Abstract: The invention relates to a device for separating a flowing medium mixture into at least two fractions with differing mass density. The device comprises an inlet for the medium mixture to be separated, which connects to first separating means for separating the flowing mixture in at least a first and a second fraction, and that connect to first and second outlet means for discharging the first and second fractions. The device further comprises a feedback loop comprising second separating means between the second outlet means and the inlet means of the first separating means. The invention also relates to a method for separating a flowing medium mixture into at least two fractions with differing mass density, using the claimed device. The device and method allow to obtain a more selective separation, particularly in purifying natural gas.

Abstract: The present invention is directed to a method and a system for separating oxygen from air. A compressible air stream that contains oxygen is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which oxygen is capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the oxygen is absorbed from other compressible components of the air stream. The compressible air stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: The present invention is directed to a method and a system for separating hydrogen or helium from gas having a mixture of gaseous components. A compressible feed stream that contains at least one target compressible component and hydrogen or helium is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which the target component(s) is/are capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the target component is absorbed from a compressible product stream containing the hydrogen or helium. The compressible feed stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: The invention relates to cryogenic engineering. The inventive device for liquefying and separating gas and for releasing one or more gases from a mixture thereof, comprises, in series axially positioned, a prechamber (1) with gas flow whirling means (2) arranged therein, a subsonic or supersonic nozzle (3) with a working segment (4), which is abutted thereto and to which liquid phase extracting means (5) is connected, and a subsonic diffuser (7) or the combination of a supersonic (6) and the subsonic diffuser (7). The length of the working segment (4) is selected according to a condition of forming condensate drops with a size greater than 0.5 mkm and of drifting them, by centrifugal forces, from the axial area of the working segment to the walls of the drop extracting means. The device is provided with an additional nozzle (8) arranged in the prechamber. The invention makes it possible to increase the separation efficiency.

Abstract: High molecular weight (HMW) gases are separated from an exhaust gas of a combustion source using a blower and an interior vent within the exhaust stack. The interior vent includes a vent wall having a top portion attached to the interior surface of the exhaust stack along the entire inner perimeter of the exhaust stack and a lower portion that extends downward into the exhaust stack to form an annular space or gap between the vent wall and the interior surface of the exhaust stack, and at least one opening in the interior surface of the exhaust stack between the top and bottom portions of the vent wall. The blower creates a tangential flow of the exhaust gas with sufficient centrifugal force to concentrate substantially all of the HMW gases along the inner surface of the exhaust stack. A transfer pipe removes the HMW gases from the interior vent.

Abstract: The invention relates to a separation system comprising a flow inlet (16). The separation system comprises a swirl valve (100), arranged to receive and control the flux of a fluid flow via the flow inlet (16) and to generate a swirling flow, swirling about a central axis (11). The separation system further comprises a separation chamber (40) positioned downstream with respect of the swirl valve (100) to receive the swirling flow from the swirl valve (100), wherein the separation chamber (40) comprises a first and second flow outlet (41, 42). The first flow outlet (41) is positioned to receive an inner portion of the swirling flow and the second outlet (42) is positioned to receive an outer portion of the swirling flow.

Abstract: High molecular weight (HMW) gases are separated from an exhaust gas of a combustion source using a blower and an interior vent within the exhaust stack. The interior vent includes a vent wall having a top portion attached to the interior surface of the exhaust stack along the entire inner perimeter of the exhaust stack and a lower portion that extends downward into the exhaust stack to form an annular space or gap between the vent wall and the interior surface of the exhaust stack, and at least one opening in the interior surface of the exhaust stack between the top and bottom portions of the vent wall. The blower creates a tangential flow of the exhaust gas with sufficient centrifugal force to concentrate substantially all of the HMW gases along the inner surface of the exhaust stack. A transfer pipe removes the HMW gases from the interior vent.

Abstract: The present invention is directed to low emission power plant. A compressible feed stream is provided that is derived from a power production unit, where the compressible feed stream contains at least one target compressible component and at least one non-target compressible component, is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which the target component(s) is/are capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the target component is absorbed from a compressible product stream containing the non-target compressible component(s). The compressible feed stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: A process and apparatus for separating a gas mixture comprising providing a slot in a gas separation channel (conceptualized as a laterally elongated Clusius-Dickel column), having a length through which a net cross-flow of the gas mixture may be established; applying a higher temperature to one side of the channel and a lower temperature on an opposite side of the channel thereby causing thermal-diffusion and buoyant-convection flow to occur in the slot; and establishing a net cross-flow of a gas mixture comprising at least one higher density gas component and at least one lower density gas component along the length of the slot, wherein the cross-flow causes, in combination with the convection flow, a spiraling flow in the slot; and wherein the spiral flow causes an increasing amount of separation of the higher density gas from the lower density gas along the length of the channel. The process may use one or more slots and/or channels.

Abstract: A separation system including a source of a gaseous mixture, the gaseous mixture comprising at least a first constituent and a second constituent, and a separation unit in communication with the source to receive the gaseous mixture and at least partially separate the first constituent from the second constituent, wherein the separation unit comprises at least one of a vortex separator and a pressure vessel.

Abstract: A process and apparatus for separating a gas mixture comprising providing a slot in a gas separation channel (conceptualized as a laterally elongated Clusius-Dickel column), having a length through which a net cross-flow of the gas mixture may be established; applying a higher temperature to one side of the channel and a lower temperature on an opposite side of the channel thereby causing thermal-diffusion and buoyant-convection flow to occur in the slot; and establishing a net cross-flow of a gas mixture comprising at least one higher density gas component and at least one lower density gas component along the length of the slot, wherein the cross-flow causes, in combination with the convection flow, a spiraling flow in the slot; and wherein the spiral flow causes an increasing amount of separation of the higher density gas from the lower density gas along the length of the channel. The process may use one or more slots and/or channels.

Abstract: A cyclonic fluid separator has a tubular housing (10) in which the fluid is accelerated and swirl imparting means (2) for inducing the fluid to swirl through an annular space between the housing and a central body (1) mounted within the housing (10), wherein a low pressure fluid (80) is injected through a central opening (82) in the central body (1).

Abstract: Devices for separating dispersed particles from gases or vapors by centrifugal force are disclosed. The vortex tube comprises a body, an inlet duct, outlet ducts for the cold and hot gases, a liquid discharge duct, and a power separator. The inlet duct has a device for the introduction of methanol. The body comprises a vortex generator at the inlet duct. The body comprises a separator and a diaphragm with an inner conical surface, both defining an annular channel. The surface of the streamlined end of the separator comprises flutes. The separator is mounted to be capable of moving along the axis of the body and is pressed against the diaphragm by a spring. The inner portion of the body and the outer portion of the separator define a liquid chamber. A vortex reducer having a cross shape is mounted on the end of the power separator opposite the body.

Abstract: The invention relates to a cyclonic separator comprising a throat portion (4) arranged between a converging fluid inlet section and a diverging fluid outlet section, to generate a swirling fluid flow in a downstream direction. The diverging fluid outlet section comprises an inner primary outlet (7) for condensables depleted fluid components and an outer secondary outlet for condensables enriched fluid components (6). The cyclonic separator comprises a volute diffuser (9, 9?) connected to one of the outlets (6, 7), which comprises a volute outlet duct (90, 90?) defined by a volute axis (I1), forming a spiral shape around the central axis (I). The outlet duct (90, 90?) comprises a vortex chamber 95. The vortex chamber is provided to transform axial momentum of the swirling fluid flow with respect to the central axis (I) into tangential momentum with respect to the volute axis (I1).

Abstract: The invention relates to fluid separator comprising:—a throat portion (4) which is arranged between a converging fluid inlet section and a diverging fluid outlet section, the diverging fluid outlet section comprising an inner primary outlet (7) for condensables depleted fluid components and an outer secondary outlet for condensables enriched fluid components (6); and—a central body (10) provided upstream of the throat portion (4) in the fluid inlet section, the central body (10) being arranged substantially coaxial to a central axis I of the fluid separator. The fluid separator is arranged to facilitate a main flow through the converging fluid inlet section, the throat portion towards the diverging fluid outlet section. The central body (10) comprises an outlet (13), directed towards the tubular throat portion (4) and is arranged to add a central flow towards the throat portion (4).

Abstract: An apparatus and method for providing a hydrogen rich gas stream at a high pressure for use by hydrogen vehicles or other devices requiring hydrogen rich feed streams are disclosed in the present invention. As the pressure of gaseous hydrogen is increased, the temperature of the gaseous hydrogen also increases due to the heat of compression. The apparatus and method of the present invention utilize localized cooling via a vortex tube to cool the gaseous hydrogen caused by the increase in pressure.

Abstract: High molecular weight (HMW) gases are separated from an exhaust gas of a combustion source using a blower and an interior vent within the exhaust stack. The interior vent includes a vent wall having a top portion attached to the interior surface of the exhaust stack along the entire inner perimeter of the exhaust stack and a lower portion that extends downward into the exhaust stack to form an annular space or gap between the vent wall and the interior surface of the exhaust stack, and at least one opening in the interior surface of the exhaust stack between the top and bottom portions of the vent wall. The blower creates a tangential flow of the exhaust gas with sufficient centrifugal force to concentrate substantially all of the HMW gases along the inner surface of the exhaust stack. A transfer pipe removes the HMW gases from the interior vent.

Abstract: The invention relates to a device for separating a flowing medium mixture into at least two fractions with differing mass density. The device comprises an inlet for the medium mixture to be separated, which connects to first separating means for separating the flowing mixture in at least a first and a second fraction, and that connect to first and second outlet means for discharging the first and second fractions. The device further comprises a feedback loop comprising second separating means between the second outlet means and the inlet means of the first separating means. The invention also relates to a method for separating a flowing medium mixture into at least two fractions with differing mass density, using the claimed device. The device and method allow to obtain a more selective separation, particularly in purifying natural gas.

Abstract: The present invention is directed to a method and a system for separating oxygen from air. A compressible air stream that contains oxygen is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which oxygen is capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the oxygen is absorbed from other compressible components of the air stream. The compressible air stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: The present invention is directed to a method and a system for separating hydrogen or helium from gas having a mixture of gaseous components. A compressible feed stream that contains at least one target compressible component and hydrogen or helium is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which the target component(s) is/are capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the target component is absorbed from a compressible product stream containing the hydrogen or helium. The compressible feed stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: The present invention is directed to low emission power plant. A compressible feed stream is provided that is derived from a power production unit, where the compressible feed stream contains at least one target compressible component and at least one non-target compressible component, is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which the target component(s) is/are capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the target component is absorbed from a compressible product stream containing the non-target compressible component(s). The compressible feed stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: The present invention is directed to a method and a system for separating gas components of a combustion gas. A compressible feed stream derived from a combustion gas that contains at least one target compressible component and at least one non-target compressible component is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which the target component(s) is/are capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the target component is absorbed from a compressible product stream containing the non-target compressible component(s). The compressible feed stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: The present invention is directed to a method and a system for separating gas components of a gas containing a plurality of gaseous components. A compressible feed stream containing at least one target compressible component and at least one non-target compressible component is mixed in a substantially co-current flow with an incompressible fluid stream comprising an incompressible fluid in which the target component(s) is/are capable of being preferentially absorbed. Rotational velocity is imparted to the mixed streams, separating an incompressible fluid in which at least a portion of the target component is absorbed from a compressible product stream containing the non-target compressible component(s). The compressible feed stream may be provided at a stream velocity having a Mach number of at least 0.1.

Abstract: A cyclonic fluid separator has a tubular housing (10) in which the fluid is accelerated and swirl imparting means (2) for inducing the fluid to swirl through an annular space between the housing and a central body (1) mounted within the housing (10), which central body (1) is provided with resonance abatement means, such as: tensioning means (20,22) which apply a tension load to an elongate tail section (8) of the central body (1) such that the natural frequency of the central body (1) is increased; vibration dampening means (31,50,60), which inhibit vibration of at least part (8) of the central body (1); solid particles (31) arranged in a segmented tubular tail section (8) of the central body (1), a viscous liquid (50) arranged between a tubular tail section (8) of the central body (1) and a tensioning rod (51), apertures (60) drilled radially through a tail section (8) of the central body (1); and/or a low pressure fluid (80) injected through a central opening (82) in the central body (1).

Abstract: A mechanism configured to interact with air, which has been sucked through a device that imparts turbulence to the air, causes a redistribution of components (e.g., oxygen and nitrogen) in the air so that when the air arrives at a location where the oxygen is to be consumed there is an enriched supply of oxygen available. The effects of a first stage of turbulence of the induced air is reduced, resulting in a higher density supply to the atomization point and to the combustion chamber, in the case of an internal combustion engine.

Abstract: The present invention relates to a method and a plant for CO2 enrichment of a CO2 containing gas, such as an exhaust gas from an industrial plant or a thermal power plant, by means of serially connected centrifuges of cyclones. Enrichment of CO2 reduces the volume of the exhaust gas, increases the partial pressure of CO2 therein and makes a less expensive and more effective capture of CO2 possible. The invention also relates to plants for carrying out the method.

Abstract: A module mountable in the crankcase of a vehicle for removing gases therefrom including a housing having an opening communicable with the crankcase, a set of bearings disposed in such housing, a hollow shaft journaled in such bearing having first and second partitions providing first and second axially disposed chambers, cooperating with said housing to provide first and second annular chamber, such shaft having a passageway intercommunicating the first axial chamber and the first annular chamber, a passageway intercommunicating the first axial chamber and the second annular chamber and a passageway intercommunicating the second axial chamber and the second annular chamber, a spiral, centrifugal separator mounted on such shaft in the first annular chamber, and a pillar mounted on the shaft in the second annular chamber and means connectable to motive means for rotating such shaft.

Abstract: A rotary phase separator system generally includes a step-shaped rotary drum separator (RDS) and a motor assembly. The aspect ratio of the stepped drum minimizes power for both the accumulating and pumping functions. The accumulator section of the RDS has a relatively small diameter to minimize power losses within an axial length to define significant volume for accumulation. The pumping section of the RDS has a larger diameter to increase pumping head but has a shorter axial length to minimize power losses. The motor assembly drives the RDS at a low speed for separating and accumulating and a higher speed for pumping.

Abstract: The invention relates to a method for separating gas mixtures by means of an inventive gas centrifuge during which a compressible working fluid from an axial central supply tube (1) is introduced into the enlarging casing space (2) whereby passing through the flow channels (6) of the compression area (A) of a double-walled centrifuge rotor (3) and, in the axially distant area (B) inside the double tube, is guided in flow channels (6) having a constant flow cross-section (4) when in the centrifuged state. The flow of gas is separated into a specifically heavier and a specifically lighter gas fraction at a separating barrier (8) that is dependent on the individual gas volume portion. Inside the flow channels (6), the separated gas fractions are forcibly guided, slowed down and diverted in a separate manner with decreasing axial distance. The acceleration of the gas molecules in compression area (A) and the slowing down of the gas fractions in expansion area (C) ensue in a manner that is proportional to mass.

Abstract: A process in connection with a pipe (1) for transforming a dispersed gas/liquid flow into laminar stratified flow. The solution involves a first set of stationary guide blades (6) arranged in the pipe (1) and designed to rotate the liquid/gas flow. The pipe (1) is, in turn, connected to a second pipe (2) with the same or a different diameter and, in the transition between the pipe (1) and the second pipe (2), there is a second set of blades or a device (8) that is designed to stop the rotation of the gas. The natural flow pattern of the gas/liquid in the second pipe (2) then becomes stratified over a predefined distance.

Abstract: A mechanism configured to interact with air, which has been sucked through a device that imparts turbulence to the air, causes a redistribution of components (e.g., oxygen and nitrogen) in the air so that when the air arrives at a location where the oxygen is to be consumed there is an enriched supply of oxygen available. The effects of a first stage of turbulence of the induced air is reduced, resulting in a higher density supply to the atomization point and to the combustion chamber, in the case of an internal combustion engine.

Abstract: A compressor fuel gas conditioner for a natural gas well having a compressor which utilizes natural gas from the well as a fuel. The conditioner includes a vortex tube having an inlet to receive compressed natural gas from the compressor, a warm gas outlet for gas which has been heated by circular motion in the vortex tube, and a cool gas outlet for cool gas exiting the vortex tube after passing through the tube wherein the warm gas is returned to an inlet side of the compressor. A salt dryer includes a dryer inlet to receive the cool gas exiting the cool gas outlet of the vortex tube and a dryer outlet to deliver gas from the salt dryer as fuel gas to the compressor.

Abstract: The subject of the present invention is a method and a device for the separation of fuel-vapor/air mixtures into their components, in particular for purification of vapor mixtures, such as occur in fuel tanks of motor vehicles. A preseparator is arranged between the fuel tank and the filter. In the preseparator, the hydrocarbons are separated from the mixture and are supplied to the fuel tank again. The remaining mixture is supplied to the filter.

Abstract: An apparatus and method of removing a selected component from a stream of fluid containing a plurality of components is provided. The stream is induced to flow at supersonic velocity through a conduit so as to decrease the temperature of the fluid to below a selected temperature at which one of condensation and solidification of the selected component occurs, thereby forming particles of the selected component. The conduit is provided with a structure for imparting a swirling motion to the stream of fluid thereby inducing the particles to flow to a radially outer section of a collecting zone in the stream. A shock wave is created in the stream so as to decrease the axial velocity of the fluid to subsonic velocity, and to increase the swirling motion of the particles which are extracted into an outlet stream from the radially outer section of the collecting zone downstream of the shock wave.

Abstract: An apparatus for liquefying a gas has a nozzle having a convergent nozzle portion and a nozzle throat, and a divergent nozzle portion (in the case of supersonic flow), and a working section. Vanes or another mechanism for creating a swirl velocity are connected to the nozzle, to create a strong swirl velocity in gas fed to the nozzle. In the nozzle, the gas adiabatically expands, gas velocity increases and gas temperature drops, to promote the condensation of gas with formation of droplets. The gas then passes through a working section having a wall, whereby further condensation of at least a portion of the gas flow occurs and droplets of condensed gas grow. Centrifugal effects generated by the swirl velocity drive the droplets towards the wall of the working section. Condensed liquid gas droplets are separated from remaining gas in the gaseous state at least adjacent the wall of the working section.

Abstract: A method and apparatus are provided for removing solid particles from a particle containing stream of fluid, the method including the steps of: inducing the stream to flow at supersonic velocity through a conduit; inducing a swirling motion to the supersonic stream of fluid thereby causing the particles to flow to a radially outer section of a collecting zone in the stream; and extracting the solid particles into an outlet stream from the radially outer section of the collecting zone. The apparatus is an apparatus effective for performance of this method.

Abstract: A charged particle selector having first and second circular electrical mobility selector portions is shown to include directing portions for directing particles selected by the first circular electrical mobility selector to the input of the second circular electrical mobility selector. These selectors may be combined to be in parallel instead of in series. The charged particle selector can be used to make in-line measurement of the mass and/or density of aerosol particles, to make measurements of the size of the particles and/or their distribution as well as the distribution of aerosol electrical charges.

Abstract: The invention concerns a dynamic particle mobility selector comprising two separate and parallel coaxial disks (30, 32) defining a dynamic selection zone (31), the upper disk comprising an annular slit with radius r.sub.1 and a central suction intake (38) in order to circulate a laminar, centripetal and stable air flow in the dynamic selection zone. An annular opening (36) with average radius r.sub.2 <r.sub.1 may be provided in the lower disk (32). Application to a dynamic mobility spectrometer, to a device for measuring the particle size of an aerosol and a mono-dispersed aerosol generator.

Abstract: A fluid centrifuge device for separating fluids and/or solids comprises a non-rotatable containment vessel (6) and a rotatable shroud (6A) of conical or other form within said vessel (6). The vessel (6) is located between an inlet assembly (2) including a manifold (8) which leads to the interior of a tubing housing (14) of a turbocharger and an outlet assembly (4) including two outlets (10, 10A) for respectively clean and dirty gases. The shroud (6A) is mounted on a drive shaft (20) for rotation therewithin. The shaft (20) and the shroud (6A) are driven by turbine blades (16) or by other drive.

Abstract: An apparatus and method for separating chemical species of a mixture. A partially liquefied mixture having a mass fraction of less than 30% liquid is provided. This mixture is introduced in a tangential direction relative to and adjacent an inner surface of an elongated enclosure. The enclosure has a first end, an opposite second end, and a longitudinal axis. The inner surface has a substantially circular cross-section. The introduction of the mixture is at a sufficient velocity to form a vortex region in the enclosure. The vortex region contains at least two phases which interact. A first of the phases is a gas comprising a relative volatile chemical species, and the second of the phases is a relatively less volatile chemical species. The relatively volatile first gas phase exits from the first end of the enclosure and the relatively less volatile second phase exits from the second end of the enclosure. The present invention provides separation in an inexpensive, lightweight, low maintenance environment.

Abstract: Removal NO.sub.x and SO.sub.x from the flue gas utilizing a transport line adsorber through which sorbent is transported by pressurized flue gas to cause the sorbent to absorb NO.sub.x and SO.sub.x from the flue gas while the flue gas is transporting the sorbent particles through the transport line adsorber. A plurality of interconnected cyclones may be utilized to contact sorbent saturated with NO.sub.x and SO.sub.x removed from the flue gas with a heated gas to heat the sorbent and remove the NO.sub.x from the sorbent and separate the sorbent and the heated gas to produce an off stream of heated gas carrying the removed NO.sub.x away; the heated gas and gravity combine to pass the sorbent through the plurality of cyclones and which cyclones are positioned vertically and successively downwardly with respect to each other. A plurality of interconnected cyclones is also utilized to contact heated sorbent having the NO.sub.x and SO.sub.

Abstract: Removal of NO.sub.x and SO.sub.x from flue gas utilizing a transport line adsorber through which sorbent is transported by pressurized flue gas to cause the sorbent to adsorb NO.sub.x and SO.sub.x from the flue gas while the flue gas is transporting the sorbent through the transport line adsorber A plurality of interconnected cyclones is utilized to contact sorbent saturated with NO.sub.x and SO.sub.x removed from the flue gas with a heated gas to heat the sorbent and remove the NO.sub.x from the sorbent and separate the sorbent and the heated gas to produce an off stream of heated gas carrying the removed NO.sub.x away; the heated gas and gravity combine to pass the sorbent through the plurality of cyclones and which cyclones are positioned vertically and successively downwardly with respect to each other. A plurality of interconnected cyclones is also utilized to contact heated sorbent having the NO.sub.x and SO.sub.

Abstract: Novel aromatic polyimide, polyamide and polyamide-imide gas separation membranes and the process of using such membranes to separate one or more gases from a gaseous mixture is disclosed. The polyimides, polyamides and polyamide-imides are formed from diamines of the formula ##STR1## where Ar' is ##STR2## Q is nothing or an aromatic group and Z is independently alkyl groups having 1 to 10 carbon atoms, most preferably a tertiary butyl group, n is an integer from 0 to 4, preferably 1.

Abstract: By using AVLIS or other methods capable of providing a depleted isotopic mixture, troublesome isotopes such as Gd.sup.154, Gd.sup.156 and Er.sup.166 are selectively removed from naturally occurring isotopic mixtures, while avoiding the additional costs associated with complete fractionation of the mixture. Such mixtures can be used to provide a burnable nuclear fuel absorber having a selectively depleted isotope or isotopes. In particular, the invention concerns burnable absorbers containing erbium with a depleted 166 isotope, gadolinium with a depleted 156 isotope or with depleted 154 and 156 isotopes, and methods for making such absorbers.