Patent Application
20120000201
This invention relates generally to organic Rankine cycle (ORC) plants, and more particularly to methods and apparatus for using the thermal mass of the ORC, the working fluid, the oil loop, the water loop and all components, to provide additional transient power.
Rankine cycles use a working fluid in a closed cycle to gather heat from a heating source or a hot reservoir by generating a hot gaseous stream that expands through a turbine to generate power. The expanded stream is condensed in a condenser by rejecting the heat to a cold reservoir. The working fluid in a Rankine cycle follows a closed loop and is re-used constantly.
Electric grids do not incorporate any intrinsic storage capability. Demand and supply therefore are required to be balanced at every moment. This characteristic requires power plants constantly follow the electric grid load. Since not all types of power plants are able to achieve such tracking, some power plants operate at constant load, and provide a so-called base-load. Power plants that are able to accommodate such fast changing power requirements are called peaking power plants. Peak power is more expensive to generate and is of high value since it ensured the grid stability. Peak power plants therefore provide a technical and economic advantage over base-load power plants.
ORC plants are presently either base-load power plants, or strictly follow the heat input from a heat source. Such ORC plants are able to provide only a base load to the electric grid, and thus generate relatively low revenue for the generated electricity.
In view of the foregoing, it would be advantageous to provide an ORC plant with an improved operation strategy that is capable of operating with varying temperatures and pressures to enable the production of transient power. The ORC plant should be capable of generating power corresponding to the demand on an electric grid, thus providing a more economical and profitable power system and helping to stabilize the electric grid.
According to one embodiment, an organic Rankine cycle (ORC) plant comprises:
an internal combustion engine or gas turbine (engine/turbine) cooling fluid loop configured to transfer engine/turbine cooling fluid heat to a low temperature (LT) ORC loop, the engine/turbine cooling loop and the LT ORC loop together configured to generate transient power via at least one LT expander; and
a thermal oil loop configured to transfer heat generated via the engine/turbine to a high temperature (HT) ORC loop, the thermal oil loop and the HT ORC loop together configured to generate transient power via at least one HT expander.
According to another embodiment, an organic Rankine cycle (ORC) plant comprises an internal combustion engine or gas turbine (engine/turbine) cooling fluid loop configured to transfer engine/turbine cooling fluid heat from an engine/turbine to a low temperature (LT) ORC loop working fluid, the engine/turbine cooling loop and the LT ORC loop together configured to generate transient power via at least one LT expander.
According to yet another embodiment, an organic Rankine cycle (ORC) plant comprises a thermal oil loop configured to transfer heat from an internal combustion engine or gas turbine (engine/turbine) to a high temperature (HT) ORC loop working fluid, the thermal oil loop and the HT ORC loop together configured to generate transient power via at least one HT expander.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawing, wherein:
While the above-identified drawing figure sets forth a particular embodiment, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
Looking now at thermal oil loop 12, an engine/turbine 20 generates an exhaust gas 22 at a high temperature (e.g. 450° C.) that is received by a heat exchanger 24 that cools the exhaust gas by transferring at least some of its heat to a thermal oil 26 passing through the heat exchanger 24. The heated thermal oil 26 enters an evaporator 28 where it is re-cooled as it transfers heat to the HT ORC loop 16 working fluid to generate a saturated vapor stream 38 that may have a temperature for example, of about 210° C. according to one embodiment. Common heat sources for organic Rankine cycles are exhaust gases from combustion systems (power plants or industrial processes), hot liquid or gaseous streams from industrial processes or renewable thermal sources such as geothermal or solar thermal. The cooled thermal oil re-enters a thermal oil pump 30 to generate the high-pressure thermal oil, and the thermal oil loop cycle repeats.
The resultant HT ORC loop 16 saturated vapor stream 38 expands through a high temperature expander (turbine) 32 that forms part of the HT ORC loop 16 to generate output power. In one embodiment, this expansion is isentropic and the output power is sufficient to produce about 190 KW of electrical output power. The expansion decreases the temperature and pressure of the vapor stream. The resultant vapor stream 40 then enters a condenser 34 where it is cooled to generate a liquid stream 36 by transferring residual heat to the LT ORC 18 working fluid. This liquid stream 36 re-enters a pump 42 to generate the high-pressure HT ORC loop 16 working fluid, and the cycle repeats.
Moving now to the engine/turbine cooling fluid loop 14, the engine/turbine 20 heats a known cooling fluid such as water to a high temperature (e.g. 90° C.) that is subsequently received by a pre-heater unit 44 that re-cools the engine/turbine cooling fluid by transferring at least some of its heat to the LT ORC loop 18 working fluid 46 passing through the pre-heater 44. The heated working fluid 48 enters the evaporator 34 where it is further heated via resultant vapor stream 40 to generate a saturated vapor stream 50 that may have a temperature for example, of about 90° C. according to one embodiment. Common heat sources for organic Rankine cycles are exhaust gases from combustion systems (power plants or industrial processes), hot liquid or gaseous streams from industrial processes or renewable thermal sources such as geothermal or solar thermal, as stated herein.
The resultant LT ORC loop 18 saturated vapor stream 50 expands through a low temperature expander (turbine) 52 that forms part of the LT ORC loop 18 to generate output power. In one embodiment, this expansion is isentropic and is sufficient to produce about 183 KW of electrical output power. The expansion decreases the temperature and pressure of the vapor stream. The resultant vapor stream 54 then enters a condenser 56 (e.g. air blown finned tubes) where it is re-cooled to generate a saturated liquid stream 58. This saturated liquid stream 58 re-enters a pump 60 to generate the high-pressure LT ORC loop 18 working fluid, and the cycle repeats.
In summary explanation, techniques for using the thermal mass of an ORC, the working fluid, the oil loop, the water loop and all components, to provide additional transient power to an electrical grid according to particular embodiments have been described herein. The embodiments described herein provide for improved ORC operation strategies in response to varying temperatures and pressures to enable the production of transient power. More power can be produced by, e.g. further cooling down heat transfer fluids for a limited period of time. Thus, when less power is demanded from the grid, the ORC can follow the demand and help to stabilize the grid. Transient power in the range of up to a few minutes can be produced when using all the flexibility of the ORC. According to one embodiment, the thermal oil loop provides about two minutes of power to drive the ORC at full power.
Harvesting the incentives for peak power can be more easily achieved using the principles described herein by increasing the size and capacity of one or more ORC loops 16, 18 and/or providing one or more additional backup expanders/turbines 82, 84 such as depicted in
The embodiments described herein advantageously provide backup power capability in the case of a grid loss event. The ORCs can immediately provide power for systems during the time periods when engines need to start-up. Such time periods can be, for example, up to about ten minutes for large Jenbacher engines. The thermal energy stored from previous engine operations or from other industrial heat sources can provide the requisite backup power capability using the principles described herein.
The embodiments described herein are particularly useful for maintaining operation of an ORC plant, even during short periods of time while the heat source, e.g. internal combustion engine, gas turbine, and the like, is already turned off. The embodiments are also useful to provide additional thermal peak power from a thermo oil loop if required by the ORC plant operation. The embodiments described herein are further particularly useful in island applications, to supply auxiliary power if the power plant is off. Embodiments described herein are capable of providing short time increases and/or decreases of output power if demanded from the grid side when operated according to the principles described herein. Further, the foregoing embodiments can compensate for power fluctuations due to day/night ambient temperature fluctuations.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
