EP2518423A2 - Method for heating heat transfer media and supercritical heat pump - Google Patents

Abstract

The method involves setting inlet temperature greater than 70[deg] C and outlet temperature greater than 120[deg] C by a joule process. The pressure in the low pressure side is adjusted to the value equal to or twice the value of the critical pressure of the used working material. The pressure value in the low pressure side is set in range of 74-110 bar. An independent claim is included for supercritical heat pump.

Description

The invention relates to a method for heating heat transfer media, for. As of water in a heating circuit, from inlet temperatures greater than 40 ° C to outlet temperatures greater than 80 ° C by means of a Jouleprozesses with internal recuperation. The working according to the method heat pump preferably uses a natural agent such. As carbon dioxide, and makes it possible to generate heating and process heat, the temperature on a z. B. suitable for district heating networks high level, with performance figures of at least 3 can be achieved.

Supercritical heat pumps are known as so-called. Cold gas engines. They work according to the Jouleprozess with internal recuperation. They are mainly used in the low temperature range (below -70 ° C). Supercritical heat pumps for the normal temperature range (25 to 80 ° C) are considered by experts to be ineffective compared to subcritical heat pumps, which work subcritically with evaporating and condensing agents (cold vapor process) (see Heat pump application in industry, agriculture, corporate and residential construction, Ed. Heinrich et al., VEB Verlag Technik, 1982, p. 41 to 44 ).

The only exception is air-conditioning cabin air conditioning cabinets, which are operated with compressed air from the engine compressor. By using the cold air air conditioning units, the system weight can be sustainably reduced compared to conventional air conditioning units; the comparatively poor efficiency is accepted. For supercritical heat pumps for higher outlet temperatures (80 ° C and higher), no solutions are known from the prior art so far.

Out DE 10 2006 007 119 A1 is a trans-critical CO ₂ heat pump is known, with a heat transfer medium from a low inlet temperature (10 ° C to 40 ° C) to a high outlet temperature (from 60 ° C to well above 100 ° C) is heated. Since the carbon dioxide on the high-pressure side is supercritical in this heat pump, the temperature profile of the carbon dioxide adapts to the temperature profile of the heat transfer medium (Temperaturglide), whereby high performance figures are possible. By arranging a plurality of gas coolers connected in series on the gas side, all of which operate at the same high pressure level, different useful temperature levels are realized.

With such heat pumps can, in comparison to the conventional, subcritical heat pumps with constant condensation temperature, significantly higher power ratios, d. H. Higher ratios of benefit (heating) to effort (drive energy) can be achieved.

However, the efficiency of these heat pumps decreases sharply with increasing inlet temperature of the heat transfer medium, so that their use at inlet temperatures greater than 50 ° C, as they are commonly found today in many heating networks, district heating networks and process heat consumers, no longer makes sense.

In DE 10 2010 004 187 Therefore, a transcritical CO ₂ heat pump with a two-stage compression and a heat extraction at different high pressure levels is proposed, with which even at inlet temperatures of 50 to 60 ° C, a sufficient efficiency is achieved. In district heating networks, however, inlet temperatures of 70 ° C and higher often occur; There, too, this process is not effective.

The invention has for its object to find a method and a working heat pump according to the method, with which heat transfer media with inlet temperatures of greater than 40 ° C can be heated to outlet temperatures of greater than 80 ° C and higher. It should be achievable performance figures of at least three.

The object of the invention is achieved by the characterizing features of claims 1 and 4. Further advantageous embodiments and uses of the invention will become apparent from the claims 2 and 3 and 5 to 11.

According to the invention, in the process by means of a Joule process with internal recuperation (use of an internal heat exchanger), a heat transfer medium, the inlet temperature of at least 40 ° C has heated to an outlet temperature of at least 80 ° C, wherein on the low pressure side of the pressure is controlled to a value which corresponds to at least the value of the critical pressure and at most twice the value of the critical pressure of the working substance used ,

As working substances natural agents such. As carbon dioxide, ammonia or propene can be used. Likewise suitable are synthetic agents.

The method is particularly suitable for use in heating networks, district heating networks and process heat consumers, in which water (or water vapor) is used as a heat transfer medium.

It has surprisingly been found that the effectiveness (coefficient of performance) of Joule processes (with internal recuperation) at inlet temperatures of at least 40 ° C. and outlet temperatures both compared to conventional subcritical processes with constant condensation temperature and to trans-critical processes operating with one or more pressure levels in the gas coolers can be sustainably improved by at least 80 ° C, if on the low pressure side, a pressure is set, which is slightly above the critical pressure of the material used.

The principle of keeping the lower pressure level slightly above the critical pressure in order to obtain a particularly effective, supercritical process can also be used for the right-handed force process according to the Joule principle.

A Jouleprozess proved particularly efficient, which operates with carbon dioxide as working means and in which the low-pressure side is regulated to a pressure, the value of the 1,0 to 1,5 times (73,8 to 110,7 bar, rounded 74 to 110 bar) corresponds to the critical pressure of carbon dioxide. On the high pressure side set 140 to 160 bar.

The operating according to the inventive method, supercritical heat pump (cold gas engine) includes a gas heater, a gas cooler, at least one Compressor, a relaxation device, (at least) a motor that allows the required for the operation of the heat pump energy input, a recuperator, which is used for internal heat transfer from the high pressure side to the low pressure side, and a controller. During operation of the heat pump, the controller sets the pressure on the low-pressure side to a value that corresponds at least to the simple and at most twice the critical pressure of the working fluid used.

To increase the coefficient of performance of the supercritical heat pump, the expansion device is usually designed as a relaxation machine, by means of which the relaxation work formed during the Joule process is converted into mechanical energy and supplied to the engine or at least one compressor.

In a preferred embodiment, the expansion machine with generator is mechanically separated from the engine of the compressor.

In a further preferred embodiment, the engine has two diametrically extending force transmission axes. The motor used is usually an electric motor, to whose armature the two diametrically extending power transmission axles are attached. The first power transmission axle acts as a drive axle and is connected to the compressor while the second power transmission axle is connected to the expansion machine so that the work done by the expansion machine is supplied to the engine.

In a heat pump (cold gas machine), the mechanical energy to be provided by the compressor is greater than the work of expansion formed in the Joule process. The difference between the power consumed by the compressor and the power delivered by the decompression machine, d. H. the residual power required for the operation of the compressor is provided by the engine.

In an alternative embodiment, a first compressor, which is driven exclusively by the expansion machine, is used as the first compressor stage. The first compressor stage is followed by a second compressor stage (cascade), which consists of a compressor driven exclusively by the engine.

Single-stage turbomachines are preferably used as compressors since they are of compact construction and their paddle wheel can be mounted directly on the end of the first power transmission shaft of the engine (a compressor stage) or on the end of a shaft driven by the expansion machine (two compressor stages). Thus, the relaxation work recovered in the Joule process can be transferred to the compressor virtually without mechanical losses. The use of other compressors is also possible in principle.

The expansion machine may also be a single-stage turbomachine, e.g. drives a generator.

The supercritical heat pump can indeed be set up without a relaxation machine. The associated disadvantages, namely comparatively lower performance figures, however, outweigh the advantages achieved (simplification of the structure of the heat pump).

Furthermore, the invention can be advantageously used in a heat-cooling coupling by cooling power is taken from the Joule process not only on the gas cooler heat output but also via the gas heater on direct or indirect (via a DC link).

The supercritical heat pump can also be advantageous for direct or (via a DC link) indirect heating of gases as a heat transfer medium, eg. B. for heating air for drying processes or in preheaters used.

Since the Jouleprozess can also be readily operated right-handed, the inventive method can also be used to generate mechanical work from waste heat, solar and geothermal heat, combustion heat or heat from material conversion processes.

Fig. 1:

Schaltbild einer überkritischen CO₂-Wärmepumpe,

Fig.2:

Temperatur-Entropie-Schaubild des in der Wärmepumpe ablaufenden Jouleprozesses.

The invention will be explained in more detail with reference to two embodiments; show:

Fig. 1:

Circuit diagram of a supercritical CO ₂ heat pump,

Figure 2:

Temperature-entropy diagram of the Joule process taking place in the heat pump.

The supercritical CO ₂ heat pump ( Fig. 1 ), like all the heat pumps operating according to the Joule process, has the compressor 1, the gas cooler 2, the gas heater 3, the expansion machine 4 and the motor 5, via which the mechanical energy required for the Joule process (heat pump: left process) is introduced. In order to achieve high performance figures at outlet temperatures of greater than 80 ° C and inlet temperatures of greater than 40 ° C, the supercritical heat pump is also equipped with a recuperator 6, which serves to heat the exiting from the gas heater carbon dioxide from the gas cooler exiting carbon dioxide.

As from the temperature-entropy diagram (Ts-diagram; Fig. 2 ), the compressor 1 driven by the engine via the power transmission axle 7 draws in carbon dioxide at the first state point A (pressure: 80 bar and temperature: 79.5 ° C.) and reaches the second state point B (150 bar and 145 ° C). With unchanged pressure / temperature, the carbon dioxide passes into the gas cooler 2 and is cooled there by countercurrently guided water 8 (= heat transfer medium) to 80.9 ° C. The water 7 enters the gas cooler 2 at 70 ° C. and out of it at 120 ° C. (third state point C).

In order to achieve the highest possible temperature of the carbon dioxide before the compressor 1 and consequently a sufficiently high compression end temperature after the compressor stage (for the useful heat output), an internal heat transfer from carbon dioxide on the high pressure side to the carbon dioxide on the low pressure side is performed by means of the recuperator 6. After the recuperator 6, the carbon dioxide in the fourth state point D has a temperature of 70.3 ° C, is in the Turbine 4 to the fifth state point E (80 bar and 36.3 ° C) relaxes and enters the gas heater 3. The work of relaxation obtained by the turbine 4 is supplied to the compressor 1 via the first power transmission axis 7.2 of the motor 5.

In the gas heater 3, heat from a heat source (industrial waste heat or geothermal water, not shown) is supplied to the carbon dioxide by means of a heat transfer medium, whereby the carbon dioxide is heated to 60 ° C. (sixth state point F). The heat transfer medium cools in turn in the gas heater 3 from 65 ° C to 40.8 ° C from.

Finally, the carbon dioxide on the low-pressure side in the recuperator 6 absorbs heat from the carbon dioxide on the high-pressure side and again reaches the state point A (79.5 ° C.). The cycle is closed.

With the current levels of efficiency of the components, performance figures greater than 3 can be achieved with the illustrated process, with lower performance figures being accepted if technical, ecological and / or economic conditions justify lower performance figures.

List of reference numbers used

1

compressor

2

gas cooler

3

gas heater

4

Expansion device / expansion machine

5

engine

6

recuperator

7.1

First power transmission axle

7.2

Second power transmission axle

8th

heating water

A

First state point

B

Second state point

C

Third state point

D

Fourth state point

e

Fifth state point

F

Sixth state point

Claims (13)

Process for heating heat transfer media, e.g. B. of water in a heating circuit, at inlet temperatures of the heat transfer medium in a gas cooler greater than 40 ° C outlet temperatures of the heat transfer medium from the gas cooler greater than 80 ° C by means of a Jouleprozesses with internal recuperation, being controlled on the low pressure side of the pressure to a value that at least equal to or less than or equal to twice the critical pressure of the material used. A method according to claim 1, characterized in that is operated with inlet temperatures of 40 ° C to 80 ° C and outlet temperatures of 80 ° C to 130 ° C. Method according to one of claims 1 and 2, characterized in that carbon dioxide used as the working substance and the pressure on the low pressure side is adjusted to a value of 74 to 110 bar. Supercritical heat pump for carrying out the method according to claim 1, which works after a cold gas process with a natural working substance and is suitable for outlet temperatures of greater than 80 ° C and inlet temperatures greater than 40 ° C, with a gas heater (3), a gas cooler (2), at least one compressor (1), a relaxation device (4), at least one motor (5), which allows the entry of the energy required for the operation of the heat pump, a recuperator (6), which is used for internal heat transfer from the high pressure side to the low pressure side, and a controller which, in operation of the low pressure side heat pump, sets the pressure to a value at least equal to the value of the critical pressure and at most twice the critical pressure of the used agent. Supercritical heat pump according to claim 4, characterized in that the expansion device is a relaxation machine (4), by means of which the expansion work formed in the Jouleprozess is converted into mechanical energy. Supercritical heat pump according to claim 5, characterized in that the expansion machine (4) and the motor (5) of the compressor (1) are designed to be mechanically separated. Supercritical heat pump according to claim 5, characterized in that the engine (5) has two diametrically extending power transmission axles (7.1, 2.7), the first power transmission axle (7.1) with the compressor (1) and the second power transmission axle (7.2) with the expansion engine (7). 4), whereby the relaxation power performed by the expansion machine (4) supplied to the motor (5) and by the motor (5) for the operation of the compressor (1) required residual power is applied. Supercritical heat pump according to claim 7, characterized in that the motor (5) is designed as an electric motor, at the armature of the two diametrically extending power transmission axes (7.1, 7.2) are attached. Supercritical heat pump according to one of claims 4 and 5, characterized in that a first compressor (1), which is driven exclusively by the expansion machine (4), is used as the first compressor stage, and the first compressor stage is followed by a second compressor stage, the consists of an exclusively motor-driven compressor (1). Supercritical heat pump according to one of claims 4 to 9, characterized in that the at least one compressor (1) is a single-stage turbomachine. Supercritical heat pump according to one of claims 4 to 10, characterized in that the expansion machine (4) is a turbomachine. Use of the supercritical heat pump according to claim 4 in heat-refrigeration coupling, by simultaneously providing by means of the gas heater (3) cooling capacity and by means of the gas cooler (2) heat output available. Use of the supercritical heat pump according to claim 4 for drying processes and preheaters of gases.

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