Cleaning and liquid contact with solids – Processes – Including melting
Reexamination Certificate
2001-03-12
2002-02-19
El-Arini, Zeinab (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including melting
C134S019000, C134S022110, C134S105000, C134S16600C
Reexamination Certificate
active
06348102
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the removal of deposits, in particular in pipelines, and to apparatus for that removal.
Pipelines for liquids, especially crude oil or wet gases such as natural gas, often pass through cold areas, either on the surface in Arctic areas or on the sea bed e.g. in North Sea or Gulf of Mexico. These cold conditions can result in formations of deposits of wax from the oil or gas hydrate crystals from the natural gas, the deposits forming when fluid flow is stopped e.g. during shut down or in extreme cases when fluid is still flowing. The deposits reduce the flow rate and ultimately if they build up sufficiently can block the line. Existing methods of removing the deposits are mechanical using “pigs” to scrape out the wax, physical, such as use of hot oil flushes, or chemical such as addition of alcohols and/or chemical deposition inhibitors. None of these is completely satisfactory.
SUMMARY OF THE INVENTION
A method and apparatus has now been devised to remove the deposit in a different way, namely by localized heating of the pipe (and hence its elements) using a reusable heat source.
The present invention provides an apparatus comprising an elongate pipe for use in the transfer of fluids susceptible to form deposits on cooling, and a container comprising a reusable heat source comprising a supercooled solution, said container being in heat conducting contact with a surface of said pipe, preferably on at least one surface of said container.
The present invention also provides a method of removing from inside a pipe a deposit formed on cooling a fluid passing through said pipe, said method comprising locating in heat conducting relation to said pipe a reusable heat source comprising a supercooled solution, and activating crystallization in said solution liberating heat which causes at least some of the deposit to melt and/or dissolve. The method preferably comprises subsequently passing fluid through said pipe to cause the crystals in said heat source to form into a solution, followed by allowing the solution to cool to reform the supercooled solution.
The present invention also provides a container for a reusable heat source, said container having at least one surface adapted to be capable of being in heat conducting relation to a pipe.
The pipe may be for transfer of crude oil with or without gas and/or water, or transfer of wet gas. The pipe may be on land e.g. Arctic tundra or underwater e.g. on the sea bed, or may be involved in production rather than transport of the oil/gas e.g. the production annulus in a well bore. The pipe is usually metallic e.g. of ferrous metal such as steel, but may be of other heat conducting material e.g. fibre reinforced polymer, such as carbon fibre reinforced material. The pipe is usually at least 8 cm in diameter, such as 8-80 in particular at least 10 cm, such as 25-50 cm.
The container for the heat source is usually an elongate body of which an elongate surface is in contact with the pipe. That section of pipe may be one with or preferably without joints, though the pipe may have one or more bends, especially shallow bends. Particular shaped containers are preferred for a pipe with sharp bends e.g. one of 45-145° such as right angled ones, those containers preferably conforming to one or more parts of the bend. The container inner surface usually has a concave shape adapted to receive the pipe. The container surface may contact the pipe circumference over only a part of the total circumference of the pipe such as at least 15% e.g. when only one wall of the pipe is in contact with a source of cold e.g. sea, so deposits only form on that wall. There may be more than one of such containers, each contacting past of the pipe circumference at that location, the totality of said surfaces of the containers surrounding the pipe circumference. Thus there may be 2-4 elongated containers, each with an inner concave surface adapted to receive a part of the pipe circumference; in this case the 2-4 containers fit in sections around the pipe. These sections may be removably or non removably attached to the pipes. Thus they may be strapped to the pipe and/or to each other e.g. with a clamping strip with means to locate and receive that strip on the outsides of the containers, but preferably the sections have reversibly releasable means to attach the sections to each other, e.g. with appropriate clips and corresponding latches to enable the sections in total to fit round the pipe.
The part section elongate containers with the inner concave surface may also adapted to be fitted over the pipe, in particular when the pipe is laying on the ground or on a partly immersed in a sea bed, rather than round the pipe. In this aspect of the invention the containers may be in the form of part annular elongate caps or covers e.g. of arch or horseshoe shaped cross section and in particular with a top hemispherical inner surface for receiving and fitting over the pipe; the heat source would then be located in the annulus and the container could conveniently for ease of handling be fitted with one or more means for suspension e.g. hooks on its top outer curved surface.
The container may contact the pipe around its entire circumference i.e. surround the pipe, and in this case the container is in the form of an annulus surrounding the pipe. The shape of the outer transverse surface of the pipe may be the same or different from that of the external shape of the container, conveniently the container and pipe are coaxial, especially with spacers between them to maintain a substantially constant separation between the container outer wall and the pipe. When the container surrounds the pipe the container may be removable from the pipe, but it is preferably not so removable. The annular container may have an inner surface for contacting the pipe, e.g. be in the form of a sleeve or sheath, and in this form may be removable. The outer surface of the container may be arcuate e.g. cylindrical or may be rectangular e.g. square. In a modification the heat source in the annulus is in direct contact with the exterior wall of the pipe so the inner surface of the container is the outer surface of the pipe; the container and pipe then become a double walled container e.g. double walled pipe.
Advantageously the container has heat insulation on at least one and preferably substantially all of its sides not to be in contact with the pipe. The insulation may be on the inside of the outer wall of the container but is preferably on its outer wall. The insulation may be inorganic e.g. fibrous as in rock wool or particulate as in fly ash powder, aluminium silicate microspheres or expanded vermiculite, or pumice or glass wool or organic as in foamed polymer or with larger voids as in laminated sheets enclosing separate gas bubbles e.g. “bubble wrap”. Preferably the container and pipe are such that in use the external surfaces of the container are heat insulated from the environment e.g. the sea. Advantageously on the inside of the outer wall of the container are one or more reflective surfaces to focus the heat back towards the pipe.
The container which is usually rigid and of metal has within it the supercooled solution, which may be in contact with the walls of the container, or retained inside one or more bags constructed preferably of flexible impermeable plastics material, e.g. fibre reinforced rubber, PVC or nylon.
The container itself may also be in the form of an elongated flexible body capable of being wrapped around the pipe e.g. helically in one or more strips, preferably substantially to cover the pipe's outer circumference or lain e.g. axially over the length of the pipe or transversely across the pipe. Accordingly an apparatus may be provided which comprises a container extending around the pipe. The body may contain the solution with free fluid movement throughout, but the body such be divided with more than one section restricting or inhibiting such movement; the subdivision may be by bringing opposing sides of the elongate body tow
BP Exploration and Oil, Inc.
El-Arini Zeinab
Nixon & Vanderhye
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