Natural circulation evaporator for water supply lines for decentralized geothermal heat recovery

Abstract

The main claims comprise two types of natural circulation evaporators for water supply lines, both of which permit a functional extension for decentralized recovery of the near-surface geothermal energy that is regeneratively contained in the supply water. This includes, on the one hand, the application to existing pipelines and, on the other hand, a new construction application using a combination pipeline. As a result, heat pumps in the utility buildings in contact with lines can be supplied with low-temperature geothermal heat, from which they generate high-temperature useful heat.

Description

[0001] Natural circulation evaporator for water supply lines for decentralized geothermal energy generation

[0002] Description

[0003] The invention relates to two types of natural circulation evaporators for water supply pipes, both of which enable a functional extension for the decentralized extraction of the near-surface geothermal energy contained in the supply water. This includes, on the one hand, application on existing pipelines and, on the other hand, application in new construction using a combined pipeline. This allows heat pumps in the adjacent utility buildings to be supplied with low-temperature geothermal energy, which then generate high-temperature useful heat.

[0004] The state of the art is documented in the following publications:

[0005] DE 10 2007 054472 A1 discloses the extraction of heat from a water supply line using a heat exchanger within the supply line. In contrast, in the present invention, such a heat exchanger is arranged outside the water supply line in the form of an evaporator heat exchanger.

[0006] DE 10 2013 000213 A1 describes a heat exchanger for electronic components, which is designed as an open-pore metallic body through which a single-phase liquid or gaseous temperature control fluid flows. The single-phase circulating volume flow is regulated as forced convection by means of a pump or valve. In contrast, the present invention generates an automatic two-phase liquid / gas natural circulation flow in the evaporator heat exchangers, which are constructed from a porous-permeable solid. Furthermore, the heat transfer processes from a turbulent liquid flow (supply water) to a two-phase, single-component heat transfer fluid are fundamentally different from the heat transfer from a solid body (electronics) to a single-phase heat transfer fluid.

[0007] According to DE 20 2008 017 571 U1, a tubular hollow profile is encased by a hollow profile channel spirally along the outer surface of the hollow profile, wherein the hollow profile channel is designed as a heat exchanger through which a heat transfer fluid flows. In contrast, the present invention does not use a hollow profile channel, but rather a porous-permeable solid within an evaporator heat transfer body.

[0008] DE 27 47 356 A1 discloses that heat is extracted from the surrounding standing surface and groundwater of a packed-layer storage tank (underground well) via a heat exchanger coil in an open cladding tube. In contrast, the present invention uses a porous-permeable solid within an evaporator heat transfer body for heat transfer.

[0009] DE 10 2006 001 169 A1 describes a method for improving heat recovery from near-surface geothermal energy through water infiltration. For this purpose, known geothermal heat exchanger devices in the form of horizontal coil collectors are used, which are to be installed in the ground below the sewer. In contrast, the present invention uses porous-permeable evaporator heat exchangers on the supply water pipeline to recover geothermal energy. EP 2 223 020 B1 discloses a method for extracting geothermal energy from a water supply network, wherein partial water volume flows are diverted via bypass lines parallel to the main line and flow through the heat exchanger tanks connected there.A metal pipe is installed in the tanks, through which a liquid refrigerant flows from top to bottom according to the heat pipe principle, where it is evaporated, and the refrigerant gas rises in the same pipe, allowing the natural refrigerant circulation between the evaporator and the heat pump to be achieved via a single connecting pipe. In practice, however, there are problems with the space restrictions for the bypass lines and the limited heat energy recovery due to partial volume flows.

[0010] The object of the invention is to solve the corresponding problems by means of a particularly advantageous technical implementation that is functional and quality-assured for drinking water supply.

[0011] This problem is solved by the features of the two independent main claims.

[0012] Natural circulation evaporator for existing pipelines of water supply networks as a functional extension for decentralized geothermal energy production, characterized in that

[0013] • no evaporator compartments are located within the supply water pipeline,

[0014] • the existing supply water pipes embedded in the ground are partially encased by two similar evaporator half-shell heat transfer bodies, which are connected to each other via their vertically arranged boundary surfaces and thermally coupled around the existing pipe,

[0015] • the evaporator half-shell heat transfer bodies consist of a single piece made of a porous-permeable solid with good thermal conductivity, preferably open-pore metal foam, which are each hydraulically sealed and pressure-resistant by an enclosing wall,

[0016] • the enclosing wall consists of a solid material with good thermal conductivity, preferably solid metal, which completely and firmly fills the pore space structure of the porous-permeable solid in its edge zone, so that a high thermal coupling is formed over a large contact inner surface,

[0017] • a single-component heat transfer fluid, preferably carbon dioxide (R744), is formed in the permeable pore space of the evaporator half-shell heat transfer body due to a large number of nucleation sites and bubble dynamics as a self-acting two-phase natural circulation flow, whereby at the same time the liquid phase flows in from below due to gravity, is converted into steam and the gaseous phase rises due to density-buoyancy and flows out at the top as a gas,

[0018] • the geothermal energy stored in the supply water is transferred to the colder heat transfer fluid circulating in the pore space of the porous-permeable solid due to the convective water flow, heat conduction from the existing pipe wall, the enclosing wall and the solid matrix of the evaporator heat transfer bodies as well as the developed temperature gradient, and

[0019] • via building connection lines for the heat transfer fluid, consisting of a gas riser line and a liquid return line, the convective heat energy transfer between the evaporator half-shell heat transfer bodies located below and the decentralized heat pumps located above in the heat utilization buildings adjacent to the supply line is generated through natural circulation.

[0020] In particular, the natural circulation evaporator is designed in such a way that there is no heat exchanger within the existing pipeline. Instead, the evaporator half-shell heat transfer bodies, which can be designed in particular as described above, are always located outside the existing pipelines. This means that they do not need to be structurally modified. In particular, there are no compartments, also called divisions, volumes, or areas, within the existing pipelines that serve for heat transfer.

[0021] Natural circulation evaporator integrated into a combined pipeline designed as a new pipeline for water supply and decentralized geothermal energy production, characterized in that

[0022] • no evaporator compartments are located within supply water compartments and vice versa,

[0023] • the combined pipeline laid in the ground consists of an outdoor pipe for the flow transport of the supply water and an evaporator-internal heat transfer body for the circulation of the heat transfer fluid,

[0024] • the external space duct is made up of a good thermally conductive outer wall and a good thermally conductive inner wall, which corresponds to the enclosing wall and spacers,

[0025] • the evaporator's internal heat transfer body consists of a porous-permeable solid, preferably open-pore metal foam, which is hermetically sealed by the enclosing wall and divided into equidistant longitudinal internal sections by highly thermally conductive, hydraulically sealed vertical partition walls,

[0026] • the enclosing wall consists of a solid material with good thermal conductivity, preferably solid metal, which completely and firmly fills the pore space structure of the porous-permeable solid in its edge zone, so that a high thermal coupling is formed over a large contact inner surface,

[0027] • a single-component heat transfer fluid, preferably carbon dioxide (R744), is formed in the permeable pore space of the evaporator's internal heat transfer body as a self-acting two-phase natural circulation flow due to a large number of nucleation sites and bubble dynamics, whereby at the same time the liquid phase flows in from below due to gravity, is converted into steam, and the gaseous phase rises due to density buoyancy and flows out at the top as a gas, • the geothermal energy stored in the supply water is transferred to the colder heat transfer fluid circulating in the pore space of the porous-permeable solid due to the convective water flow, heat conduction from the enclosing wall and solid matrix of the evaporator heat transfer body, as well as the developed temperature gradient,

[0028] • via building connection lines for the heat transfer fluid, consisting of gas rise line and liquid return line, the convective heat energy transfer between the evaporator interior heat transfer bodies and the decentralized heat pumps in the heat utilization buildings adjacent to the supply line is generated by the natural circulation and

[0029] • the building connection pipes for the consumption water are connected to the outside of the combined pipeline.

[0030] The ecological and economic benefits achieved with the invention are related to the energy and climate transition. There is significant market potential for upgrading to combined water supply and geothermal energy networks. This can be achieved directly in residential buildings by adding additional pipes to existing pipelines or by constructing new pipelines or replacing sections. The combined pipeline thus forms the basis for innovative meshed ring networks that can simultaneously fulfill the functions of transport, distribution, development, transmission, extraction, and sustainable regeneration of low-temperature geothermal energy. This enables the emission-free, decentralized generation of high-temperature useful heat using climate-neutral heat pump electricity.

[0031] Compared to a district heating network, this results in significant savings in investment and operating costs, as well as in planning and construction time for centralized fossil-free heat sources and pipe laying. Further advantages include the high efficiency and the associated electricity savings, as well as high flow temperatures in the heating circuit, which are required for use in old buildings that have not been renovated for energy efficiency, i.e., without insulation when using existing radiators, and generally for hygienic reasons (Legionella) for hot water preparation (at least 60°C). The seasonal performance factor (SPF) is important here, which evaluates the heat pump in conjunction with the heat source. Due to the consistently high ground temperature of approximately 10 to 14°C, even in the colder winter months, this factor is significantly higher for the geothermal source according to the invention (SPF approx. 4-5) than for the use of ambient air (-3 to 3°C) as a heat source (SPF approx. 2-2.5).Furthermore, the one- to two-month phase shift between the negative peak in air temperature (highest heat consumption) and the subsequent negative peak in geothermal temperature has the positive effect that relatively high supply water temperatures still prevail in the coldest winter months, while their slight decrease towards the end of winter is no longer relevant because higher air temperatures already prevail. Due to the low temperature level, the air-source heat pump is at a disadvantage, as technical optimization is physically and thermodynamically limited. Use in unrenovated old buildings is therefore not economical in winter when the air is cold, as high power consumption is required. In addition, particularly in urban areas, there are problems with the installation of the outdoor unit in terms of space requirements, appearance, and noise pollution.

[0032] Geothermal sources are also superior to the use of open bodies of water as central heat sources, such as seawater, river and lake water, as well as raw and stored water, which must be operated in conjunction with a central high-temperature large-scale heat pump and a high-temperature district heating network with supply and return pipes. The very low water temperature in the cold winter months of approximately -3 to 3 °C (similar to the air temperature), additional energy consumption for the operation of district heating network pumps (in addition to the heat pump drive), heat losses during district heating distribution, and limited heat extraction rates lead to inefficient seasonal efficiency ratios of approximately 2.5 to 3. The invention is explained in more detail below using exemplary embodiments with reference to the accompanying figures.

[0033] It shows:

[0034] Fig. 1 shows in cross section the schematic structure of a natural circulation evaporator for an existing pipeline and

[0035] Fig. 2 shows in cross section the schematic structure of a natural circulation evaporator integrated into a new combined pipeline and

[0036] According to Fig. 1, an existing underground water supply pipeline 1, consisting, for example, of a cast iron pipe wall 5, is encased and thermally coupled by two identical, one-piece prefabricated evaporator half-shell heat transfer bodies 2. These half-bodies are each constructed internally from a porous-permeable solid 3 (e.g., metal foam), which is completely hermetically sealed by an enclosing wall 4 (e.g., solid metal). Due to the transfer of geothermal energy from the warmer supply water to the heat transfer bodies, the colder heat transfer fluid (e.g., carbon dioxide) contained in the porous-permeable metal foam is evaporated, creating a self-convective, two-phase natural circulation.At the same time, starting from the heat pump installed at the top of the heat utilization building, the heat transfer fluid is fed in liquid phase 6a via the return line 7b, following gravity through the two lower connections, into the evaporator, where it is converted into vapor 6b, and returned upwards in gaseous phase 6c due to density and buoyancy via the two upper connections and the riser line 7a to the heat pump. According to Fig. 2, the warmer supply water is conducted in an annular outdoor pipe 8 within a coaxial combination pipe, while the colder heat transfer fluid circulates in a central evaporator-internal heat transfer body 10 within a two-phase natural circulation, as described in Fig. 1. The outdoor pipe comprises an outer wall 9 and an inner wall, which corresponds to the enclosing wall 4, as well as individual spacers 11 between the two walls.The building connection line 12 for the consumption water is connected to the outside pipe.

[0037] List of reference symbols

[0038] Existing water supply pipeline

[0039] Evaporator half-shell heat transfer body

[0040] Porous-permeable solid

[0041] Enclosing wall of the evaporator heat transfer bodies

[0042] Existing pipeline wall a Liquid phase of the heat transfer fluid b Vapor of the heat transfer fluid c Gaseous phase of the heat transfer fluid a Gas riser line of the heat transfer fluid building connection b Liquid return line of the heat transfer fluid building connection

[0043] Outdoor pipe for the supply water

[0044] Outside wall of the outdoor pipe 0 Evaporator-inside heat transfer body 1 Spacer in the outdoor pipe 2 Building connection pipe for the consumption water

Claims

Patent claims 1 . Natural circulation evaporator for existing pipelines of water supply networks as a functional extension for decentralized geothermal energy generation, characterized in that a) evaporator compartments are arranged outside the supply water pipeline, b) the supply water-carrying existing pipelines (1) embedded in the ground are partially encased by two similar evaporator half-shell heat transfer bodies (2) which are connected to one another via boundary surfaces and thermally coupled around the existing pipe, c) the evaporator half-shell heat transfer bodies (2) consist of a one-piece, highly thermally conductive, porous-permeable solid (3), which are each closed off hydraulically and pressure-tight by an enclosing wall (4), d) the enclosing wall (4) consists of a highly thermally conductive solid material which defines the pore space structure of the porous-permeable solid (3) in its Fills the edge zone completely and firmly,so that a high thermal coupling is formed over a large contact inner surface, e) a single-component heat transfer fluid in the permeable pore space of the evaporator half-shell heat transfer bodies (2) is formed as an automatic two-phase natural circulation flow due to a large number of nucleation sites and bubble dynamics, wherein at the same time the liquid phase (6a) flows in from below due to gravity, is converted into steam (6b) and the gaseous phase rises due to density-buoyancy and flows out at the top as gas (6c), f) the geothermal energy stored in the supply water, due to the convective water flow, heat conduction from, standpipe wall (5), enclosing wall (4) and solid matrix of the evaporator heat transfer bodies as well as the developed temperature gradient, is transferred to the colder heat transfer fluid, which circulates in the pore space of the porous-permeable solid, and g) via building connection lines for the heat transfer fluid, consisting of gas rise line (7a) and liquid return line (7b), the convective heat energy transfer between the evaporator half-shell heat transfer bodies (2) located below and the decentralized heat pumps located above in the heat utilization buildings adjacent to the supply line is generated by the natural circulation.

2. Natural circulation evaporator integrated into a combined pipeline designed as a new pipeline for water supply and decentralized geothermal energy generation, characterized in that a) evaporator compartments are arranged outside of supply water compartments and / or vice versa, b) the combined pipeline laid in the ground consists of an external pipe (8) for the flow transport of the supply water and an evaporator internal heat transfer body (11) for the circulation of the heat transfer fluid, c) the external pipe is constructed from a highly thermally conductive outer wall (9) and a highly thermally conductive inner wall, which corresponds to the enclosing wall (4), as well as spacers (11), d) the evaporator internal heat transfer body (10) consists of a highly thermally conductive porous-permeable solid (3),which is hermetically enclosed by the enclosing wall (4) and is divided into equidistant longitudinal inner sections by hydraulically sealed vertical partition walls, e) the enclosing wall (4) consists of a solid material with good thermal conductivity, which completely and firmly fills the pore space structure of the porous-permeable solid in its edge zone, so that a high thermal coupling is formed over a large contact inner surface, f) a single-component heat transfer fluid in the permeable pore space of the evaporator's internal heat transfer body is formed as a self-acting two-phase natural circulation flow due to a large number of nucleation sites and bubble dynamics, whereby simultaneously the liquid phase (6a) flows in from below due to gravity, is converted into vapor (6b), and the gaseous phase rises due to buoyancy and flows out at the top as gas (6c), g) the geothermal energy stored in the supply water, due to the convective water flow, heat conduction from the enclosing wall (4) and the solid matrix of the evaporator heat transfer body, as well as the developed temperature gradient,is transferred to the colder heat transfer fluid circulating in the pore space of the porous-permeable solid, h) via building connection lines for the heat transfer fluid, consisting of a gas riser line (7a) and a liquid return line (7b), the convective heat energy transfer between the evaporator interior heat transfer bodies and the decentralized heat pumps in the heat utilization buildings adjacent to the supply line is generated by natural circulation, and i) the building connection lines for the consumption water (12) are connected to the outside of the combined pipeline.

Images