EP0000135A1 - Plant for the centralised generation of thermal energy - Google Patents

Abstract

An installation for the central production of useful thermal energy for the remote supply of loads (10) has a turbine (16), after which one or more heat exchangers (22, 23) are connected. In these heat exchangers (22, 23), the heat transfer medium used for the remote supply is heated. In order to be able to use the mechanical energy of the turbine (16) for heating the heat transfer medium also, the turbine (16) drives a heat pump (8) which draws heat from the environment, raises it to a higher temperature level and imparts it to the heat transfer medium as useful heat. As a result, the consumption of primary energy is lower than in the case of direct heating of the heat transfer medium by primary energy alone. <IMAGE>

Description

The invention relates to a system for the central generation of thermal energy for the remote supply of consumers with at least one turbine, in particular a back pressure steam turbine, which is followed by at least one heat exchanger for delivering useful heat to at least one heat transfer medium.

In known plants of this type, which are designed as district heating plants with gas or steam turbines, the generation of thermal and mechanical useful energy is coupled, which means that this required effort of primary energy is less than with a separate generation of these types of energy. The mechanical useful energy is converted into electrical energy and supplied to consumers by generators which are connected to the turbine. This advantage of generating useful energy with a reduced expenditure of primary energy is offset by some disadvantages.

If such systems primarily serve to generate useful heat and the electrical energy generated is fed into public power supply networks, in many cases it is not possible to achieve a cost-covering price for this electrical energy, so that the overall economic viability of such a system is questioned.

Finally, in order to counter malfunctions, reserve units for the power supply have to be provided, which further reduces the economy.

On the other hand, if you equip power plants that are intended for the generation of electrical energy and are usually located far away from residential areas with additional devices for the production of heating energy, this heating energy must be conducted over long distances to the individual consumers, which means mainly at low loads and Capacity considerable - costs arise. In addition, a reduction in power generation is to be expected for a given output size of the heat source of the power plant, so that additional expenses for the procurement of backup power are necessary, which influence the economy.

The main reason for the disadvantages of the well-known Hei.z power plants is, however, that the daily and seasonal fluctuating demand for electrical and thermal useful energy does not cover each other.

The invention is based on the object of specifying a system for the central generation of useful thermal energy of the type mentioned, in particular a system for the remote supply of consumers, which has at least largely the thermodynamic advantages of the coupled generation of mechanical and thermal useful energy with simultaneous independence from the generation of electrical energy. In addition, the structure of the system should be simple and fully meet the operational requirements.

The solution to this problem in "a system of the type mentioned in the present invention is that the turbine is designed to drive the compressor of a heat pump that raises the ambient heat to a higher temperature level and emits useful heat to the heat transfer medium.

The heat energy obtained from fossil and / or nuclear fuels and transferred to a working medium such as steam or propellant gas is converted into mechanical drive energy in the steam or gas turbine and used to drive the heat pump, whereby the ambient heat raised by the heat pump to a higher temperature level, and at least the waste heat of the turbine, is given off as useful heat to the heat transfer medium. Dynamic advantages of cogeneration of thermal and mechanical usable maintained, at the same time, however, connected to a power generation disadvantages, such as high equipment and operation costs as well as the problems of the current sale of the known plants omitted according to the prior art _- thereby the thermoelectric are.

Since a considerable part of the primary energy consumed is used to cover thermal useful energy, the system according to the invention gains importance because of its economy and its simple structure with regard to efforts to save energy and substitute high-quality fossil fuels.

A system according to the invention can of course also have several, possibly multi-stage compressors, and several heat pumps can also be provided.

One of the known systems with a compressor can serve as the heat pump, but it is particularly advantageous if the heat pump has an expansion turbine which is coupled to the compressor designed as a turbocompressor and which via at least one heat exchanger which emits the compression heat to the heat transfer medium to the pressure side of the compressor connected. By relaxing the ver sealed working medium in the expansion turbine and by using the mechanical energy obtained in this way to drive the compressor, the drive energy to be supplied by the turbine is reduced. As a result, the turbine can be designed with lower power, ie cheaper.

According to a further development of the invention, the heat pump can have a closed circuit for the working medium with at least one second heat exchanger, which is connected into the circuit between the expansion turbine and the compressor, for the supply of ambient heat. A steam can be used as the working medium, e.g. Refrigerant and gas such as Serve carbonic acid or air.

If the ambient heat is extracted from a coolant, the system can also be used to generate useful cooling.

A particularly recommendable further development can consist in the heat pump having an open circuit for the working medium, the compressor being used to draw in ambient air. is formed and the air outlet of the expansion turbine opens into the environment. Since the ambient heat is fed into the system with the ambient air drawn in, no heat exchanger is required for the supply of ambient heat and the construction effort is reduced.

The main advantage of the aforementioned design of the heat pump is, however, that high heat carrier temperatures in the range around 100 ° C can be reached with a good performance figure and the performance figure deteriorates only slightly with falling temperature of the ambient heat.

At least one third heat exchanger through which a coolant can flow can also advantageously be connected to the air outlet of the expansion turbine. As a result, the system can be used in a simple manner to generate useful cold and / or useful heat.

• Fig. 1 eine Anlage zur Erzeugung von Nutzwärme mit einem Dampferzeuger und einer Gegendruckdampfturbine und einer Wärmepumpe mit geschlossenem Kreislauf,
• Fig. 2 den Gegenstand der Fig. 1 mit einer Wärmepumpe mit offenem Kreislauf und
• . Fig. 3 eine Ausführungsvariante des Gegenstandes der Fig. 2 mit einer Gas-Turbine.

Further advantages and recommended features of the invention emerge from the following description of exemplary embodiments in conjunction with the schematic figures. Here show:

• 1 is a system for generating useful heat with a steam generator and a back pressure steam turbine and a heat pump with a closed circuit,
• Fig. 2 shows the subject of Fig. 1 with a heat pump with an open circuit and
• . Fig. 3 shows a variant of the subject of Fig. 2 with a gas turbine.

In the drawings, the same parts are given the same reference numerals.

According to the embodiment of FIG. 1, the working medium of the heat pump 8 is supplied to the compressor 2 via an intake line 1. In this compressor, which is designed as a turbocompressor, the gaseous working medium is increased pressure specified by the design of the system is compressed, whereby the working medium heats up. This is then fed to the first heat exchanger 4 via a line 3. The heat exchange between the working medium and the colder heat carrier introduced into the first heat exchanger 4 via the line 5 takes place via heat exchange surfaces. In the present exemplary embodiments, heating water is provided as the heat transfer medium, which is supplied to the heat consumer (s) 10 via the heating water supply line 9 at a predetermined flow temperature. The cooled heating water is fed via line 11 and pump 12 into the heating water return line 13. A predetermined portion of the returning heating water can be regulated via a valve 14 or a regulating element and can be supplied to the first heat exchanger 4 via the line 5.

The working medium cooled in the first heat exchanger 4 is fed to the expansion turbine 7 via the line 6. Here it expands and cools down through the expansion process. The cooled and relaxed working medium is introduced via line 40 into the second heat exchanger 41. Here, the working medium is supplied with ambient heat, for example through ambient air, which is supplied to the second heat exchanger 41 via a line 50. The ambient air is conveyed by a fan, not shown. However, it is cheaper to extract the ambient heat from a supplied coolant such as water, brine or refrigerant and to use the cooled coolant, for example for the Air conditioning or commercial purposes. Finally, the working medium loaded with ambient heat is discharged through the suction line 1, so that the circuit of the heat pump 8 is closed.

The expansion of air in the relaxation. Turbine 7 released mechanical energy is used to drive the compressor 2. For this reason, the shafts of the compressor and expansion turbine are mechanically connected to one another via a common shaft piece 1.5.

The power requirement for driving the compressor 2 is greater than the power released by the expansion of the air in the expansion turbine 7. The still missing drive power for the compressor 2 is applied by the turbine 16, which in the exemplary embodiment according to FIG. 1 is designed as a tap-back pressure steam turbine. The turbine 16 is mechanically connected to the compressor 2 via a shaft section 17. Deviating from these representations, the turbine 16 could, however, also be equipped with its own generator for generating electricity and the machine group consisting of the compressor 2 and the expansion turbine 7 could be driven by an electric motor which is fed by the generator.

The working steam of the turbine 16 is obtained in a steam generator 18 by using fossil or nuclear fuel. The steam generator 18 is equipped with an overheating device 19 for overheating the working steam. The working steam is supplied to the turbine 16 via the live steam line 20 and the turbine inlet valve 21.

The turbine 16 supplies the heat exchangers 22 and 23 with the required exhaust steam and / or tapped steam for heating a partial heat flow, which is removed from the heating water return line 13 and via the shut-off and control element 24 and the line 25 to the heat exchangers 22 and 23 is supplied. The heating steam pressures at the steam extraction points 26, 27 of the turbine are chosen so that approximately the same heating margins of the heat transfer medium occur in the heat exchangers 22 and 23 and the required flow temperature is reached. The heated partial flow of the heat transfer medium is then introduced into the common heating water supply line 9.

The extraction points 26 and 27 provided on the turbine 16 for the exhaust steam or bleed steam are connected to the heat exchangers 22 and 23 via lines 29 and 30. The steam condensate from the heat exchanger 23 is introduced via line 31 into the steam space of the heat exchanger 22 which is at a lower vapor pressure and together with the condensate of the heat exchanger 22 via line 32, the condensate pump 33 and the line 34 into the degassing mixer preheater 35 headed. This is via a heating steam line 36 from a suitable heating steam extraction point, e.g. Tapping point 27, supplied with heating steam.

Another tapping point 28 is provided for supplying heating steam to a surface feed water preheater 37. Analogously, several feed water heaters connected in series on the feed water side can also be used. Instead of the shown two-stage heating water heating can also be selected one-stage or heating water heating with still further stages. Contrary to the illustration, the working steam of the turbine can be reheated after part expansion, or the working steam can be completely overheated. The details of the circuit in the steam section of the proposed system can be modified according to the respective requirements.

In the present exemplary embodiment, the feed pump 38 conveys the feed water via the feed water preheater 37 and the line 39 into the steam generator 18, whereby the water-steam cycle of the system is closed.

The arrangement of the turbine 16, the compressor 2 and the expansion turbine 7 on a common shaft 15 and 17 which is in power equilibrium offers the possibility of low-loss speed control of this machine group.

As can be seen from the above, a partial stream of the heat transfer medium is taken from the heating water return line 13 during operation of the system, heated in the heat exchangers 22 and 23 and 4 and fed to the heating water supply line 9. The heat required for the heating is taken from the exhaust steam and / or bleed steam from the turbine 16 and the heat pump 8. Since the heat pump 8 is essentially driven by the turbine 16, it is thus possible with the present system to take advantage of the thermodynamic advantages of the coupled energy generation for the sole generation of thermal useful energy.

FIG. 2 shows an embodiment variant of the system according to FIG. 1. The difference between the two systems is that the system according to FIG. 2 has an open circuit heat pump for the working medium. For this purpose, the intake line 1 opens into the environment, and the compressor 1 thus draws in ambient air with ambient pressure and temperature. Accordingly, the line 40, which is connected to the air outlet of the expansion turbine 7, opens into the environment.
A third heat exchanger 44, through which a coolant flows, is switched on in line 40. The heated coolant coming from the cold consumers, for example air conditioning systems, enters the third heat exchanger 44 via the line 42, is cooled here with the release of ambient heat and flows to the cold consumers via the line 45. A pump 43 maintains the circulation. The fluids already mentioned can be used as the coolant.

FIG. 3 finally shows an embodiment variant of the plant according to FIG. 2, the plant according to FIG. 3 having a gas turbine for generating the mechanical energy.

Accordingly, a gas turbine is used as the turbine 16, which is supplied with propellant gas as working medium via a line 46, which is generated in a combustion chamber 47.

The air required for the combustion of the fuel, such as gas or oil, is compressed together with the secondary air required to maintain the specified design temperature of the working gas in a turbocompressor 48 and is fed to the combustion chamber 47 together with the fuel. The turbocompressor 48 is coupled to the turbine 16 for driving, so that the compressor 2, expansion turbine 7, turbine 16 and turbocompressor 48 are connected to one another on the drive side.

After exiting the turbine 16, the expanded propellant gas is supplied to the heat exchanger 49 which, like the heat exchangers 22, 23 in the exemplary embodiment according to FIG. 1 or 2, is acted upon by the heat transfer medium.

The main advantage of the systems according to the invention is, above all, the reduction in the use of primary energy in the supply of useful heat compared to known heating plants or compared to individual furnaces and in avoiding the disadvantages of known heating plants.

The advantage of the lower use of primary energy compared to known heating plants or individual firing systems is to be demonstrated on the basis of the exemplary embodiment according to FIG. 2 by drawing up the external heat balance:

• Hierin ist Q_H(WP) [KJ/S] ; die im ersten Wärmetauscher 4 nutzbar an das Heizwasser übertragene Wärme
• Q_WP [KW] ; die Leistungsaufnahme der Wärmepumpe

For the machine group acting as a heat pump with compressor 2 and expansion turbine 7, the performance figure applies:

• Herein is Q _{H (WP)} [KJ / S]; the heat transferred in the first heat exchanger 4 usable to the heating water
• Q _WP [KW]; the power consumption of the heat pump

• Hierin bedeuten Q_H(DT) [KJ/S] ; die in den dampfbeheizten Wärmetauschern 22 und 23 nutzbar an das Heizwasser übertragene Wärme
• P_DT [KW] ; die Leistungsabgabe der Dampfturbine

The performance index of the steam turbine 16 is:

• Here, Q means _{H (DT)} [KJ / S]; the heat transferred to the heating water in the steam-heated heat exchangers 22 and 23
• P _DT [KW]; the power output of the steam turbine

The required fuel heat that is to be supplied to the steam generator 18 is calculated from:

• Here is Q _BR [KJ / S]; the fuel heat to be supplied to the steam generator
• η _DE [-]; the efficiency of the steam generator

• Leistungsabgabe der Dampf-Turbine = Leistungsaufnahme der Wärmepumpe
  
• gesamte Heizleistung Q_H = im ersten Wärmetauscher 4 nutzbar an das Heizwasser übertragene Wärme plus in den Wärmetauschern 22 und 23 nutzbar an das Heizwasser übertragene Wärme

bzw.

If minor other external losses are neglected:

• Power output of the steam turbine = power consumption of the heat pump
  
• Total heating power Q _H = heat transferred to the heating water in the first heat exchanger 4, plus heat transferred to the heating water in the heat exchangers 22 and 23

or.

als dimensionslose Kenngröße ein, so ergibt sich mit den vorher definierten Größen für das Ausführungs_- beispiel gemäß Fig. 1 die'Beziehung:

If one leads the fuel utilization factor

as a nondimensional parameter, we obtain with the previously-defined sizes for the execution _- for example according to Fig 1 die'Beziehung.

Hierin bedeuten

• η_HW [-] ; der Wirkungsgrad der Wärmeübertragung vom Brennstoff an das Heizwasser, z.B. in einem Heißwasser-Kessel

For a heating plant according to the prior art, the fuel utilization factor is appropriate

Mean here

• η _HW [-]; the efficiency of heat transfer from the fuel to the heating water, e.g. in a hot water boiler

The ratio of the fuel utilization factors is a measure of the possible reduction in the primary energy use of a system according to the invention compared to a heating supply with known heating plants.

und setzt man in.obige Beziehung realisierbare Werte, z.B.

ein, so ergibt sich der Zahlenwert für dieses Beispiel mit

If you put simplifying '

and if one sets realizable values in the above relationship, e.g.

, the numerical value for this example is given with

This means that the expenditure of primary energy in a system according to the invention is considerably less than in known heating plants.

gerechnet werden.In the case of individual firing, the average efficiency of the heat transfer to the heating water can be approximately at best

can be expected.

so ist das Verhältnis der Brennstoffausnutzungsfaktoren einer Anlage nach der Erfindung gegenüber der Heizwärmeversorgung mit Einzelfeuerung:

oder mit den entsprechenden Zahlenwerten:

Assume a steam generator efficiency of

the ratio of the fuel utilization factors of a system according to the invention to the heating supply with individual firing is as follows:

or with the corresponding numerical values:

This provides quantitative evidence of the possible fuel savings of the systems according to the invention compared to competing known methods of heating supply.

In addition, there are other advantages of using the cold side of the heat pump for cooling purposes.

Claims (7)

1. Plant for the central generation of useful thermal energy for the remote supply of consumers with at least one turbine (16), in particular a back pressure steam turbine, which is followed by at least one heat exchanger (22, 23, 49) for delivering useful heat to at least one heat transfer medium, characterized that the turbine (16) is designed to drive the compressor (2) at least one heat pump (8) which raises the ambient heat to a higher temperature level and emits useful heat to the heat transfer medium, 2. Plant according to claim 1, characterized in that the heat pump (8) has an expansion turbine (7) which is coupled to the compressor designed as a turbocompressor (2) and which via at least one of the heat of compression emitting to the heat transfer medium first heat exchanger (4th ) is connected to the pressure side of the compressor (2). 3. Plant according to claim 2, characterized in that the heat pump (8) has a closed circuit for the working medium with at least one between the expansion turbine (7) and compressor (2) in the circuit switched on second heat exchanger (41) for the supply of Ambient heat. (Fig.1) 4. Plant according to claim 3, characterized in that the second heat exchanger (41) for the supply of ambient heat can be flowed through by a refrigerant. 5. Plant according to claim 2, characterized in that the heat pump (8) has an open circuit for the working medium, the compressor (2) is designed for the suction of ambient air and the air outlet of the expansion turbine (7) opens into the environment. (Fig. 2) 6. Plant according to claim 5, characterized in that at least one third heat exchanger through which a coolant can flow is connected to the air outlet of the expansion turbine (7). 7. Plant according to one of claims 1 to 6, characterized in that the speed of the turbine (16) is adjustable.

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