Liquid purification or separation – Processes – Chromatography
Reexamination Certificate
2002-12-17
2004-09-28
Hopkins, Robert A. (Department: 1724)
Liquid purification or separation
Processes
Chromatography
C210S661000, C210S198200, C210S266000, C210S283000, C210S284000, C210S285000, C210S541000
Reexamination Certificate
active
06797175
ABSTRACT:
The present invention relates to a device for injecting a stream of fluid used as a diverted fluid in a separation process employing a plurality of beds of adsorbant, a main fluid stream and a plurality of secondary fluid streams, the beds being separated by at least one fluid distributor plate, the plate possibly comprising one or more distributor-mixer-extractor panels, DME panels, which can inject and/or mix and/or extract one or more secondary fluids via a single distribution chamber.
The invention is of particular application to the device and process described in the Applicant's French patent application FR-A-2 772 634, when secondary fluids are injected and extracted by means of a single distribution network, normally termed a distribution “spider”.
The invention also relates to all processes in which the purity of at least one constituent in a mixture moving through a solid adsorbant or solid catalyst is to be improved.
It can also be applied to processes for separating at least one constituent from a mixture for which any chromatographic adsorption or ion exchange separation, for example, is carried out.
Throughout the description, the term “main fluid” designates a stream of fluid that moves through the beds of adsorbant, and the term “secondary fluid” designates fluids that are used within the separation process, for example desorbant, feed, extract or raffinate and which pertain to the exterior.
The invention is of particular application to separating n-paraffins containing 10 to 13 carbon atoms from sweetened kerosene type feeds.
The prior art describes different devices and processes that can separate feeds using a simulated moving bed. The following can be cited: U.S. Pat. Nos. 2,985,589, 3,214,247, 3,268,605, 3,592,612, 4,614,204, 4,378,292, 5,200,075, 5,316,821, European patent application 0,769,316, French patent application FR-A-2 772 634 and International patent application WO-A-95 03867.
As a general rule, a simulated moving bed comprises at least three chromatographic zone, advantageously four or five, each zone being constituted by at least one bed or column section.
Between two zones there is either a point for injecting a feed to be fractionated, or a point for injecting an eluent or desorbant, or a point for drawing off an extract between the point for injecting eluent and the point for injecting feed which is located downstream (in the direction of movement of the eluent), or a point for drawing off a raffinate between each point for injecting mixture and the point for injecting eluent which is located downstream in the direction of movement of the eluent.
The assembly of beds or column sections forms a closed loop including at least one flow regulated pump for recycling the main fluid, for example between the first and last section.
During the separation process, the injection points and drawing off points of at least one section or column are generally displaced in the same direction (upstream or downstream, again in the direction of movement of the main fluid). This forms the basis of the simulated moving bed operation.
During that process, it is important for the fluid distribution in each of the beds of adsorbant to be as uniform as possible and as homogeneous as possible.
Distribution over each of the beds necessitates collecting the streams from the preceding bed (main fluid moving along the main axis of the column), the possibility of injecting an accompanying fluid or a secondary fluid while mixing the two fluids to the best possible extent, or the possibility of removing a portion of the collected fluid, or drawing it off to send it outside the device and to re-distribute a fluid over the subsequent bed.
To this end, it is possible either to convey all of the main fluid or stream in the adsorber in accordance with a scheme described in U.S. Pat. No. 2,985,589, or to remove a large portion or all of that stream outside using the process described in U.S. Pat. No. 5,200,075.
As described in patent application FR-A-2 772 634, a further solution consists, of moving the majority of the main stream internally and a minority of the stream externally, typically 2% to 20% of the stream. One advantage of such a system is that the injection and withdrawal circuits for the secondary fluids permanently have substantially the same composition. Two distributor plates are connected via an external circuit known as a synchronous bypass circuit. That circuit circulates a minority of the removed stream, ensuring an identical composition. On-off valves are connected to the bypass circuit for removing secondary fluids, along with a non-return valve. Optionally, the circuit can be provided with an on-off valve or a control valve to inject and draw off from a single plate.
Continuous rinsing of the distribution spiders of the distributor plates for the simulated moving bed separation units can be carried out in two manners:
1) when each plate is provided with at least two independent distribution networks (D
1
and D
2
), network D
1
of plate P is brought into communication with network D
2
of the plate P+1, and the network D
1
of plate P+1 is brought into communication with network D
2
of plate P+2, so that on each distributor plate, all of the distribution networks have a permanent fluid circulation, and each plate experiences a flow of a stream of fluid diverted from one distribution network to the main fluid and a second fluid stream diverted in substantially the same manner from the main fluid to the second distribution network. The driving force for such flows is provided by the pressure drop caused by the flow of main fluid in the granular porous medium located between two successive distributor plates;
2) when each distributor plate is provided with a single distribution network, the bypass circuits can only be established in every other bed, for example from plate P to plate P+1, then from plate P+2 to plate P+3. If a bypass line connected plates P+1 to P+2, this would result in parallel circulation to the adsorber from the top bed to the bottom bed. The disadvantage of establishing only one bypass circuit in every other bed is that the internal flow rates would vary from one bed to the other: on beds including a bypass circuit, there would be a flow rate D, while on beds not including a bypass circuit, there would be a flow rate D+b.
A further patent FR-A-2 794 663 described a device for injecting a diverted fluid originating from a distribution, mixing and/or extraction chamber from an upstream plate in a region Ri of an adsorbant bed downstream of that plate.
The present invention concerns a device and process that are particularly suitable for separation devices in which the plates are provided with a single network for distributing secondary fluids, distributor-mixer-extractor or DME panels comprising a single distribution, extraction and/or mixing chamber.
Since users' demands for quality have increased, the purity standard to be achieved has been raised from values in the range (98.1-99%) to 99.5% for C10 to C13 n-paraffins. As a result, operators have to modify existing separation units to satisfy those new requirements.
The invention can be applied to existing units and to new units. It is used in processes and devices for separation, by adsorption in counter-current simulated moving bed processes and optionally in units comprising a rotary valve. It is applicable, for example, in a device comprising a central distribution described in U.S. Pat. No. 4,378,292, for example, in which the distributor plates are provided with a single distribution spider, when revamping a unit or during a significant change in the composition of the feed which results in a change in the configuration of the unit. The invention is also applicable to debottlenecking a unit.
More generally, the modification supplied by the scheme of the invention is particularly applicable in the case of debottlenecking operations in a unit to replace the molecular sieve and/or to mechanically strengthen the distributor plates
Hopkins Robert A.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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