DE19651289C2 - Chiller or heat pump with compressor - Google Patents

Description

The invention relates to a refrigerator or Heat pump and a corresponding chiller or Heat pump process with compressor according to the respective Preamble of claims 1 and 8.

State of the art

From JUNGNICKEL, Heinz; AGSTEN, Rainer; KRAUS, wolf Eberhard: Fundamentals of refrigeration technology; 3rd edition, Berlin, Verlag Technik GmbH, 1990, pages 176 to 181, are for the Refrigeration and heat pump technology compression circuits known in which a compressor between the evaporator and Capacitor is connected. From the literature, for example from DE-OS 43 31 145, are also Refrigeration or heat pump processes known for Heat transformation gas-solid reactions or the Use adsorption of gases on solids. Doing so at a lower pressure level in an evaporator liquid refrigerant evaporates. This gas is the Solid (reactor) fed where it gives off heat reacts with the solid (synthesis phase). By feeding of gas at a higher temperature level can at a higher pressure level again from the solid be expelled (decomposition phase). The gas is in a condenser giving off the heat of condensation condenses and the liquid refrigerant is on the relaxed pressure level in the evaporator. So is the cycle closed.

Since the solid reacts with the steam in the reactor, then it must be completely regenerated again. This results in a cyclical behavior of the process. A quasi-continuous process can be achieved through use  of two reactors, one in synthesis phase and one in Decomposition phase.

The power density of such a solid-state reactor depends essentially on two transport parameters: The The thermal conductivity of the solid in the reactor determines the Heat transport, gas permeability, mass transport.  

A high thermal conductivity is therefore desirable Heat already with small temperature differences in the Reactor can be coupled in or out. It is one high gas permeability desired to high To achieve flow rates of the refrigerant. The flow acts directly on the reaction rate and thus on the evaporator capacity (= cooling capacity) or in Reactive heat output released from the reactor.

This mass transfer of the steam from the evaporator directly to the reaction centers in the synthesis phase located reactor depends on the one hand on the Gas permeability of the reactor and from the other to the Transport available pressure. However, it will Working pressure level usually through the application (Temperatures) and the pair of substances used (gas-solid Reaction, adsorbent). Should z. B. with Water provided as a refrigerant refrigeration at 5 ° C the working pressure is in accordance with the Vapor pressure curve for water, at a maximum of 8.7 mbar. At this resistance is affected by the pressure strongly that the construction of the reactor afterwards must be aimed at reducing these resistances, d. H. short and as large as possible flow channels realize. This limits the design in terms of considerable compactness and low material costs a.

To increase the efficiency of solid heat pumps increase, it is suggested evaporator and condenser through another pair of reactors with if necessary to replace other solids. This is also a Lowering pressure connected.

To improve both heat conduction and the gas permeability of the fixed bed were different  Matrices in which the solid is stored, suggested, e.g. B. a matrix of pressed expanded graphite (U.S. Patent 4,852,645). The matrix component and the bulk density of the matrix as well as the gas permeability as well as influence the thermal conductivity, however in opposite effect: an increase in volume density causes an improvement in thermal conductivity, however also a reduction in gas permeability. With little Working pressure level must therefore have a low volume density Matrix and a manufacturing related also reduced Volume density of the sorbent / reactive solid used will. This improvement therefore leads to a Reduction in energy density. A decrease in Energy density of the reactor leads to that Loss processes caused by periodic warming up and Cool down result, increase relatively and the efficiency reduce a sorption refrigeration system.

In addition, there is an upper limit for for each matrix the gas permeability caused by stability reasons specified minimum volume density of the matrix becomes. Cases therefore occur (e.g. with water as Work equipment) in which the mass transfer in gas Solid reactions / adsorption through the use of a Matrix cannot be improved to the extent that a economically attractive power density is possible. In In these cases, the mass transport must be carried out by other measures be improved. The increase in pressure, which is yes the evaporator is determined, but is naturally one Limit by the heat source temperature at the evaporator given.

Discontinuous cycles have been proposed that work with various gases and solids, e.g. B. H ₂ O / zeolite, H ₂ O / CaO, NH ₃ / ammonia salts. However, a disadvantageous property of such periodically operating cycles is a time-varying performance. Fig. 1 shows a typical reaction rate measurement of a reaction bond with water vapor. The sharply falling reaction rate (and thus performance) can be seen.

Interconnections from compressors and sorption circuits [Proceedings of Absorption Hegt Pump Conference '91, Ziegler: Compression-Absorption Cycles with R22 / E181 and NH ₃ / H ₂ O] are known. However, in contrast to the present invention, these are continuously working sorption cycles in which the compressor itself contributes significantly to the generation of cold or heat or to the shifting of their temperature levels. The problem of the reaction rate dropping does not exist in these systems.

It is the object of the present invention, a Chiller or heat pump and a corresponding one Specify refrigeration machine or heat pump process at who the reaction rate and thus the power density of a sorption reactor can be increased and also stabilized can without changing the energy density of the reactor degraded.

This problem is solved by the features of claims 1 and 8, respectively.

The basic idea of the present invention will now be explained with reference to FIG. 2. Fig. 2 shows the process and the refrigerator or heat pump according to the present invention in an Inp-1 / T diagram with an evaporator 2 , a compressor 4 , a reactor in synthesis phase 6 , a reactor in decomposition phase 8 , a condenser 10 and a choke 12 . By the compressor 4 , which works between the evaporator 2 and the reactor 6 currently working in the synthesis phase, the pressure level of the vapor at the evaporator pressure p ₀ is raised to p _'2 to such an extent that the mass transport within the reactor 6 is improved to such an extent that the reactor 6 has a sufficient power density.

By using a compressor, the Power density of a reactor during the synthesis phase increased and a constant cooling capacity becomes possible produce.

The compressor 4 is preferably designed so that it only serves to overcome pressure losses p _'2- p _{2 of} the reactor 6 in the synthesis phase. That is, the higher pressure p _{'2 present} at the reactor 6 allows on the one hand a higher pressure drop in the reactor 6 and on the other hand the mass transport increases due to the higher density of the steam. For this purpose, it makes sense to adapt the pressure stroke p _'2- p _{0 to} the changing flow resistances so that the reaction rate remains constant, which means a constant performance in the synthesis phase. This adjustment also minimizes the use of mechanical work.

In addition, the temperature T ₂ in the synthesis reactor can be varied as desired by varying the pressure p ₂ , which increases the flexibility and usability of the circuit.

The remaining sub-claims relate to others advantageous embodiments of the invention.

More details, features and advantages of the Invention result from the following description exemplary embodiments with reference to the drawing.

It shows:  

FIG. 1 is reaction rate of the reaction of water vapor with CaO in a graphite-composite reaction without further measures;

Fig. 2 is an Inp-1 / T diagram for explaining the basic principle of the invention;

Fig. 3 is a lnp-1 / T diagram for explaining a second embodiment of the invention in the form of a multi-stage refrigeration machine / heat pump;

Fig. 4 shows the relationship between reaction progress and pressure readjustment;

FIG. 5 shows the performance of the AKM or AWP as a function of time; and

Fig. 6 shows the pressure curve at the reactor to achieve a constant power as a function of time.

example 1

The behavior of the solid-state reactor to a pressure increase by a compressor was simulated on a test facility for measuring the reaction rate of gas-solid reactions. This first exemplary embodiment of the invention corresponds to the single-stage system / process according to FIG. 2. It comprises the solid-state reactor 6 , which can be separated from the rest of the system by a valve (not shown), a thermostatic evaporator 2 , a pressure sensor and a flow meter ( not shown).

The reacting solid consists of CaO, which is embedded in a matrix of pressed expanded graphite (diameter: 42 mm). There are three holes (diameter 10 mm each) in the matrix for gas supply. The density of the CaO expanded graphite composite is 200 g / l (without gas supply). The sample is kept at a constant temperature of 200 ° C. The evaporator 2 is filled with water and is initially kept at 4 ° C. (= 8 mbar water vapor pressure). After opening the valve to the reactor 6 , water vapor can flow to the reactor 6 and react there with the CaO. As soon as the reaction rate decreases, measurable via the reduced flow, the evaporator temperature is increased and thus also the pressure over the reactor 6 .

As FIG. 4 shows, 70% of the CaO could react in this way with a constant reaction rate, which is illustrated by the linear increase in the progress of the reaction. Surprisingly, as shown in FIG. 6, only a maximum pressure of 30 mbar was necessary for this, ie only a small amount of compression work had to be used in order to achieve an approximately constant reaction rate, as shown in FIG. 5.

Example 2

The specified circuit can be used as a preliminary circuit for other sorption refrigeration circuits. Fig. 3 shows the connection of a solid circuit working with water as a refrigerant (with a power density improved by a compressor) and a double-effect sorption refrigerator to a quintuple-effect refrigerator. The condensation and synthesis heat from the solids circuit is fed into the generator of the double-effect refrigeration system. An improvement in the heat ratio from 1.2 to 2.0 can thus be achieved. In order to operate the DE with a high heat ratio, an almost constant course of the drive heat, ie also the heat emission in the synthesis phase, is required. This is possible by connecting the compressor to the solids circuit as described above.

Claims (9)

1. Chiller or heat pump with a sorption circuit with solid sorbent or reactant, at least one evaporator, at least one condenser, at least one reactor, which work alternately in the synthesis phase and decomposition phase, and a compressor, characterized in that the compressor between the evaporator and is arranged in the reactor working in the synthesis phase and thereby improves the mass transfer in the reactor working in the synthesis phase. 2. Chiller or heat pump according to claim 1, characterized characterized in that the compressor with sliding Pressure stroke works so that a constant cooling capacity is made possible. 3. Chiller or heat pump according to claim 2, characterized characterized in that the pressure stroke of the compressor so it is regulated that the heat extraction from the reactor in Synthesis phase takes place at a higher temperature T2 than the reaction or Adsorption equilibrium temperature of the reactor in Synthesis phase at the pressure of the evaporator corresponds. 4. Chiller or heat pump according to at least one of the Claims 1 to 3, characterized in that Evaporator and condenser by at least one another reactor with possibly another Sorbent to be replaced (absorption). 5. Chiller or heat pump according to at least one of the Claims 1 to 4, characterized in that in the Reactors as a graphite-solid reaction composite Sorbent or reactant is used.   6. Chiller or heat pump according to at least one of the Claims 1 to 5, characterized in that the Working water and the sorbent one or several of the following are: CaO, MgO, zeolite, Silica gel. 7. Chiller or heat pump according to at least one of claims 1 to 5, characterized in that the working agent NH ₃ and the sorbent is one or more of the following substances: ZnCl ₂ , NaCl, PbCl ₂ , NaBr, BaCl ₂ , CaCl ₂ , SrCl ₂ , MnCl ₂ , FeCl ₂ , NiCl ₂ , MgCl ₂ , MgBr ₂ , NiBr ₂ , MgBr ₂ . 8. Chiller or heat pump process with one Sorption cycle, in which a phase change continuous work equipment alternating from one solid sorbent is sorbed or with a solid reactant reacts, thereby characterized that the gaseous working fluid before Feed to the solid sorbent or reactant is compressed. 9. refrigerator or heat pump process according to claim 8, characterized in that this process as Upstream process for any other sorption processes is used in such a way that the heat from the Condensation and / or from the reactor in the synthesis phase serves to drive these sorption processes.