Process and equipment for electricity storage using gerotors

Abstract

This system stores and generates electricity using heat pumps and heat engines that interconvert thermal energy and mechanical energy via gerotor compressors and expanders. The gerotors have advanced features that allow for variable pressure ratios, reduced leakage via improved seals, and longer bearing life from mechanisms that unload the bearings.

Description

ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 1 PROCESS AND EQUIPMENT FOR ELECTRICITY STORAGE USING GEROTORS Inventors: Mark Holtzapple 8601 Rosewood Dr. College Station, TX 77845 Jeff Breedlove P.O. Box 348 Grantham, NH 03753 Daniel Micka 16 Hetzel Rd Lebanon, NH 03766 Elliot Goodman 3 Grant Rd Hanover, NH 03755 Applicant: StarRotor Corporation 8601 Rosewood Dr. College Station, Texas 77845 Attorney: Ryan Loveless Loveless Law Group 4760 Preston Road | No.244-357 Frisco, TX 75034 ryan@lovelesslawgroup.com 9782.292.8303ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 2 PROCESS AND EQUIPMENT FOR ELECTRICITY STORAGE USING GEROTORS TECHNICAL FIELD

[0001] This invention relates to energy storage systems and, more particularly, to process and equipment for electricity storage using gerotors. RELATED APPLICATIONS / PRIORITY

[0002] This application claims priority to United States Provisional Application No. 63 / 582,500 filed on September 13, 2023. United States Provisional Application No.63 / 582,500 is hereby incorporated by reference for all purposes. BACKGROUND

[0003] As intermittent renewable electricity (e.g., wind, solar) becomes a larger portion of the grid, economical and reliable electricity storage assumes greater importance. SUMMARY OF THE DISCLOSURE

[0004] The present disclosure relates to a system that stores and generates electricity using heat pumps and heat engines that interconvert thermal energy and mechanical energy via gerotor compressors and expanders. The gerotors have advanced features that allow for variable pressure ratios, reduced leakage via improved seals, and longer bearing life from mechanisms that unload the bearings.

[0005] Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and / or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] For a more complete understanding of this disclosure and its features, reference is now made to the following description, taken in conjunction with the accompanying drawings and tables, in which:ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 3

[0007] Figure 1A shows a system of heat pumps and heat engines, according to aspects of the disclosure;

[0008] Figure 1B shows a system of heat pumps and heat engines in charge mode, , according to aspects of the disclosure;

[0009] Figure 1C shows a system of heat pumps and heat engines in discharge mode, according to aspects of the disclosure;

[0010] Figure 1D shows a system of heat pumps and heat engines in generate mode, according to aspects of the disclosure;.

[0011] Figure 2 shows a configuration of a gerotor compressor and expander, according to aspects of the disclosure;

[0012] Figure 3 shows the efficiency of a gerotor compressor as a function of power input;

[0013] Figure 4 shows the efficiency of a Carnot engine;

[0014] Figure 5A shows electricity out / electricity in for 95% efficiency;

[0015] Figure 5B shows electricity out / electricity in for 90% efficiency;

[0016] Figure 5C shows electricity out / electricity in for 85% efficiency;

[0017] Figure 6 shows a lined water tank, according to aspects of the disclosure;

[0018] Figure 7 shows a lined water tank buried in the ground, according to aspects of the disclosure;

[0019] Figure 8A and 8B show a lined water tank in (a) heating mode and (b) cooling mode, according to aspects of the disclosure;

[0020] Figure 9 shows charge Option 1, according to aspects of the disclosure;

[0021] Figure 10 shows a TS diagram for Charge Option 1, according to aspects of the disclosure;

[0022] Figure 11 shows a Charge Option 2, according to aspects of the disclosure;

[0023] Figure 12. TS diagram for Charge Option 2, according to aspects of the disclosure;

[0024] Figure 13. Charge Option 3, according to aspects of the disclosure;

[0025] Figure 14. TS diagram for Charge Option 3, according to aspects of the disclosure;

[0026] Figure 15. Charge Option 4, according to aspects of the disclosure;

[0027] Figure 16 shows a TS diagram for Charge Option 4, according to aspects of the disclosure;ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 4

[0028] Figure 17 shows a Discharge Option 1, according to aspects of the disclosure;

[0029] Figure 18 shows a TS diagram for Discharge Option 1, according to aspects of the disclosure;

[0030] Figure 19 shows a Discharge Option 2, according to aspects of the disclosure;

[0031] Figure 20 shows a TS diagram for Discharge Option 2, according to aspects of the disclosure;

[0032] Figure 21 shows a Discharge Option 3, according to aspects of the disclosure;

[0033] Figure 22 shows a TS diagram for Discharge Option 3v.

[0034] Figure 23 shows a Discharge Option 4, according to aspects of the disclosure;

[0035] Figure 24 shows a TS diagram for Discharge Option 4, according to aspects of the disclosure;

[0036] Figure 25 shows a Generate Option 1, according to aspects of the disclosure;

[0037] Figure 26 shows a TS diagram for Generate Option 1, according to aspects of the disclosure;

[0038] Figure 27 shows the dimensions and mass of a gerotor compressor / expander, according to aspects of the disclosure;

[0039] Figure 28A, 28B, and 28C show a gerotor compressor / expander with replaceable plugs, according to aspects of the disclosure;

[0040] Figure 29A, 29B, 29C, and 29D show an actuated segmented plug, according to aspects of the disclosure;

[0041] Figure 30 shows four leakage paths, according to aspects of the disclosure;

[0042] Figure 31A, 31B, and 31C show configurations of abrading, according to aspects of the disclosure;

[0043] Figure 32 shows a rotary compression seal with smooth bore and light sensors, according to aspects of the disclosure;

[0044] Figure 33 shows a rotary compression seal with labyrinth bore and light sensors, according to aspects of the disclosure;

[0045] Figure 34 shows a rotary compression seal with labyrinth bore and light sensors and evacuated chamber, according to aspects of the disclosure;ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 5

[0046] Figure 35 shows a rotary compression seal with labyrinth bore and light sensors and swept chamber, according to aspects of the disclosure;

[0047] Figure 36 shows a rotary compression seal with labyrinth bore and pressure sensors, according to aspects of the disclosure;

[0048] Figure 37 shows a rotary compression seal with labyrinth bore and pressure sensors and evacuated chamber, according to aspects of the disclosure;

[0049] Figure 38 shows a rotary compression seal with labyrinth bore and pressure sensors and swept chamber, according to aspects of the disclosure;

[0050] Figure 39 shows a Perspective view of smooth-bore rotary compression seal with tabs, according to aspects of the disclosure, according to aspects of the disclosure;

[0051] Figure 40 shows a perspective view of smooth-bore rotary compression seal with pins, according to aspects of the disclosure;

[0052] Figure 41 shows a perspective view of smooth-bore rotary compression seal with slots, according to aspects of the disclosure;

[0053] Figure 42 shows a top view of thin-wall rotary compression seal with pins on extensions, according to aspects of the disclosure;

[0054] Figures 43A, 43B, and 43C shows a rotary compression seal with hydraulic shrink ring, according to aspects of the disclosure;

[0055] Figure 44 shows a rack-and-pinion pressure actuator, according to aspects of the disclosure;

[0056] Figure 45 shows a piezoelectric pressure actuator, according to aspects of the disclosure;

[0057] Figure 46 shows a gas pressure actuator, according to aspects of the disclosure;

[0058] Figure 47 shows an oil pressure actuator, according to aspects of the disclosure;

[0059] Figure 48 shows sliding bodies illustrating Archard’s law;

[0060] Figure 49 shows wear rates calculated from interrupted mass measurements;

[0061] Figure 50 shows a conformal seal with and O-ring, according to aspects of the disclosure;

[0062] Figure 51 shows a spring-loaded O-ring;ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 6

[0063] Figure 52 shows a single conformal seal on an inner rotor, according to aspects of the disclosure;

[0064] Figure 53 shows a seal for axial leakage in a circumference configuration and flat face configuration;

[0065] Figures 54A and 54B show a conformal seal made from copper and polymer, according to aspects of the disclosure;

[0066] Figure 55 shows high- and low-pressure zones, according to aspects of the disclosure;

[0067] Figure 56 shows high and low-pressure zones of alternative configuration, according to aspects of the disclosure;

[0068] Figure 57 shows a distribution of high- and low-pressure zonec, according to aspects of the disclosure;

[0069] Figure 58A shows a contact seal with the same shape as the rotor, but slightly smaller;

[0070] Figure 58B shows that the metal support structure is spring loaded so that it applies a force to the sacrificial material and thereby effects a seal;

[0071] Figure 59 shows a double conformal seal on inner rotor, according to aspects of the disclosure;

[0072] Figure 60 shows an alternative embodiment that employs a center hub and spokes to reduce leakage across the faces of the inner rotors, according to aspects of the disclosure;

[0073] Figure 61 shows a finite-element analysis of a lobe that spans the outer rotor, according to aspects of the disclosure;

[0074] Figure 62 shows the specific stiffness (modulus of elasticity divided by density or density squared) of a number of candidate materials;

[0075] Figure 63 shows forces act on rotors from difference between inlet and outlet pressure;

[0076] Figure 64A and 64B shows a net force as a function of angle in unbalanced and balanced configurations;

[0077] Figure 65 shows a coupled rolling bearing and plain journal bearing, according to aspects of the disclosure;ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 7

[0078] Figure 66 shows a cross-section of a shaft rotating in a plain journal bearing, with the pressure profile indicated in the squeezed space;

[0079] Figures 67A through 67D show mechanisms for adjusting the gap in a plain journal bearing;

[0080] Figure 68 shows a single journal bearing supplied with lubricant through a single valve;

[0081] Figure 69 shows multiple journal bearings supplied with lubricant through multiple valves.

[0082] Figure 70 shows variations on the plain journal bearing, according to aspects of the disclosure;;

[0083] Figure 71 shows a hydrostatic oil bearing, according to aspects of the disclosure;;

[0084] Figure 72 shows a hydrostatic oil bearing with oil spray, according to aspects of the disclosure;;

[0085] Figure 73 shows a hydrostatic gas bearing, according to aspects of the disclosure;

[0086] Figure 74 shows a permanent magnet bearing (circumferential), according to aspects of the disclosure;

[0087] Figure 75 shows an electromagnet bearing (circumferential), according to aspects of the disclosure;

[0088] Figure 76 shows laminates for magnetic bearing (circumferential), according to aspects of the disclosure;

[0089] Figure 77 shows a permanent magnetic bearing (axial), according to aspects of the disclosure;

[0090] Figure 78 shows an electromagnetic bearing (axial), according to aspects of the disclosure;

[0091] Figure 7974 shows laminates for magnetic bearing (axial), according to aspects of the disclosure;

[0092] Figure 80 shows a single panel of a heat exchanger, according to aspects of the disclosure;

[0093] Figure 81 shows multiple panels of heat exchangers arranged in parallel inside of a tank, according to aspects of the disclosure;ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 8

[0094] Figure 82 shows a top view of the tank, which includes multiple panels of heat exchangers and baffles that direct the fluid flow over the panels, according to aspects of the disclosure;

[0095] Figure 83 shows an alternate embodiment of the heat exchanger in which the fluid enters a tank to be cooled or heated, and then exits;

[0096] Figure 84 shows a gas liquefaction process, according to aspects of the disclosure;

[0097] Figure 85 shows additional details of a gas liquefaction process, according to aspects of the disclosure;

[0098] Figure 86 shows the vapor pressure of three liquefied gases (nitrogen, oxygen, methane) and liquid air;

[0099] Figure 87 shows the heat capacity of methane and nitrogen; and

[0100] Figure 88 shows additional details of a gas liquefaction process, according to aspects of the disclosure. DETAILED DESCRIPTION

[0101] The FIGURES described below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure invention may be implemented in any type of suitably arranged device or system. Additionally, the drawings are not necessarily drawn to scale.

[0102] As intermittent renewable electricity (e.g., wind, solar) becomes a larger portion of the grid, economical and reliable electricity storage assumes greater importance. Typical methods for storing electricity include the following:

[0103] Pumped hydraulic storage – This method pumps low-elevation water to a high- elevation lake. During the charge cycle, the equipment functions as a motor / pump, and during the discharge cycle it functions as a generator / turbine. These systems have large capacity and good round-trip efficiency of approximately 80%; however, they are limited to hilly geographies. Pumped hydraulic storage comprises about 95% of current energy storage systems.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 9

[0104] Compressed-air energy storage – During the charge cycle, a motor / compressor is used to store compressed air in sealed caverns. During the discharge cycle, the compressed air is combined with fuel, combusted, and expanded in a gas turbine to drive a generator. Alternatively, it is possible that a motor / compressor (charge) can also function as a generator / expander (discharge) and recover energy without the need to combust fuel.

[0105] Batteries – Numerous battery technologies can store electrical energy; however, they often contain toxic materials and have several challenges: low energy densities, low power capacity, high maintenance costs, and short cycle life. Flow batteries have a fixed electrode area that is sized to provide a given amount of power; the electrolyte is stored in large tanks, and increasing the tank volume increases the amount of energy storage. Molten metal batteries employ two molten metals with dissimilar densities and a layer of molten salt between them; they are designed to use inexpensive earth-abundant elements and can cycle repeatedly with little degradation in performance.

[0106] Fuel cells – Water can be electrolyzed to hydrogen and oxygen (charge) and then reacted to form water and electricity (discharge). Unfortunately, the cycle efficiency is low.

[0107] Flywheels, superconductors, and supercapacitors – These technologies have high power densities and are efficient, but energy densities are low. They are best suited for instantaneous power conditioning, but are not practical long-term energy storage.

[0108] Liquid air – During the charge cycle, liquid air is created and stored in an insulated tank. During the discharge cycle, the air is gasified using thermal energy from the surroundings.

[0109] Heat pump storage – Figures 1A to 1D show a schematic of heat pump storage. During the charge cycle (Figure 1B), a heat pump transfers heat from a medium-temperature source (Tm) to a high-temperature “thermal battery” (Th). During the discharge cycle (Figure 1C), a heat engine withdraws thermal energy from the high-temperature “thermal battery” (Th) to produce electricity while rejecting heat to the environment (Tc). If the low-temperature source is waste heat from an industrial process, then Tm> Tc. In this scenario, because of energy input from the waste heat, thermodynamics allows the output of electricity to be greater than the input of electricity. When the high-temperature (Th) “thermal battery” is exhausted, the system can be configured to generate electricity (Figure 1D) by combusting fuel.

[0110] Compared to other options, electricity storage by heat pumps is very attractive:ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 10 ^ When waste heat is available well above ambient temperature, this storage system has the potential to produce more electricity than was invested; thus, the round-trip efficiency can be effectively greater than 100%. ^ When the thermal storage reservoir is exhausted, the system can produce electricity from fuels thus serving as an electricity generator in addition to an electricity storage system. This versatility makes excellent use of capital.

[0111] To realize the full benefits of heat pump storage, the rotating equipment in the heat pumps and heat engines must satisfy the following requirements: ^ Accommodate varying speeds – To match power production to power demand, the rotation rate must vary in response to instantaneous temperatures (Th, Tm, Tc) and grid conditions. ^ Accommodate varying pressure ratio – The rotating equipment must maintain efficiency over a wide range of pressure ratios. ^operating life. ^ Provide dual function – To save capital, the rotating equipment must function both as an expander and compressor. ^ of ^ be

[0112] These requirements can be met with gerotor compressors / expanders (Figure 2), which are very efficient compared to other options (Figure 3). The inventive improvements described herein will increase both efficiency and functionality.

[0113] While select configurations will be described with particular configurations of gerotor compressors / expanders, other configurations may utilize other configurations of gerotor compressors / expanders. Additionally, while heat pump storage will be described with particular configurations, aspects of this disclosure may be utilized with other types of energy storage.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 11 Heat Pump Storage In Sadi Carnot a heat of the steps: 1. 2. 3.4. Adiabatic expansion

[0115] When these four steps are plotted on a temperature-entropy (TS) diagram, a “Carnot box” results.

[0116] The Carnot heat engine is the most efficient heat engine allowed by nature. If there are no irreversibilities (e.g., friction, turbulence, finite temperature differences associated with heat transfer), the efficiency  ^ is determined strictly by the temperature of the heat source (Th) and the temperature of the heat sink (Tc)  ^^W eng^ Th ^Tc(1)Q h T h is not by^engW eng^T ^ h^T c Q eng h T h (2) T T W^^ h^c eng eng Q T h h

[0118] In this simple model, ^eng^accounts for inherent irreversibilities that prevent a real heat engine from achieving the full work output calculated by the Carnot equation. Figure 4 shows the engine efficiency calculated from this simple model assuming waste heat is rejected at Tc= 25°C.

[0119] A Carnot heat pump is the most efficient heat pump allowed by nature. TheATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 12 ^ Q ^ T PF h ^ h W hp hp T h^T m m the nd. ridwhen demand is high. The efficiency of Heat Engine 1 is modeled by Equation 2 and the performance factor of Heat Pump 1 is modeled by Equation 3. The ratio of work output from Heat Engine 1 compared to the work input to Heat Pump 1 is calculated as follows: Th ^ T ^ c eng Q W eng T h T^T ^ h^^ h c W en ^ (4) hp 1 ^T g hp h^T m ^ T ^ T Qh m^ T h hp h

[0121] Figures 5A to 5C show the predictions of Equation 4 under a variety of combinations of temperature and efficiency. In many scenarios where Tm > Tc , more electricity is produced by the heat engine than is consumed by the heat pump; thus, the source of waste heat is able to “amplify” electricity production.

[0122] Figure 6 shows the liquid water storage tank consists of a sloped pit dig in the soil. To reduce the chance of wall collapse, the walls are cut to the angle of repose (or less steep). To prevent water leakage, the walls may be constructed of an impermeable liners consisting of the following potential materials: Material Maximum use Supplier temperature (°C) EPDM90 https: / / therubbercompany.com / rubber-sheeting / epdm-rubber-sheeting / epdm-geomembrane-pond-liner High-density 100 https: / / nilex.com / products / high-temperature-hdpe- polyethylene geomembrane-linersATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 13 https: / / www.geosynthetica.com / high-temperature- geomembrane-patent-gse / https: / / www.agru.at / en / news / article / article / high- temperature-resistant-geomembrane / http: / / www.gseworld.com / Products / Geomembranes / High- Temperature / Silicone 150 https: / / www.rubbercal.com / sheet-rubber / silicone-rubber / PTFE (Teflon) 316 https: / / www.textilescoated.com / high-temperature- geomembrane-liners

[0123] Figure 7 shows that the water-filled tank may be buried in the ground. For each 10 meters of soil above the tank, an additional ~1 atm of pressure can be sustained and thereby maintain the liquid state. To provide insulation, a double liner can be employed with a dry lose material filling between the liners. Examples of potential insulating materials include sand, perlite, vermiculite, porous lava stone, and foamed glass. Potentially, liquid water may be trapped between the liners. Heat from the hot water tank will vaporize this trapped liquid water, and allow it to vent and thus ensure the insulating material is maintained dry and thereby provide good insulating properties.

[0124] Figures 8A and 8B show that the tank is thermally stratified with hotter water (less dense) on top of the cooler water (more dense). During the charge cycle (Figure 8A), cooler water is drawn from the bottom, heat is added, and hotter water is placed in the top. During the discharge cycle (Figure 8B), hotter water is drawn from the top, heat is removed, and cooler water is placed in the bottom. Charge

[0125] Figure 9 shows Charge Option 1. Heat is withdrawn from the ambient environment at cold temperature (Tc) or from waste heat at moderate temperature (Tm). The working fluid (e.g., ammonia, hydrocarbons, refrigerants) vaporizes in the evaporator. The vapors are compressed through a series of compressors, each of which adds superheat to the working fluid. The high- pressure vapors condense in a condenser, which charges the “thermal battery” at high temperature (Th) by heating the water. The condensed working fluid flows through an expander (shown) or aATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 14 throttling valve (not shown). The low-pressure liquid (plus some flashed vapor) returns to the evaporator and thus completes the cycle.

[0126] Figure 10 shows the temperature-entropy TS diagram for Charge Option 1 using ammonia as the working fluid. The shaded area represents the deviation from a Carnot box and is the energy penalty required to compress superheated vapors.

[0127] Figure 11 shows Charge Option 2. Heat is withdrawn from the ambient environment at cold temperature (Tc) or from waste heat at moderate temperature (Tm). The working fluid (e.g., ammonia) vaporizes in the evaporator. The vapors are compressed through a series of compressors. The superheated vapors exiting each compressor pass through a liquid contactor where the superheat is removed by direct contact with evaporating liquid. The high- pressure vapors condense in a condenser, which charges the “thermal battery” at high temperature (Th) by heating the water. The condensed working fluid flows through a series of expanders (shown) or throttling valves (not shown). The liquid that exits each expansion stage contacts the superheated vapors exiting each compressor stage. The low-pressure liquid (plus some flashed vapor) returns to the evaporator and thus completes the cycle.

[0128] Figure 12 shows the temperature-entropy TS diagram for Charge Option 2 using ammonia as the working fluid. The shaded area represents the deviation from a Carnot box and is the energy penalty required to compress superheated vapors in each stage. The shaded area in Option 2 is less than Option 1, so Option 2 is more efficient.

[0129] Figure 13 shows Charge Option 3. Heat is withdrawn from the ambient environment at cold temperature (Tc) or from waste heat at moderate temperature (Tm). The working fluid (e.g., ammonia) vaporizes in the evaporator. The vapors are compressed through a series of compressors. Atomized liquid working fluid from the condenser is sprayed into the compressor inlet as a high-surface area “fog.” During the compression, the liquid evaporates thus preventing the vapors from superheating. Ideally, the vapors exiting each compression stage are saturated. The high-pressure vapors condense in a condenser, which charges the “thermal battery” at high temperature (Th) by heating the water. The condensed working fluid flows through a series of expanders (shown) or throttling valves (not shown). The low-pressure liquid (plus some flashed vapor) returns to the evaporator and thus completes the cycle.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 15

[0130] Figure 14 shows the temperature-entropy TS diagram for Charge Option 3 using ammonia as the working fluid. The cycle is a Carnot box and thus has the potential to approximate the theoretical limits of efficiency.

[0131] Figure 15 shows Charge Option 4. Heat is withdrawn from the ambient environment at cold temperature (Tc) or from waste heat at moderate temperature (Tm). The working fluid (e.g., ammonia) vaporizes in the evaporator. The vapors are compressed through a series of compressors. Atomized liquid working fluid from each expansion stage is sprayed into the compressor inlet as a high-surface area “fog.” During the compression, the liquid evaporates thus preventing the vapors from superheating. Ideally, the vapors exiting each compression stage are saturated. The high-pressure vapors condense in a condenser, which charges the “thermal battery” at high temperature (Th) by heating the water. The condensed working fluid flows through a series of expanders (shown) or throttling valves (not shown). A portion of the liquid from each expansion stage is sprayed into the compressor to maintain nearly saturated conditions. The low- pressure liquid (plus some flashed vapor) returns to the evaporator and thus completes the cycle.

[0132] Figure 16 shows the temperature-entropy TS diagram for Charge Option 4 using ammonia as the working fluid. The cycles are a series of Carnot boxes and thus have the potential to approximate the theoretical limits of efficiency. Discharge

[0133] Figure 17 shows Discharge Option 1. Heat is withdrawn from the “thermal battery” at high temperature (Th) or from waste heat at moderate temperature (Tm). The high-pressure working fluid (e.g., ammonia) vaporizes in the evaporator. The vapors expand through a series of expanders, each of which expels a mixture of saturated liquid and vapor. The low-pressure vapors condense in a condenser, which discharges waste heat into the ambient environment at cold temperature (Tc). Using a liquid pump, the condensed working fluid is pressurized. The high- pressure liquid returns to the evaporator and thus completes the cycle.

[0134] Figure 18 shows the temperature-entropy TS diagram for Discharge Option 1 using ammonia as the working fluid. The shaded area represents the deviation from a Carnot box and is the work that could have been realized if the cycle were Carnot efficient.

[0135] Figure 19 shows Discharge Option 2. Heat is withdrawn from the “thermal battery” at high temperature (Th) or from waste heat at moderate temperature (Tm). The high-pressureATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 16 working fluid (e.g., ammonia) vaporizes in the evaporator. The vapors expand through a series of expanders, each of which expels a mixture of saturated liquid and vapor. The expelled liquid is vaporized by contacting hot fluid from the “thermal battery” at Thor the waste heat source at Tm. The low-pressure vapors condense in a condenser, which discharges waste heat into the ambient environment at cold temperature (Tc). Using a liquid pump, the condensed working fluid is pressurized. The high-pressure liquid returns to the evaporator and thus completes the cycle.

[0136] Figure 20 shows the temperature-entropy TS diagram for Discharge Option 2 using ammonia as the working fluid. The shaded area represents the deviation from a Carnot box and is the work that could have been realized if the cycle were Carnot efficient. Discharge Option 2 is less efficient than Discharge Option 1, but the reheat between expansion stages allows it to produce more power per cycle.

[0137] Figure 21 shows Discharge Option 3. Heat is withdrawn from the “thermal battery” at high temperature (Th) or from waste heat at moderate temperature (Tm). The high-pressure working fluid (e.g., ammonia) vaporizes in the evaporator. The vapors expand through a series of expanders, each of which expels a mixture of saturated liquid and vapor. The low-pressure vapors exiting the final expansion stage partially condense in a condenser, which discharges waste heat into the ambient environment at cold temperature (Tc). Using a liquid pump, the condensed portion of the working fluid is pressurized and flows through a venturi that sucks in vapors that mix with the liquid. The mixture of liquid and vapor is compressed through a series of compressors. The amount of added vapors is specified so the fluid exiting the final compressor is substantially free of vapor. The high-pressure fluid returns to the evaporator and thus completes the cycle.

[0138] Figure 22 shows the temperature-entropy TS diagram for Discharge Option 3 using ammonia as the working fluid. The cycle is a Carnot box and thus has the potential to approximate the theoretical limits of efficiency.

[0139] Figure 23 shows Discharge Option 4. Heat is withdrawn from the “thermal battery” at high temperature (Th) or from waste heat at moderate temperature (Tm). The high-pressure working fluid (e.g., ammonia) vaporizes in the evaporator. The vapors expand through a series of expanders, each of which expels a mixture of saturated liquid and vapor. The vapor and liquid are separated using a knock-out drum or cyclone. Most of the separated vapors flow into the next expansion stage. A small portion of the vapors are sucked into the throat of a venturi and mix withATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 17 liquid fed to a compressor. In each compression stage, the amount of added vapors is specified so the fluid exiting the each compressor is substantially free of vapor. Low-pressure vapors exiting the final expansion stage partially condense in a condenser, which discharges waste heat into the ambient environment at cold temperature (Tc). Using a liquid pump, the condensed portion of the working fluid is pressurized and flows through a venturi that sucks in vapors that mix with the liquid. This mixture of liquid and vapor is compressed in the first-stage compressor. The high- pressure fluid the emerges from the multiple compression stages returns to the evaporator and thus completes the cycle.

[0140] Figure 24 shows the temperature-entropy TS diagram for Discharge Option 4 using ammonia as the working fluid. The cycles are a series of Carnot boxes and thus have the potential to approximate the theoretical limits of efficiency. Generate

[0141] When the “thermal battery” is depleted and can no longer supply heat, the equipment can continue to operate from supplemental heat such as would be realized by burning fuel.

[0142] Figure 25 shows Generate Option 1, which uses a hot gas that serves as a source of sensible heat. The hot gas can be provided from multiple sources, such as burning fuel in a burner or from hot exhaust gas from an engine (e.g., gas turbine, diesel engine). Liquid pressurizes the working fluid (e.g., ammonia), which countercurrently contacts the hot gas and vaporizes. The hot high-pressure vapors flow through a series of expanders. The final low-pressure fluid is completely condensed and then pumped to high pressure, thus completing the cycle.

[0143] Figure 26 shows the temperature-entropy TS diagram for Generate Option 1 using ammonia as the working fluid. The working fluid is superheated and does not enter the two-phase dome. The temperature difference between the hot exhaust gas and the high-pressure working fluid is an irreversibility, and is shown in the shaded area. A heat exchanger with a small approach temperature can minimize the irreversibility and thus has the potential to extract nearly all of the thermal energy available in the hot gas and convert it to work.

[0144] Generate Option 2 combusts fuel in a boiler that produces high-pressure steam. The condensing high-pressure steam can be used as a source of latent heat in any of the discharge options described above.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 18 Rotating Equipment

[0145] As described previously, the rotating equipment must satisfy the following requirements: ^ Accommodate varying speeds ^ Accommodate varying pressure ratio ^ Resist large pressure differences ^ Provide dual function ^ Be reconfigurable ^ Be efficient

[0146] Uniquely, gerotor compressors and expanders can meet these requirements.

[0147] Figure 27 shows the exterior housing of a gerotor compressor / expander coupled to an electric motor / generator. The indicated size can process about 1 m3 / s based on the flow measured at the low-pressure side. The shaft speed is about 1800 rpm (30 Hz).

[0148] Figures 28A and 28B show the interior of the gerotor compressor / expander. The inner rotor has five lobes and the outer rotor has six lobes. The inner and outer rotors rotate about their respective centers, which are offset from each other. During the rotation of the inner and outer rotor, a void opens and then closes causing gas to flow through the tips of the outer rotor. Referring to Figure 28A, when functioning as a compressor, the rotors rotate counterclockwise with the following functions: ^ Intake – 12:00 to 8:00 ^ Compression – 8:00 to 4:00 ^ Exhaust – 4:00 to 2:00 Referring to Figure 28A, when functioning as an expander, the rotors rotate clockwise with the following functions: ^ Intake – 2:00 to 4:00 ^ Expansion – 4:00 to 8:00 ^ Exhaust – 8:00 to 12:00 The gerotor compressor / expander can be improved using the inventive features described below. Variable Pressure Ratio

[0149] Figure 28C shows a plug that is inserted into the housing that determines the pressure ratio. Figure 28A has a plug that seals the tip of the outer rotor from 4:00 to 8:00, andATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 19 gives a larger pressure ratio (4:1). Figure 28B has a plug that seals the tip of the outer rotor from 5:00 to 8:00, and gives a smaller pressure ratio (2:1).

[0150] Figures 29A to 29D show an actuated plug that is divided into moveable segments. Each segment is independently actuated using a mechanism such as a solenoid, hydraulic piston, or screw driven by a servo motor. Figure 29A shows all the segments fully engaged, which gives a larger pressure ratio (e.g., 4:1). Figure 29D shows all the segments are fully retracted, which gives a smaller pressure ratio (e.g., 2:1). Figures 29B and 29C show some segments fully engage and some retracted, which provides intermediate pressure ratios (e.g., 3:1). Increasing the number of segments increases the resolution and allows a more precise pressure ratio to be obtained, thus preventing energy losses from mismatches between the pressure ratio of the gerotor compressor / expander and the pressure ratio of the inlet and outlet pipes. Improved Sealing

[0151] In rotating equipment, it is common to require a fluid seal between a rotating circular surface (e.g., shaft) and a circular stationary surface (e.g., housing). For example, the shaft of a compressor, turbine, pump, or hydraulic motor must penetrate through the housing, but maintain a seal that prevents the fluid from leaking into the environment.

[0152] Common approaches to sealing are described below: 1. Labyrinth seal – A labyrinth seal has numerous grooved circumferential chambers in the region where the shaft and the housing are in close proximity. As fluid flows from one groove to the next, there are significant flow losses, which reduces the leakage rate. Because of potential temperature differences between the shaft and the housing, the dimensions of the labyrinth can change. Should the gap open, leakage increases. These seals reduce leakage between the circular surfaces. 2. Lip seal – A circular elastomer seals between the shaft and housing. In some designs, a spring forces the elastomer to contact the shaft. If surface speeds are high, these seals tend to wear giving them short life. These seals reduce leakage between the circular surfaces. 3. Contact seal – A spring-loaded stationary seal contacts the rotating surface, or a spring- loaded rotating seal contacts the stationary surface. In either case, the contact seal causesATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 20 friction (energy loss) and wear (limited life). These seals reduce leakage between two flat faces and not on the circular surfaces. 4. Lift-off seal – A small flow of gas leaks between the rotating and stationary surfaces. Forces generated in the seal gap cause the spring-loaded component to lift away from the other surface. These seals reduce leakage between two flat faces and not on the circular surfaces. 5. Magnetic seal – Within the housing, the shaft has a set of permanent magnets. Outside the housing, the shaft has another set of permanent magnets. The north and south poles align, thus creating a magnetic coupling between the interior and exterior shafts. A wall separates the interior and exterior permanent magnets, thus providing a hermetic seal. Torque transmission is limited by magnetic strength. High-strength magnets are very costly. The maximum use temperature is limited by the Curie temperature of the magnet.

[0153] Other rotating circular surfaces that benefit from a seal include the outer diameters of the following: ^ centrifugal compressors ^ centrifugal expanders ^ axial compressors ^ axial expanders ^ outer rotor of gerotor compressors ^ outer rotor of gerotor expanders

[0154] In the above applications, the surface speeds are high, so a contact seal is impractical because of high wear and friction. Furthermore, the temperature can be high, which reduces the range of acceptable materials.

[0155] Often, in the above applications, an abradable seal is employed. Should a touching event occur, one of the surfaces abrades away, which theoretically allows for a very small, near- zero gap. In practice, the gap depends upon the speed and temperature history of the machine. In the most extreme operating conditions, the gap can be near-zero; however, in less extreme operating conditions, the gap can open. For example, at high rotation rates, the diameter of the rotating equipment will enlarge from centrifugal forces and carve away some abradable coating. When operated at lower rotation rates, the diameter of the rotating equipment will reduce becauseATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 21 centrifugal forces are lower and the gap will open. In the case of thermal excursions, if the rotating component is hot and the housing is cold, the rotating component will thermally expand and carve away some abradable coating. Later, if the housing temperature increases, then it will expand and open the gap.

[0156] In most cases, the gaps are small measuring only a few thousandths of an inch; however, even with such small gaps, the leakage rate can be significant and adversely affect performance. Ideally, the gaps will be so small they are limited only by the eccentricity of the rotating equipment and bearing precision.

[0157] Figure 30 shows the four leakage mechanisms in a gerotor compressor / expander: ^ Leakage Mechanism A – Port-to-port leakage from the high-pressure port to the low- pressure port. ^ Leakage Mechanism B – Chamber-to-chamber leakage from the high-pressure chamber to the low-pressure chamber. ^ Leakage Mechanism C – Flat-face leakage from high-pressure regions to low-pressure regions. ^ Leakage Mechanism D – Axial leakage from the high-pressure regions of the compressor / expander to low-pressure regions in the housing. Abradable Coating

[0158] A universal sealing approach that addresses all of the above loss mechanisms is to place an abradable coating onto one surface that moves relative to another uncoated surface. The uncoated surface can be grit blasted to provide roughness that helps abrade away the surface layers of the abradable coating; however, this approach is limited because the surface can gall.

[0159] To prevent galling, the abradable surface can be cut away using a knife edge (Figure 31A) typically made from a hard material such as Stellite. The dislodged particles collect in a pocket in front of the blade, which prevents galling. A continuous blade and pocket (Figure 31B) provides a leakage path. To overcome this problem, a discontinuous blade and pocket (Figure 31C) can be employed. Compressed RingsATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 22

[0160] To reduce the gap to near zero, a sensor is required that determines the gap. This information is fed to an actuator that changes the diameter of the non-contact seal embedded in the stationary component, thus allowing the gap to approach zero.

[0161] Examples of sensing techniques that can determine the gap include the following: capacitance, inductance, sound, light, and pressure. In principle, any of these techniques (and others) could be employed to sense the gap dimension; however, the following embodiments will describe only light and pressure.

[0162] The following description describes various embodiments that allow a near-zero gap using a non-contact seal suitable for rotating circular surfaces. The following illustrations will use shaft seals as an example, but it is understood that the same methods can be applied to seal the outer diameters of compressors and expanders, and other rotating equipment.

[0163] Figure 32 shows a rotary compression seal with a smooth bore and light sensors. The compression seal (filled with dots) is located between the parallel faces of the housing. O- rings in the housing ensure there is no leakage across the flat faces of the seal. (In an alternative embodiment, it is understood that the O-rings could be located on the seal rather than the housing.) A hollow chamber between the seal and the housing is filled with a pressurized fluid. As the fluid pressure increases, it compresses the compression seal and closes the gap. An external seal (solid black) prevents dirt and grit from contacting the compression seal (filled with dots). To ensure the stationary compression seal does not touch the rotating shaft, a light emitter is placed on one side of the compression seal and a light detector is placed on the other side. As pressure increases, the gap closes and less light is detected. The pressure is adjusted to minimize the amount of light detected. The detected light should not be zero, which would indicate the seal directly contacts the shaft and thereby prevents it from rotating freely. For this system to work properly, it is important that extraneous light not enter from external sources.

[0164] Figure 33 shows a rotary compression seal with labyrinth bore and light sensors. The function and operation are identical to Figure 32. The only difference is that labyrinths are incorporated into the seal to reduce the leakage rate.

[0165] Figure 34 shows a system identical to Figure 33, except that the void between the compression seal and external seal is evacuated to purge potential harmful fluids that might leak past the compression seal.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 23

[0166] Figure 35 shows a system identical to Figure 34, except that a sweep gas is used to purge potential harmful fluids that might leak past the compression seal.

[0167] Figure 36 shows a system that is identical to Figure 33, except that the gap is sensed by pressure rather than light. The pressure difference across the external seal is measured. If the compression seal is working properly, the leakage will be very small, thus the measured pressure difference will be small as well.

[0168] Figure 37 is identical to Figure 36, except that a vacuum can be applied to a second chamber to remove leaked fluids that are potentially harmful.

[0169] Figure 38 is identical to Figure 37, except that a sweep gas is used to remove potentially harmful fluids.

[0170] To function properly, it is important that the compression seal be concentric with the rotating equipment. To maintain concentricity, Figure 39 shows an embodiment employing tabs machined into the compression seal that ride in radial groves in the housing (not shown). These centering tabs are shown on one surface, but they could also be located on both surfaces.

[0171] Figure 40 is similar to Figure 39, except that pins are used rather than tabs. The pins ride in radial groves in the housing (not shown). The pins are shown on one surface, but they could also be located on both surfaces.

[0172] Figure 41 is similar to Figures 39 and 40, except the grooves are located in the compression seal and the pins or tabs are located in the housing.

[0173] To minimize the magnitude of the pressure required to compress the seal, the radial thickness should be as thin as possible. Figure 42 shows examples of thin-wall compression seals in which the pins are located on extensions. It is understood that the extension may contain tabs (as in Figure 39) or grooves (as in Figure 41).

[0174] Figure 43A shows a rotor that rotates within a stationary housing, a model system that illustrates methods for reducing gas leakage between a rotor and stationary housing. High- pressure gas is fed to the lower side of the rotor. A non-contacting circumferential seal reduces leakage between the rotor and housing. The housing has a hydraulic shrink ring in close proximity to the rotor. Behind the hydraulic shrink ring, the housing has a chamber filled with fluid (e.g., hydraulic oil). When the fluid is pressurized, the hydraulic shrink ring deforms and closes the gap between the housing and rotor (Figure 43B). Figure 43C shows an alternative embodiment inATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 24 which an abradable seal ring is inserted between the hydraulic shrink ring and the rotor. Optionally, the rotor has grooves that serve as labyrinths to reduce leakage, particularly when they cut into the abradable seal ring. Optionally, the abradable seal ring has an attached sensor that measures the gap between the abradable seal ring and the rotor.

[0175] The gap measurement (e.g., light, pressure) is fed to a controller that regulates the pressure actuator that compresses the compression seal. The pressure can be provided by any fluid, such as gas (e.g., process gas) or liquid (e.g., oil).

[0176] Figure 44 shows a pressure actuator consisting of a fluid reservoir (e.g., oil) in sendson the measured gap. Figure 44 illustrates the non-contact circumferential seal using the embodiments described in Figure 32; however, it is understood that the other embodiments described in Figures 33 and 43 could be employed as well.

[0177] Figure 45 shows a pressure actuator consisting of a fluid reservoir (e.g., oil) equipped with a piezoelectric material in which the volume changes depending on the applied voltage. The controller sends a voltage to the piezoelectric material, which either pressurizes or de-pressurizes the fluid, depending on the measured gap.

[0178] Figure 46 shows a pressure actuator consisting of a source of pressured gas (e.g., gas and theother gas gap more gas is added. If the gap needs to be opened, pressurized gas is released.

[0179] Figure 47 shows a pressure actuator consisting of a source of pressured oil in a high-pressure accumulator. The oil is supplied from a low-pressure storage tank; a pump or hydraulic intensifier pressurizes the oil. Two valves are employed. One valve connects the high-seal. If gap more gap pressurized oil is released.

[0180] In all cases, the controller can establish a “lock-down mode.” When the shaft is not a tightATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 25

[0181] For the embodiments described in Figures 32 and 33, materials for the compression seal must be compressed when pressure is applied to the outside surface. Stiff materials (e.g., ceramics) are not desirable whereas as springy materials (e.g., metals, polymers) are suitable. Ideally, the material should be “forgiving” in the case of an accidental touching event. For example, if a soft material (e.g., polymer) were used, during a touching event, the surface that contacts the rotating shaft would abrade away or melt.^^ (5)2 t where ^ = hoop stress (Pa) ^P = pressure difference across cylindrical wall (Pa) D = diameter of pressure vessel (m) in length^ ^ ^ E ^^^(6)L / L where in length (m)length (m)

[0184] The change in length can be calculated by manipulating Equation 6 ^L ^^ L(7)E

[0185] The change in length can be expressed in terms of the pressure difference across the^L ^ ^ (8)E 2 tE

[0186] The original length of the compressive seal is its circumferenceATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 26 L ^ ^ D (9) and the change in length is related to the change in diameter as follows: ^ L ^ ^ ^ D (10)

[0187] The change in gap g is half the change in diameter ^g ^1^D(11)2 which is readily rearranged ^D ^ 2 ^ g (12)

[0188] Substituting Equation 12 into Equation 10 gives ^L ^ ^ ^2 ^ g ^ ^ 2 ^ ^ g (13)

[0189] Substituting Equations 9 and 13 into Equation 8 gives ^^ PD^^ D^22^ ^g ^^ ^ PD2 tE 2 tE (14) ^P ^2tE2 ^^ g^ 4tE^g^ D 2 D 2

[0190] Sample Calculation 1 – The compression seal is made from brass with a diameter of 0.2 m (20 cm) and a thickness of 0.005 m (0.5 cm). The Young’s modulus is 102 GPa. Calculate the pressure required to reduce the gap by 0.0000254 m (0.001 inch) ^P ^4 tE^g ^4^0.005 m^ ^102 ^ 109Pa^ ^0.0000254 m^^ 1, 295,000 PaD2 ^ 2 0.2 m^This pressure difference is 12.8 atm (188 psi), which is readily achieved.

[0191] Sample Calculation 2 – The compression seal is made from PTFE (Teflon) with a diameter of 0.2 m (20 cm) and a thickness of 0.005 m (0.5 cm). The Young’s modulus is 0.4 GPa. Calculate the pressure required to reduce the gap by 0.0000254 m (0.001 inch) 40.005 m9 ^P ^4 tE^g ^^ ^^0.4 ^ 10 Pa^^0.0000254 m^^ 5080 PaD2^0.2 m^2This pressure is 0.05 atm (0.74 psi), which is very small.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 27

[0192] The required pressure for metal (e.g., brass) is significantly different from polymer (e.g., PTFE). Composites of metal and polymer can “tune” the required pressure for a given application. For example, at a specified “transition radius” (TR), the compression seal could be tes by led EK FE ersthat have appeared in the literature.

[0195] Assume the applied pressure P is 10,000 N / m2and the surface speed v is 8 m / s. (Note: the relative speed between the inner to be 8 m / s.)ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 28 Table 1. Unlubricated wear rates and coefficients of friction Wearing surface Counter surface Wear rate, k Coefficient Ref (mm3 / (N ^m) of friction, ^ ^ Mild steel 0.62 [4] Leaded brass 0.24 [4] PTFE 0.18 [4] Stellite 0.60 [4] Ferritic stainl 0.53 [4] Graphite (ZX 0.28 [5] Polyethylene 0.53 [4] Graphite (Gr 0.11 [5] Tungsten car 0.35 [4] Diamond 0.02–0.2 [2] PEEK / PTFE 0.12 [1] Diamond-lik .05–0.07 [3] metalV ^ kWL A ^ ^ kW ^ vt ^ ^ ^k^^W ^^v^kPvt^A^^mm3^ 1–3^ 3 ^^ ^^2.3^10–9^ 0 m ^ ^10,000N ^ ^ m ^  ^ N ^m^ ^^mm^ ^ ^^ ^m 2^^ ^ 8^s^^^1.84^10^ 13m^3600 s^24 h^365 ds h d yr ^5.8^10^ 6myr

[0196] This is an acceptable wear rate. A significantly larger applied pressure could be used and the wear rate is still acceptable.

[0197] The material combinations shown in Table 1 are examples and are not limiting. Table 2 shows the coefficients of friction for other material combinations.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 29 Table 2. Coefficients of friction for various seal face materials

[0198] In Figure 50, the black element is the sacrificial material that wears upon sliding. For example, the black element could be 20:80 PEEK:PTFE. It is sealed by an O-ring (filled with lines), which could be a conventional elastomer O-ring, or a spring-filled O-ring (Figure 51). This sealing system can be deployed to reduce leakage across the flat faces of the inner rotor (Figure 52) and the continuous surfaces (either circumference or flat face) of the outer rotor (Figure 53).

[0199] Both PEEK and PTFE are high-temperature polymers; however, they do not conduct heat very well, so there is potential for over-heating at the contact interface. As shown in Figures 54A and 54B, a way to prevent overheating at the contact interface is to make the PEEK / PTFE layer thin and bond it to a conducting material such as copper (orange). The gaps can be filled with thermally conductive grease (yellow) to help dissipate heat into the bulk material. As shown in Figure 54A, to improve bonding of the PEEK / PTFE to the thermally conductive metal (e.g., copper), the metal interface can be porous sintered material. Surface Finish

[0200] The surface finish of the mating counter surface is an important consideration. Smoother surfaces will result in less wear and less gas leakage. Table 3 describes some surface finishes that can be achieved.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 30 Table 3. Surface roughness SurfaceSurface roughness ( ^m)ReferenceLapped stainless steel 0.161 [1] Electropolish (N1 surface) 0.025 [6, 7] Electroless or electroplated Ni–P 0.002 to 0.004 [8]

[0201] Exceptional smoothness can be obtained using the following steps in sequence: (1) lapping, (2) electropolishing, and (3) plating with Ni-P.

[0202] Plating with Ni-P-PTFE has the advantage that PTFE is also in the mating surface. The literature often describes the fact that the polymer creates a “transfer film” on the mating metal surface, which reduces friction and wear. By placing PTFE in the mating surface, this enhances the transfer film process. Mounting Systems

[0203] To minimize the wear rate, it is important to reduce the force acting on the sealing member. If the pressure difference between the upstream and downstream gas pressures is large, then the force acting on the seal can be very large and will accelerate the wear rate (Figure 55). This problem can be avoided by adding a static seal that can accommodate small movements, such as an O-ring seal (Figure 56).

[0204] If the sliding seal is less than perfect, gas will leak between the seal and the sliding surface. As a result, there will be a pressure profile under the seal. To create a self-balancing seal, the forces acting on the seal must be countered by an appropriate pressure profile above the seal (Figure 57). The sharp edge of the sliding seal (red) contacts the compliant seal (filled with lines) at spacings x and y. If x = y, the net downward pressure would be the arithmetic average of the low and high pressures, and would be the appropriate spacing for a linear pressure profile between the seal and the sliding surface. If x > y, the downward force is increased. If x < y, the downward force is decreased. For a given application, either through calculation or experimentation, the appropriate values of x and y can be determined.

[0205] Figure 58A shows a contact seal with the same shape as the rotor, but slightly smaller. The sacrificial material (black) is secured by a metal support structure with a web that extends toward the center. The web stiffens the metal support structural, which is subjected to centrifugal loads. Figure 58B shows that the metal support structure is spring loaded so that itATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 31 applies a force to the sacrificial material (black), and thereby effects a seal. To ensure that excess pressure is not applied, the metal support structure is pressure balanced. The O-ring separates the high-pressure gas (outer surface) from the low-pressure gas (inner surface), and therefore balances the pressure similar to the approach described in Figure 57.

[0206] Figure 59 shows a double seal. The space between the two seals can be supplied with a pressurized fluid (e.g., water, oil) that flows under the seals so they lift off the sliding surface, which reduces wear and provides cooling. In the case of water, Vesconite is an attractive material option for the seal material.

[0207] Figure 60 shows an alternative embodiment that employs a center hub and spokes to reduce leakage across the faces of the inner rotor. Alternatively (not shown), each spoke could be replaced with a circular ring. Increase stiffness

[0208] Figure 61 shows a finite-element analysis of a lobe that spans the outer rotor. When rotating at high speeds, centrifugal forces cause the lobe to deform to a bow shape. The deformation opens gaps that increase leakage, so stiffer low-density materials will improve performance.

[0209] Figure 62 shows the specific stiffness (modulus of elasticity divided by density or density squared) of a number of candidate materials. Those materials with a higher specific stiffness will deform less under centrifugal loads. In addition to the stiff materials described in Figure 62, ceramic-metal composites (cermets) can be formulated to be stiff.

[0210] In addition to making the lobe from stiff materials, hollowing the lobe reduces deformation. Radial High-Load Bearings

[0211] Figure 63 shows a gerotor compressor that intakes low-pressure gas (left) and discharges high-pressure gas (upper right). In the case of the inner rotor, the average pressure on the right side of the rotor is higher than the left side, thus there is net force acting in the leftward radial direction. Similarly, there are net leftward radial forces acting on the outer rotor. Although Figure 63 illustrates a gerotor compressor, similar net radial forces act on gerotor expanders.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 32

[0212] The radial loads on the rotating rotors must be resisted by bearings. If the pressure difference between the discharge and inlet is large, the radial loads can be substantial. The following is an example: D = inner rotor diameter = 12 inches L = inner rotor length = 1.5 inches Pin = inlet pressure = 100 psig = 115 psia Pout = outlet pressure = 450 psig = 465 psia

[0213] The entire left side of the inner rotor is exposed to the inlet pressure Pin whereas a portion of the right side of the inner rotor is exposed to the outlet pressure Pout. Simplistically, if it is assumed that the entire right side of the inner rotor is exposed to the high-pressure outlet, then the radial load is easily calculated: F^ DL( Pout^ Pin) ^^12 in^ ^1.5 in^(450 psig ^ 100 psig) ^ 6300 lbf

[0214] In actuality, considering the fact that the entire right side of the inner rotor is not exposed to the full outlet pressure, the side load is slightly less. Analysis of the pressure in each lobe indicates that the radial force is about 4000 lbf, or about 2 / 3 of the force calculated in the simple analysis.

[0215] This radial force is about 2 tons, and can be readily handled by a plain journal bearing. However, plain journal bearings have a gap of a few thousands of an inch. (As a rule of thumb, the gap is 0.001 inch per 1.0 inch of shaft diameter.) If plain journal bearings are used to support the rotors, the centers of rotation are not sufficiently precise to maintain small gaps between the inner and outer rotor, and between the outer rotor and the housing. The large gaps would allow for too much gas leakage and thereby reduce the efficiency of the compressor (or expander).

[0216] Rolling bearings (e.g., ball bearings, angular-contact bearings, cylindrical roller bearings, needle bearings, tapered roller bearings, spherical roller bearings) establish very precise centers of rotation, and therefore allow the compressor to operate with small gaps, low gas leakage, and high efficiency. However, rolling bearings are unable to handle large radial loads. To achieve a desired service life, a given rolling bearing operating at a given speed with a given lubricant hasATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 33 a maximum allowable radial force Fmax. In service, if the radial force exceeds Fmax, the bearing life is shortened and therefore requires expensive maintenance to replace the bearings frequently.

[0217] Figure 64A shows an example of the radial loads acting on the bearing. The loads are cyclic and vary with the rotation angle of the inner and outer rotors. In many cases, the cyclic loads exceed Fmax and lead to a shortened service life.

[0218] The best features of the journal bearing (high load) and the rolling bearing (high precision) can be achieved by employing both bearings simultaneously as a hybrid (Figure 65). If the journal bearing is designed properly, it will counter the majority of the radial load and allow the rolling bearing to operate below Fmax (Figure 64B).

[0219] Figure 66 shows the cross section of a conventional plain journal bearing. The annular space between the bearing and the shaft is filled with lubricating fluid. As the load is applied to the shaft, the rotating shaft pumps lubricating fluid into the squeezed space, which causes the pressure to increase and push back on the shaft. If properly designed, the shaft never touches the bearing, allowing for very long operating life.

[0220] In a plain journal bearing, the system self regulates. As the squeezed space gets smaller, the pressure increases and therefore pushes the rotating shaft towards the center. When a plain journal bearing is coupled to a rolling bearing, the shaft does not have the ability to move within the plain journal bearing, so the self-regulating function is lost. To ensure that the appropriate amount of counterbalancing force is applied to the rotating shaft, it is desirable to have a feedback system. As shown in Figure 65, a strain gauge can be located near the rolling bearing to measure the applied radial load. Appropriate changes are made in the plain journal bearing to provide the required force that unloads the rolling bearing. The following are some possible methods for altering the unloading force using the plain journal bearing:

[0221] Option 1 – With a constant offset, alter the viscosity of the lubricating fluid by altering its temperature or composition.

[0222] Option 2 – Adjust the gap between the shaft and the plain journal bearing. Figures 67A through 67d shows some alternative methods for implementing this option. Figure 67A shows a screw that directly sets the position of the bearing. Figure 67B shows a screw-actuated incline that sets the position of the bearing. (Note: A shallow slope allows for very accurate positioning.) Figures 67C and 67D show a positioning system that employs two rotatable rings. The OD of theATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 34 outer ring (grey) has the same centerline as the shaft. The outer ring has an offset hole that contains the plain journal bearing (black), which also has an offset hole. The relative rotation of the outer ring with respect to the plain journal bearing set the gap. The relative rotation of the outer ring with respect to the housing locates the angular position of the gap. The angular position of the outer ring and plain journal bearing can be set by a worm gear, one of which is shown.

[0223] Option 3 – With a constant offset, adjust the flowrate of lubricating fluid into the plain journal bearing (Figure 68).

[0224] Option 4 – With a constant offset, design the plain journal bearing so that it is segmented into various sections along the axial length (Figure 69). Each section is supplied with its own lubrication ports. By flowing oil to fewer or more of the lubrication ports, the number of sections that are engaged can be varied. The design of each journal bearing can be different so that some add coarse adjustment and others add fine adjustment.

[0225] Figure 70 shows variations on the plain journal bearing including lemon bore, pressure dam, and tilting pad designs

[0010] . Pressure dams have a high load capacity and have reduced whirl.

[0226] The mean pressure generated by the oil film squeezed between the rotating shaft and the journal is typically 100 to 300 psi. It can be as high as 3000 to 5000 psi in automotive and other severely loaded applications. The maximum pressure is typically about twice the mean pressure

[0011] .

[0227] In the case study, the radial load is about 4000 lbf. The plain journal bearing needs an area of only about 1 to 2 in2if it is designed as a severely loaded bearing and about 10 to 40 in2if lightly loaded. The area is determined as the shaft diameter times the bearing length.

[0228] The plain journal bearings discussed thus far are examples of hydrodynamic bearings in which large radial forces are generated by the bearing itself. In essence, the hydrodynamic bearing is a pump that forces lubricant into the tight gap. Another approach is a hydrostatic bearing (Figure 71). In this case, an external high-pressure pump forces lubricant into a chamber that directly contacts the shaft and exerts a radial load. Figure 72 shows a variant of the hydrostatic bearing in which a small hole is placed in the wall that allows a spray of oil to lubricate the adjacent rolling bearing. Figure 73 shows another variation that employs high-ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 35 pressure gas or vapor in the hydrostatic bearing. Leakage can be reduced by placing grooves along the edge of the chamber, which act as labyrinthian seals.

[0229] Magnetic bearings can be employed to apply a radial load through the force of attraction between the shaft and the magnet. Figure 74 shows an example of a permanent magnet bearing in which the force of attraction is varied by adjusting the gap between the magnet and the shaft. Figure 75 shows an example of an electromagnet in which the force of attraction is varied by adjusting the current that flows through the coil. In both Figures 74 and 75, the magnet bridges the circumference of the shaft.

[0230] Figure 764 shows laminates that can be used with the circumferential magnets to reduce eddy currents, and hence increase efficiency. While an example configuration of laminates have been shown, others may also be utilized.

[0231] Figures 77 and 78 show permanent magnet and electromagnet bearings, respectively, that span the axis.

[0232] Figure 79 shows laminates that can be used with the axial magnets to reduce eddy currents, and hence increase efficiency. Again, while example laminates are shown, others may be utilized.

[0233] Figure 80 shows a single panel of a heat exchanger. The heat exchanger is constructed from pipes, although tubing could also be used. The top and bottom headers are constructed from pipes with a larger diameter, whereas the vertical pipes are a smaller diameter. Holes are drilled in the headers that allow the vertical pipes to be welded in place, which provides both structural support and sealing.

[0234] Figure 81 shows multiple panels of heat exchangers arranged in parallel inside of a tank. The tank is filled with fluid, typically water. In other configurations, the tank may be filled with other fluids.

[0235] Figure 82 shows a top view of the tank, which includes multiple panels of heat exchangers (black), as described previously, but also baffles (filled with dots) that direct the fluid flow over the panels.

[0236] The interior of the pipes contains the heat transfer fluid, which can transfer either latent (phase change) or sensible (no phase change) heat.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 36

[0237] Example 1 – If the fluid entering the tank is to be cooled using sensible heat, the heat transfer fluid would be colder than the fluid in the tank, and it would not undergo a phase change.

[0238] Example 2 – If the fluid entering the tank is to be heated using sensible heat, the heat transfer fluid would be warmer than the fluid in the tank, and it would not undergo a phase change.

[0239] Example 3 – If the fluid entering the tank is to be cooled using latent heat, the heat transfer fluid would evaporate. In this case, the vertical pipes would be nearly filled with liquid heat transfer fluid, which is boiling. Because the liquid heat transfer fluid can be easily entrained with the vapors, a separation device (not shown) can be employed to separate entrained liquid from the high-velocity vapors. Examples of separation devices include knock-out drums, cyclones, and demisters. Once the liquid is separated, it is returned to the heat exchanger.

[0240] Example 4 – If the fluid entering the tank is to be heated using latent heat, the heat transfer fluid would condense. In this case, the vertical pipes would be nearly empty of liquid heat transfer fluid and would be nearly filled with vapor.

[0241] Figure 83 shows an alternate embodiment of the heat exchanger in which the fluid (typically water) enters a tank to be cooled or heated, and then exits. Ideally, the fluid level in the tank is unchanged from the fluid entering and exiting the tank.

[0242] The heat exchanger is constructed from pipes, although tubing could be used as well. The top and bottom headers are constructed from pipes with a larger diameter, whereas the vertical pipes are a smaller diameter. Holes are drilled in the headers that allow the vertical pipes to be welded in place, which provides both structural support and sealing. The headers form a closed loop that is circular, or nearly circular. For example, a nearly circular header could be constructed from straight pipe connected by elbows of 90°, 45°, 30°, or 15°. The elbows can be welded in place, or the large-diameter pipe can be bent to form a circular or nearly circular shape.

[0243] As shown in Figure 83, the heat exchanger can consist of a single circle of vertical pipes; however, the heat exchanger can be constructed from nested circles of increasing diameter. Nesting the heat exchangers creates multiple rows of vertical pipes along the radius.

[0244] An agitator is located at the center or near center of the circular header, which increases the fluid velocity at the exterior surface of the pipes, and thereby enhances heat transfer.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 37 Figure 83 shows a single agitator on the motorized shaft; however, multiple agitators can be used as well. A standard Rushton impeller can be used as the agitator; however, other impellor designs (e.g., marine impellers) can be used as well, depending on upon the desired circulation pattern.

[0245] The interior of the pipes contains the heat transfer fluid, which can transfer either latent (phase change) or sensible (no phase change) heat.

[0246] Example 1 – If the fluid entering the tank is to be cooled using sensible heat, the heat transfer fluid would be colder than the fluid in the tank, and it would not undergo a phase change.

[0247] Example 2 – If the fluid entering the tank is to be heated using sensible heat, the heat transfer fluid would be warmer than the fluid in the tank, and it would not undergo a phase change.

[0248] Example 3 – If the fluid entering the tank is to be cooled using latent heat, the heat transfer fluid would evaporate. In this case, the vertical pipes would be nearly filled with liquid heat transfer fluid, which is boiling. Because the liquid heat transfer fluid can be easily entrained with the vapors, a separation device (note shown) can be employed to separate entrained liquid from the high-velocity vapors. Examples of separation devices include knock-out drums, cyclones, and demisters. Once the liquid is separated, it is returned to the heat exchanger.

[0249] Example 4 – If the fluid entering the tank is to be heated using latent heat, the heat transfer fluid would condense. In this case, the vertical pipes would be nearly empty of liquid heat transfer fluid and would be l fill d ith

[0250] In some case production. As a liquid, oil can be conveniently bro d networks. In contrast, natural gas requires pipelin ral gas pipelines are not available, particularly in remq y, g .

[0251] By liquefying the remote natural gas, it can be trucked to market. Normally, the amount of gas flared at a particular site is relatively small, so it is difficult to install a cost-effective liquid natural gas (LNG) plant.

[0252] This challenge can be overcome by installing a centralized air liquefaction plant that is large enough to achieve economies of scale and cost-effective operation. U.S. Patent Publication 2015 / 0211788 A1, which is hereby incorporated by reference, describes a gasATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 38 liquefaction process that is efficient, even at moderate scale (Figure 84). The liquid air is transported to the remote sites using specialized trucks equipped with pressurized cryogenic tanks (Figure 85).

[0253] Once the truck arrives at the oil well site, it unloads the liquid air into a pressurized (~10 atm) cryogenic tank located at the well site. The liquid air surrounds a tank of 1-atm liquid natural gas (LNG); thus, any heat losses through insulation vaporize air rather than LNG. Figure 85 shows the liquid air is pumped to the jacket of the LNG tank; however, it could be fed by gravity if the liquid air tank were elevated with respect to the LNG tank.

[0254] A pump circulates liquid air through a latent heat exchanger where a portion evaporates. When the circulating fluid is returned to the liquid air tank, the vapor disentrains. The natural gas that enters the latent heat exchanger condenses and enters the LNG tank.

[0255] Because liquid air is a mixture of gases—primarily nitrogen and oxygen—it does not have a unique boiling point. The normal boiling points of nitrogen, oxygen, methane, and carbon dioxide are shown in Table 4. Of these gases, nitrogen is the most volatile; as the liquid air boils off, nitrogen will boil off preferentially compared to oxygen. Methane and carbon dioxide are the least volatile gases. If carbon dioxide is present in the natural gas, it will condense with the methane. Table 4. Normal boiling points Gas Normal boiling point* (K) Nitrogen 77.35 Oxygen 90.15 Methane 111.55 Carbon dioxide 194.69 * Pressure = 1 atm

[0256] As a function of temperature, Figure 86 shows the vapor pressure of three liquefied gases (nitrogen, oxygen, methane) and liquid air. Because it is composed primarily of nitrogen, the vapor pressure of liquid air is similar to that of nitrogen. If the natural gas is composed of 100% methane and the pressure of the LNG tank is 1 bar, then the temperature on the LNG tank is 111.51 K. Allowing for a 5 K approach temperature in the latent heat exchanger, the pressure of liquid air is about 10 bar. As the nitrogen preferentially boils off, to maintain the set-point temperature, the tank pressure must be reduced. Figure 85 shows a control loop that regulates theATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 39 set-point temperature of the liquid air tank to achieve the desired condensation rate of natural gas. A lower temperature increases the rate that natural gas liquefies.

[0257] Compared to liquid air, methane has a higher latent heat of vaporization; consequently, the mass of liquid air evaporated is about 3.45 times greater than the mass of natural gas condensed.

[0258] The vaporized air exiting the liquid air tank is very cold. It flows countercurrently through the sensible heat exchanger, which pre-cools the natural gas in preparation for The heat of methane is about 2 times that of (Figure 87). Becausethere is excess thermal capacity in the vented gases. Consequently, the sensible heat exchanger can operate with a large approach temperature, which reduces the size of the equipment. The vented air will be cold and could be used productively to cool equipment or buildings located at the well site.

[0259] Because of the cryogenic temperatures, it is necessary for the natural gas to be dry prior to entering the sensible heat exchanger; otherwise, ice will form and reduce heat transfer. The can conventional such as solid (e.g., zeolite, silica gel) or liquid well site or remotely. be removed from the raw gas. Numeroustechnologies exist for removing these gases, such as the following: ^ Amine scrubbing (CO2, H2S) ^ Iron or (H2S)^ Porous absorbents (H2S)

[0261] The above list is meant to be exemplary and not limiting. The appropriate technology for removing the acid gases depends on the initial concentration, the volumetric flowrate, and the end use of the LNG.

[0262] While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or

Claims

ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 40 constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure. References [1] David L. Burris, W. Gregory Sawyer, A low friction and ultra low wear rate PEEK / PTFE composite, Wear, 410–418 (2006) [2] https: / / ocw.mit.edu / courses / mechanical-engineering / 2-800-tribology-fall- 2004 / readings / ultra_low_fricti.pdf [3] Y. Liu, A. Erdemir, E.I. Meletis, A study of the wear mechanism of diamond-like carbon films, Surface and Coatings Technology, 82, 48–56 (1996). [4] M.B. Peterson, W.O. Winer, Wear Control Handbook, The Research Committee on Lubrication, American Society of Mechanical Engineers, page 38. [5] Peter J. Blau, Rebecca L. Martin, Friction and wear of carbon-graphite materials against metal and ceramic counterfaces, Tribology International, 27(6), pp.413–422 (1994). [6] http: / / www.harrisonep.com / electropolishing-ra.html [7] http: / / www.worldstainless.org / Files / issf / non-image- files / PDF / Euro_Inox / Electropolishing_EN.pdf [8] P. Peeters, G.v.d. Hoorn, T. Daenen, A. Kurowski, G. Staikov, Properties of electroless and electroplated Ni–P and its application in microgalvanics, Electrochimica Acta, 47, 161–169 (2001). [9] http: / / www.bearingsindustry.com / aboutbearing / jb.htm [10] http: / / www.reliabilitydirect.com / appnotes / jb.html [11] http: / / www.machinerylubrication.com / Read / 779 / journal-bearing-lubricationATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 42 4. A thermal battery charging system comprising: an evaporator for receiving a working fluid and vaporizing the working fluid by withdrawing heat from an ambient environment at a cold temperature or from waste heat at a moderate temperature; a plurality of compressors configured to sequentially compress the vaporized working fluid, each compressor adding superheat to the working fluid; a condenser configured to receive the compressed, superheated working fluid and condense the working fluid to charge a thermal battery at a high temperature by heating water within the thermal battery; an expander or a throttling valve configured to receive the condensed working fluid and reduce the pressure of the condensed working fluid; and a return path for returning the low-pressure liquid working fluid, and any flashed vapor, to the evaporator to complete a cycle.

5. The thermal battery charging system of Claim 1, wherein the working fluid is ammonia.

6. A thermal battery charging system comprising: an evaporator for receiving a working fluid and vaporizing the working fluid by withdrawing heat from an ambient environment at a cold temperature or from waste heat at a moderate temperature; a plurality of compressors configured to sequentially compress the vaporized working fluid; a plurality of liquid contactors, each liquid contactor configured to receive superheated vapors exiting a corresponding one of the plurality of compressors and to remove superheat from the superheated vapors by direct contact with evaporating liquid; a condenser configured to receive the compressed working fluid and condense the working fluid to charge a thermal battery at a high temperature by heating water within the thermal battery;ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 43 a series of expanders or throttling valves configured to receive the condensed working fluid and reduce the pressure of the condensed working fluid in stages; wherein liquid exiting each expansion stage contacts the superheated vapors exiting a corresponding compressor stage; and a return path for returning the low-pressure liquid working fluid, and any flashed vapor, to the evaporator to complete a cycle.

7. The thermal battery charging system of Claim 3, wherein the working fluid is ammonia.

8. A thermal battery charging system comprising: an evaporator for receiving a working fluid and vaporizing the working fluid by withdrawing heat from an ambient environment at a cold temperature or from waste heat at a moderate temperature; a plurality of compressors configured to sequentially compress the vaporized working fluid; a condenser configured to receive the compressed working fluid and condense the working fluid to charge a thermal battery at a high temperature by heating water within the thermal battery; a liquid atomizer configured to atomize condensed liquid working fluid from the condenser and spray the atomized liquid working fluid into an inlet of at least one of the plurality of compressors as a high-surface area fog to prevent superheating of the vapors during compression; a series of expanders or throttling valves configured to receive the condensed working fluid and reduce the pressure of the condensed working fluid in stages; and a return path for returning the low-pressure liquid working fluid, and any flashed vapor, to the evaporator to complete a cycle.ATTORNEY DOCKET NO. PCT PATENT STAR07-00033WO APPLICATION 44 9. The thermal battery charging system of Claim 5, wherein the working fluid is ammonia.

Images