MEMBRANE GAS SEPARATOR

Description

[0001] The invention relates to the separation of flammable gases in a heating circuit or brine cooling circuit. It is known that heating circuits occasionally need to be vented because air can accumulate in the system. This usually occurs due to leaks at elevated points in the heating circuit, where a leak combined with negative pressure leads to air being drawn into the water circuit. In some cases, the air is dissolved in the top-up water and is released when it is heated. The same applies to brine split systems where brine is present in the heating circuit.

[0002] If air is present in the system, this often leads to malfunctions and damage to system components due to corrosion. Components with wear parts, such as circulation pumps, are particularly affected. Furthermore, air pockets can impede circulation and disrupt or even interrupt heat distribution. These malfunctions are often accompanied by flow and cavitation noises. Air vents are therefore commonly used to remove such air from the system. However, these vents become problematic when the system contains other substances besides air.

[0003] In newer refrigeration systems, such as those used in heat pumps, flammable natural refrigerants like R290 and R1270 are no longer used. Their operating pressure is typically higher than the usual pressure in heating circuits, both on the heat-receiving and heat-emitting sides. Depending on the configuration and operating mode, leaks in the condenser or evaporator can therefore lead to the escape of gaseous, flammable working fluid from the refrigeration circuit into the heating or brine circuit. This could then result in the release of a flammable mixture during venting. For safety reasons, this must be prevented at all costs. The same applies, of course, to conventional flammable refrigerants such as R32, should these still be in use.

[0004] In the prior art, this is prevented by using double-walled stainless steel heat exchangers as condensers and evaporators. In the event of a leak, the flammable working fluid enters the space between the two walls, where it is extracted separately and subjected to post-treatment. This post-treatment can also be omitted if there is a safe venting path to the atmosphere, where mixing with air occurs in such a quantity that an ignitable mixture cannot form. The gap is usually only a few tenths of a millimeter. However, these designs are expensive and also impede heat transfer because the gap acts like thermal insulation, thus reducing the achievable efficiency. Moreover, leaks can affect both walls. For these reasons, the invention focuses on the vents.

[0005] A distinction must be made between manual and automatic air vents, which are also known as quick-release air vents. Manual venting is achieved using vent valves. These are simply taps that are opened and closed as needed, once the gas in the system, usually air, has completely escaped. However, the system can also be vented automatically using quick-release air vents. These are available in a wide variety of designs.

[0006] DE 10 2006 015 263 A1 describes an automatic air vent valve with a diaphragm that is permeable to gaseous media. The diaphragm material is a plastic, such as PTFE or PP, and is oleophobic and / or hydrophobic and non-wettable at very low surface tensions. The diaphragm material is impermeable to liquids and, depending on the design, can withstand the high pressures of a heating system. The diaphragm can be designed either as a porous ring through which flow is radial or as a disc through which flow is axial. For other designs, reference is made to the extensive prior art presented in DE 10 2006 015 263 A1.

[0007] DE 10 2009 048 402 A1 and DE 10 2010 024 107 A1 describe further developments of automatic venting devices as modular systems. DE 10 2006 021 454 A1 describes an improved embodiment compared to DE 10 2006 015 263 A1, which also includes a float. Other known embodiments involve the capture of fine gas bubbles by means of brushes or Pall rings, or other packings and bulk materials in the flow path, which lead to coagulation and improved separation from the liquid medium.

[0008] Automatic air vents without floats typically consist of an upper part, a middle part, and a lower part, the latter containing the connections to the water circuit. The middle part has a receptacle for a diaphragm assembly facing the lower part and a connection for gas to the upper part. The escaping gas from the water circuit enters the watertight pipe diaphragm from below, passes through it, and exits through a perforated disc.

[0009] The automatic air vents with floats function as follows: When liquid is circulated or pumped through the system, the existing gas is forced into the vent by the flow pressure as soon as the system starts up. During this process, the float ball initially remains in the lower position. This opens the valve fully, allowing any accumulated air to escape. Once the automatic air vent has completed the initial venting, liquid flows into the vent. As the liquid level rises, the float's position also moves upwards, and the vent valve closes. If air then accumulates again, the liquid level and the float drop. This causes the valve to reopen to remove the air from the system. When more liquid flows in, the float rises and closes the valve.A membrane is not required for this.

[0010] The float and diaphragm can also be used together. Venting is carried out via a diaphragm, while the float provides protection against system overpressure, such as that encountered during a pressure test, as shown in DE 20 2018 003 488 U1.

[0011] DE 10 2011 120 002 A discloses a rapid air vent with membrane for air separators for heating technology.

[0012] However, known membranes for air vents allow both air and propane gas to pass through, thus preventing the formation of a flammable mixture after passage through the membrane. Furthermore, no membranes are known that are selective with respect to the individual gas components when these are to be separated from a liquid.

[0013] However, it is possible to separate gaseous propane from air components using a membrane. DE 600 32 610 T2 describes a method for producing such a membrane and shows in Example 5, Section

[0051] on page 33 how propane can be obtained using such a membrane. This is due, among other things, to the fact that the working diameters of lighter gases such as oxygen, nitrogen, and carbon dioxide are smaller than those of propane.

[0014] As is known, the working diameters of oxygen are 3.46 angstroms, nitrogen 3.64 angstroms, carbon dioxide 3.3 angstroms, methane 3.8 angstroms, and propane 4.3 angstroms. Other flammable components of R290, R600a, or R1270 therefore always have molecular sizes greater than 3.7 angstroms. Consequently, a porous film with a working diameter of 3.7 angstroms retains methane, ethane, propane, isobutane, and butane, while allowing the other air components, oxygen and nitrogen, to pass through. With a pore size of 3.5 angstroms, the porous film can be made permeable to oxygen but impermeable to nitrogen and propane. This would also reliably prevent the formation of a flammable gas mixture, but would normally increase the amount of gas to be removed due to the nitrogen produced.

[0015] The object of the invention is therefore to provide a vent that separates gaseous air components and gaseous flammable components from the fluid circulation of a heat transfer medium and releases them separately from each other.

[0016] The invention solves this problem by means of a vent for air conditioning, heating, and ventilation technology, comprising two connections for a water-carrying circuit, means for separating gas bubbles and separating gas components and liquid while retaining the liquid in the water-carrying circuit, from an aqueous liquid, at least one chamber for collecting separated gas components, furthermore a vent for separated air components, wherein a retention membrane is additionally provided in the flow path of the gas to be separated, the pores of which are such that oxygen molecules can pass through, but flammable gas components are retained, and between the first means which separates the liquid from the gas space and the retention membrane a further chamber with a gas vent is provided.

[0017] Otherwise, the vent corresponds to known designs for manual and automatic vents with or without a float. The invention works by first capturing all the gas that bubbles out of the aqueous solution in the chamber formed between the means for separating gas bubbles and the gas components and liquid. Subsequently, at least a large portion of the oxygen is removed from this chamber through a membrane. It is not necessary for the oxygen to be completely removed; it is entirely sufficient if the gas mixture drawn from the chamber is flammable but no longer explosive, and if it is ensured that no flammable gas components escape into the atmosphere via the vent during normal venting.

[0018] Two different membrane types are used alternatively for gas separation in the containment membrane. These are, on the one hand, semipermeable walls and, on the other hand, size-selective membranes. With semipermeable walls, the gas dissolves in the solid wall and diffuses through it. Gases that do not dissolve do not diffuse. Depending on the working fluid, a semipermeable wall is selected in which alkanes cannot dissolve, unlike oxygen and, ideally, also nitrogen.

[0019] For size-selective membranes, which are typically constructed from thin films, the diameter is crucial. Selective oxygen removal is possible if the pore diameter of the retention membrane is dimensioned larger than 3.46 angstroms but smaller than 3.64 angstroms, with outgassing carbon dioxide also being removed along with the oxygen. In this case, a mixture of nitrogen and flammable alkanes, depending on the working fluid used in the refrigeration circuit, collects in the chamber between the gas bubble separator and the retention membrane, along with a small amount of oxygen corresponding to the partial back pressure of the atmosphere.

[0020] However, it is also possible to design the retention membrane so that nitrogen is also carried away through the second membrane by dimensioning the pore size to be smaller than 3.8 angstroms. This concentrates all flammable components in the chamber, while the air components all escape through the retention membrane until a partial pressure equilibrium with the atmosphere is reached. In this case, the same collection and disposal device used in conventional state-of-the-art systems with the spaces between double-walled heat exchangers can be used for the gas extracted from the chamber. This could, for example, be a duct to the outside or an activated carbon adsorber.

[0021] If the flammable components are not methane or ethane, but propane and / or butane, a pore distribution can also be used where the largest pores are smaller than 4.3 angstroms. Such a membrane with a pore distribution of 3.5 to 4.3 angstroms is more cost-effective to manufacture than one with a narrow distribution.

[0022] In one embodiment of the invention, the gas space formed jointly by the chamber and the exhaust is equipped with a sensor for flammable gas. This allows for the detection of undetected leaks, which have resulted in flammable working fluid entering the heating or cooling water. Because it is insoluble, it then travels as gas bubbles to the vent, where it is separated into a gaseous state and enters the gas space formed jointly by the chamber and the vent. Since there are no other points of entry, this can be considered a reliable indicator of a leak in one of the heat exchangers and can lead to the initiation of appropriate measures, such as shutting down the water circuit.

[0023] The passage of molecules through pores requires, on the one hand, a sufficient surface area and, on the other hand, a pressure difference between the partial pressures. With regard to oxygen, this means that the atmospheric partial pressure of oxygen also leads to the introduction of oxygen into the chamber, provided the pressure in the chamber is not higher than the ambient pressure. It is therefore advantageous not to position the vent at the highest point of the water circuit, as is currently the norm, but rather at the point of highest water pressure downstream of the heat exchanger through which the working fluid flows. Furthermore, it is beneficial to maintain the chamber in which the combustible gas mixture is collected under elevated pressure by equipping the gas outlet with an adjustable pressure relief valve and ensuring that the pressure reduction to the environment occurs only within or after the second membrane.In this way, a sufficient reduction of the oxygen content in the chamber's exhaust is achieved and the ignition limits of the gas mixture extracted for post-treatment are reliably undercut.

[0024] The arrangement of the two membrane surfaces can be carried out according to known state of the art, either in a tubular or ring shape, with the gas passing radially through, or in a disc shape, with the gas passing axially through. Due to the pressure conditions, it can therefore be advantageous for the first membrane between the liquid and the chamber to be disc-shaped, as it only needs to withstand small pressure differences, and for the second membrane to be designed as a ring membrane with a supporting structure. A construction consisting of two concentric tubes, two parallel discs, or other designs is also possible.

[0025] The invention is explained in more detail below with reference to three schematic diagrams. These show: Fig. 1 a membrane separator for flammable gas, Fig. 2 a float-free air vent with membrane separator, Fig. 3 a deaerator with float and membrane separator.

[0026] Fig. 1 Figure 1 shows a membrane separator for flammable gas as a module, which in this form can be attached to or integrated into a conventional automatic air vent. The gas mixture 1, which comes from an automatic or manual air vent, normally consists of air, but in the event of a leak, it also contains flammable components. If the water circuit is connected to a refrigeration circuit operating with the refrigerant R290, this is, for example, propane. When using R600a or R1270, it can also be other alkanes or alkenes.

[0027] The gas mixture enters the round inner chamber 2, which is enclosed on the outside by the annular containment membrane 3. The containment membrane 3 has a pore diameter of 4 angstroms and is permeable to oxygen, nitrogen, and carbon dioxide, but not to propane and higher hydrocarbons. Due to the pressure differential, it is constructed in two layers. On the inner side, it has a film whose pores retain the combustible gas components; behind this, it has a supporting structure that can absorb the forces resulting from the pressure differential.

[0028] Normally, all the gas, provided it consists only of degassing air, passes through the retaining membrane 3 into the outer chamber 4, which is kept under pressure. In the event of a leak, however, some of the gas remains in the inner chamber 2. In this case, the gas sensor 5 indicates that flammable gas is accumulating in the inner chamber 2. This triggers an alarm, and some of the gas is released from the inner chamber 2, with the pressure being monitored by the pressure gauge 6. The pressure relief valve 7 ensures that the pressure does not drop too low during the release, and the remaining pressurized flammable gas 8 undergoes standard post-treatment.

[0029] The degassing air is kept in the outer chamber 4 at a pressure lower than that of the inner chamber, with the pressure difference acting as the driving force for transport through the retention membrane. However, the pressure difference must not become too high to avoid damaging the sensitive retention membrane, and it must be large enough to prevent the oxygen back pressure from causing excessive oxygen to remain in the inner chamber 2. The pressure in the outer chamber is measured by the pressure gauge 9 and adjusted accordingly using the adjustable pressure relief valve 10. The degassing air 11 is then released.

[0030] Fig. 2 Figure 1 shows a floatless air vent with a membrane separator. The air vent consists of a water inlet 12, a lower section 13 connected to it in which the separation of gas bubbles from the water flow takes place by known means, a water outlet 14 connected to it, a middle section 15 in which water and gas are located, a water-impermeable membrane 17 which is held in place on its lower and upper sides by support discs 16 and 18, and an upper section 19 to which the membrane separator with the retention membrane is connected.

[0031] When gas bubbles in the water enter the lower section 13, they are coagulated, e.g., by means of Pall rings, brushes, or similar devices, and then rise into the middle section 15, where they displace the water in contact with the impermeable membrane. The gas can then pass through the impermeable membrane and enter the upper section 19, and from there into the inner chamber 2 of the membrane separator. The further process is as described in Fig. 1 As described. As soon as the water level in the middle section 15 reaches the water-impermeable membrane 17 again, the cycle starts again from the beginning.

[0032] Fig. 3 Figure 1 shows a deaerator with a float and diaphragm separator. Instead of a watertight diaphragm, the separation of water and gas is achieved by a float 20 in the central section 15. Initially, the float is pushed upwards by the water pressure, and the lever mechanism 21 causes the valve 22 to close tightly. As soon as gas accumulates in the central section, the float is pushed downwards in accordance with the falling water level, and the lever mechanism 21 opens the valve 22. The gas can then flow into the inner chamber 2 of the diaphragm separator; the subsequent process is described in Figure 2. Fig. 1 and Fig. 2 Described. Reference symbol list

[0033] 1 Gas mixture 2 Inner chamber 3 Retaining membrane 4 Outer chamber 5 Gas sensor 6 Pressure measurement 7 Pressure holding valve 8 Flammable gas 9 Pressure measurement 10 Pressure holding valve 11 Degassing air 12 Water inlet 13 Bottom part 14 Water outlet 15 Middle part 16 Support disc 17 Waterproof membrane 18 Support disc 19 Top part 20 Float 21 Lever mechanism 22 Valve

Claims

1. Vent for air conditioning, heating and ventilation technology, comprising - two connections (12, 14) for a water-carrying circuit, - means for separating gas bubbles and separating (17, 20) gas components and liquid from an aqueous liquid while retaining the liquid in the water-carrying circuit, - at least one chamber (19) for collecting separated gas components, - furthermore at least one outlet (11) for separated air components, characterised in that - a retention membrane (3) is additionally provided in the flow path of the gas to be separated, the pores of which are designed so that oxygen molecules can pass through but combustible gas components are retained, - a further chamber (2) with a gas outlet (8) is provided between the means separating the liquid from the gas space and the retention membrane (3).

2. Vent according to claim 1, characterised in that the pore diameter of the retention membrane (3) is selected to be greater than 3.46 Ångström but less than 4.3 Ångström.

3. Vent according to claim 1, characterised in that the pore diameter of the retention membrane (3) is selected to be greater than 3.46 Ångström but less than 3.8 Ångström.

4. Vent according to claim 1, characterised in that the pore diameter of the retention membrane (3) is selected to be greater than 3.46 Ångström but less than 3.64 Ångström.

5. Vent according to one of claims 1 to 4, characterised in that the gas space (2) formed jointly by the chamber and the extractor (8) is equipped with a sensor (5) for combustible gas.

6. Vent according to one of claims 1 to 5, characterised in that the gas extractor (8) from the chamber (2) is equipped with an adjustable pressure maintenance valve (7).

7. Vent according to any one of claims 1 to 6, characterised in that the retaining membrane (3) is designed as a ring membrane.

8. Vent according to one of claims 1 to 6, characterised in that the retaining membrane (3) is designed as a disc membrane.