U.S. patent application number 13/434169 was filed with the patent office on 2013-10-03 for chiller or heat pump with a falling film evaporator and horizontal oil separator.
This patent application is currently assigned to JOHNSON CONTROLS TECHNOLOGY COMPANY. The applicant listed for this patent is Paul M. DE LARMINAT. Invention is credited to Paul M. DE LARMINAT.
Application Number | 20130255308 13/434169 |
Document ID | / |
Family ID | 47291224 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130255308 |
Kind Code |
A1 |
DE LARMINAT; Paul M. |
October 3, 2013 |
CHILLER OR HEAT PUMP WITH A FALLING FILM EVAPORATOR AND HORIZONTAL
OIL SEPARATOR
Abstract
A refrigerant circuit using a vapor compression cycle, the
circuit usable for air conditioning, refrigeration or heat pump
purposes. The circuit includes a lubricated compressor connected to
an oil separator vessel separate from the compressor, a falling
film or hybrid falling film evaporator and a condenser. The oil
separator vessel extends substantially horizontally. The oil
separator vessel is separated into a primary space and a secondary
space by a filter pad configured to substantially remove entrained
oil droplets of about 5 .mu.m and larger from the refrigerant
entering the oil separator vessel. The primary space is in fluid
connection with a discharge of the compressor. The secondary space
is in fluid connection with an inlet of the condenser. The circuit
has an oil entrainment flow discharge of lubricant from the
compressor of at least about two percent by mass relative to
refrigerant flow.
Inventors: |
DE LARMINAT; Paul M.;
(Nantes, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DE LARMINAT; Paul M. |
Nantes |
|
FR |
|
|
Assignee: |
JOHNSON CONTROLS TECHNOLOGY
COMPANY
Holland
MI
|
Family ID: |
47291224 |
Appl. No.: |
13/434169 |
Filed: |
March 29, 2012 |
Current U.S.
Class: |
62/470 |
Current CPC
Class: |
F25B 2400/23 20130101;
F25B 43/02 20130101; F25B 1/047 20130101; F25B 31/004 20130101 |
Class at
Publication: |
62/470 |
International
Class: |
F25B 43/02 20060101
F25B043/02 |
Claims
1. A refrigerant circuit using a vapor compression cycle, the
circuit usable for air conditioning, refrigeration or heat pump
purposes, comprising a lubricated compressor connected to an oil
separator vessel separate from the compressor, a falling film or
hybrid falling film evaporator and a condenser, wherein the oil
separator vessel extends substantially horizontally, the oil
separator vessel separated into a primary space and a secondary
space by a filter pad configured to substantially remove entrained
oil droplets of about 5 .mu.m and larger from the refrigerant
entering the oil separator vessel, the primary space being in fluid
connection with a discharge of the compressor; the secondary space
being in fluid connection with an inlet of the condenser, the
circuit having an oil entrainment flow discharge of lubricant from
the compressor of at least about two percent by mass relative to
refrigerant flow.
2. The refrigerant circuit of claim 1, wherein a bottom of the oil
separator vessel is used as an oil sump, and the oil sump is in
fluid connection with oil supply orifices of the compressor.
3. The refrigerant circuit of claim 1, wherein the compressor has a
discharge directed substantially downwards and suction from above
or sideways from the compressor, and wherein a compressor driveline
is positioned at least partially above the oil separator, and the
evaporator is positioned at least partially above the
condenser.
4. The refrigerant circuit of claim 1, wherein the compressor has a
downwardly directed suction and a discharge from a side of the
compressor, and wherein the compressor is positioned at least
partially above the evaporator, and the oil separator positioned at
least partially above the condenser.
5. The refrigerant circuit of claim 1, wherein an inlet of the oil
separator vessel is bifurcated, the oil separator vessel separated
into three spaces by two filter pads.
6. The refrigerant circuit of claim 5, wherein refrigerant flow is
bifurcated.
7. The refrigerant circuit of claim 5, wherein the three spaces
include two secondary spaces that are not adjacent to each
other.
8. The refrigerant circuit of claim 1, wherein the filter pad is
located perpendicular to a longitudinal axis of the oil separator
vessel.
9. The refrigerant circuit of claim 8, wherein the filter pad is
located at about mid-length of the longitudinal axis of the oil
separator vessel and including a second filter pad at one end of
the oil separator vessel.
10. The refrigerant circuit of claim 1, wherein the filter pad is
positioned non-perpendicular of the longitudinal axis of the oil
separator vessel.
11. The refrigerant circuit of claim 10, wherein the filter pad is
composed of two or more portions arranged at an angle to each
other.
12. The refrigerant circuit of claim 11, wherein the two or more
portions are of unequal length.
13. The refrigerant circuit of claim 1, wherein the filter pad
permits between about 50 to about 100 PPM of oil entrained in
refrigerant flowing from the oil separator vessel.
14. The refrigerant circuit of claim 1, used as a heat pump, and
using a halogenated fluid as the refrigerant.
15. The refrigeration circuit of claim 14, wherein the halogenated
fluid is an HFC or an HFO as the refrigerant.
16. The refrigeration circuit of claim 1, wherein the refrigerant
is a hydrocarbon.
Description
BACKGROUND
[0001] This invention deals with machines used for refrigeration
and air conditioning or heat pumps with medium to high cooling
capacity (typically about 100 kW and higher), using vapor
compression cycles, including falling film or hybrid falling film
evaporators, in conjunction with lubricated compressors connected
to oil separators that are separate from the compressor.
[0002] In the context of research for energy savings and reduction
of the emissions of greenhouse gasses, high equipment efficiency
and low refrigerant charges are being sought. To achieve these
goals, improvements are being made to all the components of the
systems: compressors, variable speed drives, optimized choice of
refrigerant, oil separators, heat exchangers, etc. Most of the
compressors require an amount of lubrication, which lubrication
similarly generates carry-over of an amount of oil from the
compressor into the refrigerant circuit. This oil that is entrained
into the refrigerant circuit must then be returned to the
compressor by and adequate oil return system, in order to avoid
different adverse effects like the deterioration of the performance
of the heat exchangers. It is especially so for screw compressors:
these machines require a particularly large amount of lubrication
in order to insure proper sealing of the gas between the rotors and
to avoid the need for additional synchronization gears between the
rotors. Therefore, screw compressors typically require a vessel,
also commonly referred to as an oil separator, positioned between
the compressor discharge and the inlet of the condenser. One
challenge associated with refrigeration machines and heat pumps is
the management of the oil in the refrigerant circuits. This
requires a careful combination between the oil carry-over, the oil
return system and the technology of the heat exchangers.
[0003] Besides separating the oil from the discharge gas, this
vessel or oil separator or separator vessel usually also has the
function of being the oil sump for the compressor. Separator
vessels or oil separators can be based on several operating
principles. The most common include: [0004] Impingement separation:
the two-phase mixture of oil and gas is projected onto a wall or to
the end of the vessel, providing a first stage of separation.
[0005] Gravity separation: the gas mixed with oil is allowed to
travel in the vessel, either horizontally or vertically upwards;
this permits the larger droplets of oil in liquid phase sufficient
time to be urged by gravity toward the bottom of the vessel. [0006]
Filter pad separation: the mix is forced through a pad of closely
spaced and/or finely interwoven filaments or wires that acts as a
filter. In one embodiment, the filter pad may include a wire mesh.
Per the instructions of such filter manufacturers, filter pads are
normally installed horizontally, with gas circulation directed
upwards. The filtration level of filter pads is relatively coarse;
it would not stop very fine droplets entrained in the gas or mist,
but still removes smaller droplets than gravity separation. [0007]
Centrifugal separation: the two-phase oil and gas mixture is
introduced tangentially in a cylindrical vessel. The whirling
motion tends to project the oil droplets onto the cylindrical wall
of the vessel where the droplets coalesce and fall to the bottom of
the vessel. Like gravity separation, centrifugal separation allows
removing the largest droplets of oil. [0008] Coalescing filters:
the two-phase mixture of oil and gas is forced through a cartridge
acting as a filter. The filter material is typically fiberglass.
The filtration is much finer as compared with the filter pads (see
above). For example, coalescing filters substantially prevent
droplets of 1 .mu.m (micrometers) or larger in diameter from
passing through the coalescing filter during operation of a
refrigerant circuit. In a typical embodiment, the coalescing
filters generally permit about 1 to 10 parts per million (PPM) by
mass of oil droplets entrained in refrigerant flow to discharge
from the separator.
[0009] Several different principles are often implemented
simultaneously in a single separator. For instance, when coalescing
filters are used, they are normally installed to supplement a
filter/separator that can incorporate one or more operating
principles such as impingement, gravity, centrifugal, and/or filter
pad separation. In the design of an oil separator, the challenge is
to find the best compromise between various parameters such as
price, size, ease of installation, pressure drop, reliability, and
of course, efficiency of the separation.
[0010] Typical designs of oil separators include: [0011] A
horizontal design with coalescing filters. FIG. 1 shows an example
of this well-known design. The separation begins with impingement
at one end of the vessel, continues with a gravity separation
section that is also used as the oil sump, and is completed by
coalescing filters. [0012] A vertical cyclone design with a
coalescing filter (not shown).
[0013] When properly implemented, these designs normally provide a
highly efficient oil separation thanks to the coalescing elements.
Yet, coalescing filters have some drawbacks. They tend to be
relatively expensive. If the coalescing filters are not mounted
properly, some separators in a series may not meet operating
specifications. If the possibility of inspection and filter removal
is desired, costly additional flanges or access-providing man holes
are required that also increase the risk of refrigerant leaks. In
addition, hydraulic pressure safety testing of vessels having
internal coalescing filters raises risk of damaging these filters,
as well as associated difficulties in emptying and drying the
vessel properly after completing the testing.
[0014] In case of accidental high fluid mass flow, coalescing
filters can also suffer loss of performance, and are susceptible to
clogging and/or destruction under the effect of elevated fluid
forces. Increased fluid mass flow is especially a problem for heat
pump applications with high pressure halogenated refrigerants such
as HFC's. Even when used in air conditioning applications,
coalescers or coalescing filters need to be oversized when high
pressure HFC's, such as R-410A or R-507 are used. Use of high
temperature heat pumps increases problems associated with such
applications. In such high temperature heat pumps, the evaporating
temperature is substantially higher than when using the same
machines and refrigerant in corresponding air conditioning
applications, due to higher temperature of the water or other
medium being cooled at the evaporator. In high temperature heat
pumps, the leaving water from the evaporator is typically above
20.degree. C., and can reach up to 60.degree. C. or even higher.
The resulting higher evaporation temperatures substantially
increase density and hence the mass flow of refrigerant, even when
using a relatively low pressure refrigerant such as R-134a or even
lower pressure refrigerants like R-245fa for instance.
[0015] For heat pumps or chillers using compressors, such as a
screw compressor, what is desirable is an oil separator having a
radically simplified design that does not include coalescing
filters, while providing a sufficient oil separation during
operation.
SUMMARY
[0016] For heat pumps or chillers using a screw compressor, the
present disclosure is directed to the use of falling film
evaporators or hybrid falling film evaporators, such as described,
for instance, in U.S. Pat. No. 7,849,710, which is incorporated by
reference in its entirety. These evaporators offer the best state
of the art compromise between optimized performance and reduced
refrigerant charge. In addition, falling film and hybrid falling
film evaporator performance is less sensitive to oil carry-over
than traditional flooded evaporators, permitting an oil separator,
such as the filter pad, to be used without sacrificing evaporator
performance.
[0017] For purposes of the present disclosure, the term filter pad
generally incorporates the following performance characteristics:
substantially prevents droplets of about 5 .mu.m (micrometers) in
diameter or larger from passing through the filter pad during
operation of a refrigerant circuit. In one embodiment, the filter
pad operates between about 50 to about 100 parts per million (PPM)
of oil entrained in refrigerant flow from the separator. In another
embodiment of the filter pad, the void percentage of the filter pad
is between about 97 and about 99 percent. In a further embodiment
of the filter pad, the diameter of filaments and/or wires generally
ranges from between about 0.15 mm to about 0.35 mm (millimeters) in
diameter.
[0018] The present invention is directed to a refrigerant circuit
using a vapor compression cycle, the circuit usable for air
conditioning, refrigeration or heat pump purposes. The circuit
includes a lubricated compressor connected to an oil separator
vessel separate from the compressor, a falling film or hybrid
falling film evaporator and a condenser. The oil separator vessel
extends substantially horizontally. The oil separator vessel is
separated into a primary space and a secondary space by a filter
pad configured to substantially remove entrained oil droplets of
about 5 .mu.m and larger from the refrigerant entering the oil
separator vessel. The primary space is in fluid connection with a
discharge of the compressor. The secondary space is in fluid
connection with an inlet of the condenser. The circuit has an oil
entrainment flow discharge of lubricant from the compressor of at
least about two percent by mass relative to refrigerant flow.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1 and shows a prior art oil separator.
[0020] FIG. 2 shows an exemplary embodiment of an oil separator of
the present disclosure.
[0021] FIG. 3 shows an exemplary embodiment of an oil separator of
the present disclosure.
[0022] FIG. 4 shows an exemplary embodiment of an oil separator of
the present disclosure.
[0023] FIG. 5 schematically shows an exemplary embodiment of a
vapor compression system of the present disclosure.
[0024] FIG. 6 schematically shows an exemplary embodiment of a
vapor compression system of the present disclosure.
[0025] FIG. 7 shows an exemplary embodiment of an oil separator of
the present disclosure.
[0026] FIG. 8 shows an exemplary embodiment of an oil separator of
the present disclosure.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0027] FIG. 2 shows a horizontal vessel 1 with a filter pad 2
providing a longitudinal separation of the vessel into two spaces:
a primary space 3 having an inlet 4 to receive discharge from the
compressor, and a secondary space 5 having an outlet 6 in
communication with an inlet of a condenser (not shown). In an
exemplary embodiment, inlet 4 receives compressor discharge in
which a gas and oil mixture 15 entering separator vessel 1 can be
arranged to provide impingement separation at an end of vessel 1 in
primary space 3. In addition, a second filter pad 7 can be disposed
on or near end 17 of vessel 1 where this impingement occurs, to
limit the re-entrainment of liquid with gas discharged from the
compressor after the gas discharge collides with the end of the
vessel.
[0028] In this arrangement, as further shown in FIG. 2, the oil
that is separated from the gas is allowed to move freely from
primary space 3 to secondary space 5. In one embodiment, filter pad
2 is installed across the complete cross section of vessel 1,
transverse to the longitudinal direction of vessel 1. The lower
part of vessel 1 is collecting liquid oil 19 and performing the
function of an oil sump. As filter pad 2 offers very little
resistance to the circulation of liquid oil 19 between primary
space 3 and secondary space 5, the level of liquid oil 19 is
essentially the same for both spaces. It is generally better to
collect the liquid oil 19 from secondary space 5 through an oil
pipe 8 to be returned to the compressor for lubrication, because
the oil has an opportunity to become separated from foam and
bubbles by filter pad 2 while migrating from primary space 3 to
secondary space 5. With this arrangement, evaporators 12 (FIG. 5),
such as falling film evaporators or hybrid falling film
evaporators, a circuit having an oil entrainment flow discharge of
lubricant from the compressor of about two percent or more by mass
relative to refrigerant flow, i.e., percentage of mass flow total
of refrigerant plus lubricant, such as associated with screw
compressor operation, can be accommodated by the oil separator. In
one embodiment, the oil separator is separate from the
compressor.
[0029] In one arrangement, a filter pad 2 separating respective
primary and secondary spaces 3, 5 is substantially planar and is
installed vertically, i.e., perpendicular to a longitudinal axis of
vessel 1, and about at mid-length of the separator vessel. In
alternative arrangements, this filter pad 2 can be positioned
non-perpendicular with respect to the vessel axis, such as shown in
FIG. 3. This arrangement has an advantage of reducing the velocity
of the gas flowing through filter pad 2. As a result, a vessel of
the present disclosure can have a smaller vessel diameter in
comparison to the diameter of a vessel of conventional
construction, with the smaller diameter vessel of the present
disclosure operating with a gas flow velocity through the filter
pad 2 that may be similar to the operating gas flow velocity
through the filter pad 2 of the larger, conventional vessel of FIG.
2. In one embodiment, the smaller diameter vessel of the present
disclosure may operate with a gas flow velocity through the filter
pad 2 that may be less than the gas flow velocity of the larger,
conventional vessel. In another embodiment, filter pad 2 may be
composed of two or more portions 2a, 2b arranged at an angle to
each other, e.g., in the shape of a "V" as shown in FIG. 4, which
is a plan view of the vessel. In yet another embodiment, portions
2a, 2b may be of unequal length.
[0030] In still a further arrangement, two oil separation sections
or spaces utilizing the same principle can be integrated in a
single vessel 1, each section or space or secondary space 5
receiving approximately one half of the volume of discharge gas and
oil from primary space 3. In this arrangement, there is one vessel
1 with two filter pads 2, and two possible options about the
direction of the flow. In one embodiment as shown in FIG. 7, there
is one primary space 3 positioned substantially in the middle of
vessel 1 and between the two filter pads 2, and two secondary
spaces 5, with one secondary space 5 arranged at each end of the
vessel. As shown, there is one common gas inlet 4 substantially
positioned in the middle of primary space 3, and one outlet 6
positioned in each of opposed secondary spaces 5, which secondary
spaces 5 are positioned at each end of primary space 3. These two
outlets 6 are connected to the condenser inlet (not shown). The
interconnection piping between both outlets can be internal or
external to vessel 1. In another embodiment (FIG. 8) the flows are
reversed: there is one primary space 3 positioned at each end of
vessel 1 with an end of gas inlet 4 extending into each respective
primary space 3, and one common secondary space 5 positioned
between opposed primary spaces 3 with a common gas inlet 4 entering
secondary space 5. In this embodiment, sections of inlet 4
connected to the compressor discharge are divided into two pipes or
portions extending to each of the two primary spaces, one at each
end of vessel 1. The interconnected piping or portions of inlet 4
can be arranged internal or external of the vessel. For instance,
in FIG. 8, there is one common inlet 4 extending to a bifurcated
internal pipe 13 distributing the gas to each end of vessel 1.
[0031] In an alternate embodiment of FIG. 7, both outlets 6 can be
connected to form a single pipe that extends to one condenser
inlet. In an alternate arrangement, the condenser (not shown) can
have two inlets, one inlet at each end; with each of the two
separator outlets 6 being connected to one of the condenser
inlets.
[0032] The arrangement with two sections or spaces in a common
vessel offers several advantages. As the flow to each section or
space is reduced, such as being reduced by a factor of two, so too
is a reduction of the required cross section of the vessel.
Therefore, in spite of the additional length, the reduction in
diameter will result in a less expensive vessel. A further
advantage is that a vessel of smaller diameter will typically
radiate less noise, because there is less potential for wall
resonance in a shell of smaller diameter. Finally, the added length
to the vessel does not raise packaging problems with other system
components as long as the length of the separator or vessel does
not substantially exceed that of the heat exchangers, such as the
condenser and/or evaporator.
[0033] As the oil separator vessel is horizontal, the arrangement
lends itself to easy packaging with horizontal shell and tube heat
exchangers, and with a horizontal screw compressor driveline. In a
possible arrangement as shown in FIG. 5, the discharge of
compressor 9 is directed downwards to separator vessel 1. In
another embodiment as shown in FIG. 6, the discharge of compressor
9 may be directed from one side of compressor 9 to oil separator
vessel 1. In yet another embodiment, the compressor discharge may
be directed at an orientation that is between the downward
direction and the side direction of the compressor to the oil
separator vessel (not shown). In this arrangement, the compressor
driveline can be installed at least partially above the oil
separator vessel. As further shown in FIG. 5, evaporator 12 is
positioned above condenser 11 and arranged near the compressor
driveline and separator vessel. In other embodiments (not shown),
evaporator 12 and condenser 11 may be positioned in different
arrangements with respect to each other and/or to the compressor
driveline and oil separator vessel. In another arrangement, such as
shown in FIG. 6, the compressor suction is directed vertically,
such that compressor 9 is installed on top of evaporator 12, with
compressor discharge from one side of the compressor to oil
separator vessel 1. In another embodiment (not shown) the
compressor suction may extend outwardly from the side, or in yet
another embodiment, the compressor suction may extend between a
vertical and a side orientation with respect to the oil separator
vessel 1. In this arrangement, compressor 9 can be installed at
least partially above evaporator 12. As further shown in FIG. 6,
oil separator vessel 1 is shown positioned laterally beside
compressor 9 and on top of condenser 11. In other embodiments,
other arrangements between the compressor, oil separator vessel,
condenser and evaporator may be utilized.
[0034] This use of filter pads is especially advantageous for use
with heat pumps using halogenated refrigerants like HFC's or HFO's,
and when the evaporation temperature is significantly greater than
evaporator temperatures normally associated with air conditioning
applications (e.g., 5.degree. C.). For such heat pumps, the
evaporation temperature can be up 30.degree. to about 40.degree. C.
with HFC refrigerant R-134a or possible equivalents, and even
higher temperatures associated with lower pressure refrigerants
such as R-245fa.
[0035] In another embodiment, the refrigerants may include
hydrocarbons such as R-290 or R-1270.
* * * * *