High-temperature dual-source organic Rankine cycle with gas separations

• US 20100300093A1
• Filed: 11/25/2007
• Published: 12/02/2010
• Est. Priority Date: 10/12/2007
• Status: Active Grant

• Current Assignee: Doty Scientific, Inc.
• Original Assignee: Doty Scientific, Inc.
• Inventors: Doty, F. David
• Granted Patent: US 8,046,999 B2
• Time in Patent Office: Days
• US Class Current: 60/641.2
• CPC Class Codes: F01K 17/06 Returning energy of steam, in exchanged form, to process, e.g. use of exhaust steam for drying solid fuel or plant
• CPC Class Codes: F01K 19/10 Cooling exhaust steam other than by condenser; Rendering exhaust steam invisible
• CPC Class Codes: F01K 25/10 the vapours being cold, e.g. ammonia, carbon dioxide, ether
• CPC Class Codes: F01K 3/12 having two or more accumulators
• CPC Class Codes: F22G 1/005 the heat being supplied by steam
• CPC Class Codes: Y02E 10/46 Conversion of thermal power into mechanical power, e.g. Rankine, Stirling or solar thermal engines
• CPC Class Codes: Y02E 20/16 Combined cycle power plant [CCPP], or combined cycle gas turbine [CCGT]
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

In a dual-source organic Rankine cycle (DORC), the condensed and slightly sub-cooled working fluid at near ambient temperature (˜300 K) and at low-side pressure (0.1 to 0.7 MPa) is (1) pumped to high-side pressure (0.5-5 MPa), (2) pre-heated in a low-temperature (LT) recuperator, (3) boiled using a low-grade heat source, (4) super-heated in a high-temperature (HT) recuperator to a temperature close to the expander turbine exhaust temperature using this exhaust vapor enthalpy, (5) further super-heated to the turbine inlet temperature (TIT) using a mid-grade heat source, (6) expanded through a turbine expander to the low-side pressure, (7) cooled through the HT recuperator, (8) cooled through the LT recuperator, (9) mostly liquefied and slightly subcooled in a condenser, and (10) the condensed portion is returned to the pump to repeat this cycle.

Claims

1. A Dual-source Organic Rankine Cycle (DORC) for converting thermal power from the combination of a low-grade thermal source and a mid-grade thermal source to electrical power, said method characterized by:

condensing a working fluid from a low-pressure cool vapor at total pressure p₁ to a low-pressure condensed working fluid at temperature T₁ in a condenser, where p₁ is greater than 100 kPa but less than 1 MPa, and where T₁ is greater than 260 K but less than 340 K,

producing pressurized working liquid by pumping said low-pressure condensed working fluid to pressure p₂, where p₂ is greater than 1.3p₁ but less than 5 MPa,

heating and boiling at least a portion of said pressurized condensed working fluid in a boiler using thermal power that originates from said low-grade source to create pressurized vapor at temperature T₅,

using a high-temperature (HT) recuperator to produce preheated vapor at temperature T₆, greater than T₅, utilizing heat from an expander exhaust vapor flow,

using thermal power that originates from said mid-grade source to produce final superheated vapor at temperature T₇, greater than T₆,

expanding said super-heated vapor at temperature T₇ through a turbine to low-pressure hot vapor of temperature T₈ and pressure near p₁ to produce shaft power for subsequent conversion to electrical power,

cooling hot vapor through said HT recuperator to warm vapor at temperature T₉, greater than T₅,

further cooling said warm vapor to at least its condensing temperature and repeating the above cycle.

2. The DORC of 1 further characterized in that the condensed working fluid in said condenser has mean molecular mass between 45 and 90.

3. The DORC of 1 further characterized as utilizing selective membranes and a vacuum pump for separation of non-condensable light gases from a vapor mixture in said condenser.

4. The DORC of 1 further characterized as including means for separating a portion of the heavy hydrocarbons (HHCs) from said working fluid, where HHCs arc defined as having molecular mass greater than 79 and normal boiling point greater than 354 K.

5. The DORC of 1 further characterized in that the condensed working fluid in said condenser has isobutane molar fraction greater than 0.2, benzene molar fraction greater than 0.01, and molar fraction less than 0.05 of other hydrocarbons having more than 5 carbon atoms.

6. The DORC of 1 further characterized as including a low-temperature (LT) recuperator for preheating said pressurized condensed working fluid using heat from the partially pre-cooled low-pressure vapor flow.

7. The DORC of 1 further characterized in that the ratio of the mass of its working fluid at temperature above (T₆+T₇)/2 to its total working fluid mass is less than 0.03.

8. The DORC of 1 further characterized as utilizing a first tank containing gravel and oil for low-grade sensible thermal storage and a second tank containing gravel and a high-boiling liquid for mid-grade sensible thermal storage.

9. The DORC of 1 further characterized in that the low-grade thermal source is selected from the set comprised of solar, geothermal, oceanic, and industrial waste.

10. The DORC of 1 further characterized in that surfaces of said final superheater and turbine which contact said working fluid are coated with a thin layer of material of low catalytic activity.

11. The DORC of 1 further characterized in that the mass fraction of lubricants in the condensed fluid in said boiler is greater than 0.003 but less than 0.03.

12. The DORC of 1 further characterized as utilizing a molten alloy comprised of at least 40% lead (Pb) for transferring heat into said final superheater.

13. The DORC of 1 in which said condenser is further characterized as comprising a plurality of cross-flow finned-tube heat exchangers in parallel.

14. The DORC of 4 in which the HHC separation process is further characterized as including:

draining boiler liquid from the boiler,

flashing low-boiling components from the drained boiler liquid in a flash drum, compressing at least a portion of the flashed low-boiling components,

performing an additional separations process on the bottoms product from the flash drum.

15. The DORC of 6 in which said LT recuperator is further characterized as comprising a series of cross-flow finned-tube heat exchangers in a counter-flow arrangement.

16. The DORC of 7 further characterized in that:

the low-grade thermal source is selected from the set comprised of solar and geothermal,

the mid-grade thermal source is concentrated solar heat,

the condensed working fluid has isobutane molar fraction greater than 0.5,

T₅ is greater than 370 K but less than 440 K,

T₇ is greater than 650 K but less than 820 K,

the critical temperature of the working fluid is greater than T₅ but less than T₆,

the critical pressure of the working fluid is less than twice p₂ but greater than p₂,

the partial pressure of said light gases in said condenser is greater than 0.02p₁ but less than 0.2p₁.

17. The DORC of 8 in which said high-boiling liquid is further characterized as having normal boiling point greater than 660 K, autoignition temperature greater than 660 K, pour point below 320 K, and including a substantial component selected from the set comprised of polyphenyl ethers, polyalphaolefins, polyol esters, silicones, fluorocarbons, polymer esters, and alkylated polynuclear aromatics of normal boiling point greater than 660 K.

18. The DORC of 11 further characterized in that said lubricants are selected from the set comprised of alkylated benzenes and polyalphaolefins.

19. An Organic Rankine Cycle (ORC) for converting thermal power from a mid-grade thermal source to electrical power, said method characterized by:

condensing a working organic fluid from a low-pressure cool vapor to a low-pressure working liquid,

producing pressurized working liquid by pumping the low-pressure working liquid to a higher pressure,

heating and boiling the pressurized working liquid to produce a high-pressure vapor from a boiler,

expanding the vapor through a turbine to low-pressure vapor to produce shaft power for subsequent conversion to electrical power,

cooling the hot vapor to near its condensing temperature,

separating light gases from the cooled vapor mixture using selective membranes and a vacuum pump,

repeating the above cycle,

said ORC further characterized as including means for separation of heavy hydrocarbons from the organic working fluid.