WO2009068993A1

WO2009068993A1 - Method for the fluidisation of sediment and the recovery of hydrocarbons from hydrocarbon storage tanks

Info

Publication number: WO2009068993A1
Application number: PCT/IB2008/003609
Authority: WO
Inventors: Humberto Vidales Olaya; Luz Edelmira Afanador Rey; Martha Josefina Parra Ramirez; Lilia Rodriguez Rodriguez; Elena Losik; Jose Isaias Vargas Navarro
Original assignee: Ecopetrol S.A.
Priority date: 2007-11-29
Filing date: 2008-12-01
Publication date: 2009-06-04
Also published as: ECSMU10010202U; CO6140033A1; PE20091661A1

Abstract

The invention relates to a method for the fluidisation of sediment and the recovery of hydrocarbons from hydrocarbon storage tanks. The method comprises the following steps: diagnosis and definition of the detection process, measurement and characterisation of the sediment or oily sludge, adaptation or installation of the fluidisation system, fluidisation by means of agitation, and hydrocarbon recovery. During the adaptation or installation step, the direction of the agitators is varied if the tank includes such elements or a fluidisation system is installed in the manhole of the tank. The system includes a manhole cover (1), the outer surface of which is designed to receive a manifold (3) connected to a pump (4), which recirculates the product through the manhole. Said manifold is coupled to the manhole cover (1) by means of flanges (5a, 5b) and includes three pipes connected to three independent valves (2) and, on the inner surface thereof, one or more nozzle tubes (6) coupled to a nozzle (7) by means of flanges.

Description

METHOD FOR THE FLUIDIZATION OF BORRAS AND RECOVERY OF HYDROCARBONS OF STORAGE TANKS OF

HYDROCARBONS

FIELD OF THE INVENTION

The present application relates to a fluidization method for removing oily sludges or sludges that are deposited in the bottoms of the hydrocarbon storage tanks and which also includes the recovery of the hydrocarbons.

In oil fields, once the oil is extracted from the subsoil, it must be subjected to processes to remove the water and salt associated with it. After these treatments, the crude ones are stored in tanks to later be transported to the refining centers or to the ports for export. In addition to water, the oil contains well sand and other materials, such as pipe oxides. Once the crude oil arrives at the refineries, they are subjected to distillation and treatment processes to obtain products such as gasoline, diesel, kerosene, naphtha, etc. During the development of these processes, water formation and entrainment of solid materials, such as catalyst residues and metal oxides, are presented. The distilled products obtained are also stored in tanks before being dispatched to distribution centers for consumption.

For the storage of these hydrocarbons tanks are used that can be from low capacity (180 m ³ ) to high capacity (40,000 m ³ ), which can have diameters between 4 and 60 meters. The tanks, depending on the product they store, can be fixed roof (conical, oval) or floating roof.

During the storage of the different types of hydrocarbons, sedimentation processes occur where the densest compounds, such as water, heavy and solid hydrocarbons accumulate at the bottom of the tank to form pasty and viscous materials, which are called borras or oily sludge, hereinafter oily sludge. The hydrocarbon present in the oily sludge is formed by some heavy compounds, such as asphaltenes, resins and / or paraffins, which precipitate due to different mechanisms trapping water and solids in this process. The sediments or solids can be oxides, sands, fine particles and metallic waste.

In the oil industry, generally, tanks are maintained every five years. Maintenance implies unoccupying the tank, removing it from service and proceeding to clean it, that is, removing the oily sludge, until it is left in conditions that allow the entry of personnel for inspection, maintenance and repair, if required. Oily sludge has always been considered as polluting industrial waste.

The method of the present invention allows the cleaning of tanks containing light, semi-heavy or heavy hydrocarbons, removing oily sludge, which reduces the need for personnel to remove them and the days when the tank is out of service, improving Ia recovery of the hydrocarbons that formed them and minimizing the emission of pollutants.

STATE OF ART

When storing hydrocarbons in tanks, due to the differences in densities of the compounds that make up the oil and due to thermal effects, resting times or flow patterns in the tank, the heavier compounds or paraffinic compounds settle, which they are known by the name of "erase" or "oily sludge". Oily sludges are composed of hydrocarbons, water and sediments. The hydrocarbons can be paraffins, asphaltenes, resins and the sediments can be metal residues caused by oxidation of the pipes or the tanks themselves, inorganic materials, sands, fine particles and metallic residues of different kinds. This situation produces deposits in storage tanks which generate pollutants that affect subsequent refining and transportation processes. The type and consistency of oily sludge depends on the product stored. Those of distillates are colloidal oily sludges of low viscosity and easy fluidization; those of light hydrocarbons and paraffinic media are oily and pasty sludges of low fluidity, which require recirculation and / or heating to eliminate their paraffinic characteristic, which makes them solid at the temperature inside the storage tank. To melt or disperse the present paraffin, additives must be heated or added and subjected to stirring processes to ensure fluidization. The oily sludges of semi-heavy and heavy hydrocarbons are of low fluidity and high viscosity, so dilution and / or heating is required for their fluidization, since they have a high content of asphaltenes and resins.

The presence of oily sludge causes various inconveniences to the storage operation generating loss of hydrocarbons trapped in the sludge, trapping water that prevents it from draining, decreases the storage capacity of the tank, promotes the corrosion of tank bottoms , contaminate the products of dispatch and cause problems in the pumping units due to erosion.

A conventional way of cleaning tanks is basically the manual sludge removal. Said cleaning consists of entering personnel crews inside the tank for short periods of time (10 minutes) to proceed to the removal of oily sludge or sludge manually, using shovels and buckets.

This methodology is inappropriate from several points of view: it is a delayed and expensive process, it works in highly hazardous conditions for human health and most of the time the hydrocarbon present in the oily sludge is not recovered but is available in areas where It generates pollution. This causes higher costs because for its treatment the concentration of hydrocarbon in oily sludge must be decreased by mixing with large amounts of soil before subjecting it to bioremediation processes, because microorganisms are only able to biodegrade material with hydrocarbon. in low concentration That is, in the conventional method hydrocarbon is not recovered, it is contaminated, and cleaning only generates costs. As mentioned earlier, the tanks depending on the product they store can be fixed roof (conical, oval) or floating roof. Fixed roof tanks have a design that allows the entire weight of the tank roof to be deposited on its walls. Floating roof tanks are designed so that the roof floats on the fluid they store and has hollow guides or tubes distributed throughout the roof area that are used to seat the roof to the tank floor when they are in the maintenance position.

At present, different methods and apparatus for removing oily sludge, sediment or sludge deposited at the bottom of hydrocarbon storage tanks are known in the state of the art.

Among them is the method described in US Patent 4,770,711, which uses a portable hydraulic device or vehicle for cleaning the sludges containing hydrocarbons from a crude oil storage tank. It uses a fluidizing agent, based on water and emulsifying agent, applied in a mud to fluidizing agent ratio of 70/30.

On the other hand, US Patent 5,335,395 describes an apparatus for removing sludge, which is inserted through the manhole to the storage tank. The apparatus includes a platform connected to a pump and two channels connected to the platform, which have a kind of drill or endless, which cuts the sludge and leads to the entrance of the pump.

The cleaning methods that employ devices such as those mentioned above have the disadvantage that they cannot be used in floating roof tanks because they contain guides or bars inside the tank that hinder the movement of the vehicle inside.

For its part, US Patent 5,008,035 relates to a process of fluidization of heavy crudes and grouts composed of catalyst, coke and asphalt residues. The process comprises a heating stage with mixing at a temperature of up to 6O ⁰ C, the addition of a fluidizing agent comprising the following compounds: water (15-85%), a nonylphenoxylated additive, formaldehyde with a molecular weight between 1000 and 25000, surfactants with HLB between 40 and 5, such as condensed alkanolamides, ethoxylated fatty alcohol phosphates and mixtures thereof, and organic solvents such as naphtha, aromatic naphtha, heavy naphtha, alkylated or light aromatic and mixtures thereof, with these ingredients and residues hot grouts are formed, which are mixed until their fluidization

The previous process focuses on tanks that store heavy hydrocarbons, which is why the use of a specific chemical is claimed and additionally, does not raise the recovery of the hydrocarbon. In addition, the aforementioned patent application uses an additive of a chemical composition different from that which is part of the process claimed herein.

US 5,611, 869, discloses a method and composition for the cleaning of oily sludges in storage tanks in refineries. The process forms an emulsion, which cleans the mud. The cleaning solution is formed of a resin of an alkylphenol formaldehyde of molecular weight 500 to 5000, dialkyl polyethylene or glycol, and a solvent selected from the group consisting of alcohols aqueous solution Ci to C ₈ as alcohol, glycol, or glycol ether. The emulsion formed is sent to another container, where an emulsion breaker is added, such as a polyalkylamine or polyamine or aluminum salts. Said patent claims an emulsifying additive and the method of breaking the emulsion.

Unlike what is established in the previous paragraph, the present patent application does not require the formation of an emulsion and its subsequent rupture for hydrocarbon recovery, which implies a greater number of stages, additives, time, costs and control of the emulsion. The invention of this application only requires hydrocarbons similar to that stored in the tank or, in the case of heavy crude, refining diluents are used which allows the hydrocarbon to be recovered at the end of the fluidization stage. On the other hand, there are methods that employ microorganisms for the cleaning process, as is the case of US patent 6,069,002, which describes a method for removing sludge from storage tanks and the recovery of hydrocarbon from said sludge. The method is applied in the tank. First, the sludge is studied to define the treatment, then the treatment consists of adding a biological system (microorganisms) and the nutrients required for its development (water, nitrogen, phosphorus) to the tank, then the tank is vigorously agitated, after which it is left at rest until the separation of the phases, then the tank is sampled and the hydrocarbon is removed, finally the rest of the content of the tank is removed.

This type of method is basically for light or medium hydrocarbons, that is to say with densities higher than water, but for heavy hydrocarbons (<IO ° API) it does not apply because a good definition of the phases cannot be achieved and the hydrocarbon will not float , but it will be deposited in the bottom of the tank or in its intermediates. Additionally, the nutrients required for the development of microorganisms can affect the quality of the recovered hydrocarbon.

In addition to the above, the use of microorganisms implies strict control of process conditions (pH), since these organisms are very sensitive to this factor. This method includes the addition of the treatment fluid at pressures of 0.02 MPa to 0.14 MPa, while the present invention is carried out at low pressures (0.01 MPa) and does not include the incorporation of a biological system.

For its part, US 6,142,160 discloses a method and an apparatus that is used for the internal cleaning of crude oil tanks, where hydrocarbons accumulate by sedimentation over time. The apparatus consists of two concentric tubes with a nozzle to inject wash fluid and produce a spray. The apparatus has a system that allows its displacement, however, it has the disadvantage that the displacement of the tube can only be carried out in one direction, that is, towards the front of the manhole entrance, which prevents a total sweep of the tank . US Patent 6,033,901 describes a method for removing sludge from a crude storage tank and the recovery of mud hydrocarbons. The method is developed inside the tank. The mud is initially studied to determine the method of treatment. Once the sludge treatment is placed in the tank, it is mixed and shaken vigorously. A heating and addition process of diluent hydrocarbon and / or surfactant or enzymes is included. Subsequently the hydrocarbons are recovered from the tank and then the rest of the contents of the tank are removed, which can be filtered. They use discharge pressures from 0.07 MPa to 0.14 MPa.

The previous method has the disadvantage of requiring high pressures (0.07 to 0.14 MPa), which can affect the integrity of the tank. As mentioned above, the present invention is carried out at low pressures and does not use a biological system.

Application WO06 / 001797 describes a method for cleaning the walls of a tank using pressurized air, which is injected into the tank by means of nozzles. It also uses liquids in the form of drops such as water or detergents or disinfectants or antifungal, which are charged by the air flow. It also uses solids such as sand or plastic or glass to clean.

Document RU 2,150,341 describes a process that consists of the installation of a stirrer in the tank and the injection of diluent and steam. Once the mixture is homogenized, it is pumped into a decanter to perform a centrifugal separation.

US Patent 3,436,263 relates to a process for cleaning tanks that consists of applying a chemical liquid inside the internal surface of the tank, leaving a residence time to optimize the efficiency of the chemical and then washing the walls with water to remove the chemical and the deposits contained in the surface of the tank walls. Said patent does not perform fluidization of the oily sludge, it only raises the cleaning of the tank walls, that is, it is only applied after the oily sludge has been removed from the tank.

For its part, the US patent 1, 891, 592, relates to a method and an apparatus for cleaning tanks, which consists of installing devices inside the tank, before starting the cleaning process, and then sealing the tank and proceed to inject a volatile non-combustible vapor (carbon tetrachloride) or a gas, which acts as a detergent on the hydrocarbon. They also inject calcium chloride and steam to condense and precipitate the gaseous mixture and subsequently, remove all these liquids from the tank.

Reference CA 2295723 describes a method for removing sludge from tanks and recovering the hydrocarbon from the mud. It consists of placing a treatment for the fluid, the injection of this treatment is performed at high pressure (0.02-0.14 MPa), then vigorously stirred and subsequently, the liquids are removed from the tank. It also includes heating.

Document KR 040031477 discloses an apparatus for removing sludge from tanks, which prevents sludge deposits at the bottom of the tank. The apparatus consists of a guide that is installed on the top of the tank, a roller installed in the guide, a movable panel, a pump, and suction and discharge lines connected to the pump. This device requires installing a somewhat complex and careful infrastructure, and does not apply to conical fixed roof tanks.

In order to meet the needs and deficiencies of the methods and devices existing in the state of the art, specifically those that require the installation of a complex infrastructure, the total unemployment of the tank and a previous cleaning for the installation of equipment; The inventors of the present application developed a fluidization method to remove oily sludges from any type of hydrocarbon storage tank, either fixed roof or floating roof, which can be operated for both tanks that store hydrocarbons heavy as for tanks that store light, or light heavy hydrocarbons and that also includes the recovery of the hydrocarbon.

In this way, the occupational risks associated with this type of processes are reduced, while at the same time it is possible to generate income from the recovery of the hydrocarbon contained in the oily sludge and the times required for the cleaning of the tanks are reduced.

SUMMARY OF THE INVENTION

A method has been developed that consists of the following stages: diagnosis and definition of the process of detection, measurement and characterization of oil sludges or sludge, adaptation or installation of the fluidization system, fluidization by agitation and hydrocarbon recovery.

In one embodiment of the invention, the adaptation or installation stage comprises the variation of the direction of the agitators in the case that the tank has these elements.

If the tank to be cleaned lacks its own stirrers, a fluidization system is installed through the tank manhole. Said system comprises: a manahole cover (1) adapted to receive on its external side a manifold (3), which is connected to a pump (4), which takes product from the tank and recirculates it through the manhole. Said manifold comprises three pipes connected to independent valves (2) and is coupled to the manhole cover (1) by means of flanges (5a, 5b). On the other hand, said manhole cover (1) comprises on its inner side, one or more nozzle tubes (6), preferably three nozzle tubes, to which the nozzles (7) are coupled by means of flanges, as can be see in Figures 1 to 4.

The method disclosed here has slight variations in some of its stages, depending on the type of tank and the type of hydrocarbon it contains. In the case of light distillates, the fluidization stage comprises three steps: agitation (usually by recirculation of the same crude in the tank), separation and withdrawal of the resulting product.

If the tank to be treated stores light crudes (> 28 ° API), the crudes are removed to the minimum level allowed by the tank specifications and the fluidization stage comprises the steps of diluent addition, agitation (usually by recirculation of the crude or by means of the fluidization system adapted to said tank), separation and removal of the resulting product.

When the method is applied to tanks with semi-heavy crudes, between 18 ⁰ API at 28 ° API, the product is removed to the minimum level allowed by the tank specifications and the fluidization stage comprises the steps of light crude oil treatment, which are repeated for several cycles.

Finally, for tanks with heavy crudes (° API <18), the method differs from that used for semi-heavy crudes in that after removal of the product the tank is opened, in the fluidization stage the diluent is mixed with solvents and heats, prior incorporation into the tank that you want to treat.

It is an objective of the present invention to provide a simple and low-cost oily sludge treatment method, which allows the removal of said oily sludges from any type of hydrocarbon storage tanks, either fixed roof or floating roof, with one or several manholes, and with capacities from 18O m ³ to 4000O m ³ .

It is another objective of the present invention to condition a fluidization system to the tank with hydrocarbons or to use the existing attachments, such as the side stirrers or the recirculation lines.

Another objective of the present invention is to provide a method of removing oily sludge in storage tanks that contain different types of hydrocarbons (light or light heavy or heavy) and that can be carried out both in tanks with internal elements, as in tanks without any internal elements.

As another objective of the present invention is to provide a method of removal of oily sludges deposited in storage tanks, which allows the recovery of the hydrocarbon contained in the oily sludge, thus reducing the environmental liability that generates its disposal and generating savings and benefits for the recovery of the hydrocarbon.

It is another objective of the present invention to reduce the times for cleaning the tanks and improve the occupational health conditions in which the method is performed.

In the search to achieve these objectives and carry out the cleaning of oily slips or sludges deposited in storage tanks, the applicant has surprisingly found that the treatment of the tank with the same hydrocarbon and agitation achieves better fulfill the proposed objectives.

DESCRIPTION OF THE FIGURES

Figure 1. Front view of the manhole cover, which comprises three pipes for connecting, on the one hand, the nozzles of the fluidization system and on the other the manifold of the recirculation system.

Figure 2. Top view of the fluidization system with recirculation showing the arrangement of the nozzles adapted to the manhole.

Figure 3. Side view of the section of the tank where the location of the fluidization nozzles is shown.

Figure 4. Top view of the detail of the fluidization system of the invention installed in a manhole. DETAILED DESCRIPTION OF THE INVENTION

The method for the removal of oily sludges from hydrocarbon storage tanks depends on the type of tank, the kind of hydrocarbon it stores and the arrangement of the internal elements that each tank has. These internal elements can be dynamic stirrers and / or a pump recirculation system. Likewise, there are also tanks without any internal elements.

Based on the above, the specific method to be followed is defined below, the type of hydrocarbon to which it applies and whether it requires performing the pre-fluidization process or not.

The method of the present invention is characterized in that it comprises the following steps:

a) diagnosis and definition of the detection process, b) measurement and characterization of oily sludges or sludges, c) adaptation or installation of the fluidization system, d) fluidization by agitation, and e) hydrocarbon recovery.

Each of the stages of the process is detailed below, specifying the sub-stages or steps that are carried out in them:

a) Diagnosis and definition of the detection process.

During the stage a) corresponding to the diagnosis and definition of the process, the characteristics of the tank are evaluated, to establish the best way to carry out the fluidization process and the requirements or not for adjustments or the installation of additional systems to achieve the fluidization. b) Measurement and characterization of borras or oily sludge.

Stage b), for measuring and characterizing oily sludge, comprises the characterization of oily sludge to determine: hydrocarbon content, water and solids in order to justify and establish a process of hydrocarbon recovery after fluidization and / or treatment of the remaining sludge.

Additionally, in said stage the rheology of the oily sludge and of the mixtures with diluents is established, to predict the dilution and manageability of the mixture during the fluidization. The oily sludge density is also evaluated to determine the amount of diluent required to obtain a good phase separation, when heavy hydrocarbons are fluidized.

Finally, at this stage the requirement for heating and / or chemical dosing is evaluated. In the case of oily sludge with paraffinic content, it is necessary to determine the temperature and / or amount of additive necessary to disperse the crystals and in this way, avoid their aggregation and subsequent precipitation.

c) Adaptation or installation of the fluidization system.

When the tanks have agitation systems installed inside, the stage of adaptation of the fluidization system consists of adjusting the existing agitators so that, instead of remaining in a fixed direction as is usually provided for hydrocarbon storage tanks, these periodically change orientation so that the greater amount of the cross-sectional area of the tank is covered.

If the tank to be cleaned lacks its own agitators, a fluidization system is installed through the tank manhole. Said system comprises: a manahole cover (1) adapted to receive on its external side a manifold (3), which is connected to a pump (4), which takes product from the tank and recirculates it through the manhole. Said manifold comprises three pipes connected to independent valves (2) and is coupled to the manhole cover (1) by means of flanges (5a, 5b). On the other hand, said manhole cover (1) comprises on its inner side, one or more nozzle tubes (6), preferably three nozzle tubes, to which the nozzles (7) are coupled by means of flanges, as can be see in Figures 1 to 4.

The steps to follow to adapt the tank with the fluidization system are the following: remove the hydrocarbon from the tank, up to a level below the manhole. Remove the lid from the manhole and replace said lid with a properly modified one to receive both the manifold (3) and the nozzles (6).

Install the suction line (7) with valve (8) so that it leaves the dispatch or receipt line of the tank, towards the recirculation pump (4) to take the product. Install the portable diesel recirculation pump (4), which preferably has a capacity of 2.27 m ³ / minute at 4.54 m ³ / minute (600 GPM and 1200 GPM) and minimum discharge pressure of 1.38 MPa ( 200 Psi). Install the line from the discharge of the portable recirculation pump (4) to the recirculation manifold (3) in the manholes of the tank. Finally, install the modified lids (1) in each manhole with the fluidization system to carry out the fluidization of the oily sludge contained in the tank, see figures 2 and 4. For tanks with a capacity greater than 11,924 m ³ (100 KBLS ) fluidization systems must be installed in all manholes.

For the operation of the fluidization system described in the previous paragraphs, the nozzles conditioned in the tank manhole are located at three different angles, to generate flow patterns that will allow fluidizing the oily sludge, as seen in Figure 2. The Figures 3 and 4 show the side view of the fluidization system in the tank and the front view of the modified manhole respectively. In a preferred embodiment of the invention, these fluidization systems are installed in all manholes, in order to ensure fluidization throughout the entire tank area. d) Fluidization.

The fluidization stage in turn comprises three main steps, agitation, separation and removal of the resulting product. Depending on the tank to be treated and the kind of hydrocarbon stored in it, this stage may include additional steps to achieve the total removal of the oily sludge. The different steps of the fluidization stage are described below, depending on the kind of hydrocarbon stored in the tank:

In the case of treatment of oily sludges from light distillates, the fluidization stage c) comprises the three basic steps, mentioned above, and with them the reduction and in some tanks, the total removal of the oily sludge is achieved.

When the tank to be treated stores light crudes (> 28 ⁰ API), the hydrocarbons are removed from the tank, to the minimum level allowed by the tank specifications, diluent is added to the tank and the stirring, separation and removal steps are carried out. resulting product.

The fluidization stage when the oily sludges come from semi-heavy crudes, between 18 ⁰ API at 28 ° API, comprises the same steps of the fluidization stage of the light crude treatment and repeats the entire sequence of steps one or more times, depending on the composition of the oiled sludge.

Finally, for tanks with heavy crudes (° API <18), the fluidization differs from that used for semi-heavy crudes in that it is performed with the tank open and the diluent is mixed with solvents and heated before joining the tank What do you want to try?

The diluent used for the treatment of oily sludges derived from light and medium crudes is the same crude stored in the tank; For heavy crude or heavy products, such as fuel oil, the diluent will be the light hydrocarbon available in the area, preferably mixed with Light Cycle Oil (ALC) or other aromatic diluents. If you have paraffinic oily sludge, a mixture of paraffin dispersant additives and asphalt from refinery products is used, which are added in quantities of 100 to 800 ppm.

To determine the amount of diluent, laboratory tests with a sample of stored oily sludge and different types and ratios of solvent are required. Tests carried out with different types of oily sludge and diluents allowed us to establish that the minimum amount for fluidization, that is, so that the oily sludge is dispersed or diluted, is in the ratio 1: 0.5 to 2 erasure: diluent.

The amount of diluent to carry out the process on an industrial scale is described below: For tanks without agitator but using the fluidization nozzle system (light and medium hydrocarbons) between 1.0 meters and 1.2 meters high are required, for properly form the flow patterns generated by the nozzles.

For tanks with heavy hydrocarbons, without agitator, which are fluidized with open manhole (open tank), the volume required is that necessary to obtain a product recovered with an API greater than 15, it is estimated that a minimum ratio between 1: 1 must be achieved , 5 to 1: 2 between the amount of oily sludge and solvent.

Based on the above information on the differences in the sub-stages of the fluidization stage depending on the hydrocarbons stored in the tank to be cleaned, the preferred modalities of the invention are considered, in which the presence or no of agitators or recirculation with pump.

Fluidization stage for tanks with agitators or pump recirculation.

In an embodiment of the method of the invention, for tanks that already have a mechanical agitator, the fluidization stage comprises the periodic agitation by changing the direction of the agitators with a certain frequency. If said tank contains Light distillates, it is possible that the agitation of the tank modifying the directions of agitation achieves the total elimination of oily sludge.

For light and medium hydrocarbons (° API> 18) stored in tanks with mechanical stirrers, periodic agitation in different directions constitutes a first part of the fluidization that has been called pre-fluidization. This can be carried out with any level of crude in the tank, to the minimum that allows the use of mechanical agitators. If there are paraffinic oily sludges, a mixture of paraffin dispersant additives and asphaltenes from refinery products, in an amount of 100 ppm and 800 ppm, is used in addition to the diluent.

Preferably, when the tank already has stirrers, the fluidization stage consists of the following steps: stir the tank permanently for 90 hours using the side stirrers and varying the mixing angle every 10 hours, at least three times before removing it To maintenance, combine angle changes with filling and emptying intervals of the tank.

Subsequently, the tank is left at rest for a period between 5 hours and 24. hours, then the free water is drained and the tank is vacated to a minimum level. During this process the quality of the pumped oil is monitored (API and BS&W Gravity). The manhole is opened, the tank is inspected and the hydrocarbon is finished using an auxiliary pump. If remaining oily sludges remain, they will be fluidized with emulsified washing.

For the treatment of the remaining oily sludges, they are characterized, an anionic dispersant additive is added, preferably an aqueous solution consisting of a strong base, a weak acid and polymer, on the oily sludge, water is added and recirculated under pressure. , to achieve the fluidization of oily sludge.

A pump is installed to send the fluidized oily sludge to the tank intended for the separation of hydrocarbon and water. The tank for floor and wall cleaning is delivered as stipulated, and the separation tank is left at rest for 24 hours to separate the hydrocarbon by decantation, the water is drained from the tank, treated with known physicochemical methods and controlled its quality. The remaining hydrocarbon is recirculated and characterized to determine and adjust its quality.

Fluidization stage for tanks without agitators or pump recirculation.

In another alternative of the invention, the method is carried out in tanks without agitator and without pump recirculation, to which the fluidization system shown in Figures 1 to 4 has been adapted. In these cases, for sludge fluidization Oils produced by light and medium hydrocarbons (API> 18), the process is carried out with a closed tank.

To fluidize the oily sludges produced by heavy hydrocarbons (API <18,) in tanks with the aforementioned fluidization system, the fluidization must be carried out in an open tank, using diluents from mixtures of refinery streams and applying heat to the diluent before of incorporating it into the tank.

Fluidization with closed tank without agitator and with pump recirculation

Once the fluidization system is ready and installed, the process for the fluidization of the oily sludge begins with the following steps: connect the manhole cover (1) that already has the fluidization manifold (3) with the portable pump (4) and the recirculation system, see Figure 2. Fill the tank with diluent, until it reaches a height of 1.2 meters to 2.0 meters, preferably 1.5 meters, if it is a conical tank or, 8 to 2.3 meters, preferably 2 meters if it is floating roof.

If the service time of the tank is less than three years, start the recirculation for 72 hours by alternating the direction of the recirculation nozzles. The direction of each pair of nozzles is changed every 24 hours. If the service time of the tank is more than three years, start the recirculation for 24 hours for each nozzle independently, in each of the four manholes. This operation must be repeated for one month before leaving service. Taking samples and evaluate the variation of density at different time intervals fluidization, if the density is in the approved limit value (15 ⁰ suggested API) process, opposite ends Io is continued recirculation Ia.

e) Hydrocarbon recovery.

After the fluidization process, the product of the tank is allowed to decant for at least three hours. The product is removed from the tank until the transfer pump loses suction.

After the fluidization cycles, proceed to: open manhole (S), vent until obtaining permissible levels of organic vapors and enter the tank. On the first entry into the tank, the atmosphere of the container will be monitored internally and completely; Samples should be taken to ensure that there is no presence of gas bags. According to the values of% LEL (minimum explosive level) (<10%), the percentage of oxygen (19.5% - 23.5%) and the percentage of sulfur (10 ppm maximum) obtained in this first entry, the personnel is admitted to the tank for the inspection of oily sludge or the degassing of the tank is continued.

Take samples of the remaining oily sludge and if oily sludge is found, these can be fluidized by dispersing them in water with the help of additives and withdrawing completely. For this, water must be added to a level higher than the lower part of the manhole, in order to facilitate the evacuation of the supernatant hydrocarbon and leave the tank only with water and the remaining oily sludge. Add the anionic dispersant additive. The recirculation process will be restarted with a movable nozzle and the same fluidization pump or by installing a pump in the tank pit or sump. This process is performed until the entire tank is fluidized, a process that can take between 6 hours and 10 hours. Then it is allowed to decant, the supernatant hydrocarbon is removed. Water is drained from the tank to The wastewater treatment plant. Finally, a tank for cleaning floors and walls with sawdust is delivered or as stipulated.

Open tank method without agitator and with pump recirculation

In an alternative modality, the specific method to be followed for the fluidization of oily sludge of oil with an open tank consists in recirculating the diluent in the tank by means of two or more nozzles located on the floor thereof, the position of said nozzles will change in the as the process of the fluidization of the heavy hydrocarbon evolves. Then, the hydrocarbons are extracted from the tank, the fluids are removed to the treatment system or to the relief tank, the water is allowed to decant and then it is drained, the cleaning of the tank will be finished in the traditional way.

For the treatment of this type of tanks, the fluidization system consists of at least two diesel pumps, which suck the supernatant hydrocarbon (diluent + fluidized oily sludge) through the manhole and recirculate it to the same tank by means of nozzles, forming the patterns of flow required to fluidize the oily sludge. The aforementioned pumps are self-priming, provide continuous flow at a flow rate greater than 1, 14 m ³ per minute (300 gpm) and 1.38 MPa discharge. The nozzles are eductors mounted on bronze skates that allow their manual mobilization at the bottom of the tank.

In this case, for the adequacy of the fluidization system the following activities must be carried out: decrease the tank level to a minimum volume, open the tank manhole, take the sample and characterize it, then at least one recirculation pump with capacity is installed between 1.14 m ³ at 2.27 m ³ per minute (300 GPM and 600 GPM) and discharge pressure greater than 1.38 MPa. Then, the hoses are installed from the recirculation pump to the center of the tank and to the left side and the nozzles are installed. The tank must remain grounded. Once the fluidization system is ready and installed, in this case with recirculation, the process for the fluidization of the oily sludge is started, which comprises the steps of closing and blindly positioning the valve that communicates the dispatch line of the tank with the pumps of dispatch The attachments for the discharge and / or receipt of the diluent tank and / or line to the tank near the suction of the recirculation pump must be taken. Perform the gas test inside the tank and vent, if required, to obtain permissible levels. Start the recirculation by suctioning with the pump through the nozzles installed from the center towards the suction of the tank and the pump to the left side. Recirculate for at least 2 hours, stop the process to check fluidity, if you can walk without problems and the floor feels clean in front of the nozzles, proceed to change the nozzles to more viscous points and restart recirculation.

Perform this operation until total fluidity. Take samples in the recirculation and evaluate the BS&W variation at different time intervals. Perform gas test inside the tank and vent, if required, until permissible levels of organic vapors are obtained. Once the fluidization stage is completed, the decanting process begins. Take samples at different heights of the fluidized tank in order to determine the volume of hydrocarbon to be dosed. The recovered hydrocarbon will be injected into the selected tank and the parameters arranged for this operation will be controlled. Perform venting until permissible levels of organic vapors are obtained and enter the tank to quantify the remaining sludge.

The treatment of the remaining sludge comprises the characterization of the remaining oily sludge, followed by the addition of anionic dispersing additive of an anionic character on the oily sludges. Then add and recirculate the water under pressure using nozzles until fluidization of the oily sludge. Install the pump to send fluidized oily sludge in the dike of the tank. Pump the fluidized oily sludge into the tank intended for this treatment and deliver the tank for floor and wall cleaning as stipulated.

Leave the tank that stores the remnant at rest for 24 hours to separate the hydrocarbon by decantation. Drain water from the tank and treat it with methods physicochemicals and control their quality. Recirculate and characterize the remaining hydrocarbon to determine and adjust its quality.

Below are some examples that illustrate some of the preferred embodiments of the invention. It should be understood that such examples are not of a limiting nature and the person skilled in the art can carry out modifications that are not contemplated therein, without them departing from the scope of the present invention.

EXAMPLE 1

A method of cleaning the oily sludges of a tank that stored diesel (API> 35 °) was performed, with a storage capacity of 1156.27 m ³ (10,000 barrels and had a conical roof). The fluidization system was installed for the recirculation of the oily sludge through the manhole, as described in Figures 1 to 4. The oily sludge was fluidized and pumped out of the tank, allowed to decant to recover the hydrocarbon.

The initial hydrocarbon content in the oily sludge was 25%, recovering 84%. The recovered hydrocarbon remained with a BS&W of 0.5%. The methodology carried out allowed to reduce the volume of oily sludge to be treated, and the residual oily sludge that was sent to the biodegradation process had a hydrocarbon content of 5%. This hydrocarbon content allows the application of the biodegradation process without diluting the residual oily sludge with soil.

EXAMPLE 2

A second method was taken to remove and treat the oily sludge from a 5781, 35 m ³ (50,000 barrels) tank with a conical roof that stored diesel (API> 35 °). It contained 660.81 m3 (5715 barrels) of oily sludge. The hydrocarbon content in the oily sludge was 53%. The fluidization system was installed for the recirculation of the oily sludge through the manhole, as described in Figures 1 to 4, the oily sludge was recirculated and pumped out of the tank and allowed to decant to recover the hydrocarbon.

The methodology carried out allowed to recover 98% of the diesel present in the initial oily sludge. The residual waste was 5.32 m ³ (46 barrels) with a hydrocarbon content of 15%.

EXAMPLE 3

The crude oil storage tank cleaning method with storage capacity of 28906.77 m ³ (250,000 barrels) was performed, the treated tank is floating roof, stored 26 ° API crude, is 61 m in diameter, 12, 8 m high, three lateral agitators and 4 lateral manholes, 3 of them located 48 cm from the floor and one at ground level. The tank had been maintenance free for 5 years.

The cleaning method was performed as follows:

The water contained in the tank is drained. The oily sludge was sampled and quantified through the roof of the tank, to do this some of the supports that support the roof were removed when it is in a maintenance position, and a sampling system was introduced by the support guide that allowed sucking sample of oily sludge

The content of oily sludge was calculated at 1156.27 m ³ (10,000 barrels), then 0.93 m ³ (8 barrels) of hydrocarbon-aromatic diluent (preferably ALC) and crude was added until having 5203.22 in the tank m ³ (45,000 barrels) of liquid. Stirring of the tank was started using the side stirrers in 30 ° position to the right. After approximately 24 hours of stirring the stirrers were turned off and follow-up sampling was performed, in order to determine the effect of the diluent and the stirrers on the homogenization and fluidization of oily sludge. Sampling results indicated decreased oily sludge content. The samples were analyzed for BS&W content and viscosity.

The position of agitators was varied by placing them forward and agitation of the tank was restarted. After 24 hours of stirring the agitators were turned off and follow-up sampling was performed. There was evidence of a decrease in the content of oily sludge. The position of agitators was varied by placing them 30 ° to the left. After approximately 24 hours of stirring the agitators were turned off and follow-up sampling was performed. The tank level is low by draining 3468.81 m ³ (30000 BIs) of crude oil to another tank.

4625.08 m ³ (40,000 BIs) of new crude oil were added to the tank, until a level of 3 meters equivalent to 6359.49 m ³ (55000 BIs) was obtained. This operation was performed with the agitators on, then the tank was left at rest for approximately 24 hours.

About 4393.83 m ³ (38000 BIs) were pumped from the tank into another tank. Water was added by the drainage of the tank, approximately 809.39 m ³ (7000 BIs), in order to make the oil overflow and be able to pump the largest amount of hydrocarbon into the other tank.

The oil continued to be pumped until the transfer pumps lost suction, the tank had a height of 86 cm of liquid equivalent to 1850.03 m ³ (16000 BIs).

Since at that height of liquid the tank did not allow the manholes to open to locate the transfer pump to the relief tank, the injected water was drained. Once the height of the liquid in the tank was less than 40 cm, manholes were opened, a pump was installed and the hydrocarbon continued to be sent to the relief tank. Venting was performed until permissible levels of organic vapors were obtained and the tank was entered, using self contained air equipment, to quantify the remaining oily sludge.

The presence of oily sludge was found towards the central part of the tank, the remaining oily sludge was characterized and fluidized by adding 0.48 m ³ (110 gallon) anionic dispersant additive and pressurized water through the fluidizing nozzles. This process took approximately 3 hours.

Pumping of the fluidized oily sludge and water to the relief tank began. For this, a pump was used that was installed through one of the manholes. The process was completed without the presence of oily sludge in the tank.

The follow-up sampling verified the effect of the diluent and the mixing in the homogenization of the oily sludge. The process used to fluidize the oily sludge was successful and allowed to recover 96% of the hydrocarbon present in the oily sludge.

Once the water that was sent to the relief tank has been drained, it remains in the specific cleaning specifications. The homogenization time of the oily sludge was 72 hours. The total cleaning time of the tank was 48 hours. In this time it is counted from the opening of the manholes until the delivery of the tank for sweeping with sawdust. In addition to the reduction of the operating times, the method of cleaning tanks claimed here allowed to generate revenue from the sale of the recovered hydrocarbons and not only expenses, as usually happens when the oily sludges of the storage tanks are cleaned.

From the examples mentioned above, the recovery of the hydrocarbon present in oily sludge is greater than 84%. It is also important to note that through this method there is an additional saving in resources and time due to the use of oily sludge biodegradation processes.

Claims

1. A method for the removal of oily sludge from hydrocarbon storage tanks, characterized in that it comprises the following steps:

2. The method according to claim 1, characterized in that in stage a) of diagnosis and definition of the detection process the characteristics of the tank are evaluated, to establish the best way to perform the fluidization process and the requirements or not of adjustments or the installation of additional systems to achieve fluidization.

3. The method according to claim 1, characterized in that in step b) of measurement and characterization of the oily sludges comprises the characterization of the oily sludges to determine: hydrocarbon content, water and solids in order to establish a process of hydrocarbon recovery after fluidization and / or treatment of the remaining sludge.

4. The method according to claim 3, characterized in that in step b) of measurement and characterization of oily sludges the requirement or not of heating and / or dosage of chemical is evaluated.

5. The method according to claim 1, characterized in that in step c) of adaptation or installation of the fluidization system is to establish the most suitable fluidization system according to the characteristics of the tank determined in step a).

6. The method according to claim 5, characterized in that if in stage a) the presence of mechanical agitators is established within the tank, in stage c) said mechanical agitators are adjusted by periodically varying their angle.

7. The method according to claim 6, characterized in that the mechanical stirrers are adjusted such that sweeping currents with different angles are generated.

8. The method according to claim 5, characterized in that if in step a) the need for a fluidization system is established, in step c) said system is mounted in at least one of the manholes of the tank.

9. The method according to claim 8, characterized in that the recirculation injection system is installed in all manholes of the tank.

10. The method according to claim 9, characterized in that for tanks with a capacity greater than 11,924 m ³ (100KBLS) fluidization systems must be installed in all manholes.

eleven . The method according to claim 8, characterized in that the fluidization system comprises: a manahole cover (1) adapted to receive on its external side a manifold (3), which is connected to a pump (4), which Take product from the tank and recirculate it through the manhole. Said manifold comprises three pipes connected to independent valves (2) and is coupled to the manhole cover (1) by means of flanges (5a, 5b). In addition, said manhole cover (1) contains on its inner side, one or more nozzle tubes (6), to which the nozzles (7) are coupled by means of flanges.

12. The method according to claim 11, characterized in that it consists of installing a suction line (7) with valve (8), which leaves the dispatch or receipt line of the tank, towards the recirculation pump (4) connects with the manifold (3).

13. The method according to claim 12, characterized in that the recirculation pump (4) has a capacity of 2.27 to 4.54 m ³ / minute (600 and 1200 GPM) and a minimum discharge pressure of 1, 38 MPa (200 Psi).

14. The method according to claim 11, characterized in that it comprises 3 nozzle tubes.

15. The method according to claim 5, characterized in that the fluidization system comprises a pump (4) and two flexible tubes for the recirculation of the contents of the tank.

16. The method according to claim 1, characterized in that step d) of

The fluidization comprises mechanical or hydraulic agitation.

17. The method according to claim 16, characterized in that in the case that the tank does not have mechanical agitators, the claimed method includes a preparation step that consists in extracting the hydrocarbon from the tank to a level below the manhole and removing the lid from the manhole.

18. The method according to claim 17, characterized in that it optionally comprises replacing said cover (1) with a duly modified one to receive both the manifold (3) and the nozzles (6).

19. The method according to claim 16, characterized in that for the treatment of oily sludges of light distillates, the fluidization stage c) comprises agitation only.

20. The method according to claim 19, characterized in that for the stirring step it is carried out with mechanical stirrers or with a recirculation system consisting of a pump and two flexible tubes.

21. The method according to claim 16, characterized in that for the treatment of oily sludges from light crudes (> 35 ° API), the hydrocarbons are removed from the tank, to the minimum level allowed by the tank specifications, diluent is added to the tank and agitation is carried out.

22. The method according to claim 21, characterized in that for the stirring step it is performed with mechanical agitators, with a recirculation system consisting of a pump and two flexible tubes or with the fluidization system defined in claim 1 1 .

23. The method according to claim 16, characterized in that for the treatment of oily sludges of semi-heavy crudes, between 18 and 28 ° API, it comprises the steps of the fluidization stage of the treatment of light crudes and repeats the entire sequence of steps one or more times, depending on the composition of the oiled sludge.

24. The method according to claim 23, characterized in that for the stirring step it is carried out with mechanical stirrers or with the fluidization system defined in claim 1 1.

25. The method according to claim 23, characterized in that, optionally, a pre-fluidization process is carried out in which the mechanical stirrers generate currents in different directions which facilitates the subsequent fluidization of the oily sludge.

26. The method according to claim 23, characterized in that for the stirring step it is carried out with mechanical stirrers or with the fluidization system defined in claim 1 1.

27. The method according to claims 23 to 26, characterized in that the diluent used is the same fluid stored in the tank

28. The method according to claim 16, characterized in that for the treatment of oily sludges of heavy crudes (° API <18), the fluidization is carried out with the tank open and diluent mixed with solvents is added.

29. The method according to claim 28, characterized in that the solvents are heated before incorporation into the tank to be treated and the diluent is recirculated the fluidization system defined in claim 15.

30. The method according to claims 28 and 29, characterized in that the diluent used will be the light hydrocarbon available in the area, preferably mixed with Light Cycle Oil (ALC) with other aromatic diluents.

31. The method according to claims 28 and 30, characterized in that if the oily sludges comprise paraffinic compounds, a mixture of paraffin dispersing additives and asphaltenes from refinery products are used, which are added in amounts of 100 to 800 ppm.

32. The method according to claim 16, characterized in that the minimum amount of diluent for fluidization is in the ratio of 1: 1 to 1: 5 of oily sludge to diluents.

33. The method according to claims 16 to 32, characterized in that the separation stage comprises filtration and decantation stages.

34. The method according to claim 33, characterized in that the decantation is carried out in a tank independent of the tank in which the cleaning of oily sludges is carried out.

35. The method according to claim 1, characterized in that the step e) of hydrocarbon recovery comprises a separation step that consists of leaving the tank at rest for a period between 5 and 24 hours, to separate the free water present in oily sludge and the tank is vacated to a minimum level.

36. The method according to claim 35, characterized in that the hydrocarbon without water is treated with known physicochemical methods, to finally recirculate it to the refining plant.

37. The method according to claim 35, characterized in that the remaining oily sludges are treated with a dispersion additive of an anionic nature, adding water and recirculating it under pressure using nozzles until fluidization of the remaining oily sludges, additionally, the water is separated by Decanting and drained for further treatment.