Molecular sieve abstract
A monitoring system for determining the concentration of oxygen
in the product gas of an oxygen enriching system includes differential
pressure regulator means for reducing the pressure of the product
gas, for regulating the pressure of the product gas at a preset
level, and for referencing the regulated pressure to atmospheric
pressure. Solenoid valves allowing product gas to pressurize the
monitoring system in a first condition and to allow product gas
to vent the monitoring system to the atmosphere in a second condition
are also included. Restrictive orifices upstream and downstream
of a bed of molecular sieve material eliminate pressure spikes in
the monitoring system. A bed of molecular sieve material to adsorb
oxygen from the product gas wherein, in a first condition, with
the system pressurized, the upper pressure limit is attenuated as
the molecular sieve bed absorbs oxygen from the product gas, and,
in a second condition, with the system vented to the atmosphere,
the lower pressure limit is attenuated by the rate of desorption
of the oxygen from the molecular sieve bed. Further included is
a pressure transducer with means for converting the system pressure
to an electrical analog of that pressure including means for comparing
the electrical analog to a reference and inferring oxygen concentration.
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 differential pressure regulator means for reducing the pressure
of said product gas, and for regulating the pressure of said product
gas at a preset level, and for referencing said regulated presssure
to atmospheric pressure,
solenoid valves for allowing product gas to pressurize said monitoring
system in a first condition and to allow product gas to vent the
monitoring system to the atmosphere in a second condition,
restrictive orifices upstream and downstream of a bed of molecular
sieve material to eliminate pressure spikes in said monitoring system,
a bed of molecular sieve material to adsorb oxygen from said product
gas which
in a first condition, with the system pressurized, the upper pressure
limit is attenuated as the molecular sieve bed adsorbs oxygen from
the product gas, and
in a second condition, with the system vented to the atmosphere,
the lower pressure limit is attenuated by the rate of desorption
of the oxygen from the molecular sieve bed, and
a pressure transducer with means for converting the system pressure
to an electrical analog of that pressure including means for comparing
said electrical analog to a reference and inferring oxygen concentration.
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 differential pressure regulator means for reducing the pressure
of said product gas, and for regulating the pressure of said product
gas at a preset level and for referencing said regulated pressure
to atomospheric pressure,
solenoid valves for allowing product gas to pressurize said monitoring
system in a first condition and to allow product gas to vent the
monitoring system to the atmosphere in a second condition,
restrictive orifices upstream and downstream of a bed of molecular
sieve material to eliminate pressure spikes in said monitoring system,
a bed of molecular sieve material to adsorb said particular gas
from said product gas which
in a first condition, with the system pressurized, the upper pressure
limit is attenuated as the molecular sieve bed adsorbs particular
gas from the product gas, and
in a second condition, with the system vented to the atmosphere,
the lower pressure limit is attenuated by the rate of desorption
of the particular gas from the molecular sieve bed, and
a pressure transducer with means for converting the system pressure
to an electrical analog of that pressure including means for comparing
said electrical analog to a reference and inferring the particular
gas concentration.
3. A monitoring system as recited in claim 1 wherein the temperature
of said molecular sieve bed is monitored and is compensated to maintain
the bed temperature constant.
4. A monitoring system as recited in claim 1 wherein the temperature
of said molecular sieve bed is monitored and is used to generate
a correction to said electrical analog means.
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 bed of molecular
sieve material such as 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 system or any other enriched product gas for
which a suitable absorber 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.
It is still further an object of this invention to provide a monitor
which functions independent of product gas system pressure and ambient
pressure, altitude in the case of aircraft.
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 variation in pressure excursions
between oxygen and nitrogen enriched product gas.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 the molecular sieve oxygen monitor 10 includes
a differential pressure regulator 12 which regulates the pressure
of the effluent gas samples P.sub.s from an oxygen enriching supply
(not shown). The differential pressure regulator 12 references its
output pressure to the atmospheric pressure and maintains a constant
differential thereto. In applications where the atmospheric pressure
can vary, such as in aircraft, the constant differential pressure
establishes a reference system flow-through rate from which the
nitrogen or oxygen concentrations of the effluent gas can be inferred
as more fully explained below.
The gas flow from the regulator 12 is controlled by an input solenoid
valve 14 which is driven by an electrical timing circuit (not shown),
which circuit holds the solenoid valve open for a first period of
1.5 seconds of a 3.0 second sampling cycle time. In order to prevent
pressure spikes, a restrictive orifice 16 allows for a gradual system
pressure increase over the 1.5 seconds when the input solenoid valve
14 is open.
The effluent sample flows through a bed 18 of molecular sieve material
and on through a restrictive orifice 20 to an output solenoid valve
22. The ouput solenoid 22 is held closed for the first period of
1.5 seconds and is opened for a second period of 1.5 seconds of
the 3 second sampling time cycle. During this second 1.5 second
period, the input solenoid valve 14 is held closed.
The temperature of the molecular sieve bed 18 is monitored by a
temperature transducer 24. The output of the transducer 24 is used
to either control the temperature of the bed 18 or to correct the
system pressure output readings. A pressure transducer 26 converts
the pressure of the oxygen monitor 10 to an electrical signal which
is fed to a signal conditioner (not shown). The signal conditioner
interprets the system pressure swing limits from which oxygen concentrations
are inferred and displayed.
MODE OF OPERATION OF THE PREFERRED EMBODIMENT
To start the oxygen monitor 10 a timing circuit (not shown) is
activated, and alternately, electrically excites the solenoid valves
14 and 22 for 1.5 second periods holding the first open while the
second is closed and closing the first when the second is open.
The pressure of the gas sample P.sub.s is reduced to a preset level
by the regulator 12. The regulated pressure is referenced to the
atmospheric pressure maintaining a constant differential pressure
across the monitor 10 from the source P.sub.s to the system vent
P.sub.v. When the solenoid valve 14 is cycled open for 1.5 seconds,
the monitor 10 pressure is gradually increased as the gas flows
through the restrictive orifice 16. With the solenoid valve 22 closed
during this first 1.5 second period, the pressure in the monitor
10 reaches a level proportional to the adsorptive capabilities of
the molecular sieve material in the bed 18. If the product gas is
oxygen-rich and a molecular sieve material which adsorbs oxygen,
such as a zeolite 4A, is selected, the upper pressure limit attained
in the system will be less than that which would be attained by
a nitrogen-rich gas or by air as the oxygen is adsorbed.
As the system vents through the restrictive orifice 20 to the atmosphere
when the solenoid valve 22 opens and the valve 14 closes in the
second 1.5 second period, the lower pressure limit reached by the
monitor 10 will be decreased as a function of the rate of desorption
of the sieve material in bed 18. Both the upper and lower limit
pressure attenuation of an oxygen-rich product gas acting through
a monitor whose bed 18 is charged with a molecular sieve material,
such as a zeolite 4A which readily adsorbs oxygen, are illustrated
in FIG. 2. FIG. 2 also illustrates the pressure swing of air or
any nitrogen-rich gas flowing through that same system using a zeolite
4A.
The calibration of the monitor 10 includes establishing a correlation
between the pressure swing of nitrogen and that of oxygen in an
oxygen adsorbing system. The pressure transducer 26 provides an
electrical signal which is an analog of the monitor 10 system pressure.
This electrical signal is compared to an equivalent signal for the
reference gas, in this example, nitrogen, and an oxygen concentration
is inferred. Should the temperature of the bed change from that
at which the monitor 10 was calibrated, a correction is applied
to the inferred concentration level.
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. |