Electric heating – Metal heating – Of cylinders
Patent
1991-04-30
1993-08-31
Reynolds, Bruce A.
Electric heating
Metal heating
Of cylinders
219 1057, 219 1079, H05B 636, H05B 664
Patent
active
052411478
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for heating a transport pipeline. The invention also relates to a transport pipeline with heating.
TECHNICAL FIELD
The invention is developed in connection with so-called multiphase transport, i.e. transport of mixtures of gas, oil and water through pipelines. Such multiphase transport has increasingly been regarded as more attractive over longer distances. The main reason is the desire to be able to reduce the number of platforms in the sea and/or the size of them. In this way, it will be economically viable to develop more oil and gas fields. Multiphase transport from subsea installations to central platforms or directly to land, offers many new challenges.
One of the problems to be faced in the case of transport of unprocessed well stream, is the risk of hydrate formation. At low temperatures, under 20.degree. C., and high pressure, hydrocarbons (gas) and water can form a solid phase which can prevent flow in pipes, pumps and valves. Hydrate formation can be prevented by removing water from the well stream. Such processing is very difficult to carry out on the sea bed. Other known methods are injection of methanol or glycol. Where there are large volumes of water in the well stream, the consumption of such inhibitors will be very great. The cost of regeneration through distillation is also high. In addition there are costs for installation, operation and maintenance of pipelines, pumps and valves for injection. Deposits of wax can cause problems for the operational stability.
An alternative to the use of inhibitors is insulation of pipelines combined with heating. In order to prevent the formation of hydrate during prolonged unforeseen operational stand-stills or to achieve the melting of hydrate which has been formed, energy must be supplied. The need for power will be strongly dependent on the total heat transfer coefficient of the pipeline and the length of the pipeline. Calculations show that for long pipelines, very good insulation materials are required, e.g. foamed polyurethane. In the case of operational stand-stills, typical power requirement for keeping the temperature at 25.degree. C. in a 20" pipeline on the seabed, where there is an ambient temperature of 4.degree. C., is 50-100 W/m.
The use of a few electrically heated pipelines on the sea bed is known. These pipelines are all relatively short, they have a length of less than 5 km and they are installed in one single towed-out length. For longer pipelines, the problems increase, partly due to a greater power requirement and partly due to a considerable increase in the number of electric joints when conventional laying technique is used.
Heating of pipelines can take place in several ways:
Currently known techniques, using conventional heating cables or the mentioned induction method SECT (Skin Effect Current Tracing CHISSO Engineering, Japan) is not known to have been utilized over long distances. These known methods appear to have a low reliability underwater due to a large number of joints.
DISCLOSURE OF INVENTION
The present invention aims at using inductive heating, particularly combined with the use of conventional laying methods, so-called S- and J-laying, combined with thermal insulation of the pipeline.
According to the invention, a method is therefore suggested for heating a transport pipeline by induction, and the method is characterized in that a magnetic field is provided, which magnetic field in the case of induction generates heat in the transport pipeline, in such a way that mutual, preferably parallel conductors are utilized as induction wires. The power supply can be single-phase or three-phase and the frequency either available grid frequency (50 or 60 Hz) or an optimized frequency provided by a particular converter. The physical basis for the calculation of heat generation in the pipes in Maxwell's equations expressed in differential form. These equations provide the relation between electric and magnetic quantities. The arrangement of the conductor in or on the surface of the ins
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Electric Heating System for pipelines . . . Sectracing, Pipe Heating Systems, Inc.
Moving the Arctic Oil; Donald F. Othmer and John W. E., Griemsmann Mechanical Engineering, Nov. 1971 pp. 27-31.
Heating Pipelines With Electrical Skin Current, Masao Ando and Donald R. Othmer Chemical Engineering Mar. 9, 1970.
Skin Effect Current Tracing Ric-Wil Incorporated.
Den Norske Stats Oljeselskap A.S.
Reynolds Bruce A.
Switzer Michael D.
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