Patent Application
20060118644
This invention relates to the field of oil and gas separation, specifically to methods and apparatuses for igniting a burner for controlling heat the temperature of the contents of a separator.
Petroleum flowing from a well is not refined product. It is a mixture of crude oil and gas, and impurities such as brine, sand, and other suspended solids. The mixture flows into a separator where gravity can be utilized to separate the mixture into product (oil, gas) from the impurities. The product is then moved, generally by pipelines into storage tanks that are close to the production well(s). From here it is transported to refineries for processing.
Some oil wells produce considerable salt water along with the oil. Gas also bubbles out of the oil. In order to separate the oil, water, and gas, the fluids can be put into a separator. The separator is a tank, often using gravity to separate the fluids. Gas goes to the top, and the heavier salt water goes to the bottom. In the past, where there was no market for the gas, it was often flared (i.e. burned at the well site). Today, casing gas is used to power pump engines or heat storage tanks. Heating the separator can help separate water and oil if they are mixed in an emulsion.
Current gas-heated separators use a pilot light to ignite gas. The pilot light is kept burning by a small flow of gas. The pilot light ignites the gas in a main burner when a temperature control system indicates that heating is needed. Pilot light systems can be very simple, and consequently are currently in widespread use with oilfield separators, where ruggedness and simplicity can be important. Alternative ignition systems, in use in other applications, have not been adopted for oilfield separators due to their increased cost and complexity.
Pilot ignition systems must be kept lit and maintained by human operators. The pilot light can be extinguished by wind or other weather conditions. Also, the small pilot orifice can be easily obstructed, e.g., by sand, extinguishing the pilot light. Cleaning the orifice and relighting it requires time and resources. Also, if the pilot light is extinguished, then the main burner will not ignite, and the separator will not be heated. This can lead to freezes in the separator, interrupting the oil/gas/water flow through the separator. Interrupted flow results in lost revenue.
Accordingly, there is a need for ignition methods and apparatuses that are sufficiently simple and rugged for oilfield separator applications, and that avoid the shortcomings of current pilot light systems.
The present invention provides methods and apparatuses for controlling a heater for an oil and gas separator. According to the present invention, a spark is provided for igniting a gas burner. The spark is controlled such that the gas burner is ignited, without unduly complex control or sensor requirements. In the description below, generally an entire temperature-controller separator is described to provide context for the discussion. The invention also contemplates just the heating subsystem, e.g. to mount with existing separators. The invention also contemplates just the heating control subsystem, e.g., to retrofit existing pilot ignition subsystems.
Advantages and novel features will become apparent to those skilled in the art upon examination of the following description and can be learned by practice of the invention.
The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The present invention provides methods and apparatuses for controlling a heater for an oil and gas separator. According to the present invention, a spark is provided for igniting a gas burner. The spark is controlled such that the gas burner is ignited, without unduly complex control or sensor requirements. In the description below, generally an entire temperature-controller separator is described to provide context for the discussion. The invention also contemplates just the heating subsystem, e.g. to mount with existing separators. The invention also contemplates just the heating control subsystem, e.g., to retrofit existing pilot ignition subsystems.
In operation, when the temperature of the contents of the vessel 101 falls below a determined value, for example a value that indicates impaired performance or potential flow reduction, the vessel temperature sensor 105 generates a signal indicating that heat is needed. That signal initiates gas flow from the gas supply to the gas burner 102 through the gas control valve 104. That signal also initiates enablement of the spark generator 108 by the spark control subsystem 107. The spark generator 108 can generate a continuous electric discharge, or can generate a periodic discharge (i.e., a sequence of sparks) to reliably ignite the burner 102. Ignition of the burner 102 will generate heat 103 therefrom. The burner temperature sensor 106 generates a signal indicative of the heat output from the burner, e.g., a signal indicating that the burner temperature has exceed a determined threshold. The spark control subsystem 107 then disables the spark generator 108 since the burner 102 is known to have ignited by the elevated temperature signal. If the burner 102 loses ignition, then the spark control subsystem 107 can re-enable the spark control generator 108. After the burner 102 has supplied sufficient heat to the vessel, the vessel temperature sensor 105 can generate a signal that indicates that heat is no longer required, which signal can cause the gas control valve 104 to cease gas supply to the burner 102 and can cause the spark control subsystem 107 to disable the spark generator 108.
In operation, when the temperature of the contents of the vessel 201 falls below a determined value, for example a value that indicates impaired performance or potential flow reduction, the vessel temperature sensor 205 generates a signal indicating that heat is needed. That signal initiates gas flow from the gas supply to the gas burner 202 through the gas control valve 204. The gas valve sensor 209 indicates that the gas valve 204 is supplying gas to the burner 202, and initiates enablement of the spark generator 208 by the spark control subsystem 207. A flow restrictive device (not shown) such as a needle valve, can mount between the valve 209 and the burner 202, which can increase the time from the opening of the valve 209 and the gas reaching the burner 202 and decrease or eliminate any time that gas is flowing through the burner before a spark is generated. The spark generator 208 can generate a continuous electric discharge, or can generate a periodic discharge (i.e., a sequence of sparks) to reliably ignite the burner 202. Ignition of the burner 202 will generate heat 203 therefrom. The burner temperature sensor 206 generates a signal indicative of the heat output from the burner, e.g., a signal indicating that the burner temperature has exceed a determined threshold. The spark control subsystem 207 then disables the spark generator 208 since the burner 202 is known to have ignited by the elevated temperature signal. If the burner 202 loses ignition, then the spark control subsystem 207 can re-enable the spark control generator 208. After the burner 202 has supplied sufficient heat to the vessel, the vessel temperature sensor 205 can generate a signal that indicates that heat is no longer required, which signal can cause the gas control valve 204 to cease gas supply to the burner 102, causing the gas valve sensor 204 to indicate that gas is not being supplied to the burner 202 and cause the spark control subsystem 207 to disable the spark generator 208.
In operation, when the temperature of the contents of the vessel 301 falls below a determined value, for example a value that indicates impaired performance or potential flow reduction, the vessel temperature sensor 305 generates a signal indicating that heat is needed. That signal initiates gas flow from the gas supply to the gas burner 302 through the gas control valve 304, and causes the spark control subsystem 307 to enable the spark generator 308. The spark generator 308 can generate a continuous electric discharge, or can generate a periodic discharge (i.e., a sequence of sparks) to reliably ignite the burner 302. Ignition of the burner 302 will generate heat 303 therefrom. Heat 303 from the burner 302 will cause a rise in the temperature of the contents of the vessel 301. The vessel temperature sensor 305 can generate a signal that indicates that the temperature of the contents has risen above a determined threshold, e.g., a threshold that has been determined to be adequately indicative of reliable burner operation. The spark control subsystem 307 then disables the spark generator 308 since the burner 302 is known to have ignited by the elevated temperature signal. If the burner 302 loses ignition, and the contents consequently cool, then the spark control subsystem 307 can re-enable the spark control generator 308. After the burner 302 has supplied sufficient heat to the vessel, the vessel temperature sensor 305 can generate a signal that indicates that heat is no longer required, which signal can cause the gas control valve 304 to cease gas supply to the burner 302, and cause the spark control subsystem 307 to disable the spark generator 308.
Q1, D1, R1, D2, and T1 provide a self-oscillating circuit, where the output of the secondary side of T1 is rectified and used to charge C4 to approximately 200VDC. R5, R4, R3, C2, NE1, D6, and SCR1 provide a voltage level sensing and trigger circuit. When the proper voltage is sensed, NE1 fires, which turns on SCR1 and dumps the voltage built up in C4 across the primary side of pulse transformer T2, which outputs a high voltage to generate a spark across the gap of a spark plug. C1 and R6 serve as a ground return and noise reduction for the high voltage spark (a snubber circuit). Q2, R6, R7, D6, and R8 all for a charge regulator to keep a three volt battery charged using a solar panel. T3 provides a noise filter, to help prevent noise from getting back into the DC charging circuit.
The present invention can be used with any gas-powered separator, including without limitation those marketed by Tesco Corporation, Allman Heath, Natco, American, and Weatherford. The invention is suitable for use in inclement weather, with both vertical and horizontal separators. Contemporary separators are typically approximately three feet in diameter and approximately none feet long, although the present invention is not limited to those sizes.
The temperature at which the burner is desired is generally in the range of 80 to 120 degrees Fahrenheit, although the present invention is suitable for use outside that range. Generally an output stack temperature of about 140 degrees Fahrenheit indicates that the burner is ignited, and that the spark generator can be stopped, although the present invention is suitable for use with various indications of main burner ignition. In typical environmental conditions, the time after burner ignition until the output stack reaches 140 degrees Fahrenheit can be about two to three minutes.
In some embodiments of the present invention, a 0.25 inch needle valve between the main gas valve and the burner to delay the arrival of gas to the burner. A 2 pound pressure switch was found to be suitable for initiating the spark circuitry, with a 10 pound burner supply pressure. A variety of spark devices can be used; spark igniters like those used in some water heaters can be suitable. A T12 thermostat made by Kimray was suitable as a temperature sensor in an embodiment of the present invention. A bimetallic strip sensor can be used to sense the temperature of the outlet stack.
The particular sizes and equipment discussed above are cited merely to illustrate particular embodiments of the invention. It is contemplated that the use of the invention may involve components having different sizes and characteristics. It is intended that the scope of the invention be defined by the claims appended hereto.
