GB2469319A

GB2469319A - Exhaust treatment for a marine engine

Info

Publication number: GB2469319A
Application number: GB0906166A
Authority: GB
Inventors: John David Young
Original assignee: Hamworthy PLC; Kittiwake Developments Ltd; Krystallon Ltd
Current assignee: Wartsila Hamworthy Ltd
Priority date: 2009-04-08
Filing date: 2009-04-08
Publication date: 2010-10-13
Also published as: GB0906166D0

Abstract

A system for removing contaminants from exhaust gas emitted by a marine combustion engine, the system comprises an exhaust gas inlet 4 and an exhaust gas outlet 7, between the them is a quenching section 6 for mixing the exhaust gas stream with a quenching liquid stream and a scrubbing section 8 downstream of the quenching section for mixing the exhaust gas stream with a scrubbing liquid stream to remove liquid soluble contaminants from the exhaust gas, where the quenching system comprises a packed region 16 comprising packing material through which the exhaust gas and quenching liquid streams pass before entering the scrubbing section. The quenching section may comprise a nozzle 14 for providing the quenching liquid, a curved inlet 18 and a flow restriction 19 upstream of the packing material. The scrubbing section preferably comprises multiple of sub-regions 26 28 30 32, where each region has structured packing material with fluid passageways. After the scrubbing section there may be a sump 34 to collect liquid and a demister 38 to remove moisture from the gas. The quenching and scrubbing liquid may be sea water.

Description

EXTRACTION DEVICE AND METHOD

The present invention relates to systems and methods for the removal of contaminants from combustion engine exhaust gases, and more particularly from exhaust gases emitted by marine engines.

Reciprocating combustion engines, and in particular diesel combustion engines for example using a two or four stroke diesel cycle are commonly used as a source of motive and/or auxiliary power for marine vessels. The requirement to remove certain contaminant components from an exhaust gas stream derives from their potential to harm the environment or represent a toxic hazard when released into the environment. Some of those harmful components are soluble in liquid, especially in water. It is common practice, therefore, that exhaust gas streams containing polluting components i.e. contaminants are treated in some way with liquid streams to promote the absorption of gas into liquid and therefore generate a gas-liquid solution that may be subsequently separated from the exhaust gas stream and treated to reduce the dangerous effect of the contaminants. Such processes may be referred to as exhaust gas "scrubbing". One exhaust gas scrubbing system is disclosed in WO 2007/068944.

The various hydrocarbon fuels used commonly in combustion engines contain varying amounts of impurities and, in particular, sulphur. Following combustion sulphur dioxide (SO2) is one of the components of the exhaust gas in concentrations proportional to the original sulphur content of the fuel. Once released in this way the sulphur dioxide may be absorbed by water in the atmosphere and contribute to acid rain. Sulphur dioxide is therefore a significant contaminant which may be present in exhaust gases emitted by combustion engines, and which it is desirable to remove before the exhaust gas is released into the environment.

In exhaust gas treatment systems, the hot exhaust gas may be quenched, or cooled by water sprays, before entering the scrubbing section. Hot gases, which are above ambient temperature, are often cooled to near the saturation level. If the exhaust gas is not cooled before scrubbing is carried out, the hot gas stream may evaporate portions of the scrubbing liquid, adversely affecting absorption efficiency and potentially damaging scrubber internal parts. For example, if the gases entering the scrubber are too hot, some liquid droplets may evaporate before they have a chance to contact contaminants in the exhaust stream, and others may evaporate after contact, causing captured particles to be released back into the gas stream.

A quenching system can be as simple as spraying liquid into a duct through which the exhaust gas flows just preceding the main scrubbing section, or it can be a separate column e.g. tower with its own spray system.

One traditional quench tower design consisted of an open vessel in which liquid is sprayed to contact the gas. The gas typically enters the bottom of the tower through a side nozzle and flows upwards, counter-current to liquid that has been sprayed from the top of the tower. By the time the gas has reached the top gas outlet, it has been cooled to its adiabatic saturation temperature. A variation of this design is to have the gas entering the top of the tower and contacting the liquid co-currently as it travels down through the tower. Quench towers have also been designed using the reverse jet scrubbing principle. The gas enters the top of the reverse jet scrubber barrel and flows downwards where it contacts a liquid that has been sprayed from the bottom.

The present invention may provide improved methods and systems for removing contaminants from exhaust gases emitted by marine engines. The present invention is, in certain aspects and embodiments, alternatively or additionally concerned with providing improved quenching of the exhaust gas prior to scrubbing.

In accordance with a first aspect of the invention, thee is provided a system for removing contaminants from exhaust gas emitted by a marine combustion engine, the system comprising: an exhaust gas inlet and an exhaust gas outlet, wherein a stream of exhaust gas flows through the system along a path from the inlet to the outlet in use; a quenching section located between said inlet and said outlet for mixing the exhaust gas stream with a quenching liquid stream in use, a scrubbing section located downstream of said quenching section for mixing the exhaust gas stream with a scrubbing liquid stream for removing liquid soluble contaminants from the exhaust gas in use; wherein the quenching section comprises a packed region comprising packing material through which the exhaust gas and quenching liquid streams pass in use before entering the scrubbing section, the packed region being arranged to promote contact between the liquid and gas streams.

Thus, in accordance with the invention, the exhaust gas flows sequentially through the quenching and scrubbing subsections in its path between the inlet and outlet of the system. In accordance with the invention, the quenching section includes a packed region through which the exhaust gas passes after mixing with the quenching liquid stream, and before the main scrubbing stage.

The provision of a quenching section which includes a packed region in this manner, has been found to be advantageous for a number reasons, as described in more detail below. This packed region upstream of the scrubbing section has been found to promote contact between the liquid stream introduced in the quenching section and the exhaust gas stream, improving heat and mass transfer therebetween in the quenching section. In this way, the temperature of the exhaust gas stream entering the scrubbing section may be reduced in comparison to that which may be achieved using conventional systems. It has also been found that this packed region may remove certain contaminants, particularly solid contaminants such as carbon particles, before the exhaust gas reaches the main scrubbing stage and the demister, where provided. This has been found to address problems associated with prior art devices in which solid particles tended to build up on and clog up filters or packing used in the scrubbing stage and the demister.

The quenching section is arranged to mix the exhaust gas with a liquid stream. Thus, the quenching section comprises means for providing a liquid stream for mixing with the gas stream. The main function of the quenching means is to cool the exhaust gas stream before it passes downstream to the other sections of the system. This may occur as a result of heat and/or mass transfer from the exhaust gas stream to the liquid stream. Mixing of the gas and liquid streams may also result in some contaminants within the exhaust gas stream becoming entrained or dissolved in the liquid. This may result in a liquid-gas mixture or solution being formed which may subsequently be separated from the exhaust gas stream thereby removing the contaminants from the exhaust gas stream in the same manner as later takes place in the scrubbing section. Thus, the quenching section may provide some initial mixing of the exhaust gas with liquid to allow some separation of contaminants from the exhaust gas stream in this manner prior to the main scrubbing stage. The quenching section may also help to draw exhaust gas into the system through the inlet e.g. by eduction as a result of the presence of the liquid stream.

Preferably the liquid stream of the quenching section moves in the same direction as the exhaust gas stream flowing through the quenching section.

The liquid stream may be of any suitable type. The mass/heat transfer process as a result of the mixing between the gas and liquid phases in the quenching section will proceed more effectively the greater the surface area of contact between the liquid and gas phases. Preferably the liquid stream is in the form of a spray, and the quenching section comprises means for providing a liquid spray for mixing with the exhaust gas stream. Preferably the spray is a fine spray e.g. mist. In preferred embodiments, the quenching section comprises at least one nozzle for providing the liquid stream in use.

Preferably the quenching liquid is water, most preferably sea water.

Preferably the quenching section comprises a conduit through which the exhaust gas passes and means for providing a liquid stream for mixing with the exhaust gas as it moves through the conduit. The length of the conduit will define the residence time for the mixing process, and may be selected as appropriate.

In some embodiments the upstream end of the quenching section is configured to facilitate drawing in of the exhaust gas stream through the inlet.

Preferably the quenching section comprises a curved section extending from the exhaust gas inlet to promote drawing of the exhaust gas into the quenching section for mixing with the liquid stream in use. The exhaust gas therefore follows a curved path through this inlet section. The curved section may extend to the portion of the quenching section in which the liquid and gas streams are mixed.

Preferably the curved section terminates upstream of the liquid stream, e.g. upstream of a nozzle outlet. The curved section may therefore extend in embodiments from the exhaust gas inlet to an outlet of a nozzle for providing the liquid stream. In preferred embodiments the exhaust gas follows a linear path through the quenching section during and after mixing with the liquid stream.

Preferably the quenching section comprises a curved portion in the region of the inlet and a non-curved portion downstream thereof in which mixing of the liquid and gas streams occurs.

Preferably the quenching section comprises a flow constriction in the path along which the exhaust gas flows. Such a constriction may further promote mixing between the liquid and gas streams to increase the heat and/or mass transfer between the streams, enhancing cooling of the exhaust gas stream, and to a degree entrainment of contaminants from the exhaust gas stream in the liquid stream. In some embodiments, the quenching section comprises a conduit through which the exhaust gas and liquid streams flow, the conduit having a waist which defines the constriction. In embodiments the conduit decreases in diameter from end nearest the inlet, tapering to a narrow waist which defines the constriction before tapering outwardly again increasing the diameter of the conduit. The rate of decrease in diameter of the conduit from the inlet end of the conduit to the constriction is preferably greater than the rate of increase of the diameter of the conduit downstream of the constriction. The increase in diameter of the conduit may increase pressure recovery.

In accordance with the invention, the quenching section comprises a packed region comprising packing material through which the liquid and gas streams pass. The packed region promotes contact between the liquid and gas streams. This may increase the effectiveness of the quenching section, facilitating heat and/or mass transfer between the liquid and gas streams.

It has been found that the liquid from the air/gas mixture incident upon the quenching section packed region will tend to temporarily collect upon the surface thereof, and spread across the surface, promoting contact between the liquid and gas streams, and resulting in improved entrainment between the liquid and gas phases before the scrubbing section is reached. The quenching section packed region may therefore act to diffuse the liquid stream. The packed region may result in increased contact time between the liquid and gas phases, as it acts to slow down the liquid and gas streams. This may allow a reduction in the size e.g. diameter of the system required to provide a given level of mixing of the liquid and gas streams. The quenching section packed region may also further reduce the temperature of exhaust gases prior to the scrubbing section compared to the temperature on leaving the quenching section if such a packed region were not present. This is beneficial, as if the exhaust gases, are too hot, some liquid mixed with the exhaust gas in the scrubbing section may evaporate before contacting contaminants in the exhaust gas stream, preventing contaminants from being entrained in the liquid stream. Reduced operating temperatures may also allow reduction in the dimensions of the system as a result of the lower volume of gases.

It is believed that a quenching section including a packed region of this type is advantageous in its own right. Thus, from a further aspect of the invention there is provided; a quenching section for a system for removing contaminants from exhaust gas emitted by a marine combustion engine, the quenching section comprising: an exhaust gas inlet through which exhaust gas enters the quenching section in use; and means for providing a liquid stream for mixing with the exhaust gas stream; the quenching section further comprising; a curved inlet section extending from the exhaust gas inlet to promote drawing of exhaust gas into the quenching section for mixing with the liquid stream; and a packed region comprising packing material through which the exhaust gas and liquid streams pass in use for promoting contact between the liquid and gas streams.

The present invention in accordance with this further aspect of the invention may include any or all of the features described in respect of the other aspects and embodiments of the invention.

In accordance with the present invention in any of its aspects or embodiments, in order to maximise mixing between the liquid and gas streams, and hence mass and heat transfer therebetween in the region of the quenching section packed region, the liquid stream should be arranged to extend over as great a surface area of the packed region as possible, ideally as uniformly as possible.

This may result in a film of liquid building upon the upstream surface of the packed region. Preferably the liquid stream providing means of the quenching section is arranged to cause liquid to be distributed over a significant portion, and preferably the entire surface area of the upstream end of the packed region. For example, this may be achieved by selecting the angle of discharge of the liquid stream providing means appropriately. In preferred embodiments, the liquid stream providing means comprises a full cone nozzle.

The packed region of the quenching section may comprise any suitable packing material or materials which may promote contact between the liquid and gas phases. The packed region may do this by causing the fluid streams i.e. the liquid and gas streams to take a more complicated route through the region, for example increasing the potential surface area of contact between the liquid and gas phases. The packed region may provide a packed bed through which the fluid streams pass. The packed region may be selected to provide a desired flow speed and pressure head loss of the exhaust gas as it passes therethrough. This may be controlled by choosing the packing material, e.g. the configuration e.g. size and density of fluid passages through the packed material and/or the area and length of the packed region appropriately. Suitable packing materials may be known as "column packingt'.

The packed region may comprise one or more sub-regions of packing material of the same or different construction along the path of the gas flow through the packed region.

The packed region preferably extends over the entire cross sectional area of the quenching section.

The packing material may be of any composition, e.g. metal, ceramic, plastic etc. In some embodiments, the packing material comprises a mesh material, preferably a metallic mesh material. The metal may be steel.

While the packing material may be random packing, the packing material preferably comprises structured packing material, As known in the art, a structured packing material may comprise layers of material defining channels therebetween through which the liquid and gas pass. The layers may be porous e.g. a mesh, or may be solid layers. The layers may be configured to increase the time required for the liquid and gas phases to pass through the packed region to enhance mixing. For example, in some embodiments the layers may comprise corrugations out of the plane of the layers. The corrugations may be of any configuration desired to provide suitable residence times and levels of mixing.

The layers may be arranged parallel to and/or inclined to the axis of the packed region. In preferred embodiments the packing material is a mesh structured packing material, preferably a metallic mesh e.g. steel.

Preferably the quenching section packed region is arranged to promote turbulence in the gas and liquid streams to promote mixing thereof. This may be achieved by configuring the packing material thereof appropriately, e.g. by providing turbulence promoting formations. In embodiments in which the quenching section packed region comprises structured packing, the structured packing material may comprise turbulence promoting formations. The turbulence promoting formations may oppose the movement of fluid through the fluid passageways defined through the packed region. The turbulence promoting formations may be of any desired type. For example, the material may comprise baffles for this purpose. The baffles may be inclined to the axis along which the gas and liquid streams move, or perpendicular thereto. In embodiments in which the quenching section packed region comprises structured packing, the layers of the packing may comprise such baffles.

The packed region is located downstream of the point at which the liquid stream is mixed with the exhaust gas stream, and downstream of the inlet section of the quenching section. In embodiments the packed region is at the downstream end of the quenching section. In embodiments in which the quenching section comprises a conduit having a restriction, the packed region is located downstream of the restriction.

It will be appreciated that the quenching section packed region may provide a pre-scrubbing stage before the exhaust gas is subjected to the main scrubbing process in the scrubbing section. The quenching section packed region is therefore upstream of the scrubbing section, and the packed region of the quenching section is separate from any packed region of the scrubbing section.

The quenching section packed region is an additional packed region to any packed region of the scrubbing section. In embodiments in which the scrubbing section comprises a packed region, preferably the quenching section packed region is spaced axially from an upstream end of the packed region of the scrubbing section. Where there are a plurality of packed regions in the scrubbing section, it will be appreciated that the packed region of the quenching section is axially spaced from the upstream end of the most upstream of the packed regions. The packed regions may be axially spaced along the length of a conduit connecting the quenching section and scrubbing section. There is therefore a region between the quenching section packed region and the scrubbing section packed region in which there is no packing material. Preferably the quenching section and the scrubbing section are defined within a conduit which extends between quenching section packed region and the scrubbing section. The conduit is preferably the same conduit as that defining the quenching section.

It will be appreciated that the quenching section may comprise a plurality of packed regions through which the liquid and gas streams pass in use. The packed regions may be located in series or parallel.

After passing through the quenching section packed region, the exhaust gas and liquid streams (which by this stage will include entrained gas), reach the scrubbing section. The scrubbing section preferably comprises means for providing a liquid stream and a packed region for promoting contact between the gas and liquid streams. The main function of the scrubbing section is to remove contaminants from the exhaust gas as a result of entrainment of the contaminants with the scrubbing liquid. This may remove at least liquid soluble contaminants, but there may also be some flushing of solid contaminants from the gas.

The scrubbing liquid stream is a different liquid stream to the liquid stream provided in the quenching section, and may be referred to as the scrubbing liquid stream. The liquid stream may be of the same type described in relation to the quench section, and to avoid repetition the features thereof will not be repeated here, although it will be appreciated that any of the features of the liquid stream and means for providing the liquid stream described in relation to the quenching section may be used in the scrubbing section. Preferably the liquid stream is in the form of a spray, and the scrubbing section comprises a nozzle for producing a spray of liquid. Preferably at least the outlet of the nozzle is located between quenching section packed region and the upstream end of the packed region of the scrubbing section. Preferably the scrubbing liquid is water, more preferably sea water.

Preferably the liquid stream in the scrubbing section moves in the same direction as the direction of flow of exhaust gas through the system, i.e. the gas and liquid streams are concurrent. It is believed that this may be advantageous in its own right, and, from a further aspect the present invention provides; a system for removing contaminants from exhaust gas emitted by a marine combustion engine; the system comprising; -Il-an exhaust gas inlet and an exhaust gas outlet, wherein a stream of exhaust gas flows along a path from the inlet to the outlet in use; the system further comprising a scrubbing section located between said inlet and outlet, the scrubbing section being arranged to mix the exhaust gas stream with a scrubbing liquid stream in use for removing liquid soluble contaminants from the exhaust gas, wherein the scrubbing liquid stream flows through the scrubbing section in the same direction as the exhaust gas stream.

The present invention in accordance with this further aspect may include any of all of the features described in relation to the first aspect of the invention.

For example, the system may further comprise a quenching section upstream of the scrubbing section, and other sections as discussed in relation to the overall system. In preferred embodiments the system may include a quenching section having a packed region and preferably an curved inlet section as described above.

However, it will be appreciate that this is optional in accordance with this further aspect. The components downstream of the scrubbing section in accordance with each aspect of the invention may be identical.

The use of concurrent gas and liquid streams in these further aspects and embodiments of the invention is advantageous in that it allows the exhaust gas to pass through the system at a higher velocity than in arrangements in which the liquid stream opposes the gas stream. This is advantageous in that it may allow a higher level of gas and liquid mixing and hence scrubbing effect to be achieved for a given set of conditions. Hence, it has been found that the dimensions of the system may be reduced with respect to a similar system in which the gas velocity is lower. For example, if the diameter of the conduit in which mixing occurs is made smaller, this will reduce the surface area of contact between the liquid and gas streams, and hence the degree of mixing obtainable. However, this decrease is offset by the increase in mixing obtained by the greater velocity of the gas stream. By way of example, it was found that by increasing the gas velocity through the scrubbing section from 3.2 m/s to 5.4 rn/s the diameter of the conduit in which the scrubbing section was provided could be reduced from 1.5m to im with comparable levels of scrubbing being achieved. Such size reductions are -12-desirable in the context of marine exhaust systems, in which there are space and weight constraints imposed by the on ship environment. Reductions in size and weight may reduce the load which must be carried by the vessel, and hence fuel demands, providing environmental and cost benefits.

The scrubbing section packed region is preferably arranged to promote liquid and gas contact over a predetermined length of the path of the exhaust gas through the scrubbing section. Thus, the packed region preferably extends a predetermined distance axially e.g. along a conduit defining the scrubbing section.

In accordance with any of the aspects and embodiments of the system, in which the scrubbing section comprises a packed region comprising packing material, the packed region of the scrubbing section may be of any suitable type.

The packed region may be of any of the types described with respect to the quenching section packed region, and may include any of the types of packing material described in relation thereto.

While the packing may be random packing, the packing material preferably comprises structured packing material. As known in the art, a structured packing material may comprise layers of material defining channels therebetween through which the liquid and gas pass. The layers may be of a continuous or apertured e.g. mesh material. In this way, contact between the liquid and gas phases is promoted. The layers may be arranged to increase the time required for the liquid and gas phases to pass through the packing material to enhance mixing. For example, the layers may comprise corrugations out of the plane of the layers. The corrugations may be of any configuration desired to provide suitable residence times and levels of mixing. The layers may be arranged parallel to and/or inclined to the axis of the scrubbing section. The configuration of passageways through the packed region may be selected as desired to allow the gas and liquid streams to pass at a desired velocity therethrough, and to result in an appropriate pressure drop. The packing material may comprise a mesh material, as described in relation to the quenching section packing material. In some embodiments, the scrubbing section packed region comprises a plurality of packed subregions -13 -through which the exhaust gas passes sequentially, the passages in the respective subregions having different orientations.

As described in relation to the quenching section, the liquid stream of the scrubbing section should be arranged to distribute liquid over as great a portion of the upstream surface of the scrubbing section packed region. as possible.

It will be appreciated that the scrubbing section may comprise a plurality of packed regions, which may be the same or different. The packed regions may be axially spaced from one another. The packed regions may be located in series or parallel.

Preferably the scrubbing section comprises a packed region having a plurality of sub-regions arranged sequentially along the path of the exhaust gas through the packed region, each sub-reion comprising different packing material.

The sub-regions may be located one above the other. The packing material of each sub-region may differ e.g in the configuration of fluid passageways therethrough, the composition of the material itself etc. Each sub-region may extend a predetermined distance along the axis of the system. In some preferred embodiments, the packing material of each sub-region is structured packing material having fluid passageways therethrough, wherein the alignment of the fluid passageways of the structured packing material of adjacent sub-regions is different.

The scrubbing section results in contaminants of the exhaust gas becoming entrained or dissolved in the scrubbing liquid stream, resulting in a liquid/gas mixture which may be separated from the exhaust gas thereby removing contaminants from the exhaust gas as known in the art. This scrubbing liquid stream may be separated from the exhaust gas stream and treated to render it safe for discharge e.g. into the sea.

Preferably the scrubbing section comprises a sump below the packed region e.g. at the bottom of the scrubbing section, for collecting scrubbing and/or quenching liquid, and a scrubbing section gas outlet for exhaust gas. In this way, the exhaust gas may continue towards the outlet of the system while the majority of the scrubbing and quenching liquid will drain into the sump. In embodiments -14-the system comprises a conduit having the scrubbing section in a lower region thereof, and the sump is located at the bottom of the conduit.

The exhaust gas leaving the scrubbing section will comprise some liquid droplets. Preferably the system further comprises a demister section located in the path of the exhaust gas stream between said scrubbing section and said outlet for removing liquid from the exhaust gas stream. As known in the art, the demister defines passageways through which the exhaust gas passes, but which present a barrier to the passage of liquid droplets. The liquid droplets tend to build up and conglomerate on the demister surfaces until they reach a sufficient weight that they fall away from the demister, and thereby becoming disentrained from the gas stream. The liquid droplets may then drop to the bottom of the demister, and subsequently may fall back into the sump.

The demister may be of any suitable construction. The demister may comprise a plurality of plates defining channels therebetween through which the exhaust gas passes. In preferred embodiments the demister is a vertical demister i.e. the plates are arranged vertically. In preferred embodiments the exhaust gas stream moves along a horizontal path through the demister. The demister may comprise hooks or other formations to cause the gas to take a more difficult path through the demister increasing the likelihood of liquid droplets being removed from the gas stream.

In this manner, the level of moisture in exhaust gas leaving the demister is reduced, rendering it suitable for emission. The exhaust gas continues downstream to the exhaust gas outlet where it leaves the system.

The system may comprise other components not described, e.g. further filters etc It will be appreciated that single or multiple combinations of quenching and scrubbing sections may be combined in series or parallel as desired. Likewise, it is envisaged that a single quenching or scrubbing section may comprise multiple packed regions in series or parallel.

It will be appreciated that in preferred embodiments the direction of liquid and exhaust gas flow throughout the system is the same. Thus, the direction of -15-the liquid stream introduced in the quenching section and also that introduced in the scrubbing section is the same as that of the exhaust gas flow. The exhaust gas flows in a single direction between the inlet and outlet of the device. Preferably the exhaust gas flows downward from the inlet of the device through the quenching, and scrubbing sections. The quenching and scrubbing sections are then located one above the other.

Preferably the system comprises a conduit which defines the quenching, and scrubbing sections. Preferably the conduit is a vertical conduit i.e. column.

Preferably the quenching section is therefore located towards the top of the conduit and the scrubbing section towards the bottom thereof. In embodiments the diameter of the conduit is constant in the region downstream of the quenching section.

Preferably the system comprises a single first conduit defining the quenching and scrubbing sections. The scrubbing section gas outlet may be connected to a second conduit through which exhaust gas may flow towards the exhaust gas outlet of the system, preferably via a demister unit, after passing through the scrubbing section. In embodiments the second conduit is perpendicular to the first conduit in which the quenching and scrubbing sections are disposed. In preferred embodiments the gas follows a horizontal path through the second conduit. One or more additional conduits may be joined thereto to result in the exhaust gas leaving the system in a desired direction. In preferred embodiments the gas leaves the system in a vertical direction. There may be a third vertical conduit connected to a second horizontal conduit through which the exhaust gas passes after leaving the scrubbing section disposed in a first vertical conduit. The various conduits may be integrally formed with one another, or may be provided by separately formed conduits which are attached to one another. It will be appreciated that these embodiments are merely exemplary, and any configuration of conduits may be used. Likewise, the conduits may be integrally formed or separately formed and attached to one another.

Preferably the system comprises an outlet for discharging scrubbing and/or quenching liquid into the sea after passing through the scrubbing section. -16-

In accordance with its various aspects and embodiments, the present invention provides a system for removing contaminants from the exhaust gas of a marine engine. Preferably the engine is a diesel engine. Preferably the engine is an engine of a marine vessel.

The system is arranged to receive exhaust gases from a marine engine.

Preferably the inlet of the system is connected to (the exhaust) of a marine engine.

There may be an indirect or direct connection via any number of intermediate connectors.

The contaminants removed from the exhaust gas in accordance with the invention may be of any type. Preferably the system is arranged to remove at least sulphur dioxide from the exhaust gas. This is achieved by dissolving of this soluble gas in the scrubbing and/or quenching liquid.

The present invention extends to a system in accordance with the invention in any of its aspects or embodiments mounted to a marine vessel.

The present invention extends to the use of a system in accordance with any of the aspects or embodiments of the invention to remove contaminants, preferably sulphur dioxide, from exhaust gas emitted by a marine engine The present invention extends to a method of removing contaminants from exhaust gas emitted by a marine engine using the system of any of the aspects or embodiments of the invention. The method may comprise the steps of providing exhaust gas emitted by a marine engine to the inlet of the system, and passing the exhaust gas through the system. The method may further comprise providing liquid streams in each of the quenching and scrubbing sections for mixing with the exhaust gas stream.

In accordance with the invention in any of its aspects and embodiments, the system may be formed of any suitable materials, e.g. metal, plastics materials, ceramics or any combinations thereof. The various sections e.g. quenching section, scrubbing section and, in embodiments, inlet section, may be defined by separately formed components which have been attached to one another, or may be defined by parts of an integral structure.

-17 -Any references to components being "upstream" or "downstream" herein should be understood as being with respect to the direction of flow of the exhaust gas through the system from the inlet to the outlet. References to features being between one another are in reference to the axial direction i.e. the direction along which the exhaust gas flows unless the context demands otherwise. The terms "up" and "down" or similar should be understood with reference to the orientation of the system in its normal operating condition.

Some preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a side on view of an exhaust gas contaminant removal system in accordance with a first embodiment of the invention with the column containing the quenching/scrubbing sections shown in cross section; and Figure 2 is a vertical sectional view showing the part of the system in the region of the inlet and quenching system in more detail.

The system 1 comprises a vertical column 2 including an inlet 4 for exhaust gas emitted by a marine combustion engine at its top. The inlet 4 leads into a quenching section 6 and a scrubbing section 8 located below the quenching section 6. The exhaust gas passes sequentially through the quenching section 6 and the scrubbing section 8 in the direction of the arrow in Figures 1 and 2 in the direction from the top of the bottom of the column and then through a further column 10 perpendicular to the column 2, and finally through a vertical discharge pipe 12 to a system exhaust gas outlet 7.

As may be seen in more detail in relation to Figure 2, the quenching section 6 comprises a 90 degree curved inlet section 18 at the top extending from the exhaust gas inlet 4 to the top of the column 2 for drawing the exhaust gas into the system. The curved portion terminates in the region of the outlet of a nozzle 14. The curved portion may be provided by a separate inlet duct inserted into the top of the column 2. Below the curved portion 18, the column 2 has straight sides. -18-

The nozzle 14 provides a quenching stream in the form of a fine spray of seawater for mixing with the exhaust gas stream passing through the quenching section 6. The quenching liquid stream flows in the same direction as the exhaust gas downwards through the column 2. In the embodiment shown the nozzle is inserted through the curved inlet section 18 into the interior of the column 2. At the downstream end of the section 6 there is a packed region including packing material 16. The nozzle is arranged to distribute liquid over the upstream surface of packed region 16. To this end, the spray nozzle is an overhead full cone non-clogging type of sufficient capacity to try to maximise coverage of the packing region surface and to reduce the possibility of gas bypassing the liquid spray. A full-cone nozzle has been found to provide good spray coverage and distribute the liquid evenly through the packing filter.

In the quenching section 6 below the outlet of nozzle 14, the liquid and gas streams mix. This results in cooling of the hot exhaust gas stream prior to entry into the scrubbing section as a result of heat transfer between the liquid and gas streams. There may also be some mass transfer between the streams with gas becoming entrained or dissolved in the liquid stream. This may result in some contaminants e.g. soluble gases from the exhaust gas stream, including e.g. sulphur dioxide, being entrained in the gas stream in the same manner as occurs later, and to a greater extent in the scrubbing section 8.

It will be seen from Figures 1 and 2 that the quenching section 6 has a particular shape downstream of the nozzle 14 and the curved section 18. The quenching section includes a flow constriction 19 in the form of a waist which is followed by a widening of the diameter of the quenching section.

The nozzle 14 is used to direct a water jet parallel to the gas flow at a volumetric flow rate sufficient to provide a continuous layer of water to a specific depth on the upstream surface of the packed region 16, in the absence of the exhaust gas flow. The packed region 16 is provided by structured packing material defining a plurality of passageways through which the liquid and gas may pass as they move downstream towards the scrubbing section. This may promote -19-contact between the liquid and gas phases, and hence increases mass and het transfer between the phases. There may also be some removal of solid particulate contaminants from the exhaust gas stream as it passes through the packed region 16 reducing the problem of clogging in the downstream scrubbing packed region or demister.

The packed region 16 includes baffles arranged perpendicular or inclined to the direction of flow of the gas to result in turbulence in the gas flow, further increasing mixing between the liquid and gas streams. The structure of the packed region 16 is chosen to result in a desired level of mixing between the gas and liquid streams, e.g. taking into account factors such as the gas and liquid velocities, and the dimensions of the system. The presence of the packed region 16 will result in slowing of the gas further increasing levels of mixing attainable prior to the scrubbing section 8. The configuration of the packed region may be chosen to provide a particular flow speed and pressure head loss across the packed region.

After passing through the quenching packed region 16, the exhaust gas and liquid streams, which will now be mixed to some extent, enter the scrubbing section 8 defined in the lower part of the column 2.

The scrubbing section 8 is intended to provide the bulk of the contaminant removal by mixing the gas stream with a further stream of seawater emitted by nozzle 22. The nozzle 22 is similar to the nozzle 14 of the quenching section 6.

The scrubbing section 8 includes a packed region 24 including sub-regions 26, 28, 30, 32. The sub-regions include structured packing material with passageways therethrough with different alignments, as shown schematically in Figure 1. This promotes further mixing between the exhaust gas and scrubbing liquid streams (and also the residual quenching liquid). The nozzle 22 is arranged to provide a spray in the same direction as the direction of gas flow. This may enable the exhaust gas to reach relatively higher velocities than in systems using opposed liquid and gas streams, enabling a reduction in the overall size of the system for providing a given level of mixing and contaminant removal. The system is -20 -designed such that the exhaust gas flow speed through the packing is sufficient to prevent water flow back through the packed region 24.

After passing through the scrubbing section 8, the liquid and its entrained gas falls into the sump 34 at the bottom of the column 2. This liquid contains contaminants removed from the exhaust gas, and is passed on to a treatment plant, before being safely discharged into the sea. The main liquid removed from the exhaust gas by the scrubbing process is sulphur dioxide.

The exhaust gas continues through a scrubbing section outlet 36 to enter a horizontal conduit 10 placing the interior of column 2 in fluid communication with the discharge pipe 12. As it passes through the conduit 10 the exhaust gas moves through a vertical demister unit 38 for removing residual moisture from the exhaust gas.

Operation of the system involves connecting the inlet 4 to the outlet of a marine diesel engine so that exhaust gas flows into the inlet 4, and supplying seawater to the nozzles 14 and 22 to provide the quenching and scrubbing liquid sprays for mixing with the gas. The curved portion 18 of the quenching section together with the liquid spray act to draw the exhaust gas into the system.

It will be appreciated that the present invention may, in embodiments, provide systems which utilise seawater as a medium for absorption and chemical reactions that convert the sulphur dioxide to calcium suiphite in solution.

Seawater is readily available as a scrubbing medium. Seawater is commonly used in land based power stations, typically in the form of sprays, to remove SO2.

However, where space is limited and capacity to carry stocks of additional chemicals as buffers or acid neutralisers is not available, such as on ships, traditional engineering approaches cannot be applied.

It will be appreciated that the present invention may provide systems and methods which allow the removal of substantial quantities of SO2 from combustion engines burning hydrocarbon fuel containing compounds of sulphur as impurities within the limited space and gas flow requirements afforded by the engine exhaust system and ship structure, and using seawater only as the chemical medium. Each -21 -stage of the system may contribute to the processing of the exhaust gas in a different way and may be selected to perform a function which interrelates with the requirements of the following stage. Each stage may contain more than one similar device to perform the particular function required at that stage.

The overall geometry of the system may be of any section, circular or rectangular, as best suits the layout of the plant. More than one scrubbing section may be combined in paraLlel within a single exhaust gas stream to provide the required scrubbing capacity. Similarly, single or multiple combinations of quench sections may be combined (i.e. a single quench sections feeding two scrubber sections in parallel). The quenching section may contain more than one such quench section, connected in series, or parallel, within the exhaust gas stream.

Claims

-22 -CLAIMS: 1. A system for removing contaminants from exhaust gas emitted by a marine combustion engine, the system comprising: an exhaust gas inlet and an exhaust gas outlet, wherein a stream of exhaust gas flows along a path in a direction from the inlet to the outlet in use; a quenching section located between said inlet and said outlet for mixing the exhaust gas stream with a quenching liquid stream, a scrubbing section located downstream of said quenching section in the path of said exhaust gas stream between said inlet and outlet for mixing the exhaust gas stream with a scrubbing liquid stream for removing liquid soluble contaminants from the exhaust gas in use; wherein the quenching section comprises a packed region comprising packing material through which the exhaust gas and quenching liquid streams pass in use before entering the scrubbing section.
2. The system of claim 1 wherein the quenching section comprises a nozzle for providing a quenching liquid stream in the form of a spray.
3. The system of any preceding claim wherein said quenching section comprises a curved inlet section extending from exhaust gas inlet to promote drawing of exhaust gas into the quenching section for mixing with the liquid stream.
4. The system of claim 2 wherein said curved section terminates upstream of the outlet of a nozzle for providing said quenching liquid.
5. The system of any preceding claim wherein said packing material of said packed region comprises structured packing material.

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6. The system of any preceding claim wherein the packing material of said packed region is arranged to induce turbulence in the exhaust gas flow.
7. The system of any preceding claim wherein the quenching section comprises a flow restriction in the region where the liquid and gas streams flux in use, the flow restriction being located upstream of the packed region.
8. The system of any preceding claim wherein the quenching liquid and exhaust gas streams flow in the same direction through said quenching section.
9. The system of any preceding claim wherein the scrubbing section comprises a packed region comprising packing material, and means for providing said scrubbing liquid stream.
10. The system of claim 9 wherein said packing material of the scrubbing section is structured packing material.
11. The system of claim 9 or 10 wherein the packed region of said scrubbing section comprises a plurality of sub-regions arranged sequentially along the path of the exhaust gas through the packed region, each sub-region comprising structured packing material having fluid passageways, wherein the fluid passageways of the structured packing material of adjacent sub-regions is different.
12. The system of any preceding claim comprising a sump at the bottom of the scrubbing section for collecting liquid.-24 -
13. The system of any preceding claim wherein the quenching section is located above the scrubbing section
14. The system of any preceding claim further comprising a demister, preferably a vertical demister, downstream of the scrubbing section for removing moisture from the exhaust gas.
15. A quenching section for a system for removing contaminants from exhaust gas emitted by a marine combustion engine, the quenching section comprising: an exhaust gas inlet through which exhaust gas enters the quenching section in use; and means for providing a liquid stream for mixing with the exhaust gas stream; the quenching section further comprising; a curved inlet section extending from the exhaust gas inlet to promote drawing of exhaust gas into the quenching section for mixing with the liquid stream; and a packed region comprising packing material through which the exhaust gas and liquid streams pass in use for promoting contact between the liquid and gas streams.
16. The quenching section of claim 15 wherein the quenching section comprises a flow restriction through which the liquid and gas streams pass in use, the flow restriction being located upstream of the packed region.
17. A system for removing contaminants from exhaust gas emitted by a marine combustion engine; the system comprising; an exhaust gas inlet and an exhaust gas outlet, wherein a stream of exhaust gas flows along a path in a direction from the inlet to the outlet in use; -25 -the system further comprising a scrubbing section located between said inlet and outlet, the scrubbing section being arranged to mix the exhaust gas stream with a scrubbing liquid stream in use for removing liquid soluble contaminants from the exhaust gas, wherein the scrubbing liquid stream flows in the same direction as the exhaust gas stream.
18. The system or quenching section of any preceding claim wherein the inlet of the system is connected to the exhaust gas outlet of a marine engine for supplying exhaust gas to the system in use.
19. The system or quenching section of any of claims 1 to 18 wherein the system is mounted to a marine vessel.
20. The system of claim 17 further comprising a quenching section upstream of said scrubbing section for mixing the exhaust gas with a stream of quenching liquid.
21. A method of removing contaminants from marine exhaust gas using the system or quenching section of any of claims 1 to 14 or 17 to 20, the method comprising supplying exhaust gas from an engine, preferably a marine engine to the exhaust gas inlet of the system.
22. The method of claim 21 further comprising mixing the exhaust gas stream with quenching liquid and scrubbing liquid streams in the quenching and scrubbing sections.
23. A method of removing contaminants from marine exhaust gas using the quenching section of claim 15 or 16, the method comprising supplying exhaust gas from an engine, preferably a marine engine to the exhaust gas inlet of the quenching section.
24. The method of claim 23 further comprising connecting an outlet of said quenching section to the inlet of a scrubbing system.
25. The method or system of any preceding claim wherein said quenching liquid and/or said scrubbing liquid comprises sea water.
26. The use of the system or quenching section of any of claims 1-20 to remove contaminants, preferably sulphur dioxide, from exhaust gas emitted by a marine engine
27. A system, quenching section or method substantially as herein described, and with reference to any one of the accompanying drawings.