Gas separation: processes – Degasification of liquid
Reexamination Certificate
2000-08-23
2002-07-02
Smith, Duane S. (Department: 1724)
Gas separation: processes
Degasification of liquid
C095S260000, C096S155000, C096S204000
Reexamination Certificate
active
06413299
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method and apparatus for facilitating the dissipation of a liquid slug that is flowing together with compressed gas in a pipeline; and in particular to a method and apparatus for dividing a liquid slug into two liquid slugs, one of which is facilitated to dissipate into a two phase flow of separate liquid and separate gas, and then recombining the two phase flow with the remaining liquid slug in a manner that facilitates the dissipation of that other liquid slug into a two phase flow of separate liquid and separate gas.
2. Description of the Related Art
To the best of the Inventor's knowledge this is a unique invention which has no related prior art. There is tangential prior art relating to methods and apparatuses for the removal of liquids or liquid slugs from a gas pipeline which has a liquid slug and liquid/gas flow. The Inventor's prior invention, disclosed in U.S. Pat. No. 5,525,133, and in Canadian Patent #2,129,306, is one such invention. However the present invention does not deal with the removal of a liquid slug from a gas pipeline, the present invention is a method and apparatus to facilitate the dissipation of a liquid slug that is flowing in a gas pipeline, and therefore, if that liquid slug was traveling in the gas pipeline together with gas, in a substantially unified flow stream, on the dissipation of the liquid slug the liquid (which was traveling as a slug) will thereafter have a unique and distinguishable flow stream from the gas with which it had been traveling, which gas will thereafter also then have its own unique and distinguishable flow stream.
Liquid can exist as single molecules or as droplets, and when liquid molecules of the same or similar types have a sufficient cohesion for each other, liquid can also exist in a mass. In gas pipelines there often exists sufficiently cohesive liquids, which, as they travel through the pipeline develop into liquid slugs that travel through the pipeline substantially intact or growing in size.
The flow regime of a gas pipeline that is carrying both gas and liquid can have more than one configuration depending on several factors, the most significant of which are: the operating gas pressure, liquid viscosity, liquid density, surface tension, gas/liquid velocities, and the vertical rise/fall of the pipeline. At low gas and low liquid flow rates, the flow regime is generally stratified (i.e. a two phase flow) with the gas phase flowing at a faster rate above the liquid phase, and the liquid flowing along the bottom of the pipeline. The difference in phase velocity is due to slip that occurs at the gas/liquid interface. At higher gas flow rates and low liquid flow rates, the flow regime is generally an annular flow in which the liquid flows mainly near the inside wall of the pipeline and the gas flows mainly in the center of the pipeline. The annular flow regime is two phase and the gas phase velocity is higher than the liquid phase velocity. However, at low to high gas flow rates and high liquid flow rates the liquid can develop into a liquid slug and will travel down the pipeline as a single phase liquid flow and at or near the same velocity as the gas phase flowing in the pipeline. The liquid slug usually develops from a stratified two phase flow in a gas pipeline when waves form at the gas/liquid interface and grow to the point where they fill the cross-section of the pipeline, blocking the gas flow. Typically, the flow rate of the gas phase is much higher than that of the liquid phase, the liquid slugs are therefore accelerated by the gas phase to approximately the same velocity as the gas phase. The liquid slugs thus travel at a much higher flow rate than the non-slug portion of the liquid phase. As a result, the piping and related equipment downstream of the slugs may experience intermittent surges and subsequent impact from the slugs. Such surging may place stresses on the pipeline and processing equipment and may lead to the pipeline or the processing equipment or both becoming damaged.
In addition to the potential for causing damage, the liquid slugs are difficult to remove by conventional liquid separation equipment, and therefore in gas pipelines it is desirable, to as far as possible, reduce the existence of liquid slugs. When a liquid slug flowing through a gas pipeline is changed to a two phase gas/liquid flow regime, it facilitates the separation and removal of the liquid phase from the gas pipeline.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention was to design a method and a means to cause a liquid slug and gas that is traveling down a pipeline to divide into two liquid slug and gas flows traveling in two pipelines.
A second object of the present invention is to devise a method and a means to facilitate the dissipation of the liquid slug in one of the two liquid slug and gas flows into a separate liquid flow and a separate gas flow.
A third object of the present invention is to devise a method and a means to combine the created separate liquid flow and separate gas flow with the other liquid slug and gas flow in a manner that facilitates the dissipation of that other liquid slug into a two phase flow of separate liquid and separate gas.
A fourth object of the present invention was to achieve the first two objects by an apparatus which is relatively inexpensive, and easy construct, install and operate.
A fifth object of the present invention was to achieve the first four objects by an apparatus that is relatively maintenance free.
Where there is a primary gas pipeline in which gas and any liquids and any liquid slugs in the pipeline are traveling through the primary gas pipeline in the pipeline's downstream direction, the method of the present invention that accomplishes the above objects is comprised of constructing a phase separation pipe, hereinafter also referred to as a “secondary gas pipeline”, and then communicatively connecting the secondary gas pipeline in parallel with the primary gas pipeline, wherein the secondary gas pipeline is of a configuration such that a significant percentage of a liquid slug traveling through it, from its input end to its output end, will not remain as a liquid slug, but will become a two phase flow of liquid and gas, and which secondary gas pipeline is of such a configuration and of a length, and is located along the primary gas pipeline such that any liquid slug and gas “LSG” which arrives at the upstream point of connection of the primary gas pipeline with the secondary gas pipeline will divide into LSG
1
that continues traveling down the primary gas pipeline and LSG
2
that enter the secondary gas pipeline; wherein LSG
1
is a portion of LSG and LSG
2
is the remaining portion of LSG such that LSG
1
+LSG
2
=LSG; and wherein the secondary gas pipeline is connected to the primary gas pipeline at the appropriate downstream location such that when LSG
2
leaves the secondary gas pipeline and re-enters the primary gas pipeline it will re-enter the primary gas pipeline at the time of the arrival, at the location at which LSG
2
re-enters the primary gas pipeline, of the front portion of the largest LSG
1
that is anticipated to be traveling through the primary gas pipeline.
The apparatus of the present invention that accomplishes the above objects, when said apparatus is connected in parallel with a primary gas pipeline in which gas and any liquids and any liquid slugs in the primary gas pipeline are traveling through the pipeline in the pipeline's downstream direction, is a phase division pipe, which, as previously mentioned herein is also referred to as a “secondary gas pipeline”, which secondary gas pipeline is comprised of: an input end; and a first section that is in continuous communication with the input end, which first section is of a smaller diameter than is the diameter of the primary gas pipeline; and a second section that is in continuous communication with the first section, which second section is of
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