SYSTEM AND METHOD FOR TREATING SHIP EXAUST

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of U.S. Patent Application 62/472,285 filed on March 16, 2017, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

BACKGROUND

Field of the Disclosure

The present disclosure generally relates to systems and methods for treating exhaust from ship engines and more specifically to an exhaust treatment system that includes a wet scrubber and a washwater treatment system for treating contaminated washwater produced by the wet scrubber.

Description of Related Art

The need to reduce the amount of pollutants emitted in exhaust gas from engines is well understood. This is reflected by increasingly stringent environmental regulations. For example, the International Chamber of Shipping (ICS) has currently proposed regulations to reduce the permitted sulphur content in marine fuel to 0.5%. Coastal areas of northwest Europe and North America already have emission control areas that require use of fuel having a sulfur content of no more than 0.1%. An option is to use a wet scrubber to clean the exhaust to remove pollutants such as SO2 from the exhaust gas allowing the use of fuel having higher sulphur content. Wet scrubbers use a liquid washwater to remove water-soluble pollutants from the exhaust stream. Various contaminants, such as sulfates, nitrates, heavy metals, organics including hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), and the like, become dissolved or suspended in the washwater during scrubbing. Before contaminated washwater can be discharged, it must be treated to remove at least some of these contaminants.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure provides a system for treating exhaust gasses of a marine vessel. The system comprises: (a) a wet scrubber configured for receiving the exhaust gasses and washwater and scrubbing the exhaust gasses using the washwater to produce scrubbed exhaust gasses and contaminated washwater; and (b) a pressure filter system fluidly coupled to the wet scrubber to receive the contaminated washwater, the pressure filter system including a filter media and being configured to deliver the contaminated washwater through the filter media under pressure to filter contaminants from the contaminated washwater and produce a clean washwater filtrate.

The present disclosure also provides a method of cleaning exhaust gasses of a marine vessel. The method comprises: (a) scrubbing the exhaust gasses with a wet scrubber using washwater to produce scrubbed exhaust gasses and contaminated washwater; and (b) filtering the contaminated washwater under pressure using the pressure filtering system as described in the present disclosure.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments are illustrated in the accompanying figures to improve understanding of concepts as presented herein.

FIG. 1 is a schematic showing an exhaust treatment system and engines as installed in a stern of a ship.

FIG. 2 is a schematic illustration of a wet scrubber of the exhaust treatment system.

FIG. 3 is a process flow diagram of a washwater treatment system and the scrubber.

FIG. 4 is a perspective of the washwater treatment system.

FIG. 5 is an elevation of the washwater treatment system.

FIG. 6 is a process flow diagram of an indexing filter of the washwater treatment system shortly after a housing thereof is closed.

FIG. 7 is a process flow diagram of the indexing filter while contaminated washwater is being supplied to the filter.

FIG. 8 is a process flow diagram of the indexing filter while air is being pumped into the filter to flush the filter of liquids.

FIG. 9 is a process flow diagram of the indexing filter while filter media is being indexed.

FIG 10 is a control schematic for the washwater treatment system.

Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION

Referring now to the drawings, and in particular to Fig. 1, a stern section of a ship S (broadly, "a marine vessel") is shown in phantom as the structure in which an exhaust treatment system constructed according to the principles of the present invention is generally indicated by reference numeral 11. The illustrated portion of the ship S includes a superstructure U, a funnel F, a hull H, which is broken away forward of the superstructure, a rudder R, a propeller P and a shaft SH mounting the propeller on the hull. A power generation system 13 of the ship S mounted within the hull H includes a main engine 15, a first auxiliary engine 17 and a second auxiliary engine 19. The main engine 15 is a diesel engine and is connected to the shaft SH for driving rotation of the propeller P. The first and second auxiliary engines 17, 19 are also diesel engines that can be used for electrical power generation, backup or in other ways understood by those of ordinary skill in the art. Other sources of exhaust gas may be attached to the exhaust treatment system 11. For example and without limitation, instead of an internal combustion engine, the source of exhaust gas could be a boiler. Internal combustion engines, boilers and other heat engines are broadly considered "engines." The engines 15, 17, 19 are connected to the exhaust treatment system 11 for cleaning the exhaust of the engines prior to being discharged to the atmosphere at the funnel F. The main engine 15 is connected to the exhaust treatment system 11 by an exhaust pipe 21. The first auxiliary engine is connected to the exhaust treatment system 11 by an exhaust pipe 23. The second auxiliary engine 19 is connected to the exhaust treatment system 11 by an exhaust pipe 25. In the illustrated embodiment, a mixing vessel 37 connects the exhaust pipes 21, 23, 25 to the exhaust treatment system 1 1 for mixing the exhaust streams from each of the engines 15, 17, 19 as they flow into the exhaust treatment system as described in International Patent Application No. PCT/US2016/034019, the disclosure of which is incorporated herein by reference in its entirety for all purposes. However, in other embodiments, the engines can be separately connected to the exhaust treatment system 11 as is known in the art. It will be understood that the number, the type, the location and/or use of engines may be other than described without departing from the scope of the present invention.

The exhaust treatment system 11 includes an in-line, wet scrubber, generally indicated at 29 and a washwater treatment system, generally indicated at 30. As will be explained in further detail below the wet scrubber 29 is configured to receive and scrub the hot exhaust gasses from the diesel engines 15, 17, 19, oil fired steam boilers, and engine recycled gas (ERG) sources to produce a treated exhaust stream that is suitable for being discharged to atmosphere. The wet scrubber 29 also receives washwater for cooling the exhaust gasses as they flow through the scrubber. As is known in the art, the washwater interacts with the exhaust inside the scrubber 29 and various contaminants from the exhaust gas dissolve or become suspended in the washwater. The washwater treatment system 30 is fluidly connected to a drain 59 of the scrubber 29 to receive the contaminated washwater. As explained in further detail below, the washwater treatment system 30 is configured to filter the contaminants from the contaminated washwater to produce filtered washwater (i.e., a filtrate) that is suitable for being discharged into the sea, lake, or other body of water (broadly, marine environment) on which the ship S is sailing. In the illustrated embodiment, all the components of the exhaust scrubbing system 11 are located in the stern of the ship S on the same deck, and the wet scrubber 29 extends into the funnel F. It is understood that components of the exhaust treatment system 11 could be located at other locations on the ship (e.g., different decks, etc.) in other embodiments. In still other

embodiments, components of the exhaust treatment system 11 could be located offshore. For example, in one or more embodiments, contaminated washwater is stored on board the ship S until the ship reaches port. The ship S can thus offload the contaminated washwater at port for treatment at a washwater treatment facility located onshore.

Referring to Fig. 2, the scrubber 29 includes a generally cylindrical housing 31 having an inlet fitting 33 at a first (bottom) longitudinal end of the scrubber housing and an outlet fitting 35 at a second, opposite (top) longitudinal end of the scrubber housing. Parts of the housing 31 are broken away to reduce the height of the scrubber 29 for illustration. The overall shape of the scrubber 29 and its normal (vertical) operating position make it ideal for use in the ship S. The elongate configuration of the scrubber 29 corresponds closely to the configuration of the funnel F. The scrubber 29 can fit in the place conventionally used for a silencer (not shown). The scrubber 29 can function to silence engine noise, thereby replacing the function of the silencer. The slender configuration of the scrubber 29 also facilitates the installation of more than one scrubber in the funnel F, should that be required. A large diameter, with a short, swatted scrubber configuration may also be used, depending on ship type and cargo being carried, to avoid using valuable cargo space or increasing the installation cost by necessitating

modifications to the ship to fit the scrubber size. All three of the exhaust pipes 21, 23, 25 are attached to the inlet fitting 33 by the exhaust mixer 37 (Fig. 1). The exhaust mixer 37 is mounted directly on the scrubber inlet fitting 33. All three engines 15, 17, 19 are serviced by one scrubber 29 in the illustrated embodiment. But in other embodiments, different scrubbers could be used for different engines. The outlet fitting 35 may be connected to a discharge stack 36 for release of cleaned exhaust gas to the atmosphere as shown in Fig. 1.

Internal components of the scrubber 29 are shown in hidden lines in Fig. 2. The inlet fitting 33 extends into the interior of the housing and opens in the interior at a mouth 39. The mouth is covered by a diverter cap 41 that prevents washwater used in the scrubber 29 from entering the mouth 39. A lower absorber spray head 43, a middle absorber spray head 45 and an upper absorber spray head 47 each include nozzles (designated 43 A, 45A and 47A, respectively) to spray washwater within the scrubber housing 31. A droplet separator 51 is located near the top of the housing 31 to capture entrained water droplets. The droplet separator 51 includes rows of curved pieces (sometimes called "chevrons" for their general shape) that define tortuous paths for scrubbed exhaust gas leaving the scrubber facilitating water droplet removal. A separator sprayer 53 located under the droplet separator 51 can be periodically activated to spray washwater or other solution through nozzles 53 A for cleaning the chevrons forming the droplet separator. In general, it will be understood that the construction and operation of the scrubber 29 may be other than described without departing from the scope of the present invention.

In use, hot, dirty exhaust gas from one or more of the engines 15, 17, 19 (broadly, hot gas sources) enters the inlet fitting 33 of the scrubber 29 and exits the mouth 39 within the scrubber housing 31. In some instances, the entering exhaust gas might be on the order of 350°C. The diverter cap 41 alters the flow of exhaust gas from a generally vertical direction to a generally lateral direction. The diverter cap 41 also redirects water coming down from the lower, middle and upper absorber spray heads 43, 45, 47 laterally off the sides of the diverter cap. The hot exhaust moving out from under the diverter cap 41 passes through a curtain of water around the diverter cap. A substantial amount of water is evaporated so that much of the heat of the exhaust gas entering the scrubber 29 is removed immediately upon entry into the interior of the scrubber housing 31. The quenched gas and entrained water flows upward from the diverter cap 41 in the housing 31. In addition to providing further cooling of the exhaust gas, the water captures particulates in the gas. As explained below, a reagent may be added to the water sprayed from the lower, middle and upper absorber spray heads 43, 45, 47 to promote the absorption of a particular pollutant by the water. For example, an organic or inorganic reagent may be added to promote absorption of SO2. It will be understood that the particulates and SO2 are considered "constituents" of the exhaust gas. Water droplets entrained in the gas flow passing above the upper absorber spray head 47 encounter the droplet separator 51. The changes in direction of the gas flows passing through the tortuous paths defined by the chevrons of the droplet separator 51 promotes collection of water droplets from the gas flow on the surfaces of the chevrons.

Collected water on the chevrons may fall down toward the bottom of the scrubber housing 31. Water containing particulates and SO2 (i.e., contaminated washwater) from the droplet separator 51 and from the lower, middle and upper absorber spray heads 43, 45, 47 falls down within the scrubber housing 31 to a slanted floor 57 at the bottom of the housing. The floor 57 is located well below the mouth 39 of the inlet fitting 33 to inhibit the contaminated washwater collected at the bottom of the housing from entering the inlet fitting. A drain outlet 59 is located on the lowest side of the slanted floor 57 to permit contaminated washwater to exit the scrubber 29.

Referring to Fig. 3, the drain outlet 59 is fluidly connected to a residence tank 101 for receiving the contaminated washwater from the scrubber 29. In the illustrated embodiment, the exhaust treatment system 11 is configured to recirculate some of the contaminated washwater. A washwater pump 102 is configured to pump washwater from the residence tank through a heat exchanger 104 and into the scrubber 29 through the spray heads 43, 45, 47 and/or sprayer piping 53. The illustrated exhaust treatment system 11 is also an open loop system. The pump 102 is configured to draw in new seawater to deliver it with the recirculated washwater to the scrubber 29. A washwater conditioning pump 103 is configured to deliver a washwater conditioner or reagent such as caustic soda from a reservoir tank 105 to the residence tank 101 for mixing with the washwater. The caustic soda in the washwater helps neutralize acidic compounds in the exhaust gasses when it is recirculated to the scrubber 29. The washwater pump 102 or another pump is also configured to deliver some of the contaminated washwater from the residence tank to the washwater treatment system 30.

Referring to Figs. 3-5, the washwater treatment system 30 includes a buffer or feed tank 111 that is configured to receive and store contaminated washwater from the pump 102. As explained in detail below, the feed tank 111 includes a pump 112 configured to selectively deliver the contaminated washwater to an indexing filter (broadly, a pressure filter), generally indicated at 113, which forces the contaminated washwater through a filter media 115 under pressure to filter the washwater. In the illustrated embodiment, the indexing filter 113 is configured to receive contaminated washwater that has not been previously filtered or centrifugally separated to remove contaminants. As set forth below, the indexing filter 113 is also configured to produce a filtrate that is returned to the marine environment without any additional filtering, polishing, or chemical processing of the filtrate. Thus, the indexing filter 113 alone filters the contaminated washwater for storage on board until the ship makes port or for discharge overboard . As explained in greater detail below, the indexing filter 1 13 must occasionally be disconnected from the washwater feed tank 111 for a short period of time to replace spent filter media 115 with new filter media (this process is referred to as "indexing" the filter media). In the illustrated embodiment, the feed tank 111 can be disconnected from the indexing filter 113 by deactivating the pump 112, but other embodiments can disconnect the washwater supply in other ways (e.g., using a shutoff valve, etc.). Suitably, the storage volumes of the residence tank 101 and the feed tank 111, alone or in combination, are sufficiently large to contain the contaminated washwater the scrubber 29 produces during the period of time in which the filter media 115 is indexed.

The washwater treatment system 30 further includes a filter aid dispensing system 117 that is configured to provide a filter aid or conditioner to the feed tank 111 for mixing with the contaminated washwater prior to filtering. In the illustrated embodiment, the filter aid dispensing system 117 comprises a hopper 117A and an inclined screw conveyor 117B for conveying particulate solid filter aid. Other filter aid dispensing systems can be configured for delivering the same or other kinds of filter aids (e.g., liquid filter aid, etc.) without departing from the scope of the invention. The inclined screw conveyor 117B is configured to selectively deliver the filter aid from a bottom outlet of the hopper 117A through an inlet fitting at the top of the feed tank 111. In some embodiments, the filter aid is passively mixed with the contaminated washwater in the feed tank 111 or mixed in-line prior to the stream entering the feed tank; in other embodiments, the feed tank includes a motorized mixer (not shown) for mixing the filter aid with the washwater.

The filter aid dispensing system 117 may be configured to supply any suitable filter aid for conditioning, precoating and/or admixing and thus enhancing the ability of the washwater to be filtered by the filter media 115. Suitably, the filter aid can comprise at least one of diatomite (diatomaceous earth) and perlite, but other filter aid materials can also be used in other embodiments. In one or more embodiments, the filter aid is dispensed into the feed tank 111 so that the mixture of contaminated washwater and filter aid contains a ratio of about one part filter aid to one part diesel particle. However, the filter aid dispensing system 117 can dispense the filter aid at other rates in other embodiments, allowing the filter to treat a wide range of washwater qualities and characteristics.

As set forth above, in the illustrated embodiment, the washwater treatment system 30 uses an indexing filter 113 to filter the contaminated washwater under pressure. Other washwater treatment systems can use other types of pressure filters (e.g., candle filters, etc.) or gravity filters (horizontal belt, etc) or vacuum filters (drum filter, etc) to filter the contaminated washwater without departing from the scope of the invention. Referring to Figs. 6-9, the illustrated indexing filter 113 comprises a housing 119 supported on a frame 121 to define a single filtering chamber 123 for receiving the filtering medium 115 (i.e., the indexing filter 113 is a single-chambered filter). The housing 119 comprises a top (i.e., first) housing member 119A and a bottom (i.e., second) housing member 119B. In the illustrated embodiment, the top housing member 119A is fixed to the frame 121 and the bottom housing 119B is movable with respect to the top housing member and the frame between an open position (Fig. 9) and a closed position (Figs. 6-8). In the closed position, the top and bottom housing members 119A, 119B define the filtering chamber 123. In other embodiments, the orientation of the indexing filter can be reversed such that the top housing member is movable with respect to the bottom housing member or both housing members could be movable with respect to the frame.

The indexing filter 113 is configured to receive the filter media 115 inside the filtering chamber 123 so that the filter media extends generally horizontally through the filtering chamber. In the illustrated embodiment, the top and bottom housing members 119 A, 119B interface with one another at a substantially horizontal plane P. The filter media 115 has a length that extends from a new filter media roll 115A (e.g., a segment of the length of the filter media is wound on the new filter media roll) along the horizontal plane P to a spent filter media roll 115B (e.g., a segment of the length of the filter media is also wound onto the spent filter media roll). As explained in further detail below, the indexing filter 113 further includes a filter media drive mechanism 126 operatively connected to the spent filter media roll 115B to wind spent filter media 115 onto the filter media roll and thereby unwind new filter media from the new filter medial roll 115 A. When the housing 119 is closed, the portion of the filter media 115 that extends along the horizontal plane P is sealingly received between the top and bottom housing members 119A, 119B inside the chamber 123. Accordingly, when the filter media 115 is operatively positioned for filtering the contaminated washwater, it extends in a generally horizontal plane.

In one or more embodiments, the filter media 1 15 is made of a polypropylene material. In certain embodiments, the filter media 115 comprises a material having a BETA rating of less than or equal to about 9 microns. For example, when filter aid is used, a suitable filter media 115 may have a BETA rating of about 9 microns. When filter aid is not used, a suitable filter media 115 may have a BETA rating of about 2 microns. Other filter media may also be used in other embodiments.

In certain embodiments, one or both of the top and bottom housing members 119 A, 119B includes a gasket (not shown) for sealing the filter media 115 and the other of the housing members in the closed position. In the illustrated embodiment, the indexing filter 113 includes an air bag 125 operatively connected between the bottom housing member 119B and the frame 121 for forcing the bottom housing member into sealing engagement with the top housing member 119A and the filter media 115 in the closed position. The air bag 125 is configured to receive pressurized air that urges the bottom housing member 119B upward with respect to the frame 121 into opposing engagement with the top housing member 119 A.

Referring to Fig. 7, the feed tank pump 112 is configured to dispense the contaminated washwater through a washwater inlet valve 149 A into the filtering chamber 123 and through the filter media 115 under pressure. The filtered washwater exiting the filter media 115 is indicated by the arrows in Fig. 7. For example, in one or more embodiments, the feed tank pump 112 pumps the contaminated washwater to the filtering chamber 123 at a pressure in a range of from about 0 psig (0 bar) to about 40 psig (2.5 bar). As explained above, the air bag 125 maintains a seal at the interface between the top and bottom housing members 119A, 119B, even when the filtering chamber 123 is pressurized. In the illustrated embodiment, the indexing filter 113 is configured to dispense the washwater into the filtering chamber 123 in a generally vertical direction, generally perpendicular to the filter media 115 in the filtering chamber 123. The illustrated indexing filter 113 includes a washwater distributor 131 configured to dispense the washwater into the filtering chamber 123. The washwater distributor 131 is suitably configured to distribute the washwater across the surface of the filter media 115 to promote use of substantially the entire filter media received in the filtering chamber 123, allowing the uniform deposition of the first layer of accumulated solids. Non-uniform deposition could allow untreated water to pass through the filter media directly into the filtrate tank. The filter media 115 holds back the solid contaminant and resultant clean washwater known as filtrate is dispelled from the downstream side of the filter media. As shown in Figs. 3-5, the washwater treatment system 30 includes a filtrate tank 146 positioned below the indexing filter and fluidly coupled to the downstream end portion of the filtering chamber 123 for receiving the filtrate. The filtrate tank 146 provides a temporary holding for storing the filtrate while it is sampled and tested before discharging the filtrate as effluent. As shown in Fig. 7, the filtrate tank 146 includes a level sensor 148 configured to sense the level of filtrate in the tank. The level sensor 148 can be used to ensure the amount of filtrate provided to the filtrate tank 146 does not exceed the capacity of the tank.

Referring to Fig. 10, the indexing filter 113 includes a controller 145 that is operatively connected to various components of the washwater treatment system 30 to automate the washwater treatment system. Although Fig. 10 depicts a single controller 145 that controls several components of the washwater treatment system 30, it will be understood that other embodiments can use more than one controller to control various aspects of the system. The controller 145 is configured to determine when the filter media 115 is in need of replacement (i.e., when the filter is "spent"). Referring to Figs. 7 and 10, the controller 145 is operatively connected to a differential pressure sensor 147 configured to sense a differential pressure across the filter media 115. The differential pressure sensor 147 transmits a differential pressure signal representative of the sensed differential pressure to the controller 145. When the signal indicates the differential pressure has reached a differential pressure set point, the controller 145 determines the filter media is spent, e.g., has captured a maximum amount of solid particulate for effective filtering.

As shown in Fig. 8, when the controller 145 determines that the filter media 115 in the filtering chamber 123 is spent, it automatically executes a control routine that flushes the chamber of any remaining wastewater and dries the retained solids. Once the spent filter media determination is made, the controller 145 sends a deactivation control signal to the washwater supply pump 112 operative to deactivate the pump and shutoff filter inlet valve 149A to shut off the flow of washwater into the filtering chamber 123. The controller 145 then transmits a flushing/drying activation signal to air valve 149B, which opens the air valve to deliver pressurized air (e.g., air at a pressure in a range of from about 30 psig to 35 psig (2- 2.5 Bar) to the chamber 123. In the illustrated embodiment, the controller 145 is operatively connected to the differential pressure sensor 147 and internal controller timer. The plant air flowing through the air valve 149B forces out the remaining washwater in the filter chamber. The controller 145 maintains the air valve 149B in the open position until the differential pressure detected by the sensor 147 falls below the air dry set point, indicating free air flow is occurring. The controller 145 then activates an internal timer (e.g., an internal timer set in a range of from about 30 seconds to about 60 seconds) to allow air to continue to pass through the solids and filter paper to insure dryness. The moisture content of the filtered scrubber solids and media is less than about 30% by wt. and contains no free water meeting the standards of an EPA "Paint Filter" for standing water. After the timer times out, the controller 145 closes air valve 149B.

In some embodiments, after the filtrate has been dispelled from the filtering chamber 123, the controller 145 is configured to execute a control routine that opens the housing 119. In some embodiments, once the liquid washwater has been dispelled from the filtering chamber 123, the controller 145 sends a chamber release control signal to depressurize the air bag. The air bag 125 deflates and moves the bottom housing member 119B to the open position. In some

embodiments, after the air valve 149B is closed, the controller 145 is configured to execute a control routine that depressurize the air bag 125 and opens the housing 119.

After the housing 1 19 has been opened as shown in Fig. 9, the controller 145 is configured to execute a control routine that is operative to index the filter media 115. After liquid washwater has been emptied from the filtering chamber 123, a layer of dry, solid particulate that was filtered out of the contaminated washwater forms a residual layer or "cake" atop the dried filter media 115. The controller 145 is configured to transmit an indexing control signal to the filter media drive mechanism 126 operative to activate the drive mechanism to wind spent filter media onto the spent filter media roll 115B. The controller 145 also receives a feedback signal from a filter media roll counter 127 representative of the amount of filter media being unwound from the new filter media roll 115 A. The controller 145 uses the signal from the roll counter 127 to for example, determine when the filter media roll 115A should be replaced. As the spent filter media is wound onto the spent filter media roll 115B, the spent filter media is pulled downward over a tensioning roller 161 such that the orientation of the spent filter media changes from a generally horizontal orientation to a substantially inclined orientation. This change of orientation is what causes the cake to fall off the spent filter media 115 onto a chute 163, which directs the particulate into a dry storage vessel 165. The dry cake can be stored onboard in the dry storage vessel 165 until it is possible to offload the vessel onshore for disposal. As the drive mechanism 126 winds spent filter media 115 onto the roll 115B, new filter media is unwound from the new filter media roll 115 A. The roll counter 127 senses the paper movement. In one embodiment, the controller activates the drive mechanism 126 for a predetermined number of counts (e.g., about 10 counts ) that corresponds with winding a length of spent filter media 115 onto the roll 115B sufficient to position a new segment of filter in alignment with the filtering chamber 123.

Referring to Figs. 4 and 10, the controller 145 is also configured to control the filter aid dispensing system 117. The controller 145 is operatively connected to the filter aid screw conveyor 117B to adjust a rate at which the conveyor delivers filter aid from the hopper 117A to the feed tank 111. In general, the controller 145 can be configured to control the filter aid conveyor 117B on a time basis. For example, the controller 145 can be configured to activate the conveyor 117B at a predetermined frequency and for a predetermined period to deliver the desired amount of filter aid to the washwater feed tank 111. In certain embodiments, the controller 145 monitors one or both of the rate at which the differential pressure across the filter media 115 increases during filtering (based on the differential pressure signal received from the sensor 147) and the amount of time the controller opens the air valve 149B before the chamber 123 is determined to be dry (e.g., based on the differential pressure signal received from the sensor 147). If the rate at which the differential pressure increases is too fast or too slow and/or the air pump activation time period is too long or too short, the controller 145 can automatically adjust the period and frequency for dispensing filter aid to increase or decrease the amount of filter aid that is mixed into the contaminated washwater. In addition or in the alternative, the controller 145 can be configured to adjust the differential pressure set point for indexing the filter media based on the rate at which the differential pressure increases or the air pump activation time period.

Having described the illustrated components of the exhaust treatment system 11, a method of using the exhaust treatment system to treat exhaust gasses from the ship S will now be briefly described. As the ship S uses the engines 15, 17, 19, they produce exhaust that is carried through the exhaust lines 21, 23, 25 to the exhaust scrubber 29. The washwater pump 102 provides washwater from the residence tank 101 and the marine environment (sea, lake, etc.) to the scrubber 29, and the scrubber uses the washwater to scrub the exhaust and produce a cleaned gaseous exhaust stream. The cleaned exhaust is dispelled to atmosphere through the exhaust stack 36. Contaminated washwater produced by the scrubber 29 is drained through the drain line 59 into the residence tank 101, and the pump 102 continuously pumps washwater back into the scrubber from the residence tank 101. A small portion of the washwater stream is directed to the washwater treatment system 30 to limit the contaminate concentration in the washwater recirculating through the scrubber. The filter aid dispensing system 117 dispenses filter aid into the feed tank at the rate dictated by the controller 145 to mix filter aid into the contaminated washwater.

In the embodiment discussed herein, the controller 145 automatically controls the washwater treatment system 30 to perform the method of treating the contaminated washwater. However, it will be understood that one or more aspects of the washwater treatment method can be carried out manually instead of automatically without departing from the scope of the invention. If not already closed, the controller 145 closes the filtering system housing by actuating the air bag 125. As shown in Fig. 6, the air bag 125 inflates to position the bottom housing member 119B in the closed position, thereby forming a seal at the interface between the housing members 119A, 119B and the filter media. Once the chamber 123 is closed and sealed, the controller activates the feed pump 112 to deliver contaminated washwater to the chamber 123 under pressure. The pressurized washwater is forced through the filter media 115 to produce liquid filtrate and a particulate cake.

The controller 145 monitors the differential pressure signal from the sensor 147 as the washwater is delivered to the chamber 123 and filtered. When the differential pressure reaches the set point, the controller 145 shuts off the feed pump and activates the air valve 149B as shown in Fig. 8 to dispel the filtrate from the chamber 123 until the differential pressure signal from the pressure sensor 147 indicates that the filtering chamber 123 is substantially free of liquid and free air is passing through the solids and filtering media. The filtrate is directed into the filtrate tank 146 and, after sampling and testing, is eventually fed back to the marine environment. In one or more embodiments, the washwater treatment system 30 is configured to expel the filtrate into the marine environment after filtering with the indexing filter 113 and without any post processing to further enhance the quality of the filtrate. For example, after the index filter 113 filters the washwater, the resulting filtrate can be expelled into the marine environment without additional treatment including filtering, polishing, or being chemically processed in any other way (e.g., agglomeration, flocculation, neutralization, etc.). The controller 145 then closes the air valve 149B and deflates the air bag 125 to open the housing 119. Subsequently, the controller 145 activates the filter media drive mechanism 126 to wind spent filter media 115 onto the spent filter media roll 115B and position new filter media in the chamber 123. The steps of closing the chamber 123, pumping and filtering the washwater, emptying the chamber, opening the chamber, and indexing the filter media 115 are repeated as needed so long as the scrubber 129 is producing contaminated washwater. When the scrubber is not producing contaminated washwater, the washwater treatment system sits idle in stand-by mode ready to receive additional washwater for treatment. During use, the controller 145 continuously monitors the rate of increase of the differential pressure signal and the amount of time the air pump is activated to empty the filtering chamber 123 of liquid and makes adjustments to the rate at which filter aid is added to the contaminated washwater and/or the differential pressure set point used to signal the end of a filtration cycle in order to optimize the process.

As can be seen, the illustrated exhaust treatment system 11 reduces the pollutant content of two waste streams produced by the ship S to permit them to be directly discharged into the environment. The wet scrubber 29 scrubs sulfur and other pollutants from the ship exhaust gasses, and the washwater treatment system 30 filters contaminated washwater to allow it to be directly discharged to the marine environment. The exhaust treatment system 11 can use seawater and does not rely on onboard stores of fresh water for treatment. Moreover, the total number of waste streams is kept to a minimum because no liquid sludge or wet waste is separated from the contaminated washwater. Using the indexing filter 113 provides an automated mechanism for replacing spent filter media 115 so that the washwater treatment system 30 can effectively filter the contaminated washwater for extended durations, without substantial operator input. Because the indexing filter 113 indexes the filter media 115 based on differential pressure and cycle time, it self-compensates for changes in the content of the washwater. That is, when engine load (MCR) changes, consuming more or less fuel increasing or decreasing the concentration of sulfur in the hot exhaust gas, the indexing filter 113 automatically increases or decreases the cycle duration and time between filter changes to account for increases or decreases in the contaminant content of the washwater because the time it takes for the differential pressure across the filter media to reach the set point increases or decreases. By using the appropriate combination of filter aid and filter media, the washwater treatment system 30 can effectively filter suspended solids, along with attached PAHs, in one filtering step so that the filtrate can be discharged in compliance with various regulations, without further filtering or post-treatment. Thus, the washwater treatment system 30 provides a single-step process, end-of-pipe solution for treating contaminated washwater without operator attention. Although the illustrated washwater treatment system 30 is used as an end-of-pipe solution, other embodiments could adapt the washwater treatment system for use as a side stream system. Likewise, though the illustrated washwater treatment system 30 is used with a closed loop scrubber 29, a pressure filter system could also be configured for use to treat the

contaminated washwater from an open loop or hybrid designed scrubber.

Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

EMBODIMENTS

For further illustration, additional non-limiting embodiments of the present disclosure are set forth below.

For example, embodiment 1 is a system for treating exhaust gasses of a marine vessel, the system comprising:

(a) a wet scrubber configured for receiving the exhaust gasses and washwater and

scrubbing the exhaust gasses using the washwater to produce scrubbed exhaust gasses and contaminated washwater; and

(b) a pressure filter system fluidly communicated with the wet scrubber to receive the contaminated washwater, the pressure filter system including a filter media and being configured to deliver the contaminated washwater through the filter media under pressure to filter contaminants from the contaminated washwater and produce a clean washwater filtrate.

Embodiment 2 is a system as set forth in embodiment 1 further comprising a filter aid dispensing system configured to mix filter aid into the contaminated washwater before the contaminated washwater is delivered through the filter media.

Embodiment 3 is a system as set forth in embodiment 2 wherein the filter aid comprises at least one of a diatomite and a perlite.

Embodiment 4 is a system as set forth in either of embodiments 2 and 3 wherein the filter aid dispensing system comprises a hopper and a screw conveyor.

Embodiment 5 is a system as set forth in any of embodiments 2-4 further comprising a filter aid dispensing control system configured to control the filter aid dispensing system to adjust an amount of filter aid that is mixed into the contaminated washwater.

Embodiment 6 is a system as set forth in embodiment 5 wherein the filter aid dispensing control system is configured to monitor a change in a differential pressure across the filter media and to control the filter aid dispensing system to adjust the amount of filter aid that is mixed into the contaminated washwater based on said monitored change in the differential pressure across the filter media.

Embodiment 7 is a system as set forth in any preceding embodiment wherein the pressure filter system comprises an indexing filter.

Embodiment 8 is a system as set forth in embodiment 7 wherein the indexing filter is a single-chamber indexing filter.

Embodiment 9 is a system as set forth in either of embodiments 7 and 8 wherein the indexing filter comprises a housing defining a filtering chamber, the housing comprising a first housing member and a second housing member movable with respect to the first housing member between an open position and a closed position in which the first and second housing members define the filtering chamber.

Embodiment 10 is a system as set forth in embodiment 9 wherein the filtering chamber is configured to receive the filter media and said contaminated washwater under pressure.

Embodiment 11 is a system as set forth in either of embodiments 9 and 10 wherein the indexing filter further comprises an air bag that is selectively inflatable to urge the second housing member into sealing engagement with the first housing member in the closed position to seal the chamber.

Embodiment 12 is a system as set forth in any of embodiments 9-11 wherein the washwater is configured to be delivered through the filtering chamber and the filter media in a generally vertical direction.

Embodiment 13 is a system as set forth in any of embodiments 9-12 wherein the indexing filter further comprises a washwater distributor configured to distribute the washwater across a surface of the filter media.

Embodiment 14 is a system as set forth in any of embodiments 7-13 wherein the filter media extends generally in a horizontal plane.

Embodiment 15 is a system as set forth in any of embodiments 7-14 wherein the pressure filter system is configured to monitor a differential pressure across the filter media and the indexing filter is configured to dry the contents and index the filter media when the differential pressure reaches a set point.

Embodiment 16 is a system as set forth in any of embodiments 7-14 wherein the pressure filter system is configured to monitor a differential pressure across the filter media and the indexing filter is configured to determine that the filter media is spent when the differential pressure reaches a set point.

Embodiment 17 is a system as set forth in embodiment 15 wherein the indexing filter is configured to remove the spent filter media and to install new filter media after the differential pressure reaches the set point.

Embodiment 18 is a system as set forth in embodiment 17 wherein the spent filter media and the new filter media are formed from a single sheet of filter media.

Embodiment 19 is a system as set forth in embodiment 18 wherein the single sheet of filter media is wound on a roll.

Embodiment 20 is a system as set forth in either of embodiments 18 and 19 wherein the indexing filter is configured to wind the spent filter media onto a spent filter media roll as it is removed from the indexing filter.

Embodiment 21 is a system as set forth in any preceding embodiment wherein the filter media is comprised of a polypropylene. Embodiment 22 is a system as set forth in any preceding embodiment wherein the filter media has a BETA rating of less than or equal to about 9 microns.

Embodiment 23 is a system as set forth in any of embodiments 1-22 wherein the filter media has a BETA rating of about 2 microns.

Embodiment 24 is a system as set forth in any preceding embodiment further comprising a tank fluidly coupled between the wet scrubber and the pressure filter system for storing a volume of contaminated washwater.

Embodiment 25 is a system as set forth in embodiment 1 wherein the pressure filter system is configured to discharge the clean washwater filtrate as effluent without the contaminated washwater passing through another filter media or separator.

Embodiment 26 is a method of cleaning exhaust gasses of a marine vessel, the method comprising:

(a) scrubbing the exhaust gasses with a wet scrubber using washwater to produce

scrubbed exhaust gasses and contaminated washwater; and

(b) filtering the contaminated washwater under pressure using the pressure filtering system set forth in any of embodiments 1-25.