Diffusion barrier by means of protective layers

Description

[0001] The invention relates to irregular states in refrigeration circuits in which a working fluid acting as a refrigerant is circulated in a thermodynamic cycle, such as the Clausius-Rankine cycle, and to their adsorptive safety devices. These are primarily heat pumps, air conditioners, and refrigeration units commonly found in residential buildings. Residential buildings are defined here as private homes, apartment complexes, hospitals, hotels, restaurants, and combined residential and commercial buildings where people live and work permanently, as distinct from mobile devices such as automotive air conditioners or transport containers, or industrial plants or medical devices. These cycles have in common that they generate useful heat or cooling using energy and form heat transfer systems.

[0002] The thermodynamic cycles involved have long been known, as have the safety problems that can arise when using suitable refrigerants. Apart from water, the most common refrigerants used at that time were flammable and toxic. In the last century, this led to the development of safety refrigerants consisting of fluorinated hydrocarbons. However, it turned out that these safety refrigerants contributed to global warming and that their perceived safety led to design oversights. Up to 70% of sales were attributable to the need to refill leaking systems and the associated leakage losses, which was tolerated as long as it was considered economically justifiable in individual cases and encouraged replacement purchases.

[0003] Modern refrigeration systems are equipped with these safety refrigerants of safety class A1, meaning they are non-toxic and non-flammable. The most common refrigerants used in heat pump applications are R134a, R407C, and R410A, all of which are fluorocarbon compounds. Until January 2015, the use of these refrigerants was not subject to any restrictions. However, the introduction of the F-Gas Regulation (EU) 517 / 2014 on January 1, 2015, restricts the use of fluorocarbon refrigerants in the European Union through quantity limits, causing the prices of existing refrigerants to rise significantly. The aim of the F-Gas Regulation is the medium-term phase-out of greenhouse gas-producing refrigerants and their replacement with natural refrigerants or chemical refrigerants with significantly reduced global warming potential.

[0004] However, a disadvantage is that almost all refrigerant alternatives belong to the group of flammable refrigerants, especially the most technically promising refrigerants such as R290 (propane) and R1270 (propylene).

[0005] It is therefore extremely problematic, on the one hand, to adopt the design principles for refrigerant-carrying thermodynamic processes that have seemingly proven successful with safety refrigerants, and on the other hand, to rely on system concepts from the time before the introduction of safety refrigerants. This is also due to the fact that individual devices have now become complex systems, which has multiplied the number of potential malfunctions and their consequences.

[0006] DE 10 2011 116 863 A1 describes a method for securing a device for a thermodynamic cycle, which is operated with a process fluid containing or consisting of at least one environmentally hazardous, toxic, and / or flammable substance. In the event of a leak in the device for the 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, and CuBTC are proposed as adsorbents; the adsorbent can be in the form of a bed, a molded body, a coating, a spray film, or a coating.The supporting structure of the molded body can consist of a microstructure, lamellar structure, tube bundle, tube register, and sheet metal, and must be mechanically stable and offer a large surface area. Circulation of the potentially contaminated air typically occurs continuously, but can also be initiated by a sensor that activates the ventilation after a threshold value is reached or in the event of a detected emergency. Adsorption can be carried out inside or outside an enclosed space.

[0007] DE 195 25 064 C1 discloses a device for the safe execution of a left-hand thermodynamic cycle according to the preamble of independent claim 1, and describes a refrigeration machine with a gas-tight housing that accommodates all refrigerant-carrying components of the machine. A space is provided connecting the interior of the gas-tight housing to an outlet, and this space is filled with a refrigerant-absorbing substance. The quantity of the absorbing substance is dimensioned such that all potentially escaping refrigerant can be absorbed and kept away from the environment. The space filled with the absorbing substance is open to the surroundings. For refrigerants heavier than air, the space is open at the bottom; for those lighter, it is open at the top, so that a circulating fan is not required.The sorbent is introduced into the housing and completely encloses the refrigeration unit or the refrigerant-carrying components. Baffles are incorporated along its path to the outside to prevent short-circuiting and force escaping gas through the sorbent. A double-walled design, in which the sorbent is located within the double jacket, is also possible. A refrigerant meter can be installed at the outlet of the space filled with the sorbent to the environment.

[0008] EP 3 106 780 A1 describes a heat pump system housed in an airtight casing lined with a binding agent. An adsorption unit with forced ventilation can be located within this casing, which cleans the air inside the casing during recirculation. This recirculation can occur continuously, only in the event of a malfunction, or at regular intervals. Downstream of this sorption stage, an ignition burner, a pilot flame, a catalytic burner, or a heating wire can also be installed to combust any remaining combustible contaminants. A fresh air supply combined with the exhaust of cleaned air is also conceivable.

[0009] JP 2000 105003 A describes a refrigeration unit operated with a flammable working fluid. The unit may consist of two parts, one located inside a building and the other outdoors. To prevent the escape of working fluid in the event of a leak, the inner walls of the inner housing are lined with an adsorbent material, and the pipes of the outdoor unit are coated with an adsorbent material. Activated carbon is among the proposed adsorbents.

[0010] A problem with using activated carbon as an adsorbent is that it ages over time in air due to slow oxidation processes. Because of the safety requirements for availability throughout the lifetime of devices operating counterclockwise cycles, such as heat pumps, degradation of the adsorbent must be strictly avoided, especially if it could go unnoticed.

[0011] Depending on the design, installation location, and operating mode of, for example, a heat pump, different requirements arise regarding the potential exposure of the adsorbent to co-adsorbents, such as VOCs, water vapor from humidity, atmospheric oxygen, temperature fluctuations, and others. A distinction must be made between linings and flow-through sorption beds. With flow-through sorption beds, a further distinction is made between those that operate within a housing in recirculated air mode and those that vent to the outside. The invention relates to the latter, although combinations with the aforementioned recirculated air-operated sorption beds and linings are also possible. It is assumed below that the sorption bed is located in a channel with an inlet side and an outlet side, and is open at both ends, the design of a device according to the invention being defined by the features of independent claim 1.

[0012] Contamination of sorption beds open to the inside and outside of the casing is caused by diffusion and convection of contaminants, or, in the case of co-adsorbents, by both channel openings into the sorption bed. These contaminants can cause reversible or irreversible degradation of the sorption capacity of the sorption bed relative to the escaping refrigerant. Diffusion flow is driven solely by the concentration gradient, while convective input is caused by weather-induced air pressure or temperature gradients between the casing and the environment. The resulting pressure differences lead to equalizing flows through the sorption bed and thus to the transport of contaminants into the sorption bed.

[0013] Potential contaminants from the housing in which the cycle is carried out include: mono- and polyhydric alcohols, moisture, drawing greases, cutting oils, foaming agents and RCM oils.

[0014] Potential contaminants from the environment of the housing in which the cycle is carried out include: ketones, aldehydes, aromatics, mono- and polyhydric alcohols, siloxanes, moisture, fine dust, cigarette smoke.

[0015] When installed in buildings, the load from the installation room is generally considered to be a greater input of contaminants over the system's lifetime. Consequently, the degradation of the sorption bed occurs from both channel openings into the bed at different rates and degrees of degradation, resulting in the development of degradation zones into the bed from both sides. These zones reduce the loading capacity of the sorption bed over time until the function of the sorptive safety solution is so severely impaired that working fluid could escape into the installation room in the event of leaks.

[0016] The object of the invention is therefore to provide a safe device that no longer exhibits the described disadvantages. The invention solves this problem by providing a device for the safe execution of a left-handed thermodynamic cycle using a flammable working fluid, which is circulated in a closed, hermetically sealed working fluid circuit and which is contained within the device. at least one compressor for working fluid, at least one expansion device for working fluid, at least two heat exchangers for working fluid, each with at least two connections for heat transfer fluids, a housing which includes all devices connected to the closed working fluid circulation and may include further devices, at least one sorption channel with an adsorber through which gas which may contain the working fluid can flow, wherein the adsorber (12) includes a main adsorber (19) and the working fluid can be absorbed by the main adsorber (19) and flow through it, the sorption channel connects directly to the housing and is open to it, the sorption channel is open to the environment of the housing for gas, wherein the adsorber in the sorption channel has, in addition to the main adsorber, protective layers which are designed in such a way that the main adsorber and the adsorbent in the adsorber are protected from contamination,and the adsorber in the sorption channel consists of a main adsorber made of activated carbon, with at least one protective layer both upstream and downstream of the main adsorber.

[0017] Therefore, the sorption channel is to be extended and additional protective layers added to both sides. These protective layers are designed to target the respective contaminants and bind them permanently, preferably via chemisorption. Due to the different classes of contaminants, stacks of protective layers tailored to specific substance classes are also possible, allowing for selective sorption of each. In this way, the actual sorption bed, which is intended to bind the working fluid, is permanently protected.

[0018] Selective sorption of moisture, for example, is achieved using zeolites of types 3A, 4A, and 5A, as well as aluminum or silica gel. Ketones, aldehydes, aromatics, and mono- and polyhydric alcohols can be captured by zeolites with larger pore diameters or a semipermeable membrane. Fine dust can be removed by a HEPA filter, and oxygen by a copper bed. Sulfur compounds and acidic gases, if present, are removed by activated carbon impregnated with potassium carbonate or potassium iodide.

[0019] Different geometries and arrangements of the protective layers must be provided, adapted to the flow conditions in the sorption bed. In some designs, protective layers are arranged not only at the inlet and outlet openings of the sorption bed, but also section by section within the sorption bed itself.

[0020] The sorption bed is typically constructed as a packed bed of shaped particles, and the sorption channel is designed vertically. The shaped particles rest on an inlet screen, provided the flow through the sorption bed is from bottom to top. A top-mounted flow outlet is advantageous because a simple top-mounted hinged lid, which is lifted and opened by very low gas pressure, can prevent a large proportion of the contaminants from diffusing into the packed bed.

[0021] In some embodiments, the sorption channel is designed with multiple channels and features a deflection on the underside or top side. Specially designed sorption layers can be arranged within this deflection, with a higher flow resistance on the inner radius side than on the outer radius side. Alternatively, the deflection can simply contain an air layer. In other embodiments, the packing material is arranged in sieve baskets that can be removed individually. To further shape the flow, deflectors or baffles can be arranged within the sieve baskets. These baffles are themselves formed from sieve baskets containing packing material that is finer-grained and exhibits higher flow resistance.

[0022] Furthermore, a gas-permeable flap can be provided at the outlet opening of the sorption channel to prevent objects from entering the sorption channel from the outside. The invention is explained in more detail below with reference to two figures. These show: Figure 1 a heat pump with a single-pass sorption channel, Figure 2 a heat pump with a double-pass sorption channel.

[0023] Fig. 1Figure 1 shows a heat pump with an external adsorber, illustrated by a schematic diagram of a refrigeration circuit 1 with a compressor 2, a condenser 3, a pressure reducer 4, and an evaporator 5 in a housing consisting of an inner housing 6 and a directly adjoining single-pass sorption channel 11. The adsorber 12 is located in the sorption channel 11. The housing 6 is open at the bottom towards the sorption channel 11 and closed on all other sides, while the sorption channel 11 is open at the top. The heat pump has a heat source connection 7, a heat source flow 8, a heat sink flow 9, and a heat sink connection 10.

[0024] In this example, refrigeration circuit 1 is operated with the flammable working fluid propane, also known as R290. Propane is heavier than air; therefore, in the event of a leak in refrigeration circuit 1, it tends to sink to the bottom of the housing 6, although it mixes well in the case of small leaks. An opening with an inlet area 14 is therefore provided in the lower part of the housing 6, through which an air-propane mixture from the interior 13 enters the sorption channel 11 with the adsorber 12.

[0025] In the sorption channel 11, three protective layers 16, 17, and 18 are arranged in the direction of flow. These layers separate various contaminants originating from the interior 13 of the housing 6, thus preventing degradation of the main adsorber 19. The three protective layers 16, 17, and 18 rest on a screen 15 and are inserted into the sorption channel 11 in precisely fitting wire baskets. In the event of a leak, the flammable components of the working fluid, in the case of R290, propane, are adsorbed in the main adsorber 19. Further downstream in the direction of flow, three protective layers 20, 21, and 22 are arranged, preventing degradation of the main adsorber 19 by contaminants from the installation room. The three protective layers 16, 17 and 18 together with the main adsorber 19 and the three protective layers 20, 21 and 22 form the adsorber 12. Downstream in the direction of flow is the outlet opening 23, which is protected by a flap 24.The flap is not airtight, because otherwise, in the event of high pressure due to weather conditions, an overpressure could build up against the interior of the housing 13. However, it does provide mechanical protection.

[0026] Fig. 2Figure 1 shows a two-pass variant of the sorption channel 11. Such a multi-pass variant is used when the amount of adsorption material forming the main adsorber 19 cannot be accommodated simultaneously with the protective layers in a single-pass sorption channel due to space constraints. In the deflection layer 25, an additional protective layer can be placed, or it can be left empty, with the protective layer consisting of air. Without additional measures, a short-circuit flow would occur on the inside of the deflection, since the flow resistance is lower on the shortest path than further out, leading to uneven flow. Therefore, the deflection area must either be left empty, or a baffle layer 26, which provides increased flow resistance, is inserted on the inside.

[0027] Such baffle layers can also be installed within the fill material or on the walls to influence the flow. The material of the protective layers can also be partially mixed with or enriched with the adsorption material of the main adsorber to achieve improved protective effectiveness. Reference symbol list

[0028] 1 Refrigeration circuit 2 Compressor 3 Condenser 4 Pressure reducer 5 Evaporator 6 Inner casing 7 Heat source connection 8 Heat source supply 9 Heat sink supply 10 Heat sink connection 11 Sorption channel 12 Adsorber 13 Interior 14 Inlet area 15 Screen 16 Protective layer 17 Protective layer 18 Protective layer 19 Main adsorber 20 Protective layer 21 Protective layer 22 Protective layer 23 Outlet opening 24 Flap 25 Deflection layer 26 Baffle layer

Claims

1. Device for safely performing a counter-clockwise thermodynamic cycle (1) using a combustible working fluid, which is circulated in a closed, hermetically sealed working fluid circuit and which is contained in the device, comprising - at least one compressor (2) for working fluid, - at least one expansion device (4) for working fluid, - at least two heat exchangers (3, 5) for working fluid, each with at least two connections (7, 8, 9, 10) for heat exchanger fluids, - a housing (6) which comprises all devices connected to the closed working fluid circuit and may comprise further devices, - at least one sorption channel (11) with an adsorber (12) through which gas, which may contain the working fluid, can flow, wherein the adsorber (12) contains a main adsorber (19) and the working fluid can be absorbed by the main adsorber (19), - the sorption channel (11) is directly connected to the housing (6) and is open to it, - the sorption channel (11) is open to the environment of the housing for gas, characterised in that - the adsorber (12) in the sorption channel (11) has, in addition to the main adsorber (19), protective layers (16, 17, 18, 20, 21, 22) which are designed such that the main adsorber (19) in the adsorber (12) is protected against contamination, - the main adsorber (19) is made of activated carbon, and at least one of the protective layers (16, 17, 18, 20, 21, 22) is arranged in the sorption channel (11) both upstream and downstream of the main adsorber (19) in the direction of flow.

2. Device according to claim 1, characterised in that the protective layers (16, 17, 18, 20, 21, 22) are formed from materials or mixtures containing zeolites of type 3A, 4A and 5A, aluminium, silica gel, HEPA filters, copper, activated carbon impregnated with potassium carbonate or potassium iodide, or zeolites with larger pore diameters or a semipermeable membrane .

3. Device according to one of claims 1 or 2, characterised in that the sorption channel (11) has multiple passages and at least one deflection (25).

4. Device according to claim 3, characterised in that the deflection (25) contains a further protective layer, which is made of air.

5. Device according to one of claims 1 to 4, characterised in that the individual protective layers and the main adsorber are arranged in individually removable mesh baskets.

6. Device according to one of claims 1 to 5, characterised in that the sorption channel (11) contains flow-equalising elements or baffles (26).

7. Device according to one of claims 1 to 6, characterised in that the sorption channel (11) has a gas-permeable flap (24) at its outlet opening (23).