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:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       REFERENCE TO A “SEQUENCE LISTING” 
       [0003]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0004]     1. 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.  
         [0006]     2. Description of Related Art  
         [0007]     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.  
         [0008]     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.  
         [0009]     As seen in  FIG. 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.  
         [0010]     Generally, the ejector converts pressure energy, for example, a motive stream, into kinetic energy (velocity). Referring to  FIG. 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  FIG. 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.  
         [0011]     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.  
         [0012]     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  
       [0013]     The present ejector provides a compressible gas ejector with an improved motive gas mass flow to load mass gas flow ratio.  
         [0014]     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.  
         [0015]     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.  
         [0016]     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)  
       [0017]      FIG. 1  is a cross-sectional view of a prior art steam ejector.  
         [0018]      FIG. 2  is a cross-sectional view of the present ejector.  
         [0019]      FIG. 3  is a cross sectional view of a regulator for controlling flow through the motive funnel.  
         [0020]      FIG. 4  is a cross sectional view of an alternative regulator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Referring to  FIG. 2 , the present compressible gas ejector  10  is shown. For purposes of description, a motive gas  12  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.  
         [0022]     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.  
         [0023]     As seen in  FIG. 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.  
         [0024]     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.  
         [0025]     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 .  
         [0026]     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  12  to the load gas  14 .  
         [0027]     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 .  
         [0028]     The motive funnel  20  is selected to provide substantially unexpanded motive gas  1   2  at the exit port  24 . Thus, the particular convergence within the motive funnel  20  is at least partially determined by the intended operating parameters.  
         [0029]     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°.  
         [0030]     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.  
         [0031]     In selected configurations as seen in  FIG. 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  12  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 ejector  10 , thereby maintaining efficiency of the ejector.  
         [0032]     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  FIG. 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=√ {square root over (0.008)}(x) . In an alternative configuration, the spike  36  defines a conical cross-section, as seen in  FIG. 4 .  
         [0033]     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.  
         [0034]     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  12  increases, with the downstream end of the motive funnel  20  remaining within the length of the converging section of the diffuser.  
         [0035]     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.  
         [0036]     As seen in  FIG. 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.  
         [0037]     Therefore, a flow path of the motive gas  12  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  12  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.  
         [0038]     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 .  
         [0039]     Further, it has been found that the motive funnel  20  can discharge the motive gas  12  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 .  
         [0040]     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.