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 like 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 impede heat transfer because the space acts like thermal insulation, thus reducing the achievable efficiency. Moreover, leaks can affect both walls. For these reasons, the invention focuses on the venting of heating circuits.

[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. However, such an air vent valve would separate both air and flammable gases simultaneously, which could lead to an ignitable mixture.

[0007] German patent applications 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 designs involve the capture of fine gas bubbles using 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. However, the problem of separating a potentially ignitable mixture also exists in these designs.

[0008] However, the known membranes for vents allow both air and flammable gases such as propane to pass through, so the formation of a flammable mixture after passing through the membrane cannot be prevented.

[0009] The processes of gas permeation and pervaporation will be used for this purpose. The only difference between these processes is that in pervaporation, the substance to be separated is additionally evaporated, which requires the input of heat and the application of a partial pressure vacuum. In both cases, gases are separated, and two coupled transport mechanisms are present within the membrane. First, the substance to be separated, in this case the working fluid or refrigerant, must adhere to or adsorb onto the membrane. Subsequently, the substance must diffuse through the membrane. High selectivity is desirable for both mechanisms, and low transport resistance is desirable for the substance to be separated.

[0010] The separation of gas bubbles from the flammable refrigerant can be achieved from either the liquid or the gaseous state. In the first case, two gas separators are required: the first is a diaphragm gas separator, and the second is a conventional air vent. The diaphragm gas separator serves to selectively remove gas bubbles from the flammable working fluid in the heating circuit water before the air is separated in the conventional air vent. While the conventional air vent is typically placed at the highest point of the heating circuit, the upstream diaphragm gas separator should be positioned at the lowest point, as this is where the highest pressure differential across the diaphragm exists, thus achieving the best possible separation efficiency.

[0011] In the second case, a conventional automatic air separator is modified so that the flammable gas is separated from the air while still under pressure, before the separated air is depressurized and released into the atmosphere. Both separation processes share the characteristic that the separation occurs from a gas phase. In the first case, it is gas bubbles of undissolved or insoluble gas that adhere to the membrane before being adsorbed by it; in the second case, it is a homogeneous gas phase. Whether the phase is homogeneous or heterogeneous is irrelevant, but gases dissolved in the heating circuit fluid are not separated in this way, only flammable refrigerants in gas bubbles.

[0012] For this purpose, a composite membrane is used. A similar membrane is described in EP 3 483 526 A1 and EP 3 483 527 A1, but the substances to be separated differ from those described here. The methods described in those two documents involve separating air introduced into a refrigeration circuit from the refrigerant and recovering the refrigerant, whereas here the refrigerant introduced into an aqueous heat transfer medium is to be separated together with the introduced air. Therefore, the application is different.

[0013] A hydrophobic, ceramic layer of zeolite is used as the surface facing the side where the working fluid or refrigerant to be separated accumulates; preferred zeolites are NaY zeolite, ZSM-5 zeolite, and silicalite-1 zeolite. These can also be combined in multiple layers. A rubber-like polymer membrane is used as the core material; preferably polydimethylsiloxane, polyetherblockamide, or polybutadiene, either individually or in mixtures.

[0014] The object of the invention is therefore to provide a separator for air conditioning, heating and ventilation technology that separately separates and removes gaseous flammable components from the fluid circulation of a heat transfer medium.

[0015] The invention solves this problem by using a membrane gas separator for air conditioning, heating, and ventilation technology, comprising Means for separating gas bubbles, which may contain a flammable gas, from a flowing aqueous liquid, and at least one chamber for collecting separated gas components, a vent for the separated gas components, wherein a composite membrane is provided in the flow path of the gas to be separated, the membrane being composed of at least two layers, of which at least one layer is formed from a ceramic layer of zeolite and at least one further layer from a rubber-like polymer membrane, and the at least one layer of the ceramic layer of zeolite is provided in the flow path of the gas to be separated as the first layer in which the flammable gas is adsorbed either from the gas phase or from the liquid phase, the further layer being formed subsequently in the flow path of the gas to be separated as a diffusion layer,The chamber for collecting separated gas components is arranged downstream in the flow path, and the chamber for collecting separated gas components is connected to a fume hood operating under negative pressure.

[0016] The ceramic layer of the zeolite composite membrane is formed in a known manner from layers of NaY-zeolite, ZSM-5-zeolite, or silicalite-1-zeolite, or from a mixture thereof. This mixture can also consist of several individual layers and be equipped with a hydrophobic surface coating.

[0017] Special features relate to the rubber-like polymer membrane of the composite membrane. This can be made of polydimethylsiloxane, polyetherblockamide, or polybutadiene, or a mixture thereof. If the mechanical properties of the composite membrane are insufficient to stably support the applied pressure difference, an inactive and permeable support layer can, of course, be added.

[0018] In a known manner, a vacuum pump is provided at the exhaust of the chamber for collecting separated gas components. This vacuum pump ensures that a sufficient partial pressure gradient is always present across the composite membrane; the vacuum pump only needs to be switched on when flammable gas is actually detected on the outside of the membrane.

[0019] The invention is explained in more detail below with reference to two schematic diagrams. These show: Fig. 1 a membrane gas separator for separation from a homogeneous gas phase, Fig. 2 a membrane gas separator for separating gas bubbles from liquid.

[0020] Fig. 1 Figure 1 shows a membrane gas separator for flammable gas as a module, which in this form can be 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.

[0021] The gas mixture 1 enters the round inner chamber 2, which is enclosed on the outside by a ring-shaped composite membrane. The composite membrane consists of the inner ceramic layer 3 made of zeolite, the rubber-like polymer membrane 4, and the supporting framework 5. Only if flammable gas is present in the gas mixture 1 does it diffuse through the composite membrane into the outer collection chamber 6, which is kept under vacuum. The vacuum is measured by the pressure gauge 7; if it exceeds a predefined value, it is removed by the vacuum pump 8 for further use 9 or disposal.

[0022] The remaining gas from the gas mixture, which is not flammable, is released into the atmosphere 13 via a reducing valve 12 after a concentration measurement 10, in which it is checked whether there are residual components of flammable gas in the gas mixture, and a pressure measurement 11.

[0023] Fig. 2 Figure 1 shows a membrane gas separator for separating gas bubbles from liquid 14, typically a heating circuit or a brine circuit. To coagulate the gas bubbles in the liquid, which are often very fine, the liquid is passed through a tangle 16, where Pall rings or brushes may also be used. A flow element 15 then creates an annular flow in the membrane to shorten the path of the gas bubbles to the membrane wall. The bubbles then adhere to the ceramic layer 3, and the flammable gas diffuses through the composite membrane in a manner analogous to that described in Figure 2. Fig. 1 described.

[0024] The liquid 17, now depleted of flammable gas and still containing air bubbles, is conveyed further and can be fed to a standard automatic air separator where air can be safely separated. Reference symbol list

[0025] 1 Gas mixture 2 Inner chamber 3 Ceramic layer 4 Polymer membrane 5 Support frame 6 Collection chamber 7 Pressure measurement 8 Vacuum pump 9 Further use 10 Concentration measurement 11 Pressure measurement 12 Reducing valve 13 Atmosphere 14 Liquid 15 Flow section 16 Tangles 17 Liquid

Claims

1. Use of a membrane gas separator for air conditioning-heating-ventilation technology for separating gas bubbles, which may contain a flammable gas, from a flowing aqueous liquid for transferring heat from or to a refrigeration circuit, the refrigeration circuit being operated with a flammable refrigerant, the membrane separator comprising - at least one chamber (6) for collecting separated gas components containing refrigerant, - a fume cupboard for the separated gas containing refrigerant - a composite membrane in the flow path of the gas to be separated, which is composed of at least two layers, of which at least one layer (3) is formed from a ceramic layer of zeolite and at least one further layer (4) is formed from a rubber-like polymer membrane - and the at least one layer of the ceramic layer of zeolite is provided as the first layer in the flow path of the gas to be separated, - downstream of the further layer of a rubbery polymer membrane in the flow path is the chamber for collecting separated gas components, which has a connection that is connected to an exhaust under negative pressure. characterised in that - the flammable gas components containing refrigerant are adsorbed in the ceramic zeolite layer either from the gas phase or from the liquid phase, - subsequently in the flow path of the gas to be separated, the further layer of a rubber-like polymer membrane is formed as a diffusion layer.

2. Use of a gas separator according to claim 1, characterised in that the rubber-like polymer membrane is formed from polydimethylsiloxane.

3. Use of a gas separator according to claim 1, characterised in that the rubber-like polymer membrane is formed from polyether block amide4. Use of a gas separator according to claim 1, characterised in that the rubber-like polymer membrane is formed from polybutadiene5. Use of a gas separator according to one of claims 2 to 4, characterised in that the rubber-like polymer membrane is formed from a mixture of polydimethylsiloxane, polyether block amide and polybutadiene.