WO2003036099A1

WO2003036099A1 - Ejector

Info

Publication number: WO2003036099A1
Application number: PCT/NO2002/000353
Authority: WO
Inventors: Tom Jacobsen; Terje Fagervold; Gunnar Fagervold; Olav Kvalvaag
Original assignee: Gto Subsea As
Priority date: 2001-10-04
Filing date: 2002-10-02
Publication date: 2003-05-01
Also published as: NO20014843D0; NO20014843L

Abstract

An ejector comprising a tubing (2) for transporting material from the tubing inlet to the tubing outlet, with an ejector nozzle connected externally in relation to said tubing and with an angle of incline relative to the tubing (2) in a plane common with a longitudinal axis of the tubing. The ejector comprises two or more nozzles (31, 32, ...) arranged substantially symmetrically around the tubing (2) periphery, said ejector nozzles preferably having equal angles relative to the axis of the tubing and providing equal amounts of motive power (injecting equal rates of fluid).

Description

Ejector

The present invention concerns an ejector as defined by the preamble of claim 1. Background

It is well known in varies applications to use an ejector nozzle arranged in a tubing for creating an energetic force or pump effect in the tubing, so that the tubing is useful for transporting therethrough materials of different kinds. The materials to be transported may be solid particulates or the like, while the pumping medium supplied to the tubing through the nozzle is a fluid. There is, however, no limit to the combinations of phases (solids, liquids, gases) that are transportable through an ejector, and in the following we only refer to these as "materials". An important utilisation among many others is the transportation of sediments under water (dredging)

A disadvantage connected with common ejector tubings is the volume occupied by the nozzle within the tubing, thereby effectively limiting the maximum size of the particles that may be transported through the tubing. To overcome this problem it has been suggested to arrange the ejector nozzle completely externally of the tubing. In order to obtain the required direction of the jet from the nozzle, a technique involving an inclined arrangement of the nozzle relative to the tubing has been used. In addition the tubing has been arranged with a moderate bend at the point where the nozzle is attached. These measures combined have ensured that most of the energy supplied has been transformed to an energetic power within the tubing. This has in turn enabled transportation of rocks with a size close to the diameter of the tubing.

The solution is, however, not ideal, and even though the bend is quite moderate, it provides a shape that departs from the ideal, straight configuration, and involves a level of risk that large particles will become jammed in the tubing. Furthermore, it is a problem that wear is not uniform, since the particles transported with the water have to pass through a bend where turbulence is higher. In addition, in many applications it is desirable that the mix chamber (the region downstream of the nozzle) is as short as possible.

Objective Thus, the object of the present inventive is to provide a new principle for the design of an ejector powered tubing, where the above mentioned disadvantages are eliminated, providing uniform How conditions in a tubing with no cross-section reduction. The invention

The invention comprises an ejector as defined by claim 1. Preferred embodiments of the invention are disclosed by the dependent claims. As will be readily understood from the subsequent description with reference to the accompanying drawings, the present invention provides an ejector that is completely straight at least with respect to the requirements related to the ejector nozzles establishing the energetic force in the tubing. Figure 1 is a schematic side view of an ejector according to the invention, Figure 2 is a cross- sectional view of the ejector, along the line II-II in Fig. 1.

Figure 3 is a cross-sectional view of an embodiment of the ejector according to the invention that differs from that of Figure 1 and 2.

Figure 4 is a cross-sectional view of a third embodiment of the ejector according to the invention.

Figure 1 shows an ejector 1 comprising an ejector tubing 2 and two ejector nozzles 3,, 3, that are arranged on opposite sides of the tubing 2. The nozzles 3,, 3₂ have a mutual acute angle relative to the longitudinal axis of the tubing 2. The nozzles are connected to a water pump or the like, and will in operation inject water into the tubing 2 as indicated by arrows.

Figure 2 depicts a cross-section of the embodiment of the invention shown in figure 1.

Figure 3 is a cross-sectional view substantially the same as Figure 2, but showing an embodiment with three ejector nozzles, 3,, 3₂ og 3₃ connected to the tubing 2, each displaced 120° relative to the other two around the circumference of the tubing, thereby forming a symmetrical pattern around the tubing.

Figure 4 is a cross-sectional view substantially the same as Figures 2 and 3, but showing an embodiment with four ejector nozzles connected to the tubing and distributed at 90° intervals around the circumference of the tubing, thereby forming a symmetrical pattern around the tubing.

Furthermore it is possible to include more than four nozzles along the circumference of the tubing. F.ven with no more than four nozzles, the effective length of the mix zone will be reduced to one half of that obtainable with solely one nozzle, irrespective of whether such a single nozzle be arranged internally in the tubing or externally in relation to the tubing.

According to the invention, one would normally arrange a number of nozzles that are all equally powerful and are all mounted at the same angle of incline relative to the tubing 2, in order to obtain an optimized symmetry for the system and thereby minimal loss of effect. It is, however, also within the scope of the invention to accept minor deviations while still maintaining the general principle of the invention, so that the forces induced by the nozzles are not lost and in a way which ensures that no significant deviations from a symmetrical flow pattern are induced in the tubing. In this connection it should be mentioned that it is natural, but not a requirement, that the nozzles are all arranged on one common circle on the periphery of the tubing, the circle being defined by the intersection of the tubing and an imaginary plane perpendicular to the axis of the tubing.

A simple variation from the case of perfect symmetry is one where two and two of a total of four nozzles are equally powerful and mounted at equal angles relative to the tubing, but where the pairs of equal nozzles are different from each other. With such a variant it is still possible to obtain symmetrical conditions within the tubing.

Correspondingly, it is possible to maintain substantial symmetry even if the angle between one of the nozzles and the tubing is changed somewhat, provided that the same nozzle be moved somewhat upstream or downstream in relation to the other nozzles to compensate for the deviating nozzle angle. optionally also allowing individual adjustment of the power to each of the nozzles. All such not-far- from symmetrical designs shall be considered to be covered by the term "substantially symmetrically^" used in claim 1.

When using an ejector according to the invention, a complete mixing of the fluid from the nozzles and the material in the tubing is obtained in a region corresponding to 4-5 times the tubing diameter. A normal length of mix zone or mix chamber is 7-8 times the tubing diameter. The invention thus enables use of significantly shorter mix chambers compared to the ones previously known and this may be crucial for some demanding applications. It is thus a preferred embodiment of the invention that the mix chamber (i.e. the straight portion of the tubing downstream of the nozzles) does not exceed 6 times the tubing diameter.

The optimal nozzle angle depends on geometrical parameters of the system, particularly the ratio between the cross-sectional area of the nozzles and the cross-sectional area of the tubing. The optimal nozzle angle therefore needs to be determined separately for each application ol the invention. Experience shows that particularly good results are obtained with a nozzle angle, i.e. the angle between each of the nozzles and the longitudinal axis of the tubing, in the range 8 to 25 degrees, which therefore constitutes a preferred embodiment of the invention. Often the optimal nozzle angle is within the range 13 to 18 degrees. In this range the shortest possible mix zone is obtained and this thus constitutes a particularly preferred embodiment of the present invention.

Claims

1. An ejector comprising a tubing (2) for transporting material from a tubing inlet to a tubing outlet, with an ejector nozzle connected externally in relation to said tubing and with an angle of incline ("nozzle angle") relative to a longitudinal axis of the tubing (2) in a plane common with said longitudinal axis of the tubing, characterized in that the ejector comprises two or more nozzles (3,, 3₂) arranged substantially symmetrically around the tubing (2) periphery.

2. Ejector as claimed in claim 1 , characterized in that it comprises two ejector nozzles with approximately equal nozzle angles relative to the tubing (2), said nozzles providing mutually equal forces (rate of powering fluid) and being mutually displaced 180 ° relative to each other around the tubing (2) periphery.

3. Ejector as claimed in claim 1, characterized in that it comprises three ejector nozzles ( 3,, 3₂, 3₃) with equal nozzle angles relative to the tubing (2), said nozzles providing mutually equal forces (rate of powering fluid) and being mutually displaced 120 ° relative to each other around the tubing (2) periphery.

4. Ejector as claimed in claim 1, characterized in that it comprises four ejector nozzles ( 3,, 3₂, 3₃, 3₄) pairs of each having equal nozzle angles relative to the tubing (2), said nozzles providing mutually equal forces (rate of powering fluid) and being mutually displaced 90 ° relative to each other around the tubing (2) periphery.

5. Ejector as claimed in claim 1, characterized in that it comprises five or more ejector nozzles with approximately equal nozzle angles relative to the tubing (2).

6. Ejector as claimed in any one of the preceding claims, characterized in that the ejector nozzles ( 3,, 3₂, ..) each has a nozzle angle in the range between 8 and 25 degrees relative to the axis of the tubing (2).

7. Ejector as claimed in any one of the preceding claims, characterized in that the ejector nozzles ( 3,, 3₂, ..) each has a nozzle angle in the range between 13 and

18 degrees relative to the axis of the tubing (2).

8. Ejector as claimed in any one of the preceding claims, characterized in that the tubing downstream of the nozzles ( 3,, 3₂, ..) has the shape of a linear mix chamber with a length not exceeding six times the tubing (2) diameter.