WO2003046449A1

WO2003046449A1 - Method and device for solar thermal refrigeration

Info

Publication number: WO2003046449A1
Application number: PCT/EP2002/013436
Authority: WO
Inventors: Marcus Reuss; Peter Noeres; Daniel HÖLDER; Bernd Dietz
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2001-11-30
Filing date: 2002-11-28
Publication date: 2003-06-05
Also published as: AU2002352174A1

Abstract

The invention relates to a method of refrigeration by solar thermal means. On implementing the method, parabolic channel collectors are preferably employed. An adsorption refrigeration unit is preferably employed in the refrigeration process, in particular a two-stage water/NH3 absorption process. The above is embodied for the direct connection to a parabolic channel collector field and the high operating temperatures thus achievable. Very high back-cooling conditions of up to 50 °C and more are also achievable. The latter is particularly essential for hot countries. As temperatures of below 0 °C can also be achieved with said method, multiple application possibilities are given.

Description

Method and device for solar thermal refrigeration

description

The invention relates to a method for solar thermal refrigeration according to the preamble of claim 1 and an apparatus for performing such a method.

Processes for thermal cooling are part of the known prior art and are used primarily in the context of the recovery of waste heat and the associated secondary energy. Reference is made to a method for the use of waste heat from heating power plants according to the teaching according to DE 199 40 465 AI. Here, an absorption refrigeration device is described, which among other things. is also used for cooling a photovoltaic device.

Thermal refrigeration processes can be used wherever there is sufficient thermal energy, either in the form of waste heat or as primary energy.

The benefit of thermal refrigeration processes results from the fact that energy forms which are otherwise unused in the environment, in particular thermal energy, can be used for technical purposes. As a result, higher-quality forms of energy, such as electrical energy or chemical energy stored in fuels, can be saved and / or the environmental pollution associated with energy generation due to pollutant emissions or carbon dioxide emissions can be reduced. Thermal cooling processes therefore play an important role in energy projects for the purpose of environmental protection.

The method proposed here is used for solar thermal cooling and can e.g. for storage cooling, food cooling, air conditioning using ice stores, production of artificial snow, provision of cold for pumpable brine-ice mixtures as well as for process cooling.

Another interesting energy saving effect of solar thermal refrigeration is that the regenerative solar energy available in nature is as possible can be used directly and not via the detour of generating electricity.

The use of solar energy is simple, inexpensive and thus offers particularly in areas of the third world, which are mostly in areas with a high

Annual sunshine duration, a possibility either to produce electrical energy inexpensively or to use the solar energy directly technically.

The object on which the invention is based is therefore to specify an inexpensive and effective method and a device for cooling, which is based on the use of solar energy.

The object of the invention is achieved with a method for solar thermal refrigeration according to claim 1, wherein the subclaims contain at least useful refinements and developments.

According to the invention, the method is based on the principle of a two-stage absorption refrigerator known per se. This comprises a refrigerant circulating in a refrigerant circuit, as well as an absorption or solvent circulating in two solvent circuits, together with evaporator, condenser, two expellers and two absorbers. According to the invention, the thermal energy required for operating the desorber is collected in the form of solar energy within a solar heating system and supplied to the absorption medium in the solar heating system.

The method according to the invention can thus be used in any case emission-free and independent of existing electrical and district heating supply networks.

The cooling is preferably carried out continuously as part of the method. For this reason, an absorption chiller is used as the refrigeration system, which is designed as a two-stage water-ammonia AKM.

Here, the mixture of substances called absorbent and refrigerant is separated within the solar heating system by their different evaporation temperatures in a desorber. The refrigerant will then liquefied in a condenser and evaporated in an evaporator, whereby heat is extracted from the environment. Then the refrigerant vapor is absorbed again by the absorbent.

The absorption medium heated in the solar heating system can in principle be used for other purposes. For example, a hot or hot water supply based on these, as well as solar thermal power generation by means of a steam turbine coupled to a generator, is possible. This ensures flexible use of the thermal energy collected by the solar heating system, depending on the existing application.

For the solar heating or energy recovery system, a parabolic trough collector is provided as part of a desorber, the focal point of which is extended to a focal line by the extruded parabolic shape of a collector mirror. With the help of parabolic trough collector systems, by focusing the direct

Solar radiation temperatures of 180 ° C with collector efficiencies of over 50% can be achieved. At these high temperatures, absorption cooling processes such as the water-NH3 absorption process presented here can be carried out in two stages. This can almost double the effectiveness of the process, also in the literature as COP (cooling capacity / thermal drive power, coefficient of performance). According to estimates for the operating case considered here (evaporator temperature 0 ° C, condenser and absorber 1 at 50 ° C and temperature of desorber 2 at approx. 180 ° C), the COP can achieve a COP of 0.9 to 1. The working pair is heated and evaporated within a heating pipe located in the focal line. Alternatively, a steam generator can be connected downstream of the parabolic trough collector.

A heating section is thus formed within the focal line of the collector mirror, in which the absorbent flowing through is continuously heated. The use of the parabolic trough collector is a particularly easy to implement, therefore inexpensive and particularly efficient due to the high concentration factor of the solar thermal energy within the focal line of the collector mirror of the solar thermal energy use. Ammonia water is used as the working pair. This system has been known for a long time and can be mastered with existing technology. Both substances are available at low cost. Ammonia can be used without any problems, since with existing technology and due to the low odor threshold, NH3 leakages can be detected early.

A refrigerant is cooled in the evaporator to transport the cold to the actual place of use, then transported to the customer site and then returned to the evaporator. The coolant can be an aqueous brine, water at temperatures above 0 ° C or a pumpable water (brine) - ice system. With this process, coolant temperatures down to -40 ° C are possible under favorable conditions.

To remove the heat absorbed by the refrigeration system from the environment and the solar heat, the arrangement of the condenser and the absorber is actively cooled.

In a first embodiment, the active cooling of the condensers and / or the absorbers takes place by means of a liquid flow, for example a cooling water circuit. Furthermore, cooling can be carried out by means of evaporative cooling systems.

In a further embodiment of the active cooling, this is designed by air cooling. Here, the refrigerant / absorbent / vapor mixture is passed over a heat exchange surface, which enables the most intensive possible thermal contact with the surrounding air. By a blower

Ambient air sucked in and brought into thermal contact with the heat exchange surface.

On the device side, the invention is formed by an arrangement of a desorber of an absorption refrigeration machine, which contains a heating section, which is located in a combustion zone of a solar collector or collector field and through which a medium flows, with a coupling to an arrangement comprising at least one rectification column and / or a steam separator, these components are connected in a solar circuit. The solar collector or the collector array is expediently designed as a parabolic collector array with a linear tubular heating section. The method according to the invention for solar thermal refrigeration will be explained in more detail using an exemplary embodiment. The accompanying illustrations in FIGS. 1 and 2 serve to illustrate this.

Here shows:

Fig. 1 is a schematic overview of an embodiment of the solar thermal refrigeration according to the invention, including, among other things, a solar heating system designed as a parabolic trough collector field as part of a desorber and

Fig. 2 is a schematic representation of a parabolic trough collector.

Fig. 1 shows a basic embodiment for solar thermal refrigeration. In a solar circuit with flow paths 1, 2, 3, 4, 5, a mixture of water and ammonia is circulated by means of a circulation pump P4, which flows through a parabolic trough collector field PRK in a plurality of line branches 2, 3, 4 and via a throttle valve VI Flow path 5 is supplied to a desorber Des2 with a steam separator DA and a rectification column RK.

The solvent, water in the application example described here, is conducted via flow paths 6, 7, 8, 9 in a solvent circuit with the desorber Des2, a solution heat exchanger LWT2, an absorber Abs2 and a throttle valve V3, which is circulated by a solvent pump P2.

Furthermore, a further desorption process is provided, which is designated in FIG. 1 by the flow paths 10, 11, 12, 13, 14, 15 and which contains a desorber Desl, another solution heat exchanger LWT1, and another absorber Absl with a throttle valve V2, which is circulated by a further solvent pump Pl. Absorber Abs2 from the first solvent circuit and Desorber Desl from the further solvent circuit are included via a heat transfer circuit O

Flow paths 16, 17 coupled, which is driven by a circulation pump P3 and in which heat is transported from the absorber Abs2 to the desorber Desl.

The ammonia expelled from the desorbers Des2 and Des2 is fed via the flow paths 11, 20, 21, 22, 23, 24 to a refrigerant circuit, the one

Contains capacitor Koni and a precooler VK1. The refrigerant circuit is connected to a circuit for cooling water 18, 19, which actively cools the absorber Absl and the condenser Koni, in a heat-transferring manner.

Furthermore, a coolant circuit 25, 26 is provided, which introduces the heat extracted from the environment into the evaporator Verl and is used, for example, as a coolant in the brine or cold water.

In the two-stage process, the Desorber Des2 provides the actual parabolic trough collector field PRK with the additional steam separator DA or

RK rectification column. Ammonia is an uncritical medium compared to steel and the use of the two-stage process means that the operating pressures in a range of less than 25 bar overpressure are selected and therefore easy to control. The almost water-free ammonia vapor released from the Desorber Des2 is deposited in the Koni condenser and expanded into the evaporator via the throttle valve V4. The low-ammonia solution flowing out of the desorber Des2 flows into the absorber Abs2. There, ammonia evaporating at low vapor pressure is absorbed again from the evaporator Verl. The heat of absorption released in this process is conveyed via the heat transfer circuit into the further solvent circuit to the desorber Desl. In this

The solvent cycle has a significantly lower average water content, so that ammonia can be expelled from the solution at almost the same temperature level as in Absorber Abs2. The steam released in the Desorber Desl is also deposited in the condenser Koni together with the steam from the Desorber Des2. The solution depleted in ammonia from the desorber Desl is conveyed to the absorber Absl at a low pressure level. There the absorber takes up some of the ammonia released in the evaporator. The solution, now enriched with ammonia, is conveyed back to the desorber and the solution cycle closes. The solution cycle composed of Desorber Des2 and Absorber Abs2 works analogously. To increase the efficiency or process effectiveness (COP), temperature changers are used both in the solution circles and in the line between the condenser Koni and the evaporator Verl. These can partially compensate for the heat loss from the higher to the lower temperature or pressure level.

2 shows the parabolic trough collector PRK used for steam generation in more detail. A trough-shaped parabolic rail PS, the cross section of which is essentially parabolic and the surface of which is reflective, produces a focal line in which there is a heating tube HR, through which the absorption medium flows continuously. The absorption medium W occurs in liquid form as condensate W-KON. The application example described here and shown in FIG. 1 is a mixture of ammonia and water. The diameter of the header pipe, the throughput and the pipe lengths are determined in such a way that the medium reaches the desired pressures and temperatures in accordance with the required thermal performance, while maintaining the permissible flow velocities. The medium can evaporate partially or not at all. In the latter case, a vapor container is connected downstream of the parabolic trough collector, in which flash evaporation with integrated rectification can take place.

In order to achieve the greatest possible efficiency of the refrigeration system, it is advantageous to reduce the operating load, i.e. to keep the temperature difference between the immediate vicinity of the condenser Koni and the evaporator Verl as low as possible. For this reason, air cooling can be carried out as active cooling, in which a fan continuously draws in air and ensures a continuous flow around the heat-emitting walls between the condenser Koni and the ambient air and prevents the formation of an insulating air layer. Even higher performance data and efficiencies are achieved if the process is recooled with river water, sea water or also with evaporative cooling systems.

LIST OF REFERENCE NUMBERS 1 ... 5 solar circuit

12 ... 15 first solvent cycle

10, 11, refrigerant circuit

21 ... 24

16, 17 heat transfer circuit

18, 19 cooling water circuit

27, 26 refrigerant circuit

Absl absorber 1

Abs2 absorber 2

DA steam separator

Desl Desorber 1

Des2 Desorber 2

HR heating tube

Koni capacitor

LWT solution heat exchanger

RK rectification column

Pl, P2 solvent pumps

P3 Pump heat transfer circuit

P4 circulation pump collector array

PRK parabolic trough collector, parabolic trough collector field

PS parabolic trough

VI ... V4 throttle valves

Leave vaporizer

VK1 precooler

W-KON absorption medium, liquid

W-D absorption medium, steam

Claims

claims

1. Process for thermal refrigeration, d a d u rch g e ke n n ze i ch n et that - for refrigeration one on the principle of a two-stage

Absorption refrigerator based refrigeration system is used, wherein

- For evaporation of the working couple, heat is supplied via a heating system operated with solar energy

- Is designed as part of a desorber (Des2) of the absorption refrigerator.

2. The method of claim 1, d a d u rc h g e ke n n ze i c h n et that continuous refrigeration takes place in the absorption refrigerator.

3. The method according to any one of claims 1 or 2, so that the absorption medium heated by the solar heating system is also used to generate electrical energy by means of a generator coupled to a steam turbine or a device comparable to it.

4. The method according to claim 2, so that the absorption medium heated by the solar heating system is optionally also used for heating tasks.

5. The method according to any one of claims 2 to 6, such that the desorber's heating system operated with solar energy is designed as a parabolic trough collector (PRK), wherein

- The working pair is heated and evaporated within a heating tube (HR) located in a focal line of a parabolic mirror;

- Or is evaporated in a steam generator downstream of the parabolic trough collector.

6. The method according to any one of the preceding claims, dadu rc h ge ken n ze ichn et that water as the solvent and ammonia as the refrigerant can be used as the working pair.

7. The method according to any one of the preceding claims, since d u rch g eken nzei ch net that consumers connected to the refrigeration system are supplied by a refrigerant, in particular brine, water, ammonia or the like refrigerant by means of a refrigerant circuit (25, 26).

8. The method according to any one of the preceding claims, since d u rch g eken nzeich net that an arrangement within the refrigeration system existing condensers (Koni) and absorbers (Absl) is actively cooled.

9. The device according to claim 8, so that the active cooling of the condenser (Koni) is realized by means of a liquid flow.

10. The method according to any one of claims 8 or 9, since it is characterized by the fact that the active cooling of the condenser (Koni) and / or the absorber takes place by means of a cooling water circuit (18, 19) and / or evaporative cooling systems.

11. Device for performing the method according to one of the preceding

Claims, since it is characterized by the fact that for the active cooling of the condenser (Koni) and the absorber (Absl) there is a blower and a heat transfer surface which is in thermal contact with the air flow generated by the blower.

12. Device according to one of the preceding claims, g eke nn zei ch n et du rch a desorber from a solar collector field with a heating section arranged within a combustion zone of the collector and through which a medium flows and with a coupling to an arrangement comprising at least one rectification column (RK ) and / or a steam separator (DA) in a solar circuit (1,2,3,4,5)

12. The apparatus according to claim 11, characterized as a parabolic collector field (PRK) designed collector field with a linear flow, tubular heating section (HR).