U.S. patent application number 12/525104 was filed with the patent office on 2010-06-10 for air cycle refrigeration capacity control system.
Invention is credited to Ron Lee, Stephen A. McCormick.
Application Number | 20100139297 12/525104 |
Document ID | / |
Family ID | 39925987 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100139297 |
Kind Code |
A1 |
McCormick; Stephen A. ; et
al. |
June 10, 2010 |
AIR CYCLE REFRIGERATION CAPACITY CONTROL SYSTEM
Abstract
The present invention describes a method and apparatus for
controlling the operating pressure of a Reverse Brayton type
refrigeration device 70 for the purposes of regulating cooling
capacity and coolant inventory control.
Inventors: |
McCormick; Stephen A.;
(Warrington, PA) ; Lee; Ron; (Bloomsbury,
NJ) |
Correspondence
Address: |
The BOC Group, Inc.
575 MOUNTAIN AVENUE
MURRAY HILL
NJ
07974-2082
US
|
Family ID: |
39925987 |
Appl. No.: |
12/525104 |
Filed: |
April 25, 2008 |
PCT Filed: |
April 25, 2008 |
PCT NO: |
PCT/US08/05321 |
371 Date: |
January 12, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60914056 |
Apr 26, 2007 |
|
|
|
Current U.S.
Class: |
62/89 |
Current CPC
Class: |
F25B 9/004 20130101;
F25B 9/06 20130101; F25B 9/006 20130101; F25B 9/10 20130101 |
Class at
Publication: |
62/89 |
International
Class: |
F25D 17/04 20060101
F25D017/04 |
Claims
1. A method for controlling the operating pressure of a
refrigeration system, the method comprising: a) passing a cryogen
through a closed loop Reverse Brayton refrigerator; b) passing the
cryogen through a condensation vessel; and c) passing the cryogen
through a refrigerated space.
2. The method of claim 1, wherein the closed loop Reverse Brayton
refrigerator comprises a compressor, a chiller, a heat exchanger
and a turbine.
3. The method of claim 1, wherein the condensation vessel comprises
a condensation coil.
4. The method of claim 3, wherein the condensation coil is capable
of condensing a cryogen.
5. The method of claim 4, wherein the cryogen is a gas selected
from the group consisting of air; nitrogen; oxygen-nitrogen
mixtures; argon; helium; and any combination of the air, nitrogen
and oxygen-nitrogen mixtures, argon and helium.
6. The method of claim 4, wherein the cryogen is nitrogen.
7. The method of claim 3, wherein the cryogen that passes through
the condensation coil is passed to vent.
8. A method for controlling the operating pressure of a
refrigeration system, the method comprising a) passing a cryogen
through a condensation vessel to form a gaseous cryogen to vent and
a condensate to pass to a refrigerated space; b) passing the
condensate from step a) through a heating element in a refrigerated
space, and then passing the resulting heated condensate to a heat
exchanger in a Reverse Brayton refrigerator; c) passing the heated
condensate from step b) to a compressor in the Reverse Brayton
refrigerator; d) passing the heated condensate from step c) to a
chiller to form a cooled condensate; e) passing the cooled
condensate from step d) to the heat exchanger in opposite flow from
the flow in step b); f) passing the cooled condensate from step e)
through a turbine to form a used condensate; and g) passing the
used condensate from step f), which splits into a condensate for
passing through the condensation vessel, and a condensate for
joining the condensate from step a) into the heating element in the
refrigerated space.
9. A method for controlling the operating pressure of a
refrigeration system, the method comprising: a) passing a gaseous
first cryogen through a condensation vessel; cooling the gaseous
first cryogen to condense some of said first cryogen into a liquid
first cryogen and to establish a first pressure within said
condensation vessel; passing any remaining gaseous first cryogen to
a vent; and passing said liquid first cryogen to a refrigerated
space; b) passing the first cryogen from step a) through a heating
element in the refrigerated space; heating the first cryogen; and
passing the first cryogen to a regenerative heat exchanger within a
reverse Brayton refrigerator, wherein said regenerative heat
exchanger uses heated cryogen and chilled cryogen from the same
reverse Brayton refrigerator for fluids which exchange heat
therein; c) passing the first cryogen from step b) to a compressor
within the reverse Brayton refrigerator; d) passing the first
cryogen from step c) to a chiller; chilling said first cryogen; e)
passing the first cryogen from step d) to the regenerative heat
exchanger; f) passing the first cryogen from step e) through a
turbine; and g) passing a first fraction of the first cryogen from
step f) to the refrigerated space, and passing a second fraction of
the first cryogen from step f) to the condensation vessel.
10. The method for controlling the operating pressure of a
refrigeration system of claim 9, wherein said vent is an output to
the external atmosphere.
11. The method for controlling the operating pressure of a
refrigeration system of claim 9, wherein said vent outputs to a
buffer vessel capable of returning vented material to the
system.
12. The method for controlling the operating pressure of a
refrigeration system of claim 9, wherein said cryogen is a gas
selected from the group consisting of air; nitrogen; mixtures of
oxygen and nitrogen; argon, helium; and combinations thereof.
13. The method for controlling the operating pressure of a
refrigeration system of claim 9, wherein said cryogen consists
essentially of nitrogen.
14. The method for controlling the operating pressure of a
refrigeration system of claim 9, wherein said first pressure within
said condensation vessel is adjusted to provide the cooling demand
required.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a refrigeration system. In
particular, this invention is related to a method and apparatus for
controlling the operating pressure of a Reverse Brayton type
refrigeration device for the purposes of regulating cooling
capacity and coolant inventory control.
BACKGROUND OF THE INVENTION
[0002] In the food freezing industry, high food quality with low
dehydration losses is obtained using low temperature liquid
nitrogen freezing systems which operate at about -320.degree. F.
Ammonia and freon vapor compression mechanical systems, which
operate at relatively high temperatures, such as -40.degree. F.,
are commonly used to freeze food in an economical manner, but with
high freezing times and high dehydration losses. Recently, high
performance vapor compression, mechanical systems have emerged
which produce high quality frozen foods with low dehydration losses
at relatively high temperatures of from -40.degree. F. to
-60.degree. F. Because they operate at such relatively high
temperatures, dehydration losses associated with high performance
mechanical freezers leave room for improvement. Common mechanical
systems typically also cannot operate at low temperatures due to
limitations associated with common refrigerants. If a low
temperature refrigerant system could be developed, dehydration
losses can be appreciably reduced.
[0003] Refrigeration capacity control for refrigeration systems are
routinely used and well known. They include rotating equipment
(e.g., compressor/expanders) speed control and coolant loop
pressure control. The use of reverse Brayton refrigerators for
applications such as food freezing, as in the following arts.
[0004] U.S. Pat. No. 5,524,442 discloses a cooling system includes
a unit for processing product to be cooled or frozen. A secondary
refrigeration loop is connected to this unit and introduces a
refrigerant at or near atmospheric pressure into the unit. The
secondary refrigeration loop may be open or closed. The secondary
loop includes a secondary heat exchanger for cooling the
refrigerant. A primary, closed refrigeration loop, operating at a
pressure of not less than 2 atmospheres, includes a forward flow
path which comprises a primary refrigerant compressor for producing
compressed primary refrigerant, a primary heat exchanger for
receiving and cooling the compressed primary refrigerant and an
expander for further cooling and transferring the compressed
refrigerant to the secondary heat exchanger to enable cooling of
the secondary refrigerant. The primary loop further includes a
return flow path from the secondary heat exchanger to the primary
refrigerant compressor and to the primary heat exchanger. The
primary heat exchanger thereby provides heat exchange from the
return flow path to the forward flow path to accomplish a cooling
action.
[0005] U.S. Pat. No. 3,868,827 discloses a refrigeration system for
freezing of food products, utilizing air as the working fluid. The
system includes a freezing chamber having entrance and exit ports
for passing a food product therethrough. A refrigerant supply main
provides low temperature air to the freezer chamber, which air
exits from the chamber via a return main. The warmed air passes
through first and second stage compressors and aftercoolers
positioned in line beyond each said compression stage. The high
pressure output from the second stage compressor and aftercooler is
also passed in countercurrent relationship through a heat
exchanger, the cooler side of which carries the low pressure return
flow of air refrigerant on its way to the first stage compressor.
The compressed and cooled air from the compressor stages passes
through an expansion turbine where the work performed thereby cools
the air to the desired low temperature, and the cold air is then
lead into the supply main leading back to the freezer chamber. A
make-up and drier system, including a pair of drying beds, is
connected to provide dry make-up air to the refrigerant return main
to replace air lost at the product entrance and exit ports of the
freezer chamber.
[0006] U.S. Pat. No. 5,267,449 discloses a method and system for
cooling air to cryogenic temperatures [e.g., below -100.degree. F.
(-730.degree. C.)] for use as a refrigerant medium for direct
contact cooling of articles such as foodstuffs for fast
freezing.
[0007] U.S. Pat. No. 5,483,806 discloses a refrigeration system
using air as the refrigerant comprises a compressor which
compresses air to 84 bar g. The compressed air is cooled first by
cooling water and then by returning air in a plate-fin heat
exchanger before being expanded to 59 bar g in an expander. The
expanded air at -61.degree. C. is passed through indirect cooling
coils in a cold store which it leaves at -45.degree. C. This air is
then passed through the plate-fin heat exchanger before being
recycled to the compressor. The refrigeration delivered is about
1.05 kw refrigeration/kw power input.
[0008] Prior art refrigeration capacity control methods that use
pressure control can be wasteful of coolant gas, requiring a buffer
vessel, and/or have limited turndown services. Thus, there remains
a need in the art for improved simple and effective refrigeration
capacity control methods for providing pressure control.
SUMMARY OF THE INVENTION
[0009] The present invention describes a method and apparatus for
controlling the operating pressure of a Reverse Brayton type
refrigeration device for the purposes of regulating cooling
capacity and coolant inventory control.
[0010] An embodiment of this invention is directed to a method for
controlling the operating pressure of a refrigeration system, the
method comprising: a) passing a cryogen through a closed loop
reverse Brayton refrigerator; b) passing the cryogen through a
condensation vessel; and c) passing the cryogen through a
refrigerated space. The closed loop reverse Brayton refrigerator
comprises a compressor, a chiller, a heat exchanger, and a turbine.
The condensation vessel comprises a condensation coil therein, and
is capable of condensing a cryogen. The cryogen may be many of the
cryogen known to the skilled artisan. In one embodiment, the
cryogen is liquid nitrogen. The cryogen that passes through the
condensation coil is passed to vent.
[0011] In another embodiment, the present invention is directed to
a method for controlling the operating pressure of a refrigeration
system, the method comprising a) passing a cryogen through a
condensation vessel to form a gaseous cryogen to vent and a
condensate to pass to a refrigerated space; b) passing the
condensate from step a) through a heating element in a refrigerated
space, and then passing the resulting heated condensate to a heat
exchanger in a reverse Brayton refrigerator; c) passing the heated
condensate from step b) to a compressor in the reverse Brayton
refrigerator; d) passing the heated condensate from step c) to a
chiller to form a cooled condensate; e) passing the cooled
condensate from step d) to the heat exchanger in opposite flow from
the flow in step b); f) passing the cooled condensate from step e)
through a turbine to form a used condensate; and g) passing the
used condensate from step f), which splits into a condensate for
passing through the condensation vessel, and a condensate for
joining the condensate from step a) into the heating element in the
refrigerated space.
BRIEF DESCRIPTION OF THE DRAWING
[0012] The above and other feature of the present invention will
become more apparent by describing in detail exemplary embodiment
thereof with reference to the attached drawings in which FIG. 1 is
a schematic illustration of the apparatus and method according to
an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] Reverse Brayton type refrigerators are well known systems
that can provide refrigeration through a sequence of compression,
heat removal, and reversible de-compression. The reversible
de-compression is typically through a turbo-expander and the
overall cycle is often termed a Turbo-Brayton cycle. There are many
modifications possible for these type of systems, including
multi-stage compression and/or expansion and heat exchange
processes. At least an embodiment of the present invention is best
described using a simple example that employs the least mechanical
complexity. It will be evident to those skilled in the art that
numerous modifications and additions are possible within the scope
of the present invention.
[0014] FIG. 1 is a schematic of a simple, closed loop, Reverse
Brayton refrigerator that is directed toward a refrigeration
application (here shown as a simple heat exchanger inside an
enclosure to be refrigerated). While not limited to any particular
operating temperature, the present invention will be described in
the context of a low temperature refrigeration application in the
temperature range of about 0.degree. C. to about -150.degree. C.
The typical working fluids for this temperature range are air,
nitrogen, oxygen-nitrogen mixtures, or combinations of these gases
as well as other gases such as argon and helium.
[0015] For the system shown in FIG. 1, the closed loop cycle
operates at a maximum pressure downstream of the compressor (P1)
and a minimum pressure downstream of the turbine (P2). The overall
cooling capacity of the system can be controlled during operation
by a variety of techniques, including speed and pressure control.
The technique of at least one embodiment is through pressure
control. The pressure ratio (P1/P2) is typically a constant value
for a particular set of equipment, equipment speed, and
refrigeration temperature (T). The amount of cooling is
substantially a linear function of the absolute pressure of either
P1 or P2. That is, if P2 (and, hence, P1) is reduced by a factor of
two, then the overall cooling produced is also reduced by a factor
of two. Typical operating pressures (P2) are between atmospheric
(about 1 bara) and several hundred bar. Similarly, the pressure
ratio may be from about 1.5 to 5. The higher pressure ratios will
typically require multiple stage compression and/or expansion.
[0016] Pressure control, at constant operating temperatures,
implies that coolant (gas) mass must be added or removed. Typical
prior art techniques include venting gas to reduce pressure, and
introducing compressed gas to increase pressure. The vented gas can
be lost, or may possibly be stored in a separate buffer volume. The
gas introduced to increase pressure may either be new gas or gas
from a buffer volume that may be further compressed to raise its
pressure. Certain arrangements are possible where the gas is
removed from the system from the high pressure side (P1) into an
intermediate pressure buffer vessel, then reintroduced when the
pressure is to be raised into the low pressure side (P2) without
the need for a compressor. The problems associated with these
techniques are that they can be wasteful of coolant gas, require
additional compression equipment, require a large buffer vessel,
and/or have limited turndown capability.
[0017] The present invention provides a simple and effective means
for providing pressure control, without introducing the limitations
associated with prior art techniques. In an embodiment, the method
is illustrated with an example where the operating fluid is
nitrogen 10, the operating pressure (P2) 54 is between about 1 and
20 bara, and the refrigeration temperature is about -50.degree. C.
to -150.degree. C.
[0018] Pressure control is achieved through the use of an attached
condensation vessel 20 as shown in FIG. 1. Generally, in one
embodiment, liquid cryogen 10 passes through first valve (V1) 12
into condensing coil 14 inside of the condensation vessel 18. The
liquid cryogen 10 emerges from condensation vessel 18 as gaseous
cryogen 16 and is passed to vent 11.
[0019] Condensed cryogen 20 passes from condensation vessel 18
through second valve (V2) 22 as cryogen 24 for passage into
refrigerated space 26. Cryogen 60 combines with cryogen 24 to pass
into heat exchange coils 28 in refrigerated space 26. Condensed
cryogen 30 passes from refrigerated space 26 and passes onto heat
exchanger coil 32 in central heat exchanger 46, emerging as cryogen
stream 34. Cryogen stream 34 passes onto compressor 36 emerging as
cryogen stream 38, which in turn passes through chiller 40 emerging
as cryogen stream 42. Cryogen stream 42 returns to heat exchanger
coil 44 in central heat exchanger 46, emerging as cryogen stream
48. Cryogen stream 48 passes through first operating pressure (P1)
51 prior to passing onto turbine 52 and then second operating
pressure (P2) 54, emerging as cryogen stream 50. Cryogen stream 50
splits into cryogen streams 58, 60. Cryogen stream 58 recycles back
onto condensation vessel 18, and cryogen stream 60 recycles back
onto refrigerated space 26 by joining with cryogen stream 24 for
passage into refrigerated space 26. In an embodiment, the part of
the system containing legends 32 to 56 may be described as a
Reverse Brayton Refrigerator.
[0020] In an embodiment, for pressure reduction, liquid nitrogen,
at a pressure lower than second operating pressure (P2) 54, is
introduced through first valve 12 into the condensing coil 14
inside the condensation vessel 18. The relatively low pressure of
the liquid nitrogen 10 will create a low temperature surface inside
the condensation vessel 18 that is sufficiently cold to cause the
higher pressure nitrogen gas at a second pressure (P2) 54 to
condense. The rate of condensation will generally be proportional
to the flow rate of liquid nitrogen 10. Condensation is possible as
long as the coolant gas is at a second pressure (P2) 54 below the
critical pressure associated with the gas, which for nitrogen is 34
bara. The nitrogen 16 that is vented from the condensing coil 14
will be a gas at a temperature of about -150.degree. C. to
-196.degree. C. The refrigeration capacity, on average, of this
cold gas will likely be small compared to the amount of
refrigeration being supplied by the Reverse Brayton refrigerator
70. However, its cooling capacity may be usefully captured by
simply introducing it directly or indirectly via a heat exchanger
into the refrigerated space.
[0021] The condensation vessel 18 will be insulated in order to
prevent the condensed coolant fluid from rapidly vaporizing and
raising the system pressure. In an embodiment, the condensation
vessel 18 will be insulated with vacuum jacketing. To raise the
system's second pressure (P2) 64, some or all of the condensed
coolant fluid is vaporized. While the vaporization can be achieved
through a variety of heating techniques, in at least one
embodiment, it may be accomplished by vaporizing the condensed
coolant fluid 24 in the refrigerated space 26. As shown in FIG. 1,
this may be accomplished by opening second valve (V2) 22 and
allowing the condensed liquid 24 to drain or be drawn into the heat
exchanger 28 inside the refrigerated space 26. The vaporization of
the condensed liquid 30 is then easily accomplished while
performing useful refrigeration.
[0022] At least one embodiment of the present invention is to
adjust the operating pressure, either (P1) 51 or (P2) 54, according
to the cooling demand required. The opening and closing of first
and second valves, (V1) 12 and (V2) 22, either lower or raise the
operating pressure accordingly. An associated benefit to the
present arrangement is ensuring the system pressure does not rise
to an unacceptable level during periods on non-usage when the
overall system temperature warms and the coolant gas expands. The
condensation vessel 18 and associated pressure control will
continue to perform whether or not the Reverse Brayton refrigerator
70 is operating. In addition, the overall inventory of coolant gas
can easily be adjusted during periods when the refrigeration system
is not operating. A simple technique is to pre-calibrate the level
of condensed liquid in the condensation vessel that is present when
the refrigerator is not operating and the system (outside the
condensation vessel) is entirely at ambient temperature. The system
pressure (P1) 51 and/or (P2) 54 can also be reduced during this
time to a pressure sufficiently low by use of first valve (V1) 12
to allow introduction of relatively low pressure bulk gas (e.g.,
liquid or gaseous nitrogen). The point where replenishing gas or
liquid is introduced can be anywhere in the system, but if it is
liquid it would be preferably introduced directly into the
condensation vessel 18.
[0023] In at least one embodiment, a variety of refrigeration
cycles can employ this method of pressure control. In addition to
recuperative cycles such as the Reverse Brayton, regenerative type
cycles such as Stirling and Pulse Tube cycles can utilize the
method of the present invention. For the Turbo-Brayton cycle, any
number of compression and/or expansion stages may be employed. In
addition, these compression/expansion stages may be coupled
together for cycle optimization.
[0024] In another embodiment, a wide variety of working fluids may
be used, in addition to the normal atmospheric gases (oxygen,
nitrogen, argon, air) any number of gases are possible. In
addition, these gases may be combined to form specific mixtures
with specific properties.
[0025] In another embodiment, the orientation and arrangement of
the condensation vessel may be modified in a number of ways, and
the particular design of the condensing coil may be accomplished
through any number of heat exchanger designs.
[0026] In another embodiment, the method for re-vaporization of the
condensed liquid, whether economized thermally within the system or
not, may be changed. Including, for example, the use of electric or
ambient vaporizers.
[0027] In another embodiment, the use of the overall refrigeration
system is not limited to providing refrigeration to a refrigerated
space (e.g., a food freezer), but may by any number of cooling
applications. This may also employ heat exchange designs that do
not include a forced air circulation, but may, for example, use
another intermediate heat exchange fluid.
[0028] In yet another embodiment, the overall process refrigeration
may include more than one refrigeration system, which may employ
multiple refrigeration zones and sources. The use of the
refrigeration may also be provided to multiple destinations, such
as multiple food freezers or even different processes.
[0029] In another embodiment, a method is provided for controlling
the operating pressure of a refrigeration system, the method
comprising:
a) passing a gaseous first cryogen through a condensation vessel;
cooling the gaseous first cryogen to condense some of said first
cryogen into a liquid first cryogen and to establish a first
pressure within said condensation vessel; [0030] passing any
remaining gaseous first cryogen to a vent; and [0031] passing said
liquid first cryogen to a refrigerated space; b) passing the first
cryogen from step a) through a heating element in the refrigerated
space; [0032] heating the first cryogen; and [0033] passing the
first cryogen to a regenerative heat exchanger within a reverse
Brayton refrigerator, wherein said regenerative heat exchanger uses
heated cryogen and chilled cryogen from the same reverse Brayton
refrigerator for fluids which exchange heat therein; c) passing the
first cryogen from step b) to a compressor within the reverse
Brayton refrigerator; passing the first cryogen from step c) to a
chiller; [0034] chilling said first cryogen; e) passing the first
cryogen from step d) to the regenerative heat exchanger; f) passing
the first cryogen from step e) through a turbine; and g) passing a
first fraction of the first cryogen from step f) to the
refrigerated space, and passing a second fraction of the first
cryogen from step f) to the condensation vessel.
[0035] In this method, the vent may be an output to the external
atmosphere. Alternatively, the vent may output to a buffer vessel
(not shown) capable of returning vented material to the system. As
discussed above, the cryogen may be a gas selected from the group
consisting of air; nitrogen; mixtures of oxygen and nitrogen;
argon, helium; and combinations thereof. In one embodiment, the
cryogen may consist essentially of nitrogen. According to this
method, said first pressure within said condensation vessel may be
adjusted to provide the cooling demand required.
[0036] It will be understood that the embodiment(s) described
herein are merely exemplary, and that one skilled in the art may
make variations and modifications without departing from the spirit
and scope of the invention. All such variations and modifications
are intended to be included within the scope of the invention as
described hereinabove. Further, all embodiments disclosed are not
necessarily in the alternative, as various embodiments of the
invention may be combined to provide the desired result.
* * * * *