Method for separating material flows

Abstract

Methods for separating a first material flow containing a dissolved substance are already known in which said first material flow is divided into a second material flow and a third material flow such that the third material flow has an increased concentration of the dissolved substance compared to the second material flow. In such methods, this is achieved by means of a freezing process in which the first material flow is pre-cooled in a heat exchanger and solidified in a heat pump, whereupon the ice is mechanically crushed and centrifuged, allowing the extraction of a liquid fraction containing the dissolved substance which does not integrate into the ice lattice. In such a method, the invention provides a second heat pump which only takes over the heat transfer in the region of the freezing point, meaning that its efficiency is particularly high due to the substantially constant temperature on both sides.

Description

[0001] PROCESS FOR SEPARATION OF MATERIAL FLOWS

[0002] The present invention relates to a method for separating a first material stream of a solution of a solvent and a substance dissolved therein into a second material stream and a third material stream, wherein the dissolved substance in the third material stream is more concentrated than the second material stream, wherein the first material stream is pre-cooled in a heat exchanger, is further cooled in a first heat pump and finally is at least partially solidified into ice with inclusions of the dissolved substance, thereafter the ice is mechanically crushed and separated by mechanical separation into the second material stream and the third material stream and the second material stream and the third material stream jointly absorb the heat released by the first material stream in the heat exchanger and in the first heat pump.

[0003] Such a process is already known from WO 2022 / 064161 A1. It is a combined system for generating thermal energy and desalinating seawater using the freezing process. When seawater cools, ice crystals free of salts form. The freezing process exploits the fact that the salt ions do not fit into the lattice of the ice crystals. For this reason, the frozen ice consists of freshwater. However, the ice, trapped between the crystals, still contains salt, which is released back into the water during melting. The ice crystals must therefore be separated from the mother liquor, which can be particularly advantageous when the water is a mixture of freshwater ice and brine. A pre-cooling system cools the water to near zero degrees before freezing, and after freezing, a centrifuge is used to separate the water-ice mixture.

[0004] Furthermore, with regard to the state of the art, reference is made to the documents DE 29 21 728 A1 and WO 2018 / 211037 A1.

[0005] There is still enough drinking water in this country. However, due to global warming, many regions around the world are slowly drying out. Providing clean water to the ever-increasing number of people will be a major challenge for the future, and seawater desalination will play a key role in this. Seawater desalination is the extraction of drinking or industrial water from seawater by reducing its salinity. Various desalination processes are known for removing the salts and minerals from the water.

[0006] In some places, drinking water is predominantly obtained from gas- or oil-fired desalination plants. Alternatives to this include combined turbine power plants with connected desalination plants, which operate with multi-stage flash evaporation. Reverse osmosis, in which the natural osmosis process is reversed under pressure, is also practiced. In this process, seawater is forced under pressure through a semipermeable membrane to remove salts and impurities. This is achieved by forcing the water through a microscopic sieve with a mesh size smaller than the diameter of a salt ion, thereby desalinating the salt water. The advantage of this technology is that it completely purifies the water of salt and all contaminants, including bacteria and viruses. Furthermore, it is currently considered the most energy-efficient method among available technologies.

[0007] However, energy consumption is still very high, and reverse osmosis requires careful pretreatment of the seawater to protect the sensitive membrane from contamination, which can increase operating costs. Despite such preparation, the membranes' service life is limited, and their replacement is costly.

[0008] Reverse osmosis and evaporation processes are mainly used industrially.

[0009] In addition to these processes, which require high energy consumption and extensive water treatment, intensive research is being conducted into the development of energy-efficient processes for seawater desalination. Current experiments include experiments using plastic evaporation tubes, electrodialysis, and biofuel cells, as well as freezing processes of the type mentioned above.

[0010] Against this background, the object of the present invention is to create a process for separating a material stream of a solution of a solvent, preferably water, and a substance dissolved therein, which is easier to maintain and at the same time more energy-efficient, and which functions particularly effectively on smaller scales on the basis of known freezing processes.

[0011] This object is achieved by a separation process according to the features of independent claim 1. Useful embodiments of such a process can be found in the subsequent dependent claims.In this respect, a method is provided for separating a first material stream of a solution of a solvent and a substance dissolved therein into a second material stream and a third material stream, wherein the dissolved substance in the third material stream is more concentrated than in the second material stream, wherein the first material stream is pre-cooled in a heat exchanger, further cooled in a first heat pump and finally at least partially solidified into ice with inclusions of the dissolved substance, thereafter the ice is mechanically crushed and separated by mechanical separation into the second material stream and the third material stream, and the second material stream and the third material stream jointly absorb the heat emitted by the first material stream in the heat exchanger and in the first heat pump.

[0012] Such a method is characterized according to the invention in that the first material stream is cooled to a liquid around the freezing point of the first material stream by means of the first heat pump and solidified to ice by means of a second heat pump, wherein the second material stream and the third material stream absorb the heat emitted by the first material stream by means of the second heat pump and are thereby liquefied.

[0013] The process according to the invention consists of several steps. First, a first material stream is sucked in. This consists of a solution containing a high concentration of a dissolved substance. The first material stream is first pre-cooled using a heat exchanger, for which purpose the heat exchanger transfers the solvent coming from the process, preferably water, to the second material stream and / or the third material stream, which absorb the heat of the first material stream. This is then passed on in a cooled state to a first heat pump. Here, the first material stream is further cooled to its freezing point in the region of 0°C, with further heat being released to the second material stream and / or the third material stream, before being subsequently frozen into ice in a second heat pump, which also includes cooling to just an ice slurry.Since the solute is not incorporated into the ice crystals, the ice itself does not contain the solute, but there are amounts of the solute trapped between the ice crystals. By means of mechanical separation, the ice, from which the second stream is formed, can be separated from the solvent with the still present solute, which forms the third stream. If the cooling takes place to a completely solid ice, this must first be crushed. If, however, the first stream remains as ice slurry, this step can be omitted. In this situation, mechanical separation takes place so that a concentrated third stream is created, with which the solute is carried away, and a purified second stream, which essentially consists of the ice with a few remaining inclusions.

[0014] The use of two heat pumps is crucial here. While the first heat pump cools the first material stream from a temperature reduced by the heat exchanger down to the freezing point, resulting in a coefficient of performance of around 6 due to the similar temperature conditions, the second heat pump carries out the actual freezing process, during which the first material stream can release a lot of energy without the temperature changing. The released energy is released when the ice crystals form. The already separated and frozen material from the second material stream and the third material stream is available to cool the first material stream. Both of these material streams have more or less the same temperature of 0°C and can therefore absorb almost all of the energy from the first material stream without changing their temperature.This is because the energy required to freeze the first stream is more or less exactly the same as the energy required to thaw the second stream and the third stream. Due to the very small temperature changes in the process, the second heat pump only needs to transfer the required cooling energy from two substances with almost the same temperature to freeze the solvent containing the dissolved substance. The coefficient of performance for such a small temperature difference can be approximately 60 to 70.

[0015] This results in a particularly energy-efficient process, comparable to reverse osmosis in this respect, but without the membrane maintenance required for reverse osmosis. Furthermore, the solvent is not completely freed from the dissolved substance, but rather the dissolved substance content is simply reduced. This also makes it possible to combine it with other processes to increase their efficiency.

[0016] In a first embodiment, the mechanical separation can be achieved by centrifuging the ice, whereby the ice is collected in a centrifuge drum, the second material stream is retained in the centrifuge drum, and the third material stream is removed as a liquid. The resulting centrifugal forces push the ice outwards within the centrifuge drum, whereby the centrifuge drum has openings through which material can escape from the centrifuge drum. The ice remains in the centrifuge drum, while molten solvent is carried away together with the solute. The remaining ice, which still contains solute between its crystals, thus has a reduced concentration of the solute and forms the second material stream, while the solute is concentrated in the discharged liquid, the third material stream.

[0017] In a second embodiment, the mechanical separation can also be achieved by washing the ice, preferably with liquid from the second and / or third stream. The known freezing processes have the problem that the ice crystals are washed by the mother liquor, which in turn requires a significant amount of clean solvent, such as fresh water, which has rendered the known processes unfeasible in practice. Such purification can be achieved in the present case using liquid obtained from the second stream or even the third stream.

[0018] Furthermore, it is advantageous to run the process in a cascade fashion, using the second stream of the previous cascade as the first stream in each cascade. This makes it possible to enhance the positive, yet limited, effect of the proposed process through repeated application and to discontinue it when the desired degree of solute removal is achieved.

[0019] The second material stream and the third material stream can be present as separate liquid streams at the outlet of the second heat pump and fed to the heat exchanger to cool the first material stream. The energy absorbed by the first material stream can therefore be sufficient to heat the second material stream and the third material stream to 2°C. In addition, the waste heat from the heat pump must also be transported away with the second material stream and the third material stream. To continue the flow of the second material stream and the third material stream, it is advantageous if they are in liquid form, and the separation of the material streams is necessary because the dissolved substance is present in different concentrations in the two material streams.

[0020] In a specific embodiment, the second material stream and the third material stream can be present at the output of the second heat pump at a temperature in the range of 0°C to 4°C, preferably at a temperature in the range of 0°C to 2°C, most preferably at a temperature of at least approximately 2°C. In this case, the temperature absorption is sufficient to extract sufficient energy from the first material stream to convert it from 0°C in the liquid state to 0°C in the solid state.

[0021] Furthermore, the second material stream and the third material stream can be present at the exit of the heat exchanger at a temperature in the range of 14°C to 18°C, preferably at a temperature in the range of 15°C to 17°C, most preferably at a temperature of at least approximately 16°C. This temperature range is particularly advantageous and energy-efficient because the second and third material streams can then be used to cool the first material stream to approximately 0°C while still in the first heat pump. By cooling the first material stream, the second material stream and the third material stream are each heated to approximately 23°C with the help of the heat exchanger.

[0022] Preferably, the second and third streams should be conducted in parallel within a cascade and at approximately the same temperature in the heat exchanger. This ensures that the first stream is cooled evenly.

[0023] In a specific embodiment, the first material stream exiting the heat exchanger should have a temperature in the range of 2°C to 6°C, preferably in the range of 3°C to 5°C, and most preferably at a temperature of 4°C. In this temperature range, the first material stream is ideally pre-cooled, allowing the first heat pump to cool the first material stream particularly energy-efficiently.

[0024] The dissolved substance can be a salt, such as sodium chloride, but also other dissolved substances such as ethanol, caffeine, or sugar. Thus, the process is suitable not only for the separation of salts from aqueous solutions but also for the separation of other dissolved substances in aqueous solutions, especially in the field of food chemistry, so that harmful, but also otherwise undesirable ingredients can be specifically reduced without having to add anything else to the product.

[0025] The invention described above is explained in more detail below using an exemplary embodiment.

[0026] Figure 1 shows a method known in the prior art for

[0027] Separation of material flows in a schematic representation,

[0028] Figure 2 shows the process according to the invention for the separation of

[0029] Material flows in a schematic representation, as well as

[0030] Figure 3 shows a centrifuge as a means for mechanically separating a first material stream into a second material stream and a concentrated third material stream in a plan view.

[0031] Figure 1 shows a process known from the prior art, upon which the process according to the invention is based. For this purpose, a first material stream 1 is initially provided. At feed 8, seawater is considered the first material stream 1 from which salt is to be removed by the process according to the invention. However, this process can also treat very different material streams, such as coffee to be decaffeinated, fruit juice to be sweetened, and the like. The only essential factor in the selection is that the substance dissolved in the first material stream 1 cannot be incorporated into the lattice of the solvent in which the substance is dissolved.

[0032] In a first step, the first material stream 1 is cooled in a heat exchanger 4, whereby incoming seawater at 20°C can be cooled to 2°C by the second and third material streams 2 and 3, which are created later in the process. The second material stream 2 and the third material stream 3 initially exist as solid ice and absorb energy from the seawater, so that by cooling the seawater to 2°C, the solid ice becomes liquid water, but also at 0°C. This is because a large amount of energy can be used to break up the lattice structure of the ice without increasing the temperature.

[0033] In the next step, material streams 1, 2 and 3 are fed to a first heat pump 5, in which energy is extracted from the first material stream 1, so that it solidifies into ice, while the second and third material streams 2 and 3 are heated to approximately 23°C. The second and third material streams 2 and 3 are then fed to a removal point 9 and leave the process, while the ice from the first material stream 1 is fed to a mechanical separation 7. There, the ice from the first material stream 1 is converted into the second material stream 2, which essentially comprises rinsed ice and thus fresh water, while the third material stream 3 comprises liquid at approximately 0°C, as well as rinsed-off salt or generally washed-out dissolved substance. These are fed to the heat exchanger 4 to cool the seawater, thus closing the cycle. The mechanical separation 7 can be carried out using a centrifuge 10, for example, as described below.

[0034] The problem with this process is that a large amount of energy must be expended in the first heat pump 5 to transfer the heat energy from the first material stream 1 to the second and third material streams 2 and 3, thereby heating them. To transfer the energy for this process, the first heat pump must reach a refrigerant temperature of at least 25°C, preferably 30°C. This is possible with a coefficient of performance of approximately 6. To transfer 1 kWh of heat, one-sixth of this energy must be absorbed as electrical energy.

[0035] To freeze 1 kg of salt water at 2°C, which is pre-cooled by heat exchanger 4, 8.4 kJ are required to cool it from 2°C to 0°C. The freezing process requires another 335 kJ. A total of 343.4 kJ are therefore required per kilogram of salt water. Since the first heat pump 5 has a coefficient of performance of 6, it requires 57.23 kJ per kg of salt water.

[0036] Figure 2, however, shows the modified process according to the invention. Here, too, the solvent with the dissolved substance, seawater as an example below, is first fed in at 8 and cooled using the heat exchanger 4, which is also provided here. However, since the cooling second and third streams 2 and 3 are present at 2°C, they cool the first stream 1 from 20°C to only 4°C, while heating up to 16°C. The heat exchanger 4 can be operated in a manner known per se according to the countercurrent or crosscurrent principle. The first heat pump 5 is also provided in the modified form of the process, whereby the first stream 1 is cooled from 4°C to 0°C, but in the liquid state, while the second and third streams 2 and 3 heat up from the 16°C present at the outlet of the heat exchanger 4 to approximately 23°C and are then fed to a discharge 9.The second material stream 2 can be used in a next cascade as the first material stream from which further dissolved substance, in this case further salt, is to be removed.

[0037] A first difference to the already known process are the temperature levels mentioned at which the material flows 1, 2 and 3 move. These also lead to a coefficient of performance of approximately 6 in the first heat pump 5. However, since here only the temperature reduction and not the formation of the lattice structure needs to be achieved, the energy required in the first heat pump 5 is considerably lower. 16.76 kJ of thermal energy are required per kg of water. Since the heat pump has a coefficient of performance of approximately 6, this results in an energy absorption of 2.79 kJ per kg of water. A coolant temperature of approximately 25°C must also be assumed here. Cooling using the first heat pump 5 takes place from 4°C down to a liquid at 0°C, i.e. it stops after cooling and before the lattice formation.This occurs for the first material stream 1 with the aid of a second heat pump 6, in which further energy is extracted from the first material stream 1, causing it to solidify into ice. Subsequently, a mechanical separation takes place, from which the first material stream 1 is separated into the second material stream 2, essentially ice crystals made of fresh water and residues of dissolved matter trapped between the crystals, and the third material stream 3, essentially separated water with the residue of the concentrated dissolved matter.

[0038] The energy for solidifying the first material stream 1 is provided by the second and third material streams, initially in the form of ice, before leaving the second heat pump 6 as liquid water, ideally at 0°C, but up to approximately 2°C. Since the heat energy required to freeze the first material stream 1 more or less corresponds to the amount of heat required to thaw the second and third material streams 2 and 3, the second heat pump can operate at a very low coolant temperature of 2°C and, due to this small temperature difference, achieves a coefficient of performance of approximately 60-70. While the first heat pump 5 requires approximately 2.79 kJ per kg of salt water, the second heat pump 6 requires another approximately 5.15 kJ per kg of salt water, so that a total of only 7.94 kJ per kg of salt water is required per kg of salt water using the adapted process, i.e. just under 14% of the energy required in the known process.

[0039] Finally, Figure 3 shows a centrifuge 10, which can be used for the mechanical separation of the first material stream 1 into the second material stream 2 and the third material stream 3. The frozen material of the material stream 1 is collected in a centrifuge drum 11 of the centrifuge 10, which is set in rotation. Due to the centrifugal force, the material is pushed outwards, so that the liquefied material migrates more strongly outwards due to its greater density and is not stopped there by the perforated centrifuge drum 11. The substance dissolved in it, in this case salt, is carried along, while the ice retained in the centrifuge drum is pure freshwater, which merely contains deposits of the dissolved substance, i.e. salt.The third material stream 3, which is present in a largely liquefied state, therefore contains significantly larger amounts of the dissolved substance than the second material stream 2, which can be fed to a further cascade of the present process as described above.

[0040] The above describes a process for separating a material stream of a solution consisting of a solvent, preferably water, and a substance dissolved therein, which is easier to maintain and at the same time more energy-efficient, and which also functions effectively on smaller scales based on known freezing processes.

[0041] LIST OF REFERENCE SYMBOLS

[0042] I First material stream 2 Second material stream

[0043] 3 Third material stream

[0044] 4 heat exchangers

[0045] 5 First heat pump

[0046] 6 Second heat pump 7 Mechanical separation

[0047] 8 Feed

[0048] 9 Withdrawal

[0049] 10 Centrifuge

[0050] II Centrifuge drum 12 outlet

Claims

P A T E N T A N S P R Ü C H E 1. A method for separating a first material stream (1) of a solution of a solvent and a substance dissolved therein into a second material stream (2) and a third material stream (3), wherein the dissolved substance in the third material stream (3) is more concentrated than in the second material stream (2), wherein the first material stream (1) is pre-cooled in a heat exchanger (4), further cooled in a first heat pump (5) and finally at least partially solidified into ice with inclusions of the dissolved substance, thereafter preferably the ice is mechanically crushed and then separated by means of mechanical separation (7) into the second material stream (2) and the third material stream (3), and the second material stream (2) and the third material stream (3) jointly absorb the heat released by the first material stream (1) in the heat exchanger (4) and in the first heat pump (5), characterized in thatthat the first material flow (1 ) is cooled by means of the first heat pump (5) to a liquid around the freezing point of the first material flow (1 ) and solidified to ice by means of a second heat pump (6), wherein the second material flow (2) and the third material flow (3) absorb the heat emitted by the first material flow (1 ) with the aid of the second heat pump (6) and are thereby liquefied.

2. Method according to claim 1, characterized in that the mechanical separation is carried out by centrifuging the ice, the ice being taken up in a centrifuge drum (11), the second material stream (2) being retained in the centrifuge drum (11) and the third material stream (3) being removed as a liquid.

3. A method according to claim 1, characterized in that the mechanical separation is carried out by washing the ice, preferably with liquid from the second material stream (2) or the third material stream (3).

4. Process according to one of the preceding claims, characterized in that the process proceeds in a cascade-like manner and in each cascade the second material stream of the preceding cascade is used as the first material stream (1).

5. Method according to one of the preceding claims, characterized in that the second material stream (2) and the third material stream (3) at the output of the second heat pump (6) are present at a temperature in the range from 0°C to 4°C, preferably at a temperature in the range from 0°C to 2°C, most preferably at a temperature of at least approximately 2°C.

6. Process according to one of the preceding claims, characterized in that the second material stream (2) and the third material stream (3) are present at the outlet of the heat exchanger (4) at a temperature in the range from 14°C to 18°C, preferably at a temperature in the range from 15°C to 17°C, most preferably at a temperature of at least approximately 16°C.

7. Process according to one of the preceding claims, characterized in that the first material stream (1) at the outlet of the heat exchanger (4) is at a temperature in the range from 2°C to 6°C, preferably at a temperature in the range from 3°C to 5°C, most preferably at a temperature of 4°C.

8. A process according to any one of the preceding claims, characterized in that the dissolved substance is ethanol, caffeine, fine, sugar or a salt, preferably sodium chloride.

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