Note: Descriptions are shown in the official language in which they were submitted.
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COMPRESSOR INTER-STAGE TEMPERATURE CONTROL
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of the filing
of U.S. Provisional Patent
Application Serial No. 61/476,099, entitled "Compressor Inter-Stage
Temperature Control", filed on April
15, 2011, and the specification thereof is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention (Technical Field):
[0002] Embodiments of the present invention relate to a method, system,
and apparatus for
providing inter-stage temperature control of a compressor, particularly at
least partially via the use of an
air cooler.
Description of Related Art:
[0003] One of the major problems encountered with known vapor recovery
systems is
condensation of the vapors in the air-cooled compressor, which compressor is
used to raise the
pressure of the recovered vapors to the pressure of the sales line. In known
systems, some of the
recovered vapors are at liquid phase at the typical sales line pressures, but
change to a vapor phase
when the sales line pressure is reduced to the atmospheric pressure of the
storage tank. Known
systems prevent the recovered vapors from going back to the liquid phase
during the compression cycle
by maintaining, through all stages of compression, the temperature of the
recovered vapors above the
hydrocarbon dew-point of the recovered vapors. In order to control, during the
compression cycle, the
temperature of the recovered vapors the air cooler is removed from the
compressor and is replaced by a
system that utilizes the recovered liquids instead of the atmosphere as a heat
sink.
[0004] Failure to adequately maintain proper temperature of gasses
between stages of
compression can result in recycle loops being formed. There is thus a need for
a method, apparatus,
and system of vapor recovery that can be used in temperate climates and will
prevent the formation of
recycle loops, be simple to install on an existing compressor setup, or
incorporated into the design of a
new vapor recovery unit and which uses ambient air to cool one or more
portions of the system.
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[0005] Objects, advantages and novel features, and further scope of
applicability of the
present invention will be set forth in part in the detailed description to
follow, taken in conjunction with
the accompanying drawing, and in part will become apparent to those skilled in
the art upon
examination of the following, or may be learned by practice of the invention.
BRIEF SUMMARY OF EMBODIMENTS OF THE PRESENT INVENTION
[0006] An embodiment of the present invention relates to a method for
regulating temperature
of a gas between stages of compression which includes providing a control
valve between stages of
compression; providing an air-cooled heat exchanger; monitoring the
temperature of the gas in at least
one location; and manipulating the control valve such that at least a portion
of compressed gas from a
first stage of compression can be selectively caused to flow through the air-
cooled heat exchanger
before being introduced into a second stage of compression. The at least one
location can be
downstream of an outlet of the second stage of compression. The at least one
location can be between
an outlet of the air-cooled heat exchanger and an inlet of the control valve.
Manipulating the control
valve can include modulating the control valve.
[0007] In one embodiment, the control valve can include a first inlet
which is coupled to an
outlet of the first stage of compression, the control valve can include a
second inlet which is coupled to
an outlet of the air-cooled heat exchanger, and/or manipulating the control
valve can include adjusting a
flow ratio, the ratio being a formed between a flow rate of gas entering the
first inlet of the control valve
and a flow rate of gas entering the second inlet of the control valve.
[0008] In one embodiment, manipulating the control valve can include
modulating the control
valve with a modulating valve, and the modulating valve can optionally be
controlled in response to a
temperature monitored in a second location and the control valve can be
adjusted in response to a
combination of the temperature that is monitored at the first location and a
temperature that is monitored
at the second location. The first location can include a location that is
downstream of the second stage
of compression and the second location can include a location between an
outlet of the air-cooled heat
exchanger and the second inlet of the control valve.
[0009] Optionally, the control valve can be manipulated so as to maintain
a temperature of the
gas after having passed through the second stage of compression within a
predetermined temperature
range and/or to maintain a temperature of gas exiting the air-cooled heat
exchanger above a
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predetermined set point. In one embodiment, the second stage of compression is
a third stage of
compression of a multi-stage compressor and the first stage of compression is
a second stage of
compression of the multi-stage compressor. Optionally, the control valve can
include an outlet that is
communicably coupled to an inter-stage scrubber.
[0010] An embodiment of the present invention also relates to an apparatus
for controlling
temperature of gases between stages of compression for a multi-stage
compressor which includes a
control valve having first and second inlets and an outlet, the first inlet
coupled to an outlet of a first
stage of the multi-stage compressor, the second inlet coupled to an outlet of
an air-cooled heat
exchanger, and the outlet of the control valve coupled to an inter-stage
scrubber; and a modulating
valve communicably coupled to the control valve; the modulating valve
configured to manipulate the
control valve based on a temperature of the gases at a location between an
outlet of the air-cooled heat
exchanger and the second inlet of the control valve. In one embodiment, the
control valve can be
manipulated based on a temperature of the gases at a location that is
downstream from a second stage
of the multi-stage compressor. Optionally, process control logic can be
connected to the modulating
valve. The control valve preferably adjusts a mixture of gas having passed
through the air-cooled heat
exchanger with hot gas exiting the first stage of the multi-stage compressor.
[0011] In one embodiment, the control valve and the air-cooled heat
exchanger are positioned
such that at least a portion of hot gas from the first stage of compression
can be caused to flow through
the air-cooled heat exchanger before entering the second inlet of the control
valve and at least a portion
of hot gas from the first stage of compression of the multi-stage compressor
enters the second inlet of
the control valve.
[0012] In one embodiment, each of the components are duplicated and placed
on another inter-
stage of compression such that, rather than being disposed between the first
and second stages of
compression of the multi-stage compressor, the duplicated components are
instead disposed between
second and third stages of the multi-stage compressor.
[0013] Objects, advantages and novel features, and further scope of
applicability of the
present invention will be set forth in part in the detailed description to
follow, taken in conjunction with
the accompanying drawings, and in part will become apparent to those skilled
in the art upon
examination of the following, or may be learned by practice of the invention.
The objects and
advantages of the invention may be realized and attained by means of the
instrumentalities and
combinations particularly pointed out in the appended claims.
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BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0014] The accompanying drawing, which is incorporated into and forms a
part of the
specification, illustrates one or more embodiments of the present invention
and, together with the
description, serves to explain the principles of the invention. The drawing is
only for the purpose of
illustrating one or more embodiments of the invention and is not to be
construed as limiting the
invention. Fig. 1 is a flow diagram illustrating an embodiment of the present
invention as applied to a
two-stage compressor.
DETAILED DESCRIPTION OF THE INVENTION
[0015] An embodiment of the present invention is directed to a method,
system, and apparatus
for vapor processing that utilizes a compressor equipped with an air cooler.
Embodiments of the
present invention can be used in conjunction with a new compressor, can be
incorporated into the
design of a compressor, or can be retrofitted to an already-installed
compressor system.
[0016] In one embodiment, for a multi-stage compressor, an air cooled
compressor can be
equipped with temperature control valves on each stage of compression. The
temperature control
valves can be controlled by a thermostat installed in the piping downstream of
the compression stage
that is being controlled. The temperature control valves preferably mix a
portion of the hot gas of
compression with a portion of the cool gas from the air cooler to provide a
gas temperature at each
stage of compression that is high enough to prevent or inhibit the formation
of recycle loops. This can
be done by monitoring a temperature of the compressed gas and adjusting the
one or more valves such
that a greater or lesser amount of the compressed gas is caused to flow
through an air-cooled heat
exchanger. In one embodiment wherein multiple inter-stages of compression
exist and wherein a
control valve is provided for each of the multiple inter-stages of
compression, the valve for each inter-
stage of compression preferably acts independently of the other inter-stages.
Thus, each valve can
have two inlets such that hot gas directly from a stage of compression enters
in one inlet and cooled
compressed gas from an air-cooled heat exchanger enters at a second inlet and
the valve is
manipulated to adjust the ratio there between. Optionally, the one or more
control valves can be
adjusted based on sensed temperatures in relation to one or more predetermined
temperature set-
points. In one embodiment, a desired temperature set-point can be established
and the valve can
continuously and/or periodically adjust the mix ration in order to maintain
that set-point or within a
margin of error of that set point.
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[0017] In one embodiment, for a two stage compressor, one temperature
control valve can
optionally be used. In one embodiment, for a three stage compressor, two
temperature control valves
can be used. In one embodiment for multiple stage compressors, one temperature
control valve less
than the number of stages of compression can be used.
[0018] The term "PICT valve" and/or "process inter-stage controlled
temperature" is used
throughout this application to mean a temperature control valve or any other
mechanism, system,
assembly, circuit, sensor, combination thereof, or the like, which can be used
in place of a temperature
control valve and which will perform substantially the same operation.
[0019] In one embodiment, because the PICT valve can be made to divert
only a portion of the
hot compressed gas to a 1st stage cooler, the volume of gas flowing through
the cooler is thus less than
if all of the hot compressed gas were directed therethrough. Because
comparatively less gas is flowing
through the 1st stage cooler, the cooling coil is thus comparatively over-
sized. Therefore, the gas
flowing through the cooling coil is cooled more than would be the case if all
of the hot compressed
gases were directed therethrough. The gas flowing through the cooling coil is
subject to hydrate
formation, so the temperature of the gas flowing through the cooling coil is
preferably maintained above
the gas hydrate formation temperature. This can be accomplished by monitoring
the temperature of the
gas exiting the cooler and adjusting the PICT valve in response to
predetermined temperature
parameters.
[0020] To maintain the temperature of the gas flowing through the cooling
coil to a temperature
above hydrate formation, a thermocouple, transducer, or other sensor, method,
system, circuit,
apparatus, or combination thereof is optionally installed in the piping
downstream of the cooling coil
outlet. The sensor preferably monitors the temperature of the gas exiting the
cooling coil. As long as
the gas exiting the cooling coil is above the hydrate formation temperature of
the gas, the thermostat
downstream of the compression stage preferably controls the operation of the
PICT valve.
[0021] If the ambient temperature becomes low enough to cause the
temperature of the gas
exiting the cooling coil to approach hydrate formation temperature, the
transducer through a process
logic control unit ("PLC") preferably overrides the thermostat and the PLC
takes control of the PICT
valve and sends more hot compressed gas through the cooling coil. Of course
other circuits, and
control mechanisms can be used in place of the transducer and PLC to effect
the same actions. As
long as the ambient temperature is low enough to create a potential problem
with hydrate formation in
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the cooling coil, the transducer and PLC can control the PICT valve to
maintain the gas temperature in
the cooling coil above hydrate formation temperature.
[0022] During the times that the PLC is controlling the PICT valve, some
condensation of the
recovered vapors can occur. The amount of condensation that can occur, though,
is much less than the
amount of condensation that would occur, under the same ambient temperature
conditions, on an
uncontrolled compressor, and the small amount of condensation that can occur
is not enough to affect
the vapor recovery process.
[0023] In one embodiment, the PICT valve can be designed for use in the
piping connecting
the compression stages of a compressor, the design of the valve can optionally
be specialized. For
example, the valve can be powered by a motor system, or formed from another
non-diaphragm
mechanism. In one embodiment, the PICT valve preferably has as low of a
pressure drop as practical.
In one embodiment, the PICT valve can optionally incorporate a diaphragm
opposed by a spring. The
movement of the diaphragm can optionally be controlled by a gas signal from a
temperature control
device. In one embodiment, the PICT valve does not shut off the flow of gas,
movement of the
diaphragm does not change the flow capacity of the PICT valve, and completely
closing either the cool
or hot port does not change the flow capacity of the PICT valve because each
port is capable of
providing the full flow capacity of the of the compressor through PICT valve.
[0024] Referring now to Fig. 1 a flow diagram of the present invention as
applied to a two-
stage compressor is illustrated. Gas flow line 1 preferably moves the vapors
to be compressed into the
inlet scrubber 2. Liquid level control 3 and dump valve 4 are preferably
installed in inlet scrubber 2.
Tubing line 5 preferably sends an output signal from liquid level control 3 to
motor valve 4. Liquid flow
line 6 preferably sends the liquids separated by inlet scrubber 2 to point 7.
Gas flow line 8 preferably
moves the vapors from inlet scrubber 2 to the suction port 44 of first stage
of compression 9. First stage
of compression 9 preferably discharges through discharge port 45. Flow line 10
preferably moves the
hot compressed vapors from discharge port 45 of first stage of compression 9
to point 11. Gas flow line
12 preferably moves at least a portion of the hot compressed vapors from point
11 to inlet 13 of first
stage gas cooler 14.
[0025] First stage gas cooler 14 is preferably cooled by force draft air
driven by fan 15. Fan 15
is driven by the compressor power source, which can optionally include, but is
not limited to an engine,
an electric motor, a pneumatic motor, a hydraulic motor, combinations thereof,
and the like (note that
the compressor power source is not illustrate in Fig. 1). The hot compressed
vapors preferably flow
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through the radiator type air cooling section of first stage air cooler 14 and
exit at outlet 16 of first stage
air cooler 14. Gas flow line 17 preferably moves the cooled compressed vapors
from outlet 16 of gas
cooler 14 to cool port 18 of PICT valve 19.
[0026] In one embodiment, PICT valve 19 comprises a three-way gas
temperature control
valve. Gas flow line 20 preferably moves hot compressed vapors from point 11
to hot port 21 of PICT
valve 19. Port 22 is the common port of PICT valve 19. Flow line 23 is a flow
line that carries the
temperature controlled, compressed vapors to inter stage scrubber 24. Flow
line 25 preferably carries
the temperature controlled, compressed vapors to the inlet port 26 of second
stage of compression 27.
Second stage of compression 27 preferably discharges through discharge port
28. Flow line 29
preferably carries the hot compressed vapors from second stage of compression
27 to either be further
controlled by another PICT valve for temperature control of a third stage of
compression or else to the
discharge of the compressor. Thermostat 30 preferably senses the temperature
of the vapors being
carried in flow line 29. Thermostat 30 preferably increases output pressure to
increase the temperature
of the vapors flowing in line 29. Tubing line 47 preferably carries supply gas
to thermostat 30. Line 31
is a tubing line that carries the output signal of thermostat 30 to modulating
control valve 38, the
modulating control valve 38 preferably receives an electrical signal from PLC
32. Line 39 is a tubing
line that carries the pneumatic control pressure signal to the diaphragm of
PICT valve 19. Temperature
transmitter 33 is a temperature transducer. Line 34 is an electrical line that
connects transducer 33 to
PLC 32. Line 36 is an electrical line that connects PLC 32 to modulating
control valve 38.
[0027] In operation, the vapors in line 1 enter inlet scrubber 2. Inlet
scrubber 2 removes any
free liquids contained in the vapors. The free liquids fall to the bottom of
inlet scrubber 2 and, when a
fluid level is sensed by liquid level controller 3, a pneumatic signal is sent
to motor valve 4. The
pneumatic signal opens motor valve 4 causing excess liquids to be dumped
through motor valve 4 and
line 6 to point 7. (The flow of the liquids will be further described).
[0028] The liquid free vapors exit inlet scrubber 2 and flow through line
8 to the suction port 44
of first stage of compression 9. First stage of compression 9 increases the
pressure and temperature of
the vapors. The hot compressed vapors exit first stage of compression 9 at
discharge port 45 and flow
through line 10 to point 11. At point lithe volume of vapors being carried in
line 10 can split into two
proportions. One of the proportions of the vapors can flow through line 12, to
the inlet 13 of first stage
gas cooler 14, and through cooler 14, outlet 16, and line 17 to the cool port
18 of PICT valve 19. The
other proportion of the volume of vapors being carried in flow line 10 can
flow from point 11 through flow
line 20 to the hot port 21 of PICT valve 19. PICT valve 19 preferably controls
the volume of gas flowing
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through flow lines 12 and 20. Depending upon the temperature requirement of
the discharged gas from
second stage of compression 27, all or none of the volume of gas in flow line
10 can flow through either
flow line 12 or flow line 20 to common port 22 of PICT valve 19.
[0029] In one embodiment, the temperature controlled vapors from first
stage of compression 9
can flow from common port 22 of PICT valve 19 through flow line 23 into inter
stage scrubber 24. In
inter stage scrubber 24 any free liquids can be removed from the vapors. The
free liquids preferably fall
to the bottom of inter stage scrubber 24. When liquid level controller 40
senses a liquid level in inter
stage scrubber 24 it can optionally send a signal, which can be pneumatic or
electrical, through line 46
to motor valve 41. The signal preferably opens motor valve 41 to dump the
liquids through line 42 to
point 7. At point 7 the liquids from inlet scrubber 2 and inter stage scrubber
24 preferably join and flow
through line 43 for further processing or storage. In one embodiment, the
temperature controlled vapors
preferably flow from inner stage scrubber 24 through flow line 25 to suction
port 26 of second stage of
compression 27. Second stage of compression 27 preferably increases the
pressure and temperature
of the vapors.
[0030] The vapors can exit second stage of compression 27 through
discharge port 28 into
flow line 29. Thermostat 30 senses the temperature of the gas in flow line 29
and pneumatically
controls the positioning of PICT valve 19 to maintain a set discharge
temperature. Thermostat 30 is
preferably set to maintain the discharge temperature above the dew-point
temperature of the vapors
being compressed. Depending upon the composition of the vapors and the amount
of compression, the
dew-point temperature of the vapors can vary widely. On a three-stage
compressor a discharge
temperature of about 200 to about 280 degrees Fahrenheit is typically high
enough to be above the
dew-point of the vapors.
[0031] When ambient temperatures decrease to a point where the
temperature of the gas
exiting gas cooler 14 approaches gas hydrate temperature (hydrate temperature
depends on the
composition and pressure of the gas), temperature transducer 33 preferably
sends through line 34 an
electrical signal to activate PLC 32 (the hydrate temperature at which PLC 32
will activate is preferably
predetermined and pre-set). When PLC 32 is activated it preferably sends an
electrical signal to
modulating valve 38, which can optionally include an electro-pneumatic
modulating valve, to begin
controlling PICT valve 19 to send more hot gas through air cooler 14. As long
as the ambient
temperature is low enough to cause possible gas hydrating in gas cooler 14,
PLC 32 and modulating
control valve 38 will preferably continue controlling PICT valve 19. As soon
as the ambient temperature
increases and the gas temperature exiting gas cooler 14 increases
approximately five degrees above
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the gas hydrate temperature, PLC 32 opens modulating control valve 38 and
thermostat 30 again takes
over control of PICT valve 19.
[0032] Although the foregoing description made reference to such things as
transducers,
pressure signals, motor valves, and a PLC, other components and configurations
can be used in place
thereof. For example, one or more sensors can be used in place of the
transducers, the use of a
pressure signal can be replaced by electrical, pneumatic, hydraulic, and
hydraulic lines, and/or a
combination thereof. Optionally, a pressure signal can also optionally be
replaced with a mechanical
linkage. Motor valves, can be replaced with mechanical valves, including
valves operated via a
mechanical linkage. The PLC can optionally be replaced with pneumatic logic, a
microcontroller, a
microprocessor, an electrical circuit, a mechanical logic device, a computer,
combinations thereof, and
the like.
[0033] In one embodiment, modulating control valve 38 is not provided. In
this embodiment,
one or more sensors and/or transducers are connected to an electrical,
pneumatic or other type of
circuit that monitors temperature and adjusts PICT valve 19. For example, PICT
valve 19 can be
electrically controlled and can be adjusted from a circuit, such as PLC 32,
which circuit preferably
monitors thermostat 30 and transducer 33 and which adjusts valve 19 in
response to predetermined
temperature set points or temperature ranges.
[0034] Although the invention has been described in detail with particular
reference to these
preferred embodiments, other embodiments can achieve the same results.
Variations and modifications
of the present invention will be obvious to those skilled in the art and it is
intended to cover in the
appended claims all such modifications and equivalents. The entire disclosures
of all references,
applications, patents, and publications cited above are hereby incorporated by
reference.
