Method and apparatus for the treatment of water polluted by hydrocarbons

Abstract

Method and apparatus for the purification of water polluted by hydrocarbons and / or mineral oils, in particular bilge water, which can also be carried out on board a vessel. The method comprises a series of treatment cycles of the water with a hydrophobic adsorbent material and regeneration of the adsorbent material with a series of desorption cycles of the hydrocarbons and oils by flushing with a liquefied gas. The hydrocarbons and oils are separated from the liquefied gas by means of evaporation of the liquefied gas, which is then condensed and made available in liquefied form for new regeneration cycles of the adsorbent material.

Description

[0001] METHOD AND APPARATUS FOR THE TREATMENT OF WATER POLLUTED BY HYDROCARBONS

[0002] DESCRIPTION

[0003] The present invention relates to a method and an apparatus for the treatment of water polluted by hydrocarbons, mineral oils and the like.

[0004] Background of the invention

[0005] There are numerous situations of water pollution by hydrocarbons, both in the industrial sector, where hydrocarbons and mineral oils used in production processes come into contact with process water, and in the civil sector, as a consequence of accidental leaks or spills of hydrocarbons and / or oils in water intended for civil uses, or more simply of washing water of surfaces polluted by hydrocarbons and oils.

[0006] The reuse of such water in an industrial sector, or its introduction into the urban mains or watercourses, or the purification of polluted marine surfaces, therefore, entails the abatement of the polluting load, in compliance with current legislation.

[0007] An example of water polluted by hydrocarbons, mineral oils and the like consists of run-off water from port areas, such as docks and surrounding areas. These areas are subject to the transit of vehicles which bring the loss of fuel, lubricants and the like, which are then washed away by rainwater or water used for washing such areas. This water polluted by hydrocarbons, mineral oils and the like is collected in tanks or reservoirs and must be treated before being released into the environment.

[0008] Another example of water polluted by hydrocarbons is the drainage water of the sludge produced in the extraction of oil from oil wells. In fact, this water contains hydrocarbons which must be treated before being released into the environment. In the case of offshore wells, in fact, the water is released into the sea.

[0009] A particular case of water polluted by hydrocarbons is represented by bilge water.

[0010] The bilge is a part located in the lower part of the hull of a vessel, intended to collect water infiltrations and the drainage of various liquids, such as lubricants, engine oils, residual washing water and other waste liquids, also deriving from maintenance activities regularly carried out on ships.

[0011] Since the current regulations prohibit the discharge of polluting liquids into the sea, the water collected in the bilge, polluted with hydrocarbons and the like, must be discharged in ports through special pipes and pumps connected to the sewer system, or treated on board so as to reduce the polluting load below established limits. Therefore, bilge water treatment systems are known which can be placed on board ships, in particular systems for the separation of hydrocarbon residues and mineral oils so as to reduce the content thereof to a level which allows the bilge water to be discharged into the sea without harming the marine environment.

[0012] US 2009 / 0090473 Al describes a complex system for the treatment of bilge water which comprises the evaporation of such water.

[0013] WO 2018 / 0177795 Al discloses a treatment and regeneration system for extracting organic solutes from water by using a filter media which is then regenerated by a displacement fluid. The organic solute is then separated from the displacement fluid, which can be re-used. Although mentioned among the possible filter media, activated carbon is described as difficult to regenerate and reuse since it requires very high treatment temperatures (T ~ 900°C), or it must be discarded and replaced with fresh material. Backwashing, or backflushing the filter media with a solvent, is mentioned to regenerate granulated filter media other than active carbon.

[0014] Smathers C. et al, “Removing Dispersed and Dissolved Hydrocarbons from Water Using Adsoprtion Media Systems with Multiple Regeneration Processes”; Society of Petroleum Engineers - 192355 - MS; 23 April 2018, disclose removing hydrocarbon contaminants from water by using a material designated as “Osorb”.

[0015] The need is therefore felt to provide a system for the treatment of water polluted by hydrocarbons and lubricating oils, which allows the drawbacks of the known systems to be eliminated or reduced.

[0016] The object of the present invention is therefore to provide a method and an apparatus for the treatment of water polluted by hydrocarbons and lubricating oils which represent an improvement on the systems currently available, in particular which is effective in removing hydrocarbon residues and mineral oils from bilge water, and can be made in sufficiently compact dimensions, so that it can be placed and managed on board vessels which are not particularly large, as well as on board off-shore platforms.

[0017] Summary of the invention

[0018] An aspect of the invention consists of a method for the treating water polluted by hydrocarbons and / or mineral oils comprising the following steps: a) flowing said water polluted by hydrocarbons and / or oils through a hydrophobic material having adsorbent capacity of said hydrocarbons and / or oils, thereby obtaining the adsorption of said hydrocarbons and / or oils in said adsorbent material; b) at the end of said step a), flowing a liquefied gas having solvent capacity for said hydrocarbons and / or oils through said hydrophobic material, thereby obtaining the desorption of said hydrocarbons and oils from said adsorbent material; c) transferring said liquefied gas containing said hydrocarbons and / or oils into an evaporation chamber in which said liquefied gas is evaporated, thereby releasing said hydrocarbons and oils; and d) sucking said evaporated gas from said evaporation chamber, compressing it and cooling it so as to condense it and obtain said liquefied gas; characterized in that said liquefied gas of said step b) is a halogenated hydrocarbon belonging to the class of hydrofluoroolefins fed at a temperature of from 30 to 50°C and at a pressure of from 5 to 10 bar.

[0019] Another aspect of the invention consists of an apparatus for carrying out the treatment method of water polluted by hydrocarbons and / or oils as defined above, comprising:

[0020] A. a treatment chamber suitable for containing an absorption material of hydrocarbons and mineral oils, said chamber being hydraulically connected to a storage tank of said water polluted by hydrocarbons and / or oils;

[0021] B. an evaporation chamber for a solvent liquid, hydraulically connected to said treatment chamber;

[0022] C. means for compression, cooling and condensation of a gas, connected to said evaporation chamber and to said treatment chamber;

[0023] D. a storage tank for a liquefied gas, hydraulically connected to said compression, cooling and condensation means, said tank being hydraulically connected to said treatment chamber; and

[0024] E. a series of valves for managing the flow of said water and said liquefied gas.

[0025] According to an embodiment of the invention, the method and the apparatus for treating water polluted by hydrocarbons and / or mineral oils are particularly advantageous in the treatment of bilge water.

[0026] In such an embodiment of the apparatus of the invention, the treatment chamber suitable for containing the hydrocarbon and / or mineral oil absorption material is hydraulically connected to a storage tank for said water polluted by hydrocarbons and / or oils, which can directly be the bilge of a vessel.

[0027] Brief description of the figure

[0028] The invention is described in detail below, in which: Fig. 1 schematically depicts a non-limiting embodiment of both the method according to the invention and an apparatus for carrying out such method; and

[0029] Fig. 2 shows the shape of the adsorbent material according to an embodiment of the invention.

[0030] Detailed description of the invention

[0031] In its most general aspect, the present invention relates to a method and an apparatus for treating water polluted by hydrocarbons and / or mineral oils and the like.

[0032] A particular case of water which can be advantageously treated with the method and the apparatus of the invention consists of bilge water. Therefore, in the following description, specific reference is made to the treatment of bilge water containing hydrocarbons, oils, greases and other hydrophobic organic pollutants, so as to purify such water and allow the discharge thereof into the sea, following analysis so as to verify that the residual content of pollutants complies with current regulations. Furthermore, the hydrocarbons and oils separated from the water can be advantageously reused as fuel in marine engines, obviously after carrying out the appropriate compatibility checks.

[0033] However, the treatment of bilge water is merely a non-limiting example of the type of water which can be treated with the method and apparatus according to the invention.

[0034] In the nautical field, the term "bilge water" refers to water consisting essentially of mixtures of water and oil resulting from leaks from equipment (machinery and pipes) on board ships, including those used to manage fuels and lubricants, including the purification thereof.

[0035] In the present description, the term “vessel” means a vessel of any size, as long as it has sufficient and suitable space to house the apparatus for carrying out the treatment method.

[0036] The method of the invention comprises a series of steps which can be repeated cyclically until the minimum pollutant content made possible by the method itself is reached. This allows the use of an apparatus of relatively compact dimensions, such that it can be housed on board the ship, even if the same apparatus can advantageously be placed on land, for example in the port area.

[0037] Step a)

[0038] In a first step a) of the method according to the invention, the bilge water is taken either directly from the bilge of the vessel or from a bilge water storage tank provided on board the vessel itself, collectively designated with 4 in Fig. 1, and sent to a treatment chamber 6.

[0039] According to the present invention, the term “treatment chamber” designates a containment space for the adsorbent hydrophobic material which can consist of either a single chamber or a plurality of chambers connected in series or in parallel, all containing the adsorbent hydrophobic material.

[0040] A total volume Qi of the treatment chamber; either a single chamber or a plurality of interconnected chambers, is filled with the adsorbent hydrophobic material.

[0041] In the treatment chamber, the bilge water is flowed through a hydrophobic material 10 having adsorbent capacity of hydrocarbons and oils, which are then absorbed in such material. Due to the hydrophobic nature of the adsorbent material, water is not absorbed but flows through it and is released with less or free of hydrocarbon and oil pollutants.

[0042] In an embodiment of the treatment method, the flow of bilge water through the adsorbent material is carried out continuously with a series of passages of the same water, which, after being discharged from the treatment chamber 6, is recirculated in the same chamber and on the same adsorbent material 10, until the desired purification level is obtained, for example until a residual content of hydrocarbons and oils of no greater than 5 ppm is obtained.

[0043] The water recirculation is obtained, for example, with a pump El inserted in a recirculation circuit 7 provided with three-way valves VI, V2 and V3.

[0044] In an embodiment, the hydrophobic adsorbent material consists of expanded granules obtained from siliceous rocks and treated with hydrophobic polymers, so as to retain the capacity to absorb hydrocarbons and mineral oils typical of siliceous rocks but - thanks to the treatment with hydrophobic polymers - acquire a hydrophobic character and thus become water-repellent. Therefore, water flows through the material 10 without being absorbed. These characteristics make the material 10 suitable for use in step a) of the method of the invention.

[0045] An adsorbent material advantageously used for this purpose is produced by the company Airbank S.r.l. and marketed under the brand name H2OIL SORB.

[0046] In another embodiment, the hydrophobic adsorbent material described above is advantageously mixed with activated carbon.

[0047] In a further embodiment, the adsorbent material is activated carbon.

[0048] Step b)

[0049] In the second step b), a liquefied gas is fed into the treatment chamber 6 and flowed through the hydrophobic material 10, which has absorbed the hydrocarbons and oils. The liquefied gas has a solvent capacity for hydrocarbons and oils, which are therefore desorbed from the material 10 also due to the stripping action exerted by the flow of the liquefied gas, and dissolved in the liquefied gas. The amount of liquefied gas flowed through the hydrophobic material that fills the volume Qi of the treatment chamber is defined by the volume Q2. Both volumes Qi and Q2 are expressed as Litres.

[0050] According to an aspect of the present invention, the ratio Q2 / Q1 varies from 4 to 3, preferably from 3.8 to 3.2, and is preferably about 3.5. The liquefied gas is a halogenated hydrocarbon belonging to the hydrofluoroolefin (HFO) class, normally used in refrigeration, which at ambient temperature and pressure, is in gaseous form. Preferably, the HFO is in gaseous form even in the temperature range from -5 to -15°C and pressure from 1 to 4 bar.

[0051] The HFO is introduced in the treatment chamber 6 in liquefied form at a temperature from 30 to 50°C, preferably from 35 to 40°C, and at a pressure from 5 to 10 bar, preferably 6 to 8 bar.

[0052] In an embodiment of the method of the invention, the HFO is trans-l,3,3,3-tetrafluoropropene, commonly referred to by the acronym ASHRAE R1234ze.

[0053] In another embodiment of the method of the invention, the HFO is trans 2, 3,3,3- tetrafluoropropene, commonly referred to by the acronym HFO-1234yf, having the molecular formula CH2=CFCF3.

[0054] At the end of step b), the adsorbent material is regenerated and can be reused for a new bilge water treatment cycle.

[0055] In one embodiment of the method of the invention, the adsorbent material 10 is packed in the treatment chamber with a cylindrical shape, as shown in Fig. 2. Preferably, also the treatment chamber, or each single chamber if there are more than one, has a cylindrical shape.

[0056] According to a preferred aspect, as shown in Fig. 2, the adsorbent material of cylindrical shape has an axial inner channel 30 through which the liquefied hydrofluoroolefin is fed, so that it flows from the inner channel through the adsorbent material to the outside of the adsorbent material. It has been surprisingly found that this flow path allows minimizing the amount of liquefied gas required for dissolving the adsorbed hydrocarbons and oils.

[0057] Step c)

[0058] In the third step c) the liquefied gas containing hydrocarbons and oils is transferred to an evaporation chamber 3, where the liquefied gas is evaporated, releasing the hydrocarbons and oils dissolved or entrained therein.

[0059] The evaporation is obtained by expanding the liquefied gas due to the suction exerted by a compressor 8 placed downstream of the evaporation chamber 3. The hydrocarbons collect in the evaporation chamber 3, from which they can subsequently be withdrawn.

[0060] The temperature of the gas in the evaporation chamber is preferably from -5 to - 15°C, preferably from -2 to -9°C. The pressure in the evaporation chamber is preferably from 1 to 4 bar, preferably from 1.5 to 3.5 bar.

[0061] Step d)

[0062] In step d) the gas evaporated in the evaporation chamber 3 is sucked and transferred to a condenser 5. The suction is performed by connecting the evaporation chamber 3 to the suction side of a compressor 8. The compression and cooling of the gas cause the condensation thereof, resulting in liquefied gas.

[0063] At the end of step d) it is therefore possible to reuse the liquefied gas for the regeneration of the adsorbent material after a new treatment of other bilge water polluted by hydrocarbons and oils. Steps a), b), c) and d) are repeated for a number of cycles necessary to ensure maximum efficiency in removing hydrocarbons and oils from the bilge water. The method thus allows to obtain bilge water, which is no longer polluted, and thus reusable on board the vessel, for example as washing water, and to obtain hydrocarbons and oils which can also be used on board the vessel, for example as combustible or fuel, depending on their characteristics. The apparatus according to the invention comprises a bilge water treatment chamber 6, suitable for containing a material 10 for absorbing hydrocarbons and mineral oil, hydraulically connected to the vessel's bilge or to a bilge water storage tank, collectively designated with 4 in Fig. 1, for example by means of a pipeline 19. An electric pump El is present in a recycling line 7 connected to the pipeline 19, so as to allow the treated bilge water, taken from the bottom of the chamber 6, to be pumped to the inlet of the chamber itself and flowed over the adsorbent material 10 again.

[0064] A series of three-way solenoid valves VI, V2, V3, V4 allows to manage the recycling circuit and the discharge of the liquefied gas from the chamber 6.

[0065] The treatment chamber 6 is connected to the bottom of an evaporation chamber 3 by means of a pipeline 21. As described above, the evaporation chamber is suitable for allowing the evaporation of a liquefied gas thanks to the connection to the suction side of a compressor 8 by means of a pipeline 23. Downstream of the evaporation chamber 3 and upstream of the compressor 8, there is a filter 17 suitable for retaining any hydrocarbon and oil residues still present in the gas exiting from the evaporation chamber.

[0066] Downstream of the compressor 8, a condenser 5 is placed which cools the fluid and condenses it, restoring the liquefied gas introduced into the treatment chamber 6.

[0067] The apparatus further comprises a liquefied gas storage tank 2, hydraulically connected to the compressor 8. A three-way valve 9 allows the liquefied gas to be fed either to the tank 2 or directly to the treatment chamber 6, by means of a pipeline 12 provided with a valve VI. The liquefied gas tank 2 is connected to the treatment chamber 6 by means of a line 13 provided with a valve 15.

[0068] The treatment chamber 6 is connected to a vacuum pump 25, for example a two-stage rotary oil pump, whose function is to evacuate the non-condensable gases, essentially consisting of oxygen, nitrogen and water vapour, from the liquefied gas inlet chamber 6, so as to prevent the latter from being contaminated.

[0069] A programmable logic controller PLC allows to manage the various components of the system in an automated manner.

[0070] As regards the treatment chamber 6, in an embodiment not illustrated, it can consist of several chambers connected in series or in parallel, each containing the adsorbent material.

[0071] The method and apparatus according to the invention therefore involve the alternation of treatment cycles of polluted bilge water using an adsorbent material with regeneration cycles of the adsorbent material by means of suitable halogenated hydrocarbons, in particular those belonging to the class of hydrofluoroolefins (HFO).

[0072] Furthermore, the evaporation and condensation cycles of the liquefied gas allow the hydrocarbons and oils to be obtained for possible reuse.

[0073] Hydrofluoroolefins are currently used as refrigerants and have the following advantages:

[0074] 1) They are not toxic or harmful;

[0075] 2) They have low environmental impact (ODP = 0; GWP = 7);

[0076] 3) Being gaseous at room temperature and pressure, they can be easily removed from the solid matrix consisting of the hydrophobic adsorbent material and from the pollutants recovered at the end of the treatment (oils and hydrocarbons).

[0077] 4) They are nontoxic and non-flammable or mildly flammable.

[0078] 5) The quantity of hydrofluoroolefins used for the regeneration of the adsorbent is very limited, and is of the same order of magnitude as the quantity of adsorbent material used, whereby the subsequent recovery of the fluid at the end of the treatment process is facilitated, also appropriately exploiting the transition from liquid to gas and vice versa.

[0079] As it appears from step b) above, it has been found that the method according to the invention allows regenerating the adsorbent material at a temperature of from 30 to 50°C and at a pressure of from 5 to 10 bar. These are relatively low values of temperature and pressure, so that the method is both effective and efficient from a cost perspective.

[0080] Furthermore, the amount Q2 of liquefied gas used to regenerate the volume Qi of adsorbent material is limited, as the ratio Q2 / Q1 is no more than 4. The aforesaid characteristics allow the method to be implemented in a relatively compact apparatus, therefore suitable for being housed on board a vessel. The possibility of making a relatively compact apparatus is also advantageous for installation in port areas, where the available space is limited, or in any other suitable site, or on off-shore platforms.

Claims

CLAIMS1. Method of treatment of water polluted by hydrocarbons and / or mineral oils for the removal of said hydrocarbons and / or mineral oils, characterized by comprising the following steps: a) flowing said water through a hydrophobic adsorbent material having adsorbent capacity of said hydrocarbons and / or oils, thereby obtaining the absorption of said hydrocarbons and / or oils in said adsorbent material; b) at the end of said step a) flowing a liquefied gas having solvent capacity for said hydrocarbons and / or oils through said hydrophobic material, thereby obtaining the desorption of said hydrocarbons and oils from said adsorbent material; c) transferring said liquefied gas containing said hydrocarbons and / or oils into an evaporation chamber in which said liquefied gas is evaporated, thereby releasing said hydrocarbons and oils; and d) sucking said evaporated gas from said evaporation chamber, compressing it and cooling it so as to condense it and regenerate said liquefied gas; characterized in that said liquefied gas of said step b) is a halogenated hydrocarbon belonging to the class of hydrofluoroolefins fed at a temperature of from 30 to 50°C and at a pressure of from 5 to 10 bar.

2. Method according to claim 1, characterized in that said hydrophobic adsorbent material consists of expanded granules obtained from siliceous rocks and treated with hydrophobic polymers.

3. Method according to one or more of the previous claims, characterized in that said liquefied gas of said step b) is a halogenated hydrocarbon belonging to the class of hydrofluoroolefins (HFO) selected from trans-l,3,3,3-tetrafluoropropene and trans- 2,3 ,3 ,3-tetrafluoropropene .

4. Method according to one or more of the previous claims, characterized in that said liquefied gas of said step b) is in gaseous form in the temperature range from -5 to -15°C and pressure from 1 to 4 bar.

5. Method according to claim 4, characterized in that said liquefied gas of said step b) is in liquefied form at a temperature of from 35 to 40°C, and at a pressure of from 6 to 8 bar.

6. Method according to one or more of the previous claims, characterized in that said liquefied gas is evaporated in said evaporation chamber because of the suction exerted by a compressor placed downstream of said evaporation chamber.

7. Method according to one or more of the previous claims, characterized in that in said step c) the temperature of the gas in the evaporation chamber is from -5 to -15°C, preferably from -2 to -9°C.

8. Method according to one or more of the previous claims, characterized in that in said step c) the pressure in the evaporation chamber is from 1 to 4 bar, preferably from 1.5 to 3.5 bar.

9. Method according to any claims 1 and 3-8, characterized in that said adsorbent material is activated carbon.

10. Method according to any claims 1-9, characterized in that said adsorbent material is contained in a treatment chamber having a cylindrical shape and that the adsorbent material has also a cylindrical shape, and is formed with an axial inner channel.

11. Method according to claim 10, characterized in that said liquefied gas belonging to the class of the hydrofluoroolefins is fed into said axial inner channel and flows from inside to the outside of the adsorbent material.

12. Method according to any claims 1-11, wherein the adsorbent material occupies a volume Qi of said treatment chamber and the liquefied gas flowed through the adsorbent material in said step b) has a volume Q2, characterized in that the ratio Q2 / Q1 varies from 4 to 3, preferably from 3.8 to 3.2, and more preferably is about 3.5.

13. Apparatus for carrying out a method of treating water polluted by hydrocarbons and / or oils, including:A. a treatment chamber (6) suitable for containing an absorption material (10) of hydrocarbons and mineral oils, said chamber being hydraulically connected to a storage tank (4) of said water polluted by hydrocarbons and / or oils;B. an evaporation chamber (3) for a solvent liquid, hydraulically connected to said treatment chamber (6);C. means for compression (8), cooling and condensation (5) of a gas, connected to said evaporation chamber (3) and to said treatment chamber (6);D. a storage tank (2) for a liquefied gas, hydraulically connected to said compression (8), cooling and condensation means (5), said tank (2) being hydraulically connected to said treatment chamber (6); AndE. a series of valves for managing the flow of said water and said liquefied gas.

14. Apparatus according to claim 13, characterized by the fact of comprising a recycling circuit (7) of said water, comprising an electric pump (El) and a series of three-way solenoid valves VI, V2, V3, V4 for the management of bilge water recycling.

15. Apparatus according to claim 13 or 14, characterized by the fact that said treatment chamber (6) is connected to a vacuum pump (25), for the evacuation of non-condensable gases.

16. Apparatus according to one or more of claims 13 - 15, characterized in that said storage tank (4) is the bilge of a boat.

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