Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B9/00—Cleaning hollow articles by methods or apparatus specially adapted thereto 
  • B08B9/08—Cleaning containers, e.g. tanks
  • B08B9/093—Cleaning containers, e.g. tanks by the force of jets or sprays
  • B08B9/0933—Removing sludge or the like from tank bottoms

Definitions

• the present invention relates to a method for cleaning a floating roof tank containing crude oil and to a device for carrying out said method.
• crude oil storage tanks are generally cylindrical tanks with floating roofs.
• the roof structure is therefore at a higher or lower level relative to the ground depending on the amount of crude oil that is in the tank.
• the periphery of the floating roof has sealing members making it possible to prevent the oil from passing around the periphery of the roof. It has been found that in these storage tanks, a sediment is progressively deposited on the bottom of the tank, consisting largely of the heaviest fractions of the stored crude oil, in particular paraffinic compounds, and inorganic elements such as l water, sand, rust particles or the like.
• This sediment is likely to constitute on the tank bottoms very thick layers of 1 or 2 meters or more and it is necessary to clean the tanks by removing this sediment. Indeed, if the sediment accumulates on the bottom of the tank and the floating roof descends towards the bottom as the tank is emptied, the risk is to have contact between the floating roof and a point on the deposit of sediment, which unbalances the roof and blocks it in an oblique position in the side wall of the tank; however, the weight of a floating roof being several hundred tonnes, it is understandable that the repair of such an incident involves considerable costs.
• the invention is based on the fact that the sediment can be resuspended in the crude oil which overcomes it, provided that turbulence and / or vortices are generated in the entire volume of liquid oil which overcomes the sediment and to send jets of petroleum powerful enough on the sediment so that this one, gradually, is resuspended and maintained in this state by the turbulence imposed in the liquid crude oil.
• the layer of sediment gradually disappears and is found inside the liquid crude oil, which revalorizes the sediment since there is no longer any sedimentary material to be evacuated from the tank to be destroyed.
• the reinjection into the tank is carried out by rotary lances arranged vertically under the floating roof, these lances being equipped with nozzles which send jets of oil in the direction of the layer of sediment; the rotation of the lances generates vortices having for axis the axis of the lances and one makes so that these vortices interest the whole of the tank.
• the crutches of the floating roof are replaced by the lances which ensure the reinjection of the crude oil, the bottom of the lances arriving in the vicinity of the mean plane of the upper face of the sediment layer.
• the present invention therefore relates to a process for resuspending a sediment which has, by deposition, formed a layer on the bottom of a floating roof tank containing crude oil, said floating roof comprising a plurality crutch holes regularly distributed over its surface, said holes making it possible to secure crutches capable of supporting the roof by pressing on the bottom of the tank when the level of crude oil in the tank is less than the length of the crutches, characterized by the fact that :
• the level of crude oil in the tank is brought to a distance L from the highest level of the sediment on the bottom of the tank, with L between 2 and 5 meters approximately,
• the crude oil is drawn into the tank by at least one pump with an overall hourly flow rate equal to V / n, V being the volume remaining in the tank below the floating roof and n being a number between 8 and 15 approximately, - the pumped crude is reintroduced into the tank by injecting it using lances carried by the floating roof and put in place vertically in the tank above the sediment, each of said lances having, below the floating roof, a length less than L, being driven in rotation about its axis, being closed at its lower end and comprising at least one nozzle disposed above the sediment, nozzle whose jet is oriented towards the bottom of the tank, the outlet section of the nozzle (s) of the same lance being sufficiently small so that, with the flow rate delivered by the ( the) pump (s), the output pressure of the crude jet is sufficient for the vortex volume generated by a lance to intersect the vortex volumes relating to the adjacent lances,
• the implementation of the process is continued until the density of the pumped crude oil is equal to a predetermined value which corresponds to an almost complete resuspension of the sediment.
• n which defines the overall hourly flow aspirated and reintroduced into the tank is a function of the characteristics of the tank to be cleaned by resuspending the sediment, the physicochemical characteristics of the sediment itself and the immobilization time that we accept to proceed with cleaning the tank.
• the lances are rotated at a speed of between 0.25 and 4 revolutions / minute.
• the lances can be rotated about their axis by explosion-proof electric motors, one motor being assigned to each lance.
• the present invention also relates to a device for implementing the method as defined above, this device being characterized in that the lances are arranged in the sleeves of the stand holes of the floating roof of the tank.
• the essential advantage of installing the rotary lances in the crutch holes that is to say in the sleeves which usually hold the crutches integral with the floating roof, allows the installation of the cleaning device according to the invention, without any modification having to be made to the floating roof of the tank to be cleaned: it is enough to remove the crutches one by one and replace them progressively with rotating lances.
• the crutch holes being sufficiently close together, the rotary jets from these lances cause the entire volume of crude oil remaining in the tank to be mixed, thus causing the erosion of the sediment fragments until they are completely resuspended.
• each lance comprises a plurality of nozzles situated at different levels relative to the tank bottom, the jets of the nozzles of the lower level being directed towards the tank bottom while the jets nozzles of the upper level are directed towards the floating roof; advantageously, each lance has three nozzle levels, a nozzle of the median level generating a substantially horizontal jet while the nozzles of the two other levels generate jets whose axis is inclined by 50 to 70 ° relative to the axis of the lance that carries the nozzle. Provision can be made for each nozzle level to have two diametrically opposite nozzles.
• the lower level nozzle (s) is (are) placed at a level between 20 and 50 cm above the average level of the sediment layer.
• the pump (s), which sucks (s) the crude in the tank is (are) volumetric (s); it can be, for example, screw pumps.
• This type of pump provides a given flow rate and the pressure obtained at the outlet of the nozzles is therefore a function of the outlet section of all the nozzles supplied by the pump.
• the volume interested in the turbulence around a lance is obviously all the more important as the jet ejection pressure is higher.
• these volumes which are substantially cylinders having for axis the axis of the lances, overlap with the volumes pertaining to the adjacent lances so that no part of the liquid petroleum contained in the tank remains outside the turbulence assembly created according to the invention.
• the mixing of the sediment also causes the inorganic elements contained in the sediment to be resuspended.
• a filter is therefore provided at the suction of the pumps to remove these inorganic elements, the parts which pass through the filter being, in any case, ground by the screws of the pump.
• the operator of the tank empties the liquid content of the tank by transferring it to another tank containing a similar crude, this emptying being, of course, only carried out after having replaced the crutches of the floating roof at the place of the lances used for the implementation of the method according to the invention. After this mixing with the content of another tank has been carried out, the refining of the crude oil used for cleaning according to the invention can take place.
• the device according to the invention comprises at least two pumps each preceded by at least one filter and each followed by a distributor, each outlet channel of which outputs on an enclosure which supplies p lances, p being the same integer for all the speakers of the device.
• FIG. 1 schematically shows a device for implementing the method according to the invention
• FIG. 2 shows schematically in section a crude oil tank with floating roof in which a lance has been put in place for the reinjection of the crude oil pumped as indicated in Figure 1, the other lances not being shown;
• FIG. 3 shows a plan view of the floating roof of the tank according to Figure 2, this view showing the crutch sleeves provided on said floating roof and, in dotted lines, the circles delimiting the cylindrical volumes of turbulence generated by each of lances inserted in said crutch sleeves.
• a crude oil storage tank has been designated by 1 as a whole; the tank 1 consists of a cylindrical side wall la, the base lb of which constitutes the bottom of the tank.
• the tank is equipped with a floating roof 2, the periphery of which comprises sealing members, not shown.
• the tank 1 is intended for the storage of crude oil, the roof 2 floating on the crude.
• a tank can have a diameter of about 50 m and a height of 15 m.
• the crude gradually settles and gives rise to a sediment 3 which constitutes a layer on the bottom of the tank 1b, a layer which can reach several meters in thickness; the diaper surface is relatively uneven.
• the sediment is generally of a thyxotropic nature.
• the tank is partially emptied; if we assume a layer of sediment with an average thickness of 1 m, we leave in the tank above the sediment about 3 m of crude oil, that is to say that the roof 2 is located about 4 m above the bottom of the tank.
• the floating roof 2 is equipped with 72 crutches which pass through the roof by crutch sleeves designated by 4 in FIG. 3. These crutches have a length of between 1.8 and 2.2 m and come in support on the tank bottom when the floating roof descends sufficiently low.
• each lance 5 is a tube which is pivotally placed in a crutch sleeve.
• the lance 5 is driven in rotation about its axis by an explosion-proof electric motor 6 located at the head of the lance, above the floating roof 2.
• the crude oil is supplied to the lance 5 by a pipe 7.
• the lance 5 has on three levels of nozzles making it possible to evacuate the crude oil brought into the tube which constitutes the lance by the pipe 7. These nozzles orient the outlet jets. Each level has two diametrically opposite nozzles on the lance.
• the two nozzles of the lower level provide jets 8a whose axes are 60 ° with the axis of the lance 5, these jets being oriented towards the bottom of the tank; the two upper level nozzles provide 8c jets. whose axes make with the axis of the lance 5 an angle of 60 °, these jets being oriented towards the floating roof 2; the two nozzles of the median level form jets 8b whose axes are substantially horizontal.
• the nozzles on the lower level are approximately 30 cm above above the mean plane of the sediment layer 3; the median level nozzles are approximately 60 cm above those of the lower level and the upper level nozzles are also approximately 60 cm above those of the median level.
• the base of the lances 5 is closed.
• the motors 6 drive the lances 5 at two revolutions / minute.
• the pumping in the tank 1 is carried out by means of two pumps 8; the pumps 8 are positive displacement pumps and which each flow 400 m 3 / h.
• the pumps 8 are arranged in parallel and, upstream of each pump, there is a filter 9.
• the two filters 9 are connected to the outlet of a 2000 liter tank 10, the inlet of which is connected by a pipe 11 to the lower part of the side wall 1a of the tank 1.
• the filters 9 are intended to remove the inorganic elements which are present in the pumped oil.
• Each of the two pumps 8 delivers on a distributor 12.
• Each distributor 12 has three outlets, each of which delivers on a 200-liter enclosure 13; each enclosure 13 has six outputs fitted with a valve

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• 1997
  • 1997-12-15 LU LU90183A patent/LU90183B1/fr active
  • 1997-12-18 AU AU55645/98A patent/AU5564598A/en not_active Abandoned
  • 1997-12-18 EP EP97952101A patent/EP1091812B1/de not_active Expired - Lifetime
  • 1997-12-18 BR BR9714913-6A patent/BR9714913A/pt not_active IP Right Cessation
  • 1997-12-18 WO PCT/FR1997/002347 patent/WO1999032238A1/fr active IP Right Grant
  • 1997-12-18 UA UA2000074275A patent/UA68367C2/uk unknown
  • 1997-12-18 PT PT97952101T patent/PT1091812E/pt unknown
  • 1997-12-18 DE DE69738052T patent/DE69738052T2/de not_active Expired - Fee Related
  • 1997-12-18 ES ES97952101T patent/ES2293666T3/es not_active Expired - Lifetime
  • 1997-12-18 DK DK97952101T patent/DK1091812T3/da active
  • 1997-12-18 EA EA200000668A patent/EA003659B1/ru not_active IP Right Cessation
  • 1997-12-18 AT AT97952101T patent/ATE370801T1/de not_active IP Right Cessation
• 1998
  • 1998-07-20 PT PT98113513T patent/PT975148E/pt unknown
• 2000
  • 2000-06-19 NO NO20003169A patent/NO322452B1/no not_active IP Right Cessation
• 2001
  • 2001-08-27 HK HK01106015A patent/HK1035509A1/xx not_active IP Right Cessation

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