Abstract:
An improved heat engine that includes an organic refrigerant exhibiting a boiling point below −35° C.; a heat source having a temperature of less than 82° C.; a heat sink; a sealed, closed-loop path for the organic refrigerant, the sealed, closed-loop path having both a high-pressure zone that absorbs heat from the heat source, and a low-pressure zone that transfers heat to the heat sink; a positive-displacement decompressor providing a pressure gradient through which the organic refrigerant in the gaseous phase flows continuously from the high-pressure zone to the low-pressure zone, the positive-displacement decompressor extracting mechanical energy due to the pressure gradient; and a positive-displacement hydraulic pump, which provides continuous flow of the organic refrigerant in the liquid phase from the low-pressure zone to the high-pressure zone, the hydraulic pump and the positive-displacement decompressor maintaining a pressure differential between the two zones of between about 20 to 42 bar.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry under 35 U.S.C. §371 of International Patent Application PCT/US2014/014965, filed Feb. 5, 2014, designating the United States of America and published in English as International Patent Publication WO 2014/124061 A1 on Aug. 14, 2014, which claims the benefit under Article 8 of the Patent Cooperation Treaty and under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. Nos. 61/841,610, filed Jul. 1, 2013, 61/817,862, filed Apr. 30, 2013, and 61/761,115, filed Feb. 5, 2013. The disclosures of each of these applications are hereby incorporated herein in their entireties by this reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to organic Rankine cycle systems and, more particularly, to an improved heat engine that includes an organic refrigerant exhibiting a boiling point below −35° C. 
     BACKGROUND 
     The Rankine cycle is a thermodynamic cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid. This cycle generates about 80% of all electric power used throughout the world, and is used by virtually all solar, thermal, biomass, coal and nuclear power plants. It is named after William John Macquorn Rankine, a Scottish engineer and physicist (Jul. 5, 1820-Dec. 24, 1872). William Thomson (Lord Kelvin) and Rudolf Clausius were the founding contributors to the science of thermodynamics. Rankine developed a complete theory of the steam engine and, indeed, of all heat engines. His manuals of engineering science and practice were used for many decades after their publication in the 1850s and 1860s. He published several hundred papers and notes on science and engineering topics, from 1840 onward, and his interests were extremely varied, including, in his youth, botany, music theory and number theory, and, in his mature years, most major branches of science, mathematics and engineering. A Rankine cycle describes a model of a steam-operated forward heat engine most commonly found in power generation plants. The combustion of coal, natural gas and oil, as well as nuclear fission, commonly provides the heat for power plants employing the Rankine cycle. Rankine cycle power systems typically transform thermal energy into electrical energy. A conventional Rankine cycle power system employs the following four basic steps: (1) thermal energy is used, in a boiler, to turn water into steam; (2) the steam is sent through a turbine, which, in turn, drives an electric generator; (3) the steam is condensed back into water by discharging the remaining thermal energy in the steam to the environment; and (4) the condensate is pumped back to the boiler. In the ideal Rankine cycle, the expansion is isentropic and the evaporation and condensation processes are isobaric. However, the presence of irreversibilities in the real world lowers cycle efficiency. Those irreversibilities are primarily attributable to two factors. 
     The first is that during expansion of the gas, only a part of the energy recoverable from the pressure difference is transformed into useful work. The other part is converted into heat and is lost. The efficiency of the expander is stated as a percentage of work that would be performed by a theoretical isentropic expansion, in which entropy remains constant. The second cause is heat exchanger inefficiency caused by pressure drops associated with the long and sinuous paths that ensure good heat exchange, but lower the power recoverable from the cycle. 
     The efficiency of a Rankine cycle is a function of the physical properties of the working fluid. Without the pressure reaching super critical levels for the working fluid, the temperature range the cycle can operate over is quite small: turbine entry temperatures are typically 565° C. (the creep limit of stainless steel) and condenser temperatures are around 30° C. This gives a theoretical Carnot efficiency of about 63% compared with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry temperature (compared with an internal-combustion gas turbine) is why the Rankine cycle is often used as a bottoming cycle in combined cycle gas turbine power stations. The working fluid in a Rankine cycle follows a closed loop and is re-used continually. While many working fluids can and have been used in the Rankine cycle, water is usually the fluid of choice because it is abundant, inexpensive, nontoxic, generally non-reactive, and possesses favorable thermodynamic properties. Organic Rankine cycles have been developed to enable recovery of energy from lower temperature sources, such as industrial waste heat, geothermal heat, solar ponds, and so forth. The Organic Rankine cycle (ORC) is named for its use of an organic, high molecular mass fluid having a liquid-vapor phase change, or boiling point that occurs at a lower temperature than the water-steam phase change. Using the ORC, low-temperature heat can be converted to useful work, which, for example, can be harnessed to generate electricity. A prototype ORC power system was first developed and exhibited in 1961 by Israeli solar engineers Harry Zvi Tabor and Lucien Bronicki. 
     The organic Rankine cycle technology has many possible applications. Among them, the most widespread and promising fields are the following: waste heat recovery is the most important development field for the ORC. It can be applied to heat and power plants, or to industrial and farming processes such as organic products fermentation, hot exhausts from ovens or furnaces, flue gas condensation, exhaust gases from vehicles, intercooling of a compressor, and the condenser of a power cycle. 
     Biomass is available all over the world and can be used for the production of electricity on small to medium size scaled power plants. The problem of high specific investment costs for machinery such as steam boilers are overcome due to the low working pressures in ORC power plants. The ORC process also helps to overcome the relatively small amount of input fuel available in many regions because an efficient ORC power plant is possible for smaller sized plants. 
     Geothermic heat sources vary in temperature from 50° C. to 350° C. The ORC is, therefore, uniquely suited for this kind of application. However, it is important to keep in mind that for low-temperature geothermal sources (typically less than 100° C.), the efficiency is very low and depends strongly on heat sink temperature, which is typically the ambient temperature. 
     The ORC can also be used in the solar parabolic trough technology in place of the usual steam Rankine cycle. The ORC allows a lower collector temperature, a better collecting efficiency (reduced ambient losses) and, hence, the possibility of reducing the size of the solar field. 
     The selection of an appropriate working fluid is of key importance in low-temperature Rankine Cycles. Because of the low temperature, heat transfer inefficiencies are highly prejudicial. These inefficiencies depend very strongly on the thermodynamic characteristics of the fluid and on the operating conditions. In order to recover energy from low-grade heat sources, the working fluid must have a lower boiling temperature than water. Refrigerants and hydrocarbons are the two commonly used components. Unlike water, organic fluids usually suffer chemical deterioration and decomposition at high temperatures. The maximum hot source temperature is thus limited by the chemical stability of the working fluid. In addition, the freezing point should be lower than the lowest temperature in the cycle. A fluid with a high latent heat and density will absorb more energy from the source in the evaporator and thus reduce the required flow rate, the size of the facility, and energy consumption of the pump. Other important characteristics for an organic working fluid are that it has low ozone depletion and low global warming potential, that it be non-corrosive, non-flammable, non-toxic, in addition to being readily available at a reasonable cost. 
     On May 29, 2008, ElectraTherm, Inc. of Carson City, Nev. announced the successful installation of its first commercial waste heat generator at Southern Methodist University in Dallas, Tex. The generator, dubbed the “Green Machine,” makes electricity from residual industrial heat that has, heretofore, gone to waste. The U.S. Department of Energy reports that the available seven quadrillion Btu of waste heat sources exceeds the current production of all other U.S. renewable power sources combined. This includes hydroelectric, wood, biofuels, geothermal, wind, and solar photovoltaic. With a scalable output of 50 kW-500 kW and a subsidy-free payback period of less than three years, ElectraTherm&#39;s creation has the potential to significantly expand the production of electricity at very low cost at every fossil fuel burning power plant without burning additional oil, gas or coal, and without further pollution or damage to the environment. From liquids having temperatures as low as 93 degrees C., the process extracts heat to run a twin-screw expander, which is coupled to a generator. The company&#39;s twin-screw expander, which costs about one-tenth the price of a turbine, operates free of expensive gear boxes and electronics, runs at one-tenth the speed of turbines, operates with far less friction than does a turbine, and utilizes process lubrication without the need for a traditional oil pump, oil tank, oil lines and oil filter, enables the Green Machine to produce electricity at a cost of $0.03 to $0.04 per kW/hr during the payback period and for less than $0.01 per kW/hr thereafter. Although U.S. patent application Ser. No. 11/407,555, titled Waste Heat Recovery Generator, was filed by inventor Richard K. Langson on Apr. 19, 2006, covering the generator process and apparatus, with a priority date based on the filing of Provisional Patent Application No. 60/673,543, the application was finally rejected for obviousness in December of 2007. Langson also subsequently filed a related application titled Power Compounder, which covers certain aspects of the invention, and which issued as U.S. Pat. No. 7,637,108. 
     BRIEF SUMMARY 
     A heat engine employing an organic Rankine cycle includes: an organic refrigerant having a boiling point below −35 degrees Celsius; a hot water heat source having a temperature of less than 82 degrees Celsius; a heat sink; a sealed, closed-loop path for the organic refrigerant, the path having both a high-pressure zone that absorbs heat from the heat source, and that contains a first portion of the organic refrigerant in at least a gaseous phase, and a low-pressure zone that transfers heat to the heat sink, and that contains a second portion of the organic refrigerant in at least a liquid phase; a positive-displacement decompressor that provides a pressure gradient through which the organic refrigerant in its gaseous phase flows continuously from the high-pressure zone to the low-pressure zone, the decompressor maintaining a pressure differential between those zones of between about 20 bar and about 42 bar, the decompressor extracting mechanical energy from the pressure gradient; an electrical generator coupled to the decompressor that converts extracted mechanical energy to electrical energy; and a positive-displacement hydraulic pump for providing continuous flow of the organic refrigerant in its liquid phase from the low-pressure zone to the high-pressure zone. 
     The improved decompression heat engine utilizes a Rankine cycle having two multiphase differential pressure zones separated by both a positive-displacement decompressor and a positive-displacement hydraulic pump. The positive-displacement decompressor decompresses a heated organic refrigerant from a high-pressure vapor state to a lower pressure vapor state, thereby creating mechanical work. The positive-displacement decompressor reaches its maximum power potential when pressure is released by continuous flow without pistons or valves interrupting the flow. 
     While related to a conventional Organic Rankine Cycle (ORC), the improved organic Rankine cycle decompression heat engine differs because it focuses primarily on energy derived from differential pressure (Delta P) energy rather than the conventional ORC focus on high-velocity mass flow rate through an expander with a high Delta T. 
     The improved heat engine is used primarily to generate electricity from a heat source having a temperature less than 82 degrees Celsius. Because energy could heretofore not be economically extracted from such heat sources, they were largely ignored. The heat source can range from low-temperature natural geothermal heat like hot springs, waste heat from methane generators, manufacturing or any heat source or waste heat source available. 
     The improved heat engine has the ability to capture very low heat energy more abundantly available (below 82 degrees Celsius) and transfer that energy into electricity more efficiently than currently available technology. Such energy is extracted by using a very low boiling point refrigerant (such as R410a, which boils at approximately −51 degrees C.) and transforming high differential pressure of from about 20 to 42 bar into electricity generation through a positive-displacement decompressor. 
     Cooling sources provide a low-pressure zone in the improved heat engine by sinking heat to abundant cold streams and waterways, or even to the ambient air. Abundant lower heat and cooling sources will be utilized by the heat engine like never before, allowing more clean renewable energy to be available to the world. 
     A brief comparison of a conventional organic Rankine cycle (ORC) to the improved decompression heat engine is in order. The conventional ORC is a cycle that utilizes a heat source and a cooling source to operate a type of heat engine to produce mechanical work at a given Delta T. Because of the high mass flow requirements of an ORC, it is limited in the use of working fluids/refrigerants. A conventional ORC utilizes a high-velocity vapor phase change in the working fluid at a relatively low pressure to produce mechanical work. At a typical ORC low-heat temperature (about 93° C. to about 149° C.), R245a will flash or go through a vapor phase change and return back to a liquid phase at close to ambient temperatures (approximately 21° C.). During this phase change, the pressure differential ranges from approximately 0.69 bar to 1.38 bar at about 12.8° C. to 21° C. on the cool side and approximately 10.9 bar to 13.8 bar at about 93° C. to 149° C. on the hot side. The force to achieve mechanical work is a high-velocity/CFM vapor mass flow rate before the expander/driver at approximately 6.9 bar to 13.8 bar. Thus, relatively low pressure at a high CFM achieve the mechanical work from an ORC heat engine. The working fluid in an ORC must flow at a high rate through the heat exchange process to transfer heat to and from a high flowing refrigerant/working fluid, thus requiring excessive BTU to KW performance. The prime mover in an ORC is designed to provide resistance to a high-mass, high-velocity vapor force, but is not positive displacement because a positive-displacement prime mover can compress vapor to a fluid at its inlet and slow down the driver. Similar to a wind turbine blade, wind velocity must pass by the blade/driver to provide enough resistance to rotate the blade/driver. ORC prime movers/expanders allow the vapor to effectively expand through the impeller vanes in order to capture enough blow-by CFM force at low pressure to achieve mechanical work. An ORC works best at as high a temperature difference as possible (high Delta T). 
     The improved heat engine is related to a conventional ORC in that the former utilizes a heat source and a cooling source to operate a type of heat engine to produce mechanical work. While the two cycles are related, the improved heat engine is uniquely different. The decompressor for the improved heat engine is a positive-displacement device, and utilizes a lower flow/CFM higher pressure principle. High-pressure super-heated vapor (working fluid) at approximately 41.4 bar at 65.6° C. entering the positive-displacement prime mover, will decompress to approximately 13.8 bar at 21° C. lower pressure vapor and convert 27.6 bar differential pressure (Delta P) energy into mechanical work, as an example. This differential pressure energy function is similar to a refrigerant compressor operating in reverse. While a compressor that can move 105 kw of heat may require a 62 kw electrical motor to compress a refrigerant to a 41.4 bar high-pressure vapor at 65.6° C., the improved heat engine may generate more than 62 kw of power when 65.6° C. of heated compressed high-pressure refrigerant is forcing the compressor process in the opposite direction. The waste heat energy, for example, is the energy force driving the reverse compressor process to generate electricity rather than electricity being the force to compress a cool vapor/gas to a hot vapor/gas. 
     The Improved ORC Compared to a Typical ORC 
     By focusing on pressure differential (Delta P) energy when using very low-boiling point, high-pressure refrigerants, a smaller Delta T can be used to achieve an equivalent differential pressure (Delta P). The extractable energy using the improved ORC with 27.6 bar pressure differential is much greater than the energy that can be extracted using a conventional ORC with a 9.65 bar energy pressure differential. 
     ORC Refrigerant R245fa Temperature-Pressure Delta T and Delta P 
     21° C.=1.2 bar 93° C.=10.9 bar 
     Delta T of 72° C.=Delta P of 9.7 bar energy 
     HEDC Refrigerant R407c Temperature-Pressure Delta T and Delta P 
     21° C.=9.6 bar 78° C.=37.5 bar 
     Delta T of 57° C.=Delta P of 27.9 bar energy 
     HEDC Refrigerant R410a Temperature-Pressure Delta T and Delta P 
     21° C.=13.8 bar 66° C.=41.4 bar 
     Delta T of 45° C.=Delta P of 27.6 bar energy 
     HEDC Refrigerant CO 2  Temperature-Pressure Delta T and Delta P 
     20° C.=57.4 bar 38° C.=85.4 bar 
     Delta T of 18° C.=Delta P of 28.0 bar energy 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of the improved organic Rankine cycle decompression heat engine. 
     
    
    
     DETAILED DESCRIPTION 
     The present application has priority dates that are based on the filing of three separate provisional patent applications. The first, application Ser. No. 61/761,115, has a filing date of 5 Feb. 2013 and is titled HEAT ENGINE DECOMPRESSION CYCLE. The second, application Ser. No. 61/817,862, has a filing date of 30 Apr. 2013 and is titled HIGH-PRESSURE VAPOR ENHANCER. The third, application Ser. No. 61/841,610, has a filing date of 1 Jul. 2013 and is titled SCROLL DRIVER ACCELERATOR SYSTEM. All three of these provisional patent applications are hereby fully incorporated herein, in their entireties, by this reference. 
     The invention will now be described with reference to  FIG. 1 , which shows the ordered arrangement of equipment required to implement the improved organic Rankine cycle decompression heat engine  100 . The improved heat engine  100 , which employs a highly specialized organic Rankine cycle, provides a sealed, closed-loop path for an organic refrigerant  101  having a boiling point below −35 degrees Celsius. Elements of the closed-loop path will be subsequently enumerated. The improved heat engine  100  also includes a low-grade fluid heat source  103  having a temperature of less than 82 degrees Celsius. In almost all cases, it is preferable that the fluid heat source  103  be a hot water heat source, as rapid heat transfer is possible due to the high specific heat of water (1 calorie/gram ° C.=4.186 joule/gram ° C.), which is higher than any other common substance. Such low-grade heat sources are extremely plentiful. They can, for example, be geothermal water, coolant water from nuclear reactors or from industrial processes, and many other sources that have, heretofore, been considered of too low temperature to be useful in an energy recovery process. It is also certainly conceivable that the fluid heat source  103  could be hot gases. However, such a scenario would require a much larger heat exchanger than would be required for a hot water source. 
     A primary difference between the improved heat engine  100  of the present invention and previously disclosed heat engines employing conventional organic Rankine cycles is the use, in this heat engine, of organic refrigerants having very low molecular weight and very low boiling points. In essence, the improved heat engine  100  is effective because of it is ability to maintain a relatively high pressure differential of between about 20 to 42 bar on opposite sides of a highly efficient positive-displacement decompressor  105 . In an embodiment of the improved heat engine  100 , an orbital scroll decompressor is manufactured by the Danish company, Danfoss. Orbital scroll compressors (modified for use as decompressors) of other manufacturers, such as Trane, Copeland, Emerson Electric and Bristol, could also be used. In addition, other types of positive-displacement decompressors can be substituted for an orbital scroll decompressor. For example, Roots-type pumps, starrotor pumps, and dual-lobe pumps can almost certainly be used with success. In any case, the use of a highly efficient positive-displacement decompressor  105  enables the improved heat engine  100  to be used to generate electrical power from low-grade heat sources that have been heretofore ignored. The improved heat engine  100  also includes a heat sink  107 , which is at a temperature that is less than or equal to the ambient temperature. Though the heat sink  107  is, ideally, a fluid cold water source, as from a well or pond that is at less than ambient temperature, a heat sink using ambient air can be employed, but with a resulting drop in efficiency of the heat engine  100 . 
     Another component of the improved heat engine  100  that is critical to maintaining the pressure differential of between about 20 to 42 bar on opposite sides of the decompressor is a positive-displacement hydraulic pump  109 . The sole function of the hydraulic pump  109 , which is operated by a first electric motor  111 , is to transfer the refrigerant  101 , in its liquid state, from a low-pressure zone to a high-pressure zone. In such capacity, the hydraulic pump  109  must move the liquid refrigerant  101  while matching the pressure in the high-pressure zone. From the output port  113  of the hydraulic pump  109  to the intake port  115  of the decompressor  105 , the organic refrigerant  101  travels in the high-pressure zone of the heat engine  100 . Likewise, from the exhaust ports  117  of the decompressor  105  to the input port  119  of the hydraulic pump  109 , the organic refrigerant  101  travels in the low-pressure zone of the heat engine  100 . As a matter of clarification, it should be mentioned that the arrowheads near the outer edges of the rectangular block that represents the decompressor  105  symbolize the exhaust ports, as well as their relative location and direction. It will be noted that the exhaust ports  117  are covered by a first porous oil separator  121 . 
     Still referring to  FIG. 1 , from the output port  113  of the hydraulic pump  109 , the organic refrigerant  101 , generally in its liquid state, enters an eccentrically shaped cool refrigerant pressure holding tank  123 . Because of the shape of holding tank  123 , sufficient refrigerant vapor becomes trapped in the holding tank  123  so that it can serve as a pulsation dampener to mitigate the effect of fluid hammer as the hydraulic pump  109  transfers refrigerant from the low-pressure zone to the high-pressure zone. From the holding tank  123 , the refrigerant flows through a check valve  125  en route to a refrigerant-heating heat exchanger  127 . From the refrigerant-heating heat exchanger  127 , the refrigerant flows to a high-pressure vapor enhancer  129 , which is, essentially, a vertically oriented, tubular, fin-tube heat exchanger. It will be noted that hot water from the hot water heat source  103  enters near the top of the high-pressure vapor enhancer  129  through hot water input port  131  and exits near the bottom thereof through hot water output port  133 , while refrigerant enters the bottom of the high-pressure vapor enhancer  129  and exits the top thereof. The high-pressure vapor enhancer  129  ensures that refrigerant  101 , as it passes therethrough, is flashed to a superheated vapor, in which state it travels to the intake port  115  of the decompressor  105 . Piping  139  is sized to maintain this high-pressure vapor state. After hot water from the heat source  103  leaves output port  133 , it is piped to a hot water entry port  135  near the top of refrigerant-heating heat exchanger  127 . After heat is transferred to the organic refrigerant  101 , it leaves the refrigerant-heating heat exchanger  127  through hot water exit port  137 . A first actuator valve  141  serves as a pressure relief valve for superheated refrigerant vapor leaving the high-pressure vapor enhancer  129 . In such a pressure-limiting capacity, the first actuator valve  141  directs excess heat to the low-pressure zone, and also serves as bypass valve for pre-start and post-run operation. A second actuator valve  143  controls the pressure of superheated refrigerant vapor entering the decompressor  105 . 
     Still referring to  FIG. 1 , the decompressor  105  is located within a prime mover shell  145 , which also houses a high-efficiency generator  147  that is mechanically coupled to the positive-displacement decompressor  105 . Lubricating oil  149  is held in a reservoir  151  that is separated from the generator  147  by a heat shield  152  that has some small apertures therein, which enable oil to drain into the reservoir  151 . The lubricating oil  149  held in reservoir  151  is heated by a hot water loop  153  that begins at the hot water input port  131  of the high-pressure vapor enhancer  129  and ends at the hot water exit port  137  of the refrigerant-heating heat exchanger  127 . The lubricating oil temperature in reservoir  151  is controlled by a thermostat  155  and flow control solenoid  157 . The lubricating oil  149  is circulated by oil pump  159  powered by a second electric motor  161  and is injected into the intake port  115  of the decompressor  105 . The primary functions of the lubricating oil  149  are to lubricate and help seal minute gaps between the stationary scroll and the orbital scroll of the decompressor  105 , thereby enhancing the efficiency of the decompressor  105 . Alternatively, the lubricating oil  149  can be circulated by an internal oil pump within the drive shaft of the positive-displacement decompressor  105 . After refrigerant vapor has escaped the exhaust ports  117  of the decompressor  105 , it enters the low-pressure zone and passes through the first porous oil separator  121 , which removes most of the lubricating oil from the refrigerant vapor. The removed oil passes through apertures  163  in an exhaust gas barrier ring  165  and then drains through the heat shield  152  into the oil reservoir  151 . The refrigerant vapor then enters exhaust pipe  167  and travels to a vapor expansion chamber  169 , which contains a second porous oil separator  171 . Oil removed from the refrigerant vapor by oil separator  171  returns, via gravity, to the oil reservoir  151  through return tube  173 . It will be noted that the vapor expansion chamber  169  has an output tube  174  that extends into the chamber housing  175 , thereby making it more difficult for oil to escape from the expansion chamber  169  through the normal refrigerant escape path. Cooling of the generator  147 , along with pressure equalization for the prime mover shell  145 , is achieved with an actuator valve  177  and pressure equalization piping  179  from the prime mover shell  145  to the top of the chamber housing  175 . 
     Still referring to  FIG. 1 , from the vapor expansion chamber  169 , refrigerant vapor passes into an eccentrically shaped expansion chamber extension  181 , which is also connected at its apex to the pressure equalization piping  179 . It will be noted that there is a first sub-cooling coil  183  within the expansion chamber extension  181 . It will be further noted that the first sub-cooling coil  183  vents into the expansion chamber extension, where the escaping gas from the coil  183  join the refrigerant vapor that has been released from the decompressor  105 . Because of the expansion and cooling effect, the refrigerant vapor begins to condense into a liquid. It should be understood that the propensity of the refrigerant vapor to condense is directly related to the amount of liquid refrigerant charge maintained in the low pressure zone. From the expansion chamber extension  181 , the condensing vapor moves to a refrigerant-cooling heat exchanger  185 , where heat from the refrigerant is transferred to the heat sink  107 , which is preferably a cold-water source. From the refrigerant-cooling heat exchanger  185 , the condensing refrigerant vapor passes through a filter/dryer unit  187 , which removes any water moisture and any solid particles from the condensing refrigerant. From the filter/dryer unit  187 , the largely condensed refrigerant  101  enters a vertically oriented refrigerant tank  189  of downwardly tapering and downwardly decreasing cross-sectional area, which employs gravity to ensure maximum density of refrigerant  101  in its liquid state as it enters the input port  119  of the hydraulic pump  109 . It will be noted that the vertically oriented refrigerant tank  189  is also connected to the pressure equalization piping  179 . It will be further noted that a second sub-cooling coil  191 , which is installed within refrigerant tank  189 , can be used to further cool the condensed refrigerant before it enters the hydraulic pump  109 . A metering valve  193  provides a pressure drop for either pressurized liquid or vapor stored within holding tank  123 . This released liquid or vapor passes, first, through the second sub-cooling coil  191 , and subsequently, through the first sub-cooling coil  183 , thereby assisting in the condensation and cooling of the refrigerant vapor in the expansion chamber extension  181  and liquid refrigerant in the vertically oriented refrigerant tank  189 . 
     Still referring to  FIG. 1 , a mechanical pressure relief valve  195  protects the high-pressure zone from incidental or inadvertent over-pressure events. Released vapor and/or liquid refrigerant is released to the input port  197  of the filter/dryer unit  187 . In addition, an actuator valve  199  allows controlled pressure relief for system pre-start in order to purge any refrigerant vapor from the hydraulic pump  109 . Once again, released vapor and/or liquid refrigerant is released to the input port  197  of the filter/dryer unit  187 . 
     Although only a single embodiment of the improved organic Rankine cycle decompression heat engine has been shown and described, it will be obvious to those having ordinary skill in the art that changes and modifications may be made thereto without departing from the scope and the spirit of the invention as hereinafter claimed.