Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HYDROGEN SULFIDE REMOVAL METHOD AND APPARATUS
BACKGROUND OF THE INVENTION
This invention relates to gas sweetening and more
particularly to apparatuses and methods used to remove hydrogen
sulfide from petroleum gas flowing from a well and ventilated
into the atmosphere.
In the oil fields there are many small wells which produce
oil together with small amounts of sour gas or gas containing
hydrogen sulfide. The small amount of this gas makes it an
uneconomical by-product of the oil production. Small amounts of
sour gas are also sometimes produced during secondary or tertiary
recovery when water is pumped underground to increase the
recovery of oil from a field.
The problem is, then, how to economically dispose of this
sour gas. The traditional method of disposal has been to
incinerate or flare the sour gas. The problem with this method
is that it is hazardous, costly, and more costly in remote
locations. A 40' stack must be erected and a line supplying
propane to a flare at the top of the stack must be installed and
kept supplied with propane. Sometimes a carbon filled stack
catches on fire. Sometimes the tank also cathes on fire.
Sometimes when a track is sucking oil from the storage tank the
flame ignites the oil in the tank and it burns to the ground. In
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cold weather the line running to the tank may freeze. When this
happens, the emergency shut down shuts down the well.
Another viable solution to the problem of the sour gas is to
use storage tanks which can withstand pressure. Thus, the sour
gas can be stored until it is removed. The problem with this
approach is that even old railway tank trucks which are large
enough to contain at least a day or two's production are very
expensive. Another problem with this approach is that in cold
weather the controls sometimes freeze and the well is then shut
down, or that the well may be snowed in for more than the period
of its two day's storage capacity.
There have been a number of inventions which pump sour gas
through a hydrogen sulfide absorption fluid. The problem with
all of these inventions is that they are expensive to construct
and operate. This expense necessarily follows from the fact that
the sour gas must be pumped through them. The sour gas must be
pumped because it must be pressurized in order to be able to
percolate through a considerable depth of absorption fluid in
order to ensure all of the hydrogen sulphide in the gas is fully
absorbed. The motorized mechanisms must be ran continuously and
serviced regularly. In remote locations power must be generated
for their operation. In cold weather, wet gas causes them to
freeze up. When this happens, the producing well is
automatically shut down.
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OBJECTS AND STATEMENT OF INVENTION
It is an object of this invention to provide an economical
method of sweetening sour gas with a hydrogen sulfide absorption
fluid. It is an object of this invention to provide a method of
sweetening low pressure sour gas thereby avoiding the expense and
problems associated with pressurizing the sour gas. It is yet a
further object of this invention to provide an economical method
of sweetening low volumes of sour gas at the well head thereby
avoiding the expense of storing the pressurized gas or
alternatively maintaining a flare. It is yet a further object of
this invention to provide an apparatus which is cheaply
constructed and operated yet, is effective in absorbing hydrogen
sulfide from gas.
One aspect of this invention provides for a method of
sweetening sour gas comprising the steps of piping low pressure
gas into a vessel beneath a layer of structured packing in the
vessel, allowing the gas to percolate through the layer of
structured packing where it is mixed with a hydrogen sulfide
absorption fluid in the vessel and then, ventilating the gas in
the vessel through an opening in the top portion of the vessel to
atmosphere.
A more preferred aspect of the invention provides a method
comprising the steps of piping low pressure gas into a vessel,
providing a layer of structured packing immediately above the gas
outlet in the vessel, and partially filling the vessel with a
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scavenger so that the gas may percolate through the fluid filled
structured packing before being released to atmosphere.
An apparatus is provided for sweetening sour gas with a
hydrogen sulfide absorption fluid which comprises a vessel having
a top opening, a layer of structured steel packing within the
vessel, and means to conduct low pressure gas into the vessel
immediately beneath the structured steel packing, wherein use the
vessel is partially filled with the hydrogen sulfide absorption
fluid partially covering the structured packing so that when the
gas percolates through the structured steel packing any hydrogen
sulfide therein is absorbed.
Various other objects, advantages and features of this
invention will become apparent to those skilled in the art from
the following description in conjunction with the accompanying
drawings.
FIGURES OF THE INVENTION
Figure 1 is a perspective view of the invention installed
beside a storage tank.
Figure 2 is a cross-sectional view taken along lines 2-2 of
Figure 1.
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The following is a discussion and description of the
preferred specific embodiments of this invention, such being made
with reference to the drawings, wherein the same reference
numerals are used to indicate the same or similar parts and/or
structure. It should be noted that such discussion and
description is not meant to unduly limit the scope of the
invention.
DESCRIPTION OF THE INVENTION
Turning now to the drawings we have a preferred embodiment
of the Hydrogen Sulfide Removal Apparatus 20 which is ideal for
remote wells which have problematic low volumes of sour gas which
must be sweetened. It should be noted that other embodiments of
the invention which would utilize larger vessels and contain
larger volumes of hydrogen sulfide fluid are economically viable
solutions to handling larger sour gas volumes. Alternatively,
for intermediate volumes of sour gas, multiple vessels of the
type described herein could be employed in parallel, or if
pressure permitted in serial connection with a sour gas exhaust
line from a storage tank. The apparatus described herein has
been approved by the Alberta Energy Resources Conservation Board
for use in the Province of Alberta Canada based on its tested
effectiveness.
The hydrogen sulfide removal apparatus 22 is shown next to
an oil storage tank 21. When a storage tank 21 is vented to
atmosphere through the hydrogen sulfide removal apparatus 22 the
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tank 21 need not contain any pressure. Compared to a vessel that
stores pressurised petroleum it has a much lower capital cost.
The invention 20 comprises a vessel 22 constructed from rolled
steel having flat end plates 24. The vessel 22 is generally the
size of a 45 gallon drum. It is 4' in height and 2' in diameter.
Generally 20" above its bottom end plate 24 a horizontal
perforated plate 26 is tacked therein. The perforated plate 26
supports two cyllindrical layers of structured steel packing 28
each being 7" in thickness. Structured steel packing is only
available in 7" thicknesses. One manufacturer of structured
steel packing is by Nutter Engineering in Pennsylvania. A 2"
threaded drain valve 30 is screwed into a fitting 32 on a bottom
portion of the vessel 22. A means to conduct low pressure gas
into the vessel, being a 2" screwed steel inlet pipe 36 provides
an inlet opening 38 positioned immediately beneath the structured
steel packing for the sour gas 48. An outlet opening 40 is
provided by a short 3" outlet pipe 42 having an elbow 43 thereon.
The outlet pipe 42 is welded in and through the top end plate 24.
A deflector plate 44 is provided underneath the outlet pipe 42.
A sight gauge 34 constructed from 3/8" diameter plastic is
positioned on the side of the vessel extending from below to
above the structured packing 28. The sight gauge 34 enables one
to view the height of hydrogen sulfide absorption fluid 46 which
is poured through the outlet opening 40 into the vessel 22.
The hydrogen sulfide absorption fluid 46 is capable of
scavenging or absorbing hydrogen sulfide from sour gas 48 when
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the sour gas 48 is slowly percolated through the fluid 46 by
means of the structured steel packing 28. Sweet gas 50 rises out
of and above the structured steel packing 28. The hydrogen
sulfide absorption fluid 46 may be one of several known brands of
hydrogen sulfide scavengers marketed by different manufacturers.
However, it has been found that a petroleum based hydrogen
sulfide scavenger is more effective in cold temperatures than a
formaldehyde based scavenger. The height of the fluid 46 above
the inlet opening 26 is critical. As a rule of thumb generally 1
ounce of sour gas 48 pressure is required for each 1" of head of
fluid 46 which the sour gas 48 must rise through. It has also
been found that it is necessary for sour gas 48 to percolate
through at least 12" of hydrogen sulfide absorption fluid 46 in
structured steel packing 28 in order for the hydrogen sulfide to
be effectively absorbed. Therefore, a minimum of 12 ounces of
sour gas 48 pressure is required in order to utilise the
invention 20. Accordingly, when sour gas 48 pressure is the
minimal 12 oz. then it is necessary to maintain at least, but no
more than 12" of fluid 46 height above the inlet opening 26. In
addition to maintaining the proper fluid 46 height a second use
of the site gauge 34 is in viewing the color of the fluid 46. As
the fluid 46 becomes spent it becomes darker in color. It also
tends to become heavier, and settles to the bottom of the vessel
22. Accordingly, one can approximate the remaining life or
hydrogen sulfide absorbing capability of the fluid 46 in the
vessel 22 by viewing its color through the site gauge 34.
I CLAIM:
