WO2007018648A2

WO2007018648A2 - Compressible gas ejector with unexpanded motive gas-load gas interface

Info

Publication number: WO2007018648A2
Application number: PCT/US2006/017033
Authority: WO
Inventors: David William Tice; Thomas H. Mcmahon
Original assignee: Graham Corporation
Priority date: 2005-07-28
Filing date: 2006-05-04
Publication date: 2007-02-15
Also published as: WO2007018648A3; US20070025862A1

Abstract

A compressible gas ejector is configured to present unexpanded motive gas to a load gas, wherein the interface of the unexpanded motive gas and the load gas can be located in a suction chamber or within a downstream diffuser. The ejector includes a motive funnel for increasing the velocity of a relatively high pressure motive gas, the motive funnel substantially precluding adiabatic expansion of the motive gas.

Description

TITLE OF THE INVENTION

[0001 ] COMPRESSIBLE GAS EJECTOR WITH UNEXPANDED MOTIVE GAS- LOAD GAS INTERFACE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] Not applicable.

REFERENCE TO A "SEQUENCE LISTING"

[0004] Not applicable.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0005] The present invention relates to ejectors, and more particularly to a compressible gas ejector having an unexpanded motive gas exposed to a load gas, wherein the interface of the unexpanded motive gas and the load gas can be located in a suction chamber or a downstream diffuser.

DESCRIPTION OF RELATED ART

[0006] Steam jet ejectors are employed in the chemical process industries, refineries as well as power generation plants, stills, vacuum deaerator evaporators, crystallizers, steam vacuum refrigeration, flack coolers, condensers, vacuum pan dryers, dehydrators, vacuum impregnators, freeze dryers and vacuum filters. The ejector provides a vacuum that can be applied, depending upon the design of the ejector, from relatively small loads to significant loads. Ejectors can also be used to evacuate air and/or combustion products in aerodynamic and combustion processes.

[0007] Ejectors can also be used to provide the vacuum (pressure below atmospheric) for the production of natural fats and oils and derivative oleochemicals. In addition, degumming, bleaching, interestification, fractionation, winterization and deodorization are often supported by ejectors.

[0008] As seen in Figure 1 , a prior art ejector includes a motive venturi, a suction chamber and a downstream diffuser. The motive venturi includes a converging section, a throat and a diverging section, wherein the suction chamber encompasses (and is thus fluidly exposed to) the open diverging end of the motive venturi. The suction chamber is fluidly exposed to a suction inlet and hence to a load gas and the diffuser. The diffuser is also a venturi and includes a converging section beginning in the suction chamber, a throat and a diverging section.

[0009] Generally, the ejector converts pressure energy, for example, a motive stream, into kinetic energy (velocity). Referring to Figure 1 , prior art steam ejectors 1 obtain the desired by velocity by the adiabatic expansion of the motive steam through a convergent and divergent section of the motive venture 3. As seen in Figure 1 , the velocity of the motive steam continually increases as the motive steam passes along the divergent section of the motive venturi. The motive steam is typically expanded to the pressure of the load gas. The high velocity motive steam then passes into a suction chamber 5. The resulting high velocity, motive steam is then retarded in the suction chambers while the load steam is accelerated in the suction chamber and forms a mixture.

[0010] The mixture passes through the converging section, the throat and the diverging section of a diffuser 7, wherein the high velocity is converted back into pressure. Thus, the mixture can be vented to atmospheric pressure, or additional ejectors can be employed to sufficiently raise the pressure to atmospheric pressure.

[001 1 ] In certain applications, it is advantageous for the ejector to remove a certain ratio of motive gas to load gas. Historically, in sub critical flows, the ejectors are only able to provide a motive mass flow to load mass flow ratio of approximately 2.0. However, certain applications can be provided with increased efficiency, if the ratio of motive mass flow to load mass flow is on the order of 1 .5. Therefore, the need exists for a compressible gas ejector that can reduce the ratio of motive gas mass flow to load gas mass flow. BRIEF SUMMARY OF THE INVENTION

[0012] The present ejector provides a compressible gas ejector with an improved motive gas mass flow to load mass gas flow ratio.

[001 3] In one configuration, the present compressible gas ejector provides for the direct contact of unexpanded motive gas with the load gas. Depending upon the particular construction, the interface between the unexpanded motive gas and the load gas can be located in the suction chamber or a converging section of the diffuser.

[0014] Contrary to prior teachings which suggest detrimental instability upon exposing unexpanded motive flow in the suction chamber, the present configuration provides stable mass flow rates, with the unexpanded motive gas directly mixing with the load gas.

[001 5] In a further configuration, the compressible gas ejector, includes a converging motive funnel, the motive funnel having a converging section being substantially free of a downstream diverging section; a suction chamber fluidly connected to the motive funnel; and a diffuser downstream of the suction chamber, the diffuser including a converging section and a downstream diverging section. In one configuration, a downstream end of the motive funnel is disposed within the converging section of the diffuser.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0016] Figure 1 is a cross-sectional view of a prior art steam ejector. [001 7] Figure 2 is a cross-sectional view of the present ejector.

[0018] Figure 3 is a cross sectional view of a regulator for controlling flow through the motive funnel.

[0019] Figure 4 is a cross sectional view of an alternative regulator.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Referring to Figure 2, the present compressible gas ejector 10 is shown. For purposes of description, a motive gas 1 2 is introduced into the ejector to draw a load gas 14 into the ejector so as to form a mixture 16, wherein the mixture exits the ejector 10 at a downstream location. The term "motive gas" 12 is intended to encompass any of a variety of motive flows including steam, vapor or other compressible flows, as well as mixtures thereof. The term "load gas" 14 is intended to encompass any of a variety of load gases such as, but not limited to process by-products, combustion products or other compressible flows, or mixtures thereof.

[0021 ] The ejector 10 includes a suction chamber, an upstream motive funnel 20 and a downstream diffuser 60, wherein the motive gas 12 passes through the motive funnel 20 and mixes with the load gas 14 from the suction chamber and is discharged through the diffuser.

[0022] As seen in Figure 2, the upstream motive funnel 20 and the downstream diffuser 60 extend along a longitudinal axis and are generally coaxial. As the suction chamber 40 encompasses a portion of the motive funnel 20 and interfaces with the diffuser 60, the suction chamber also includes a dimension extending along the longitudinal axis.

[0023] Therefore, for definitional purposes, a component or portion of the motive funnel 20 or the diffuser 60 can be described in terms of a "length" which is a dimension extending along the longitudinal axis. A width of a component is that dimension transverse to the longitudinal axis.

[0024] The suction chamber 40 includes a suction inlet 42 fluidly connected to the load gas 14, which is to be drawn into the ejector 10 and passed through the diffuser 60.

[0025] The converging motive funnel 20 is fluidly connected to a source of the motive gas such as steam from a turbine discharge. The motive funnel 20 includes an entrance port 22 and a downstream exit port 24, wherein the entrance port is larger than the exit port. A converging section 26 extends from the entrance port 22, and in selected configurations, terminates at the exit port 24. Thus, in contrast to prior ejectors, the present converging motive funnel 20 does not include a diverging portion, and thus presents unexpanded motive gas 1 2 to the load gas 14.

[0026] In other configurations, the motive funnel 20 can include a throat 30 downstream of the converging section 26, wherein the throat defines a substantially constant cross-section along the longitudinal axis and terminates at the exit port 24 of the motive funnel. Typically, the throat 30 of the motive funnel 20 will have a length that is less than the length of the converging section 26 of the motive funnel. In this construction, a downstream end of the throat 30 defines the exit port 24, and hence the downstream end of the motive funnel 20.

[0027] The motive funnel 20 is selected to provide substantially unexpanded motive gas 12 at the exit port 24. Thus, the particular convergence within the motive funnel 20 is at least partially determined by the intended operating parameters.

[0028] In one satisfactory configuration, the diameter of the entrance port 22 can be between approximately 1 .85 to 2.25 times the diameter of the exit port 24. The inlet diameter of the entrance port 22 of the converging section of the motive funnel 20 can be greater than the length of the motive funnel. Typical angles for the converging section of the motive funnel 20 are between approximately 35° and approximately 80°, with at least one satisfactory angle of approximately 60°.

[0029] It is understood the motive funnel 20, or the downstream end of the throat 30, can include a de minimis diverging taper 32, such as along a wall thickness of the funnel. That is, the exit port 24 can include a diverging flare on the order of less than 5% of the area of the exit port. However, such diverging taper 32 does not allow a material expansion of the motive gas. [0030] In selected configurations as seen in Figure 3, the motive funnel 20 includes a regulator 34 to effectively reduce the cross sectional area of the exit port 24 without changing pressure of the motive gas. The regulator 34 thus provides for the selective reduction in the amount of motive gas 1 2 passing through the motive funnel 20. In one configuration, the regulator 34 moves relative to the exit port 24 to effectively change the cross sectional area of the exit port. The regulator 34 is selected to substantially maintain the pressure drop along the ejectorl O, thereby maintaining efficiency of the ejector.

[0031 ] In one configuration of the regulator 34, the regulator includes a generally tapered spike 36 which can be moved along the longitudinal axis towards and away from the exit port 24 of the motive funnel 20. Referring to Figure 3, the spike 36 can be curvilinear such as parabolic. In one configuration of the parabolic spike 36, the curvature is defined by the relation Y = -70.008(X) . In an alternative configuration, the spike

36 defines a conical cross-section, as seen in Figure 4.

[0032] The diffuser 60 includes a converging section 62, a throat 64 and a diverging section 68. The converging section 62 includes an inlet 61 and a downstream outlet 63 coincident with the throat 64. In contrast to prior ejectors, the present diffuser converging section 62 has a length that is less than an inlet diameter of the converging section. In certain constructions, the inlet diameter of the converging section 62 is on the order of twice the length of the converging section 62. Functionally, the diameter of the inlet 61 and the length of the converging section 62 are selected to substantially maintain a steady state operation of the ejector 10 at the intended flow rates.

[0033] It is further contemplated, that in selected configurations, the diameter of the inlet 61 of the converging section 62 is at least 1 .5, and can be greater than twice the diameter of the outlet 63 (the throat 64 of the diffuser 60). As the inlet diameter of the converging section 62 increases, the interface area between the load gas 14 and the unexpanded motive gas 1 2 increases, with the downstream end of the motive funnel 20 remaining within the length of the converging section of the diffuser.

[0034] In certain constructions, the diverging section 66 of the diffuser 60 is longer than the converging section 62 of the diffuser, wherein the diverging section can be at least twice the length of the converging section.

[0035] As seen in Figure 2, the exit port 24 of the motive funnel 20 is disposed within the inlet of the converging section 62 of the diffuser 60. That is, as the converging section 62 of the diffuser 60 extends along the longitudinal dimension, the exit port 24 is located within the same length of the longitudinal dimension. The amount of penetration of the motive funnel 20 into the converging section 62 of the diffuser 60 can range from approximately 1 % of the length of the converging section to approximately 50% of the length of the converging section. [0036] Therefore, a flow path of the motive gas 1 2 passes through the motive funnel 20 and the exit port 24, to then enter the converging section 62 of the diffuser 60. Load gas 14 is drawn in through the suction inlet 42 and mixes with the motive gas 1 2 in the converging section 62 of the diffuser 60 to form the entrained mixture 16, wherein the entrained mixture passes through the diffuser 60 and increases pressure.

[0037] It has been found advantageous to employ the present ejector 10 in a sub critical flow regime. That is, the pressure of the motive gas 12 is less than twice the pressure of the load gas 14.

[0038] Further, it has been found that the motive funnel 20 can discharge the motive gas 1 2 into the suction chamber 40, or the converging section 62 of the diffuser 60 at a pressure that is lower than the load gas 14.

[0039] While the invention has been described in connection with a presently preferred embodiment thereof, those skilled in the art will recognize that many modifications and changes may be made therein without departing from the true spirit and scope of the invention, which accordingly is intended to be defined solely by the appended claims.

Claims

CLAIM OR CLAIMS

1 . A compressible gas ejector system, comprising:

(a) a converging motive funnel, the motive funnel including a converging section and being substantially free of a downstream diverging section;

(b) a suction chamber fluidly connected to the motive funnel; and

(c) a diffuser downstream of the suction chamber, the diffuser including a converging section and a downstream diverging section.

2. The system of Claim 1 , wherein the motive funnel is selected to present substantially unexpanded motive gas to the suction chamber.

3. The system of Claim 1 , wherein the motive funnel is selected to present substantially unexpanded motive gas to the diffuser.

4. The system of Claim 1 , further comprising a load gas fluidly connected to the suction chamber, a pressure of the load gas being greater than approximately one half a pressure of the motive gas.

5. The system of Claim 1 , wherein a pressure of a motive gas passing from the motive funnel is less than a pressure of a load gas in the suction chamber.

6. A method of operating a compressible gas ejector, comprising:

(a) expressing an unexpanded motive gas into a converging section of a downstream diffuser to form an entrained flow.

7. The method of Claim 6, further comprising passing the motive gas through an upstream motive funnel and maintaining a pressure of the motive gas upstream of the motive funnel less than approximately twice a pressure of a load gas.

8. The method of Claim 6, further comprising providing a ratio of motive gas flow rate to a load gas flow rate of approximately 1 .5 or less.

9. A compressible gas ejector fluidly connected to a load gas, comprising:

(a) a motive funnel consisting essentially of a converging portion and a throat to expose a substantially unexpanded motive gas flow to the load gas.

10. The ejector of Claim 9, further comprising a downstream diffuser having a converging section, the motive nozzle throat located within the converging section of the diffuser.

1 1 . A compressible gas ejector, comprising:

(a) a diffυser having a converging section and a downstream diverging section, the converging section having an inlet diameter greater than a length of the converging section.

1 2. A method of operating a compressible gas ejector, comprising:

(a) passing a flow mixture including a motive gas and a load gas through a diffuser, the diffuser having a converging section with an inlet diameter less than a length of the converging section.

1 3. A compressible gas ejector for compressing a load gas to a higher pressure, the ejector comprising:

(a) a motive funnel having a converging portion and an exit port; and

(b) a downstream diffuser having a converging section, the exit port located within the converging section.

14. A compressible gas ejector, comprising:

(a) a diffuser having a converging section, the converging section having an inlet; and

(b) a motive funnel upstream of the diffuser, the motive funnel having an exit port sized to introduce unexpanded motive gas into the inlet.

1 5. The ejector of Claim 14, wherein the exit port is within the inlet.