Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
2001-01-18
2003-02-18
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S102000, C095S117000, C095S121000, C095S130000, C096S132000, C096S154000
Reexamination Certificate
active
06521019
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for separating the components of a gas stream, and more particularly to a cyclic adsorption process for separating oxygen from nitrogen. Specifically, the invention concerns a cyclic adsorption process, e.g. vacuum swing adsorption (VSA) or pressure swing adsorption (PSA), carried out in a system comprising at least one main adsorption vessel containing a monolith comprising an adsorbent material in the form of a wheel. In particular the adsorbent material comprises at least two layers of adsorbent material one of which is a monolith, preferably in the form of a spirally wound wheel.
BACKGROUND OF THE INVENTION
Cyclic adsorption processes are frequently used to separate the components of a gas mixture. Typically, cyclic adsorption processes are conducted in one or more adsorbent vessels that are packed with a particulate adsorbent material which adsorbs at least one gaseous component of the gas mixture more strongly than it adsorbs at least one other component of the mixture. The adsorption process comprises repeatedly performing a series of steps, the specific steps of the sequence depending upon the particular cyclic adsorption process being carried out.
In any cyclic adsorption process, the adsorbent bed has a finite capacity to adsorb a given gaseous component and, therefore, the adsorbent requires periodic regeneration to restore its adsorption capacity. The procedure followed for regenerating the adsorbent varies according to the process. In VSA processes, the adsorbent is at least partially regenerated by creating vacuum in the adsorption vessel, thereby causing adsorbed component to be desorbed from the adsorbent, whereas in PSA processes, the adsorbent is regenerated at atmospheric pressure. In both VSA and PSA processes, the adsorption step is carried out at a pressure higher than the desorption or regeneration pressure.
A typical VSA process generally comprises of a series of four basic steps that includes (i) pressurization of the bed to the required pressure, (ii) production of the product gas at required purity, (iii) evacuation of the bed to a certain minimum pressure, and (iv) purging the bed with product gas under vacuum conditions. In addition a pressure equalization or bed balance step may also be present. This step basically minimizes vent losses and helps in improving process efficiency. The PSA process is similar but differs in that the bed is depressurized to atmospheric pressure and then purged with product gas at atmospheric pressure.
As mentioned above, the regeneration process includes a purge step during which a gas stream that is depleted in the component to be desorbed is passed countercurrently through the bed of adsorbent, thereby reducing the partial pressure of adsorbed component in the adsorption vessel which causes additional adsorbed component to be desorbed from the adsorbent. The nonadsorbed gas product may be used to purge the adsorbent beds since this gas is usually quite depleted in the adsorbed component of the feed gas mixture. It often requires a considerable quantity of purge gas to adequately regenerate the adsorbent. For example, it is not unusual to use half of the nonadsorbed product gas produced during the previous production step to restore the adsorbent to the desired extent. The purge gas requirement in both VSA and PSA processes are optimization parameters and depend on the specific design of the plant and within the purview of one having ordinary skill in the art of gas separation.
Many process improvements have been made to this simple cycle design in order to reduce power consumption, improve product recovery and purity, and increase product flowrate. These have included multi-bed processes, single-column rapid pressure swing adsorption and, more recently, piston-driven rapid pressure swing adsorption and radial flow rapid pressure swing adsorption. The trend toward shorter cycle times is driven by the desire to design more compact processes with lower capital costs and lower power requirements. The objective has been to develop an adsorbent configuration that demonstrates a low pressure drop, a fast pressurization time and an ability to produce the required purity of oxygen.
Most commercial adsorption processes currently employ fixed-bed adsorbents usually in the form of beads or pellets. Typically, these beads or pellets range in size from about 1 mm to 4 mm. In two recent articles by Y. Y. Li et al., in the Trans Ichem E, Vol 76, Part A (November 1998), the authors have disclosed the use of extended zeolite monolith structure (20 mm diameter and 1 mm thickness) and their application to air separation and/or O2 enrichment. In addition, U.S. Pat. Nos. 4,758,253 and 5,082,473 are directed to the use of adsorbents having a plurality of small passages for gas separation. The present invention is directed to an improved air separation process utilizing monolithic adsorbent material.
SUMMARY OF THE INVENTION
It is the primary object of the present invention to provide a process for the separation of components in a gas mixture.
It is another object of the present invention to provide a process for the separation of oxygen from nitrogen.
It is still another object of the present invention to provide a process for the separation of oxygen from nitrogen utilizing vacuum swing adsorption (VSA).
It is a further object of the present invention to provide a process for the separation of oxygen from nitrogen utilizing pressure swing adsorption (PSA).
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description or will be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects, and in accordance with the purposes of the invention or embodied and broadly described herein, the process of the present invention comprises introducing a gaseous mixture comprising a first gaseous component and a second gaseous component into an adsorption zone containing at least two layers of adsorbent material capable of preferentially adsorbing at least one of the gaseous components in the gaseous mixture to separate the first gaseous component from the second gaseous component wherein the layers of adsorbent material are stacked in a direction parallel to the flow of the gaseous mixture through the adsorption zone and at least one of the adsorption layers is selected to be a monolith wheel having a plurality of channels throughout, the channels being aligned substantially parallel to the direction of the flow of the gaseous mixture through the adsorption zone and recovering the non-preferentially adsorbed gaseous component from the adsorption zone.
In another aspect of the present invention, and in accordance with the purposes of the invention or embodied and broadly described herein, the process of the present invention comprises introducing a gaseous mixture comprising a first gaseous component and a second gaseous component into an adsorption zone containing at least one adsorbent material capable of preferentially adsorbing at least one of the gaseous components in the gaseous mixture to separate the first gaseous component from the second gaseous component wherein the adsorbent material is selected to be a monolith wheel (non-rotating) comprising a spirally-wound sheet of adsorbent material having a plurality of channels throughout, the channels being aligned substantially parallel to the direction of the flow of the gaseous mixture through the adsorption zone and recovering the non-preferentially adsorbed gaseous component from the adsorption zone.
In still another aspect of the present invention, and in accordance with the purposes of the invention or embodied and broadly described herein, the process of the present invention comprises introducing a first gaseous component and a second gaseous component in
Acharya Divyanshu R.
Ambriano John Robert
Fitch Frank R.
Jain Ravi
LaCava Alberto I.
Neida Philip H. Von
Pace Salvatore P.
Spitzer Robert H.
The BOC Group Inc.
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