Electric heating – Microwave heating – Fluid heater
Reexamination Certificate
1999-12-30
2001-10-23
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Fluid heater
C219S679000, C219S695000, C219S746000, C166S060000, C166S248000, C137S001000, C204S157150
Reexamination Certificate
active
06307191
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a microwave heating system and, more particularly, to a system and method for removing or inhibiting the formation of inclusion complexes in a hydrocarbon fluid pipeline
BACKGROUND OF THE INVENTION
Hydrocarbon fluid pipelines which operate at elevated pressures can become occluded by inclusion complexes in the form of clathrates and, more specifically, in the form of solid-phase gas hydrates. Gas hydrate formation is a well known phenomenon which occurs when free liquid water is present in a hydrocarbon fluid stream flowing through a pipeline and the temperature of the hydrocarbon fluid stream falls below a critical value. The critical temperature value for gas hydrate formation can be in excess of 60° F. in higher pressure pipelines, although the critical temperature value for gas hydrate formation generally decreases as a function of decreasing pressure in the pipeline.
A number of techniques are known in the prior art for preventing or inhibiting gas hydrate formation in hydrocarbon fluid pipelines. One method is to dehydrate the hydrocarbon fluid stream before transporting the hydrocarbon fluid through the pipeline. Another method is to continuously inject a gas hydrate liquid inhibitor composition, such as methanol or glycol, directly into the pipeline where the inhibitor mixes with the flowing hydrocarbon fluid. Yet another method is to wrap the pipeline wall with an electric resistance, heat-tracing cable or a heat-tracing tube containing a circulating hot fluid which elevates the temperature of the pipeline wall. A more recently developed method is to induction heat the pipeline wall using an alternating current. This method requires an electrically isolated parallel conductor in addition to the pipeline itself, such as a second outer metal pipeline surrounding, but insulated from, the original pipeline or a conductor cable running parallel to, but likewise insulated from, the original pipeline.
The above-recited prior art methods for preventing or inhibiting gas hydrate formation are excessively expensive or complex for many off-shore and subsea applications. For example, the prior art method of continuously injecting a gas hydrate liquid inhibitor, such as methanol, into a subsea production pipeline requires the operator to run a separate methanol injection tube to the subsea well head. In addition large quantities of methanol must be handled by the operator and are consumed while practicing the method. The prior art method of induction heating the pipeline wall with an alternating current requires reliable electrical isolation between the original pipeline and the parallel conductor which is extremely difficult to achieve in practice. A short circuit current path could render a large portion of the induction heating system inoperative.
The present invention recognizes a need for a more cost effective and less complex system for preventing or inhibiting gas hydrate formation in hydrocarbon fluid pipelines. Accordingly, it is an object of the present invention to provide a system for inhibiting the formation of gas hydrate blockages in a hydrocarbon fluid pipeline where a liquid water phase is coexistent with one or more hydrocarbon phases. It is another object of the present invention to provide a system for removing gas hydrate blockages in a hydrocarbon fluid pipeline which have formed as the result of unusual pipeline conditions or upsets. It is still another object of the present invention to provide such a system which can be designed as a new installation or which can be readily retrofitted to an existing system. It is yet another object of the present invention to provide such a system which has particular utility to offshore deep water hydrocarbon pipeline applications and to sub sea oil and gas well production flow line applications. These objects and others are achieved in accordance with the invention described hereafter.
SUMMARY OF THE INVENTION
The present invention is a microwave heating system comprising a microwave generator, a fluid pipeline having an upstream section and a downstream section, and a waveguide assembly connected to the microwave generator. The waveguide assembly includes a microwave transition body and a microwave distributor. The microwave distributor is positioned in the fluid pipeline at a junction between the upstream section and the downstream section such that the microwave distributor is in contact with fluids passing through the junction from the upstream section to the downstream section. The upstream section has a circular internal configuration with a substantially continuous open cross-section proximal to the junction. The microwave distributor is in substantially straight line alignment with the upstream section proximal to the junction, while the downstream section is in substantially right angle alignment with the upstream section proximal to the junction. The microwave transition body is positioned between the microwave generator and the microwave distributor and conforms the propagation pattern of microwave signals transmitted by the microwave generator to the internal configuration of the upstream section.
In accordance with one embodiment of the invention, the upstream section has a pipe wall comprising a plurality of layers, including a structural layer and a transmissive layer positioned internal to the structural layer which is substantially less resistant to transmission of microwaves than the structural layer. The pipe wall also has a corrosion resistant layer positioned on the opposite side of the transmissive layer from the structural layer. The corrosion resistant layer is formed from a relatively corrosion resistant material to provide a corrosion barrier.
The microwave heating system is applicable to substantially preventing or remediating inclusion complex blockages in the upstream section of the fluid pipeline at a distance up to about 20 km, and preferably up to about 50 km, or more from the microwave generator. The microwave heating system is also applicable to simultaneously controlling a function of a remote device. The microwave generator employed in the present embodiment has means for frequency or amplitude modulating the microwave signals transmitted thereby to embed information in the microwave signals. The remote device, e.g., a flow control device, is positioned at a point on the upstream section having means for responding to the information embedded in the modulated microwave signals. Alternatively, the microwave generator has means for generating secondary signals in addition to the primary microwave signals. The microwave generator further has means for frequency or amplitude modulating the secondary signals to embed information in the secondary signals. The remote device likewise has means for responding to the information embedded in the modulated secondary signals.
The microwave heating system is also applicable to simultaneously powering an electrically-powered remote device while substantially removing or inhibiting the formation of inclusion complexes in the hydrocarbon fluid pipeline. The remote device is positioned at a point on the upstream section and coupled with an electrical storage battery which powers the remote device. A power absorbing means is coupled with the electrical storage battery to absorb power from the microwave signals propagated through the pipeline and to charge the electrical storage battery with the absorbed power.
The invention will be further understood from the accompanying drawings and description.
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patent: 4193448 (1980-03-01), Jeambey
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patent: 4678034 (1987-07-01), Eastlund et al.
patent: 4853507 (1989-08-01), Samardzija
patent: 5055180 (1991-10-01), Klaila
patent: 5625178 (1997-04-01), Rojey
patent: 62-293000 (1987-12-01), None
Ebel Jack E.
Leung Philip H.
Marathon Oil Compamy
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