Apparatus and method for utilising waste heat

Abstract

The invention relates to an apparatus for utilising waste heat, comprising: a cooling circuit (1) which is coupled to a thermal store (5); and a steam-generating unit (17), wherein the cooling circuit (1) comprises a feed line (3) for feeding a coolant into the thermal store (5) and a return line (7) for returning the coolant from the thermal store (5), such that, after heat is absorbed from a process, coolant can be fed into the thermal store (5) and coolant from the thermal store (5) can be returned to enable heat to be absorbed again, wherein the thermal store (5) contains only liquid coolant and no steam, and wherein the steam-generating unit (17) comprises an evaporator which is connected to the thermal store (5) such that a coolant flow from the thermal store (5) can be used to generate steam. The invention also relates to a method for utilising waste heat in such an apparatus.

Description

[0001] 240347W001

[0002] Device and method for utilizing waste heat

[0003] Description

[0004] The invention relates to a device for utilizing waste heat, comprising a cooling circuit for cooling a process and a steam generation device that is operated with a coolant flowing in the cooling circuit as a heat source. The invention further relates to a method for utilizing waste heat in such a device.

[0005] Heat recovery can improve process efficiency. However, particularly in discontinuous processes or continuous processes that require frequent interruptions, such as for maintenance, waste heat is currently often released without any added value, typically using river water or air for heat removal. One reason cited for the lack of utilization of waste heat from such processes is the effort required, as it results in a loss of flexibility. This is because processes must be synchronized to directly utilize waste heat from one process in another.

[0006] To bridge interruptions, it is known to use thermal storage. However, integrating thermal storage involves significant equipment complexity and varies considerably depending on the specific application. Another problem with discontinuous processes is the fluctuating temperature and the associated fluctuations in the amount of heat.

[0007] For the utilization of waste heat from discontinuous processes, it is known, for example, from KR-A 1020150032241, to use a heat transfer fluid to cool a reactor and then to heat another heat transfer fluid with this fluid, which is then fed to a flash steam generator for steam production. To ensure a continuous supply of steam in the event of a reactor interruption, a steam storage tank is connected downstream of the flash steam generator. However, the disadvantage of this method is that the steam occupies a large volume, requiring a correspondingly large steam storage tank. Furthermore, the steam storage tank must also be stable under the steam pressure.

[0008] A waste heat recovery system in which hot flue gases are cooled with a refrigerant and the heat absorbed by the refrigerant is subsequently used to generate electrical energy is known from US Patent 2010 / 0319348. To enable continuous electrical energy generation even during intermittent combustion, two heat storage units with different temperature levels are used.

[0009] A method for generating electrical energy that utilizes two thermal storage units is also known from US patent 2023 / 0287808. Here, a molten salt is used as a heat transfer medium, whereby the molten salt releases heat from the hot thermal storage unit to generate steam, which is then used to generate electrical energy. After heat transfer to a cold thermal storage unit, the process is called 240347W001.

[0010] 2

[0011] The molten salt from the cold heat storage unit is heated and transferred back into the hot heat storage unit.

[0012] The object of the present invention was to provide a device and a method for utilizing waste heat that can also be used at fluctuating temperatures and in discontinuously operated processes.

[0013] The problem is solved by a device for utilizing waste heat comprising a cooling circuit coupled to a heat storage unit and a steam generation device, wherein the cooling circuit includes a supply line for a coolant into the heat storage unit and a return line for the coolant from the heat storage unit, so that coolant can be introduced into the heat storage unit after heat absorption from a process and coolant from the heat storage unit can be returned to the process for renewed heat absorption, wherein the heat storage unit contains only liquid coolant and no steam, and wherein the steam generation device includes an evaporator connected to the heat storage unit in such a way that a coolant flow from the heat storage unit can be used for steam generation.

[0014] The method for utilizing waste heat implemented in the device includes:

[0015] (a) Cooling of a process, wherein the coolant absorbs heat from the process,

[0016] (b) Supplying at least part of the coolant to the heat storage unit via the supply line when the coolant has a temperature above a minimum storage temperature, and not supplying any coolant to the heat storage unit when the coolant has a temperature below the minimum storage temperature,

[0017] (c) Return of coolant from the heat storage unit, wherein the amount of coolant returned corresponds to the amount of coolant supplied to the heat storage unit,

[0018] (d) Extraction of part of the coolant from the heat storage and use of that part of the coolant to generate steam.

[0019] With the device according to the invention, the coolant used to cool the process is simultaneously used as a heat storage medium. For this reason, no driving temperature gradient between a storage medium and the coolant is necessary, so that heat storage can be carried out at a higher temperature level.

[0020] Another advantage is that heat can be stored by introducing coolant until the temperature in the entire heat storage unit reaches the temperature of the supplied coolant. 240347W001

[0021] This corresponds to 3. This also means that if the temperature in the heat storage unit is close to the minimum storage temperature, more waste heat can be absorbed at a lower temperature level. Furthermore, as long as the maximum temperature of the supplied coolant has not yet been reached throughout the entire storage unit, heat peaks from the process can be absorbed. Therefore, unlike known devices, this system also allows for effective heat storage even when the temperature of the process whose waste heat is being stored fluctuates.

[0022] The “minimum storage temperature” is understood to be the temperature of the coolant at the point where the return line branches off from the heat storage unit and where the coolant in the heat storage unit has the lowest temperature.

[0023] Furthermore, the use of the heat storage system allows steam to be generated continuously, even at times when no or only a small amount of waste heat is removed from the process.

[0024] To remove heat from a process, it is common to either cool the device in which the process is carried out or, alternatively, to cool material streams that are taken from the device.

[0025] Devices in which the process is carried out can be, for example, columns, vessels, or pipelines equipped with a double jacket or surface-mounted coils through which a coolant flows. Alternatively, particularly in the case of columns or vessels, cooling coils can be incorporated internally through which the coolant flows. Any process that generates heat can be carried out in the apparatus. Common processes include chemical reactions, absorption processes, adsorption processes, crystallization, dissolution of solids, and condensation.

[0026] In addition to the aforementioned devices, tube bundle systems, for example, can also be used. In these systems, one medium flows through the pipes and another medium flows around them. In this case, heat is transferred via the walls of the individual tubes in the tube bundle system, whereby it is possible for the warmer medium to flow around the tubes, or for the colder medium to flow around them. A chemical reaction, for example, can also be carried out in a tube bundle system.

[0027] When waste heat is transferred to the coolant by cooling a fluid stream, heat exchangers are typically used. Common heat exchangers include shell and tube heat exchangers, block heat exchangers, plate heat exchangers, and spiral heat exchangers. 240347W001

[0028] 4

[0029] Furthermore, waste heat from industrial plants or engines can also be utilized. In this case, the coolant is used to cool the industrial plant or the engine, absorbing the heat.

[0030] Preferably, the waste heat absorbed by the coolant originates from a chemical process, in particular a chemical reaction, for example an exothermic chemical reaction carried out in a batch process. Reactions in which the device and the process can be used include, for example, polymerizations, neutralizations, oxidations, or reductions.

[0031] To prevent heat loss from the thermal storage system by adding excessively cool coolant, coolant is only added if its temperature is above the minimum storage temperature. As soon as the coolant temperature reaches or falls below the minimum storage temperature, no further coolant is added.

[0032] Whether only part of the coolant is supplied to the heat storage unit or the entire coolant depends in particular on the temperature of the coolant taken from the heat storage unit and the temperature at which the coolant is supplied to the process.

[0033] If the temperature of the coolant supplied to the thermal storage system and the temperature of the coolant supplied to the cooling process are above a minimum storage temperature, it is advantageous to separate the coolant into a first and a second part. The first part of the coolant is supplied to the thermal storage system, and the second part is mixed with the coolant drawn from the thermal storage system and then supplied to the cooling process. By mixing the coolant drawn from the thermal storage system, whose temperature is below the temperature at which the coolant is to be supplied to the cooling process, with the second part, which is not supplied to the thermal storage system, it is possible to adjust the coolant temperature to reach the temperature at which the coolant is to be supplied to the cooling process.For this purpose, the hot coolant stream extracted from the process is divided into the first and second parts in such a way that the desired mixing temperature is achieved.

[0034] If the temperature of the coolant supplied to the thermal storage unit is above and the temperature of the coolant supplied to the cooling process is below the minimum storage temperature, it is preferred that all of the coolant be supplied to the thermal storage unit and at least a portion of the coolant withdrawn from the thermal storage unit be cooled in the radiator. Since the temperature of the coolant withdrawn from the thermal storage unit in this case is above the temperature at which the coolant is supplied to the cooling process, it is necessary to cool the coolant further after it is withdrawn from the thermal storage unit. For this reason, at least a portion of the coolant withdrawn from the thermal storage unit is first cooled in the radiator before being supplied to the cooling process again. Whether all of the coolant withdrawn from the thermal storage unit or only a portion 240347W001

[0035] The amount of coolant supplied to the radiator depends, for example, on the temperature at which the coolant is drawn from the heat storage unit. The smaller the difference between the temperature at which the coolant is drawn from the heat storage unit and the temperature at which it is supplied to the cooling process, the less heat the coolant needs to dissipate to achieve the desired temperature. Depending on the amount of heat that the coolant needs to dissipate, the temperature, and the size of the cooling current, the amount of coolant supplied to the radiator is selected to achieve the desired temperature after cooling and remixing of the coolant supplied to the radiator with the portion that was not separately cooled.

[0036] Since the temperature of the coolant supplied to the process is always lower than the temperature of the coolant extracted from the process after cooling, no coolant is added to the heat storage system, and at least a portion of the coolant in the cooler is cooled, if the coolant temperature after absorbing heat from the process falls below the minimum storage temperature. This prevents the temperature in the heat storage system from decreasing due to the addition of coolant.

[0037] As described above, the proportion of coolant supplied to the cooler depends on the temperature at which the coolant is to be supplied to the cooling process, the temperature at which the coolant is withdrawn from the process, and the temperature and size of the flow supplied to the cooler. The proportion of coolant supplied to the cooler is selected such that, after remixing the cooled and uncooled portions of the coolant, the temperature at which the coolant is supplied to the cooling process is reached.

[0038] In order to make it possible to supply only a portion of the coolant to the heat storage unit when the temperature of the coolant supplied to the heat storage unit is above and the temperature of the coolant supplied to the process for cooling is below the minimum storage temperature, and to supply no coolant when the temperature of the coolant after absorbing heat from the process is below the minimum storage temperature, it is preferred that the coolant circuit includes a bypass connecting the supply line and the return line.

[0039] Since either the coolant extracted from the heat storage unit must be cooled to adjust the temperature required for supply to the process, or the coolant bypassed by the heat storage unit when no coolant is supplied to the heat storage unit must be cooled, it is preferred that the cooler be located downstream of the return line in the cooling circuit. To allow only a portion of the coolant to be supplied to the cooler, it is further preferred that at least one additional bypass is included through which the coolant can flow past the cooler. 240347W001

[0040] 6

[0041] The at least one additional bypass can, for example, branch off from the cooling circuit between the return line and the cooler and rejoin the cooling circuit downstream of the cooler. Alternatively, or preferably additionally, a bypass is included that is arranged upstream of the supply line to the heat storage tank. In particular, if the temperature of the coolant drawn from the heat storage tank is below the temperature at which the coolant is to be returned to the process, the temperature of the coolant can be increased in this way by mixing in warm coolant taken from the process, thus setting the desired temperature at which the coolant is to be returned to the process.

[0042] In order for the coolant flow supplied to the cooling process to be equal to the coolant flow withdrawn from the process after cooling, it is necessary that the amount of coolant withdrawn from the heat storage is equal to the amount of coolant supplied to the heat storage.

[0043] To utilize the waste heat from the process, according to the invention, a portion of the coolant contained in the heat storage unit is used for steam generation. Through steam generation, heat is released from the coolant contained in the heat storage unit, so that the average temperature of the coolant in the heat storage unit is below the temperature at which the coolant is supplied to the heat storage unit.

[0044] The thermal storage system can be a stratified storage system; the coolant in the thermal storage system can have a temperature profile, or the coolant in the thermal storage system can be mixed so that the temperature of the coolant in the thermal storage system is essentially constant. "Essentially constant" in this context means that there can be deviations from the average coolant temperature, particularly at the point where the coolant is injected into the thermal storage system, and further deviations can occur, for example, at the walls of the thermal storage system, such as through heat loss to the environment.

[0045] To create a temperature profile in the thermal storage tank or to operate the thermal storage tank as a stratified storage system, it is possible, for example, to feed the coolant extracted from the process into the thermal storage tank at the top and to extract the coolant returned to the process from the bottom. Similarly, the coolant used for steam generation is extracted from the top of the thermal storage tank and, after releasing heat for steam generation, is reintroduced into the thermal storage tank at the bottom. This is particularly advantageous when the density of the hot coolant is lower than that of the cooler coolant, in order to minimize convective mixing of the coolant within the thermal storage tank. The coolant should be introduced into and extracted from the thermal storage tank in such a way that no active mixing occurs within the tank. 240347W001

[0046] 7

[0047] To efficiently store heat in the thermal storage system, it is preferred that the coolant does not evaporate due to heat absorption during the process. For this purpose, the coolant pressure is preferably selected such that it remains above the boiling point at every point in the process at the temperature to which the coolant can be heated to its maximum through heat absorption from the process. Furthermore, the thermal storage system is also operated at a pressure at which no coolant evaporates. Therefore, it is particularly preferred that the cooling circuit be operated such that the pressure throughout the entire cooling circuit remains above the boiling point. Only when the coolant is used directly for steam generation is the pressure in the evaporator itself below the boiling point; however, in the rest of the cooling circuit, it remains above the boiling point even in this case.“Essentially constant pressure” here means that pressure changes may occur, for example, through the use of feed pumps or through flow-related pressure losses as well as hydrostatic pressure, but no devices are used that compress or expand the coolant flowing in the cooling circuit.

[0048] A heat pump is preferably used as the steam generation device. The heat pump can be an open-loop heat pump or a closed-loop heat pump.

[0049] In a closed-loop heat pump, heat is extracted from the refrigerant in the heat storage unit and transferred to a working fluid in a first heat exchanger, causing the working fluid to evaporate. The evaporated working fluid is then compressed, further heating it during the compression process. In an evaporator, the working fluid releases heat to a stream of water, causing at least some of the water to evaporate and at least some of the working fluid to condense. After releasing heat to the water, the working fluid is expanded in an expansion device, such as a throttle or turbine, where it cools down and can then absorb heat again in the first heat exchanger.

[0050] As an alternative to a closed-loop evaporator, it is also possible to heat a water stream by heat transfer from the working fluid in a second heat exchanger and subsequently evaporate a portion of the water in a flash evaporator. In this case, the evaporated portion is extracted from the flash evaporator as steam, and the unevaporated portion is returned to the second heat exchanger.

[0051] Suitable working fluids for use in closed loops include, for example, synthetic working fluids such as hydrofluoroolefins, preferably R1336mzz(Z), R1233zd(E) or R1234ze(Z), as well as natural hydrocarbons, preferably R600 (n-butane), R600a (isobutane) or R601 (pentane), and inorganic compounds, preferably R717 (ammonia) or carbon dioxide. 240347W001

[0052] 8

[0053] Unlike a closed-circuit heat pump, in an open-circuit heat pump, heat is transferred from the coolant taken from the heat storage unit to the water via indirect heat transfer in a heat exchanger or evaporator.

[0054] In a first embodiment of an open-circuit heat pump, the portion of the refrigerant extracted for steam generation transfers heat to a water stream in a heat exchanger, thereby heating the water stream. The heated water stream is fed to a flash evaporator, where it expands, causing a portion of the water stream to evaporate and be extracted as steam. The unevaporated portion is returned to the heat exchanger. The heat pump with a flash evaporator is preferably used when the refrigerant extracted from the heat storage tank for steam generation has a temperature in the range of 20 to 250 °C, more preferably in the range of 70 to 200 °C, and particularly in the range of 90 to 165 °C.The water flow supplied to the heat exchanger preferably has a pressure in the range of 0.1 to 20 bar (abs), more preferably in the range of 0.6 to 16 bar (abs), and particularly in the range of 1 to 6.5 bar (abs), and is preferably heated in the heat exchanger to a temperature in the range of 40 to 210 °C, more preferably in the range of 80 to 195 °C, and particularly in the range of 95 to 158 °C. In the flash evaporator, the water flow is depressurized to a pressure below the boiling point at the temperature at which the water is supplied to the flash evaporator. Preferably, the water flow in the flash evaporator is depressurized to a pressure in the range of 0.01 to 19.9 bar (abs), more preferably to a pressure in the range of 0.3 to 15.9 bar (abs), and particularly to a pressure in the range of 0.7 to 6 bar (abs).The portion taken from the flash evaporator and returned to the heat exchanger is first compressed to the pressure at which the water stream is supplied to the heat exchanger and then mixed with the water stream.

[0055] The proportion of water that is evaporated in the flash evaporator is preferably in the range of 0.15 to 35 wt.%, more preferably in the range of 0.5 to 9 wt.% and particularly in the range of 2.3 to 5 wt.%, based on the total mass flow of water.

[0056] Any heat exchanger known to experts, in which heat is transferred indirectly from one medium to another, can be used as a heat exchanger. Suitable heat exchangers include, for example, shell and tube heat exchangers, block heat exchangers, plate heat exchangers, or spiral heat exchangers.

[0057] A flash container with a throttle at the inlet is suitable as a flash evaporator, for example, so that the water flow into the flash container is relaxed when passing the throttle.

[0058] In a second embodiment of an open-circuit heat pump, the portion of the refrigerant extracted for steam generation transfers heat to a water stream in an evaporator, causing the water stream to at least partially evaporate. The at least partially evaporated water stream is fed to a phase separator, and the evaporated portion is returned to the 240347W001

[0059] 9

[0060] The phase separator extracts the coolant as steam. The unevaporated portion is returned to the evaporator. This embodiment is preferably used when the coolant taken from the heat storage tank for steam generation has a temperature in the range of 20 to 250 °C, more preferably in the range of 70 to 200 °C, and particularly in the range of 90 to 165 °C. The water flow supplied to the evaporator preferably has a pressure in the range of 0.1 to 20 bar (abs), more preferably in the range of 0.6 to 16 bar (abs), and particularly in the range of 1 to 6.5 bar (abs). Preferably 0.15 to 100 wt.%, more preferably 20 to 100 wt.%, and particularly 80 to 100 wt.% are evaporated in the evaporator.

[0061] The phase separator downstream of the evaporator can be operated at the same pressure as the water flow entering it. Alternatively, it is also possible to operate the phase separator at a lower pressure, so that a further portion of the water flow evaporates due to expansion upon entering the phase separator. This is particularly advantageous if the amount of water already evaporated in the evaporator is insufficient to generate steam efficiently and effectively.

[0062] If not only part of the water stream is to be evaporated in the evaporator, but the entire water stream, the phase separator can be omitted, since in this case no liquid water needs to be separated from the evaporated stream.

[0063] Any suitable evaporator, as determined by those skilled in the art, can be used for at least the partial evaporation of a water stream. Suitable evaporators include, for example, shell-and-tube evaporators, falling-film evaporators, or boiler evaporators, with falling-film evaporators being preferred.

[0064] Since in the open heat pumps and closed-circuit heat pumps described above, heat is transferred from the coolant to either a working medium or water, any coolant suitable for the respective process can be used.

[0065] Suitable coolants include water or mixtures of water and an alcohol or salt. Suitable alcohols, which can be used in mixtures with water or in pure form, include glycols such as ethylene glycol or propylene glycol. Suitable salts, which can be added to water, include sodium chloride or carbonate salts. Other suitable coolants include heat transfer oils, liquid salts, or sodium. Water is the preferred coolant.

[0066] In addition to using a heat pump in which heat is transferred from the refrigerant to a working fluid or to water, it is particularly possible and preferred when using water as a refrigerant to use the refrigerant for steam generation in a flash evaporator, in 240347W001

[0067] 10. The coolant expands and is supplied to the heat storage unit so that part of it evaporates. The evaporated portion of the coolant is extracted as vapor, and the unevaporated portion is returned to the heat storage unit.

[0068] Since coolant is being extracted from the coolant circuit in this case, it is necessary to replace the extracted coolant with fresh coolant, in particular demineralized and degassed water. For this purpose, it is especially preferred to introduce the coolant to be replenished directly into the heat storage tank. If the coolant in the heat storage tank has a temperature profile, the coolant to be replenished is preferably supplied at a position where the temperature of the coolant in the heat storage tank matches the temperature of the coolant being supplied.If the coolant to be replenished has a temperature above the maximum storage temperature, it is preferably added at the point where the hot coolant is located in the thermal storage unit. If the coolant temperature is below the minimum storage temperature, it is preferably added at the point where the coolant with the lowest temperature is located in the storage unit. In a mixed thermal storage unit where the coolant has a substantially constant temperature throughout the entire unit, the coolant to be replenished can be added at any point.

[0069] As described above for the first embodiment of the open heat pump, the flash evaporator can, for example, be a flash container with a throttle at the inlet, so that when passing the throttle, the water flow into the flash container is expanded.

[0070] When the coolant is evaporated in a flash evaporator, it is preferred that the coolant is taken from the heat storage at a temperature in the range of 30 to 210 °C, more preferably in the range of 70 to 165 °C and in particular at a temperature in the range of 90 to 100 °C and a pressure in the range of 0.1 to 20 bar(abs), more preferably at a pressure in the range of 0.6 to 6.5 bar(abs) and in particular at a pressure in the range of 0.8 to 1 bar(abs).

[0071] In the flash evaporator, the coolant is then preferably expanded to a pressure in the range of 0.01 to 20 bar(abs), more preferably to a pressure in the range of 0.2 to 6 bar(abs) and in particular to a pressure in the range of 0.69 to 0.99 bar(abs), so that preferably 0.15 to 35 wt.%, more preferably 0.5 to 9 wt.% and in particular 2.3 to 5 wt.% of the coolant supplied to the flash evaporator evaporates.

[0072] Depending on the intended use of the steam and the pressure of the steam generated in the steam generation system, the steam can either be used directly or compressed to a higher pressure. In particular, if the steam was generated by evaporation in a flash vaporizer, it is usually necessary to compress the steam to a higher pressure. 240347W001

[0073] 11

[0074] To compress the steam, at least one compressor is preferably arranged downstream of the evaporator.

[0075] The steam generated in the steam generation unit can either be supplied directly to a consumer or fed into a steam network that supplies steam to various consumers. In particular, when the steam is supplied directly to a consumer, it is possible to use the steam at the pressure it has during steam generation in the unit. When feeding it into a steam network or supplying it to a consumer for whom the temperature of the steam generated in the unit is too low, it is necessary to compress the steam. It is preferable to supply the consumers directly with the steam.

[0076] Low-pressure, medium-pressure, or high-pressure steam can be generated by compression in at least one compressor. It is also possible to first compress all the steam to low-pressure steam, provided the pressure in the steam generation system is below that of low-pressure steam, then to further compress at least a portion of the low-pressure steam to medium-pressure steam, and finally to compress at least a portion of the medium-pressure steam to high-pressure steam.

[0077] In the context of the present invention, low-pressure steam is understood to mean steam having a pressure in the range of 0.9 to 4 bar(abs), preferably in the range of 1 to 2 bar(abs) and particularly in the range of 1.2 to 1.5 bar(abs) and a temperature in the range of 96 to 160 °C, more preferably in the range of 99 to 140 °C and particularly in the range of 104 to 120 °C.

[0078] Medium-pressure steam within the scope of the present invention is steam with a pressure in the range of 4 to 8 bar(abs), preferably in the range of 4.5 to 7 bar(abs) and particularly in the range of 5 to 6 bar(abs) and a temperature in the range of 143 to 220 °C, more preferably in the range of 147 to 210 °C and particularly in the range of 151 to 200 °C.

[0079] High-pressure steam within the scope of the present invention is steam with a pressure in the range of 8 to 40 bar(abs), preferably with a pressure in the range of 10 to 30 bar(abs) and in particular with a pressure in the range of 16 to 20 bar(abs) and a temperature in the range of 170 to 280 °C, more preferably in the range of 180 to 260 °C and in particular with a temperature in the range of 201 to 240 °C.

[0080] To generate low-pressure, medium-pressure, or high-pressure steam, a compressor or a compressor cascade can be used, wherein a compressor cascade with at least two compressors in which the steam is compressed in stages, or a compressor with several compressor stages, for example a geared turbo compressor, is preferred. A geared turbo compressor typically includes several compression stages and intermediate stages, with intermediate cooling in the respective intermediate stages.

[0081] 12 can take place. Even if a compressor cascade with several compressors is planned, it is advantageous to carry out intercooling between the individual compressors.

[0082] Water is typically injected into the steam for intercooling. Due to the temperature of the compressed steam, the water evaporates completely, cooling the steam and simultaneously increasing the steam volume. A sufficiently long injection section is provided to ensure that the injected water evaporates completely before subsequent compression in another compressor or compression stage.

[0083] The steam generated in this way is then extracted from the waste heat recovery device and supplied to a consumer or fed into a steam network.

[0084] Exemplary embodiments of the invention are shown in the figures and are explained in more detail in the following description.

[0085] They show:

[0086] Figure 1 shows a device for utilizing waste heat,

[0087] Figure 2 shows a control concept for the device for utilizing waste heat.

[0088] Figure 3a Temperature in the heat storage unit as a function of time;

[0089] Figure 3b Mass flow rate of the generated steam as a function of time;

[0090] Figure 3c Process return temperature, setpoint of coolant supply temperature and actual value of coolant supply temperature as a function of time;

[0091] Figure 4 shows a section of the diagram shown in Figure 3c.

[0092] Figure 1 shows a device for utilizing waste heat.

[0093] After heat absorption from a process, a coolant from a cooling circuit 1, of which only the part relating to heat storage and utilization is shown here, is introduced into a heat storage tank 5 via a supply line 3. To maintain a constant coolant flow in the cooling circuit 1, the same quantity of coolant introduced into the heat storage tank 5 is withdrawn from the heat storage tank 5 via a return line 7 and returned to the cooling circuit 1.

[0094] To allow for the possibility of feeding only a portion of the coolant or no coolant at all into the heat storage unit during operation of the process, the coolant circuit 240347W001 features

[0095] 13 a bypass 9 which connects the supply line 3 and the return line 7, so that coolant can flow directly from the branch of the supply line 3 out of the cooling circuit 1 to the inlet of the return line 7 into the cooling circuit 1.

[0096] If the coolant downstream of the return line 7 inlet has a temperature higher than the temperature at which it is to be returned to the process, the cooling circuit 1 includes a cooler 11. To adjust the coolant temperature, a further bypass 13 is included, through which at least a portion of the coolant can bypass the cooler 11. If the coolant in the cooler 11 is cooled to a temperature below the temperature at which it is to be returned to the process for further heat absorption, a portion of the warmer coolant can bypass the cooler 11 through the further bypass 13. Downstream of the cooler 11, the two flows are mixed again, resulting in a temperature higher than the temperature at which the coolant left the cooler 11.

[0097] Should the temperature of the coolant being returned from the heat storage unit 5 to the cooling circuit 1 be below the temperature at which the coolant is to be reintroduced into the process, the coolant taken from the heat storage unit 5 is routed through the further bypass 13 and, in addition, a portion of the coolant that has absorbed heat from the process is routed through a second further bypass 15 and mixed with the coolant taken from the heat storage unit, so that after mixing the coolant has a temperature that is above the temperature at which the coolant was taken from the heat storage unit and corresponds to the temperature at which the coolant is to be reintroduced into the process.Naturally, to adjust the temperature of the coolant being returned to the process, coolant that has flowed through cooler 11 can be mixed with coolant that has passed through the second bypass 15, so that the second bypass 15 is used instead of the bypass 13. Alternatively, to adjust the temperature of the coolant being returned to the process, coolant can be passed through cooler 11, the bypass 13, and the second bypass 15. The flow rates through cooler 11, the bypass 13, and the second bypass 15 depend on the quantity and temperature of the coolant being returned from the heat storage tank 5 to the cooling circuit 1, and on the temperature to which the coolant is cooled in cooler 11, if coolant is flowing through it.

[0098] To utilize the heat absorbed by the coolant from the process, a portion of the coolant is fed to a steam generation unit 17. The steam generation unit 17 includes, for example, a heat exchanger in which heat is transferred from the coolant to water. In the heat exchanger, the water is heated and then partially evaporated by expansion in a flash evaporator. The evaporated portion is extracted as steam, and the remainder is returned to the heat exchanger. 240347W001

[0099] 14

[0100] Alternatively, the steam generation device 17 may include an evaporator in which water is at least partially evaporated by heat transfer from the coolant. If the water is partially evaporated, a phase separator is connected downstream of the evaporator, in which the evaporated portion is separated from the unevaporated portion and extracted as steam. The unevaporated portion is returned to the evaporator. To increase the steam output, the phase separator can be operated at a lower pressure than the evaporator, so that further water evaporates upon entering the phase separator.

[0101] If all the water in the evaporator evaporates, the phase separator can be omitted.

[0102] When water is used as a coolant, the steam generation device 17, as shown here, includes a flash evaporator 19 in which a portion of the coolant evaporates. The evaporated portion is extracted from the flash evaporator 19 as steam and fed to a compressor 22.

[0103] In particular, if a temperature profile develops in the heat storage tank 5 in which hotter coolant, due to its lower density, is at the top and colder coolant, due to its higher density, is at the bottom, the coolant supplied to the steam generation device 17 is drawn from the top of the heat storage tank 5 via a first line 21. After heat dissipation in the heat exchanger or compressor, or, if the coolant is water, after partial evaporation in the flash evaporator 19, the cooled coolant or the unevaporated coolant is returned to the bottom of the heat storage tank 5 via a second line 23.

[0104] If steam is to be used directly, it can be drawn off, for example, via a steam line 25. Any steam not drawn off via steam line 25 is then fed to at least one compressor 22. Typically, a multi-stage compressor 22 is used to compress the steam, and additional water can be injected downstream of the compressor stages for cooling. The water injected downstream of the compression stages can be either unevaporated water taken from the steam generation unit 17 via an injection line 27, or, if the coolant is water, coolant from the heat storage unit 5, which is drawn from the heat storage unit 5 via a line 29. Alternatively, if the coolant is water, it is also possible to draw both water from the heat storage unit 5 and unevaporated water from the flash evaporator 19 and inject them into the steam.The compressed steam 31 leaving the compressor 22 can then, for example, be fed into a steam network.

[0105] Since the amount of coolant in the heat storage tank is reduced when coolant evaporates to generate steam, it must be replenished. For this purpose, for example, coolant, especially water, can be introduced into the heat storage tank via a supply line 33. 240347W001

[0106] 15

[0107] A control concept for the device for utilizing waste heat is shown in Figure 2.

[0108] In the embodiment shown in Figure 2, degassed and demineralized water is used as the coolant in cooling circuit 1. All subsequently described controls for carrying out the process are preferably PID controllers.

[0109] To prevent the temperature in the thermal storage unit 5 from falling below a minimum storage temperature, the coolant supplied to the thermal storage unit 5 must have a temperature above this minimum storage temperature. For this purpose, a temperature controller 61 receives the temperature difference between the temperature of the coolant after heat absorption from a process, such as a chemical reaction, absorption, adsorption, crystallization, condensation, or the dissolution of solids, and the temperature in the thermal storage unit 5 as measured by a second temperature controller 63. As soon as this temperature exceeds a setpoint, the coolant is supplied via a line 62 to a split point, where the line 62 is divided into the supply line 3 to the thermal storage unit 5 and the bypass 9.If the temperature difference is smaller than the setpoint, the coolant is routed past the heat storage tank 5 via a bypass line 65.

[0110] The amount of coolant flowing through cooling circuit 1 after heat absorption from the process is measured by a flow controller 67. This controls a pump 69 to establish a predetermined flow rate.

[0111] To adjust the temperature at which the coolant in cooling circuit 1 is supplied to the process being cooled, a portion of the warm coolant, after absorbing heat from the process, can be mixed with colder coolant taken from the heat storage tank 5 via the return line 7. To keep the amount of coolant in cooling circuit 1 constant, the amount of coolant supplied to the heat storage tank 5 via the supply line 3 corresponds to the amount of coolant returned to the cooling circuit via the return line 9.

[0112] To determine the ratio of coolant supplied to the heat storage tank 5 to coolant routed through the bypass 9, the mixture temperature detected by a third temperature controller 71 is first compared to a target value. The target value is the temperature specified by the process control system for the coolant flow to the process. If the temperature detected by the third temperature controller 71 is above the target value, the controller outputs a higher setpoint for the coolant supplied to the heat storage tank 5, and if the temperature detected by the third temperature controller 71 is below the target value, a lower setpoint for the coolant supplied to the heat storage tank 5 is output. 240347W001

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[0114] The second temperature controller 63 receives the temperature at the top of the heat storage unit 5 as its input. The target value for the second temperature controller 63 is a predefined value for the maximum storage temperature. If the temperature measured by the second temperature controller 63 is below the maximum storage temperature, the second temperature controller 63 increases the setpoint for the amount of coolant supplied to the heat storage unit 5. As soon as the temperature in the heat storage unit 5 approaches the target temperature, i.e., the maximum storage temperature, the setpoint is reduced so that less coolant is supplied to the heat storage unit 5 to prevent overheating.

[0115] Since the amount of coolant supplied to the heat storage unit 5 affects both the mixture temperature, which is measured by the third temperature controller 71, and the temperature in the heat storage unit 5, which is measured by the second temperature controller 63, the coupling of the second temperature controller 63 and the third temperature controller 71 is crucial for determining the setpoint for the valves that regulate the amount of coolant flowing through the bypass 9 and the amount of coolant supplied to the heat storage unit 5. For example, it is possible to always use the smaller of the setpoints determined by the second temperature controller 63 and the third temperature controller 71 for the amount of coolant supplied to the heat storage unit 5. Alternatively, the two setpoints can be multiplied, with the setpoints taking on a value between 0 and 1.“0” means that no coolant is supplied to the heat storage unit 5, but that all the coolant is routed through the bypass 9, and “1” means that all the coolant is supplied to the heat storage unit 5 and no coolant flows through the bypass 9.

[0116] For example, the second temperature controller 63 might, at a low temperature in the thermal storage tank 5, specify that all the coolant flowing through line 62 should be introduced into the thermal storage tank 5, i.e., it sets a setpoint of "1". However, since in this case the coolant temperature would be too low for feeding into the process, and a mixing temperature must be set that requires part of the coolant to flow through bypass 65, the third temperature controller 71 specifies that only part of the coolant can be supplied to the thermal storage tank 5 and the other part should flow through bypass 9. If, for example, half of the coolant is to be supplied to the thermal storage tank 5, the setpoint determined by the third temperature controller 71 is 0.5.In this case, both in the variant where the smaller control value is used and in the case of multiplication of the control values, the control value to be used would be 0.5, meaning that one half of the coolant is supplied to the heat storage tank 5 and the other half is routed through the bypass 9.

[0117] When the temperature of the storage medium approaches the maximum storage temperature, the second temperature controller 63 specifies a smaller setpoint, for example, a setpoint of 0.05. However, if, on the other hand, a larger quantity of coolant is to be supplied to the heat storage unit 5 to achieve the desired mixing temperature, for example, 70% of the coolant, the third temperature controller 71 specifies a setpoint of 0.7. At Ver- 240347W001

[0118] 17. Applying the smaller control value would in this case supply 5% of the coolant to the heat storage unit 5, or, in the case of multiplication of the control values, only 3.5% of the coolant. Due to the small amount of coolant supplied to the heat storage unit 5 and thus the small amount of cold coolant removed from the heat storage unit 5, the mixture temperature is too high, so that in this case the coolant must be cooled further downstream of the third temperature controller 71 in the cooler 11.

[0119] To regulate the flow through the cooler 11, a fourth temperature controller 73 is used to regulate the ratio of the partial flows that pass through the cooler 11 and the further bypass 13, as well as the amount of cooling medium 75 that flows through the cooler 11 to cool the coolant, based on the temperature of the coolant supplied to the process to be cooled and a setpoint that corresponds to the desired supply temperature to the process to be cooled.

[0120] A first pressure regulator 77 regulates the pressure in the return line 7 so that the inlet pressure is sufficiently high to pump the coolant from the heat storage tank 5 into the cooling circuit 1. The required pressure is set via a circuit line 79.

[0121] Since coolant is extracted during steam generation, it must be replenished for continuous operation. For this purpose, the fill level in the heat storage tank 5 is monitored by a first level controller 81. The first level controller 81 sends a setpoint to a fourth flow controller 83, which regulates the supply of fresh coolant to the heat storage tank 5 via the supply line 33.

[0122] For steam generation, coolant is drawn from the thermal storage tank 5 via the first line 21. The amount of coolant is measured by a second flow controller 85 and regulated by a second pump 87. The setpoint for the flow rate is calculated from the currently required amount of energy. This can be constant or vary with the charge level in the thermal storage tank 5, which depends on the temperature of the coolant. Both continuous energy quantity settings and discrete increments are possible. Furthermore, a cascade control system can be established, in which a controller 89 specifies the setpoint for the flow rate as the actuated value and itself regulates to a predetermined amount of energy for steam generation.

[0123] The pressure of the steam generated in the flash evaporator 19 is regulated by a second pressure regulator 91, which controls the steam withdrawal from the flash evaporator 19 to achieve a predetermined pressure. The target pressure is determined by the steam generation process and can be constant or vary depending on the storage temperature. For example, at higher storage temperatures, steam can be generated at a higher pressure, as the efficiency of steam compression increases with rising pressure. 240347W001

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[0125] To prevent overfilling of the flash evaporator 19, the fill level in the flash evaporator 19 is measured with a second level controller 93 and the return flow of coolant through the second line 23 into the heat storage tank 5 is regulated via a third flow controller 95 to adjust the fill level in the flash evaporator 19.

[0126] Example

[0127] The process for utilizing waste heat was simulated using a simulation program, whereby the control system shown in Figure 3 is modeled using the simulation program.

[0128] To simplify the simulation, the process being cooled and the compressor 22 are not included. This is achieved by specifying that the compressor 22 automatically operates within its load range of 60 to 100%, depending on the temperature in the heat storage tank 5, and that the process delivers a predetermined coolant flow derived from real operating data, with water being assumed as the coolant. The supply temperature to the process is also derived from real data.

[0129] Furthermore, heat losses to the environment are neglected in the simulation, so that, for example, the heat storage unit 5 does not release any heat to the environment.

[0130] The simulation tests the control concept shown in Figure 3, including the control loops. Impermissible temperature exceedances or other impermissible operating points become apparent.

[0131] Furthermore, the simulation checks the behavior of the fill level and temperature in the heat storage unit 5, as well as the flow temperature in the cooling circuit downstream of the cooler 11 and in the evaporator 19, the flow rate from the heat storage unit 5 in the first line 23 to the evaporator 19 and the flow rate from the cooling circuit 1 to the heat storage unit 5.

[0132] A continuous storage control system is simulated, in which the heat flow rate supplied to the evaporator for steam generation can assume all values ​​between a minimum and a maximum heat flow rate. A heat exchanger is assumed to be the evaporator.

[0133] The following input parameters are used for the simulation:

[0134] The mass flow rate and temperature of the coolant after heat absorption from the process are transmitted to the simulation model as a function of time;

[0135] The target value for the process flow temperature is transmitted to the simulation model as a function of time; 240347W001

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[0137] The target pressure is 0.4 bar (abs);

[0138] The target value for the coolant flow rate is 375 m³ / h. 3 / h

[0139] The target value for the difference between return temperature and storage temperature is 2 °C;

[0140] The heat storage unit operates within a temperature range of 90 to 100 °C;

[0141] The heat storage unit has a volume of 3000 m³ 3 up and the target value for the fill level is 90% of the total volume;

[0142] A heat transfer rate of 1072 kW / K is assumed for the heat transfer of the cooler;

[0143] The evaporation tank has a volume of 2 m³ 3 and the fluid level is regulated to 10% of the volume;

[0144] Steam generation is stopped at a temperature below 90 °C and resumed at minimum load at a temperature above 91 °C;

[0145] At temperatures of 95 °C, steam generation is increased from minimum to maximum load. When temperatures drop below 93 °C, steam generation is switched from maximum to minimum load.

[0146] The maximum energy output for the steam is 900 kW and the minimum energy output is 270 kW.

[0147] The following starting parameters are set at the beginning of the simulation:

[0148] The starting temperature of the heat storage unit is 90 °C;

[0149] The liquid volume in the heat storage tank is initially 3000 m³. 3 ;

[0150] The amount of heat supplied for steam generation is initially 0 kW.

[0151] The results of the simulation are shown in Figures 3a to 3c, where the simulation simulates operation over 270 hours.

[0152] Figure 3a shows the temperature in the heat storage tank 5 as a function of time in hours. Figure 3b shows the mass flow rate of the generated steam as a function of time, and in Figure 3c, the solid line 101 shows the process return temperature of the water. Furthermore, Figure 3c shows the setpoint 103 for the temperature at which the coolant is supplied to the process. 240347W001

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[0154] The first 50 hours of the process return temperature 101, the setpoint 103 for the temperature at which the coolant is supplied to the process for cooling, and the actual value 105 for the temperature at which the coolant is supplied to the process are shown in Figure 4. For clarity, the first 50 hours of the process return temperature 101, the setpoint 103 for the temperature at which the coolant is supplied to the process for cooling, and the actual value 105 for the temperature at which the coolant is supplied to the process are shown in Figure 4.

[0155] The simulation results shown in Figure 3a indicate that the heat storage unit is operated within the planned temperature range.

[0156] The planned switching of steam generation takes place between maximum load, reduced load and phases without operation, as can be seen in Figure 3b.

[0157] Figures 3c and 4 show that the intended temperature of the coolant is reliably reached, so that stable operation is possible even with the heat integration of batch processes.

Claims

240347W001 21 Patent claims 1. Device for utilizing waste heat comprising a cooling circuit (1) coupled to a heat storage unit (5) and a steam generation device (17), wherein the cooling circuit (1) comprises a supply line (3) for a coolant into the heat storage unit (5) and a return line (7) for the coolant from the heat storage unit (5), so that coolant can be introduced into the heat storage unit (5) after heat absorption from a process and coolant from the heat storage unit (5) can be returned to the process for renewed heat absorption, wherein the heat storage unit (5) contains only liquid coolant and no steam, and wherein the steam generation device (17) comprises an evaporator connected to the heat storage unit (5) in such a way that a coolant flow from the heat storage unit (5) can be used for steam generation.

2. Device according to claim 1, characterized in that the cooling circuit (1) comprises a bypass (9) connecting the supply line (3) and the return line (7).

3. Device according to claim 1 or 2, characterized in that a cooler (11) is included in the cooling circuit (1) downstream of the return line (7).

4. Device according to claim 3, characterized in that at least one further bypass (13, 15) is included through which the coolant can flow past the radiator (11).

5. Device according to one of claims 1 to 4, characterized in that water is evaporated in the evaporator by indirect heat transfer from the coolant to the water.

6. Device according to one of claims 1 to 4, characterized in that the coolant is water and the evaporator is a flash evaporator (19) in which a portion of the coolant is evaporated.

7. Device according to one of claims 1 to 6, characterized in that at least one compressor (22) is arranged downstream of the evaporator for compressing the steam.

8. Method for utilizing waste heat in a device according to any one of claims 1 to 7, comprising: (a) Cooling of a process, wherein the coolant absorbs heat from the process, (b) Supply of at least part of the coolant via the supply line (3) into the heat storage tank (5) when the coolant has a temperature above a 240347W001 22 minimum storage temperature, and no supply of coolant to the heat storage (5) if the coolant has a temperature below the minimum storage temperature, (c) Return of coolant from the heat storage unit (5), wherein the amount of coolant returned corresponds to the amount of coolant supplied to the heat storage unit (5), (d) Extraction of part of the coolant from the heat storage (5) and use of that part of the coolant to generate steam.

9. Method according to claim 8, characterized in that the coolant is water.

10. Method according to claim 8 or 9, characterized in that the portion of the coolant withdrawn for steam generation releases heat to a water stream in a heat exchanger, thereby heating the water stream, the heated water stream is fed to a flash evaporator in which the water stream is expanded, so that a portion of the water stream evaporates and is withdrawn as steam and the unevaporated portion is returned to the heat exchanger.

11. Method according to claim 8 or 9, characterized in that the portion of the coolant withdrawn for steam generation releases heat to a water stream in a heat exchanger, whereby the water stream is at least partially evaporated, the partially evaporated water stream is fed to a phase separator, the evaporated portion is withdrawn from the phase separator as steam, and the non-evaporated portion is returned to the heat exchanger.

12. Method according to claim 9, characterized in that the coolant for steam generation is supplied to a flash evaporator (19) in which the coolant expands, so that part of the coolant evaporates and is withdrawn as steam and the non-evaporated part of the coolant is returned to the heat storage (5).

13. Method according to one of claims 8 to 12, characterized in that the steam is compressed.

14. Method according to any one of claims 8 to 13, characterized in that the coolant is separated into a first part and a second part, the first part of the coolant is supplied to the heat storage unit (5) and the second part is mixed with the coolant withdrawn from the heat storage unit (5) and then supplied to the cooling process if the temperature of the coolant supplied to the heat storage unit (5) and the temperature of the coolant supplied to the cooling process are above a minimum storage temperature, or that the entire coolant is supplied to the heat storage unit (5) and at least a part of the coolant supplied to the heat storage unit (5) 240347W001 23 coolant extracted in the cooler (11) is cooled if the temperature of the coolant supplied to the heat storage (5) is above and the temperature of the coolant supplied to the process for cooling is below the minimum storage temperature, or if no coolant is supplied to the heat storage (5) and at least part of the coolant is cooled in the cooler (11) if the temperature of the coolant after absorbing the heat from the process is below the minimum storage temperature.

15. A method according to any one of claims 8 to 14, characterized in that the process comprises a chemical reaction, cooling of a mass flow or cooling of an apparatus.

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