Gas separation: processes – Solid sorption – Including reduction of pressure
Patent
1998-02-19
1999-10-19
Spitzer, Robert
Gas separation: processes
Solid sorption
Including reduction of pressure
95101, 95130, 96130, 96144, B01D 53047
Patent
active
059682337
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for treating a gas mixture by pressure-swing adsorption, of the type in which, in at least one vessel containing a mass of adsorbent, a cycle is implemented which comprises (a) a production phase in which the mixture is circulated, in a so-called cocurrent direction, from one end referred to as the inlet, to another end, referred to as the outlet, of the vessel, and (b) a phase of regenerating the adsorbent, by the vessel having, on the one hand, on its outlet side and beyond the mass of adsorbent in the cocurrent direction, a free volume, referred to as the production dead volume, which is in permanent communication with the outlet side end of the mass of adsorbent, and on the other hand, on its inlet side, before the mass of adsorbent in the cocurrent direction, a free volume, referred to as the feed dead volume, which is in permanent communication with the inlet side end of the mass of adsorbent.
The invention applies in particular to the production of oxygen-enriched air, in particular containing at least 90% oxygen, from atmospheric air.
The pressures referred to are absolute pressures.
The expression "pressure-swing adsorption" (PSA) is to be understood in the broad sense, that is to say the high pressure of the cycle is greater than or equal to atmospheric pressure and the low pressure of the cycle is less than or equal to atmospheric pressure.
BACKGROUND OF THE INVENTION
It is known that the performance of a PSA method can be assessed through a number of factors, which in the aforementioned example are as follows: produced to the volume of said gas contained in the gas mixture which is treated (volumes measured under standard temperature and pressure conditions); unit volume of adsorbent (unit: m.sup.3 (stp)/h.m.sup.3); product gas, measured under standard temperature and pressure conditions (unit: kWh/m.sup.3 (stp)); and method (unit: FF).
When the parameters of a PSA plant are altered, the four factors mentioned above are generally affected in different ways. It is therefore particularly difficult to predict what the final cost of the product gas (in particular oxygen) will be, and especially since a number of relatively poorly understood physical phenomena, such as the adsorption/desorption kinetics, are affected.
The cost C of the product gas can be defined by the following formula: also the maintenance, taxes, etc.
C thus represents the unit cost of the product gas.
SUMMARY OF THE INVENTION
The object of the invention is to make it possible to obtain a low production cost, in particular with minimized outlay in terms of specific energy and/or reduced investment, in a way which is particularly convenient and straightforward for designing and using the plant.
To this end, the invention relates to a method of the aforementioned type, wherein: the assembly consisting of the mass of adsorbent and the two dead volumes, and where V is the volume of the same assembly, is selected, at a value of less than 6 m.sup.-1 ; and 10% and substantially 60% of the volume of the mass of adsorbent.
If, for a given cost of the product gas, it is desired to minimize the outlay in terms of specific energy, the production dead volume will advantageously be selected to be close to 10% of the volume of the mass of adsorbent.
If, however, the intention is to favor low investment, the production dead volume will advantageously be selected to be close to 60% of the volume of the mass of adsorbent.
The invention also relates to a plant intended for implementing the method defined above.
This plant, of the type comprising at least one vessel which contains a mass of adsorbent and defines an inlet through which the mixture enters in the production phase, and an outlet through which the production gas emerges, the mixture circulating through the vessel in a so-called cocurrent direction during the adsorption phase, by the vessel having, on the one hand, on its outlet side and beyond the mass of adsorbent in the cocurrent direction, a free volume, referred
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Labasque Jacques
Letellier Jean-Yves
Rouge Dominique
L'Air Liquide, Societe Anonyme Pour L'Etude et L'Exploitation de
Spitzer Robert
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