AU689534B2

AU689534B2 - Rotary swirl cyclone scrubber

Info

Publication number: AU689534B2
Application number: AU15079/95A
Authority: AU
Inventors: Stephen Joseph
Original assignee: BIOMASS ENERGY SERVICES AND TE
Current assignee: BIOMASS ENERGY SERVICES AND TECHNOLOGY Pty Ltd
Priority date: 1994-04-13
Filing date: 1995-03-24
Publication date: 1998-04-02
Anticipated expiration: 2015-03-24
Also published as: AU1507995A

Description

P/00/01 1 Regulation 3.2

AUSTRALIA

Patents Act 1 990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

S.

S

C

*SCCSS

0*

S

0* S C

S

Invention Title: "ROTARY SWIRL CYCLONE SCRUBBER" The following statement is a full description of this invention, including the best method of performing it known to us: GH&CO REF: P23310OB/CAS 2 "ROTARY SWIRL CYCLONE SCRUBBER" Introduction This invention concerns a rotary swirl cyclone scrubber, otherwise known as a helical-flow vortex separator. Th!3 type of device is used to clean gases by removing small particles from them and absorbing gaseous or fluid solutants.

Background of the Invention Cyclone scrubbers conventionally employ a vortex chamber, or cyclone, l:hrough the centre of which flows the dirty gas to be cleaned. An auxiliary medium is introduced to move in a direction from the gas outlet towards the gas inlet of the vortex chambers while swirling in a helical flowstream around the stream of dirty gas. The auxiliary medium imparts a rotation to the dirty gas, and the resultant centrifugal forces cause dust in the dirty gas stream to move outward towards the boundary layer between the auxiliary medium and the dirty gas stream. The dust is entrained by the auxiliary stream when it reaches and passes through the boundary layer and is subsequently moved away by the auxiliary S"medium flow through a further outlet of the vortex chamber, leaving clean gas to exit the vortex chamber through the gas outlet.

There are a number of limitations in the efficiency with which particles can cross the boundary layer between the dirty gas stream and the auxiliary medium stream, and there are also limitations in the types of impurities that can be removed from the dirty gas stream by this type of equipment.

The present invention seeks to enhance impurities removal efficiency in a helical-flow vortex separator.

Summary of the Invention Accordingly, the invention provides a rotary swirl cyclone scrubber comprising: S: 23310B II I I- 3 a vortex chamber; a dirty gas inlet at one end of the vortex chamber; and a clean gas outlet at the other end of the chamber, the outlet preferablybeing co-axial with the inlet, one or more auxiliary fluid inlet jets are arranged in the sides of the vortex chamber such as to introduce an auxiliary medium and impart thereon a flowing direction from the gas outlet towards the gas inlet and a swirling motion around a stream of dirty gas flowing from the gas inlet to the gas outlet; and at least one jet nozzle positioned in the vortex chamber such as to introduce a secondary auxiliary medium into the dirty gas stream flowing through the inlet.

A second auxiliary medium is one that causes wetting of particles in the incoming dirty gas stream. As a result of the wetting some pseudo-agglomeration of particles is believed to take place, resulting in a larger effective diameter of the particles to be removed from the dirty gas stream. This assists in transferring the particles acrosi .the boundary shear layer between the dirty gas stream and the 20 hereto axially counter directed circulating auxiliary medium stream.

Furthermore, the wetting of particles in the incoming gas stream causes the con.ensation of some impurities in the gas stream, such as tars. Once condensed, these impurities eeoee S" 25 are removed in the same way as the particulate impurities.

In addition, some water soluble gases will be dissolved in the second auxiliary medium, ie water or steam, and removed.

Chemicals may also be added to the second auxiliary S" medium in order to react with specific impurities and volatile components in the dirty gas and so facilitate their removal. For instance, lime can be added to an aqueous secondary auxiliary medium to remove sulfur dioxide, and amine can be added to remove hydrogen sulfide. Alternatively, chemicals can be added to the S:23310B III I .J L, I 4 dirty gas stream to react with impurities and facilitate their removal by the scrubbing process.

A swirler may be associated with the dirty gas inlet in order to impart a swirl to that stream. The swirl may either be in the same direction as the auxiliary medium or the opposite direction.

Water may be used as the first and second auxiliary medium, in which case the jet nozzle introducing the secondary auxiliary medium may employ an atomiser in order to disperse the water into the incoming dirty gas.

To minimise cooling of the gas to be cleaned, the primary auxiliary medium may be introduced close to the walls of the vortex chamber.

Alternatively, steam may be employed as the 15 auxiliary medium, in which case there is no need for S S0 atomisation at the jet nozzle.

A jet nozzle which delivers the secondary auxiliary medium is preferably arranged in the vortex chamber coaxially with and directed towards the inlet. With this arrangement, the incoming stream of secondary auxiliary medium will assist in driving particles towards the boundary layer by a motion directed outwards from the nozzle.

It is also envisaged to provide two or more jet nozzles with axial distance from one another along the flow path of the dirty gas stream from gas inlet to gas outlet to further enhance removal of pollutants from the gas stream.

A demister may be provided at the outlet end of the vortex chamber in order to remove water vapour remaining in the clean gas.

A further jet nozzle may be provided to introduce a further auxiliary medium stream into the secondary auxiliary stream near cr upstream of the gas inlet and in a direction coinciding with the axial flow direction of the primary auxiliary medium. This arrangement will further ensure that volatile particles and dust removed from the gas stream are transported by the primary S :23310B 5 auxiliary medium to a dust discharge for the vortex chamber.

Embodiments of the invention provide an efficient and inexpensive gas clean-up to produce high quality gas, for instance of a quality suitable for dual fuel and gas engines.

Embodiments are also able to be operated in a semiautomated or fully automated fashion, and are thus safe to operate. They are of a smaller size for an equivalent gas throughput than existing scrubbers and cyclones.

Since embodiments of the invention are straightthrough devices, with the only obstruction between inlet and outlet being the jet nozzle for the secondary auxiliary medium, they are extremely easy to install and maintain. Furthermore the pressure drop through embodiments of the invention is very small, and when water is being used as a cleaning fluid, measurements indicate pressure drops of around 6 to 8 millibars (6 to er 8 centimetres of water) Units embodying the invention are very easy to manufacture and can use standard schedule pipes. No complicated shapes need to be machined or cast, and the nozzles can be purchased from commercial suppliers. Due ea to the simplicity and ingenuity of the design, high reliability and low maintenance will be achieved.

The unit can efficiently work and clean gases at very high temperatures 1200 degrees Celsius) and with high dust loadings 100 gms/Normal cubic metres). The cooling of the incoming gas can be minimised either by using steam in the tangential jets, used to introduce the primary auxiliary medium into the vortex chamber or by pointing water jets closer to the walls.

Efficiency of removal of coal dust from a boiler can be as high as 99.99%, and extraction of sulphur dioxide with lime solutions as high as 95%, none of which has been able to be accomplished with conventional vortex separators.

S: 23310B -r -II I 6 Brief Description of the Drawings The invention will now be described by way of example only, with reference to the accompanying drawings, in which: figure 1 is a schematic view of a rotary swirl cyclone scrubber embodying the present invention; and figure 2 is a schematic illustration of an alternative embodiment.

The same reference numerals have been used throughout both drawings to refer to corresponding features.

Best Modes for Carrying Out the Invention o ~Referring first to figure 1, the rotary swirl cyclone scrubber 1 comprises a vortex chamber, or 15 cyclone, 2, penetrated at its lower end by a dirty gas inlet pipe 3 and at its upper end by a clean gas outlet pipe 4.

Vanes 5 are provided in inlet pipe 3 to impart a swirling or cyclonic motion to incoming gas, indicated 20 generally at 6. The vanes 5 are angled at 45 degrees to the axes of the inlet and outlets. The inlet pipe has a diameter of approximately 50% of the diameter of the .:vortex chamber 2.

Inlet 3 and outlet 4 are arranged in-line so that dirty gas can flow through vortex chamber 2, where it is cleaned, from the inlet pipe 3 to the outlet pipe 4 in a straight line.

Inlet jets 7 are positioned in the walls of the cyclone to introduce a primary auxiliary medium. The jets 7 are oriented so as to direct the primary auxiliary medium in a direction from outlet 4 to inlet 3 along a helical path 8 surrounding the stream of dirty gas 6.

A jet nozzle 9 is arranged inside the vortex chamber 2 to direct a secondary auxiliary medium towards the incoming dirty gas stream.

A baffle 10 is provided below or upstream the upper end of inlet pipe 3 in order to separate the cyclone S:23310B L- I 7 chamber from a bunker outlet 11. A butterfly valve is provid n the bunker outlet to increase back pressure.

and ensures that, when nearly closed, very little of the dirty gas escapes that way.

In use, the incoming dirty gas stream is rotated in a first direction, and the auxiliary medium is rotated in the opposite direction around the dirty gas stream. This creates counter rotating inner and outer fluid bodies or streams separated by a boundary shear layer.

When water is used as the auxiliary medium., primary auxiliary medium is directed into the cyclone throi!gh jets 7, and secondary auxiliary medium is directed into the incoming dirty gas stream through jet nozzle 9 which .*oS includes an atomising nozzle (not shown) at its end.

S 15 The secondary auxiliary medium enters in atomised form to wet particles in the incoming dirty gas stream and causes pseudo-agglomeration of the particles. This S.o results in the particles having a larger effective dia.,eter and increased weight.

The rotation imparted to the incoming dirty gas stream by vanes 9 causes centrifugal forces to act on the

S

incoming dirty gas stream, and accordingly to drive particles radially outward. This effect is enhanced by oooo the stream of atomised spray from the nozzle at the end of jet 9, which also serves to drive the particles radially outwards as the droplets impact on particles.

Particles arriving at the boundary shear layer between the inner and outer fluid streams are thus more readily able to cross from the dirty gas stream into the auxiliary medium stream where they are entrained and driven down the outside of the cyclone past baffle and are then taken away into sump 11. The baffle prevents re-entrainment of the particles as they are removed, and assists in preventing the incoming dirty gas stream from exiting the chamber into the bunker 11.

Bunker 11 is connected to a settling tank (not shown).

Another means for assisting in the prevention of re-entrainment of the particles and enhancement of the S: 23310B Its 8 removal thereof into the bunker is the provision of one or a plurality of jets arranged such as to direct a further auxiliary medium stream into the outer fluid stream in. the region behind the opening of the inlet pipe 3 into the vortex chamber such as to impart a further axial speed component onto the particles in direction of the bunker and then provide an effective air barrier against re-entry of dust particles into the chamber 2.

Such further jets are schematically illustrated by phantom lines at Reference numeral 9a indicates a further jet nozzle for introducing secondary auxiliary medium into the dirty gas stream; this second jet nozzle, which is optional, is Slocated downstream of the first jet nozzle, i.e. near the coo0 15 gas outlet pipe opening, and serves to further enhance o scrubbing of the gas before leaving the vortex chamber.

The water droplets introduced through jet nozzle 9 will also contact tars and water soluble gases that are present in the dirty gas stream. The tars will condense on contact with the water, and soluble gases will be absorbed by the water. As a result both these types of impurities will also be removed in the cyclone.

In order to facilitate the scrubbing of some gases, chemicals can be mixed with the water. For instance, S lime may be added to remove sulfur dioxide and amine to remove hydrogen sulfide. Alternatively, powdered chemicals can be added to the dirty gas, and these powders will react with impurities in the dirty gas which is then scrubbed.

In an alternative, steam may be used as the auxiliary medium. In this case jet nozzle 9 will not require an atomising attachment.

In a second embodiment shown in figure 2, the scrubber 1' is horizontally arranged and a further chamber 12 is added at the exit of cyclone 2 before outlet pipe 4. A wire or fibre demister 13 is arranged in the second chamber to remove any droplets remaining in the clean gas prior to its leaving the vortex device.

S:23310B Fl I~ 9 A sump 14 is arranged at the bottom of cyclone 2 connected to a drain 15. A sump 16 and drain 17 are also provided at the bottom of the demisting chamber 12 to remove the captured moisture.

The residence time of the particles in the vortex separator is dependent on the angle of injection of the auxiliary jets into the chamber, and on the mass flow rates of the dirty gas and the auxiliary media. When steam is used as auxiliary medium, the temperature of incoming gas should not decrease by more than about 200 degree Celsius when leaving the chamber.

Embodiments of the invention are able to clean small gas particles and remove toxic compounds from gas streams. Applications include the cleaning of "producer ee0 gas" resulting from the gasifying of biomass. Vortex separators designed in accordance with the invention are able to ensure that particle loadings to an engine are less than 50 milligrams per normal cubic metre and that tar loadings are less than 100 milligrams per normal cubic metre. In addition, sulfur dioxide and particulates may be removed from coal fired heat and power equipment. Furthermore, fine mineral dust and aerosols are able to be removed at high temperatures during processing with minimum cooling of the gas stream.

For coal or wood ash particles with a mean diameter of 7 microns, capture efficiency can be greater than 99.9%, and the dust loading in the outlet stream can be as low as 2 milligrams per normal cubic metre. The water required to achieve this capture efficiency is approximately 1.5 to 2.2 kilograms per normal cubic metre of gas, and the pressure drop through the scrubber varies from only 40 to 60 millimetres of water.

Using lime solutions as auxiliary media, the extraction of sulfur dioxide from flue gases can be as high as 95% in a single pass. In conjunction with an impingement scrubber, tar removing from entrained flow biomass gasifiers can be as high as 95% with tar loadings S:23310B -I I I I -C -I 10 of less than 50 milligrams per normal cubic metre of gas being achieved.

Although the invention has been described with reference to particular embodiments it should be appreciated that it may be embodied in many other forms, provided the essential feature of the provision of secondary auxiliary medium into the dirty gas stream is achieved. For instance an arrangement could be envisaged where the secondary auxiliary medium is introduced in a swirling fashion rather than being sprayed from a nozzle directly into the throat of the inlet pipe.

In Lhe claims which follow and in the preceding summary of the invention, except where the context requires otherwise due to express ]anguage or necessary implication, the word 15 "comprising" is used in the sense of "including", ie the features specified may be associated with further features in various embodiments of the invention.

S*

S *r 9 0 f S:23310B I i- I I

Claims

1. A rotary swirl cyclone scrubber, comprising: a vortex chamber; a dirty gas inlet at one end of the vortex chamber; a clean gas outlet at the other end of the vortex chamber, the outlet being co-axial with the inlet; one or more inlet jets arranged in the sides of the vortex chamber such as to introduce primary auxiliary medium and impart thereon a flowing direction from the gas outlet towards the gas inlet and a swirling motion around a stream of dirty gas flowing from the gas inlet to the gas outlet; and eoee at least one jet nozzle positioned in the vortex *ag chamber such as to introduce secondary auxiliary medium into a dirty gas stream flowing through the inlet.

2. A rotary swirl cyclone scrubber according to claim 1, wherein one or more powdered or liquid chemical substances are added to the secondary auxiliary medium. C.

3. A rotary swirl cyclone scrubber according to claim 20 2 wherein lime is added to an aqueous secondary od :auxiliary medium to remove sulfur dioxide.

4. A rotary swirl cyclone scrubber according to claim 2, wherein amine is added to an aqueous secondary auxiliary medium to remove hydrogen sulfide.

5. A rotary swirl cyclone scrubber according to claim 2, wherein one or more chemical substances are added to the dirty gas stream.

6, A rotary swirl cyclone scrubber according to any preceding claims, wherein a swirler is associated with the dirty gas inlet so as to impart a helical motion onto the dirty gas entering the vortex chamber. S:23310B I 1- 12

7. A rotary swirl cyclone scrubber according to any preceding claim, wherein water is used as the auxiliary medium, and the jet nozzle introducing the secondary auxiliary medium includes an atomiser.

8. A rotary swirl cyclone scrubber according to claim 7, wherein to minimise cooling, the water used as primary auxiliary medium is introduced close to the walls of the vortex chamber

9. A rotary swirl cyclone scrubber according to any one 10 of claims 1 to 6, wherein steam is used as the auxiliary medium.

A rotary swirl cyclone scrubber according to any one of the preceding claims, wherein the secondary auxiliary medium is introduced into the vortex chamber directed 15 towards the gas inlet.

11. A rotary swirl cyclone scrubber according to any one of the preceding claims, wheiein a r-nister is provided at the outlet end of the vortex chamizr.

12. A rotary swirl cyclone scrubber according to any one of the preceding claims, wherein at least one further jet nozzle is provided to introduce a further auxiliary medium stream into the secondary auxiliary medium near or upstream of the opening of the gas inlet intc the vortex chamber in a direction away from the gas outlet.

13. A rotary swirl cyclone scrubber substantially as herein described with reference to the accompanying drawings. S :23310B II- I 13 Dated this 23rd day of March 1995 BIOMASS ENERGY SERVICES TECHNOLOGY PTY. LTD. (ACN NO. 003 443 918) By Their Patent Attorneys GRIFFITH H-ACK &CO 23310B ABSTRACT "ROTARY SWIRL CYCLONE SCRUBBER" The scrubber comprises a dirty gas inlet at one end of a vortex chamber, and a clean gas outlet at the other end, co-axial with the inlet. One or more auxiliary fluid inlet jets are arranged in the sides of the vortex chamber to introduce auxiliary medium flowing from the outlet towards the inlet and swirling around an axial stream of dirty gas flowing from inlet to outlet. The 10 scrubber also includes a jet nozzle positioned in the vortex chamber to introduce secondary auxiliary medium into the dirty gas stream. The second auxiliary medium causes wetting of particles in the incoming dirty gas stream. As a result of the wetting some pseudo- agglomeration of particles is believed to take place, resulting in a larger effective diameter. This assists in transferring the particles across the boundary shear layer between the dirty gas and the circulating auxiliary medium. 20 (Figure 1) S: 23310B I I 'I