WO2012105905A1

WO2012105905A1 - Apparatus and method for removing or reducing of gas pollutants from exhaust gas stream

Info

Publication number: WO2012105905A1
Application number: PCT/SG2011/000045
Authority: WO
Inventors: Tonci TADIC
Original assignee: Viridis Harbour Inc.
Priority date: 2011-01-31
Filing date: 2011-01-31
Publication date: 2012-08-09

Abstract

The present invention relates apparatus and method for removing or reducing of gas pollutants from an exhaust gas stream. The apparatus having a chamber with an inlet for receiving the polluted exhaust gas stream and an outlet for discharging the exhaust gas stream with reduced pollutant; a spray within the chamber for spraying wash water onto the exhaust gas stream; and a baffling means intermediate the inlet and the outlet, for reducing the flow rate of the exhaust gas stream in the chamber such that the baffling means increases the exposure of the exhaust gas stream to the wash water. The method including receiving the gas stream into the chamber; baffling the flow of the gas stream by a baffling means; spraying of wash water onto the baffled gas stream; discharging the gas stream from the chamber.

Description

APPARATUS AND METHOD FOR REMOVING OR REDUCING OF GAS POLLUTANTS FROM EXHAUST GAS STREAM

Field of Invention

The present invention relates apparatus and method for removing or reducing of gas pollutants from exhaust gas stream.

Background

Industrial processes like burning of coal for thermal power stations or heavy fuel oil in industries like the chemical industries, marine industries and refineries are known to emit pollutants into the atmosphere in the form of exhaust gas stream. Some of the common pollutants are carbon dioxide (C0₂), sulphur dioxide (S0₂) and oxides of nitrogen (NO_x) e.g. nitrogen dioxide (N0₂). The release of the pollutants into the air has adverse environmental impacts and causes harm to human beings.

To prevent or reduce the emission of such pollutants into the atmosphere, there has been many devices and apparatus made to remove them before releasing the exhaust gas streams into the atmosphere. One common apparatus is a wet scrubber. The wet scrubber typically consists of a tower with a sprayer for spraying scrubbing liquid. Polluted exhaust gas stream is passed into the tower from below and the scrubbing liquid is sprayed onto it directly to remove the pollutants before releasing the gas stream through the top of the tower. Although the wet scrubber is able to remove both gas and particulate pollutants, the tower has to be of considerable height so that there is sufficient time for the scrubbing liquid to contact the pollutant to remove the pollutants effectively. In this way, the apparatus can take up a considerable amount of space and is difficult to install in constricted areas.

There have been efforts put into reducing the size of the tower by increasing the scrubbing efficiency of the tower. In some instances, filters have been put into the tower to remove certain pollutants more quickly so that the time taken to remove other pollutants by the scrubbing method is reduced thus decreasing the height of the tower required. In other instances, the concentration and/or amount of scrubbing liquid is increased to improve the gas-to-liquid contact ratio so as to reduce the time taken to remove the pollutants. In either way, the cost to remove the pollutant would inevitably increase and it is not cost-effective in the long run thus putting a strain on the companies in cleaning up the exhaust gas stream.

Further, current systems e.g. conventional towers available in the market, are only capable of removing one gas at a time. This results in the higher cost and lower efficiency in removing more than one gas at a time.

The present invention aims to improve the effectiveness of pollutant removal without the disadvantages mentioned. Summary of Invention

An apparatus for reducing pollutants in an exhaust gas stream having a chamber with an inlet for receiving the polluted exhaust gas stream and an outlet for discharging the exhaust gas stream with reduced pollutant; a spray within the chamber for spraying wash water onto the exhaust gas stream; and a baffling means intermediate the inlet and the outlet, for reducing the flow rate of the exhaust gas stream in the chamber such that the baffling means increases the exposure of the exhaust gas stream to the wash water.

Preferably, the inlet and the baffling means are in fluid communication and the baffling means comprises at least one slot for allowing the exhaust gas stream to escape.

Preferably, the slot comprises at least one deflector for deflecting the gas so that the exhaust gas stream can be diverted away from the center of the baffling means to increase the exposure of the gas stream.

Preferably, the deflector is angle for deflecting the exhaust gas stream downwards so that the gas stream can escape from the baffling means while preventing ingress of water.

Preferably, the baffling means comprise of conical roof and a plurality of frusto-conical rings below the roof, the roof and the rings spaced apart to allow the exhaust gas stream to escape.

Preferably, the circumference of one ring is larger than an adjacent ring.

Preferably, the circumference of the rings increases towards the inlet.

Preferably, the outer circumference of one ring is larger than the inner circumference of another.

Preferably, the rings are equally spaced apart.

Preferably, the roof further comprises a cone attached to the underside of the roof, the apex of the cone pointed in a direction opposite to the apex of the conical roof so that the gas^' stream would not be trapped under the roof. Preferably, the spray is above the baffling means.

Preferably, the wash water is treated water or treated alkaline water.

Preferably, the water is treated by an ultra low frequency electrolysis process.

Preferably, the apparatus further comprises a plurality of chambers forming a tower wherein the chambers in fluid communication.

Preferably, the tower comprises three chambers.

Preferably, the tower comprises five chambers.

Preferably, each chamber removes a desired pollutant.

Preferably, there is a first chamber which removes S0₂, a second chamber removes one of C0₂ and NO_x and a third chamber removes the other of C0₂ and NO_x.

Preferably, treated water is used to remove S0₂ and treated alkaline water is used to remove C0₂ and NO_x.

Preferably, each chamber comprises an inner wall coated with a protective layer.

Preferably, the spray includes a nozzle for dispersing the wash water.

Preferably, the nozzle includes a spiral jet or a fog jet nozzle.

Preferably, the nozzle in one chamber differs from the nozzle in another chamber.

Preferably, the nozzle is made from Glass Reinforced Plastic (GRP).

Preferably, the apparatus further comprise of a base for mounting the chamber.

Preferably, the base comprises an inlet for entry of the exhaust gas stream and a drainage outlet for draining the wash water.

Preferably, the tower further comprises a demister. A method for removing pollutants from an exhaust gas stream flowing through a chamber including receiving the gas stream into the chamber; baffling the flow of the gas stream by a baffling means; spraying of wash water onto the baffled gas stream; discharging the gas stream from the chamber.

Preferably, the method further comprises the step of receiving the gas stream into a second chamber, spraying the wash water on the gas stream, deflecting the flow of the gas stream by the baffling means and discharging the gas stream from the second chamber.

Preferably, the method further comprising the step receiving the gas stream into a third chamber, deflecting the flow of the gas stream by the baffling means, spraying the wash water on the gas stream and discharging the gas stream from the third chamber.

Preferably, there is a first chamber which removes S0₂, a second chamber which removes one of C0₂ and NO_x and a third chamber which removes the other of C0₂ and NO_x.

Preferably, the method further comprises the step of treating the wash water with an ultra low frequency electrolysis process.

Preferably, the wash water in the chambers is either treated water or treated alkaline water.

Preferably, the method further comprises the step of passing the exhaust gas stream through a demister.

Brief Description of Drawings of a Preferred Embodiment

Fig. 1 shows a cross-sectional view of an. embodiment of the present invention; Fig. 3 shows another embodiment of the present invention;.

Fig. 3 shows a perspective view of an embodiment of a baffling means of the embodiment in Fig. 1 ;

Fig. 4 shows the the embodiment in Fig. 1 in a stacked configuration; Fig. 5 shows a schematic view of the embodiment of Fig. 1;

Fig. 6 shows another embodiment of the present invention;

Fig. 7 shows another embodiment of a roof in Fig. 1 ; and

Fig. 8 shows another stacked configuration of the embodiment in Fig. 1.

Description of a Preferred Embodiment of the Present Invention

Fig. 1 shows a chamber 10 having a tubular housing 100, sprays 200 and baffling means 300 within the housing 100.

The tubular housing 100 has an inlet 101 and outlet 103 at its ends. At the inlet 101 and outlet 103 are flanges 102 for connecting to another chamber. Openings 104 are located on the housing 100 for the sprays 200 to penetrate into the housing 100. There are also side flanges 106 for connecting to other apparatus for various purposes. There are wash water drainage arrangements 108 made near the bottom of the housing 100 close to the flanges 102. A drainage arrangement 108 for bottom gas entry (in-line gas entry) is shown in Fig. 1. Another drainage arrangement 108 for side or perpendicular gas entry is shown in Fig. 6. The flanges 102 of two chambers 10 are connected by conventional bolt and nuts configuration. However, other methods of holding the flanges 102 together may be contemplated.

The housing 100 is preferably made of high temperature mild steel. However, any other material suitable for the purpose can be contemplated. The housing 100 is preferably coated with a thin layer of high temperature ceramic coating to prevent corrosion so that the structural strength of the chamber can be maintained. The thickness of the coating is dependent on the purpose of the chamber and it will be known by a person skilled in the art.

Alternatively, the housing 100 may have a convex wall as shown in Fig. 2 such that the centre of the housing 100 has a wider circumference than the inlet 101 and outlet 103 of the housing. The convex wall helps to reduce the surface pressure of the housing 100.

The sprays 200 consist of piping 202 and a nozzle 204 at the end of the piping 202.

The piping 202 is preferably made of Glass Reinforced Plastics (GRP). However, other materials like coated mild steel may be used.

The nozzles 204 in Fig. 1 are positioned in the upper half of the chamber 10 facing downward to provide a downward spray. This is the preferred direction of spray for rising exhaust gas stream as it provides a maximum spray coverage in the chamber. However, other directions of spray e.g. horizontal spray from the side of chamber may be contemplated.

The nozzle 204 can be a spiral nozzle, a fog jet spray nozzle and/or a "pig tail nozzle" (see Fig. 3. As different types of nozzle provide different spray patterns and perform specific pollutant gas removal tasks, the choice of nozzle is essential to ensure high removal rates. A person skilled in the art will be able to select a suitable nozzle to handle a specific task. Preferably, the nozzle is made of stainless steel 316. However, any other material e.g. galvanized steel, GRP, suitable for the specific purpose may be used.

A perspective view of the baffling means 300 is shown in Fig. 3 which consists of a conical roof 302 and a plurality of frusto-conical rings 304. A ring bar 314 is attached to the inner circumference of the ring 304. The roof 302 and each ring 304 are stacked onto each other by vertical rods 306 mounted onto ring bars 314 of the rings 304 below thus creating a gap or slot between the roof 302 and ring 304 and between rings 304. The baffling means 300 has a cylindrical base 308 that is attached to the housing 100 and the base 308 has an inlet 310 (see Fig. 1) for the entry of exhaust gas stream into the baffling means 300 so that the baffling means 300 is in fluid communication with the inlet 101. A schematic drawing of the chamber is shown in Fig. 5. The lowest ring 304 is mounted onto the base 308 by vertical rods 306 (not shown). A cone 312 (see Fig. 5) is installed under the roof such that the vertex of the cone points in a direction opposite the direction of the vertex of the roof 302 for preventing the exhaust gas stream from being trapped under the roof 302. The number of rings 304 used for the baffling means is determined by the flow rate of the gas stream. Similarly, the baffling means 300 may be made of high temperature mild steel or any other materials suitable to withstand the heat and corrosiveness of the exhaust gas stream.

In the present embodiment as shown in Fig. 5, the roof 302 overlaps ring 304 beneath it in such a way that the diameter of the roof 302 exceeds the inner diameter of ring 304 and this arrangement allows the exhaust gas stream to escape through the gaps while preventing water from entering the baffling means 300 and causing a backflow into the inlet 310. The rings 304 have the same configuration such that the ring 304 above overlaps the ring below in the same manner. The tapering of the rings 304 serves the same function of preventing water from entering the baffling means 300 i.e. backflow. In order for the rings 304 to overlap, the diameter of the rings 304 increases towards the base 308. The increase in the diameter of the rings 304 towards the base improves the spread of the exhaust gas stream radially in the chamber 10. As the exhaust gas stream rises within the baffling means 300, the gas stream exits the baffling means 300 through the gaps between the roof 302 and ring 304 and between rings 304. Accordingly, the gas stream that exits the lowest ring 304 will be diverted to a space furthest away from the centre of the baffling means 300 and the gas stream that exits towards the top of the baffling means 300 i.e. from under the roof 302 will be closest to the centre of the baffling means. In this way, the gas stream rising in the chamber 10 can be spread out more evenly radially within the chamber as compared with the gas flow in a conventional tower whereby the gas stream is generally concentrated towards the center of the tower. The advantage of having the gas stream spread out is the increase in the exposure of the gas stream to the wash water to allow a more thorough interaction between the gas stream and wash water. Comparatively, a gas stream which flows centrally in a conventional tower having the same setup e.g. the same nozzle arrangement, has a reduced exposure to wash water.

In addition, the baffling means 300 retards the speed of the exhaust gas stream as it obstructs and diverts the gas stream. Similarly, the retardation of the exhaust gas stream increases the time for the gas stream to be exposed to the wash water.

As a result, the efficiency of chamber 10 improves over conventional towers. The improvement in the efficiency can be translated into either a more compact design of the chamber 10 or a more effective apparatus for removing pollutants.

The baffling means 300 can be configured to consist of roof 302 alone or with one or a plurality of rings 304. Alternatively, the roof 302 may be replaced by a ring 304 (see Fig. 6 and 7) so that the gas can escape from the top of the baffling means and from the centre of baffling means 300.

When in use, the exhaust gas stream enters the chamber 10 through the opening 310 as shown in Fig. 1. The exhaust gas stream exits the baffling means 300 via the gaps between the rings 304 and between the roof 302 and rings 304. Wash water 12, e.g. treated alkaline water, for removing the pollutants is pumped into the chamber 10 and sprayed onto the exhaust gas stream through the nozzles 204. Thereafter, the wash water is channeled to the drainage arrangement 108 as shown in Fig. 1.

The chamber 10 can be stacked onto another to form a tower as shown in Fig. 8. To optimize the efficiency of the chamber 10, each chamber 10 is made to remove specific pollutants e.g. S0₂, C0₂. In Fig. 4, a tower 50 having three chambers 10-1 , 10-2, 10-3 stacked vertically is shown. The first chamber 10-1 (at the bottom) is used to remove S0₂ from the exhaust gas stream. The removal of S0₂ is denoted as Stage 1. Stage 1 is also used to remove heavier particles first before channeling of the exhaust gas stream into the next chamber. The second chamber 10-2 and third chamber 10-3 is used to remove C0₂ and NO_x. The removal of both gases at this stage is denoted as Stage 2. The order of removal of the gases in Stage 2 is not important. However, the order of the stages is. At the top of the tower, a demister (not shown) is installed to retain moisture from the. exhaust gas before releasing the gas into the atmosphere. For the embodiment in Fig. 4, the wash water used in the stages is treated. It can be water or seawater when the tower is installed on a vessel at sea. The wash water 12 is treated by Ultra Low Frequency (ULF) waves and not with chemical or addictives. This causes the wash water 12 to become very reactive and reductive for all the gases. This method of treating the wash water can be found in US Patent Application No. 11/241,122. Specifically, the wash water for Stage 1 has been enhanced to increase the reactivity of the treated wash water and to improve removal efficiency and it is denoted as treated wash water. Wash water for Stage 2 is treated differently. For the wash water in Stage 2, the pH value is first excited and subsequently treated by Ultra Low Frequency Electrolysis System (ULFES), a patented system, to raise the pH value of the wash water. The wash water for Stage 2 is denoted as treated alkaline wash water and it is effective in the removal of C0₂ and NO_x.

The treatment of the wash water greatly enhances the efficiency of the removal of pollutants from the exhaust gas stream. In an example, the concentration of pollutants C0₂, S0₂ and ΝΟχ in an exhaust gas stream was taken at inlet 101 and outlet 103. The gas abatement results were recorded and the efficiency calculated below:

Table 1

The above results were taken from a vessel. Although the vessel was not running at full engine load, it is noted that the efficiency of removal of C02, S02 and NOX is about 77%, 98% and 66%.

Due to the treated wash water for each stage, the material of the apparatus used for each stage has to be suitable for each stage otherwise the pH value of the treated water will be affected. The material used for the housing, piping etc for Stage 1 includes mild steel, galvanized steel and equivalent. Material for Stage 2 includes GRP, PVC, coated mild steel etc.

The number of chambers 10 in tower 50 in Fig. 8 can be increased according to the requirement of the system. For example, there can be five chambers in a tower so that there is a spare chamber for each stage.

Also, the configuration of the chambers can vary from the embodiment in Fig. 8. The bottom chamber can be replaced by a base unit 20 with a side opening 22 for inlet of exhaust gas stream i.e. perpendicular gas entry instead of the opening 310 (inline gas entry). In this embodiment, the wash water drainage 108 is at the bottom of the base unit 20.

Preferably, a demister (not shown) between two stages can be installed to arrest moisture at each stage. Alternatively, the demister can be installed between each chamber.

There can be different types of nozzles in a chamber 10. The choice of the nozzles can be made based on the type of treated wash water used so as to compliment the nature of the fluid to more effectively remove the pollutant concerned.

Claims

1. An apparatus for reducing pollutants in an exhaust gas stream, the apparatus comprising: a chamber having an inlet for receiving the polluted exhaust gas stream and an outlet for discharging the exhaust gas stream with reduced pollutant; a spray within the chamber for spraying wash water onto the exhaust gas stream; and a baffling means intermediate the inlet and the outlet, for reducing the flow rate of the exhaust gas stream in the chamber; wherein the baffling means increases the exposure of the exhaust gas stream to the wash water.

2. An apparatus according to claim 1 wherein the inlet and the baffling means are in fluid communication and the baffling means comprises at least one slot for allowing the exhaust gas stream to escape.

3. An apparatus according to claim 2 wherein the slot comprises at least one deflector for deflecting the gas.

4. An apparatus according to claim 3 wherein the deflector is angled for deflecting the exhaust gas stream downwards.

5. An apparatus according to claim 1 wherein the baffling means comprises a conical roof and a plurality of frusto-coriical rings below the roof, the roof and the rings spaced apart to allow the exhaust gas stream to escape.

6. An apparatus according to claim 5 wherein the circumference of one ring is larger than an adjacent ring.

7. An apparatus according to claim 5 wherein the circumference of the rings increase towards the inlet.

8. An apparatus according to claim 7 wherein the outer circumference of one ring is larger than the inner circumference of another.

9. An apparatus according to claim 7 or 8 wherein the rings are equally spaced apart.

10. An apparatus according to any one of claims 5 to 9 wherein the roof further comprises a cone attached to the underside of the roof, the apex of the cone pointed in a direction opposite to the apex of the conical roof.

11. An apparatus according to any one of preceding claims wherein the spray is above the baffling means.

12. An apparatus according to any one of preceding claims wherein the wash water is treated water or treated alkaline water.

13. An apparatus according to claim 12 wherein the water is treated by an ultra low frequency electrolysis process.

14. An apparatus according to any one of preceding claims wherein the pollutant includes S0₂, C0₂ or NO_x.

15. An apparatus according to any one of the preceding claims further comprising a plurality of chambers forming a tower wherein the chambers are in fluid communication.

16. An apparatus according to claim 15 wherein the tower comprises three chambers.

An apparatus according to claim 15 wherein the tower comprises five chambers.

18. An apparatus according any one of claims 15 to 16 wherein each chamber removes a desired pollutant.

19. An apparatus according to claim 18 wherein a first chamber removes S0₂, a second chamber removes one of C0₂ and NO_x and a third chamber removes the other of C0₂ and NO_x.

20. An apparatus according to claim 19 wherein treated water is used to remove S0₂ and treated alkaline water is used to remove C0₂ or NO_x.

21. An apparatus according to any one of preceding claims wherein each chamber comprises an inner wall coated with a protective layer.

22. An apparatus according to any one of preceding claims wherein the spray comprises a nozzle.

23. An apparatus according to claim 22 wherein the nozzle includes a spiral jet or a fog jet nozzle.

24. An apparatus according to claim 22 or 23 wherein the nozzle in one chamber differs from the nozzle in another chamber.

25. An apparatus according to any one of claims 22 to 24 wherein the nozzle is made from Glass Reinforced Plastic (GRP).

26. An apparatus according to any one of the preceding claims further comprising a base for mounting the chamber.

27. An apparatus according to claim 26 wherein the base comprises an inlet for entry of the exhaust gas stream and a drainage outlet for draining the wash water.

28. An apparatus according to any one of claims 15 to 27 wherein the tower further comprises a demister.

29. An apparatus according to any one of preceding claims wherein the chamber has a convex wall.

30. A method for removing pollutants from an exhaust gas stream flowing through a chamber comprising: receiving the gas stream into the chamber; baffling the flow of the gas stream by a baffling means; spraying of wash water onto the baffled gas stream; discharging the gas stream from the chamber.

31. A method according to claim 30 further comprising receiving the gas stream into a second chamber, spraying the wash water on the gas stream, deflecting the flow of the gas stream by the baffling means and discharging the gas stream from the second chamber.

32. A method according to claim 31 further comprising receiving the gas stream into a third chamber, deflecting the flow of the gas stream by the baffling means, spraying the wash water on the gas stream and discharging the gas stream from the third chamber.

33. A method according to any one of claims 30 to 32 wherein the pollutants include S0₂, C0₂ or NO_x.

34. A method according to claim 32 wherein a first chamber removes S0₂, a second chamber removes one of C0₂ and NO_x and a third chamber removes the other of C0₂ and NO_x.

35. A method according to one of claims 29 to 34 further comprising treating the wash water with an ultra low frequency electrolysis process.

36. A method according to one of claims 29 to 35 wherein the wash water in the chambers is either treated water or treated alkaline water.

37. A method according to claim 36 wherein treated water is used to remove S0₂ and treated alkaline water is used to remove C0₂ and NO_x.

38. A method according any one of claims 28 to 37 further comprising passing the exhaust gas stream through a demister.