Patent Application
20170211806
The present disclosure relates to vent gases resulting from petroleum production and processing and in particular to the combustion of the excess vent gases using an auxiliary burner.
The venting of hydrocarbon vapors into the atmosphere has been a common practice at many petroleum production and processing facilities. Often, where the amounts are substantial, the vapors are collected, recompressed and used. There are many other locations where these vapors are vented to the atmosphere. Recently, as of 2012/2013, the United States Environmental Protection Agency (EPA) has placed an upper limit on the amount of volatile organic vapors (VOCs) that may be vented. There is also a desire to minimize the venting of methane gases or gases that decompose to methane to the atmosphere because methane has a strong greenhouse gas heat trapping effect, being twenty-one times more effective than carbon dioxide over a 100 year period.
Vent gases originate from petroleum liquids that are stored in one or more tanks but can come from many sources in the extraction, collection, storage, processing and transportation of oil and gas. A pressure relief devices that allow the gases to escape to the atmosphere if a specified pressure is exceeded. To prevent the escape of the vent gases to the atmosphere these vent gases are directed to a burner system that consumes the gas vapors at a pressure below the pressure relief set-point.
An effective method to deal with the vented gases is to combust the gases under controlled circumstances. The standard method of combusting these gases is to feed these gases to an incinerator unit or flare where a pilot, either continuous or started on demand, feeds into the vented gases in the presence of air to ignite the gases. In the case of a flare, the vent gases are directed through a vertical tube or pipe and burned as the gases contact air. Since a flare is undesirable from an environmental and public perception point of view, the general preference is to enclose the flame and to regulate the air flow to achieve combustion with good air-fuel ratio control. The disadvantage with flares and incinerators is that the heat energy from the vapor combustion is lost and not used. In addition, adding a flare or incinerator to a site may require additional effort to obtain permission for installation and operation by regulatory authorities.
In many of the petroleum production processes fired heater units are employed for a multitude of purposes. Such heaters are used on an intermittent basis in response to the process requiring the heat energy and as a result are not always available to combust the vent gases. Typically these heaters use a burner jet where the fuel is introduced and a horizontal fire tube for directing the flame and the hot combustion gases to the medium requiring the heat and then to a vertical stack for directing the exhaust gases to the atmosphere. The horizontal portion may be simply one pipe or several parallel pipes connected to a stack, a U arrangement or a multi-pass arrangement where the pipe or pipes make several passes through the medium to be heated. The use of heaters can provide an effective solution to using vent gases however varying demand requirements can result in times when heating of the medium is not required and the vent gases must be dealt with.
Accordingly, systems and methods that enable a novel way of combusting excess vent gases when a main burner is not in operation remains highly desirable.
Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
Embodiments are described below, by way of example only, with reference to
In accordance with an aspect of the present disclosure there is provided an auxiliary burner assembly for combusting excess combustible vent gases, the auxiliary burner assembly comprising: a first auxiliary burner unit housed within an exhaust stack of a main burner assembly above the main burner assembly, the first auxiliary burner unit for combusting vent gases received from a vent gas supply line; and an outer pipe for supporting the first auxiliary burner unit within a center of the outer pipe having a diameter equal to or larger than a main fire tube of the main burner assembly; and wherein the first auxiliary burner unit combusts vent gases when the main burner assembly is inactive.
In accordance with another aspect of the present disclosure there is provided a method for controlling an auxiliary burner assembly, the method comprising: initiating an auxiliary burner of the auxiliary burner assembly positioned in an exhaust stack of a main burner assembly; initiating a main pilot of the main burner assembly; initiating the main burner of the main burner assembly; determining the air flow velocity in the main burner assembly; and shutting off auxiliary burner assembly when air flow velocity reaches a pre-determined threshold.
In accordance with yet another aspect of the present disclosure there is provided an auxiliary burner assembly for combusting excess combustible gases from a vent gas tank, the auxiliary burner assembly comprising: a first auxiliary burner unit housed within an exhaust stack of a main burner assembly, the first auxiliary burner unit for combusting vent gases received from a vent gas supply line from the vent gas tank; and an outer pipe for supporting the first auxiliary burner unit within a center of the outer pipe having a diameter equal to the exhaust gas stack of the main burner assembly; and wherein the first auxiliary burner unit is utilized to combust vent gases from the vent gas tank when the vent gases exceed a first pressure set-point and the main burner assembly is inactive.
In accordance with an aspect of the present disclosure there is provided a method for controlling an auxiliary burner assembly for combusting vent gases, the method comprising: determining a state of a main burner assembly; determining a pressure value of vent gas in a vent gas tank; and initiating the auxiliary burner assembly to combust vent gas when the pressure value of gas in the vent gas tank exceeds an upper pressure set-point value and the determined state of the main burner assembly is inactive.
In accordance with another aspect of the present disclosure there is provided a controller for controlling the combusting vent gas, the controller comprising: a processor; and a memory containing instructions which when executed by the processor cause the processor to: determine a state of a main burner assembly; determine a pressure value of vent gas in a vent gas tank; and initiate an auxiliary burner assembly to combust vent gas when the pressure value of gas in the vent gas tank exceeds an upper pressure set-point value and the determined state of the main burner assembly is inactive.
In accordance with still yet another aspect of the present disclosure there is provided an auxiliary burner assembly for combusting vent gases comprising: a pilot unit; a burner unit housed within an exhaust stack of a main burner assembly for heating a medium; and an outer pipe surrounding the burner unit and pilot unit within a center of the outer pipe, the outer pipe having a flange for coupling to an exhaust gas stack of the main burner assembly wherein the auxiliary burner assembly is utilized to combust vent gases from a vent gas tank when the main burner assembly is inactive.
In accordance with still yet another aspect of the present disclosure there is provided a computer readable memory containing instructions for controlling an auxiliary burner assembly for combusting vent gases, the instructions which when executed by a processor performing the method comprising: determining a state of a main burner assembly; determining a pressure value of vent gas in a vent gas tank; and initiating the auxiliary burner assembly to combust vent gas when the pressure value of gas in the vent gas tank exceeds an upper pressure set-point value and the determined state of the main burner assembly is inactive.
An auxiliary burner can be utilized to combust vent gases from petroleum production or processing when a main burner is not required for heating of a medium. The auxiliary burner assembly is inserted within the exhaust stack of an existing main burner to eliminate the need for additional exhaust stacks to be added. A control system consisting of a set of valves, regulators, and sensors that ensure the existing main burner achieves its purpose to maintain the desired production of heat, while using the vent gas as the source of gases for the main burner. When the main burner is not on and vent gas is present, the vent gas is directed to the auxiliary burner in the stack where the heat from the combustion of the vent gases does not add heat to main burner region. A combustion zone of the auxiliary burner is less than the main burner if an internal fire tube is utilized. The diameter of the auxiliary fire tube is less than that of the exhaust stack the airflow in the exhaust stack prevents the combustion zone of the auxiliary burner from creating excessive surface temperatures in the existing exhaust stack. At times when the main burner is not being utilized and the excess vent gas needs to be combusted one or more internal auxiliary burners can be utilized to combust the gases while the main burner is inactive.
In conditions where excess vent gas may need to be dealt with and the main burner is not active, a lower capacity auxiliary burner may not be sufficient to handle the excess vent gas. To provide a high capacity auxiliary burner, rather than using a containment area with the exhaust stack, external heat shields are provided to enable larger auxiliary burners. The external heat shields allow full use of the existing exhaust stack diameter as a combustion zone for the auxiliary burner unit. This enables an existing exhaust stack to be utilized for excess gas combustion by using the same airflow as the main burner and the auxiliary burner. No auxiliary burner flow regulation is required because the main burner already has an air flow regulator. If additional air flow control is required, a limited area auxiliary burner flow regulator can be installed.
The vent control system described provides an efficient combustor for all the components of the tank gases which may include methane, ethane, propane and butane and smaller amounts of other volatile gases. If the methane escapes to the atmosphere it has a greenhouse effect. Over a 100 year time period the global warming potential, according to the International Panel on Climate Change (IPCC) of methane is some twenty-five or more times that of the same mass of carbon dioxide. When the methane is combusted 1 kg of methane, equivalent to 25 or more kg of carbon dioxide is changed to water and 44/16=2.75 kg of carbon dioxide, thus leading to a reduction in the greenhouse effect of the vented gases. In addition, the non-methane components of the tank gas may decompose, due to natural processes in the atmosphere, to products which include methane. The advantages to such a system where an auxiliary burner is added to an existing burner assembly is the combustion of volatile organic vapors to meet environmental regulations, the reduction in total gases burned, which lessens operating costs and greenhouse gas emissions, and elimination of the need to seek approval for the addition of an additional burner to a oil and gas production site
The shields 212 may comprises dimpled sheets shaped in cylindrical shapes. The dimpling is sufficient to provide physical separation by 1 mm or more of individual layers. Alternatively the fire tube 212 may be provided by a ceramic lining within the exhaust gas stack to deal with the higher temperature in the auxiliary burner flame zone approximately 0.3 to 2.2 meters above the flange. The inner lining of the lower stack portion can be composed of a heat resistant material such as fire brick reduces the surface temperature of the metal stack.
A high capacity auxiliary burner assembly 410 provides for the combustion of excess combustible gases when the main burner is not required and inactive and the pressure of the vent gas is above an upper pressure set-point value. The high capacity auxiliary burner size can approach or exceed the main burner size as no extra air that flows through the existing fire tube and the flame arrestor is needed for internal cooling. By integrating the auxiliary burners 412 and 414 into the exhaust stack 106, the combustion of the vent gases can be provided without additional exhaust stacks at the production/processing site. Burner control logic as described below is provided so that only the main burner in the fire tube 104 is active or the auxiliary burners 412 and 414 are active at one time, in this way the air 114 is available for either burner. Each auxiliary burner 412 and 414 may have gas mixer assemblies. Although the shrouds 416 and 418 are shown as commencing above the auxiliary burner at flange 206, they may be part of the auxiliary assembly 410 or provided in additional to the auxiliary assembly. Similarly the auxiliary assembly 410 may be integrated in to the exhaust stack or provided in a retrofit installation and the shroud installed around an existing exhaust stack.
The BMS 502 continuously monitors the temperature of the medium 102 needing heat by measuring the output of a thermocouple 580 in the medium 102 and subject to the low liquid level switch 584 and the gas temperature 582, turns on its pilot if heat is needed. After a delay to confirm the pilot of pilot assembly 112 is on, the BMS 502 opens the valve 506 for the main burner 110. The status of the pilot is sent to the main controller 503 by the digital input to the main controller 503. When the pilot of the pilot assembly 112 is on, the main controller 503 controls the gas flow according to the following criteria:
If vent gas pressure 501 from a vent gas, measured by the pressure sensor 530, is below the lower pressure set-point, the solenoid operated shut-off valve 532 is opened to allow the process gas 500 to flow to the main burner 110.
If vent gas 501 pressure is above a specified first pressure set-point, the solenoid operated shut-off valve 534 is opened to allow the vent gas 501 to flow to the main burner 110 until the vent gas 501 pressure drops below the lower pressure set-point. The specified first pressure set-point can either be the lower pressure set-point plus a pressure margin or an upper pressure set-point.
If the vent gas 501 pressure does not drop below a specified value within a specified period of time, the BMS 502 is remotely shut-off causing the pilot 112 and main burner 110 to go off. The auxiliary burner may then be utilized to reduce the pressure as the auxiliary burner may have higher burner capacity than the main burner.
When the main pilot 112 is off, indicating no heat is needed by the medium 102, the main controller 503 controls the gas flow according to the following criteria:
If the vent gas 501 pressure measured by the pressure sensor 530 is below the lower pressure set-point no gas flow valves are opened.
If the vent gas 501 pressure is above the upper pressure set-point, the ABCS 510 is turned on remotely. The ABCS 510 causes the pilot 216 to ignite using similar criteria to the BMS 502. When the pilot 216 is confirmed to be operating, the ABCS 510 opens solenoid operated shut-off valve 512 and solenoid operated shut-off valve 534 allowing the vent gas 501 to flow to the auxiliary burner unit 214 until the vent gas 501 pressure drops below the lower pressure set-point.
The main controller 503 monitors the low level pressure switch 540, and does now allow any parts of the system to operate if the process natural gas 500 pressure is too low. If the high-level switch 542 in the liquids knock-out container for the vent gas 501, the burner is not permitted to burn the vent gas 501. Additional pressure control regulators 566 and 568 may be provided in the system to regulate gas flow within the system. The ambient temperature may be received by the main controller 503 from sensor 586 to enable control modifications according to the ambient temperature or to enable ambient temperature corrections to orifice flow calculations. Referring to
It should be understood that there may be variations in the logic details and the choice and positioning of control and monitoring devices and the implementation disclosed should not be considered limiting in any way. The described system and method enable a desired amount of heating to be maintained by using as much vent gas as possible and ensuring the vent gas vapors are combusted to prevent the escape of the unburned vent gases to the atmosphere. Although the control functions described in relation the burner management system, ABCS, and main controller may be associated with a particular controller containing a processor, the functions may be performed by a single controller or processor; alternatively the functions may be allocated across multiple controllers or processors. The control functions are provided by at least a processor having an associated memory, the memory providing instructions for performing one or more functions associated with controlling a main burner and auxiliary burner to combust vent gases of a petroleum production and processing facility.
If the main burner and pilot assembly are not active, the auxiliary burners can be initiated if required. If the gas pressure is below the lower pressure set-point (YES at 722) no valves are opened (724) and the auxiliary burners are not initiated. Alternatively, if the auxiliary burners are already active, the associated valves are closed to shut-off the auxiliary burner assembly. If the gas pressure is below the upper pressure set-point (NO at 726) no valves are opened (724) and the auxiliary burner is not initiated. If the gas pressure is above the lower pressure set-point (NO at 722) and is above the upper pressure set-point (YES at 726) the auxiliary pilot is initiated (728) as discussed above. Once it has been confirmed that the pilot is active the valve from the vent gas to the auxiliary burner(s) is opened (730) and the decision process starting at (702) is repeated until the upper or lower vent gas pressure set-points are exceeded. Alternatively, if the medium heating requirements change (702) the auxiliary burner assembly may be turned off (705) and the main burner initiation process commenced (706). If multiple auxiliary burners are provided the selection of which of the auxiliary burners that are required may be determined based upon gas flow rates and capacity ranges of each of the auxiliary burners. If there is a need to quickly switch the vent gas flow from the main burner to the auxiliary burner, the auxiliary pilot can be on at all times.
In some cases the maximum capacity of the auxiliary burner is insufficient to meet or exceed the rate at which vent gases are generated by other processes. An example of the variability in vent gas flow rate from a petroleum liquids storage tank is shown in the graph 1000 of
A limitation in the maximum capacity of the auxiliary burner is the temperature of the stack portion adjacent to the flame zone. The maximum temperature is determined by the material properties of the stack and the self-ignition temperature of an air-fuel mixture that may exist adjacent to the stack. A vertical temperature profile of the stack surface temperatures observed when the auxiliary burner is operational is shown in graph 1100 of
The removal of the inner heat shield 212, removal of the auxiliary baffle 920, and/or an increase in the stack diameter may be used to increase the auxiliary burner capacity. However these modifications do not increase the amount of air available that must be drawn in through the existing fire-tube and flame arrestor. It is well known that an increase in stack height does increase the air flow, but there are practical and economic reasons that preclude a large increase in stack height. A further method of providing the additional air required by the auxiliary burner is the addition of a fan between the flame arrestor 108 and the main burner 110. The fan can provides the additional air required by the auxiliary burner.
Alternatively,
In some embodiments, any suitable computer readable media can be used for storing instructions for performing the methods described herein to be executed by a processor. For example, in some embodiments, computer readable media can be transitory or non-transitory. For example, non-transitory computer readable media can include media such as magnetic media (such as hard disks, floppy disks, etc.), optical media (such as compact discs, digital video discs, Blu-ray discs, etc.), semiconductor media (such as flash memory, electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), etc.), any suitable media that is not fleeting or devoid of any semblance of permanence during transmission, and/or any suitable tangible media.
Although the description discloses example methods, system and apparatus including, among other components, software executed on hardware, it should be noted that such methods and apparatus are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of these hardware and software components could be embodied exclusively in hardware, exclusively in software, exclusively in firmware, or in any combination of hardware, software, and/or firmware. Accordingly, while the fore-going describes example methods, systems and apparatus, persons having ordinary skill in the art will readily appreciate that the examples provided are not the only way to implement such methods and apparatus.
The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. In the design of the auxiliary burner section, one or more of the described embodiments may be used to meet the desired maximum vent gas flow rate to the auxiliary burner. It is recognized that variations in the described innovations are possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2822267 | Jul 2013 | CA | national |
This application is a continuation-in-part of U.S. patent application Ser. No. 14/448,492 which is incorporated by reference for all purposes which claims the benefit of Canadian Patent Application Serial No. 2,822,267, filed 31 Jul. 2013 which is hereby incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14448492 | Jul 2014 | US |
| Child | 15431288 | US |
