Gas separation: processes – Sound waves used
Reexamination Certificate
2001-11-14
2003-02-25
Smith, Duane S. (Department: 1724)
Gas separation: processes
Sound waves used
C096S389000
Reexamination Certificate
active
06524368
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to separation of one or more selected components from a stream of fluid containing a plurality of components. More particularly the invention relates to apparatus and methods for removal of selected components from a fluid stream by decreasing the temperature of the fluid to below a selected temperature at which one of condensation and solidification of the selected components occurs thereby forming particles of the selected components, and separating the particles from the stream. Such separation apparatus and methods have application in various processes, for example in drying and removal of nitrogen from natural gas, removal of noxious components from flue gas, in air-conditioning (water removal), and in concentrations or enriching vapors in front of condensors.
BACKGROUND OF THE INVENTION
Numerous methods and apparatus exist for separating components from a fluid flow containing gases, liquids and/or solids. Conventional separation apparatus include distillation columns, filters and membranes, settling tanks, centrifuges, electrostatic precipitators, dryers, chillers, cyclones, vortex tube separators, and adsorbers. There are disadvantages associated with each of these conventional apparatus which make them undesirable for certain applications.
For example, distillation columns, electrostatic precipitators and dryers are generally large in size, have long residence times, and require high energy input. In addition, these devices are relatively ineffective in separating gaseous mixtures.
Filtration and membrane separation of solid particles from a fluid includes the removal of particles from the fluid by use of a filter or membrane specifically tailored to remove particles from the fluid while allowing the fluid to pass through the filter or membrane. Thus, filters and membrane separation requires that the membrane, filter cake or other similar filtration aid be regenerated or discarded after separation adding increased costs to the process. Additionally, filters and membranes have a long residence time. Settling tanks also have a long residence time and often require additional treatment, such as filtration or centrifugation.
Centrifuges and cyclones both use centrifugal force to achieve separation. Centrifugal separators can achieve separation of immiscible or insoluble components from a fluid medium; however, centrifugal separators require mechanical acceleration of up to 20,000 G. The mechanical parts and energy needed to achieve these velocities make centrifugal separators costly to operate to effectively remove components from a fluid. Cyclones are used to separate gaseous components from gas-liquid fluid flows by way of turbulent vortex flow. Vortices are created in a fluid flow so that heavier particles and/or liquid droplets move radially outward in the vortex, thus becoming separated from gaseous components. Considerable external energy must be added to cyclones to achieve effective separation.
Apparatus and processes exist for creating droplets from a fluid, which are then separated from the fluid. Examples of such apparatus include chillers, throttling valves, turboexpanders and vortex tube separators. Chillers create droplets and may also create hydrates which can clog downstream flow systems.
A turboexpander is an apparatus which reduces the pressure of a feed gas stream. In so doing, useful work may be extracted during the pressure reduction. Furthermore, an effluent stream may also be produced from the turboexpander. This effluent may be passed through a separator or distillation column to separate the effluent into a heavy liquid stream. Turboexpanders utilize rotating equipment, which is relatively expensive. Such equipment requires a high degree of maintenance and, because of the moving parts, has a higher incidence of mechanical breakdown.
In addition, turboexpanders are poorly suited for certain applications, such as for feed gas streams with entrained water.
Vortex tube separators are devices for chilling gas by expansion. A gas is introduced into the vortex tube separator through a header across tangential inlet nozzles. The gas may reach near sonic velocity as it passes into the vortex tube. Condensation occurs during the near adiabatic expansion of the gas. The condensate is forced toward the outer wall of the vortex tube. Simultaneously, gas moves from the wall to the center of the tube. By removing the liquid phase from the tube wall it is possible to separate the gas and liquid phases. Vortex tube separators are not particularly efficient and the fluid flow is limited to subsonic velocities.
Japanese Patent Application No. 63-165849 refers to the separation of a gaseous mixture through the use of supersonic flow. The device includes a subsonic swirler positioned upstream of a supersonic nozzle. The swirling fluid stream passes through an axially symmetric expansion nozzle to reach supersonic velocity and form fine particles. In order to separate a component from the gas flow, a large upstream swirl must be initially provided by the swirler and a significant amount of energy therefore must be input to the system. The system undergoes a large pressure drop and an oblique shock wave occurs downstream after the separation.
U.S. Pat. No. 3,559,373 (Garrett) refers to a supersonic flow separator including a high pressure gas inlet, a rectangularly-shaped throat, and a U-shaped rectangular-cross sectional channel. The channel includes an outer curved permeable wall. A gas stream is provided to the gas inlet. The gas converges through the throat and expands into the channel, increasing the velocity to supersonic. The expansion of the flow in the supersonic region results in droplets which pass through the outer permeable wall and are collected in a chamber. The force available to separate out the droplets is dependent on the radius of the curvature of the channel. The radius of the curvature of the channel, however, must be limited to prevent undesirable shock waves. Therefore, the U-shaped configuration limits the force available for separating out liquid droplets from the flow stream. Further, liquid droplets are collected across only a limited area of the channel.
European Patent Publication No. 496,128 refers to a method and device for separating a gas from a gas mixture. The device includes a cylinder which converges to a nozzle. Gas enters an inlet port of the cylinder at subsonic speeds, flows through a converging section of the nozzle and then out of a diverging section at supersonic velocity. A pair of delta-shape plates arranged in the gas flow generate a vortex. The combination of the supersonic velocities and the vortex allow for condensation and centrifugal force to move a condensed component to an edge zone of the cylinder. An outlet pipe is positioned centrally within the cylinder to allow discharge of the gaseous components of the flow stream at supersonic velocity. The condensed component continues on through a second diverging section, which drops the velocity to subsonic, and through a fan, ultimately exiting the cylinder through a second outlet. The device includes some inherent flaws which inhibit its ability to effectively separate components. Specifically, the change in temperature experienced by the flow stream in the supersonic region over time is too great to grow large particles and therefore the gaseous component of the flow stream still contains substantial amounts of fine liquid particulates. Further, discharge of the gaseous components occurs at supersonic velocities, and thus no final controlled shock wave is utilized to assist in separation.
What is needed is a separation apparatus and method that provides high separation efficiency while avoiding or minimizing pressure drop, maintenance costs, and the need to supply external energy.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method to separate one or more selected components from a compressible fluid containing a plurality of components. The term “compressible fluid” herein shall be under
Betting M.
van Holten Th.
van Veen J. M. H. M.
Shell Oil Company
Smith Duane S.
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