Layered manifold pressure swing adsorption device and method

Details Layered manifold pressure swing adsorption device and method Layered manifold pressure swing adsorption device and method

2001-09-25

2003-05-20

Simmons, David A. (Department: 1724)

Gas separation: apparatus

Solid sorbent apparatus

Plural solid sorbent beds

C096S130000, C096S135000

Reexamination Certificate

active

06565635

ABSTRACT:

FIELD
Disclosed embodiments of the invention concern fluid separations from a mixture of fluids, such as oxygen separation from air or hydrogen purification, conducted by pressure swing adsorption (PSA) using a fluid separation apparatus having layered manifolds, such as a compact, rotary pressure swing adsorption apparatus operating at high apparatus cycle frequencies. Narrow channel adsorbers, reinforced so as to engage directly with valve faces, also are described that desirably may be used with various embodiments of pressure swing adsorption apparatuses.
BACKGROUND
I. General PSA Process
Fluid separation from a fluid mixture by pressure swing adsorption is achieved by coordinated pressure cycling and flow reversals over an adsorber that 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 adsorber from a first end to a second end of the adsorber, 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.
A “light” product, depleted in the more readily adsorbed component and enriched in the less readily adsorbed component, is then delivered from the second end of the adsorber. A “heavy” product enriched in the more strongly adsorbed component is exhausted from the first end of the adsorber. The light product usually is the desired product to be purified, as in the important examples of oxygen separation over nitrogen-selective zeolite adsorbents and hydrogen purification. The heavy product may be a desired product in the example of nitrogen separation over nitrogen-selective zeolite adsorbents. Typically, a fluid feed mixture is admitted to the first end of an adsorber and the light product is delivered from the second end of the adsorber when the pressure in that adsorber is elevated to a higher working pressure. The heavy product is exhausted from the first end of the adsorber at a lower working pressure. In order to obtain a highly pure light product, a fraction of the light product or fluid enriched in the less readily adsorbed component is recycled back to the adsorbers as “light reflux” fluid after pressure letdown, e.g. to perform purge, pressure equalization or repressurization steps.
The conventional process for fluid separation by pressure swing adsorption uses two or more adsorbers in parallel, with directional valving at each end of each adsorber to connect the adsorbers in alternating sequence to pressure sources and sinks, thus establishing the changes of working pressure and flow direction. The basic pressure swing adsorption process inefficiently uses applied energy, because of the irreversible expansion over the valves while switching the adsorbers between higher and lower pressures. More sophisticated conventional pressure swing adsorption devices achieve some improvement in efficiency by using multiple “light reflux” steps and other process refinements, but the valve logic complexity based on conventional 2-way valves is greatly increased. As a result, apparatus cycle frequencies are low, with 1 cycle/minute being common, and few commercial devices have cycle frequencies higher than 5 cycles/minute. Furthermore, the cycle frequency with conventional valves and granular adsorbent cannot be greatly increased, so the adsorbent inventory is large. Conventional PSA plants are accordingly bulky and heavy, and there is a need for much more compact PSA technology.
II. Rotary PSA Technology
Siggelin (U.S. Pat. No. 3,176,446), Mattia (U.S. Pat. No. 4,452,612), Davidson and Lywood (U.S. Pat. No. 4,758,253), Boudet et al. (U.S. Pat. No. 5,133,784), Petit et al. (U.S. Pat. No. 5,441,559), Keefer et al. (U.S. Pat. No. 6,051,050) and Westmeier et al. (former German Democratic Republic patent DD 259,794 A1) disclose PSA devices using rotary adsorbent bed configurations. Ports for multiple, angularly separated adsorbent beds mounted on a rotor assembly, sweep past fixed functional ports for the functions of feed admission, product delivery, exhaust discharge and pressure equalization. All of these devices use multiple adsorbent beds operating sequentially on the same cycle, with multiport distributor rotary valves for controlling fluid flows to, from and between the adsorbent beds.
The prior art includes numerous examples of pressure swing adsorption and vacuum swing adsorption devices with three adsorbers operating in parallel. Thus, Hay (U.S. Pat. No. 4,969,935) and Kumar et al. (U.S. Pat. No. 5,328,503) disclose vacuum adsorption systems that do not achieve continuous operation of compressors and vacuum pumps connected at all times to one of the three adsorbers. Such operation is achieved in other three adsorber examples provided by Tagawa et al. (U.S. Pat. No. 4,781,735), Hay (U.S. Pat. No. 5,246,676), and Watson et al. (U.S. Pat. No. 5,411,528), but in each of these latter examples there is some undesirable inversion of the ordering of light product withdrawal and light reflux steps so that process efficiency is compromised. Examples of rotary valve controlled PSA for hydrogen purification with six adsorbers in parallel are provided by Keefer (U.S. Pat. No. 6,063,161).
Some rotary PSA embodiments disclosed by Westrneier et al. (former German Democratic Republic patent DD 259,794 A1) and by Keefer et al. (U.S. Pat. No. 6,051,050) have a rotational period that is an integer multiple “M” of the cycle period (with M>1). The fixed functional ports for each function must then be provided in the same multiple “M” numerically equal to the integer quotient of the rotational period divided by the cycle period, and positioned at equal angular spacing about the rotational axis. This approach balances pressure loads on the valve faces, reduces rotor-bearing loads, and reduces the friction of sliding seal surfaces in the valve faces. Frictional torque and power required to drive the rotor are reduced by at least the factor “1/M”, since angular velocity is reduced by the same factor and contact pressure loads of balanced seals may be reduced as well. With reduced friction, seal life is extended. Consequently higher pressure applications (e.g. hydrogen purification) become more practicable for such rotary PSA devices, as seal life typically will be controlled by the product of sliding velocity (here reduced by the factor “1/M” reflecting the reduction or rotational frequency by the same factor) and contact pressure. However, this approach encounters the following problems:
For a given PSA cycle, the number of adsorbers must be increased by the factor “M”. Hence the angular width of each adsorber must be reduced by the same factor “M”, resulting in added cost and complexity if the adsorbers are separate fabricated assemblies. Pressure containment, static sealing between adsorbers, and porting of the adsorbers to the valve faces in a rotary PSA system is difficult with a very large number of separate adsorbers. Again, this consideration is more critical when the basic PSA process has a large number of steps and envisages that multiple adsorbers will simultaneously undergo each step, as in U.S. Pat. No. 6,051,050.
As the angular sector allocated to each PSA cycle is 360°/M, angular pressure gradients between the PSA cycle steps are steepened by the factor “M” when M>1. This makes valve face sealing more difficult, so that the potential for cross-leakage between adjacent PSA steps increases. The efficiency improvement of reduced sliding friction with M>1 may thus be offset by efficiency loss due to leakage, so that an important challenge will be to reduce leakage.
Complicated and costly external piping connections in “M” sets must be provided to the opposing sides of the apparatus for each process function with valve ports, while maintaining uniform flow distribution between the plurality of fixed ports Off serving each function. This

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