Method and system for purifying polluted marine exhaust gas purification liquid

Abstract

The invention provides a method (100) for purifying a contaminated purification liquid, wherein the contaminated purification liquid is a contaminated marine exhaust gas purification liquid. The method comprises the following steps: a) providing (101) the contaminated purification liquid; b) adding (102) a solid porous adsorbent to the contaminated purge liquor; c) allowing (103) the adsorbent to react with contaminants in the contaminated purge liquor; d) separating (104) the contaminated purge liquid in a centrifuge; and e) discharging (105) a clean liquid phase and a contaminant phase from the centrifuge. The invention further provides a system for purifying the polluted purification liquid, wherein the polluted purification liquid is ship waste gas purification liquid.

Description

Technical Field

[0001] The present invention relates to the field of exhaust gas purification systems and methods. Background Art

[0002] Today's shipping industry strives to reduce harmful emissions, such as those resulting from fuel combustion in engines, to minimize negative environmental impacts and meet current and upcoming emissions regulations.

[0003] Part of this is reducing nitrogen oxides (NO X ) emissions. This can be achieved by implementing exhaust gas recirculation (EGR), whereby a portion of the exhaust gas is recirculated into the engine's combustion chamber. However, it is necessary to reduce the amount of soot and particulates in the hot exhaust gas. Therefore, it is desirable to specifically cool and purify the exhaust gas, which can be achieved by using a purging fluid, which, however, produces polluted purging fluid.

[0004] Another purpose is to reduce sulfur oxides (SO X ) emissions. Sulfur oxides are produced during the combustion of fuels containing residual sulfur. Exhaust gas purification, for example by using scrubbers, can reduce the amount of sulfur oxides in the exhaust gas. However, scrubber-based exhaust gas purification processes also produce contaminated scrubbing fluids.

[0005] Equipment for purifying contaminated purge fluids includes, for example, membrane and filtration technologies, flotation devices, and centrifuges. However, equipment that relies on filtration technology has drawbacks in that it requires monitoring, servicing, and replacement of filter components.

[0006] Centrifuges are commonly used to separate liquids and / or solids from liquid or gas mixtures, utilizing the density difference between the fluid and solid phases to collect the separated fractions at different radii from the axis of rotation. For examples of using centrifuges to purify contaminated liquids, see, for example, WO 2011 / 104302 A1.

[0007] However, new regulations for NOx and SOx emissions require even better purification processes for contaminated purified water.Therefore, there is a need in the art for improved methods and systems for purifying contaminated marine exhaust gas purification fluids. Summary of the Invention

[0008] A primary object of the present invention is to provide a system and method for purifying contaminated purge fluid, such as contaminated purge water, used on board a vessel for reducing NOx or SOx emissions.

[0009] As a first aspect of the present invention, a method for purifying a contaminated purification liquid is provided, wherein the contaminated purification liquid is contaminated ship exhaust purification liquid; the method comprises the following steps: a) providing the contaminated purified liquid; b) adding a solid porous adsorbent to the contaminated purified liquid; c) allowing the adsorbent to react with contaminants in the contaminated purge fluid; and d) separating the contaminated purified liquid in a centrifuge; and e) discharging the clean liquid phase and the pollutant phase from the centrifuge.

[0010] Marine exhaust gas cleaning fluid refers to the cleaning fluid used on ships to purify exhaust gas from engines. This cleaning can be performed, for example, in an EGR unit or SOx scrubber. Therefore, the cleaning fluid that has already been used to purify exhaust gas is contaminated marine exhaust gas cleaning fluid, or simply "contaminated cleaning fluid" in this disclosure.

[0011] The purification fluid may be an aqueous purification fluid, such as water, for example tap water, fresh water or desalinated sea water.

[0012] The contaminated purified liquid provided in step a) is thus a purified liquid containing pollutants, such as solid and / or liquid particles containing organic or inorganic combustion residues, such as sulfur oxide residues, soot, partially oxidized and unoxidized marine fuel oil, and salts from oxidized metals. The contaminated purified liquid can thus be water contaminated with oil and pollutant particles, such as pollutant organic particles.

[0013] In an embodiment of the first aspect, the contaminated purified fluid comprises at least 20 mg / l oil, such as at least 50 mg / l oil, such as at least 100 mg / l oil.

[0014] As an example, the contaminated purge fluid may contain about 20-300 mg / l oil, such as 25-200 mg / l oil.

[0015] In an embodiment of the first aspect, the contaminated purified liquid comprises a suspended solids content of about 25-2000 mg / l, such as between 50-1500 mg / l.

[0016] As an example, the suspended solids content in the contaminated purge liquid may be between 50-150 mg / l.

[0017] In an embodiment of the first aspect, the contaminated purified liquid comprises an oil content of 25-200 mg / l oil and a suspended solids content of about 50-1500 mg / l.

[0018] The solid porous adsorbent added in step b) may be in the form of slurry, powder or granules. The solid porous adsorbent may have a highly porous structure that attracts molecules or ions attached to the surface.

[0019] The solid porous adsorbent can be capable of adsorbing pollutants in the contaminated purification fluid, for example, can adsorb oil. The pollutants can be adsorbed on the outer surface of the adsorbent and / or adsorbed within the adsorbent, for example, within the pores of the adsorbent.

[0020] Step b) may be performed after the purified liquid has passed through the EGR unit or the SOx scrubber.

[0021] Step c) of allowing the adsorbent to react with the contaminants in the contaminated purge liquid can be performed at least during a specific time interval, such as during at least 10 minutes, such as during at least 15 minutes, such as at least 25 minutes. As an example, step c) can include allowing the adsorbent to react with the contaminants in the contaminated purge liquid for 5-30 minutes.

[0022] The term "allowing the adsorbent to react" may thus mean allowing the adsorbent to adsorb onto the surface of the adsorbent and / or into the pores of the adsorbent.

[0023] The centrifuge of step d) can be a disc stack centrifuge. Thus, the centrifuge can include a stack of separation discs, such as frustoconical separation discs, to improve separation performance. Thus, step d) can include providing contaminated scrubber liquid to an inlet of the centrifuge, such that the contaminated purified liquid can be separated into a clean liquid phase and a contaminant phase by means of the disc stack arranged within the centrifuge.

[0024] The step e) of discharging the clean liquid phase may comprise discharging the clean liquid phase continuously, and the discharge of the pollutant phase may be continuous discharge or intermittent discharge from the centrifuge.

[0025] The solid porous adsorbent added in step b) can be discharged in the pollutant phase, for example in the sludge phase or in the pollutant liquid phase.

[0026] The clean liquid phase may have a reduced amount of contaminants, but may still contain low amounts of contaminants. Similarly, the contaminated phase separated from the contaminated purified liquid may still contain some amount of purified liquid.

[0027] In an embodiment, the method further comprises the step f) of returning the clean liquid phase or at least a portion of the clean liquid phase to a location upstream of the centrifuge. Such a location may be a tank located upstream of the centrifuge.

[0028] The terms upstream and downstream may be used to denote a direction or position seen in the direction of flow of the purge liquid. Upstream may be understood as being closer to, for example, an EGR unit or a SOx scrubber.

[0029] As an example, step e) may further comprise returning the clean liquid phase or at least a portion of the clean liquid phase to a tank upstream of the centrifuge. The tank may be the tank to which the solid porous adsorbent is added, or a tank located upstream of the location where the solid porous adsorbent is added.

[0030] In an embodiment, the clean liquid phase is further treated in a filter, such as a membrane filter. This can be done before the clean liquid phase is returned to a location upstream of the centrifuge. This can further reduce the amount of any remaining contaminants in the clean liquid phase.

[0031] A first aspect of the present invention is based on the insight that solid porous adsorbents can effectively adsorb contaminants in contaminated purified water so that they can be more easily separated in a centrifuge. As an example, it has been found that oil present in the contaminated purified water can adsorb onto the adsorbent to such an extent that it remains on or within the adsorbent even when subjected to very strong centrifugal fields in a centrifuge.

[0032] This is particularly important for modern engines meeting Tier II and Tier III NOx regulations. Such engines produce only small amounts of soot, which makes the purge fluid difficult to purify. Due to the high oil concentration that may be present in the contaminated purge fluid, the solid phase has a low density and is difficult to settle using a centrifuge without the addition of an adsorbent according to the present invention. Furthermore, it has been observed that for exhaust gas recirculation (EGR) systems, when the suspended solids concentration is low (TSS < 100 mg / l) and the oil concentration is high (C_Oil > 200 PPM), an oil film may form on top of the contaminated purge fluid. This oil film has previously been difficult to remove using prior art methods utilizing a centrifuge, for example when the centrifuge is configured as a clarifier for liquid-solid separation.

[0033] Furthermore, since the engines burn heavy fuel oil (HFO) and operate in so-called closed-loop mode, high concentrations of heavy metals are present in the contaminated purge fluid from the SOx scrubber. It has been found that using adsorbents, high amounts of harmful heavy metals such as nickel, vanadium, and zinc can be separated from the contaminated purge fluid.

[0034] In an embodiment of the first aspect, step c) is performed during stirring of the contaminated purification liquid.

[0035] Stirring can promote the adsorption of pollutants onto the added adsorbent. Stirring can be carried out during the addition of the adsorbent, or can be started immediately after the adsorbent is added in step c).

[0036] As an example, step b) is added to a tank containing the contaminated purified water. Thus, stirring can be performed in the tank to which the adsorbent is added.

[0037] However, stirring need not occur in the tank. As a further example, the addition in step b) is to the contaminated purified water being conveyed through the piping system. Thus, stirring of the contaminated purified liquid can be performed by conveying the contaminated purified liquid, for example, in a pipe. Thus, the adsorbent can be added during the recirculation of the contaminated purified liquid, for example, from the tank through the piping system and back to the same tank. Thus, the adsorbent can be added to the contaminated purified liquid while it is being conveyed, i.e., while the contaminated purified liquid is moving (flowing).

[0038] In an embodiment of the first aspect, the method further comprises the step of adding a flocculant and / or a coagulant to the contaminated clarified liquid prior to step d).

[0039] The flocculant and / or coagulant may be added between steps c) and d), ie after the addition and reaction of the contaminated purge liquid with the adsorbent, but before the contaminated purge liquid is provided to the centrifuge.

[0040] Flocculants and / or coagulants help the agglomeration of particles in the polluted liquid, and therefore make the separation of pollutants easier in a centrifuge. As an example, flocculants and / or coagulants can be polymers, for example polyelectrolytes. Therefore, flocculants can be anionic, cationic or nonionic polymer flocculants, have about for example physical length, coupling and different characteristics of intensity aspect. As an example, flocculants can be cationic flocculants.

[0041] As mentioned above, the centrifuge used may be a disc stack centrifuge. The disc stack centrifuge may have a single liquid outlet for the separated liquid phase and an outlet for the separated sludge phase. Thus, the disc stack centrifuge may be of the clarifier type.

[0042] Thus, in an embodiment of the first aspect, the separation of step d) produces a single pollutant phase and a single liquid phase, and wherein the single liquid phase is discharged as the clean liquid phase in step e).

[0043] Thus, pollutants in the contaminated purified liquid can be discharged in the same single pollutant phase. For example, pollutants in the form of oil and particles can be discharged in the same pollutant sludge phase. Furthermore, since the added adsorbent may agglomerate with the oil and particles in the contaminated purified liquid, these can also be removed in a single pollutant phase, i.e., the sludge phase, in the centrifuge.

[0044] However, a centrifuge with two liquid outlets may also be used. For example, a three-phase centrifuge may be used. Such a centrifuge may be arranged to separate the contaminated purified liquid into a clean liquid phase (e.g., an aqueous phase), a contaminated liquid phase (e.g., an oil phase), and a contaminated sludge phase.

[0045] In an embodiment of the first aspect, the contaminated purge fluid provided in step a) originates from recirculating purge fluid used in an exhaust gas recirculation (EGR) unit for marine applications.

[0046] In EGR systems used in marine applications, a portion of the exhaust gas is recirculated to the engine after a cooling and purification process. This purification and cooling process involves the use of an EGR unit, typically including an EGR cooling unit, where the recirculated exhaust gas is sprayed with a purification fluid, such as fresh water. The recirculated purge fluid, which is contaminated by excessive purge fluid, may need to be drained from the EGR unit and purified. The drained purge fluid may include excess liquid, such as water, that has accumulated in the EGR system from the combustion process.

[0047] Thus, step a) may comprise providing discharged contaminated purge fluid from an EGR unit EGR purge tank, and the adding of the adsorbent in step b) may be adding the contaminated purge fluid in the EGR purge tank.

[0048] "Discharged contaminated purge liquid" refers to contaminated purge liquid that has been discharged from the EGR system and is therefore not subsequently returned to the EGR system, but is instead purified and treated elsewhere. The centrifuge used in step d) can thus be part of a water treatment system (WHS) for the EGR system.

[0049] Furthermore, the clean liquid phase discharged from the centrifuge in step e), i.e. the purified water, can be sent directly overboard to a storage tank for later disposal or recycled back to the EGR discharge tank. Thus, the clean liquid phase discharged in step e) can comply with international requirements for effluent water, such as those set out in the 2015 Guidelines for Exhaust Gas Cleaning Systems, MEPC 259(68).

[0050] As an example, step e) may further comprise discharging the clean liquid phase overboard.

[0051] As a further example, step e) may further include discharging the clean liquid to a tank for later disposal.

[0052] As a further example, step e) may further comprise recycling the clean liquid phase to a tank for further processing in a centrifuge.

[0053] In an embodiment of the first aspect, the contaminated purge liquid provided in step a) originates from recycled purge liquid used in a SOx scrubber.

[0054] During the combustion of fossil fuels in ship engines, exhaust gases containing sulfur oxides (SOx) are formed. The exhaust gases can be passed through a SOx scrubber and / or a wet electrostatic precipitator to be scrubbed with a purification liquid, whereby the pollutants in the exhaust gases are captured in the liquid. The purification liquid is typically circulated in a circulation loop via a recirculation tank, and a centrifuge in the water treatment system (WHS) can be used to purify the contaminated purification liquid and return it to such a recirculation tank. Alternatively, the contaminated purification liquid can be purified by a centrifuge in the water treatment system (WHS) and sent overboard or to a tank for later disposal, i.e., the purified liquid is discharged from the circulation loop.

[0055] Thus, as an example, step a) may comprise providing the contaminated purge liquid used in the SOx scrubber in a circulation tank, and step e) may further comprise recycling the clean liquid phase back to the circulation tank.

[0056] The circulation tank may be a tank for storing the scrubbing liquid to be used later in the SOx scrubber.

[0057] As a further example, step a) may comprise providing the contaminated purified liquid for use in the SOx scrubber in a recycle tank, and step e) may further comprise sending the purified liquid overboard, or to a tank for later disposal.

[0058] In an embodiment of the first aspect, the solid porous adsorbent used is selected from the group consisting of activated carbon, zeolite, iron oxide coated sand, silica gel, nanoadsorbents, graphene-based adsorbents and natural adsorbents.

[0059] As an example, the solid porous adsorbent used may be selected from activated carbon, zeolites and graphene-based adsorbents.

[0060] As an example, the solid porous adsorbent may be activated carbon. The activated carbon may have been treated to have a high surface area.

[0061] As an example, the solid porous adsorbent used can be added together with other additives, for example in a composition, mixture, or dissolved in another additive. As mentioned above, the solid porous adsorbent, such as activated carbon, can be added, for example, in the form of a slurry, powder or granules.

[0062] As an example, the solid porous adsorbent may have an average particle size below 1 mm, such as below 0.5 mm, for example below 100 μm. This allows the use of a disk stack separator, as particles that are too large would clog the disk stack. Therefore, in embodiments, solid porous adsorbent particles having an average particle size above 1 mm are not used.

[0063] Additionally, step b) may comprise adding the solid porous adsorbent at a concentration of less than 2 g / L, such as less than 1 g / L, such as less than 0.7 g / L, such as about 0.5 g / L.

[0064] Therefore, in an embodiment of the present invention, the solid porous adsorbent, such as activated carbon, added to the contaminated purified liquid in step b) has an average particle size of less than 1 mm, for example less than 100 μm, and is added to the contaminated purified liquid to a concentration of less than 2 g / L.

[0065] Thus, step b) may comprise adding activated carbon in powdered form at a concentration below 2 g / L, for example below 1 g / L, such as below 0.7 g / L, for example about 0.5 g / L.

[0066] Alternatively, step b) may comprise adding activated carbon to the contaminated purified liquid to a concentration of 50-300 mg / l, such as between 100-250 mg / l.

[0067] The activated carbon may have an average particle size between 2-200 μm, for example between 5-150 μm.

[0068] The activated carbon may be powdered activated carbon.

[0069] The activated carbon may have a surface area of ​​at least 300 m 2 / g of powdered activated carbon, such as at least 500m 2 / g.

[0070] As an example, activated carbon may be a carbon having at least 500 m 2 Powdered activated carbon with a surface area of ​​1000 μm / g and an average particle size of less than 75 μm (diameter).

[0071] In embodiments, the solid porous adsorbent is added as activated sludge or activated emulsion.

[0072] As a second aspect of the present invention, a system for purifying contaminated purification fluid is provided, wherein the contaminated purification fluid is ship exhaust purification fluid. The system comprises: a centrifuge arranged to separate at least one contaminated phase and a clean phase from said contaminated purified liquid, a dosing unit comprising a solid porous adsorbent and arranged upstream of the centrifuge, for adding the solid porous adsorbent to the contaminated purified liquid, - a conveying device for conveying the contaminated purified liquid to which the adsorbent has been added to the centrifugal separator.

[0073] The terms and definitions used in relation to the second aspect are the same as discussed above in relation to the first aspect.

[0074] Thus, the system can be used to perform the method of the first aspect.

[0075] The centrifuge may be as discussed above in relation to the first aspect.

[0076] The centrifuge is arranged to separate at least one contaminated phase and a clean phase from the contaminated purified liquid. The centrifuge can thus be arranged to separate the contaminated purified liquid into a single liquid phase and a sludge phase, or into two liquid phases and a sludge phase. The centrifuge can include a fixed frame and a drive member configured to rotate a centrifuge drum within the frame. The centrifuge drum can enclose a separation space. The separation space can include a stack of separation discs centrally arranged around a rotation axis. Such separation discs form an insert with an enlarged surface in the separation space. The separation discs can have a truncated cone shape, i.e., the stack can be a stack of truncated cone-shaped separation discs.

[0077] The dosing unit may comprise a chemical or membrane dosing pump to dose the adsorbent. The dosing unit may further comprise a mixer arranged to mix the solid porous adsorbent with, for example, water prior to dosing. However, if the adsorbent is already in a slurry, only a dosing pump may be required.

[0078] As an example, a dosing unit may include a reservoir containing a solid porous adsorbent, a powder mixer, and a supply of fresh water. The dosing unit may further include a mixing unit, such as an agitator mixer, for mixing the powdered adsorbent with the fresh water prior to supply. The dosing unit may also include a membrane dosing pump and a conduit to the dosing location.

[0079] As a further example, a dosing unit may include a reservoir containing the powdered sorbent as a slurry, a membrane dosing pump, and piping to the dosing location.

[0080] The solid porous adsorbent may be as discussed above in relation to the first aspect.

[0081] The delivery means may for example comprise a pump, such as a feed pump for delivering the contaminated purified liquid to the inlet of the centrifuge.

[0082] In an embodiment of the second aspect, the system further comprises a tank, from which the contaminated purified liquid can be transferred to the centrifuge. Thus, the system can include a conduit connecting the tank to an inlet of the centrifuge. A transfer device is configured to transfer the contaminated purified liquid, to which the adsorbent has been added, from the tank to the centrifuge.

[0083] As an example, the dosing unit may be arranged to add the solid porous adsorbent to the tank, and the tank may further comprise stirring means for stirring the contaminated purified liquid in the tank.

[0084] The agitator can thus be arranged to mix the components within the tank, namely the contaminated purified liquid and the added adsorbent. The agitator can include a stirring blade arranged to rotate within the tank. The stirring blade can be attached to a shaft that is rotated by, for example, a motor. Thus, using a stirred tank facilitates the adsorption of contaminants in the contaminated purified liquid onto the adsorbent and reduces the adsorbent's settling time within the tank, thereby increasing adsorption capacity.

[0085] As an example, the tank may be a circulation tank via which contaminated scrubber water may be circulated to the centrifuge and back. The centrifuge and the circulation tank may thus form a first recirculation system.

[0086] In an embodiment of the second aspect, the system further comprises a recirculation system arranged for recirculating the contaminated purified liquid in the tank before being conveyed to the centrifuge, and wherein the dosing unit is arranged to add the solid porous adsorbent to the recirculation system.

[0087] Thus, the tank can be part of a recirculation system that does not involve a centrifuge. In this case, the adsorbent can be added to such a recirculation system. Thus, the flow of the contaminated purified liquid in such a recirculation system can facilitate mixing of the adsorbent with the contaminants in the contaminated purified liquid, thereby facilitating adsorption of the contaminants onto the adsorbent.

[0088] In the embodiment of second aspect, system also comprises the pre-treatment unit in centrifuge upstream, and is used for the contaminated purified liquid that has been added with described adsorbent to be transported to the conveying device of described centrifuge by pre-treatment unit.Such pre-treatment unit can comprise the quantitative feeding unit that is used for flocculant and / or coagulant.Therefore the quantitative feeding unit that is used for flocculant and / or coagulant can be connected to the supply unit that comprises flocculant and / or adsorbent.Flocculant and / or coagulant can be as discussed above about first aspect.Flocculant and / or coagulant can help agglomerate pollutants, make them more easily separate in centrifuge.

[0089] The pre-treatment unit may thus comprise a flocculator device, such as a static or hydraulic flocculator device, wherein flocculation of the pollutants occurs without any moving parts.

[0090] In an embodiment of the second aspect, the system further comprises a filter, such as a membrane filter, arranged downstream of the centrifuge to further purify the clean phase from the centrifuge.

[0091] In an embodiment of the second aspect, the system further comprises an exhaust gas recirculation (EGR) unit arranged to purify exhaust gases from the engine and thereby produce contaminated purified water, and wherein the system is further arranged to convey the contaminated purified water from the EGR unit to the centrifuge.

[0092] As discussed above in relation to the first aspect, such an EGR unit may be part of an EGR system for recirculating exhaust gases back to the vessel's engines. The EGR unit may be used to purify and cool the exhaust gases before they are introduced into the engine. The EGR unit may comprise an EGR cooling unit in which the exhaust gases are cooled with a purification liquid. Thus, a contaminated purified liquid may be formed from the EGR cooling unit. The system may further comprise a buffer tank in which the contaminated purified liquid from the EGR unit is collected and recycled to the EGR unit. In addition, the system may comprise an EGR discharge tank into which part of the contaminated cooling water is discharged for purification and subsequent disposal, for example overboard. Thus, the dosing unit may be arranged for adding the solid porous adsorbent to the contaminated purified liquid in the EGR discharge tank, or directly to the EGR discharge tank, or to a recirculation system involving the EGR discharge tank but not involving a centrifuge, as discussed above.

[0093] In an embodiment of the second aspect, the system further comprises a SOx scrubber arranged to clean exhaust gas from the engine and thereby produce contaminated purified water, and wherein the system is further arranged to convey the contaminated purified water from the SOx scrubber to the centrifugal separator.

[0094] SOx scrubbers can be so-called closed-loop scrubbers, which use a circulating scrubber liquid containing a combination of freshwater or seawater and an alkaline agent such as sodium hydroxide (NaOH) or magnesium hydroxide (Mg(OH)2) to scrub sulfur oxides and particulates from the exhaust gas. In such scrubbers, the amount of aqueous sulfites, sulfates, and particulates in the circulating purge liquid gradually increases. The contaminated purge liquid can be continuously purified and returned to the SOx scrubber.

[0095] The system may include a recirculation tank, and the purified liquid may be recirculated to the SOx scrubber via the recirculation tank. The system may be arranged to transfer a portion of the contaminated purified liquid in the recirculation tank to the centrifuge and back to the recirculation tank. Thus, a transfer device, such as a pump, may be used to transfer the contaminated purified liquid from the recirculation tank to the centrifuge.

[0096] The system may also be arranged to discharge a portion of the clean phase from the centrifuge overboard, or to a tank for later disposal, ie not returning all of the clean phase to the recycle tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 A schematic diagram of an embodiment of the system of the present invention for purifying contaminated purge fluid from an EGR unit is shown.

[0098] Figure 2A schematic diagram of another embodiment of the system of the present invention for purifying contaminated purge fluid from an EGR unit is shown.

[0099] Figure 3 A schematic diagram of another embodiment of the system of the present invention for purifying contaminated purge liquid from a SOx scrubber is shown.

[0100] Figure 4 A schematic diagram of a centrifuge that may be used in the systems of the present disclosure is shown.

[0101] Figure 5 The process steps of the method of the present disclosure are schematically shown. DETAILED DESCRIPTION

[0102] The method and system according to the present disclosure will be further explained through the following description with reference to the accompanying drawings.

[0103] Figure 1 A schematic diagram of an embodiment of a system 1 for purifying contaminated purge liquid is shown. In this example, the contaminated purge liquid is a ship's exhaust purge liquid, such as water, which originates from an exhaust gas recirculation (EGR) unit 20 on the ship. Thus, the EGR unit 20 can be part of a larger EGR system for recirculating exhaust gases back to the ship's engines. In the EGR unit, the purge liquid is used to cool and reduce pollutants in the exhaust gases that are transported through the EGR unit 20 (as indicated by the thick arrows), thereby producing contaminated purge liquid. The contaminated purge liquid is circulated between the EGR unit 20 and the buffer tank 21 via conduits 30 and 31. The buffer tank 21 is connected to the EGR discharge tank 22, for example via an overflow outlet 32, to prevent contaminated purge liquid in the EGR discharge tank 22 from being introduced into the EGR unit 20.

[0104] The contaminated purge liquid in the EGR discharge tank is fed to centrifuge 2 in lines 33 and 34 using liquid feed pump 25. The centrifuge is configured to separate the contaminated purge liquid into a contaminated phase and a clean phase. The clean phase, which contains the purified purge liquid, is continuously discharged to outlet pipe 35 via a single liquid outlet, while the contaminated phase, containing contaminant particles and oil, is intermittently discharged to sludge tank 18.

[0105] A pretreatment unit 23 is also installed upstream of the centrifugal separator 2, and a liquid feed pump 25 is arranged to convey the contaminated purified liquid to the centrifugal separator 2 via the pretreatment unit 23. The pretreatment unit 23 may be a flocculant device and may further include a supply unit 24 for dosing a certain amount of flocculant and / or coagulant into the contaminated purified liquid to be purified in the centrifugal separator 2. The supply unit 24 may thus contain the actual flocculant and / or coagulant to be added. The addition of flocculant and / or coagulant improves the separation capacity of the contaminants in the centrifugal separator 2.

[0106] The purified purge liquid from outlet pipe 35 can be sent overboard via pipe 37 or to a tank for later disposal, or can be returned to the EGR drain tank via pipe 36. This is controlled by valve arrangement 27. Thus, the purified purge liquid can be mixed with the contaminated purge liquid in the EGR drain tank for further purification in the centrifuge. However, the liquid that leaves system 1 via pipe 37 is discharged from system 1.

[0107] Likewise Figure 1 As illustrated in FIG, the system 1 comprises a dosing unit 26 containing a solid porous adsorbent. This is arranged upstream of the centrifuge 2 and is used to add the solid porous adsorbent to the contaminated purified liquid. Figure 1 In the example shown, the dosing unit 26 is arranged to add a solid porous adsorbent to the EGR discharge tank 22, as indicated by arrow 38. To promote mixing and adsorption of, for example, oil in the contaminated purge fluid to the adsorbent, the EGR discharge tank 22 includes a stirring device 45 for stirring the contaminated purge fluid in the EGR discharge tank 22.

[0108] The solid porous adsorbent may be activated carbon, as discussed above.

[0109] Additionally, as indicated by dashed arrow 39 , a solid porous adsorbent may be added to buffer tank 21 as a supplement or alternative.

[0110] Figure 2 Schematic diagram of an embodiment of a system 1 for purifying contaminated purge fluid. In this example, the contaminated purge fluid is also a ship exhaust purge fluid, such as water, which originates from an exhaust gas recirculation (EGR) unit 20 on board a ship. The system 1 has the same characteristics as described above with respect to Figure 1 The same components function in the same manner as discussed in the above, except that the system 1 further comprises a recirculation system 46 which is arranged to recirculate the contaminated purified liquid in the discharge tank 22 before it is conveyed to the centrifuge 2. Therefore, downstream of the liquid feed pump 25, there is a valve device 40 which is arranged to direct the contaminated purified liquid in the EGR discharge tank to a return conduit 36 ​​arranged between the centrifuge 2 and the EGR discharge tank 22. Therefore, by regulating the valve 40 and the valve 43, a recirculation system 46 can be formed which recirculates the contaminated purified liquid by using the liquid feed pump 25. When recirculating, the contaminated purified liquid is conveyed via the pipes 33, 42 and 43. With such an arrangement, the dosing unit is arranged to add the solid porous adsorbent to the recirculation system 46. Therefore, the pollutants are mixed with the adsorbent during the recirculation and are conveyed in the recirculation system 46 for a certain period of time before the valve 40 is used to direct the pollutant purified liquid to which the adsorbent has been added to it to the centrifuge 2 via the pretreatment unit 23. As shown in FIG. Figure 2As indicated by arrow 38, dosing unit 26 is arranged to add adsorbent to the contaminated purge liquid at a location downstream of liquid feed pump 25. However, as an alternative, dosing unit 26 may be arranged to add adsorbent to the contaminated purge liquid at a location upstream of liquid feed pump 25 in recirculation system 46, such as at a location between the EGR drain tank and liquid feed pump 25.

[0111] Figure 3 Shown is a schematic diagram of an embodiment of a system 1 for purifying contaminated purge fluid. In this example, the contaminated purge fluid is ship exhaust purge fluid, such as water, originating from a SOx scrubber 50 arranged to purify exhaust gases from engines on board a ship.

[0112] The exhaust gas is thus fed to be scrubbed with a purge liquid within a scrubber 50 so that pollutants from the exhaust gas can be adsorbed, thereby producing a contaminated purge liquid. The scrubber 50 also includes an electrostatic precipitator 51 to further increase the absorption of pollutants into the purge liquid. The contaminated purge liquid from the scrubber 50 is conveyed to a circulation tank 52 via a pipe 61, and the purge liquid from the circulation tank 52 is circulated back to the scrubber via a pipe 62 and to the dust collector 51 via a pipe 63. Prior to introduction into the scrubber and / or dust collector, an alkaline agent, such as sodium hydroxide (NaOH) or sodium carbonate (Na2CO3), is added to the purge liquid using a dosing unit 53.

[0113] The contents of the recycle tank 52, which therefore contains contaminated purified liquid, are purified by the centrifuge 2 and returned to the recycle tank via return line 36, or are discharged from the system via pipe 37 for off-board disposal, or sent to a tank for later disposal.

[0114] The contaminated purified liquid in the circulation tank 52 is transported to the centrifuge 2 in the pipes 33 and 34 by the liquid feed pump 25. Figure 1 and 2 As in the previously discussed systems, the centrifuge 2 is arranged to separate a polluted phase and a clean phase from the polluted purified liquid. The clean phase, thus containing the purified purified liquid, is discharged continuously to the outlet pipe 35 via a single liquid outlet, while the polluted phase, containing pollutant particles and oil, is discharged intermittently to the sludge tank 18.

[0115] A pretreatment unit 23 is also installed upstream of the centrifugal separator 2, and a liquid feed pump 25 is arranged to convey the contaminated purified liquid to the centrifugal separator 2 via the pretreatment unit 23. The pretreatment unit 23 may be a flocculant device and may further include a supply unit 24 for dosing a certain amount of flocculant and / or coagulant into the contaminated purified liquid to be purified in the centrifugal separator 2. The supply unit 24 may thus contain the actual flocculant and / or coagulant to be added. The addition of flocculant and / or coagulant improves the separation capacity of the contaminants in the centrifugal separator 2.

[0116] As mentioned above, the purified purge liquid from the outlet pipe 35 can be sent overboard via pipe 37 or to a tank for later disposal, or can be returned to the circulation tank 52 via the return pipe 36. This is controlled by the valve device 27. Thus, the circulating purge liquid used in the scrubber 50 can be continuously purified by the centrifuge 2. However, the liquid leaving the system 1 via pipe 37 is discharged from the system 1.

[0117] Likewise Figure 1 As illustrated in FIG, the system 1 comprises a dosing unit 26 containing a solid porous adsorbent. This is arranged upstream of the centrifuge 2 and is used to add the solid porous adsorbent to the contaminated purified liquid. Figure 1 In the example shown, the dosing unit 26 is arranged to add the solid porous adsorbent to the circulation tank 52, as indicated by arrow 38. Since the contents of the circulation tank are circulated to the scrubber 50 and to the centrifuge 2, no further stirring means may be required in the tank 52.

[0118] Figure 4 Describes and gives the Figure 1-3 Some more details of the centrifuge 2 used in the system 1 are shown.

[0119] The centrifuge 2 comprises a rotating part arranged for rotation about an axis of rotation (X) and includes a centrifuge bowl 3 and a main shaft 4. The main shaft 4 is supported in a bottom bearing 6 and a top bearing 7 in a stationary frame 5 of the centrifuge.

[0120] The centrifuge drum 3 forms within itself a separation chamber 8 in which, during operation, centrifugal separation of, for example, contaminated purified liquid takes place.

[0121] The separation chamber 8 is provided with a stack of frustoconical separation discs 9 for efficient liquid separation. This stack of frustoconical separation discs 9 is an example of an insert with an enlarged surface. These discs 9 are centrally mounted coaxially with the centrifuge drum 3 and include holes that form channels 10 for the axial flow of the liquid when the separation discs 9 are mounted in the centrifuge drum 3.

[0122] The contaminated purified liquid to be separated is fed into the centrifuge drum 3 from the top via a fixed inlet pipe 11 extending downwards.

[0123] The centrifuge drum 3 has a light liquid phase outlet 12 extending therefrom for the clean liquid phase separated from the contaminated purified liquid. The light liquid phase outlet 12 extends through the frame 5 at the top of the separator. In this example, the separator 2 has only one liquid outlet 12, but the separator 2 can also include more liquid outlets for liquid phases of different densities than the liquid density taken out via the outlet 12. This depends on the liquid substance to be processed. In such a case, any higher density liquid can be forced to flow out through another liquid outlet (not shown) at a radial distance greater than the radial level of the outlet 12. As an example, if oil is separated from the contaminated scrubber fluid as a separate liquid phase, another liquid outlet can be utilized.

[0124] The centrifuge drum 3 is provided with a plurality of radial sludge outlets 13 in the form of intermittently openable outlets on its outer periphery for discharging higher density components of the liquid, such as sludge or other solids. Pollutants in the form of particles and oil adhering to the particles can thus be discharged from the radially outer portion of the separation chamber 8 into the space surrounding the centrifuge drum 3.

[0125] The centrifuge 1 is further provided with a drive motor 14. Such a motor 14 may be, for example, an electric motor, which is arranged to transmit a driving torque to the main shaft 4 and thus to the centrifuge bowl 3 rotor 3. Alternatively, the drive motor 14 may be connected to the main shaft 4 by a transmission such as a belt.

[0126] exist Figure 3 During operation of the centrifuge, the centrifuge bowl 3 is caused to rotate by the torque transmitted from the drive motor 14 to the main shaft 4. For example, when the rotor is already running at its operating speed, the contaminated purified liquid to be separated is brought into the separation space 8 via the fixed inlet pipe 11. Thus, the contaminated purified liquid can be continuously introduced into the rotor 3.

[0127] The pollutant phase, which contains particles and oil agglomerated to the particles, moves radially outward between the separation discs, while the clean phase, i.e., the purified purified liquid, moves radially inward between the separation discs and is forced through the outlet 12. The pollutant phase, which contains particles and oil, accumulates at the periphery of the separation chamber 8 and is intermittently emptied from the separation space through the sludge outlet 13 being opened, whereby the pollutant phase is discharged from the separation space by means of centrifugal force.

[0128] Figure 5The various method steps of a method 100 for purifying a contaminated purge liquid, wherein the contaminated purge liquid is contaminated ship exhaust purge liquid, are described. Method 100 comprises the following steps: a) providing 101 the contaminated purge liquid; b) adding 102 a solid porous adsorbent to the contaminated purge liquid; and c) allowing 103 the adsorbent to react with the contaminants in the contaminated purge liquid. The method further comprises the step of adding 106 a flocculant and / or a coagulant to the contaminated purge liquid before, in step d), subjecting the contaminated purge liquid to separation 104 in a centrifuge. Method 100 further comprises the step of discharging 105 a clean liquid phase and a contaminant phase from the centrifuge.

[0129] The invention is not limited to the disclosed embodiments but may be varied and modified within the scope of the claims set forth below. The invention is not limited to the type of centrifuge shown in the figures. The term "centrifuge" also includes centrifuges with a substantially horizontally oriented axis of rotation and centrifuges with more than one liquid outlet.

[0130] Experimental Examples The oil adsorption efficiency of powdered activated carbon was tested. Lubricating oil was added to softened laboratory water to a concentration of 250 mg / l. The density of lubricating oil is 905 kg / m³. Two different types of powdered activated carbon were used: The surface area of ​​sample 1 is 900m 2 / g, with an average diameter of 50µm. When examined under a microscope, the particle size was found to be up to 35μm. The surface area of ​​sample 2 is 550m 2 / g, with an average diameter of 25µm. When examined under a microscope, the particle size was found to be up to 180µm.

[0131] A total of 16 tests were performed using these two different samples with different dosing rates.The oil content in water was determined in the C6-C40 range using a standard M-0153 GC-FID.

[0132] All samples showed satisfactory oil removal efficiencies ranging from 65-90%. Therefore, laboratory testing clearly demonstrated that the activated carbon samples could remove oil from water samples. This demonstrates that oil in contaminated purified water can be adsorbed onto the activated carbon and more easily separated in a centrifuge.

Claims

1. A method (100) for purifying a contaminated purification liquid, wherein the contaminated purification liquid is a contaminated ship exhaust purification liquid; the method comprising the following steps: a) providing the contaminated purified liquid (101); b) adding (102) a solid porous adsorbent to the contaminated purified liquid; c) allowing (103) the adsorbent to react with the contaminants in the contaminated purified fluid; d) separating (104) the contaminated purified liquid in a centrifuge; and e) Discharging (105) the clean liquid phase and the pollutant phase from the centrifuge.

2. The method (100) according to claim 1, wherein step c) is performed during stirring of the contaminated cleaning liquid.

3. The method (100) according to claim 2, wherein the adding in step b) is to a tank containing the contaminated purified water.

4. The method (100) of claim 2, wherein the adding in step b) is to a piping system (46) through which the contaminated purified water is conveyed.

5. The method (100) according to any one of the preceding claims, wherein the method further comprises the step of adding (106) a flocculant and / or a coagulant to the contaminated purified liquid before step d).

6. The method (100) according to any one of the preceding claims, wherein the separation of step d) produces a single pollutant phase and a single liquid phase, and wherein the single liquid phase is discharged as the clean liquid phase in step e).

7. The method (100) according to any one of the preceding claims, wherein the contaminated purge fluid provided in step a) originates from recirculating purge fluid used in exhaust gas recirculation (EGR) units for marine applications.

8. The method (100) according to any one of claims 1 to 6, wherein the contaminated purge liquid provided in step a) originates from recycled purge liquid used in a SOx scrubber.

9. The method (100) according to any one of the preceding claims, wherein the solid porous adsorbent used is selected from the group consisting of activated carbon, zeolites, iron oxide coated sand, silica gel, nanoadsorbents, graphene based adsorbents and natural adsorbents.

10. The method (100) according to any one of the preceding claims, further comprising the steps of: f) returning the clean liquid phase or at least a portion of the clean liquid phase to a position upstream of the centrifuge.

11. The method (100) according to any one of the preceding claims, wherein the solid porous adsorbent added to the contaminated purified liquid in step b) has an average particle size below 1 mm and is added to the contaminated purified liquid to a concentration below 2 g / L.

12. A system (1) for purifying a polluted purification liquid, wherein the polluted purification liquid is a ship exhaust purification liquid, the system (1) comprising: a centrifuge (2) arranged to separate at least one contaminated phase and a clean phase from the contaminated purified liquid, a dosing unit (26) comprising a solid porous adsorbent and arranged upstream of the centrifuge, for adding the solid porous adsorbent to the contaminated purified liquid, - a conveying device (25) for conveying the contaminated purified liquid to which the adsorbent has been added to the centrifugal separator (2).

13. The system (1) according to claim 12, further comprising a tank (22, 52), from which the contaminated purified liquid can be transferred to the centrifuge (2).

14. The system (1) according to claim 13, wherein a dosing unit (26) is arranged to add the solid porous adsorbent to the tank (22, 52), and wherein the tank comprises a stirring device (45) for stirring the contaminated purified liquid in the tank (22, 52).

15. The system (1) according to claim 13, further comprising a recirculation system (46) arranged for recirculating the contaminated purified liquid in the tank (22, 52) before being conveyed to the centrifuge, and wherein the dosing unit is arranged to add the solid porous adsorbent to the recirculation system (46).

16. The system (1) according to any one of claims 12 to 15, further comprising an exhaust gas recirculation (EGR) unit (20) arranged to purify exhaust gases from an engine and thereby produce contaminated purified water, and wherein the system (1) is further arranged to convey the contaminated purified water from the EGR unit (20) to the centrifugal separator (2).

17. The system (1) according to any one of claims 12 to 15, further comprising a SOx scrubber (50) arranged to clean exhaust gases from an engine and thereby produce contaminated purified water, and wherein the system (1) is further arranged to convey the contaminated purified water from the SOx scrubber (50) to the centrifugal separator (2).

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