EP4164773A1

EP4164773A1 - System comprising two scrubbers connected to an electrostatic precipitator and a method for purifying exhaust gas using it

Info

Publication number: EP4164773A1
Application number: EP21737106.1A
Authority: EP
Inventors: Jere FABRITIUS; Juha JOKILUOMA
Original assignee: Valmet Technologies Oy
Current assignee: Valmet Technologies Oy
Priority date: 2020-06-16
Filing date: 2021-06-02
Publication date: 2023-04-19
Also published as: JP2023530916A; WO2021255329A1; JP7779608B2; FI130699B1; FI20205629A1; CN115803100A; KR20230025442A

Abstract

A method for cleaning at least first exhaust gas (EG1) and second exhaust gas (EG1). The method comprising scrubbing the first and second exhaust gases (EG1, EG2) in a first and a second scrubber (710, 720) to produce scrubbed first and second exhaust gases (SEG1, SEG2); and conveying at least part of the scrubbed first and second exhaust gases (SEG1, SEG2) to an electrostatic precipitator (100). The method further comprises cleaning one or both of the at least part of the scrubbed first exhaust gas (SEG1) and the at least part of the scrubbed second exhaust gas (SEG2) in the electrostatic precipitator (100) to produce clean exhaust gas (CEG). A system for the carrying out the method.

Description

SYSTEM COMPRISING TWO SCRUBBERS CONNECTED TO AN ELECTROSTATIC PRECIPITATOR AND A METHOD FOR PURIFYING EXHAUST GAS USING IT

Technical field The invention relates to cleaning exhaust gases, in particular exhaust gases of more than one combustion engines. The invention is especially usable on a ship, which only has a limited space for the equipment, particularly on a ship comprising multiple combustion engines. The invention relates to desulphurization of exhaust gases, i.e. flue gases, by scrubbing. The invention relates to cleaning scrubbed exhaust gases.

Background

Fossil fuel combustion is used in industrial processes for many different purposes, including combustion engines. Depending on the quality of the fuel, the flue gases (i.e. exhaust gases) may contain various amounts of pollutants, including sulphur oxides (SOx). Marine vessels, i.e. ships, typically include combustion engines and use low grade fuels that both result in high levels of SOx and particles present in the exhaust gas (i.e. flue gas). One possibility to reduce the content of SOx in the exhaust gas is to use desulphurization techniques, in particular a wet scrubbing process, in which the emitted exhaust/flue gases are brought into intimate contact with an aqueous scrubbing solution. The aim of these processes is to provide high absorption efficiency and to remove, or substantially reduce, the concentration of particles, droplets or substances in the exhaust/flue gas that are scrubbed. Marine scrubbers for scrubbing gases exhausted from a marine engine are known from the publications EP 1 857 169, US 3 781 407, and W099/44722. The scrubbers disclosed therein operate in a closed-loop mode, a semi closed- loop mode, and in an open-loop mode, respectively.

However, the scrubbing does not remove all the contaminants of the exhaust gas. Small particles may escape the scrubber. Such contaminants may be hazardous to the environment. Therefore, further cleaning may be required. When the exhaust gases are produced on a ship, there is only a limited amount of space available for additional cleaning equipment. Summary

It has been found that the scrubbed exhaust gases can be further cleaned by using an electrostatic precipitator (ESP). Because the exhaust gases leave the scrubber(s) at a saturated moisture content, the ESP may be referred to as a wet ESP (i.e. WESP), because of the humidity of the scrubbed exhaust gas/gases. Moreover, it has been found that the same wet ESP can be used to further clean scrubbed exhaust gases obtainable from more than one scrubbers. Using only one wet ESP for at least two scrubbers diminishes space requirements of the equipment. Moreover, the arrangement makes it possible to use the wet ESP for cleaning only such exhaust gases that need to be cleaned. The arrangement also allows, on a ship, that whichever of the engines is in operation in harbour conditions (when typically only one or two engine(s) is running), the gases can be cleaned in the wet ESP from one or multiple combustion engines, which significantly increases flexibility in ship operation. The environmental requirements concerning a ship may be very different depending on where the ship is operated. For example, on sea, the wet ESP may not be needed at all, which enables maintenance of the wet ESP. In contrast, closer to a harbour, the wet ESP may be required because of local environmental legislation. Moreover, closer to a harbour, the ship’s engine(s) may be operated at only partial power, whereby the singe wet ESP may be sufficient near a harbour, even if the single wet ESP would not be sufficient when all the engines operate at full power (e.g. at sea).

The arrangement is disclosed in more specific terms in claim 1 . The method is disclosed in more specific terms in claim 9. The dependent claims define preferable embodiments. The description discloses further details of the embodiments.

Brief description of the drawings

Fig. 1 shows a ship having an arrangement for cleaning exhaust gases, Figs. 2a to 2d show arrangements for cleaning exhaust gases,

Figs. 3a to 3d shows arrangements for evenly spreading the scrubbed exhaust gases within the wet ESP,

Fig. 4a shows a side view of an interior of a wet electrostatic precipitator, Fig. 4b shows a top view of a precipitation zone of a wet electrostatic precipitator, Fig. 5a shows a top view of a precipitation zone of another wet electrostatic precipitator, Fig. 5b shows a top view of a precipitation zone of another wet electrostatic precipitator, Fig. 6 shows an arrangement for cleaning exhaust gases, wherein a scrubber serves multiple combustion engines, and Fig. 7 shows an arrangement for cleaning exhaust gases, wherein the wet electrostatic precipitator serves more than two scrubbers.

In the figures, the direction arrows Sz, Sx, and Sy indicate upwards vertical direction and two orthogonal horizontal directions, respectively. The direction arrow SI indicates a longitudinal direction of an electrode of the wet electrostatic precipitator, which, in use, may be substantially vertical. The direction arrows St1 and St2 indicate orthogonal directions that are transverse to the longitudinal direction SI.

Detailed description

Figure 1 shows a ship 910 being equipped with (i.e. comprising) an arrangement 900 for cleaning first exhaust gas EG1 and second exhaust gas EG2. The ship 910 is an example of a more general vehicle, wherein the arrangement 900 can also be used, as well as in other locations, wherein the space for the arrangement 900 is limited. Figures 2a to 2d show examples of an arrangement 900 usable as indicated above.

The exhaust gases EG1 , EG2 are produced in combustion processes, whereby they are hot and contain sulphur oxides (SOx). In order to diminish the amount of sulphur oxides, the arrangement 900 comprises a wet scrubber. Flowever, exhaust gas from a source is oftentimes scrubbed in a wet scrubber dedicated to scrub the exhaust gases of only that source in order to avoid conveying hot exhaust gases on the vehicle for a long distance. In what follows, the term “scrubber” refers to a wet scrubber, i.e. a scrubber in which the gases to be scrubbed are contacted with a scrubbing solution. In a typical ship (or vehicle), there are multiple different sources of exhaust gases. Thus, typically, the ship (or vehicle) is equipped with at least two scrubbers 710, 720. Therefore, the arrangement 900 comprises a first scrubber 710 and a second scrubber 720. The first scrubber 710 comprises an inlet 712 for receiving the first exhaust gas EG1 and an outlet 714 for letting out scrubbed first exhaust gas SEG1 (see Figs. 2a to 2d). The second scrubber 720 comprises an inlet 722 for receiving the second exhaust gas EG2 and an outlet 724 for letting out scrubbed second exhaust gas SEG2 (see Figs. 2a to 2d). The scrubbers 710, 720 are configured to desulphurize and clean the exhaust gases EG1 , EG2, respectively; at least to some extent.

The source of the first exhaust gas EG1 may be, but need not be, a first combustion engine 810. The source of the second exhaust gas EG2 may be, but need not be, a second combustion engine 820.

In order to clean the scrubbed exhaust gases SEG1 , SEG2, the arrangement comprises an electrostatic precipitator (ESP) 100. The ESP 100 comprises a first inlet 112 for receiving at least some of the scrubbed first exhaust gas SEG1 and a second inlet 114 for receiving at least some of the scrubbed second exhaust gas SEG2. Such inletsl 12, 114 are depicted e.g. in Figs. 2b and 4a. As will be detailed below, not all of the scrubbed first exhaust gas SEG1 needs to be cleaned in the ESP 100; and not all of the scrubbed second exhaust gas SEG2 needs to be cleaned in the ESP 100. For this reason, the arrangement 900 comprises a first primary piping 716 configured to convey at least some of the scrubbed first exhaust gas SEG1 to the first inlet 112 of the ESP 100 and a second primary piping 726 configured to convey at least some of the scrubbed second exhaust gas SEG2 to the second inlet 114 of the electrostatic precipitator 100. These pipings 716, 726 are shown in Figs. 2a to 2d. The ESP 100 is of the type of a wet electrostatic precipitator, i.e. wet ESP, i.e. WESP, in order to clean gases that are substantially saturated with humidity (i.e. after a wet scrubber).

Referring to Fig. 4a, the wet ESP 100 comprises an inlet zone Z1. The first inlet 112 and the second inlet 114 are arranged within the inlet zone Z1. In other words, the inlet zone Z1 is equipped with the first and the second inlets (112, 114). In a marine application, the inlet zone Z1 is preferably short. In more specific terms, in a preferable embodiment, a height of the inlet zone Z1 is at most 30 % of a height of the wet ESP 100. The height of the inlet zone Z1 may be e.g. at most the same as a height of a precipitation zone Z2 of the wet ESP. Moreover, preferably, the inlet zone Z1 overlaps in the direction of the height of the wet ESP with the rest of the wet ESP 100. In other words, preferably, the inlet zone Z1 does not radially protrude from the rest of the wet ESP 100. More preferably, a cross section of the inlet zone Z1 on a horizontal plane is the same as a cross section of the wet ESP 100 on a horizontal plane.

The wet ESP comprises a precipitation zone Z2. The scrubbed exhaust gases are configured to be cleaned within the precipitation zone Z2 following the principles of electrostatic precipitation. Therefore, the wet ESP 100 comprises discharge electrodes 220 and collecting surfaces 210, as will be detailed below (see e.g. Figs. 4b, 5a, and 5b). The collecting surfaces 210 are also electrodes. Thus, the discharge electrodes 220 and collecting surfaces 210 are referred to simply as electrodes, when considered feasible. The electrodes 210, 220 are for electrically precipitating at least one of the scrubbed first exhaust gas SEG1 and the scrubbed second exhaust gas SEG2. The electrodes (210, 220) are arranged within the precipitation zone Z2 of the wet ESP 100. A height of the precipitation zone Z2 may equal a length of a collecting surface 210.

The wet ESP 100 comprises an outlet 132 for letting out clean exhaust gas CEG (see Figs. 3a to 3d). In use, the scrubbed exhaust gas that is further cleaned in the wet ESP 100 flows from the inlet/inlets 112, 114 through the precipitation zone Z2 to the outlet 132. Therefore, the precipitation zone Z2 is arranged in between the inlet zone Z1 and the outlet 132 of the wet ESP 100.

In order to function well and to diminish maintenance intervals, the gas/gases SEG1 , SEG2 that are cleaned with the wet ESP 100 should be evenly distributed to the precipitation zone Z2. Therefore, in an embodiment, the wet ESP 100 comprises a perforated plate 150 in between the inlet zone Z1 and the precipitation zone Z2, as shown in Figs. 3a, 3c, and 3d. A purpose of the perforated plate 150 is to divide the gas SEG, SEG2 evenly in between the electrodes 210, 220 of the wet ESP 100. In an embodiment, the wet ESP 100 comprises at least two perforated plates 150, or more than two perforated plates 150, in between the inlet zone Z1 and the precipitation zone Z2, for dividing the gas SEG, SEG2 more evenly in between the electrodes 210, 220 of the wet ESP 100.

Another possibility, not exclusive with the perforated plate 150, is to use a perforated tube 152 or perforated tubes 152, 154 in the inlet zone Z1 . Referring to Figs. 3b and 3c, in an embodiment, the wet ESP 100 comprises, in the inlet zone Z1 , a first perforated tube 152 that is configured to deliver the first scrubbed exhaust gas SEG1 into the inlet zone Z1. Moreover, in an embodiment, the wet ESP 100 comprises, in the inlet zone Z1 , a second perforated tube 154 that is configured to deliver the second scrubbed exhaust gas SEG2 into the inlet zone Z1 . The first perforated tube 152 may comprise bends in order to spread the first scrubbed exhaust gas SEG1 more evenly into the inlet zone Z1. The second perforated tube 154 may comprise bends in order to spread the second scrubbed exhaust gas SEG2 more evenly into the inlet zone Z1. Guide plates may be arranged inside the perforated tubes 152, 154 to further level out the flow of the scrubbed exhaust gas/gases SEG1 , SEG2 into the inlet zone Z1 . The perforated tubes 152, 154 can be connected together to form a single perforated tube 152, as shown in Fig. 3d, to which both the scrubbed exhaust gases SEG1 , SEG2 are conveyed; however not necessarily simultaneously. In the Figs. 3b, 3c, and 3d, the first perforated tube 152 is configured to deliver at least the first scrubbed exhaust gas SEG1 into the inlet zone Z1 .

As depicted in Fig. 3c, the wet ESP 100 may comprise the perforated plate 150 in between the inlet zone Z1 and the precipitation zone Z2 and the first and second perforated tubes 152, 154. As depicted in Fig. 3d, the wet ESP 100 may comprise the perforated plate 150 in between the inlet zone Z1 and the precipitation zone Z2 and only the first perforated tube 152.

When the arrangement 900 is operated, a method for cleaning exhaust gases is performed. As indicated above, in an embodiment of the method, the wet electrostatic precipitator 100 is arranged on a vehicle, such as a ship 910. The method comprises scrubbing first exhaust gas EG1 in a first scrubber 710 to produce scrubbed first exhaust gas SEG1 and scrubbing second exhaust gas EG2 in a second scrubber 720 to produce scrubbed second exhaust gas SEG2. The method further comprises conveying at least part of the scrubbed first exhaust gas SEG1 to a wet electrostatic precipitator 100, and conveying at least part of the scrubbed second exhaust gas SEG2 to the wet electrostatic precipitator 100. Furthermore, the method comprises cleaning at least one of the at least part of the scrubbed first exhaust gas SEG1 and the at least part of the scrubbed second exhaust gas SEG2 in the wet electrostatic precipitator 100 to produce clean exhaust gas CEG.

A preferable embodiment of the method comprises cleaning both (i) at least the part of the scrubbed first exhaust gas SEG1 and (ii) at least the part of the scrubbed second exhaust gas SEG2 in the wet electrostatic precipitator 100 to produce clean exhaust gas CEG. However, both the first and second scrubbed exhaust gases SEG1 and SEG2 need not be present at the wet electrostatic precipitator 100 simultaneously. For example the (i) at least a part of the scrubbed first exhaust gas SEG1 and the (ii) at least a part of the scrubbed second exhaust gas SEG2 may be cleaned subsequently using the same wet ESP 100. Further details concerning the issue of “at least part” of the scrubbed exhaust gas (SEG1 , SEG2) will be given below in connection with first and second valve arrangements 754 and 764.

It has been found that the scrubbing, and thus also the wet desulphurization of the exhaust gases EG1 , EG2, is particularly efficient, when a scrubbing solution is sprayed onto the gases that are scrubbed. In the alternative or in addition, the gases may be conveyed through a bath of a scrubbing solution. However, spraying is much more efficient, since this increases the contact area between the gases EG1 , EG2 and the scrubbing solution. For these reasons, a preferable embodiment of the arrangement 900 comprises a first circulation 718 for spraying first scrubbing solution SS1 within the first scrubber 710 to scrub the first exhaust gas EG1 by contacting the first exhaust gas EG1 with the first scrubbing solution SS1 . This is depicted in all the figures 2a to 2d.

Thus, the first scrubber 710 comprises nozzles 719 (see Figs. 2a to 2d) for spraying the first scrubbing solution SS1 and for forming droplets of the first scrubbing solution SS1 into the first scrubber 710. Moreover, the first scrubber 710 comprises a pump 715 for delivering the scrubbing solution to the nozzles 719. When scrubbed, the first exhaust gas EG1 is let to make a contact with the so formed droplets of the first scrubbing solution SS1. Thus, an embodiment of the method comprises, in the first scrubber 710, spraying the first scrubbing solution SS1 to form droplets of the first scrubbing solution SS1 and letting the first exhaust gas EG1 contact the droplets of the first scrubbing solution SS1 .

The first scrubbing solution SS1 (or the second scrubbing solution SS2 as defined later) may be water, fresh water, seawater, or any other aqueous solution of one or more compounds known to bind, or absorb, one or more of the constituents of the exhaust/flue gas to be scrubbed. Acidic gases as such as SOx are normally removed from a solution by scrubbing with an alkaline solution, such as an aqueous solution of an alkaline compound, such as caustic soda or other alkaline substances.

The first circulation 718 may be an open loop circulation, as shown in Figs. 2b and 2c. Therein sea water may be used as the scrubbing solution. More specifically, sea water may be used as the common (first) scrubbing solution for both the first and the second scrubber 710, 720, as in the in the embodiment of Fig. 2b. Sea water may be used as both the first scrubbing solution SS1 used in the first scrubber 710 and a second scrubbing solution SS2 used in the second scrubber 720 in the embodiment of Fig. 2c.

The first circulation 718 may be a closed loop circulation, as shown in Figs. 2a and 2d. A closed loop circulation may be usable, when environmental restrictions are strict. If a closed loop circulation is used, the scrubbing solution SS1 or the scrubbing solutions SS1 and SS2 are formed preferably from water (sea water and/or fresh water) and alkaline. In such a case and even more preferably, the scrubbing solution SS1 or the scrubbing solutions SS1 and SS2 are formed from fresh water and alkaline. Solids may be removed from the scrubbing solution(s) SS1 , SS2 from the circulation(s) 718, 728.

When the first circulation 718 is a closed loop circulation, as shown in Figs. 2a and 2d, the temperature of the first scrubbing solution tends to rise, since the exhaust gases, which are scrubbed, are hot. Flowever, the capability of the first scrubbing solution SS1 capturing SOx from the first exhaust gas EG1 decreases, when temperature increases. Also, evaporation of water from process to the atmosphere increases, which can remarkably increase make- up water consumption and result in thick visible plume after the stack. Therefore, preferably, the first circulation 718 comprises a heat exchanger 717 for cooling the first scrubbing solution SS1 (see Figs. 2a and 2d). Coolant C1 used in the heat exchanger 717 on a ship is typically seawater. In other applications, e.g. air or water (e.g. fresh water or sea water) may be usable as the coolant C1 in the heat exchanger 717. When the arrangement comprises a second circulation 728 and the second circulation 728 is of the closed loop type, the second circulation 728 comprises a heat exchanger 727 for cooling the second scrubbing solution SS2 (see Fig. 2a).

In Figs. 2a and 2d the pump (715, 725) of the circulation (718, 728) is arranged downstream from the heat exchanger (717, 727) of the circulation. Flowever, in an embodiment, such a pump 715, 725 of the circulation 718, 728 is arranged upstream from a heat exchanger 717, 727 of the circulation 718, 728.

A hybrid mode scrubber can also be used as either one or both of the first and second scrubber. A hybrid mode scrubber includes valve(s) (not shown) so that at a first time, the scrubbing solution that is sprayed, is taken from the scrubber (as in Figs. 2a and 2d), and at a second time, the scrubbing solution that is sprayed, is taken from the sea (as in Figs. 2b and 2c).

The same (first) circulation 718 may be used to feed the same (first) scrubbing solution SS1 into both the first and the second scrubbers 710, 720, as depicted in Figs. 2b and 2d. In this embodiment, the first circulation 718 is suitable for spraying the first scrubbing solution SS1 within the second scrubber 720 to scrub the second exhaust gas EG2 by contacting the second exhaust gas EG2 with the first scrubbing solution SS1. A corresponding method comprises, in the second scrubber 720, spraying the first scrubbing solution SS1 to form droplets of the (first) scrubbing solution SS1 and letting the second exhaust gas EG2 contact the droplets of the (first) scrubbing solution SS1 .

In the alternative, the arrangement 900 may comprise a second circulation 728 (see Figs. 2a and 2c) for spraying second scrubbing solution SS2 within the second scrubber 720 to scrub the second exhaust gas EG2 by contacting the second exhaust gas EG2 with the second scrubbing solution SS2. A corresponding method comprises, in the second scrubber 720, spraying the second scrubbing solution SS2 to form droplets of the (second) scrubbing solution SS2 and letting the second exhaust gas EG2 contact the droplets of the (second) scrubbing solution SS2.

As for some structural details of the wet ESP 100, the wet ESP 100 comprises, at the precipitation zone Z2 the discharge electrodes 220 and collecting surfaces 210. The precipitation zone Z2 is shown from a side in Fig. 4a, and from and end in Fig 4b. In Fig. 4a, the reference SI indicates a longitudinal direction of the discharge electrodes 220 or collecting surfaces 210, or, in other words, the direction of flow of the scrubbed exhaust gas(es) SEG1 , SEG2 within the wet ESP. In use, the longitudinal direction SI may be substantially vertical. Flowever, when onboard a ship, the direction SI may change as the ship rolls (i.e. swings). Preferably, in use, the longitudinal direction SI forms an angle of at most 45 degrees with a vertical direction Sz.

Figs. 4b, 5a, and 5b show a transversal cross section of the precipitation zone Z2. In Figs. 4b and 3a every second electrode has a tubular shape, while the other electrodes are arranged coaxially within the tubular electrodes. In Fig. 5b, the electrodes have the shape of a plate. The tubular electrodes in Figs. 4b and 5a have a tubular shape extending in the longitudinal direction SI. The planar electrodes in Fig. 5b extend in a plane that comprises the longitudinal direction SI. Typically the wet ESP 100 comprises means 222 for discharging electric charge to particles of the at least one of the scrubbed first exhaust gas SEG1 and the scrubbed second exhaust gas SEG2.

The operation principle of the wet ESP is that e.g. the means 222 for discharging electric charge charges particles of the gas SEG1 , SEG2 that is cleaned. Thereafter, the gas is conveyed in between discharge electrodes 220 and collecting surfaces 210. As the particles have an electric charge, the electrodes 210, 220 attract the particles and the particles collide therewith. Typically, the means 222 for discharging electric charge are arranged as part of the discharging electrodes 220 (most often in a lower electric potential than the collecting surface 210), whereby they emit electrons to the particles to be removed. Correspondingly, the particles collide with collecting surfaces 210 and become arrested thereto. Thus, in a preferable embodiment, an area of the collecting surfaces 210 is greater than an area of the discharge electrodes 220, as in Fig. 4b. The means 222 for discharging electric charge may be sharp protrusions on the discharge electrode 220. For these reasons, in a preferable embodiment, the collecting surfaces 210 have a tubular shape extending in the longitudinal direction SI, and each discharge electrode 220 extends coaxially with one of the collecting surfaces 210 in the longitudinal direction SI, as shown in Fig. 4b; the discharge electrode 220 being laterally surrounded by the collecting surface 210.

In order to generate the electric field, the arrangement 900 or the wet ESP 100 comprises an electric source 230 and wiring 232 configured to convey a first electric potential V1 to the collecting surfaces 210 and a second electric potential V2 to the discharge electrodes 220. In an embodiment, the second electric potential V2 is less than the first electric potential V1 . A strength of an electric field in between the electrodes 210, 220 may be e.g. from 0.1 kV/cm to 10 kV/cm.

It has been found the wet ESP 100 is particularly useful when used after a scrubber, i.e. a wet scrubber operating with a scrubbing solution SS1 , SS2. The arrangement is useful, since the scrubbed exhaust gas SEG1 , SEG2 entering the wet ESP 100 is substantially saturated with moisture. Thus, the moisture of the gases SEG1 , SEG2 condense on the electrodes 210, 220 of the wet ESP, and in use, flush the electrodes so that at least some of the particles which collide with the electrodes, are flushed with the condensate. This increases a maintenance interval of the wet ESP. Moreover, because of the flushing, in an embodiment of the arrangement 900, the wet electrostatic precipitator 100 comprises, at a lower part of the wet electrostatic precipitator 100, a secondary outlet 140 for draining effluent EFF from the wet electrostatic precipitator 100, as depicted in Figs. 2a to 4a. The effluent EFF comprises the condensate of the scrubbed exhaust gas SEG1 , SEG2, and may further comprise rinsing solution RS, as detailed below. The aforementioned relatively small angle between the longitudinal direction SI and the vertical direction Sz is beneficial also from the point of view of flushing the electrodes.

As motivated in the background, low-grade fuels include a lot of sulphur, but are otherwise attractive, since they are cheap. The problem with high sulphur content can be diminished by using the arrangement 900 as discussed above. In particular, the low-grade fuel can be used in a combustion engine. Thus, an embodiment of the arrangement 900 comprises a first combustion engine 810 and a first secondary piping 891 configured to convey first exhaust gas EG1 of the first combustion engine 810 to the inlet 712 of the first scrubber 710. Thus, when the combustion engine is operated, at least a part of the first exhaust gas EG1 generated by the first combustion engine 810 is conveyed to the first scrubber 710 and scrubbed therein. Moreover, the embodiment comprises a second combustion engine 820 and a second secondary piping 892 configured to convey second exhaust gas EG2 of the second combustion engine 820 to the inlet 722 of the second scrubber 720. Thus, when the combustion engine is operated, at least a part of the second exhaust gas EG2 generated by the second combustion engine 820 is conveyed to the second scrubber 720 and scrubbed therein. Reference is made to Figs. 1 , 2a, 2c, 2d, 6, and 7.

As detailed above, the scrubbed exhaust gases SEG1 , SEG2 are humid. This applies also to the clean exhaust gas CEG emitted from the wet ESP 100. When emitted to atmosphere, some of the humidity may become visible, known as exhaust gas plume, or simply plume. However, oftentimes people mix up visible humidity with smoke. Since smoke emission is, in general, considered harmful for environment, an embodiment of the arrangement 900 comprises a plume diminishing device 160 configured to diminish plume of the clean exhaust gas CEG, as shown in Figs. 2a, 2c, and 2d. The plume diminishing device 160 may comprise at least a fan for mixing depluming gas DPG with the clean exhaust gas CEG. The depluming gas DPG may be dry and/or hot gas, e.g. air, in order to diminish plume of the CEG. For these reasons, an embodiment of the method comprises mixing depluming gas DPG with the clean exhaust gas CEG to diminish plume of the clean exhaust gas CEG. The plume diminishing device 160 eliminates water vapour from the clean exhaust gas after the wet ESP 100. This means that white smoke is eliminated and corrosion is avoided on the top 162 of the exhaust pipe.

The wet ESP 100 of the arrangement 900 can be used for cleaning only such exhaust gases that need to be cleaned. Environmental requirements concerning a ship may be very different depending on where the ship is operated. For example, on sea, the wet ESP may not be needed at all, which enables maintenance of the wet ESP. Closer to a harbour, the wet ESP may be required because of local environmental legislation. However, closer to a harbour, the ship’s engine(s) may be operated at only partial power, whereby the singe wet ESP may be sufficient near a harbour, even if the single wet ESP would not be sufficient when all the engines operate at full power (e.g. at sea). Moreover, closer to a harbour, the ship may run with only one engine, whereby the singe wet ESP may be used to clean exhaust gas from only one engine.

In order to enable the versatile use of the single wet ESP 100 in connection with the first 710 and second 720 scrubbers, in an embodiment of the arrangement 900, the first primary piping 716 comprises a first outlet 752 for letting out some of the scrubbed first exhaust gas SEG1 from the first primary piping 716 to elsewhere than to the wet electrostatic precipitator 100, e.g. to atmosphere. Thus, the scrubbed first exhaust gas SEG1 conveyed to the first outlet 752 bypasses the wet ESP 100. Such a first outlet 752 is shown in Figs. 2a to 2d. Moreover, the first primary piping 716 comprises a first valve arrangement 754 for conveying at least some of the scrubbed first exhaust gas SEG1 to the first outlet 752 and at least some of the scrubbed first exhaust gas SEG1 to the first inlet 112 of the wet electrostatic precipitator 100. Thus, the first valve arrangement 754 is also suitable for conveying all the scrubbed first exhaust gas SEG1 to the first outlet 752 and, correspondingly, none of the scrubbed first exhaust gas SEG1 to the first inlet 112 of the wet electrostatic precipitator 100. The first valve arrangement 754 can thus be used to convey none, only a part of, or all of the scrubbed first exhaust gas SEG1 directly to the first outlet 752, and e.g. to the atmosphere. The first valve arrangement 754 can thus be used to convey all of, only a part of, or none of the scrubbed first exhaust gas SEG1 to the first inlet 112 of the wet ESP 100. Depending on the case, further cleaning may of the SEG1 by using the wet ESP may not be required. Moreover, in an embodiment, the second primary piping 726 comprises a second outlet 762 for letting out some of the scrubbed second exhaust gas SEG2 from the second primary piping 726 to elsewhere than to the wet electrostatic precipitator 100; and a second valve arrangement 764 for conveying at least some of the scrubbed second exhaust gas SEG2 to the second outlet 762 and at least some of the scrubbed second exhaust gas SEG2 to the second inlet 114 of the wet electrostatic precipitator 100. Thus, the scrubbed second exhaust gas SEG2 conveyed to the second outlet 762 bypasses the wet ESP 100. The second valve arrangement 764 can be used in a similar manner as the first valve arrangement 754 mutatis mutandis.

The first and second valve arrangements 754, 764 can be used e.g. in such a manner that at a first period of time, both of (i) the scrubbed first exhaust gas SEG1 or a part thereof and (ii) the scrubbed second exhaust gas SEG2 or a part thereof are conveyed to the wet ESP 100. In particular the valve arrangements 754, 764 can be used such that at the first period of time, [A] both of (i) only a part of the scrubbed first exhaust gas SEG1 and (ii) all the scrubbed second exhaust gas SEG2, or [B] both of (i) only a part of the scrubbed first exhaust gas SEG1 and (ii) only a part of the scrubbed second exhaust gas SEG2 are conveyed to the wet ESP 100. Concerning the latter, when only a part of the scrubbed first exhaust gas SEG1 is cleaned with the wet ESP 100, the wet ESP 100 needs not be as large as if it would have been designed to clean all the scrubbed first exhaust gas SEG1 . Such use may be possible e.g. at sea.

The first and second valve arrangements 754, 764 can be used e.g. in such a manner that at a second period of time, only one of (i) the scrubbed first exhaust gas SEG1 or a part thereof or (ii) the scrubbed second exhaust gas SEG2 or a part thereof is conveyed to the wet ESP 100. Depending on the case, the source for the other exhaust gas may be turned off (e.g. one of the combustion engines 810, 820 is not running) or the scrubbed exhaust gas thereof is emitted directly to the atmosphere via the outlet (752, 762) of the piping.

The first and second valve arrangements 754, 764 can be used e.g. in such a manner that at a at a third period of time, neither (i) the scrubbed first exhaust gas SEG1 or a part thereof nor (ii) the scrubbed second exhaust gas SEG2 or a part thereof is conveyed to the wet ESP 100. Depending on the case, the sources for the other exhaust gas may be turned off (e.g. neither one of the combustion engines 810, 820 is running, e.g. when anchored) or the scrubbed exhaust gases or both thereof are emitted directly to the atmosphere via the outlets (752, 762) of the pipings. Thus, at the third period of time, the wet ESP 100 is not in use. This may be possible e.g. at sea, when no further cleaning of the scrubbed exhaust gases SEG1 , SEG2 is needed. When the wet ESP 100 is not used, it may be maintained. As detailed above, on a ship and at sea, the wet ESP is not necessarily used. Maintaining the wet ESP preferably includes at least washing. The wet ESP may be washed with a rinsing solution RS. The washing preferably includes at least washing of some of the electrodes 210, 220 of the wet ESP 100; in particular such electrodes that collect the contaminants, which are typically the collecting surfaces 210 (e.g. electrodes at a higher electric potential). For these reasons, in an embodiment of the arrangement 900, the wet electrostatic precipitator 100 comprises an inlet 120 for letting in rinsing solution RS, and means 122 for washing at least some of the electrodes 210, 220 of the wet electrostatic precipitator 100 using the rinsing solution RS. The means 122 may include nozzles for spraying the rinsing solution RS onto the electrodes that are washed, such as onto at least the collecting surfaces 210. Such means 122 and the inlet 120 are depicted e.g. in Figs. 2a, 2c, and 2d.

Referring to Fig. 6, it is also possible to use the first scrubber 710 for scrubbing the first exhaust gas EG1 and some third exhaust gas EG3. The third exhaust gas EG3 may be produced in a third combustion engine 830. In addition (as shown in Fig. 6) or alternatively (not shown), the second scrubber 720 can be used for scrubbing the second exhaust gas EG2 and some fourth exhaust gas EG4. The fourth exhaust gas EG4 may be produced in a fourth combustion engine 840.

Referring to Fig. 7, the wet ESP 100 may comprise a third inlet 116 for receiving at least some scrubbed third exhaust gas SEG3. The scrubbed third exhaust gas SEG3 may be received from a third scrubber 730. The third scrubber 730 may be configured to scrub third exhaust gas EG3 of a third combustion engine 830. As depicted in the figure 7, the arrangement may comprise a third valve arrangement for conveying all of, none of, or only a part of the scrubbed third exhaust gas SEG3 into the wet ESP 100, and, respectively, none of, all of, or only a part of the scrubbed third exhaust gas SEG3 to elsewhere, e.g. to the atmosphere. When the wet ESP 100 comprises the third inlet 116, the first inlet 112, the second inlet 114, and the third inlet 116 are arranged within the inlet zone Z1 . Also in this case the height of the inlet zone Z1 is preferably small as detailed above, even if not shown in Fig. 7.

Claims

Claims:

1. An arrangement (900) comprising

- a first scrubber (710) comprising an inlet (712) for receiving first exhaust gas (EG1 ) and an outlet (714) for letting out scrubbed first exhaust gas (SEG1 ),

- a second scrubber (720) comprising an inlet (722) for receiving second exhaust gas (EG2) and an outlet (724) for letting out scrubbed second exhaust gas (SEG2),

- an electrostatic precipitator (100) comprising · an inlet zone (Z1 ) equipped with a first inlet (112) for receiving scrubbed first exhaust gas (SEG1 ) and a second inlet (114) for receiving scrubbed second exhaust gas (SEG2),

• discharge electrodes (220) and collecting surfaces (210) for electrically precipitating the scrubbed exhaust gas (SEG1, SEG2), the discharge electrodes (220) and collecting surfaces (210) being arranged within a precipitation zone (Z2) of the electrostatic precipitator (100), and

• an outlet (132) for letting out clean exhaust gas (CEG), wherein

• the precipitation zone (Z2) is arranged in between the inlet zone (Z1) and the outlet (132) of the electrostatic precipitator (100) and - a first primary piping (716) configured to convey scrubbed first exhaust gas

(SEG1 ) to the first inlet (112) of the electrostatic precipitator (100) and

- a second primary piping (726) configured to convey scrubbed second exhaust gas (SEG2) to the second inlet (114) of the electrostatic precipitator (100).

2. The arrangement (900) of claim 1 , wherein

- the arrangement (900) comprises a first circulation (718) for spraying first scrubbing solution (SS1) within the first scrubber (710) to scrub the first exhaust gas (EG1) by contacting the first exhaust gas (EG1) with the first scrubbing solution (SS1) and

[A]

- the first circulation (718) is suitable for spraying the first scrubbing solution (SS1 ) within the second scrubber (720) to scrub the second exhaust gas (EG2) by contacting the second exhaust gas (EG2) with the first scrubbing solution (SS1) or

[B] - the arrangement (900) comprises a second circulation (728) for spraying second scrubbing solution (SS2) within the second scrubber (720) to scrub the second exhaust gas (EG2) by contacting the second exhaust gas (EG2) with the second scrubbing solution (SS2); preferably,

- the first circulation (718) comprises a heat exchanger (717) for cooling the first scrubbing solution (SS1 ).

3. The arrangement of claim 1 or 2, wherein

- the electrostatic precipitator (100) comprises, at a lower part of the electrostatic precipitator (100), a secondary outlet (140) for draining effluent (EFF) from the electrostatic precipitator (100).

4. The arrangement of any of the claims 1 to 3, comprising

- a first combustion engine (810),

- a first secondary piping (891 ) configured to convey first exhaust gas (EG1 ) of the first combustion engine (810) to the inlet (712) of the first scrubber (710),

- a second combustion engine (820), and

- a second secondary piping (892) configured to convey second exhaust gas (EG2) of the second combustion engine (820) to the inlet (722) of the second scrubber (720).

5. The arrangement of any of the claims 1 to 4, wherein

- the first primary piping (716) comprises

• a first outlet (752) for letting out some of the scrubbed first exhaust gas (SEG1 ) from the first primary piping (716) to another location than to the electrostatic precipitator (100) and

• a first valve arrangement (754) for conveying at least some of the scrubbed first exhaust gas (SEG1 ) to the first outlet (752) and at least some of the scrubbed first exhaust gas (SEG1 ) to the first inlet (112) of the electrostatic precipitator (100); preferably,

- the second primary piping (726) comprises

• a second outlet (762) for letting out some of the scrubbed second exhaust gas (SEG2) from the second primary piping (726) to another location than to the electrostatic precipitator (100) and • a second valve arrangement (764) for conveying at least some of the scrubbed second exhaust gas (SEG2) to the second outlet (762) and at least some of the scrubbed second exhaust gas (SEG2) to the second inlet (114) of the electrostatic precipitator (100).

6. The arrangement of any of the claims 1 to 5, comprising

- a perforated plate (150) or perforated plates (150) in between the inlet zone (Z1 ) and the precipitation zone (Z2) and/or

- a first perforated tube (152) configured to deliver at least the first scrubbed exhaust gas (SEG1 ) to the inlet zone (Z1 ).

7. The arrangement of any of the claims 1 to 6, wherein the electrostatic precipitator (100) comprises

- an inlet (120) for letting in rinsing solution (RS), and

- means (122) for washing at least some of the collecting surfaces (210) and/or the discharge electrodes (220) of the electrostatic precipitator (100) using the rinsing solution (RS).

8. A vehicle, such as a ship (910), comprising the arrangement (900) of any of the claims 1 to 7.

9. A method for cleaning at least first exhaust gas (EG1 ) and second exhaust gas (EG1 ), the method comprising

- scrubbing the first exhaust gas (EG1 ) in a first scrubber (710) to produce scrubbed first exhaust gas (SEG1 ),

- scrubbing the second exhaust gas (EG2) in a second scrubber (720) to produce scrubbed second exhaust gas (SEG2),

- conveying at least part of the scrubbed first exhaust gas (SEG1 ) to an electrostatic precipitator (100),

- conveying at least part of the scrubbed second exhaust gas (SEG2) to the electrostatic precipitator (100),

- cleaning one or both of the at least part of the scrubbed first exhaust gas (SEG1 ) and the at least part of the scrubbed second exhaust gas (SEG2) in the electrostatic precipitator (100) to produce clean exhaust gas (CEG).

10. The method of claim 9, comprising

- in the first scrubber (710), spraying a first scrubbing solution (SS1 ) to form droplets of the first scrubbing solution (SS1 ) and letting the first exhaust gas (EG1 ) contact the droplets of the first scrubbing solution (SS1), and

- in the second scrubber (720), spraying the first scrubbing solution (SS1 ) or a second scrubbing solution (SS2) to form droplets of the first or the second scrubbing solution (SS1 , SS2) and letting the second exhaust gas (EG2) contact the droplets of the first or the second scrubbing solution (SS1 , SS2); preferably, the method comprises

- cooling the first scrubbing solution (SS1 ) using a first heat exchanger (717), preferably using water, such as sea water, as a coolant (C1 ), more preferably,

- the first scrubbing solution (SS1 ) comprises water, e.g. fresh water, and alkaline.

11 . The method of claim 9 or 10, comprising

- producing first exhaust gas (EG1 ) in a first combustion engine (810),

- producing second exhaust gas (EG2) in a second combustion engine (820),

- conveying the first exhaust gas (EG1 ) to the first scrubber (710), and

- conveying the second exhaust gas (EG2) to the second scrubber (720).

12. The method of any of the claims 9 to 10, comprising

- at a first period of time, conveying both of (i) the scrubbed first exhaust gas (SEG1 ) or a part thereof and (ii) the scrubbed second exhaust gas (SEG2) or a part thereof to the electrostatic precipitator (100), and/or

- at a second period of time, conveying only one of (i) the scrubbed first exhaust gas (SEG1 ) or a part thereof or (ii) the scrubbed second exhaust gas (SEG2) or a part thereof to the electrostatic precipitator (100), and/or

- at a third period of time, conveying neither (i) the scrubbed first exhaust gas (SEG1 ) or a part thereof nor (ii) the scrubbed second exhaust gas (SEG2) or a part thereof to the electrostatic precipitator (100).

13. The method of any of the claim 12, comprising

- at the first period of time, conveying to the electrostatic precipitator (100)

• [A] both of (i) only a part of the scrubbed first exhaust gas (SEG1 ) and (ii) all the scrubbed second exhaust gas (SEG2), or • [B] both of (i) only a part of the scrubbed first exhaust gas (SEG1 ) and (ii) only a part of the scrubbed second exhaust gas (SEG2, and/or

- at the second period of time, conveying to the electrostatic precipitator (100) only one of (i) only a part of the scrubbed first exhaust gas (SEG1 ) or (ii) only a part of the scrubbed second exhaust gas (SEG2) and/or

- at the third period of time, washing the electrostatic precipitator (100) with a rinsing solution (RS).

14. The method of any of the claims 9 to 13, comprising - mixing depluming gas (DPG) with the clean exhaust gas (CEG) to diminish plume of the clean exhaust gas (CEG).

15. The method of any of the claims 9 to 14, wherein the electrostatic precipitator (100) is arranged on a vehicle, such as a ship (910).