GB2155106A

GB2155106A - Steam ejector

Info

Publication number: GB2155106A
Application number: GB08405264A
Authority: GB
Inventors: Shigeru Mitsuoka
Original assignee: Chlorine Engineers Corp Ltd
Current assignee: ThyssenKrupp Uhde Chlorine Engineers Japan Ltd
Priority date: 1984-02-29
Filing date: 1984-02-29
Publication date: 1985-09-18
Also published as: GB8405264D0

Abstract

A steam ejector 1 comprises a jet nozzle 8 that diverges toward the end thereof, through which working steam is ejected into a suction chamber to produce high-speed working steam, and a diffuser 17 with a throat section 18 connected to the suction chamber, through which diffuser the working steam and entrained gas to be extracted at inlet 13 are passed to obtain a high vacuum. Means for separating mist from the working steam is provided in the diverging part of the jet nozzle in the form of the angularly spaced vanes determinating in projections 11. Means for removing the separated mist from the system is also provided, in the form of outlet 15 for a supplied coolant liquid. Other mist-separating means, comprising mechanical incorporations, and/or coolant liquid supply and contact means, can be utilised if located at or between throat 6 of the nozzle and the inlet region of the diffuser. <IMAGE>

Description

SPECIFICATION Steam Ejector This invention relates to steam ejectors.

Asteam ejectorisa device for extraction of gases or vapours by suction. It generally comprises a nozzle blowing working steam at high speed across a suction chamber and into the throat of a diffuser outlet, thereby to entrain gases in the chamber by the high speed steam and reduce the pressure in the chamber and in.a suction duct connected thereto.

Steam ejectors have been used for many years as steam or vapour pumps, and nowadays multi-stage steam ejectors are widely used in the extraction of corrosive steam and gases at a high temperature in petroleum refinery, the deodorizing of edible oil, -synthetic fiber manufacture and the like.

As described more fully below, a problem with steam ejectors is steam mist (water vapour and/or droplets of water carried in, or formed in, the working steam) which represents a burden on the operation of the ejector and thus increases the amount of working steam needed per unit of time to rriaintain a given level of vacuum.

The present invention sets out to provide a steam ejector capable of high working efficiency in which steam mist is separated from the working steam and removed. For the same performance, therefore, the steam ejector of the present invention requires less working steam than a conventional one per unit of time.

The invention according consists in a steam ejector of the type which comprises a suction chamber; a jet nozzle for supplying working steam, from a nozzle throat and thence via a diverging portion, across at least part of the chamber; a diffuser for receiving the jet of working steam into a tapering portion thereof opposite the jet nozzle; and an inlet into the chamber for gas to be entrained in the flow of working steam; further comprising (a) means for separating mist from the working steam, located at a position from the jet nozzle throat to the diffuser inlet and (b) means for removing the separated mist from the ejector.

The invention will be further described with reference to the accompanying drawings, in which: Figure lisa longitudinal cross-section of a conventional steam ejector; Figure 2 is a longitudinal cross-section through the main parts of the ejector of a first embodiment of the present invention; Figure 3 is a section taken along the line Ill-Ill of Figure 2; Figure 4 is an exploded perspective view of the jet nozzle shown in Figure 2; Figure 5 is a longitudinal cross-section of a second embodiment of the invention, and shows a steam ejector pointing downwards; Figure 6 is a longitudinal cross-section of a third embodiment of the invention, and shows a steam ejector pointing upwards; and Figure7 is an enlarged longitudinal cross-section of the jet nozzle used in a forth embodiment of steam ejector according to the invention.

Figure 1 shows a conventional steam ejector. In this ejector, working steam (usually at 3-15 kg/ cm2G) is ejected from a jet nozzle A that broadens toward its end. The working steam reaches critical speed (that is, the speed of sound) as it passes through a throat section B, and then passes through a section C that broadens toward its end. Pressure energy is completely converted into kinetic energy.

The steam is ejected into suction chamber D at supersonic speed. This steam at supersonic speed entraps gases in the suction chamber and the mixture of steam and gas passes into a tapering section F of a diffuser E, still at high speed. The speed of a mixture again becomes supersonic at a throat section G of the diffuser. When the mixture passes through the throat section G, the steam generates shock waves. Part of the kinetic energy in the working steam is converted into pressure energy by these shock waves. The mixture is then discharged from the diffuser.

The working steam entering the suction chamber generally has a moisture content of about 30%, if the suction vacuum is less than 10 mmHg (although this moisture content depends to a certain extent on the steam pressure and the moisture content before the steam enters nozzle A). This moisture is largely evident as steam mist and plays no active part in the extraction of gas, mixing with gas, or subsequent compression of steam. The moisture content thus effectively increases the quantity to be extracted, and should be subtracted from the energy input of the working steam.

In the steam ejector shown in Figure lithe working steam ejected from the throat section B of the nozzle A reaches the inner surface of the tapering section F of the diffuser E, as shown by broken lines in Figure 1. A large proportion of the mist in the working steam proceeds onward through diffuser E. The rest of the mist in the working steam aggregates or accumulates and runs back along the inner surface of the diffuser E tending to build up in the base of the suction chamber D.

The temperature of the mist depends on the vacuum used for suction. At a vacuum of 4 mm Hg it is 0 C, and at a vacuum of 1 mm Hg it would be about - 0 C. However, the temperature of the working steam and extracted gas can exceed 100"C.

The mist otherwise aggregating in the suction chamber D is in practice re-evaporated by the effect of the temperature of these adjacent flows of hot steam and gases.

Thus, in a conventional steam ejector the mist in the working steam is not removed before it reaches the outlet of the diffuser, and reduces the extraction efficiency accordingly making it necessary to use a larger volume of the working steam for unit of time for a given performance.

In the embodiment of Figures 2-4, a suction chamber 1 for the extraction of gases is defined within a horizontally-installed cylindrical main body 2 and having at one end a flange to which a nozzle mounting is connected. A working steam supply opening 5 is provided at one end of the nozzle 8 and is connected by a throat section 6 at the other end to a diverging section 7 which opens into the suction chamber 1. A plurality of mist-separating vanes 9, arranged radially and equidistantly, are held tightly in the section 7. Extensions 10 are provided at the ends of the vanes 9. Nozzle cap 12 engages by a thread with the outer circumference of the end of the jet nozzle 8. The nozzle cap 12 has a short cylindrical body with a plurality of radial projections at one end.The configuration of the inner end of the nozzle cap 12 is such as to accommodate the extensions 10 of the vanes 9.

In use, a device such as a drying device, distribution device, deodorising device or the like (not shown) which requires the use of a high vacuum is connected to downwardlyfacing inlet 13 for extracted gas.

Coolant water-supply port 14 and a coolant waterremoving port 15 are located at the top and bottom of the suction chamber respectively. A tapering section 18 of a diffuser 17 fits into a circular aperture 16 in the side surface of the suction chamber 1 opposite to the jet nozzle 8, being conventionally so dimensioned and located that the extension of the inner surface of the section 7 would reach the inner surface ofthetapering section 18.

In use high pressure working steam is supplied to the supply opening 5 and is ejected from the jet nozzle 8, and an aqueous calcium chloride brine ora solvent that dissolves water and has a freezing point of below 0 C (such as glycerin, ethylene glycol or the like) is supplied to the suction chamber 1 from the cooling liquid supply opening 14. The working steam reaches sonic speed as it passes through the throat section 6 of the jet nozzle 8. The pressure energy of the working steam is converted into kinetic energy as it passes through section 7 and is ejected into the suction chamber 1 at supersonic speed.

A considerable amount of mist is contained in the working steam.This mist comes into contact with the vanes 9 as the working steam passes through the section 7 and part of the mist attaches to the vanes. The mist runs into contact with the inner wall surface of the section 7 or the suction chamber 1, and aggregates. This aggregation is prompted by the fact that the ends of the vanes 9 and of the nozzle cap 12 project radially.

The aggregated mist collects at the bottom of the suction chamber 1. This aggregation of the mist that has not yet been aggregated is also promoted by the coolant, and this aggregation also collects at the bottom. The temperature of the aggregated mist is usually less than 0 C but because of the employment of a coolant that does not freeze at 0 C the mist is dissolved in the coolant and removed from the system through the outlet 15.

With this set-up, the gas capable of being extracted is thus increased by an amount equal to the mist that has been removed. As a practical result the reduction of the working steam per unit time for a given performance is attained.

In Figure 5 there is shown a jet nozzle 24 installed in the upper section of a suction chamber 21 so as to face downwardly. A screen 23 is located in the section of nozzle that diverges. The screen body 23 separates the mist, which arrives at the base of the chamber 21 as liquid. A liquid extraction tube 26 connected to a receiving tank 25 for the coolant liquid is provided at one side of the lower end of the suction chamber 21. A liquid-circulation and resupply tube 28 is connected to the receiving tank 25 so that the liquid in the receiving tank 25 can be circulated back into the suction chamber 21 by a circulation pump 27.

A gas inlet 29 for the gas to be extracted is connected at one side of the suction chamber 21.

The upper end of a tapering section 30 of a diffuser 33 (which consists of the tapering section 30, a throat section 31 and a diverging section 32) fits into a circular aperture in the base of the suction chamber 21. A plurality of flow control plates 34 each provided with several apertures 35 fit into the end of section 32.

When the working steam is supplied to the ejector of Figure 5, mist in the working steam first comes into contact with the screen. The speed of the working steam drops, and it aggregates on the inner walls of the section 22 and/or on the inner walls of the suction chamber 21. The aggregated mist runs down to collect in the base of the suction chamber 21. If a coolant (of calcium chloride solution, or of ethylene glycol or the like) is circulated from the liquid circulation and re-supply tube 28, a further proportion of the mist which has not come into contact with the screen 23 contacts the coolant and aggregates and collects with coolant in the base of the suction chamber 21. Coolant in which the mist is dissolved is removed by the extraction tube 26 into the receiving tank 25.The working steam, from which part of the mist has thus been removed in the suction chamber 21, creates and maintains a high vacuum by sucking in gas from the inlet 29.

Eventually, the steam is discharged to the atmosphere through the diffuser 33.

In practice there is a tendency for the speed of the working steam in the diverging section 32 is greater at the axis than at the inner wall surface. Back flow in the working steam is therefore liable to occur. In this actual embodiment, the working steam strikes flow-control plates 34 near the outlet of the diffuser 33 and the speed is made uniform across the diffuser so that as back-flow of the working steam occurs.

In Figure 6 a suction chamber 41 is formed as a cylindrical hollow body. A horizontal inlet pipe 42 for working steam is provided about halfway up one side of the suction chamber 41. This terminates in an upward facing jet nozzle 43. Coolant recovery tube 44 is provided at one side of the suction chamber 41, below the working steam inlet pipe 42.

The coolant thus can collect in the base of the suction chamber 41 (below the recovery tube 44) where a circulation pump 46 is provided. A diffuser 50 consists of the tapering section 47, a throat section 48 and a diverging section 49 fits at one end into the upper part of the suction chamber 41. An annular coolant chamber 51 surrounds the periphery of the tapering section 47, within the suction chamber 41, and circulation tube 52 connected the circulation pump 46 with the suction chamber 41 via chamber 5, and associated small apertures 53 in the tapering section 47. A gas inlet 54 is connected at a position generally as high as the jet nozzle 43, to one side of the suction chamber 41.

As before high-pressure working steam is supplied to the ejector of Figure 6 by the working steam inlet pipe 42 ejected as a high-speed flow at 43 into the suction chamber 41, and discharged from the diffuser 50 together with the extracted gas.

Mist in the working steam comes into contact with the coolant entering from the small apertures 53 fed from the annular cooling liquid chamber 51, and eventually collects in the base of the suction chamber 41. Excess of liquid eventually overflows from the coolant recovery tube 44.

In Figure 7, flange 65 is provided on a jet nozzle 64. This nozzle consists of a working steam supply opening 61, a throat section 62 and a section 63 that diverges towards its end. A cylindrical outer tube 67 which has an internal diameter larger than the external diameter of the jet nozzle 64, and an upper end which extends beyond the upper end of the jet nozzle 64, is mounted upright by auxiliary members located by flange 65. A mist extraction tube 66 is provided at a lower part of the cylindrical outer tube 67. A pair of grooves 69 are cut in the inner wall of the diverging section 63 and each groove 69 communicates with space between the outer tube 67 and nozzle 64 by means of an extraction aperture 70.

When working steam is supplied at opening 61 it is ejected at supersonic speeds into the diverging section 63 of the jet nozzle 64. The mist in the working steam enters the grooves 69 and aggregates therein, draining into the outer tube 67 through the extraction apertures 70, and being eventually removed from the system through the extraction tube 66.

Part of the mist that passes completely through the diverging section 63 comes into contact with the inner wall of the outer tube 67 above the jet nozzle 64 and aggregates as liquid which flows down the inner wall of the outer tube 67 to join the liquid removed from the system by the mist extraction tube 66.

In the embodiments described above, vanes are in some cases provided in, or in extension of, the diverging section of the jet nozzle, as a means of separating the mist in the working steam.

Alternatively or additionally the mist may be made to come into contact with coolant. Moreover, grooves or a screen may be provided in the jet nozzle. However, the invention is not limited to these embodiments and any means can be used for the aggregation of the mist.

The present invention removes mist from the working steam at the throat section of the nozzle; or between the throat section and the inlet of the diffuser; or (preferably) in the suction chamber. It does not reduce the efficiency of the gas extraction.

When ejectors of the present invention are employed, the volume of working steam required is less than that of a conventional ejectorforthesame performance.

Working Example A steam ejector as illustrated in Figures 2--4 was employed.

The total length of the jet nozzle was 50 cm (20 inches), that of the suction chamber was 80 cm (32 inches) and that of the diffuser was 270 cm (108 inches). A screen-like body having ten vanes was provided in the diverging section of the jet nozzle.

The inside diameter of the throat section of the diffuser was 4.5 mm (0.18 inch). Steam was supplied to the working steam supply opening and a gauge pressure of 8 kg/cm2G and calcium chloride brine was supplied to the suction chamber. The supply volume of the working steam was adjusted so that the internal vacuum was 5 mmHg, and the external vacuum at the diffuser outer was 75 mmHg. The supply rate of the working steam used was 4.0 t/hr, the discharge rate of the extracted air was 10 kg/hr and the discharge rate of mist was 0.40 t/hr.

The same operation was carried out twice more.

The respective rates of working steam supply and mist discharged were 3.5 t/hr, 0.456 t/hr; and 3.1 t/hr, 0.56 t/hr.

The same operation was further carried out (not in accordance with the invention) by employing the above ejector but without the screen body or the coolant water supply. The supply rate of working steam necessary to obtain 5 mmHg vacuum was 5.1 t/hr.

Claims

1. A steam ejector of the type which comprises a suction chamber; a jet nozzle for supplying working steam, from a nozzle throat and thence via a diverging portion, across at least part of the chamber; a diffuser for receiving the jet into a tapering portion thereof opposite the jet nozzle; and an inlet into the chamber for gas to be entrained in the flow of working steam: further comprising (a) means for separating mist from the working steam, located at a position from the jet nozzle throat to the diffuser inlet and (b) means for removing the separated mist from the ejector.

2. A steam ejector as claimed in Claim 1, wherein the jet nozzle and diffuserwre aligned horizontally.

3. A steam ejector as claimed in Claim 1, wherein the jet nozzle and the diffuser are aligned vertically with the jet nozzle pointing downwards.

4. A steam ejector as claimed in Claim 1, wherein the jet nozzle and the diffuser are aligned vertically into the jet nozzle pointing upwards.

5. A steam ejector as claimed in Claim 1, wherein the means for separating the mist from the working steam is a screen or like body across the working steam passage in the nozzle whereby the mist is made to condense by coming into contact with the screen body.

6. A steam ejector as claimed in Claim 5, wherein the screen or like body is formed as a plurality of angularly spaced vanes held at least within the diverging section of the jet nozzle.

7. A steam ejector as claimed in any one preceding Claim wherein the means for separating the mist from the working steam comprises a coolant supply circuit such as to permit the mist to come into contact with the coolant liquid.

8. A steam ejector as claimed in Claim 7, wherein the circuit is suitable to supply a coolant solvent for water with a freezing point below 0 C.

9. A steam ejector as claimed in Claim 7, wherein the jet nozzle points upwards; the base of the suction chamber is such as to hold å supply of coolant; an annular coolant liquid chamber is provided around the lower periphery of the diffuser, within the suction chamber; small apertures are pierced in the lower end of the diffuser to communicate with the annular chamber; and liquid means are located to transfer liquid from the base of the suction chamber to the annular chamber so that it passes th rough the apertures to contact working steam entering the diffuser and remove mist therefrom.

10. A steam ejector as claimed in any one preceding Claim, wherein circumferential grooves are provided in the inner wall of the diverging section of the jet nozzle and wherein extraction apertures are provided to communicate with the grooves through the nozzle wall to remove mist aggregating in the said grooves.

11. A steam ejector as claimed in any one preceding Claim, wherein one or more flow control plates with a plurality of apertures are provided within the diverging section of the diffuser.

12. A steam ejector as claimed in Claim 1 and substantially as herein described with reference to Figures 2 to 7 of the accompanying drawings.