WO2012117233A1 - Exhaust scrubbing - Google Patents

Exhaust scrubbing Download PDF

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Publication number
WO2012117233A1
WO2012117233A1 PCT/GB2012/050310 GB2012050310W WO2012117233A1 WO 2012117233 A1 WO2012117233 A1 WO 2012117233A1 GB 2012050310 W GB2012050310 W GB 2012050310W WO 2012117233 A1 WO2012117233 A1 WO 2012117233A1
Authority
WO
WIPO (PCT)
Prior art keywords
scrubbing
exhaust gases
duct
water droplets
quenching chamber
Prior art date
Application number
PCT/GB2012/050310
Other languages
French (fr)
Inventor
Nicholas Galor HOLNESS
Original Assignee
Oceanox Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oceanox Limited filed Critical Oceanox Limited
Priority to GB1315568.4A priority Critical patent/GB2501663B/en
Publication of WO2012117233A1 publication Critical patent/WO2012117233A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/04—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust using liquids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/005—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for draining or otherwise eliminating condensates or moisture accumulating in the apparatus
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2252/00—Absorbents, i.e. solvents and liquid materials for gas absorption
    • B01D2252/10—Inorganic absorbents
    • B01D2252/103—Water
    • B01D2252/1035—Sea water
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/30—Sulfur compounds
    • B01D2257/302—Sulfur oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/404—Nitrogen oxides other than dinitrogen oxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/702—Hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/012—Diesel engines and lean burn gasoline engines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/12—Methods and means for introducing reactants
    • B01D2259/124—Liquid reactants
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/45—Gas separation or purification devices adapted for specific applications
    • B01D2259/4566—Gas separation or purification devices adapted for specific applications for use in transportation means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/60—Simultaneously removing sulfur oxides and nitrogen oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/77—Liquid phase processes
    • B01D53/78—Liquid phase processes with gas-liquid contact
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2590/00—Exhaust or silencing apparatus adapted to particular use, e.g. for military applications, airplanes, submarines
    • F01N2590/02—Exhaust or silencing apparatus adapted to particular use, e.g. for military applications, airplanes, submarines for marine vessels or naval applications
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to an apparatus and a process for scrubbing exhaust gases from an engine, in particular from a marine engine.
  • Engines such as diesel engines are widely used on marine vessels, either for propulsion or as a source of auxiliary power.
  • the fuel contains impurities such as sulphur
  • the exhaust gases will contain contaminants such as sulphur dioxide. If this is released into the atmosphere it may be absorbed by water and contribute to acid rain. In some situations it may be possible to remove the impurities from the fuel before it is used, but for marine applications it may instead be acceptable to remove the sulphur dioxide from the exhaust gases before they are discharged to the environment, by a scrubbing process.
  • the exhaust gases can be satisfactorily scrubbed, then it would be acceptable for ships to continue to use residual fuel oil, which is a comparatively cheap fuel source.
  • GB 2 469 319 describes a system for treating exhaust gases in which the exhaust gases are first quenched, to lower their temperature, and are then scrubbed; the quenching section includes a packed region through which a quenching liquid and the exhaust gases both pass; the scrubbing region may also included a packed region.
  • the quenching section includes a packed region through which a quenching liquid and the exhaust gases both pass; the scrubbing region may also included a packed region.
  • a system for scrubbing exhaust gases from an engine comprising:
  • quenching chamber of a high temperature resistant material, the quenching chamber containing nozzles for spraying water droplets into the exhaust gases;
  • scrubbing duct of sufficient length and cross-sectional area that the residence time for exhaust gases in the scrubbing duct is greater than 2 seconds, the scrubbing duct comprising nozzles for spraying water droplets so that water droplets fall through the flowing exhaust gases;
  • the demister unit at the downstream end of the scrubbing duct to remove water droplets from the flowing exhaust gases.
  • the total pressure drop is preferably less than 10 kPa (3" Hg); a significant proportion of the pressure drop is usually in the pipework, rather in the scrubbing system itself.
  • the treated exhaust gases may be discharged to the environment.
  • the residence time for exhaust gases in the scrubbing duct is greater than 3 seconds, and more preferably greater than 4 seconds.
  • the length of the scrubbing duct is between 3 m and 10 m, more preferably between 4 m and 6 m, and the cross-sectional area is selected in accordance with the maximum exhaust gases flow to achieve the required residence time.
  • the system is connectable into an exhaust-carrying duct by means of a diversion valve, such that when the exhaust gases scrubbing system is not operating the diversion valve may be actuated so that the exhaust gases are not passed through the scrubbing system. If there is a problem in the water supply system, the exhaust gases can be discharged directly into the atmosphere until the problem is rectified. Consequently the scrubbing duct can be made of a
  • the water droplets used in the quenching chamber and the scrubbing duct are seawater, in the case of vessels at sea. In other cases the water may be fresh water, or may contain chemical additives.
  • the direction of flow of the exhaust gases through the scrubbing duct, and indeed through the quenching chamber is preferably generally horizontal, so that the water droplets are falling in a direction substantially transverse to the gas flow direction. It is intended that the water droplets and the exhaust gases should be substantially in a crossflow relationship. More specifically, the direction of flow is preferably no more than 45° from the horizontal, more preferably not more than 30 ° from horizontal, and may indeed be less than 10 ° from the horizontal.
  • the system is primarily intended for use on a ship, so that in practice, as the ship proceeds through waves, the inclination of the direction of flow from the horizontal will in practice vary.
  • the water droplets that have passed through the quenching chamber or the scrubbing duct are collected as a waste water stream, and the system includes a hydrocyclone to separate waste water from particulates and any uncombusted oil.
  • the particulates and uncombusted oil form a sludge which can be stored for safe subsequent disposal.
  • the cleaned waste water which contains the bulk of the gaseous contaminants from the exhaust gases, may be diluted with additional seawater before being discharged into the sea.
  • the water that has passed through the quenching chamber and/or the scrubbing duct is thus, in this example, discharged as the waste water stream, without being recirculated. It will be appreciated that the contaminants such as sulphur dioxide and NO x are not detrimental to the environment when introduced in dilute form into the sea.
  • the waste water is combined with the additional seawater by means of an eductor, so as to enhance the flow of the waste water through the hydrocyclone.
  • the invention in a second aspect, provides a system for scrubbing exhaust gases from an engine, comprising a diversion valve operable to divert exhaust gases from a duct carrying the exhaust gases, a quenching unit of a high temperature resistant material to which the diversion valve diverts the exhaust gases, and a scrubbing unit, and means to supply water to the quenching unit and to the scrubbing unit.
  • the scrubbing unit is preferably of a plastic or glass-fibre reinforced plastic material, so minimising weight.
  • the invention in a third aspect, provides a process for scrubbing exhaust gases using a scrubbing system of the first aspect or of the second aspect.
  • Figure 1 shows a flow diagram of an exhaust gases scrubbing system
  • Figure 2 shows a perspective view of parts of the scrubbing system of Figure 1 ;
  • Figure 3 shows a cross-sectional view on the line A-A of figure 2;
  • Figure 4 shows a perspective view showing the underside of the parts shown in figure 2.
  • FIG 1 there is shown part of an exhaust duct 12 in a marine engine, along with a scrubbing system 10.
  • the exhaust duct 12 is modified by installing a side duct 14 of substantially the same cross-sectional area as the exhaust duct 12, and a diverter valve 16 (represented schematically).
  • a side duct 14 of substantially the same cross-sectional area as the exhaust duct 12, and a diverter valve 16 (represented schematically).
  • the diverter valve 16 can be moved into an alternative position 16a (shown in broken lines) in which the exhaust gases do not flow through the side duct 14.
  • the three-stage treatment unit 20 consists of a quenching chamber 22 constructed of heat-resistant steel such as Inconel (trade mark); a horizontally-extending scrubbing duct 24 constructed of glass reinforced vinyl ester resin; and a demisting section 26 also of glass-reinforced vinyl ester resin and enclosing a polypropylene fibre pad.
  • Seawater S is supplied by a pump 28 to injection nozzles 30 within the quenching chamber 22 and to injection nozzles 32 within the scrubbing duct 24.
  • the injection nozzles 30 are also supplied with compressed air C, so they produce a fine mist of droplets.
  • the fine mist of droplets within the quenching chamber 22 cools the exhaust gases, typically from above 400 °C down to about 30 °C, and ensures that the gas stream is saturated with water vapour as it enters the scrubbing duct 24.
  • the scrubbing duct 24 As the cooled exhaust gases pass through the scrubbing duct 24 they are exposed to sprays of droplets from the nozzles 32, the arrangement being substantially a crossflow arrangement with the droplets primarily travelling in a direction transverse to the longitudinal axis of the duct 24 and so to the flow direction of the exhaust gases.
  • the droplets remove particulate material and water-soluble contaminant gases such as S0 2 and NO x , to form a waste water stream 34.
  • the waste water stream 34 flows down under gravity into a hydrocyclone 35 which separates off a sludge stream P containing particulate material such as carbon and any unburnt hydrocarbons from the fuel.
  • the quantity of material in the sludge stream P is not large, typically being less than 20 g per tonne of fuel that has been used, more typically about 10 g/tonne.
  • This may be stored in a container for subsequent safe disposal; it may be dosed with a neutralising agent; and in some cases it may be stored in a ship's organic sludge disposal system.
  • the remainder of the waste water stream emerges through an outlet duct 36 which is connected to an eductor (or jet pump) 37 fed with a stream of seawater S by a pump 38.
  • the eductor 37 hence produces a dilute waste water stream Q which may be discharged back into the sea.
  • the eductor 37 creates suction, which enhances the flow through the hydrocyclone 35.
  • the hydrocyclone 35, the eductor 37 and the pump 38 together constitute a waste water treatment unit 33.
  • the three-stage treatment unit 20 includes a steel support frame 40 which supports the quenching chamber 22, the scrubbing duct 24 and the demisting section 26.
  • the quenching chamber 22 is of square cross-section, and is of length 2.0 m.
  • One end face of the quenching chamber 22 is closed apart from a tubular inlet 42 for connection to the side duct 14, and the opposite end face is completely open, and provided with a flange for connection to a corresponding flange 44 at the end of the scrubbing duct 24.
  • the cross-sectional area of the quenching chamber 22 is therefore larger than that of the exhaust duct 12.
  • the nozzles 30 are mounted on the side walls, and in this example there are two on each side, near the inlet end.
  • the scrubbing duct 24 includes tapered linking portions 46 at each end, and a central scrubbing portion 48 of generally square cross-section, but in which the base, as shown in figures 3 and 4, slopes gently down to define a central sump 49.
  • the central scrubbing portion 48 in this example, is of length 5.6 m, and the linking portions 46 are each of length 1 .1 m, and the cross-sectional area is sufficiently large that the residence time for the exhaust gases in the scrubbing duct 24 is just more than 4 seconds, while the residence time in the three-stage treatment unit 20 is about 7 seconds.
  • the cross-sectional area of the quenching chamber 22 would preferably be 1 m 2 and the cross-sectional area of the central scrubbing portion 48 would be preferably 2.25 m 2 ; for a 5 MW diesel engine the cross-sectional area of the quenching chamber 22 might be 4 m 2 and the cross-sectional area of the central scrubbing portion 48 might be 10 m 2 .
  • the scrubbing duct 24 is constructed of glass reinforced vinyl ester resin, in the form of two upper parts 47a and two lower parts 47b joined together at flanges, and each incorporating strengthening ribs 47c.
  • seawater S from the pump 28 is supplied via a supply pipe 50 running along below the three-stage treatment unit 20, and which is connected to pipes 52 made of a corrosion resistant metal such as Inconel (TM) that are mounted on to larger-diameter flanges 53 at the top corners of the central scrubbing portion 48.
  • the pipes 52 carry the nozzles 32, and the apertures within the flanges 53 are sufficiently large that the pipes 52 with the nozzles 32 can be withdrawn for maintenance.
  • a waste water pipe 54 also runs along below the three- stage treatment unit 20, to carry the waste water stream 34.
  • the waste water pipe 54 is connected via two U-bends 56 to the central sump 49, and as shown in figure 4 it is also connected via U-bends 56 to the base of the quenching chamber 22 and to the base of the demisting section 26.
  • the U-bends 56 will contain water, and so prevent the exhaust gases flowing out into the waste water pipe 54.
  • the U-bends 56 act as weirs.
  • the downstream end of the central scrubbing portion 48 communicates with a tapered linking portion 46 which connects to the demisting section 26. This is of the same cross-sectional area as the quenching chamber 22, and contains a
  • the pad can be inserted through a rectangular slot 58, shown in figure 2, at the side of the demisting section 26. In use this slot 58 would be covered by a cover plate (not shown).
  • the fibre pad traps small droplets from the clean gas stream, and the droplets collect at the base of the demisting section 26, and flow out into the waste water pipe 54 through the corresponding U-bend 56 shown in figure 4.
  • a tapering end portion 60 that links to an outlet port 62 which may be of the same cross- sectional area as the exhaust duct 12.
  • the scrubbing system 10 can therefore readily be retrofitted to a ship. Because the scrubbing duct 24 and the demisting section 26 extend in a horizontal direction, and are made of a relatively low-density material, the scrubbing system 10 does not affect the stability of the ship, as it does not require the installation of heavy items high up in the ship. As the quenching chamber 22 and scrubbing duct 24 do not contain any packing material to disrupt gas flow, the scrubbing system 10 does not impose a large back pressure on the exhaust duct 12.
  • the components of the waste water treatment 33 may be installed below the support frame, for example on a lower deck of the ship, for example within the ship's engine room, as may the water supply pump 28.
  • the system 10 described in relation to the figures is by way of example only.
  • a scrubbing system may differ in various ways while remaining within the scope of the present invention, for example: the quenching chamber and the scrubbing duct may be of a different cross-sectional shape to that shown; the demisting unit might utilise closely spaced zigzag plates instead of the polypropylene fibre pad.
  • the system 10 can be installed as a module.
  • the cross-sectional area of the three-stage treatment unit 20 can be selected in accordance with the gas flow to be treated, which corresponds to the power of the engine.
  • the side duct 14 might connect to two different modules operating in parallel and so providing greater capacity.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Biomedical Technology (AREA)
  • Health & Medical Sciences (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Treating Waste Gases (AREA)

Abstract

A system (10) for scrubbing exhaust gases from an engine, particularly from a marine engine, comprises a quenching chamber (22) of a high temperature resistant material, the quenching chamber containing nozzles (30) for spraying water droplets into the exhaust gases; a scrubbing duct (24) of sufficient length and cross- sectional area that the residence time for exhaust gases in the scrubbing duct is greater than 2 seconds, the scrubbing duct (24) comprising nozzles (32) for spraying water droplets so that water droplets fall through the flowing exhaust gases; and a demister unit (26) at the downstream end of the scrubbing duct (24). The system (10) can be set up to provide a substantially horizontal flow path for the exhaust gases in which the water droplets pass across the gas flow. The system (10) can be retrofitted to a ship, and does not impose a significant back pressure on the exhaust gases.

Description

Exhaust Scrubbing
The present invention relates to an apparatus and a process for scrubbing exhaust gases from an engine, in particular from a marine engine.
Engines such as diesel engines are widely used on marine vessels, either for propulsion or as a source of auxiliary power. If the fuel contains impurities such as sulphur, the exhaust gases will contain contaminants such as sulphur dioxide. If this is released into the atmosphere it may be absorbed by water and contribute to acid rain. In some situations it may be possible to remove the impurities from the fuel before it is used, but for marine applications it may instead be acceptable to remove the sulphur dioxide from the exhaust gases before they are discharged to the environment, by a scrubbing process. Hence, if the exhaust gases can be satisfactorily scrubbed, then it would be acceptable for ships to continue to use residual fuel oil, which is a comparatively cheap fuel source. For example GB 2 469 319 describes a system for treating exhaust gases in which the exhaust gases are first quenched, to lower their temperature, and are then scrubbed; the quenching section includes a packed region through which a quenching liquid and the exhaust gases both pass; the scrubbing region may also included a packed region. However it is important that any such scrubbing process does not impose a large pressure drop on the exhaust gases, as this would have a detrimental impact on the performance of the engine.
According to the present invention there is provided a system for scrubbing exhaust gases from an engine, the system comprising:
- a quenching chamber of a high temperature resistant material, the quenching chamber containing nozzles for spraying water droplets into the exhaust gases;
- a scrubbing duct of sufficient length and cross-sectional area that the residence time for exhaust gases in the scrubbing duct is greater than 2 seconds, the scrubbing duct comprising nozzles for spraying water droplets so that water droplets fall through the flowing exhaust gases; and
- a demister unit at the downstream end of the scrubbing duct to remove water droplets from the flowing exhaust gases. Neither the quenching chamber nor the scrubbing duct contain a packed region, so there is little pressure drop imposed on the exhaust gases. The total pressure drop is preferably less than 10 kPa (3" Hg); a significant proportion of the pressure drop is usually in the pipework, rather in the scrubbing system itself. After passing through the demister unit, the treated exhaust gases may be discharged to the environment. Preferably the residence time for exhaust gases in the scrubbing duct is greater than 3 seconds, and more preferably greater than 4 seconds. Preferably the length of the scrubbing duct is between 3 m and 10 m, more preferably between 4 m and 6 m, and the cross-sectional area is selected in accordance with the maximum exhaust gases flow to achieve the required residence time.
Preferably the system is connectable into an exhaust-carrying duct by means of a diversion valve, such that when the exhaust gases scrubbing system is not operating the diversion valve may be actuated so that the exhaust gases are not passed through the scrubbing system. If there is a problem in the water supply system, the exhaust gases can be discharged directly into the atmosphere until the problem is rectified. Consequently the scrubbing duct can be made of a
comparatively lightweight material such as a plastic or glass-reinforced plastic, as it is not exposed to the high temperature of the unquenched exhaust gases. Preferably the water droplets used in the quenching chamber and the scrubbing duct are seawater, in the case of vessels at sea. In other cases the water may be fresh water, or may contain chemical additives.
The direction of flow of the exhaust gases through the scrubbing duct, and indeed through the quenching chamber, is preferably generally horizontal, so that the water droplets are falling in a direction substantially transverse to the gas flow direction. It is intended that the water droplets and the exhaust gases should be substantially in a crossflow relationship. More specifically, the direction of flow is preferably no more than 45° from the horizontal, more preferably not more than 30 ° from horizontal, and may indeed be less than 10 ° from the horizontal. The system is primarily intended for use on a ship, so that in practice, as the ship proceeds through waves, the inclination of the direction of flow from the horizontal will in practice vary.
In a preferred embodiment the water droplets that have passed through the quenching chamber or the scrubbing duct are collected as a waste water stream, and the system includes a hydrocyclone to separate waste water from particulates and any uncombusted oil. The particulates and uncombusted oil form a sludge which can be stored for safe subsequent disposal. The cleaned waste water, which contains the bulk of the gaseous contaminants from the exhaust gases, may be diluted with additional seawater before being discharged into the sea. The water that has passed through the quenching chamber and/or the scrubbing duct is thus, in this example, discharged as the waste water stream, without being recirculated. It will be appreciated that the contaminants such as sulphur dioxide and NOx are not detrimental to the environment when introduced in dilute form into the sea.
Preferably the waste water is combined with the additional seawater by means of an eductor, so as to enhance the flow of the waste water through the hydrocyclone.
The invention, in a second aspect, provides a system for scrubbing exhaust gases from an engine, comprising a diversion valve operable to divert exhaust gases from a duct carrying the exhaust gases, a quenching unit of a high temperature resistant material to which the diversion valve diverts the exhaust gases, and a scrubbing unit, and means to supply water to the quenching unit and to the scrubbing unit.
The second aspect of the invention may be combined with one or more of the features described and summarised above. In particular, the scrubbing unit is preferably of a plastic or glass-fibre reinforced plastic material, so minimising weight.
The invention, in a third aspect, provides a process for scrubbing exhaust gases using a scrubbing system of the first aspect or of the second aspect.
The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which:
Figure 1 shows a flow diagram of an exhaust gases scrubbing system;
Figure 2 shows a perspective view of parts of the scrubbing system of Figure 1 ; Figure 3 shows a cross-sectional view on the line A-A of figure 2; and
Figure 4 shows a perspective view showing the underside of the parts shown in figure 2.
Referring to figure 1 , there is shown part of an exhaust duct 12 in a marine engine, along with a scrubbing system 10. The exhaust duct 12 is modified by installing a side duct 14 of substantially the same cross-sectional area as the exhaust duct 12, and a diverter valve 16 (represented schematically). In the position as shown the exhaust gases from the engines are all diverted into the side duct 14, as indicated by the arrows, but if the scrubbing system 10 is not functioning, then the diverter valve 16 can be moved into an alternative position 16a (shown in broken lines) in which the exhaust gases do not flow through the side duct 14.
The side duct 14, as indicated schematically, supplies the exhaust gases to a three-stage treatment unit 20, and the treated exhaust gases emerge as a clean gas stream R which may be discharged directly to the environment as shown, or alternatively may be fed back into the exhaust duct 12 above the diverter valve 16 for discharge into the environment. The three-stage treatment unit 20 consists of a quenching chamber 22 constructed of heat-resistant steel such as Inconel (trade mark); a horizontally-extending scrubbing duct 24 constructed of glass reinforced vinyl ester resin; and a demisting section 26 also of glass-reinforced vinyl ester resin and enclosing a polypropylene fibre pad. Seawater S is supplied by a pump 28 to injection nozzles 30 within the quenching chamber 22 and to injection nozzles 32 within the scrubbing duct 24. The injection nozzles 30 are also supplied with compressed air C, so they produce a fine mist of droplets. The fine mist of droplets within the quenching chamber 22 cools the exhaust gases, typically from above 400 °C down to about 30 °C, and ensures that the gas stream is saturated with water vapour as it enters the scrubbing duct 24.
As the cooled exhaust gases pass through the scrubbing duct 24 they are exposed to sprays of droplets from the nozzles 32, the arrangement being substantially a crossflow arrangement with the droplets primarily travelling in a direction transverse to the longitudinal axis of the duct 24 and so to the flow direction of the exhaust gases. The droplets remove particulate material and water-soluble contaminant gases such as S02 and NOx, to form a waste water stream 34.
The waste water stream 34 flows down under gravity into a hydrocyclone 35 which separates off a sludge stream P containing particulate material such as carbon and any unburnt hydrocarbons from the fuel. The quantity of material in the sludge stream P is not large, typically being less than 20 g per tonne of fuel that has been used, more typically about 10 g/tonne. This may be stored in a container for subsequent safe disposal; it may be dosed with a neutralising agent; and in some cases it may be stored in a ship's organic sludge disposal system. The remainder of the waste water stream emerges through an outlet duct 36 which is connected to an eductor (or jet pump) 37 fed with a stream of seawater S by a pump 38. The eductor 37 hence produces a dilute waste water stream Q which may be discharged back into the sea. The eductor 37 creates suction, which enhances the flow through the hydrocyclone 35. The hydrocyclone 35, the eductor 37 and the pump 38 together constitute a waste water treatment unit 33.
Referring now to figure 2 the three-stage treatment unit 20 is shown in more detail. It includes a steel support frame 40 which supports the quenching chamber 22, the scrubbing duct 24 and the demisting section 26. The quenching chamber 22 is of square cross-section, and is of length 2.0 m. One end face of the quenching chamber 22 is closed apart from a tubular inlet 42 for connection to the side duct 14, and the opposite end face is completely open, and provided with a flange for connection to a corresponding flange 44 at the end of the scrubbing duct 24. The cross-sectional area of the quenching chamber 22 is therefore larger than that of the exhaust duct 12. The nozzles 30 are mounted on the side walls, and in this example there are two on each side, near the inlet end.
The scrubbing duct 24 includes tapered linking portions 46 at each end, and a central scrubbing portion 48 of generally square cross-section, but in which the base, as shown in figures 3 and 4, slopes gently down to define a central sump 49. The central scrubbing portion 48, in this example, is of length 5.6 m, and the linking portions 46 are each of length 1 .1 m, and the cross-sectional area is sufficiently large that the residence time for the exhaust gases in the scrubbing duct 24 is just more than 4 seconds, while the residence time in the three-stage treatment unit 20 is about 7 seconds. For example for a 1 MW diesel engine the cross-sectional area of the quenching chamber 22 would preferably be 1 m2 and the cross-sectional area of the central scrubbing portion 48 would be preferably 2.25 m2; for a 5 MW diesel engine the cross-sectional area of the quenching chamber 22 might be 4 m2 and the cross-sectional area of the central scrubbing portion 48 might be 10 m2. The scrubbing duct 24 is constructed of glass reinforced vinyl ester resin, in the form of two upper parts 47a and two lower parts 47b joined together at flanges, and each incorporating strengthening ribs 47c.
As shown in figures 3 and 4 seawater S from the pump 28 is supplied via a supply pipe 50 running along below the three-stage treatment unit 20, and which is connected to pipes 52 made of a corrosion resistant metal such as Inconel (TM) that are mounted on to larger-diameter flanges 53 at the top corners of the central scrubbing portion 48. The pipes 52 carry the nozzles 32, and the apertures within the flanges 53 are sufficiently large that the pipes 52 with the nozzles 32 can be withdrawn for maintenance. A waste water pipe 54 also runs along below the three- stage treatment unit 20, to carry the waste water stream 34. The waste water pipe 54 is connected via two U-bends 56 to the central sump 49, and as shown in figure 4 it is also connected via U-bends 56 to the base of the quenching chamber 22 and to the base of the demisting section 26. In use the U-bends 56 will contain water, and so prevent the exhaust gases flowing out into the waste water pipe 54. There is typically no standing water in the central sump 49, as the water surface is within the U-bends 56, and water overflows from the U-bends 56 into the waste water pipe 54 at the same rate as the water is sprayed through the nozzles 32. The U-bends 56 act as weirs.
The downstream end of the central scrubbing portion 48 communicates with a tapered linking portion 46 which connects to the demisting section 26. This is of the same cross-sectional area as the quenching chamber 22, and contains a
polypropylene fibre pad. The pad can be inserted through a rectangular slot 58, shown in figure 2, at the side of the demisting section 26. In use this slot 58 would be covered by a cover plate (not shown). The fibre pad traps small droplets from the clean gas stream, and the droplets collect at the base of the demisting section 26, and flow out into the waste water pipe 54 through the corresponding U-bend 56 shown in figure 4. At the downstream end of the demisting section 26 is a tapering end portion 60 that links to an outlet port 62 which may be of the same cross- sectional area as the exhaust duct 12. The bulk of the scrubbing system 10, in particular the three-stage treatment unit 20 and the support frame 40, fit within the dimensions of a standard 40-foot container. The scrubbing system 10 can therefore readily be retrofitted to a ship. Because the scrubbing duct 24 and the demisting section 26 extend in a horizontal direction, and are made of a relatively low-density material, the scrubbing system 10 does not affect the stability of the ship, as it does not require the installation of heavy items high up in the ship. As the quenching chamber 22 and scrubbing duct 24 do not contain any packing material to disrupt gas flow, the scrubbing system 10 does not impose a large back pressure on the exhaust duct 12. The components of the waste water treatment 33 may be installed below the support frame, for example on a lower deck of the ship, for example within the ship's engine room, as may the water supply pump 28. It will be appreciated that the system 10 described in relation to the figures is by way of example only. A scrubbing system may differ in various ways while remaining within the scope of the present invention, for example: the quenching chamber and the scrubbing duct may be of a different cross-sectional shape to that shown; the demisting unit might utilise closely spaced zigzag plates instead of the polypropylene fibre pad.
It will be appreciated that the system 10 can be installed as a module. As described above, the cross-sectional area of the three-stage treatment unit 20 can be selected in accordance with the gas flow to be treated, which corresponds to the power of the engine. However, if a single module does not provide sufficient capacity it will be appreciated that, as an alternative, the side duct 14 might connect to two different modules operating in parallel and so providing greater capacity.

Claims

Claims
1 . A system for scrubbing exhaust gases from an engine, the system comprising:
- a quenching chamber of a high temperature resistant material, the quenching chamber containing nozzles for spraying water droplets into the exhaust gases;
- a scrubbing duct of sufficient length and cross-sectional area that the residence time for exhaust gases in the scrubbing duct is greater than 2 seconds, the scrubbing duct comprising nozzles for spraying water droplets so that water droplets fall through the flowing exhaust gases; and
- a demister unit at the downstream end of the scrubbing duct to remove water droplets from the flowing exhaust gases;
wherein the quenching chamber and scrubbing duct do not contain any packing material to disrupt gas flow.
2. A system as claimed in claim 1 wherein the residence time for exhaust gases in the scrubbing duct is greater than 3 seconds.
3. A system as claimed in claim 1 or claimed 2 also comprising a diversion valve for connection into an exhaust-carrying duct.
4. A system as claimed in any one of the preceding claims wherein the scrubbing duct is of a plastic or glass-reinforced plastic material.
5. A system as claimed in any one of the preceding claims also comprising a hydrocyclone to treat waste water from the scrubbing duct.
6. A system as claimed in any one of the preceding claims wherein waste water from the scrubbing duct is combined with additional water by means of an eductor.
7. A system for scrubbing exhaust gases from an engine, comprising a diversion valve operable to divert exhaust gases from a duct carrying the exhaust gases, a quenching unit of a high temperature resistant material to which the diversion valve diverts the exhaust gases, and a scrubbing unit, and means to supply water to the quenching unit and to the scrubbing unit.
8. A system as claimed in claim 7 wherein the scrubbing unit is of a plastic or glass- reinforced plastic material.
9. A process for scrubbing exhaust gases, the process using a scrubbing system as claimed in any one of the preceding claims.
10. A process as claimed in claim 9 wherein the water droplets are of seawater.
PCT/GB2012/050310 2011-02-28 2012-02-13 Exhaust scrubbing WO2012117233A1 (en)

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GBGB1103349.5A GB201103349D0 (en) 2011-02-28 2011-02-28 Exhaust scrubbing
GB1103349.5 2011-02-28

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FR3035440A1 (en) * 2015-04-24 2016-10-28 Claude Jules Joseph Vansuyt DEVICE FOR THE WET FILTRATION OF GASEOUS RELEASES IN THE EXHAUST PITCH OUTPUT OF A THERMALLY ENGINE VEHICLE
CN108487973A (en) * 2018-01-30 2018-09-04 福建省福船海洋工程技术研究院有限公司 Tail gas smoke eliminating device and method for offshore wind power self-elevating mounting platform generator set
FR3073894A1 (en) * 2017-11-22 2019-05-24 Michel Jean Celestin Carle DEPOLLUTION OF THE AIR: VEHICLES, INDUSTRY, FIREPLACES, LOCOMOTIVES, POLLUTED HABITATS
WO2019101286A1 (en) * 2017-11-21 2019-05-31 Wärtsilä Finland Oy A method of installing an exhaust gas scrubber system of a power plant in a marine vessel and an exhaust gas scrubber system for wet scrubbing of exhaust gas of a power plant in a marine vessel

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GB2469319A (en) 2009-04-08 2010-10-13 Krystallon Ltd Exhaust treatment for a marine engine

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EP1797943A1 (en) * 2005-12-14 2007-06-20 Atkins Limited Scrubbing system
WO2008104070A1 (en) * 2007-02-27 2008-09-04 Nxtgen Emission Controls Inc. Emission reduction system using wet scrubbing
GB2469319A (en) 2009-04-08 2010-10-13 Krystallon Ltd Exhaust treatment for a marine engine

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Publication number Priority date Publication date Assignee Title
FR3035440A1 (en) * 2015-04-24 2016-10-28 Claude Jules Joseph Vansuyt DEVICE FOR THE WET FILTRATION OF GASEOUS RELEASES IN THE EXHAUST PITCH OUTPUT OF A THERMALLY ENGINE VEHICLE
WO2019101286A1 (en) * 2017-11-21 2019-05-31 Wärtsilä Finland Oy A method of installing an exhaust gas scrubber system of a power plant in a marine vessel and an exhaust gas scrubber system for wet scrubbing of exhaust gas of a power plant in a marine vessel
KR20200087810A (en) * 2017-11-21 2020-07-21 바르실라 핀랜드 오이 Method for installing the exhaust gas scrubber system of the generator on the marine vessel and the exhaust gas scrubber system for wet scrubbing of the exhaust gas of the generator on the marine vessel
KR102395685B1 (en) 2017-11-21 2022-05-06 바르실라 핀랜드 오이 Method of installing exhaust gas scrubber system of generator on marine vessel and exhaust gas scrubber system for wet scrubbing of exhaust gas of generator in marine vessel
FR3073894A1 (en) * 2017-11-22 2019-05-24 Michel Jean Celestin Carle DEPOLLUTION OF THE AIR: VEHICLES, INDUSTRY, FIREPLACES, LOCOMOTIVES, POLLUTED HABITATS
CN108487973A (en) * 2018-01-30 2018-09-04 福建省福船海洋工程技术研究院有限公司 Tail gas smoke eliminating device and method for offshore wind power self-elevating mounting platform generator set
CN108487973B (en) * 2018-01-30 2024-01-19 福建省福船海洋工程技术研究院有限公司 Tail gas smoke abatement device and method for offshore wind power self-elevating type installation platform generator set

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GB2501663B (en) 2017-09-27
GB201315568D0 (en) 2013-10-16
GB201103349D0 (en) 2011-04-13

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