Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
2003-04-11
2004-11-02
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S105000, C095S130000, C096S109000, C096S115000, C096S130000
Reexamination Certificate
active
06811590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a gas concentrating method and apparatus using pressure swing adsorption (PSA), and more particularly, to a gas concentrating method and apparatus in which a high-pressure gas concentration is performed in a system (which means a two-adsorption-bed system, which is hereinafter referred to as a multi-bed system) where two adsorption beds (hereinafter referred to as sieve beds) alternately repeat concentration of a weak adsorption matter and washing of a strong adsorption matter, and then the two sieve beds are made to temporarily communicate with each other through a solenoid valve, at their bottoms, in such a manner that a high-pressure raw material gas moves from a high-pressure sieve bed to a low-pressure sieve bed to thus equalize pressures in the two sieve beds and perform washing and discharging of the two sieve beds.
2. Description of the Related Art
A pressure swing adsorption (PSA) process separates and concentrates a gas such as oxygen using a difference in an adsorption quantity of oxygen adsorbed to an adsorption material according to a pressure. Since the PSA process uses only compressed air and an adsorption material, it does not discharge a pollution matter and its use is easy. Thus, the PSA process has been widely used in a medical oxygen concentrator for long.
According to a concentrating principle, when compressed air is introduced and pressurized in a sieve bed filled with an adsorption material, a strong adsorption matter is adsorbed and a weak adsorption matter is concentrated. As a result, oxygen is left and separately stored as a product gas. After the product gas has been obtained, the strong adsorption matter adsorbed to the adsorption material is detached as inner oxygen and discharged externally to then be decompressed.
According to an oxygen separation principle, two sieve beds perform the above-described concentrating steps alternately. That is, the oxygen separation process includes four steps. Here, oxygen, which is a weak adsorption matter, is separated from a massive amount of nitrogen, which is a strong adsorption matter, in the sieve beds including zeolite which is an adsorption material.
Nitrogen of about 80% consisted in the air is adsorbed to zeolite more than oxygen be. Accordingly, when air is introduced in a sieve bed filled with an adsorption material, nitrogen is adsorbed to the adsorption material and oxygen in the air from which nitrogen has been reduced rises up to an exit located in the upper end of the sieve bed. The main component of the risen oxygen is composed of concentrated oxygen which is -a weak adsorption matter.
The above-described two-sieve-bed type, that is, multi-bed type oxygen separating apparatus is used as an oxygen separator. The oxygen separator includes an adsorption unit for separating nitrogen and oxygen from the air, an operator performing compression, storage and discharging of the air, a controller turning a valve on and off, and a frame portion accommodating the adsorption unit, the operator and the controller.
The oxygen separating apparatus adopts an oxygen separation method of repeating a process of supplying compressed air to a sieve bed filled with an adsorption material and adsorbing oxygen, and a process of detaching the oxygen adsorbed to the adsorption material, to thereby obtain necessary oxygen of a predetermined concentration. Here, part of the necessary oxygen obtained in the sieve bed is circulated into the sieve bed in order to perform a detachment process.
The adsorption process includes the steps of introducing compressed air through a predetermined adsorption material, adsorbing nitrogen which is a strong adsorption matter, and separating oxygen from the air. Here, once an adsorption step has been performed, the nitrogen adsorbed to zeolite which is an adsorption material should be necessarily separated (detached) from the adsorption material, in order to restore the original performance. This process is called a washing process, in which part of the oxygen adsorbed to the adsorption material is recirculated under a low-pressure state and detached therefrom, to restore an adsorption performance.
As described above, oxygen concentration and nitrogen washing are repeated to obtain concentrated oxygen of a predetermined purity.
An oxygen concentrating apparatus for concentrating oxygen through a multiple-bed type sieve bed was filed by the same applicant as shown in FIG.
1
.
The oxygen concentrating apparatus includes a compressor
50
for compressing air, a solenoid valve
40
for controlling a supply of the compressed air, sieve beds
60
-
1
and
60
-
2
for separating nitrogen and oxygen from the compressed air supplied through the solenoid valve
40
, an orifice
90
connected between the upper portions of the two sieve beds, an equilibrium valve
120
installed between the two sieve beds, making high-pressure and high-purity oxygen flow from the upper portion of the sieve bed to that of the other sieve bed, to be in equilibrium, counter-current preventive check valves
90
-
1
and
90
-
2
, a storage tank
100
, a pressure controller
70
and a needle valve
80
. In
FIG. 1
, a reference numeral
10
denotes an air intake filter, a reference numeral
20
denotes an air intake muffler, and a reference numeral
30
denotes an air discharging muffler.
When the inner portion of a first sieve bed
60
-
1
is pressurized with the air, in the oxygen concentrating apparatus, nitrogen is adsorbed to an adsorption material from the air, and the other remaining concentrated oxygen is discharged. At the same time, in the case of a second sieve bed
60
-
2
, an adsorption material to which nitrogen is adsorbed should be washed. Accordingly, part of the concentrated oxygen in the first sieve bed
60
-
1
is transferred to the upper portion of the second sieve bed
60
-
2
through an orifice
90
to then wash the inside of the second sieve bed
60
-
2
. Then, oxygen of a high-pressure and high-purity is transferred to the second sieve bed
60
-
2
for a short time to keep the oxygen concentration in equilibrium between the first and second sieve beds and discharge the internal gas after washing. Here, the internal portion of the second sieve bed
60
-
2
has a considerable pressure resistivity.
Thus, in the case of the oxygen concentrating system, a compressor continues to operate at high pressure in the first sieve bed and a pressurized concentrated oxygen at high pressure is supplied to the inside of the second sieve bed which is at the low-pressure state through an equilibrium valve. As a result, the above-described oxygen concentrating system has the following defectives.
First, since the second sieve bed is washed with a high-purity of concentrated oxygen, a mechanical energy loss becomes large due to pressurization of a compressor.
Second, when the concentrated oxygen of a high pressure is supplied from the upper portion of the first sieve bed into the inside of the second sieve bed which is at the low-pressure state after pressurization, the second sieve bed is kept to be at the high-pressure state while discharging the air. As a result, air discharging noise becomes excessive.
Referring to
FIG. 2
illustrating the above-described processes, according to a pressure curve of the first sieve bed, the pressure rises up to the point immediately before the concentrated oxygen in the first sieve bed is discharged, and then part of the high-pressure oxygen is supplied to the second sieve bed through the equilibrium valve
120
, so that the pressure is lowered from 2.5 to 1 during about 2 seconds, which is shown as a pressure difference between {circle around (
1
)} and {circle around (
2
)} in FIG.
2
. Here, the pressure equilibrium is made between both the sieve beds, and the second sieve bed is partially pressurized.
Thereafter, since a time between an intersection at which the pressure curves of the respective sieve beds cross (at a point at which the pressure is 1. 5 as shown in {circle around (
3
)} in
FIG. 2
Choi Yoon Sun
Lee Tae Soo
Liniak, Berenato & White, LLC
Oxus Co., Ltd.
Spitzer Robert H.
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