1. Field of the Invention
The present invention relates to power generation, transmission, and distribution and, more particularly, to the generation and conveyance of electric power, the recovery and storage of thermal energy, and the conversion of thermal energy into electric power.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Large central generating plants that use coal, natural gas, oil, or nuclear fuel are used in electric power systems throughout the industry in the U.S. and abroad. Generating capacities of central generating plants range from about 25 Mw to over 1,000 Mw. Central generating plants are typically located remote from end-use facilities and typically convert less than 40 percent of the energy content of fuel into electric power. A key feature of the existing power transmission and distribution system is that it is designed for power flow in only one direction: from central generating plants to the electric transmission system, to distribution substations, and then radially outward to end-use facilities.
Distributed generation, by contrast, refers to a variety of smaller power-generating technologies that are installed at or near end-use facilities. Distributed generation technologies include wind turbines, solar photo-voltaic panels, fuel cell generators, gas turbine generators, and reciprocating engine generators. Distributed generation units typically have 25 Mw or less in generating capacity.
A combined heat and power (“CHP”) generator is a type of distributed generation system that is commonly comprised of one or more gas turbine generators or reciprocating engine generators that convert a fuel, typically natural gas, into electric power and waste heat, which is also referred to as “thermal energy”. The financial feasibility of CHP generator operation is heavily dependent on the extent to which the waste heat can be beneficially utilized in an end-use facility such as for space heating or domestic water heating or industrial process heating. When waste heat can be fully utilized, power from a CHP unit can be produced at less than half of the cost of power generated by central plants that use coal, natural gas, or oil as fuel.
Conventional CHP generator year-round operation with total waste-heat utilization at full power output is currently practical only in instances where the end-use facility's year-round heat and power demand exceeds the CHP generator's maximum heat and power output. Such instances are limited to industrial plants or commercial buildings with significant year-round domestic water heating, laundry, and food service heat demand such as large hospitals or hotels. In practically all other types of commercial buildings, heat demand results almost entirely from winter space heating requirements with minimal heat demand at other times of the year. Limited heat demand renders CHP generator operation economically unattractive for the majority of commercial buildings at all times of year except during the winter months when space heat demand provides a beneficial use for CHP waste heat.
Current practice by those skilled in the art is to electrically interconnect distributed generation systems on the customer side of the electric meter so that power generated would replace power delivered by an electric utility. If the distributed generation system produces more power than the end-use facility consumes, power will flow in reverse into the electric distribution system. When this occurs, unstable voltage conditions could be experienced in some areas of the electric distribution system that could adversely impact operation of some types of electrically operated equipment in end-use facilities that are electrically interconnected to the same circuit. In addition, the electric utility would have difficulty ascertaining the direction of power flow in circuits where distributed generators are connected. This could potentially expose workers to harmful power flows when distribution system repairs must be made on these circuits. Electric utilities typically restrict distributed generation owners from producing power in excess of their use in order to prevent export of excess power into the distribution system which can burden the economics of distributed generation to such an extent that investment in distributed generation becomes unattractive and CHP economic feasibility is restricted to industrial and commercial facilities with year-round heat demand.
Other embodiments of the invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements.
One embodiment of the disclosure is a novel Distributed Heat and Power System (DHPS) architecture that (1) improves the operating efficiency of combined heat and power (“CHP”) generators and that (2) prevents unstable voltage conditions and safety concerns that arise when large numbers of distributed power generators are interconnected with electric distribution systems that represent current art. An exemplary DHPS architecture disclosed herein has (at least) two novel features: (1) a Waste Heat Recovery and Conversion System that captures substantially all of the recoverable waste heat that is rejected from one or more CHP generators and that converts said waste heat into electric power and thermal energy that can be beneficially utilized and (2) a Power Gathering System that transports power produced by a plurality of CHP power generators located at widely separated sites for the purpose of delivering their aggregate power output to the electric transmission system, at a single point of interconnection, using conventional means of electric power conveyance. The Power Gathering System operates independently and separate from utility-operated electric distribution systems. It is understood by those skilled in the art that CHP generators typically cannot operate cost-effectively during the summer months when there is no significant demand for space heating, and opportunities for other beneficial uses of waste heat in most commercial facilities are limited. CHP generators that are equipped with the Waste Heat Recovery and Conversion System disclosed herein and that are interconnected with the Power Gathering System disclosed herein would be capable of operating year-round at full power output with maximum efficiency thereby making it economically feasible for such CHP generators to serve as a financially viable alternative to central generating plants that represent current art and that use coal, natural gas, oil, or nuclear fuel.
The Power Gathering System (“PGS”) gathers power produced by a plurality of CHP generators located at widely separated sites for the purpose of conveying their aggregated power output to an electric distribution substation without directly interconnecting with an existing, electric distribution system. The aggregated power output of the CHP generators supplants power that would otherwise have been supplied by central generating plants to electric loads interconnected with an electric distribution system operated by an electric distribution utility. CHP generators are typically installed within the property boundary (the “Site Boundary”) of the end-use facility that utilizes waste heat produced by the CHP generator (“Thermal Host Facility”). The Thermal Host is also electrically interconnected with the PGS and is supplied by the aggregated power output of the CHP generators. End-use facilities that are not Thermal Host Facilities but that are interconnected with the PGS (“Offsite Electric Loads”) are also supplied by the aggregated power output of the CHP generators. The amount of power collectively produced by the CHP generators that is in excess of the power consumed by the Thermal Hosts, the Offsite Electric Loads, and the electric load interconnected with the existing electric distribution system flows into the electric transmission system supplanting power produced by central generating plants.
The Waste Heat Recovery and Conversion System captures waste heat from a conventional gas turbine generator or reciprocating engine generator and converts said waste heat into electric power, steam, and/or hot water.
The PGS and the Waste Heat Recovery and Conversion System, when used together, allow CHP generators to operate continuously at full power output with maximum efficiency, thereby making it economically feasible for CHP generators to serve as a financially viable alternative to central generating plants that represent current art and that use coal, natural gas, oil, or nuclear fuel.
Heat-transfer fluid is circulated by pump P-1A through coils in the High-Temperature Waste Heat Recovery unit E-1A, which heat-transfer fluid absorbs a portion of the heat in the gas turbine exhaust. The High-Temperature Heat Conversion System (“HTHC”) uses the heat absorbed by the heat-transfer fluid 19 to produce high-pressure steam 21 and low-pressure steam 22 for use in a Thermal Host Facility. The cooled heat-transfer fluid 20 is then returned to unit E-1A for reheating. Recovered heat that is not utilized to produce steam is converted in the HTHC system into power 24 that is conveyed to electric end-use facilities via the PGS.
The Low-Temperature Heat Recovery and Conversion (“LTHC”) section uses high-pressure water circulated by pump P-1B through coils in the Low-Temperature Heat Recovery unit E-1B, which water absorbs additional heat from the gas turbine exhaust 18 that enters unit E-1B at a temperature of approximately 475 Deg. F. The LTHC system uses the heat absorbed by the circulating high-pressure water 26 to produce hot water 28 for use in a Thermal Host Facility. The cooled high-pressure water 27 is returned to unit E-1B for reheating. Heat that is recovered in unit E-1B that is not utilized to produce hot water is converted in the LTHC system into power 29 that is conveyed to electric end-use facilities via the PGS. The power output from the LTHC system varies in response to an external control signal 30 while generator GT-1 power output 16 remains constant.
Current art is to reject this heat into the atmosphere using a conventional radiator or cooling tower, whereas, in this exemplary embodiment, this heat is converted to power in the WHC system. Pump P-2 circulates cooling water 33 through the jacket water cooling heat exchanger E-1C and through a conventional exhaust heat recovery silencer E-1D, which transfers heat from 950 Deg. F. engine exhaust gas 39 to heat the cooling water to approximately 315 Deg. F. This heated cooling water 35 circulates to the WHC system to produce low-pressure steam 36 for use in a Thermal Host Facility and electricity 38 that is conveyed to other electric end-use facilities via the PGS. The power generated by the WHC system varies in response to an external control signal 37, while generator EG-1 power output 32 remains constant. Pump P-3 conveys a portion 40 of the hot water stream 34 to the Thermal Host Facility 85, which is returned 41 to the cooling water system for reheating.
A portion 55 of high-pressure steam 53 is supplied to steam turbine N-2, which reduces the steam's pressure to levels needed to supply low-pressure steam 57 to the Thermal Host Facility. Pressure controller PC-2 measures steam 57 pressure and modulates control valve V-2 as needed to maintain steam 57 pressure at approximately 5 to 10 psig. Steam turbine N-1 drives generator G-2, which produces electricity 56 that is conveyed to electric end-use facilities via the PGS 29.
Pump P-6 is used to convey a portion 58 of HTF 19 to superheater E-3, which transfers heat from HTF 58 to superheat high-pressure steam 59 when heat loss in transit to the Thermal Host Facility is a concern.
Steam condensate 60 that is returned from the Thermal Host Facility and make-up water 61 is conveyed to deaerator D-1, where the oxygen and other non-condensable gases are removed. The combined steam condensate and make-up water flow 52 is then supplied to steam generator E-2 via pump P-5 to generate steam. Cooled HTF 20 from steam generator E-2, superheater E-3, and ORC generator ORC-1 is returned to unit E-1A of
The total power output 29 of all four ORC generators can be varied in response to an external control signal 30 by altering the thermal fluid flow rate though the ORC generators. Pump P-7 is a variable-speed pump that is capable of changing thermal fluid flow rate by changing its rotational speed. Power output controller EC-1 processes an external control signal 30 and varies the thermal fluid flow rate by causing the rotational speed of pump P-7 to vary, which in turn causes the aggregate ORC generator power output 29 to vary.
A portion 27 of the thermal fluid 67 leaving ORC generator ORC-5 returns to unit E-1B of
Pump P-1B operates at a constant flow rate, whereas pump P-7 operates at a variable flow rate depending on the level of power output required from the ORC generators. The role of heat accumulator D-2A is to accommodate the differences in flow rate between pumps P-1B and P-7 by accumulating high-temperature thermal fluid 69 when pump P-7 flow rate is less than pump P-1B flow rate. Similarly, heat accumulator D-2A discharges high-temperature thermal fluid 69 when pump P-7 flow rate is greater than pump P-1B flow rate. Heat accumulator D-2A remains full at all times. The gradient between high-temperature thermal fluid 69 at the top of heat accumulator D-2A and low-temperature thermal fluid 70 at the bottom of heat accumulator D-2A changes in response to the difference in flow rate between pumps P-1B and P-7.
Although
The total power output 38 of all six ORC generators can be varied in response to an external control signal 37 by altering the thermal fluid 73 flow rate though the ORC generators. Pump P-8 is a variable-speed pump that is capable of changing thermal fluid 73 flow rate by changing its rotational speed. Power output controller EC-2 responds to the external control signal 37 and varies the thermal fluid 73 flow rate by causing the rotational speed of pump P-8 to vary, which in turn causes the aggregate ORC generator power output 38 to vary.
Thermal fluid 79 leaving ORC generator ORC-11 flows through radiator E-5 and then returns to exchanger E-1C of
The sum of thermal fluid 70 flow rate and heated water 71 flow rate equals heated water 35 flow rate. As low-pressure steam production 36 varies, thermal fluid 70 flow rate will vary inversely. Thermal fluid 73 flow also varies with ORC generator power output 38.
The role of heat accumulator D-2B is to accommodate the differences in flow rates of thermal fluids 70 and 73 by accumulating high-temperature thermal fluid 80 when the flow rate of thermal fluid 73 is less than the flow rate of thermal fluid 70. Similarly, heat accumulator D-2B discharges high-temperature thermal fluid 80 when the flow rate of thermal fluid 73 is greater than the flow rate of thermal fluid 70. Heat accumulator D-2B remains full at all times. The gradient between high-temperature thermal fluid 80 at the top of heat accumulator D-2B and low-temperature thermal fluid 81 at the bottom of heat accumulator D-2B changes in response to the difference between in the flow rate of thermal fluid 73 and the flow rate of thermal fluid 70.
Steam condensate 84 that is returned from the Thermal Host Facility and make-up water 83 is conveyed to deaerator D-1A, where the oxygen and other non-condensable gases are removed. The combined steam condensate and make-up water flow 82 is then supplied to steam generator E-4 via pump P-9 to generate steam.
Although
The present disclosure has been discussed in the context of
In general, the PGS circuits of a PGS system could be connected to one or more of the following facilities:
Although the disclosure has been described as using ORC generators, it will be understood that other types of heat-to-electricity generators, such as a condensing steam turbine generator, can be used.
Although the architectures of
Although the PGS system is shown in
According to an example embodiment disclosed above in reference to
In some embodiments of the above electric overlay system, the amount of thermal energy used by the first thermal host facility varies over time inversely with the amount of excess thermal energy; and the first CHP generator is configured to adjust over time the amount of additional electric power generated directly with the varying amount of excess thermal energy.
In some embodiments of any of the above electric overlay systems, the electrical overlay system of claim 1, comprising one or more circuits (e.g., 11-14) including the first circuit, wherein the one or more circuits are connected to: the electric-power GTD system; one or more electric-power generators (e.g., CHP-1 to CHP-8) including the first CHP generator and each connected to provide electric power to the one or more circuits; and one or more electric-power users (e.g., H1-H8, OS1-OS4) including the first thermal host facility and each connected to receive electric power from the one or more circuits.
In some embodiments of any of the above electric overlay systems, when a total amount of electric power used by the one or more electric-power users is greater than a total amount of electric power provided by the one or more electric-power generators, then additional electric power is supplied to the one or more electric-power users by the electric-power GTD system via the one or more circuits; and when the total amount of electric power used by the one or more electric-power users is less than the total amount of electric power provided by the one or more electric-power generators, then excess electric power is supplied by the one or more electric-power generators to the electric-power GTD system via the one or more circuits.
In some embodiments of any of the above electric overlay systems, the electrical overlay system comprises one or more circuits (e.g., 11-14) including the first circuit, wherein the one or more circuits are connected to: the electric-power GTD system; one or more additional CHP generators (e.g., CHP-2 to CHP-8), each connected to provide electric power to the one or more circuits; and one or more additional thermal host facilities (e.g., H2-H8), each connected to receive electric power from the one or more circuits and thermal energy from a co-located one of the one or more additional CHP generators.
In some embodiments of any of the above electric overlay systems, the one or more circuits are further connected to at least one of: one or more non-CHP electric-power generators, each connected to provide electric power to the one or more circuits, but not any thermal energy to any thermal host facility; and one or more other facilities (e.g., OS1-OS4), each connected to receive electric power from the one or more circuits, but not any thermal energy from any CHP generator.
In some embodiments of any of the above electric overlay systems, the electric-power GTD system has one or more distribution substations, each connected to its own instance of the electrical overlay system.
In some embodiments of any of the above electric overlay systems, the CHP generator (
In some embodiments of any of the above electric overlay systems, the primary electric-power generator is a gas turbine generator or a reciprocating engine generator.
In some embodiments of any of the above electric overlay systems, the final heat recovery and conversion stage is a low-temperature heat recovery and conversion stage; the CHP generator further comprises a high-temperature heat recovery and conversion stage located between the primary electric-power generator and the low-temperature heat recovery and conversion stage; the high-temperature heat recovery and conversion stage is configured to convert at least some of the thermal energy from the primary electric-power generator into a first amount of additional electric power (e.g., 24, 25) dependent on the amount of primary electric power; and the low-temperature heat recovery and conversion stage is configured to convert at least some of the thermal energy (e.g., 18) from the high-temperature heat recovery and conversion stage into a second amount of additional electric power (e.g., 29) independent of the amount of primary electric power.
In some embodiments of any of the above electric overlay systems, the final heat recovery and conversion stage comprises: a heat recovery unit (e.g., E-1B) configured to transfer at least some of the thermal energy generated by the primary electric-power generator to a cooled fluid (e.g., 27) to generate a heated fluid (e.g., 26); and a heat conversion system (e.g., LTHC) configured to convert at least some of the thermal energy in the heated fluid into the amount of additional electric power and to provide the cooled fluid.
In some embodiments of any of the above electric overlay systems, the heat conversion system (
In some embodiments of any of the above electric overlay systems, the one or more heat-to-electricity generators comprise a plurality of organic Rankine cycle (ORC) generators connected in series.
According to another example embodiment disclosed above in reference to
In some embodiments of the above CHP generator, the final heat recovery and conversion stage is a low-temperature heat recovery and conversion stage; the CHP generator further comprises a high-temperature heat recovery and conversion stage located between the primary electric-power generator and the low-temperature heat recovery and conversion stage; the high-temperature heat recovery and conversion stage is configured to convert at least some of the thermal energy from the primary electric-power generator into a first amount of additional electric power (e.g., 24, 25) dependent on the amount of primary electric power; and the low-temperature heat recovery and conversion stage is configured to convert at least some of the thermal energy (e.g., 18) from the high-temperature heat recovery and conversion stage into a second amount of additional electric power (e.g., 29) independent of the amount of primary electric power.
In some embodiments of any of the above CHP generators, the primary electric-power generator is a gas turbine generator or a reciprocating engine generator.
In some embodiments of any of the above CHP generators, at least some of the thermal energy from the final heat recovery and conversion stage is supplied to a thermal host facility (e.g., H1) co-located with the CHP generator.
In some embodiments of any of the above CHP generators, the amount of additional electric power generated by the final heat recovery and conversion stage inversely depends on the amount of thermal energy provided to the thermal host facility.
In some embodiments of any of the above CHP generators, the final heat recovery and conversion stage comprises: a heat recovery unit (e.g., E-1B) configured to transfer at least some of the thermal energy generated by the primary electric-power generator to a cooled fluid (e.g., 27) to generate a heated fluid (e.g., 28); and a heat conversion system (e.g., LTHC) configured to convert at least some of the thermal energy in the heated fluid into the amount of additional electric power and to provide the cooled fluid.
In some embodiments of any of the above CHP generators, the heat conversion system comprises: an input port configured to receive the heated fluid (e.g., 26); an output port configured to provide the cooled fluid (e.g., 27); a heat accumulator (e.g., D-2A) having a first port connected to the input port and a second port connected to the output port and configured to receive, store, and provide fluid via its first and second ports; one or more heat-to-electricity generators (e.g., ORC-2 to ORC-5) connected between the first and second ports of the heat accumulator and each configured to convert at least some of the thermal energy in the heated fluid into electric power (e.g., 68) and to provide the cooled fluid; a variable-speed pump (e.g., P-7) connected between the first and second ports of the heat accumulator and configured to allow a selected amount of the heated fluid to flow through the one or more heat-to-electricity generators; and a controller (e.g., EC-1) configured to select the amount of the heated fluid flowing through the one or more heat-to-electricity generators and thereby control the amount of electric power generated by the one or more heat-to-electricity generators.
In some embodiments of any of the above CHP generators, the one or more heat-to-electricity generators comprise a plurality of organic Rankine cycle (ORC) generators connected in series.
According to another example embodiment disclosed above in reference to
In some embodiments of the above heat conversion system, the one or more heat-to-electricity generators comprise a plurality of heat-to-electricity generators connected in series.
In some embodiments of any of the above heat conversion systems, each heat-to-electricity generator is an organic Rankine cycle (ORC) generator.
Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value or range.
It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain embodiments of this invention may be made by those skilled in the art without departing from embodiments of the invention encompassed by the following claims.
The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures.
It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the invention.
Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”
The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.
This application claims the benefit of the filing date of U.S. provisional application No. 61/776,909, filed on Mar. 12, 2013, the teachings of which are incorporated herein by reference in their entirety.
Number | Date | Country | |
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61776909 | Mar 2013 | US |