Method for using heat from a heat transfer medium circuit of a geothermal system

Abstract

The invention relates to a method for using heat from a heat transfer medium circuit (15) of a geothermal system (1), said method comprising: (a) heating a heat transfer medium flowing through the heat transfer medium circuit (15) to a temperature in a range from 100 to 200 °C by transferring heat from hot brine (3) from a geothermal source or by transferring heat from the geothermal source; (b) evaporating water (35) in an evaporator (33) by transferring heat from at least one part of the heated heat transfer medium (31), wherein the at least one part of the heat transfer medium is cooled to a temperature in a range from 80 to 140 °C; (c) heating a heat transfer medium (41) of a district heating network in at least one heat exchanger (39) by transferring heat from at least one part of the heat transfer medium cooled to a temperature in a range from 80 to 140 °C (37; 79.1; 81).

Description

[0001] BASF SE 240597W001

[0002] Method for utilizing heat from a heat transfer circuit of a geothermal plant

[0003] Description

[0004] The invention relates to a method for utilizing heat from a heat transfer circuit of a geothermal plant.

[0005] Geothermal plants are typically used to generate electricity and provide usable heat for specific applications, such as building heating. For electricity generation, hydrothermal springs are used, from which hot brine is extracted and fed into an ORC (Organic Rankine Cycle) process. Alternatively, the hot brine can be used to generate steam or hot water in a heat transfer fluid circuit and then fed into a steam network or, for example, a district heating network.

[0006] A geothermal plant utilizing brine from a geothermal source to provide energy for electricity generation or building heating is described, for example, in I. Stober, K. Bucher, "Geothermal Energy", 3rd edition, Springer-Verlag, 2020. This description illustrates the cascaded utilization of the brine's heat at different temperature levels. The heat at the highest temperature level is used to generate electricity in a power plant. Due to the heat extraction for electricity production, the brine is cooled to a lower temperature level, and some of this heat is used for food processing or refrigeration. This heat utilization leads to a further cooling of the brine to a third temperature level, at which point the heat can be used to heat buildings or greenhouses.Due to the heat extraction, the brine is then at the lowest temperature level still usable for the system, at which the heat of the brine can then be used, for example, for fish farming, before the brine is pumped back to the geothermal source.

[0007] Particularly in the chemical industry, steam is used as a key energy source alongside electricity. Currently, steam is primarily produced using fossil fuels. Therefore, to reduce carbon dioxide emissions, alternative methods for electricity generation and, in particular, steam production are being sought.

[0008] It is known from CN-A 114321858 to utilize geothermal energy to generate steam. For this purpose, water from a geothermal source is used to heat desalinated water in a first heat exchanger. The cooled water from the geothermal source is then used as the heat transfer fluid in a heat pump before being returned to the geothermal source. The water heated in the first heat exchanger is fed into a flash evaporator, where water is evaporated. The water that has not yet evaporated is fed into a second flash evaporator, where more water is evaporated. BASF SE 240597W001

[0009] 2

[0010] The device described in CN-A 114321858 is suitable for steam generation; however, it is not possible to utilize the heat from the geothermal source for other applications. Furthermore, the direct use of water from the geothermal source can lead to mineral precipitation, and the resulting deposits can cause problems in system components.

[0011] Therefore, the task arose to provide a method for utilizing heat from a geothermal plant that, in addition to steam generation, can also enable further use of the heat.

[0012] This task is solved by a method for utilizing heat from a heat transfer circuit of a geothermal plant, comprising:

[0013] (a) Heating a heat transfer fluid flowing through the heat transfer fluid circuit to a temperature in the range of 100 to 200 °C by transferring heat from hot brine from a geothermal source or heating the heat transfer fluid flowing through the heat transfer fluid circuit to a temperature in the range of 100 to 200 °C by heat transfer from the geothermal source;

[0014] (b) Evaporation of water in an evaporator by transferring heat from at least a part of the heated heat transfer medium, wherein the at least a part of the heat transfer medium is cooled to a temperature in the range of 80 to 140 °C;

[0015] (c) Heating a heat transfer medium of a district heating network in at least one heat exchanger by transferring heat from at least a part of the heat transfer medium cooled to a temperature in the range of 80 to 140 °C.

[0016] Utilizing the heat from a geothermal heat transfer system allows the heat from the hot brine or geothermal source to be used not only to heat the heat transfer fluid in the system, but also to supply the necessary heat for a district heating network. Additionally, some of the heat from the system can be used for other purposes, such as steam generation or electricity generation.

[0017] Furthermore, it is also possible to use the heat from the heat transfer fluid in the heat transfer circuit not only for steam generation, but also for other purposes, such as directly heating plant components. BASF SE 240597W001

[0018] 3

[0019] By utilizing residual heat after its use for steam generation in step (b), it is possible to optimally utilize the heat of the heat transfer fluid circuit, so that only a small portion of the heat of the heat transfer fluid remains unused.

[0020] In one type of geothermal plant, hot brine is extracted from a geothermal source. The temperature of the brine depends on the depth from which it is extracted. For deep geothermal energy use, the brine is typically extracted from a depth of 3000 to 4000 m and has a temperature in the range of 120 to 300 °C, preferably in the range of 120 to 200 °C, and particularly in the range of 140 to 180 °C.

[0021] To reduce deposits on pipes and equipment caused by precipitated minerals, minerals are first removed from the brine. For this purpose, suitable anti-scaling agents can be added, for example. Common anti-scaling agents are familiar to professionals.

[0022] Regardless of any further use, at least a portion of the hot brine from the geothermal source is used to heat a heat transfer fluid in a heat transfer circuit to a temperature in the range of 100 to 200 °C, more preferably to a temperature in the range of 120 to 200 °C, and particularly to a temperature in the range of 140 to 180 °C. The pressure of the heat transfer fluid in the heat transfer circuit is preferably regulated so that the heat transfer fluid always remains liquid and does not evaporate.

[0023] As an alternative to heating the brine in the geothermal source, it is also possible to heat the heat transfer fluid in the heat transfer circuit by heat transfer from the geothermal source. For this purpose, the heat transfer fluid is pumped to a depth of 3000 to 5000 m, where it is then heated directly by the geothermal source, for example, hot rock. Since the density decreases with heating, the heated heat transfer fluid rises, resulting in natural circulation. Through this heat transfer from the geothermal source, the heat transfer fluid is heated to a temperature of 100 to 200 °C.

[0024] Any heat transfer fluid known to experts is suitable for use in the heat transfer circuit. Suitable heat transfer fluids include, for example, water, especially demineralized water, heat transfer oils, isobutanol, isopentanol, ammonia, mineral oils such as motor oil or Mobilotherm® 605, inorganic molten salts, or liquid metals such as sodium, lead, bismuth, potassium, or alloys thereof. Water is the preferred heat transfer fluid for use in the heat transfer circuit.

[0025] In a first embodiment, at least a portion of the heat transfer fluid heated by the brine is used to produce steam. For this purpose, water is heated in an evaporator by transferring heat from the at least BASF SE 240597W001

[0026] 4. A portion of the heat transfer fluid is evaporated. This cools the portion of the heat transfer fluid used for evaporation to a temperature in the range of 80 to 140 °C, more preferably to a temperature in the range of 100 to 130 °C, and particularly to a temperature in the range of 105 to 120 °C.

[0027] The water supplied to the evaporator for evaporation preferably has a pressure in the range of 1 to 50 bar (abs). In the evaporator, the water is at least partially, preferably completely, evaporated to saturated steam and, if necessary, superheated in a downstream heat exchanger stage.

[0028] Depending on the pressure of the water being evaporated and the desired steam temperature for further use, it is possible to further compress the steam generated in step (b). This compression takes place in at least one compressor with at least one compression stage.

[0029] Since the steam becomes highly superheated during compression, it is preferred to inject water into the steam downstream of at least one compression stage, preferably downstream of each compression stage, for cooling purposes. This has the additional advantage of also increasing the steam volume.

[0030] In addition to steam generation, it is possible to use heat from at least part of the heat transfer fluid in the heat transfer cycle in an Organic Rankine Cycle (ORC) process for power generation.

[0031] For the utilization of heat in an ORC process, a working fluid used in the ORC process, typically an organic liquid with a low evaporation temperature, for example isobutane, is first evaporated by heat transfer from the heat transfer fluid of the heat transfer circuit and then superheated. The evaporation and superheating can take place in a single heat exchanger or, preferably, in an evaporator where the working fluid evaporates and a subsequent superheater where the evaporated working fluid is superheated.

[0032] Since the heat transfer fluid of the heat transfer circuit cools down through heat transfer to the working fluid, it is preferred if the heat transfer fluid of the heat transfer circuit first flows through the superheater and then through the evaporator, and it is further preferred if the heat transfer fluid of the heat transfer circuit and the working fluid are carried in counterflow in both the evaporator and the superheater.

[0033] Through the evaporation and superheating of the working fluid by heat transfer from the heat transfer fluid in the heat transfer circuit, the heat transfer fluid in the heat transfer circuit cools down. If the temperature of the heat transfer fluid in the heat transfer circuit after heat transfer to the working fluid of the ORC process is in the range of 80 to 140 °C, more preferably in the range of 100 to 130 °C, and particularly in the range of 105 to 120 °C, the heat transfer fluid in the heat transfer circuit can be used directly to transfer heat to the heat transfer fluid of the district heating network. BASF SE 240597W001

[0034] 5

[0035] Particularly when the temperature of the heat transfer fluid after heat transfer to the working fluid is below 100°C, it is preferred to use only a portion of the heat transfer fluid in the heat transfer circuit for heat transfer to the working fluid. In this case, the portion of the heat transfer fluid in the heat transfer circuit used for heat transfer to the working fluid of the ORC process is mixed again with the heat transfer fluid not used in the ORC process after heat transfer, so that the heat transfer fluid after mixing has a temperature in the range of 80 to 140°C, more preferably in the range of 100 to 130°C, and particularly in the range of 105 to 120°C.

[0036] To generate electricity, the superheated working fluid is fed to a turbine connected to a generator. Inside the turbine, the superheated working fluid expands, thus driving the turbine. After passing through the turbine, the working fluid is condensed in a condenser. The pressure of the condensed working fluid is increased by a pump, and then the working fluid is returned to the evaporator. Any suitable coolant can be used for condensing the working fluid, preferably cooling water.

[0037] After cooling through heat transfer for water evaporation or through the use of heat in the Organic Rankine Cycle process, the temperature of the heat transfer fluid is still high enough to utilize further heat from the fluid. According to the invention, the heat from the heat transfer fluid, cooled to a temperature in the range of 80 to 140 °C, is used in a district heating network by heating the heat transfer fluid in a heat exchanger through heat transfer from at least a portion of the heat transfer fluid cooled to a temperature in the range of 80 to 140 °C.

[0038] Depending on the district heating network and the heat transfer medium used in the district heating network, the heat transfer medium of the district heating network, which has been cooled to a temperature in the range of 50 to 120 °C, more preferably to a temperature in the range of 60 to 100 °C and in particular to a temperature in the range of 60 to 80 °C, by using district heating, for example for heating buildings or for hot water preparation, is preferably heated to a temperature in the range of 90 to 140 °C, more preferably to a temperature in the range of 90 to 130 °C and in particular to a temperature in the range of 100 to 130 °C and can thus be used again in the district heating network.

[0039] Water is typically used as the heat transfer medium in district heating networks. This water is usually pressurized to such a high level that it does not evaporate when heated by heat transfer from the heat transfer fluid in the heating circuit. Even if a different heat transfer medium than water is used in the district heating network, it is preferable to heat it at a pressure at which no heat transfer fluid evaporates. BASF SE 240597W001

[0040] 6

[0041] Through heat transfer to the heat carrier of the district heating network, the heat carrier of the heat transfer circuit in step (c) preferably cools down to a temperature in the range of 60 to 100 °C. This temperature is then usually no longer sufficiently high to economically provide further energy, so the cooled heat carrier of the heat transfer circuit is returned to step (a) to be reheated by heat transfer from the brine or the geothermal source.

[0042] Since the demand for district heating usually fluctuates greatly depending on the ambient temperature, and therefore different amounts of heat are always needed to heat the heat transfer fluid of the district heating network, it is advantageous if the heat of the heat transfer fluid of the heat transfer circuit, which has been cooled to a temperature in the range of 80 to 140 °C, can also be used in other ways.

[0043] For example, the heat transfer fluid in the heat transfer circuit, cooled to a temperature between 80 and 140 °C, can be divided into a first and a second partial flow. The heat from the first partial flow is used to heat the heat transfer fluid in the district heating network, while the heat from the second partial flow is used to generate steam in an absorption heat pump. The size of the partial flows can then be selected so that the district heating network always receives sufficient heat from the heat transfer fluid in the heat transfer circuit, regardless of the outside temperature, and at least some of the heat transfer fluid not used to heat the district heating network is utilized in the absorption heat pump.In particular, if the amount of steam generated in the absorption heat pump is greater than the required amount of steam, and if all the heat transfer fluid not used for the district heating network is supplied to the absorption heat pump, it may be useful to provide a bypass through which another part of the heat transfer fluid from the heat transfer circuit, whose residual heat is not required, is routed.

[0044] A single-stage absorption heat pump is preferably used. In the absorption heat pump, a liquid working fluid is evaporated in a first step in an evaporator. The heat required for this is supplied by heat transfer from the second partial flow of the heat transfer fluid in the heat transfer circuit, which has been cooled to a temperature in the range of 80 to 140 °C. The working fluid evaporated in the evaporator is then fed to an absorber, where it is absorbed by an absorbent. The heat released during absorption is used to evaporate water and thus generate steam. After the heat is released to generate steam, the absorbent, along with the absorbed working fluid, is depressurized to a lower pressure and fed to a desorber, where the working fluid is desorbed from the absorbent by the addition of heat.The heat required for this process is also provided by heat transfer from the heat transfer fluid in the heat transfer circuit, which is cooled to a temperature in the range of 80 to 140°C, with the working fluid being driven off as steam. BASF SE 240597W001.

[0045] 7. The vaporous working fluid is then condensed in a condenser, the liquid working fluid thus obtained is brought to a higher pressure and then fed back to the evaporator.

[0046] After the working fluid has been expelled, the concentrated absorbent is also pressurized and returned to the absorber. An internal heat exchanger is preferably arranged between the absorber and the desorber, in which the warm absorbent, along with the absorbed working fluid, transfers heat to the concentrated absorbent in the desorber for preheating.

[0047] The condensation of the working fluid in the condenser occurs through heat transfer to a coolant. Cooling water is typically used as the coolant.

[0048] Water, for example, is a suitable tool.

[0049] A salt, for example lithium bromide in aqueous solution, is preferably used as the absorbent.

[0050] To enable the absorbent to be circulated between the absorber and the desorber, only enough working fluid is driven off in the desorber to obtain a concentrated brine of working fluid and absorbent, which can then be returned to the absorber. In the absorber, the brine is then diluted by absorption of working fluid, and the diluted brine is passed to the desorber.

[0051] Due to the large amount of heat released during absorption and the associated high temperatures, it is possible to supply the water to be evaporated at a pressure in the range of 1 to 10 bar(abs), more preferably in the range of 1.0 to 2 bar(abs). If the pressure of the steam generated in the absorption heat pump is still below the desired process steam pressure, it is preferred to mix the steam generated in the absorption heat pump with the steam generated in step (b) to form a total steam stream, and then to compress the total steam stream in at least one compressor with at least one compression stage.

[0052] If the pressure of the total steam flow is below the desired process steam pressure, it is further preferred to compress the steam superheated in the heat exchanger in at least one compressor with at least one compression stage.

[0053] Here too, it is preferred to inject water into the steam downstream of at least one compression stage and preferably downstream of every compression stage.

[0054] Regardless of whether steam was generated only in step (b) or additionally in the

[0055] Absorption heat pump, the generated process steam can either be supplied directly to a consumer BASF SE 240597W001

[0056] 8 or into a steam network that supplies various consumers with steam. In particular, if the process steam is supplied directly to a consumer, it is possible to use the steam at the pressure it has after evaporation in the evaporator and, if applicable, after mixing with the steam generated in the absorption heat pump, without further compression. When feeding into a steam network or supplying to a consumer for whom the temperature of the uncompressed steam is too low, it is necessary to compress the steam.

[0057] By compression in at least one compressor with at least one compression stage, low-pressure steam, medium-pressure steam, or high-pressure steam can be generated. It is also possible to first compress all the steam to low-pressure steam, provided the generated steam has a pressure below that of low-pressure steam, then to further compress at least a portion of the low-pressure steam to medium-pressure steam, and finally to compress at least a portion of the medium-pressure steam to high-pressure steam.

[0058] In the context of the present invention, low-pressure steam is understood to mean steam having a pressure in the range of 0.9 to 4 bar(abs), preferably in the range of 1 to 2 bar(abs) and particularly in the range of 1.2 to 1.5 bar(abs) and a temperature in the range of 96 to 160 °C, more preferably in the range of 99 to 140 °C and particularly in the range of 104 to 120 °C.

[0059] Medium-pressure steam within the scope of the present invention is steam with a pressure in the range of 4 to 8 bar(abs), preferably in the range of 4.5 to 7 bar(abs) and particularly in the range of 5 to 6 bar(abs) and a temperature in the range of 143 to 220 °C, more preferably in the range of 147 to 210 °C and particularly in the range of 151 to 200 °C.

[0060] High-pressure steam within the scope of the present invention is steam with a pressure in the range of 8 to 40 bar(abs), preferably with a pressure in the range of 10 to 30 bar(abs) and in particular with a pressure in the range of 16 to 20 bar(abs) and a temperature in the range of 170 to 280 °C, more preferably in the range of 180 to 260 °C and in particular with a temperature in the range of 201 to 240 °C.

[0061] The at least one compressor with at least one compression stage used to generate low-pressure, medium-pressure, or high-pressure steam can be a single compressor or a compressor cascade, wherein a compressor cascade comprises at least two compressors, each with at least one compression stage, or at least one compressor with at least two compression stages in which the steam is compressed in stages. A geared turbo compressor is preferred, for example, as the compressor with at least two compression stages. Such a geared turbo compressor typically comprises several compression stages and intermediate stages, with intercooling possible in the respective intermediate stages. Even when a compressor cascade with several compressors is provided, it is advantageous to implement intercooling between the individual compressors. BASF SE 240597W001

[0062] 9

[0063] Intercooling is achieved, as described above, by injecting water into the steam. Due to the temperature of the compressed steam, the water evaporates completely, thereby cooling the steam and simultaneously increasing the steam volume. To ensure that the injected water evaporates completely before subsequent compression in another compressor or compression stage, a sufficiently long injection section is provided.

[0064] The process steam generated in this way can then be supplied to a consumer or fed into a steam network. To minimize damage to the equipment through which the steam is passed and to the steam generation apparatus, the water used for steam generation is preferably demineralized and degassed.

[0065] In particular, if only a portion of the heat transfer fluid in the heat transfer circuit is used for evaporation and superheating of the organic heat transfer fluid, it is alternatively possible to divide the heat transfer fluid in the heat transfer circuit into a first partial flow and a second partial flow, feed the first partial flow to the evaporator, where the first partial flow is cooled to a temperature in the range of 80 to 140 °C, and use the heat from the second partial flow in an ORC process to generate electricity, and use the heat from the first partial flow, cooled to a temperature in the range of 80 to 140 °C, to heat the heat transfer fluid of the district heating network.

[0066] In this context, it is particularly advantageous to use only the first partial flow for heating the heat transfer medium of the district heating network if the second partial flow is cooled by heat utilization in the ORC process to a temperature that corresponds to or is even below the temperature of the first partial flow after heat transfer to the heat exchanger of the district heating network.

[0067] If the temperature of the second partial flow after heat transfer to the working fluid of the ORC process is above the outlet temperature of the heat transfer fluid from the heat exchanger in which heat is transferred to the heat transfer fluid of the district heating network, it is preferred if at least a portion of the second partial flow is mixed with the first partial flow upstream of the heat exchanger to heat the heat transfer fluid of the district heating network. It is particularly preferred if the portion of the heat transfer fluid from the heat transfer circuit supplied to the heat exchanger for heating the heat transfer fluid of the district heating network has a temperature in the range between 100 and 140 °C after mixing the first partial flow with at least a portion of the second partial flow.

[0068] The portion of the second partial flow not mixed with the first partial flow upstream of the heat exchanger, if only a portion of the second partial flow is mixed with the first partial flow upstream of the heat exchanger, or the entire second partial flow if no portion upstream of the heat exchanger is mixed, is fed downstream of the heat exchanger to heat the heat transfer fluid of the district heating network, cooled in the heat exchanger. BASF SE 240597W001

[0069] 10

[0070] Part of the heat transfer fluid of the heat transfer circuit is added in order to subsequently be able to return the entire heat transfer fluid of the heat transfer circuit to step (a).

[0071] Furthermore, it is also possible to divide the second partial stream, cooled to a temperature in the range of 80 to 140 °C, or, if the first partial stream is mixed back into the second partial stream after cooling in the OCR process, the entire stream cooled to a temperature in the range of 80 to 140 °C, into a first further partial stream and a second further partial stream, whereby the first further partial stream transfers heat to the heat carrier of the district heating network and the second partial stream is used to generate steam in an absorption heat pump.

[0072] Exemplary embodiments of the invention are shown in the figures and are explained in more detail in the following description.

[0073] They show:

[0074] Figure 1 shows an overview flow diagram of a geothermal plant;

[0075] Figure 2 shows a flow diagram of an embodiment of a heat transfer circuit with an evaporator and a heat exchanger for the use of residual heat in a district heating circuit;

[0076] Figure 3 shows a flow diagram of an embodiment of a heat transfer circuit with an evaporator, a heat exchanger for utilizing residual heat in a district heating circuit and in an absorption heat pump;

[0077] Figure 4 shows a flow diagram of an embodiment of a heat transfer circuit with an evaporator, a heat exchanger for utilizing residual heat in a district heating circuit and in an ORC circuit for power generation.

[0078] Figure 1 shows an overview flow diagram of a geothermal plant.

[0079] In a geothermal plant 1, hot brine 3 is extracted from a geothermal source using a pumping device 5. The pumping device 5 is, for example, a pump and, depending on the depth of the borehole from which the hot brine 3 is extracted, is located above or, as shown here, below the ground level 7.

[0080] The hot brine is usually extracted from a depth of 3000 to 4000 m and has a

[0081] Temperature in the range of 120 to 300 °C, more preferably in the range of 120 to 200 °C and especially in BASF SE 240597W001

[0082] 11

[0083] Temperature range of 140 to 180 °C. To prevent mineral precipitation and, in particular, the formation of mineral deposits, an anti-scaling agent 9 is added to the hot brine.

[0084] With a Cleaning in Place (ClP) system, it is possible to efficiently clean plant components, such as heat exchangers in cooling water circuits, without having to disassemble them. Cleaning agents circulate through pipes and plant components to remove deposits, biofilms, and other contaminants, thereby increasing the operational efficiency and service life of the plant. Automating the cleaning process not only saves time but also increases the safety of operating personnel by minimizing contact with hazardous chemicals.

[0085] Downstream of the CIP system 11, the hot brine is fed to a heat exchanger 13, where heat is transferred to a heat transfer fluid in a heat transfer circuit 15. The heat transfer fluid in the heat transfer circuit 15 is preferably heated to a temperature in the range of 100 to 200 °C, more preferably to a temperature in the range of 120 to 200 °C, and particularly to a temperature in the range of 140 to 180 °C. Through the heat transfer to the heat transfer fluid in the heat transfer circuit, the brine, which is typically circulated counter-currently to the heat transfer fluid, cools down to a temperature in the range of 60 to 120 °C, more preferably to a temperature in the range of 70 to 100 °C, and particularly to a temperature in the range of 70 to 80 °C.

[0086] Downstream of the heat exchanger 13, in which the heat transfer medium of the secondary circuit 15 is heated, lithium is removed from the brine in a lithium extraction 21.

[0087] After lithium extraction, the brine is fed into a brine treatment plant 23, where minerals are added back to the brine to obtain a composition that essentially corresponds to that of the hot brine extracted from the geothermal source. The remineralized and cooled brine 25 is then returned to the geothermal source.

[0088] To prevent the returned cold brine from being immediately extracted again, it is reintroduced into the geothermal source at a distance of 27 meters. This distance depends on the depth of the boreholes from which the hot brine is extracted and the cold brine is reintroduced, and is between 1000 and 2500 meters for borehole depths of 3000 to 4000 meters.

[0089] According to the invention, the heat transferred to the heat carrier of the heat transfer circuit 15 is used to heat a heat carrier of a district heating network. This is illustrated in a first embodiment in Figure 2. BASF SE 240597W001

[0090] 12

[0091] For steam generation, the heat transfer fluid 31 of the heat transfer circuit 15, heated in the heat exchanger 13 to a temperature in the range of 100 to 200 °C, more preferably to a temperature in the range of 120 to 200 °C, and particularly to a temperature in the range of 140 to 180 °C, is fed to an evaporator 33. In the evaporator 33, water 35, in particular demineralized and degassed water, is evaporated by heat transfer from the heated heat transfer fluid 31. Due to the heat transfer during the evaporation of the water, the heat transfer fluid cools to a temperature in the range of 80 to 140 °C, more preferably to a temperature in the range of 100 to 130 °C, and particularly to a temperature in the range of 105 to 120 °C. At this temperature, however, the heat transfer fluid still contains enough heat to be used as an energy carrier for supplying energy to a district heating circuit.

[0092] For this purpose, the heat transfer fluid 37, cooled in the evaporator 33, is fed to a heat exchanger 39. In the heat exchanger 39, a heat transfer fluid 41 of a district heating network is heated. The heat transfer fluid 43 of the district heating network, heated in the heat exchanger 39, can then be supplied to the consumers of the district heating network. Consumers include, for example, building heating systems or hot water preparation systems. Through the heat transfer to the heat transfer fluid 41 of the district heating network, the heat transfer fluid of the heat transfer circuit 15 cools down further and is returned to the heat exchanger 13.

[0093] The steam generated in the evaporator 33 can either be used directly if the steam temperature is sufficient for the desired application, or it can be further compressed in at least one compressor 45 with at least one compression stage 45.1, 45.2 to generate process steam at a higher pressure. Here too, water is preferably injected into the steam downstream of the compression stages 45.1, 45.2 for intercooling at injection points 47.1, 47.2.

[0094] The process steam 48 generated in this way can then be supplied to a consumer or fed into a steam network.

[0095] In particular, if not all of the residual heat from the heat transfer fluid in the heat transfer circuit is used to heat the heat transfer fluid in the district heating network, it is possible to use some of the residual heat, for example, for steam generation in an absorption heat pump.

[0096] A flow diagram of an embodiment of a heat transfer circuit with an evaporator, a heat exchanger for utilizing residual heat in a district heating circuit and in an absorption heat pump is shown, for example, in Figure 3.

[0097] As in the embodiment shown in Figure 2, the temperature is adjusted to a range of 100 to 200 °C, more preferably to a range of 120 to 200 °C and in particular to a BASF SE 240597W001

[0098] 13

[0099] Heat transfer medium 31, heated to a temperature in the range of 140 to 180 °C, is fed to a first evaporator 33 in which water 35 is evaporated.

[0100] The heat transfer fluid 37, cooled by evaporation to a temperature in the range of 80 to 140 °C, more preferably to a temperature in the range of 100 to 130 °C and in particular to a temperature in the range of 105 to 120 °C, is subsequently divided, unlike in Figure 2, into a first partial stream 37.1 and a second partial stream 37.2.

[0101] The first partial flow 37.1 is fed to the heat exchanger 33 to heat the heat transfer medium 41 of the district heating network, as in the embodiment shown in Figure 2, and the second partial flow 37.2 is fed to an absorption heat pump 49.

[0102] In the absorption heat pump, a working fluid is evaporated by heat transfer from the second partial flow 37.2 and fed to an absorber. In the absorber, the working fluid is absorbed by an absorbent, releasing heat of absorption. This heat of absorption is then used to evaporate water 35. Through heat transfer, the second partial flow cools to a temperature in the range of 60 to 100°C.

[0103] After absorption of the working fluid, the diluted absorbent is expanded and fed to a desorber, where the working fluid is driven off by the addition of heat. The driven-off working fluid is then condensed, and the heat of condensation released is removed by a refrigerant 51.

[0104] The steam 53 generated by the absorption heat pump is mixed with the steam generated in the evaporator 33 to form a total steam flow 55 and then compressed to the desired process steam pressure in at least one compressor 45 with at least one compression stage 45.1, 45.2. The process steam 48 thus generated can then be supplied to a consumer or fed into a steam network.

[0105] Another possible embodiment of a heat transfer circuit with an evaporator, a heat exchanger for utilizing residual heat in a district heating circuit and in an ORC circuit for power generation is shown in Figure 4.

[0106] Unlike the embodiments shown in Figures 2 and 3, in the embodiment shown in Figure 4, the heat transfer fluid 31 of the heat transfer circuit, heated to a temperature in the range of 100 to 200 °C, more preferably to a temperature in the range of 120 to 200 °C, and particularly to a temperature in the range of 140 to 180 °C, is divided into a first partial flow 31.1 and a second partial flow 31.2. The size of the first partial flow 31.1 and the second partial flow 31.2 depends on the desired amount of steam. For example, it is also possible not to generate any steam at all, so that the BASF SE 240597W001

[0107] 14 first partial flow 31.1 is zero and the second partial flow 31.2 contains the entire heat transfer fluid 31 of the heat transfer fluid circuit.

[0108] The first partial stream 31.1 is fed to the evaporator 33, in which, as described above with reference to Figures 2 and 3, water is evaporated by heat transfer from the first partial stream 31.1 and the vapor is subsequently compressed in at least one compressor 45 with at least one compression stage 45.1, 45.2.

[0109] The second partial stream 31.2 is fed to an Organic Rankine Cycle (ORC) process 61 to utilize the heat.

[0110] The ORC process 61 comprises a working fluid circuit 63 in which a liquid working fluid, typically a low-boiling organic liquid, for example isobutane, is first pressurized by a pump 65. The working fluid is then evaporated in an evaporator 67 and superheated in a superheater 69, with the heat required for evaporation and superheating being supplied by the second partial stream 31.2. Since the temperature of the second partial stream 31.2 decreases due to heat transfer to the working fluid, it is preferred that the second partial stream 31.2, as shown here, first flows through the superheater 69 and then through the evaporator 67. It is further preferred that the second partial stream 31.2 and the working fluid also flow countercurrently in the evaporator 67 and the superheater 69.

[0111] The vaporized and superheated working fluid is fed to a turbine 71. Inside the turbine 71, the working fluid expands, thereby driving the turbine 71. A generator 73 for electricity generation is connected to the turbine 71 and is driven by the turbine 71.

[0112] After passing through the turbine 73, the expanded working fluid is condensed in a condenser 75. The heat released in this process is carried away by a coolant 77, for example, a cooling water stream.

[0113] The second partial flow 79, cooled by heat transfer in the evaporator 67 and superheater 69 to a temperature in the range of 80 to 140 °C, more preferably to a temperature in the range of 100 to 130 °C and in particular to a temperature in the range of 105 to 120 °C, can be divided into a first cooled partial flow 79.1 and a second cooled partial flow 79.2, wherein the first cooled partial flow 79.1 is supplied to the heat exchanger 39, in which heat from the cooled partial flow 79.1 is transferred to the heat transfer medium 41 of the district heating network.

[0114] If the first partial flow 31.1 is greater than zero, meaning that a portion of the heat transfer fluid from the secondary flow 15 is supplied to the evaporator 33, it is possible to mix the cooled second partial flow 79 with the first partial flow 81, which has been cooled in the evaporator 33, and then supply it to the heat exchanger 39. BASF SE 240597W001

[0115] 15

[0116] In particular, if the temperature of the cooled second partial flow is equal to or lower than the temperature of the first partial flow leaving the heat exchanger 39, it is preferred to supply only the cooled first partial flow 81 to the heat exchanger 39 and to mix the entire cooled second partial flow 79 downstream of the heat exchanger 39 with the cooled first partial flow 81.

[0117] Depending on the ambient temperature and thus the heat demand for the district heating network, the size of the cooled first partial flow 79.1 can be adjusted so that, after mixing with the first cooled partial flow 81, the amount of heat required for the district heating network is transferred to the heat transfer medium 41 of the district heating network in the heat exchanger.

[0118] Accordingly, the remainder of the cooled second partial flow 79 is mixed as cooled second partial flow 79.2 downstream of the heat exchanger 39 to the remaining heat transfer fluid of the heat transfer circuit 15, so that after mixing the entire heat transfer fluid of the heat transfer circuit is returned to the heat exchanger 13.

[0119] Furthermore, it is also possible to divide the first partial stream 81, particularly after heat dissipation in the evaporator 33, into two further partial streams and to supply the first further partial stream, corresponding to partial stream 37.1 in Figure 3, to the heat exchanger 39 in order to heat the heat transfer fluid 41 of the district heating network, as in the embodiment shown in Figure 3, and to supply the second further partial stream, corresponding to the second partial stream 37.2 in Figure 3, to an absorption heat pump for steam generation. If the cooled first partial stream 79.1 is mixed with the second partial stream 81, it is preferred to divide the entire stream into the two further partial streams.

Claims

BASF SE 240597W001 16 Patent claims 1. Method for utilizing heat from a heat transfer circuit (15) of a geothermal plant (1), comprising: (a) Heating a heat transfer medium flowing through the heat transfer circuit (15) to a temperature in the range of 100 to 200 °C by transferring heat from hot brine (3) from a geothermal source or heating the heat transfer medium flowing through the heat transfer circuit to a temperature in the range of 100 to 200 °C by heat transfer from the geothermal source; (b) Evaporation of water (35) in an evaporator (33) by transferring heat from at least a part of the heated heat transfer medium (31), wherein the at least a part of the heat transfer medium is cooled to a temperature in a range of 80 to 140 °C; (c) Heating a heat transfer medium (41) of a district heating network in at least one heat exchanger (39) by transferring heat from at least a part of the heat transfer medium (37; 79.1; 81) cooled to a temperature in a range of 80 to 140 °C.

2. Method according to claim 1, characterized in that heat from at least a part of the heated heat transfer medium is used in an Organic Rankine Cycle process (61) for power generation and optionally at least a part (79.1) of the heat transfer medium used in the Organic Rankine Cycle process is mixed with at least a part of the heat transfer medium (81) not used in the Organic Rankine Cycle process, so that a heat transfer medium cooled to a temperature in a range of 80 to 140 °C is obtained.

3. Method according to claim 1 or 2, characterized in that the heat transfer medium (37; 79.1; 81) is cooled to a temperature in the range of 60 to 100 °C by the heat transfer in step (c).

4. Method according to one of claims 1 to 3, characterized in that the heat transfer medium (41) of the district heating network is water.

5. Method according to one of claims 1 to 4, characterized in that the steam generated in step (b) is compressed in at least one compressor (45) with at least one compression stage (45.1, 45.2).

6. Method according to one of claims 1 to 5, characterized in that water is injected into the steam downstream of at least one compression stage (45.1, 45.2). BASF SE 240597W001 17 7. Method according to one of claims 1 to 6, characterized in that the heat transfer fluid cooled to a temperature in a range of 80 to 140 °C is divided into a first partial flow (37.1) and a second partial flow (37.2), wherein heat from the first partial flow (37.1) is used to heat the heat transfer fluid (41) of the district heating network and heat from the second partial flow (37.2) is used to generate steam (53) in an absorption heat pump (49).

8. Method according to claim 7, characterized in that the steam (53) generated in the absorption heat pump (49) is mixed with the steam generated in step (b) to form a total steam flow (55) and the total steam flow (55) is then compressed in at least one compressor (45) with at least one compression stage (45.1, 45.2).

9. Method according to claim 8, characterized in that water is injected into the steam downstream of at least one compression stage (45.1, 45.2).

10. Method according to any one of claims 1 to 6, characterized in that the heat transfer medium (31) is divided into a first partial stream (31.1) and a second partial stream (31.2), the first partial stream (31.1) is fed to the evaporator (33) in which the first partial stream (31.1) is cooled to a temperature in the range of 80 to 140 °C, and heat from the second partial stream (31.2) is used in the Organic Rankine Cycle process (61) to generate electricity, and heat from the first partial stream (81) cooled to a temperature in the range of 80 to 140 °C is used to heat the heat transfer medium (41) of the district heating network.

11. Method according to claim 10, characterized in that at least a part of the second partial stream (31.2) is mixed with the cooled first partial stream (81) upstream of the heat exchanger (39) for heating the heat transfer medium (41) of the district heating network.

12. Method according to claim 11, characterized in that the part of the heat transfer fluid of the heat transfer circuit supplied to the heat exchanger (39) for heating the heat transfer fluid (41) of the district heating network has a temperature in a range between 80 and 140 °C after mixing the cooled first partial flow (81) with at least a part (79.1) of the cooled second partial flow (79).

13. Method according to claim 11 or 12, characterized in that at least a part (79.2) of the cooled second partial flow (79) downstream of the heat exchanger (39) is mixed with the part of the heat transfer fluid of the heat transfer circuit cooled in the heat exchanger (39) for heating the heat transfer medium (41) of the district heating network.

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