Method for utilizing heat from a secondary circuit of a geothermal system

Abstract

The invention relates to a method for utilizing heat from a secondary circuit (15) of a geothermal system (1), said method comprising: (a) heating a heat transfer medium flowing through the secondary circuit (15) to a temperature in the region of 120°C to 300°C by transferring heat from hot brine (3) from a geothermal source; (b) evaporating water (35) in a first evaporator (33) by transferring heat from at least one portion of the heated heat transfer medium (31), wherein the at least one portion of the heat transfer medium is cooled to a temperature in the region of 80°C to 140°C; (c) generating steam by using the heat of the heat transfer medium (37) cooled to a temperature in the region of 80°C to 140°C.

Description

[0001] 240595W001

[0002] Methods for utilizing heat from a secondary circuit of a geothermal plant

[0003] Description

[0004] The invention relates to a method for utilizing heat from a secondary 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 secondary 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, "Geothermie" (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 extracted 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] CN-A 114321858 discloses the use of geothermal energy to generate steam. For this purpose, water from a geothermal source is used to heat demineralized 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 unevaporated water is fed into a second flash evaporator, where more water is evaporated. 240595W001

[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 problem is solved by a method for utilizing heat from a secondary circuit of a geothermal plant, comprising:

[0013] (a) Heating a heat transfer fluid flowing through the secondary circuit to a temperature in the range of 120 to 300 °C by transferring heat from hot brine from a geothermal source;

[0014] (b) Evaporation of water in a first 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) Generating steam by utilizing heat from the heat transfer medium cooled to a temperature in the range of 100 to 140 °C.

[0016] The use of heat from a secondary circuit of the geothermal plant allows the heat of the hot brine to be used not only to heat the heat transfer medium of the secondary circuit, but also for other tasks, for example for electricity generation or, after heat transfer to the heat transfer medium of the secondary circuit, for cooling systems or heating buildings.

[0017] Furthermore, it is also possible to use the heat of the heat transfer medium in the secondary circuit not only for steam generation, but also for other purposes, for example for the direct heating of plant components.

[0018] Another advantage of the method according to the invention is that the heat of the secondary circuit can be used optimally, since the residual heat after use for steam generation in step (b) can also be used for steam generation and thus the amount of steam generated with the heat of the secondary circuit can be greatly increased.

[0019] In a 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 drawn from a depth of 3000 to 240595W001.

[0020] 3

[0021] 4000 m and has a temperature in the range of 120 to 300 °C, more preferably in the range of 120 to 200 °C and particularly in the range of 140 to 180 °C.

[0022] 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.

[0023] 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 secondary circuit to a temperature in the range of 120 to 300 °C, more preferably to a temperature in the range of 130 to 170 °C, and particularly to a temperature in the range of 140 to 160 °C. The pressure of the heat transfer fluid in the secondary circuit is preferably controlled so that the heat transfer fluid always remains liquid and does not evaporate.

[0024] Any heat transfer fluid known to experts is suitable for use in the secondary 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 the secondary circuit.

[0025] According to the invention, at least a portion of the heat transfer fluid heated by the brine is used to produce steam. For this purpose, water is evaporated in a first evaporator by transferring heat from the at least part of the heat transfer fluid. 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.

[0026] The water supplied to the first evaporator for evaporation preferably has a pressure in the range of 1 to 50 bar(abs), more preferably 1 to 30 bar(abs), and particularly 1 to 10 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.

[0027] After cooling through heat transfer during water evaporation, the temperature of the heat transfer fluid is still high enough to utilize further heat from the fluid. For this purpose, the heat from the fluid, cooled to a temperature in the range of 80 to 140 °C, is used to generate more steam. This preferably cools the fluid to a temperature in the range of 60 to 100 °C.

[0028] In a first embodiment, the heat can be utilized by evaporating water in a second evaporator. Due to the temperature of the cooled heat exchanger, it is necessary to supply water to the second evaporator at a pressure of 240595W001.

[0029] 4. rich from 100 to 1000 mbar(abs), more preferably in the range of 200 to 800 mbar(abs) and especially in the range of 300 to 500 mbar(abs).

[0030] In the second evaporator, the water is at least partially, preferably completely, evaporated, and it is also preferred that the water is completely evaporated to saturated steam and superheated if necessary.

[0031] To utilize the steam generated in the second evaporator, it is preferred to subsequently compress it. Typically, at least one compressor with at least one compression stage is used for steam compression. It is particularly preferred to compress the steam generated in the second evaporator in at least one compressor with at least one compression stage and then mix it with the steam generated in the first evaporator. For this purpose, the steam generated in the second evaporator is preferably compressed to a pressure in the range of 1 to 10 bar (abs) and, in particular, to a pressure in the range of 1 to 2 bar (abs).

[0032] For cooling, water is injected into the steam downstream of at least one compression stage, preferably downstream of every compression stage. This has the additional advantage of also increasing the steam volume.

[0033] Depending on the intended use of the steam, it may be necessary to further compress it into process steam after mixing. Here too, compression preferably takes place in at least one compressor with at least one compression stage. It is also preferred that water is injected into the steam for cooling downstream of at least one compression stage, preferably downstream of each compression stage.

[0034] In an alternative and preferred embodiment, the steam in step (c) is generated by using the heat of the heat transfer fluid cooled to a temperature in the range of 80 to 140 °C in an absorption heat pump.

[0035] Preferably, the absorption heat pump is a single-stage absorption heat pump in which 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 heat transfer fluid, which is cooled to a temperature in the range of 80 to 140 °C, more preferably in the range of 100 to 120 °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 is provided by the heat transfer fluid which, after use for steam generation, has been cooled to a temperature in the range of 60 to 120°C, more preferably in the range of 70 to 100°C and in particular to a temperature of 75 to 95°C, 240595W001.

[0036] 5. The working fluid is driven off as vapor. The vaporous working fluid is then condensed in a condenser, the resulting liquid working fluid is brought to a higher pressure and then fed back to the evaporator.

[0037] 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.

[0038] The condensation of the working fluid in the condenser occurs through heat transfer to a coolant. Cooling water is typically used as the coolant.

[0039] Water, for example, is a suitable tool.

[0040] A salt, for example lithium bromide, in aqueous solution is preferably used as the absorbent.

[0041] To enable the absorbent to be circulated between the absorber and the desorber, only enough working fluid is driven off from the desorber to obtain a concentrated brine solution 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.

[0042] 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 to the single-stage absorption heat pump at a pressure in the range of 1 to 5 bar(abs), more preferably in the range of 1 to 2 bar(abs).

[0043] In an alternative embodiment, a multi-stage, preferably a two-stage, absorption heat pump is used, in which steam can be generated that already has a pressure corresponding to the pressure of the process steam produced by compression of the steam generated in the first evaporator. In this case, the steam generated in step (b) is compressed in at least one compressor with at least one compression stage and, after compression, mixed with the steam generated in the absorption heat pump. The process steam obtained in this case is preferably low-pressure steam.

[0044] If medium-pressure or high-pressure steam is to be generated as process steam, it is possible to further compress the steam to the desired pressure in at least one additional compressor with at least one compression stage. 240595W001

[0045] 6

[0046] As already described above, it is also preferred here that water is injected into the steam both during the compression of the steam generated in the first evaporator and during the optional further compression of the steam to high-pressure steam or low-pressure steam for cooling downstream of at least one compression stage, preferably downstream of each compression stage.

[0047] When using a multi-stage, preferably two-stage, absorption heat pump, the steam generated in the absorption heat pump preferably has a pressure in the range of 1 to 10 bar(abs), more preferably in the range of 3 to 8 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 if the steam generated in the absorption heat pump is mixed with the steam generated in step (b) to form a total steam flow, and the total steam flow is then compressed in at least one compressor with at least one compression stage.

[0048] If the temperature of the steam after mixing the steam generated in the first evaporator and the steam generated in the absorption heat pump is still below the temperature of the heat transfer fluid heated by the brine, it is further preferred if the heat transfer fluid is divided into a first partial flow and a second partial flow, wherein the first partial flow passes through the first evaporator and the second partial flow passes through a heat exchanger in which the total steam flow is superheated by heat transfer from the second partial flow before compression.

[0049] Since the temperature of the partial flow of heat transfer fluid passing through the heat exchanger to superheat the steam is higher than the temperature of the steam leaving the absorption heat pump after heat transfer to the steam, it is further preferred if the first partial flow after passing through the first evaporator and the second partial flow after passing through the heat exchanger are mixed to form a total flow and the total flow is then supplied to the absorption heat pump.

[0050] 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.

[0051] Here too, in the described compression of the steam in at least one compressor with at least one compression stage, it is preferred to inject water into the steam downstream of at least one compression stage and preferably downstream of each compression stage.

[0052] The generated process steam can either be supplied directly to a consumer or fed into a steam network that supplies steam to various consumers. In particular, if the process steam is supplied directly to a consumer, it is possible to use the 240595W001

[0053] 7

[0054] To use steam at the pressure it has after evaporation in the first evaporator and, if applicable, after mixing with the steam generated in step (c), 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.

[0055] Low-pressure steam, medium-pressure steam, or high-pressure steam can be generated by compression in at least one compressor with at least one compression stage. It is also possible to first compress all the steam to low-pressure steam, provided the pressure in the steam generation device is 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 at least a portion of the medium-pressure steam to high-pressure steam.

[0056] 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 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.

[0057] 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.

[0058] 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.

[0059] 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. 240595W001

[0060] 8

[0061] 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.

[0062] 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 passes and to steam generation apparatus, the water used for steam generation is preferably demineralized and degassed.

[0063] Exemplary embodiments of the invention are shown in the figures and are explained in more detail in the following description.

[0064] They show:

[0065] Figure 1 shows an overview flow diagram of a geothermal plant;

[0066] Figure 2 shows a flow diagram of an embodiment with a first evaporator and a second evaporator;

[0067] Figure 3 shows a flow diagram of a first embodiment with an evaporator and an absorption heat pump;

[0068] Figure 4 shows a flow diagram of a second embodiment with an evaporator and an absorption heat pump.

[0069] Figure 1 shows an overview flow diagram of a geothermal plant.

[0070] 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.

[0071] The hot brine is usually extracted from a depth of 3000 to 4000 m and has a temperature in the range of 120 to 300 °C, more preferably in the range of 120 to 200 °C and particularly in the 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.

[0072] With a “Cleaning in Place” (ClP) system 11, it is possible to efficiently clean system components, for example heat exchangers in cooling water circuits, without disassembling them 240595W001

[0073] 9. For this purpose, cleaning agents circulate through pipelines and system components to remove deposits, biofilms, and other contaminants, thereby increasing the operational efficiency and lifespan of the system. Automating the cleaning process not only saves time but also increases the safety of operating personnel by minimizing contact with hazardous chemicals.

[0074] 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 of a secondary circuit 15. The heat transfer fluid of the secondary circuit is preferably heated to a temperature in the range of 120 to 300 °C, more preferably to a temperature in the range of 130 to 170 °C, and particularly to a temperature in the range of 140 to 160 °C. Through heat transfer to the heat transfer fluid of the secondary 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] According to the invention, the heat transferred to the heat carrier of the secondary circuit 15 is used to generate steam. This is illustrated in a first embodiment in Figure 2.

[0079] To generate steam, the heat transfer fluid 31, heated in the heat exchanger 13 to a temperature in the range of 120 to 200 °C, more preferably to a temperature in the range of 130 to 170 °C, and particularly to a temperature in the range of 140 to 160 °C, is fed to a first evaporator 33. In the first 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. However, the heat transfer fluid contains 240595W001.

[0080] 10 still enough heat to be used as an energy carrier for the evaporation of more water.

[0081] In the embodiment shown in Figure 2, the cooled heat transfer fluid 37 is supplied to a second evaporator 39. Due to the lower temperature of the heat transfer fluid supplied to the second evaporator 39, it is necessary that the water 41 supplied to the second evaporator for steam generation has a pressure lower than the pressure of the water 35 supplied to the first evaporator 33. Preferably, the water supplied to the second evaporator 39 has a pressure in the range of 100 to 1000 mbar (abs), more preferably in the range of 200 to 800 mbar (abs), and particularly in the range of 300 to 500 mbar (abs).

[0082] In order to make practical use of the steam generated in the second evaporator 39, it is necessary to compress it. For this purpose, at least one compressor with at least one compression stage 43.1, 43.2 is used. Preferably, the steam generated in the second evaporator 39 is compressed in the at least one compressor with at least one compression stage.

[0083] 43.1. 43.2 compressed to a pressure at which the vapor can be mixed with the vapor generated in the first evaporator 33 without reducing the pressure of the resulting total vapor flow too much. To prevent overheating, pressure is applied at injection points 44.1 ,

[0084] 44.2 downstream of compression stages 43.1 , 43.2 water is injected into the steam for intercooling.

[0085] The total steam flow can then 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.

[0086] The process steam 47 thus generated can then be supplied to a consumer or fed into a steam network.

[0087] Figure 3 shows an alternative embodiment for steam generation.

[0088] As in the embodiment shown in Figure 2, the heat transfer medium 31, heated to a temperature in the range of 120 to 300 °C, more preferably to a temperature in the range of 130 to 170 °C and in particular to a temperature in the range of 140 to 160 °C, is supplied to a first evaporator 33 in which water 35 is evaporated.

[0089] 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, however, an- 240595W001

[0090] 11 of the as shown in Figure 2, not fed to a second evaporator 39 but to an absorption heat pump 49.

[0091] In the absorption heat pump, a working fluid is evaporated by heat transfer from the heat transfer medium 37, which has been cooled 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, 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 this heat transfer, the heat transfer medium cools down to a temperature in the range of 60 to 100 °C.

[0092] 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.

[0093] When using a multi-stage absorption heat pump, steam 53 is generated which already has a pressure that preferably corresponds to the desired process steam pressure.

[0094] The steam generated in the first evaporator 33 is compressed to the desired process steam pressure in the at least one compressor 45 with at least one compression stage 45.1 , 45.2.

[0095] The steam generated in the first evaporator 33, compressed to process steam pressure, and the steam generated in the absorption heat pump 53 are mixed together and supplied as process steam 47 to a consumer or fed into a steam network.

[0096] Another embodiment with an absorption heat pump for steam generation is shown in Figure 4.

[0097] In contrast to the embodiment shown in Figure 3, the steam 55 taken from the absorption heat pump 49 has a significantly lower pressure. For this reason, the steam taken from the absorption heat pump 49 is mixed with the steam taken from the first evaporator 33 before the resulting total steam flow 57 is compressed.

[0098] Preferably, the total steam flow 57 is superheated in a heat exchanger 59 before compression. The heat required for this is provided by the heated heat transfer fluid 31. In order to use the heated heat transfer fluid as a heat source for evaporation in the first evaporator 33 and for superheating the steam in the heat exchanger 59, the heated heat transfer fluid is divided into a first partial flow 61 and a second partial flow 63. 240595W001

[0099] 12

[0100] The first partial flow 61 passes through the first evaporator 33 and the second partial flow passes through the heat exchanger 59. After passing through the first evaporator 33 and the heat exchanger 59, the first partial flow 61 and the second partial flow 63 are combined again and the total flow is supplied to the absorption heat pump 49.

[0101] The steam superheated in the heat exchanger 59 is then fed to the at least one compressor 45 with at least one compression stage 45.1 , 45.2 and compressed in this to form process steam 47.

[0102] In the embodiments shown in Figures 2, 3, and 4, two compression stages 43.1, 43.2; 45.1, 45.2 are depicted. However, depending on the desired pressure to which the steam is to be compressed and the pressure ratio between the inlet and outlet of a compression stage, it may be sufficient for a compressor with only one compression stage, or more than two compression stages may be required. If more than two compression stages are needed, either a compressor with the corresponding number of compression stages, such as a geared turbo compressor, can be used, or more than one compressor can be employed.

[0103] In addition, the generated process steam 47 can be further compressed in further compressors or compression stages in all illustrated embodiments if steam with a higher pressure is required.

Claims

240595W001 13 Patent claims 1. Method for utilizing heat from a secondary circuit (15) of a geothermal plant (1 ), comprising: (a) Heating a heat transfer fluid flowing through the secondary circuit (15) to a temperature in the range of 120 to 300 °C by transferring heat from hot brine (3) from a geothermal source; (b) Evaporating water (35) in a first 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) Generating steam by utilizing heat from the heat transfer medium cooled to a temperature in the range of 80 to 140 °C (37).

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

3. Method according to claim 1 or 2, characterized in that in step (c) water (41) is evaporated at a pressure in the range of 100 to 1000 mbar(abs) by heat transfer from the heat transfer medium cooled to a temperature in the range of 80 to 140 °C in a second evaporator (39).

4. Method according to claim 3, characterized in that the vapor generated in the second evaporator is compressed in at least one compressor with at least one compression stage (43.1 , 43.2) and subsequently mixed with the vapor generated in step (b).

5. Method according to claim 4, characterized in that the steam is compressed to process steam after mixing in at least one compressor (45) with at least one compression stage (45.1 , 45.2).

6. Method according to claim 4 or 5, characterized in that water is injected into the steam downstream of at least one compression stage (43.1 , 43.2; 45.1 , 45.2).

7. Method according to claim 1 or 2, characterized in that the steam in step (c) is generated by using the heat of the heat transfer medium cooled to a temperature in the range of 80 to 140 °C in an absorption heat pump (49). 240595W001 14 8. Method according to claim 7, characterized in that the absorption heat pump (49) is a multi-stage absorption heat pump and the steam generated in step (b) is compressed in at least one compressor (45) with at least one compression stage (45.1 , 45.2) and is mixed with the steam generated in the absorption heat pump (49) after compression.

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

10. Method according to claim 7, characterized in that the steam generated in the absorption heat pump (49) is mixed with the steam generated in step (b) to form a total steam flow (57) and the total steam flow (57) is then compressed in at least one compressor (45) with at least one compression stage (45.1 , 45.2).

11. Method according to claim 10, characterized in that water is injected into the steam downstream of at least one compression stage (45.1 , 45.2).

12. Method according to claim 10 or 11, characterized in that the heat transfer medium is divided into a first partial flow (61) and a second partial flow (63), wherein the first partial flow (61) flows through the first evaporator (33) and the second partial flow (63) flows through a heat exchanger (59) in which the total steam flow (57) is superheated by heat transfer from the second partial flow (63) before compression.

13. Method according to claim 12, characterized in that the first partial flow (61 ) after passing through the first evaporator (33) and the second partial flow (63) after passing through the heat exchanger (59) are mixed to form a total flow and the total flow is then supplied to the absorption heat pump (49).

14. Method according to claim 12 or 13, characterized in that the steam superheated in the heat exchanger (59) is compressed in at least one compressor (45) with at least one compression stage (45.1 , 45.2).

15. Method according to claim 14, characterized in that water is injected into the steam downstream of at least one compression stage (45.1 , 45.2).

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