Patent Grant
10844293
The present invention relates, in general, to the field of combustion systems, and in particular, to sparkless igniters and methods for use in heater treaters.
Crude oil is often extracted from oil wells as an oil-water emulsion that may also contain significant amounts of free water and natural gas. Gas is separated from the oil-water emulsion and free water using a gas separator. Free water may be removed using water knock-out vessels, which are also known as phase separators. The resulting oil-water emulsion, with minimal amounts of gas and free water, is then sent to a treater (also referred to as heater treater) to separate water from the emulsion. The treater dehydrates or dewaters the produced crude oil to a required basic sediment and water (BS&W) level. Oil-water separation may be enhanced by heating, adding emulsion breaking chemicals, coalescing media, and/or electrostatic fields. Most crude oils are treated to a range of 0.2% to 3.0% BS&W as determined by the ASTM Standard Test No. D96-82. Treaters typically contain water knock-out and de-gassing zones to produce crude oil of desired quality. Heating lowers the viscosity of the oil making it easier for the water to settle. It also aids in the coalescing of the water droplets, which facilitates water removal. Heater treaters are used where the emulsion cannot be broken using just retention, quiescence, and chemical demulsifiers.
Heater treaters may be vertical or horizontal in design and installation. Horizontal heater treaters have a significantly larger oil treating section, provide for longer residence times, and are used to treat heavier crudes where significant settling (residence) time is required. A schematic diagram of an exemplary vertical heater treater 100 is shown in
Heating may be accomplished using one or more firetubes 107. Fire tube 107 may be of a U-shaped design. The heat load of the burner (firetubes) is normally calculated on the assumption that the water content of the emulsion being heated will not exceed 20%. A heating shroud around the firetube may be used to minimize the heat load transferred to free water that can settle without heating. A maximum firetube heat flux is typically 10,000 BTU/h/ft2. Using a heat exchanger to recover heat from the treated crude that exits through tube 110 to heat incoming emulsion would reduce the amount of fuel required to heat the firetubes.
Ignition of fuel in the firetubes is done using a suitable fuel igniter that is removably affixed to fire tube 107. The igniter is typically fed with natural gas. Combustion product gases (flue gases) are vented through stack 113. Natural gas is a byproduct formed during oil extraction from oil wells, and is typically referred to as wellhead gas. Wellhead gas comprises a mixture of methane, ethane, propane, nitrogen, carbon dioxide, and water. Efficient operation of the treater depends on efficient firetube performance, which in turn depends on efficient igniter performance and adequate firetube design. Igniter performance depends on many factors including igniter design, durability of ignition elements, and proper adjustment of fuel gas pressure, which in turn controls fuel and air flow rates to the igniter. Firetube design depends on matching heat flux with the properties of the oil (water content etc.), selecting an optimum operating temperature and materials that provide good heat transfer without sacrificing durability. Commercially available igniters significantly reduce the durability of the firetube to less than five years in a vertical treater because the flame exiting the igniter through an igniter nozzle impinges on the bend region (U-shaped region) in the firetube, creates localized hotspots, and results in premature failure and significant replacement costs. Each leg of the U-shaped firetube is typically only about 4 feet in length before the bend. The diameter of the firetube is typically about 12 inch to about 20 inch. The flame plume obtained using these commercially available burner nozzles is approximately 5 inch to 7 inch in diameter and about 4 ft. to 6 ft. in length. The flame plume therefore impinges on the bend regions of the firetube and decreases durability of the firetube. In addition, the flame does not provide uniform heating along the length of the firetube (because the plume diameter is smaller than that of the fire tube), leading to higher fuel consumption and inefficient operation of the treater.
Ignition may be accomplished with spark igniters or sparkless igniters. In the case of spark ignition, the sparking tips require periodic cleaning to remove carbon accumulation formed as a byproduct of combustion. Further, periodic adjustment is required to maintain the spark gap between the two electrodes in a spark igniter. Therefore, there is an increasing interest in using sparkless ignition in treater firetubes.
Efficient sparkless igniters and methods to operate these igniters in conjunction with a suitable burner management system is therefore desired to improve the efficiency and reduce down time of heater treaters, and in particular, of vertical treaters.
In one aspect, a sparkless igniter comprises a fuel-air mixture inlet, a nozzle in fluid communication with the fuel-air mixture inlet and a fuel-air mixture conduit and disposed downstream of the fuel-air mixture inlet. The nozzle comprises a neck region and a throat region disposed contiguous with the neck region and separated by a boundary, a plurality of apertures characterized by a first diameter and arranged substantially in a first row in the neck region and disposed proximate to the boundary, a plurality of apertures characterized by a second diameter and arranged substantially in a second row in the throat region and disposed proximate to the boundary (the second diameter is less than the first diameter), and a plurality of apertures characterized by a third diameter and arranged substantially in a third row in the throat region and disposed between the second row and an exit end of the nozzle (the third diameter is less than the second diameter). A hot surface igniter assembly is removably disposed in the igniter such that a portion of the hot surface igniter assembly protrudes into the fuel-air mixture conduit to ignite the fuel-air mixture when the assembly is energized, and produces flue gases and a flame that exits through the plurality of apertures in at least one of the first, second, third rows of the nozzle and a nozzle orifice disposed at the exit end of the nozzle. The igniter may further comprise a flame sensor. In one embodiment, the flame sensor is a flame rod. In another embodiment, the flame sensor is a thermocouple.
In another aspect, a burner system for use in a vertical treater comprises an exemplary sparkless igniter removably affixed in the fire tube of the vertical treater, and a fuel-air mixer configured to deliver fuel-air mixture through an orifice in the mixer to the fuel-air mixture inlet of the igniter and through a nipple removably disposed between the mixer and the igniter. The length of the nipple is at least eight times the diameter of the nipple.
In another aspect, a method for heating the fire tube in a heater treater comprises providing an exemplary sparkless igniter removably affixed in the fire tube of the vertical treater to ignite a fuel-air mixture, and providing a fuel-air mixer configured to deliver fuel-air mixture through an orifice in the mixer to the fuel-air mixture inlet of the igniter and through a nipple removably disposed between the mixer and the igniter. The length of the nipple is at least eight times the diameter of the nipple. Ignition of the fuel-air mixture generates a flame plume having a diameter substantially equal to the diameter of the fire tube and a flame length less than the length of each leg of the fire tube. The heater treater may be a vertical heater treater or a horizontal heater treater.
In another aspect, a method for heating the fire tube in a heater treater comprises providing an exemplary sparkless igniter comprising a flame rod and removably affixed in the fire tube of the heater treater, energizing the hot surface igniter assembly for a first time period, providing a fuel-air mixture to the igniter, measuring a control parameter such as a flame strength value (FSV) of the igniter wherein the energizing of the hot surface igniter assembly is continued for a second time period if the FSV is greater than a threshold FSV, shutting off fuel-air mixture to the igniter if the FSV is greater than the threshold FSV after the second time period and waiting for a third time period, and repeating the ignition sequence until the FSV falls below the threshold FSV that indicates successful ignition of the fuel-air mixture in the fire tube.
In another aspect, a method for heating the fire tube in a heater treater comprises providing an exemplary sparkless igniter comprising a thermocouple and removably affixed in the fire tube of the heater treater, energizing the hot surface igniter assembly for between about 8 seconds and about 10 seconds, providing a fuel-air mixture to the igniter, monitoring the change in temperature (ΔT) relative to ambient temperature after about 30 seconds, shutting off fuel-air mixture to the igniter if ΔT is less than about 100° C. and waiting for about 2 minutes, repeating the ignition sequence until ΔT is greater than about 100° C., monitoring the flame temperature at about 10 second intervals until a maximum flame temperature is reached and shutting off fuel-air mixture if the flame temperature decreases by about 1% of the maximum temperature.
In another aspect, a nozzle for use in a sparkless igniter comprises a neck region and a throat region disposed contiguous with the neck region and separated by a boundary, a first plurality of apertures disposed in the neck region upstream of the boundary, a second plurality of apertures disposed in the throat region between the boundary and an exit end of the nozzle, and a nozzle orifice disposed at the exit end of the nozzle wherein the cross sectional area of the first plurality of apertures is between about 40% and about 45% of the total cross sectional area of the first plurality of apertures, second plurality of apertures and the nozzle orifice. Ignition of a fuel-air mixture in the sparkless igniter results in flue gases and a flame exiting through at least one of the plurality of apertures and the nozzle orifice.
Other features and advantages of the present disclosure will be set forth, in part, in the descriptions which follow and the accompanying drawings, wherein the preferred aspects of the present disclosure are described and shown, and in part, will become apparent to those skilled in the art upon examination of the following detailed description taken in conjunction with the accompanying drawings or may be learned by practice of the present disclosure. The advantages of the present disclosure may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appendant claims.
The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
All reference numerals, designators and callouts in the figures are hereby incorporated by this reference as if fully set forth herein. The failure to number an element in a figure is not intended to waive any rights. Unnumbered references may also be identified by alpha characters in the figures and appendices.
The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which igniter designs for heater treaters may be practiced. These embodiments, which are also referred to herein as “examples” or “options,” are described in enough detail to enable those skilled in the art to practice the present invention. The embodiments may be combined, other embodiments may be utilized or structural or logical changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense and the scope of the invention is defined by the appended claims and their legal equivalents.
In this document, the terms “a” or “an” are used to include one or more than one, and the term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. Further, “igniter,” and “ignitor,” should be construed to have the same meaning. “Fire tube” and “firetube” should be construed to have the same meaning. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. An emulsion is a relatively stable dispersion of water and oil which exits from flowing or pumped oil wells. For construing the scope of the term “about,” the error bounds associated with the values (dimensions, operating conditions etc.) disclosed is ±10% of the values indicated in this disclosure. The error bounds associated with the values disclosed as percentages is ±10% of the percentages indicated.
Particular aspects of the invention are described below in considerable detail for the purpose for illustrating its principles and operation. However, various modifications may be made, and the scope of the invention is not limited to the exemplary aspects described.
Exemplary nozzle 207 may be rated to support vertical treater firetube rating of about 500,000 BTU/h. Operating with about 4 vol.-% residual oxygen in the flue gas exiting the vertical treater at a flue stack temperature of about 900° F., and using natural gas with a heating value (HHV) of 1050 BTU/SCF as the fuel, yields a combustion efficiency of about 69% (API Specification 12L). The heating value of natural gas may however vary between 1000 and 1600 BTU/SCF. Under these exemplary conditions, igniter 200 comprising nozzle 207 may ignite about 700 SCF (standard cubic feet) of natural gas. Nozzle 207 comprises a fuel entry end 301 and an exit end 302 (
In a commercially available nozzle sold by the applicant, the neck region does not comprise of any apertures. Instead, the throat region comprised a first row of a plurality of apertures of diameter of about 0.25 inch and located proximate to the boundary between neck and throat regions. The throat region also comprised a second row of a plurality of apertures of diameter of about 0.22 inch and located between the second row of apertures and the exit end of the nozzle. Further the diameter of the nozzle orifice located in the exit end was about 1.42 inch.
Alternately, igniter nozzle 207 may be suitably modified to directly couple to the igniter body 200 that does not contain the neck 206. For example, one end of nozzle 207 could be configured to comprise a male threaded section that can be screwed into a mating female threaded section in body 201 that is fluid communication with the fuel-air mixture conduit 202. Further, the nozzle may be removably attached to the conduit 202 using flanges or other quick connect fittings.
A cylindrical hot surface ignition assembly (HSI) 210 is removably inserted through opening 217 in conduit 203 (
The HSI assembly is configured to fit snugly in the opening that connects conduits 202 and 203. HSI assembly 210 comprises an igniter heating element 211 that is substantially enclosed in a high temperature ceramic body 212. Wires 213 are electrically connected to the igniter heating element 211 and are used to energize the igniter heating element using preferably a DC (direct current) electrical source. A portion of element 211 protrudes from the ceramic body 212. A high temperature alloy guard (e.g. Inconel guard) 214 protects the ceramic body, and the exposed part of heating element 211. The diameter of the Inconel guard is preferably 0.4 inch to 0.5 inch in diameter, and more preferably 0.4 inch to 0.45 inch. HSI assembly (not including the length of the wires 213) is preferably 2 inch to 3 inch in length and more preferably between 2 inch and 2.5 inch in length. The length of the heating element 211 that protrudes from the ceramic body 212 is preferably between 0.3 inch and 0.6 inch and more preferably between 0.4 inch and 0.55 inch.
The igniter element may be made of durable, high temperature materials such as silicon carbide or silicon nitride. Other transition metal carbides or nitrides may also be used. When a suitable voltage (preferably DC voltage) is applied to the element 211, it heats up to enable auto ignition of the fuel or wellhead gas flowing in conduit 202. The HSI element is heated for a predetermined time before it is exposed to the fuel-air mixture. The predetermined time for energizing the HSI may be in the order of a few seconds, and preferably between 5 seconds and 15 seconds. If ignition is not detected within the predetermined time, the gas valve closes and the burner management system will repeat the start-up sequence. HSI assemblies are available from sources that include, but are not limited to, Robertshaw, Crystal Technica, Honeywell, and the like. These igniters may be energized using 12 to 24 VDC or 120 to 280 VAC. The heating elements may be enclosed proprietary ceramic composite materials.
Igniter 200 is equipped with a flame sensor 223, which senses the presence or absence of a flame, and feeds the signal to a burner management system. Flame sensors include, but are not limited to, flame rods and thermocouples. At start-up, the HSI element is energized before fuel feed is started. Fuel pressure is controlled to about 5-15 psig using a suitable regulator. Auto-ignition of the fuel-air mixture on the hot surface of the HSI element is detected using the flame sensor. If a flame is not detected within the predetermined time, the fuel valve close and the system recycles. If a flame is extinguished for any reason during operation, the fuel valve closes and the system recycles.
In the case of a flame rod, an AC current is applied to the flame rod such as Kanthal flame rods rated to 2600° F. (available for example, from Honeywell), which then flows through the ions in the flame, and to the igniter assembly/head to ground. Because the surface area of the flame rod is much smaller than that of the igniter head, the AC current is rectified to DC current in the process commonly known as flame rectification. The magnitude of this current could vary from 0.25 to 8 mA. Armored wiring harness rated at 500° F. or above is used. The burner management system opens the main gas valve to the igniter if it detects a DC current (which may be converted to a suitable voltage reading using resistors) of pre-determined magnitude. As an alternative to flame rods, thermocouples may be used to sense the temperature of the flame and/or exhaust gases. An exemplary thermocouple is the K-type thermocouple, which is rated to 2400° F. Because these thermocouples are located in the flame, they are usually sheathed in high temperature metal sheaths such as Inconel.
Other variations in nozzle design may be used to achieve similar results. In fact, nozzles that provide for different flame length and flame diameter may be interchangeably used with the exemplary igniter. For example, one or more rows of apertures of varying diameters may be used depending on at least one of desired fuel flow rate, fire tube design, and heat duty of the fire tubes. Apertures need not be circular in shape. Other shapes such as oval shaped apertures may be used. Any single row may comprise a plurality of apertures of varying diameters. The nozzle may comprise a plurality of neck and throat regions. Further, apertures of varying diameters may be located in the neck and throat regions with their centers offset from one another instead of being arranged in rows. That is, the apertures need not be arranged in rows. While exemplary nozzles have been demonstrated in vertical heater treaters, they may be also used in horizontal treaters. The disclosed sparkless igniter can be scaled up or scaled down in size depending on the heat duty that is desired for the particular application.
Exemplary nozzle 207 that comprise a plurality of apertures arranged in rows or in other patterns, may also comprise elements such as shutters to selectively open and close one or more aperture rows to obtain the desired flame plume shape to optimize heat transfer efficiency and durability of firetubes of various dimensions. This feature eliminates the need to replace nozzle 207 in igniters whenever the dimensions of the firetube and heat duty changes. Shutter type elements may also be used to change the size of the nozzle orifice 303. The exemplary nozzle may be used in spark igniters wherein the HSI element is replaced with a sparking mechanism.
Igniter operation may be controller using a burner management system (BMS). During start-up, the HSI element in exemplary igniter 200 is energized for about 8 seconds to 10 seconds, preferably using a DC voltage of about 12 to about 24 volts. The HSI element temperature rapidly increases to auto-ignition temperature of the fuel. The burner management system then initiates fuel flow to the igniter and monitors the signal from the flame sensor. When the igniter is equipped with a flame rod as the sensor 223, the BMS checks whether ignition has occurred by monitoring Flame Strength Value (FSV) of the igniter as a control parameter. An FSV of about 3 to about 4 (equivalent to 555 mV) indicates that ignition has occurred. An FSV of greater than about 250 (threshold value) indicates that ignition failed to occur, in which case, the igniter stays energized for an additional time period of about 5 seconds to about 10 seconds. Typically, in the absence of a flame, the FSV is about 504 to about 505 (equivalent to about 4700 mV). If ignition continues to fail, the BMS shuts off fuel flow, waits for 1-3 minutes, preferably about 2 minutes, and initiates the above sequence once again. A burner management system as disclosed in U.S. application Ser. No. 11/047,794 entitled “METHOD, APPARATUS AND SYSTEM FOR CONTROLLING A GAS-FIRED HEATER,” may be used to control operation of the exemplary igniter. Instead of monitoring a calculated parameter such as FSV, the BMS may monitor the output of the flame rod in terms of current (mA) or voltage (mV). FSV is generally a function of electrical resistance of the HSI element and exhibits a linear relationship with measured electrical resistance.
If a thermocouple is used as the flame sensor (instead of a flame rod), during start-up, the HSI element in exemplary igniter 200 is energized for between about 8 seconds and about 10 seconds, preferably using a DC voltage of about 12 to about 24 volts. The HSI element temperature rapidly increases to auto-ignition temperature of the fuel. The burner management system initiates fuel flow to the igniter. After about 30 seconds, the BMS monitors the change in flame temperature (ΔT) relative to ambient temperature. A ΔT value of about 100° C. in about 30 seconds (ΔT/Δt of about 3.3 degrees/second) indicates the presence of a flame. If ignition failed to occur, the fuel flow is shut off and the sequence is repeated again. If ignition was successful, the BMS monitors flame temperature at intervals of about 10 seconds until the temperature levels off at a maximum temperature (typically 600° F. to 2000° F. depending on the heating value of the fuel and the application). The BMS continues to monitor temperature at 10 second intervals. A decrease in temperature by at least 1% of maximum temperature indicates that the absence of a flame. The BMS shuts off fuel flow and the sequence is repeated again.
The BMS also measures the resistance of the HSI element. The measured resistance of the HSI element can also be used to predict if the HSI element or assembly is wearing out. Aging of the resistance wires may occur at high temperatures due to cyclic operation, and possibly due to some carbon formation. The resistance of the HSI element is also a function of the age of the HSI element. Aging generally causes an increase in the resistance of the HSI element. The resistance of a fresh HSI element is about 2 ohms, and more typically between 1.6 and 2.4 ohms at a reference temperature of 50° C. An aged igniter element is characterized by a resistance of about 3.5 ohms at a reference temperature of 50° C. An increase in measured resistance at a reference temperature would suggest that the heating element is aging. As a remedial measure, the energizing voltage to the HSI element can be increased in steps of about 0.5 volts (when DC voltage is used) to compensate for the aging of the heating element. Increasing the energizing voltage is warranted if the measured resistance at a reference temperature exceeds the baseline resistance by more than 50%, and preferably by more than 75% to compensate for ageing of the hot igniter surface assembly. If this action fails, replacement of the HSI element would be required. The control methods in the burner management system can also keep track of the service time of the HSI element, and increase resistance accordingly to offset the effects of aging to achieve a predetermined ignition temperature.
In another aspect, the igniter body may comprise of more than one subassemblies that are removably coupled to form the igniter body assembly. One or more of the subassemblies may be opened to replace or swap out worn out or malfunctioning hot surface elements if needed. This permits the user to use the same sparkles igniter, while changing out the HSI elements, when needed and could lead to cost savings.
The disclosed sparkless igniter requires no cleaning and adjustments once installed and commissioned in a burner management system. The use of the disclosed igniter in burner management systems is particularly beneficial when operating at remote sites (often at freezing conditions in winter) because traveling to these sites is difficult and often hazardous.
The Abstract is provided to comply with 37 C.F.R. § 1.72(b), to allow the reader to determine quickly from a cursory inspection the nature and gist of the technical disclosure. It should not be used to interpret or limit the scope or meaning of the claims.
Although the present disclosure has been described in connection with the preferred form of practicing it, those of ordinary skill in the art will understand that many modifications can be made thereto without departing from the spirit of the present disclosure. Accordingly, it is not intended that the scope of the disclosure in any way be limited by the above description.
It should also be understood that a variety of changes may be made without departing from the essence of the disclosure. Such changes are also implicitly included in the description. They still fall within the scope of this disclosure. It should be understood that this disclosure is intended to yield a patent covering numerous aspects of the disclosure both independently and as an overall system and in both method and apparatus modes.
Further, each of the various elements of the disclosure and claims may also be achieved in a variety of manners. This disclosure should be understood to encompass each such variation, be it a variation of an implementation of any apparatus implementation, a method or process implementation, or even merely a variation of any element of these.
Particularly, it should be understood that the words for each element may be expressed by equivalent apparatus terms or method terms—even if only the function or result is the same. Such equivalent, broader, or even more generic terms should be considered to be encompassed in the description of each element or action. Such terms can be substituted where desired to make explicit the implicitly broad coverage to which this disclosure is entitled. It should be understood that all actions may be expressed as a means for taking that action or as an element which causes that action. Similarly, each physical element disclosed should be understood to encompass a disclosure of the action which that physical element facilitates.
In addition, as to each term used it should be understood that unless its utilization in this application is inconsistent with such interpretation, common dictionary definitions should be understood as incorporated for each term and all definitions, alternative terms, and synonyms such as contained in at least one of a standard technical dictionary recognized by artisans and the Random House Webster's Unabridged Dictionary, latest edition are hereby incorporated by reference.
Further, the use of the transitional phrase “comprising” is used to maintain the “open-end” claims herein, according to traditional claim interpretation. Thus, unless the context requires otherwise, it should be understood that the term “compromise” or variations such as “comprises” or “comprising,” are intended to imply the inclusion of a stated element or step or group of elements or steps, but not the exclusion of any other element or step or group of elements or steps. Such terms should be interpreted in their most expansive forms so as to afford the applicant the broadest coverage legally permissible.
This application is related to and claims the benefit of and priority to U.S. Provisional Patent Application No. 62/562,732, filed Sep. 25, 2017, and entitled “Sparkless Igniters And Methods For Heater Treaters,” the entire disclosure of which is hereby incorporated herein by reference in its entirety.
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