Abstract:
A dual-pressure flare system and a method of its use. The dual-pressure flare system includes a dual-pressure flare stack having a central axis that is aligned with the center of a high-pressure outlet; a high-pressure flue having a central axis that is co-linear with the central axis of the dual-pressure flare stack; and a low-pressure flue connected to a low-pressure tip. Some exemplary embodiments of the system further include an air-assist assembly having an air-supply connection connected to an air blower and a mixing chamber, wherein the mixing chamber surrounds the low-pressure tip. In some exemplary embodiments, the air-supply connection is disposed outside the dual-pressure flare stack and the high-pressure flue.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims priority from U.S. Ser. No. 13/967,082 filed on Aug. 14, 2013. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates in general to a gas flare and more particularly to a dual-pressure gas flare system. 
       BACKGROUND 
       [0003]    In oil and gas operations (e.g., oil and gas processing plants, wells, offshore rigs, and landfills), situations arise that may necessitate burning of combustible waste gases from time to time. Environmental laws and regulations and ecological considerations require that these gases be burned with a smokeless efficiency before being released into the atmosphere. For example, the United States Environmental Protection Agency (EPA) regulations (40 C.F.R. §60.18) require that a gas flare operate at the destruction and removal efficiently (DRE) of 98% or greater. DRE is the percent removal of hydrocarbon from the flare vent gas. The EPA regulations provides empirically derived equations that use variables such as flare type, the net heating value of the gas being combusted, and the exit velocity of the gas to indirectly determine if a flare is operating at a DRE of 98%. In other words, the EPA assumes that a flaring meeting the operating condition requirements of 40 C.F.R. §60.18 operates at a DRE of 98%. But even if a flare is operating at the regulatory criteria, the actual DRE can often be lower than 98%. So a system that operates in compliance with the regulations can still produce a significant amount of smoke, which may raise environmental concerns. 
         [0004]    The gases that need to be flared vary in composition and pressure. High-pressure gases generally have sufficient kinetic energy and do not require additional energy to be imparted to the flaring system to burn smokelessly. But low-pressure hydrocarbon gases, having a hydrogen-to-carbon molecular weight ratio of less than 0.3, 0 produce smoke as a result of incomplete combustion and the formation of free carbon. Various systems and methods for coping with smoke generation have been proposed. One method uses steam or water as smoke suppressant. Others use a supply of high-pressure gas to increase hydrogen-to-carbon ratio. Another method uses forced air to provide turbulent mixing of air with the hydrocarbon gas for complete smokeless combustion. Providing additional kinetic energy and oxygen to the low-pressure gas supply can increase the DRE. This method is typically referred to as “air-assist flaring.” This type of air-assisted flaring is advantageous when neither steam nor assist gas is available because a simple air blower can be used to provide forced air. Some air-assisted flare systems suffer from inefficiencies due to over-assisting, i.e., providing more assist air than is necessary or providing assist air but not actually increasing the DRE. 
         [0005]    An oil and gas operation may need to vent both high- and low-pressure gases at various times. Because low-pressure gases require additional assist systems (e.g., steam, gas, or air), separate flare systems are often used for the different pressure waste gases. Some have proposed designs for a single flare system that is capable of processing both low and high pressure waste gases, but these systems have certain limitations and inefficiencies. U.S. Pat. No. 3,822,985 issued to John F. Straitz, III (“Straitz patent”) discloses a flare stack gas burner for waste combustible gases at both low and high pressure with separate delivery systems for each. The Straitz patent teaches a central flare stack with a low-pressure gas delivery tube disposed inside. A separate tube feeds air into the central flare stack to mix with the low-pressure gas with a swirling action caused by the burner tip design. High-pressure gas delivery tube is disposed entirely outside of the central stack, and feeds into a manifold at the burner tip. There are several major inefficiencies associated with the system as disclosed in Straitz patent. First, the blown air must travel the entire inner space/volume of the central stack before it mixes with the low-pressure gas. This results in a significant loss of kinetic energy, which in turn results in smoke formation. Second, a blower with a large capacity and high power must be used to deliver sufficient forced air through the central stack. Third, to be operative, one must use the specialized burner assembly with a plurality of low-pressure and high-pressure apertures organized in a ring fashion at the burner tip. Finally, an existing gas flare cannot be retrofitted to provide for a system that is capable of processing both low- and high-pressure gases. 
         [0006]    U.S. Pat. No. 4,105,394 issued to Robert D. Reed (“Reed patent”) discloses a smokeless burner apparatus for single structure flare systems capable of burning waste gases from high and low pressure sources. Like the Straitz patent, the Reed patent teaches a specialized burner assembly with a hub-and-spokes design. The low-pressure gas delivery pipe is again disposed within the central stack. Forced air is blown through the entire inner space of the central stack before mixing with low-pressure gas. High-pressure gas delivery pipe is disposed within the central stack. The apparatus of the Reed patent suffers from several of the same inefficiencies as the apparatus of the Straitz patent. 
         [0007]    Another problem faced by previous gas flares is the presence of liquids in the waste gases from the oil or gas production stream or from storage tank battery. Most oil and gas operations have a gas-liquid separator (also known as a “knockout drum” or a “scrubber”) upstream of the flare to remove water or oil from the waste gas being combusted. Often, even with the upstream scrubbing step, not all of the liquid is removed. This can be due to the inefficiencies, overload, or failure of the upstream gas-liquid separator. The free liquids entrained in the gas streams travel and build up in the gas delivery system. This can cause inefficient burning of the gases, and may necessitate cleanup or replacement of gas flare system. 
         [0008]    Another problem posed by previous gas flares is the level of noise produced by the system. While some flaring units are used in rural settings where the noise is of little concern, many flaring units are used quite close to residential areas. Furthermore, even in sparsely populated locations, the operators of the flaring units will have to approach the system from time to time. Extended exposure to a high level of noise can be detrimental to human auditory system. 
       SUMMARY 
       [0009]    The following is a summary of some aspects and exemplary embodiments of the present technology, of which a more detailed explanation is provided under the Detailed Description section, here below. In accordance with one aspect of an exemplary embodiment, a dual-pressure flare system and the method of its use are provided which substantially eliminates or reduces disadvantages associated with previous gas flare systems and methods. 
         [0010]    In accordance with one aspect of an exemplary embodiment, a dual-pressure flare system is disclosed, which includes: (a) a dual-pressure flare stack having a central axis, a high-pressure chamber having a high-pressure inlet and a high-pressure outlet, a low-pressure chamber having a low-pressure inlet and a low-pressure outlet, wherein the center of the high-pressure outlet is aligned with the central axis; (b) a high-pressure flue having a central axis that is co-linear with the central axis of the dual-pressure flare stack, a first end connected to the high-pressure outlet, a second end connected to a high-pressure tip; and (c) a low-pressure flue having a first end connected to the low-pressure outlet, a second end connected to a low-pressure tip. Some exemplary embodiments of the system further includes an air-assist assembly having an air-supply connection having a first end connected to an air blower and a second end connected to a mixing chamber, wherein the mixing chamber surrounds the low-pressure tip. In exemplary embodiments, the air-supply connection is disposed outside the dual-pressure flare stack and the high-pressure flue. 
         [0011]    In accordance with another aspect of an exemplary embodiment, a method of operating a dual-pressure flare is disclosed, which includes: (a) providing a dual-pressure flare system having a dual-pressure flare stack, a high-pressure flue, a low-pressure flue, an air-assist assembly, a pilot assembly, and remote control panel; wherein the dual-pressure flare stack having a central axis, a high-pressure chamber having a high-pressure inlet and a high-pressure outlet, a low-pressure chamber having a low-pressure inlet and a low-pressure outlet, wherein the center of the high-pressure outlet is aligned with the central axis; wherein high-pressure flue having a central axis that is co-linear with the central axis of the dual-pressure flare stack, a first end connected to the high-pressure outlet, a second end connected to a high-pressure tip; and wherein low-pressure flue having a first end connected to the low-pressure outlet, a second end connected to a low-pressure tip; (b) supplying a high-pressure gas stream into the high-pressure inlet; (c) supplying a low-pressure gas stream into the low-pressure inlet; (d) mixing assist-air to the low-pressure gas stream near the low-pressure tip; (e) igniting a pilot light using the pilot assembly; and (f) combusting the high-pressure gas stream and the low-pressure gas stream at a hydrocarbon destruction and removal efficiency of at least 98 percent. 
         [0012]    Exemplary embodiments may provide a number of technical advantages. For example, according to an exemplary embodiment, the assist air is blown through a narrower conduit of a smaller volume, which reduces the amount of kinetic energy that is lost. With the assist air being blown only through the low-pressure flue that is outside dual-pressure stack, an air blower with a smaller capacity and lower power can be used because the assist air need not flow through the entire volume of the central stack. The presence of multiple transitions in the high-pressure flue combined with efficient delivery of assist air through the smaller volume of the low-pressure flue results in hydrocarbon destruction efficiency that is far superior to previous flare systems. 
         [0013]    Another technical advantage associated with an exemplary embodiment is its flexibility and versatility. In an exemplary embodiment of the gas flare system, the flare tip does not use a complex or specialized burner tip assembly as is required in previous dual-pressure gas flare systems. The high-pressure flare tip and the low-pressure tip operate substantially independently of each other, and one can be replaced with a new part without having to replace the other. Similarly, the air blower can easily be replaced in the event of its failure without the need to interrupt the operations of the high-pressure flare. 
         [0014]    Yet another technical advantage associated with an exemplary embodiment is its additional safety measures. Even in the event of the failure of an upstream gas-liquid separator, the dual-pressure gas flare system according to some exemplary embodiments is capable of removing liquids entrained in both the high-pressure and low-pressure gas streams. 
         [0015]    Exemplary embodiments may enjoy some, all, or none of these advantages. Other technical advantages may be readily apparent to one skilled in the art from the following figures, description, and claims. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0016]    The foregoing aspects and many of the attendant advantages, of the present technology will become more readily appreciated by reference to the following Detailed Description, when taken in conjunction with the accompanying simplified drawings of exemplary embodiments. The drawings, briefly described here below, are not to scale, are presented for ease of explanation and do not limit the scope of the inventions recited in the accompanying patent claims. 
           [0017]      FIG. 1  illustrates a perspective view of a dual-pressure gas flare system according to an exemplary embodiment. 
           [0018]      FIG. 2  illustrates an elevation view of a dual-pressure gas flare system according to an exemplary embodiment 
           [0019]      FIG. 3A  illustrates a vertical cross-sectional view of the dual-pressure gas flare system along the line shown on  FIG. 1  according to an exemplary embodiment. 
           [0020]      FIG. 3B  illustrates a horizontal cross-sectional view of the dual-pressure gas flare system along the line shown on  FIG. 2  according to an exemplary embodiment. 
           [0021]      FIG. 4  illustrates a detailed elevation view of a dual-pressure gas flare system according to an exemplary embodiment. 
           [0022]      FIG. 5  illustrates a partial elevation view of a dual-pressure gas flare system shown in  FIG. 4  according to an exemplary embodiment. 
           [0023]      FIG. 6  illustrates a partial elevation view of a dual-pressure gas flare system shown in  FIG. 4  according to an exemplary embodiment. 
           [0024]      FIG. 7  illustrates a process flow diagram for method of using a dual-pressure gas flare system according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     I. Overview of the System 
       [0025]      FIG. 1  and  FIG. 2  illustrate an exemplary embodiment of the dual-pressure flaring system  100  that is capable of flaring both low-pressure and high-pressure gases independently. System  100  includes a base  101  that supports a dual-pressure stack  102 . In some exemplary embodiments, the base  101  is fastened or mounted on to a concrete slab or an immovable platform (e.g., of an oil rig). In other embodiments, the base  101  is fastened or mounted on to a movable platform, such as a truck flatbed. In such embodiment, the dual-pressure flaring system  100  may be used as a temporary replacement system during a failure or outage of an existing, permanent system. The system  100  can be moved to a new location at a hydrocarbon production field or a tank battery based on the changes in the need for a flaring system. 
         [0000]    A. Dual Stack with Integrated Gas-Liquid Separator 
         [0026]    As illustrated in  FIG. 3A , the dual-pressure stack  102  is divided into two chambers: one for LP gas and the other for HP gas. As used herein, high-pressure gas means gas that has sufficient kinetic energy and do not require additional energy imparted to it to burn smokeless. In an exemplary embodiment, high-pressure gas has a pressure level of about 10 psi to about 100 psi. As used herein, low-pressure gas means gas that does not have sufficient kinetic energy and require additional energy to be imparted to it to burn smokelessly. In an embodiment, low-pressure gas has a hydrogen-to-carbon molecular weight ratio of less than 0.30 and produces smoke as a result of incomplete combustion and the formation of free carbon. In an exemplary embodiment, low-pressure gas has a pressure level of about 0.1 psi to about 0.75 psi. In an exemplary embodiment, the dual-pressure stack  102  has a low-pressure (LP) gas inlet  103  and a high-pressure (HP) gas inlet  104 . 
         [0027]    In some exemplary embodiments, the LP gas inlet  103  and the HP gas inlet  104  are designed and configured to cause the inflowing gas streams to travel in a vertical (or helical) flow. For example, in the embodiment illustrated in  FIG. 3B , the LP gas inlet  103  has a pipe that extends into the interior of the dual-pressure stack  102  and is capped on the end. The LP gas inlet  103  pipe has an opening  105  that is directionally disposed towards the interior wall of the dual-pressure stack  102 . As the inflowing gas exits the LP gas inlet opening  105 , the gas stream substantially follows the circumferential path along the interior wall of the dual-pressure stack  102  as indicated by the inward spiraling arrow. The inlet opening  105  can be any other device known to be cable of imparting a vorticular flow to fluid in other embodiments. Because the inflowing gas has lower density compared to the interior environment of the dual-pressure stack  102 , the gas stream rises as it follows the circumferential path. This results in the gas stream forming a vortex as it travels up the dual-pressure stack  102 . The vorticular flow of the gases generate centrifugal force that causes the liquids entrained in the gas stream to separate out during the upward travel along the vorticual path. 
         [0028]    Similarly, the HP gas inlet  104  has an opening  106  that is directionally disposed towards the interior wall of the dual-pressure stack  102 . As with the inflowing LP gas, the inflowing HP gas follows a circumferential path along the interior wall of the dual-pressure stack  102  and travels up in a vorticular path. The entrained liquid in the HP gas stream falls out due to the centrifugal force. The liquids that fall out of HP gas stream collects on the HP base surface  107 , and the liquids that fall out of the LP gas stream collects on the LP base surface  108 . The HP base surface  107  acts as a separator between the LP chamber and the HP chamber of the dual-pressure stack  102 . The liquid that collects and accumulates in the LP and HP chambers is removed through the liquid evacuation outlets  109  and  110 , respectively (as shown more clearly in  FIG. 6 ). 
         [0029]    In an exemplary embodiment, the dual-pressure stack  102  has a height of about 10 feet. In some embodiment, the dual-pressure stack  102  has outer diameter of about 4 inches to about 15 inches. In an exemplary embodiment, the dual-pressure stack  102  has an inner diameter of about 12 inches. The diameter of the dual-pressure stack  102  can be varied to increase the volume of gas processed. The thickness of the dual-pressure stack  102  wall ranges from about 0.250 inch to about 0.375 inch in an exemplary embodiment. Because the HP chamber is in a vertically stacked arrangement over the LP chamber, the dual-pressure stack  102  has a reduced footprint. The dual-pressure stack  102  can be formed from any material that is able to withstand the pressure levels of the gases flowing through the system  100 . Such materials include, in some embodiments, carbon steel and stainless steel. 
       B. High-Pressure Gas Flue 
       [0030]    Returning to  FIG. 1  and  FIG. 2 , the dual-pressure stack  102  narrows in diameter at the transition  111  as it approaches the HP outlet  112 . While not being bound by any theory, it is believed that the narrowing of the diameter causes the HP gas to flow at a a higher velocity. In some exemplary embodiments, the transition  111  reduces the inner diameter from the dual-pressure stack  102  to the HP outlet  112  by about 33% to about 66%. In an exemplary embodiment, the inner diameter of the HP outlet  112  is about 6 inches. The HP outlet  112 , connects to HP flue  113 . In an exemplary embodiment, HP outlet  112  and HP flue  113  have flanges that allows them to detachably connect. This allows the replacement of the HP flue without the need to change the dual-pressure stack. In some exemplary embodiments, the HP flue  113  height ranges from about 10 feet to about 40 feet. In an exemplary embodiment, the HP flue  113  height is about 20 feet. 
         [0031]    In some exemplary embodiments of the system  100 , the HP flue undergoes further reduction in diameter through one or more transitions  114 . The HP flue transition  114  reduces the HP flue inner diameter by about 25% to about 50%. In an exemplary embodiment, the post-transition HP flue  115 . diameter is about 3 inches. In some exemplary embodiments, the post-transition HP flue  115  height ranges from about 10 feet to about 35 feet. In an exemplary embodiment, the HP flue  113  height is about 15 feet. 
         [0032]    The post-transition HP flue  115  has flanges  116  that connects to the HP tip  117  in some exemplary embodiments. The flanges allow the HP tip  117  to detachably connect to the HP flue  115 . In some exemplary embodiments, the tip  117  is narrower in diameter by about 25% to about 50% than the post-transition HP flue  115  further increasing the gas velocity. In some exemplary embodiments, the HP tip  117  height ranges from about 18 inches to about 24 inches. In an exemplary embodiment, the HP tip  117  height is about 20 inches. The HP tip  117  has an opening, which further narrows the exit diameter of the HP gas. In some embodiment, the HP tip  117  has a plurality of small openings as illustrated in  FIG. 4  and  FIG. 5 . The decrease in diameter from HP outlet  112  to the tip  117  increases the exit velocity of the HP gas, which increases the DRE. This contributes to a cleaner burn of the HP gas compared to prior gas flare systems. 
         [0033]    As used herein, HP flue means the portion from the point of the HP outlet  112  to the HP tip  117 . In some exemplary embodiments, the height of the total height from the HP base  107  to the HP tip  117  ranges from about 25 feet to about 50 feet overall length. The heavier the hydrocarbon being combusted and the more volume of gas flowing through the system  100 , the more heat is liberated by the flame. Thus, in exemplary embodiments, the height from the HP base  107  to the HP tip  117  is adjusted to maintain a safe level of heat for the operation personnel at the ground level. 
       C. Low-Pressure Gas Flue 
       [0034]    The dual-pressure stack  102  has an LP outlet  118  that connects to the LP flue  119 . The narrowing of the diameter from the dual-pressure stack  102  to the LP outlet  118  increases the LP gas velocity. In some exemplary embodiments, the LP outlet  118  is about 25% to about 50% narrower than the HP outlet  112 . This further helps to increase the exit velocity of the LP gas. In an exemplary embodiment, the inner diameter of the LP outlet  118  is about 3 inches. The LP flue  119  has one or more transition(s)  120  that narrow the diameter of the LP flue  119 . In some exemplary embodiments, the pre-transition LP flue  119  diameter ranges from about 4 inches to about 12 inches. In an exemplary embodiment, the pre-transition LP flue  119  diameter is about 3 inches. In some exemplary embodiments, the post-transition LP flue  119  diameter ranges from about 2 inches to about 6 inches. In some exemplary embodiments, the LP flue transition  120  narrows the inner diameter of the LP flue  119  by about 25% to about 50%. While  FIG. 1  and  FIG. 2  illustrate an embodiment of the 100 that has the transition  120  located towards the top, the transition  120  can be located substantially anywhere along the length of the LP flue  119 . 
         [0035]    In some exemplary embodiments, the LP flue  119  bends at substantially 90 degrees at the bend  121 . In another embodiment, the LP flue  119  connects to a separate bend  121  piece (e.g., elbow) that is detachable. The LP flue bend  121  has flanges  122  that allows the LP tip  123  to detachably connect. In some exemplary embodiments, the LP tip  123  diameter ranges from about 2 inches to about 6 inches. As used herein, LP flue means the portions from the point of the LP outlet  118  to the LP tip  123 . In some exemplary embodiments, the height of the LP flue matches the height of the HP flue so that the HP tip  117  and the LP tip  123  is substantially aligned. Thus, when compared to previous flares, the LP gas travels through a much smaller internal volume of the LP flue and is retains higher velocity. 
         [0036]    The LP tip  123  has an opening  124 , which further narrow the exit diameter of the LP gas. In some exemplary embodiments, the LP tip opening  124  diameter reduces the diameter by about 25% to about 50% compared to the diameter of the LP tip  123 . As with the HP flue, the decrease in diameter in the LP flue  119  and at the LP tip opening  124  increases the exit velocity of the LP gas, which increases the DRE. While not being bound by any theory, it is believed that this contributes to a cleaner burn of the LP gas compared to prior gas flare systems. The bend  121  allows the LP tip opening  124  to be facing up towards the direction of the flow of the assist-air, which promotes a more efficient mixing of the LP gas with the assist air. It also prevents the blow-back of the LP gas and the assist air into the LP tip  123 . Because the LP gas that exists the opening  124  and the assist air travels in the same direction, the assist air imparts additional kinetic energy to the LP gas and increases exit velocity. 
       D. Air-Assist Assembly 
       [0037]    In an exemplary embodiment, the air-assist assembly includes an air blower  125 , which provides additional kinetic energy and oxygen to the LP gas before the LP gas is burned. As illustrated in  FIG. 1  and  FIG. 2  and shown in further detail in  FIG. 4 , the blower  125  is connected to an air-assist supply hose  126  that connects to an air-assist pipe  127  in some exemplary embodiments. The air supply hose  126  diameter ranges from about 2 inches to about 4 inches in some exemplary embodiments. In some exemplary embodiments, the supply hose  126  allows for a tighter and more secure connection with the blower  125  than connecting the blower  125  directly to the pipe  127 . The supply hose  126  also provides flexibility in placement or location of the blower  125 . In other embodiments, the air blower  125  is connected directly to the air supply pipe  127 . 
         [0038]    The air-assist pipe  127  is attached to the HP flue  113 ,  115  and the LP flue  119  via support brackets  128  in an exemplary embodiment. In other embodiments, the air-assist pipe  127  is attached to the HP flue  113 ,  115  or the LP flue  119  using other suitable supporting mechanism. The air-assist pipe  127  is connect to the air-LP gas mixing chamber  129 . In some exemplary embodiments, the air supply hose  126  is connected directly to the mixing chamber  129 . The air-supply connection includes air supply hose  126 , air-assist pipe  127 , alone or in combination. As shown in detail in  FIG. 5 , the LP tip  123  is disposed inside the mixing chamber  129 . In an exemplary embodiment, the mixing chamber ranges from about 12 inches to about 24 inches in diameter and from about 6 feet to about 12 feet in length. As noted above, the LP tip opening  124  is oriented upward so that the LP gas exits in the same direction as the flow of the air. This facilitates better mixing of the LP gas and the assist air, which results in a cleaner burn. Also, because the assist air is not blowing directly into the LP tip opening  124 , it prevents the blow-back of the LP gas and the assist air into the LP tip  123 . This promotes a more efficient use of the assist air. The top opening of the mixing chamber  129  is substantially at the same height as the HP tip  117  opening. 
         [0039]    As used herein, air-assist assembly means the collection of components that supply the assist air to the system  100 , including the air blower  125 , air-supply connection, and the mixing chamber  129 . 
       E. Hood Assembly 
       [0040]    In some exemplary embodiments, the HP tip  117  and the opening of the mixing chamber  129  is surround by a flame hood  130 . The flame hood  130  is a substantially cylindrical tube with the upper end substantially open, which directs the flames to flow upward. On the other end, the flame hood  130  has a sleeve  131  that prevents the flames from blowing down towards the HP tip  117 , the mixing chamber  129 , and the LP flue  119 . The flame hood sleeve  131  thus reduces the wear and damage of the parts. In some exemplary embodiments, the flame hood sleeve  131  is detachable from the flame hood  130  so that the sleeve  131  can be replaced without having to replace the entire hood  130 . In some exemplary embodiments, the flame hood  130  has one or more air holes  132 . These flame hood air holes  132  allows ambient air to be drawn in to further facilitate a cleaner burn. The air that is drawn in through the air holes  132  also pushes the flames up toward the top opening of the flame hood  130 . The flame hood  130  also acts to dampen the noise produced by the flaring operation. 
       F. Pilot Assembly 
       [0041]    Gas flaring operations can be both continuous and intermittent. A pilot assembly  133  is used to maintain a constant source of flame in intermittent operations or in the event of a flame blow out in continuous operation. In an exemplary embodiment, as shown in detail in  FIG. 5 , a pilot pipe  134  on the flame hood  130  directs the pilot toward the HP tip  117  and the LP tip  123  in an exemplary embodiment. In some exemplary embodiments, the pilot assembly  133  houses a pilot igniter  135 . The pilot igniter is raised up through the pilot assembly  133  through the guide rail  136  using the pilot winch  137  in an exemplary embodiment. The pilot guide rail  136  is attached to the HP flue  113 ,  115  at one or more points using support brackets  138 . In other embodiments, the support brackets  138  are attached to  102  or the LP flue  119 . The pilot igniter  135  is connected to pilot gas supply hose  139  in on embodiment. As used herein, pilot assembly means the collection of components that enable the system  100  to maintain and ignite a pilot light, including the pilot igniter  135 , the pilot guide rail  136 , and the pilot gas supply hose  139 . 
       II. Operation of the System 
       [0042]    Air-assisted flares increase the exit velocity of the low-pressure gas to facilitate a clean, smokeless burn. It is important to note, however, that regulatory limits exist as to how high the exit velocity can be. One such regulatory limits are outlined in the EPA regulation, 40 C.F.R. §60.18, which is incorporated herein by reference. For example, 40 C.F.R. §60.18(f) dictates that the maximum permitted velocity, V max , for an air-assisted flare is to be determined by the following equation: 
         [0000]        V   max =8.706+0.7084( H   T )  Eqn. 1
 
         [0000]    V max  is the maximum permitted velocity (in meters per second, m/s). H T  is the net heating value of the gas being combusted, which is calculated by the following equation: 
         [0000]        H   T   =KΣ   i=1   n   C   i   H   i   Eqn. 2
 
         [0000]    H T  is the net heating value of the sample (in megajoules per standard cubic meter, MJ/scm), where the net enthalpy per mole of offgas is based on combustion at 25° C. and 760 mm Hg, but the standard temperature for determining the volume corresponding to one mole is 25° C. K is the constant: 
         [0000]    
       
         
           
             
               
                 
                   K 
                   = 
                   
                     1.740 
                     × 
                     
                       10 
                       
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                         7 
                       
                     
                      
                     
                       ( 
                       
                         1 
                         ppm 
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         
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                            
                           
                               
                           
                            
                           mole 
                         
                         scm 
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         MJ 
                         kcal 
                       
                       ) 
                     
                   
                 
               
               
                 
                   Eqn 
                   . 
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
         [0000]    where the standard temperature for 
         [0000]    
       
         
           
             ( 
             
               
                 g 
                  
                 
                     
                 
                  
                 mole 
               
               scm 
             
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       is 20° C. 
       [0043]    C i  is the concentration of sample component i in ppm on a wet basis. H i  is the net heat of combustion of sample component i (in kilocalories per mole, kcal/mole) at 25° C. and 760 mm Hg. In English units, Equation 1 is converted as follows: 
         [0000]        V   max =28.54+0.087( H   T )  Eqn. 4
 
         [0000]    where V max  is measured in feet per second (ft/s) and the H T  is measured in British thermal units per standard cubic feet (Btu/scf). 
         [0044]    For air-assisted flares, by regulation, only gases with net heating value of 11.2 MJ/scm (300 Btu/scf) or greater can be combusted. In a typical oil and gas production setting, the flare gas composition is dominated by methane, followed by ethane and some higher molecular weight hydrocarbons. The heating values for some component gases are provided below: 
         [0000]                                                Heating Value           Gases   (Btu/scf)                           methane   1010.0           ethane   1769.6           propane   2516.1           i-butane   3251.9           n-butane   3262.3           i-pentane   4000.9           n-pentane   4008.9           n-hexane   4755.9                        
In an exemplar calculation, a mixture of gas having the net heating value, H T , of 1500 Btu/scf would allow the air-assisted flare to operate at the maximum exit velocity, V max , of 159 ft/s (48 m/s). For a gas mixture having H T  of 2000 Btu/scf, the V max  would be 202 ft/s (62 m/s).
 
         [0045]    Thus, it can be seen that increasing the DRE of the air-assisted flares is not merely a matter of supplying more kinetic energy and increasing the velocity of the low-pressure gas. The embodiments of the system  100  utilize the assist air more efficiently compared to previous flares. For example, in an exemplary embodiment, the assist air need only travel through a 2-inch diameter air-assist supply hose  126  and air-assist pipe  127  to reach the mixing chamber  129 . Comparatively, previous flares require the use blowers with a very high capacity sufficient to fill the entire the inner volume of a wide (e.g., about 12 inches or greater) and long stack. Furthermore, in system  100 , the loss of kinetic energy of LP gas is minimized because it travels through the narrow LP flue  119 . Previous flares, on the other hand, routed the LP gas through the primary stack and mixed it with air in the large inner volume of the primary stack. In order to impart sufficient energy to send the gas up to the top of the stack, previous flares required high-capacity blowers, which often over-assisted without increasing the DRE. In an exemplary embodiment, system  100  uses a centrifugal blower  125  having a 1 horsepower motor supplying from about 200 to about 350 cubic feet per minute of assist air. This is significantly lower than typical previous air-assisted flares. 
         [0046]    Another reason why it would be undesirable to simply increase the assist air capacity is the noise produced by the flaring system. Previous air-assist flares typically produce from about 96 decibels at about 100 feet away from the flare. Exemplary embodiments of the system  100 , on the other hand, produce only about 90 to about 116 decibels of noise at about 100 feet away from the system  100 . By using the assist air more efficiently—combined with the dampening effect provided by the flame hood  130 —the noise level is greatly reduced. 
         [0047]    The following is an exemplar description of the operation of system  100  in the context of use in an oil and gas production field. One such embodiment is illustrated in in  FIG. 6  and  FIG. 7 . But system  100  can be used in any industry or field where both high- and low-pressure waste gases need to be flared from time to time, including oil and gas exploration, production, and processing operations, chemical plants or industrial plants. 
         [0048]    In the production field, the fluid extracted from a well typically have high pressure. The extracted well fluid goes through a separator that separates the liquid oil from the gas. The extracted gases sometimes need to be flared off whenever the processing equipment items are over pressured. This gas stream comprises the HP gas inlet stream  140  in an exemplary embodiment. As a precautionary measure, the HP gas inlet stream  140  passes through a flame arrestor  141  before feeding into the HP inlet  104 . Even though the well fluid goes through a separator, some of the oil and/or water are entrained in the fast-traveling HP gas. Thus, the HP inlet opening  106  of the dual-pressure stack  102  causes the inflowing gas stream to travel in a vortical flow (as described above in Section I-A). The vortex naturally separates the entrained water and oil from the HP gas stream before the HP gas flows out of the HP outlet  112  into the HP flue  113 . 
         [0049]    In some oil and gas operations, the extracted oil is stored in tank battery until it is used or transported. The stored oil has dissolved gases that separate out of the liquid phase over time. This tank vapor comprises the LP gas inlet stream  142  in an exemplary embodiment. As with the HP inlet stream  140 , the LP inlet stream  142  also passes through a flame arrestor  143  before feeding into the LP inlet  103 . The LP gas inlet stream  142  sometime has entrained oil or water, which is removed by the vortical motion imparted by the LP inlet opening  105 . The removal of entrained oil and water facilitates cleaner, smokeless burning of the gases. 
         [0050]    To control the various components of the system  100  and to fuel the pilot assembly  133 , the tank  144  provides the supply gas. The supply gas is pure methane in an exemplary embodiment; in other embodiments, the supply gas is any purified or mixture of hydrocarbon gases sufficient to serve as the pilot gas. The supply gas is fed into the supply gas tank  144  through the inlet  145 . In some embodiment, the supply gas is pressurized to 40 to 80 pounds per square inch gauge (psig). In an exemplary embodiment, the supply gas tank  144  has three outlets  146 . One of the outlets  146  feeds into the supply gas tank pressure relief line  147 , which routes the excess gas to the LP inlet stream  142  when the tank  144  becomes over pressurized. In an exemplary embodiment, the supply gas tank pressure relief line  147  is controlled by a pressure relief valve  148 . The second outlet  146  feeds into the pilot gas supply line  149 . The amount of supply gas that feeds into the pilot gas supply line  149  is controlled by the pilot gas pressure regulator  150  and a pilot gas solenoid valve  151  in an exemplary embodiment. The third outlet  146  feeds into the control gas supply line  152 . The control gas controls the liquid evacuation lines (described below). The control gas supply line  152  is regulated by a pressure regulator  153  in an exemplary embodiment. 
         [0051]    When the dual-pressure stack  102  separates out the entrained oil and water from the HP and the LP gas streams, the liquid is collected and pumped out of the stack  102  through the liquid evacuation line  154 . The amount of liquid collected on the LP base surface  107  will differ from that collected on the HP base surface  108 . In some exemplary embodiments, when the field gas stream is particularly “wet,” liquid will accumulate faster in the HP chamber than the LP chamber. System  100  accounts for this difference, determines when the two chambers need to be evacuated of the collected liquids, and independently controls the HP side and the LP side of the liquid evacuation line  154 . This is enabled by using two separate liquid control valves, which uses the pressurized gas from the control gas supply line  152  that diverges into to separate control gas lines. 
         [0052]    The LP control gas solenoid valve  155  controls the flow of the supply gas that is fed through the LP control gas supply line  156  in an exemplary embodiment. Similarly, the HP control gas solenoid valve  157  controls the flow of the supply gas that is fed through the HP control gas supply line  158  in an exemplary embodiment. These solenoid valves  155 ,  157  can also build up excess pressure upstream of the valve, which can be relieved to the LP gas inlet stream  142  through the solenoid valve pressure relief line  159 . 
         [0053]    The liquid that accumulates on the LP base surface  107  is removed or pumped out through the LP liquid evacuation line  160  in an exemplary embodiment. Similarly, the liquid that accumulates on the HP base surface  108  is removed or pumped out through the HP liquid evacuation line  161  in an exemplary embodiment. The two liquid evacuation lines  160 ,  161  are independently controlled by a LP liquid level controller  162  and a HP liquid level controller  163 , respectively, in an exemplary embodiment. These liquid level controllers  162 ,  163  are triggered by LP level gauge  164  and HP level gauge  165 , respectively. When the level gauges  165 ,  164  trigger their respective liquid level controllers  162 ,  163 , the liquid evacuation pump  166  is activated to pump out the accumulated liquid from the dual-pressure stack  102 . The liquid evacuation pump  166  thus only needs to operate when the liquid level controllers  162 ,  163  are triggered. This is a marked improvement over liquid evacuation pumps that are constantly pumping out minimal amounts liquid. As used herein, the liquid evacuation system means the collection of components that enable the accumulated liquids in the LP and HP chamber to be pumped out, including the control gas lines  152 ,  156 ,  158 , regulator  153  and solenoid valves  155 ,  157 , liquid evacuation lines  154 ,  160 ,  161 , solenoid valve pressure relief line  159 , level controllers  162 ,  163 , level gauges  165 ,  164 , and the liquid evacuation pump  166 . 
         [0054]    In some exemplary embodiments, a remote control panel  167 , illustrated in  FIG. 7 , controls and monitors various components of the system  100 . For example, in an exemplary embodiment, a temperature sensor  168 , such as a thermocouple, senses whether the pilot light is on. If the sensor  168  indicates a temperature below a predetermined threshold, a pilot failure alarm  169  is activated. This allows an operator (or an automated system) to reignite the pilot light using a flare ignition controller  170 , which activates the pilot igniter  135 . This ensures that a flame will be present at all times, ready to combust any gas that is flared. 
         [0055]    In some exemplary embodiments, the remote control panel  167  monitors a sensor  171  that detects the operation of the air blower  125 . If the blower sensor  171  detects that the air blower  125  is not in operation or has suffered a failure, the remote control panel  167  activates an air blower failure alarm  172  in an exemplary embodiment. This will alert an operator to attend to the blower  125  and replace it if necessary. In other embodiments, when the air blower failure alarm  172  is activated, the remote control panel  167  switches on a secondary (or back-up) blower that is connected to the air supply hose  126  or the air supply pipe  127 . This ensures that the LP gas will not be combusted without the assist air. 
         [0056]    In an exemplar embodiment, the system  100  is capable of combusting from about 2000 to about 3000 standard cubic feet per day. This requires the supply of from about 250 to about 375 cubic feet per minute. In some embodiment, the system  100  operates at a DRE of from at least 98% to about 99%. 
       III. Alternate Embodiments 
       [0057]    Although several exemplary embodiments have been described, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present 7 disclosure encompass such changes, variations, alterations, transformations, and modifications as fall within the spirit and scope of the appended claims. Alternative embodiments that result from combining, integrating, or omitting features of the embodiments are also within the scope of the disclosure. 
         [0058]    For example, instead of the various solenoid valves and regulators described above, system  100  can be controlled by various different types of control valves, including without limitation: back-pressure regulator with external tap, differential pressure reducing regulator, self-contained pressure regulator, piston-actuated shutdown valve, positioner with solenoid, electronic solenoid-operated valve, or diaphragm-actuated control valve. Various fluid inlets and outlets can be monitored and controlled using different types of flow meters and instruments, including without limitation: venturi, coriolis, turbine, roots, orifice flow meter, annubar flow meter, in-line flow meter, or other types of flow instruments. Similarly, the liquid evacuation system can be controlled by various types of level instruments, including without limitation: level gauge, level transmitter (differential-pressure type or external displacer chamber), magnetic level indicator with level switches, level control with internal displacer, level switch with an internal displacer or an external displacer chamber, or other types of level controllers. Various types of pressure indicators, gauges, regulators, diaphragms, or sensors can be used. The pilot sensor  168  can utilize various types of temperature instruments, including without limitation: temperature indicator, temperature transmitter, thermowell, thermocouple, temperature recorder, or temperature indicating controller can be used. Various valves can be places in several locations along the fluid inlets and outlets to further control the flow of the gas or liquid streams, including without limitation: ball valve, globe valve, check valve, gate valve, plug valve, butterfly valve, needle valve, or other types of valves. The length, width, height, depth, diameter, temperature, pressure, or flow measurements given herein are illustrative and not meant to be limiting. While the air-supply connection  127 ,  126  and the pilot guide rail  136  were disclosed as being connected with a set of support brackets  128 ,  138 , the air-supply connection  127 ,  126  and the pilot guide rail  136  can be connected to the HP flue  113 , the dual-pressure stack  102 , or the LP flue  119  using any supporting mechanism capable of bearing the weight of the he air-supply connection  127 ,  126  or the pilot guide rail  136  and stably supporting them. 
         [0059]    In order to assist the United States Patent and Trademark Office (USPTO) and any readers of any patent issued on this application in interpreting the claims appended hereto, Applicant wishes to note that the Applicant: (a) does not intend any of the appended claims to invoke paragraph six (6) of 35 U.S.C. section 112 as it exists on the date of the filing hereof unless the words “means for” or “step for” are specifically used in the particular claims; and (b) does not intend, by any statement in the specification, to limit the scope of any inventions in any way that is not otherwise reflected in the appended claims.