ATOMISER

Abstract: An atomiser for use in the combustion of liquids, particularly liquids containing particulate material, comprises a body (10) through which a duct (11) for the liquid to be atomised and flow passages (12) for a supply of atomising gas such as air or natural gas, the flow passages (12) intersecting with the duct at such positions and at such angles that the atomising gas has a significant proportion thereof directed along paths tangential to the duct (11).

Description: ATOMI SER This invention relates to an atomiser which can be used to introduce a gas. usually air into a liquid, such as oil, to form a fine "atomised" spray. This will normally be a combustible mixture of oil and water which is ignited. However, the atomiser can be used in other environments wherein a liquid has to be atomis-sd. A known atomiser includes a body having within it a first plurality of flow paths for the liquid to be atomised all leading to parts at a surface of the body, and a second plurality of flow paths for atomising gas intersecting the first plurality of flow paths. Where each of the first plurality of flow paths is intersected by a gas path there is usually a sharp difference in direction between the two paths which are usually of comparable cross—sectional size. Such a known atomiser has several disadvantages. Firstly, the angled intersection of the two flow paths results in a deal of turbulence and frictional energy loss, which means that relatively high pressures have to be used to achieve atomisation of a liquid of a given viscosity. Secondly, the fluid flow passages tend to be rather small in cross- sectional area and this makes them unsuitable for use with liquids containing entrained solids, such as slurries and waste oil. It is an object of the present invention to provide an improved atomiser. The invention provides an atomiser comprising a body having a duct for a fluid to be atomised and a plurality of flow passages for an atomising gas, the flow passages intersecting the duct at an angle to allow tangential flow of gas from passages to duct. A preferred atomiser of the invention can have one or more of the following optional features: The duct has the form of a venturi, comprising a convergent section, a constricted section and a divergent section, some or all of the passages intersecting the duct in the constricted section. The convergent section may be omitted on small fluid throughputs. The divergent section is preferably constructed to constitute a diffuser. The convergent section is desirably constructed to be a diffuser. The divergent section is frusto conical with a cone angle from 20° to 30°, preferably 25°. The cross sectional area of each flow passage is <_ 33.3%, preferably <. 25% of the cross sectional area of the duct. The duct is normally circular in cross section and each passage is also circular in cross section, the diameter of each passage being equal to or less than one half of the diameter of the duct. Each passageway has a wall portion which meets a wall portion o the duct tangentially or as close to tangentially as is mechanically convenient. The gas passages are arranged in groups spaced along the duct. There are two, three or more such groups. Each group can contain a number of passages arranged generally in a common plane disposed radially relative to the duct axis. The number of passages in each group can be two or more and those in the group can be radially spaced around the axis, preferably equall radially-spaced. When the number of passages in each group is the same, the set of passages of each group is preferably radially offset relative to the passages in the adjacent group or groups. The gas passages are arranged each to direct a stream of gas into the liquid duct in a direction transverse to an axis of the duct and tangential to side walling of the duct. The duct can be annular in cross section or may be circular, polygonal, elliptical or curved. In cases of non-circuitry "tangential" is to be interpreted as meaning with a substantial portion at grazing incidence to a wall part of the liquid duct. The invention will be described further, by way of example, with reference to the accompanying drawings, wherein:- Figure 1 is a longitudinal cross section through a preferred atomiser of the invention; Figure 2 is a cross section on line II—II of Figure 1; Figure 3 is a cross section on line III—III of Figure 1; and Figure 4 is a cross section on line IV—IV of Figure 1. A preferred atomiser of the invention includes a body 10 wherein is a duct 11 for liquid, particularly viscous, solids- contaminated waste oil, to be atomised for combustion. A plurality of flow passage 12 intersect with duct 11 and are connected to a source of compressed air, such as air. Flow of liquid through the duct 11 is from top to bottom in the draining, and considered in this direction the duct 11 has, sequentially, a converging section 11a, a constricted section lib and a divergent diffusing section lie. An annular manifold (not shown) can surround the body 10 ad cent section lib to supply gas to passages 12. Section lie is a diffuser to connect dynamic pressure in the flow to static pressure and the angle of the frusto-conical lie C ) can be from 20° to 30°, preferably 25°. As best seen in Figures 2, 3 and 4, the passages 12 are arranged in three groups 13, 14, 15 spaced along the axis 16 of duct 11. The passages in each group are circular in cross- section and lie in a plane at right angles to axis 16. The passages 12 in each group are spaced equidistantly about the axis 16 and the respective groups 13, 14, 15 are radially mutually spaced at 30 intervals as will be seen in Figures 2 to 4. The angle can be from 20° up to 40°. The atomiser of the invention is a considerable improvement over known atomisers in that because its liquid flow passage 11 is of significant size, for example from 5 to 10mm in diameter, it can be used with very viscous liquids, and with liquids contaminated with solids. It can cope with waste oils which are so thick and contaminated that normal atomisers cannot cope. When used with thinner liquids, atomisation can be achieved at lower pressures of liquid and gas than have been previously necessary. This results in savings in pump power and installation strengths. The atomiser of the invention is suitable for burning coal/water slurries. The use of the tangential impingement of the gas jets to the peripheral walls of the duct is beneficial in destroying the laminar surface flow layer which tends to develop on the surface of the duct, and convert it to a turbulent gasified mixture. Further, improved atomisation is achieved because a considerable part of the energy disipated by the expanding atomising gas appears as rotational velocity in the fluid stream. Liquid in the diffuser house has a rotational velocity component in addition to the longitudinal velocity generated by the expanding gas/liquid mix. Since it is shear stresses generated by liquid velocity which breaks up the liquid into fine droplets, the rotational component materially assists atomisation compared with what could be achieved by longitudinal velocity alone. The flexibility in number and size of gas parts relative to the liquid passages permitted by the basic shape of the nozzle enables a wider range of atomising gas to fluid flow ratios than a conventional atomiser can achieve. This is of value in achieving improved burning of difficult products, particularly in reducing the formation of unburnt carbon particles and smut in the stack gases. The invention is not limited to the precise details of the foregoing and variations can be made thereto. For example, the dimensions of and the cross-sectional shapes of the duct and of the passages can vary widely. The passageways can have angles to the axis 16 different from 90°. There can be any convenient number of groups of passageways 12. The atomising gas can, in certain circumstances, be a fuel gas, such as natural gas, for use in circumstances where a user has insufficient waste oil to burn to meet heating needs. The atomised liquid can be a coal/water slurry. The atomiser of the invention creates a flame which, because of the swirl, is of short axial length compared with conventional flames. This firstly reduces the length of combustion chamber required, but, more importantly, exposes wide area of flame to impingement by secondary air, giving rise to a high flame temperature with consequent efficient main combustion close to the nozzle, with the remainder of the combustion chamber being free for "polishing", i.e. oxidation of a small fraction of remaining products. The increased efficiency of atomisation also contributes to the short axial flame length. The time for a liquid product to burn is dependent upon droplet size because liquid droplets burn only on their surfaces. The atomiser of the inve-ntion produces smaller droplets which therefore burn faster contributing to a hotter, shorter flame. This has enabled poly chlorinated biphenyls (PCB/s) to be incinerated without the production of dioxin. The atomiser of the invention is also very tolerant of variations in its operating parameters. Probably because of the aspirating effect of the venturi, the air pressure can be reduced from (in a typical installation) its nominal value of 4.6 Bar down to 3.6 Bar without significant delineaticn in its performance.

Claims: CLAIMS 1. An atomiser comprising a body having a duct for a fluid to be atomised and a plurality of flow passages for an atomising gas, the flow passages being directed to intersect the duct at such positions and at such angles that the atomising gas flowing into the duct has a significant proportion thereof directed along paths tangential to the duct. 2. An atomiser as claimed in claim 1, wherein the duct has the form of a venturi, comprising a convergent section, a constricted section and a divergent section. 3. An atomiser as claimed in claim 2, wherein some or all of the passages intersect the duct in the constricted section. 4. An atomiser as claimed in claim 2 or 3, wherein the divergent section is constructed to constitute a diffuser. 5. An atomiser as claimed in claim 2, 3 or 4 wherein the convergent section constitutes a diffuser. 6. An atomiser as claimed in any of claims 2 to 5, wherein the divergent section is frusto conical with a cone angle from 20° to 30°. 7. An atomiser as claimed in claim 6 wherein the angle is 25°. 8. An atomiser as claimed in any of claims 1 to 7 wherein the cross sectional area of each flow passage is _< 33.3%. 9. An atomiser as claimed in claim 8 wherein the cross-sectional area of each flow passage is < ^ 25% of the cross-sectional area of the duct. 10. An atomiser as claimed in any preceding claim wherein the duct is circular in cross section and each passage is also circular in cross section, the diameter of each passage being equal to or less than one half the diameter of the duct. 11. An atomiser as claimed in any preceding claim, wherein each passageway has a wall portion which meets a wall portion of the duct tangentially. 12. An atomiser as claimed in any preceding claim, wherein 10 the passages are straight. 13. An atomiser as claimed in any preceding claim, wherein the gas passages are arranged in groups spaced along the duct. 14. An atomiser as claimed in claim 13, wherein there are l-* two, three or more such groups. 15. An atomiser as claimed in claim 14 wherein each group contains a number of passages arranged generally in a common plane disposed around the duct axis. 16. An atomiser as claimed in claim 14 or 15, wherein the 0 number of passages in each group is two or more. 17. An atomiser as claimed in claim 15 or 16 wherein the passageways of each group are equally radially-spaced. 18. An atomiser as claimed in any of claims 14 to 17 wherein the set of passages in each group is radially offset relative 5 to the passages in the adjacent group or groups. 19. An atomiser as claimed in any preceding claim, wherein the gas passages are arranged each to direct a " stream of gas into the liquid duct in a direction transverse to an axis of the duct and tangential to side walling of the duct. 20. An atomiser as claimed in any preceding claim wherein the duct is annular in cross-section or circular or polygonal, or elliptical, or curved. 21. An atomiser as claimed in claim 20 when appended to claim 19, wherein in cases of non-circularity "tangential" means with a substantial portion at grazing incidence to a wall of the duct. 22. An atomiser substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: SUNIEWSKI STANISLAW EDWARD, SUNIEWSKI, STANISLAW, EDWARD
Applicants: HIRT COMBUSTION ENG, HIRT COMBUSTION ENGINEERS LTD.
Application year: 1988
Main classification: B05B7
IPC codes: B01F5, B05B7, F23D11