Note: Descriptions are shown in the official language in which they were submitted.
CA 02281610 1999-08-17
WO 98/39078 PCT/US97/03295
-1-
METHOD AND APPARATUS UTILIZING HYDROCARBON
POLLUTANTS
Technical Field
1 This invention relates to glycol dehydrators and more
2 particularly to a method and apparatus which eliminates noxious
3 gasses normally exhausted to the atmosphere from the still
4 column of a gas dehydrator.
Natural gas produced from gas wells contains entrained
6 water and oil droplets, water vapor, and condensable hydrocar-
7 bons .
8 It is necessary to remove the water and water vapor from
9 the natural gas before it passes into a pipeline to prevent
clogging and corrosion of the pipeline and downstream equip
11 ment .
12 Glycol dehydrators are used to remove water and water
13 vapor from gas by contacting the wet gas with glycol absorbing
14 the water and vapor. The desiccant then flows to a reboiler
regenerating the glycol by driving off the water vapor,
16 allowing the reconcentrated desiccant to be returned to the
17 dehydration phase.
18 An unintentional by-product of the dehydration process is
19 the absorption of hydrocarbons with water and water vapor.
CA 02281610 1999-08-17
WO 98/39078 PCT/US97/03295
-2-
1 These hydrocarbons are normally released to the atmosphere with
2 water vapor from the regenerator. Many of these aromatic
3 hydrocarbons are hazardous to the environment, benzene, ethyl-
4 benzene, toluene, and xylene for example.
Background Art
6 Some prior patents, such as United States Patent No.
7 3,875,019 issued April 1, 1975 to Cocuzza et al, and United
8 States Patent No. 5,163,981 issued November 17, 1992 to Choi,
9 disclose removing noxious gasses from the vapors emitted by a
still column from a reboiler and passing these noxious gasses
11 to the burner of the reboiler. However, a problem occurs in
12 admitting the gasses to the reboiler burner and obtaining
13 combustion since these noxious gasses do not readily burn, as
14 does natural gas. This invention overcomes this problem.
The maj ority of the prior art patents are directed toward
16 the reclaiming and/or reconcentrating ethylene glycol.
17 United States Patent No. 4,273,620 issued June 16, 1981
18 to Knobel, United States Patent No. 4,225,394 issued September
19 30, 1980 to Cox et al, and United States Patent No. 4,322,265
issued March 30, 1982 to Wood, are considered good examples of
21 the further state-of-the-art in reclaiming and reconcentrating
22 used ethylene glycol.
23 Disclosure Of The Invention
24 A glycol dehydrating system includes a reboiler having an
upstanding still column receiving vapors having temperatures as
26 high as 177° C. In this invention the still column vent is
27 closed to prevent the normal escape of noxious gasses and water
28 vapor. These vapors are piped through a heat exchanger sized
29 to drop the temperature to less than 66° C. The condensed
water and condensable hydrocarbons flow by gravity to tank
31 storage through a self emptying container. The remaining
32 hydrocarbon vapors flow through a secondary separator to remove
33 remaining liquids, and through either of two thermostatically
CA 02281610 1999-08-17
WO 98/39078 PCT/US97/03295
-3-
1 controlled valves for use as dehydrator fuel. In some instal-
2 lations, the uncondensed hydrocarbons have been found to be of
3 sufficient quantity to substantially fuel the dehydrator,
4 replacing the natural gas normally used for fuel.
Hrief Description Of The Drawings
6 Figure 1 is a schematic of the apparatus;
7 Figure 2 is a fragmentary side elevational view of a
8 dehydration reboiler fuel and air mixing fire-tube burner inlet
9 tube connected with a noxious gas and air mingle unit;
Figure 3 is a fragmentary exploded isometric view of the
11 noxious gas and air mingle unit, per se; and,
12 Figure 4 is a vertical cross sectional view taken
13 substantially along the line 4---4 of Fig. 2.
14 Best Mode For Carrving,0ut The Invention
Referring first to Fig. 1, the reference numeral 10
16 indicates the apparatus as a whole which includes a glycol
17 regenerating apparatus 12 comprising a reboiler 16 having an
18 over temperature controller 15, and a thermostatic temperature
19 controller 17 and having a still column 14 mounted thereon
receiving wet glycol from a contactor tower, not shown, via a
21 line 18. The reboiler 16 contains a fire-tube 19 having a
22 burner 20 (Fig. 2), in its burner entrance 19', supplied with
23 fuel gas by a line 21 having a fuel control valve 22 and
24 terminating in an upstanding exhaust stack 23 for heating the
glycol.
26 Water vapor and aromatic hydrocarbons vaporized from the
27 wet glycol are normally exhausted to the atmosphere through a
28 vent, not shown, in the wall of the still column 14. However,
29 in this invention, the still column vent is closed, and water
vapor and aromatic hydrocarbon gasses pass via a line 26 to an
31 air cooled heat exchanger or vapor condenser 28 where the vapor
32 volume is reduced by condensation.
33 The terms "line" and "piping" as used herein refer to
CA 02281610 2003-04-24
tubular pipes for conducting fluids.
Liquid~r f low by gravi ty f rom the vapor condenser through
a drain line 30 to a:z standpipe 3;? which drains to a self
emptying liquid conta:ir~er 34 through a check valve 3:5. The
upper end portion of t:he standpipe is normally closed by a
thermostat controlled fluid pressure valve 31 and a pressure
relief valve 33. Air ~~rapor or gas displaced by liquid entering
the liquid container ::34 is vented t.o the upper end portion of
the stand pipe 32 via:r a line 36. 'The self emptying liquid
container 34 is fully disclosed ira United States Patent No.
4,948,010 The container 34
is connected with the fuel gas line 21 via line 37 so that a
float, not shown, within the container 34 opens an internal
valve, similarly not shown,, when the float is lifted to a
predetermined level by contained liquid to allow gas pressure
from the line 3'7 to d:isc:harcy=_ contained 3_iquid to storage
through a check valve 93 in a drain line 38.
Vapor and aromat.i.c hydra~arbon gasses in the upper end
portion of the stand ~:yipe 32 pass to a separator 39 via a line
90. Condensed liquids in the separator drain by gravity through
a line 42 to the depending end portion of the stand pipe 32 and
to the liquid container 34. Hydrocarbons leaving the separator
39 are filtered by a fi:Yter 48 in a conduit 44 connected to the
burner 20 through a no:~r~mally open tehermoetat- control valve 47.
Separated liquids in t:he filter 48 drain to the separator drain
line 42 via a line 45~. A flame arrestor 50 is interposed in
the conduit 44 downst~.eam from the filter 48. A branch line 55,
connected with the t:-ondu~.t 44 upstream from the valve 47
diverts gasses, under c~ertaird conditions as presently ex-
plained, to the exhaust stack 23 through a normally closed
thermostat controlled v~a:lwe 56.
The over temperature controller 15 is connected with the
fuel gas supply :~?1 up~~3t::c.-earn frcnn tkna_ -valv-e~ 22 by a line 13 and
CA 02281610 2003-04-24
C~ _
with the thermostatic temperature control 17 by a line 11.
During normal operation, the teroperature control 17 supplies
fuel gas pressure to operate the valves 22, 47 and 56, by gas
piping 53, 5'7 arid 58, respeetively_ Other gas piping 59
connects the line 11 <;:o the vent valve 3:1. In the event of
reboiler temperature r:~bove a pi:edetermined limit, the over
temperature controller :L5 removes gas supply pressure to the
thermostat temperature control valve 17 and vent valve 3.L , thus
closing fuel and unconciensed hydzo~arbons supply valves 22 and
47 and opening exhaust: stack valve 56 arid vent
valve 31.
Referring also to the remaining Figures, the burner 2o is
provided with an inlet opening defined by a laterally project-
ing boss 60 connected with the fuel line 21. The fuel burner
mixer end 62 is open for' admitting air to be mixed with the
fuel from the lime 2:L, the qu~intity of air being manually
adjusted by a baffle plate 63 can a threaded stem 64.
An aromatic gas and air mingle element 65 is interposed
between the burner end 62 and the air inlet control plate 63.
The mingler 65 is provided with a tubular end portion 66 which
receives aromatic gasses from the conduit 44. The mingle
element 65 has opposing aide walls 68 and 70 provided with
axially aligned openings ?2 and 74 surrounding the burner stem
64. The wall forming the side wall opening 72 slidably
surrounds the burner stem 64. The side wall 68 is provided with
a plurality of radial openings 73, four in the example shown,
admitting gas from the mixer 65 to the burner 20. The diameter
of the side wall opening 74 is substantially equal with the
diameter of the baffle plate 63.
A cylindrical flame arresting element 75 is axially
interposed between the burner end c~2 and the mingler side wall
68. A nut 76 on the stem 64 holds the side wall 68 in contact
with the adjacent surface of the element 75. In addition to its
CA 02281610 1999-08-17
WO 98/39078 PCT/US97/03295
-6-
1 flame arresting characteristics, the element 75 acts to
2 thoroughly mix or commingle the aromatic gasses with air to
3 form a combustible mixture as they enter the burner 20. A
4 manually operated control valve 67 is interposed in the condui-t
44 downstream from the flame arrestor 50, and a manual bleed
6 valve 69 is interposed in the gas piping 59 upstream from the
7 vent valve 31.
8 As an example, the above described system was installed
9 on a glycol dehydrator and operated for 90 days. The dehydra
for has a 375,000 BTU heater, a 76.2 cm contactor, and dries 20
11 mmcf natural gas per day. Gas temperature is 43° C. Contactor
12 pressure is 1,000 psi. Total liquid hydrocarbons recovered,
13 3.33 bbls/day x 90 = 299.7 bbls. Total natural gas fuel saved
14 by using the aromatic hydrocarbons as fuel is: 18 mcf/day x 90
= 1.620 mmcf.
16 Under normal conditions the apparatus continuously
17 operates under a predetermined temperature controlled by the
18 temperature controller 17. In the event of a malfunction, such
19 as the temperature rising or falling to a temperature range
beyond the setting of the temperature control, the over temp-
21 erature controller 15 closes the burner valve 22 and uncon-
22 densed hydrocarbon gas valve 47 and opens the uncondensed
23 hydrocarbon gas valve 56 to the exhaust stack 23 and opens the
24 vent valve 31 to atmosphere. Uncondensed hydrocarbon gasses
diverted to the exhaust stack are mingled with a thermal draft
26 in the presence of an igniter, not shown.
27 Obviously the invention is susceptible to changes or
28 alterations without defeating its practicability. Therefore,
29 we do not wish to be confined to the preferred embodiment shown
in the drawings and described herein.
