Methods for district and local heating supply using heat pumps

Abstract

A method for district and local heating supply using heat pumps, characterized in that a mechanical heat transformation (22) is integrated between the heat pump cycle (21) and the heat sink (23), which extracts heat transfer fluid from the heating return (23.2), raises its temperature and then feeds it into the heating supply (23.1), wherein the gaseous working fluid circuit (22.1) of the heat transformation (22) is, after an expansion (22.6) performing technical work (22.8), recuperatively heated (22.4) by a partial flow of the heat transfer return (23.5) and then subjected to a single- or multi-stage compression (22.2 and 22.3), which raises the temperature of the working fluid of the heat transformation (22) above the supply temperature of the heat supply and then heats another partial flow of the heat return (23.4) to supply temperature (22.5) and feeds it into the heating supply. (23.1) leads to.

Description

[0001] The invention relates to a method for supplying heating and hot water via local and district heating pipeline systems.

[0002] The field of application of the invention is the municipal, commercial and industrial heat and hot water supply, in particular with water as a heat carrier.

[0003] At the current state of the art, the application area and provision of cooling are sectors of the energy supply with high consumption of primary and electrical energy, although it is known that heat pumps in heat supply and via combined cooling / heating can significantly reduce primary energy consumption.

[0004] The main reasons that hinder the use of heat pumps are the methods used to absorb ambient heat for the evaporation of the working fluids in the heat pump cycle and the usually high temperatures of the heat transfer medium in the return flow of the district and local heating supply.

[0005] The absorption of ambient heat through recuperative cooling of water from near-surface, aquifers, bodies of water, and wastewater is well known. However, these methods also have disadvantages, which usually consist in the minerals contained in the water, particularly lime, salts, and iron, blocking the heat exchanger surfaces, which makes it difficult or impossible to absorb ambient heat and shortens the life cycle of the required devices.

[0006] Methods are also known for cooling the heat transfer medium return, which, in the state of the art, mainly consist of enlarging the heating surfaces of the heat sinks and connecting heat sinks with falling temperature levels in series, e.g. underfloor heating systems after convection heating surfaces.

[0007] DE 25 16 560 A1, EP 0 215 966 ​​A1, AT 337 938 B, EP 0 093 826 A1 and DE 28 29 134 B1 show a generic state of the art.

[0008] The aim and task of the invention are therefore to propose new methods for absorbing and coupling ambient heat into heat pump processes and for beneficially cooling the heat transfer medium return without having to significantly intervene in the structure of the existing heat sinks.

[0009] According to the invention, the absorption of ambient heat in heat pump cycle processes takes place as in Fig. 1 by • Water is taken from sources such as near-surface layers of the earth, bodies of water or sewage systems, such as sewers or clarifiers, via filter wells or filters and is subjected to vacuum evaporation under reduced pressure, • part of the sensible heat of the water is removed by flash evaporation from vacuum evaporation, • the vacuum of the flash evaporation, and thus the boiling temperature of the water under vacuum, is adjusted by recuperative evaporation of heat pump working fluid through recuperative condensation of the flash steam on the rear evaporator surfaces, • the heat pump working fluid is supplied in liquid form, in the supercritical state, via a throttle device in the heat pump cycle to its evaporation and then, in the subcritical state, in vapor form to the compression of the heat pump cycle, • the flash steam condensate is fed to an external recycling facility, e.g. drinking water treatment, • the water cooled by flash evaporation from the vacuum evaporation is returned to the extraction sources under increased pressure, avoiding short-circuit flows, e.g. via seepage wells, • the performance difference between the supply and discharge of the vacuum evaporator in the heat pump cycle is compensated by mechanical work.

[0010] The integration of the heat pump cycle, especially in existing district and local heating systems, such as in Fig. 2, is carried out according to the invention by incorporating a heat transformation, arranged between the flow and return of the heating supply, which in the form of a gas circuit, preferably with compressed air, combines a single- or multi-stage compression with an upstream recuperative gas heating, and in the case of multi-stage compression, with an intermediate gas cooling, and a gas expansion with upstream recuperative gas cooling as follows: • The gas, advantageously as a compressed gas, is heated recuperatively after expansion by a partial flow of the return flow of the heat supply system and then heated by compression above the temperature level of the flow flow. • Through the recuperative transfer of sensible heat after expansion from the heat return to the gas circuit, - on the one hand, the enthalpy difference of the cycle gas is increased so that the temperature of the gas after compression already rises above that of the heating flow at a pressure ratio of less than 2, so that a first partial flow of the heat return can be warmed up by the gas or raised above the temperature of the heating flow and fed into the heating flow, bypassing the heat pump, and - on the other hand, a third partial flow of the heat return is cooled by up to 50 K according to the invention before being fed to the heating steam condenser of the heat pump, which increases the ability of the heat pump working fluid to absorb ambient heat. • With optional multi-stage gas compression, the gas is cooled according to the invention by a second partial flow of the heat return in a gas cooling system arranged between the compression stages, whereby this second partial flow is also heated above the temperature of the heating heat flow and is fed to this, bypassing the heat pump. • According to the invention, the 4th partial flow remaining in the heating heat return warms up the heat pump working fluid after its evaporation, i.e. before its compression in the heat pump compressor, and cools down to the temperature of the heating circuit desired upstream of the heat pump heating condenser before it is also fed to the heating condenser of the heat pump.

[0011] Furthermore, according to the invention, a heat storage tank, preferably a hot water stratified storage tank, is optionally integrated in the bypass in the heat flow upstream of the heat sink.

[0012] The economic advantage of the invention lies in the economically advantageous substitution of fossil fuels with environmental energy when converting heat supply to renewable electricity and in the expansion of the possibilities for storing renewable energy through known methods of hot water storage. Example

[0013] The first part of this exemplary description of the invention describes the absorption and use of ambient heat for heating purposes by means of Fig. 1, when using carbon dioxide as a heat pump working fluid, as follows: • Water is taken from water-bearing layers of the earth near the surface via filter wells (7) as surface filtrate (1) with a temperature of 10 °C and fed to a vacuum evaporator (2). • At a vapor pressure in the vacuum evaporation (2) of 0.009 bar, corresponding to a boiling temperature of water of 5 °C, approx. 8 kg water / m 3 Filtrate is converted into steam (3) by flash evaporation and the filtrate (1) is cooled by approx. 5 K. • The cooled filtrate (4) is removed from the vacuum evaporation (2) with an energy consumption of approx. 120 kJ / m 3 pumped out via the pump (9), of which 70 kJ / m 3 can be recovered via the pressure reduction (11). Flash evaporation therefore requires approximately 6 kJ of technical work per kg of flash steam (3), which is condensed in the flash steam condensation chamber (6) of the evaporation (5) of the heat pump cycle. • The evaporation of carbon dioxide at approximately 40 bar requires a heat of vaporization of approximately 230 kJ / kg, ie per m 3 Surface filtrate (1) can evaporate approximately 75 kg of carbon dioxide. Or, in other words, over 1 m 3 Surface filtrate (1) can supply more than 19,000 kJ of ambient heat (5.4 kWh) to the heat pump process via (13). • When using seawater, this means that the described flash evaporation produces 8 kg of desalinated condensate (10) per m 3 can be obtained for freshwater supply, associated with an energy consumption of 6 kJ / I (1.7 kWh / m 3 ).

[0014] In the following second part of the embodiment, the inventive exergetic upgrading of the ambient heat to heating heat for a heating supply with a spread between flow and return temperature of 90 to 60 °C is carried out with the help of Fig. 2 as follows: • The heat pump working medium carbon dioxide is preheated from 5 to 55 °C in the preheater (21.2) after evaporation (21.5). With a specific mass of carbon dioxide of 85 kg / m 3 Approximately 3825 kJ of filtrate, ie 20 kg of return water (23.6) are required. • The carbon dioxide, preheated to 55 °C, is fed to the compression stage (21.6) and compressed there from 40 to 70 bar. With an isentropic compression efficiency (21.6) of 85%, the compression effort is 43 kJ / kg carbon dioxide or approximately 3,700 kJ / m 3 Surface filtrate. • In the heating condensation (21.4) there are approximately 26,525 kJ / m 3 Surface filtrate is available for heating the cooled heating heat return (21.1), which is cooled to 10 °C in the recuperator (22.4) of the heat transformation (22) and the working fluid preheating (21.2). • The heat requirement for heating the heat carrier water from 10 to 90 °C is 335 kJ / kg, ie if 95% of this is used technically, the heat condensation (21.4) of the heat pump can produce approx. 75 kg of heating water / m 3 Feed surface filtrate into the flow line (23.1), for which the preheater (21.2) 20 kg / m 3 Filtrate and the pressure gas heating (22.4) of the 3rd partial flow of the return (23.5) 55 kg / m 3 provide filtrate. • The recooling of 55 kg of return water in (22.4) is achieved by air at a pressure of 10 bar, which the expansion machine (22.6) supplies at 10 °C for the compressed gas heating (22.4), which heats the air from 10 to 55 °C. In the recuperator (22.4), 10,340 kJ of heat are transferred from the return water (23.5) to the compressed air circuit (22.1) of the heat transformation (22). This results in a compressed air mass of 230 kg / m 3 filtrate. • The heated compressed air is compressed in the 1st stage of air compression (22.2) to a temperature of 95 °C, for which, with an isentropic efficiency of 85%, a technical work of 43 kJ / kg air, i.e. a total of 9,890 kJ / m 3 filtrate is required. • After the first compression stage (22.2), the compressed air is cooled from 98 to 65 °C in the recuperator (22.5). With a compressed air mass of 230 kg, 7500 kJ / m 3 Filtrate is transferred to the return water (23.4), which is heated from 60 to 90 °C. The return mass flow for the recuperator (22.5) is calculated to be 60 kg / m 3 filtrate. • In a second compression stage (22.3), the compressed air mass flow is compressed from 14 bar to 21 bar, which increases the temperature of the compressed air to 114 °C with an isentropic efficiency of 85%. • The compressed air, which has a temperature of 114 °C and is present after the second compression stage (22.3), is cooled from 114 to 65 °C in the recuperator (22.7). In the process, 11,270 kJ of heat is transferred to 89 kg of return water (23.3) at a temperature of 60 °C, which is then added to the heating flow (23.1) at a temperature of 90 °C. • After the compressed air cooling in the recuperator (22.7), the air mass flow at 20 bar and 65 °C is fed to the compressed air expansion (22.6) and there, releasing technical work (22.8) in the amount of 11,960 kJ / m 3 Filtrate depressurized to 10 bar.

[0015] Due to the return cooling in (21.2 and 22.4), the heat pump (21) achieves a heat pump coefficient of approx. 7.2 kWh / kWh el , while the heat transformation (22) operates with a heat pump coefficient of approximately 2. However, the heat pump (21) only supplies 33% of the district heating flow (23.1), while the heat transformation (22) provides 67% of the heating flow via (22.5) and (22.7).

[0016] The heat pump / heat transformer combination according to the invention can thus be operated with a heat pump index of >3 when absorbing ambient heat at a temperature of 4 °C and releasing district heat at a flow temperature of 90 °C. List of reference symbols 1 surface filtrate 2 Vacuum evaporation 3 Flash steam 4 Cooled filtrate 5 Working fluid evaporation (heat pump) 6 Flash steam condensation 7 filter wells 8 soakaway wells 9 Water pump 10 Flash steam condensate 11 Pressure reduction 12 Pump drive 13 Vaporous working fluid (heat pump) 14 throttle valve 21 Heat pump cycle / heat pump 21.1 Cooled heating return 21.2 Working fluid preheating after evaporation / preheater / preheating / return cooling 21.3 Preheated working fluid heat pump / vaporous working fluid heat pump 21.4 Heat pump heating condensation / heating condenser / heat pump condenser / heating heat condensation 21.5 Working fluid evaporation / evaporator 21.6 Working fluid compression 22 Heat transformation 22.1 Compressed gas circuit / gaseous working fluid circuit 22.2 Primary pressure gas compression 22.3 Secondary pressure gas compression 22.4 Compressed gas heating / recuperator / recuperative heating / return cooling 22.5 Compressed gas intercooling / recuperator 22.6 Compressed gas expansion / expansion machine / compressed air expansion 22.7 Compressed gas cooling 22.8 Technical work 23 Heat sink 23.1 Heating flow / heat carrier flow / district heating flow 23.2 Heating heat return 23.3 1. Partial flow return water withdrawal (for heating in 22.7) / hot return water 23.4 2nd partial flow return water withdrawal (for heating in 22.5) / return water 23.5 3. Partial flow return withdrawal (for pressure gas preheating in 22.4) / return water 23.6 4. Partial flow return withdrawal (for preheating heat pump working fluid in 21.2) / return water

Claims

[1] Processes for district and local heating supply with heat pumps, characterized by that a mechanical heat transformation (22) is integrated between the heat pump cycle (21) and the heat sink (23), which takes heat transfer medium from the heating heat return (23.2), raises its temperature and then feeds it into the heating heat flow (23.1), wherein the gaseous working medium circuit (22.1) of the heat transformation (22) is heated recuperatively (22.4) by a partial flow of the heat transfer medium return (23.5) after an expansion (22.8) which performs technical work and is then fed to a single-stage or multi-stage compression (22.2 and 22.3), which raises the temperature of the working medium of the heat transformation (22) to above the flow temperature of the heat supply and then heats a further partial flow of the heat return (23.4) to flow temperature (22.5) and feeds it to the heating heat flow (23.1). [2] Method according to claim 1, characterized bythat the working fluid in the heat pump cycle (21) is evaporated (21.5) by recuperative condensation of flash steam generated from surface filtrate, river, sea or waste water under vacuum. [3] Method according to claim 1 and 2, characterized by that a partial flow (23.6) of the heat transfer medium return, which is to be heated in the heat pump condenser (21.4), is cooled down by the vaporous heat pump working medium after the evaporator (21.5) in the working medium preheater (21.2) before being fed to the heating condenser (21.4) of the heat pump and in the process heats up the vaporous working medium of the heat pump (21.3) before the compression (21.6). [4] Method according to claim 3, characterized bythat a further heat transfer medium partial flow (23.5) is used for the recuperative heating (22.4) of the gaseous working medium of the heat transformation (22) and is then raised together with the partial flow (23.6) according to claim 3 in the heating condenser of the heat pump process (21.4) to the temperature of the heating heat flow (23.1), and in the process the heat pump working medium is cooled to near the temperature of its evaporation before it is reduced to the pressure of its evaporation in the throttle valve of the heat pump cycle. [5] Method according to claim 1, characterized by that in the case of multi-stage compression (22.2 and 22.3), the working medium of the heat transformation (22) is cooled recuperatively (22.5) between the compression stages and in the process raises a further partial flow (23.4) of the heat transfer medium return to flow temperature and feeds it to the heat transfer medium flow (23.1) in front of the heat sink (23) of the heating system. [6] Method according to claims 1 to 5, characterized by that a heat storage device is integrated in the bypass in the heat flow (23.1) in front of the heat sink (23). [7] Method according to claim 6, characterized by that the heat storage tank is a hot water stratified storage tank. [8] Method according to claim 1, characterized by that the flash steam condensate from the evaporation of the heat pump working fluid (21.5) is supplied for external use.

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