Geothermal installation with cascaded water vapour generators for industrial installations

Abstract

The invention relates to a geothermal installation with cascaded water vapour generators for industrial installations, comprising: (a) a geothermal source which is designed such that it provides a brine with a temperature in the range from 120 to 300 °C, (b) at least two heat exchangers (2, 3, 4) through each of which the brine can flow on their primary side, the primary side of the respective heat exchangers (2, 3, 4) being arranged in a cascaded manner with respect to its adjacent heat exchanger (2, 3, 4), wherein the respective heat exchanger (2, 3, 4) has a secondary side which is configured such that either supplied water (c1, c2, c3) evaporates as a result of the heat exchange from the primary to the secondary side, or circulating water heats up in a secondary circuit and as a result an evaporator (15, 16, 17) arranged in the secondary circuit evaporates supplied water (c1, c2, c3), (c) a first pipeline, which fluidically connects the withdrawal location (a) of the geothermal source to the cascaded primary sides of the heat exchangers (2, 3, 4), (d) each of the provided heat exchangers (2, 3, 4) has a downstream mineral withdrawal unit (12, 13, 14), (e) a first brine pump (1) which is arranged between the withdrawal location (a) and the primary side of the first heat exchanger (2) in the main flow direction, by way of which the brine is conveyed from the source to the respective cascaded primary sides of the heat exchangers (2, 3, 4) and their respective downstream mineral withdrawal unit (12, 13, 14), and (f) an outflow pipeline which is fluidically connected to the last mineral withdrawal unit (14) in the main flow direction, wherein the outflow pipeline opens into the geothermal source such that the outlet of the outflow pipeline (b) has a distance of at least 100 m, preferably at least 1500 m and particularly preferably at least 2500 m, to the withdrawal location (a). The invention further provides a method of operating a geothermal installation according to the invention.

Description

[0001] Geothermal plant with cascaded steam generator for industrial plants

[0002] The invention relates to a geothermal plant with cascaded steam generators for industrial plants, comprising a geothermal source designed to provide a brine having a temperature in the range of 120 to 300 °C, at least two heat exchangers, each of which can be flowed through by the brine on its primary side, and the primary side of the respective heat exchanger is arranged in cascade to its adjacent heat exchanger, wherein the respective heat exchanger has a secondary side configured so that either supplied water evaporates by heat transfer from the primary to the secondary side, or that circulating water is heated in a secondary circuit and thereby an evaporator arranged in the secondary circuit evaporates supplied water.

[0003] Heat pumps are generally known for generating heat, and in particular for generating steam. A special type of heat pump is a geothermal system. This uses the hot brine of a geothermal source as a heat source to generate steam or useful heat.

[0004] The Springer-Verlag textbook "Geothermal Energy" by Ingrid Stober and Kurt Bucher, in its third edition from 2020, introduces geothermal plants. Page 179 describes a geothermal plant that uses the brine from a geothermal source to provide energy for a power plant or for buildings. The use of the brine's heat is presented in a cascaded manner at different temperature levels, with the brine heat at the highest temperature being used to generate electricity in a power plant. Due to the heat extraction for electricity production, the brine is then at a correspondingly lower temperature level, where the heat from the brine is used for food processing or refrigeration systems.Due to the heat extraction, the brine is then at an even lower temperature, at which point the heat from the brine is used for building heating or greenhouse heating. Due to the heat extraction, the brine is then at the lowest temperature still usable for the system, at which point the heat from the brine is used for fish farming before the brine is pumped back to the geothermal source.

[0005] Such geothermal plants have the disadvantage that they cannot generate steam for industrial plants. This is because they only provide electricity and useful heat for specific applications, such as building heating. The generation of industrial steam is not intended. Furthermore, such geothermal plants have the disadvantage that mineral precipitation can clog the geothermal plant.

[0006] CN114321858A discloses a geothermal plant for steam generation with a heat pump and a waste heat system with multi-stage steam generators. In this geothermal plant, the heat pump generates steam at a higher temperature than the steam generated by the plant's multi-stage, cascaded steam generators. Each of the multi-stage steam generators represents a flash tank.

[0007] Such geothermal systems have the disadvantage that a complex and expensive heat pump with a separate working fluid is required to generate steam. Furthermore, the brine flows through a first heat exchanger, the heat exchanger of the heat pump's evaporator, and a second heat exchanger for waste heat recovery. Neither chemical treatment of the brine nor consideration is given to possible mineral precipitation. This therefore leads to the risk of problems arising from mineral precipitation in, for example, the heat exchangers. Excessive precipitation can clog the heat exchangers due to the resulting deposit formation, necessitating the system shutdown.

[0008] The challenge was therefore to develop a geothermal plant that could efficiently and reliably generate steam for industrial plants. Furthermore, the task was to create a geothermal plant that could operate stably throughout its entire operating life without deposit formation leading to a significant increase in the pressure drop for pumping the brine through the geothermal plant. Furthermore, the task was to create a geothermal plant that could extract minerals from the brine.

[0009] These objects are achieved according to the present invention by a geothermal plant according to claim 1 and by a method for operating the geothermal plant according to claim 6. Advantageous embodiments of the geothermal plant are given in claims 2 to 5, whereas advantageous embodiments of the method for operating the geothermal plant are given in claims 7 to 15.

[0010] The geothermal plant with cascaded steam generator for industrial plants according to the invention comprises:

[0011] (a) a geothermal source designed to provide a brine having a temperature in the range of 120 to 300 °C, (b) at least two heat exchangers, each of which can be flowed through by the brine on its primary side, and the primary side of the respective heat exchanger is arranged in cascade to its adjacent heat exchanger, wherein the respective heat exchanger has a secondary side configured so that either supplied water is evaporated by the heat transfer from the primary to the secondary side, or that circulating water is heated in a secondary circuit and thereby an evaporator arranged in the secondary circuit evaporates supplied water,

[0012] (c) a first pipeline that fluidically connects the extraction point (a) of the geothermal source with the cascaded primary sides of the heat exchangers,

[0013] (d) each of the existing heat exchangers has a downstream mineral extraction unit,

[0014] (e) a first brine pump arranged between the extraction location (a) and the primary side of the first heat exchanger in the main flow direction, whereby the brine is conveyed from the source to the respective cascaded primary sides of the heat exchangers and their respective downstream mineral extraction unit, and

[0015] (f) an outflow pipeline which is fluidically connected to the mineral extraction unit arranged last in the main flow direction, wherein the outflow pipeline opens into the geothermal source in such a way that the outlet of the outflow pipeline is at a distance of at least 100 m, preferably at least 1500 m and particularly preferably at least 2500 m from the extraction location (a).

[0016] The advantage of the geothermal plant according to the invention lies in the efficient treatment of the brine during its operation, preventing the flow channel walls of the cascaded heat exchangers from becoming clogged by deposits that would significantly increase the pressure loss across the respective heat exchanger or even clog the heat exchanger. At the same time, various minerals are extracted in the mineral extraction unit downstream of the respective heat exchanger due to the different temperature levels of the heat exchangers. At the same time, efficient, safe, and robust steam generation for industrial use as industrial steam is ensured.

[0017] In this document, a "geothermal source" includes a production well for extracting brine and an injection well for returning the treated brine.

[0018] The extraction point corresponds to the lowest end of the production well, whereas the return point corresponds to the lowest end of the injection well. If the geothermal source is located at a depth of 3,000 to 4,000 m, the distance between the extraction point and the return point should preferably be between 1.0 and 2.5 km.

[0019] In this document, a "pipeline" includes one or more pipes, which may be joined together to form a pipeline by pipe connections. The pipeline may also contain, for example, pipe support systems, fittings, and thermal and mechanical insulation. A pipeline serves to transport fluids and transfer mechanical and / or thermal energy. For example, a pipeline may be located in the production well or in the injection well to fluidically connect the corresponding extraction or return point with a brine pump and / or with other pipes or pipelines of the geothermal plant.

[0020] In this document, a "heat exchanger" refers to a device that can transfer heat from one fluid to another. Examples include plate heat exchangers or shell-and-tube heat exchangers.

[0021] In this document, a "mineral extraction unit" represents a facility that extracts minerals or other substances from a brine. In principle, any suitable separation process can be used to extract minerals or other substances from a brine, such as filtration, phase separation, extraction, adsorption, absorption, or precipitation. The minerals or other substances can be reused. For example, lithium can be used in the production of batteries.

[0022] The detailed design of a mineral extraction unit also depends on the type of minerals to be separated. On the one hand, a mineral extraction unit serves to separate solids that are formed by cooling the brine or by adding precipitants, such as

[0023] Sulfuric acid is used to precipitate barium sulfate from the brine. The separation of the finely dispersed, precipitated minerals follows the well-known principles of solid-state processing.

[0024] Either discontinuous or continuous operation is used. These can be discontinuous filter presses, Nutsche filters, sedimentation tanks, and the like, or continuously operating centrifuges, decanters, belt filters, and the like.

[0025] On the other hand, a mineral extraction unit can also be designed to separate substances in solution. In this case, ion exchangers or adsorption devices, each of which can be operated regeneratively, can be used.

[0026] In both cases, the mineral extraction units contain, in addition to the core equipment or machines mentioned, the necessary peripheral equipment, such as solvent reservoirs, rinse water tanks, pumps and the corresponding piping and fittings, etc.

[0027] In this document, “brine purification” is a process that removes minerals or other substances from the brine in order to reduce the formation of deposits in the geothermal plant, such as in the cascaded heat exchangers, so that the geothermal plant does not become clogged or the pressure loss of the brine between the production well and the injection well does not become too great during operation.

[0028] In this document, "extraction from brine" refers to a process that extracts minerals or other substances from the brine for further use. In this case, deposit formation can also occur in geothermal systems, such as cascaded heat exchangers. Here, too, it is important to reduce potential deposit formation to prevent the geothermal system from becoming clogged or to prevent the pressure loss of the brine between the production well and the injection well from becoming excessive during operation.

[0029] In this document, a “secondary circuit” represents a circuit mass flow that receives a heat flow from the primary side of the heat exchanger.

[0030] The secondary circuit may also contain branches, for example, a bypass parallel to an evaporator. There may also be multiple evaporators in the secondary circuit, which are fluidically connected to each other, for example, in parallel circuits, series circuits, or combinations of parallel and series circuits.

[0031] An "evaporator" in this document represents a heat exchanger or a flash tank. If the evaporator is a heat exchanger, the heat exchanger transfers a heat flow from its primary side to its secondary side, whereby a liquid supplied to the secondary side, preferably water and particularly preferably demineralized water, is at least partially evaporated.

[0032] The evaporator can also contain other standard components, such as control valves, pressure reducers, flow regulators, or sensors. The evaporator can therefore also include a control system. In general, the term "evaporator" can also refer to multiple evaporators that are fluidically connected to each other in series or parallel.

[0033] Examples of suitable heat exchangers as evaporators include thin-film, Robert, falling-film, natural circulation, and forced circulation evaporators. These evaporators can be designed as shell-and-tube heat exchangers or plate heat exchangers. Suitable evaporators are known to those skilled in the art and are described, among others, in: SPX, Evaporator Handbook, APV Americas, Engineered Systems, Separation Technologies, 4th Edition, available at (accessed on November 20, 2023).

[0034] A "flash tank" represents one possible form of evaporator in this document. The flash tank has a tank that preferably contains an expansion nozzle in the upper region. A fluid, preferably water and particularly preferably demineralized water, is fed to the flash tank. The fluid is superheated upstream of the expansion nozzle with respect to the pressure in the flash tank. If an expansion nozzle is present, the fluid is fed to the flash tank through the inlet of the expansion nozzle. The fluid that has not evaporated in the flash tank collects in the lower region of the flash tank and is discharged through a flash tank outlet. The fluid that has evaporated in the flash tank is discharged through a vapor outlet in the upper region of the flash tank. Furthermore, a separate fluid, preferably water and particularly preferably demineralized water, can be fed to the flash tank via a supply line.

[0035] In this document, a “compressor” is understood as a machine that compresses gases.

[0036] An example of a suitable compressor is a geared turbo compressor. The compressor is usually designed with several compression stages and intermediate stages, with each intermediate stage being equipped with a device for intercooling.

[0037] In this document, the term "fluidically connected" generally refers to two or more flow-through components, such as several flow pipes, being connected in such a way that a fluid can flow through these connected components. As a rule, sufficient technical tightness should be ensured when a fluid flows through them.

[0038] In this document, a "liquid" is defined as a single-phase or multi-phase fluid. The liquid is therefore free-flowing and can be pumped through the primary circuit. The liquid may also contain gas and / or solid components, provided such a liquid is still pumpable.

[0039] In this document, a "heat transfer fluid" is defined as a single-phase or multi-phase fluid, for example, a liquid, a gas, a vapor, or mixtures thereof. The heat transfer fluid is therefore fluid. The heat transfer fluid may also contain solids, provided such a heat transfer fluid is still pumpable. Examples of heat transfer fluids include heating steam, air, demineralized water, filtered river water, or a reaction mixture from a reactor.

[0040] The following fluids are preferably used as heat transfer fluids: water, demineralized water, heat transfer oils such as Therminol VP1, Xceltherm 600, Syltherm XLT, Dowtherm A, Calorie HAT 43 or Marlotherm SH, sunflower oil, organic liquids such as ethanol, propane, butane, isobutanol, isopentanol or octane, ammonia, mineral oils such as motor oil or Mobiltherm 605, inorganic molten salts, liquid metals such as sodium, lead, bismuth, potassium and alloys thereof.

[0041] In a preferred embodiment of the geothermal plant according to the invention, a second brine pump is arranged between the mineral extraction unit arranged last in the main flow direction and the outlet of the outflow pipeline, whereby the treated brine is conveyed to the outlet of the outflow pipeline.

[0042] This has the advantage that the treated brine is transported directly and safely to the return point.

[0043] In a preferred embodiment of the geothermal system according to the invention, if a secondary circuit is present, the respective heat exchanger contains a pump for circulating the water in the secondary circuit, thereby ensuring water circulation. Furthermore, the water mass flow can be adjusted, for example, using a variable-speed pump.

[0044] In a preferred embodiment of the geothermal plant according to the invention, the heat exchangers on their secondary side or the evaporators in the secondary circuits each have a downstream compressor, each configured to compress the generated steam. This compresses the steam to a level that allows it to be used in many industrial processes. By connecting multiple compressors or by varying the number of compressor stages, the steam can be compressed to the level required for the intended application.

[0045] In a preferred embodiment of the geothermal plant according to the invention, exactly three cascaded heat exchangers are provided for steam generation, each of the three heat exchangers having a downstream mineral extraction unit. With exactly three cascaded heat exchangers, exactly three temperature levels for mineral separation are set by the downstream mineral extraction units.

[0046] This allows minerals to be separated from the brine at three different temperature levels, which automatically results in the concentration of the separated minerals depending on the three temperature levels, since the respective solubility of the individual minerals in the brine is strongly dependent on the temperature. To extract minerals from the brine, the minerals are already preselected accordingly by the three different temperature levels. The economic outlay, especially with three cascaded heat exchangers, remains in proportion to the mineral extraction and steam generation. Another subject of the invention relates to the method according to the invention for operating a geothermal plant according to the invention.

[0047] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the method comprises the following steps: a) conveying the brine by the first brine pump from the geothermal source to the cascaded primary sides of the respective heat exchangers, wherein the temperature of the brine at the inlet of the primary side of the first heat exchanger arranged in the main flow direction is in the range of 120 to 300 °C, b) transferring at least part of the heat of the brine from the primary side of the respective heat exchanger

[0048] I. on the water supplied to the secondary side, whereby the supplied water is evaporated, or

[0049] II. in the case of an existing secondary circuit: on the circulating water in the secondary circuit of the respective heat exchanger, whereby the temperature of the water in the respective secondary circuit upstream of the evaporator is in the range from 40 to 195 °C, and thereby the water supplied to the evaporator is evaporated, c) extraction of minerals by the mineral extraction unit downstream of the respective heat exchanger, and d) conveying the treated brine from the outlet of the mineral extraction unit arranged last in the main flow direction to the outlet of the outflow pipe, whereby the temperature at the outlet of the outflow pipe is in the range from 35 to 115 °C.

[0050] The advantage of the method according to the invention for operating the geothermal plant lies in the efficient treatment of the brine, preventing the flow channel walls of the cascaded heat exchangers from becoming clogged by deposits that would significantly increase the pressure loss across the heat exchanger or even clog the heat exchanger. At the same time, various minerals are extracted in the mineral extraction unit downstream of the heat exchanger due to the different solubilities of the minerals at the different temperature levels of the heat exchangers.

[0051] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the temperature of the brine at the inlet of the primary side of the first heat exchanger arranged in the main flow direction is in the range of 120 to 200 °C, preferably in the range of 140 to 180 °C. The temperature of the brine at the outlet of the primary side of the first heat exchanger is in the range of 105 to 155 °C.

[0052] As a result, the first minerals are separated from the brine by the downstream mineral extraction unit, whereby the pressure loss across the first heat exchanger does not increase significantly due to possible deposit formation on the flow channel walls of the first heat exchanger.

[0053] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the temperature of the brine at the inlet of the primary side of the second heat exchanger arranged in the main flow direction is in the range of 105 to 155 °C, and the temperature of the brine at the outlet of the primary side of the second heat exchanger is in the range of 75 to 120 °C.

[0054] As a result, further minerals are separated from the brine by the downstream mineral extraction unit, whereby the pressure loss across the second heat exchanger does not increase significantly due to possible deposit formation on the flow channel walls of the second heat exchanger.

[0055] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the temperature of the brine at the inlet of the primary side of the third heat exchanger arranged in the main flow direction is in the range of 75 to 120 °C, and the temperature of the brine at the outlet of the primary side of the third heat exchanger is in the range of 35 to 115 °C, preferably in the range of 40 to 85 °C and particularly preferably in the range of 45 to 55 °C.

[0056] As a result, further minerals are separated from the brine by the downstream mineral extraction unit, whereby the pressure loss across the third heat exchanger does not increase significantly due to possible deposit formation on the flow channel walls of the third heat exchanger.

[0057] In a preferred embodiment of the method according to the invention for operating a geothermal plant, exactly three heat exchangers are present for generating steam, each of the three heat exchangers having a downstream mineral extraction unit. With exactly three cascaded heat exchangers, exactly three temperature levels for separating minerals are set by the downstream mineral extraction units. This allows minerals to be separated from the brine at three different temperature levels, which automatically results in the concentration of the separated minerals depending on the three temperature levels. To extract minerals from the brine, the minerals are already pre-selected accordingly by the three different temperature levels. The economic outlay, especially with three cascaded heat exchangers, still remains proportional to the mineral extraction and steam extraction.

[0058] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the first mineral extraction unit in the main flow direction separates at least partially, preferably predominantly, one of the substances: Fe, Pb, and Al silicates from the brine to purify the brine. For extraction, the first mineral extraction unit in the main flow direction separates at least partially, preferably predominantly, one of the substances: Zn, Sr, CaF, and Mn; from the brine to purify the brine. As a result, the downstream heat exchangers are not so heavily burdened by the deposit formation that occurs during operation of the geothermal plant that the pressure loss across the downstream heat exchangers increases significantly. In addition, one or more substances selected from the group: Zn, Sr, CaF, and Mn; can be at least partially extracted from the brine.In addition, the heat flow extracted by the first heat exchanger is also used for steam generation.

[0059] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the second mineral extraction unit in the main flow direction separates at least partially, preferably predominantly, one of the substances: Mg, P, and Zn; from the brine for purification of the brine. For extraction, the first mineral extraction unit in the main flow direction separates at least partially, preferably predominantly, one of the substances: Mg, Mn, F, P, Sr, and Zn; from the brine.

[0060] This prevents the downstream heat exchangers from being exposed to the deposits that occur during operation of the geothermal plant, significantly increasing the pressure drop across the downstream heat exchangers. Furthermore, one or more substances selected from the group consisting of Mg, Mn, F, P, Sr, and Zn can be extracted at least partially from the brine. Furthermore, the heat flow extracted by the second heat exchanger is also used for steam generation.

[0061] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the third mineral extraction unit in the main flow direction separates at least partially, preferably with a predominant proportion, one of the substances: Mn, Sr, F and Ba2+; from the brine for extraction.

[0062] As a result, one or more substances selected from the group consisting of Mn, Sr, F, and Ba2+ are at least partially extracted from the brine. Furthermore, the heat flow extracted by the third heat exchanger is simultaneously used for steam generation. In a preferred embodiment of the method according to the invention for operating a geothermal plant, the Ba2+ is at least partially, preferably predominantly, precipitated from the brine as Ba sulfate by adding H2SO4. This efficiently extracts the substance Ba sulfate.

[0063] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the precipitated Ba sulfate serves as a filler in plastics, as a filler in plastic masses, as a white pigment for, for example, paints, or as a whitener.

[0064] In a preferred embodiment of the method according to the invention for operating a geothermal plant, the brine is kept at such a pressure that neither evaporation of the brine nor outgassing from the brine can occur. This offers the advantage that no precipitation from the brine occurs and no liquid-gas mixture is formed, which has a lower energy density due to its lower density.

[0065] The invention is explained in more detail below with reference to the drawings. The drawings are to be understood as schematic representations. They do not represent a limitation of the invention, for example, with regard to specific dimensions or design variants. They show:

[0066] Fig. 1 : Geothermal plant for the generation of steam for industrial plants, whereby the secondary side of the respective heat exchanger evaporates water supplied by the heat transfer from the primary to the secondary side.

[0067] Fig. 2: Geothermal plant for the generation of steam for industrial plants, whereby the secondary side of the respective heat exchangers is designed in such a way that circulating water is heated in a secondary circuit and thereby evaporates water supplied to an evaporator arranged in the secondary circuit.

[0068] List of reference symbols used:

[0069] 1 First brine pump

[0070] 2 First heat exchanger

[0071] 3 Second heat exchanger

[0072] 4 Third heat exchanger

[0073] 5 First pump

[0074] 6 Second pump

[0075] 7 Third pump 8 Second brine pump

[0076] 9 First compressor

[0077] 10 Second compressor

[0078] 11 Third compressor

[0079] 12 First mineral extraction unit

[0080] 13 Second mineral extraction unit

[0081] 14 Third Mineral Extraction Unit

[0082] 15 First evaporator

[0083] 16 Second evaporator

[0084] 17 Third evaporator a Production well to the geothermal source as extraction point b Injection well to the geothermal source as return point c1 First water supplied for evaporation c2 Second water supplied for evaporation c3 Third water supplied for evaporation d1 Steam generated by the first evaporator d2 Steam generated by the second evaporator d3 Steam generated by the third evaporator e1 Steam compressed by the first compressor e2 Steam compressed by the second compressor e3 Steam compressed by the third compressor

[0085] Fig. 1 shows a first embodiment of the geothermal plant according to the invention for generating steam for industrial plants, wherein the respective secondary side of the three cascaded heat exchangers 2, 3 and 4 is designed so that supplied water c1, c2, c3 can evaporate by heat transfer from the primary to the secondary side.

[0086] In detail, the geothermal plant is connected to the brine of the geothermal source through the extraction point a. A first pipeline is fluidly connected to a first brine pump 1, with the first pipeline fluidly connecting the extraction point a to the respective primary side of the three cascaded heat exchangers 2, 3, and 4 and their respective downstream mineral extraction units 12, 13, and 14.

[0087] The secondary side of the first heat exchanger 2 is designed to allow a first water c1 to be supplied, allowing the supplied first water c1 to evaporate. A downstream first compressor 9 is configured to compress the generated steam into a higher-energy water vapor e1.

[0088] The secondary side of the second heat exchanger 3 is designed to allow a second water c2 to be supplied, allowing the supplied second water c2 to evaporate. A downstream second compressor 10 is configured to compress the generated steam into a higher-energy water vapor e2.

[0089] The secondary side of the third heat exchanger 4 is designed to allow a third water c3 to be supplied, allowing the supplied third water c3 to evaporate. A downstream first compressor 11 is configured to compress the generated steam into a higher-energy water vapor e3.

[0090] An outflow pipeline fluidly connects the third mineral extraction unit 14 to the return point b, with a second brine pump 8 fluidly connected to the outflow pipeline to pump the brine to the return point b. The distance between the extraction point a and the return point b is 1500 m.

[0091] Fig. 1 further shows a first embodiment of the method according to the invention for operating the geothermal plant for generating steam for industrial plants, wherein the respective secondary side of the three cascaded heat exchangers 2, 3 and 4 evaporates supplied water c1, c2, c3 by the heat transfer from the primary to the secondary side.

[0092] In detail, a brine is pumped at the extraction point a through a first pipeline with a first brine pump 1 to the primary side of the three cascaded heat exchangers 2, 3 and 4 and their respective downstream mineral extraction units 12, 13 and 14.

[0093] A first water c1 is supplied to the secondary side of the first heat exchanger 2, causing the supplied first water c1 to evaporate. A downstream first compressor 9 compresses the generated steam into a higher-energy water vapor ei.

[0094] A second water c2 is supplied to the secondary side of the second heat exchanger 3, causing the supplied second water c2 to evaporate. A downstream second compressor 10 compresses the generated steam into a higher-energy water vapor e2. A third water c3 is supplied to the secondary side of the third heat exchanger 4, causing the supplied third water c3 to evaporate. A downstream third compressor 11 compresses the generated steam into a higher-energy water vapor e3.

[0095] The brine is conveyed through an outflow pipeline from the third mineral extraction unit 14 to the return point b, with a second brine pump 8 fluidly connected to the outflow pipeline so that it can convey the brine to the return point b. The distance between the extraction point a and the return point b is 1500 m.

[0096] Fig. 2 shows a second embodiment of the geothermal plant according to the invention for generating steam for industrial plants, wherein the respective secondary side of the three cascaded heat exchangers 2, 3 and 4 is designed such that circulating water is heated in a secondary circuit and as a result an evaporator 15, 16 and 17 arranged in the secondary circuit can evaporate water c1, c2 and c3 supplied to the geothermal source. In detail, the geothermal plant is connected to the brine of the geothermal source via the extraction point a. A first pipeline is fluidically connected to a first brine pump 1, wherein the first pipeline fluidically connects the extraction point a to the respective primary side of the three cascaded heat exchangers 2, 3 and 4 and their respective downstream mineral extraction units 12, 13 and 14.

[0097] The secondary circuit of the first heat exchanger 2 is fluidly connected to a pump 5 and a first evaporator 15. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated in the secondary circuit by the pump 5. Furthermore, the secondary side of the first heat exchanger 2 is designed such that a first water c1 can be supplied to the first evaporator 15, whereby the supplied first water c1 can evaporate into water vapor d1.

[0098] The secondary circuit of the second heat exchanger 3 is fluidly connected to a pump 6 and a second evaporator 16. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated in the secondary circuit by the pump 6. Furthermore, the secondary side of the second heat exchanger 3 is designed so that a second water c2 can be supplied to the second evaporator 16, whereby the supplied second water c2 can evaporate into water vapor d2.

[0099] The secondary circuit of the third heat exchanger 4 is fluidically connected to a pump 7 and a third evaporator 17. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated in the secondary circuit by the pump 7. Furthermore, the secondary side of the third heat exchanger 4 is designed so that a third water c3 can be supplied to the third evaporator 17, whereby the supplied third water c3 can evaporate into water vapor d3.

[0100] An outflow pipeline fluidly connects the third mineral extraction unit 14 to the return point b in the geothermal source, with a second brine pump 8 fluidly connected to the outflow pipeline to pump the brine to the return point b. The distance between the extraction point a and the return point b is 1500 m.

[0101] In principle, in this second embodiment, the evaporators 15, 16 and 17 can each have a downstream compressor which is configured to compress the correspondingly generated vapor d1, d2 or d3 into a water vapor with a higher energy value.

[0102] Fig. 2 further shows a second embodiment of the method according to the invention for operating the geothermal plant for generating steam for industrial plants, wherein the respective secondary side of the three cascaded heat exchangers 2, 3 and 4 is designed such that circulating water is heated in a secondary circuit, thereby evaporating water c1, c2 and c3 supplied to an evaporator 15, 16 and 17 arranged in the secondary circuit. In detail, a brine is conveyed at the extraction point a through a first pipeline with a first brine pump 1 to the primary side of the three cascaded heat exchangers 2, 3 and 4 and their respective downstream mineral extraction units 12, 13 and 14.

[0103] The secondary circuit of the first heat exchanger 2 is fluidly connected to a pump 5 and a first evaporator 15. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated in the secondary circuit by the pump 5. Furthermore, a first water c1 is supplied to the first evaporator 15, whereby the supplied first water c1 evaporates into water vapor d1.

[0104] The secondary circuit of the second heat exchanger 3 is fluidly connected to a pump 6 and a second evaporator 16. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated in the secondary circuit by the pump 6. Furthermore, a second water c2 is supplied to the second evaporator 16, whereby the supplied second water c2 evaporates into water vapor d2.

[0105] The secondary circuit of the third heat exchanger 4 is fluidly connected to a pump 7 and a third evaporator 17. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated in the secondary circuit by the pump 7. Furthermore, a third water c3 is supplied to the third evaporator 17, whereby the supplied third water c3 evaporates to water vapor d3.

[0106] The brine is conveyed through an outflow pipeline from the third mineral extraction unit 14 to the return point b, with a second brine pump 8 fluidly connected to the outflow pipeline to convey the brine to the return point b. The distance between the extraction point a and the return point b is 1500 m.

[0107] In principle, in this second embodiment, the evaporators 15, 16 and 17 can each have at least one downstream compressor which compresses the correspondingly generated vapor d1, d2 or d3 into a water vapor with a higher energy value.

[0108] Examples

[0109] The following examples use the PhreeQC software, which enables geochemical modeling and calculations related to the chemistry of aqueous solutions and rocks. PhreeQC can also be used to calculate the possible types of precipitation after cooling an aqueous solution, such as a brine. The composition of the brine is calculated as molarity in mol / L. From the molarity n, the molar mass M, and the correction factor k, the amount of ions contained is calculated using the formula ß = M * n * k. The mass concentration of the precipitated ions at each temperature level is determined by subtracting the previous mass concentration from the current ß value. Documentation of the PhreeQC software is available at: https: / / pubs.usgs.gov / publication / tm6A43 (accessed on November 10, 2023).

[0110] Example 1

[0111] In this Example 1, the method according to the invention for operating the geothermal plant for generating steam for industrial plants according to Fig. 1 is described.

[0112] Here, water c1, c2, c3 supplied to the respective secondary side of the three cascaded heat exchangers 2, 3 and 4 is evaporated by the heat transfer from the primary to the secondary side.

[0113] In detail, a brine is pumped at the extraction point a through a first pipeline with a first brine pump 1 to the primary side of the three cascaded heat exchangers 2, 3 and 4 and their respective downstream mineral extraction units 12, 13 and 14.

[0114] The brine is extracted at an absolute pressure of 10 bar and at a temperature of 160 °C at its extraction point a with a mass flow of 360 t / h.

[0115] The brine contains the following substances in mg / L: The temperature of the brine at the inlet of the first heat exchanger 2 is 155 °C and is cooled by the first heat exchanger 2 to a temperature of 120 °C.

[0116] The first mineral extraction unit 12 extracts the following substances in mg / L from the brine for purification, whereby the respective substance from the brine refers to the element specified in the third column of the table that is separated:

[0117] The first mineral extraction unit 12 extracts the following substances in mg / L from the brine for extraction, whereby the respective substance from the brine refers to the element specified in the third column of the table that is extracted:

[0118] A first water c1 with a mass flow of 24 t / h at a temperature of 96.6 °C is supplied to the secondary side of the first heat exchanger 2, whereby the supplied first water c1 evaporates, the water vapor having an absolute pressure of 1 bar and a temperature of 100 °C. A downstream first compressor 9 compresses the generated steam to a higher-energy water vapor ei, the water vapor having an absolute pressure of 2 bar and a temperature of 181 °C.

[0119] The temperature of the brine at the inlet of the second heat exchanger 3 is 119 °C and is cooled by the second heat exchanger 3 to a temperature of 85 °C.

[0120] The second mineral extraction unit 13 extracts the following substances in mg / L from the brine for purification:

[0121] The second mineral extraction unit 13 extracts the following substances in mg / L from the brine, whereby the respective substance from the brine refers to the value shown in the third column of the

[0122] The element specified in the table refers to the element being separated: A second water c2 with a mass flow of 22 t / h at a temperature of 79.5 °C is supplied to the secondary side of the second heat exchanger 3, whereby the supplied second water c2 evaporates, the water vapor having an absolute pressure of 0.525 bar and a temperature of 82.5 °C. A downstream second compressor 10 compresses the generated steam to a higher-energy water vapor e2, the water vapor having an absolute pressure of 1.1 bar and a temperature of 167 °C.

[0123] At the inlet of the third heat exchanger 4, the temperature of the brine is 84 °C and is cooled by the third heat exchanger 4 to a temperature of 50 °C

[0124] The third mineral extraction unit 14 extracts the following substances in mg / L from the brine for purification, whereby the respective substance from the brine refers to the element specified in the third column of the table that is separated:

[0125] The third mineral extraction unit 14 extracts the following substances in mg / L from the brine for extraction, whereby the respective substance from the brine refers to the element specified in the third column of the table that is extracted:

[0126] Furthermore, the remaining barium ions can be converted into sparingly soluble barium sulfate by precipitation with sulfuric acid. The barium sulfate can then be recovered as a valuable material.

[0127] A third water c3 with a mass flow of 21 t / h at a temperature of 45.7 °C is supplied to the secondary side of the third heat exchanger 4, whereby the supplied third water c3 evaporates, the water vapor having an absolute pressure of 0.11 bar and a temperature of 47.7 °C. A downstream third compressor 11 compresses the generated steam to a higher-energy water vapor e3, the water vapor having an absolute pressure of 0.22 bar and a temperature of 120.2 °C.

[0128] The brine is conveyed through an outflow pipeline from the third mineral extraction unit 14 to the return point b, with a second brine pump 8 fluidly connected to the outflow pipeline to convey the brine to the return point b. The distance between the extraction point a and the return point b is 1500 m. Example 2

[0129] In this example 2, the method according to the invention for operating the geothermal plant for generating steam for industrial plants according to Fig. 2 is described. Furthermore, the three evaporators 15, 16, and 17 each represent a flash tank.

[0130] The respective secondary side of the three cascaded heat exchangers 2, 3 and 4 is designed in such a way that circulating water is heated in a secondary circuit and thereby evaporates water c1, c2 and c3 supplied to an evaporator 15, 16 and 17 arranged accordingly in the secondary circuit.

[0131] In detail, a brine is pumped at the extraction point a through a first pipeline with a first brine pump 1 to the primary side of the three cascaded heat exchangers 2, 3, and 4 and their respective downstream mineral extraction units 12, 13, and 14. The brine is extracted at an absolute pressure of 10 bar and a temperature of 160 °C at its extraction point a with a mass flow of 360 t / h.

[0132] The brine contains the following substances in mg / L: The temperature of the brine at the inlet of the first heat exchanger 2 is 155 °C and is cooled by the first heat exchanger 2 to a temperature of 120 °C.

[0133] The first mineral extraction unit 12 extracts the following substances in mg / L from the brine for purification, whereby the respective substance from the brine refers to the element specified in the third column of the table that is separated:

[0134] The first mineral extraction unit 12 extracts the following substances in mg / L from the brine for extraction, whereby the respective substance from the brine refers to the element specified in the third column of the table that is extracted:

[0135] The secondary circuit of the first heat exchanger 2 is fluidly connected to a pump 5 and a first evaporator 15. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated by the pump 5 in the secondary circuit at a mass flow rate of 267 t / h. Furthermore, a first water c1 with a mass flow rate of 24 t / h at a temperature of 97.6 °C is supplied to the first evaporator 15, whereby the supplied first water c1 evaporates to water vapor d1 with an absolute pressure of 1 bar and a temperature of 100 °C.

[0136] The temperature of the brine at the inlet of the second heat exchanger 3 is 119 °C and is cooled by the second heat exchanger 3 to a temperature of 85 °C.

[0137] The second mineral extraction unit 13 extracts the following substances in mg / L from the brine for purification, whereby the respective substance from the brine refers to the element specified in the third column of the table that is separated: The second mineral extraction unit 13 extracts the following substances in mg / L from the brine for extraction, whereby the respective substance from the brine refers to the element specified in the third column of the table that is extracted:

[0138] The secondary circuit of the second heat exchanger 3 is fluidly connected to a pump 6 and a second evaporator 16. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated by the pump 6 in the secondary circuit at a mass flow rate of 412 t / h. Furthermore, a second water c2 with a mass flow rate of 22 t / h at a temperature of 78 °C is supplied to the evaporator 16, whereby the supplied second water c2 evaporates to water vapor d2 with an absolute pressure of 0.5 bar and a temperature of 81.3 °C.

[0139] The temperature of the brine at the inlet of the third heat exchanger 4 is 84 °C and is cooled by the third heat exchanger 4 to a temperature of 50 °C.

[0140] The third mineral extraction unit 14 extracts the following substances in mg / L from the brine for purification, whereby the respective substance from the brine refers to the element specified in the third column of the table that is separated:

[0141] The third mineral extraction unit 14 extracts the following substances in mg / L from the brine for extraction, whereby the respective substance from the brine refers to the element specified in the third column of the table that is extracted:

[0142] Furthermore, the remaining barium ions can be converted into sparingly soluble barium sulfate by precipitation with sulfuric acid. The barium sulfate can then be recovered as a valuable material. The secondary circuit of the third heat exchanger 4 is fluidically connected to a pump 7 and to a third evaporator 17. The heat transfer fluid in the secondary circuit is demineralized water, which is circulated by the pump 7 in the secondary circuit at a mass flow of 405 t / h. Furthermore, a third water c3 with a mass flow of 21 t / h at a temperature of 43.8 °C is fed to the third evaporator 17, whereby the supplied third water c3 evaporates to water vapor d3 with an absolute pressure of 0.1 bar and a temperature of 45.8 °C.

[0143] The brine is conveyed through an outflow pipeline from the third mineral extraction unit 14 to the return point b, with a second brine pump 8 fluidly connected to the outflow pipeline to convey the brine to the return point b. The distance between the extraction point a and the return point b is 1500 m.

Claims

Patent claims 1. Geothermal plant with cascaded steam generator for industrial plants comprising: (a) a geothermal source designed to provide brine with a temperature in the range 120 to 300 °C, (b) at least two heat exchangers (2, 3, 4), each of which has brine flowing through it on its primary side, and the primary side of the respective heat exchanger (2, 3, 4) is arranged in cascade to its adjacent heat exchanger (2, 3, 4), wherein the respective heat exchanger (2, 3, 4) has a secondary side configured such that either supplied water (c1, c2, c3) is evaporated by heat transfer from the primary to the secondary side, or that circulating water is heated in a secondary circuit and thereby an evaporator (15, 16, 17) arranged in the secondary circuit evaporates supplied water (c1, c2, c3), (c) a first pipeline fluidically connecting the extraction point (a) of the geothermal source with the cascaded primary sides of the heat exchangers (2, 3, 4), (d) each of the existing heat exchangers (2, 3, 4) has a downstream mineral extraction unit (12, 13, 14), (e) a first brine pump (1) arranged between the extraction point (a) and the primary side of the first heat exchanger (2) in the main flow direction, whereby the brine is conveyed from the source to the respective cascaded primary sides of the heat exchangers (2, 3, 4) and their respective downstream mineral extraction unit (12, 13, 14), and (f) an outflow pipeline which is fluidically connected to the mineral extraction unit (14) arranged last in the main flow direction, wherein the outflow pipeline opens into the geothermal source in such a way that the outlet of the outflow pipeline (b) is at a distance of at least 100 m, preferably at least 1500 m and particularly preferably at least 2500 m from the extraction location (a).

2. Geothermal plant according to claim 1, wherein a second brine pump (8) is arranged between the mineral extraction unit (14) arranged last in the main flow direction and the outlet of the outflow pipeline (b), whereby the treated brine is conveyed to the outlet of the outflow pipeline (b).

3. Geothermal plant according to claim 1 or 2, wherein the respective heat exchanger (2, 3, 4) contains, in the case of an existing secondary circuit, a pump (5, 6, 7) for circulating the water.

4. Geothermal plant according to one of the preceding claims, wherein the heat exchangers (2, 3, 4) on their secondary side or the evaporators (15, 16, 17) in the secondary circuits each have a downstream compressor, which is each configured so that the generated water vapor is compressed.

5. Geothermal plant according to one of the preceding claims, wherein exactly three cascaded heat exchangers (2, 3, 4) are present for steam generation, and wherein each of the three heat exchangers (2, 3, 4) has a downstream mineral extraction unit (12, 13, 14).

6. A method for operating a geothermal plant according to one of the preceding claims, comprising the steps of: a) conveying the brine by the first brine pump (1) from the geothermal source to the cascaded primary sides of the respective heat exchangers (2, 3, 4), wherein the temperature of the brine at the inlet of the primary side of the first heat exchanger (2) arranged in the main flow direction is in the range of 120 to 300 °C, b) transferring at least part of the heat of the brine from the primary side of the respective heat exchanger (2, 3, 4) I. on the water supplied to the secondary side (c1, c2, c3), whereby the supplied water (c1, c2, c3) is evaporated, or II. in the case of an existing secondary circuit: on the circulating water in the secondary circuit of the respective heat exchanger (2, 3, 4), wherein the temperature of the water in the respective secondary circuit upstream of the evaporator (15, 16, 17) is in the range from 40 to 195 °C, and thereby the water (c1, c2, c3) supplied to the evaporator (15, 16, 17) is evaporated, c) removal of minerals by the mineral removal unit (12, 13, 14 downstream of the respective heat exchanger, and d) conveying the treated brine from the outlet of the mineral removal unit (14) arranged last in the main flow direction to the outlet of the outflow pipe (b), wherein the temperature at the outlet of the outflow pipe (b) is in the range from 35 to 115 °C.

7. A method for operating a geothermal plant according to claim 6, wherein the temperature of the brine at the inlet of the primary side of the first heat exchanger (2) arranged in the main flow direction is in the range of 120 to 200 °C, preferably in the range of 140 to 180 °C, and the temperature of the brine at the outlet of the primary side of the first heat exchanger (2) is in the range of 105 to 155 °C.

8. A method for operating a geothermal plant according to claim 6 or 7, wherein the temperature of the brine at the inlet of the primary side of the second heat exchanger (3) arranged in the main flow direction is in the range of 105 to 155 °C, and the temperature of the brine at the outlet of the primary side of the second heat exchanger (3) is in the range of 75 to 120 °C.

9. A method for operating a geothermal plant according to one of claims 6 to 8, wherein the temperature of the brine at the inlet of the primary side of the third heat exchanger (4) arranged in the main flow direction is in the range from 75 to 120 °C, and the temperature of the brine at the outlet of the primary side of the third heat exchanger (4) is in the range from 35 to 115 °C, preferably in the range from 40 to 85 °C and particularly preferably in the range from 45 to 55 °C.

10. A method for operating a geothermal plant according to one of claims 6 to 9, wherein exactly three heat exchangers (2, 3, 4) are provided for generating steam, and wherein each of the three heat exchangers (2, 3, 4) has a downstream mineral extraction unit (12, 13, 14).

11. A method for operating a geothermal plant according to one of claims 6 to 10, wherein the first mineral extraction unit (12) in the main flow direction separates at least partially, preferably predominantly, one of the substances: Fe, Pb and Al silicates; from the brine for purification of the brine, and separates at least partially, preferably predominantly, one of the substances: Zn, Sr, CaF and Mn; from the brine for extraction.

12. A method for operating a geothermal plant according to one of claims 6 to 11, wherein the second mineral extraction unit (13) in the main flow direction separates at least partially, preferably with a predominant proportion, one of the substances: Mg, P and Zn; from the brine for purification of the brine, and separates at least partially, preferably with a predominant proportion, one of the substances: Mg, Mn, F, P, Sr and Zn; from the brine for extraction.

13. A method for operating a geothermal plant according to one of claims 6 to 12, wherein, in the case of a third heat exchanger (4) present in the main flow direction, the third mineral extraction unit (14) separates at least partially, preferably with a predominant proportion, one of the substances: Mn, Sr, F and Ba2+; from the brine for extraction.

14. A method for operating a geothermal plant according to claim 13, wherein the Ba2+ is precipitated from the brine as Ba sulfate at least partially, preferably with a predominant proportion, by the addition of H2SO4.

15. A method for operating a geothermal plant according to claim 14, wherein the precipitated Ba sulfate serves as a filler in plastics, as a filler in plastic masses, as a white pigment for, for example, paints, or as a whitening agent.

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