U.S. patent application number 11/921341 was filed with the patent office on 2009-05-21 for oil separation in a cooling circuit.
This patent application is currently assigned to Johnson Controls Denmark ApS. Invention is credited to Istvan Knoll.
Application Number | 20090126376 11/921341 |
Document ID | / |
Family ID | 36822341 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090126376 |
Kind Code |
A1 |
Knoll; Istvan |
May 21, 2009 |
Oil Separation in a Cooling Circuit
Abstract
The invention concerns a method and a cooling system for oil
separation in a cooling circuit, including compression means (4)
that supply coolant under a first high pressure through means for
oil separation (10) and further on through condensing means (12),
from where coolant is applied restriction means (16), from where
coolant is conducted to flooded evaporation means (18), from where
the compression means (4) suck gaseous coolant back, where
remaining oil in the flooded evaporation means is returned to the
cooling circuit through an oil removal circuit (26). It is the
purpose of the invention to achieve an efficient oil separation
from a flooded evaporator (18). This may be attained by the cooling
system according to the invention, in that the oil removal circuit
(26) includes a pump (24), the suction side of which being
connected to the flooded evaporator (18), where the pressure outlet
of the pump is connected to a pressure connection (9) between the
pressure outlet of the compressor (4) and the oil separator
(10).
Inventors: |
Knoll; Istvan; (Hojbjerg,
DK) |
Correspondence
Address: |
JAMES C. WRAY
1493 CHAIN BRIDGE ROAD, SUITE 300
MCLEAN
VA
22101
US
|
Assignee: |
Johnson Controls Denmark
ApS
|
Family ID: |
36822341 |
Appl. No.: |
11/921341 |
Filed: |
May 26, 2006 |
PCT Filed: |
May 26, 2006 |
PCT NO: |
PCT/DK2006/000287 |
371 Date: |
November 30, 2007 |
Current U.S.
Class: |
62/84 ;
62/472 |
Current CPC
Class: |
F25B 2400/05 20130101;
F25B 43/02 20130101; F25B 2339/024 20130101; F25B 31/004
20130101 |
Class at
Publication: |
62/84 ;
62/472 |
International
Class: |
F25B 43/02 20060101
F25B043/02; F25B 43/00 20060101 F25B043/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2005 |
DK |
PA 2005 00783 |
Claims
1. A method for oil separation in a cooling circuit (2), including
compression means (4) that deliver coolant under a first high
pressure through means for oil separation (10) and further on
through condensing means (12), from where coolant in liquid state
is applied restriction means (16), from where coolant under a
second lower pressure is conducted to at least one flooded
evaporation means (18), from where coolant, which is mainly in
gaseous state, is conducted to the suction side of the compression
means (4), where remaining oil in the flooded evaporation means
(18) is returned to the cooling circuit (2) through an oil removal
circuit (22, 24, 26, 28, 30), characterised in that the oil removal
circuit (22, 24, 26, 28, 30) includes means (24) for pumping oil
from the flooded evaporation means (18) and to a point (9) in a
pressure connection forming a coolant connection between the
pressure outlet of the compression means (4) and at least one oil
separation means (10).
2. A cooling system (2) containing at least one compressor (4)
having a pressure outlet (6), which is connected to an oil
separator (10), where the oil separator (10) is further connected
to at least one condenser (12), from where the coolant is conducted
through a coolant line (14) to at least one restriction element
(16) communicating with at least one flooded evaporator (18), from
where primarily gaseous coolant flows to the suction side (6) of
the compressor, where an oil removal circuit (22, 24, 26, 28, 30)
connected to the coolant circuit (2) is provided in connection with
the flooded evaporator (18), characterised in that the oil removal
circuit (22, 24, 26, 28, 30) includes a pump (24), the suction side
(22) of which being connected to the flooded evaporator (18), where
the pressure outlet of the pump is connected to a point (9) in a
pressure connection between the pressure outlet of the compressor
(8) and the oil separator (10).
3. Cooling system according to claim 1, characterised in that the
outlet (8) of the pump (24) communicates with pressure control
valves (28-32), from where excess coolant is conducted to the
flooded evaporator (18) via pressure control valves (32).
4. Coolant (2) according to claim 1, characterised in that the
cooling system (2) contains a number of compressors (4) having
coolant communication through oil separators (10) and further on
through at least one condenser (12) to a number of expansion
elements (16), from where coolant is conducted to a number of
independent evaporators (18) where flooded evaporators (18) are
connected to the oil removal circuit (22, 24, 26), where an outlet
connection (26) from the oil removal circuit forms a connection to
a central oil distribution circuit, where oil is conducted to the
active compressors depending on the actual oil level in each
individual compressor.
5. Cooling system according to claim 1, characterised in that the
mixture of oil and fluid and/or gaseous coolant flows through a
preheater (42) before the mixture is supplied to the pressure
connection (8) between the pressure outlet of the compressor and
the oil separator (110).
6. Cooling system according to claim 5, characterised in that the
preheater (42) is contained in the oil separator (110).
Description
[0001] The invention concerns a method for oil separation in a
cooling circuit, including compression means that supply coolant
under a first high pressure through means for oil separation and
further on through condensing means, from where coolant, mainly in
liquid state, is applied restriction means, from where coolant is
conducted to flooded evaporation means under a second lower
pressure, from where the compression means suck gaseous coolant
back, where remaining oil in the flooded evaporation means is
returned to the cooling circuit through an oil removal circuit.
[0002] Moreover, the invention concerns a cooling system containing
at least one compressor having a pressure outlet, which is
connected to an oil separator, where the oil separator is further
connected to at least one condenser, from where the coolant is
conducted through a coolant line to at least one restriction
element communicating with at least one flooded evaporator, from
where primarily gaseous coolant flows to the suction side of the
compressor, where an oil removal circuit from the coolant circuit
is provided in connection with the flooded evaporator.
[0003] In cooling systems, coolant and oil used for lubricating the
compressor come into contact with each other. Thus a certain amount
of oil is conducted on to the cooling system. In well-known systems
with so-called flooded evaporators, oil will be concentrated and
accumulated in the evaporator. Coolant vapours sucked from the
flooded evaporator to the compressor contain practically no oil.
Therefore, oil from the flooded evaporator is to be returned to the
compressor.
[0004] Depending on properties and quantitative ratio between oil
and coolant, the oil may remain in a separate state or be mixed
partly or wholly with the coolant. In the first case, the oil is
immiscible; in the second case, the oil is wholly or partly
miscible. Irrespectively of the miscibility, oil is normally
unwanted in the evaporator as the oil reduces the heat transmission
coefficient and thus the efficiency of the evaporator, and the oil
disappearing from the compressor is to be substituted by refilling.
The oil is therefore to be removed from flooded evaporators. If the
oil is not miscible, and if the oil is heavier than the coolant,
the oil is collected on the bottom of the evaporator due to the
force of gravity. From here, the oil is removed manually by
draining off. Due to the manual operation, this method is rarely
used today. Alternatively, the draining can be automatised in that
the oil by means of the force of gravity is collected in a small
container connected in proximity of the evaporator, from where it
is pressed to the suction side or the crank housing of the
compressor, preferably by means of hot gas. The system can be
activated when the collected amount of oil exceeds a determined
value.
[0005] The disadvantage of the last-mentioned solution is that
compressors, and particularly piston compressors, cannot stand up
to liquid coolant or oil at the suction side of the compressor due
to the risk of hammering. Therefore, strict requirements are made
for indicating when only oil is present in the collecting
container. It is also a problem that the only force driving the oil
to the container is the force of gravity, which means that the
driving force may be insufficient at low temperatures when the oil
viscosity is high.
[0006] For systems with coolant miscible with oil, there is
described a solution in "ASHRAE HANDBOOK System Practices for
Halocarbon Refrigerants", 2.29 (FIG. 1.), published 2002. By this
solution, the suction line of the compressor is to be passed under
the liquid level of the evaporator in order to ensure sufficient
driving height for liquid transport, implying a difficult
disposition of the suction line.
[0007] Another solution for removing miscible oil is found in
"Pohlmann Taschenbuch der Kaltetechnik", 16. Auflage punkt 7.9.4.4.
Bild 7-138, published 1978. In this case, a small dry evaporator is
used, also called an oil heater for coolant evaporation, which is
connected to the coolant circulation pump and in parallel with the
flooded evaporator. A dry evaporator is capable of transporting the
oil due to a high coolant gas speed from the dry evaporator/oil
heater. The capacity of the small dry evaporator/oil heater is
selected so that the maximum oil content in the flooded evaporator
is not exceeded. The oil heater is mounted below liquid level in
the flooded evaporator. If the oil heater is filled up with clean
oil in case by a interruption of operation, the system cannot start
up again by itself as the clean oil does not evaporate and
therefore has to be removed manually from the oil heater.
Furthermore, it is rare that flooded evaporators have a coolant
recirculation pump.
[0008] In connection with miscible oils and with regard to both
solutions there is, however, still the drawback that hammering may
occur in the compressor.
[0009] A common problem to all solutions for both miscible and
immiscible oils is that oil is transported to the suction side of
the compressor. Since flooded evaporators form saturated vapours
practically without superheating, there is only very little
opportunity of adding extra liquid coolant for oil removed from the
evaporator. As the added liquid cannot evaporate in saturated
vapours, it remains in liquid state and may cause hammering which
may destroy the compressor.
[0010] It is the purpose of the invention to achieve an efficient
oil separation and returning of oil from a flooded evaporator. A
further purpose may be to control the oil level in a
compressor.
[0011] This may be attained by the cooling system according to the
invention, in that the oil removal circuit includes at least one
pump, the suction side of which being connected to the flooded
evaporator, where the pressure outlet of the pump is connected to a
pressure connection between the pressure outlet of the compressor
and the oil separator.
[0012] By the invention, the oil accumulated in the evaporator is
not supplied to the suction side of the compressor with the
resulting risk of hammering. The pump delivers a mixture of cold
liquid coolant and oil to the pressure side of the compressor in
the circuit, where the coolant is present in superheated gas state,
and therefore the coolant in gaseous state may absorb and evaporate
the liquid coolant while the oil remains in liquid state. When the
mixture of superheated coolant and oil subsequently passes through
the oil separator, the larger part of the oil is removed. At the
same time it happens that the efficiency of the oil separator
rises, as the coolant gas mixture has lower temperature due to the
heat energy used for evaporating the liquid supplied to the
compressed hot coolant gas.
[0013] The oil removal circuit may advantageously be designed so
that the pressure side of the pump communicates with pressure
control valves from where excess coolant is conducted to the
flooded evaporator. Hereby may be achieved that the oil removal
circuit can remove a substantial amount of liquid coolant from the
bottom of the evaporator, without substantially reducing the
efficiency of the cooling system.
[0014] The cooling system may contain a number of compressors
having coolant communication through oil separators and further on
through at least one condenser to a number of expansion elements,
from where coolant may be conducted to a number of independent
evaporators where flooded evaporators advantageously may be
connected to the oil removal circuit, where an outlet connections
from the oil removal circuit may form a connection to a central oil
distribution circuit, from where oil is conducted to the active
compressors, depending on the actual oil level in each individual
compressor. Hereby may be achieved an efficient automatic
regulation of the oil supply to a number of compressors. The need
for checking and refilling oil on individual compressors is thus
reduced.
[0015] The mixture of oil and liquid and/or gaseous coolant may
advantageously flow through a preheater. Before the mixing, the
pressure connection between the pressure outlet of the compressor
and the oil separator is provided. Hereby may be achieved that the
mixture of oil, liquid and gaseous coolant returning from oil
removal circuit is preheated, whereby a part of the fluid coolant
is provided in gaseous state.
[0016] Advantageously, the preheater may be contained in an oil
separator. Hereby may be achieved a cooling of the oil collected in
the oil separator.
[0017] The method and circuit according to the invention may be
used for both miscible and immiscible oil, and the pumps used in
the oil removal circuit may transport both of these oils.
Furthermore, it is possible to suck an oil/coolant mixture from the
evaporator, where the amount of coolant is substantially greater
than the amount of oil, and thus a coolant circulation arises in
the evaporator itself as replacement to the sucked off coolant.
This extra internal coolant flow also entrains oil located far from
the suction branch. In that way, the oil removal action is
increased in case of immiscible oil, compared with other technical
solutions where the oil flow toward the oil removal circuit is only
based on the force of gravity. This has particularly significance
with low temperatures where the viscosity of the oil can be high
and the oil flow thus be impeded.
[0018] By using screw compressors in the cooling circuit, a
considerably amount of oil may also be circulated for compressor
lubrication and for cooling pressurised gases. The oil itself may
therefore also be cooled. In many cases, this is effected by
injection of coolant. If the amount of the pumped coolant is
selected so great that, besides removing the oil, the need for
cooling pressurised gases is also covered, the extra equipment for
cooling pressurised gases may be done without. In that way, a
combined oil removal/oil cooling system may be provided.
[0019] As pump in the oil removal circuit, one may use the common
mechanical pumps, e.g. gear wheel pumps, but other alternatives are
possible, e.g. ejector pumps, MHD-pumps, gas-driven pumps etc.
[0020] In the following, the invention is explained from
[0021] FIG. 1 showing a possible embodiment of the invention, and
from
[0022] FIG. 2 showing an alternative embodiment of the
invention.
[0023] On FIG. 1 is shown a cooling system 2 containing at least
one compressor 4 having a coolant inlet 6 and a coolant outlet 8.
The coolant outlet of the compressor 4 communicates with an oil
separator 10, where the oil separator 10 conducts oil back to the
compressor 4 over a connection 20. From the oil separator 10 the
coolant is conducted through a condenser unit 12, where the coolant
changes its state from mainly gaseous to mainly liquid state. With
a coolant connection 14, coolant is conducted to a restriction
element 16, whereafter coolant is conducted to a flooded evaporator
18 where it evaporates. From the evaporator 18, the coolant is
conducted to the compressor 4 through coolant inlet 6. At the
bottom of the flooded evaporator 18 there is provided an oil drain
in the shape of a connection 22 communicating with a pump 24. A
connection 26 is shown from the pump 24, connected to a restriction
element 28 from where a connection 30 forms connection further on
to a point 9 in the connection between the pressure outlet 8 of the
compressor 4 and the oil separator 10. Possibly redundant coolant
is conducted from the connection 26 back to evaporator 18 through
restriction element 32 and connection 34.
[0024] The exemplified cooling system 2 can be provided with a
miscible or an immiscible oil.
[0025] An oil removal circuit 20, 22, 26, 30 is arranged for
transporting oil mixed with coolant away from the flooded
evaporator 18. The connecting line 22 may advantageously be
situated below the liquid level in the evaporator 18 and form a
connection to a point 9 in the line or the flowpath between the
pressure outlet 8 of the compressor and the inlet of the oil
separator 10. The liquid transport in the oil removal circuit is
effected by means of a gear wheel pump 24 that imparts a suitably
high pressure to the oil/coolant mixture, the pressure being
further regulated by a orifice plate/control valve 28 for
controlling the circulated amount of liquid before discharge at the
point 9.
[0026] In order to separate the possible excess coolant, this is
returned to the evaporator through a bypass line 34, and through a
control valve 32.
[0027] By the method according to the invention, the pump 24 sucks
a limited amount of coolant/oil mixture from the flooded evaporator
18 and pumps it into the pressure line of the compressor at the
point 9, whereby hammering in the compressor 4 is avoided, as the
superheated gas in the pressure line can absorb liquid which is
evaporated due to the high temperature. At the same time, the
superheating of the coolant is reduced, enhancing the efficiency of
the oil separator. In the existing oil separator 10, the oil is
separated and led to the compressor 4.
[0028] The system may be automatically restarted, as the pump may
start with clean oil.
[0029] FIG. 2 shows an alternative embodiment of the invention,
where the compressor 4, as shown on FIG. 1, has a pressure outlet 8
connected to an oil separator 110. From the oil separator 110,
coolant is conducted on towards a not shown condenser via a
connection 14. A pump 24 is shown with a connection to a not shown
flooded evaporator. From the pump 24, there is a connection to
restriction elements 28 and 32. From the restriction element 28
there is shown a connection 130 containing a heat exchanger 42
disposed inside the oil separator 110. From the heat exchanger, the
connection 130 continues to a connecting point 9 in the pressurised
gas connection 8. The oil separator 110 contains an oil separator
element 40 disposed uppermost in the oil separator, and below there
is shown an oil level 44 where oil is conducted to the compressor 4
via the connection 20.
[0030] By the embodiment shown on FIG. 2 is achieved that the
mixture of oil, liquid and gaseous coolant contained in the
connection 130 is preheated, whereby a part of the liquid coolant
is provided in gaseous state. At the same time, cooling of the oil
collected in the oil separator may be achieved.
* * * * *