US20160153318A1 - Use of highly efficient working media for heat engines - Google Patents

Use of highly efficient working media for heat engines Download PDF

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US20160153318A1
US20160153318A1 US14/902,224 US201414902224A US2016153318A1 US 20160153318 A1 US20160153318 A1 US 20160153318A1 US 201414902224 A US201414902224 A US 201414902224A US 2016153318 A1 US2016153318 A1 US 2016153318A1
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working medium
heat engine
heat
temperature
orc
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Jens Busse
Joern ROLKER
Muhammad Irfan
Gregor Westphal
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Evonik Operations GmbH
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Evonik Degussa GmbH
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Assigned to EVONIK DEGUSSA GMBH reassignment EVONIK DEGUSSA GMBH ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: Busse, Jens, IRFAN, MUHAMMAD, ROLKER, JOERN, WESTPHAL, Gregor
Publication of US20160153318A1 publication Critical patent/US20160153318A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K25/00—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for
    • F01K25/08—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/02—Materials undergoing a change of physical state when used
    • C09K5/04—Materials undergoing a change of physical state when used the change of state being from liquid to vapour or vice versa
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K25/00—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for
    • F01K25/08—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours
    • F01K25/10—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours the vapours being cold, e.g. ammonia, carbon dioxide, ether
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/14—Combined heat and power generation [CHP]

Definitions

  • the invention relates to a heat engine for performing an organic Rankine cycle (ORC) which comprises an evaporator, an engine, a condenser and a circuit comprising a fluid working medium and to the use of a working medium for a heat engine.
  • ORC organic Rankine cycle
  • ORC stands for organic Rankine cycle “organischer Rankine-Kreisrind” (1994.
  • An ORC process is a thermodynamic cycle for converting heat into mechanical work using an organic working medium.
  • An ORC process is a simple thermodynamic cycle in which the working medium is evaporated and optionally superheated by supplying heat at a high pressure level.
  • the superheated vapour undergoes expansion cooling to a lower pressure in an expander (in particular an engine such as a piston engine or a turbine) thus performing work.
  • the work may be directly mechanically utilized or is converted into electrical current using a generator.
  • the vapour exiting the expander may still be in the superheated state or may already be decompressed to such an extent that it occupies the wet vapour region so that some of it is already in the liquid state. Complete liquefaction takes place in the condenser.
  • the electricity-generating cycle is operated not with water but with an organic working fluid which can utilize the heat generated at a low temperature level with greater thermodynamic efficiency.
  • the working medium employed thus has a key role since the optimal interaction between the working medium and the process configuration has a determining influence on the efficacy and thus on the efficiency of the entire process.
  • the working medium influences the plant configuration.
  • Optimal selection of a working medium can enhance the utilization of the heat source and the efficiency of the plant.
  • Suitable working media for ORC processes include especially (hydro)chlorofluorocarbons and hydrocarbons and also mixtures of fluids (hydrocarbons and water, (hydro)fluorocarbon mixtures) and organic silicon components.
  • the existing industrially realized prior art employs not only hydrocarbons such as pentane, but also siloxanes such as octamethyltrisiloxane or chlorinated hydrocarbons such as R134a or R245fa (Quoilin, S., Lemort, V., Technological and Economical Survey of Organic Rankine Cycle, 5th European Conference Economics and Management of Energy in
  • the disadvantages of the prior art working fluids include possible hazards to the environment (CFCs: harmfulness to the ozone layer and global warming) and to workplace safety (hydrocarbons: flammability, explosion prevention) and also thermodynamic limitations due to insufficient optimization of plant design and fluid properties.
  • the fluorinated hydrocarbons are some of the most extensively described working media.
  • a substantial advantage of these substances lies in their physical properties. For instance these substances are generally not flammable and nontoxic.
  • the disadvantage of such substances is that the boiling point of fluorinated hydrocarbons is generally very low since said substances were usually developed as coolants and are thus of only limited suitability for use in an ORC system at relatively high use temperatures.
  • ORC working media are hydrocarbons, for example toluene, pentane and isobutane. Hydrocarbons are very well known as suitable ORC working media and are employed in ORC engines. However, when utilizing these media their properties must be taken into account. The main disadvantage of these substances is that they are usually flammable and hazardous to the environment. Said substances generally also have a highly deleterious effect on climate.
  • ethanol is currently used in an ORC vapour engine from DeVeTec GmbH as the most efficient working medium in a temperature range starting at about 250° C.
  • the problem addressed by the invention is that of providing a working fluid for an organic Rankine cycle (ORC) comprising a vapour-expansion engine using waste heat streams from DeVeTec GmbH in extended temperature ranges between 80° C. to 250° C., in particular from 80° C. to 200° C., particularly preferably from 80° C. to 150° C.
  • ORC organic Rankine cycle
  • This broad temperature range is a result of the different temperature levels of the waste heat streams.
  • offgases from biogas, biomass or mine gas combustion are present at temperatures in the region of 450° C.
  • the industrial sphere is host to many lower temperature streams in the range from 100° C. to 200° C. which can no longer be utilized in many chemical sites but whose potential can be enhanced via an ORC cycle. Different working fluids are thus utilized depending on the application.
  • the working medium In addition to suitable thermodynamic properties (inter glia thermal stability, enthalpy of vapourization, vapour pressure and heat capacity) the working medium must meet further requirements such as low toxicity and low environmental impacts (for example with regard to innocuousness towards the ozone layer and climate) and must not be flammable nor corrosive towards components of the heat engine.
  • a further problem addressed by the invention is that of providing a working medium employable with heat engines at low temperatures with a high degree of efficiency.
  • the working medium shall simultaneously exhibit good environmental compatibility, in particular in terms of harmfulness towards the ozone layer and climate.
  • the working medium should further effect as little attack and corrosion as possible on the components of such a heat engine.
  • the working medium shall moreover be as nonhazardous as possible in its application, i.e. should exhibit the lowest possible flammability and present no risk of explosion.
  • a heat engine for performing an organic Rankine cycle which comprises an evapourator, an engine, a condenser and a circuit comprising a fluid working medium, wherein the working medium has a critical pressure (pc) between 4000 kPa and 6500 kPa, preferably between 4200 kPa and 6300 kPa, the working medium has a critical temperature (Tc) between 450 K and 650 K, preferably between 460 K and 600 K, the working medium has a molar mass between 50 g/mol and 80 g/mol, preferably between 60 g/mol and 75 g/mol, and the gaseous working medium partially condenses out during adiabatic expansion.
  • ORC organic Rankine cycle
  • the working medium is cyclopentene or at least one alkyl formate or a mixture thereof, preferably methyl formate and/or ethyl formate.
  • the heat engine is an expansion machine which preferably comprises a vapour expansion engine comprising pistons as the engine or which comprises at least one turbine as the engine.
  • the engine may thus be realized either as a piston engine or as a turbine.
  • Other types of heat engines may also be employed as the engine provided they are capable of converting the expansion work of the working medium into mechanical work utilizable outside the process. It is thus also possible to employ a rotary engine.
  • a vapour expansion engine having reciprocating pistons is particularly preferred in accordance with the invention since the wet behaviour of the working medium makes it possible to eschew a recuperator and the conversion of the ORC process may thus be carried out in particularly cost-effective fashion.
  • the mechanical work delivered by the engine may be directly mechanically utilized or converted into electrical current using a generator.
  • a pump is disposed between the condenser and the evapourator in the circuit of the heat engine, said pump allowing the fluid working medium to be conveyed from the condenser to the evapourator.
  • a particularly preferred embodiment of the invention may provide that the circuit of the heat engine does not comprise a recuperator.
  • recuperator heat exchanger
  • the erosion rate of the working medium towards unalloyed steel is less than 0.05 mm/a at 150° C. and/or that the erosion rate of the working medium towards alloyed steel (1.4571) is less than 0.005 mm/a at 150° C.
  • the working medium exhibits no endothermic or exothermic reactions or first or second order phase transitions in the temperature range between 70° C. and 200° C. when subjected to temperature changes over time, preferably not even when subjected to tenfold repetition of a temperature/time profile between 70° C. and 200° C.
  • a working medium having a critical pressure (pc) between 4000 kPa and 6500 kPa, preferably between 4200 kPa and 6300 kPa, having a critical temperature (Tc) between 450 K and 650 K, preferably between 460 K and 600 K, and having a molar mass between 50 g/mol and 80 g/mol, preferably between 60 g/mol and 75 g/mol, in a heat engine, wherein the gaseous working medium partially condenses out during adiabatic expansion within a cycle of the ORC process.
  • pc critical pressure
  • Tc critical temperature
  • methyl formate and/or ethyl formate are employed as the alkyl formate, preference being given to employing methyl formate or ethyl formate as the working medium in the heat engine.
  • the process according to the invention is easy to implement and thus cost effective in its realization.
  • the use of mixtures may be highly advantageous for reducing the energy losses during heat transfer since the evaporation thereof does not occur at constant temperature.
  • Uses according to the invention may preferably provide that the heat engine is operated with an ORC process.
  • the substances and substance classes at issue are particularly suitable for ORC processes.
  • the heat engine employed is an expansion machine, preferably a vapour expansion engine comprising pistons or at least one turbine as the engine.
  • the heat engine is operated with a heat source in a low-temperature range between 80° C. and 200° C., preferably between 80° C. and 150° C.
  • the working media intended for use are particularly suitable for the low temperature range.
  • ⁇ Lv is the enthalpy of vaporization at constant volume
  • c p is the heat capacity at constant pressure
  • T c,Fluid is the critical temperature of the working medium
  • T process is the process temperature
  • T is the temperature
  • S is the entropy.
  • a heat engine filled with a working medium according to the invention for example the piston expansion engine from DeVeTec GmbH
  • a working medium according to the invention for example the piston expansion engine from DeVeTec GmbH
  • so-called “wet” working fluids which may be decompressed into the wet vapour region, may be employed. Recuperation is not necessary for such a fluid and the engine for performing the process may therefore be markedly simplified.
  • FIG. 1 shows a simplified schematic representation of an ORC process/a heat engine for implementing a process according to the invention
  • FIG. 2 shows an ideal-type representation of the changes of state for wet, dry and isentropic fluids in the ORC process in a temperature-entropy diagram
  • FIG. 3 shows a schematic representation of a setup for determining the vapour pressure of suitable working media
  • FIG. 4 shows the temperature/time profile for a calorimetric measurement (DSC) for analyzing suitable working media
  • FIG. 5 shows a vapour pressure/time diagram for determining the thermal stability of 1-propanol at 195° C. to 180° C.
  • FIG. 6 shows a vapour pressure/time diagram for methyl formate at 150° C.
  • FIG. 7 shows a vapour pressure/time diagram for ethyl formate at 150° C.
  • FIG. 8 shows cyclic differential thermal analysis diagrams (DSC curves) for ethyl formate.
  • FIG. 1 shows a simplified schematic representation of an ORC process for implementing a process according to the invention, i.e. an ORC process, such as is carried out in a heat engine according to the invention.
  • the ORC process depicted is a simple thermodynamic cycle in which a working medium is evaporated and optionally superheated at a high pressure level by supplying heat.
  • the superheated vapour undergoes expansion cooling to a lower pressure in an engine (for example a turbine or piston engine) thus performing work.
  • the vapour exiting the expander may still be in the superheated state or may already be decompressed to such an extent that it occupies the wet vapour region so that some of the working medium is already in the liquid state.
  • Complete liquefaction takes place in the condenser.
  • the electricity-generating cycle is operated not with water but with an organic working fluid which can utilize the heat generated at a low temperature level with greater thermodynamic efficiency.
  • a parameter of central importance is the vapour pressure of the components which firstly permits general classification for the low- or high-temperature range. Efficient working fluids make it possible to realize, for a given temperature of the heat source and the heat sink, the greatest possible pressure ratio between the upper and lower process pressure. This requirement may readily be shown in a logarithmic representation of the vapour pressure via the negative reciprocal absolute temperature as is shown in FIG. 2 . Since the gradient of the vapour pressure curve in the Raoult diagram is proportional to the enthalpy of vaporization in accordance with the Clausius-Clapeyron equation, working media having large enthalpies of vaporization promise advantages on account of the greater expected pressure ratio in the expander. Together with the heat capacity there are also methods of estimation that allow predictions to be made regarding the fluid type (wet, dry or isentropic).
  • the changes of state of the working fluid in the cycle may be depicted in the temperature (T) entropy (S) diagram.
  • FIG. 2 shows the advancement of the process for different fluid types in the T-S diagram with the simplification that the fluids are decompressed in isentropic fashion.
  • the working fluids may be categorized according to the path of the saturation line and the dew line into wet (negative gradient dew line), dry (positive gradient dew line) and isentropic (vertical dew line) working fluids.
  • the substantial difference when using these different fluid types in the ORC process lies in the state of the vapour after the decompression.
  • the vapour is in the superheated state only to a very limited extent, if at all, after the decompression, i.e. the fluid is decompressed into the wet vapour region so that liquid droplets are already present.
  • a superheated vapour is present which is at a temperature higher than the condensation temperature.
  • Process costs may simultaneously be increased by about 30% due to the use of the additional heat exchanger.
  • recuperator heat exchanger
  • a medium is referred to as a wet fluid when the gradient of the dew line in the T-S diagram is negative ( FIG. 2 ). This results in the formation of wet vapour upon isentropic decompression starting from the dew line.
  • the medium When the dew line is vertical the medium is referred to as isentropic and when the gradient is positive the medium is referred to as dry.
  • thermodynamic suitability of new working media in the ORC process a model of the cycle was constructed in the “Aspen Plus” computer simulation program which allows the thermal efficiency to be calculated as a function of the medium employed and the temperature of the available heat source.
  • the maximum temperature in the evaporator is accordingly a degree of freedom.
  • the simulations were performed for various temperatures: 100° C., 150° C., 200° C. and 250° C.
  • the thermal efficiency of the process was evaluated for the various conditions.
  • the efficiency is generally defined as:
  • the utility is the output of the expansion machine.
  • the input is composed of the power of the pump and the supplied heat.
  • Ethanol was defined as the reference medium.
  • the particularly suitable working media found in the context of the present invention were compared with the working medium ethanol for various temperatures. In general terms it should be noted that the choice of working medium is dependent on the heat source available. Depending on the evaporator temperature certain working media are more or less suitable for use as the working medium in a heat engine.
  • the vapour pressure is the pressure established when a vapour is in thermodynamic equilibrium with the associated liquid phase in a sealed system.
  • the vapour pressure increases with increasing temperature and is a function of the substance/mixture present.
  • the vapour pressure of a liquid is equal to the ambient pressure in an open system the liquid begins to boil.
  • the vapour pressure is one of the crucial substance properties for the design and operation of an ORC plant. Due to the operating conditions defined for the vapour engine the vapour pressure of a suitable liquid should be below 35 bar.
  • vapour pressures of the working media are determined in a sealed and temperature-controlled high-pressure autoclave. This comprises heating the liquid and measuring the pressure at the particular temperature setting. The more accurate the measurement of these two values the better the determined vapour pressure data. Calculations may be performed with “Aspen Plus” for comparison with the literature values. In the case of deviations in the data, in-house measurements of the vapour pressure may then be performed.
  • Specific heat capacity indicates the amount of heat that needs to be supplied to a kilogram or a mole of a particular substance to raise its temperature by 1 Kelvin.
  • Viscosity is a measure of the resistance of a fluid to deformation and influences heat transfer and pump performance in an ORC system.
  • water has a viscosity of about one mPas
  • edible oils have a viscosity of about 100 mPas
  • honey has a viscosity of about 1000 mPas. The lower the viscosity the more mobile a liquid and the quicker said liquid can flow under constant conditions.
  • Suitable ORC working media should therefore have a low viscosity of less than 10 mPas at 20° C.
  • the chosen working media all have a rather low viscosity which is comparable to the viscosity of water (about 1 mPas at 20° C.). In the region above about 100° C. which is of interest for an ORC system the viscosities of the preselected working media hardly differ from one another anymore.
  • thermodynamic cycle One of the further important substance properties for the design of a thermodynamic cycle is the density of the liquid and gaseous phase of the working medium.
  • the density of the working media is essential to the design of the circulation pumps. Volume flow is converted into mass flow using the density of the substances.
  • the data for the cited physical parameters of the various substances are obtainable from the literature and/or from databases concerning the working media analyzed.
  • the enthalpy of vaporization is the amount of heat required to effect the transition of a liquid from the liquid into the gaseous state.
  • the converse process in which the gaseous medium is reliquefied gives off the heat of condensation. Both parameters are of great importance for a thermodynamic cycle in which a liquid is continually evaporated and recondensed.
  • the enthalpy of vaporization may be obtained from the literature or, similarly to the heat capacity, measured by calorimetric methods (for example by DSC).
  • the vapour pressure is one of the most important physical substance properties of a working medium. Designing an ORC system and validating the simulation data require accurate knowledge of the vapour pressure curve. Equipment allowing accurate measurement in an absolute pressure range from 0 bar to 100 bar and at temperatures from 20° C. to 400° C. was constructed for the experimental determination of said curve. Since accurate measuring means for such a large measurement range are not available the equipment was divided into three measurement regions. Table 2 which follows summarizes the permissible operation data for the individual autoclaves.
  • Measurement accuracy was enhanced by using pressure sensors (from Endress & Hauser) calibrated for the relevant pressure and temperature range.
  • the autoclaves were heated using an electric heating collar. Temperature control was effected by measuring the temperature in the individual autoclave and in the heating collar using precise Ni-Cr temperature sensors and comparing these temperatures with one another.
  • the autoclaves were sealed using special copper washers and copper paste.
  • the apparatus and the conduits were fully insulated to reduce heat losses and achieve improved controllability.
  • the integrated vacuum pump makes it possible to obtain measurements under high vacuum.
  • the vacuum is also required in particular when changing the fluids for cleaning purposes and for purging the measuring means with nitrogen for avoiding explosive atmospheres. Readings were acquired using an automatic data acquisition means with a sampling rate of one second for the entire duration of the test.
  • a basic schematic construction of the measuring means is shown in FIG. 3 .
  • the actual suitability as a working medium depends not only on the maximum obtainable efficiency but also to a substantial extent on the long-term stability of the substances when in use. Thermal decomposition of the substances can result in undesired byproducts which can lead, for example, to a reduction in the vapour pressure or to corrosion of the materials employed in the heat engine.
  • the working media were subjected to short-term stress and analyzed in terms of a plurality of criteria. Four substances were selected therefrom for further tests.
  • the second test phase comprised carrying out extensive corrosion and material compatibility tests.
  • the third test phase comprised carrying out long-term tests.
  • the working media were charged into an autoclave at room temperature and inertized with nitrogen.
  • the temperature of the medium was subsequently increased up to a maximum use temperature and sustained for a prolonged period.
  • the vapour pressure of the substance was initially determined at room temperature and compared with literature values. This was followed by continuous determination of the vapour pressure as a function of temperature and long-term measurement at the maximum temperature.
  • the working medium was cooled and analyzed by gas chromatography.
  • the gas chromatograph allows the composition of substance mixtures to be determined. This results in a chromatogram in which all substances are unambiguously assigned. The measurement is performed for an untreated laboratory-tested substance. This makes any decomposition products formed unambiguously determinable. The measurement makes it possible to determine not only the type of byproducts but also the percentage fraction thereof.
  • DSC differential scanning calorimetry
  • DSC comprises heating two sealed crucibles (first crucible containing about 10 mg of sample and second empty crucible as reference) at a predetermined heating rate (10 Kelvin/minute in this case) up to a target temperature (up to 200° C. in this case). Both crucibles are subjected to the same temperature program.
  • the energy absorption or decrease is analyzed during heating.
  • the energy balance changes in comparison to the empty sample depending on the the heat capacity of the sample or exothermic and endothermic processes in the sample such as melt or vaporization.
  • Once heating is complete the sample is held at a constant maximum temperature. For a thermally stable substance no energy changes occur during this time. Decomposition of the substance is observed via a change in the energy absorption or energy decrease.
  • FIG. 4 shows the employed temperature/time profile for the DSC. Over the time period from 0-20 minutes the temperature is increased as a constant heating rate and energy is correspondingly absorbed. In the range between 20-50 minutes the temperature is kept constant. For a stable medium no absorption or emission of energy occurs. Between 50-70 minutes the sample is cooled down again and the temperature is reduced with a corresponding energy decrease.
  • the reproducibility of the measurement was confirmed by carrying out a plurality of cycles per medium. This is because the decomposition products may also arise only after a prolonged operating time and a plurality of cycles.
  • FIG. 5 depicts the investigation of the thermal stability of 1-propanol at 195° C. and 180° C.
  • the measured vapour pressure increases with time at constant temperature (lower curve) at various temperatures between 195° C. and 180° C. This shows that 1-propanol is not stable at these use temperatures. Below 180° C. the vapour pressure becomes too low (less than 20 bar) to be usefully employable as the working medium in a heat engine.
  • methyl formate was stored at a temperature (upper curve) of about 150° C.
  • the vapour pressure (lower curve) remains constant and the fluid may therefore be described as stable at this temperature.
  • the working media methyl formate, ethyl formate and cyclopentene are particularly advantageous on account of these investigations for example.
  • the extended investigations tested the thermal stability of the preselected working media in a longer test of two months in duration.
  • the working media tested were stored in high-pressure autoclaves at an operating temperature of 150° C. After the test the decomposition rate of all samples was investigated by GC analysis to determine thermal stability. The results of this analysis are summarized in table 3. The maximum decomposition of the working media methyl formate, ethyl formate and cyclopentene was about 2% and is therefore in an industrially acceptable range.
  • the following materials were tested in the corrosion tests: unalloyed steel (P265GH) and alloyed steel (1.4571) including a weld seam.
  • the materials were employed in the form of sheet-metal (90 mm ⁇ 10 mm ⁇ 6 mm).
  • the test specimens were weighed in a materials engineering laboratory and characterized by optical microscopy. The test was then carried out in the abovedescribed apparatus for measuring vapour pressure. Once the samples were removed evaluation was once again performed in the materials engineering laboratory. The results of the first corrosion investigation are shown in table 4.
  • FIG. 8 shows the cyclic DSC curves of ethyl formate, with methyl formate and cyclopentene also showing similar curves.
  • the upper curve once again shows the employed temperature profile for the DSC measurement.
  • the lower set of curves represents the results of the DSC measurement. All three working media therefore show sufficient long-term storage.
  • T c critical temperature
  • Such fluids are also usable with a high degree of efficiency at low temperatures of the offgas to be utilized/at a low temperature of the evaporator. It has been found that to simplify the construction of the heat engine the use of a recuperator (heat exchanger) may be eschewed when a “wet” working medium is employed.
  • the working medium is referred to as a “wet” working medium when the gaseous working medium undergoes partial condensation upon adiabatic expansion.
  • the critical temperature (T c ) of methyl formate is 487 K, that of ethyl formate is 508 K and that of cyclopentene is 507 K.
  • the critical pressure p c of methyl formate is 5998 kPa, that of ethyl formate is 4742 kPa and that of cyclopentene is 4820 kPa.
  • the molar mass of methyl formate is 60 g/mol, that of ethyl formate is 68 g/mol and that of cyclopentene is 74 g/mol. All three of these working media undergo partial condensation upon adiabatic expansion and it is therefore possible to eschew a recuperator in the circuit of the ORC.
  • the efficiency of the inventive working media in a heat engine at an offgas temperature (evaporator temperature) between 80° C. and 200° C. is superior to prior art working media for heat engines, for example ethanol.

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DE102013212805.3A DE102013212805A1 (de) 2013-07-01 2013-07-01 Verwendung von hoch effizienten Arbeitsmedien für Wärmekraftmaschinen
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PCT/EP2014/062516 WO2015000678A2 (de) 2013-07-01 2014-06-16 Verwendung von hoch effizienten arbeitsmedien für wärmekraftmaschinen

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Cited By (8)

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US9840473B1 (en) 2016-06-14 2017-12-12 Evonik Degussa Gmbh Method of preparing a high purity imidazolium salt
US9878285B2 (en) 2012-01-23 2018-01-30 Evonik Degussa Gmbh Method and absorption medium for absorbing CO2 from a gas mixture
US10105644B2 (en) 2016-06-14 2018-10-23 Evonik Degussa Gmbh Process and absorbent for dehumidifying moist gas mixtures
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