot flame latching valve  60  is closed by the microcomputer  100  pulsing line  102  low which causes an H-bridge to drive a current pulse through the valve&#39;s coil  61  in the closing direction. 
     The main gas latching valve  20  is opened by the microcomputer  100  pulsing line  103  low which causes an H-bridge to drive a current pulse through the valve&#39;s coil  71  in the opening direction. The main gas latching valve  20  is closed by the microcomputer  100  pulsing line  104  low which causes an H-bridge to drive a current pulse through the valve&#39;s coil  71  in the closing direction. 
     The microcomputer  100  detects flame through line  105 , which is connected to the flame sensor  16 . In a preferred embodiment, the flame sensor  16  is a flame ionization detector which draws no power. 
     The microcomputer  100  controls the igniter  17 , typically a high voltage circuit  170  via line  160 . The high voltage circuit  170  causes a pulsating high voltage current to be applied to a spark gap  180  in the proximity of a nozzle (not shown) of the pilot burner  15 . 
     A microcontroller, or low power watchdog timer circuit  110 , controls the power for the system  1 . Power from a battery  80  is connected to the latching valve&#39;s control circuits  90  via a switch  130 . At prescheduled intervals, switch  130  is closed by the watchdog timer circuit  110 . Switch  130  is opened by the microcomputer  100  through line  120  when the microcomputer  100  has completed the interval interrogation using the flame sensor  16  and the ignition sequence, if required. In operation, the switch  130  is closed several times per second by timer  110 . In a preferred embodiment, the timer  110  is internal to the microcomputer  100 . 
     If flame is detected at the flame sensor  16 , all is operating properly, and the microcomputer  100  opens switch  130 , thus turning the power off to the control circuits  90 . If no flame is detected, the microcomputer  100 , checks for a demand for heat through line  190 , and if so the main burner  14  needs to be restarted. Microcomputer  100  closes both latching valves  20 ,  21  and waits a prescribed amount of time to clear the area of gas. The microcomputer  100  then actuates the pilot flame latching valve  21  and shortly thereafter activates the igniter circuit  170  to ignite the pilot gas flow. Subsequently, following ignition and when a flame is detected, the igniter circuit  170  is turned off and the main gas latching valve  20  is opened. Typically the pilot flame latching valve  21  is left open, however, in some other instances, an operator may wish to also close the pilot flame latching valve  21  and pilot gas flow on proof of ignition of the main gas burner  13 . The microcomputer  100  then opens switch  130 , turning off the power. 
     There may be many different operational scenarios for the burner, all of which rely on at least one latching valve.