Note: Descriptions are shown in the official language in which they were submitted.
CA 02372987 2002-02-25
1 "METHOD FOR DISPOSAL OF LIQUID
2 FROM GAS WELLS"
3
4 FIELD OF THE INVENTION
The invention relates to method and apparatus for disposal of liquid
6 such as water and condensate recovered from gas wells, more particularly, to
7 the processing of the liquid and its incineration in a flare.
8
9 BACKGROUND OF THE INVENTION
Gas wells are known to accumulate liquids. The liquid imposes a
11 hydrostatic pressure which adversely retards the flowing characteristics of
the
12 well, reducing the rate and quantity of gas which can be produced.
13 Accumulation of sufficient liquid can kill the well. Accordingly, various
methods
14 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
16 the water is directed to a tank. Another known method of liquid removal is
to
17 periodically blow down the well to the lower pressure surface tank.
18 The liquid, usually water, is typically salty or otherwise unsuitable
19 for direct surface disposal. Today, environmental respect requires proper
20' disposal. One time consuming and expensive form of disposal is to collect
the
21 water and haul it to approved dump sites. Another form of disposal is to
cause
22 the water stored in a tank to evaporate, possible hastened through the
23 application of waste heat such as that from compressor exhaust. The
24 evaporative tank approach is subject to salt and scale build up which must
be
manually removed.
CA 02372987 2002-02-25
1 In another area related to the handling of gas wells, it is known to
2 use flares to deal with excess gas and vapors. Sometime water disposal is
dealt
3 with by periodically flowing high gas rates for entrairiing water with the
gas and
4 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
6 are being used more frequently as regulations are being tightened with
respect
7 to the emissions from flaring, venting of tank vapors and venting of BTEX
8 emissions (benzene, toluene, ethylbenzene and xylene) from the glycol
9 dehydrators on natural gas wells. The problem with all flares to date
include the
inability to co-process water and gas.
11 In light of the above, it is a desirable characteristic to simplify the
12 apparatus of ground flare stacks, improve combustion and to provide a
highly
13 dispersed exhaust from the flare stack without interfering' with the
operation of
14 the burners.
16 SUMMARY OF THE INVENTION
17 In a preferred form of the invention, liquids, produced from a gas
18 well, are processed in a. ground flare. The flare forms a primary
combustion
19 zone sustained by maintaining a substantially continuous flow of
combustible
gas produced from the well. Liquids for disposal are introduced and atomized
21 into the primary combustion zone. The method produces environmentally sound
22 exhaust. Preferably, the apparatus comprises a wellhead separator and a
23 ground flare having at least one set of burners. The burners are fired with
a first
24 combustible fluid, such as gas from the well or supplementary commercial
pilot
gas. A nozzle atomizes and directs liquids, possibly containing both water and
2
CA 02372987 2002-02-25
1 some condensate, into the combustion zone formed by the burners. The liquid
is
2 incinerated and its combustion or vaporized products are discharged with the
3 burned gas.
4
BRIEF DESCRIPTION OF THE DRAWINGS
6 Figure 1 is a schematic cross-sectional view of an embodiment of
7 the invention illustrating the combustion of well gases and the incineration
of
8 liquids recovered from the well annulus;
9 Figure 2 is a side cross-sectional view of a ground flare stack
suitable for implementing an embodiment of the present invention, with
11 secondary burners being fitted with liquid atomization nozzles; and
12 Figure 3 is a cross-sectional downward view along line III-III of Fig.
13 2, showing two side-by-side burners, one of which is illustrated in a
14 disassembled form.
16 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
17 Having reference to Fig. 1, two streams of fluids from a well 109
18 are directed through a first gas conduit 110 and a second conduit 111 to a
19 ground flare 112.
The flare 112 uses combustible gas recovered from the first
21 conduit 110 to fuel a combined combustion and incineration process. The
22 second conduit 111 conducts liquid which has been recovered from the well
109
23 and which is directed for disposal.
24 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
3
CA 02372987 2002-02-25
1 (entrained with the gas) or is specifically recovered using known processes
such
2 as gas lift, or blow-down. As shown, the liquid may be obtained from the
well
3 annulus 109b or other well site location, from a separator 113 downstream
from
4 the production tubing 109a, or from tankage 114 of previously stored well
liquids.
At the separator, fluids in the second conduit 111 are subject to
6 liquid-gas separation. The separated liquid is directed to conduit 111 and
then to
7 the flare 112 for disposal. Separated gas is directed to conduit 110 for
8 combustion at the flare 112.
9 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
11 incinerating the liquid from the second conduit 111.
12 Combustible gas is directed through conduit 110 to first burners
13 120 Combustion of the gas forms a high temperature combustion zone 121.
14 Liquid from the second conduit 111 is directed through second burners or
suitable atomizing nozzles 122 into the combustion zone 121, ensuring the
liquid
16 is dispersed and substantially consumed therein. The heat balance of the
17 combustion zone 121, losses and enthalpy of the liquid is such that the
18 combustion zone 121 is maintained at a temperature high enough to ensure
19 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
21 109 having a natural gas flow of m3/hr, then 2-10 bbl/hr of liquid can be
22 consumed in the flare (typically the liquid is 90% water, 10% condensate).
For a
23 typical natural gas well, 200 USGaI of water can be incinerated using
solely the
24 gas flow from the well 109.
4
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1 While it is anticipated that other flare configurations or commercial
2 incinerators could be applied, a preferred flare is that described in US
Patent
3 6,146,131, issued to Applicant, the contents of which are incorporated
herein in
4 their entirety.
For convenience, portions of the disclosure are described again as
6 follows. The reference numerals are maintained per US 6,146,131 for
continuity.
7 Having reference to Fig. 2, the flare 112 is a ground flare utilizing
8 primary and secondary burners. Herein, it is understood that the second
burner
9 is modified as necessary to atomize liquid which is substantially water but
may
also include condensate. Such modification includes adding atomizing nozzles,
11 typically having 1/16" or 5132" orifices.
12 The first conduit 110 is a gas conduit 1 which forms a header 3
13 which splits into two or more burner feed lines 4a,4b. A first burner 4a
feed line
14 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
16 second burners 5a,5b respectively. Both burners can be selected
17 simultaneously. The lines 4a,4b shown extending between the valves 6a,6b
and
18 the burners 5a,5b are flexible.
19 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.
21 Each upwardly adjacent shell 7b has a greater diameter than the preceding
shell
22 7a so that an annular space 9 is formed between adjacent shells 7b,7a. The
23 lower edge 10 of the adjacently higher shell 7b overlaps the upper edge 11
of
24 the lower shell 7a. Combustion air enters the system through a plurality of
circumferentially spaced vents 12 and secondarily through the annular spaces 9
5
..~.. n~-
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1 between the adjacent shells 7. The one or more hoops 10a act as a bell-mouth
2 intake for smoothing the incoming annular combustion air so as to result in
an
3 improved intake of secondary air.
4 This annular air is provided in several stages described below.
One or more of the shells 7 above the burners 5a,5b form a bum
6 chamber 14 which houses the combustion done 121. One or more nozzles 15
7 are fitted to the burners 5a,5b for distributing the waste gas in a manner
suitable
8 for most efficient combustion. The nozzles 15 ensure atomization of the
waste
9 gases and direct and discharge combustible waste gases upwardly into the bum
chamber 14. Combustion air from the annular spaces 9 mix with the waste
11 gases as they exit the nozzles 15. An exhaust stack 16 is fitted to the
burner
12 chamber 14 for removing products of combustion formed in the combustion
13 zone. Conventional pilot, ignition systems and flame sensors (not shown)
initiate
14 and monitor combustion above the burners 5a,5b.
When the flare 2'is in operation, a draft is created in the stack 8,
16 drawing air upwardly and inwardly through the vents 12 and annular spaces
9.
17 At the lower end of the stack, generally below the. burners, the vents 12
and the
18 annular spaces 9 admit primary combustion air. The annular spaces 9 above
19 the burners admit secondary combustion air for burners 5a,5b; one, for
improved
efficiency of combustion, and secondly, for admitting volume-building air for
21 improved dispersion and stack cooling.
22 Having reference to Figs. 2 and 3, two burners 5a,5b are shown in
23 a laterally side-by-side arrangement and horizontally extending
orientation. The
24 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.
6
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1 One or more nozzles 55,55a,55b, which can be of conventional
2 liquid fuel burner design, or having specialized nozzles, are positioned in
the
3 stack's upper portion 8b for incineration of the liquid from second conduit
111.
4 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
6 bore 50 and can conveniently form the header 53, the bore 50 being of
sufficient
7 internal diameter to distribute and supply the necessary volumetric flow to
the
8 nozzles 55,55a,55b. The header 53 can be located at the lower edge 10 (at
9 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
11 header 53 through feed lines 54a,54b. Corresponding valves 56a and 56b
12 enable selective use of one or more of the nozzles 55 or 55a and 55b.
13 Using the flare 112 of the present invention, high volumes of waste
14 liquid can be cleanly incinerated having combustion zone temperatures in
the
burn chamber 14 of about 1100° C while the post bum incorporation of
additional
16 volumes of annular air contribute to increased dispersion and achieve same
with
17 stack surface temperatures which are typically at temperature of less than
18 250° C.
19
7
