Abstract:
Liquids recovered from a gas well processed in a ground flare for avoiding the expense of offsite disposal. Well gases are burned in first burners to form a primary combustion zone. Liquids for disposal are introduced and atomized through second burners or nozzles into the primary combustion zone. Preferably, a wellhead separator further separates liquids from gas recovered from the well. Liquids are stored in a tank and delivered to the second burners as the heat capacity in the flare permits. Supplementary commercial pilot gas can provide sufficient heat capacity if the well gas is temporarily insufficient. The liquid is incinerated and its combustion or vaporized products are discharged with the burned gas.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to method and apparatus for disposal of liquid such as water and condensate recovered from gas wells, more particularly, to the processing of the liquid and its incineration in a flare.  
         BACKGROUND OF THE INVENTION  
         [0002]    Gas wells are known to accumulate liquids. The liquid imposes a hydrostatic pressure which adversely retards the flowing characteristics of the well, reducing the rate and quantity of gas which can be produced. Accumulation of sufficient liquid can kill the well. Accordingly, various methods are applied to remove the liquid from the well. Liquid may be entrained with the gas. Preferably liquid, containing both water and condensate is separated and the water is directed to a tank. Another known method of liquid removal is to periodically blow down the well to the lower pressure surface tank.  
           [0003]    The liquid, usually water, is typically salty or otherwise unsuitable for direct surface disposal. Today, environmental respect requires proper disposal. One time consuming and expensive form of disposal is to collect the water and haul it to approved dump sites. Another form of disposal is to cause the water stored in a tank to evaporate, possible hastened through the application of waste heat such as that from compressor exhaust. The evaporative tank approach is subject to salt and scale build up which must be manually removed.  
           [0004]    In another area related to the handling of gas wells, it is known to use flares to deal with excess gas and vapors. Sometime water disposal is dealt with by periodically flowing high gas rates for entraining water with the gas and to the flare. The water can end up being discharged at the flare and fall to earth, resulting in a continuing well-abandonment liability. More efficient ground flares are being used more frequently as regulations are being tightened with respect to the emissions from flaring, venting of tank vapors and venting of BTEX emissions (benzene, toluene, ethylbenzene and xylene) from the glycol dehydrators on natural gas wells. The problem with all flares to date include the inability to co-process water and gas.  
           [0005]    In light of the above, it is a desirable characteristic to simplify the apparatus of ground flare stacks, improve combustion and to provide a highly dispersed exhaust from the flare stack without interfering with the operation of the burners.  
         SUMMARY OF THE INVENTION  
         [0006]    In a preferred form of the invention, liquids, produced from a gas well, are processed in a ground flare. The flare forms a primary combustion zone sustained by maintaining a substantially continuous flow of combustible gas produced from the well. Liquids for disposal are introduced and atomized into the primary combustion zone. The method produces environmentally sound exhaust. Preferably, the apparatus comprises a wellhead separator and a ground flare having at least one set of burners. The burners are fired with a first combustible fluid, such as gas from the well or supplementary commercial pilot gas. A nozzle atomizes and directs liquids, possibly containing both water and some condensate, into the combustion zone formed by the burners. The liquid is incinerated and its combustion or vaporized products are discharged with the burned gas.  
           [0007]    In a broad aspect, the invention is a method for the disposal of liquid produced from a gas well comprising the steps of recovering liquid from the well, burning combustible gas recovered from the well in a flare for producing a combustion zone in the flare, and incinerating the liquid in the combustion zone of the flare.  
           [0008]    Further, the apparatus for the disposal of liquid produced from a gas well comprises:  
           [0009]    a ground flare having a burner, a burn chamber and an atomizing nozzle and an exhaust;  
           [0010]    a gas conduit between the burner and the gas well so that gas from the well is burned to form a combustion zone in the burn chamber and flue gas which is discharged at the exhaust; and  
           [0011]    a liquid conduit between the liquid recovery means and the atomizing nozzle so that recovered liquid is atomized and directed into the combustion zone and incinerated therein, the incinerated byproducts being discharged with the flue gas.  
           [0012]    In a preferred embodiment of the invention, the liquid is entrained with the gas or alternatively, the liquid can be recovered using gas lift or blow-down and is obtained for combustion from the well annulus, a downstream separator or a storage tank.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic cross-sectional view of an embodiment of the invention illustrating the combustion of well gases and the incineration of liquids recovered from the well annulus;  
         [0014]    [0014]FIG. 2 is a side cross-sectional view of a ground flare stack suitable for implementing an embodiment of the present invention, with secondary burners being fitted with liquid atomization nozzles; and  
         [0015]    [0015]FIG. 3 is a cross-sectional downward view along line III-III of FIG. 2, showing two side-by-side burners, one of which is illustrated in a disassembled form. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Having reference to FIG. 1, two streams of fluids from a well  109  are directed through a first gas conduit  110  and a second conduit  111  to a ground flare  112 .  
         [0017]    The flare  112  uses combustible gas recovered from the first conduit  110  to fuel a combined combustion and incineration process. The second conduit  111  conducts liquid which has been recovered from the well  109  and which is directed for disposal.  
         [0018]    The second conduit  111  conducts fluids from the well  109  which contain liquid. The liquid is removed from the well  109  as a matter of course (entrained with the gas) or is specifically recovered using known processes such as gas lift, or blow-down. As shown, the liquid may be obtained from the well annulus  109   b  or other well site location, from a separator  113  downstream from the production tubing  109   a , or from tankage  114  of previously stored well liquids.  
         [0019]    At the separator, fluids in the second conduit  111  are subject to liquid-gas separation. The separated liquid is directed to conduit  111  and then to the flare  112  for disposal. Separated gas is directed to conduit  110  for combustion at the flare  112 .  
         [0020]    In a first embodiment, the first conduit  110  conducts combustible gas from the well  109  to the flare  112 , providing the entire heat demand for incinerating the liquid from the second conduit  111 .  
         [0021]    Combustible gas is directed through conduit  110  to first burners  120  Combustion of the gas forms a high temperature combustion zone  121 . Liquid from the second conduit  111  is directed through second burners or suitable atomizing nozzles  122  into the combustion zone  121 , ensuring the liquid is dispersed and substantially consumed therein. The heat balance of the combustion zone  121 , losses and enthalpy of the liquid is such that the combustion zone  121  is maintained at a temperature high enough to ensure complete combustion of the gas and vaporization of the liquid. Temperatures in the combustion zone  121  of 850-1200 C are typical. For example for a well  109  having a natural gas flow of 2300 m3/hr, then 2-10 bbl/hr of liquid can be consumed in the flare (typically the liquid is 90% water, 10% condensate). For a typical natural gas well, 200 USGal of water can be incinerated using solely the gas flow from the well  109 .  
         [0022]    While it is anticipated that other flare configurations or commercial incinerators could be applied, a preferred flare is that described in U.S. Pat. No. 6,146,131, issued to Applicant, the contents of which are incorporated herein in their entirety.  
         [0023]    For convenience, portions of the disclosure are described again as follows. The reference numerals are maintained per U.S. Pat. No. 6,146,131 for continuity.  
         [0024]    Having reference to FIG. 2, the flare  112  is a ground flare utilizing primary and secondary burners. Herein, it is understood that the second burner is modified as necessary to atomize liquid which is substantially water but may also include condensate. Such modification includes adding atomizing nozzles, typically having {fraction (1/16)}″ or {fraction (5/32)}″ orifices.  
         [0025]    The first conduit  110  is a gas conduit  1  which forms a header  3  which splits into two or more burner feed lines  4   a , 4   b . A first burner  4   a  feed line supplies a first burner  5   a  and the second feed line  4   b  supplies a second burner  5   b . First and second valves  6   a , 6   b  permit selection and use of the first or the second burners  5   a , 5   b  respectively. Both burners can be selected simultaneously. The lines  4   a , 4   b  shown extending between the valves  6   a , 6   b  and the burners  5   a , 5   b  are flexible.  
         [0026]    The ground flare  2  comprises a stack  8  formed of a plurality of concentric tubular shells  7 , each shell  7   a , 7   b  . . . being displaced spaced axially. Each upwardly adjacent shell  7   b  has a greater diameter than the preceding shell  7   a  so that an annular space  9  is formed between adjacent shells  7   b , 7   a . The lower edge  10  of the adjacently higher shell  7   b  overlaps the upper edge  11  of the lower shell  7   a . Combustion air enters the system through a plurality of circumferentially spaced vents  12  and secondarily through the annular spaces  9  between the adjacent shells  7 . The one or more hoops  10   a  act as a bell-mouth intake for smoothing the incoming annular combustion air so as to result in an improved intake of secondary air.  
         [0027]    This annular air is provided in several stages described below.  
         [0028]    One or more of the shells  7  above the burners  5   a , 5   b  form a burn chamber  14  which houses the combustion zone  121 . One or more nozzles  15  are fitted to the burners  5   a , 5   b  for distributing the waste gas in a manner suitable for most efficient combustion. The nozzles  15  ensure atomization of the waste gases and direct and discharge combustible waste gases upwardly into the burn chamber  14 . Combustion air from the annular spaces  9  mix with the waste gases as they exit the nozzles  15 . An exhaust stack  16  is fitted to the burner chamber  14  for removing products of combustion formed in the combustion zone. Conventional pilot, ignition systems and flame sensors (not shown) initiate and monitor combustion above the burners  5   a , 5   b.    
         [0029]    When the flare  2  is in operation, a draft is created in the stack  8 , drawing air upwardly and inwardly through the vents  12  and annular spaces  9 . At the lower end of the stack, generally below the burners, the vents  12  and the annular spaces  9  admit primary combustion air. The annular spaces  9  above the burners admit secondary combustion air for burners  5   a , 5   b ; one, for improved efficiency of combustion, and secondly, for admitting volume-building air for improved dispersion and stack cooling.  
         [0030]    Having reference to FIGS. 2 and 3, two burners  5   a , 5   b  are shown in a laterally side-by-side arrangement and horizontally extending orientation. The burners are positioned in one shell  7  and are sandwiched between a cap  35  and first nipple  32 . Nipple  32  connects to the gas conduit  1 .  
         [0031]    One or more nozzles  55 , 55   a , 55   b , which can be of conventional liquid fuel burner design, or having specialized nozzles, are positioned in the stack&#39;s upper portion  8   b  for incineration of the liquid from second conduit  111 . The nozzles  55  are directed into the combustion zone. A plurality of nozzles  55   a , 55   b  can be fed from a header  53 . Accordingly, a hoop  10   a  is formed with a bore  50  and can conveniently form the header  53 , the bore  50  being of sufficient internal diameter to distribute and supply the necessary volumetric flow to the nozzles  55 , 55   a , 55   b . The header  53  can be located at the lower edge  10  (at  10   a ) of each shell for also aiding in air flow, or can be located elsewhere (at  10   b ) for serving only as header  53 . The second conduit  111  is fed to nozzles  55  and header  53  through feed lines  54   a , 54   b . Corresponding valves  56   a  and  56   b  enable selective use of one or more of the nozzles  55  or  55   a  and  55   b.    
         [0032]    Using the flare  112  of the present invention, high volumes of waste liquid can be cleanly incinerated having combustion zone temperatures in the burn chamber  14  of about 1100° C. while the post burn incorporation of additional volumes of annular air contribute to increased dispersion and achieve same with stack surface temperatures which are typically at temperature of less than 2500° C.