HEAT PUMP WITH ADSORBER AND CATALYST

Description

[0001] The invention relates to a device for the safe implementation of a left-handed thermodynamic cycle in a heat pump suitable for installation in a building using a hydrocarbon-containing working fluid, which is circulated in a closed, hermetically sealed working fluid circuit in a thermodynamic cycle, such as the Clausius-Rankine cycle. These are primarily heat pumps, air conditioning systems, and refrigeration units commonly used in residential buildings.

[0002] Residential buildings include private homes, apartment complexes, hospitals, hotel complexes, restaurants, and combined residential and commercial buildings in which people live and work permanently, as opposed to mobile devices such as car air conditioning systems or transport crates, or even industrial plants or medical devices. What these cyclic processes have in common is that they use energy to generate useful heat or cooling and form heat transfer systems. The heat pump itself, as well as its user-facing installations, are installed within a building, which results in high safety requirements.

[0003] In such systems, adsorbers are used, among other things, to bind working fluid that has escaped due to leakage. DE 10 2011 116 863 A1 describes a method for securing a device for a thermodynamic cycle, which is operated with a process fluid that contains or consists of at least one environmentally hazardous, toxic and / or flammable substance. In the event of a leak in the device for a thermodynamic cycle, an adsorbent is brought into contact with the process fluid, in particular ammonia, propane or propene, and the substance is selectively bound by the adsorbent. The adsorbent is regenerated after use. Zeolite, also in combination with imidazole or phosphates, as well as CuBTC and activated carbon, are proposed as adsorbents. The adsorbent can be in the form of a bed, a shaped body, a paint, a spray film, or a coating.The support structure of the molded body can consist of a microstructure, a lamellar structure, a tube bundle, a pipe register, or sheet metal and must be mechanically stable and significantly increase the surface area. Circulation of the potentially contaminated air is usually continuous, but can also be initiated by a sensor that activates the ventilation when a threshold is reached or when an emergency is detected. Adsorption can be carried out inside or outside an enclosed space.

[0004] Many other documents also teach the use of adsorbers to separate working fluid that has leaked from a leak in the refrigeration circuit into the housing of a heat pump, which contains the refrigeration circuit and heat exchanger. EP 3 486 564 A1 describes the lining of the heat pump housing with activated carbon, where the activated carbon is pre-charged with an inert gas that is displaced by the leaked working fluid during loading. This reduces the heat development that occurs during adsorption. EP 3 486 582 A1 describes a system with which the loading of the adsorber can be determined using a weight measurement. EP 3 581 861 A1 describes a heat pump vessel stuffed with molded activated carbon cushions. EP 3 748 257 A1 describes a device in which adsorbers open a gas outlet via an adsorber in the event of a pressure increase in the heat pump vessel.EP 3 693 683 A1 describes protective layers in an adsorber that is open to the environment. EP 3 693 687 A1 describes an adsorber arranged in the heat pump housing that has a cooling system.

[0005] The technical-physical problem addressed in these documents is that it is impossible to know the concentration of refrigerant vapor that will result from a leak in the heat pump casing, since the leak cannot be known in advance. However, the partial pressure of the respective adsorptive and the flow velocity of the gas flowing through it are crucial for dimensioning the adsorption system with regard to the amount of adsorbent and the required cross-sections.

[0006] At low partial pressure and high flow rate, the breakthrough curve moves quickly through the adsorption, but remains relatively flat. The advantage of this is that the adsorbate heats up only slightly; the disadvantage is that very large quantities of adsorbent would be required for complete separation, which would be uneconomical and impractical. At high partial pressure, on the other hand, a lot of adsorption can take place, but the adsorbate heats up considerably, which reduces its absorption capacity. This results in an unwanted feedback loop. The heating simultaneously desorbs already separated adsorptive, so the breakthrough curve pushes a kind of bow wave ahead of it as it moves through the adsorber.

[0007] In both cases, however, the adsorbed working fluid desorbs from the adsorbate as soon as the partial pressure drops again, since the counterpressure is then absent. The open, flow-through adsorber, as well as inserted adsorber pads or walls coated with adsorbent, cannot permanently retain the adsorbed working fluid, but can only ensure that no ignitable mixture can form. It would therefore be desirable if the adsorber were capable of immediately destroying the separated substance after the separation process, i.e., switching to chemisorption after adsorption. The dilemma, however, is that oxidation of the adsorptive could lead to considerable heat generation, since alkanes are ideal fuels as working fluids. Using activated carbon as an adsorbent would also pose the risk of toxic carbon monoxide formation or even ignition.This must be avoided at all costs, no matter how large the hypothetical leak and thus the loading situation may be in rare cases.

[0008] The problem is also known in freezers and refrigerators, which have air flowing through them in the cooling chamber. JP 2000 320 950 A describes such a device, which uses a hydrocarbon as the refrigerant and an adsorption layer to adsorb any refrigerant that may have leaked out due to a leak and catalytically destroy or convert it. To achieve the required temperature for the catalytic reaction, the existing defroster heater is used. Above this is a small element with an adsorption layer and a catalytic layer made of platinum supported on aluminum. Unlike a heat pump, the extremely low temperatures in the freezer compartment mean that the refrigerant pressure is below atmospheric pressure, and in the event of a leak, practically no refrigerant escapes.Such a leak into the good compartment could occur during the defrosting process, however, and the heater used to defrost the good compartment would then simultaneously heat the catalyst for any necessary catalytic decomposition of the refrigerant. Unfortunately, this trick cannot be transferred or applied at the temperatures typically encountered in a heat pump.

[0009] It is also known that air filters first capture VOCs and then decompose them catalytically. US 2021 / 0108810 A1 describes a device and method for air purification, especially in vehicle cabins. The problem here is that the potentially multi-stage catalytic treatment must take place at high temperatures, and the resulting waste heat must be controlled. A combination with adsorption is not taught. Such air filters are unsuitable for heat pumps or for refrigerant leaks.

[0010] DE 69 60 740 T2 describes a filtration process for gas in the engine compartment of a vehicle. It provides, among other things, a catalytic treatment of hydrocarbons. Precious metals such as platinum, palladium, and rhodium, as well as metallic, high-melting supports, serve as catalysts. In the case of hydrocarbons, this requires an auxiliary heated surface. The design can be similar to conventional honeycomb catalysts, which have long been state-of-the-art in vehicle exhaust gas purification. The catalytic reaction can also be preceded by adsorption followed by desorption.

[0011] DE 10 2019 118984 A1 describes a device according to the preamble of claim 1; wherein a heat pump with at least one sorption channel with an adsorber through which gas can flow is disclosed; wherein the sorption channel directly connects to the housing and is open to it, the sorption channel is open to the environment for gas, the adsorber in the sorption channel has at least one adsorption layer of activated carbon, at least one protective layer at the connection to the housing and at least one protective layer at the outlet of the adsorber to the environment.

[0012] The object of the invention is therefore to provide a device for safe and efficient adsorptive gas treatment in a heat pump installed in a residential building, in which a left-handed thermodynamic cycle is carried out in a closed, hermetically sealed working fluid circuit using a flammable, hydrocarbon-containing working fluid. This device should no longer exhibit the problems described above.

[0013] The invention solves this problem by a device for the safe implementation of a left-turning thermodynamic cycle in a heat pump suitable for installation in a building by means of a hydrocarbon-containing working fluid which is guided in a closed, hermetically sealed working fluid circuit, wherein an enclosed adsorption zone into which the air-hydrocarbon mixture can flow, around or through, a gas-permeable enclosure of this enclosed adsorption zone, an adsorbent and an oxidation catalyst are provided within the enclosed adsorption zone, and the ratio of oxidation catalyst to adsorbent is between 1 to 10 and 1 to 1000, calculated on a mass fraction basis.

[0014] This catalyzes the oxidation of the adsorbed hydrocarbon, and the oxidation catalysts added to the adsorbent in small quantities cause a slow oxidation. Although catalytic oxidation results in heat development in addition to the heat of adsorption, this is kept to a minimum by the small amount of catalyst and thus remains easily manageable.

[0015] When the adsorption process is applied in the housing of a heat pump or in conjunction with it within a building, the adsorptive is slowly degraded at low leakage rates, resulting in a very flat breakthrough curve in the adsorber, assuming that atmospheric oxygen is present for oxidation.

[0016] Embodiments relate to an enclosed adsorption zone, which can be flowed against, around or through by the air-hydrocarbon mixture, and a gas-permeable enclosure of this enclosed adsorption zone, wherein an adsorbent and an oxidation catalyst are provided within the enclosed adsorption zone.

[0017] The design of the device relates to the catalysts used. Oxidation catalysts for alkanes are predominantly used industrially to produce alkenes. For example, propane is processed into propylene in propane dehydrogenation, or butane is partially oxidized to butylene or butadiene. These known processes are carried out catalytically, ensuring the highest possible selectivity and avoiding the formation of oxidation products such as carbon monoxide or carbon dioxide. The catalysts used for this purpose achieve the desired activity in temperature windows of at least 150 degrees Celsius.

[0018] In this case, however, the most complete oxidation possible at room temperature is desired. Even incomplete oxidation in the form of partial oxidation is acceptable, provided the partially oxidized products remain on the adsorbent, i.e., are also adsorbed, are liquid, or form solids, and the heat of reaction remains low. The amount of catalyst should therefore be small compared to the adsorbent. Therefore, the ratio of oxidation catalyst to adsorbent is intended to be between 1:10 and 1:1000, based on mass fraction. However, the ratio does not have to be the same everywhere.

[0019] The device uses catalytic compounds containing Fe(III), Cu(II), Ce(IV), PB(IV), Rh, or Pd, or mixtures thereof. They are either applied directly to the adsorbent, thus using the adsorbent as a carrier substance, or other carrier materials are used that are mixed with the adsorbent. Activated carbon serves as the adsorbent.

[0020] In one embodiment, the oxidation catalyst is supported on the adsorbent. This includes shaped bodies of a bed, such as cylindrical pellets, or honeycomb shaped bodies with flow channels, or shaped cushions, or foams, or other known supports for adsorbents and catalysts. Alternatively, the oxidation catalysts can also be applied to separate shaped bodies, which are, for example, mixed into a bed. If, for example, activated carbon is used as an adsorbent in the form of a bed, small amounts of other shaped bodies on which catalysts are applied can be mixed into the bed.

[0021] In one embodiment, the adsorption zone is formed by a sorption channel with a gas inlet, insert baskets filled with adsorbent bed and oxidation catalyst, and a gas outlet open to the environment. The sorption channel can be equipped with additional features, such as protective layers, baffles, etc.

[0022] Independently of this, one embodiment provides for the catalyst bulk density to increase with the bed height, i.e., the flow length, and for the catalyst bulk density to reach its highest value at the adsorber outlet. This ensures that the lowest reaction heat is added at the adsorber inlet, where the most adsorption heat is generated, while the catalytic degradation is greatest at the adsorber outlet, where initially only minimal adsorption occurs. This ensures the best possible distribution of the heat load across the adsorber bed height.

[0023] If adsorber pads are used, the covers can be coated with a catalyst. If adsorber walls are used, the catalyst should be positioned on the side facing the vessel wall, as the reaction heat can best be dissipated via the vessel wall or other walls. If shaped bodies are used for adsorption, the catalyst should be applied at the flow outlet or on the side walls in a higher concentration than in the center or at the flow inlet. The adsorption zone is then formed by a shaped body with inner and outer flow surfaces. It is also possible for the shaped body to be attached to the inner wall of the housing of a heat pump, with the bulk density of oxidation catalyst on the adsorbent increasing with proximity to the wall. All of these measures and designs can also be used in combination.

[0024] In some embodiments, the temperature of the adsorbent is measured. If this rises too much, a small amount of inerting nitrogen is added; this slows oxidation by lowering the partial pressures of the reactants, especially that of oxygen. If the added amount is small, this has little effect on adsorption. The temperature measurement and the addition of nitrogen can also take place at different points or layers. Any nitrogen that may be added is kept under high pressure, which, when the pressure is released during addition, also leads to a cooling of the adsorbent due to the Joule-Thomson effect. In this case, which indicates a high leakage rate, it can absorb more adsorptive than would be possible if it were heated due to the heat of adsorption. The cooling effect locally compensates for the heat of adsorption and, if applicable, the heat of reaction.

[0025] Furthermore, cooling of the adsorber can alternatively or additionally be carried out using known cooling devices according to the state of the art, as described above.

[0026] The invention is illustrated by an example in Fig. 1 explained in more detail. Fig.1 shows a heat pump 1 with an encapsulated housing 2, in which a refrigeration circuit 3 is operated with the flammable refrigerant R290. This refrigeration circuit comprises a compressor 4, a condenser 5, an expansion valve 6, and an evaporator 7. The encapsulated housing is provided with a connection 8 to a sorption channel 9. The sorption channel 9 contains a bed of the adsorbent activated carbon and an oxidation catalyst made of iron (III) applied to the activated carbon. The doping concentration increases along the length of the channel. Purified air can leave the sorption channel 9 via the outlet 10. Normally, there is hardly any flow through the sorption channel.

[0027] Should a leak occur, the pressure in the encapsulated housing 2 increases, forcing the resulting air-R290 mixture into the sorption channel 9, where it is adsorbed in the lower section. This heats up the adsorbent, and the applied catalyst initiates a slow reaction, producing oxidation products of the R290, including carbon dioxide. Should larger quantities occur due to a major leak, which is extremely rare, the adsorption heat causes significant heating, which also accelerates the oxidation and can cause further heating.

[0028] For this case, an injection 11 of nitrogen or another inert gas is provided to modulate this reaction. In the case of nitrogen, pressure relief during the injection can also achieve a temperature reduction, which, on the one hand, increases the capacity of the adsorbent and, on the other hand, reduces the reaction heat of oxidation. To detect such excessive heating in a timely manner, a temperature measuring point T is provided in the sorption channel 9. List of reference symbols

[0029] 1Heat pump 2Housing 3Refrigerant circuit 4Compressor 5Condenser 6Expansion valve 7Evaporator 8Connection 9Sorption channel 10Outlet 11Connection / injection TTemperature measuring point

Claims

1. Device for safely carrying out a counterclockwise thermodynamic cycle (3) in a heat pump (1) suitable for installation in a building by means of a hydrocarbon-containing working fluid which is guided in a closed, hermetically sealed working fluid circuit, containing an enclosed adsorption zone (9), which can be flowed against, around or through by an air-hydrocarbon mixture, and a gas-permeable enclosure of this enclosed adsorption zone (9), an adsorption agent being provided within the enclosed adsorption zone, characterised in that - within the enclosed adsorption zone and an oxidation catalyst is provided, - and the ratio of the mass fractions of oxidation catalyst to adsorbent is between 1 to 10 and 1 to 1000.

2. Device according to claim 1, characterised in that the oxidation catalysts are catalytic compounds containing Fe(III), CU(II), Ce(IV), PB(IV), Rh or Pd or mixtures thereof and in that the adsorbent is activated carbon.

3. Device according to one of claims 1 or 2, characterised in that the oxidation catalyst is supported on the adsorbent.

4. Device according to one of claims 1 to 3, characterised in that the adsorption zone (9) is formed by a sorption channel (9) which has a gas inlet (8), furthermore insert baskets which are filled with adsorbent bulk and oxidation catalyst, and a gas outlet (10) which is open to the environment.

5. Device according to claim 4, characterised in that the density of oxidation catalyst on the adsorbent increases with the length of the sorption channel.

6. Device according to claim 4, characterised in that the density of oxidation catalyst on the adsorbent increases with the proximity to the wall of the sorption channel.

7. Device according to claim 1, characterised in that a temperature measuring point (T) is arranged in the adsorbent, with which the temperature is measured.

8. Device according to claim 1, characterised in that a connection (11) and a distribution device for pressurised nitrogen are provided.