WO2013033082A1 - Moteur thermique osmotique - Google Patents

Moteur thermique osmotique Download PDF

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Publication number
WO2013033082A1
WO2013033082A1 PCT/US2012/052642 US2012052642W WO2013033082A1 WO 2013033082 A1 WO2013033082 A1 WO 2013033082A1 US 2012052642 W US2012052642 W US 2012052642W WO 2013033082 A1 WO2013033082 A1 WO 2013033082A1
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Prior art keywords
draw solution
energy recovery
osmotic
membrane
recovery device
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PCT/US2012/052642
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English (en)
Inventor
Robert Mcginnis
Aaron Mandell
Richard STOVER
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Oasys Water, Inc.
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Publication of WO2013033082A1 publication Critical patent/WO2013033082A1/fr

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03G—SPRING, WEIGHT, INERTIA OR LIKE MOTORS; MECHANICAL-POWER PRODUCING DEVICES OR MECHANISMS, NOT OTHERWISE PROVIDED FOR OR USING ENERGY SOURCES NOT OTHERWISE PROVIDED FOR
    • F03G7/00—Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for
    • F03G7/005—Electro-chemical actuators; Actuators having a material for absorbing or desorbing gas, e.g. a metal hydride; Actuators using the difference in osmotic pressure between fluids; Actuators with elements stretchable when contacted with liquid rich in ions, with UV light, with a salt solution

Definitions

  • the present invention relates to an osmotic heat engine for converting thermal energy into mechanical work that uses a semi -permeable membrane to convert osmotic pressure into electrical power.
  • PRO Pressure retarded osmosis
  • Salinity power is a membrane-based osmotic pressure energy conversion process.
  • PRO utilizes osmotic flow across a semi-permeable membrane to generate electricity.
  • PRO processes are discussed, for example, in U.S. Patent No. 3,906,250 to Loeb, U.S. Patent No. 3,587,227 to Weingarten et al., and U.S. Patent No. 3,978,344 to Jellinek, the disclosures of which are hereby incorporated by reference herein in their entireties.
  • PRO processes at river deltas also known as "open loop" PRO
  • open loop PRO have several operational and design limitations.
  • River delta PRO also runs in an open-loop configuration. This means that the feed and the draw solutions are returned to the ocean after the PRO process is complete.
  • seawater and river water When the seawater and river water are brought into the PRO system, they must be filtered and disinfected to prevent fouling and biofilm formulation, respectively.
  • any chemicals that are added to these waters must either be flushed out to sea or be removed through physical or chemical means. Disposal of disinfection chemicals and disinfection byproducts can have unforeseen environmental impacts. Diversion of river water may also have an environmental impact on delicate river delta ecology.
  • the draw solution is a solution of an ionic salt, such as sodium chloride, as described for example in U.S. Patent No. 3,906,250 to Loeb. Heat applied to the OHE would re-concentrate the draw solution by vaporizing a portion of the water into steam, which would then be condensed to form the deionized working fluid.
  • a primary difficulty faced by these OHEs is poor thermal efficiency due to high heat input requirements for water and organic solute vaporization.
  • chemical feed stock consumption can pose difficulties to economic operation.
  • An additional challenge is the difficulty of obtaining solute separation complete enough to avoid concentration polarization (CP) effects in the feed water. This is not a problem when water is vaporized and re-condensed as distilled working fluid, but could pose a significant problem when using removable draw solutes that are difficult to remove completely.
  • CP concentration polarization
  • the invention described herein attempts to overcome some of the noted problems of the prior art by proposing an alternative means of power production that uses osmotic pressure to generate electrical power from sources of low-grade heat. While several prior investigations of the use of osmotic phenomena to produce power have been conducted, such as those used to convert "salinity power" from the mixing of natural saline and fresh water streams, relatively few studies have focused on the use of osmotic phenomena to produce power through the conversion of heat.
  • the present invention relates generally to a closed loop PRO process that utilizes a recyclable draw solute.
  • the present invention relates to a method of generating power using an ammonia-carbon dioxide osmotic heat engine.
  • the method includes the steps of pressurizing a concentrated draw solution to a hydraulic pressure lower than its osmotic pressure on a first side of a semi-permeable membrane, introducing a dilute (nearly deionized) working fluid on an opposite side of the semi-permeable membrane, causing a portion of the dilute working fluid to flow through the semi-permeable membrane into the pressurized draw solution to create a water flux that expands the volume of the draw solution, inducing flow of the expanded volume of the draw solution through a turbine to produce power, and processing the expanded volume of the draw solution through a distillation column at a suitable temperature and pressure to separate the solutes from the draw solution, thereby producing new draw solution and working fluid streams for reuse in the system.
  • the invention in another aspect, relates to a method of generating power using an osmotic heat engine.
  • the method includes the steps of introducing a concentrated draw solution to a first side of a semi-permeable membrane, introducing a working fluid to a second side of the semi -permeable membrane, causing a portion of the working fluid to flow through the semi-permeable membrane into the pressurized draw solution to create a water flux that expands the volume of the draw solution, inducing flow of the expanded volume of the draw solution to a first side of a first energy recovery device and to a first side of a second energy recovery device to depressurize the expanded volume of the draw solution, introducing a turbine driving fluid to a second side of the first energy recovery device to pressurize the turbine driving fluid and induce the flow thereof through a turbine to produce power, introducing the concentrated draw solution to a second side of the second energy recovery device to pressurize the concentrated draw solution and induce flow thereof to the first side of the semi-permeable membrane, and processing the
  • the first and second energy recovery devices are connected in parallel; however, other quantities and arrangements of the energy recovery devices are contemplated and considered within the scope of the invention.
  • one or more energy recovery devices could be used with the working fluid introduced to the membrane system and/or between any combinations of fluid sources.
  • the second energy recovery device pressurizes the concentrated draw solution to a hydraulic pressure lower than its osmotic pressure on the first side of the semi-permeable membrane.
  • the concentrated draw solution includes ammonia and carbon dioxide in ratio of greater than 1 : 1 and in one or more embodiments at a ratio between about 1: 1 to 2.5: 1.
  • the concentrated draw solution comprises a non-aqueous solvent.
  • Other draw solutions, such as amine-based solutions are contemplated and considered within the scope of the invention.
  • the invention in another aspect, relates to an osmotic heat engine.
  • the osmotic heat engine includes a pressure retarded osmosis unit having a semi-permeable membrane, a source of concentrated draw solution in fluid communication with the pressure retarded osmosis unit, a source of working fluid in fluid communication with the pressure retarded osmosis unit, a first energy recovery device in fluid communication with the pressure retarded osmosis unit for receiving a first portion of an expanded volume of a dilute draw solution therefrom, a source of turbine driving fluid in fluid communication with the first energy recovery device, a turbine in fluid communication with the first energy recovery device and the source of turbine driving fluid; wherein the first energy recovery device transfers the pressure from the expanded dilute draw solution to the turbine driving fluid to rotate the turbine, a second energy recovery device in fluid communication with the pressure retarded osmosis unit for receiving a second portion of the expanded volume of the dilute draw solution therefrom, and a solute recycling system in fluid communication with the
  • FIG. 1 depicts an osmotic heat engine system in accordance with one or more embodiments of the invention
  • FIG. 2 depicts an alternative osmotic heat engine system in accordance with one or more embodiments of the invention
  • FIG. 3 depicts flux data and demonstrates the relationship between water flux and draw solution concentration for the membrane
  • FIG. 4 depicts the membrane power density relative to hydraulic and osmotic pressures in the osmotic heat engine of the invention.
  • FIG. 5 depicts the osmotic heat engine efficiency as a percentage of Carnot engine efficiency, relative to the difference between the hydraulic and osmotic pressures of the draw solution.
  • the present invention relates generally to a method of generating power using an ammonia-carbon dioxide osmotic heat engine.
  • the method includes the steps of
  • the osmotic heat engine described herein is designed to compete with other types of heat engines including gas turbines (Bray ton Cycle), steam turbines (Rankine Cycle), internal combustion engines (gasoline, diesel), and external combustion engine (Stirling engines).
  • gas turbines Bit ton Cycle
  • steam turbines Rankine Cycle
  • internal combustion engines gasoline, diesel
  • Stirling engines external combustion engine
  • the present invention relates to a closed cycle osmotic heat engine.
  • the system uses an ammonia-carbon dioxide draw solution and a deionized working fluid.
  • the deionized working fluid may include water that is substantially (or nearly) deionized. What is meant by nearly deionized is that the deionized working fluid contains less than 1 ppm ammonia and carbon dioxide (or alternative draw solutes) and no other solutes.
  • the draw solution is highly soluble, osmotically efficient and contains entirely removable and recyclable solutes.
  • the use of deionized water as a working fluid maximizes membrane mass transfer by eliminating internal concentration polarization effects.
  • the draw solution includes ammonium salts formed by the introduction of ammonia and carbon dioxide into water and is used in the OHE of the invention to generate electrical power; however, other thermolytic solutes are contemplated and considered within the scope of the invention.
  • the draw solution is formulated by mixing ammonium bicarbonate salt with ammonium hydroxide to form a complex solution of ammonium salts including ammonium bicarbonate, ammonium carbonate, and ammonium carbamate. The amount of ammonium hydroxide added is minimized to minimize the concentration of unionized ammonia in the draw solution.
  • the concentrated draw solution has an ammonia to carbon dioxide ratio of between about 1 : 1 to 2.5: 1.
  • the draw solution has a concentration of between 0.1 and 12 molar, preferably between about 3 to about 6 molar.
  • This draw solution has several desirable characteristics, including: (1) high solubility of the ammonium salts; (2) relatively low molecular weight and high diffusivity of the chemical species leading to high osmotic pressures and moderate external concentration polarization effects; (3) solutes that are almost completely removable in that the ammonium salts, upon heating with the draw solution at an appropriate temperature and pressure (for example 60° C at 101.3 kPa (1 atm), decompose to ammonia and carbon dioxide gases that may be readily removed to levels of less than 1 ppm; and (4) the thermal energy required for the removal and recycling of these solutes from a quantity of water is significantly less than that required to vaporize the water itself.
  • the concentrated draw solution is pressurized to a hydraulic pressure lower than its osmotic pressure
  • a dilute working fluid e.g., deionized water containing less than 1 ppm ammonia and carbon dioxide
  • this water flux expands the volume of the draw solution, inducing flow through a turbine, producing power.
  • Heat is introduced to the osmotic heat engine to drive a separation of the solutes from the draw solution, resulting in renewed draw solution and working fluid streams.
  • a pressure exchanger similar to those used in reverse osmosis (RO) desalination may be used to maintain the pressure of the draw solution side of the membrane in steady state operation.
  • the present invention uses a recyclable draw solute in PRO, where heat is input to the system which serves to regenerate the draw solute and excess heat is rejected to the environment in some way.
  • the system is known as an "osmotic heat engine" because heat is absorbed and rejected and work is produced. While different conceptions of this type of system have previously been configured, ether poor membrane performance and/or inefficient use of heat limited further development, due in part to the inadequate performance of the selected draw solution agents and severe internal concentration polarization effects.
  • the present invention proposes the use of ammonia-carbon dioxide (NH 3 -CO2) osmotic heat engine. This heat engine 10 is illustrated in FIG.
  • the OHE 10 includes a membrane system 12 in fluid communication with a source of the draw solution 11 and a source of the feed or working fluid 13.
  • the membrane system 12 is also in fluid communication with one or more pressure exchangers 16, a turbine 20, and a system for recycling the draw solutes 22.
  • Various systems of this type are described in U.S. Patent Publication Nos. 2010/0024423 and 2010/0183903, the disclosures of which are hereby incorporated by reference herein in their entireties.
  • a pressure exchanger or combination of pressure exchangers may be used to, for example, pressurize the draw solution side of the membrane system 12 and/or as an interface between the dilute draw solution and a turbine.
  • the osmotic heat engine of the invention relies on the use of a deionized (i.e., containing little or no dissolved solutes) working fluid.
  • a deionized (i.e., containing little or no dissolved solutes) working fluid is advantageous, because no ICP occurs. While salt leakage from the draw solution through the membrane may cause ICP, the membrane is chosen to reject salt to a high degree, which will serve to counteract this tendency.
  • the membrane is a semipermeable membrane that has an active layer oriented toward the draw solution and a backing layer oriented toward the feed solution.
  • the water flux that expands the volume of the draw solution is typically at least about 25 x 10 ⁇ 6 m3/m2 -s.
  • One of the keys to the efficient osmotic heat engine process of the invention is the heat required to separate pure water from the diluted draw solution. This is where the benefit of using an ammonia and carbon dioxide draw solution (or similar) becomes apparent, because these gases may be successfully stripped from water using low temperature steam.
  • Modeling of gas removal using Aspen HYSYS ® (available from Aspen Technology, Burlington, MA) has shown that steam with temperatures as low as 40°C can be utilized under a vacuum gas stripping process. This allows for the utilization of a variety of heat sources that have typically little utility and very low to no cost.
  • Low grade heat sources come from a variety of industries including, for example, metal manufacturing (steel mills), glass manufacturing, oil refining, and thermoelectric power generation. All of these industries use elaborate methods of reclaiming their waste heat, but low grade heat is always lost to the environment through water cooling or flue gases.
  • renewable sources of heat may also be used. Geothermal heat sources are abundant, but are rarely of high enough quality to directly generate electricity. Typically, these sources may be used to heat and cool homes, but can also be used in a binary cycle configuration that utilizes the heat to vaporize a secondary liquid, such as ammonia, and expand that vapor through a turbine. The vapor can then by condensed by rejecting heat to the air or surface water.
  • OTEC ocean thermal energy conversion
  • This system includes an engine that utilizes the warm surface ocean water as a heat source and the cold deep ocean water as a heat sink.
  • OTEC uses warm water to vaporize a liquid, like ammonia, which then expands through a turbine. The gas is then condensed with the cold deep ocean water and recycled. For both of these processes, a gas is being used as the working fluid and hence a large turbine must be used (i.e., at least about 10 meters in diameter for steam turbine OTC). This is a design limitation that can be alleviated replacing the ammonia vapor system commonly used with the osmotic heat engine of the invention. By using the warm water to strip the NH 3 -CO2 draw solution and the cold water to condense these gases, the working fluid directed through the turbine to generate power is instead a liquid. This is of significant benefit, as hydroturbines are much smaller than turbines designed to use lower density gases, and are very efficient at converting work into electricity.
  • a benefit of the osmotic heat engine of the present invention is the ability to successfully convert low grade heat sources into electrical energy.
  • the configuration of the heat engine of the invention solves many of the previous economic and environmental issues of river outlet PRO due to its closed loop configuration and recyclable draw solute.
  • Utilizing low grade heat sources also provides an essentially cost-free energy source, because the cost of the energy is related only to the capital cost of the equipment amortized over the life of the equipment and maintenance.
  • the heat required for separating the draw solutes from solution is typically introduced at a temperature of between about 35 and 250°C.
  • the temperature required for separating the draw solutes from solution is proportional to pressure and pressure is typically introduced at about 0.05 to about 10 atm.
  • FIG. 2 depicts an alternative OHE 100 that uses isobaric energy recovery devices in the PRO process to replace the use of a high-pressure draw solution that drives the turbine in the earlier described embodiments of the invention with high-pressure pure water or other solution chosen for its particular compatibility and/or operating characteristics.
  • the use of the pure water (or other non-aqueous solutions) may reduce or eliminate the need for specialized materials for the turbine and related equipment, as may be required with certain draw solutions.
  • the OHE 100 of FIG. 2 includes a membrane system 112, a source of a feed or working fluid 113, a source of a draw solution 111, a turbine 120, and a draw solute recycling system 122.
  • the OHE 100 also includes two isobaric energy recovery (i.e., pressure transfer) devices 116, 118, a pump 110, and a source of turbine driving fluid 124.
  • the working fluid 113 is introduced to a first side of the membrane system 112 and the concentrated draw solution 111 is introduced to a second side of the membrane system 112, via pump 110, and provides an osmotic pressure differential.
  • the pump 110 assists in pressurizing the concentrated draw solution.
  • a solvent generally moves across the membrane via osmosis, thus increasing the volume on the pressurized draw solution side of the membrane system 112.
  • the increased volume of the pressurized draw solution may be decreased by flow through the turbine 120, which reduces the solution pressure and produces power.
  • the depressurized solution may then be treated via the solute recycling system 122, as previously described.
  • the pressurized dilute draw solution is directed to one side of each of the two energy recovery devices 116, 118.
  • a second side of one device 116 is in fluid communication with the solute recycling system 122, in particular a source of concentrated draw solution therefrom, and the pump 110.
  • the first side of device 116 is also in fluid communication with the solute recycling system 122 to return the depressurized dilute draw solution to the recycling system 122.
  • the pressured dilute draw solution passes through the device 116, pressurizing the concentrated draw solution from the recycling system 122 to the pump 110, thereby reducing the need for additional energy for transferring and pressurizing the concentrated draw solution.
  • a second side of the other device 118 is in fluid communication with the turbine 120 and the source of turbine driving fluid 124.
  • the first side of device 118 is also in fluid communication with the solute recycling system 122 to return the depressurized dilute draw solution to the recycling system 122.
  • the pressurized dilute draw solution directed to the second device 118 pressurizes the turbine driving fluid 124, which may be pure water or other fluid compatible with the turbine 120, to spin the turbine and generate electricity.
  • the reduced pressure dilute draw solution is directed to the recycling system 122.
  • the pressurized dilute draw solution passes through the two energy recovery devices 116, 118 in parallel.
  • the source 124 may also be in fluid communication with the recycling system 122.
  • the foregoing OHEs were described with respect to using aqueous solutions; however, the systems described herein can also be used with non-aqueous solutions.
  • the non-aqueous solvent could have the following properties: high surface tension, a high ability to dissolve a volatile solute, and low volatility.
  • the solutes used could have the following properties: high solubility, capable of generating a high osmotic pressure, volatile when heated, and low enthalpy of vaporization.
  • DMSO dimethyl sulfoxide
  • the OHE would use a polar non-aqueous solvent with ammonium salts.
  • the use of various polar and non-polar solvents and various salts are contemplated and considered within the scope of the invention.
  • the data was taken with the NH 3 -CO2 draw solution on the active layer of the membrane.
  • a deionized water feed was used to simulate osmotic heat engine conditions. Two temperatures were evaluated: 20°C and 40°C, and the feed and draw solutions were maintained at identical temperatures for both series of tests. The results are shown in FIG. 3.
  • power generation data can be estimated by modeling the process in Aspen HYSYS ® (available from Aspen Technology, Burlington, MA). Using various draw solution concentrations over a range of permeate pressurization, the amount of energy generation can be calculated by using the following equation:
  • FIG. 4 illustrates this feature for a range of draw solution concentrations and demonstrates how various draw solution concentrations perform in the osmotic heat engine of the invention over a range of permeate side hydraulic pressure.
  • the energy production was modeled using Aspen HYSYS® (available from Aspen Technology, Burlington, MA).
  • Measurements of water flux through semi-permeable membranes oriented in the PRO configuration provide data for estimations of engine performance.
  • Membrane water flux data was obtained using a cross flow membrane cell and associated system components. The dimensions of the channel were 77 mm long by 26 mm wide by 3 mm dep. Mesh spacers were inserted within both channels to improve support of the membrane as well as to promote turbulence and mass transfer.
  • a viable speed peristaltic pump (available from Masterflex of Vernon Hills, IL) with a dual pump head was used to pump both the feed and draw solutions in a closed loop.
  • a constant temperature water bath (available from Neslab of Newington, NH) was used to maintain both the feed and draw solution temperatures.
  • Osmotic water flux was determined for a range of draw solution concentrations.
  • the draw solution was made by mixing ammonium bicarbonate salt (NH 4 HCO 3 ) with ammonium hydroxide (NH 4 OH), forming a complex solution of ammonium salts, comprised of ammonium bicarbonate, ammonium carbonate and ammonium carbamate, with the latter being the most abundant in concentrated solutions.
  • the amount of NH 4 OH added was varied depending on the concentration of the draw solution and the temperature at which it was to be used.
  • the amount of NH 4 OH was minimized to minimize the concentration of unionized ammonia in the draw solution.
  • Properties of the draw solutions used in modeling of the OHE including osmotic pressure, density, viscosity, and pH, were obtained with Aspen HYSYS ® , in conjunction with an electrolyte property package from OLI Systems, Inc.
  • A is the water permeability coefficient
  • ⁇ the reflection coefficient
  • ⁇ ltm the difference in osmotic pressures across the membrane between the draw and feed solution at the separation interface (i.e., the membrane active layer surface)
  • ⁇ is the hydraulic pressure difference between the draw solution side and the working fluid.
  • ⁇ is calculated from the bulk osmotic pressure of the draw solution after accounting for ECP effects as discussed above.
  • the turbine efficiency E is typically greater than 90%.
  • the efficiency of the pressure exchanger used to maintain steady state pressurization of the draw solution is typically greater than 95%.
  • the combined efficiency of these two components is approximated, in the modeling effort described herein, to an overall efficiency of 90% for projections of power production, captured in the value of 0.90 for E in Equation 2 above.
  • the volume flowing through the turbine per unit time (V) is equal to the product of the water flux through the membranes of the OHE (Jw) and the total membrane surface area. This flux is a function of both the hydraulic and osmotic pressures of the system, as shown by Equation 1 above. Increasing the hydraulic pressure relative to the osmotic pressure increases the power output per unit volume of water through the turbine, but will also reduce the total volume of water by reducing membrane water flux. Reducing hydraulic pressure will have the inverse effect.
  • Thermal efficiency is calculated by measuring the quantity of power produced relative to the quantity of heat used (for the separation and recovery of the draw solution). There are two measures of efficiency that may be considered in evaluating an engine's performance: thermal efficiency and Carnot efficiency. Thermal efficiency is simply the ratio of engine power output over heat input. Carnot efficiency is a measure of the efficiency of an engine relative to that of a Carnot engine, one which produces the maximum theoretical quantity of work from a given heat flow, based on a perfectly reversible process.
  • the "quantity of heat" component of engine efficiency can be calculated based on the heat duty of the distillation column used to separate the ammonia and carbon dioxide from the dilute draw solution, producing a re-concentrated draw solution and deionized working fluid.
  • the column heat duty was modeled with Aspen HYSYS ® in conjunction with an electrolyte property package from OLI Systems, Inc. (Morris Plains, NJ), following the procedures used in estimating the energy demands of forward osmosis desalination.
  • T H is the absolute temperature of heat delivered to the engine (from fuel combustion, for example) and TL is the absolute temperature at which heat is rejected to the environment.
  • Measuring OHE efficiency against the efficiency of a Carnot engine establishes how effective the OHE is relative to the quantity of heat it uses.
  • the Carnot efficiency of such an engine would be 55%, approximately equally to the Carnot efficiency of a coal fired power plant operation at 537°C. This is a particularly useful method of comparison between heat engine technologies when considering heat sources as low as 20°C above ambient temperatures, where maximum theoretical thermal efficiencies are quite low.
  • FIG. 3 illustrates the relationship between water flux and draw solution concentration for the membrane.
  • One criterion for optimizing the OHE is to select hydraulic and osmotic pressures which produce the highest power output per membrane area, or highest membrane "power density.”
  • the power density is calculated based on membrane water flux, draw solution hydraulic pressure, and anticipated ECP effects in the OHE membrane system.
  • the ECP effects were calculated using a fitted mass transfer coefficient of 1.78 x 10-5 m/s, determined through experimental flux measurements in the PRO mode.
  • the combined efficiency of the hydroturbine and pressure recovery device was assumed to be 90%.
  • the relationship between the osmotic and hydraulic pressures in the OHE, relative to the membrane power density is shown in FIG. 4. Each curve corresponds to a fixed ammonia-carbon dioxide draw solution concentration.
  • the power density may be further increased by increasing the cross flow velocity of the draw solution stream (to reduce ECP effects) or the hydraulic pressure of the OHE membrane system.
  • the maximum power density would be about 274 W/m 2 in this scenario.
  • Modeling of an OHE with a 20.26 MPa (200 atm) hydraulic operating pressure indicates that power densities would be increased by an additional 47% over those of a 10.13 MPa (100 atm) system. Increased crossflow velocity, however, will result in additional power consumption, and increased hydraulic pressure will require more expensive process components. These operating conditions will necessarily be factors in process optimization, balanced against correlating factors of process fluid pump power consumption and equipment capital and replacement costs.
  • the Carnot efficiency of the OHE was modeled over a range of osmotic and hydraulic pressures.
  • the heat and electrical duties of the draw solution separation and recycling process are compared to the electrical production of the OHE power generating turbine for the combination of osmotic and hydraulic pressures examined.
  • the thermal efficiency is practically the ratio between the electrical energy produced by the OHE and the thermal energy required for the draw solute separation. This efficiency is compared to the theoretical efficiency of a Carnot engine operating with the same high and low temperature heat streams, giving a "percentage of Carnot efficiency" measure of OHE performance.
  • a draw solution of sufficient concentration to produce the osmotic pressure desired is specified in a HYSYS ® chemical simulation model.
  • This solution stream is directed to a distillation column with characteristics appropriate for the removal.
  • One example of such a model specifies a single distillation column, effecting the separation of draw solutes from a 6 M (C0 2 basis) draw solution stream (which generates 31.94 MPa (315.26 atm) osmotic pressure in the OHE membrane system, containing structured packing 2.35 m (7.7 ft.) in height (30 theoretical stages) supplied with heat at 50°C.
  • a column of this type operates at a bottom pressure and temperature of 10.62 kPa (0.1 048 atm) and 46.96°C (given a 3°C ⁇ in the reboiler heat exchanger), and a top pressure and temperature of 10.54 kPa (0.1040 atm) and 35.55°C.
  • the stream fed to the top of the column is preheated to 32°C with an energy requirement of 3196.8 MJ/m 3 (per m working fluid produced).
  • the column heat duty is 3454.6 MJ/m 3 , supplied to the reboiler. Supplementary heating required to maintain all streams at specified temperatures is 385.7 MJ/m 3 , for a total heat duty of 7037.1 MJ/m 3 .
  • FIG. 5 represents OHE engine efficiency as a percentage of Carnot engine efficiency, relative to the difference between the hydraulic and osmotic pressures of the draw solution.
  • the percentage of maximum theoretical engine efficiency (Carnot) reaches a maximum of approximately 16% as the net driving force ( ⁇ - ⁇ ) approaches zero.
  • the osmotic pressure ⁇ is based on the bulk osmotic pressure of the draw solution.
  • the distillation column used for the solute recycling system is however inefficient in its removal of N3 ⁇ 4 and C0 2 from the dilute draw solution. Some water vapor is also removed, requiring heat which may not be converted to power production. As the concentration of the draw solution is increased, the amount of water vapor created in the distillation column increases as well, and this inherent inefficiency of separation results in decreasing OHE efficiency overall. However, as previously discussed, using a non-aqueous draw solution can eliminate this inefficiency. This increase in osmotic pressure does, however, result in increased water flux, which benefits OHE operation through increased membrane power density. Higher membrane power densities require less membrane area for a given energy capacity and thus less membrane cost. This represents a tradeoff between membrane capital cost and engine efficiency, which must be optimized in the design of an OHE system.
  • ammonia-carbon dioxide osmotic heat engine of the invention allows for power production from diverse energy sources such as heat from the reject streams of existing power plants, otherwise unproductive low temperature geothermal heat sources, low-concentration solar thermal energy, biomass heat (non-combustion) and ocean thermal energy conversion, among others. In all of these cases the process of the invention produces power that is renewable and carbon- free.

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  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
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Abstract

L'invention concerne un moteur thermique osmotique pour convertir l'énergie thermique en énergie mécanique, qui utiliseune membrane semi-perméable pour convertir la pression osmotique en courant électrique.
PCT/US2012/052642 2011-08-31 2012-08-28 Moteur thermique osmotique WO2013033082A1 (fr)

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ITAN20130198A1 (it) * 2013-10-28 2015-04-29 New Energy World S R L Impianto per la generazione di energia elettrica.
WO2016022602A1 (fr) * 2014-08-05 2016-02-11 Monarch Power Corp. Quadri-génération d'électricité, de chaleur, de refroidissement et d'eau pure
WO2016037999A3 (fr) * 2014-09-08 2016-05-26 Applied Biomimetic A/S Procédé de génération d'électricité
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US10968128B2 (en) 2016-03-04 2021-04-06 Applied Biomimetic A/S Power generation process
US11231019B2 (en) 2016-03-04 2022-01-25 Applied Biomimetic A/S Electricity generation process
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US11231020B2 (en) 2017-07-12 2022-01-25 Saltkraft Aps Power generation process
WO2021239701A1 (fr) * 2020-05-26 2021-12-02 Saltpower Holding Aps Saturateur de saumure

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