Exhaust gas purification system, method for purifying exhaust gas, and use of exhaust gas purification system

Abstract

An exhaust gas cleaning system (1, 49, 77, 107), method and use are provided for cleaning exhaust gas (EG) on a ship, comprising an exhaust gas inlet (5, 79) for receiving exhaust gas to be cleaned and a scrubber (9, 51, 83) arranged to clean the exhaust gas from pollutants in a scrubbing section (11, 53, 89) of the scrubber. The scrubbing section comprises an exhaust gas inlet (19) for receiving the exhaust gas and an exhaust gas outlet (15, 57) for discharging the exhaust gas. The exhaust gas cleaning system further comprises a wet electrostatic precipitator (39) arranged to further clean the exhaust gas from pollutants after it has been cleaned in the scrubbing section. The wet electrostatic precipitator includes a flue gas inlet (40) arranged in communication with the flue gas outlet of the scrubbing section for receiving the flue gas, a flue gas outlet (42) for discharging the flue gas, and at least one channel (38) arranged to direct the flue gas from the flue gas inlet to the flue gas outlet of the wet electrostatic precipitator. The flue gas cleaning system also includes a flue gas outlet (7, 81) for discharging the purified flue gas. The flue gas cleaning system further includes one or more second number of first ejection devices (43) arranged between the scrubbing section and the at least one channel (38), each of the first ejection devices facing the wet electrostatic precipitator (39) and including an ejection port arranged to eject liquid toward the at least one channel when the flue gas flows through the flue gas cleaning system to clean the at least one channel from pollutants deposited by the flue gas as the flue gas is directed through the at least one channel.

Description

Technical Field

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[0003]

[0001] The present invention relates to an exhaust gas purification system for purifying exhaust gas from, for example, a marine engine, combustor or boiler on board a ship. The present invention also relates to a method for purifying exhaust gas from, for example, a marine engine, combustor or boiler on board a ship using such an exhaust gas purification system. Further, the present invention relates to the use of such an exhaust gas purification system on board a ship for reducing pollutants in exhaust gas from a marine combustion engine, combustor or boiler.

Background Art

[0002] Large ships are usually driven by engines operating on sulfur-containing fuels, more particularly heavy fuel oil with a high sulfur content. In the combustion of such fuels, exhaust gas containing sulfur oxides (SOx) is formed. The exhaust gas also usually contains particulate matter such as black carbon (BC) which is mainly composed of soot, oil, heavy metals, and sub-micron elemental carbon particles. In order to reduce the impact of the exhaust gas on the environment, the exhaust gas needs to be purified from these pollutants before it is released into the atmosphere. For example, the exhaust gas can be passed through a scrubber and washed with a scrubbing fluid in which pollutants in the exhaust gas are trapped.

[0003] The scrubber can be a so-called open loop scrubber which uses the natural alkalinity of seawater to wash sulfur oxides from the exhaust gas. Seawater is supplied from the ocean, sent through the scrubber to absorb SOx and particulate matter from the exhaust gas, and then discharged and returned to the ocean.

[0004] Alternatively, the scrubber could be a so-called closed-loop scrubber, which uses circulating freshwater or seawater to wash away sulfur oxides and particulate matter from the exhaust gas, typically in combination with an alkaline agent such as sodium hydroxide (NaOH) or sodium carbonate (Na2CO3). Within such a scrubber, the amounts of hydrated sulfites, sulfates, and particulate matter in the circulating freshwater or seawater gradually increase. Therefore, to control the quality of the circulating freshwater or seawater, a small amount of it may be replaced from time to time or continuously with clean freshwater or seawater, or it may be stored on board the vessel or discharged overboard after being purified from particulate matter.

[0005] Today, scrubbers used for this purpose can remove most sulfur oxides and some less particulate matter from exhaust gases. SOx emissions are already regulated globally by the IMO, and regulations on black carbon are expected in the future. From this perspective, exhaust gas purification technologies are needed that will enable the removal of more particulate matter from ship exhaust gases.

[0006] SE540530 discloses equipment for purifying exhaust gas by feeding exhaust gas through a scrubber and then passing it through a wet electrostatic precipitator to collect particulate matter still present in the exhaust gas after it has passed through the scrubber. The purified exhaust gas then passes through a demister and then leaves the equipment. A nozzle for rinsing off particulate matter from the wet electrostatic precipitator with fresh water is positioned between the wet electrostatic precipitator and the demister. The demister is provided to minimize the release into the atmosphere of droplets generated by the nozzle and contaminated with exhaust gas. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] SE540530 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide an improved exhaust gas purification system for purifying exhaust gas on a ship, an improved method for purifying exhaust gas on a ship by such a system, and an improved use of such an exhaust gas purification system on a ship. [Means for solving the problem]

[0009] The fundamental concept of the present invention is to achieve exhaust gas purification by a scrubber combined with a wet electrostatic precipitator, also known as a wESP, with arrangement of means for purifying the wet electrostatic precipitator to minimize the release of contaminated droplets into the atmosphere. The exhaust gas purification system, method, and use according to the present invention are defined in the appended claims and described below.

[0010] The exhaust gas purification system according to the present invention is deployed to purify exhaust gas on a ship. The exhaust gas purification system includes an exhaust gas inlet for receiving exhaust gas to be purified, and a scrubber arranged to purify the exhaust gas from contaminants within a scrubbing section of the scrubber. The scrubbing section includes an exhaust gas inlet for receiving exhaust gas before purification and an exhaust gas outlet for discharging the purified exhaust gas. The exhaust gas purification system further includes a wet electrostatic precipitator arranged to further purify the exhaust gas from contaminants after the exhaust gas has been purified within the scrubbing section. Thus, the wet electrostatic precipitator includes an exhaust gas inlet, arranged in communication with the exhaust gas outlet of the scrubbing section, for receiving exhaust gas before the further purification step, and an exhaust gas outlet for discharging exhaust gas after the further purification step. Furthermore, the wet electrostatic precipitator includes at least one channel arranged to transport exhaust gas from the exhaust gas inlet to the exhaust gas outlet of the wet electrostatic precipitator. The exhaust gas purification system also includes an exhaust gas outlet for discharging the purified exhaust gas. The exhaust gas purification system further comprises one or more second numbers of first ejection devices, such as nozzles or sprayers, positioned between the scrubbing section and the at least one channel. Each of the first ejection devices includes an outlet, aperture, or opening that faces a wet electrostatic precipitator and is arranged to eject a liquid toward the at least one channel to purify the exhaust gas from contaminants deposited as the exhaust gas is carried through the at least one channel, when the exhaust gas is flowing through the exhaust gas purification system intermittently or continuously.

[0011] The liquid ejected by the first ejection device may be an alkaline fluid, i.e., having a pH value greater than 7 to achieve optimal removal of SOx from the exhaust gas. For example, the liquid may be seawater, a mixture of freshwater and an alkaline agent, a mixture of seawater and an alkaline agent, or any combination thereof. The exhaust gas purification system may be installed to purify exhaust gas from an onboard marine engine, an onboard marine combustor, or an onboard marine boiler.

[0012] The scrubber may be a wet scrubber, configured to clean the exhaust gas with a scrubbing fluid in the form of a scrubbing solution.

[0013] The scrubber in the exhaust gas purification system may be of the open-loop type, and the scrubbing fluid may be seawater. Next, seawater is collected from the ocean, passed through the scrubber once, and then discharged back into the ocean immediately or after purification.

[0014] Alternatively, the scrubber in the exhaust gas purification system may be of a closed-loop type, and the scrubbing fluid may be either seawater or freshwater mixed with an alkaline agent such as Mg(OH)2, MgO, Na2CO3, CaCO3, NaOH, or Ca(OH)2, or a combination thereof. In such a closed-loop scrubber, the scrubbing fluid inlet of the scrubber may be in communication with the scrubbing fluid outlet of the scrubber to allow recirculation of the scrubbing fluid through the scrubber. The exhaust gas purification system including a closed-loop type scrubber may further include a circulation tank. The circulation tank may be in communication with the scrubber, for example, its scrubbing fluid outlet, to receive the scrubbing fluid from the scrubber after exhaust gas purification. Furthermore, the circulation tank may be in communication with the scrubber, for example, its scrubbing fluid inlet, to supply the scrubbing fluid to the scrubber. Some of the scrubbing fluid may be intermittently or continuously withdrawn from the closed loop for purification before being discharged or supplied back into the closed loop.

[0015] Whether the scrubbing fluid originates from an open-loop or closed-loop scrubber, it may be purified, for example, by one or more separators and / or filters.

[0016] The at least one channel is defined by at least one wall that at least partially encloses the channel. A first ejection device ejects liquid toward the at least one channel, thereby removing contaminants from the at least one wall. The at least one channel may, for example, be formed by at least one plate extending inside the wet electrostatic precipitator. For example, several channels may be formed by several plates arranged parallel to each other inside the wet electrostatic precipitator. As another example, the at least one channel may be formed by a tube extending inside the wet electrostatic precipitator, which may be designed to have any suitable cross-section, such as circular, oval, or polygonal, for example, a hexagonal cross-section. For example, several channels may be formed by a bundle of parallel tubes arranged inside the wet electrostatic precipitator.

[0017] It should be emphasized that throughout the text, "connected" and "connected" mean "connected directly or indirectly" and "direct or indirect connection," respectively. Similarly, throughout the text, "receive," "supply," and "discharge" mean "receive directly or indirectly," "supply directly or indirectly," and "discharge directly or indirectly," respectively.

[0018] The pollutants may include sulfur oxides as well as particulate matter such as soot, oil, heavy metals, and black carbon. In the scrubbing section, the exhaust gas is cooled and purified from most of the sulfur oxides and some less of the particulate matter. In the wet electrostatic precipitator, the exhaust gas is further purified from the particulate matter and remaining sulfur oxides.

[0019] Throughout this text, whenever a ejection device is said to be arranged to eject liquid toward something, the ejection device is directed toward that something; that is, the ejection device has an ejection direction toward that something.

[0020] When liquid is ejected by the first ejection device, it absorbs particulate matter and sulfur oxides from the exhaust gas, forming contaminated droplets. Since the first ejection device is positioned before or upstream of the wet electrostatic precipitator with respect to the flow direction of the exhaust gas through the exhaust gas purification system, the droplets enter the wet electrostatic precipitator and are collected thereby. Thus, very few contaminated droplets pass through the wet electrostatic precipitator. The wet electrostatic precipitator then performs a "demister function" to prevent droplets from escaping the exhaust gas purification system. In contrast, in the equipment according to SE540530, the nozzle for flushing the wet electrostatic precipitator is positioned after or downstream of the wet electrostatic precipitator with respect to the flow direction of the exhaust gas through the equipment. Thus, relatively light droplets generated by the nozzle and contaminated by the exhaust gas do not reach the wet electrostatic precipitator and are not captured thereby.

[0021] Due to the nozzle arrangement in SE540530, a demister downstream of the wet electrostatic precipitator is essential for capturing relatively light droplets; otherwise, they could escape the equipment with the exhaust gas. According to one embodiment of the present invention, the exhaust gas purification system lacks a demister between the exhaust gas outlet of the wet electrostatic precipitator and the exhaust gas outlet of the exhaust gas purification system. In this case, the exhaust gas outlet of the wet electrostatic precipitator is in direct communication with the exhaust gas outlet of the exhaust gas purification system. Because there is no demister, the exhaust gas purification system according to the present invention can be made smaller and more space-efficient, which is particularly advantageous when space is limited, such as when installed on a ship.

[0022] The exhaust gas purification system can be constructed such that the scrubbing cleaning section and the wet electrostatic precipitator are arranged continuously inside the scrubber. According to such an embodiment, the outer shell structure or housing that surrounds and defines the scrubbing cleaning section can also surround the wet electrostatic precipitator. Thereby, a particularly small exhaust gas purification system can be enabled that can allow the reuse of the scrubbing cleaning liquid and can be easier and less expensive to construct. In such a system, the outlet of such an exhaust gas system may coincide with the exhaust gas outlet of the scrubber.

[0023] According to an alternative embodiment, the exhaust gas purification system is constructed such that the scrubber includes an exhaust gas outlet for discharging the exhaust gas after purification, and the exhaust gas outlet is arranged in communication with the exhaust gas outlet of the scrubbing cleaning section for transferring the exhaust gas after purification. Further, the exhaust gas inlet of the wet electrostatic precipitator is arranged in communication with the exhaust gas outlet of the scrubber for receiving the exhaust gas after purification before the further purification. This means that the wet electrostatic precipitator is arranged outside the scrubber. For example, the scrubber including the scrubbing cleaning unit and the wet electrostatic precipitator may be arranged separately and connected by appropriate piping. This embodiment is advantageous in that it allows a simple retrofit of an existing scrubber system to the system according to the present invention.

[0024] The exhaust gas purification system may also include a first sub-scrubbing cleaning section and one or a third number of second ejection devices such as nozzles or sprayers arranged inside the first sub-scrubbing cleaning section. The second ejection device may be arranged to eject the scrubbing cleaning fluid or scrubbing cleaning liquid into the exhaust gas to clean the exhaust gas. Such a first sub-scrubbing cleaning section may form a so-called jet section or sprayer section in the wet scrubber.

[0025] Furthermore, the exhaust gas purification system may be such that the scrubbing section includes a second sub-scrubbing section, one or more third ejection devices, such as nozzles or atomizers, of a fourth number, and a random or structured packing or packing layer disposed inside the second sub-scrubbing section. The third ejection device may be arranged to supply a scrubbing fluid or scrubbing liquid to the packing to wash the exhaust gas when passing through the packing. The second sub-scrubbing section may be disposed between the wet electrostatic precipitator and the first sub-scrubbing section. The third ejection device may be arranged to form a fluid film or a liquid film on the particles of the packing to increase the contact area between the exhaust gas and the fluid or liquid, thereby enhancing the pollutant absorption capacity of the second sub-scrubbing section. Such a second sub-scrubbing section may form a so-called packing section or packing layer section within the wet scrubber.

[0026] The scrubbing fluid ejected within the first and second sub-scrubbing sections of the scrubbing section may be the same type of scrubbing fluid or different types of scrubbing fluids.

[0027] The first sub-scrubbing section may include a scrubber chamber in which the exhaust gas is washed internally, and the scrubber chamber has an essentially constant cross-section along the main part of its longitudinal extension. This embodiment includes a "uniform" scrubber chamber that is easy to manufacture, small in size, and associated with low back pressure compared to, for example, a venturi-type scrubber chamber or a U-shaped scrubber chamber with or without a venturi.

[0028] The second sub-scrubbing section and the wESP section of the exhaust gas purification system including the wet electrostatic precipitator may have an essentially similar outer shape along the longitudinal central axis of the second scrubbing section and the wESP section. This embodiment enables a small and easily manufacturable exhaust gas system.

[0029] The scrubbing fluid may be an alkaline fluid, i.e., having a pH value greater than 7, to achieve optimal removal of SOx from exhaust gas. For example, the scrubbing fluid may be seawater, a mixture of freshwater and an alkaline agent, a mixture of seawater and an alkaline agent, or any combination thereof.

[0030] The exhaust gas purification system may further include one or more fifth fourth ejection devices, such as nozzles or sprayers, positioned between the exhaust gas outlet of the exhaust gas purification system and the at least one channel. These fourth ejection devices may be arranged to eject liquid toward the at least one channel when exhaust gas is not flowing through the exhaust gas purification system, thereby purifying the at least one channel from contaminants that accumulate in the exhaust gas as it is being delivered through the at least one channel. Thus, the fourth ejection devices may be activated, for example, for purification or maintenance when the exhaust gas purification system is shut down.

[0031] Exhaust gas purification systems can be designed such that the direction of exhaust gas flow through at least most of the wet electrostatic precipitator and the scrub cleaning section is essentially vertical, for example, upward. For example, the wet electrostatic precipitator can be positioned straight above or above at least most of the scrub cleaning section. Such a vertical exhaust gas purification system may require a relatively small installation area, which is beneficial on ships with limited space. Furthermore, a vertical exhaust gas purification system may allow for oppositely oriented flow, i.e., parallel counterflow, of the exhaust gas and scrub cleaning fluid within the exhaust gas purification system. Such parallel counterflow may allow for longer contact times between the exhaust gas and the scrub cleaning fluid, and thus enable more efficient scrubbing than the direct alternating current, i.e., vertical flow of exhaust gas and scrub cleaning fluid typically achieved in horizontal exhaust gas purification systems.

[0032] The present invention relates to a method for purifying exhaust gas on a ship using an exhaust gas purification system as defined above. The method includes the steps of purifying the exhaust gas from contaminants in a scrubbing section of a scrubber, and further purifying the exhaust gas from contaminants in a wet electrostatic precipitator after the exhaust gas has been purified in the scrubbing section. The wet electrostatic precipitator includes at least one channel arranged to deliver the exhaust gas through the wet electrostatic precipitator. The method further includes the step of ejecting a liquid toward the at least one channel through the nozzles of one or more second-number first ejection devices located between the scrubbing section and the at least one channel, while the exhaust gas is flowing through the exhaust gas purification system, wherein the nozzles are facing the wet electrostatic precipitator.

[0033] In this method, the liquid ejected by the first ejection device may be an alkaline fluid.

[0034] This method may be prepared to purify exhaust gases from a marine engine, a marine combustor, or a marine boiler installed on a ship.

[0035] This method can be prepared for wet scrubbing, that is, for cleaning exhaust gas with a scrubbing fluid in the form of a scrubbing solution. The scrubbing solution can be passed through the scrubber only once or recirculated.

[0036] This method may include, after the step of purifying from pollutants and the step of further purification, releasing the exhaust gas into the atmosphere without passing it through a demister.

[0037] The scrubbing section and the wet electrostatic precipitator may be arranged in succession inside the scrubber such that the step of purifying the exhaust gas from contaminants and the step of further purification are performed inside the scrubber.

[0038] Alternatively, the wet electrostatic precipitator may be located outside the scrubber such that the step of purifying the exhaust gas from contaminants is performed inside the scrubber, while the step of further purifying the exhaust gas from contaminants is performed outside the scrubber.

[0039] This method may include the step of injecting a scrubbing fluid into the exhaust gas within a first sub-scrubbing section of the scrubbing section and into the exhaust gas to clean the exhaust gas.

[0040] The method further includes the step of supplying a scrubbing fluid to a packing located inside a second sub-scrubbing section of a scrubbing section to scrub the exhaust gas as it passes through the packing. The second sub-scrubbing section may be located between a wet electrostatic precipitator and the first sub-scrubbing section.

[0041] The method may further include the step of purifying at least one channel from contaminants deposited by the exhaust gas when the exhaust gas is delivered through the at least one channel, by ejecting a liquid through one or more fifth fourth ejection devices located between the exhaust gas outlet of the exhaust gas purification system and the at least one channel of the wet electrostatic precipitator, i.e., downstream of the wet electrostatic precipitator, when the exhaust gas is not flowing through the exhaust gas purification system.

[0042] In this method, the scrubbing fluid may have a pH value greater than 7.

[0043] This method may include the step of supplying exhaust gas through a wet electrostatic precipitator and at least most of the scrubbing section in an essentially vertical direction of exhaust gas flow.

[0044] The use of the aforementioned exhaust gas purification system on a ship according to the present invention is for the purpose of reducing pollutants in exhaust gases from a ship's combustion engine, combustor, or boiler.

[0045] The advantages described in the preceding section of the various embodiments of the exhaust gas purification system according to the present invention also apply to the corresponding various embodiments of the method and use of exhaust gas purification according to the present invention.

[0046] Further objects, features, embodiments, and advantages of the present invention will become apparent from the following detailed description and drawings.

[0047] The present invention will now be described in more detail with reference to the accompanying schematic drawings. [Brief explanation of the drawing]

[0048] [Figure 1] This is a schematic diagram of the exhaust gas purification system and engine according to the present invention. [Figure 2] Figure 1 is a schematic cross-sectional view of the exhaust gas purification system. [Figure 3] This is a schematic diagram of another exhaust gas purification system and engine according to the present invention. [Figure 4] This is a schematic cross-sectional view of yet another exhaust gas purification system. [Figure 5] This is a schematic cross-sectional view of yet another exhaust gas purification system. [Modes for carrying out the invention]

[0049] Figure 1 shows an exhaust gas purification system 1 for purifying exhaust gas (EG) from an engine 3 installed in a ship (not shown) from particulate matter such as sulfur oxides and black carbon. The exhaust gas is supplied from the engine 3 to the exhaust gas purification system 1 through the exhaust gas inlet 5 of the exhaust gas purification system and passes through the exhaust gas purification system 1 at a speed of 0.1 to 6 m / s, preferably 1 to 4 m / s, in the vertically upward direction of exhaust gas flow. The purified exhaust gas is supplied from the exhaust gas purification system 1 to the atmosphere through its exhaust gas outlet 7 via a chimney (not shown). The exhaust gas purification system, shown in detail in Figure 2, includes a wet scrubber 9, which includes a housing 2 defining a scrubber chamber 4 (Figure 2) in which the exhaust gas is purified. The scrubber chamber 4 has an essentially constant cross-section along the main part of its longitudinal extension. The exhaust gas system includes a scrubbing section 11 and a wESP (wet electrostatic precipitator) section 13. The scrub cleaning section 11 and the wESP section 13 are arranged in a straight line and continuous manner inside the scrubber 9, with the exhaust gas outlet 15 of the scrub cleaning section 11 connected to the exhaust gas inlet 17 of the wESP section 13. The exhaust gas inlet 19 of the scrub cleaning section 11 is connected to or actually coincides with the exhaust gas inlet 5 of the exhaust gas purification system 1, while the exhaust gas outlet 21 of the wESP section 13 is connected to the exhaust gas outlet 7 of the exhaust gas purification system 1. Thus, the exhaust gas to be purified is fed first through the scrub cleaning section 11 for the removal of most of the sulfur oxides and some of the particulate matter, and then through the wESP section 13 for the removal of the remaining sulfur oxides and most of the remaining particulate matter.

[0050] Referring to Figure 2, the scrubbing section 11 includes a first sub-scrubbing section, more specifically a so-called jet section 23, and a second sub-scrubbing section, more specifically a so-called packing section 25, the packing section 25 being located between the jet section 23 and the wESP section 13. The packing section 25 and the wESP section 13 have similar outlines along the longitudinal vertical central axis C of the packing section 25 and the wESP section 13. The jet section 23 includes a third number, e.g., about 2 to 10 per square meter of cross-sectional area, of second ejection devices or nozzles 27 arranged along the bridge, nine of which are shown in Figure 2. The nozzles 27 are positioned downward at the top of the jet section 23, that is, each outlet 27a of the nozzles 27 faces downward. When the exhaust gas purification system 1 is operating and exhaust gas is being fed through the scrubber 9, the nozzle 27 continuously sprays a scrubbing fluid in the form of seawater into the jet section 23, thereby purifying the exhaust gas as it passes through the jet section 23. Contaminants in the exhaust gas are absorbed into the scrubbing fluid so that the exhaust gas is purified as it passes through the jet section 23. The packing section 25 includes a fourth number of third ejection devices or nozzles 29, for example 14 to 60 depending on the size of the packing section, arranged along the bridge, nine of which are shown in Figure 2, and packing 31 in the form of a gas and liquid permeable structure made of stainless steel, plastic, or any other suitable material. The nozzles 29 are positioned at the top of the packing section 25 and facing downwards; that is, each outlet 29a of the nozzles 29 faces downwards. When the exhaust gas purification system 1 is operating and exhaust gas is being supplied through the scrubber 9, the nozzle 29 continuously sprays a scrubbing fluid in the form of seawater into the packing section 25, forming a thin liquid film on the surface of the packing structure. As the exhaust gas passes through the packing section 25 and the packing 31, contaminants in the exhaust gas are absorbed into the scrubbing fluid, thereby further purifying the exhaust gas.

[0051] As indicated by arrows 33 and 35 in Figure 2, the scrubbing fluid, i.e., seawater, is supplied directly from the ship's sea chest to nozzles 27 and 29. After passing through one or both of the sub-scrubbing sections 23 and 25, the seawater is discharged from the scrubber 9, as indicated by arrow 37, depending on whether it is supplied from nozzle 27 or nozzle 29, and, if necessary, purified before being returned to the ocean. Thus, the scrubber 9 is of the open-loop type.

[0052] The wESP section 13 includes a wet electrostatic precipitator 39, which includes a bundle of a first number of pipes 41, for example, about 10 pipes per square meter of cross-sectional area, 12 of which are shown in Figure 2. Each of the pipes 41, more specifically its pipe wall 36, defines a channel 38 having a hexagonal cross-section, which is arranged to deliver exhaust gas from the exhaust gas inlet 40 to the exhaust gas outlet 42 of the wet electrostatic precipitator 39. The exhaust gas inlet 40 and exhaust gas outlet 42 of the wet electrostatic precipitator 39 are connected to the exhaust gas inlet 17 and exhaust gas outlet 21 of the wESP section 13, respectively. As the exhaust gas is delivered through the pipes 41, any contaminants remaining in the exhaust gas adhere to the walls of the pipes 41, thereby further purifying the exhaust gas. The design and function of wet electrostatic precipitators are well known and will not be described in detail herein.

[0053] During exhaust gas purification, contaminants from the exhaust gas are collected by the pipe 41, which could adversely affect the operation of the wet electrostatic precipitator 39. To avoid the accumulation of a layer of contaminants on the wall of the pipe, purification of the pipe 41 is necessary. For this purpose, the wESP section 13 includes a second number of first ejection devices or nozzles 43, e.g., about 2 to 13 per square meter of cross-sectional area, six of which are shown in Figure 2. The nozzles 43 are located at the bottom of the wESP section 13, more specifically between the scrubbing section 11 and the pipe 41, and are oriented upward. That is, each outlet 43a of the nozzles 43 is directed upward and therefore toward the wet electrostatic precipitator 39. When the exhaust gas purification system 1 is operating and exhaust gas is being fed through the scrubber 9 and the wet electrostatic precipitator 39, the nozzles 43 continuously spray a purification fluid in the form of seawater toward the pipe 41, purifying the pipe from contaminants.

[0054] Nozzles 29 and 43 are located along the same bridge, but they could instead be located along two different bridges. Thus, the purification fluid, i.e., seawater, is supplied directly from the sea chest to nozzle 43, as indicated by arrow 35. The purification fluid is sprayed upward from nozzle 43 into pipe 41 and collected on the wall of pipe 41, after which the purification fluid flows downward, bringing contaminants with it from the pipe wall. The contaminated purification fluid flowing downward passes through both sub-scrub washing sections 23 and 25 while absorbing further contaminants from the exhaust gas. Thus, the purification fluid also performs a scrubbing function when passing through scrub washing section 11. Finally, the contaminated purification fluid, along with the scrubbing fluid, is discharged from scrubber 9, as indicated by arrow 37, and optionally, after purification, is returned to the ocean.

[0055] As the purification fluid is ejected from the nozzle 43, droplets of the purification fluid are formed. To a small extent, these droplets of the purification fluid absorb pollutants from the exhaust gas. Thus, in this embodiment as well, the purification fluid also performs a scrubbing function within the wESP section 13. The droplets are ejected into the pipe 41, and most of them are collected on the wall of the pipe 41 and purified in the manner described above. More specifically, less than 5% of the droplets pass through the wet electrostatic precipitator. Since most of the droplets are collected on the pipe wall, the wet electrostatic precipitator 39 performs a "demister function" that eliminates the need for a separate demister after or downstream of the wet electrostatic precipitator.

[0056] The exhaust gas purification system 1 further includes a fifth number of fourth ejection devices or nozzles 45, e.g., 2 to 13 per square meter of cross-sectional area, arranged along the bridge, six of which are shown in Figure 2. The nozzles 45 are positioned at the top and downward of the wESP section 13; that is, each nozzle 45a faces downward. When the exhaust gas purification system 1 is not operating and no exhaust gas is being supplied through the scrubber 9, the nozzles 45 can spray a purification fluid in the form of seawater to achieve complete purification of the upper part of the pipe that is not exposed to the purification fluid ejected by the wet electrostatic precipitator 39, particularly the nozzles 43. More specifically, the nozzles 45 are arranged to spray the purification fluid onto the wall of the pipe 41 to purify the pipe wall from contaminants. The purification fluid, i.e., seawater, is supplied directly from the sea chest to the nozzles 45, as indicated by arrows 47. After purification, the contaminated purification fluid is discharged as indicated by arrow 37 and, if necessary, can be returned to the ocean after purification.

[0057] Therefore, the exhaust gas purification system shown in Figures 1 and 2 can be used to implement a method for purifying exhaust gas on a ship. The exhaust gas is purified from contaminants by passing it through a scrubber and further purified from contaminants by passing it through the tubing of a wet electrostatic precipitator. The exhaust gas is efficiently purified within the exhaust gas purification system because it is fed through the exhaust gas purification system in a vertical upward flow direction, and the scrubbing fluid and purification fluid flow through the exhaust gas purification system in a reverse downward direction due to gravity as well as the direction of the downward-facing nozzles. To ensure proper operation of the wet electrostatic precipitator, the tubing of the wet electrostatic precipitator is purified during the operation of the exhaust gas purification system by spraying the purification fluid towards the tubing from nozzles located upstream of the tubing. Contaminated droplets of the purification fluid can be captured by the wet electrostatic precipitator by positioning nozzles upstream of the tubing so that a demister is not required to prevent these small contaminated droplets from leaking out into the atmosphere downstream of the wet electrostatic precipitator. The exhaust gas purification system, method, and use of the present invention can remove approximately 70-99% of particulate matter, 70-99% of black carbon, and 70-99% of sulfur oxides from exhaust gas.

[0058] Figure 3 shows a different embodiment of the exhaust gas purification system 49 according to the present invention. Exhaust gas purification systems 1 (Figures 1 and 2) and 49 are very similar, differing only in a few points. The differences between exhaust gas purification systems 1 and 49 will be explained below.

[0059] The exhaust gas purification system 49 includes a wet scrubber 51, a scrubbing section 53, and a wESP (wet electrostatic precipitator) section 55. The scrubbing section 53 is located inside the scrubber 51, while the wESP section 55 is located outside the scrubber 51. Thus, the exhaust gas outlet 57 of the scrubbing section 53 is connected to, or actually coincides with, the exhaust gas outlet 59 of the scrubber 51. Furthermore, the exhaust gas inlet 61 of the wESP section 55 is connected to the exhaust gas outlet 59 of the scrubber 51 by appropriate piping (circularly shown by the arrow extending from the scrubber 51 to the wESP section 55).

[0060] Similar to the scrub cleaning section 11, the scrub cleaning section 53 includes a jet section, such as the jet section 23, and a packing section, such as the packing section 25. The difference here is that the nozzles in the jet section and packing section spray a scrub cleaning fluid in the form of a mixture of fresh water and sodium hydroxide instead of seawater. As shown by arrows 63 and 65 in Figure 3, this mixture is supplied from the circulation tank 67 to the nozzles in the jet section and packing section. After passing through one or both of the jet section and packing section, the mixture is supplied back to the circulation tank 67, as shown by arrow 69. Thus, the scrubber 51 is of a closed-loop type. Continuously or intermittently, such as at regular intervals, some of the mixture can be drawn from the exhaust gas purification system 49 and purified (not shown). The purified mixture is then discharged or supplied back to the exhaust gas purification system 49.

[0061] Similar to wESP section 13, wESP section 55 includes nozzles at its bottom. The difference here is that these nozzles spray a purification fluid in the form of a mixture of fresh water and sodium hydroxide instead of seawater. Furthermore, since wESP section 55 is located outside the scrubber 51, the nozzles at the bottom of wESP section 55 are not positioned along the same bridge as the nozzles in the packing section. This mixture is supplied from the circulation tank 67 to the nozzles at the bottom of wESP section 55, as shown by arrow 71 in Figure 3, and drained from wESP section 55 to the scrubbing section 53 through appropriate piping, as shown by arrow 73. In an alternative embodiment, the mixture may instead be supplied from wESP section 55 to the circulation tank 67, as shown by the dashed arrow.

[0062] Similar to exhaust gas purification system 1, exhaust gas purification system 49 includes nozzles at the top of the wESP section 55. The difference here is that these nozzles spray a purification fluid in the form of a mixture of fresh water and sodium hydroxide instead of seawater. This mixture is supplied from the circulation tank 67 to the nozzles in the wESP section 55, as indicated by arrow 75, and drained from the wESP section 55 to the scrub cleaning section 53 through appropriate piping, as indicated by arrow 73. Again, in an alternative embodiment, the mixture may instead be supplied from the wESP section 55 to the circulation tank 67, as indicated by the dashed arrow.

[0063] Both the exhaust gas purification systems 1 and 49 described above include an in-line type scrubber, i.e., a scrubber in which the first scrubbing section and the second scrubbing section are aligned in a straight line. In exhaust gas purification systems 1 and 49, the direction of exhaust gas flow through the wet electrostatic precipitator and the scrubbing sections is vertically upward. Naturally, the present invention is equally applicable to exhaust gas purification systems that include other types of scrubbers, such as U-type scrubbers. Figure 4 shows such an exhaust gas purification system 77. In the exhaust gas purification system 77, the direction of exhaust gas flow is initially vertically downward, and then directed again to vertically upward. Thus, the direction of exhaust gas flow is vertical throughout most of the wet electrostatic precipitator and the scrubbing sections of the exhaust gas purification system 77. Exhaust gas purification systems 1 and 77 (Figures 2 and 4) are very similar and differ only in a few further points. The following will focus on the further differences between exhaust gas purification systems 1 and 77.

[0064] The exhaust gas to be purified is supplied to the exhaust gas purification system 77 through its exhaust gas inlet 79. The purified exhaust gas is supplied from the exhaust gas purification system 77 to the atmosphere through its exhaust gas outlet 81 via a chimney (not shown). The exhaust gas purification system 77 includes a wet scrubber 83, which includes a housing 85 that defines a scrubber chamber 87 in which the exhaust gas is purified. The housing 85, and therefore the scrubber chamber 87, is essentially U-shaped. The exhaust gas system 77 includes a scrub cleaning section 89 and a wESP section 91 which are arranged in a continuous manner inside the scrubber 83. The scrub cleaning section 89 then includes a first sub-scrub cleaning section, more specifically a so-called jet section 93, and a second sub-scrub cleaning section, more specifically a so-called packing section 95, which is located between the jet section 93 and the wESP section 91. Furthermore, since the scrubber chamber 87 is essentially U-shaped, the jet section 93 and the packing section 95 are located side by side.

[0065] The jet section 93 includes a third number of second ejection devices or nozzles 97 positioned along the bridge at the top of the jet section 93 and oriented downward. When the exhaust gas purification system 77 is operating and exhaust gas is being fed through the scrubber 83, the nozzles 97 continuously spray a scrubbing fluid in the form of seawater to purify the exhaust gas. The packing section 95 includes a fourth number of third ejection devices or nozzles 99 positioned along the bridge and packing 101. The nozzles 99 are positioned at the top of the packing section 95 and oriented downward. When the exhaust gas purification system 77 is operating and exhaust gas is being fed through the scrubber 83, the nozzles 99 continuously spray a scrubbing fluid in the form of seawater to further purify the exhaust gas.

[0066] As shown by arrows 103 and 35 in Figure 4, the scrubbing fluid, i.e., seawater, is supplied directly from the ship's sea chest to nozzles 97 and 99. After passing through one of the sub-scrubbing sections 93 and 95, and depending on whether it was supplied from nozzle 97 or nozzle 99, the seawater is discharged back into the ocean from the scrubber 83, possibly after purification, as shown by arrow 105.

[0067] The wESP sections 13 and 91 of exhaust gas purification systems 1 and 77 have similar designs and functions. The purification fluid flowing downward from the wESP section 91 of exhaust gas purification system 77 passes through the packing section 95 and is discharged at arrow 105.

[0068] Figure 5 shows another exhaust gas purification system 107 according to the present invention. Exhaust gas purification systems 77 and 107 have a similar design with one exception. Exhaust gas purification system 107 includes a venturi-type jet section 109, i.e., a jet section having a locally decreasing cross-section in the center of the jet section, which is not the case with the jet section 93 of exhaust gas purification system 77. The design and purpose of venturi-type scrubbing sections are well known and will not be described herein.

[0069] The components of the exhaust gas purification system described above are connected by appropriate piping that allows them to communicate in the manner specified above. Furthermore, the exhaust gas system described above may include additional components that enable its components to operate properly, such as pumps, valves, sensors, purification equipment, water quality analysis units, and control units.

[0070] The first, second, third, and fourth ejection devices may be of similar or different types. The first, second, third, fourth, and fifth numbers mentioned in the preceding paragraph may be the same or different.

[0071] The embodiments described herein should be viewed merely as examples. Those skilled in the art will notice that the embodiments described can be modified in numerous ways without departing from the concept of the present invention.

[0072] For example, the exhaust gas purification system shown in Figure 1 may include a closed-loop scrubber and / or a circulation tank (which may be omitted), and / or be operated with a mixture of fresh water or seawater and an alkaline agent as the scrubbing fluid and / or purification fluid. Furthermore, the exhaust gas purification system shown in Figure 3 may include an open-loop scrubber and / or be operated with seawater as the scrubbing fluid and / or purification fluid.

[0073] The scrub cleaning fluid and the purification fluid do not need to be of the same type, but they may be of different types, requiring that the scrub cleaning fluid be kept separate from the purification fluid at all times, and therefore the purification fluid be separated from the scrub cleaning fluid and drained from the exhaust gas purification system and not drained through the scrub cleaning section as described above.

[0074] The scrubbing section of the aforementioned embodiment of the present invention includes a jet section and a packing section that makes the associated scrubber a so-called packed-bed scrubber. However, alternative scrubbing sections are possible. For example, the packing section may be omitted and replaced, or not replaced, with another jet section that makes the associated scrubber a so-called sprayer-based scrubber. As another example, the packing section may be replaced with a section that includes a tray.

[0075] It should be emphasized that the definite adjectives "first," "second," "third," etc., are used herein solely for distinguishing purposes and do not represent any particular order. It should also be emphasized that details unrelated to the present invention have been omitted, and that the drawings are schematic, simplified, and not based on scale. [Explanation of Symbols]

[0076] 1, 49, 77, 107 Exhaust gas purification systems 2.85 Housing 3 Engines 4.87 Scrubber Room 5.79 Exhaust gas inlet of exhaust gas purification system 7.81 Exhaust gas outlet of exhaust gas purification system 9, 51, 83 Scrubber 11, 53, 89 Scrub washing section 13, 55, 91 wESP sections 15, 57 Exhaust gas outlet in the scrub cleaning section 17, 61 wESP section exhaust gas inlet 19. Exhaust gas inlet for scrub cleaning section 21 Exhaust gas outlet in the wESP section 23, 93, 109 First sub-scrub washing section, jet section 25, 95 Second sub-scrub cleaning section, filler section 27, 97 Second ejection device, nozzle 27a, 29a, 43a, 45a, 97a, 99a spout 29, 99 Third ejection device, nozzle 31, 101 Filling 33, 35, 37, 47, 63, 65, 69, 71, 75, 103, 105 Arrows 36 Wall 38 channels 39 Wet electrostatic precipitator 40 Exhaust gas inlet of wet electrostatic precipitator 41 tube 42 Exhaust gas outlet of wet electrostatic precipitator 43. First ejection device, nozzle 45. Fourth ejection device, nozzle 59 Scrubber exhaust outlet 67 Circulation Tank 73 Piping C Longitudinal central axis of the second scrub washing section and wESP section

Claims

1. An exhaust gas purification system (1, 49, 77, 107) for purifying exhaust gases (EG) on a ship, An exhaust gas inlet (5, 79) for receiving the exhaust gas (EG) to be purified, A scrubber (9, 51, 83) is provided with a scrubbing section (11, 53, 89) of the scrubber (9, 51, 83) that is arranged to purify the exhaust gas (EG) from contaminants, wherein the scrubbing section (11, 53, 89) includes an exhaust gas inlet (19) for receiving the exhaust gas (EG) and an exhaust gas outlet (15, 57) for discharging the exhaust gas (EG), A wet electrostatic precipitator (39) is provided to further purify the exhaust gas (EG) from the contaminants after the exhaust gas (EG) has been purified in the scrub cleaning section (11, 53, 89), and the wet electrostatic precipitator (39) includes an exhaust gas inlet (40) provided to communicate with the exhaust gas outlets (15, 57) of the scrub cleaning section (11, 53, 89) for receiving the exhaust gas (EG), an exhaust gas outlet (42) for discharging the exhaust gas (EG), and at least one channel (38)(41) provided to transport the exhaust gas (EG) from the exhaust gas inlet (40) to the exhaust gas outlet (42) of the wet electrostatic precipitator (39), An exhaust gas outlet (7, 81) for discharging the purified exhaust gas (EG), In exhaust gas purification systems (1, 49, 77, 107), The aforementioned exhaust gas purification system (1, 49, 77, 107) One or more first ejection devices (43) are arranged between the scrubbing sections (11, 53, 89) and the at least one channel (38), each of the first ejection devices (43) facing the wet electrostatic precipitator (39) and including an outlet (43a) that is arranged to eject liquid toward the at least one channel (38) when the exhaust gas (EG) is flowing through the exhaust gas purification system (1, 49, 77, 107) to purify the at least one channel from contaminants deposited by the exhaust gas (EG) as the exhaust gas (EG) is delivered through the at least one channel (38). It further includes, The scrub cleaning section (11, 53, 89) includes a first sub-scrub cleaning section (23, 93, 109) and one or more second ejection devices (27, 97) located inside the first sub-scrub cleaning section (23, 93, 109), the second ejection devices (27, 97) being configured to eject scrub cleaning fluid into the exhaust gas (EG) to clean the exhaust gas (EG). The scrub cleaning section (11, 53, 89) includes a second sub-scrub cleaning section (25, 95), one or more third ejection devices (29, 99), and packing materials (31, 101) located inside the second sub-scrub cleaning section (25, 95), wherein the third ejection devices (29, 99) are arranged to supply scrub cleaning fluid to the packing materials (31, 101) to clean the exhaust gas (EG) as it passes through the packing materials (31, 101), and the second sub-scrub cleaning section (25, 95) is located between the wet electrostatic precipitator (39) and the first sub-scrub cleaning section (23, 93, 109). The aforementioned scrubbing fluid is seawater or freshwater mixed with one of Mg(OH)2, MgO, Na2CO3, CaCO3, NaOH, or Ca(OH)2, or a combination thereof. An exhaust gas purification system (1, 49, 77, 107) characterized in that the exhaust gas flows vertically upward or downward through a jet section which is a first sub-scrub cleaning section, and flows vertically upward through a packing section which is a second sub-scrub cleaning section and a wet electrostatic precipitator (wESP) section.

2. The exhaust gas purification system (1, 49, 77, 107) according to claim 1, wherein the exhaust gas purification system (1, 49, 77, 107) lacks a demister between the exhaust gas outlet (42) of the wet electrostatic precipitator (39) and the exhaust gas outlet (7, 81) of the exhaust gas purification system (1, 49, 77, 107).

3. The exhaust gas purification system (49) according to claim 1 or 2, wherein the scrubber (51) includes an exhaust gas outlet (59) for discharging the exhaust gas (EG), the exhaust gas outlet (59) is configured to communicate with the exhaust gas outlet (57) of the scrubbing section (53) for transferring the exhaust gas (EG), and the exhaust gas inlet (40) of the wet electrostatic precipitator (39) is configured to communicate with the exhaust gas outlet (59) of the scrubber (51) for receiving the exhaust gas (EG).

4. The exhaust gas purification system (1, 49, 77, 107) according to any one of claims 1 to 3, wherein the second sub-scrub cleaning section (25, 95) and the wet electrostatic precipitator (wESP) section (13, 91) of the exhaust gas purification system (1, 49, 77, 107) including the wet electrostatic precipitator (39) have similar external shapes along the longitudinal central axis (C) of the second sub-scrub cleaning section (25, 95) and the wet electrostatic precipitator (wESP) section (13, 91).

5. The exhaust gas purification system according to any one of claims 1 to 4 (1, 49, 77, 107), wherein the scrubbing fluid has a pH value greater than 7.

6. The exhaust gas purification system (1, 49, 77, 107) according to any one of claims 1 to 5, further comprising one or more fourth ejection devices (45) disposed between the exhaust gas outlet (7, 81) of the exhaust gas purification system (1, 49, 77, 107) and the at least one channel (38), and configured to eject liquid toward the at least one channel (38) when the exhaust gas (EG) is not flowing through the exhaust gas purification system (1, 49, 77, 107) to purify the at least one channel from contaminants deposited by the exhaust gas (EG) as the exhaust gas (EG) is delivered through the at least one channel (38).

7. A method for purifying exhaust gas (EG) on a ship using the exhaust gas purification system (1, 49, 77, 107) described in Claim 1, A step of purifying the exhaust gas (EG) from contaminants within the scrubbing sections (11, 53, 89) of the scrubber (9, 51, 83), A further purification step comprising: after the exhaust gas (EG) has been purified in the scrubbing sections (11, 53, 89), the exhaust gas (EG) being further purified from contaminants in a wet electrostatic precipitator (39), wherein the wet electrostatic precipitator (39) includes at least one channel (38) arranged to deliver the exhaust gas (EG) through the wet electrostatic precipitator (39); In a method including, The aforementioned method, Steps to purify the at least one channel (38) from contaminants deposited by the exhaust gas (EG) as the exhaust gas (EG) flows through the exhaust gas purification system (1, 49, 77, 107), wherein, when the exhaust gas (EG) is flowing through the exhaust gas purification system (1, 49, 77, 107), liquid is ejected toward the at least one channel (38) through the nozzles (43a) of one or more first ejection devices (43) located between the scrubbing section (11, 53, 89) and the at least one channel (38), the nozzles (43a) facing the wet electrostatic precipitator (39), It further includes, The steps include: cleaning the exhaust gas (EG) in the first sub-scrub cleaning section (23, 93, 109) of the scrub cleaning section (11, 53, 89) by injecting a scrub cleaning fluid into the exhaust gas (EG) of the first sub-scrub cleaning section (23, 93, 109) through the nozzles (27a) of one or more second ejection devices (27); A method comprising the step of supplying the scrubbing fluid to packing materials (31, 101) located inside the second sub-scrubbing section (25, 95) of the scrubbing section (11, 53, 89) through the respective nozzles (29a) of one or more third ejection devices (29) to clean the exhaust gas (EG) as it passes over the packing materials (31, 101), wherein the second sub-scrubbing section (25, 95) is located between the wet electrostatic precipitator (39) and the first sub-scrubbing section (23, 93, 109).

8. The method according to claim 7, further comprising the step of releasing the exhaust gas (EG) into the atmosphere without passing it through a demister, after the step of purifying it from the pollutants and the step of further purification.

9. The method according to claim 7 or 8, wherein the wet electrostatic precipitator (39) is located outside the scrubber (51, 83) such that the step of purifying the exhaust gas (EG) from the contaminants occurs inside the scrubber (51, 83), while the step of further purifying the exhaust gas from the contaminants occurs outside the scrubber (51, 83).

10. The method according to any one of claims 7 to 9, wherein the scrubbing fluid has a pH value greater than 7.

11. The method according to any one of claims 7 to 10, comprising the step of supplying the exhaust gas in a vertical exhaust gas flow direction through at least most of the wet electrostatic precipitator (39) and the scrubbing sections (11, 53, 89).

12. Use on a ship of an exhaust gas purification system (1, 49, 77, 107) according to any one of claims 1 to 6 for reducing pollutants in exhaust gas (EG) from a marine combustion engine (3), combustor or boiler.

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