EP0101109B1

EP0101109B1 - Mix atomizer

Info

Publication number: EP0101109B1
Application number: EP83201033A
Authority: EP
Inventors: Hendrikus Johannus Antonius Hasenack
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1982-08-09
Filing date: 1983-07-12
Publication date: 1988-03-23
Also published as: JPS5952557A; CA1228013A; DE3376053D1; EP0101109A3; ZA835789B; JPH0315491B2; NZ205182A; EP0101109A2

Description

The invention relates to a mix atomizer for the atomization of a liquid with gas. The invention further relates to an apparatus for the atomization of a liquid, which apparatus is provided with a plurality of such mix atomizers.
The term liquid is taken throughout the specification and claims also to include dispersions of solid particles in a liquid and emulsions.
Atomizers are applied on a large scale in combustion engineering, especially for atomizing heavy liquid fuel, to promote intensive contact of liquid with combustion air for a proper combustion. In an atomizer liquid fuel is broken up into very small droplets which droplets may be subsequently mixed with oxygen or an oxygen- containing gas, for example air, in a combustion chamber for combustion of the fuel. Atomization is normally effected by causing a liquid to spurt under pressure from one or more orifices with a special shape and dimensions. Addition of a gas, for example steam, to the liquid in the atomizer itself promotes the atomization of the liquid. An atomizer wherein gas is added to the liquid to be atomized is in the specification and claims indicated with the expression mix atomizer. When a fuel is to be atomized it is of importance to generate sprays of liquid droplets which are substantially uniformly distributed over the outlet area of the atomizer, in order to promote an optimal combustion of the liquid in the combustion chamber.
Although the elucidation of the present invention to be given hereinafter will deal mainly with steam atomization of liquid, such as oil, it is explicitly stated here that the application of the proposed atomizer is not restricted thereto. Steam may be replaced by, for example, air or refinery fuel gas. The steam may also be saturated to wet. Apart from application in combustion installations atomizers of the proposed type can also be used in spraying installations, for instance, for the purpose of the vaporization of a volatile component.
US patent specification 2,764,455 discloses a mix atomizer for the atomization of a liquid with gas comprising a first mixing chamber, a second mixing chamber into which the first mixing chamber debouches having a cross-sectional area which is substantially larger than the cross-sectional area of the first mixing chamber, and an outlet nozzle into which the second mixing chamber debouches having a cross-sectional area which is substantially smaller than the cross-sectional area of the second mixing chamber, wherein the first mixing chamber, the second' mixing chamber and the outlet nozzle have substantially coinciding central longitudinal axes, wherein the first mixing chamber is provided with one inlet for liquid and separate inlet means for primary gas, the central longitudinal axes of the inlet means for primary gas intersecting the central longitudinal axis of the inlet for liquid in the first mixing chamber, and wherein the second mixing chamber is provided with means for introducing secondary gas and with a tapering end wall portion for smoothly guiding secondary gas to the outlet nozzle.
It is an object of the present invention to provide a mix atomizer for the atomization of a liquid with a gas which is so designed that the velocity and flux of the liquid leaving the atomizer during normal operation are substantially uni-- formly distributed over the outlet area of the atomizer in order to generate homogeneous liquid sprays and promoting optimal use of the liquid for combustion or other purposes.
To this end the mix atomizer according to the invention is characterized in that the means for introducing secondary gas are means for tangen- .tially introducing secondary gas, which are arranged near the tapering end wall portion of the second mixing chamber.
The invention further relates to an apparatus for the atomization of a liquid with gas, comprising a member being internally provided with a plurality of mix atomizers, wherein each mix atomizer comprises a first mixing chamber and an outlet nozzle in fluid communication therewith terminating at the outer surface of a head of the member, the first mixing chamber and the outlet nozzle having coinciding central longitudinal axes, wherein the mix atomizer is provided with one inlet for liquid and separate inlet means for primary gas, the central longitudinal axis of the inlet means for primary gas intersecting the central longitudinal axis of the inlet for liquid, and wherein the member further comprises one liquid supply channel and one gas supply channel, first passages for supplying liquid from the liquid supply channel to the liquid inlets, and second passages for supplying primary gas from the gas supply channel to the inlet means for primary gas.
Such an apparatus is known from USA patent specification No. 3,072,344.
It is an object of the present invention to provide an apparatus for the atomization of a liquid with a gas which is so designed that the velocity and flux of the liquid leaving each mix atomizer during normal operation are substantially uniformly distributed over the outlet area of the mix atomizer in order to generate homogeneous liquid sprays and promoting optimal use of the liquid for combustion or other purposes.
To this end the apparatus for the atomization of a liquid with gas according to the invention is characterized in that the mix atomizers further comprise second mixing chambers into which the first mixing chambers debouch, wherein the second mixing chambers debouch into the outlet nozzles, wherein the cross-sectional areas of the second mixing chambers are substantially larger than the cross-sectional areas of the first mixing chambers and also substantially larger than the cross-sectional areas of the outlet nozzles, wherein the first mixing chambers, the second mixing chambers and the outlet nozzles have substantially coinciding longitudinal axes, and wherein the second mixing chambers are provided with tapering end wall portions for smoothly guiding secondary gas to the outlet nozzles and with means for tangentially introducing secondary gas which are arranged near the tapering end wall portions, and in that the member further comprises third passages for supplying secondary gas from the gas supply channel to the means for tangentially introducing secondary gas pertaining to the second mixing chambers of the mix atomizers.
The invention will now be described by way of example only in more detail with reference to the accompanying drawings, in which

Figure 1 shows a longitudinal section of a mix atomizer according to the invention.
Figure 2 shows a longitudinal section of an apparatus for the atomization of a liquid provided with a plurality of mix atomizers according to the invention, and
Figure 3 shows a top view of the apparatus shown in Figure 2.

Figure 1 shows a mix atomizer, generally indicated by reference numeral 1, for atomizing a liquid, such as heavy liquid fuel, with a gas. The mix atomizer 1 has as main components a first mixing chamber 2, a second chamber 3 being in fluid communication with the first mixing chamber 2, and an outlet nozzle 4 connected with the second mixing chamber 3. These three components have substantially coinciding longitudinal axes, while the cross-sectional areas of the second mixing chamber 3 and those of the outlet nozzle 4 are both substantially larger than the cross-sectional areas of the first mixing chamber 2. Further, the cross-sectional areas of the outlet nozzle 4 are chosen smaller than the cross-sectional areas of the second mixing chamber 3. Channels 5 and 6 are arranged in the atomizer for supplying a liquid to be atomized and atomizing gas, respectively, into the first mixing chamber 2 at or near the free end thereof. The channels 5 and 6 are positioned at an angle with respect to one another to promote intensive break-up of the liquid flow issuing from channel 5 by the gasflow from channel 6.
For supplying gas into the second mixing chamber 3 the mix atomizer is provided with a ring-shaped channel 7 with passages 8 forming fluid communications between the channel 7 and said mixing chamber 3. These passages 8, being preferably uniformly distributed over the circumference of the second mixing chamber 3, are so positioned with respect to said second mixing chamber that gas from the ring-shaped channel 7 is tangentially introduced into said mixing chamber 3.
Downstream of the ring-shaped channel 7 the second mixing chamber 3 has a substantially frusto-conically shaped side wall 9 tapering towards the outlet nozzle 4 thereby providing a smooth guiding for fluid from the channel 7 and the passages 8 towards the outlet nozzle 4.
During the operation of the mix atomizer shown in Figure 1 for the atomization of liquid fuel with steam, the liquid to be atomized and steam are introduced into the first mixing chamber 2. Owing to the impact of the steam flow on the supplied liquid flow, the liquid flow is broken up into small liquid fragments in the first mixing chamber 2. The breaking up of the liquid flow is promoted by causing the steam from the channel 6 to contact the liquid flow from the channel 5 at an angle. The so formed mixture of liquid fragments and steam enters the second mixing chamber 3, where secondary steam is added at sonic velocity to said mixture. Since the secondary steam is tangentially introduced at a high velocity into the second mixing chamber at a wide part thereof, the secondary steam will form an annulus around the core formed by the mixture of liquid fragments and primary steam from the first mixing chamber 2. The major part of the tangentially introduced steam flows substantially along the frusto-conically shaped wall 9 of the second mixing chamber 3 and follows its way along the wall of the outlet nozzle 4, thereby preventing direct contact of liquid with said walls. Such a contact might easily reduce the velocity of the liquid flowing close to said walls, resulting in an irregular outflow pattern of the liquid over the outlet nozzle 4.
Since the cross-sectional areas of the outlet nozzle 4 are substantially smaller than the cross-sectional areas of the second mixing chamber 3, the velocity of the mixture of steam and liquid fragments is substantially increased in the outlet nozzle 4, causing a further break-up of the liquid fragments. Owing to the presence of a shield of the tangentially supplied secondary steam the velocity and the density of the liquid fragments over the cross section of the outlet nozzle 4 will be substantially uniform, which feature enables an effective combustion of the liquid in a not shown combustion chamber arranged downstream of the outlet nozzle 4. Upon leaving the mix atomizer the liquid/steam mixture will rapidly expand, resulting in the formation of a mist of very fine droplets in the combustion space, where the liquid droplets are contacted with blast for the combustion of the fuel.
Reference is now made to Figures 2 and 3 showing an apparatus for atomizing liquid, which apparatus is provided with a plurality of mix atomizers of a type discussed in the above with reference to Figure 1.
This atomization apparatus comprises a member 10 provided with a central channel 11 for the supply of atomization fluid to a plurality of mix atomizers 12, and with a concentrically positioned annular channel 13 for the supply of liquid, such as oil, to be atomized. The mix atomizers 12 are arranged in a head 14 of the apparatus 10.
The distance between the outlet nozzles of adjacent mix atomizers 12 should be chosen sufficiently large to prevent interference between adjacent outflowing streams of liquid droplets. A suitable arrangement of the mix atomizers 12 is the one shown in Figure 3, wherein the centres of the outlet nozzles of the mix atomizers 12 are positioned in a circular pattern, and wherein adjacent outlet nozzles are spaced apart from one another at 120 degrees. As shown in Figure 2 the head 14 of the apparatus 10 is frusto-conically shaped whereas the mix atomizers 12 are arranged perpendicular to the outer surface of said head 14. This arrangement enables the application of more mix atomizers without the risk of interference between adjacent mix atomizers than possible when using an apparatus having a flat head and the mix atomizers being arranged perpendicular to the flat outer surface of the head.
Each mix atomizer 12 is provided with a first mixing chamber 15, a second mixing chamber 16 and an outlet nozzle 17, wherein the second mixing chamber 16 is substantially wider than the first mixing chamber 15. The first mixing chamber 15, the second mixing chamber 16 and the outlet nozzle 17 of each mix atomizer 12 have coinciding longitudinal axes, positioned perpendicular to the frusto-conically shaped outer surface of head 14.
For supplying primary atomization fluid to the mix atomizers 12, a plurality of passages 18 are provided forming fluid communications betwen the central channel 11 and the frist mixing chambers 15. Secondary atomization fluid is supplied via tangentially arranged passages 19 to the second mixing chambers 16 of the mix atomizers 12. These passages 19 form fluid communications between the mix atomizers 12 and a substantially ring-shaped channel 20 connected to the central channel 11 via a passage 21. For the supply of secondary atomization, fluid to the mix atomizers 12 via tangentially arranged passages 19 as shown in Figure 2, the ring-shaped channel 20 surrounds the mix atomizers 12.
Fluid to be atomized is supplied to the first mixing chambers 15 of the mix atomizers 12 via a plurality of passages 22 forming a fluid communication between the annular liquid channel 13 and the first mixing chambers 15.
The operation of the apparatus shown in Figures 2 and 3 is substantially the same as discussed with reference to the separate mix atomizer shown in Figure 1. When using the apparatus shown in Figures 2 and 3 for the atomization of oil with steam, the mix atomizers 12 are supplied with oil and steam via a common liquid supply, viz. annular channel 13, and a common steam supply, viz. central channel 11, respectively.
It should be noted that the present invention is not restricted to mix atomizers having second mixing chambers with frusto-conically shaped walls downstream of the secondary steam inlets. Instead thereof, other shapes of tapering walls may be applied, provided that there is a smooth passage for the secondary steam from the secondary steam inlets to the outlet nozzle of the mix atomizer, guaranteeing that the secondary steam will form a shield flowing along the walls of the second mixing chamber and the outlet nozzle.
Although in the embodiments shown the mix atomizers are provided with central primary inlets in combination with side inlets for liquid, these inlets may also be otherwise arranged, for example a combination of central liquid inlets with side primary steam inlets may be chosen for.
Further, the invention is not restricted to an apparatus with mix atomizers having the particular arrangement of a central steam channel and an annular liquid channel as shown in Figure 2. Any other suitable arrangement may be applied, provided that the mix atomizers can be supplied with steam and liquid from a common steam channel and a common liquid channel, respectively.
Finally it is noted that the invention is not restricted to an apparatus for atomization of a liquid having a frusto-conically shaped head. Instead thereof the apparatus can be provided with a flat-shaped head. With such a head the mix atomizers are preferably arranged at an angle with respect to the outer surface of the head having their outlet nozzles pointing away from one another to enable the positioning of a relatively large number of mix atomizers in the apparatus without the risk of interference between the fluid flows issuing from the atomizers during operation.

Claims

1. Mix atomizer for the atomization of a liquid with gas comprising a first mixing chamber, a second mixing chamber into which the first mixing chamber debouches having a cross-sectional area which is substantially larger than the cross-sectional area of the first mixing chamber, and an outlet nozzle into which the second mixing chamber debouches having a cross-sectional area which is substantially smaller than the cross-sectional area of the second mixing chamber, wherein the first mixing chamber, the second mixing chamber and the outlet nozzle have substantially coinciding central longitudinal axes, wherein the first mixing chamber is provided with one inlet for liquid and separate inlet means for primary gas, the central longitudinal axes of the inlet means for primary gas intersecting the central longitudinal axis of the inlet for liquid in the first mixing chamber, and wherein the second mixing chamber is provided with means for introducing secondary gas and with a tapering end wall portion for smoothly guiding secondary gas to the outlet nozzle, characterized in that the means for introducing secondary gas are means for tangentially introducing secondary gas, which are arranged near the tapering end wall portion of the second mixing chamber.

2. Mix atomizer as claimed in claim 1, wherein the mix atomizer is provided with a plurality of tangentially disposed passages for tangentially introducing secondary gas into the second mixing chamber, said passages being substantially uniformly distributed over the circumference of the second mixing chamber.

3. Mix atomizer as claimed in claim 1 or 2, wherein the cross-sectional area of the outlet nozzle is substantially larger than the cross-sectional area of the first mixing chamber.

4. Apparatus for the atomization of a liquid with gas, comprising a member being internally provided with a plurality of mix atomizers, wherein each mix atomizer comprises a first mixing chamber and an outlet nozzle in fluid communication therewith terminating at the outer surface of a head of the member, the first mixing chamber and the outlet nozzle having coinciding central longitudinal axes, wherein the mix atomizer is provided with one inlet for liquid and separate inlet means for primary gas, the central longitudinal axis of the inlet means for primary gas intersecting the central longitudinal axis of the inlet for liquid, and wherein the member further comprises one liquid supply channel and one gas supply channel, first passages for supplying liquid from the liquid supply channel to the liquid inlets, and second passages for supplying primary gas from the gas supply channel to the inlet means for primary gas, characterized in that the mix atomizers further comprise second mixing chambers into which the first mixing chambers debouch, wherein the second mixing chambers debouch into the outlet nozzles, wherein the cross-sectional areas of the second mixing chambers are substantially larger than the cross-sectional areas of the first mixing chambers and also substantially larger than the cross-sectional areas of the outlet nozzles, wherein the first mixing chambers, the second mixing chambers and the outlet nozzles have substantially coinciding longitudinal axes and wherein the second mixing chambers are provided with tapering end wall portions for smoothly guiding secondary gas to the outlet nozzles and with means for tangentially introducing secondary gas which are arranged near the tapering end wall portions, and in that the member further comprises third passages for supplying secondary gas from the gas supply channel to the means for tangentially introducing secondary gas pertaining to the second mixing chambers of the mix atomizers.

5. Apparatus as claimed in claim 4, wherein mix atomizers are provided with a plurality of tangentially disposed passages for tangentially introducing secondary gas into the mixing chambers, said passages being substantially uniformly distributed over the circumference of the second mixing chambers.

6. Apparatus as claimed in claim 4 or 5, wherein the cross-sectional areas of the outlet nozzles are substantially larger than the cross-sectional areas of the first mixing chambers pertaining thereto.

7. Apparatus as claimed in claims 4-6, wherein the centres of the outlet nozzles are positioned in circular pattern substantially equally spaced apart from each other.

8. Apparatus as claimed in claims 4-7, wherein the head of the member has a substantially frusto-conical shaped outer surface, and wherein the mix atomizers are arranged substantially perpendicular to the outer surface of the head.

9. Apparatus as claimed in claims 4-7, wherein the head of the member has a substantially flat outer surface, and wherein the mix atomizers are arranged at an angle with respect to the outer surface of the head and have their outlet nozzles pointing away from each other.

10. Apparatus as claimed in any one of the claims 4-9, wherein one of the supply channels is substantially centrally arranged in the member, and wherein the other supply channel is ring-shaped, the supply channels having substantially coinciding longitudinal axes.