Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
  • B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
  • B01D29/117—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements arranged for outward flow filtration
  • B01D29/118—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements arranged for outward flow filtration open-ended
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
  • B01D29/50—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with multiple filtering elements, characterised by their mutual disposition
  • B01D29/52—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with multiple filtering elements, characterised by their mutual disposition in parallel connection
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
  • B01D29/62—Regenerating the filter material in the filter
  • B01D29/66—Regenerating the filter material in the filter by flushing, e.g. counter-current air-bumps
  • B01D29/668—Regenerating the filter material in the filter by flushing, e.g. counter-current air-bumps with valves, e.g. rotating valves for coaxially placed filtering elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2201/00—Details relating to filtering apparatus
  • B01D2201/20—Pressure-related systems for filters
  • B01D2201/204—Systems for applying vacuum to filters
  • B01D2201/208—Systems for applying vacuum to filters by venturi systems

Definitions

• the present invention relates to a method for cleaning filters for filtering liquids during continous operation of the filters, and improved filter devices implementing said method.
• seawater is used for injection into oil or gas fields.
• Seawater includes algae, plankton in addition to organic and inorganic particles that have to be removed before injection to avoid clogging of the oil or gas well.
• filters for removing particles for injection purposes are that all particles larger than 50 - 70 microns have to be removed.
• the filter comprises a plurality of filter rods that are arranged together in a filter house.
• the filter rods are arranged parallel to each other and to the length axis of the filter house.
• the filter rods are cylindrical rods having cylinder walls comprising a mechanical filter.
• the water to be filtered flows into the interior of the filter rods through their open end faces.
• the water in the interior of the filter rods flows through the mechanical filter of the cylinder walls and into a clean water chamber that surrounds the filter rods.
• the water in the clean water chamber is removed from the device, whereas the filtered particles are left in the filter rod.
• the water flows through the mechanical filter due to the difference in pressure between the interior of the rods and the clean water chamber. This difference in pressure is normally provided by means of pumps delivering pressurized water.
• the filter rods To remove the particles in the interior of the filter rods, the filter rods have to be cleaned and the particles removed.
• the supply of water to be filtered through the end surface(s) of one or more of the filter rods is temporarily closed. Flushing water is then added trough one end face and flushing water including particles are drained through a drainage tube connected to the closures used to close the end face(s). Additional cleaning of the filter rods is achieved by backwashing, i.e. reversing of the flow over the filter so that clean water from the clean water chamber flows through the filter surface and into the interior of the filter rod. The clean water effectively releases particles withheld by the filter into the interior of the filter rods.
• the backwash is effected by the pressure drop in the interior of the filter rods due to closing of the end faces.
• the present invention comprises a method for cleaning a filter for filtration of a fluid during continuous operation of the filter, the filter device comprising a plurality of filter rods, the cylinder walls of which rods are mechanical filters, the rods being arranged so that a fluid to be filtered flows into the interior of the filter rods through one or both of the end faces of the filter rods and is filtered by flowing through the cylinder walls of the filter rods, the method comprising temporary closing of the supply of liquid to be filtered into one or more of the filter rods, reversing the direction of flow through walls of the closed filter rods so that filtered water flows into the interior of the filter rod(s) to remove particles adhered to the filter, and removing water and particles from the interior of the filter rods, wherein the pressure in the interior of the closed filter rod(s) is (are) reduced and that water and particles are withdrawn through one of the end faces of the filter rod(s) by means of a vacuum provided by means of a water jet pump.
• a water jet pump to provide a lower pressure inside the filter rods to be cleaned compared with its (their) surroundings, assures that the pressure inside the filter rod is lower than the pressure in the clean water surrounding the filter rods, thus resulting in a backwash of clean water through the filter into the interior of the filter rods to loosen and bring out particles from the filter.
• additional flushing water is supplied to the interior of the filter rods through the end face thereof that is opposite of the end face from which water and particles are removed. Addition of additional water may be preferred in certain installations to ensure sufficient flushing of the inner walls of the filter rods to enhance the cleaning.
• the present invention relates to a filter device that may be cleaned during continuous operation, the filter device comprising a filter chamber for water to be filtered, a plurality of substantially parallel, cylindrical filter rods, that are open to the filter chamber through their end faces, and the cylinder walls of which rods comprise mechanical filters, a clean water chamber for filtered water surrounding the filter rods, and a cleaning device comprising means for temporarily closing the connection between the interior of one or more of the filter rods and the filter chamber, and said means for temporarily closing one of the end faces comprises means for removal of water and particles from the interior of the filter rod(s), wherein water jet pump is arranged on the sludge line for generation of vacuum in the interior of the filter rod.
• the means for temporarily closing hi the end of the filter rod(s) that is opposite to the sludge line is arranged a flush water line for supplying flush water to the interior of the filter rod.
• the filter rods are arranged in concentric circles, and that the means for temporarily closing are arms rotably arranged in the filter chamber about the length axis of the device and which are equipped with closing devices that are adapted to rest against the end faces of the filter rods.
• FIG. 1 illustrates the principle of the filter device according to the present invention
• Figure 2 is a length section through a part of a filter device according to the present invention.
• FIG. 3 illustrates a filter device according to the prior art.
• the filter device 1 comprises a filter housing 2.
• a filter housing 2 in a subsea installation is surrounded by pressurized water, the pressure being dependent on the sea depth.
• the water to be cleaned enters the device through one or more openings 18 into a filter chamber 4 in the interior of the filter housing 2.
• a plurality of filter rods 7, 7', are placed, preferably in concentric circles relative to a cross section perpendicular to the filter rods, as described for the filters according to the prior art.
• the filter rods are tubular bodies, the tubular walls of which comprise or consist of a mechanical filter, such as e.g. a filter comprising spiral slits.
• the water in the filter chamber 4 flows into the interior of the filter rods 7 through the open end faces thereof.
• the water in the interior of the filter rods 7 flows through the filter walls of the filter rod and into a clean water chamber 6 that surrounds the filter rods and where filtered water is collected.
• the filtered water in the clean water chamber is removed through a clan water pipe 5.
• the flow through the filter walls of the filter rods is caused by the pressure drop over the filter by withdrawing water from the clean water chamber 6 by means of a not shown pump downstream for the present pumping device.
• This not shown pump is the pump that is used to pump the water down into a formation for injection into a gas or oil field.
• the end faces of the filter rods are closed the same way as described for the prior art solutions.
• the water and particle sludge inside the filter rod are removed by means of a water jet pump 17 connected to the bottom of the filter rod.
• the water jet pump effectively withdraws water and sludge of particles from the interior of the filter rod and reduces the pressure therein. Accordingly, water in the clean water chamber 6 will flow through the filter surface into the interior of the filter rods together with particles that has fastened to the filter surface.
• additional flushing water may be added e.g as described for the prior art solution, by introducing of flushing water through the end face opposite to the end face where water and particle sludge are removed.
• FIG. 1 illustrates a filter device where two filter rods are illustrated. One of the rods 7' is being cleaned, whereas the other rod 7, is in filtering operation.
• a rotating cleaning device is arranged within the filter device.
• the rotating cleaning device comprises a shaft 10 rotating about an axis that coincides with the axis of the concentrical circles of filter rods.
• a upper arm 11 and lower arm 13 including a upper closing device 12 and a lower closing device 14, respectively, are arranged on said rotating shaft.
• the closing devices, 12, 14, are adopted to rest against the upper end face and the lower end face of the filter rod, respectively, to close the end faces and prevent flow of water to be filtered from the filter chamber into the filter rods during the cleaning procedure. Any additional water for flushing is introduced after closing of the end faces to the interior of the filter rods through a flushing line 8 running through the shaft 10, the arm 11 and through the upper closing device 12.
• the removed particle and water are removed through a sludge line 15, running through the lower closing device 14, the lower arm 13 and the lower part of the shaft 10.
• a water jet pump 17 is provided on the sludge line 15 downstream for the filter rods to assure that particles and water are removed, and to provide a lower pressure in the interior of the filter rod than in the clean water chamber to effect a backwash of the filter rods.
• Pressurized water in an amount and at a pressure that is necessary to produce the required pressure drop in the interior of the filter rods is supplied through a pressurize water line 16.
• the pressurized water for the water jet pump supplied trough line 16 may suitably be provided from the above mentioned not shown pump for generation of pressurized water for injection.
• the pressurized water for the water jet pump may, however, be supplied form any other source for pressurized, cleaned water.
• additional flushing water may be supplied through an optional flushing line 8 to make the cleaning more effective.
• the amount of water flowing through the filter and the interior of the filter rod during the flushing will depend on the difference of the pressure between the interior of the filter rod and the clean water chamber, and thus on the negative pressure generated by means of the water jet pump 17.
• the water and particles that are withdrawn from the interior of the filter rods are preferably released into the surroundings.
• FIG. 2 is a longitudinal section through the lower part of a filter device according to the present invention.
• the filter device is protected by an outer shield 20 having a plurality of openings 21 to allow flow of water into the device. Only two filter rods 7, T surrounded by the clean water chamber 6 are illustrated.
• the water to be filtered may flow freely into the device through the openings 21, into the filter chamber 4 and into the interior of the filter rods 7.
• Pressurized water for the water jet pump is introduced through the pressurized water line 16 running through the shaft 10, and into a nozzle 22 leading the pressurized water into a venturi restriction 23.
• the venture restriction do not need to be integrated into filter device as illustrated in figure 2, but may be arranged on a tube for removing the water and particles from the filter device.
• the pressure in the filter chamber 4 and in the interior of the filter rods are substantially equal to the pressure of the surrounding sea at the depth of installation.
• water is withdrawn from the clean water chamber by means of a not shown pump. This results in a pressure difference over the walls of the • filter rods that is essential for the flow of water from the interior of the filter rods to the clean water chamber 6.
• the pressure in the interior of the filter rod is rapidly equalized with the pressure inside the clean water chamber, i.e. the pressure in the interior of the closed filter rod becomes lower than the ambient pressure and makes it impossible to drain the water and particles out to the surroundings. Draining the inside of the filter rod by means of vacuum provided by the water jet pump 17 reduces the pressure inside the filter rod to a pressure lower than the pressure inside the clean water chamber resulting in a backwash of the filter.
• a water jet pump may also be used for filter devices of the described type operating at a pressure above the ambient pressure. The water jet pump will reduce the pressure inside the filter rods more effectively than simple drainage and assure an effective backwash of the filter wall.
• Tests are performed both on a traditional filter device according to figure 3, produced and delivered by the present applicant, and a device according to the present invention.
• the device according to figure 3 comprises most of the features described with reference to the present invention.
• Water to be filtered is, however, supplied through a crude water line 3.
• the device according to figure 3 for surface applications normally operates at a pressure of about 10 to 15 bar.
• the water is driven through the filter by means of the pressure drop over the filter surface. Flushing and backwashing is performed against the ambient pressure, i.e. about 1 bar.
• the pressure inside the filter bar during cleaning is substantially lower than the pressure in the clean water chamber resulting in an effective backwash of the filter so that the inside of the filter rod is washed both by means of the flushing water and water flowing through the filter into the interior of the filter rod.
• the prior art device according to figure 3 do not fulfill the requirements for equipment that are to be placed at the sea bed as the equipment has to be replaced or undergo a major maintenance and cleaning procedure at a regular basis as the filters are clogged.
• the present improved filter device where a negative pressure is created in the interior of the filter rod compared with the clean water chamber during the washing results in a backwash of the filter due to the cleaned water flowing reverse to the direction during filtering operation, results in an effective backwash of the filter loosening and removing particles from the filter.
• the removal of particles from the filters of the present device is so effective that the filter device may be placed at the sea bottom at full operation for several years without any need for stop and cleaning as needed for the alternative filter devices.
• the cleaning device will, like on the device illustrated in figure 3, rotate at a steady speed and will not stop over the filter rods.
• the cleaning device will, however, have an effective washing time per rod per revolution assuring adequate cleaning of the rods.
• the rotational speed of the washing device may be adjusted dependent on the number of rods per concentric circle and the amount of particles in the water.
• the cleaning device may also comprise more than one upper arm and lower arm and corresponding closing devices and sludge lines, to increase the total washing time per filter rod. Accordingly, the frequency of cleaning and thus the rotational speed of the device may be varied according to the amount of particles and flow through the filter and is a question of optimalization.
• the requirement for filtering seawater for injection is that particles larger than 50 to 80 microns are to be removed.
• the present invention is, however, applicable for other limits of exclusion at the given limits are illustrative only.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Filtration Of Liquid (AREA)

Applications Claiming Priority (2)

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• 2005
  • 2005-05-26 NO NO20052522A patent/NO20052522L/no not_active Application Discontinuation
• 2006
  • 2006-05-26 WO PCT/NO2006/000198 patent/WO2006126892A1/en not_active Ceased
  • 2006-05-26 EP EP06747657A patent/EP1885471A1/de not_active Withdrawn

Non-Patent Citations (1)

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