Molecular sieve abstract
A monitoring system for determining the concentration of oxygen
in the product gas of an oxygen enriching system comprises a plurality
of pneumatic nor gates. Means are provided for coupling the outlet
port of each gate to the control port of the subsequent gate to
form a closed loop and a plurality of molecular sieve beds are pneumatically
connected one each to the control port of the nor gates. The molecular
sieve beds adsorb oxygen from the product gas to attenuate the rate
of pressure change in the control ports and thus, the oscillation
frequency of the monitor. The oxygen concentration of the product
gas may be inferred from the oscillation frequency of the monitor.
Molecular sieve claims
What is claimed is:
1. A monitoring system for determining the concentration of oxygen
in the product gas of an oxygen enriching system comprising:
a plurality of pneumatic nor gates coupled in series to form a
closed loop each nor gate in a first open condition, directing the
flow of said product gas to an outlet port of said gate and, in
a second closed condition, blocking the flow of said product gas
and coupling the outlet port of said gate to a vent port of said
gate,
means for coupling the outlet port of each gate to the control
port of the subsequent gate to form said closed loop thereby causing
the gates to sequentially open and close such that each subsequent
gate assumes an open or closed condition opposite to the condition
of the preceding gate,
the pneumatic pressure means at said outlet port for causing the
subsequent gate to go to either an open or closed condition,
a corresponding plurality of molecular sieve beds each pneumatically
connected to the control port of said nor gates to adsorb oxygen
from said product gas,
in said first open condition attenuate the rate of pressure rise
in said control ports, and
in said second closed condition attenuate the rate of pressure
decay in said control port, and
means for inferring the oxygen concentration of said product gas
from the oscillation frequency of the monitor.
2. A monitoring system for determining the concentration of any
particular gas in a system for producing a product gas enriched
in that particular gas comprising:
a plurality of pneumatic nor gates coupled in a series to form
a closed loop each nor gate in a first open condition, directing
the flow of said product gas to an outlet port of said gate and,
in a second closed condition, blocking the flow of said product
gas and coupling the outlet port of said gate to a vent port of
said gate,
means for coupling the outlet port of each gate to the control
port of the subsequent gate to form said closed loop thereby causing
the gates to sequentially open and close such that each subsequent
gate assumes an open or closed condition opposite to the condition
of the preceding gate,
the pneumatic pressure means at said outlet port for causing the
subsequent gate to go to either an open or closed condition,
a corresponding plurality of molecular sieve beds each pneumatically
connected to the control port of said nor gates to adsorb said particular
gas from said product gas,
in said first open condition attenuate the rate of pressure rise
in said control ports, and
in said second closed condition attenuate the rate of pressure
decay in said control port, and
means for inferring the particular gas concentration of said product
gas from the oscillation frequency of the monitor.
3. The monitoring system of claims 1 or 2 wherein said means for
coupling comprises a restrictive orifice.
Molecular sieve description
BACKGROUND OF THE INVENTION
Oxygen enriched breathing systems such as are found in hospitals
and aircraft use as oxygen sources bottled high pressure gas, liquid
oxygen, solid oxygen generators, commonly referred to as "candles",
or fractionalized air. It can become critical that the user know
the oxygen concentration in the breathing system to avoid a catastrophic
event such as could occur in high alitude aircraft.
Air fractionalizing is normally accomplished by alternating the
flow of high pressure air through each of two beds of molecular
sieve material such as a zeolite. This process is identified as
the pressure swing adsorption technique. Systems employing this
technique can be made to produce either a nitrogen or an oxygen
enriched effluent based on the type of zeolite chosen. Some zeolites
adsorb oxygen and others nitrogen. In an oxygen enriching system,
a zeolite which adsorbs nitrogen would be selected.
These same adsorption characteristics of a zeolite can be used
in monitoring the effluent concentrations of product gas from an
air fractionalizing system or any other source.
SUMMARY AND OBJECTS OF THE INVENTION
According to the invention, a molecular sieve oxygen monitor is
used to determine the oxygen concentration of the product gas of
an oxygen enriching system through the application of a plurality
of beds of molecular sieve material such as a zeolite to adsorb
oxygen from samples of the system effluent.
Though the description of the monitor focuses principally on oxygen
enriching systems, it is understood that the monitor applies equally
to nitrogen enriching systems or any other enriched product gas
for which a suitable adsorber exists.
It is therefore an object of this invention to provide a monitor
for determining the oxygen concentration of the product gas of an
oxygen enriching system.
It is another object of this invention to provide a monitor which
continuously samples the product gas to monitor oxygen concentration.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a molecular sieve oxygen
monitor according to the invention.
FIG. 2 is a pressure swing profile of the molecular sieve oxygen
monitor of FIG. 1 illustrating the control line pressure excursions
of the pneumatic nor gate circuits comprising the monitor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 a molecular sieve oxygen monitor 10 is a pneumatic
oscillator which includes a plurality of nor gates 11 12 and 13
interconnected such that the output of each gate is the control
of a subsequent gate in a closed loop series. The output of the
gate 11 is connected to the control of the gate 12 as the output
of the gate 11 passes through a restrictive orifice 14 the output
of the gate 12 is connected to the control of the gate 13 passing
through a restrictive orifice 16 and the output of the gate 13
is connected to the control of the gate 11 passing through a restrictive
orifice 18. In parallel with each of the gate controls are beds
21 22 and 23 of molecular sieve material such as a zeolite which
adsorb oxygen. Effluent gas samples P.sub.s from an oxygen enriching
supply (not shown) are continuously provided to each of the gates
11 12 and 13. The effluent gas P.sub.s flows through each of the
gates 11 12 and 13 when the gate control pressure is reduced to
a preset lower limit allowing the gate to open. Conversely, the
flow of effluent gas is blocked when the control pressure reaches
a preset upper limit and the gate closes. The rise and decay rate
of the control pressure is a function of the oxygen concentration
of the effluent gas samples P.sub.s. Pressure decay takes place
when the gate output is allowed to vent to the atmosphere through
vent ports P.sub.v.
MODE OF OPERATION OF THE PREFERRED EMBODIMENT
The pneumatic nor gates 11 12 and 13 function in response to
control pressure levels. When the control pressure in lines 24
26 or 28 is at a predetermined low level, the output pressure of
the respective gate in lines 30 32 or 34 is at the pressure of
the sample gas P.sub.s and the gate is said to be open. Conversely,
when the pressure in the control lines 24 26 or 28 reaches a predetermined
high pressure, the output of the respective gate in the lines 30
32 or 34 is dropped to the pressure at the vent ports P.sub.v and
the gate is said to be closed.
The beds 21 22 and 23 of molecular sieve material adsorb oxygen
from the sample gas P.sub.s when the respective gate 11 12 or
13 is open. The beds 21 22 and 23 desorb oxygen when the respective
gate 21 22 or 23 is closed and the lines 30 32 and 34 are at
pressure at the vent ports P.sub.v. The adsorption and desorption
of oxygen by the molecular sieve beds 21 22 and 23 inhibits the
rate of pressure rise and decay in the control pressure in lines
24 26 and 28 in a direct proportion to the concentration of oxygen
in the effluent gas samples P.sub.s. FIG. 2 illustrates the pressure
rise and decay profile of the control pressure at lines 24 26
and 28 as the gates 11 12 and 13 open and close.
In addition to the pressure rise and decay rate restriction created
by the molecular sieve beds 21 22 and 23 restrictive orifices
14 16 and 18 also inhibit the rate of pressure rise and decay.
The molecular sieve monitor 10 is a pneumatic oscillator whose frequency
of oscillation is a function of the time required for the control
pressure to reach its predetermined high and low pressure levels
to close and open the gates 11 12 and 13. Should the molecular
sieve beds 21 22 and 23 not inhibit the rate of pressure rise
and decay, such as would occur when the sample gas P.sub.s was nitrogen
rich, the restrictive orifices 14 16 and 18 introduce a time delay
in the pressure rise and decay to establish a set maximum oscillation
frequency.
The monitor 10 is activated when the sample gas P.sub.s pressure
is applied to the gates 11 12 and 13. With no control pressure
in the lines 24 26 and 28 the gates are all open and sample gas
P.sub.s pressure appears at the gate output lines 30 32 and 34.
The pressure in the control lines 24 26 and 28 rises as a function
of the flow through the restrictive orifices 14 16 and 18 which
flow is a function of the pressure of the sample gas P.sub.s. The
rate of pressure rise in the control lines is further inhibited
by the adsorption of oxygen from the sample gas P.sub.s in the molecular
sieve beds 21 22 and 23. Due to slight differences in the size
and adsorptive rates of each of the sieve beds 21 22 and 23 each
control line 24 26 and 28 reaches the predetermined pressure level
at which it closes its gate at a different point in time. When any
one gate closes first, its output line vents through its port P.sub.v
holding the subsequent gate open. When the control pressure in the
remaining gate reaches the predetermined level at which it closes,
its output pressure vents through its port P.sub.v causing the control
pressure of the gate first closed to decay, reopening the first
gate, closing the second gate, opening the third, closing the first
and so on.
The rate of pressure rise and decay of each of the control lines
varies as a function of the amount of oxygen adsorbed from the sample
gas P.sub.s by the sieve beds 21 22 and 23 and the frequency
of the gates opening and closing is a function of the rate of pressure
rise and decay. The oxygen content of the sample gas P.sub.s can
be inferred as the oscillation frequency decreases as oxygen content
increases. The level of the oxygen concentration of the sample gas
P.sub.s can be inferred if an oscillation frequency for the monitor
10 is first determined for a given level of nitrogen enrichment
and for a given level of oxygen enrichment. The oscillation frequency
is read and displayed by a suitable counter 36.
It is clear that this molecular sieve adsorptive technique is equally
applicable to any enriched product gas for which an adsorber is
available for the enriching component of that gas.
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