Method for disposal of liquid from gas wells

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] 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] 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] 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 109b or other well site location, from a separator 113 downstream from the production tubing 109a, 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 4a,4b. A first burner 4a feed line supplies a first burner 5a and the second feed line 4b supplies a second burner 5b. First and second valves 6a,6b permit selection and use of the first or the second burners 5a,5b respectively. Both burners can be selected simultaneously. The lines 4a,4b shown extending between the valves 6a,6b and the burners 5a,5b are flexible.

[0026] The ground flare 2 comprises a stack 8 formed of a plurality of concentric tubular shells 7, each shell 7a,7b . . . being displaced spaced axially. Each upwardly adjacent shell 7b has a greater diameter than the preceding shell 7a so that an annular space 9 is formed between adjacent shells 7b,7a. The lower edge 10 of the adjacently higher shell 7b overlaps the upper edge 11 of the lower shell 7a. 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 10a 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 5a,5b form a burn chamber 14 which houses the combustion zone 121. One or more nozzles 15 are fitted to the burners 5a,5b 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 5a,5b.

[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 5a,5b; 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 5a,5b 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 55,55a,55b, which can be of conventional liquid fuel burner design, or having specialized nozzles, are positioned in the stack's upper portion 8b for incineration of the liquid from second conduit 111. The nozzles 55 are directed into the combustion zone. A plurality of nozzles 55a,55b can be fed from a header 53. Accordingly, a hoop 10a 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 55,55a,55b. The header 53 can be located at the lower edge 10 (at 10a) of each shell for also aiding in air flow, or can be located elsewhere (at 10b) for serving only as header 53. The second conduit 111 is fed to nozzles 55 and header 53 through feed lines 54a,54b. Corresponding valves 56a and 56b enable selective use of one or more of the nozzles 55 or 55a and 55b.

[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.

Claims

1. A method for the disposal of liquid produced from a gas well comprising the steps of:

(a) recovering liquid from the well;

(b) burning combustible gas recovered from the well in flare for producing a combustion zone in the flare; and

(c) incinerating the liquid in the combustion zone of the flare.

2. The method of claim 1 wherein the incineration step further comprising the steps of:

(a) atomizing the liquid in a nozzle;

(b) injecting the atomized liquid into the combustion zone.

3. The method of claim 2 wherein the production of the combustion zone is supplemented with the use of commercial gas.

4. The method of claim 2 wherein the liquid is recovered periodically from the well.

5. The method of claim 4 further comprising the steps of:

(a) providing a temporary liquid storage;

(b) periodically recovering liquid from the well and depositing it into the liquid storage;

(c) recovering liquid from the liquid storage and incinerating the liquid.

6. The method of claim 1 further comprising the steps of:

(a) providing burners and atomizing nozzles in the flare;

(b) burning the gas in the burners and forming an upward column of hot gas in the combustion zone;

(c) atomizing the liquid in the nozzles and directing atomized liquid into the combustion zone.

7. The method of claim 6 wherein the combustible gas from the well is supplemented with commercial gas.

8. Apparatus for the disposal of liquid produced from a gas well comprising:

(a) a ground flare having a burner, a burn chamber and an atomizing nozzle and an exhaust;

(b) 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

(c) 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.

9. The apparatus of claim 8 further comprising:

(a) a first gas burner located upstream of the burn chamber; and

(b) a second liquid burner directed into the burn chamber.

10. The apparatus of claim 8 further comprising a liquid-gas separator for processing gas from the well and producing

i) a gas product for recovery by the gas conduit, and

ii) a liquid product for recovery by the liquid conduit.

11. The apparatus of claim 8 further comprising

(a) a storage tank for storing liquid recovered from the well;

(b) means for directing liquid from the tank to the second burner only as the heat capacity combustion zone can accept it.

12. The apparatus of claim 8 wherein the burn chamber is formed of a plurality of telescoping shells having annular inlets therebetween.