Gas separation: apparatus – Solid sorbent apparatus – Plural solid sorbent beds
Reexamination Certificate
1999-12-16
2002-06-04
Hopkins, Robert A. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
Plural solid sorbent beds
C095S096000, C095S101000, C095S102000, C095S105000, C095S113000
Reexamination Certificate
active
06398853
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to centrifugal turbomachinery for use with gas separation systems. In particular, the present invention relates to split-stream centrifugal compressors, vacuum pumps and expanders in which the flow exiting or entering the centrifugal turbomachinery comprises multiple flows at different total pressures.
BACKGROUND OF THE INVENTION
Gas separation by pressure swing adsorption (PSA) is achieved by coordinated pressure cycling and flow reversals over an adsorbent bed which preferentially adsorbs a more readily adsorbed component relative to a less readily adsorbed component of the mixture. The total pressure is elevated during intervals of flow in a first direction through the adsorbent bed from a first end to a second end of the bed, and is reduced during intervals of flow in the reverse direction. As the cycle is repeated, the less readily adsorbed component is concentrated in the first direction, while the more readily adsorbed component is concentrated in the reverse direction.
Many prior art PSA systems have low energy efficiency, because feed gas for adsorber pressurization as well as for the high pressure production step is provided by a compressor whose delivery pressure is the highest pressure of the cycle. Energy expended in compressing the feed gas used for pressurization is then dissipated in throttling across valves over the instantaneous pressure difference between the adsorber and the high pressure supply. Similarly, in vacuum swing adsorption (VSA) where the lower pressure of the PSA cycle is established by a vacuum pump exhausting gas at that pressure, energy is dissipated in throttling over valves during countercurrent blowdown of adsorbers whose pressure is being reduced. A further energy dissipation occurs in throttling of light reflux gas used for purge, equalization, cocurrent blowdown and product pressurization or backfill steps. The energy dissipation in irreversible throttling becomes more important when such throttling takes place over larger pressure differences between an adsorber and a feed source or an exhaust sink.
Energy efficiency has been improved in more modern VSA air separation systems, by using feed compressors (or blowers) whose delivery pressure follows the instantaneous pressure of art adsorber being pressurized, and by using vacuum pumps whose suction pressure follows the instantaneous pressure of an adsorber undergoing countercurrent blowdown. In effect, the feed compressor rides each adsorber in turn to pressurize it with reduced throttling losses, and likewise the vacuum pump rides each adsorber in turn to achieve countercurrent blowdown with reduced throttling losses. In such systems, each feed compressor can only supply gas to a single adsorber at any time, and each vacuum pump can only exhaust a single adsorber at a time. The working pressure in each such feed compressor or vacuum pump will undergo large variations, stressing the machinery and causing large fluctuations in overall power demand. Further, compression efficiency is compromised by the unsteady operating conditions.
Since centrifugal or axial turbomachinery cannot operate under such unsteady conditions, rotary positive displacement machines are typically used in VSA systems. However, such machines have lower efficiency than modem centrifugal turbomachinery working under steady conditions, particularly for larger plant ratings (e.g. 50 tons per day oxygen VSA systems). Further, scale up above single train plant capacities of about 80 tons per day oxygen is inhibited by the maximum capacity ratings of single rotary machines.
Other modem VSA air separation systems have used multiple individual impellers to increase the enthalpy of the individual streams. However, these latter systems increase system complexity and capital cost. Furthermore, machine efficiency is reduced since the flow rates are smaller for each machine.
Accordingly, there is a need for centrifugal turbomachinery which can be used in PSA and VSA gas separation processes for maintaining steady conditions of gas flow and pressure, while minimising energy dissipation in irreversible throttling.
SUMMARY OF THE INVENTION
According to the invention, there is provided a gas separation system which addresses the deficiencies of the prior art gas separation systems.
As herein mentioned, the term “centrifugal turbomachinery” includes centrifugal compressors, vacuum pumps and expanders.
The gas separation system, according to the invention, separates a feed gas mixture into a first gas component and a second gas component and comprises a stator, and a rotor rotatably coupled to the stator. The stator includes a first stator valve face, a second stator valve surface, and a plurality of function compartments opening into the stator valve surfaces. The rotor includes a first rotor valve surface in communication with the first stator valve surface, and a second rotor valve surface in communication with the second stator valve surface. The rotor also includes a plurality of rotor flow paths for receiving gas adsorbent material therein for preferentially adsorbing the first gas component in response to increasing pressure in the rotor flow paths in comparison to the second gas component.
Each rotor flow path includes a pair of opposite ends opening into the rotor valve faces for communication with the function compartments. The gas separation system also comprises centrifugal turbomachinery coupled to a portion of the function compartments. The centrifugal turbomachinery includes an impeller which has a plurality of impeller flow paths for exposing each rotor flow path to a plurality of discrete pressures as the rotor rotates for separating the first gas component from the second gas component.
In a first embodiment of the invention, the centrifugal turbomachinery comprises a split stream centrifugal compressor for delivering the feed gas mixture to the first stator valve surface at a plurality of different feed gas pressure levels. The centrifugal compressor comprises a gas inlet for receiving the feed gas mixture, a plurality of blades extending radially outwards from the axis of rotation of the impeller, and a channel disposed within the impeller in communication with the gas inlet and extending between adjacent pairs of the blades. The blades include a plurality of steps positioned at differing radial distances from the rotational axis and define impeller flow paths for ejecting the feed gas mixture from the channel at a plurality of different angular momentums. The centrifugal compressor also includes a plurality of diffusers in communication with the channel for providing gas flows at a plurality of different pressures. In one variation of the centrifugal compressor, instead of the blades having steps, the blades have respective blade angles which define the impeller flow paths.
In a second embodiment of the invention, the centrifugal turbomachinery comprises a split stream centrifugal vacuum pump for producing a first product gas from gas flows which are enriched in the first gas component and which are received at a plurality of different sub-atmospheric gas pressure levels from the first stator valve surface. In a third embodiment of the invention, the centrifugal turbomachinery comprises a split stream centrifugal expander for producing a first product gas at atmospheric pressure from gas flows which are enriched in the first gas component and which are received at a plurality of different superatmospheric exhaust gas pressure levels from the first stator valve surface. The centrifugal vacuum pump and the centrifugal expander are structurally similar to the centrifugal compressor except that the direction of gas flow through the impeller flow paths is reversed. In two variations, the centrifugal vacuum pump and the centrifugal expander are coupled to the centrifugal compressor for assisting the centrifugal compressor in delivering the feed gas mixture to the first stator valve surface.
In another embodiment of the invention, the centrifugal turbomachinery comprise
Kaupert Kevin Arnold
Keefer Bowie Gordon
Hopkins Robert A.
Katten Muchin & Zavis
Quest Air Gases Inc.
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