Method for selective extraction of highly viscous or solidified oils from storage tanks

Abstract

A method for the selective extraction of highly viscous or solidified oils from storage tanks is provided. The method comprises: heating, by means of a first perimetral device, a section of a metal wall of the tank located between a selective oil extraction line and a contact point between the tank's metal wall and a line of coils, such that a continuous flow of hot oil is established from the line of coils toward a pump connected to the selective extraction line; and sending, via the pump, the hot oil to receiving points for usable oil or degraded oil. The perimetral device comprises electrical heating equipment or gas injection equipment that heats the section of the metal wall. The line of coils comprises a built-in tank heating system and / or coils or electrical resistors inserted into the tank.

Description

[0001] SELECTIVE EXTRACTION PROCEDURE FOR HIGHLY VISCOSITY OR SOLIDIFIED OILS FROM STORAGE TANKS

[0002] Field of technology

[0003] The present invention relates to a selective extraction process for highly viscous or solidified oils from storage tanks, which can be applied to both vegetable oils and crude oil and petroleum products that are highly viscous or solidified at room temperature, including crude palm oil, used cooking oil (UCO), heavy fuel oil, and highly viscous or solidified hydrocarbons at room temperature that precipitate and accumulate at the bottom of crude oil tanks.

[0004] Background of the invention

[0005] In recent years, there has been a significant increase in the demand for vegetable oils for biofuel production, which has been accompanied by a corresponding increase in the number of vegetable oil storage tanks. Meanwhile, storage tanks for petroleum and petroleum products are widespread in refineries, petrochemical plants, thermal power plants, metallurgical plants, port terminals, and other facilities.

[0006] Storage tanks must be cleaned regularly for inspection, repair, cargo change, etc., but there are vegetable oils that degrade more quickly at the bottom of the tanks and require more frequent emptying of the tanks.

[0007] Patent ES2391183B1, by the same inventor as the present invention, discloses a procedure for selective extraction of high viscosity hydrocarbons by means of the following operations: application of risk prevention measures (measurement of explosivity inside the tank), heating of the tank contents by means of flexible coils slightly submerged in the hydrocarbons, and heating of the surface layer of hydrocarbons by injecting hot air into the tank.

[0008] Patent ES2544575B1, by the same inventor as the present invention, discloses a method for the selective extraction of viscous hydrocarbons remaining in storage tanks. The operations involved are as follows: measuring the explosivity inside the tank, heating the hydrocarbons using devices located inside the tank, and heating the surface layer of hydrocarbons by injecting hot air.

[0009] Patent application WO2017118766A1, from the same inventor as the present invention, discloses a method for extracting viscous hydrocarbons from tanks by injecting a stream of hot air and steam into the tank. A centrifugal fan or blower is used for the injection, passing the stream through an electric heater with baffles that creates turbulent flow. This heats the air, absorbs moisture, and superheats the steam to facilitate hydrocarbon extraction.

[0010] Application WO2019197690, also from the same inventor as the present invention, describes a procedure for extracting viscous hydrocarbons from storage tanks and process equipment, which proposes injecting an inert gas into the tank or equipment until an oxygen concentration is achieved that ensures a zero flammability range, and then injecting into the tank or equipment a stream of gases homogenized by an irreversible turbulent diffusion process, the stream being made up of gases in recirculation from the tank or equipment itself and by the quantities of water vapor and inert gas that are required to maintain the oxygen concentration at values ​​that ensure a zero flammability range and to make the hydrocarbons flow in an amount equivalent to that demanded by an extraction pump suitable for use in explosive atmospheres.

[0011] Patent ES2796092B2, by the same inventor as the present invention, describes a system and method for the selective extraction of viscous hydrocarbons from tanks and other containers. The operations that characterize it are as follows: using a steam ejector that injects a homogenized gas stream into the tank or container to heat the surface layer of hydrocarbons and facilitate their extraction; and using a perimeter conduit for localized heating of the hydrocarbons, which facilitates their extraction and causes the precipitation of any unemulsified water that may be present in the hydrocarbons and the water supplied by the steam ejector.

[0012] Accordingly, documents ES2796092B2 and ES2544575B1 describe, respectively, the use of a perimeter heating duct and heating devices installed inside the tank (specifically, flexible coils). However, the combination of both systems—that is, a perimeter duct together with a line of heating coils—is presented for the first time in the present invention.Furthermore, the present invention introduces the additional feature that the perimeter conduit heats at least a section of a metal wall of the tank located between a selective oil extraction line and the point of contact between said wall and the coil line inserted into the tank. This achieves a reduction in the viscosity of the oil in contact with the heated metal wall section and establishes a continuous flow of heated oil from the coil line to a first pump connected to the selective oil extraction line. Moreover, in the processes described in ES2391183B1 and ES2544575B1, hot air is injected to heat the surface layer of the hydrocarbons, thus avoiding the polluting effect of water vapor.Although both documents refer to the term "selective", they have the limitation of having a lower capacity to heat the surface layer of hydrocarbons compared to procedures that inject water vapor into the tank.

[0013] In the procedures described in WO2017118766A1 and WO2019197690, the surface layer of the hydrocarbons is heated with steam, which is very effective due to the high heat transmission capacity of steam, but the extraction is not selective because the hydrocarbons are contaminated with condensates from the steam injected into the tank or vessel.

[0014] Regarding the procedure proposed in ES2796092B2, although water vapor is also injected into the tank using a steam ejector, it does refer to the term "selective" because selective extraction is achieved by using a perimeter heating duct that causes the precipitation of the water supplied by the steam ejector. Therefore, this latter procedure is the most effective and complete of all the inventor's previous selective extraction procedures and the one most similar to the present invention due to the aforementioned use of a perimeter heating duct.

[0015] However, a major drawback of this latter procedure, and also of the previous ones, arises when applied to tanks of highly viscous or solidified oil. This is due to the difficulty of lowering the oil level below at least one manhole, which prevents its necessary opening for the installation of the steam ejector. In fact, the patent in question refers to viscous hydrocarbons, not to highly viscous or solidified hydrocarbons at ambient temperature. This drawback is resolved by the present invention.Regarding differences in the use of the perimeter conduit, this latter procedure includes the use of a perimeter conduit for localized heating of the hydrocarbons to facilitate their extraction and cause the precipitation of any unemulsified water that may be present in the hydrocarbons and the water supplied by the steam ejector. However, its use for removing the barrier of highly viscous or solidified oil existing between the coil line and the selective extraction line to which the pump is connected is not indicated anywhere. Furthermore, there is no reference to coil lines belonging to the tank or introduced through an inspection hatch in the tank roof, since the use of coils is usually exclusive to tanks that store highly viscous or solidified hydrocarbons at ambient temperature.

[0016] Other differences between all the previous procedures described and the present invention are the use of a flow and viscosity meter to control selective extraction and detect density variations that determine the shipment of the extracted oil to the different receiving points, and the use of an external heat exchanger to return a portion of the extracted oil to the tank very hot and avoid the formation of solidified oil slopes.

[0017] Therefore, new, more efficient selective extraction procedures are needed for highly viscous or solidified oils from storage tanks. These procedures should also allow for the selective extraction of oil located at any height within the tanks and the selective removal of a large portion of the degraded oil from the bottom of the tanks without the need to empty and decommission them. This would allow for adaptation to diverse applications, such as selectively extracting highly viscous or solidified hydrocarbons at ambient temperature that precipitate and accumulate at the bottom of crude oil tanks, or homogenizing the UCO oil from the bottom of the tanks, which has the highest percentage of animal fats, with the rest of the oil load in the tanks.

[0018] Exposition of the invention

[0019] To this end, the present invention provides a method for the selective extraction of highly viscous or solidified oils from storage tanks. The extraction is described as "selective" because the oil is extracted using operations that prevent its mixing with degraded oil and contaminants at the bottom of the tank. Furthermore, in some embodiments, a flow and density meter is used to detect variations in oil density, determining whether the oil is sent to receiving points for usable oil, degraded oil, or highly contaminated oil. The selective nature of the extraction is further enhanced by the fact that the present invention includes an embodiment of the method that allows for the selective extraction of oil located at any height within the tank, with particular application to the selective extraction of a large portion of the degraded oil from the bottom of the tanks without the need to drain and decommission them.

[0020] The viscosity of a liquid is a measure of its resistance to flow, so a pump prioritizes extracting the least viscous oil from the tank, provided there is no barrier of highly viscous or solidified oil in the way. This barrier of highly viscous or solidified oil at ambient temperature is eliminated by installing a perimeter heating device on a section of the tank's metal wall. This drastically reduces the viscosity of the oil between the selective extraction line and the heating coils.

[0021] The proposed process, according to a first embodiment, comprises heating, by means of at least one first perimeter device, at least one section of the metal wall of the tank between a selective oil extraction line and a point of contact between the metal wall of the tank and a coil line (heating which drastically reduces the viscosity of the oil and eliminates the barrier of highly viscous or solidified oil existing between said point of contact and the selective extraction line), so as to establish a permanent flow of hot oil from the coil line to at least one first pump, connected to the selective oil extraction line, which sends the hot oil to a receiving point for usable oil or to a receiving point for degraded oil.

[0022] The condition described above—consisting of heating, by means of a perimeter duct, a section of the metal wall of the tank located between the selective oil extraction line and the point of contact between said wall and the coil line—is equivalent to compliance with the following three conditions:

[0023] 1. That the installed perimeter duct comes into thermal contact and heats at least one point of the selective oil extraction line;

[0024] 2. That the coil line comes into contact with and heats at least one point on the metal wall of the tank. This operation is particularly complex, since it generally must be carried out from the inspection hatch located on the roof of the tank, which can reach more than 20 meters in height and 60 meters in diameter. Usually, it is necessary to make a hole in the outer perimeter area of ​​the tank roof to insert a guide rope, which ensures that the coil line, inserted through the inspection hatch in the roof, remains in constant contact with the inner wall of the tank during its descent and final positioning;

[0025] 3. That the perimeter heating duct comes into external contact and heats the point of contact or intersection between the coil line and the internal metal wall of the tank.

[0026] Only when these three conditions are met together is it possible to heat and reduce the viscosity of the oil between the selective extraction line and the coil line, thus eliminating the blockages of highly viscous or solidified oil that prevent the flow of hot oil between these lines and establishing a permanent flow of the oil heated by the coil line into the selective extraction line connected to the pump.

[0027] If one or more of these conditions are not met, the resulting blockages of highly viscous or solidified oil will prevent the heated oil from flowing through the coil line to the selective extraction line. Instead, a slow flow of heat and hot oil will rise to the surface layer of the oil stored in the tank, preventing its extraction until virtually the entire volume of oil in the tank has been heated and its viscosity reduced.

[0028] This scenario, at best, results in a slowdown in oil extraction from the tank and higher energy costs. In large tanks (with storage capacities of tens of thousands of tons), complete heating of the contents is not feasible using only the limited thermal capacity of the perimeter duct and the coil line. Furthermore, over time, the oil tends to solidify inside the tank because the heat transfer capacity of the tank's coil line is negated by the accumulation of grease and other burnt and solidified contaminants, which act as a thermal barrier, virtually insulating the entire heat transfer surface of the coils.According to the present invention, the perimeter heating device may consist of one or more of the following elements: electric heating equipment, such as industrial heating blankets assembled using Velcro joints to seamlessly cover the section of the metal wall to be heated. In this case, straps or cables tensioned to structural elements of the tank or to anchoring elements provided for this purpose may be used as a fastening system to the tank; a perimeter duct covering the section of metal wall to be heated, into which hot gases (water vapor, hot air, or a mixture of air and water vapor) are injected, supplied, for example, by a steam ejector connected to a steam boiler, the steam ejector drawing in air from the atmosphere or air previously heated by an electric gas heating element using the Venturi effect.In some embodiments, the perimeter duct may consist of a synthetic fabric cover supported by semicircular arches distributed along the entire length of the duct, so that the perimeter duct takes on a semicylindrical shape with its flat section coinciding with the metal wall section of the tank to which it is attached and is fixed by means of two cables tensioned to structural elements of the tank or anchor points enabled for this purpose; a perimeter line of water vapor injectors covered with a perimeter band that retains the water vapor that heats the metal wall section.In particular, the perimeter line is attached to the metal wall section to be heated and the perimeter band comprises a synthetic fabric band covering the injector line (or a synthetic fabric cover as described above), so that it retains the water vapor that transmits heat to said metal wall section.

[0029] Likewise, the coil line may consist of the tank's own heating system, coils or electric resistors that are introduced into the tank, for example, through an inspection port in the tank roof or through another point that the tank's filling level allows, or a combination of both.

[0030] In particular, in the present invention, the heating temperature is limited by the flash point of the oil.

[0031] In some embodiments, the proposed procedure can be adapted to selectively extract oil located at any height in the tank by introducing through the inspection port in the tank roof the line of coils or electric resistances that is suspended at the height at which the oil is to be extracted and in such a way that it maintains at least one point of contact with the metal wall of the tank, then installing the aforementioned perimeter heating device that reduces the viscosity of the oil and eliminates the barrier of very viscous or solidified oil existing between said point of contact and the selective oil extraction line, and connecting to said selective extraction line the first pump to selectively extract the oil located at the height that heats the line of coils or electric resistances.

[0032] In some implementation examples, the proposed procedure can also be applied to extract a large part of the degraded oil from the tanks, without the need to empty and take them out of service, which provides great operational and economic advantages over alternative procedures.

[0033] The procedure for extracting degraded oil from the bottom of the tanks may include the following operations: heating the degraded oil by means of at least one line of coils or electric resistances, inserted through the inspection mouth of the tank roof and positioned at the bottom of the tank, so that it only heats the degraded oil and makes contact with at least one point of the metal wall of the tank.In tanks with a coil line located very close to the bottom, this line can be used as a complement to or replacement for the line introduced through the inspection port in the tank roof. A perimeter heating device is installed to heat the section of the tank's metal wall between this contact point and the selective extraction line. This drastically reduces the viscosity of the oil closest to this metal section and eliminates the barrier of highly viscous or solidified oil at ambient temperature. The degraded oil is then selectively extracted by heating the coil line or electric resistance heaters using a pump connected to the selective extraction line, which sends the heated oil to the receiving point for the degraded oil. Once selective extraction has begun, the perimeter heating device can be disconnected.

[0034] In some implementations, the proposed procedure also includes the installation of a flow and density meter, inserted in the discharge line of at least one pump connected to the selective extraction line. This meter monitors the flow rate extracted by the pump and detects variations in oil density, determining whether the oil is sent to the receiving point for usable oil or to the receiving point for degraded oil. In some cases, the meter may include a visual and / or audible alarm that is activated upon detection of values ​​outside the programmed range.

[0035] In some embodiments, the procedure also comprises performing additional heating with at least one external heat exchanger, interposed in the drive lines of the pump(s) assigned for selective extraction, so that any of the pumps, separately or using a manifold, can return very hot oil to the tank.

[0036] In some embodiments, the external heat exchanger can be supplemented by or replaced with a suction heater from the tank itself. In any case, the heating temperature is limited by the flash point of the oil.

[0037] Recirculation of degraded oil should be avoided to prevent agitation and mixing of degraded oil with usable oil. This significantly reduces the viscosity of the oil's surface layer and prevents the formation of solidified oil slabs that cause cavitation in the pumps. The formation of a slab near the suction heater often prevents the complete oil extraction using the tank's own pumping system, thus also preventing the necessary opening of the tank's manholes.

[0038] The invention includes another embodiment that enables the opening of at least one manhole in tanks containing solidified oil. In this case, the perimeter device makes tangential contact with the manhole. Therefore, when the hot oil is extracted by the pump, solidified oil is also extracted from the vicinity of the manhole, maintaining selective extraction until the flow and density readings on the flow meter are practically zero due to the formation of a solidified oil slope at the manhole, allowing it to be opened.

[0039] In some embodiments, the process also includes the following operations: heating by means of at least one hot gas injection unit installed in at least one manhole of the tank where the oil level in the tank allows it to be opened, such that said heating maintains a low viscosity in the surface layer of oil to prevent the formation of solidified oil slopes that cause cavitation of the pumps. The gas injection unit may consist of an electric resistance heater with an associated centrifugal fan, a steam ejector connected to a steam boiler, or a combination of both. Preferably, the steam ejector is installed in a manhole of the tank so that it draws gases from the tank by Venturi effect, homogenizes them by turbulent diffusion with the steam supplied by the steam boiler, and injects the resulting homogenized gas mixture into the tank.The boiler pressure is limited by a regulating valve between 2 and 30 bar. However, while this is effective, only hot air injection into the tank will be carried out using the electric heating element and centrifugal fan to minimize condensation of water vapor in the tank, especially during the oil transfer phase to the receiving point for usable oil. Water will be extracted from the tank during gas injection with the steam ejector, periodically, or based on density readings similar to that of water on the flow and density meter. For these extractions, a pump will send the water to a designated water receiving point.and said pump being connected to a tank purge line or to a suction device immersed in water and introduced through a manhole of the tank; heating the oil with at least one peripheral device attached externally to a section of the metal wall of the tank located below the manhole, thereby reducing the viscosity of the oil and causing the unemulsified water and a significant portion of the solids immersed in the oil to precipitate; selective extraction of the usable oil by means of at least one pump that sends the oil heated by the hot gases injected into the tank and said peripheral device to the designated receiving point for usable oil, the pump having a suction line connected to a manhole of the tank and having a suction device attached at one end that is immersed in the usable oil,with its suction nozzle facing upwards to cause a downward flow of oil that prevents the suction of degraded oil and contaminants from the bottom, and maintaining the delivery of oil to said receiving point until the flow and density meter detects density values ​​characteristic of degraded oil in different positions of the suction device, including a position where the suction device is minimally introduced into the oil, since the detection of densities greater than that of usable oil in this last position would confirm that all the oil below is degraded, and selective extraction of the degraded oil by means of at least one pump whose suction line is connected to the manhole of the tank and has attached at one end the suction device that is submerged in the degraded oil heated by the perimeter device, the hot gases injected into the tank,and the coil or electrical resistance lines, so that said pump sends the extracted oil to the degraded oil receiving point until the flow and density meter readings indicate very low oil extraction rates.

[0040] Once the selective extraction of usable oil and degraded oil is completed, the highly contaminated oil, generally with water, sludge and oily sediments, remains segregated at the bottom of the tank. This oil is extracted from the tank by means of a procedure that also includes the following operations: heating with steam injector lines immersed in the highly contaminated oil to facilitate extraction;Extraction and transfer of oil and water to external containers, using a pump connected to the tank's purge line or to suction devices located at the lowest points at the bottom of the tank, and separation in the containers of the water and oil extracted from the tank by difference in densities, sending the highly contaminated oil to its reception point and subjecting the precipitated water to additional heating to return it very hot to the tank and cause the oil to flow towards the purge line or the installed suction devices, until the oil is completely sent to the reception point for highly contaminated oil.

[0041] In another example of embodiment of the invention, the procedure further includes the installation of an intermediate tank as a prior receiving point for usable oil and the installation of two pumps, one pump intended to send the decanted usable oil in the tank to the receiving point for usable oil or return it to the tank and a second pump intended to send the degraded oil that precipitates in the tank to its corresponding receiving point.

[0042] The procedure of the invention is also applicable to thermally insulated tanks, where a temporary or permanent modification of the tank's thermal insulation is made to install perimeter heating devices or lines of hot gas injectors distributed along the section of the metal wall to be heated. The metal structure of the thermal insulation itself may be used as a perimeter heating conduit, after prior removal of the thermal insulation material covering the section of the metal wall to be heated. Hot air will preferably be used for the injection of hot gases if the thermal insulation materials may be altered or are susceptible to corrosion when moistened by water vapor. In all cases, sufficient openings for the hot gases to escape must be left to prevent stresses that could deform the metal structure of the tank's thermal insulation.

[0043] In another embodiment of the invention, the procedure further includes: installing a heat exchanger interposed in suction or discharge lines of the pumps to subject the oil that said pumps send to the usable oil receiving point and the degraded oil receiving point to additional heating; installing at least one filter interposed in suction lines of the pumps having a mesh size smaller than the solids passage tolerances of the flow and density meter, the pumps and the heat exchangers, and the installation of at least one solids retention filter interposed in suction or discharge lines of the pumps.However, the best filters are those attributable to the application of the procedure itself because agitation and heating operations of the bottom of the tank are avoided, and because at the end of the selective extraction more solids remain segregated at the bottom of the tank than existed at the beginning, as a result of the precipitation of solids that occurs in the perimeter heating devices.

[0044] In another example of embodiment of the invention, the procedure includes the treatment of oil degraded by emulsified water, where a dosing pump is used to inject demulsifiers into a pump drive line and a tank with a heating system is used as the receiving point of the oil with emulsified water, where the precipitation of the demulsified water occurs.

[0045] In some embodiments, the procedure also includes the use of a centrifuge as a receiving point for the degraded oil, where the oil, water, and contaminating solids are separated. A dosing pump can be used to inject demulsifiers into the pump's discharge line to improve the centrifuge's effectiveness. Finally, a major operational and economic advantage of the present invention, compared to all prior procedures, is that it allows for the selective extraction of a large portion of the degraded oil from the bottom of the tanks without the need to empty and take them out of service. This avoids the risk of contamination from mixing the oil in the tank with the degraded oil from the bottom during tank emptying and associated transfers, contamination that could prevent the oil's sale and its use as fuel or raw material in production processes.The invention can also be adapted to other applications, such as selectively extracting highly viscous or solidified hydrocarbons at room temperature that precipitate and accumulate at the bottom of crude oil tanks, selectively extracting UCO oil with a higher percentage of animal fats that accumulates at the bottom of the tanks, and mixing the UCO oil from the bottom of the tanks with the rest of the oil load in the tanks to homogenize the percentage of animal fats.

[0046] Brief description of the drawings

[0047] Figure 1 schematically illustrates a storage tank for application of the proposed procedure.

[0048] Detailed explanation of the invention and some examples of its implementation

[0049] Figure 1 shows a storage tank (1), particularly with a fixed roof and metal wall, in whose suction heater (2) a slope (3) of solidified oil has formed, which makes it difficult to completely empty the tank (1).

[0050] As illustrated in the figure, the procedure that is the subject of the invention comprises the installation of one or more perimeter devices (4a, 4b), particularly consisting of industrial heating blankets attached to at least one section of the metal wall of the tank (1), for its heating and, consequently, of the oil existing between a selective oil extraction line (5a) and some contact points (6a, 6b) of the metal wall.

[0051] The contact points (6a, 6b) include coil lines of the tank itself (1) which are connected to a steam boiler (7), so that a flow of hot oil is established from the coils to a first pump (8a), which sends it to a receiving point of usable oil (9a) or returns it to the tank (1), after passing, for example, through a collector (10) and after further heating by means of an external heat exchanger (11), thus avoiding the formation of slopes (3).

[0052] In some embodiments, when the oil level permits, two manholes (12a, 12b) are opened. Through the first manhole (12a), air heated by an electric heating element (13) and propelled by a centrifugal fan (14) is injected. A suction device (15) is also installed in this first manhole (12a), immersed in the oil and slightly above the degraded oil at the bottom, to extract usable oil with a second pump (8b) and send it to the usable oil receiving point (9a). A steam ejector (16a) is installed in the second manhole (12b), which draws gases from the tank (1) by Venturi effect and injects them back into the tank (1) after homogenizing them with steam supplied by the steam boiler (7).

[0053] Near the first manhole (12a), another perimeter device (4c) is installed, consisting of a duct through which hot gases circulate, propelled by a small steam ejector (16b). This causes the precipitation of unemulsified water and solids suspended in the oil. Additionally, a flow and density meter (17) detects variations in oil density, thus determining the appropriate oil delivery points.

[0054] Finally, the procedure may include removing the heavily contaminated oil from the tank (1), which is sent to a heavily contaminated oil receiving point (9c) using the same pumps, suction devices and the purge line (5b).

[0055] The proposed procedure also includes the possibility of introducing the coil line through an inspection opening (12c) in the roof of the tank (1).

[0056] In a preferred embodiment of the present invention, the highly viscous oil contained in the tank is used cooking oil (UCO). According to this embodiment, the proposed procedure comprises: installing a flow and density meter (17) inserted in the pump discharge lines (8a, 8b) to monitor the flow rate of oil extracted by each pump and detect variations in oil density that determine its destination to the receiving points for usable oil (9a), degraded oil (9b), or heavily contaminated oil (9c). Additionally, filters are installed in the pump suction lines to retain solids typically present in the UCO oil. These filters must have a mesh size smaller than the solids passage tolerances of the meter, the pumps, and the heat exchangers. A section of the tank's metal wall (1) is then heated by at least one of the peripheral devices (4a, 4b).so that the first pump (8a) sends the oil that heats the coil line to the usable oil receiving point (9a) until the oil level in the tank (1) is below the contact point (6a, 6b) or the selective oil extraction line (5a). If densities higher than that of the usable oil are initially detected in the gauge (17), the oil will be sent to the degraded oil receiving point (9b). When density values ​​similar to those of the usable oil at the same temperature are detected again in said gauge, the oil will be sent to the usable oil receiving point (9a), since these density values ​​similar to those of the usable oil imply that the degraded oil level is below the coil line. The coil lines or electric resistors can be inserted through the manholes (12a, 12b), once they have been opened.to facilitate oil extraction; heating the oil with another perimeter conduit (4c) attached externally to a section of the metal wall of the tank (1) located below the first manhole (12a), heating which reduces the viscosity of the oil and causes the precipitation of the unemulsified water and a significant part of the solids immersed in the viscous oil; opening the first manhole (12a), once the oil level in the tank (1) allows it, installing equipment consisting of the electric resistance (13) associated with the centrifugal fan (14) to inject hot air into the tank (1) and raise its internal temperature, and installing a suction device (15), immersed in the usable oil and connected to the second pump (8b), which sends the hot oil to the usable oil receiving point (9a),maintaining the flow of oil to said receiving point until readings from the flow and density meter (17) reveal densities characteristic of degraded oil with the suction device (15) minimally inserted into the oil; further heating the oil with at least the external heat exchanger (11), so that any of the pumps (8a, 8b), separately or in combination using the manifold (10), can return very hot oil to the tank (1), recirculation of degraded oil being avoided so that no mixing of degraded oil with usable oil occurs; opening the second manhole (12b), installing the steam ejector (16a) connected to the steam boiler (7),The ejector draws gases from the tank (1) by means of the Venturi effect and injects a homogenized mixture of air and water vapor into the tank (1). The water vapor condensate can be extracted periodically or automatically due to density increases detected by the gauge (17), using a pump that sends the water to a designated receiving point. This pump (8a) is connected to the purge line (5b) or to the suction device (15), which is immersed in the water and is inserted through the first (12a) or second manhole (12b). An added advantage of the selective extraction procedure is that the steam ejector cleans the walls and structural elements along the entire height of the tank, due to the combined effect of tank heating.the turbulent flow of the homogenized mixture of air and water vapor and the washing effect of the condensates; selective extraction of the degraded oil using the second pump (8b) connected to the suction device (15), such that said pump sends the oil to the degraded oil receiving point (9b) until the readings of the meter (17) indicate very low degraded oil extraction rates, then proceeding with the operations necessary for the extraction of the heavily contaminated oil; heating the heavily contaminated oil with at least one of the coil lines or with steam injector lines immersed in the heavily contaminated oil; extracting and sending the oil and water to containers, using the first pump (8a) connected to the purge line (5b), or to suction devices located at the lowest points of the bottom of the tank (1); and separating the water and oil in the containers, by difference in densities,sending the heavily contaminated oil to the heavily contaminated oil receiving point (9c) and subjecting the precipitated water to further heating to return it to the tank (1) and causing the remaining oil in the tank (1) to flow towards the purge line (5b) or the installed suction devices, until the sending of the heavily contaminated oil to the receiving point (9c) is complete.

[0057] The scope of the present invention is defined in the appended claims.

Claims

1. CLAIMS 1. A method for selectively extracting highly viscous or solidified oils from storage tanks, comprising: heating, by means of at least a first peripheral device (4a), at least a section of a metal wall of the tank (1) comprised between a selective oil extraction line (5a) and a contact point (6a) between the metal wall of the tank and a coil line, so as to establish a permanent flow of hot oil from the coil line to at least a first pump (8a), connected to the selective oil extraction line (5a); and sending, by means of the first pump (8a), the hot oil to a receiving point for usable oil (9a) or to a receiving point for degraded oil (9b);where: the first perimeter device (4a) comprises electric heating equipment covering the metal wall section, and / or a perimeter duct covering the metal wall section through which hot gases are injected, and / or a perimeter line of water vapor injectors covered with a perimeter band that retains the water vapor that heats the metal wall section, and the coil line comprises a tank heating system (1) and / or electric coils or resistors inserted into the tank (1).; 2. The method according to claim 1, further comprising: installing a flow and density meter (17) interposed in a discharge line of the first pump (8a), which is at least one; and detecting, by means of the flow and density meter (17), variations in the density of the oil that determine its dispatch to the receiving point of usable oil (9a) or of degraded oil (9b).

3. The method according to claim 1 or 2, further comprising: additionally heating the oil by means of at least one external heat exchanger (11) and / or with a suction heater (2) of the tank (1), arranged in the discharge line of the first pump (8a), which is at least one; and returning the heated oil to the tank (1) using the first pump (8a) and / or a second pump (8b) and / or a manifold (10), wherein a heating temperature is limited by the flash point of the oil.

4. The method according to any one of claims 1 to 3, wherein the The first perimeter device (4a) is in contact, tangentially, with a first manhole (12a) of the tank (1).

5. The method according to any one of claims 1 to 4, further comprising: heating the oil by means of at least one hot gas injection unit, installed in the first manhole (12a) or in a second manhole (12b), the hot gas injection unit comprising an electric heating element (13) with a centrifugal fan (14) and / or a steam ejector (16a) connected to a steam boiler (7), and the pressure of the steam boiler (7) being limited to between 2 and 30 bar by means of a regulating valve; periodically extracting water from the tank (1) using at least the first pump (8a) and sending the extracted water to a designated water receiving point, the first pump (8a) being connected to a purge line (5b) of the tank (1) or to a suction device (15) immersed in the water;heating the oil by means of at least a third perimeter device (4c), attached externally to a section of the metal wall of the tank (1), located below the first manhole (12a); selectively extracting the usable oil by means of at least the second pump (8b), which sends it to the usable oil receiving point (9a), the second pump (8b) having a suction line coupled at one end to the suction device (15), and maintaining the delivery of selectively extracted oil to the usable oil receiving point (9a) until increases in the readings of the flow and density meter (17) indicate densities characteristic of degraded oil, the suction device (15) being minimally introduced into the oil;and selectively extracting the degraded oil by means of at least the second pump (8b), which sends it to the degraded oil receiving point (9b), and maintaining the sending of selectively extracted oil to the degraded oil receiving point 9b) until the readings of the flow and density meter (17) indicate practically zero flows of degraded oil.; 6. The method according to claim 5, further comprising extracting from a tank bottom (1) oil heavily contaminated with water, sludge and oily sediments by performing the following operations: heating the heavily contaminated oil with steam injector lines immersed in the heavily contaminated oil; extract and send the oil and water to containers using the first pump (8a) and / or the second pump (8b); and separate the water and oil in the containers, by difference of densities, sending, through the first pump (8a) and / or the second pump (8b), the highly contaminated oil to a highly contaminated oil receiving point (9c), and subjecting the water to additional heating to return it very hot to the tank (1) and cause the remaining oil in the tank (1) to flow towards the purge line (5b) or towards the installed suction devices, until the oil is sent to the highly contaminated oil receiving point (9c).

7. The method according to any one of claims 1 to 6, further comprising installing an intermediate tank as a pre-receiving point for usable oil, and two pumps, a first pump for sending decanted usable oil from the intermediate tank to the usable oil receiving point (9a) or returning it to the tank (1), and a second pump for sending degraded oil precipitated in the intermediate tank to the degraded oil receiving point (9b).

8. The method according to any one of claims 1 to 7, wherein the tank (1) has thermal insulation, and wherein the method further comprises modifying, temporarily or permanently, the thermal insulation to install the first (4a) and / or third (4c) perimeter heating device or lines of hot gas injectors, the injectors being distributed along the metal wall section.

9. The method according to any one of claims 1 to 8, further comprising using a dosing pump to inject demulsifiers into the drive line, and employing a tank with a heating system as a receiving point for the degraded oil (9b), resulting in precipitation of the demulsified water.

10. The process according to any one of claims 1 to 9, further comprising employing at least one centrifuge as a receiving point for the degraded oil (9b), where separation of the oil, water and contaminating solids takes place.

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