Systems and methods for selective extraction of viscous hydrocarbons from tanks and other containers

Abstract

A system and method for selectively extracting viscous hydrocarbons from tanks and other containers (1), the system comprising the following components for heating hydrocarbons: a steam ejector (3) in which the driving steam of the steam ejector and the gas sucked by it by the Venturi effect undergo vortex diffusion; and a peripheral heating conduit (5) connected to the outside of the tank or container. The method comprises the following operations: heating the surface layer of the hydrocarbons by the gas injected by the steam ejector (3), causing the heated hydrocarbons to flow selectively to the peripheral conduit (5); locally heating the hydrocarbons with the peripheral conduit to precipitate water and cause the hottest hydrocarbons to flow selectively to the extraction pumps (7, 8); and selectively extracting the precipitated water and hydrocarbons flowing out of the peripheral conduit by two pumps (7, 8).

Description

Technical Field

[0001] The present invention relates to systems and methods for selectively extracting viscous hydrocarbons from storage tanks and other vessels that must be periodically emptied and cleaned to perform periodic inspections, repairs, load changes, removals, and the like.

[0002] The system and method of the present invention are applicable to storage tanks and other containers containing viscous hydrocarbons in refineries, petrochemical plants, thermal power plants, port terminals, etc. Floating roof tanks and hydrocarbon process units, including distillation columns, reactors, fan coolers, vessels equipped with gaseous hydrocarbon "demisters", interconnecting piping, etc., constitute representative examples of the application of the present invention.

[0003] Among the viscous hydrocarbons to which the system and method for selective extraction are applicable, it must be pointed out that are hydrocarbons accumulated at the bottom of the oil tank (Class B hydrocarbons, flash point <55°C), fuel oil (Class C hydrocarbons, flash point between 55°C and 100°C) and asphalt (Class D hydrocarbons, flash point >100°C). Background Art

[0004] US 3,874,399 A discloses a method for discharging high viscosity hydrocarbons from a tank by recirculating preheated discharged hydrocarbons in the tank to reduce the viscosity of the contents of the tank and facilitate their discharge.

[0005] ES417373A1 describes a method for removing combustible waste from a container, the method comprising passing a gas stream containing water vapor and an inert gas (e.g. nitrogen) through the container, wherein the gas stream introduced into the container has a water vapor content of 4-50% by volume; and introducing sufficient heat into the container to reach a temperature of at least 50°C.

[0006] US5085242A discloses a method and apparatus for removing residues from a storage tank by locally heating the tank with steam, water or electrical energy and causing hydrocarbons to flow into the heated area.

[0007] GB2101475A describes a method for cleaning a tank by heating the sludge by contacting it with hot water (injection and recirculation of hot water) to reach a temperature of 70°C, making it possible to extract the residue due to the reduced viscosity of the sludge.

[0008] ES2391183B1 (P201100464), belonging to the same inventor as the present application, discloses a method for selectively extracting high-viscosity hydrocarbons using the following steps: applying hazard precautions (for floating roof tanks, the explosiveness inside the tank needs to be measured), heating the contents of the tank by a flexible coil slightly immersed in the hydrocarbons, and heating the surface layer of the hydrocarbons by injecting hot air into the tank.

[0009] ES2544575B1 (P201400060), also belonging to the same inventor as the present application, discloses a method for selectively extracting residual viscous hydrocarbons in a storage tank. It comprises the following operations: measuring the explosiveness inside the tank, heating the hydrocarbons by means located inside the tank, and heating the surface layer of the hydrocarbons by injecting hot air. As a further step, after extracting the hydrocarbons and maintaining the injection of hot air, hot water is injected on the residual hydrocarbons to facilitate their subsequent extraction.

[0010] Patent document WO2017118766A1 (P201600007), also belonging to the same inventor as the present application, discloses a method for extracting viscous hydrocarbons in a tank by injecting a gas flow consisting of hot air and water vapor into the tank. A centrifugal fan or a gas circulator is used for injection, which causes the gas flow to pass through an electric heater with a deflector to induce a vortex. By doing so, the air is heated, moisture is absorbed by the air, the water vapor is superheated, and then the extraction of hydrocarbons is carried out. In addition, the hydrocarbons can be further heated by means of a device for local heating near the suction line.

[0011] Patent document WO2019197690 (P201800095) belonging to the same inventor as the present application describes a method for extracting viscous hydrocarbons from storage tanks and process equipment, which method proposes injecting inert gas into parts of the tank or equipment until an oxygen concentration that ensures a zero flammability range is reached; then injecting a gas flow homogenized by an irreversible eddy diffusion process into the tank or parts of the equipment, the gas flow consisting of gas recycled from the tank or parts of the equipment themselves, and requiring a certain amount of water vapor and inert gas to always keep the oxygen concentration at a value that ensures the zero flammability range and to allow the hydrocarbons to flow in an amount equal to that required for an extraction pump suitable for potentially explosive environments.

[0012] Utility model RU 25176U discloses a device for removing viscous oil and sediments or deposits of petroleum products from a tank, the device comprising: means for heating, liquefying, moving and mixing the deposits, including an injection means comprising a hollow rod through which water vapor, gas or liquid circulates, the hollow rod being located above the bottom of the deposits; and an injection head for transporting the water vapor, gas or liquid to the surface of the tank.

[0013] The method of the present invention differs from the above-mentioned prior art method in that it uses a combination of steam ejectors and peripheral heating conduits connected to the outer wall of the tank, which allows heating of the hydrocarbons on the surface and heating in a localized manner the hydrocarbons adjacent to the entire extension of the peripheral conduit, with the aim of precipitating the non-emulsified water by this double heating, so that the non-emulsified water can be extracted separately from the hydrocarbons, and two selective hydrocarbon flows are established, namely, one from the surface to the zone heated by the entire extension of the peripheral conduit, and the second from the said zone heated by the peripheral conduit to the suction device of the pump for selectively extracting the hydrocarbons.

[0014] Two components characterizing the process of the present invention, namely, steam ejectors and peripheral heating conduits, are not used in any prior art process and provide results that cannot be obtained by any one or combination of prior art processes because prior art processes are unable to produce two selective hydrocarbon streams from the surface and are unable to produce precipitation and separate extraction of non-emulsified water.

[0015] Thus, the method of the present invention achieves a more selective extraction than can be achieved by any prior art method or combination thereof. The extraction of hydrocarbons is called "selective" because it satisfies two conditions: the hydrocarbons are extracted separately from the non-emulsified water, and the hydrocarbons from the surface are prevented from mixing with the hydrocarbons closest to the bottom of the tank or container, which are usually emulsified by water or contaminated by sludge and sediment during the extraction process.

[0016] In the case of prior art methods based on general heating of the hydrocarbons in the tank, such as the method in US Pat. No. 3,874,399 A, the extraction performed is not selective due to the general reduction in the viscosity of the hydrocarbons, and therefore an undesirable flow of contaminated hydrocarbons from the bottom of the tank to the suction duct of the pump occurs.

[0017] Concerning the prior art methods based on local heating of hydrocarbons in a tank, for example in US5085242A, they are much less efficient since the flow of hydrocarbons to the heating zone is very slow or non-existent and, in addition, an undesirable flow of the most contaminated hydrocarbons from the bottom of the tank to the heating zone occurs, so that the extraction is no longer selective.

[0018] In the case of the prior art methods in which heating is established by injecting water vapor, as in ES417373A1, or in which recirculation of hot water is established, as in GB2101475A, the extraction is not selective in any case, since an undesirable flow of the most contaminated hydrocarbons from the bottom of the tank to the extraction zone occurs, and the condensate with the injected water vapor or the hydrocarbons with the recirculated hot water are contaminated by water.

[0019] When the method is applied to fuel tanks, preventing water contamination and the flow of undesired contaminated hydrocarbons from the tank bottom is very important to be able to sell the extracted fuel in compliance with legal specifications regarding water and sediment content, since a small flow of contaminated fuel from the tank bottom to the suction duct of the pump is usually sufficient to make the fuel non-compliant with said legal specifications and all extracted fuel has to be disposed of as waste.

[0020] Regarding the other four prior art methods mentioned above (ES2391183B1, ES2544575B1, WO2017118766A1 and WO2019197690), all four methods correspond to the same inventors as the present application. In the latter two (WO2017118766A1 and WO2019197690), the surface layer of hydrocarbons is heated with water vapor, which is very effective due to the high heat transfer capacity of water vapor, but the extraction is not selective because the hydrocarbons are contaminated by the condensate of water vapor injected into the tank or container. For this reason, neither the title nor the description describing the methods of WO2017118766A1 and WO2019197690 mentions that the extraction of hydrocarbons is selective. In contrast, the term "selective" does appear in the title and description of the present invention, as does the first and second prior art methods (ES2391183B1 and ES2544575B1), the latter two methods establishing the injection of hot air for heating the hydrocarbon surface so that no contamination with water vapor occurs, but they do have the disadvantages of a much lower capacity for heating the hydrocarbon surface and much higher costs invested in the equipment and implementation of the method.

[0021] The equipment used for the system of the invention is very simple relative to the costs mentioned and requires only a supply of water vapor for operation. This advantage becomes even more evident when it is taken into account that water vapor is generally freely available in viscous hydrocarbon storage facilities. In contrast, the four prior art methods mentioned above and belonging to the same inventor require the use of a large amount of electrical equipment: ATEX electric heaters, centrifugal fans, gas circulators, high-power generator sets, variable frequency drives, electrical cabinets, etc. In contrast, the steam ejector and the peripheral duct are very low-cost equipment that does not require maintenance because they have no mechanical or electrical parts; moreover, the steam ejector alone performs multiple functions: it draws gas from a certain position of the tank or container by means of the Venturi effect, it subjects the drawn gas to a vortex diffusion process using its driving steam, and it injects the resulting homogeneous mixture of heated gas into another position of the same tank or container.

[0022] The method of the invention, in addition to performing selective extraction with a much higher heating capacity and at a much lower cost, allows a more efficient selective extraction than the only two prior art methods capable of achieving this (ES2391183B1 and ES2544575B1). The double heating (heating of the surface layer with the driving steam of the ejector and local heating of the hydrocarbons adjacent to the entire extension of the peripheral conduit) significantly reduces the viscosity of the hydrocarbons, which prevents the undesired flow of the most polluted hydrocarbons and the hydrocarbons closest to the bottom of the tank, which remain viscous and almost stationary due to the lack of heating, to the pump. In contrast, by using either of the two prior art methods mentioned above, the hydrocarbons flow more viscous to the suction means of the pump, and an undesired flow of hydrocarbons from the bottom of the tank to the suction means of the pump does occur to a certain extent, especially when the level of hydrocarbons in the tank drops, and at certain times of the year (winter in the northern hemisphere), when the hydrocarbons closest to the bottom of the tank have a higher temperature than the hydrocarbons on the surface.

[0023] Furthermore, it should be mentioned that the method of extracting viscous hydrocarbons from tanks most commonly used by refineries is based on dilution with crude oil or with low-viscosity hydrocarbons supplied by the refineries themselves. The method of the present invention has significant advantages over said method, since it allows the hydrocarbons to be extracted without mixing with pollutants from the bottom of the tank, allows avoiding the dangerous leaks inherent in said method in tanks with unsealed bottoms, and allows the separation of the hydrocarbon layer that contaminates the walls of the tank and the inner surface of the floating roof, as an additional cleaning effect. Moreover, the application of the method of the present invention requires the use of simpler equipment, which significantly reduces equipment investment costs and implementation costs. With regard to other containers, the most common methods are cleaning with pressurized water and chemical cleaning, in which respect the present method has the advantage of being more effective and generating less waste. Summary of the invention

[0024] The present invention relates to systems and methods for selectively extracting viscous hydrocarbons from storage tanks and other containers. The extraction of hydrocarbons is called "selective" because it satisfies two conditions: the hydrocarbons are extracted separately from the non-emulsified water, and the hydrocarbons from the surface are prevented from mixing with the hydrocarbons closest to the bottom of the tank or container, which are usually emulsified by water or contaminated by sludge and sediment during the extraction process.

[0025] According to a first embodiment, the system for selectively extracting viscous hydrocarbons from a tank or container is characterized in that it comprises a combination of the following components:

[0026] a steam boiler having control means configured to regulate the amount and temperature of the water vapour it supplies, the temperature being between 120° C. and 200° C. (between approximately 2 bar and 15 bar);

[0027] at least one steam ejector for heating the surface layer of hydrocarbons to be extracted, the driving steam nozzle of the steam ejector being connected to said steam boiler so that in the diffuser of the steam ejector there occurs a vortex diffusion of driving steam supplied by the boiler with gas sucked in by the ejector through its suction port by means of the Venturi effect, said gas coming from the tank or container itself, from the atmosphere, from the steam boiler (water vapor for increasing the temperature of the gases discharged by the ejector) or from a combination of said sources, with the result that at the ejector outlet a homogeneous mixture of heated gases is obtained, which the steam ejector itself injects into the tank or container through the gas discharge duct for heating the surface layer of hydrocarbons; and

[0028] - at least one pump for selectively extracting hydrocarbons from the surface layer heated by the homogeneous mixture of heated gases injected by the steam ejectors, the suction conduit of the pump being connected to a tank or container in a peripheral zone towards which hydrocarbons from the surface layer heated by the gases injected by the steam ejectors flow.

[0029] In the case where the boiler supplies water vapor to the gas intake conduit of the ejector in order to increase the temperature of the gas injected into the tank or container, said water vapor must be decompressed so as not to impair the normal operation of the ejector and not to cause danger due to overpressure. The danger caused by overpressure can be eliminated by using a pressure reducing valve at the boiler outlet, a conduit of sufficient diameter to expand the water vapor, or by a second steam ejector, the gas discharge of which is connected to the gas intake of the ejector which injects the gas into the tank or container.

[0030] With regard to this system, it should be mentioned that the uniform gas mixture produced by eddy diffusion prevents the water vapor injected into the tank or container from moving freely upward, so most of the injected driving steam condenses on the surface of the hydrocarbons, and a large amount of latent heat (539.4 cal / g at 100°C) is transferred to the hydrocarbons.

[0031] According to another embodiment of the present invention, the system further comprises:

[0032] - at least one peripheral conduit for locally heating the hydrocarbons, the peripheral conduit being externally connected to a portion of the metal wall of the tank or container situated below the level determined by the hydrocarbons to be extracted, a portion of the peripheral conduit consisting of the actual portion of the metal wall of the tank or container to which it is connected, so that the heated gas circulating through said peripheral conduit is in direct contact with said metal wall portion and heats the hydrocarbons adjacent to the tank or container in a locally manner, this heat transfer being a function of the area of ​​the metal wall in contact with the hot gas, the temperature of the gas circulating through the peripheral conduit and the thermal conductivity of the metal wall of the tank or container;

[0033] - at least a second pump for extracting settled water in a tank or container, the suction duct of the first pump and the suction duct of the second pump being connected to the tank or container in a surrounding area close to the area heated by the peripheral duct; and

[0034] - a gas duct connected to the gas suction and gas discharge of the ejector and connected to two different positions of the periphery of the tank or container located above the level determined by the hydrocarbons to be extracted, at least one of the said connection positions of the duct of the steam ejector being close to the peripheral connection zone of the hydrocarbon extraction duct and the sediment water extraction duct.

[0035] In another embodiment, the present invention further comprises:

[0036] - a first suction device connected to one end of the hydrocarbon suction conduit and having its suction opening facing upwards, and a second suction device connected to the sediment water suction conduit and having its suction opening facing the bottom of the tank or container;

[0037] - a peripheral heating duct consisting of a synthetic fabric covering supported by semicircular arches distributed along the entire duct, so that the peripheral duct acquires a semi-cylindrical shape, the flat part of which coincides with a part of the metal wall of the tank or container, the peripheral duct being connected and sealed to the tank or container by two straps, said semicircular arches having at their ends support plates on which are welded rings for guiding and holding the two straps passing through them, so that when the two straps are tightened at their ends at two anchoring points, they press and seal against the cylindrical wall of the tank or container the said support plates of all the arches and the upper and lower edges of the synthetic fabric, said synthetic fabric being located over the entire length of the peripheral duct (for example, a roll of siliconized fabric capable of withstanding temperatures greater than 200° C. and having dimensions of about 50 m long and 1 m wide can be used as synthetic fabric);

[0038] - a steam ejector, the discharge of which is connected to the heating gas inlet from the peripheral duct via a gas duct, the driving steam nozzle of which is connected to the boiler and the gas intake of which sucks in air from the atmosphere by means of the Venturi effect, so that the sucked air is uniformly mixed with the driving steam and is injected by the ejector itself into the heating gas inlet in the peripheral duct;

[0039] - at least one centrifugal fan or gas circulator installed in the gas suction duct of the steam ejector and configured to increase the flow rate of the gas injected into the tank or container;

[0040] at least one steam injector or connection point for injecting reduced pressure water vapor, installed in the gas intake duct of the steam injector, which injects gas into the tank or container, for increasing the temperature of the gas injected into the tank or container; and

[0041] - a nitrogen box connected to the gas intake duct of a steam ejector injecting gas into a tank or container to prevent fire or explosion hazards of hydrocarbons with a flash point below 55° C. (Class B), the nitrogen box having control means configured to regulate the amount of nitrogen supplied to the tank or container.

[0042] The present invention is also applicable to the selective extraction of viscous hydrocarbons and other substances, among which asphalt emulsions, oily emulsions, oily sludge and soot can be mentioned as non-limiting examples, wherein, due to the conditions of gas circulation and heating to which the mentioned hydrocarbons and substances are subjected, they tend to flow to the peripheral area of ​​the tank or container to which a conduit to at least one extraction pump is connected.

[0043] Furthermore, the method of the present invention for selectively extracting viscous hydrocarbons from storage tanks and other containers is characterized by the following operations:

[0044] - heating the surface layer of the hydrocarbons to be extracted by means of a steam ejector connected to a boiler, the water vapor supplied by the boiler having a temperature between 120°C and 200°C, so that the ejector, by means of the Venturi effect, sucks in gas from one position of the tank or container, subjecting the sucked gas to vortex diffusion with its driving steam and injecting the resulting homogeneous mixture of heated gas into another position of the same tank or container, the gas suction position and the discharge position of the ejector being above the level determined by the hydrocarbons to be extracted, and then regulating the amount of steam supplied to the ejector so that, during extraction, a selective flow of heated hydrocarbons from the surface layer to the local heating zone of the hydrocarbons is established, the amount of which is equal to the amount sucked in by the pump for selective extraction of the hydrocarbons;

[0045] - local heating of the hydrocarbons emanating from the surface layer by means of peripheral ducts connected externally to the tank or container through which hot gases circulate, so that precipitation of non-emulsified water occurs during the extraction process and a selective flow of the hydrocarbons heated by the peripheral ducts is established towards a suction device connected by means of ducts to a pump for selective extraction of the hydrocarbons; and

[0046] - A first pump is used to selectively extract hydrocarbons heated by a peripheral conduit, and a second pump is used to periodically extract precipitated water, wherein the conduit for extracting hydrocarbons is connected to a suction device at one end, and the suction port of the suction device is facing upward, and the conduit for extracting precipitated water is connected to a suction device at one end, and the suction port of the suction device is facing the bottom of the tank or container, the hydrocarbon suction device is immersed in the hydrocarbons heated by the peripheral conduit, and the water suction device is located at the bottom of the tank, and its suction port is slightly separated from the bottom.

[0047] As soon as the heat supply is no longer effective and the hydrocarbons stop flowing to the suction means of the pump, the extraction is ended and the interior of the tank or container is checked. If a large amount of hydrocarbons remains in certain areas of the tank or container, the extraction will continue, appropriately choosing the installation location of the device defining the system of the invention. At the end of the hydrocarbon extraction, water, oily sediments or hydrocarbons with a high melting point remain at the bottom of the tank or container, which substances are removed by conventional methods. On the contrary, it should be emphasized that when applying this method, the hydrocarbon layer initially adhering to the inner surface of the tank wall and the tank roof is removed, separated by the circulation of hot gases inside the tank or container, in particular by heating and entrainment when water vapor condenses on the hydrocarbon layer.

[0048] With regard to this method, it should be mentioned that the homogeneous mixture of gases produced by vortex diffusion in the steam ejector diffuser prevents the water vapor injected into the tank or container from moving freely upwards, so most of the injected driving steam condenses on the surface of the hydrocarbons, and a large amount of latent heat (539.4 cal / g at 100°C) is transferred to the hydrocarbons.

[0049] In another embodiment of the present invention, the hot gas circulating through the peripheral heating duct is supplied by a steam ejector, the gas discharge port of which is connected to the heating gas inlet in the peripheral duct, its driving steam nozzle is connected to the boiler, and its gas intake port sucks air from the atmosphere by means of the Venturi effect, so that the sucked air is uniformly mixed with the driving steam and is injected into the gas inlet in the peripheral duct by the ejector itself.

[0050] When the tank or container contains viscous hydrocarbons with a flash point below 55°C (Class B), the following operations should also be included:

[0051] - Initially inject nitrogen into the tank or container until the oxygen concentration is below 8%, and

[0052] - Regulate the nitrogen supply in the suction conduit of the steam ejector to keep the oxygen concentration in the tank or container always below 8%. Injecting water vapor into the tank or container also helps to keep the oxidizing oxygen concentration below 8% (the component oxygen in water vapor is not an oxidant).

[0053] As previously described, when the system and method are applied to the selective extraction of Class B viscous hydrocarbons (flash point <55°C), such as those accumulated at the bottom of an oil tank, nitrogen must be injected into the tank or container to keep the oxygen concentration therein always below 8%, whereas in the case of Class C and Class D viscous hydrocarbons (flash point ≥55°C), such as fuel oil and asphalt, there is no need to inject nitrogen into the tank or container since there is no risk of fire and explosion by applying the system and method of the present invention.

[0054] The system and method of the present invention are applicable to storage tanks and other containers containing viscous hydrocarbons in refineries, petrochemical plants, thermal power stations, port terminals, etc. The manner in which the invention is applied to other containers is virtually the same as for storage tanks, except that the installation of the equipment must be adapted to a variety of configurations and sizes in each case. Examples of these latter applications include processing units of refineries and petrochemical plants, including distillation columns, reactors, fan coolers, vessels equipped with "demisters" for gaseous hydrocarbons, interconnecting pipes, etc. The system and method can be applied to the complete processing unit or to its components individually, in both cases appropriately selecting the gas intake and gas discharge locations of one or more steam ejectors and the local heating areas of the hydrocarbons, and injecting nitrogen as a fire and explosion hazard prevention measure. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A floating roof oil tank-1- is shown, whose manhole is installed with a cover-2a- and a cover-2b-, which have the connection fittings required for installing the system and applying the method. The steam ejector-3- sucks gas from a given position of the tank through a gas suction conduit-3a- connected to the cover-2a- by means of the Venturi effect, and after the gas is uniformly mixed and heated with driving steam at a temperature between 120 and 200°C supplied by a steam boiler-4-, the gas is injected using a gas discharge conduit-3b- connected to the cover-2b-, and the boiler has a valve-4a- for regulating the amount of water vapor it supplies to the ejector.

[0056] Furthermore, a peripheral conduit-5- is installed, which is connected to the outer metal wall of the tank for heating the oil adjacent to the entire extension of the peripheral conduit. In one embodiment of the present invention, the peripheral conduit is connected to a second steam ejector-6-, which sucks air from the atmosphere-6a- by means of the Venturi effect and discharges it into the peripheral conduit through a gas discharge conduit-6b-, uniformly mixing with the driving steam supplied by a steam boiler-4-, which has a regulating valve-4b-.

[0057] The pump 7 selectively extracts the oil heated by the peripheral conduit through the suction conduit 7a, and the second pump 8 extracts the sediment water through the suction conduit 8a. The extracted oil and water are pumped to a determined storage, transportation or treatment location through the oil delivery conduit 7b and the water delivery conduit 8b, respectively. The suction conduits of the pumps are connected at their respective ends with an oil suction device 7c and a sediment water suction device 8c, which are located inside the tank near the area heated by the peripheral conduit and are designed so that the suction port of the oil suction device is upward, while the suction port of the water suction device is toward the bottom of the tank and slightly separated therefrom.

[0058] Considering that the hydrocarbons accumulated at the bottom of the tank belong to the class B hydrocarbons (flash point < 55°C), in order to eliminate the risk of fire and explosion, a nitrogen tank -9- is provided, which supplies a regulated amount of nitrogen to the gas intake duct of the ejector -3a- through a control valve -9a-. In this way, the uniform heated gas flow injected into the tank thus has a high nitrogen concentration, which helps to keep the oxygen concentration in the tank below 8% at all times. Similarly, the injection of driving steam from the ejector also helps to keep the oxidizing oxygen concentration in the tank below 8% (oxygen, as a component of water vapor, is not an oxidant). DETAILED DESCRIPTION

[0059] The preferred application of this method is the extraction of viscous hydrocarbons (Class B hydrocarbons, flash point < 55°C) accumulated at the bottom of floating roof tanks.

[0060] The order of operations for this method is as follows:

[0061] - Initially nitrogen is injected into the tank until the oxygen concentration is below 8%. Subsequently, during the extraction of the oil, a nitrogen tank -9- provided with a control valve -9a- supplies a regulated amount of nitrogen so that the oxygen concentration in the tank is always kept below 8%;

[0062] - heating the surface layer of the oil by means of steam ejectors -3- which draw in gas from the tank itself at a position above the level of the oil to be extracted, returning it after homogeneous mixing with its driving steam and the amount of nitrogen required to keep the oxygen concentration below 8%. The amount of driving steam supplied to the ejectors is regulated so that the amount of oil from the surface layer sufficient not to slow down the selective extraction of the oil selectively flows to the area adjacent to the peripheral heating duct -5-;

[0063] - local heating of the oil by means of said peripheral conduit connected externally to the tank, so that when the viscosity of the adjacent hydrocarbons decreases with heating, precipitation of non-emulsified water occurs and a selective flow of the oil heated by the peripheral conduit to a suction device -7c- connected to an oil extraction pump -7- is established. Heating gas is injected into the peripheral conduit using a second steam ejector -6-, which sucks air from the atmosphere by means of the Venturi effect and injects it into the peripheral conduit after homogeneously mixing it with its driving steam, the water vapor being supplied by said steam boiler -4-, said supply being regulated by a valve -4b-; and

[0064] - The oil heated by the peripheral conduit is selectively extracted, and the settled water is extracted separately, by means of two pumps -7- and -8-, whose respective suction means -7c- and -8-c are located inside the tank, close to the zone heated by the peripheral conduit. The pumps thus allow the oil and the water to be conveyed separately to designated locations for storage, transportation or treatment.

[0065] As soon as the supplied heat is no longer effective and the oil stops flowing towards the oil suction device -7c-, the extraction is ended and the interior of the tank is checked. If a large amount of oil remains in certain areas of the tank, the extraction will continue, appropriately choosing the location of the positioning of the equipment. In large tanks, the equipment can have several locations, or two or more steam ejectors with their corresponding peripheral heating ducts and extraction pumps can be used simultaneously. At the end of the oil extraction, water, oily sediments or high-melting-point hydrocarbons always remain at the bottom of the tank, these substances are removed by conventional methods. On the contrary, it should be emphasized that when applying this method, the oil layer that initially adheres to the inner surface of the tank wall and the tank roof is removed, separated by the circulation of heated gases in the tank and in particular by heating and entrainment when water vapor condenses on the oil layer.

Claims

1. A system for extracting viscous hydrocarbons from a container, comprising: - a steam boiler (4) having a control member configured to adjust the amount and temperature of water vapor supplied by the steam boiler (4) so ​​that the temperature of the supplied water is between 120° C. and 200° C.; - means for homogenizing the steam supplied by the steam boiler (4) with the gas flow, arranged to recirculate the gas from the steam boiler (4) itself and to inject the resulting homogeneous gas mixture into the container and to heat the surface layer of the hydrocarbons to be extracted; and - at least one first pump (7) for selectively extracting hydrocarbons from the surface layer heated by the injected homogeneous gas mixture, said first pump (7) having a suction duct (7a) connected in a peripheral region to a container for extracting heated hydrocarbons from the surface layer therein, Features - said means for homogenizing and injecting the gas flow into the container comprises at least one steam injector (3) configured to provide vortex diffusion of driving steam of a steam boiler (4) with recirculating gas from the container, said steam injector (3) having: a driving steam nozzle connected to a steam boiler (4); a gas intake conduit (3a) connected to a location in the vessel above the surface of hydrocarbons to be removed; and a gas discharge conduit (3b) through which the homogeneous gas mixture is injected into the container, In the diffuser of the steam ejector (3), the driving steam supplied by the steam boiler (4) and the gas sucked by the steam ejector (3) through the gas suction conduit (3a) by the Venturi effect are subjected to eddy diffusion, the gas coming from the container itself, from the atmosphere or from a combination of these sources, and at the discharge port of the gas discharge conduit (3b) of the steam ejector (3), the uniform mixture of heated gas produced by the eddy diffusion is injected into the container to heat the surface layer of the hydrocarbon, This eddy diffusion thereby prevents the free upward movement of the steam injected into the vessel, with the result that a large part of the injected driving steam condenses on the surface of the hydrocarbons and transfers its latent heat to the hydrocarbons.

2. The system according to claim 1, further comprising: - a peripheral conduit (5) for locally heating the hydrocarbons, the peripheral conduit (5) being externally connected to a portion of the metal wall of the container situated below the level determined by the hydrocarbons to be extracted, a portion of the peripheral conduit (5) consisting of a portion of the metal wall of the container to which it is connected, so that the heated gas circulating through said peripheral conduit (5) is in direct contact with said metal wall portion and heats the hydrocarbons adjacent to the container in a locally manner; - at least one second pump (8) for extracting settled water in the container, the suction duct (7a) of the first pump (7) and the suction duct (8a) of the second pump (8) being connected to the container in a peripheral area close to the area heated by the peripheral duct (5); and - a gas conduit connected to the gas intake and gas discharge of the steam ejector (3) and to two different locations on the periphery of the vessel above a level determined by the hydrocarbons to be extracted, at least one of the two locations being close to the peripheral area.

3. The system according to claim 1, wherein the suction conduit (7a) of the first pump (7) is connected to an oil suction device (7c) at one end, and its suction port faces upward; the suction conduit (8a) of the second pump (8) is connected to a sedimentation water suction device (8c) at one end, and its suction port faces the bottom of the container.

4. System according to claim 2, wherein the peripheral duct (5) consists of a synthetic fabric covering supported by semicircular arches distributed along the entire peripheral duct (5), so that the peripheral duct (5) acquires a semi-cylindrical shape, the flat part of which coincides with the part of the metal wall of the container, the peripheral duct (5) being connected and sealed to the container by two straps, the semi-cylindrical shape having support plates at its two ends on which are welded rings for guiding and holding the two straps passing through them.

5. The system according to claim 4, wherein: The heating gas circulating through the peripheral duct (5) is supplied by a second steam ejector (6), the gas discharge port of the second steam ejector (6) being connected to the heating gas inlet in the peripheral duct (5), the driving steam nozzle of the second steam ejector (6) being connected to the steam boiler (4), and the gas suction port of the second steam ejector (6) sucking in air from the atmosphere by means of the Venturi effect, so that the sucked in air is uniformly mixed with the driving steam and injected into the heating gas inlet in the peripheral duct (5) by the second steam ejector (6) itself.

6. The system according to claim 1, wherein: At least one gas circulator is installed in the gas intake conduit of the steam injector (3), and the gas circulator is configured to increase the flow rate of the gas injected into the container by the steam injector (3).

7. The system according to claim 1, wherein: At least one other steam injector or a connection position for injecting reduced-pressure water vapor is installed in the gas intake conduit of the steam injector (3).

8. A system according to any one of claims 1 to 7, configured to process hydrocarbons having a flash point equal to or greater than 55°C, ie, Class C and D hydrocarbons.

9. A system according to any one of claims 1 to 7, configured for treating hydrocarbons having a flash point below 55°C, i.e. Class B hydrocarbons, wherein a gas intake conduit of a steam ejector (3) for injecting gas into a container is connected to a nitrogen box having a control member configured for regulating the amount of nitrogen supplied.

10. A method for extracting viscous hydrocarbons from a container, wherein the method comprises: Heating the surface layer of the hydrocarbons to be extracted by means of a steam ejector (3) connected to a steam boiler (4) supplying water vapor at a temperature of 120-200°C; The steam ejector (3) draws in gas from the container itself, from the atmosphere, or from a combination of these sources through its suction port by means of the Venturi effect; The sucked gas and the driving steam provided by the steam boiler (4) are subjected to vortex diffusion; injecting the resulting homogeneous mixture of heated gases into another location in the same container; and The amount of steam supplied to the steam ejector (3) is adjusted so that a selective flow of hot hydrocarbons from the surface to the suction duct (7a) of the first pump (7) for selectively extracting hydrocarbons is established.

11. The method according to claim 10, further comprising: - locally heating the hydrocarbons selectively emanating from the surface layer by means of a peripheral duct (5) through which a heated gas circulates externally connected to the container, so that precipitation of non-emulsified water occurs during the extraction process, and establishing a selective flow of the hydrocarbons heated by the peripheral duct (5) to an oil suction device (7c) connected via a suction duct (7a) to a first pump (7) for selectively extracting hydrocarbons; and - The hydrocarbons heated by the peripheral conduit (5) are selectively extracted by the first pump (7), and the precipitated water is periodically extracted by the second pump (8), wherein the conduit for extracting hydrocarbons is connected to an oil suction device (7c) at one end, and the suction port of the oil suction device (7c) faces upward, and the conduit for extracting precipitated water is connected to a precipitated water suction device (8c) at one end, and the suction port of the precipitated water suction device (8c) faces the bottom of the container, the hydrocarbon suction device is immersed in the hydrocarbons heated by the peripheral conduit (5), and the water suction device is located at the bottom of the container, and the suction port of the water suction device is slightly separated from the bottom.

12. The method according to claim 11, wherein: The hot gas circulating through the peripheral duct (5) is supplied by a second steam ejector (6), the gas discharge port (6b) of the second steam ejector (6) being connected to the heating gas inlet in the peripheral duct (5), the driving steam nozzle of which is connected to the steam boiler (4), and the gas suction port of which sucks air from the atmosphere by means of the Venturi effect, so that the sucked air is uniformly mixed with the driving steam and is injected into the gas inlet in the peripheral duct (5) by the second steam ejector (6) itself.

13. A method according to any one of claims 10 to 12, suitable for treating hydrocarbons having a flash point equal to or greater than 55°C, i.e., Class C and D hydrocarbons.

14. The method according to any one of claims 10 to 12, which is suitable for treating hydrocarbons with a flash point below 55°C, i.e., Class B hydrocarbons, further comprising: - initially injecting nitrogen from a nitrogen tank (9) into the container until an oxygen concentration of less than 8% is reached; and - Regulate the nitrogen supply to keep the oxygen concentration in the container below 8% at all times.

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