EP2243934A1 - Thermodynamic multi-phase method for gaining exergy - Google Patents

Abstract

The method involves selectively expanding a working medium at a gravitational field over a geodetic pressure difference, where a part of the working medium is exchanged at a vapor state. Vapor portion is used in a steam power plant to produce mechanical and/or electrical energy. Advanced stroke work at the gravitational field is obtained by a fluid turbine. A feed pump for the steam power plant is saved, and geodetic level difference of the steam power plant is used for pressure increase.

Description

The invention describes a method in which in an evaporator in front of a steam power plant, e.g. a steam turbine, in addition to the steam mechanical or electrical energy is generated. Thereby, the exergy content of a heat-delivering medium, e.g. Thermal water, optimally used.

Steam power plants draw their thermal energy from specially provided, or the plants supplied, energy. For example, they are fed by the energy of a combustion. The heat energy for producing the working medium vapor is usually obtained by cooling a heat transfer medium, e.g. Flue gases or in special cases, thermal water, based. The supply of energy is dimensioned so that a sufficient amount of steam is produced as a working medium at a given temperature and vapor pressure. The height of the temperature are generally set technological limits, but this does not apply to thermal water as a heat carrier, here the steam temperature can be selected thermodynamically meaningful.

Although the working medium can absorb heat at the highest possible temperature, which results in a high degree of thermodynamic efficiency, only a correspondingly small amount of heat energy can then be removed by cooling the heat transfer medium.

The maximum efficiency of a thermodynamic cycle is described by the so-called Carnot efficiency. It depends only on the absolute temperature at which the heat is absorbed, and the absolute temperature at which the heat is released from the cycle again. The part of the heat energy that can be converted into mechanical energy is called exergy.

State of the art and the disadvantages compared to the solution according to the invention

In accordance with the state of the art, a variety of thermodynamic machines and system solutions have been known for over 200 years to extract the exergy, e.g. in the form of propulsion, compressed air or electric power.

By way of example, some methods and their disadvantages compared with the solution according to the invention will be discussed.

In the known steam power plants, a liquid working medium located therein is vaporized at a predetermined pressure in the simplest case by supplying heat energy in steam boilers or suitable evaporator systems. A thermally highly stressed vaporous working medium is generated which is conveyed via the steam engine, e.g. a steam turbine, is relaxed. The steam engine gains the mechanical workability of the steam and decouples it from the process. Subsequently, the condensation of the expanded steam is again to the liquid, which is then fed by means of feed pumps to the pressure level of the steam generator this again. Thus the cycle is closed.

Depending on the type of power plant, various systems are known as suitable evaporator systems. In earlier times, to produce steam at pressure higher than the atmospheric pressure, shell boilers (steamboat, steam locomotive) were used. They were first heated by fire under the boiler, later the firing was carried out by means of smoke or flame pipes.

Today dominate in the Steam generators in power plants Forced-circulation boiler (see eg: W. Beitz, K.-H. Küttner: Dubbel, Springer Verlag, Berlin 1990 ), which are referred to in the subcritical area as Sulzerkessel and in the supercritical range of water as Bensonkessel.

The feed water is conveyed by the feed pump into the boiler and, in succession, the feedwater pre-heater, the evaporator and the superheater are flowed through, e.g. consist of tube bundles.

The oldest type of water tube boiler, developed at the end of the 19th century, is the natural circulation boiler. See, for example: Helmut Effenberger: steam generator. Springer publishing house, ISBN 3-540-64175-0.

This steam generator has certain common construction elements with the method presented here and also with the convection generator, s. in Renewable Energies, August 2008, 18 Volume S. 56-59, "Geothermal Energy: Energy Source with Perspective ".

In the natural circulation boiler, the liquid working medium to be evaporated rises while boiling continuously in boiling and rising pipes. At the top, the vapor is separated from the remaining liquid in the so-called drum. The steam is supplied after passing the superheater of the steam engine and the unevaporated liquid flows through unheated downcomers in the lower part of the natural circulation boiler. The liquid medium in the downpipe has a higher density than the liquid under boiling heat in the boiling riser located liquid-vapor mixture, which under the effect of the gravitational field of the earth, the so-called convective natural circulation in the boiler comes even without an additional pump to conditions.

All of these described steam generators deliver only steam as a working medium for the actual cycle and it is accepted exergy loss, because the amount of heat is not transferred to the temperature of the heat transfer medium, but mainly at significantly lower temperatures to the working fluid. This results in an exergy loss.

The thermodynamic cycle or the heat engine, for example, increases Rankine cycle (see eg: W. Beitz, K.-H. Küttner: Dubbel, Springer Verlag, Berlin 1990 ) In the sub-critical range of the working medium, the vast amount of heat energy through the phase transition at boiling temperature. Therefore, the efficiency of the heat engine is largely determined by the boiling point. This is for example typical of ORC systems (O rganic C R ankine ircle) operating with a low boiling organic working fluid and, for example, be used in the production of electricity from thermal water at Geothermalkraftwerken.

The Rankine cycle is usually used in all modern steam power plants even in the supercritical range of water as a working medium. In the supercritical region analogous to the boiling point there is a clear maximum of the heat capacity at which a predominant part of the heat has to be transferred for heating. As a rule, in the normal power plants, even those in the supercritical region of the working medium, the steam temperature of the working medium is anyway chosen to be lower than the combustion temperature for technological reasons.

The loss of exergy ultimately results because the thermal power plants, e.g. a steam turbine, no multiphase mixtures such as e.g. Tolerated drops in live steam. The droplets do not follow the steam flow sufficiently to the turbine blades, but impinge on the surface, dissipating the kinetic energy of the droplet, i. lost mechanically. In addition, wear can destroy the turbine blades. The same applies to piston engines. For a permanent operation so completely evaporated working fluid must be forwarded to the steam turbine.

General description of the invention

These disadvantages with regard to exergy losses are avoided in the method according to the invention.

The heat energy of the heat transfer medium is transferred to the working medium without phase change. For example, with the help of a countercurrent heat transfer. The working medium is now directed into the lower end of a boiling riser. The pressure in the boiling riser increases due to the hydrostatic or geodetic pressure component of the working medium from the top down. The working medium falls below the boiling pressure and evaporates as you continue to rise, it cools down further and further. The resulting amount of steam ensures the transport of the mixture against gravity upwards. Part of the thermal energy or part of the exergy contained is thus converted into lifting. At the end of the boiling riser pipe, the mixture ideally reached the live steam temperature and pressure for the steam power plant. Now, with the vapor fraction, which is separated from the liquid working medium in a separator, the steam power plant operated.

For example, depending on the steam power plant, the steam fraction passes through the normal Rankine process: it passes through a turbine, possibly a recuperator, is condensed out in the condenser and the heat is condensed at low temperature, for example. delivered to a cooling circuit. Then this part of the liquefied working medium is e.g. brought back to the live steam pressure with the help of a feed pump. Before this liquefied portion is returned to the evaporator circuit, it is expedient to increase its temperature to the level of the liquid fraction in the separator.

The vapor content can therefore be a suitable steam power plant, e.g. be fed to an ORC turbine plant. The evaporator section used here has innovations over the known evaporator systems. Not only live steam for the steam power plant is produced but also mechanical or electrical energy. Because the lifting work, which was done on the working medium, can now be obtained with a liquid turbine, which works on the height of the boiled ear.

The evaporator part is therefore also called evaporator generator. The process described here is called the SCHWARK-BECKER process, abbreviated SBP.

This additional energy comes from the higher exergy content of the heat transfer medium, which primarily has a much higher temperature than the solid boiling point of a feed boiler of a normal steam generator.

In the case of the evaporator generator, the boiling temperature is increasing progressively from top to bottom in the boiling riser. So it corresponds better to the ideal of the highest possible boiling temperature.

In contrast to the boiling riser pipe of the evaporator generator in the SBP, the riser pipes in the natural circulation boiler serve to absorb heat and not to specifically convert thermal energy under relaxation and cooling into lifting work. Accordingly, the boiling riser pipes typically overcome large differences in altitude at the SBP, while the riser pipes in the natural circulation boiler only go through the height of the firing. The natural circulation boiler therefore also eliminates the liquid turbine in the downpipe.

embodiments

At some embodiments and the FIG. 1 the invention will be explained in more detail.

According to the patent claim 1 circulates through the entire system, so both through the evaporator generator and by the steam turbine plant, the same working fluid. In the phase separator (s. FIG. 1 ) there is a splitting of the volume flow in the vaporous and liquid remaining partial flow. The steam flow is used to work through the turbine of the steam power plant or ORC plant (s. FIG. 1 ) and then condensed. This condensed substream is then combined with the liquid remaining partial stream and re-enters the evaporator generator. The whole works as a closed continuous cycle with steam branching loop.

• oben der Phasenseparator,
• daran anschließend in absteigender Richtung das Fallrohr,
• im unteren Bereich die Flüssigkeitsturbine,
• daran anschließend in aufsteigender Richtung das Siedeaufstiegsrohr, welches oben in den Phasenseparator mündet und
• im Flüssigkeitsfallrohr befindet sich an einer anlagentechnisch- und thermodynamisch zweckmäßig gewählten Position der Thermalwasser Wärmetauscher zum Eintragen der Wärmeenergie in das Arbeitsmedium.

The designated as evaporator part of the system has in the vertical direction, the largest geometric extent. The evaporator generator is corresponding FIG. 1 composed of the following basic components:

• above the phase separator,
• then in descending direction the downpipe,
• in the lower area the liquid turbine,
• then in ascending direction the Siedstiegstiegsrohr, which opens up into the phase separator and
• in the liquid downpipe is located at a plant technically and thermodynamically appropriately selected position of the thermal water heat exchanger for entering the heat energy in the working medium.

This suitably selected position is selected for structural reasons, especially for thermodynamic reasons so that the registered heat under the action of the geodetic pressure of the liquid column in the downpipe no longer causes the downwardly flowing medium to boil.

In the lower part of the evaporator generator is the liquid turbine.

The working medium heated on the way down flows through the turbine and then enters the boiling riser. As it flows through the liquid turbine, the working fluid undergoes a pressure drop, which leads to falling below its vapor pressure on entering the boiling riser.

The working medium begins a boiling climb upwards. It now flows a multiphase mixture, consisting of vapor and liquid content upwards. With increasing ascent, the volume fraction of the vapor phase increases. The heat of vaporization comes from the liquid content, which thereby permanently cools on the way up.

Upon reaching the phase separator, the temperature of the vapor-liquid mixture has decreased so much that it corresponds to the live steam temperature for the steam turbine.

In the phase separator, the ascended volumetric flow of the multiphase mixture is split into the vapor and liquid fractions. The former is fed to the steam turbine and the ascending liquid content is immediately returned to the descent process, whereby the circulation process in the evaporator generator is closed again.

The circulation in the evaporator generator is due to the different geodetic pressure, which prevails over the downpipe and the Siedstiegstiegsrohr. Because the boiling and increasingly evaporating phase in the ascent has a lower density than the descending liquid phase, which is why it comes under the action of gravity to the convective self-circulation of the multiphase mixture.

The doing over the vertical extent of lifting work is obtained by the liquid turbine as exergy. It is the Exergieanteil, which lies between the thermal fixed point of the operation of the steam turbine and the inlet temperature of the heat transfer medium in the evaporator generator. This Exergieanteil could indeed not be used by the state of the art steam power plants.

The evaporator generator thus not only produces the live steam for the steam turbine but also additional energy.

The branched off in the phase separator steam flow is sent through the steam turbine, where it undergoes a pressure reduction from the inlet pressure to the vapor pressure of the vapor condensation temperature in the cooler.

The condensed vapor is brought to the pressure level of the inlet pressure with a feed pump, then reheated to the temperature of the working medium in the downcomer, and e.g. injected at the outlet of the phase separator in the descending liquid flow.

This closes the entire cycle including the steam flow loop as SBP.

Special plant and process engineering designs at the SBP can further optimize the process.

If, for example, the evaporator generator is erected not only below the surface level of the earth, but also upwards, then, as stated in claim 3, according to the first exemplary embodiment of the SBP, the feed pump can be saved.

In this case, the vertical course of gravity and gravity riser would be e.g. in the upper part of a tower open into the phase separator. The steam turbine and the steam condenser are also on top. The condensed liquid now flows down. Under the action of the geodesic pressure, the partial stream may be e.g. be preheated to ground level and is fed without feed pump back to the working medium flow.

The working medium stream in the evaporator generator can be added suitable solid or liquid additives. If these additives have a lower specific heat capacity and a higher density than the working medium can be realized with the same performance characteristics of the power plant smaller sizes of the evaporator, or it can be exergeto be used with the same size with an evaporator generator a larger temperature ranges.

Finally, it should be mentioned that for the exergetic exploitation of a large temperature range of the heat transfer medium, for example, from the input temperature value at 150 ° C to 10 K above ambient temperature or and a large volume flow several SBP systems are grouped thermally and fluidically in series and parallel systems.

Claims (5)

Method for obtaining mechanical or electrical energy from the heat of a heat transfer medium,
characterized, - That a working medium is deliberately expanded in the gravitational field on the geodesic pressure difference, wherein a part of the working medium changes to the vapor state, - That the vapor content is used in a steam power plant for the production of mechanical or electrical energy, - That the lifting work performed in the gravitational field is obtained with a liquid turbine. Method according to claim 1,
characterized, - That a change in media of the vapor portion is carried out by the first working medium is condensed out and thus the steam of the second working medium is generated for the steam power plant Method according to claim 1 or 2,
characterized, - That the feed pump for the steam power plant is saved by using the geodetic height difference of the plant to increase pressure. Method according to claims 1 to 3,
characterized, - That the boiling, first working medium additional substances, such as liquids or solid particles are added. Method according to claims 1 to 4,
characterized, - That multi-stage systems are used according to the method described.

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