Patent Application
20070025862
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1. Field of the Invention
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.
2. Description of Related Art
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.
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.
As seen in
Generally, the ejector converts pressure energy, for example, a motive stream, into kinetic energy (velocity). Referring to
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.
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.
The present ejector provides a compressible gas ejector with an improved motive gas mass flow to load mass gas flow ratio.
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.
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.
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.
Referring to
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.
As seen in
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.
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.
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.
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.
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.
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°.
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.
In selected configurations as seen in
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
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.
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.
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.
As seen in
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.
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.
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.
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.
