1. Field of the Invention
Embodiments of the present invention generally relate to power generation systems and, more particularly, to Organic Rankine Cycle (ORC) systems having a solar power source and a saturated liquid storage.
2. Description of the Prior Art
Rankine cycles use a working organic fluid in a closed cycle to gather heat from a heating source or a hot reservoir and to generate power by expanding a hot gaseous stream through a turbine or an expander. The expanded stream is condensed in a condenser by transferring heat to a cold reservoir and pumped up to a heating pressure again to complete the cycle. Solar power sources are known to be used as the heating source or the hot reservoir. For example, Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as the heat source for a conventional power plant. A wide range of concentrating technologies exists. The most developed are the parabolic trough, the concentrating linear fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the Sun and focus light. In all of these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage.
A generic ORC system is discussed with regard to
One working fluid that can be used in a Rankine cycle is an organic working fluid. Such an organic working fluid is referred to as an ORC fluid. ORC systems have been deployed as retrofits for engines as well as for small-scale and medium-scale gas turbines, to capture waste heat from the hot flue gas stream. This waste heat may be used in a secondary power generation system to generate up to an additional 20% power on top of the power delivered by the engine producing the hot flue gases alone.
With the development of solar power sources, the ORC cycle has been applied to such a system as described. For example, in
However, the existing solar power systems are not efficient. In addition, the existent solar power systems have difficulties in producing energy when the sun is not available. Accordingly, systems and methods for improving the efficiency of ORC systems in power generation systems are desirable.
According to an embodiment of the present invention, there is provided a closed loop system for producing energy using an Organic Rankine Cycle (ORC) and an ORC fluid. The system comprises a first solar power source configured to heat an ORC liquid to a saturated ORC liquid, a second solar power source fluidly connected to the first solar power source and configured to vaporize the saturated ORC liquid to become ORC vapor, and a turbo-machine configured to receive ORC vapor and produce mechanical energy by expanding the ORC vapor.
According to an embodiment of the present invention, there is provided a closed loop system for producing energy using an Organic Rankine Cycle (ORC) and an ORC fluid. The system comprises a turbo-machine configured to transform heat into mechanical energy, a recuperator fluidly connected to an output of the turbo-machine and configured to remove heat from the vaporized ORC fluid, a cooling device fluidly connected to the recuperator and configured to transform the vaporized ORC fluid back to the ORC liquid, a pump fluidly connected between the cooling device and the recuperator and configured to pump the ORC liquid to the recuperator, a first solar power source configured to transform by heating the ORC liquid to a saturated ORC liquid, and a second solar power source fluidly connected to the first solar power source and configured to vaporize the saturated ORC liquid to become ORC vapor, wherein the turbo-machine is configured to receive the ORC vapor from the second solar power source.
According to another embodiment of the present invention, there is provided a method for generating energy using an Organic Rankine Cycle (ORC). The method comprises transforming ORC liquid through heating within a first solar power source into a saturated ORC liquid in a closed loop system, storing the saturated ORC liquid in a storage tank, controlling a flow of the saturated ORC liquid to a second solar power source or another device for transforming the saturated ORC liquid to ORC vapor, expanding the ORC vapor in a turbo-machine to produce the energy, and cooling the ORC vapor to change it back to the ORC liquid and returning the ORC liquid back to the first solar power source.
Embodiments of the present invention will be more apparent to those skilled in the art upon reading the following description with reference to the accompanying drawings, in which:
The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. For simplicity, the following description refers to an ORC cycle used with a solar power source for producing energy with an expander. However, the solar power source may be different, or the expander may be replaced with another turbo-machine for producing energy.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
According to an exemplary embodiment illustrated in
The medium may be an organic fluid traditionally used in ORC systems. However, for an improved efficiency, a cyclopentane based fluid may be used as the medium according to an application. Cyclopentane is a highly flammable alicyclic hydrocarbon with chemical formula C5H10. It consists of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occurs as a colorless liquid with a petrol-like odor. Its melting point is −94° C. and its boiling point is 49° C. Other mediums may also be used. According to an exemplary embodiment, the ORC medium includes cyclopentane mixed with one or more of 2-Methyl Pentane, npentane and isopentane. For example, one possible combination is cyclopentane around 95%, 2-Methyl Pentane around 3.5%, npentane 0.75% and isopentane around 0.75%.
The solar power source 52 may be any of the known solar sources. However, the embodiments to be discussed next are optimized for concentrated solar power (CSP) systems. A CSP system is different from a photovoltaic system as the photovoltaic system directly transforms the solar energy into electricity. A CSP system needs a medium to be vaporized based on the solar energy and then that energy is extracted with an appropriate turbo-machine, e.g., an expander or a turbine. Thus, the medium used in the embodiment shown in
The turbo-machine 54 may be any machine that is configured to extract energy from the vaporized medium and transform this energy into, e.g., mechanical energy. In this regard, an expander is configured to receive a vaporized medium which determines airfoils or an impeller of the expander to rotate around a transversal axis. Thermodynamic energy of the gas (vaporized medium) is extracted during the expansion process which makes a shaft (that holds the airfoils or impeller) of the expander to rotate, thus generating the mechanical energy. This mechanical energy may be used to activate a power device 60, for example, a compressor or an electrical power generator for producing electricity. In other words, the system discussed in the exemplary embodiment may be used to generate power or to drive a machine, e.g., turbo-machine.
The expander may be a single stage or plural stages expander. A single stage expander has only one impeller and the vaporized gas is provided to the exhaust of the expander after passing the single impeller. A multi-stage impeller has plural impellers and the expanded medium from one impeller is provided to a next impeller for further extracting energy from the medium. The expander may be a centrifugal or an axial machine. A centrifugal expander receives the vaporized medium along a first direction (e.g., Y axis) and discharges the expanded medium at a second direction (e.g., X direction) substantially perpendicular to the first direction. In other words, a centrifugal force is used to rotate the shaft of the expander. In an axial expander the medium enters and exits the expander along the same direction, similar to the jet engine of an airplane.
The condenser 56 may be air cooled or water cooled and its purpose is to further cool the expanded medium from the turbo-machine 54 so that the medium becomes liquid. The pump 58 may be any pump known in the art and suitable for increasing the pressure of the medium to a desired value. Heat from the medium exhausted from the expander 54 may be removed in a recuperator 64 and provided to the liquid medium being provided to the solar power source 52. The recuperator 64 may be as simple as a container having two pipes that share a same ambient. For example, the liquid medium (from the pump) flows through a first pipe while the vaporized medium (from the expander) flows through a second pipe. Because the same ambient is present around the first and second pipes, heat from the second pipe migrates to the first pipe, thus heating the liquid medium. Other more sophisticated recuperators may be used.
The flow of the medium through the system 50 is now discussed in more details. Assume that the medium flow is followed from point A. At this point the liquid medium is at a high pressure (e.g., 40 bar) due to the pump 58 and at a low temperature (e.g., 55° C.). After the liquid medium passes through the solar power source 52, its temperature is increased (e.g., at 250° C.). The numbers used in this and other exemplary embodiments are for illustration purposes and not intended to limit the embodiments. Those skilled in the art would recognize that these numbers change from system to system as the characteristics of the system changes.
While passing the solar power source 52, the medium may undergo a phase transformation, i.e., from liquid medium to vaporized medium. During the passing through the solar power source 52, the solar energy is transferred from the sun light to the medium. The vaporized medium arrives at point B and enters an inlet 54a of the expander 54 and makes the shaft of the expander to rotate, transforming the solar energy into mechanical energy. The expanded medium, which may be still a gas and not a liquid (e.g., temperature at point C is about 140° C. and pressure is about 1.3 bar) is then released from the expander at outlet 54b.
As there is still energy (heat) left in the vaporized medium at point C, this medium is directed to the recuperator 64 to further remove heat from it. The heat removed in the recuperator 64 from the vaporized medium at point D is provided to the liquid medium at point E (inside the recuperator) prior to providing the liquid medium to the solar power source. The cooled vaporized medium at point F, is now cooled down in the condenser 56 to bring it back to a liquid phase. Then, the liquid medium is provided to the pump 58 and the cycle repeats. It is noted that the piping 66 that takes the medium from a component to the other is sealed so that the medium does not escape outside the system 50. In other words, the system shown in
The above discussed system increases the conversion efficiency of the solar energy to electrical energy when an electric power generator 60 is used. Also, the present system does not need water for its medium and the medium may be directly vaporized by the solar power source. If using the cyclopentane based fluid, it is noted that this medium is directly vaporized in the solar power source as the boiling temperature of cyclopentane is around 49° C.
Some modifications of the system 50 shown in
In another application, a storage tank 72 may be provided for storing the cyclopentane based medium. In one exemplary embodiment, the storage tank is provided downstream the condenser 56. Various valves 74 and 76 may be provided along the piping system for controlling the amount of the medium flowing in the system. In still another exemplary embodiment, a balancing line 78 and a valve 80 may be provided for controlling the flow of the medium through the system.
A different system is presented in
The first closed loop system 102 may include a solar power source 120, similar to the solar power source 52 of
In this regard, the oil based substance from the solar power source 120 vaporizes in the vaporizer 114 the medium of the second closed loop system and provides the vaporized medium to the turbo-machine 106. In addition, it is possible to further use the oil based substance to pre-heat the medium of the second closed loop cycle in one or more heat exchanging devices 116 and 118. However, according to an exemplary embodiment, the heat exchanging devices 116 and 118 may be omitted. The cooled oil based substance arrives then at an expansion vessel 124 from which it flows to the pump 122 for being again provided to the solar power source 120. The oil based substance does not mixes up with the medium of the second closed loop system or with the ambient. The expansion vessel 124 may be in fluid communication with a nitrogen source 126 that is configured to nitrogen blanket a top portion (inside) of the expansion vessel 124. Although the nitrogen enters inside the expansion vessel, the nitrogen does not flow through the first closed loop system 102 as it flows above the oil based substance.
According to an exemplary embodiment illustrated in
Methods for operating such systems are now discussed. According to an exemplary embodiment illustrated in
According to another exemplary embodiment illustrated in
According to still another exemplary embodiment, it is possible to provide a new arrangement that is not limited to cyclopentane but may use any ORC fluid (e.g., any organic based fluid). In this embodiment, two distinct solar power sources are used to heat the ORC fluid. The first solar power source is configured to heat an incoming ORC liquid to become saturated and the second solar power source is configured to further heat the saturated ORC liquid to become ORC vapor. A liquid is said to be saturated when it is about to boil. A storage tank for the saturated ORC liquid may be provided between the first and second solar power sources. During periods when the solar power sources are inactive, e.g., cloudily, a secondary power source may be used to transform the saturated ORC liquid into vapor to be provided to the turbo-machine. Alternatively, a throttling wall (or throttling device) may be used to partially transform the saturated ORC liquid (by partially reducing pressure isenthalpically) to vapor as will be discussed later.
According to an exemplary embodiment illustrated in
The flow of the ORC fluid is now discussed with regard to
From here the saturated ORC liquid is directed to and stored in tank 214. If the second solar power source 212 is active, the control device 216 is configured to allow the saturated ORC liquid from the tank 214 to proceed to the second solar power source 212 and not to the secondary heat source 218. The second solar power source 212 is configured to vaporize the saturated ORC liquid so that at point C the entire flow is in the form of vapors. Thus, heat is added during the transition A to B and also during the transition B to C. In a particular example, not intended to limit the invention, when the temperatures are, at A around 50° C., at B around 230° C., and at C around 250° C., the added heat between A and B is around 400 kJ/kg and a latent heat added between B and C is around 40 kJ/kg. It can be seen that the latent heat is low. The ORC vapor is then provided to the turbo-machine 202 for producing mechanical energy.
When the second solar power source 212 is not available, the control device 216 is configured to provide the saturated ORC liquid to the secondary heat source 218 so that the liquid is transformed to vapor and provided to the turbo-machine 202. It is noted that instead of the secondary heat source 218 a throttle wall (or a throttling device) 220 may be used to reduce a pressure isenthalpically of the saturated ORC liquid for transforming it into vapor as shown in
In this way, the embodiments illustrated in
According to an exemplary embodiment illustrated in
The disclosed exemplary embodiments provide a system and a method for transforming solar energy into mechanical energy or electrical energy even when the solar polar is temporarily not available. It should be understood that this description is not intended to limit the present invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the present invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the present invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.
Number | Date | Country | Kind |
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941/DEL/2011 | Apr 2011 | IN | national |
This is a national stage application under 35 U.S.C. §371(c) of prior-filed, co-pending, PCT application serial number PCT/EP2012/055760, filed on Mar. 30, 2012, which claims priority to Indian patent application serial number 941/DEL/2011, filed on Apr. 1, 2011, the entire contents of which are incorporated by reference herein.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2012/055760 | 3/30/2012 | WO | 00 | 8/13/2014 |