WO2018197420A1

WO2018197420A1 - Ballast water uv treatment unit

Info

Publication number: WO2018197420A1
Application number: PCT/EP2018/060353
Authority: WO
Inventors: Mark KALHØJ; Bjarne Tandrup KROGHOLM; Rasmus FOLSØ
Original assignee: Desmi Ocean Guard A/S
Priority date: 2017-04-25
Filing date: 2018-04-23
Publication date: 2018-11-01

Abstract

The present invention relates to a ballast water UV treatment unit (1) including: an inlet (2) for ballast water to be treated, an outlet (3) for treated ballast water, and a UV treatment chamber (4) disposed in-between said inlet (2) and said outlet (3) and having a longitudinal axis (L) extending between said inlet (2) and said outlet (3), said UV treatment chamber (4) having a plurality of elongated UV light sources extending perpendicularly to or essentially perpendicular to said longitudinal axis (L), said UV treatment chamber (4) defining within its interior a UV treatment volume by two opposite first walls extending parallel to or essentially parallel to said elongated UV light sources spaced therefrom, at least one of said opposite first walls being configured such that said UV treatment chamber (4) in the direction along said longitudinal axis (L) has a varying internal distance (D) between said opposite first walls perpendicularly to said longitudinal axis (L), said UV light sources extending between a pair of second walls (9) of said chamber (4),<b>characterized in</b>sharp turns or course alterations (8) forming transitions between outwardly and inwardly extending portions of at least one of said opposite first walls, to define one or more outwardly bulging portions of said chamber (4), an elongated UV light source extending at least partly in a corresponding outwardly bulging portion, spaced therefrom.

Description

Ballast water UV treatment unit

TECHNICAL FIELD

The present invention relates to a ballast water UV treatment unit. BACKGROUND ART On ships, such as cargo ships or passenger ships, it is often, for various technical reasons, required to carry water ballast.

Water ballast typically serves to oppose an unfavourable resulting centre of gravity resulting from a high or off-centre centre of gravity of the loaded cargo or even the ship itself. Further, in cargo ships, in so called ballast conditions, water ballast is often used to obtain sufficient draft in order to submerge the propeller and rudder. A ballast condition is a loading condition of a ship where the weight of the stowed cargo by itself does not result in a sufficient draft of the ship.

Another typical application of water ballast is for stabilizing or anti heeling purposes where a part of the carried seawater is shifted from side to side in order to counteract rolling of a ship. Seawater is widely used as ballast medium because of its ability to be easily loaded and unloaded via pumping arrangements.

Seawater is typically pumped on board the ship directly from the environments wherein the ship is located. Hereby various species of organisms are, together with the ballast water, moved together with the ship from the place of loading the water to a non-native place of unloading the water.

A part of the living organisms carried in the ballast tanks die during the pumping process as well as and under the voyage, and more die when the organisms are released at the place of unload, however, a substantial part of the organisms survive both the voyage as well as being unloaded in a foreign environment. The introduction of foreign organisms into a new and, for the foreign organisms', unnatural environment has been known to have catastrophic consequences to the environment wherein the organisms are released. It is estimated that about 3-5 billion tonnes of ballast water each year are moved from its natural environment and pumped out in foreign environments.

New directives for treatment of ballast water, aimed at rendering the organisms carried by the ballast water systems harmless for the environment wherein they are released, have been adopted by the International Maritime Organisation (IMO). The directives dictate that measures should be taken such that abovementioned relocation of living organisms is hindered, and further, the directives emphasize that any applied treatment of ballast water must be safe and environmentally acceptable.

IMO have developed and setup specific requirements to performance of the ballast water treatment systems. The requirements dictate a performance framework for the actual treatment of the ballast water as well as limits for toxic content in the ballast water discharged.

In particular, the directives state that any applied technique must show convincing effects as well as be environmentally friendly. Further, the directives state that any applied technique must be economically and technically reasonable to apply. Present ballast water treatment systems are configured for filtration and subsequent after treatment of water to be stored in ballast water tanks. Today's systems typically filtrates the ballast water only when pumping in or loading, meaning that the de-ballasting water is discharged without filtering.

As per the above, it is common to expose an intake stream of ballast water, after filtration, to a subsequent after treatment in order to render living organisms passing through the filter nonviable.

The after treatment may constitute vacuum treatment, chlorination, exposure to ultraviolet light, ozone treatment and cavitation etc.

According to one prevailing after treatment technique applied for purposes of rendering living organisms carried by ships ballast water nonviable, the intake ballast water is pumped through a UV treatment chamber for sterilizing the ballast water with UV rays.

KR20140095302 discloses a UV ballast water treatment system comprising a rectangular column-shaped UV treatment chamber comprising two opposite planar walls extending between an inlet and an outlet to facilitate a flow of ballast water through the chamber. Multiple ultraviolet lamps are installed across the middle portion of the chamber and are arranged parallel to the planar walls. The planar walls are reinforced by multiple ribs mounted consecutive on their outside surface to compensate for the internal water pressure when ballast water is flowing through the chamber.

WO2014/033478 discloses another ballast water treatment plant.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved ballast water UV treatment unit providing a ballast water treatment effect complying with the above requirements. A further object of the invention is to provide a ballast water UV treatment unit capable of providing an optimised minimum UV radiation dose to the ballast water flowing there through, in that zones with stagnant ballast water, i.e. "dead zones", are avoided.

Yet an object of the invention is to provide a UV treatment unit facilitating an optimised flow of ballast water through the unit, including a uniform flow. Furthermore, an object of the invention is to provide a structurally stable UV treatment chamber for a UV treatment unit.

According to one aspect of the invention, there is provided a ballast water UV treatment unit including an inlet for ballast water to be treated, an outlet for treated ballast water, and a UV treatment chamber disposed in-between said inlet and said outlet and having a longitudinal axis extending between said inlet and said outlet, said UV treatment chamber having a plurality of elongated UV light sources extending perpendicularly to or essentially perpendicular to said longitudinal axis, said UV treatment chamber defining within its interior a UV treatment volume by opposite first walls extending parallel to or essentially parallel to said elongated UV light sources spaced therefrom, at least one of said opposite first walls being configured such that said UV treatment chamber in the direction along said longitudinal axis has a varying internal distance between said opposite first walls perpendicularly to said longitudinal axis, said UV light sources extending between a pair of second walls of said chamber, characterized in turns forming transitions between outwardly and inwardly extending portions, when progressing along said longitudinal axis from said inlet, of at least one of said first walls, to define one or more outwardly bulging portions of said chamber, an elongated UV light source extending at least partly in a corresponding outwardly bulging portion, spaced therefrom.

One or both of the two first wall(s) may follow a zig-zag like configuration, alternating in course inwardly and outwardly relative to said longitudinal axis, straight portions of the first wall extending along the longitudinal axis intersecting at an angle straight portions of the first wall extending outwardly and inwardly, respectively, relative to the longitudinal axis.

Such a configuration of the first walls also provides an increased structural bending resisting of the first walls by an increased moment of inertia of bending.

The first wall configuration may be obtained in a casting procedure, or by bending or folding otherwise plane or substantially plane plates to form the opposite walls.

The chamber portions having larger values of the distance between the opposite first walls may be defined by two opposite outwardly bulging portions in the respective opposite walls.

The outwardly bulging portions have a reinforcing effect on the opposite walls. Hereby is provided a ballast water UV treatment unit being light weight as there is no - or for larger ballast water UV treatment units at least a reduced - need for mounting external reinforcement ribs or the like to obtain an UV treatment chamber being able to withstand the internal pressure from the ballast water flowing there through.

The outwardly bulging portions according to the invention facilitates an optimised flow of ballast water through the UV treatment chamber and around the elongated UV light sources whereby the ballast water flowing there-through is exposed to larger minimum UV radiation dose than with the prior art treatment chambers. This is the result of a higher degree of mixing of the ballast water flowing through the ballast water UV treatment unit whereby the ballast water to a larger degree is treated by essentially the same UV radiation dose or at least a more uniform UV radiation dose compared to the prior art such that the minimum treatment dose to which the water is exposed is increased, the difference between that the values of the minimum and maximum UV radiation doses being reduced.

Furthermore all ballast water, when passing the plurality of elongated UV light sources, may in one embodiment flow within a maximum distance from at least one of the plurality of elongated UV light sources, wherein the maximum distance is smaller than the diameter of an elongated UV light source. The maximum distance may be about 50% of the diameter of an elongated UV light source.

Both of the opposite first walls may be configured with the aforementioned course alterations. Alternatively the pair opposite first walls may comprise one plane wall and one wall hav- ing course alterations.

Both of the opposite walls may each comprise uninterrupted surfaces. Alternatively at least one of the opposite first walls may comprise an opening configured for mounting of or receiving a UV sensor. The opening may be a cylindrical opening. The UV sensor may be a UV intensity sensor. The longitudinal axis may define and/or be coinciding with the centre axis of the ballast water UV treatment unit. The longitudinal axis may extend straight through the inlet, UV treatment chamber and the outlet.

The elongated UV light sources may extend essentially crosswise or perpendicular to the stream of ballast water flowing from the inlet to the outlet. According to one embodiment, a pair of further walls defining opposite ends of the UV treatment chamber receive the UV lamps.

According to one embodiment, a smallest one of the distance between the opposite walls perpendicularly to the longitudinal axis is between 10% and 90% of a largest one of the distance between the opposite walls perpendicularly to the longitudinal axis. According to one embodiment, UV treatment chamber portions having smaller values of the distance between the opposite walls perpendicularly to the longitudinal axis receive a smaller number of the elongated UV light sources compared to UV treatment chamber portions having larger values of the distance between the opposite walls perpendicularly to the longitudinal axis. The UV treatment chamber portions having smaller values of the distance between the opposite walls perpendicularly to the longitudinal axis may for example receive one elongated UV light source, and the UV treatment chamber portions having larger values of the distance be- tween the opposite walls perpendicularly to the longitudinal axis may for example receive two elongated UV light sources.

The outline of the UV treatment chamber portion, in the direction along the longitudinal axis, may be as follows, starting from the inlet: - first a gradually increasing distance between the opposite first walls,

secondly an essential constant distance between the opposite walls, and

finally a decreasing distance between the opposite walls.

The opposite walls may each define several UV treatment chamber portions. According to one embodiment, two or more UV treatment chamber portions having larger values and smaller values of the distance between the opposite walls are arranged consecutively in the direction along the longitudinal axis, i.e. a similar/identical outline as described above may be repeated consecutively in the direction along the longitudinal axis toward the outlet.

Hereby is provided a ballast water UV treatment unit wherein the ballast water is exposed to the largest possible minimum UV radiation dose. According to one embodiment, a group of three elongated UV light sources is arranged, seen in a cross-sectional view, in a triangular configuration within the UV treatment chamber such that two of the elongated UV light sources are arranged in a UV treatment chamber portion having larger values of the distance between the opposite walls and the third of the UV light sources is arranged closer to the inlet. The two of the elongated UV light sources may be arranged in one plane essentially perpendicular to the longitudinal axis and spaced from the centre axis of the UV treatment chamber. The third elongated UV light sources may be arranged along the centre axis of the UV treatment chamber.

The ballast water UV treatment unit may comprise at least one sub-section comprising the group of three elongated UV light sources as described above or two or more consecutive subsections in the direction along the longitudinal axis having essentially an identical configuration. Hereby is provided a ballast water treatment unit with an optimized use of the UV light from the elongated UV light sources around all 360 degree of the elongated UV light sources. This as the flow of ballast water is guided onto a "rear side" of the third elongated UV light source by the two elongated UV light sources arranged in one plane essentially perpendicular to the longitudinal axis and spaced from the centre axis of the UV treatment chamber such, that zones with stagnant ballast water, i.e. "dead zones", are avoided around the third elongated UV light source. Likewise is the flow of ballast water guided onto a "rear side" of the two elongated UV light sources arranged in one plane essentially perpendicular to the longitudinal axis and spaced from the centre axis of the UV treatment chamber by the internal configuration of the UV treatment chamber, such that zones with stagnant ballast water, i.e. "dead zones", are avoided around the two elongated UV light sources. This is an advantage as stagnant ballast water causes that the UV light coming from parts of the elongated UV light sources provide no or minimal effect on the ballast water treatment. Consequently when optimizing the use of the UV light from the elongated UV light sources less energy may be used to treat the same amount of ballast water.

According to one embodiment, a first free flow passage area in a plane perpendicular to the longitudinal axis going through the centre axis of an elongated UV light source arranged in the chamber portion having smaller values of the distance is between 40%-100% of a second free flow passage area in a plane perpendicular to the longitudinal axis going through the centre axis of another elongated UV light source(s) arranged in the chamber portion having larger values of the distance.

The opposite first walls may have an constant or substantially constant wall thickness wherein at least one of the opposite walls may be shaped, i.e. cast, folded or bend, to comprise said outwardly bulging portion. The opposite walls may have an constant or substantially constant wall thickness between the inlet and outlet. The opposite walls may have an constant or substantially constant wall thickness all the way between the inlet and outlet or in part of the length of the opposite walls between the inlet and outlet.

According to one embodiment, the ballast water UV treatment unit further comprises a baffle plate arranged between the inlet and the UV treatment chamber. The baffle plate may alternatively be arranged in the inlet or in the UV treatment chamber close to the inlet.

The baffle plate may preferably be a baffle plate/flow distribution plate with a pattern of through-going apertures. Alternatively two baffle plates may be provided, wherein the inlet may be a pipe section comprising two openings, a first opening pointing away from the UV treatment chamber and a second opening pointing toward and being connected or configured to be connected to or assembled with the UV treatment chamber. One of the two baffle plates may be arranged in or close to the first opening and the other one of the two baffle plates may be placed in or close to the second opening.

Hereby is provided a ballast water UV treatment unit wherein the baffle plate provides a more uniform flow of ballast water flowing through the inlet and into the UV treatment chamber. This allows for a more controlled and uniform treatment of the ballast water.

According to one embodiment, ballast water UV treatment unit further comprises an elongated bar extending parallel or essentially parallel to the elongated UV light sources accommodated within the UV treatment chamber and connecting a set of opposite walls.

Hereby is provided a ballast water treatment unit with an optimized use of the UV light from the elongated UV light sources around all 360 degree of the elongated UV light sources. This as the flow of ballast water is guided onto the "rear side" of the elongated UV light sources such that zones with stagnant ballast water, i.e. "dead zones", are avoided. This is an advantage as stagnant ballast water causes that the UV light coming from parts of the elongated UV light sources provide no or minimal effect on the ballast water treatment. Consequently when optimizing the use of the elongated UV light from the elongated UV light sources less energy may be used to treat the same amount of ballast water.

The elongated bar may be arranged such that the elongated bar forms a barrier in the UV treatment chamber and leads the ballast water towards the elongated UV light sources arranged closest to the outlet of the ballast water UV treatment unit before the ballast water enters the outlet. The above mentioned third elongated UV light source may be replaced by an additional elongated bar.

According to one embodiment, said inlet and/or outlet comprise a funnel-shaped or essentially funnel-shaped inlet and/or outlet pipe section. According to an aspect of the invention, a ballast water UV treatment unit includes an inlet for ballast water to be treated, an outlet for treated ballast water, and a UV treatment chamber disposed in-between said inlet and said outlet and having a longitudinal axis (L) extending between said inlet and said outlet, said UV treatment chamber having a plurality of elongated UV light sources extending perpendicularly to or essentially perpendicular to said longitudinal axis (L), said UV treatment chamber defining within its interior a UV treatment volume by two opposite first walls extending parallel to or essentially parallel to said elongated UV light sources spaced therefrom, at least one of said opposite first walls being configured such that said UV treatment chamber in the direction along said longitudinal axis (L) has a varying internal distance (D) between said opposite first walls perpendicularly to said longitudinal axis (L), said UV light sources extending between a pair of second walls of said chamber, characterized in course alterations along said longitudinal axis (L) forming transitions between portions of at least a first wall of said opposite first walls, to define one or more outwardly bulging portions of said chamber, an elongated UV light source extending at least partly in a corresponding outwardly bulging portion, spaced therefrom, a straight portion of said first wall extending along said longitudinal axis (L) intersecting at an angle at said transitions straight portions of the first wall extending outwardly and inwardly, respectively, relative to said longitudinal axis (L), to define said treatment chamber or a treatment chamber sub-section.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in further details with reference to the figures showing an aspect thereof.

Figure 1 illustrates a perspective view of a ballast water UV treatment unit according to the invention.

Figure 2 illustrates an end view of the ballast water UV treatment in figure 1. Figure 3 illustrates a cross-sectional front view B-B of the ballast water UV treatment in figure 1 being configured for receiving elongated UV light sources.

Figure 4 illustrates a cross-sectional end view A-A of the ballast water UV treatment in figure 1 being configured for receiving elongated UV light sources. Figure 5 illustrates a bottom view of the ballast water UV treatment in figure 1 being configured for receiving elongated UV light sources.

Figure 6 illustrates a top view of the ballast water UV treatment in figure 1 being configured for receiving elongated UV light sources.

Figure 7 illustrates a cross-sectional front view B-B of the ballast water UV treatment in figure 1 comprising elongated UV light sources.

Figure 8 illustrates a cross-sectional end view A-A of the ballast water UV treatment in figure 1 comprising elongated UV light sources.

Figure 9 illustrates a sectional area of the UV treatment chamber through the centre axis of an elongated UV light source in a plan perpendicular to the longitudinal axis. Figure 10 illustrates a sectional area of the UV treatment chamber through the centre axis of two elongated UV light sources in a plan perpendicular to the longitudinal axis.

Figure 11 illustrates an end view of an alternative embodiment of a ballast water UV treatment unit.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE FIGURES Figures 1 to 8 illustrate a ballast water UV treatment unit 1 according to the invention configured for receiving a plurality of elongated cylindrical UV light sources/lamps 10, shown in figure 7 and 8. The ballast water UV treatment unit 1 comprises an inlet 2 for receiving ballast water to be treated, a UV treatment chamber 4 configured for treating the ballast water and an outlet 3 for the treated ballast water. A longitudinal axis L extends through the UV treat- ment chamber 4 between the inlet 2 and the outlet 3.

The inlet 2 and the outlet 3 may comprise an essentially funnel-shaped inlet and/or outlet pipe section wherein the pipe sections each comprises two openings, a first opening being circular and pointing away from the UV treatment chamber 4 and a second opening being rectangular and pointing toward and being connected or configured to be connected or assembled with the UV treatment chamber 4. The inlet 2 and/or outlet 3 may at their first opening be configured to be assembled with a cylindrical pipe section (not shown) by means of any suitable fas- tening means (not shown).

The UV treatment chamber 4 extends between the inlet 2 and the outlet 3 and defines within its interior a UV treatment volume 5 by two opposite first walls 6 and two second walls 9 that may define chamber 4 ends. The UV treatment chamber 4 is configured for receiving the plurality of elongated UV light sources 10 through respective opposite openings 11 in the oppo- site end walls 9 such that the elongated UV light sources 10 extend perpendicularly to the longitudinal axis L.

The UV treatment chamber 4 has varying internal distances D between the opposite first walls 6 perpendicularly to the longitudinal axis L; the distance D may vary linearly. The UV treatment chamber portions having larger values of the distance D form outwardly bulging portions 7 of the chamber 4. The drawings show the first walls 6 each having two such outwardly bulging portions 7 defining two chamber 4 sub-sections with one following the other in the general direction of flow from the inlet 2 to the outlet 3; alternatively only one of the opposite first walls 6 may have outwardly bulging portions 7.

The two opposite first walls 6 of the UV treatment chamber 4 preferably have a constant or substantially constant wall thickness T (see fig. 8) along the length thereof between the inlet 2 and the outlet 3.

The opposite first walls 6 are shaped, such as in a metal casting or metal plate folding/bending procedure, to define the outwardly bulging portions 7. Short sharp turns or course alterations, illustrated by lines marked by numeral 8 in fig. 3, form transitions between portions 7 of the first walls 6 whereby the walls 6 follow a zig-zag like configuration along the longitudinal axis L.

The UV treatment chamber 4 as presently illustrated has two essentially identical subsections. Each sub-section is configured to receive three elongated UV light sources 10 arranged in a triangular configuration. Two of the three elongated UV light sources 10 are arranged in opposite outwardly bulging portions 7 of the opposite second walls 6, and the third elongated UV light source 10 is arranged closer to the inlet 2 in a UV treatment chamber portion having smaller values of the distance D between the opposite first walls 6. Two of the three elongated UV light sources 10 are arranged with their centre axes in a plane perpendicular to the longitudinal axis L, each offset from the line of symmetry of the UV treatment cham- ber 4 (in the drawing being coincident with the longitudinal axis L), partly being received in the outwardly bulging portions 7. The third elongated UV light source 10 may be arranged in the centre of the UV treatment chamber 4, i.e. centrally between the opposite second walls 6. The UV treatment chamber 4 may comprise more than two such sub-sections such as three or four sub-sections, or only one. The sub-sections as presently illustrated and starting from the inlet 2, have three portions, the first portion 7 of the first wall 6 extending at a gradually increasing internal distance D from the opposite first wall 6, the second portion 7 of the first wall 6 extending at an essentially constant internal distance D from the opposite first wall 6 and the third portion 7 of the first wall 76 extending at a gradually decreasing internal distance from the opposite first wall 6, measured perpendicularly to the longitudinal axis L.

The two opposite second walls 9 may comprise opposite openings configured for receiving an elongated bar 30. The elongated bar 30 may extend essential parallel with the elongated UV light sources 10 when inserted. The elongated bar 30 may be arranged in the centre of the UV treatment chamber 4, i.e. centrally between the opposite first walls 6. The elongated bar 30 extends through the UV treatment chamber 4 and is placed close to the outlet 3 so that the elongated bar 30 guides the flow of ballast water to an otherwise "dead zone" on the rear/downstream side of the elongated UV light sources 10.

A baffle plate 20, preferably with a pattern of through-going apertures, may be arranged between the inlet 2 and the UV treatment chamber 4 covering the second opening of the inlet 2. The baffle plate 20 may be inserted, replaced and/or cleaned by separating the inlet 2 and the UV treatment chamber 4. The assembly of the inlet 2 and the UV treatment chamber 4 may be accomplished by any suitable fastening means 12 such as bolts and screws.

One of the opposite first walls may comprise an opening 40 configured for receiving a UV sensor (not shown). The UV sensor may be a UV sensitivity sensor. The UV sensor may be used to monitor the UV intensity within the UV treatment chamber 4, i.e. the "amount" of UV energy actually penetrating through the ballast water being treated. The UV sensor may be used to monitor whether the UV intensity in UV treatment chamber 4 passes a determined UV intensity minimum limit and/or a determined UV intensity maximum limit, so that an approximately constant UV intensity is obtained. If the UV intensity passes the UV intensity minimum limit, i.e. so that it is below the determined UV intensity minimum limit, the flow of ballast water may be reduced such that the UV dose is kept constant while the UV intensity is below the determined UV intensity lower limit. If the UV intensity passes the UV intensity maximum limit, i.e. so that it is above the determined UV intensity maximum limit, the elongated UV light sources 10 may be dimmed, such that the UV intensity in the UV treatment chamber 4 is de- creased and energy may be saved.

Alternatively the opposite first walls 6 may both define a continuous surface.

Figures 9 and 10 illustrate two cross-sectional areas including a first free flow passage area 51 and a second free flow passage area 52 between the elongated light source(s) 10 and the opposite first walls 6, when seen in a cross-sectional view perpendicular to the longitudinal axis L, taken at the level of the elongated UV light source 10. The first free flow passage area 51 being in the chamber portion having smaller values of the distance D and being divided into or comprising a first and second area section Al, A2 and the second free flow passage area 52 being in the chamber portion having larger values of the distance D and being divided into or comprising a third, fourth and fifth area section A3, A4, A5. The first free flow passage area 51, i.e. the total area of the first and second area section Al, A2, may be between 40%-100% of the second free flow passage area 52, i.e. the total area of the third, fourth and fifth area section A3, A4, A5.

The width of the first and the second area section Al, A2 may be essentially the same or smaller than the diameter of the elongated light source(s) 10. The width of the third and the fifth area section A3, A5 may be essentially 50% of the diameter of the elongated light source(s) 10. And the fourth area section A4 may essentially be the same as the diameter of the elongated light source(s) 10.

Figure 11 illustrates an end view of an alternative embodiment of a ballast water UV treatment unit 1 wherein the UV treatment chamber 4 is divided into three essential identical sub- sections, each internally having the distance D variations discussed above. The two subsections closest to the inlet 2 are configured to receive three elongated UV light sources (not shown) through opposite openings 11 in the opposite second (end) walls 9, being arranged in a triangular configuration as discussed above. A third sub-section closest to the outlet 3 is con- figured to receive two elongated UV light sources (not shown) through opposite openings 11 in the opposite second (end) walls 9 and an additional elongated bar 30' in a triangular configuration as discussed above wherein the additional elongated bar 30' is arranged closer to the inlet 2, i.e. to replace the third elongated UV light source arranged closer to the inlet 2. The two elongated UV light sources in the third sub-section is arranged with their centre lines in a plane essentially perpendicular to the longitudinal axis L and spaced from the centre axis of the UV treatment chamber 4 in the UV treatment chamber portion having larger values of the distances D between the opposite walls 6 and the additional elongated bar 30' is arranged in the UV treatment chamber portion having smaller values of the distances D between the opposite walls 6. The ballast water UV treatment unit 1 in Figure 11 comprises two uninterrupted opposite walls 6, i.e. with no opening for receiving a UV sensor. Alternatively at least one of the opposite walls 6 may comprises an opening for receiving a UV sensor as discussed above.

The term "comprises/comprising/comprised of" when used in this specification incl. claims is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

1. A ballast water UV treatment unit (1) including:

- an inlet (2) for ballast water to be treated,

- an outlet (3) for treated ballast water, and - a UV treatment chamber (4) disposed in-between said inlet (2) and said outlet (3) and having a longitudinal axis (L) extending between said inlet (2) and said outlet (3), said UV treatment chamber (4) having a plurality of elongated UV light sources (10) extending perpendicularly to or essentially perpendicular to said longitudinal axis (L), said UV treatment chamber (4) defining within its interior a UV treatment volume (5) by two opposite first walls (6) extending par- allel to or essentially parallel to said elongated UV light sources (10) spaced therefrom, at least one of said opposite first walls (6) being configured such that said UV treatment chamber (4) in the direction along said longitudinal axis (L) has a varying internal distance (D) between said opposite first walls (6) perpendicularly to said longitudinal axis (L), said UV light sources (10) extending between a pair of second walls (9) of said chamber (4),

characterized in sharp turns or course alterations (8) along said longitudinal axis (L) forming transitions between portions (7) of at least one of said opposite first walls (6), to define one or more outwardly bulging portions (6) of said chamber (4),

- an elongated UV light source (10) extending at least partly in a corresponding outwardly bulging portion (7), spaced therefrom.

2. A unit according to claim 1, said pair of second walls (9) defining opposite ends of said UV treatment chamber (4) and receiving said UV light sources (10).

3. A unit according to claim 1 or 2, wherein a smallest one of said internal distance (D_s) between said opposite first walls (6) perpendicularly to said longitudinal axis (L) is between 10% and 90% of a largest one of said internal distance (D_L) between said opposite first walls (6) perpendicularly to said longitudinal axis (L).

4. A unit according to any one or more of the preceding claims, wherein UV treatment chamber portions having smaller values of the internal distance (D) between said opposite first walls (6) perpendicularly to said longitudinal axis (L) receive a smaller number of said elongated UV light sources (10) compared to UV treatment chamber portions having larger values of said internal distance (D) between said opposite first walls (6) perpendicularly to said longitudinal axis (L).

5. A unit according to any one or more of the preceding claims, wherein two or more UV treatment chamber sub-sections, each having larger values and smaller values of said internal distance (D) between said opposite first walls (6), are arranged consecutively in said direction along said longitudinal axis (L).

6. A unit according to any one or more of the preceding claims, wherein a group of three elongated UV light sources (10) within said UV treatment chamber (4) has a triangular configuration in that two of said elongated UV light sources (10) are arranged in a UV treatment cham- ber portion having larger values of said internal distance (D) between said opposite walls (6) and said third of said UV light sources (10) is arranged closer to said inlet (2).

7. A unit according to any one or more of the preceding claims, wherein a first free flow passage area (51) in a plane perpendicular to the longitudinal axis (L) going through the longitudinal centre axis of an elongated UV light source (10) arranged in a chamber portion having smaller values of said internal distance (D) is between 40%-100% of a second free flow passage area (52) in a plane perpendicular to the longitudinal axis (L) going through the longitudinal centre axis of another elongated UV light source(s) (10) arranged in the chamber portion having larger values of said distance (D).

8. A unit according to any one or more of the preceding claims, wherein said outwardly bulg- ing portion (7) is formed by one or more fold lines (8).

9. A unit according to any one or more of the preceding claims, further comprising a baffle plate (20) arranged between said inlet (2) and said UV treatment chamber (4).

10. A unit according to any one or more of the preceding claims, further comprising an elongated bar (30) extending parallel or essentially parallel to said elongated UV light source ac- commodated within said UV treatment chamber and connecting said pair of further walls (9).

11. A unit according to any one or more of the preceding claims, wherein said inlet and/or outlet comprises a funnel-shaped or essentially funnel-shaped inlet and/or outlet pipe section.

12. A unit according to any one or more of the preceding claims, said outwardly and inwardly extending portions (7) being plane, the first wall thickness (T) of said portions (7) preferably being constant or substantially constant.

13. A unit according to any one or more of the preceding claims, one or both of said two first wall(s) (6) alternating in course inwardly and outwardly relative to said longitudinal axis (L), a straight portion (7) of said first wall (6) extending along said longitudinal axis (L) intersecting at an angle at said transitions straight portions (7) of the first wall (6) extending outwardly and inwardly, respectively, relative to said longitudinal axis (L), to define said treatment chamber or a treatment chamber sub-section.