Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: Gas Compressor with Drier and Radio Emission Controls
FIELD OF THE INVENTION
This invention relates to the compression of gases.
More particularly, it relates to the compression of natural
gas and/or hydrogen for use in vehicles propelled by such
gases. Specifically, it relates to an apparatus and methods
for removing moisture vapor as part of the compression
procedure and separating removed moisture from contaminants
therein. It also relates to minimizing the release of
electromagnetic radiation.
BACKGROUND OF THg INVENTION
It is known to remove moisture from gas in order to
store such gas for use in a motor vehicle. Moisture is also
removed from compressed gases for a variety of other
applications. Typically, during the gas compression cycle
the gas being compressed is passed over a desiccant bed
which effects the removal of moisture from the gas.
Eventually, the desiccant bed will saturate. A moisture
sensor may be employed to detect the amount of moisture
present in the gas exiting the compressor, sensing when the
measured moisture content at the output of the compressor
rises beyond a permissible range, above an upper limit.
Alternately, a drying bed may be employed for a
predetermined period of time. In either case a regeneration
stage for recharging the desiccant bed is eventually
required.
The technology for drying gas streams is well
established. It includes absorption and condensation
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methods and the use of membrane separation systems.
Examples of these technologies, used separately and in
combination are United States patent Nos. 5,034,025;
5,071,451 and 5,240,472 as well as the prior art referred to
therein.
Existing compressors of this type have employed
gas drying arrangements that operate on a continuous basis,
using a two-bed system. Examples of this type of technology
include US patent 6,117,211.
The present invention addresses the object of
compressing natural gas with a reduced amount of moisture
being present in the compressed gas by employing gas drying
arrangements that operate on a dis-continuous basis, using a
single-bed system wherein the compression of gas is
eventually interrupted to allow the system to effect
regeneration.
In the treatment of gas streams, de-watering
processes generate extracted water that may contain traces
of contaminants originating from the principal stream. In
20' the case of natural gas, these contaminants include hydrogen
sulphide, sulphur dioxide and mercaptans. Disposal of water
containing contaminants of this type can be subject to
environmental restraints.
The extracted' water being produced cannot be
released locally into the environment because of the
contaminants present therein. Apart from issues relating to
hazards, even trace smells of organic or sulphurous
components from a natural gas stream would suggest to a
consumer that a leak existed in the compressor system.
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It is an object of this invention to address the convenient
disposal of separated water under these circumstances.
It is a further object of this invention to minimize the release
of electromagnetic radiation during operation of the compressor
system.
The invention in its general form will first be described, and
then its implementation in terms of specific embodiments will be
detailed with reference to the drawings following hereafter. These
embodiments are intended to demonstrate the principle of the
invention, and the manner of its implementation. The invention in
its broadest and more specific forms will then be further
described, and defined, in each of the individual claims which
conclude this Specification.
SUMMARY OF THE INVENTION
In one aspect of the present invention, there is provided a
compressor system for gas which normally operates on a gas
compression cycle but which also operates in a drier regeneration
cycle, the system comprising: 1) a compressor driven by a motor,
the compressor having at least a first stage inlet through which
passes a flow of gas being compressed from a gas supply inlet: 2)
a gas delivery outlet at the outlet of the compressor, for
supplying gas to a delivery line; 3) a gas drier stage comprising
a desiccant bed located in-line with the flow of gas passing
through the compressor during the gas compression cycle; 4) a
condenser also located in-line with the flow of gas passing
through the compressor during the gas compression cycle which
condenser, during the compression cycle, is normally inactive; 5)
temperature control means to control the temperatures of the
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desiccant bed and condenser which means are, during the
compression cycle, inactive but, upon entering into a regeneration
cycle, such means being actuatable to cause the desiccant bed to
be heated and the condenser to be cooled; and 6) valve means for
switching the flow of gas from the delivery outlet to recirculate
through the compressor, whereby, during the regeneration cycle
arising from activation of the valve means, gas trapped within the
compressor, desiccant bed and condenser is redirected from the
outlet of the compressor for circulation in a closed loop as a
recirculating gas flow through the compressor, with at least a
portion of such recirculating gas flow passing through the
desiccant bed and condenser to permit water evolved from the
desiccant bed to be carried by the
recirculating gas to the condenser where it condenses due to the
low temperature condition maintained within the condenser by the
temperature control means.
According to the present invention in one aspect, a compressor for
a gas which normally operates on a gas compression cycle is
provided with a gas drier stage comprising a single desiccant bed
located in-line with the flow of gas passing through the
compressor during the gas compression cycle. Also located in-line
with such gas flow is a condenser which, during the compression
cycle, is inactive. The temperatures of the desiccant bed and
condenser are both controllable, preferably by electrical means.
During the compression cycle, such temperature controls are
preferably inactive. However, upon entering
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into a regeneration cycle, the gas bed is heated and the
condenser is cooled.
During the regeneration cycle arising from
activation of a valve means, gas trapped within the
compressor, desiccant bed and condenser is redirected from
the outlet of the compressor for circulation in a closed
loop as a recirculating gas flow through the compressor,
with at least a portion of such recirculating gas passing
through the dessicant bed and condenser. This permits
water evolved from the desiccant bed to be carried by the
recirculating gas to the condenser where it condenses due to
the low temperature condition maintained within the
condenser by the temperature control means.
More specifically, in a preferred embodiment the
outlet from the compressor is connected through an
electronically controlled valve to the delivery line which
carries compressed gas off to a storage reservoir during the
compression cycle. When the compressor ceases operating in
compression mode, the electronically controlled delivery
valve switches the flow of gas from the delivery line into
the interior volume of a casing cavity for the compressor.
The compressor draws its input from the casing cavity.
The resulting drop of pressure in the delivery
line causes a check valve at the external reservoir, which
contains high pressure gas, to close. The compressed gas
trapped in the delivery line then "blows down" into the
interior volume of the casing, producing a pressure
condition that is moderately elevated above that of the
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supply line pressure 'eg 30-60 psi. The check valve at the
supply line inlet to the interior volume then closes as the
source gas pressure is only of the order of 0.2 to 0.5 psi.
With output of the compressor redirected into the
casing volume, the trapped gas is now capable of circulating
in a closed loop through the compressor, desiccant bed,
condenser, and casing volume with the trapped gas serving as
a sweep gas for regenerating the dessicant bed. Circulation
of the gas within this closed loop is effected at a low gas
flow rate so that the circulating gas passing through the
condenser is substantially, preferably fully, chilled when
it exits the condenser. This maximizes the efficiency of
transferring moisture from the desiccant bed to the
condenser as a preferred mode of operation.
Circulation may be effected at a low flow rate by
reducing the speed of the compressor motor. Alternately,
one or more valve-controlled bypass lines may divert a
portion of the circulating gas around the dessicant bed,
and/or the condenser, allowing only a limited amount of gas
flow through these components. The permitted flow rate over
the bed, established by the valve or by other flow-limiting
means, is set so as to be commensurate with the condensation
of vapor from such gas. This arrangement allows the system
to operate with a fixed speed motor.
In the regeneration process water evolves from
the desiccant bed, raising the moisture content of the
circulating gas. The desiccant bed is heated at.this stage
to enhance its release of moisture. The released water, in
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vapor form, is then carried by the gas flow to the condenser
where it condenses due to the low temperature condition
maintained within the condenser. Circulating gas exiting.
the condenser leaves the condenser in a cooled, vapor
saturated, condition. By the time the circulating gas
reaches the heated desiccant bed, its temperature has been
raised and the gas is no longer vapor saturated. The heated
circulating gas is therefore able to absorb further moisture
from the desiccant bed as it passes over such bed.
In order to dispose of water condensing within the
condenser such water may simply be collected. However, to
achieve extended, stand-alone operation, the condensed water
is directed, preferably flowing under gravity, into contact
with a semi-permeable membrane which allows the water to
evaporate. At the same time, aromatic compounds present
within the condensate are retained by the membrane *within
the condenser. To enhance the rate of evaporation and flow
of water through the semi-permeable membrane; an external
fan and optional heater element may be preferably positioned
to circulate warm air past the membrane surface.
It is important to note that the condenser,
according to the invention, is located in-line with the gas
flow during the compression cycle. This. exposes the
condenser and semipermeable membrane to an elevated pressure
condition. In a preferred variant of the invention, the
compressor is a multi-stage compressor and the desiccant bed
and condenser are positioned in-line between consecutive
stages, preferably between the first and second stages of
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the compressor. Thus, although the condenser is exposed to
an elevated pressure condition, this is not the final,
maximum pressure produced by the compressor. Rather, it is
an intermediate pressure arising after only the first stage
of compression.
This limitation on the pressure to which the
condenser is exposed is particularly significant in the
preferred embodiment of the invention wherein the condenser
is directly connected to a semi-permeable membrane through
which condensed water is allowed to evaporate into the
environment. Such membranes are only capable of
withstanding a modest pressure differential. In the case of
a multistage compressor, the pressure developed between the
first and second stage is not so high as to preclude use of
such a semi-permeable membrane as a means to dispose of
water condensate. A preferred form of membrane is tubing
made of Hydroscopic Ion Exchange Membrane.
Thus, according to this preferred embodiment,
condensed water accumulating in the condenser is directly,
or eventually, disposed of by release into the environment,
preferably through the semi-permeable membrane. Use of
such a membrane ensures separation and retention of complex
odorous molecules that may be present in the water
condensate, with only pure water being released into the
environment.
Once the desiccant bed has been recharged, heating
for the bed is terminated. As well, chilling of the
condenser and heating for the semi-permeable membrane, if
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employed, are terminated. Thereafter the valve means is
actuated to reconnect the outlet stage of the compressor to
the delivery line. The compressor motor is then speeded up
to resume the compression cycle if it has been slowed down,
and the inlet to the supply line automatically reopens.
Alternately, if a fixed speed motor is employed, the bypass
lines is/are closed-off allowing the regular compression
cycle to resume.
In a further preferred variant, the compressor is
contained within a sealed metal casing.- Supply gas enters
the interior volume of this casing through a check valve and
is' drawn into the compressor from the crank-portion of this
interior volume. Also located within the casing is the
motor, preferably a variable speed motor, and preferably
control circuitry f or delivering current to the motor. In
these preferred scenarios, the motor is an alternating
current induction motor, and in the variable speed situation
the control circuitry. produces an alternating current of
varying frequency, whereby the speed of the motor is varied
in accordance with system requirements.
It is a further preferred feature of the invention
that not only is the electrical motor operating the
compressor mechanism contained within the same' casing as the
compressor, but also the control circuitry for delivering
power to the motor is contained within the casing. An
advantageous result achieved by this arrangement is that
electromagnetic emissions arising from current being
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delivered from the motor controller to the motor are
confined within the metallic casing.
The control circuitry, which may deliver current
at 360 volts DC to the motor, is itself provided with
current through a sealed penetration of the casing wall.
The motor control circuitry operates to create alternating
current having a frequency of on the order 60 Hz but with
multiple harmonics. The electrical power delivered to the
motor provides current, at a typical maximum level, of on
the order of 8 to 10 amps. The electromagnetic radiation
from the wiring extending- between the control circuitry of
the motor carrying a such current at such frequencies is a
source of electromagnetic radiation. By confining this
wiring to within the metallic casing, electromagnetic
radiation from this source is shielded from entering into
the environment.
On start-up, low motor speeds are preferably
adopted to reduce otherwise high start-up current drains on
the electrical supply system. This enables the unit to
operate off of a standard household voltage, e.g. 110-120
volt, moderately .fused electrical supply system. After
start-up, initial compression can be effected with a high
motor speed. Once higher pressures have been established in
the motor vehicle fuel reservoir or other delivery
receptacle, the motor speed is reduced in order to moderate
ring wear and limit power consumption. This procedure is
especially suited to oil-less compressors as the wear rate
of the sealing rings within the compressor cylinders of such
units increases when the compressor system is operated at
high speed against a high-back pressure.
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Furthermore in the case of use a continuously
controllable, variable speed motor, the speed of the
electric motor may also be controlled to avoid natural
resonant frequencies arising from its mechanical components
that would otherwise increase the noise and vibration
generated by the unit.
The foregoing summarizes the principal features of
the invention and some of its optional aspects. The
invention may be further understood by the description of
the preferred embodiments, in conjunction with the drawings,
which now follow.
SUMMARY OF THE FIGURES
Figure 1 is a pictorial representation of a
gaseous fuel motor vehicle parked in a garage having a home
refueling appliance according to the invention mounted on
its inner wall.
Figure 2 is a schematic for the basic components
of the appliance showing besides the motor and compressor,
the desiccant bed, the main logic controller, the motor
control circuitry and various sensors.
Figure 3 is a schematic variant of Figure 2
showing gas flow during the compression cycle.
Figure 4 is a schematic as in Figure 2 showing the
basic flow diagram of the appliance during the regeneration
cycle wherein the desiccant bed is recharged and the motor
speed is variable.
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Figure 5 is a cross-sectional side view of the
compressor/motor assembly within its immediate case and the
drier components. This compressor casing contains the
motor, a blow-down volume, and the motor control circuitry.
Also shown is an additional, outer case or ventilation
shroud to contain cooling air flow.
Figure 6 is a detailed schematic cross-sectional
front view of the drier, condenser, and semi-permeable
membrane portions of Figure 2 with the semi-permeable
membrane in the form of a tube through which water
condensate enters under gravity.
Figure 6A is a cross-sectional front view of the
drier, condenser, and semi-permeable membrane portions of
Figure 6 showing the semi-permeable membrane tube through
which water condensate evaporates in the presence of a
heated airflow created by a fan.
Figure 7 is a detailed, close-up, cross-sectional
side view of the semi permeable membrane of Figures 5 and 6a
showing airflow around the coiled tubing.
Figures 8A and 8B are schematics as in Figure 2
showing the basic flow diagram of the appliance during the
regeneration cycle wherein the motor speed is fixed and the
drier-condenser has a bypass line that can divert flow past
the drier-condenser by switching flow into the circulating
loop or to the casing cavity, or both, to permit a reduced
gas flow rate to occur within the condenser.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
In Figure 1 the home refueling appliance 1 is
shown mounted on a garage wall with the high-pressure
discharge or delivery hose 2 connected to a car, the inlet
or supply hose 3 providing a source of gas 6, and the
electrical cord 4 plugged into a standard household
receptacle.
Figure 2 schematically depicts the unit operating
in compression mode. In Figure 2 line gas 6 which may
contain contaminants 8, enters the interior volume 14 of the
casing 26 from which it drawn into the first of a series of
four
compression stages 28, 32, 33, 34 of compressor 5. The line
gas 6, which typically has a.pressure of between 0.2 and 0.5
psi is drawn into the interior volume 14 by the suction
created by the first compression stage 28. A line gas
pressure sensor 21 detects the line gas pressure, providing
a signal to the main logic controller 46..
On leaving the first stage 28, the gas 6 passes through
20- a desiccant bed 7 contained within an absorption chamber 29.
This bed of desiccant material 7, such as activated alumina
or zeolite, adsorbs the moisture in the gas 6, including at
least some of the contaminants 8. Upon exiting the
absorption chamber 29, the dried gas continues into the
volume of a condenser 30 which is, at this stage, passive.
Exiting the condenser 30 through conduit 55, the gas 6
proceeds to the next, second stage 32 of the compressor S.
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The flow of gas in this compression cycle is shown in Figure
3.
As shown in Figure 4,' and in greater detail in
Figures 6 and 6A, the desiccant 7 is regenerated by being
exposed to a sweep gas 13 originating from the gas stream
trapped in the compressor 5, motor 27, desiccant bed 7 and
condenser 30 when the compression cycle is terminated. As
shown in Figure 4 the sweep gas 13 is drawn at a reduced
flow rate through the absorbent bed 7, optionally by the
slow speed operation of the change to motor 27. Moisture in
the adsorbent bed 7 is encouraged to vaporize into the
sweep gas 13 by its dry condition, as described further
below, by its pressure and the by the additional supply of
heating to the absorbent bed 7.
Upon exiting the bed 7 the gas flows into
condenser 30 which contains a heat-exchange surface. This
heat-exchange surface is preferably cooled by an electrical-
actuated cooling block 53 operating on the basis of the
Peltier effect.
Cooled, circulating sweep gas 13, which has now been de-
moisturized in the condenser 30, then passes into a return
conduit 55 that leads to the second stage 32 of the
compressor. The slow operation of the motor 27 and
compressor 5 causes this sweep gas 13 to circulate endlessly
until the regeneration cycle is terminated.
To speed the regeneration process and assist in
recovery of the water subsequently, a thermostatically
controlled electrical element 52 warms the desiccant 7. The
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warmed, moisturized sweep gas more effectively releases
moisture as it passes through the condenser 30.
As shown in Figures 2, and 6 liquified water 54
accumulates in the bottom of the condenser 30 as a
condensate, below the level of the return conduit 55 within
the condenser. The condensed water 54 will contain some
residual contaminants 8a. This water condensate 54,
including residual contaminants 8a present therein, may be
simply accumulated and collected or it may then be passed to
a separation chamber preferably in the form of tubing 31
that has walls formed of a semi-permeable membrane 61. The
semi-permeable membrane 61 allows only the penetration of
water as the permeate. On the other side of the membrane
61, water diffusing therethrough evaporates. This process-
may be accelerated by an airflow originating from a fan 42.
In this case the shroud 43 serves to duct a constant air
flow over the membrane 61. Optionally the air flow in the
vicinity of the membrane may be heated by a membrane heater
56.
The circulating airflow 60 from the fan 42 may
also be used to cool the condenser 30, preferably using
separate ducting (not shown).
As water diffuses through the membrane 61, some
contaminants 8a may accumulate on the interior surface of
the
membrane 61. Eventually, the rate of diffusion may drop to
a level where the membrane 61 must be cleaned or replaced.
In the foregoing description the semi-permeable
membrane 61 could be in the form of a plate fitted as part
of a wall of a separation chamber. Figures 6 and 7 show a
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preferred variant in which the semi-permeable membrane is
shown as a tube 31. This tube 31 is preferably has a wall
formed of semi-permeable hydroscopic ion exchange membrane
material. Membranes in the form of tubes. made of modified
Teflon(TM) have been found suitable for this application,
showing life-times of practical duration.
It is noted that the absorbent chamber 29 and
condenser 30 are contained within the high pressure zone of
the compressor 5, between the first stage 28 and the second
stage 32. The pressure in this zone is only on order of 200
psi during the compression cycle. In fact, this pressure
level enhances the gas drying effect. It has been found
that, at these pressure levels, the semi-permeable membrane
61 in tubing format can extend outside this pressurized
zone, relying on secure couplings 57 to seal the connection
between the tubing 31 and the condenser, chamber 30. The use
of the multistage compressor especially facilitates this
arrangement.
Further components as shown in Figure 2 include
an inlet filter 22, a high pressure transducer 24, a
pressure relief valve 25 leading to a vent opening 50, a
burst disc 35 in the fourth stage 34 to relieve excessive
over-pressure, an in-line breakaway connector 36,. the
vehicle connection nozzle 38, a gas leak-detecting sensor
39, an air flow sensor 40, and an ambient air temperature
sensor 41.
In Figures 8A and 8B a fixed speed motor variant
is shown wherein a bypass line 60 or 60A is opened by valve
61 actuated by the main logic controller 46 during
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regeneration. Due to this bypass, the sweep gas 13 passes
through the desiccant material 7 and condenser 30 at a
preferred flow rate. The amount of sweep gas 13 allowed by
valve 61 and associated flow-limiting means to pass through
this regeneration branch is set to maximize the efficiency
of the vapor evaporation and condensation process.
Recirculating gas 13 is either diverted to the second stage
32 through bypass .line 60, or to the casing volume 14
through bypass line 60A, or both bypass lines may be used in
combination.
Referring to Figure 2, the compressor 5, motor 27
and motor control circuitry 45 are all located within the
casing 26, (counting the compressor block as part of the
casing), which is in turn, surrounded by an outer shroud 43.
According to one variant of the invention the electronic
motor controller 45, which supplies current to the
electrical motor '27, is preferably located within the
totally contained environment of ' the motor/compressor
assembly.. This sealed environment is provided by the same
metal casing 26 that surrounds the motor and compressor
parts. The motor control circuitry 45 is, in particular,
located in the blow-down volume 14, sealed entirely within
the casing 26. The metallic wall of the casing 26 acts as
heat sink for the heat produced by the motor control
circuitry 45 and as a shield for outgoing electromagnetic
emissions arising from wiring extending between the motor 27
and motor controller 45.
As shown in Figure 2, the main logic controller
46, fed power from a power supply 47, is able to activate
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the motor 27, and govern its speed in the variable speed
version, through motor control circuitry 45. Signals
between the, main logic controller 46 and motor control
circuitry 45 penetrate the casing 26 at a sealed entry point
44. The command logic circuitry 46 sends and receives
commands and data through digitally encoded signals
transmitted along optical fibers. This minimizes the
electrical penetrations made into the interior 14 of the
metal cavity of the casing 26 which contains natural gas in
a slightly pressurized condition.
CONCLUSION
The above disclosed embodiments are only
exemplary. The invention in its broadest, and more specific.
aspects, is further described and defined in the claims
which now follow.
These claims, and the language used therein, are
to be understood in terms of the variants of the invention
which have been described. They are not to be restricted to
such variants, but are to be read as covering the full scope
of the invention as is implicit within the invention and the
disclosure that has been provided herein.
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