EP1281445A1 - Method of emptying and cleaning an oil tank - Google Patents

Abstract

The procedure consists of pumping most of the oil out of the storage tank (1), leaving a minimal residual quantity of oil (5) mixed with sediment (6). This is liquefied by the addition of an auxiliary liquid (9) which separates the oil from the sediment and allows them to be extracted separately from the tank, allowing its inner surfaces to be cleaned. The auxiliary liquid used for the procedure is water, which is not soluble in oil and has a specific gravity greater than that of the oil, causing the oil to rise to the surface. Before it is added to the tank the water is heated in an external circuit (14, 16) with a heat exchanger (17).

Description

The present invention relates to a method for cleaning and the emptying of a storage tank for petroleum.

More specifically, the invention relates to a method for the cleaning and emptying a storage tank of the type that it is used for the storage of crude oil in petroleum refineries.

Sometimes tanks have to be completely emptied storage of this type and clean them to remove sand sediments and rust particles that have deposited over time in the bottom of the reservoir storage and / or to be able for example to undertake required maintenance work.

To be able to clean a storage tank of this type, the content of the latter must first be emptied.

In this case, according to a known method, we transfer in a first stage a maximum quantity of crude oil from the storage tank to another storage tank; in doing so, we must ensure that a minimum amount of crude oil remains above the sediment layer so to prevent entrainment of a quantity of sediment during the decanting.

In a following step, we proceed, if necessary, to the liquefaction of the residual quantity which remains and which includes, next to a fraction of sediment, another large fraction of oil, for example 50%, by the addition of and, where appropriate, by mixing with a auxiliary liquid, and then the tank is removed from storage the mixture obtained in order to finally be able to clean the internal structures of the storage tank with for example an installation working under high pressure.

The rest of the mixture which consists of the quantity residual and by the auxiliary liquid is subjected, according to this known process, that is to say an evacuation integral for further processing towards a recognized waste treatment facility, i.e. further processing in the separation plant the refinery. A major drawback related to this way of to proceed nevertheless lies in the fact that it is very expensive given the high costs of transport, packaging and processing large quantities of products from waste obtained.

Another element, which also comes decisively into account for the high cost price of such known method lies in the fact that, for the activities in the storage tank, for example for installation of the aforementioned suction apparatus and others equipment, and for cleaning internal structures, maintenance personnel must be equipped with the devices required respiratory and protective clothing, being given the possible presence of vapors in the storage which are harmful when inhaled.

Wearing such equipment also complicates the execution of the works by negatively influencing the labor output so that the cost of labor is high.

It is also known to sometimes use diesel as a auxiliary liquid to dilute the residual amount of tank and get a liquid mixture.

The additional disadvantage of using diesel nevertheless lies in the fact that vapors very easily flammable forms in the storage tank, so that the risk of fire or even the risk of explosion during of the whole procedure concerning the elimination of the quantity residual, increase dramatically.

In other known applications of the aforementioned process, it is first splits the residual quantity, which has a some consistency, in pieces by spraying using of a device working under high pressure to obtain a mass capable of being aspirated.

The downside to this way of working is the that to operate this device, maintenance personnel must work inside the storage tank for a relatively long period of time by being equipped with breathing apparatus and protective clothing necessary protection, so the cost of labor is also increasing significantly.

The object of the present invention is to provide a solution for the aforementioned drawbacks, as well as others.

To this end, the invention contemplates a process for emptying and cleaning a storage tank for petroleum, consisting of the maximum pumping of oil up to a minimum residual quantity remaining consisting of a fraction of petroleum and a fraction of sediment, followed by liquefying the residual amount by adding a auxiliary liquid that has been heated, followed by disposal of the mixture obtained, and finally followed by the subsequent cleaning internal structures of the storage tank, the characteristic being that the auxiliary liquid that we use after mixing the residual amount results a separation of the petroleum fraction, so that this fraction of oil, which represents a significant part of the residual amount, may be subjected to separation at for recovery purposes.

More specifically, the auxiliary liquid can be mixed with the residual amount by shaking.

Mixers can be used for this purpose. incorporated in most storage tanks, so you don't need devices additional and so that we can avoid the decomposition into pieces of the residual quantity by spraying using a device working under high pressure, which represents a work that is linked to a workforce important.

In particular, in accordance with the invention, a auxiliary liquid which is not soluble in the fraction of petroleum and whose specific gravity is greater than that of the petroleum fraction, so that after mixing auxiliary liquid and the residual quantity, the fraction of oil is subjected to vertical flotation if although the petroleum fraction can be recovered as useful oil, in a relatively simple way.

The fraction of sediment that remains and the auxiliary liquid added are then moved away from the storage tank, submitted to decantation and carried away by further treatment.

Therefore, the maximum separation of waste and recyclable product takes place at source, unlike known methods.

Consequently, one must transport and treat less large quantities of waste products, so that can also save money on these items.

In addition, the skimming of the oil fraction can take place. automatically, for example by making use of what one calls a "scum container", which results in a significant reduction in the number of working hours for the continued emptying of the storage tank, resulting in to a dramatic reduction in the cost of workforce.

More specifically, water represents an auxiliary liquid particularly suitable for carrying out the process according to the invention. The use of water offers advantage, the fact that it is available in large quantities in refineries and the fact that in addition it is relatively inexpensive. In addition, water does not present not the disadvantages associated with diesel in the field of safety and water is not a factor additional pollution for the environment.

More specifically, we use hot water to obtain maximum mixing and maximum separation of the fraction of oil, so we also get a quantity lower residual noxious oil after recovery of the petroleum fraction. Consequently, the further treatment of the remaining sediment fraction and water that has been added, will be cheaper, being since lesser quantities should be processed and that in addition lower quantities of hydrocarbons must be subjected to distillation. The lower hydrocarbon content ensures that the maintenance staff should use less time the breathing apparatus, so that we improve considerably the working comfort.

According to a particular embodiment, water is circulated from the storage tank via an external heating circuit and is recovered after reheating with steam.

Therefore, unlike a number of known applications, no water should be supplied continuously and after recovery of the fraction of oil, we will also get a lower amount of waste products to be treated, so that the overall operation emptying the storage tank is more economical.

In addition, steam is mostly readily available in refineries, so there is no need or additional heating element, or supply extra energy.

The invention also relates to a device which is particularly suitable for emptying and cleaning a petroleum storage tank, in accordance with process indicated above, the characteristic of which resides in the fact that this device is constituted by means for add an auxiliary liquid to the residual amount of a storage tank, preferably in the form of a addition of water; by means for heating the liquid auxiliary, more specifically in the form of one or several hot water bottles which are mounted in the food of the water ; by mixing means intended to mix the auxiliary liquid to the residual amount, which are constituted in particular by mixing devices which are present in the storage tank; by means intended to move the upper layer away from the contents of the tank and separate the oil fraction from it preferably by transferring this layer into what we calls a "scum container"; and finally by means to remove the remaining mixture from the fraction of sediment and auxiliary liquid outside the storage tank, preferably by making use of vacuum tankers.

In order to better indicate the characteristics of The invention is described below, by way of example, without any limiting character, a preferred device which allows the setting implementing the method according to the invention, with reference to the attached figure which represents this device in a way schematic.

In this figure, we represent oil tank 1 and 2, for example from an oil refinery, which are respectively fitted with a float 3 which closes so sealing the upper side of such a storage tank 1 - 2.

The first storage tank 1 represents the tank which must be emptied and cleaned, while the second tank storage 2 represents a storage tank that acts storage tank to store the recovered oil at from the first storage tank 1.

After emptying the storage tank 1 to maximum using a pumping circuit 4, the storage tank 1 still includes a residual amount consisting of petroleum fraction 5 and by a residual fraction 6, the two fractions in question to be removed from the container using a device 7 according to the invention.

The device 7 consists of elements 8 intended for add an auxiliary liquid 9, in particular water, to the residual quantity of a storage tank 1; by means 10 for heating the auxiliary liquid 9; through mixing means 11 intended to mix the liquid auxiliary 9 to the residual quantity; by means 12 intended to move the upper layer away from the contents of the tank and separate the oil fraction 5 therefrom; by suction means 13 for removing the remaining mixture from the fraction of sediment 6 and auxiliary liquid 9 outside the storage tank 1.

The means 8 intended to convey the auxiliary liquid 9, in particular water to the tank, are constituted by a circuit 14 of nozzles and / or flexible pipes which connect the storage tank 1 to the water distribution network 15 of the oil refinery.

In this circuit 14, the aforementioned means 10 are present which heat the auxiliary liquid 9.

These means 10 preferably consist of hot water bottles 16 in which the auxiliary liquid circulates 9 via a heat exchanger 17 which is connected to the steam facility 18 of the petroleum refinery.

Preferably, the mixing means 11 for mixing the auxiliary liquid 9 to the residual amount of the storage 1 are formed by mixing devices 19 which are present most of the time in the form of mixers in storage tanks. In the case where mixers of this type are not present in the storage tank, you can install separate mixers or other mixing devices in the storage tank 1.

The means 12 for moving the upper layer away from the contents of the tank and to separate the oil fraction 5, are constituted by a pump 20 including the suction duct 21 opens into the storage tank 1 and which is connected to using a pressure line 22, to a first compartment 23 of a so-called skimming container 24 in which the oil is separated from the liquid that has been transported, so that this oil is collected in a second compartment 25 of this skimming container.

The first compartment 23 of the skimming container is connected, in its lower part, using a pumping circuit 26 comprising a pressure line 27, at the connection water supply 28 from the hot water bottle 16.

This pumping circuit 26, like the connection to the aforementioned water supply 28, are fitted with taps connection 29 - 30 which allow alternating connection one of the two circuits 27 - 28 to the hot water bottle 16, the pipe under pressure 27 which can, if necessary, be connected, via an exhaust duct 31 and a shut-off valve 32 to a water purification tank 33 of the refinery of oil.

A pumping installation 34, which opens into the container storage 2, is connected to the second compartment 25 of the skimming container 24.

The aforementioned suction means 13 intended to eliminate the fraction of sediment 6 which remains, as well as the liquid auxiliary 9 outside the storage container 1, are constituted for example by one or more 35 vacuum tankers which are fitted with a suction hose 36, the orifice of which can be connected to the base of the tank storage 1.

How the tank empties and cleans storage 1 using the aforementioned device 7 is relatively simple and is as shown below.

Via pumping circuit 4, first transfer to the maximum the oil that is present in storage tank 1 in the second operational storage tank 2.

Next, water 9 is conveyed from the distribution of water 15 through hot water bottles 16 in which water is first heated before being routed via the water circuit 14 in the storage tank 1.

When the level of the liquid mixture is high enough above the mixing devices 19, the water supply to from the water distribution network 15 is stopped in closing the shut-off valve 30 fully.

The water supplied 9 is mixed with the petroleum fraction remaining 5 and with the sediment fraction 6 via the mixing equipment service 18.

Since the oil present is lighter than water, it is subjected to a vertical flotation before being transferred using the pumping installation 20 in direction of the first compartment 23 of the skimming container 24.

In this case, water is inevitably entrained by pumping. In this first compartment 23, the oil is subject to further separation from water via the vertical flotation of lighter oil, so that the oil that has been separated flows overflow into the second compartment 25 and from there is pumped using from the pumping installation 34, towards the second oil storage tank 2.

The water which collects at the base of the first compartment 23 of the oil separator 24 and ideas after opening the tap 29, via pumping circuit 26, through the hot water bottles 16 and is then reinserted, via circuit 14, in storage tank 1 to be re-mixed with the residual contents of the tank.

When the oil fraction 5 has been recovered in a sufficient measure, we end what is called skimming and residual contents of the tank, which is still mainly consisting of the sediment fraction 6 and the water 9 that has been added, is pumped in full or is vacuumed using vacuum tankers 35 out of the storage tank 1, and thus subjected to decantation natural, the two components, in a more or less separate state, also being issued for further processing.

Following this step, the internal structure of the storage 1 may still be subject to further cleaning depth using for example a working installation under high pressure.

The wastewater obtained in this case can also be vacuumed using vacuum tankers and thus be evacuated or, if necessary, can also be transferred, via the pumping installation 20, towards the skimming vessel, from which they may be subsequently evacuated by pumping using the pumping circuit 26 via the conduit drain 31 towards the water purification basin 33.

In the event that the aforementioned installations 16, 17 and 18 do not are not present near storage tank 1 or are not available, we can of course provide autonomous means to supply water and add it to the tank, for heating water and mixing liquids in the storage tank 1.

The present invention is in no way limited to the embodiment described by way of example and shown in the appended figure, but on the contrary, a method and a device of this type can be implemented in accordance to different variants without departing from the scope of the invention.

Claims (12)

Method for emptying and cleaning a storage tank for petroleum, consisting of the maximum pumping of petroleum to a minimum residual quantity consisting of a petroleum fraction (5) and a sediment fraction (6), followed by the liquefaction of the residual amount by addition of an auxiliary liquid (9), followed by the elimination of the mixture obtained, and finally followed by the subsequent cleaning of the internal structures of the storage tank (1), characterized in that the auxiliary liquid (9), after mixing with the residual amount, causes separation of the petroleum fraction (5) and in that the petroleum fraction (5) and the remaining mixture are removed separately from the storage tank (1 ). Method according to claim 1, characterized in that the mixing of the auxiliary liquid (9) with the residual amount takes place by stirring. Method according to claim 1 or 2, characterized in that the auxiliary liquid (9) is not soluble in petroleum and has a specific weight greater than that of the petroleum fraction (5) so that the petroleum fraction (5) is subjected to vertical flotation. Method according to any one of the preceding claims, characterized in that the auxiliary liquid 9 is water. Method according to claim 4, characterized in that the auxiliary liquid 9 is hot water. Method according to claim 5, characterized in that the water is circulated and is heated via an external heating circuit (14 - 16). Method according to claim 6, characterized in that the water is heated in the external heating circuit (14 - 16) using a heat exchanger (15). Process according to any one of Claims 3 to 7, characterized in that the fraction of petroleum (5) subjected to vertical flotation is recovered on site outside the storage tank (1) as petroleum usable via skimming of this petroleum fraction (5). Method according to any one of Claims 3 to 8, characterized in that the mixture coming from the storage tank (1) is transferred to a scum container (24) to obtain a separation of the petroleum fraction (5) which is recovered as usable petroleum, the petroleum fraction (9), after heating in the above-mentioned external heating circuit (14 - 16), being added to the storage tank. Method according to claim 8 or 9, characterized in that the remaining fraction of sediment (6) and the water (9) from the storage tank (1) are removed and taken away for further treatment. Method according to any one of the preceding claims, characterized in that , after the storage tank 1 has been emptied, the last remains are eliminated by pressure cleaning and in that the rinsing water is sucked up and removed for the purpose of treatment. Device for emptying and cleaning a petroleum storage tank according to the method according to any one of the preceding claims, characterized in that the said device consists of means (8) for adding an auxiliary liquid (9) the residual amount of a storage tank (1), preferably in the form of an addition of water; by means (10) for heating the auxiliary liquid (9), more specifically in the form of one or more hot water bottles (16) which are mounted in the water supply; by mixing means (11) for mixing the auxiliary liquid (9) with the residual quantity, which are constituted in particular by mixing devices (19) which are present in the storage tank (1); by means (12) intended to move the upper layer away from the contents of the tank and to separate the petroleum fraction (5) therefrom, preferably by transferring this layer into a so-called scum container (24) ; and by suction means (13) to move the remaining mixture of the sediment fraction (6) and the auxiliary liquid (9) out of the storage tank (1), preferably by making use of vacuum tankers ( 35).

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