FI73818B - FOERFARANDE FOER VAERMEUPPTAGNING UR TILLFRYSANDE VAETSKA. - Google Patents

Description

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The present invention relates to a method for extracting heat from a liquid having a temperature close to the freezing point. The invention can be applied, for example, to heat pumps whose heat source is sea, river or lake water close to 0 ° C. In addition, the invention can also be applied to seawater desalination. Crystallization of substances other than water by the process according to the invention can also be considered.

Interest in heat pumps has recently increased for both energy and environmental reasons, quite as a result of acid rain caused by the burning of fossil fuels. In our northern climate, however, nature places difficult constraints on the efficient use of heat pumps during the coldest season, when heat is most needed. Conventional heat pumps that use water as a heat source are then only able to operate at insufficient capacity to prevent the heat exchangers from freezing.

There are also known heat pump solutions that allow water to freeze. The simplest such solution is to freeze the water as a solid layer on the surface of the heat transfer medium evaporator of the heat pump.

20 When the ice layer has grown thick enough, a warm heat transfer medium is introduced into the evaporator, whereby the ice layer detaches and falls off the heat exchange surface. The resulting ice is crushed and transported to the water body. The ice is removed by melting the different parts of the evaporator in turn, so that part of the heat surface of the evaporator has to be passive for the heat-25 pump at all times. The formation of an ice layer also substantially impairs heat transfer. For example, a 3 mm thick layer of ice reduces the heat transfer coefficient to less than half. Thus, the heat sinks have to be built more than double compared to the ice-free alternative, also taking into account the above-mentioned defrosting step. In addition, 30 crushing ice also causes inconveniences in practice.

Another solution is also known, the evaporation of the liquid acting as a heat source and the simultaneous crystallization in a low-pressure tank, i.e. a crystallizer. If the heat source is water, the crystallizer pressure is 0.6 kPa and the temperature is 0 ° C, which corresponds to the triple point of water where liquid, steam and solid ice are in equilibrium. As the ice crystals form, the heat released is transferred to steam at 0 ° C, which is condensed into an ice layer on the surface of the heat pump evaporator. This layer of ice also grows gradually, which reduces the average heat transfer and causes the heat surface required for the evaporator to increase 2-3 times compared to preventing ice from forming on the heat exchange surfaces.

10 Ice must therefore be removed from time to time, which can happen in at least two known ways. The second is the periodic conduction of warm steam into the common steam space of the crystallizer and the frozen evaporator, whereby, as it condenses, it melts the ice from the heat surfaces. Another way is to divide the evaporator into several sectors, each of which in turn is led to 15 warm steam to melt the ice. In either case, intermittent adjustments can easily cause malfunctions in a plant operating under difficult conditions corresponding to the triple point of water.

It is typical of the present invention that the freezing of the steam on the heat pipes is prevented by increasing the pressure of the steam generated in the crystallizer by means of an steam jet before it flows into the evaporator of the heat pump. In this case, the temperature of the steam rises somewhat above the freezing point and the steam condenses as water, which drains away from the heating surfaces. In this way, the disadvantages of the known methods described above can be claimed. The heat transfer remains good at all times, so the heat exchanger can be built relatively smaller. In addition, the entire heat exchanger remains active and the periodic adjustments required to defrost the ice are unnecessary. The essential features of the invention are defined in more detail in the characterizing part of the first claim 30.

The invention is described in more detail with the aid of the accompanying drawings. In the embodiment of Figure 1, the steam generated in the crystallizer is compressed to a higher pressure and temperature by means of a steam jet ejector, the driving force of which is the warmer steam produced in the heat exchange with the heat transfer medium of the heat pump. Figure 2 shows an application for seawater desalination and Figure 3 shows a solution for a crystallizer

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3 1 structure. 73 818

In the embodiment of Figure 1, the actual heat pump is a Compressor 10 of known construction, which includes an evaporator 22 and a condenser 23 for a heat exchanger (e.g. freon). flowing external medium, for example water from a district heating network. The heat transfer medium continues to flow to the heat exchanger 25, 10 where it transfers some of its heat to the water in the water evaporator 14 which evaporates. The heat transfer medium flows through the expansion valve 13 to the heat transfer medium evaporator 22, where it evaporates when it receives heat in the water vapor condenser 11 from the condensing steam. The heat transfer fluid steam continues to flow to the compressor 10.

A liquid acting as a heat source for the system, for example seawater, flows into the crystallizer 17 from the pipeline 18. A pressure corresponding to the freezing point of the liquid prevails in the crystallizer, whereby part of the liquid freezes into crystals and transfers its melting heat to steam. 20 As the heat of vaporization of water is 2500 kJ / kg and the heat of melting 334 kJ / kg, 7.5 times the amount of ice is formed compared to steam. Ice crystals and water leave the pipeline 19. Various stirrers 26 can be used in the crystallizer 17 to promote evaporation and to prevent ice crystals from sticking together.

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With water as the heat source, the crystallizer 17 has a temperature of 0 ° C and a pressure of 0.6 kPa. The water evaporator 14 can be dimensioned, for example, to have a temperature of 40 ° C and a corresponding vapor pressure of 7.4 kPa. This steam flows along a pipeline 27 to a steam jet-30 to an ejector 15, which also draws colder steam down the pipe 28 from the crystallizer 17. The ejector discharges to a water condenser 11, to which the steam flows more warmly than the steam leaving the crystallizer 17. In the water condenser 1, for example, a pressure of 0.75 kPa can be selected, whereby the steam temperature is + 3 ° C and the steam condenses into water.

In the above-mentioned pressure ratios, the amount of steam flowing from the water evaporator 14 to the ejector is about 1/4 of the amount of steam 35 4 73818 1 flowing from the crystallizer 17. Depending on the dimensioning of the plant, the temperature differences can be even lower than the evaporator pressures, in which case the ratio of the feed steam to the steam sucked from the crystal core can be even more advantageous. The necessary negative pressure 5 is maintained in the crystallizer and water vapor condenser by removing uncondensed gases from the system by a vacuum pump 16. Condensate 14 is fed to the water evaporator 14 down the pipe 20 and 19 to their own.

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When the method is applied to make fresh water from salt water, part of the seawater is frozen into ice-free ice crystals and melted with essentially the same energy that was released when the water froze. Figure 2 shows this schematically. The condenser of the previous embodiment 15 is not present in this application, but the heat pump 10 pumps the heat transfer medium steam directly to the water evaporator 14. The ejector 15 operates in exactly the same way as in the embodiment of Fig. 1 and transfers steam from the crystallizer 17 to a higher pressure to a separator 29 where the ice crystals are separated from the water, rinsed with clean water and transferred in a tube 31 to a water condenser 11. Here the ice crystals melt into pure water exiting the tube 21. The ice crystals are discharged from the separator 29 to the tube 32 and exits through a preheat exchanger 33. .

In a three-point crystallizer of a liquid, problems can easily arise from the freezing of the liquid as a solid layer on the walls of the crystallizer if droplets are splashed on them. Figure 3 shows one way to avoid this inconvenience. The liquid flows into the crystallizer 17 in a flow channel, from which it divides into several flow channels 34 before flowing into the crystallizer vapor space 37. It is essential for the crystallizer to flow from each channel through its upper opening 35 to the crystalline vapor space 37. In this case all 35 contacts 36 under adequate rinsing, so that ice crystals do not form on the walls but are formed in the flowing liquid. The whole crystallizer can be I! 5 73818 1 places at a barometric height, so that a pump placed at the lower end of the statue can circulate relatively large amounts of liquid with low power consumption and the rinsing of the crystallizer remains sufficient. To this closed circuit, liquid is added from the heat source and sludge formed by the liquid and ice crystals is removed.

The invention has been described above primarily applied to a heat pump using water as a heat source. In principle, the invention can also be applied to the crystallization of other substances.

Claims (4)

A method for extracting heat from a liquid by evaporating this liquid in a crystallizer (17) having a pressure at most equal to the vapor pressure of the freezing point of the liquid and at the same time some of the liquid crystallizes, and by condensing the released steam from 17) with a steam jet ejector (15) and the steam discharged from the ejector at a pressure and temperature higher than the freezing point of the liquid is led to a condenser (11) where it condenses into a liquid. 10 2. A method according to claim 1, which comprises a crystal crystallization cell (17) with an angular projector (15), which can be secured in an upright position from 15 to 15 angles (14) by means of a color pump with a color pump in the form of a ring. fran ejektorn utströmmande, under högre tryck och i högre temperatur än i Vätskans fryspunkt befintliga angan leds til condensatorn (11) där den kondenseras tilts. 3. A patent according to claims 1 or 2, which can be used to compress a memory and a high temperature compressed by a capacitor with crystal crystals from a crystalline crystal (17) and a crystallization crystal (17) and (11), varvid ren 25 vätska bildas av angan och kriststalina. A method according to claim 1, characterized in that the steam is sucked from the crystallizer (17) by a steam jet ejector (15) into which the warmer the steam is passed to a condenser (11) where it condenses into a liquid. Method according to Claim 1 or 2, characterized in that at least part of the steam compressed by the steam jet ejector (15) to a higher pressure and temperature is condensed with ice crystals generated in the heat exchange in the crystallizer (17) and passed from there to the condenser (11). clean liquid. 25 A method of extracting heat from a liquid by evaporating this liquid in a crystallizer (17) having a pressure at most equal to the vapor pressure of the freezing point of the liquid and at the same time some of the liquid crystallizes, and condensing the released steam to the crystallizer (17) through one or more vertical flow channels (34) and discharges into the crystallizer vapor space (37) from the upper edges 35 (35) of these flow channels so that the liquid continuously flushes everything in the crystallizer I! 7 73818 1 solid walls (36) below the liquid inflow points (35), whereby ice crystals form in the flowing liquid and not on the solid walls. Apparatus for carrying out a method according to any one of the preceding claims, comprising a heat pump compressor (10), a heat transfer medium evaporator (22), a condenser (23) and a subcooler (25), a heat transfer liquid crystallizer (17) and a steam jet injector (15), characterized in that the pressure nozzle of the steam jet-10 ejector communicates with the subcooler (25) in a heat exchanger evaporator (14), the ejector inlet communicates with the crystallizer (17) and the ejector diffuser communicates with the evaporator (22) in the heat exchanger 1 1. For the purpose of uptake of the color genome by means of a crystal crystal (17) of the radiators (17) of the radiators and crystals of the crystalline crystal (11) the fungus of the color-pumping fungus, that is to say the color of the crystal sationskärlet (17) medelst en angstralejektor (15) och den fran ejektom utströmmande, under högre tryck och hogre temperatur än i vtskans fryspunkt befintliga angan leds account 10 capacitor (11) där den condenseras account vtska. 4. For the purpose of uptake of the color genome by means of a crystal crystal (17), the radar and the three crystals of the crystal crystal in which the crystal is crystallized in the condenser. 11) in the case of a solid pump, the transmission of which does not exceed the color of the crystal crystallization (17) and the number of crystals in the crystallization channel (37) 35) pa sa sätt att vätskan kontinuerligt spolar alla stationära II