WO2014032814A1

WO2014032814A1 - Exhaust gas purifying device and method

Info

Publication number: WO2014032814A1
Application number: PCT/EP2013/002631
Authority: WO
Inventors: Branko Tanfara
Original assignee: Lmb Kotlovski Inzenjering d o o
Current assignee: Lmb Kotlovski Inzenjering d o o
Priority date: 2012-08-31
Filing date: 2013-09-02
Publication date: 2014-03-06
Anticipated expiration: 2015-02-28
Also published as: HRP20120691A2; EP2912286A1

Description

Exhaust Gas Purifying Device and Method

Description of the Invention

Field to which the Invention pertains

The invention pertains to an exhaust gas purifying device and a method for purifying exhaust gas, in particular exhaust gases generated by combustion of fossil fuels in ship^'s engines and boilers.

Technical Problem

By combustion of fossil fuels containing sulfur there develop oxides (SOx, NOx) and solid particles in form of soot, ashes and non-combusted hydrocarbons. All those combustion products are harmful to the environment. IMO organization (International Maritime Organisation) started to introduce limitations in use of heavy fuels (masut) with high contents of sulfur in harbors and some protected zones which will be significantly extended in 2015, whereas till 2020 all world seas will be covered. Ships have the possibility to use low sulfur, expensive fuels (Euro Diesel) or heavy cheap fuels with high contents of sulfur, however with built in device for desulfurization and filtering solid particles, in particular soot.

State of Art

There are known marine devices for desulfurization of exhaust gases (marine SOx scrubber), where exhaust gases from engines or boilers in ports are mixed with water for cooling, whereupon they are brought to the bottom of the desulfurization device and brought vertically upwards (to the wet filter) where now the heavier wet soot falls to the bottom of the device. Sooty water is then purified from soot in separators, which is then stored in tanks. Upon passing wet filters where sulfuric oxides are chemically bound with water and form sulfuric acid, neutralization of the same is performed by dosing sodium hydroxide solution (NaOH). At the end of the device there is built in the steam heater which heats now cooled exhaust gases to a certain temperature, in order to avoid creating a white cloud of condensate when exiting the ship's chimney. This presents a high energy consumption.

Explanation of the Invention

The objective of the invention is finding a new solution of eliminating soot and of desulfurization of combustion gases, mainly for the purpose of environment protection, saving energy and increasing safety of the ship, and also for avoiding risk of bursting fire in exhaust gas fired boilers of engines.

According to a first embodiment of the invention, exhaust gases are purified from soot and other solid particles in a specially constructed fan-separator (radial ventilator) and are brought to the upper part of the desulfurization (scrubbing) device, where there is placed the cross heat exchanger gas - gas, i.e. hot combustion gases entering the device are cooled and heat in the process cooled gases exiting the device. By such a construction of a heat exchanger, the device cools itself, resp. heats by energy that is in other systems thrown to the environment.

When a device is applied for desulfurization of exhaust gases of a ship's engine, behind which there is as a rule always built in the exhaust gas fired boiler 12, serving for utilization of energy, the fan-separator, as the integral part of the filter, is built in before the engine exhaust gas fired boiler 12 (illustrated in Fig. 2). By this solution the exhaust gas fired boiler is protected from forming layers of soot and there is avoided the risk of fire in the exhaust gas fired boiler. The fan-separator of the first embodiment is also described as the radial ventilator of the second embodiment.

According to a second embodiment of the invention, an exhaust gas purifying device, in particular for combustion exhaust gas, comprises: a radial ventilator having a rotor driveably supported in a housing for rotation about a rotation axis; the housing defining an axially directed inlet passage and an outlet passage; the rotor having inlet blades for receiving an axially directed inlet flow of exhaust gas, and having outlet blades for delivering an outlet flow of purified exhaust gas out of the outlet passage; each inlet blade having an inlet end facing the inlet flow and an outlet end; at an outlet end of at least one of the inlet blades, a longitudinal channel being formed, the channel extending in an outlet direction along the outlet end of the inlet blade for receiving part of the inlet flow and having a longitudinal inlet opening extending along at least part of the channel; the inlet opening being formed adjacent to a forward facing surface of the inlet blade, the channel having a radially outward output end which is open towards an outlet port of the housing receiving the part of the inlet flow from the channel; the outlet port being connected to an inlet of a collection means for collecting particulate matter entrained with the part of the inlet flow; an outlet of the collection means being connected to the inlet passage of the housing for recirculating the part of the inlet flow.

The collection means can be a bag filter or other mechanical filter, or can be a particle separator forming a second stage of particle or soot removal. The particle separator can be a rotating separator or a cyclone type separator.

The purifying device is particularly suitable for purifying combustion exhaust gas at elevated temperatures, e.g. higher than 100°C, 200°C, 300°C, 400°C, 500°C or 600°C.

Preferably, the inlet blades form a first compression section of the housing.

Preferably, the outlet blades form a second compression section of the housing and are arranged adjacent to the outlet ends of the inlet blades. An axial space can be provided between the outlet end of an inlet blade and an inlet end of an adjacent outlet blade, or alternatively at least one inlet blade and an adjacent outlet blade can be integrally formed as one blade. A first number of inlet blades and a second number of outlet blades can be provided, and the first number can be equal to, less than or larger than the second number.

The outlet flow of purified exhaust gas can be directed radially having a tangential and/or axial component.

A longitudinal axis of the channel preferably extends in a radial plane. An angle can be formed between the longitudinal axis and a radial direction of less than 45°, 30°, 20° or 10°. Adjacent to and upstream of the inlet opening of the channel, a further longitudinal channel can be formed parallel to the channel, and a further inlet opening of the further channel can be formed upstream of the inlet opening of the channel. The further channel forms a first stage, and the channel, positioned downstream of the further channel, forms a second stage of soot or particle removal. The part of the inlet flow received in the channels (and in the further channels) may be 1% to 20%, preferably 2% to 10% and most preferably 3% to 6% or 5% of the inlet flow. The inlet opening and/or the further inlet opening can be formed flush with a forward facing surface of the inlet blade. Alternatively, the inlet opening and/or the further inlet opening can be formed to define a cross section extending normally to the forward facing surface of the inlet blade. Preferably, the inlet opening of an inlet blade is formed flush with the forward facing surface of the inlet blade, i.e. a cross section of the inlet opening extends within the forward facing surface, and the further inlet opening of the inlet blade is formed to define a cross section extending normally to the forward facing surface.

The channel can be formed by forwardly bending a sheet material forming the inlet blade. The further channel can be formed by a bent sheet material fixed on the forward facing surface of the inlet blade adjacent to the channel.

The channels and/or the further channels preferably extend along a full radial length or height of the inlet blades.

Preferably, the rotor has a rotor body comprising an inlet portion and an outlet portion positioned adjacent to an downstream end of the inlet portion. The inlet portion has a peripheral inlet surface and bears the inlet blades. The peripheral inlet surface can be cylindrical or can have a diameter that smoothly or stepwise increases in an axial direction from a first inlet diameter to a second inlet diameter. The outlet portion has a peripheral outlet surface and bears the outlet blades. The peripheral outlet surface preferably has an outer diameter that smoothly increases in the axial direction.

Preferably, the inlet blades have a first portion extending to a first radial distance from the rotation axis, and a second portion comprising the channel and extending to a second radial distance. The second radial distance can be equal to or larger than the first radial distance. A step can be formed between the first portion and the second portion. A forward facing surface of the first portion of the inlet blades can form an angle between 45° and 35° with a radial plane.

The first portion of the inlet blades can have a first axial length equal to or greater than a second axial length of the second portion of the inlet blades.

The first portion of the inlet blades can form a first angle, or average angle, with a radial plane, and the second portion can form a second angle, or average angle, with a radial plane, where the second angle preferably is greater than the first angle.

The inlet blades form a first compressor stage of the ventilator, and the outlet blades form a second compressor stage of the ventilator. The pressure ratio of the first compressor stage (total pressure of the flow downstream of the first compressor stage, or immediately downstream of the inlet blades, divided by the total pressure of the inlet flow) can be in a range between 1 ,01 and 1 ,20, preferably less than 1 ,10. A pressure ratio of the second compressor stage (total pressure of the flow downstream of the second compressor stage or in the outlet passage divided by the total pressure of the flow downstream of the first compressor stage or between the inlet blades and the outlet blades) can be in a range between 1,01 and 1,20, and preferably is between 1 ,05 and 1 ,15. Preferably, the pressure ratio of the second compressor stage is higher than the pressure ratio of the first compressor stage.

An overall pressure ratio of the radial ventilator can be in a range between 1 ,01 and 1 ,40, and preferably is between 1,10 and 1 ,20 (total pressure of the exiting purified exhaust gas in the outlet passage divided by the total pressure of the inlet flow upstream of the inlet blades).

Radially outward ends of the inlet blades can be connected by a circumferentially extending peripheral cover plate, the cover plate having openings adjacent to the channels of the inlet blades, each opening corresponding at least to a section of the corresponding channel in order to form an unrestricted radial passage in continuation of the channel. Preferably, an outer surface of the cover plate is cylindrical.

A cover flange can be connected to an upstream end of the cover plate, the cover flange extending radially inwardly from and along an inner circumference of the cover plate and pref- erably along a radial plane. The cover flange can be connected to a step between the first portions and the second portions of the inlet blades. A radial extension of the cover flange can be equal to a difference of radial heights of the first and second portions, respectively, of the inlet blades, and can be between 20% and 50% of a maximum radial height of the inlet blades, i.e. of the second portions thereof. Similar to the cover flange, a further cover flange can be connected to a downstream end of the cover plate, extending radially inwardly from and along the inner circumference of the cover plate. The cover plate and the cover flange, possibly in combination with the further cover flange, form a collecting space for soot and particulate matter to be removed from the inlet flow. Soot and other particles collecting downstream of the cover flange and against an inner surface of the cover plate will ultimately exit in a radial direction through the openings provided in the cover plate.

Preferably, the exhaust gas purifying device comprises a scrubbing or gas washing device for further purifying the purified exhaust gas by removing harmful gas components like SOx and/or NOx, by contacting the purified exhaust gas with a scrubbing liquid, an inlet of the scrubbing device being coupled to the outlet passage of the radial ventilator, the scrubbing device having a scrubber housing in which nozzles for spraying scrubbing liquid are arranged, the scrubbing device having an outlet for discharging further purified exhaust gas. Advantageously, the purified exhaust gases to be scrubbed contain only little quantities of soot due to the soot removing device installed ahead of the scrubbing device.

Preferably, a heat exchanger is provided, a first inlet of the heat exchanger being connected to the outlet passage of the radial ventilator for receiving purified exhaust gas, in particular having a temperature of at least 100°C, 200°C, 300°C, 400°C or 500°C, a first outlet of the heat exchanger being connected to the inlet of the scrubbing device for delivering cooled purified exhaust gas, a second inlet of the heat exchanger being connected to the outlet of the scrubbing device for receiving further purified exhaust gas, and a second outlet of the heat exchanger being provided for discharging heated further purified exhaust gas, in particular to the surroundings. Since the temperature of the purified exhaust gases to be scrubbed is reduced before contacting the scrubbing liquid, the solubility of gases like SOx to be scrubbed is increased, i.e. more SOx and/or NOx can be solubilized in the scrubbing liquid in comparison with a construction without cooling of the exhaust gases before the scrubbing step. Preferably, the heat exchanger is arranged on top of the scrubbing device, and the heat exchanger is a cross- flow heat exchanger.

The scrubbing device can have multiple horizontal levels, multiple nozzles being arranged in each level for spaying scrubbing liquid.

A vertical supply line, corresponding to the connecting part of the first embodiment, constituting a first scrubber stage and comprising first nozzles can be provided, connecting the first outlet of the heat exchanger to an inlet of the scrubber housing, the inlet being positioned at a bottom of the scrubber housing, the scrubber housing constituting or comprising a second scrubber stage having second nozzles. Preferably, the first scrubber stage is mainly used to reduce the temperature by spraying scrubbing liquid, e.g. sea water, into the exhaust gas, preferably in a counter-flow arrangement. In the first and/or in the second scrubber stage additives like chemical agents may be added.

The first and second embodiments are particularly useful in off-shore and marine applications adapted for use on-board of ships or platforms, but can also be used in stationary land applications.

Another aspect of the invention is a method of purifying exhaust gas, comprising the following steps: supplying an inlet flow of exhaust gas to a radial ventilator arranged for separating soot and/or particulate matter by centrifugating a part of the inlet flow of exhaust gas, compressing the inlet flow and diverting the part of the inlet flow containing soot and/or particulate matter, collecting separated soot and/or particulate matter and returning the part of the flow to the radial ventilator, and wet scrubbing a flow of purified exhaust gas exiting the radial ventilator by contacting the flow of purified exhaust gas with scrubbing liquid.

The method is particularly suitable for purifying exhaust gas at elevated temperatures, without cooling before the soot separating step, wherein the exhaust gases can have temperatures above 100°C, 200°C, 300°C, 400°C, 500°C or 600°C. The method can be arranged so that the part of the flow comprises 1% to 20%, preferably 2% to 10% and more preferably 3%, to 6% or 5% of the inlet flow of exhaust gas supplied to the radial ventilator. Preferably, a radial ventilator is used that has blades provided with radial channels in which the part of the flow is received and soot is centrifugally separated.

In particular, sea water can be used as scrubbing liquid.

Preferably, the flow of purified exhaust gas to be scrubbed is conducted in a loop comprising a downward flow portion, an upward flow portion and a cross flow portion, wherein a heat exchange is conducted in the cross flow portion for transferring heat from the flow of purified exhaust gas to a flow of further purified exhaust gas, obtained after wet scrubbing the flow of purified exhaust gas thereby cooling the purified exhaust gas before scrubbing and heating the further purified exhaust gas before discharging, e. g. to the environment.

Preferably, by scrubbing the flow of purified exhaust gas, pollutants as SOx, NOx and remaining particulate matter like soot and dust are removed by the scrubbing liquid.

The scrubbing liquid can be conducted in a closed cycle with collection of soot and other particulate matter on the one hand and collection of used, possibly concentrated, scrubbing fluid on the other hand. Alternatively, in particular when using sea water and in marine applications, the scrubbing liquid can be conducted in an open cycle made up by a step of drawing in fresh sea water, using the sea water as a scrubbing liquid in a scrubbing step, and pumping the used and pollutant loaden sea water into the sea, possibly preceded by a dilution step of mixing the used scrubbing liquid with fresh sea water. Since sea water has a pH value between 7.5 and 8.4, used scrubbing liquid having a pH of about 3.0 . .. 3.5 can be brought to a (neutral) pH of 7 by mixing with sea water.

Between the radial ventilator and the scrubbing device, an exhaust gas fired boiler can be arranged.

Preferably, the device is used to purify combustion exhaust gases from an internal combustion engine, in particular of a marine engine, at elevated temperatures.

Short List of Drawings Fig. 1 Cross-section of an exhaust gas purifying device according to a first embodiment,

Fig. 2 Modification of the device according the Fig. 1 showing the position of the fan- separator in relation to the engine and an exhaust gas fired boiler,

Fig. 3a Longitudinal cross-section of the fan-separator,

Fig. 3b Cross-section A-A of Fig. 3a,

Fig. 3 c Longitudinal cross-section of a modified version of the fan-separator,

Fig. 4 Construction of the heat exchanger on the top of the desulfurization device,

Fig. 4a Alternative construction of the heat exchanger,

Fig. 4b Part of the alternative embodiment of Fig. 4a,

Fig. 5 Construction of wet filters,

Fig. 6 Cross-section of second embodiment of the fan-separator, Fig. 6a Detail of Fig. 6,

Fig. 7 Perspective view of part of the rotor of the fan-separator of Fig. 6,

Fig. 7a Detailed view of the inlet blade of Fig. 7 in cross-section,

Fig. 8 Perspective view of part of a modified rotor,

Fig. 8a Detailed view of the inlet blade of Fig. 8 in cross-section,

Fig. 9 Perspective view of part of a modified rotor, Fig. 9a Detailed view of the inlet blade of Fig. 9 in cross-section, Fig. 9b Detailed view of an inlet blade similar to Fig. 9a, Fig. 10 Perspective view of a rotor having peripheral and side plates, Fig. 1 1 Perspective view of a fan-separator with its housing. Detailed Description of Embodiments of the Invention

According to a first embodiment of the invention shown in Fig. 1 to 5, by means of a fan- separator 1 exhaust gases are purified from soot which is through a tube 10 from the separator port introduced to the bag filter 1 1, and collected in the vessel. In this case there is dry separation of soot and other solid particles, other than in existing devices having wet separation of soot. At a first inlet 2a of the heat exchanger 2, purified gases enter the heat exchanger 2, which construction is shown in Fig. 4, placed on top of a desulfurization device (scrubbing device) 5 and which comprises a large number of rectangular tubes 5.3 with pins 5.4 on both sides, the inner and outer side, for the purpose of increasing the heat exchange surface. Hot gases enter inner ports of a rectangular tube 5.3 and are cooled by gases previously cooled in the desulfurization device 5 and which pass outer ports of the rectangular tube provided with pins 5.4. As it is visible, it is a cross heat exchanger. Cooled gases then enter the connecting port 3 of the upper and lower part of the filter, in which by sea water supplied through nozzles 4.1, 4.2 placed in the counter current, a temperature of gases is additionally reduced in the port. An upper end 3 a of the connecting port 3 forms an inlet 5 a of the scrubbing device connected to a first outlet 2b of the heat exchanger. In the port 3 at the same time starts the desulfurization process by chemical binding of sulfuric oxides with the sea water and formation of sulfuric acid. Sulfuric acid is at the same time neutralized because of alkaline characteristics of the sea water.

Instead of the bag filter 1 1 , a particle separator forming a second stage of particle or soot separation can be provided. Mechanical filter can be provided, preferably made of ceramic material. Fig. 4a shows a heat exchanger 2' similar to that of Fig. 4, made up by two parts 2.1 as shown in Fig. 4b and connected along a plane of symmetry or divisional plane 2.2.

From the port 3 (downward flow portion), now already fully cooled exhaust gases at inlet 5d of housing 5b (upward flow portion) enter the lower part of the filter 5 and pass towards upwards through the first wet filter 5.1 , construction visible in Fig. 5, washed by the dispersed (sprayed) sea water from the nozzles 6.1. In the first stage the main part of desulfurization takes place. In the second wet filter 5.2, construction visible in Fig. 5, additional desulfurization to a very high percentage takes place with nozzles 6.2. Wet filters 5.1 and 5.2 comprise a large number of plates, preferably polypropylene plates, on which there is a large number of pins or tentacles for the purpose of achieving a large exchange surface. Upon passing the second stage, exhaust gases exit through outlet 5 c of the housing 5b and pass the cross heat exchanger 2 (cross flow portion) shown in Fig. 4, entering at second inlet 2c and being discharged at second outlet 2d, where they are heated and through the ship's chimney (outlet 7 of gases from the filter) exhaust to the atmosphere. Dispersed (used) sea water is collected on the bottom of the filter and through the outlet tube 8 is thrown out of the ship. If the pH value is less than 6, it is additionally neutralized by mixing with sea water from the ship^'s cooling system. The sea water thrown out of the ship is clear because the soot was separated before by the fan-separator, and it contains only sulfates as a product of neutralization of sulfuric acid. It is permitted to throw sulfates to the sea, as they are harmless in the whole. Connection 9 (drain opening) is provided for complete emptying the filter in case of need.

The fan-separator 1 as one of the most important parts of the filter is made in following way (Fig. 3a, b, c). The rotor is by means of the hub 1.1 console like suspended on an electric motor. On the hub there is by screws fastened the basic plate 1.2 to which there is welded the tube 1.3, serving as the bearer of blades 1.6 (outlet blades or main centrifugal blades), 1.7 and 1.8. 1.5 is the conical entry of the rotor. Between the basic plate 1.2 and the tube 1.3 there is welded the conical tube 1.4 (conical sheet metal) shaped with a radius for the purpose of minimizing a resistance of the current. The rotor is of axial-radial type. On the entrance to the rotor there are placed inlet blades or axial blades 1.7 which are distorted to a radial part 1.8 (separator's blades) which is in this case the separator's part. The number of blades 1.7 is selected in the way that the blades catch the soot from exhaust gases before the exhaust gases leave the separator's part. The separator's part 1.8 is on its end bended 1.8.1 to form a radially extending channel having an upstream facing inlet opening formed as a slot in order to catch the soot and to throw it out centrifugally through an outlet port 1.12. The cross-section A-A in Fig. 3b shows that among separator^'s blades 1.8 there is welded a bulkhead 1.10 and a bulkhead 1.1 1 through which in this way runs out a small quantity of exhaust gases mixed with separated solid particles. The separator^'s blades have peripherally arranged side conical covers 1.9 and partition sheet metals 1.10, 1 .11. forming passages 1.12 tapering both in a radial- ly outward direction and in a circumferential direction and ending in outlet opening 1.13. Fig. 3c shows a slight modification of the form (cross-section) of the channel formed inside the bent portion 1.8.1 which longitudinally extends in the axial direction.

Fig. 2 shows an exhaust gas fired boiler 12 arranged between an exhaust gas purifying device and a heat exchanger 2 connected to a scrubbing device.

Separated solid particles are led out by tube 10 of the outlet of separated solid particles, and tube 10a is to return the exhaust gas to the fan-separator's inlet or suction side.

The following aspects characterize the first embodiment:

Exhaust gases filter or scrubber which on the top has built in heat exchanger gas - gas (2) in form of rectangular tubes with pins inside and outside for the purpose of increasing the heating surface and can be made of corrosion resistant aluminium alloys.

Exhaust gases filter or scrubber in which the heat exchanger is on the top (2) connected with the filter by the port (3) in which there are built in nozzles (4.1) and (4.2).

Exhaust gases filter or scrubber that has built in wet filters (5.1) and (5.2), preferably made of polypropylene plates which on the one side have a large number of pins-tentacles.

Fan-separator (1) of the filter which on the inlet has placed bended axial blades (1.7) welded on separator's blades (1.8) at the end bended (1.8.1) for the purpose of catching soot and centrifugal ejecting to the separator port (1.12). Separator^'s blades (1.8) of the fan-separator as the integral of the filter, which at the outlet are laterally connected and closed with taper sheet metals (1.9) and partition sheet metals (1.0) and (1.1 1).

Rotor of the fan-separator as the integral part of the filter which on the inlet bearing tube of blades (1.3) has built in a taper cap (1.5) for reducing gas flow resistance.

Rotor of the fan-separator as the integral part of the filter, in which the bedplate (1.2) and the tube of the blades^' girder (1.3) are connected by the by radius formed taper tube (1.4) on which there are welded main centrifugal blades (1.6).

A second embodiment of an exhaust gas purifying device is schematically shown in Fig. 6, 6a in a longitudinal sectional view. An electric motor 20 is coupled by coupling 22 with a rotor or impeller 24 rotating inside a housing 25, forming a radial ventilator 1. The motor 20 and the rotor 24 rotate about a rotation axis 27. The rotor 24 comprises a rotor body 26 having a cylindrical inlet portion 28 and an outlet portion 30 adjacent to a downstream end of the inlet portion 28. The inlet portion 28 has a peripheral or outer inlet surface 32 and bears inlet blades 34. The outlet portion 30 has a peripheral outlet surface 36 the outer diameter of which increases in an axial downstream direction 40. The outlet portion 30 bears outlet blades 42.

For the purpose of the present invention, the inlet blades 34 are also described as axial blades and correspond to the axial blades .7 of the first embodiment, receiving an inlet flow 38 of exhaust gas flowing in the axial downstream direction 40, and the outlet blades 42 are also described as radial blades and correspond to the centrifugal blades 1.6 of the first embodiment.

Figs.7 to 10 show the inlet portion 28 of the rotor 24 and the inlet blades 34 in several modifications. The inlet blades 34 are arranged on the peripheral inlet surface 32 of the inlet portion 28, where Fig. 7a, 8a, 9a and 9b show cross-sections of the inlet blades in detail. Channels 50 (Fig. 7-9) and further channels 52 (Fig. 9, 9a, 9b) are provided in the inlet blades. A longitudinal axis of each channel 50 and further channel 52 extends in a radial plane 29 (which is vertical to the rotation axis 27). The channels 50 and further channels 52 may have a tangential component of orientation, i.e. the longitudinal axes of the channels 50 and further channels 52 can be arranged, within a radial plane, to form an angle relative to a radial direction, the angle being between 0° and 10°, 20°, 30° or more, in order to reduce a tangential velocity component of a gas flow exiting the channels.

Each channel 50 has an inlet opening, in particular in form of a generally radially extending slot 54, extending along the channel 50. The inlet opening or slot 54 is formed adjacent a forward facing surface 34d or front surface of the inlet blade, as seen in a direction 56 of rotation of the rotor 24.

When a channel 50 and a further channel 52 are provided (Fig. 9, 9a, 9b), it is preferred to arrange the inlet opening 54 of the channel 50 to be flush with (within the plane of) the forward facing surface (front surface) 34d of the inlet blade 34, while arranging a further inlet opening 54a of the channel 52 which is upstream of the inlet opening 54 so as to define a cross section extending normally to the forward facing surface 34d.

Each inlet blade 34 comprises a first, upstream portion 34a (also described as axial blade 1.7 in the first embodiment) extending to a first radial distance from the rotation axis, and a second, downstream portion 34b (also described as separator's blade 1.8 in the first embodiment) comprising the channel 50 and the further channel 52, if provided. The second portion 34b extends to a second radial distance from the rotation axis 27, which can be larger than the first axial distance. A step 34c can be formed between the first portion 34a and the second portion 34b, as shown in Fig. 7 to 10.

The first portion 34a of the inlet blades 34 can be curved (Fig. 7, 7a) or straight (Fig. 8, 8a and 9, 9a), forming an angle 34e with a radial plane that preferably is between 45° and 35°.

In the embodiments according to Fig. 9a and 9b, the inlet blades 34 are formed so as to cause a deflection of the flow of gas between circumferentially adjacent inlet blades, from a first or upstream flow portion 58.1 between adjacent first portions 34a of two adjacent inlet blades to a second or downstream flow portion 58.2 between the second portions 34b of two inlet blades. This flow deflection causes particulate matter suspended in the flow to tend to follow a flow direction of the first flow portion 58.1 and to enter the inlet openings 54, and 54a, if provided. This effect is caused by the first portions 34a of the inlet blades 34 preferably being arranged to form an (average) first angle 34e with a radial plane that is inferior to a second (average) angle 34f formed between the second portions 34b and a radial plane. As shown in Fig. 10, a circumferentially extending peripheral cover plate or shroud 60 connects radially outward ends of the inlet blades, in particular the outward ends of the second portions 34b of the inlet blades. Openings 62 adjacent to the channels 50 are provided in the cover plate 60. A cover flange 64 or side plate is provided adjacent to and connected to an upstream end 60a of the cover plate 60, the cover flange 64 or side plate extending along an inner circumference of the cover plate 60 and along the step 34c of the inlet blades 34 along a radial plane. Also, a reinforcement ring 66 is provided to connect edges of the inlet blades 34.

Fig. 6 also shows the housing 25. A cylindrical, axially directed inlet passage 70 receives the inlet portion 28 and the inlet blades 34 of the rotor 24. Adjacent to the inlet passage 70, a collecting channel 72 is formed, circumferentially extending around the second portions 34b of the inlet blades 34 for receiving the part of the inlet flow radially ejected through the channels 50 and, if provided, further channels 52. The collecting channel 72 forms an outlet port for discharging a port of the inlet flow and separated particles.

Different from Fig. 10, the inlet blades 34 shown in Fig. 6 and Fig. 3a, 3c have first and second portions 34a, b extending to one and the same radial distance from the rotation axis 27. A cover plate 60 can be provided on the second portions 34b. Also different from the embodiment shown in Fig. 10, a circumferential cover 74 being triangular or trapezoid in cross section is attached to an outer surface of the cover plate 60, forming a circumferentially extending space 73 tapering in a radial direction and ending in a circumferentially extending slot 76. The purpose of the tapering space 73 provided by the cover 72 is to accelerate the radial flow exiting the channels 50 or 52 and to improve the transfer of soot or particulate matter into the collecting channel 72. The space 73 corresponds to the port 1.12 of the first embodiment (Fig. 3b), and the cover 74 corresponds to the side conical cover 1.9 (Fig. 3a, 3c). The slot 76 can be replaced by a number of circumferencially spaced outlet openings 1.13 as in the first embodiment.

The collecting channel 72 generally is U-shaped in cross-section, limited by a front wall 72a, a peripheral wall 72b and a back wall 72c which is provided by a radial flange depending from a front wall 25a of the housing 25. The collecting channel 72 in its circumferential direction is spirally formed and ends in an outlet section 72d. The part of the inlet flow received in the channels of the inlet blades, together with soot and particulate matter separated from the inlet flow, is discharged through the outlet section 72d and is guided to soot filters 1 1 by a tube 10, as shown in Fig. 2 in connection with the first embodiment. Ultimately, the part of the inlet flow, separated soot and particulate matter having been deposited in the filter 1 1 , is returned to the inlet passage 70 by a tube 10a (cf. Fig. 2).

Fig. 6 further shows outlet blades 42 downstream of the inlet blades 34, adjacent to an outlet passage 80. The outlet passage 80 is formed by the front wall 25a, a circumferentially extending peripheral wall 25b and a back wall 25c of the housing 25. The peripheral wall 25b is arranged in a spiral form in order to form spiral outlet passage 80. On a back side of the outlet passage 80, a conical transition wall 25d is arranged adjacent to and in continuation of the peripheral outlet surface 36 of the outlet portion 30 of the rotor 24. The outlet passage 80 is provided with a tangentially arranged outlet opening 82 (Fig. 1 , 1 1), which can be connected to a first inlet 2a of the heat exchanger 2 (Fig. 1) or to an inlet of the gas fired boiler 12 (Fig. 2), the outlet of which can be connected to the first inlet 2a of the heat exchanger 2.

Fig. 1 1 shows a perspective view of the exhaust gas purifying device according to the second embodiment, comprising the inlet portion 28 of the rotor, provided with inlet blades 34, the collection channel 72 with its outlet section 72d, and the housing 25 provided with the outlet passage 80 and outlet opening 82. The device can be combined with a scrubbing device 5 and an optional heat exchanger 2 is illustrated in the first embodiment.

List of Reference Numerals

Claims

1. Exhaust gas purifying device, comprising:

- a radial ventilator (1 ) having a rotor (24) driveably supported in a housing (25) for rotation about a rotation axis (27);

- the housing (25) defining an axially directed inlet passage (70) and an outlet passage

(80);

- the rotor (24) having inlet blades (34) for receiving an axially directed inlet flow (38) of exhaust gas, and having outlet blades (42) for delivering an outlet flow of purified exhaust gas out of the outlet passage (80);

- each inlet blade (34) having an inlet end facing the inlet flow (38) and an outlet end;

- at an outlet end of at least one of the inlet blades (34), a longitudinal channel (50) being formed, the channel (50) extending in an outlet direction along the outlet end of the inlet blade (34) for receiving part of the inlet flow (38) and having a longitudinal inlet opening (54) extending along at least part of the channel (50);

- the inlet opening (54) being formed adjacent to a forward facing surface (34d) of the inlet blade (34);

- the channel (50) having a radially outward output end which is open towards an outlet port (72) of the housing (25) for receiving the part of the inlet flow from the channel (50);

- the outlet port (72) being connected to an inlet of a collection means (1 1) for collecting particulate matter entrained with the part of the inlet flow; - an outlet of the collection means (1 1 ) being connected (10a) to the inlet passage (70) of the housing (25) for recirculating the part of the inlet flow.

2. Purifying device according to claim 1, characterized in that the device is adapted for purifying combustion exhaust gas at elevated temperatures of at least 100°C, 200°C, 300°C, 400°C, 500°C or 600°C.

3. Device according to claim 1 or 2, characterized in that the inlet blades (34) form a first compression section of the housing (25).

4. Device according to any of the preceding claims, characterized in that the outlet blades (42) form a second compression section of the housing (25).

5. Device according to any of the preceding claims, characterized in that an axial space is provided between the outlet end of an inlet blade (34) and an inlet end of an adjacent outlet blade (42).

6. Device according to any of claims 1 to 4, characterized in that at least one inlet blade and an adjacent outlet blade are integrally formed as one blade.

7. Device according to any of claims 1 to 5, characterized in that a first number of inlet blades (34) and a second number of outlet blades (42) is provided, the second number being equal to or less than the first number.

8. Device according to any of the preceding claims, characterized in that a longitudinal axis of the channel (50) extends in a radial plane (29).

9. Device according to any of the preceding claims, characterized in that an angle formed between a longitudinal axis of the channel (50) and a radial direction is less than 45°, 30°, 20° or 10°.

10. Device according to any of the preceding claims, characterized in that adjacent to and upstream of the inlet opening (54) of the channel (50), a further longitudinal channel (52) is formed parallel to the channel (50), and a further inlet opening (52a) of the further channel (52) is formed upstream of the inlet opening (54) of the channel (50) adjacent to the forward facing surface (34d).

1 1. Device according to any of the preceding claims, characterized in that the channels (50, 52) and the inlet openings (54, 52a) are arranged so that the part of the inlet flow received in the channels is between 1% and 20%, preferably 5% of the inlet flow.

12. Device according to any of the preceding claims, characterized in that the channel (50) is formed by forwardly bending a sheet material forming the inlet blade (34).

13. Device according to any of claims 10 to 12, characterized in that the further channel (52) is formed by a bent sheet material fixed on the forward facing surface (34d) of the inlet blade (34) adjacent to the channel (50).

14. Device according to any of the preceding claims, characterized in that the inlet blades (34) have a first portion (34a) extending to a first radial distance from the rotation axis (27), and a second portion (34b) comprising the channel (50) and extending to a second radial distance, larger than the first radial distance, from the rotation axis (27).

15. Device according to claim 14, characterized in that a step (34c) is formed between the first portion (34a) and the second portion (34b).

16. Device according to any of the preceding claims, characterized in that a forward facing surface (34d) of the first portion (34a) of the inlet blades forms an angle (34e) between 45° and 35° with a radial plane (29).

17. Device according to any of the preceding claims, characterized in that a circumferen- tially extending peripheral cover plate (60) is connected to radially outward ends of the inlet blades (34), the cover plate (60) having openings (62) adjacent to the channels (50, 52) of the inlet blades (34).

18. Device according to claim 17, characterized in that a cover flange (64) is connected to an upstream end (60a) of the cover plate (60), the cover flange (64) extending radially inwardly from and along an inner circumference of the cover plate (60).

19. Device according to claim 18, characterized in that the cover flange (64) is connected to a step (34c) between the first portions (34a) and the second portions (34b) of the inlet blades (34).

20. Device according to claim 18 or 19, characterized in that a radial extension of the cover flange (64) is equal to a difference of radial heights of the first portions (34a) and the second portions (34b) of the inlet blades (34).

21. Device according to any of claims 18 to 20, characterized in that a further cover flange is connected to a downstream end of the cover plate (60), extending radially inwardly from and along the inner circumference of the cover plate (60).

22. Device according to any of the preceding claims, comprising a scrubbing device (5) for further purifying the purified exhaust gas by contacting the purified exhaust gas with a scrubbing liquid, an inlet (5a) of the scrubbing device (5) being coupled to the outlet passage (80) of the radial ventilator (1), the scrubbing device (5) having a scrubber housing (5b) in which nozzles (4.1, 4.2) for spraying scrubbing liquid are arranged, the scrubbing device having an outlet (5c) for discharging further purified exhaust gas.

23. Device according to claim 22, characterized in that a heat exchanger (2) is provided for exchanging heat between the purified exhaust gas exiting the radial ventilator (1) and the further purified exhaust gas exiting the scrubbing device (5), a first inlet (2a) of the heat exchanger (2) being connected to the outlet passage (80) of the radial ventilator (1) for receiving purified exhaust gas, a first outlet (2b) of the heat exchanger (2) being connected to the inlet (5a) of the scrubbing device (5) for delivering cooled purified exhaust gas, a second inlet (2c) of the heat exchanger (2) being connected to the outlet (5c) of the scrubbing device (5) for receiving further purified exhaust gas, and a second outlet (2d) of the heat exchanger (2) being provided for discharging heated further purified exhaust gas.

24. Device according to claim 23, characterized in that the heat exchanger (2) is arranged on top of the scrubbing device (5), the heat exchanger (2) preferably being a cross-flow heat exchanger.

25. Device of any of claims 22 to 24, characterized in that a vertical supply line (3) constituting a first scrubber stage and comprising first nozzles (4.1 , 4.2) connects the first outlet (2b) of the heat exchanger (2) to an inlet (5d) of the scrubber housing (5b), the inlet (5d) being positioned at a bottom of the scrubber housing (5b), the scrubber housing (5b) comprising a second scrubber stage having second nozzles (6.1 , 6.2).

26. Method of purifying exhaust gas, comprising the following steps:

- supplying an inlet flow of exhaust gas (38) to a radial ventilator (1) arranged for separating soot and/or particulate matter by centrifugating a part of the inlet flow of exhaust gas,

- compressing the inlet flow (38) and diverting the part of the inlet low containing soot and/or particulate matter,

- collecting separated soot and/or particulate matter and returning the part of the inlet flow to the radial ventilator (1), and wet scrubbing a flow of purified exhaust gas exiting the radial ventilator (1) by contacting the flow of purified exhaust gas with scrubbing liquid.

27. Method according to claim 26, characterized in that a radial ventilator (1) is used having blades (34) which are provided with radial channels (50, 52) in which the part of the flow is received and soot is centrifugally separated.

28. Method according to claim 26 or 27, characterized in that sea water is used as scrubbing liquid.

29. Method according to any of claims 26 to 28, characterized in that the flow of purified exhaust gas being scrubbed is conducted in a loop comprising a downward flow portion (3), and upward flow portion (5b) and a cross-flow portion (2), wherein a heat exchange is con- ducted in the cross-flow portion (2) for transferring heat from the flow of purified exhaust gas to a flow of further purified exhaust gas obtained after wet scrubbing the flow of purified exhaust gas, thereby cooling the purified exhaust gas before scrubbing and heating the further purified exhaust gas before discharging.

30. Method according to any of claims 26 to 29, characterized in that the scrubbing liquid is conducted in a closed cycle with collection of soot and other particulate matter on the one hand and collection of used, possibly concentrated, scrubbing liquid on the other hand.

31. Method according to claim 28, characterized in that the scrubbing liquid is conducted in an open cycle made up by a step of drawing in fresh sea water, using the sea water in a scrubbing step, and pumping the used sea water into the sea, possibly preceded by a dilution step of mixing the used sea water with fresh sea water.

32. Method according to any of claims 26 to 31 , characterized in that combustion exhaust gas is introduced into the radial ventilator (1), the exhaust gas being at an elevated temperature of at least 100°C, 200°C, 300°C, 400°C, 500°C or 600°C.