Gas separation: processes – With control responsive to sensed condition – Pressure sensed
Reexamination Certificate
1999-09-27
2001-05-29
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
With control responsive to sensed condition
Pressure sensed
C095S022000, C095S101000, C095S102000, C095S105000, C095S130000
Reexamination Certificate
active
06238458
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for treatment of a gaseous mixture by Pressure Swing Adsorption or PSA, of the type in which there is used at least one adsorber and in which, in each adsorber, there is carried out, for a predetermined nominal production, a cycle comprising the following successive phases:
a production phase by co-current admission of mixture into the adsorber and recovery of a fraction enriched in the least adsorbable compounds, for supply to a production gas conduit, in the course of which phase the maximum pressure PM of the cycle is reached;
a regeneration phase comprising at least one step of depressurization and in the course of which the minimum pressure Pm of the cycle is reached;
a repressurization phase of the adsorber to the initial pressure of the production phase; and
at least one of the extreme pressures PM and Pm of the cycle being substantially different from atmospheric pressure.
The invention is applicable particularly to trans-atmospheric cycles for the production of impure oxygen, having typically a purity of the order of 90 to 95%, from atmospheric air. This production of gas will be called “oxygen” in what follows.
The pressures in question here are absolute pressures.
BACKGROUND OF THE INVENTION
The mentioned adsorption cycles are used in PSA installations which comprise a large number of valves having a high frequency of opening/closing.
Given that the good operation of the cycle depends on the sequences of opening and closing these valves, which permit obtaining the foreseen pressure cycle, it will be easily seen that the malfunction of one of these valves which are manipulated at each cycle, can cause serious problems in the operation of a PSA installation.
By way of example, there can be distinguished in particular two cases of malfunction relating to these valves:
1) A first malfunction can consist of mechanical blockage of the valve, resulting in that either the valve remains closed despite receiving an opening signal (or conversely), or it opens or closes only very slowly.
Such incidence can be detected by end of path detector installed at the level of the veins and if desired connected to timers.
Moreover, given that this type of malfunction generally causes substantial unbalance in the pressure cycle of the various adsorbers, such an incident is relatively easy to identify.
2) A second malfunction can result from a defect of sealing of a closed valve, which leads to internal loss either between adsorbers or between one adsorber and the production line or the residual line.
In contrast to mechanical blockage, unsealed closed valve losses are difficult to detect in an operating unit.
They nevertheless translate to decreased performance of the PSA installation due either to unbalanced operation of the adsorbers, or directly a production loss in the residual gas line.
To detect valves having in their closed position a sealing fault, there are conventionally used periodic stoppages of the operation of the installation to carry out tests of sealing.
But these controls have the drawback that they are long and intricate. Moreover, given the duration of stoppage of the installation, these controls can only be carried out at spaced time intervals.
However, given that the loss of production caused by a sealing defect of a valve and translating into a loss of several percent of the extraction output can last several months, the loss can be very great.
SUMMARY OF THE INVENTION
The invention has for its object providing a PSA process, typically of trans-atmospheric type, permitting economical adaptation to a variable production flow rate, as well as easy detection of the sealing of the valves.
To this end, the invention has for its object a process of the mentioned type, characterized in that, upon a reduction of production flow rate, there is added to the cycle, substantially at an extreme pressure PM and/or Pm of the cycle, at least one idle time in the course of which the adsorber is isolated.
The process according to the invention can comprise one or several of the following characteristics, taken alone or in all possible combinations:
upon reduction of flow rate, there is added an idle time substantially at the maximum pressure PM of the cycle, typically immediately following the production phase;
upon a flow rate reduction, there is added an idle time substantially at the minimum pressure Pm of the cycle, typically immediately before the repressurization phase;
the pressure of the adsorber during at least an idle time for at least certain cycles, is monitored;
in a process using two adsorbers, there is provided a step of partial balancing between the two absorbers from their respective extreme pressures and, typically upon said reduction of production flow rate, there is added to the cycle two concomitant idle times having the same duration.
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L'Air Liquide Societe Anonyme pour l'Etude et l'E
Spitzer Robert H.
Young & Thompson
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