U.S. patent application number 12/600913 was filed with the patent office on 2010-06-24 for rankine system with gravity-driven pump.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Joseph J. Sangiovanni, Michael F. Taras, Igor B. Vaisman.
Application Number | 20100154421 12/600913 |
Document ID | / |
Family ID | 40129973 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100154421 |
Kind Code |
A1 |
Vaisman; Igor B. ; et
al. |
June 24, 2010 |
RANKINE SYSTEM WITH GRAVITY-DRIVEN PUMP
Abstract
A gravity-driven pumping unit has an inlet valve connected to a
condenser, an outlet valve connected to a boiler, and a staging
zone between the inlet and outlet valves. The inlet valve, the
outlet valve, the liquid line and entire path established between
the condenser and boiler are oriented, sized and shaped to allow
for the vapor refrigerant to freely move upward from the boiler to
the condenser and to allow for the liquid refrigerant to freely
drain downwards from the condenser to the boiler by gravity. A
control system opens and closes the inlet and outlet valves in a
proper sequence, which enables gravity-driven movement of liquid
refrigerant from the condenser to the staging zone and then from
the staging zone to the boiler, against a positive pressure
differential between the boiler and condenser.
Inventors: |
Vaisman; Igor B.; (West
Hartford, CT) ; Sangiovanni; Joseph J.; (West
Suffield, CT) ; Taras; Michael F.; (Fayetteville,
NY) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
Carrier Corporation
Farmington
CT
|
Family ID: |
40129973 |
Appl. No.: |
12/600913 |
Filed: |
May 25, 2007 |
PCT Filed: |
May 25, 2007 |
PCT NO: |
PCT/US07/12567 |
371 Date: |
November 19, 2009 |
Current U.S.
Class: |
60/670 ;
417/12 |
Current CPC
Class: |
F01K 25/10 20130101;
Y02E 20/14 20130101 |
Class at
Publication: |
60/670 ;
417/12 |
International
Class: |
F01K 25/00 20060101
F01K025/00; F04B 49/00 20060101 F04B049/00 |
Claims
1. A Rankine system comprising: a closed-loop refrigerant cycle
having an expansion machine, at least one condenser unit, at least
one gravity-driven pumping unit, at least one boiler unit, and a
control system; said boiler unit providing thermal contact and heat
transfer interaction between a fluid carrying enthalpy of available
thermal energy and a liquid refrigerant; said condenser unit
providing thermal contact and heat transfer interaction between a
fluid to be heated and a refrigerant vapor to be condensed; said
gravity-driven pumping unit having an inlet valve, an outlet valve,
and a staging zone between said inlet valve and said outlet valve;
said inlet valve being connected to said condenser unit and; said
outlet valve being connected to said boiler unit; one of said inlet
valve and outlet valve being a normally open valve and the other
being designed for bi-directional operation; said condenser unit
being disposed at a higher elevation than that of said boiling
unit; said inlet valve, said outlet valve, and the entire path
between said condenser unit and said boiler unit being oriented
downwardly to allow vapor refrigerant to freely move upward from
said boiler unit to said condenser unit and to allow liquid
refrigerant to freely drain by gravity downwards from said
condenser unit to said boiler unit; said control system
facilitating operation of said gravity-driven pumping unit by
opening and closing said inlet valve and said outlet valve in a
sequence which enables gravity-driven movement of liquid
refrigerant from said condenser unit to said staging zone and then
from said staging zone to said boiler unit, against a positive
pressure differential between said boiler unit and said condenser
unit.
2. A Rankine system with as recited in claim 1 wherein said at
least one gravity-driven pumping unit includes a liquid receiver
positioned upstream of said inlet valve.
3. A Rankine system as recited in claim 1 wherein said control
system is programmed to open said inlet valve, allow for a time
interval to fill said staging zone with liquid refrigerant, close
said inlet valve, allow a time delay prior to opening said outlet
valve, open said outlet valve, allow for a time interval to
discharge refrigerant from said staging zone, close said outlet
valve, allow for a time delay prior to opening said inlet valve,
and repeat the above sequence.
4. A Rankine system as recited in claim 3, wherein said control
system is further programmed to assign nominal values to said time
to fill the staging zone with refrigerant and to said time to
discharge refrigerant from said staging zone, assign nominal values
to said time delay prior to opening said outlet valve and to said
time delay prior to opening said inlet valve, to provide maximal
pumping capacity; assign values different from said nominal values
of said time to fill staging zone with refrigerant and said time to
discharge refrigerant from said staging zone, assign values larger
than said nominal values of said time delay prior to opening said
outlet valve and to said time delay prior to opening said inlet
valve, to decrease pumping capacity.
5. A Rankine system as recited in claim 1 wherein said control
system is programmed to maintain superheat at an inlet to said
expansion machine based on pressure and temperature monitored by a
pressure sensor and a temperature sensor at said inlet to said
expansion machine, and to accordingly decrease pumping capacity if
superheat is decreased and increase pumping capacity if superheat
is increased.
6. A Rankine system as recited in claim 1 wherein said control
system is programmed to open said inlet valve and said outlet
valve, in order to relieve excessive pressure from a high pressure
side of said Rankine system to a low-pressure side of said Rankine
system, when at least one pressure sensor positioned within the
system indicates excessive pressure elevation.
7. A Rankine system as recited in claim 1 wherein said at least one
gravity-driven pumping unit comprises a plurality of gravity driven
pumps, with each gravity-driven pump housing an inlet valve, an
outlet valve, and a staging zone.
8. A Rankine system as recited in claim 7 wherein said control
system is programmed to regulate pumping capacity by engaging a
different number of said gravity-driven pumps.
9. A Rankine system as recited in claim 1 wherein a number of
boiling pressure levels is provided; said expansion machine has an
inlet associated with a highest boiling pressure level, and a
number of inlets introducing refrigerant streams into an expansion
process associated with other boiling pressure levels; said boiler
unit has a plurality of boilers connected in sequence, with respect
to said fluid carrying enthalpy of available thermal energy; said
gravity-driven pumping unit has a plurality of said gravity-driven
pumping units; a number of said boiling pressure levels, a number
of said boilers, total number of said inlets to said expansion
machine, and a number of said gravity-driven pumps are the same;
and each said gravity-driven pump feeds one boiler and one inlet to
said expansion machine.
10. A Rankine system as recited in claim 1 wherein a number of
boiling pressure levels is provided; said expansion machine has a
plurality of expansion machines, said boiler unit has the same
plurality of boilers connected in sequence, with respect to said
fluid carrying enthalpy of available thermal energy; said
gravity-driven pumping unit has the same plurality of said
gravity-driven pumping units; a number of said boiling pressure
levels, a number of said boilers, a number of said expansion
machines, and a number of said gravity-driven pumps are same; and
each said gravity-driven pump feeds one boiler and one expansion
machine.
11. A Rankine system as recited in claim 10 wherein said plurality
of expansion machines is connected in series.
12. A Rankine system as recited in claim 10 wherein said plurality
of said expansion machines is connected in parallel.
13. A Rankine system as recited in claim 1 wherein said at least
one condenser unit comprises a plurality of condensers connected in
sequence, with respect to the fluid to be heated and with respect
to refrigerant stream exiting said expansion machine; said
gravity-driven pumping unit has the same plurality of said
gravity-driven pumping units; each said condensers feeds one
gravity-driven pumping unit with refrigerant liquid and feeds a
next downstream condenser, if any, with refrigerant vapor.
14. A Rankine system as recited in claim 1 wherein said outlet
valve is installed to stop refrigerant flow in both directions and
said inlet valve is installed to stop refrigerant flow in a
direction from said boiler unit to said condenser unit.
15. A Rankine system as recited in claim 14 wherein said inlet
valve is a normally open flow control device and said outlet valve
is a normally closed flow control device.
16. A Rankine system as recited in claim 14 wherein said inlet
valve is a normally closed flow control device and said outlet
valve is a normally open flow control device.
17. A Rankine system as recited in claim 14 wherein said outlet
valve is a co-axial solenoid valve.
18. A Rankine system as recited in claim 14 wherein said outlet
valve is a motorized valve.
19. A Rankine system as recited in claim 14 wherein said outlet
valve is a modulation valve actuated by a stepper motor.
20. A Rankine system as recited in claim 1 wherein said inlet valve
is installed to stop refrigerant flow in both directions and said
outlet valve is installed to stop refrigerant flow in a direction
from said boiler unit to said condense unit.
21. A Rankine system as recited in claim 20 wherein said inlet
valve is a normally open flow control device and said outlet valve
is a normally closed flow control device.
22. A Rankine system as recited in claim 20 wherein said inlet
valve is a normally closed flow control device and said outlet
valve is a normally open flow control device.
23. A Rankine system as recited in claim 20 wherein said inlet
valve is a co-axial solenoid valve.
24. A Rankine system as recited in claim 1 wherein said inlet valve
and said outlet valve are installed to stop refrigerant flow in
both directions.
25. A Rankine system as recited in claim 24 wherein said inlet
valve is a normally open flow control device and said outlet valve
is a normally closed flow control device.
26. A Rankine system as recited in claim 24 wherein said inlet
valve is a normally closed flow control device and said outlet
valve is a normally open flow control device.
27. A Rankine system as recited in claim 24 wherein said inlet
valve and said outlet valve are co-axial solenoid valves.
28. A Rankine system as recited in claim 14 wherein said outlet
valve is an assembly of two solenoid valves; a first solenoid valve
exposed to said inlet valve and installed to stop refrigerant flow
in a direction from said condenser unit to said boiler unit and; a
second solenoid valve exposed to said boiler unit and installed to
stop refrigerant flow in a direction from said boiler unit to said
condenser unit.
29. A Rankine system as recited in claim 28 wherein said inlet
valve is a normally open flow control device and said second
solenoid valve is a normally closed flow control device.
30. A Rankine system as recited in claim 20 wherein said inlet
valve is a normally closed flow control device and said second
solenoid valve is a normally open flow control device.
31. A Rankine system as recited in claim 14 wherein said outlet
valve is an assembly of two solenoid valves; a first solenoid valve
exposed to said inlet valve and installed to stop refrigerant flow
in a direction from said boiler unit to said condenser unit and; a
second solenoid valve exposed to said boiler unit and installed to
stop refrigerant flow in a direction from said condenser unit to
said boiler unit.
32. A Rankine system as recited in claim 13 wherein said condenser
unit has a two condensation stages having a vapor inlet, an inlet
header, an outlet header, a plurality of refrigerant channels
extending between said inlet header and said outlet header and
sealed inside said inlet and outlet headers, an intermediate liquid
outlet, a liquid outlet, means to route refrigerant flow from said
vapor inlet to said intermediate liquid and liquid outlets, a first
condensation stage associated with one portion of said refrigerant
channels, a second condensation stage associated with another
portion of said refrigerant channels, and means to remove a
condensed liquid portion after said first condensation stage.
33. A Rankine system as recited in claim 32 wherein said means to
route refrigerant flow from said vapor inlet to said intermediate
liquid and liquid outlets consist of at least one of a phase
separator, a baffle, and a collector inside said inlet header and
said outlet header.
34. A Rankine system as recited in claim 32 wherein said means to
remove condensed liquid portion after said first condensation stage
consist of at least one of a phase separator, a baffle, and a
collector inside said inlet header and said outlet header.
35. A Rankine system as recited in claim 32 wherein said
condensation stage has a plurality of coils, and a plurality of
vapor inlets of said coils are connected to said vapor inlet of
said condenser unit, a plurality of intermediate liquid outlets of
said coils are connected to said intermediate liquid outlet of said
condenser unit, and a plurality of liquid outlets of said coils are
connected to said liquid outlet of said condenser unit.
36. A Rankine system as recited in claim 32 wherein said two-stage
condenser unit has a plurality of two-stage condenser coils.
37. A Rankine system as recited in claim 1 and including a vapor
compression system with a compressor wherein said expansion machine
is connected at least to assist in driving said compressor and
further wherein the capacity of said vapor compression system is
regulated by the pumping capacity of said gravity-driven pumping
unit.
38. A Rankine system as recited in claim 18 wherein said staging
zone has a relief valve connected to a point outside said
gravity-driven pumping unit.
39. A Rankine system as recited in claim 1 wherein said vapor
compression system is a heat pump.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to combined heat and power
systems operating on the Rankine cycle that may or may not
incorporate cogeneration. More particularly, the present invention
relates to a pumping method and apparatus therefor.
BACKGROUND OF THE INVENTION
[0002] The Rankine cycle comprising a closed refrigerant loop, a
condenser unit, a liquid refrigerant pump, a boiler unit, and an
expansion machine is well known in the art. The condenser unit
provides thermal contact and heat transfer interaction between a
fluid to be heated and refrigerant to be condensed. The boiler unit
provides thermal contact and heat transfer interaction between a
fluid carrying enthalpy of available thermal energy and refrigerant
vapor to be boiled. Such a system is described, for instance, in
U.S. Pat. No. 3,393,515.
[0003] The liquid refrigerant pump recycles the condensed
refrigerant to the boiler unit, substantially elevating pressure
from a condensing pressure to a boiling pressure. Performing this
function, the liquid refrigerant pump needs substantially subcooled
liquid at the pump inlet to avoid cavitation, consumes noticeable
amount of power, and requires maintenance expenses to handle
reliability issues.
[0004] The power consumed by the pump is a deductible from the
power obtained in the expansion machine, and reduces the overall
refrigerant system thermodynamic efficiency.
[0005] Usually the required refrigerant subcooling is provided by
elevating the condenser pressure, which also reduces the amount of
generated power and thermodynamic efficiency of the refrigerant
system. In addition, having subcooled refrigerant at the outlet of
the condenser unit is associated with additional refrigerant charge
and increased size of the condenser unit. In other words, all these
factors increase the system cost.
[0006] Pumping capacity adjustments are typically provided by
variable speed drives or any other known capacity reduction
methods, such as throttling or pulse width modulation controlled
valves. This also adds cost, reduces thermodynamic efficiency and
may introduce reliability issues. Similarly, if bypass technologies
are applied to reduce pumping capacity, the system efficiency and
operating cost will suffer.
[0007] International application number PCT/US97/20229 published
under the Patent Cooperation Treaty (International Publication
Number WO99/24766) discloses a solar powered heating and cooling
system containing a high temperature heat source with an
arrangement to allow for a low-pressure liquid to flow from a
condenser to a vaporizer by way of gravity. However, although the
concepts related to refrigerant flows driven by gravity are known
in the art, this application doesn't disclose or suggest any
particular component design, system configuration, valve
arrangement or any other means of how this can be accomplished.
SUMMARY OF THE INVENTION
[0008] Briefly, in accordance with one aspect of the invention, a
Rankine system comprises a closed-loop refrigerant cycle with an
expansion machine, a condenser unit, a gravity-driven pumping unit,
and a boiler unit. The gravity driven pumping unit has an inlet
valve, an outlet valve, and a staging zone therebetween. The inlet
valve is connected to the condenser unit and the outlet valve is
connected to the boiler unit. The condenser unit is located above
the boiler unit, with respect to gravity direction. The inlet
valve, the outlet valve, the liquid line and entire path
established between the condenser and boiler units are oriented
progressively downwards, with respect to gravity direction, and are
sized and shaped to allow for vapor refrigerant to freely move
upward from the boiler unit to the condenser unit, and to allow for
liquid refrigerant to freely drain downwards from the condenser
unit to the boiler unit by way of gravity. The control system
facilitates operation of the gravity-driven pumping unit by opening
and closing of the inlet and outlet valves in a sequence, which
enables gravity-driven movement of liquid refrigerant from the
condenser unit to the staging zone and then from the staging zone
to the boiler unit, against a positive pressure differential
between the boiler and condenser units.
[0009] The gravity-driven pumping unit does not require substantial
subcooling at the pump inlet, and this is another aspect of the
invention that overcomes design and operation difficulties
associated with the prior art.
[0010] In yet another aspect of the invention, the control system
operates with a timer to sequentially fill the staging zone with
the refrigerant during one time interval and to subsequently
discharge the refrigerant from the staging zone during another time
interval. Further, there could be a time delay prior to opening the
outlet valve and a time delay prior to opening the inlet valve
incorporated into the control logic. The control system assigns
normal values to the time intervals to provide maximal pumping
capacity, and changes time intervals to decrease pumping capacity.
A plurality of gravity driven pumping units may be used in
combination with each other.
[0011] In yet another aspect of the invention, a Rankine system
with a gravity-driven pump has a number of boiling pressure levels.
The expansion machine has a single inlet associated with the
highest boiling pressure level, and a number of other intermediate
inlets introducing refrigerant streams into the expansion processes
that are associated with other intermediate boiling pressure
levels.
[0012] In yet another aspect of the invention, a Rankine system
with a gravity-driven pump has a condenser unit with a number of
condenser sections connected in sequence. Each condenser section is
feeding one gravity-driven pumping unit with the refrigerant liquid
and feeding a next downstream condenser (if any) with the
refrigerant vapor.
[0013] In the drawings as hereinafter described, preferred and
alternate embodiments are depicted; however various other
modifications and alternate constructions can be made thereto
without departing from the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic illustration of a Rankine system with
a gravity-driven pump, in accordance with the present
invention;
[0015] FIG. 2 is a graphic illustration of the timing sequence in
the operation thereof;
[0016] FIGS. 3A and 3B are schematic illustrations of a coaxial
valve in closed and in opened positions, respectively;
[0017] FIG. 4 is a staging zone with an in-line pressure relief
device, in accordance with the present invention;
[0018] FIG. 5A-5D are gravity-driven pumps with valve assemblies
made of two adjacent solenoid valves with different normal flow
directions, in accordance with the present invention;
[0019] FIG. 6 is a schematic illustration of a Rankine system with
a plurality of gravity-driven pumps, in accordance with the present
invention;
[0020] FIG. 7 is a graphical illustration of the timing sequence of
the control logic for the operation of a gravity-driven pumping
unit with a plurality of pumps;
[0021] FIG. 8 is a schematic illustration of a Rankine system with
two boiling pressure levels, in accordance with the present
invention;
[0022] FIGS. 9A and 9B are schematic illustrations of a two-stage
expansion machine with two turbines connected in sequence and two
turbines connected in parallel, respectively;
[0023] FIG. 10 is a schematic illustration of a Rankine system with
a gravity-driven pump as providing cogeneration of thermal and
mechanical energy, in accordance with the present invention;
[0024] FIG. 11 is a schematic illustration of a Rankine system with
a gravity-driven pump and staged condensation, in accordance with
the present invention;
[0025] FIG. 12 is a schematic illustration of a Rankine system with
a gravity-driven pump, two boiling pressure levels, and staged
condensation, in accordance with the present invention;
[0026] FIG. 13 is a schematic illustration of a two-stage
condensation coil with one pass in each condensation stage, in
accordance with the present invention;
[0027] FIG. 14 is a schematic illustration of a two-stage
condensation coil with two passes in the first condensation stage
and one pass in the second condensation stage;
[0028] FIG. 15 is a schematic illustration of a two-stage
condensation coil with two passes in the first condensation stage
and three passes in the second condensation stage;
[0029] FIG. 16 is a schematic illustration of a two-stage
condensation coil with five passes in the first condensation stage
and four passes in the second condensation stage;
[0030] FIG. 17 is a schematic illustration of a three-stage
condensation shell-and-tube heat exchanger with vertical
baffles;
[0031] FIG. 18 is a schematic illustration of a three-stage
condensation shell-and-tube heat exchanger with horizontal
baffles;
[0032] FIG. 19 is a schematic illustration of a combined vapor
compression and Rankine cycle with a gravity-driven pump.
DETAILED DESCRIPTION OF THE INVENTION
[0033] As shown in FIG. 1, a Rankine system with a gravity-driven
pump includes a condenser unit 1, a gravity-driven pumping unit 2,
a boiler unit 3, and an expansion machine 4.
[0034] The condenser unit 1 provides thermal contact and heat
transfer interaction between a fluid to be heated (e.g. air, water,
or brine) and refrigerant vapor to be condensed. The condenser unit
1 delivers a subcooled liquid at the condensing pressure P.sub.1 at
the condenser outlet.
[0035] The gravity-driven pumping unit 2 is installed on a liquid
line 5, which connects the condenser unit 1 and the boiler unit 3
through the pumping unit 2.
[0036] The boiler unit 3, which provides thermal contact and heat
transfer interaction between a fluid carrying enthalpy of available
thermal energy and refrigerant vapor to be boiled, delivers
superheated vapor at the boiling pressure P.sub.2, which is higher
than the condensing pressure P.sub.1.
[0037] The expansion machine 4, for instance of a turbine, scroll,
screw, reciprocating, rotary or any other type, expands refrigerant
vapor and produces useful mechanical work. A high-pressure vapor
line 6 connects an outlet from the boiler unit 3 and an inlet to
the expansion machine 4. A low-pressure vapor line 7 connects an
outlet from the expansion machine 4 and an inlet to the condenser
unit 1.
[0038] The gravity-driven pumping unit 2 has an inlet valve 8, a
staging zone 9, and an outlet valve 10. The inlet valve 8 is
connected to a source of liquid refrigerant, which is, in this
case, the condenser unit 1. The outlet valve 10 is connected to the
boiler unit 3. The condenser unit 1 is located above, with respect
to gravity (i.e. at a higher elevation), the boiler unit 3. The
liquid line 5 and the gravity-driven pumping unit 2 are oriented
downwardly (vertically or inclined) to enable operation of the
gravity-driven pumping unit 2.
[0039] The gravity driven pump may have a receiver 55 located
upstream of the inlet valve 8. Also, the receiver may be a part of
the condenser unit 1.
[0040] Utilizing the Archimedes and gravity forces as described
below, the gravity-driven pumping unit 2 receives liquid
refrigerant at the condensing pressure P.sub.1 from the condenser
unit 1 and pumps it into the boiler unit 3, where the boiling
pressure P.sub.2>P.sub.1 is maintained. In the boiler unit 3,
liquid refrigerant is boiled due to heat transfer interaction with
the fluid carrying enthalpy of available thermal energy. From the
boiling unit 3, superheated vapor enters the expansion machine 4
through the high pressure vapor line 6, is expanded there from the
boiling pressure P.sub.2 to the condensing pressure P.sub.1,
producing useful mechanical energy that can be obtained from the
shaft of the expansion machine 4. The generated mechanical work may
be transferred into electrical power or may be directly applied to
other mechanically driven devices. The expanded refrigerant vapor,
arriving in the condenser unit 1 through the low-pressure vapor
line 7, is desuperheated, condensed, and subcooled at the
condensing pressure P.sub.1, due to heat transfer interaction with
the fluid to be heated. Liquid from the condenser unit 1 is pumped
through the liquid line 5 by the gravity-driven pumping unit 2, and
the sequence of the thermal processes of the Rankine cycle is
repeated.
[0041] Operational principles of the gravity-driven pumping unit 2
shown in FIG. 1 are illustrated in FIG. 2, which consists of graphs
representing an idealized pressure diagram, position diagram for
the inlet valve 8, and a position diagram for the outlet valve 10,
with respect to time. The pressure diagram indicates changes in
pressure in the staging zone 9, with respect to pressure P.sub.1 in
the condenser unit 1 and pressure P.sub.2 in the boiler unit 3. The
valve position diagrams indicate opened and closed positions of the
inlet and outlet valves 8 and 9.
[0042] Initially, the inlet valve 8 is opened and the outlet valve
10 is closed. This facilitates the filling process. A portion of
the vapor refrigerant from the staging zone 9 moves upward to the
condenser unit 1, due to the Archimedes force, while the liquid
refrigerant from the condenser unit 1 drains downwards to the
staging zone 9, due to the gravity effect, at a relatively slow
drainage rate. Thus, the drained portion of liquid refrigerant
replaces the vapor refrigerant in the staging zone 9. During the
filling process, pressure in the staging zone 9 becomes equal to
the pressure P.sub.1 of the condenser unit 1 as shown on FIG.
2.
[0043] Next, the inlet valve 8 is closed, and there is no vapor or
liquid flow associated with the staging zone 9, since the inlet
valve 8 and the outlet valves 10 are closed.
[0044] When the outlet valve 10 is opened, the staging zone 9 and
the boiler unit 3 are brought into communication. Liquid
refrigerant in the staging zone 9 is pressurized by the vapor in
the boiler unit 3, so that pressure in the staging zone 9 becomes
equal to the pressure P.sub.2 in the boiler unit 3, and the
discharge process is initiated. After the pressure equalization, a
portion of the vapor refrigerant moves upward from the boiler unit
3 to the staging zone 9, due to the Archimedes force, and the
liquid refrigerant from the staging zone 9 drains downwards to the
boiler unit 3, due to the gravity effect. The drained liquid
refrigerant is boiled in the boiler unit 3. The pressure diagram on
FIG. 2 demonstrates the pressure elevation to the value P.sub.2 in
the staging zone 9.
[0045] Next, the outlet valve 10 is closed and there is no vapor or
liquid flow associated with the staging zone 9. Opening of the
inlet valve 8 initiates the filling process again, and the
above-described gravity-driven pumping cycle is repeated.
[0046] A design challenge of the gravity-driven pumps is a
consideration of the impact of a wall temperature of the staging
zone 9. The wall temperature is established as a result of thermal
interaction with the ambient environment, liquid refrigerant
received from the condenser unit 1, vapor refrigerant received from
the boiler unit 3, and the result of thermal bridges between the
condenser unit and the staging zone 9, and between the boiler unit
3 and the staging zone 9. If pressure in the staging zone 9 appears
to correspond to the saturation conditions at the wall temperature,
the condensation of vapor inside the staging zone during the
discharge process takes place. A portion of the vapor refrigerant
from the boiler unit 3 moves upwardly, replaces the drained liquid
in the staging zone 9, and is condensed there at a certain
condensation rate when it contacts the staging zone wall. Liquid
refrigerant drains downwardly to the boiler unit 3 at a certain,
relatively low drainage rate. The condensation rate reduces the
amount of refrigerant delivered from the boiling unit 3 and
ultimately may be equal to the liquid drainage rate. The
condensation process is terminated when the liquid refrigerant is
sufficiently heated up by the refrigerant vapor that is moved up by
the Archimedes force. Insulating of the gravity-driven pump may
reduce the rate of the condensation process and improve the pump
efficiency.
[0047] It is appropriate to introduce volumetric efficiency of the
staging zone 9 as a ratio
.eta. v = m a - m 0 m max = .rho. ' ( t a ) - .rho. ( p 2 ; t 2 )
.rho. ' ( t amb ) , ( 1 ) ##EQU00001##
where .eta..sub.v--volumetric efficiency of the staging zone;
m.sub.a--actual mass of liquid refrigerant filled the staging zone
9 at actual refrigerant temperature t.sub.a; m.sub.0--mass of
refrigerant vapor remained in the staging zone 9, defined at the
boiler pressure p.sub.2 and temperature t.sub.2, prior to closing
of the outlet valve 10; m.sub.a-m.sub.0--mass of refrigerant pumped
to the boiler unit 3 during one pumping cycle; m.sub.max--is
maximal mass of liquid refrigerant filling the staging zone when
temperature of refrigerant inside the staging zone is equal to
ambient temperature t.sub.aamb; .rho.'(t.sub.a)--density of
saturated liquid refrigerant filled the staging zone at actual
refrigerant temperature t.sub.a; .rho.(p.sub.2;t.sub.2)--density of
refrigerant vapor at temperature t.sub.2 and pressure p.sub.2;
.rho.'(t.sub.amb)--density of saturated liquid refrigerant at
temperature t.sub.amb of ambient environment.
[0048] Volumetric efficiency of the staging zone 9 is reduced if a
portion of liquid refrigerant remains in the staging zone 9. Longer
opening of the outlet valve 10 reduces the amount of liquid
refrigerant remaining in the staging zone, but extends the
discharge time and reduces the pumping capacity.
[0049] The lower the wall temperature of the staging zone 9 is, the
lower the temperature of liquid refrigerant filling the staging
zone 9 is, the higher the liquid refrigerant density is, and the
greater the liquid refrigerant mass m.sub.a filling the staging
zone 9 is. This causes volumetric efficiency to increase. On the
other hand, the lower the wall temperature of the staging zone 9
is, the higher the condensation rate is, and the larger the mass
m.sub.0 is. This causes volumetric efficiency to decrease.
[0050] Oppositely, the higher the wall temperature of the staging
zone 9 is, the higher the temperature of liquid refrigerant filling
the staging zone 9 is, the lower the liquid refrigerant density is,
the lower the liquid refrigerant mass m.sub.a filling the staging
zone 9 is. This causes volumetric efficiency to decrease. On the
other hand, the higher the wall temperature of the staging zone 9
is, the lower the condensation rate is, and the smaller the mass
m.sub.0 is. This causes a volumetric efficiency to increase.
[0051] Maximal volumetric efficiency is achieved when wall
temperature of the staging zone 9, during the filling process, is
equal to the ambient temperature and the wall temperature of the
staging zone 9, during the discharge process, is equal to the
boiler temperature. However, taking into account that ambient
temperature is close to the condenser temperature, the best
practical compromise is obtained when the staging zone 9 is placed
as close to the boiler unit 3 as possible. In this case, during the
discharge process, the wall temperature of the staging zone 9 is
established as close to the boiler temperature as possible, due to
the thermal conductivity of the wall material. During the filling
process, the wall temperature of the staging zone 9 is established
as close to the ambient temperature as possible, due to high
specific capacity of liquid refrigerant filling the staging zone
9.
[0052] If ambient temperature is close to boiling temperature, the
best practical compromise is obtained when the staging zone 9 is
placed as close to the condenser unit 3 as possible.
[0053] Vertical orientation reduces the wall temperature effect, in
comparison with inclined orientations.
[0054] Operation of the gravity-driven device in the above
embodiments implies the use of two-way solenoid valves.
Conventional solenoid valves are the devices that stop fluid flow
against a rated pressure differential in one direction, which is a
normal flow direction. Usually, they do not stop flow in the
opposite direction. Solenoid two-way valves that stop fluid flow in
both directions are called bi-directional valves. If rated pressure
differentials are different for each direction, the direction,
which is rated for a higher pressure differential is called a
normal flow direction. Otherwise, a normal flow direction does not
exist.
[0055] In order to efficiently provide the pumping duty, the
gravity-driven pump should meet the following requirements: 1) the
inlet valve 8 and the outlet valve 10 should have the ability to
stop refrigerant flow in the direction from the boiler unit 3 to
the condenser unit 1; 2) at least one valve should have the ability
to stop refrigerant flow in both directions (that is, at least one
valve should be a bi-directional flow control device); 3) internal
ports of the inlet valve 8 and outlet valve 10, and internal
dimensions of the liquid line 2 should be sized and shaped to allow
for refrigerant vapor to flow upwardly, due to the Archimedes
force, and for liquid refrigerant to flow downwardly, due to the
gravity force; and 4) the orientation of the path inside the inlet
valve 8, the outlet valve 10, the liquid line 2, and a line
connecting the outlet valve 10 and the boiler unit 13 should allow
refrigerant vapor to flow upwardly, due to the Archimedes force and
liquid refrigerant to flow downwardly, due to the gravity
force.
[0056] Gravity-driven pumps are operational when the inlet valve 8
is a conventional normally open solenoid valve and the outlet valve
10 is a normally closed bi-directional solenoid valve.
Alternatively, gravity-driven pumps may operate when the outlet
valve 10 is a conventional normally open solenoid valve and the
inlet valve 8 is a normally closed bi-directional solenoid valve.
If no valve is normally open, the trapped liquid may boil out
during off-cycle and destroy the gravity-driven pump.
[0057] Conventional solenoid valves are usually either
direct-acting or pilot-operated devices. The direct-acting solenbid
valves have the ports that are too small to be applicable here. An
increase of the port size is associated with an increase of force
keeping the valve seat in an appropriate position, since the force
is proportional to the valve port area. The coil actuating the
valve limits the force. The pilot-operated valve uses available
pressure to keep the valve seat in an appropriate position.
Although this operational principle significantly reduces the
force, the pilot-operated valves are one-directional devices
only.
[0058] An example of the bi-directional valve is a coaxial valve,
as is shown in FIGS. 3A and 3B. As shown in FIG. 3A the coaxial
valve consists of a casing 11, a seat 12 (which is not a moving
part), and a hollow tube 13 (which is a moving part). The area
between the casing 11 and the seat 12 is a cross-section of an
inlet port 14. An outlet port 15 is located at the opposite end.
The hollow tube 13 has sealing rings 16 between the hollow tube 13
and the casing 11.
[0059] When the hollow tube 13 is positioned against the seat 12,
creating a seal, the co-axial valve is in the closed position, as
shown in FIG. 3A. In the closed position, the valve stops the flow
from the inlet port 14 to the outlet port 15, and from the outlet
port 15 to the inlet port 14. When the hollow tube 13 is moved to
other end, as shown in FIG. 3B, the co-axial valve is in the open
position. In the open position, the valve allows refrigerant
streams to flow from the inlet port 14 to the outlet port 15, and
from the outlet port 15 to the inlet port 14, as indicated by the
arrows in FIG. 3B. The force moving the hollow tube 13 to or from
the seat 12, or keeping the hollow tube 13 against the seat 12, is
not proportional to the port size, therefore the port size may be
as large as needed.
[0060] Hollow tubes of co-axial valves have short strokes between
the open and closed positions. Therefore, sizing of the co-axial
valves for the gravity-driven pump should be based on either the
cross-sectional area around the seat 12 or the cross-sectional area
between the seat 12 and the hollow tube 13 in the open position,
whichever is smaller. The internal diameter of the hollow tube 13
is usually larger than those cross-sectional areas.
[0061] Motorized ball valves and modulation valves actuated by
stepper motors may perfectly meet all four requirements stated
above. However, since the position of these valves cannot be
controlled when power is off, liquid may be trapped between the
inlet valve 8 and the outlet valve 10. The trapped liquid may cause
dangerous pressure elevation in the staging zone 9 when the
temperature around the zone and inside the zone is raised during
the off-cycle. In this case, an in-line pressure relief device 9a
connecting the staging zone 9 with any point of the Rankine system,
outside the staging zone 9, and preferably to a point on the low
pressure side, shall be provided, as shown on FIG. 4.
[0062] FIGS. 5A-5D show options to use conventional solenoid valves
in gravity-driven pumps. It is assumed that the third and the
fourth requirements mentioned above are provided.
[0063] In FIG. 5A, the inlet valve 8 is a conventional solenoid
valve installed to provide normal flow direction from the boiler
unit 3 to the condenser unit 1. The outlet valve arrangement
provides bi-directional operation and is configured of two adjacent
conventional valves, which are a first valve 10a and a second valve
10b. The first valve 10a is a conventional solenoid valve installed
to provide normal flow direction from the condenser unit 1 to the
boiler unit 3. The second valve 10b is a normally closed
conventional solenoid valve installed to provide normal flow
direction from the boiler unit 3 to the condenser unit 1. If the
inlet valve 8 in FIG. 5A is a normally open solenoid valve, the
first valve 10a may be either normally open or normally closed
solenoid valve; the second valve 10b should be a normally closed
solenoid valve. If the inlet valve 8 in FIG. 5A is a normally
closed solenoid valve, the first valve 10a should be a normally
open solenoid valve; the second valve 10b may be either a normally
open or normally closed solenoid valve.
[0064] The first valve 10a in FIG. 5B is a conventional solenoid
valve installed to provide normal flow direction from the boiler
unit 3 to the condenser unit 1. The second valve 10b is a
conventional solenoid valve installed to provide normal flow
direction from the condenser unit 1 to the boiler unit 3. If the
inlet valve 8 in FIG. 5B is a normally open solenoid valve, the
first valve 10a should be a normally closed solenoid valve; the
second valve 10b may be either a normally open or normally closed
solenoid valve. If in FIG. 5B the inlet valve 8 is a normally
closed solenoid valve, the first valve 10a should be a normally
opened solenoid valve; the second valve 10b may be either a
normally open or normally closed solenoid valve.
[0065] Operational principles of gravity-driven pumps with adjacent
conventional solenoid valves are the same as the operational
principles of the gravity-driven pump as shown in FIG. 1, except
that the opening and closing of adjacent valves happens
simultaneously.
[0066] FIG. 5C has the inlet valve arrangement providing
bi-directional operation and is made of two adjacent conventional
valves, which are a first valve 8a and a second valve 8b. The first
valve 8a is a conventional solenoid valve installed to provide
normal flow direction from the condenser unit 1 to the boiler unit
3. The second valve 8b is a conventional solenoid valve installed
to provide normal flow direction from the boiler unit 3 to the
condenser unit 1. If the outlet valve 10 is a normally closed
solenoid valve, the first valve 8a and the second valve 8b may be
either normally closed or normally open solenoid valves. If the
outlet valve 10 as a normally open solenoid valve, the first valve
8a may be either a normally closed or normally open, but the second
valve 8b should be a normally closed solenoid valve.
[0067] In FIG. 5D, the first valve 8a is a conventional solenoid
valve installed to provide normal flow direction from the boiler
unit 3 to the condenser unit 1. The second valve 8b is a
conventional solenoid valve installed to provide normal flow
direction from the condenser unit 1 to the boiler unit 3. If the
outlet valve 10 is a normally closed solenoid valve, the first
valve 8a and the second valve 8b may be either normally closed or
normally open. If the outlet valve 10 is a normally open solenoid
valve, the second valve 8b may be either a normally closed or
normally open valve, but the first valve 8a should be a normally
closed solenoid valve.
[0068] In accordance with FIG. 1, the gravity-driven pumping unit 2
of the Rankine system has one gravity-driven pump. When the pump
discharges a portion of liquid refrigerant into the boiler unit 3,
the boiling process begins and a certain boiling pressure is
established. During the boiling process, the amount of liquid in
the boiling unit 3 is reduced. The reduced amount of boiling liquid
refrigerant causes a reduced amount of generated refrigerant vapor.
As a result, the boiling pressure is reduced. This causes a
reduction of condensing pressure and rotating speed of the
expansion machine 4. When a new portion of liquid refrigerant
arrives, the boiling and condensing pressures and rotating speed
are recovered and the pumping cycle is repeated. Thus, fluctuations
of the boiling and condensing pressures as well as in a rotating
speed of the expansion machine 4 between pumping cycles are taking
place.
[0069] In order to reduce fluctuations of pressures and in a
rotating speed and provide continuous pumping operation, a
plurality of gravity-driven pumps is used. Acceptable levels of
pressures and rotating speed fluctuations dictate a number of
gravity-driven pumps.
[0070] The Rankine system having a plurality of gravity driven
devices is shown in FIG. 6. A gravity driven pumping unit 2
consists of a first gravity driven pump 2a, a second gravity driven
pump 2b, and a third gravity driven pump 2c operating in parallel.
A liquid refrigerant receiver 55 is installed at the inlet to the
gravity driven pumping unit 2 to ensure availability of liquid at
the inlet to the pumping unit. A control system 112 regulates
operation of the gravity-driven pumps 2a, 2b, and 2c.
[0071] Control system 112 regulates the following sequence of
operation for each gravity-driven pump: opening the inlet valve 8,
allowing a sufficient time interval to fill the staging zone 9 with
liquid refrigerant, closing the inlet valve 8, allowing a
sufficient time delay prior to opening of the outlet valve 10,
opening the outlet valve 10, allowing a sufficient time interval to
discharge refrigerant from the staging zone 9, closing the outlet
valve 10, allowing a sufficient time delay prior to opening of the
inlet valve 8, and continuously repeating this sequence, which is
illustrated by FIG. 2.
[0072] In accordance with the sequence described above, the pumping
capacity of each gravity-driven pump depends on a filling time
interval .tau..sub.f, which is the time of filling the staging zone
9 with liquid refrigerant; a discharging time interval .tau..sub.d,
which is the time of discharging refrigerant from the staging zone
9 to the boiler unit 3; the time delay .tau..sub.1 prior to opening
the inlet valve 8 (including time of the opening); and the time
delay .tau..sub.2 prior to opening the outlet valve 10 (including
time of the opening).
[0073] The control logic of the control system 112 is shown in FIG.
7, which illustrates the sequence of opening and closing the inlet
and outlet valves and the time intervals .tau..sub.f, .tau..sub.d,
.tau..sub.1, and .tau..sub.2 mentioned above.
[0074] Let us define the pumping cycle as a process utilizing one
discharging action. In accordance with FIG. 7, the duration of the
pumping cycle of one gravity-driven pumping device is equal to
.tau..sub.0=.tau..sub.f-.tau..sub.d-.tau..sub.1+.tau..sub.2 (3)
[0075] When a number of gravity-driven pumps operate in sequence,
one discharge operation happens during time calculated as
.tau..sub.0=.tau..sub.d+.tau..sub.3, (4)
where .tau..sub.3--is the time interval between the closing of an
outlet valve of one gravity-driven pump and the opening of an
outlet valve of another gravity-driven pump (including the closing
and opening times), which operates in a sequential order, with
respect to the first pump. In FIG. 7, it is shown that
.tau..sub.3=.tau..sub.2; however, this particular relationship is
not required.
[0076] The time calculated per formula (4) implies that there are
to be a number of pumps operating in sequential order
n = r .tau. f + .tau. d + .tau. 1 + .tau. 2 .tau. d + .tau. 3 , ( 5
) ##EQU00002##
where r--is a correction factor adjusting n to an integer value;
for instance, it may happen that r=1.
[0077] Each sequential step may include a number of pumps operating
in parallel, with either simultaneous or overlapping cycles. In
general, the mass flow rate provided by the gravity-driven pumping
unit is
G = ( m a - m 0 ) k n .tau. 0 = .eta. v m max k n .tau. 0 , ( 6 )
##EQU00003##
where k--is a number of gravity-driven pumps operating in parallel
at the moment.
[0078] At certain filling and discharge times
(.tau..sub.f=.tau..sub.f0 and .tau..sub.d=.tau..sub.d0), and when
time delays prior to opening inlet and outlet valves 8 and 10 are
minimal (.tau..sub.1.fwdarw.0 and .tau..sub.2.fwdarw.0), the mass
flow rate provided by one gravity-driven device is at its maximum.
These times are called nominal times. The mass flow rate is reduced
when .tau..sub.f.noteq..tau..sub.f0,
.tau..sub.d.noteq..tau..sub.d0, .tau..sub.1>0 and
.tau..sub.2>0. If .tau..sub.f<.tau..sub.f0 or
.tau..sub.d<.tau..sub.d0, the flow capacity is reduced, because
the filling process or the discharge process is incomplete. If
.tau..sub.f>.tau..sub.f0 or .tau..sub.d>.tau..sub.d0, the
mass flow rate is reduced, because the pumping cycle duration is
increased. For the same reason, the mass flow rate is reduced when
time delays .tau..sub.1 and .tau..sub.2 are increased.
[0079] The same conclusions are applicable for a plurality of
gravity driven pumps, even though formula (4) includes .tau..sub.d
and .tau..sub.3 only. This is because time .tau..sub.3 depends on
time .tau..sub.f, .tau..sub.d, .tau..sub.1, and .tau..sub.2, in
accordance with formula (5). Also, time .tau..sub.3 depends on the
number of gravity-driven pumps n operating in a sequential order.
Thus, having a plurality of gravity-driven pumps, allows an
additional option to engage a different number of pumps, in order
to change the pumping capacity. The changed number of pumps may
need changing time .tau..sub.f, .tau..sub.d, .tau..sub.1, or
.tau..sub.2.
[0080] A control system 112 makes adjustments of the mass flow rate
with time .tau..sub.f, .tau..sub.d, .tau..sub.1, and .tau..sub.2
based on readings from a temperature sensor 113 and a pressure
sensor 114. The boiler unit 3 is sized to maintain a certain
nominal superheat at maximal flow capacity. If the refrigerant
superheat, as monitored by the temperature sensor 113 and the
pressure sensor 114 is decreased, the control system 112 decreases
the refrigerant mass flow rate. If the superheat is increased, the
control system 112 increases the refrigerant mass flow rate.
[0081] The gravity-driven pumping unit may be operated in a
pressure relief mode. If pressure on the high-pressure side of the
Rankine system is undesirably increased, based on readings as
provided by the pressure sensor 114, the control system 112 opens
the inlet valve 8 and the outlet valve 10 and releases the
undesirably increased refrigerant pressure into the condenser unit
1.
[0082] The higher the pressure at the inlet to the expansion
machine 4 is, the higher the potential efficiency of the Rankine
cycle is. On other hand, the higher the boiling pressure is, the
higher the temperature of the fluid at the outlet from the boiler
unit 3 is, and the lower the extent of utilization of the thermal
energy is.
[0083] In FIG. 8, a boiler unit 3 is comprised of a first boiler 3a
operating at a high boiling temperature and a second boiler 3b
operating at a low boiling temperature. A gravity-driven pump 2a
feeds the first boiler 3a and a gravity-driven pump 2b feeds the
second boiler 3b. A fluid 115 carrying thermal energy is cooled in
the first boiler 3a to an intermediate temperature and is further
cooled in the second boiler 3b to a temperature approaching the low
boiling temperature. Refrigerant exiting the first boiler 3a feeds
a main inlet 116 of the expansion machine 4. Refrigerant from the
second boiler 3b feeds an intermediate inlet 117 to the expansion
machine 4, introducing a portion of refrigerant at a low boiling
pressure into the expansion process. Thus, the expansion machine 4
is fed through the main inlet with the same amount of vapor
refrigerant at a high boiling pressure as a boiler operating in the
Rankine cycle with one boiling pressure level, and, at the same
time, the low boiling temperature allows an extraction of power
from the thermal energy source to a greater extent. As a result,
efficiency of the Rankine system is significantly improved.
[0084] Ultimately, the Rankine system may have a number of boiling
pressure levels, and the same number of boilers, inlets to the
expansion machine 4, and gravity-driven pumping units.
[0085] Alternatively to the expansion machine 4 with the main inlet
116 and the intermediate inlet 117, a two-stage (or multistage)
expansion machine 4 having two turbines or two expanders 4a and 4b
may be used as shown in FIGS. 9A and 9B.
[0086] FIG. 9A relates a two-stage expansion machine 4 with a first
stage 4a and a second stage 4b connected in sequence. Each stage 4a
and 4b may have a plurality of turbines or other expansion devices.
Refrigerant vapor at a high boiling pressure enters the first stage
4a through an inlet 116. The first stage 4a expands the entered
portion of refrigerant to an intermediate pressure equal to a low
boiling pressure. The expanded portion of refrigerant at the low
boiling pressure is mixed with portion of refrigerant incoming
through the intermediate inlet 117 from the second boiler,
similarly to the Rankine system in FIG. 7. Further expansion to a
condensing pressure is executed in the second stage 4b. Ultimately,
the expansion machine 4 may have a number of turbines or other
expansion devices, such as scrolls, screws or reciprocating
pistons, connected in sequence, and the same number of
gravity-driven pumping units, boiling pressure levels and
boilers.
[0087] In FIG. 9B, a first stage 4a and a second stage 4b operate
in parallel. Each stage 4a and 4b may have a plurality of turbines
or other expansion devices. Refrigerant vapor at a high boiling
pressure enters the first stage 4a through an inlet 116 and is
expanded to a condensing pressure. Refrigerant vapor at a low
boiling pressure enters the second stage 4b through an intermediate
inlet 117 from the second boiler, similarly to the Rankine system
in FIG. 7, and is expanded to a condensing pressure as well.
Ultimately, the expansion machine 4 may have a number of turbines
or other expansion devices, such as scrolls, screws or
reciprocating pistons, connected in parallel, and the same number
of gravity-driven pumping units, boiling pressure levels and
boilers.
[0088] In both cases shown on FIG. 9A and FIG. 9B, the two
expansion stages may be attached to one shaft, or they may have
independent shafts with independent distribution of the recovered
mechanical energy.
[0089] Two levels of boiling pressure may be utilized in the
Rankine system providing co-generation of thermal and mechanical
energy, as shown in FIG. 10. The Rankine system recovers energy in
the expansion machine 4 and, at the same time, it executes heating
duties in a condenser unit 1a and condenser unit 1b through the
thermal and heat transfer interaction with the fluid 115. The
condenser unit 1a heats a fluid 118a providing high quality thermal
output; the condenser unit 1b heats a fluid 118b providing low
quality thermal output. Optionally, the condenser units 1a and 1b
may heat a single fluid with two steps of heating 118a and
118b.
[0090] Thermal energy is absorbed in a boiler unit 3 at two boiling
pressure levels. A high boiling pressure is maintained in a boiler
3b, which feeds the expansion machine 4 through an inlet 116. A low
boiling pressure is maintained in a boiler 3a, which feeds the
expansion machine 4 through an intermediate inlet 117. The boiler
3a is fed by a gravity-driven pumping units 2b, and the boiler 3b
is fed by gravity-driven pumping units 2a and 2c.
[0091] Refrigerant condensation occurs at two pressure levels as
well. The condenser unit 1a operates at a condensing pressure which
corresponds to a pressure at the outlet of the expansion machine 4.
The condenser unit 2a operates at a pressure which is equal to the
low boiling pressure.
[0092] The condenser unit 1a feeds the gravity-driven pumping units
2a and 2b, or alternatively may feed the gravity-driven pumping
unit 2b only. The condenser unit 2a feeds the gravity-driven
pumping units 2c.
[0093] Ultimately, the Rankine system providing co-generation of
thermal and mechanical energy has a number of condensers and
condensing pressure levels and the same number of boilers, boiling
pressure levels, and inlets to the expansion machine 4 (or
expansion machines as shown in FIGS. 9A and 9B). The number of
gravity-driven pumping units should be at least the same; however,
it may vary. For example, if there are n pressure levels: P.sub.1,
P.sub.2, P.sub.3, P.sub.N-1, and P.sub.N, where P.sub.1 is the
lowest pressure level and is a condensing pressure only; P.sub.N is
the highest pressure level and is the boiling pressure only. The
number of boiling pressures is n-1: P.sub.2, P.sub.3, . . . ,
P.sub.N-1 and P.sub.N. The number of condensing pressures is the
same and they are: P.sub.1, P.sub.2, P.sub.3, . . . , and
P.sub.N-1. Thus, pressures P.sub.2, P.sub.3, . . . , and P.sub.N-1
are boiling pressures and, at the same time, they are condensing
pressures. A condenser operating at the pressure level P.sub.1 may
have n-1 pumps, a condenser operating at the pressure level P.sub.2
may have n-2 pumps, a condenser operating at the pressure level
P.sub.3 may have n-3 pumps, and so on. Thus, n pressure levels
ultimately allow for
i = 1 n - 1 i ##EQU00004##
pumps.
[0094] It is known that liquid refrigerant condensed inside
refrigerant channels occupies an insignificant portion of the
entire internal condenser unit volume, but it is primarily
positioned at the condenser unit walls and covers up a significant
portion of internal heat transfer area. As a result, vapor
refrigerant, which occupies a significant part of the entire
internal volume, does not contact the condenser unit walls, and
overall heat transfer coefficient is substantially reduced. Removal
of the condensed refrigerant from the condenser unit may
significantly improve performance characteristics of the entire
system.
[0095] FIG. 11 relates to the Rankine system with staged
condensation. The condenser unit 1 includes a first condenser 1a, a
second condenser 1b, and a third condenser 1c cooled by a fluid
118, which could be, for instance, water, air, or brine. Each
condenser feeds its own receiver and gravity-driven pump. A first
receiver 55a and a first gravity-driven pump 2a are associated with
the first condenser 1a, a second receiver 55b and a second
gravity-driven pump 2b are associated with the second condenser 1b,
and a third receiver 55c and a third gravity-driven pump 2c are
associated with the third condenser 1c. The first, second, and
third pumps 2a, 2b, and 2c may include pluralities of pumps.
[0096] Refrigerant vapor exiting the expansion machine 4 is
partially condensed in the third condenser 1c. The condensed liquid
portion is directed into the third receiver 55c and the remaining
portion of the refrigerant vapor enters the second condenser 1b,
where it is partially condensed. Subsequently, the condensed liquid
portion is routed into the second receiver 55b and the remaining
portion of the refrigerant vapor enters the first condenser unit
1c. In the first condenser 1c, the refrigerant is completely
condensed and then fills the first receiver 55a.
[0097] FIG. 12 is another illustration of utilization of the staged
condensation, although combined with two boiling pressure levels.
The condenser unit 1 comprises a first condenser 1a and a second
condenser 1b and is cooled by a fluid 118, which could be, for
instance, water, air, or brine. The boiler unit 3 consists of a
first boiler 3a and a second boiler 3b, heated by a fluid 115
carrying enthalpy of available thermal energy. Each condenser feeds
its own receiver, pump, and boiler. A first receiver 55a, a first
gravity-driven pump 2a, and a first boiler 3a are associated with
the first condenser 1a. A second receiver 55b, a second
gravity-driven pump 2b, and a second boiler 3b are associated with
the second condenser 1b. This system requires an expansion machine
4 with two inlets, or an expansion machine 4 as shown in FIGS. 9A
and 9B.
[0098] This system combines the advantages of two levels of boiling
pressure, which improve efficiency of the Rankine system, and
removal of liquid from the condensation process, which improves
performance of the condensers and, ultimately, efficiency of the
entire Rankine system.
[0099] There are different opportunities in providing staged
condensation in the condenser units.
[0100] FIGS. 13-16 relate to air-cooled condenser units. Each
condensation stage may be circuited to have a number of passes.
[0101] FIG. 13 shows a two-stage condenser unit with one pass in
each stage. The condenser unit has an inlet header 24, an outlet
header 25, and plurality of refrigerant channels 26 extending
between the inlet and outlet headers 24 and 25. The refrigerant
channels 26 are sealed within the inlet and outlet headers 24 and
25. The external surface of the channels is thermally exposed to a
cooling fluid. The inlet header 24 has a vapor inlet 27 and a
liquid outlet 29. The outlet header 25 has an intermediate liquid
outlet 28. The inlet header 24 contains a baffle 30 splitting it
into two portions 31 and 32 and routing the condensing refrigerant
stream into two passes 33 and 34. One portion is associated with
the pass 33 and the vapor inlet 27; another portion is associated
with the pass 34 and the liquid outlet 29.
[0102] While the condenser unit in FIG. 13 has only one pass in
each condensation stage, FIG. 14 presents a condenser unit having
two passes 33a and 33b in a first condensation stage 33 and one
pass in a second condensation stage 34. An inlet header 24 has a
phase separator 30. The phase separator 30 splits the inlet header
24 into an upper chamber 31 associated with the vapor inlet 27 and
a lower chamber 32 associated with an intermediate outlet 28. An
outlet header 25 has a phase separator 35, which splits the outlet
header into an upper chamber 36 and a lower chamber 37. The upper
chamber 36 is associated with a first condensation stage 33. The
lower chamber 37 is associated with a second condensation stage 34
and a liquid outlet 29.
[0103] It is possible to have a condenser unit with multiple passes
in each condensation stage. For example, FIG. 15 shows two passes
33a and 33b in a first condensation stage 33 and three passes 34a,
34b, and 34c in a second condensation stage 34. Phase separators 30
and 36 in an inlet header 24, and phase separators 35 and 37 in an
outlet header 25, are employed. Also, a collector 29a is employed
near a liquid outlet 29.
[0104] FIG. 16 shows five passes 33a, 33b, 33c, 33d, and 33e in a
first condensation stage 33 and three passes 34a, 34b, and 34c in a
second condensation stage 34. Phase separators 30, 36, 38, and 40
in an inlet header 24 and phase separators 35, 37, 39, and 41 in an
outlet header 25 are employed. Also, a collector 29a is employed
near a liquid outlet 29.
[0105] In FIG. 15, the intermediate liquid outlet 28 is located in
the outlet header 25 and the liquid outlet 29 is located in the
inlet header 24, but in FIG. 16 the intermediate liquid outlet 28
and the liquid outlet 29 are located in the outlet header 25. Also,
there are possible constructions when the intermediate liquid
outlet 28 is located in the inlet header 24 and the liquid outlet
29 is located in the outlet header 25, and constructions when the
intermediate liquid outlet 28 and the liquid outlet 29 are located
in the inlet header 24.
[0106] Usually, the number of passes in the first condensation
stage is larger than in the second condensation stage.
[0107] In the condenser units shown in FIGS. 12-15, the refrigerant
channels extending between the inlet header 24 and outlet header
25, are oriented horizontally and the condensing refrigerant flow
is routed from top to bottom. There is an option to use the
condenser units shown in FIGS. 13-16 in a reverse direction, where
the vapor inlet is at 29 instead of being at 27, the vapor outlet
is at 27 instead of being at 29; and the intermediate liquid outlet
28 remains the same. In this case, the condensing refrigerant flow
is routed from bottom to top.
[0108] Configurations as mentioned in U.S. Pat. No. 5,988,267 and
in U.S. Pat. No. 5,762,566 are possible as well.
[0109] FIGS. 17-18 relate to shell-and-tube condenser units cooled,
for instance, by water or brine. The shell-and-tube heat exchangers
have one refrigerant pass, one pass for heated fluid, and three
condensation stages.
[0110] The shell-and-tube condenser in FIG. 17 has an elongated
cylindrical housing or shell 40. Inside the shell 40, there are a
bundle of longitudinal heat transfer tubes 41. The shell 40 and the
heat transfer tubes 41 are extended between a first tube sheet 42
and a second tube sheet 43. A first bonnet 44 is attached to the
first tube sheet 42 at one end of the shell 40. A second bonnet 45
is attached to the second tube sheet 43 at the opposite end of the
shell 40. The tube side is intended for a water stream. The first
bonnet 44 has a water inlet 46 and the second bonnet 45 has a water
outlet 47. The shell side is intended for a refrigerant stream. A
refrigerant inlet 48, and three refrigerant outlets 49, 50, and 51,
are arranged in the shell 40. Three vertical baffles 52a, 52b, and
52c are installed inside the shell 40, providing three condensation
zones. The refrigerant inlet 48 and the first refrigerant outlet 49
are located in the first condensation zone between the first tube
sheet 42 and the first vertical baffle 52a. The second refrigerant
outlet 50 is located in the second condensation zone between the
first vertical baffle 52a and the third vertical baffle 52c, and
including the second vertical baffle 52b. The third refrigerant
outlet 51 is located in the third condensation zone between the
third vertical baffle 52c and the second tube sheet 43. The
vertical baffles 52a, 52b, and 52c direct refrigerant streams as
shown by the arrows in FIG. 17.
[0111] The shell-and-tube condenser in FIG. 18 has longitudinal
baffles 53a and 53b and vertical baffles 54a and 54b. A refrigerant
inlet 48, and three refrigerant outlets 49, 50, and 51, are
arranged in the shell 40. The refrigerant inlet 48 and the first
refrigerant outlet 49 are located in the first condensation zone
between the first vertical baffle 54a and the second vertical
baffle 54b. The second refrigerant outlet 50 is located in the
second condensation zone between a first end 42 and the first
vertical baffle 54a. The third refrigerant outlet 51 is located in
the third condensation zone between the second vertical baffle 54b
and the second tube sheet 43. The longitudinal baffles 53a and 53b
and the vertical baffles 54a and 54b direct refrigerant stream as
shown by the arrows in FIG. 18.
[0112] In both FIG. 17 and FIG. 18, a first portion of refrigerant
is condensed in the first condensation zone and the condensed
portion is removed from the shell side through the first
refrigerant outlet 49. A second portion of refrigerant is condensed
in the second condensation zone and the condensed portion is
removed from the shell side through the second refrigerant outlet
50. A third portion of refrigerant is condensed in the third
condensation zone and the condensed portion is removed from the
shell side through the third refrigerant outlet 51.
[0113] FIG. 19 combines a Rankine loop and a vapor compression
loop. The Rankine loop includes a condenser unit 1, a receiver 55,
a gravity-driven pumping unit 2 installed on a liquid line 5, a
boiler unit 3, a high-pressure pipe 6, an expansion machine 4, and
a low-pressure pipe 7. The vapor compression loop consists of a
compressor 22, a discharge line 23, a portion of a low-pressure
line 7 (which is a high-pressure line for the vapor compression
loop), the condenser unit 1, the receiver 55, an expansion device
19, an evaporator unit 20, and a suction line 21. The compressor 22
and the expansion machine 4 may share a common shaft, and the
energy obtained from the expansion process in the expansion machine
4 is used to drive, or assist in driving, the compressor 22. The
compressor 22 and the expansion machine 4 may have a common casing,
forming a hermetic unit. The Rankine loop generates mechanical
energy and operates between a boiling (high) pressure and a
condensing (low) pressure. The obtained mechanical energy is used
to drive, or assist in driving, the compressor 22 operating between
the condensing (high) and evaporating (low) pressures. The vapor
compression loop driven by the compressor 22 provides cooling in
the evaporator unit 20 and/or a heating in the condenser unit 1.
The vapor compression loop may have a reversing valve to enable
operation of the loop as a heat pump. Cooling and/or heating
capacities generated by the vapor compression loop are regulated by
the gravity-driven pumping unit 2.
[0114] While certain preferred embodiments of the present invention
have been disclosed in detail, it is to be understood that various
modifications in its structure may be adopted without departing
from the spirit and scope of the invention as defined by the
following claims.
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