RANKINE SYSTEM WITH GRAVITY-DRIVEN PUMP
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.
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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 INVENTIONThe 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.
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.
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.
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.
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.
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 INVENTIONBriefly, 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.
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.
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.
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.
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.
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.
As shown in
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 P1 at the condenser outlet.
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.
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 P2, which is higher than the condensing pressure P1.
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.
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.
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.
Utilizing the Archimedes and gravity forces as described below, the gravity-driven pumping unit 2 receives liquid refrigerant at the condensing pressure P1 from the condenser unit 1 and pumps it into the boiler unit 3, where the boiling pressure P2>P1 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 P2 to the condensing pressure P1, 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 P1, 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.
Operational principles of the gravity-driven pumping unit 2 shown in
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 P1 of the condenser unit 1 as shown on
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.
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 P2 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
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.
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.
It is appropriate to introduce volumetric efficiency of the staging zone 9 as a ratio
where ηv—volumetric efficiency of the staging zone; ma—actual mass of liquid refrigerant filled the staging zone 9 at actual refrigerant temperature ta; m0—mass of refrigerant vapor remained in the staging zone 9, defined at the boiler pressure p2 and temperature t2, prior to closing of the outlet valve 10; ma-m0—mass of refrigerant pumped to the boiler unit 3 during one pumping cycle; mmax—is maximal mass of liquid refrigerant filling the staging zone when temperature of refrigerant inside the staging zone is equal to ambient temperature taamb; ρ′(ta)—density of saturated liquid refrigerant filled the staging zone at actual refrigerant temperature ta; ρ(p2;t2)—density of refrigerant vapor at temperature t2 and pressure p2; ρ′(tamb)—density of saturated liquid refrigerant at temperature tamb of ambient environment.
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.
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 ma 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 m0 is. This causes volumetric efficiency to decrease.
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 ma 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 m0 is. This causes a volumetric efficiency to increase.
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.
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.
Vertical orientation reduces the wall temperature effect, in comparison with inclined orientations.
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.
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.
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.
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.
An example of the bi-directional valve is a coaxial valve, as is shown in
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
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.
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
In
The first valve 10a in
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
In
In accordance with
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.
The Rankine system having a plurality of gravity driven devices is shown in
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
In accordance with the sequence described above, the pumping capacity of each gravity-driven pump depends on a filling time interval τf, which is the time of filling the staging zone 9 with liquid refrigerant; a discharging time interval τd, which is the time of discharging refrigerant from the staging zone 9 to the boiler unit 3; the time delay τ1 prior to opening the inlet valve 8 (including time of the opening); and the time delay τ2 prior to opening the outlet valve 10 (including time of the opening).
The control logic of the control system 112 is shown in
Let us define the pumping cycle as a process utilizing one discharging action. In accordance with
τ0=τf−τd−τ1+τ2 (3)
When a number of gravity-driven pumps operate in sequence, one discharge operation happens during time calculated as
τ0=τd+τ3, (4)
where τ3—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
The time calculated per formula (4) implies that there are to be a number of pumps operating in sequential order
where r—is a correction factor adjusting n to an integer value; for instance, it may happen that r=1.
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
where k—is a number of gravity-driven pumps operating in parallel at the moment.
At certain filling and discharge times (τf=τf0 and τd=τd0), and when time delays prior to opening inlet and outlet valves 8 and 10 are minimal (τ1→0 and τ2→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 τf≠τf0, τd≠τd0, τ1>0 and τ2>0. If τf<τf0 or τd<τd0, the flow capacity is reduced, because the filling process or the discharge process is incomplete. If τf>τf0 or τd>τd0, 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 τ1 and τ2 are increased.
The same conclusions are applicable for a plurality of gravity driven pumps, even though formula (4) includes τd and τ3 only. This is because time τ3 depends on time τf, τd, τ1, and τ2, in accordance with formula (5). Also, time τ3 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 τf, τd, τ1, or τ2.
A control system 112 makes adjustments of the mass flow rate with time τf, τd, τ1, and τ2 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.
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.
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.
In
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.
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
In
In both cases shown on
Two levels of boiling pressure may be utilized in the Rankine system providing co-generation of thermal and mechanical energy, as shown in
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.
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.
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.
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
pumps.
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.
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.
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.
There are different opportunities in providing staged condensation in the condenser units.
While the condenser unit in
It is possible to have a condenser unit with multiple passes in each condensation stage. For example,
In
Usually, the number of passes in the first condensation stage is larger than in the second condensation stage.
In the condenser units shown in
Configurations as mentioned in U.S. Pat. No. 5,988,267 and in U.S. Pat. No. 5,762,566 are possible as well.
The shell-and-tube condenser in
The shell-and-tube condenser in
In both
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.
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.
Type: Application
Filed: May 25, 2007
Publication Date: Jun 24, 2010
Applicant: Carrier Corporation (Farmington, CT)
Inventors: Igor B. Vaisman (West Hartford, CT), Joseph J. Sangiovanni (West Suffield, CT), Michael F. Taras (Fayetteville, NY)
Application Number: 12/600,913
International Classification: F01K 25/00 (20060101); F04B 49/00 (20060101);