DE3427219A1 - Supercritical steam engine cycle - Google Patents

Abstract

According to the invention, a supercritical steam engine cycle is proposed for gas turbines and/or reciprocating steam engines, in which a hot or cold gas, which is used as working material, is obtained directly from the liquid phase in the supercritical temperature range and pressure range <IMAGE> and further superheated in the event of a constant supercritical pressure (P0 = constant, P0 > Pk), is fed to a gas turbine, expanded adiabatically or polytropically in the latter up to near the critical point (Tk, Pk) of the working material (Tu > Tk, Pu > Pk), and the further cooling of the gas down to its complete liquefaction is undertaken by means of a heat pump and/or expansion chamber - at or below the critical temperature (T </= Tk), but still above the critical pressure (Pu > Pk). All the heat which can be absorbed from outside by the supercritical steam engine cycle (liquefaction heat, superheating heat and the heat qf + qu + qis = Qzu absorbed via the turbine walls during expansion in the case of operation with cold steam) can be converted into work and be profitably delivered to the outside by the cycle (Wab = Qzu). Application, in particular, for stationary hot steam and/or cold steam plants (steam power stations). Possibilities and advantages in the use of higher-quality energy carriers (fossil and/or nuclear fuels) and of lower-quality energy carriers (inherently thermally balanced water heat and/or air heat) ... Original abstract incomplete.

Description

Supercritical Steam Engine Cycle The invention relates to a steam engine cycle that occurs in the supercritical state range (Po # Pk <Pu To # Tk <Tu) of the working substance is operated, especially for stationary Superheated steam and / or cold steam power plants (steam power plants).

(The following mean: PO = upper pressure, T0 = upper temperature, Pk = crit. Pressure Pu = lower pressure, Tu = lower fl, Tk = critical temp.) The exclusively The steam power cycle process operated in the supercritical state range has the purpose of the waste heat losses that inevitably occur with subcritical steam power operation, which arise on a large scale and mostly have to be discharged unused, yes to avoid completely with their emergence, and thus primary energy on a large scale To save scale. This is especially true for those powered by coal and nuclear energy Thermal power plants, i.e. for those that use superheated steam, e.g. B. water vapor, as a working substance use.

Since the steam power process operated in the supercritical state range Even when using cold steam, it has the desired freedom from waste heat, This means that everything above the critical temperature of the working substance used can also be achieved Use lying heat sources, provided that one only chooses one working material, its critical one Temperature reasonably well below that of the heat source (work source) lies. This means that heat sources can also be used in principle, their temperature are in the range of the ambient temperature, for example thermally balanced Water or air heat reservoirs.

To date, there are no satisfactory ones to meet these requirements Proposals have become known about the waste heat generated in steam power cycle processes to be usefully eliminated or to be avoided completely from the start.

Recently, however, steam power cycle processes have become known, the can work on the environment without waste heat loss and in the subcritical pressure and temperature range are operated. Use such steam power cycle processes the enthalpy of one located between the superheated area and the saturated steam area Heating surface by using heat pumps to remove the condensation heat from the low-temperature lower pressure range is transferred to the high-temperature upper pressure range. However, there is a relatively high heat gradient (between the evaporation and Condensation isotherms) and the drive work for the heat pump very large. As a result of the resulting heat losses in the heat pump the usable heat surface, which comes from the overheating area, remains relative small, so that there is only a relatively small difference work from the two work processes can be used with a relatively low energy density and a relatively large amount of machinery.

To remedy these disadvantages and the greatest possible gain in work To achieve a heat-free steam power process, it is necessary that the Evaporation and condensation isotherms as close as possible, or better still on the same Temperature level. It would also be an additional benefit if neither an evaporation nor a condensation takes place, since both isotherms are on should be the same temperature level.

Such a cycle has the advantage of the same evaporation and Eondensation isotherms, i.e. both evaporation at the same temperature level as well as the condensation takes place, offers an exclusively supercritical state range operated so-called "supercritical steam engine cycle".

However, there is no evaporation or condensation in the edge Meaning instead, but an immediate "gasification" from the liquid phase and a immediate "liquefaction" 1 from the gas phase.

For this purpose, it is known from theory, from specialist books, that with the evaporation of liquids (high or low boiling points) the heat of evaporation (r) against the liquid and superheat share (qf + qü) becomes smaller, the closer one approaches the critical pressure and the critical temperature, to finally in the crit.

Point to disappear completely (rk = 0)). Even at higher pressures (P> Pk at T = Zip Tk) no more heat of evaporation is required and the transition from the area of the liquid to that of the gas takes place very gradually.

On the other hand, it is known that a and further superheated gas (T) Tk) only the same amount of heat is withdrawn again by cooling must be until a complete liquefaction of the gas when reaching the critical Temperature and in the range above the critical pressure occurs before it during the transition from the liquid phase to the gas phase and during the further Overheating.

This process of gas generation, known from theory, is immediate from the liquid phase, without the intermediate phase of evaporation, now also shows the Way of reversing the process, i.e. to return directly from the gas phase to to get the liquid phase, d. H. without committing the intermediate phase of condensation to have to. This would also avoid all of the disadvantages associated with condensation can be.

This is achieved, according to the invention, by using the cycle operates exclusively in the supercritical temperature and pressure range (i.e. the The expansion temperature and the expansion pressure at the outlet of the gas turbine are somewhat higher kept as the critical temperature and the critical pressure of the working substance used).

For this purpose, the liquid used as the working substance (high or low boiling point) in the supercritical state range (PO Pk and To 5 Tk) is transferred from the liquid phase directly into the gas phase via an overpressure valve at the end of a liquid flow heater (with a slight pressure drop), and the gas obtained at a constant level upper pressure (PO) in a further flow heater (gas flow-1) The following table shows the decrease in r with p for water vapor: p / bar 1 10 100 200 221.3 t / ° C 99.6 180 311 366 374.1 r / kJ / kg K 2256.0 2015 1318 589 0.0 heater) overheated to the upper working temperature T0 (To> Tk) and finally expanded adiabatically or polytropically in any subsequent expansion machine - preferably in a gas turbine The residual heat to be dissipated until the critical temperature is reached is achieved either by means of an expansion chamber (with a corresponding pressure and thus temperature reduction) or by means of a heat pump, in that this residual or waste heat is extracted from the gas at a constant lower pressure (Pu ~ constant) and after liquefaction again at high pressure (between feed pump and flow heater or boiler). Since the temperature of the liquefied working material is the same as that on which the residual heat is directly imposed, there is theoretically no temperature gradient to be overcome at the heat pump with which this residual heat must be transferred. In practice, however, a temperature gradient has to be overcome, which must be established with the heat pump and which is required for the two heat transitions on the heat exchanger surfaces (on the condenser and evaporator of the heat pump). Since the coefficient of performance of a heat pump can be made very large with the low temperature differences required in this case (at e.g. dT = 10 OC, according to the exemplary embodiment according to Fig. 13, a coefficient of performance of E75 = T5 / T5 - T7 = 198 / 198-188 = 19, 8 possible), the differential work resulting from the turbine work and the compression work of the heat pump also remains large, ie

the supercritical steam engine circuit operated in this way process works economically: firstly because of the complete conversion of the Cycle process absorbed heat in mechanical work 1) The cooling of the working gas up to close to the critical temperature is here for the most part by decoupling mechanical work achieved by means of the gas turbine.

2) This is necessary because there is a liquefaction of the gas within the turbine must be avoided because of the very disadvantageous for the turbine blades so-called "droplets" r.

and secondly because of the relatively low additional outlay on machinery for the heat pump.

The proposed "supercritical steam engine cycle resembles the 'tClausius-Rankine process' known and proven in steam engine processes. However, it has the great advantage over this that basically no heat (Heat of condensation or other waste heat) must be dissipated to the environment and thus that amount of heat can be saved that is usually unused is discharged to the environment. This, to be dissipated in the form of condensation heat The amount of heat in today's modern steam power plants is around 47% of the total primary heat or (after deducting the boiler and radiation losses of 9 + 2 = 11%) approx. 47/89 = 52.8% of the heat supplied to the cycle (cf. man Fig. 275, Winter, Techn. Heat theory).

The saving in condensation heat (47% here) is the same Scale also linked to a reduction in pollution by pollutants, since one now has to generate the same power plant output power (el. power) according to the example, use 47% less primary energy (coal or nuclear fission materials) must than before.

To assess the quality of a thermal power plant where the Waste heat can be returned to the steam cycle, it is useful to the thermal efficiency on the entire cycle (not just on the expansion machine) to expand, d. H. to take into account all the amounts of energy involved in the conversion process.

It is therefore appropriate for the proposed cycle to have a Thermal efficiency for the ?? cyclic process ?? define.

The quotient is thus to be formed from that from the cycle to the outside dissipated work to the heat supplied from the outside of the cycle, i.e. Wab qtho cycle process Qz -Da in the supercritical steam power process because of the complete Heat recirculation the heat supplied from the outside to the cycle is the same as after corresponds to the mechanical work carried out externally, is in accordance with the Conservation of energy law, the theoretical thermal efficiency for the entire thermal power plant for each one thermodynamic heat gradient on the expansion machine always 100%.

Because the use of water vapor as a working substance when using of high-quality energy sources (coal, Cl) because of the high critical point of the Water (Tk = 374 OG, Pk = 221 bar) the stress on the components (machines, Pipelines etc.) is very large, it is advantageous for high-quality energy sources to use a substance with a correspondingly lower critical point, z. B.

Ethylene, acetylene or ethane, their critical temperatures in the vicinity the temperature level of the environment.

To use low-quality energy sources, for example from Water and / or air heat, on the other hand, must have relatively low critical substances Temperatures, the rel. are far below the ambient temperature level will. The one to absorb environmental heat in the supercritical cold steam engine cycle " The required heat gradient would thus be given from the outset and thus also the "second" Corresponding to the main law of the heat reel? 1e ", since the heat now moves from a higher to a lower temperature level "of its own accord, i.e. without any effort.

Since the proposed supercritical steam power cycle no waste heat even when operated as a "supercritical cold steam engine cycle" Has to give up to the environment but only mechanical work, one comes to the point so far necessary heat dissipation side also with the second law not in trouble, because it is not applicable to mechanical structures! Mechanical work can be done just 1) dissipate to the environment even at cold end expansion temperatures 1) Since none Heat is dissipated but only mechanical work, and this both when feeding is possible with high-temperature as well as with low-temperature heat, you are in both operating cases completely independent of the so-called "lower heating container" the environment ".

The thermal power plant can thus from a single upper heat container operate. This means that the heat transferred to the cycle can be completely converted into mechanical work. This is also the case in both operating cases Condition that the critical temperature is below the temperature of the "upper heat tank ?? respectively the source of work is relocated.

A working material suitable for the use of environmental heat is available, for example. B.

in the refrigerant R14 (CF4), its critical point at Tk = 45.5 ° C, Pk = 37.4 bar. His Siedep. is at 760 Torr (= 1.013 bar) at t5 = -130 00. The properties of CF4 = tetrafluoromethane are: Colorless, odorless, non-toxic and incombustible.

With these specified characteristics of the substance R14, practically at the cold steam gas turbine a differential pressure drop of z. B.P = 100 bar and a thermodynamic heat gradient of around #T = 30 ° C (see example Fig.15), if the working gas is previously brought to the upper superheating temperature To # -10 ° C, e.g. with water heat by 4 ° C (see examples according to Fig. 13 to Fig. 15).

This means that practically all of them can be reasonably well above this crit.

Temperature (Tk45.5 -45.5 ° C) use lying heat reservoirs resp. convert into mechanical work, such as the water heat of the seas, Lakes and rivers. Even in areas with cold air temperatures (t <0 ° C) there is still enough energy below the ice sheet of the water at + 40C win, especially if the latent heat (80 kcal / kg K) of the water is still used becomes even more favorable operating conditions for the supercritical. Cold steam engine cycle would be obtained if methane (CH4) were used as the working substance, since the crit. Temperature is even lower here than with refrigerant R14. This would be a too Allow use of air heat at lower temperatures.

The critical point for methane is Tk = -82.2 OC, Pk = 46.3 bar, the boiling point (1.013 bar) is t5 = -161.7 00.

This would allow a differential pressure gradient across the cold steam gas turbine from Z. B. 2 P = 150 bar and a thermody. Temperature gradient (due to relaxation) of around #T = 65 ° C (Fig. 13 and 14). A use of air heat right down at about -40 ° C would still be possible 1) The obtainable mech. Work arises at 20 ° C water temperature with incl. use of latent heat from 1 m3 to: Wmech./ Qzu / kcal. nth. Cycle 105 kcal. 1 m³ 860 kcal / kWh pr 860 kcal / kWh = 116.3 kWh / m3, or ~ 100 kWh / m3 electrical work.

The main advantages that can be achieved with the invention are: a) Saving of primary energy in thermal power plants (fossil and nuclear power plants) in the order of magnitude of the current condensation heat losses (approx. 47% of the primary energy) and pollutant emissions reduced by the same order of magnitude for the same power plant output power; b) Operation of the thermal power plants independently of any cooling systems (e.g. cooling towers, rivers, lakes etc.), since no heat (condensation or compression heat) must be released into the environment; c) Provision of a new, regenerative one Energy source from environmental heat, especially with balanced water or air heat, by building supercritical cold steam power plants with completely environmentally friendly Operating mode; d) Generation of electricity and hydrogen with that according to c) sufficient mechanical work that can be generated with continuous - and thus more economical - Utilization of the cold steam power plants, and thus a complete solution for today's Energy problem ?? without environmental pollution ?? through the construction of many supercritical cold steam power plants.

Three embodiments of the invention are shown in the drawings and are described in more detail below. Fig. 1 shows the circuit diagram of the supercritical Steam engine cycle with predominantly adiabatic relaxation via a Gas turbine; Fig.1.1 a partial drawing for Fig. 1 (use of an expansion chamber instead of a heat pump); Fig. 2 the temperature-entropy diagram belonging to Fig. 1 (T, s diagram); Fig.2.1 a partial drawing for Fig. 2 (indication of the temperature profile the residual heat when using an expansion chamber according to Fig.1.1); Fig. 3 that too Fig. 1 corresponding pressure-volume diagram (P, v-Diagr.); Fig. 4 that of Figs. 1 and 2 corresponding energy flow diagram; Fig. 5 the same as Fig. 1, but with predominantly isothermal expansion via a gas turbine (application esp Use of low-temperature heat and use of cold steam as a working substance; Fig. 6 the T, s diagram belonging to Fig. 5; Fig. 7 the P, v diagram belonging to Fig. 5; FIG. 8 shows the energy flow diagram associated with FIG. 5; Fig. 9 the same as Fig. 1, but with reheating (with the use of a high and low pressure gas turbine); Fig.10 the T, s diagram belonging to Fig. 9; Fig.11 the P, v diagram belonging to Fig. 9; Fig.12 the energy flow diagram belonging to Fig. 9; Fig.13 the same as Fig.10, but with information on status values when using cold steam (methane = CH4) as Working substance; Fig.14 the same as Fig.11, but with information on condition values at Use of cold steam methane (CH4) as a working substance; Fig.15 the same as Fig.3, but with information on condition values when using cold steam R14 (CF4); Fig.16 Construction (sectional view) of a possible "supercritical cold steam power plant" when using sea, lake or river water.

The supercritical steam power cycle according to Fig. 1, 1.1, 5 and 9 consists of the following, fundamentally required system parts: a heat sensor (Instantaneous liquid heater) for feeding in the residual heat q2 by means of the heat pump from the low-pressure to the high-pressure part of the cycle; b heat absorber (instantaneous liquid heater) to absorb the liquid heat supplied from the outside qf; c pressure relief valve for Setting the upper critical pressure P0 '; d heat absorber (gas water heater) to absorb the externally supplied overheating qü; e Expansion machine (in the version according to Fig. 9: high pressure gas turbine) f reheater (Gas water heater), only with version Fig.9; g low-pressure gas turbine (only with version Fig.9); h Condenser (condensation through residual heat extraction q1 at constant lower pressure Pu. In the design according to Fig.1.1, this is an expansion chamber in which the temperature decrease is generated by lowering the pressure. The lower pressure Pu must remain greater than the critical pressure Pk so that no evaporation ' of the substance can occur); h1 Waste heat emitter in version Fig.5 (with predominantly isothermal expansion); h2 condenser (for residual heat dissipation q1 for version Fig.5); i Feed liquid pump (return of the liquid with simultaneous production the upper critical pressure P '); 0 k Compressor of the heat pump 1 condenser the heat pump m control valve of the heat pump and n evaporator of the heat pump; z Insulated container (shown in Fig. 9, it serves to prevent unintentional heat absorption from the environment with cold steam operation).

To put the thermal power plant into operation as shown in Fig. 1.5 or 9, must you first the full amount of energy in the form of mech. Work and warmth from fed externally, d. H. the heat engine must be "started up".

After the necessary condensing temperatures by means of the heat pump (or the critical temperature generated by expansion by means of the expansion chamber according to Fig.1.1) are reached, the system can operate independently. The one with it the individual labor and heat amounts involved in the energy conversion process entered in the energy flow diagram (Figs. 4, 8 and 12). The individual amounts of energy were taken from the T, s and P, v diagrams (Figures 2, 3, 6, 7, 10, and 11).

The exemplary embodiments for possible supercritical cold steam power processes according to Fig. 13, 14 and 15, the general gas equation (V1P1 / Tl = V2P2 / T2) calculated.

Further details can be found in the drawings and diagrams are and are sufficiently understandable for a person skilled in the art, so that a further Description unnecessary.

As we have seen, it can only be used in the supercritical State-operated steam engine cycle from almost all in nature feed occurring heat sources, provided that only the crit.

Temperatures of the working materials are chosen so that they are appropriate far below that of the heat source. It does not matter whether the warmth is available at high or low temperature, d. H. whether she is from a highly exergetic or low-exergetic heat source is provided. So you can use the energy also come from the ambient heat at low and thermally balanced temperatures, like energy from fossil or nuclear fuels at high temperatures. There In the present supercritical steam power process, no heat is dissipated to the environment has to be, but only mechanical work, it also needs for its operation only a single, so-called "upper heating container". Since the energy is only in Form of mech. Work carried away from the plant to the environment is the law of entropy (2.HS) for the so-called "lower heat container of the environment? Not applicable. The entropy law of course still applies to all thermal power cycle processes, which have to give off their waste heat to the environment.

For the functional operation of the im exclusively supercritical Area operated circular process can be summarized three essential conditions point out: 1. The critical temperature of the working material must be reasonably high lie below the temperature of the heat source (source of work); 2. The working substance must return to the cycle after the cycle has ended without releasing heat to the environment be entered; 3. The working gas must be completely liquefied after expansion is complete be, d. H. occupy its smallest possible volume (so that it is with the smallest possible Workload can be re-entered into the cycle process).

Claims (3)

Claims Supercritical steam engine cycle, in particular for stationary superheated steam and cold steam power plants (steam power plants), characterized in that that a material that serves as a working substance, in an over-critical state, immediately results Working gas transferred to the liquid phase and further superheated at constant pressure for the most part through adiabatic or polytropic expansion within an expansion machine ~ - preferably in a gas turbine - cools, and the further cooling outside the expansion machine by means of a heat pump or expansion chamber to the critical point Temperature (but still above the critical pressure, lower final expansion pressure) made and brought to the liquefaction. 2. Supercritical steam engine cycle according to claim 1, characterized in that the liquid used as the working substance (high or low boiling) in the supercritical state range (PO Pk, T Tk) in a liquid water heater Heated to above the critical temperature via an adjustable pressure relief valve immediately gasified with a slight pressure drop, the gas obtained in another Instantaneous water heater (gas instantaneous water heater) at constant pressure = constant) the final temperature (To> overheated and in the downstream gas turbine is expanded. 3. Supercritical steam engine cycle according to claim 1 and 2, characterized in that at least one, but preferably two, reheating are provided, and at the outlet of the gas turbine between the expansion temperature and the residual or waste heat generated by the heat pump at the critical temperature from the low-pressure to the high-pressure area of the liquefied working medium with each other approximately the same temperatures is transmitted (In Fig. 1 and 2 is T4-T5 and