Apparatus and method for utilising waste heat

Abstract

The invention relates to an apparatus for utilising waste heat, comprising at least one heat exchanger (3) for transferring heat from a process to a heat transfer medium, a first container (7) for storing the heat transfer medium at a first temperature, and a second container (13) for storing the heat transfer medium at a second temperature, wherein the first temperature is higher than the second temperature, wherein the heat exchanger is accommodated in a first line (5), which connects the second container to the first container, and an expansion member (11) is accommodated in a second line (9), which connects the first container (7) to the second container (13), wherein a pump is also accommodated in the first line (5), with which liquid can be compressed and pumped from the second container (13) into the first container (7), and the second container (13) comprises a vapour line (15) for vapour extraction. The invention further relates to a method for utilising waste heat with such an apparatus.

Description

[0001] 240384W001

[0002] Device and method for utilizing waste heat

[0003] Description

[0004] The invention relates to a device for utilizing waste heat, comprising a heat transfer circuit with at least one heat exchanger for transferring heat from a process to a heat transfer medium and a first container for storing a heat transfer medium. 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 devices is also known from US patent A 2023 / 0287808. Here, a molten salt is used as the heat transfer medium, as described in 240384W001.

[0010] 2. The molten salt releases heat from the hot heat storage unit to generate steam, which is then used to generate electrical energy. After releasing heat, it is transferred to a cold heat storage unit. The molten salt from the cold heat storage unit is then heated and transferred back to the hot heat storage unit.

[0011] 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.

[0012] The problem is solved by a device for utilizing waste heat comprising at least one heat exchanger for transferring heat from a process to a heat transfer medium which is heated in the heat exchanger but does not evaporate, a first container for storing the heat transfer medium at a first temperature and a second container for storing the heat transfer medium at a second temperature, wherein the first temperature is higher than the second temperature, wherein the heat exchanger is included in a first line connecting the second container to the first container and an expansion device is included in a second line connecting the first container to the second container, wherein a pump is also included in the first line with which liquid can be compressed and pumped from the second container to the first container, and the second container includes a steam line for steam extraction.

[0013] The method for utilizing waste heat carried out with the device includes:

[0014] (a) Transferring heat from the process to the heat transfer medium in the heat exchanger, whereby the heat transfer medium is heated but not evaporated;

[0015] (b) Feeding the heated heat transfer fluid into the first container;

[0016] (c) Extraction of heat transfer fluid from the first container and expansion of the heat transfer fluid extracted from the first container, so that the heat transfer fluid is partially evaporated and a liquid phase and a gaseous phase are obtained, wherein the heat transfer fluid is expanded in an expansion device in the second line or upon entry into the second container;

[0017] (d) Separating the liquid phase and the gaseous phase in the second container;

[0018] (e) Extraction of the gaseous phase as steam via the steam line.

[0019] Because the heat transfer fluid partially evaporates upon expansion, and the second container contains both a gaseous and a liquid phase, it is possible to dispense with an additional evaporator positioned between the first and second containers. 240384W001

[0020] 3

[0021] The use of a first container, in which the heat transfer fluid is stored at the initial temperature, has the advantage that the device and the process can also be used in discontinuous processes, such as batch processes or processes where temperature fluctuations occur, to continuously generate steam. Because the heat transfer fluid is stored at the initial temperature in the first container, it acts as a heat reservoir from which further heat transfer fluid can be drawn for steam generation until a minimum fill level is reached or the first container no longer contains any heat transfer fluid.

[0022] For continuous steam generation when utilizing waste heat from discontinuous processes, it is necessary that the size of the first container and the amount of heat transfer fluid stored in the first container are large enough to ensure that sufficient heat transfer fluid is available for steam generation during an interruption of the process.

[0023] In order to transfer heat from the process to the heat transfer medium, the heat from the process must first be removed. This is typically achieved by cooling either the apparatus in which the process takes place or the material streams drawn from the apparatus. If the waste heat to be utilized is generated directly by equipment used in the process, such as motors, then the corresponding equipment is cooled.

[0024] 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 provided internally through which the coolant flows. Furthermore, it is possible, and preferably preferred, to provide an external heat exchanger in which a process stream drawn from the apparatus is cooled by indirect heat transfer to the coolant and then returned to the apparatus. Any process requiring heat dissipation can be carried out in the apparatus. Common processes include, for example, chemical reactions, absorption processes, adsorption processes, extractions, condensations, crystallizations, dissolving solids, or cooling hot material streams.

[0025] Chemical reactions in which the device and method according to the invention can be used to utilize waste heat include, for example, polymerizations, neutralizations or oxidations.

[0026] In addition to the aforementioned apparatus, tube bundle apparatuses can also be used, for example. In these, 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 apparatus, whereby it is possible for the warmer medium to flow around the tubes as well as for the colder medium to flow around them. A chemical reaction can also be carried out in a tube bundle apparatus, for example. However, it is more common to use 240384W001

[0027] 4 especially in batch reactions, to feed a mass flow from a reactor to the tube bundle apparatus, to cool the mass flow in the tube bundle apparatus by transferring heat to a cooling medium and then to return the mass flow back to the reactor.

[0028] 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, plate heat exchangers, and spiral heat exchangers.

[0029] Furthermore, waste heat from industrial plants or engines can also be used. 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, or oxidations.

[0031] To ensure efficient use of the coolant and minimize coolant consumption, it is preferable for the process to include a cooling circuit in which the coolant flows, absorbing heat from the process. The heat absorbed by the coolant is then transferred to the heat transfer fluid in the heat exchanger. If the coolant temperature is still too high after heat transfer to the heat transfer fluid to be reused for cooling the process, it is possible to further cool the coolant in a cooler. Suitable coolers include, for example, air coolers or coolers through which river water flows.

[0032] After the process has cooled, the heat absorbed by the coolant is transferred to the heat transfer fluid in the heat exchanger.

[0033] 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, plate heat exchangers, or spiral heat exchangers.

[0034] As an alternative to using a coolant that then transfers the heat to the heat transfer medium, it is also possible and preferred to cool the apparatus in which the process is carried out, the process equipment, or a process stream, for example, a reaction product, using the heat transfer medium as a coolant. In this case, the apparatus to be cooled, the device to be cooled, or the heat exchanger in which the process stream is cooled is the heat exchanger in which the heat of the process is transferred to the heat transfer medium. 240384W001

[0035] 5

[0036] To increase the usable temperature range for steam generation, it is also possible to further heat the coolant after absorbing heat from the process, or, if the heat transfer fluid absorbs heat directly from the process, to further heat the heat transfer fluid before introducing it into the first container. For further heating of the coolant or the heat transfer fluid, electric heaters or heating with a heat transfer medium, such as steam, can be used, for example.

[0037] In addition to the utilization of waste heat from a single process as described above, the inventive method and device have the advantage that waste heat from several different processes can also be utilized. For example, it is possible for more than one heat exchanger to be incorporated in the first line, with each heat exchanger capable of transferring heat from one process to the heat transfer medium. It is possible for at least one heat exchanger to be the process device, the apparatus, or the heat exchanger for cooling a material stream of the process, and for at least one heat exchanger to be a heat exchanger in which a coolant, used to absorb heat from the process, transfers heat to the heat transfer medium.Of course, it is also possible that every process includes a cooling circuit and that heat is transferred from the coolant to the heat transfer medium in every heat exchanger, or that no process includes a cooling circuit and the heat transfer medium serves as a coolant for the individual devices, apparatus and / or material flows of the process, so that no additional cooling circuit is required.

[0038] The heat exchangers, in which the heat is transferred to the heat transfer medium, can be connected in such a way that the heat transfer medium flows through at least two heat exchangers in series or in such a way that the heat transfer medium flows through at least two heat exchangers in parallel.

[0039] A flow through the heat exchangers in series is particularly possible when the temperature of the heat transfer fluid after a heat exchanger is still sufficiently low that the heat transfer fluid can also absorb the heat from the subsequent process.

[0040] In addition to arranging all heat exchangers so that the heat transfer fluid flows through them in series or in parallel, it is also possible to have at least two heat exchangers connected in series and at least two heat exchangers connected in parallel. It is also possible to provide several parallel-connected series of at least two heat exchangers each.

[0041] When multiple heat exchangers are used, they can all be of the same type, or different types of heat exchangers can be used. The size of each heat exchanger depends on the amount of heat transferred to the heat transfer fluid in the respective heat exchanger, the mass flow rates of the fluid stream to be cooled and the heat transfer fluid, and the temperature difference between the fluid stream to be cooled and the heat transfer fluid. 240384W001

[0042] 6

[0043] Instead of using multiple heat exchangers, each transferring heat from a process to the heat transfer medium, it is also possible to use only one cooling circuit through which a coolant flows, absorbing heat from multiple processes and then transferring it to the heat transfer medium in the heat exchanger.

[0044] When a coolant absorbs heat from multiple processes, it can flow through them in series or in parallel. Flowing through the processes in series is particularly feasible if the coolant temperature, after absorbing heat from one process, is still low enough to absorb heat from the subsequent process, for example, if the processes are operated at different temperatures. Especially when processes are operated at the same temperature, it is advantageous for the coolant to flow through them in parallel. Furthermore, as described above for heat exchangers where heat is transferred to the heat transfer medium, it is also possible for the coolant to flow through at least two processes in parallel and at least two processes in series, or for several parallel series of at least two processes each to be provided, through which the coolant flows.

[0045] To efficiently store heat in the first vessel, the heat transfer fluid is not evaporated by absorbing heat from the at least one process. For this purpose, the pressure of the heat transfer fluid is selected such that it is above the boiling point at the temperature to which the heat transfer fluid can be heated to its maximum by absorbing heat from all processes. Furthermore, the first vessel is also operated at a pressure at which no heat transfer fluid evaporates. Therefore, it is particularly preferred if the at least one heat exchanger and the first vessel are operated such that the pressure in all heat exchangers and in the first vessel is essentially the same, or if the pressure in the first vessel is higher than in all heat exchangers.

[0046] “Essentially equal pressure” here means that pressure changes may occur, for example, through the use of feed pumps or through flow-related pressure losses, but no devices are used that compress or expand the heat transfer fluid flowing from the heat exchanger to the first container.

[0047] In order to do without a separate evaporator, according to the invention, heat transfer fluid is taken from the first container and partially evaporated by expansion to a lower pressure, so that a gaseous phase and a liquid phase are formed.

[0048] To evaporate the heat transfer fluid taken from the first container by expansion, an expansion device is incorporated in the second line connecting the first and second containers. The heat transfer fluid flowing from the first to the second container through this second line passes through the expansion device and is thereby expanded. The 240384W001

[0049] 7

[0050] The pressure to which the heat transfer fluid is expanded is a pressure below the boiling point at the temperature at which the heat transfer fluid is stored in the first container. Expansion can be achieved either through an expansion valve (throttle valve) or through a turbine. When using a turbine, some of the work done by the volume change can be converted into usable mechanical work and used to drive a generator.

[0051] The pressure at which the heat transfer fluid is stored in the first container is preferably in the range of 0.5 to 220 bar (abs), more preferably in the range of 1 to 25 bar (abs), and particularly in the range of 3 to 10 bar (abs), depending on the heat transfer fluid used. The temperature of the heat transfer fluid in the first container is preferably in the range of 70 to 300 °C, more preferably in the range of 90 to 200 °C, and particularly in the range of 100 to 150 °C. In order to evaporate a portion of the heat transfer fluid by expansion, the heat transfer fluid is preferably expanded in the expansion device to 0.2 to 24 bar (abs), more preferably to 0.5 to 10 bar (abs), and particularly to 1 to 4 bar (abs). Due to the expansion, the temperature of the heat transfer fluid drops to 60 to 180 °C, more preferably to 80 to 180 °C and especially to 100 to 140 °C.

[0052] The expansion element can be located at any point in the second line, however, it is preferred if the second container is a flash container and the expansion element is located at the inlet to the flash container, so that the heat transfer medium expands upon entering the second container and is partially evaporated.

[0053] The proportion of heat transfer fluid that is evaporated by the expansion is preferably in the range of 0.5 to 20 wt.%, more preferably in the range of 1 to 10 wt.% and in particular in the range of 2 to 5 wt.%, based on the total mass flow rate of heat transfer fluid.

[0054] To avoid removing the unevaporated portion of the heat transfer fluid from the process after evaporation, it is preferred to return the liquid phase from the second container to the first container. For this purpose, the liquid phase of the heat transfer fluid taken from the second container is passed through the heat exchanger, where the heat transfer fluid absorbs heat from the process, and then, after heat absorption, is directed into the first container.

[0055] To prevent the temperature in the first container from dropping due to the addition of colder heat transfer fluid, it is further preferred that the return of the heat transfer fluid from the second container to the first container be interrupted when the process is not releasing heat. With constant steam generation and extraction, this interruption causes the liquid level in the first container to decrease and the liquid level in the second container to increase until the process starts releasing heat again and the return of the liquid phase from the second container to the first container is restarted. 240384W001

[0056] 8

[0057] As steam is drawn from the second tank, the amount of liquid heat transfer fluid decreases. For continuous operation, it is therefore necessary to replace the withdrawn heat transfer fluid with fresh heat transfer fluid. This fresh heat transfer fluid can be added at any point in the heat transfer fluid circuit, which consists of the first tank, the first line, the second tank, and the second line. For example, it can be added directly into the first tank, the second tank, the first line connecting the first and second tanks, or the second line connecting the second and first tanks.Preferably, the fresh heat transfer fluid is added to the first container or to the second container, preferably to the first container if the temperature of the fresh heat transfer fluid is above the temperature in the first container, to the second container if the temperature of the fresh heat transfer fluid is below the temperature in the first container and above the temperature in the second container, and to the second line connecting the second container to the first container if the temperature of the fresh heat transfer fluid is below the temperature in the second container, wherein the addition to the second line is preferably made downstream of the second container and upstream of the heat exchanger.

[0058] The heat transfer medium can be any heat transfer medium known to a person skilled in the art that is suitable for steam generation. Suitable heat transfer media include, for example, water or organic liquids, such as butanediol. Water is the preferred heat transfer medium.

[0059] 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 evaporator, it is usually necessary to compress the steam to a higher pressure.

[0060] To compress the steam, preferably at least one compressor is arranged downstream of the evaporator.

[0061] The steam generated in the steam generation plant 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 steam generation plant. When feeding into a steam network or supplying a consumer for whom the temperature of the steam generated in the steam generation plant is too low, it is necessary to compress the steam. Direct supply to the consumers is preferred.

[0062] 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 that the pressure in the steam generation device is below that of low-pressure steam, at least in part 240384W001

[0063] 9 to further compress the low-pressure steam to medium-pressure steam and further compress at least a part of the medium-pressure steam to high-pressure steam.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] To generate low-pressure, medium-pressure, or high-pressure steam, a compressor or a compressor cascade can be used. A compressor cascade with at least two compressors, in which the steam is compressed in stages, or a compressor with multiple compressor stages, such as a geared turbo compressor, is preferred. A geared turbo compressor typically includes several compression stages and intermediate stages, with intercooling possible in the respective intermediate stages. Even when a compressor cascade with multiple compressors is used, it is advantageous to implement intercooling between the individual compressors.

[0068] 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.

[0069] 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.

[0070] For safe operation of steam generation and the at least one process to be cooled, the amount of heat transfer fluid flowing from the second container through the heat exchanger into the first container is regulated so that the temperature of the heat transfer fluid 240384W001

[0071] 10 Downstream of the heat exchanger, the temperature is within a predetermined setpoint range. The amount of heat transfer fluid flowing from the first tank through the second line into the second tank, and the pressure in the second tank, are regulated so that, depending on the fill level in the first tank, enough heat transfer fluid evaporates to ensure that the amount of vapor produced, which is taken from the second tank and fed to the compressor, remains within the compressor's operating limits. This shifts the load between the minimum and maximum load of the compressor, minimizing the frequency with which the compressor needs to be switched off.For example, it is possible to adjust the amount of steam extracted from the second container based on the fill level in the first container, so that when the fill level in the first container is high, as much steam as possible is generated and extracted, and when the fill level is falling, the amount of steam generated and extracted is reduced in order to be able to operate the compressor for as long as possible even if less or no heat is extracted from the process, before it has to be switched off because there is no longer enough heat transfer medium in the first container to be able to generate sufficient steam in the second container.

[0072] For control purposes, it is possible, for example, to provide a temperature controller that measures the temperature of the heat transfer fluid in the first line downstream of the heat exchanger. This temperature is then fed as a setpoint to a first flow controller, which, based on the temperature of the heat transfer fluid, adjusts the amount of heat transfer fluid flowing through the heat exchanger, for example, via a control valve.

[0073] A level controller monitors the fill level in the first tank. This fill level is fed as a setpoint to a load controller, which uses the fill level and the amount of steam required for safe compressor operation (which must be set within minimum and maximum limits) to calculate a setpoint for a second flow controller. Based on this calculated setpoint, the second flow controller regulates the heat transfer fluid flow from the first tank to the second tank. This ensures that the amount of steam generated remains within the compressor's operating limits and simultaneously guarantees the compressor's continuous operation, thus minimizing the frequency of shutdowns due to insufficient steam production.

[0074] Since compressors generally cope well with fluctuating flow rates but not with fluctuating pressures, it is preferable to provide a pressure regulator in order to keep the pressure of the steam supplied to the compressor, and thus the pressure and temperature in the second container, constant even with fluctuating steam volumes.

[0075] To adjust the pressure, the amount of steam drawn from the second vessel and the amount of fresh heat transfer fluid supplied to the process can be set. For this purpose, the pressure regulator sends a setpoint to a third flow regulator to adjust the amount of steam drawn from the second vessel and to a fourth flow regulator to adjust the amount of fresh heat transfer fluid supplied. When setting the pressure 240384W001

[0076] 11 However, care must be taken to ensure that the amount of steam taken from the second heat carrier does not fall below the minimum amount of steam required for the operation of the compressor and does not exceed the maximum amount of steam required for the safe operation of the compressor.Should this be the case, if too much steam is generated, it is necessary either to reduce the amount of heat transfer fluid that is pumped from the first container to the second container, or, if this is not possible, to divert some of the steam out of the process, or, if too little steam is generated and the amount of heat transfer fluid that can be transported from the first container to the second container cannot be increased, to switch off the compressor, or, if possible, to at least pump some of the steam back to the inlet of the compressor via a bypass from the compressor outlet, with the steam being expanded in the bypass so that the compressor can continue to operate and does not have to be switched off.

[0077] Exemplary embodiments of the invention are shown in the figures and are explained in more detail in the following description.

[0078] They show:

[0079] Figure 1 shows a simplified schematic representation of the device for utilizing waste heat,

[0080] Figure 2 shows a control concept for the device for utilizing waste heat.

[0081] Figure 1 shows a simplified schematic representation of a device for utilizing waste heat.

[0082] To utilize waste heat from a process, heat absorbed by a coolant in a cooling circuit 1 is transferred to a heat transfer medium, in particular water, in a heat exchanger 3.

[0083] Cooling circuit 1 is connected, for example, to an apparatus used in the process, such as a reactor, a column in which heat is released, a motor to be cooled, or a heat exchanger in which a material stream from the process is cooled.

[0084] The heat transfer fluid, which has absorbed heat from the process in the heat exchanger 3, is fed via a first line 5 to a first container 7. The first container 7 serves as a heat storage medium. To minimize the amount of heat released from the container to the environment, the first container 7 is thermally insulated.

[0085] To utilize the heat stored in the first container 7, a heat transfer fluid is fed via a second line 9 to an expansion device 11, where it is expanded to a pressure at which the heat transfer fluid partially evaporates. 240384W001

[0086] 12

[0087] The expansion element 11 can be positioned at any position in the second line 9, as shown here. Preferably, however, the expansion element 11 is positioned at the inlet to a second container 13, so that the heat transfer fluid expands and partially evaporates as it flows into the second container 13. In this case, the second container 13 acts as a flash apparatus.

[0088] In the second container 13, a gaseous phase and a liquid phase form. The gaseous phase is extracted as steam from the second container 13 via a steam line 15.

[0089] The liquid phase is extracted via the first line 5, compressed with a pump 17 and fed back to the heat exchanger 3 to absorb heat from the process again.

[0090] To prevent the temperature of the heat transfer fluid in the first container 7 from dropping due to the addition of cold heat transfer fluid when no heat is being released by the process (for example, if the process is a batch process or if heat is generated discontinuously during the process for any other reason), it is preferred that heat transfer fluid from the second container 13 is only returned to the first container 7 via the heat exchanger 3 when the process releases heat that is absorbed by the heat transfer fluid. As soon as the process ceases to release heat, the return of the liquid heat transfer fluid from the second container 13 is interrupted and only resumed when the process again releases heat.

[0091] The gaseous phase, which is extracted as steam from the second container 13 via the steam line 15, can be used directly if the steam pressure is sufficiently high to allow it to be used, for example, as a heat transfer medium for heating a material flow or a process. However, it is preferred to compress the steam to a higher pressure in at least one compressor 19. A cascade of at least two compressors or a single compressor with at least two compression stages is preferred, and it is further preferred to inject water into the compressed steam after each compressor or compression stage. This steam injection cools the steam and simultaneously increases the steam volume.

[0092] Since the amount of heat transfer fluid in the device decreases due to steam extraction, it is necessary to replace the extracted amount with fresh heat transfer fluid. The fresh heat transfer fluid is supplied via a supply line 20. Depending on the temperature of the fresh heat transfer fluid, the supply line can open into the first container 7 as shown here. If the fresh heat transfer fluid has a temperature lower than the temperature of the heat transfer fluid in the first container 7, it is preferred to feed the fresh heat transfer fluid either into the second container 13 or into the first line 5, with the feed point being determined by the heat transfer fluid pressure, either before or after the pump 17.

[0093] 13 of the pump 17. However, it is preferred to introduce the fresh heat transfer fluid either into the first container 7 as shown here or alternatively into the second container 13.

[0094] Figure 2 shows a control concept for the inventive method in connection with the use of the heat released during an exothermic chemical reaction.

[0095] The process, the heat from which is to be utilized according to the invention, comprises a reactor 21 to which several reactants are supplied. In the embodiment shown here, a first reactant 23 and a second reactant 25 are mixed in a mixer 27 and introduced into the reactor 21. Additionally, a third reactant 29 is supplied to the reactor 21.

[0096] If the reaction is carried out as a batch reaction, a reaction product 31 is withdrawn from reactor 21 after completion of the reaction, discharged from the process via an outlet line 33, and optionally subjected to further treatment, such as purification. During the reaction, the outlet line 33 remains closed, and the reaction product withdrawn from reactor 21 is cooled and returned to reactor 21 via a return line 35. Alternatively, the return line 35 can also lead into the mixer 27, and the reaction product can be introduced into the mixer 27 and mixed there with the first reactant 23 and the second reactant 25.

[0097] In addition to withdrawing the reaction product, it is also possible to withdraw a portion of the reaction product via outlet line 33 during the reaction itself. In this case, while a portion of the reaction product is withdrawn, the remaining reaction product is returned via return line 35.

[0098] Reactions that can be carried out in reactor 21 include, for example, polymerizations, neutralizations or oxidations.

[0099] For cooling, it is possible to feed all of the reaction product removed from reactor 21 and not discharged into heat exchanger 3 and cool it there by transferring heat to the heat transfer medium. If, after heat transfer in heat exchanger 3, the reaction product has a temperature higher than the temperature at which it is to be returned, it is possible to feed it into a further heat exchanger 37 and cool it there.

[0100] To continue the reaction when no heat is to be released in heat exchanger 3, for example, when steam generation is switched off, for instance for maintenance or repair, or when the first vessel 7 is completely full, it is also possible, as shown here, to cool and return all of the reaction product taken from reactor 21 and not discharged in the secondary heat exchanger 37. Depending on the temperature to which the reaction product is to be cooled and the amount of heat released in heat exchanger 3 and the secondary heat exchanger 37, it is also possible to feed only a portion of the reaction product into heat exchanger 3 and return it to the secondary heat exchanger 37.

[0101] 14

[0102] The cooling in heat exchanger 3 is mixed again with the part not supplied to heat exchanger 3 and then supplied to the further heat exchanger 37.

[0103] In addition to the variant shown here, it would also be possible to cool part of the reaction mixture in heat exchanger 3, cool the other part of the reaction mixture in the further heat exchanger 37, and combine the two parts again after cooling in heat exchanger 3 and in the further heat exchanger 37 respectively.

[0104] To ensure that the process continues to be cooled when the first container 7 is full and can no longer accept any more heat transfer fluid, the first container 7 is equipped with a level controller 39. Depending on the fill level in the first container 7, and thus the amount of heat transfer fluid that can still be added, a first valve 41 and a second valve 43 can be switched so that only a portion of the reaction product is passed through the heat exchanger 3 and the remainder through the second heat exchanger 37, or, if no more heat transfer fluid can be added to the first container 7, the entire reaction product is passed through the second heat exchanger 37 and no reaction product passes through the heat exchanger 3.

[0105] Additionally, a lower fill level in the first container 7 is preferably also detected in order to stop the withdrawal of heat transfer fluid when this level is reached. Depending on the position of the expansion device 11, it can, for example, also be closable, so that the expansion device 11 is closed to stop the withdrawal of heat transfer fluid from the first container 7. Alternatively, particularly if the expansion device is arranged directly at the inlet to the second container 13, it is preferred to provide an additional closing element, for example a valve or a tap, to close the second line 9 when no more heat transfer fluid is to be withdrawn from the first container 7. A pump 45 can be provided to pump the heat transfer fluid from the first container 7 to the second container 13.This is particularly necessary if the pressure difference between the first container 7 and the second container 13 is insufficient to ensure a sufficient mass flow of heat transfer fluid from the first container 7 to the second container 13.

[0106] In the first line 5, a first flow controller 47 measures the flow rate of the heat transfer fluid, and a third temperature controller 49 measures the temperature of the heat transfer fluid. The temperature allows the system to determine whether heat is being released from the process in the heat exchanger 3. Furthermore, the flow rate of the heat transfer fluid can be controlled in this way, so that the amount of heat transfer fluid can be adjusted depending on the amount of heat transferred in the heat exchanger 3, thus ensuring that the temperature of the heat transfer fluid supplied to the first container 7 remains essentially constant.

[0107] For example, if the amount of reaction product passing through heat exchanger 3 decreases, the temperature of the heat transfer fluid downstream of heat exchanger 3 decreases. 240384W001

[0108] 15 with the same flow rate of heat transfer fluid. Therefore, to heat the heat transfer fluid to a higher temperature, it is necessary to reduce the amount of heat transfer fluid flowing through the heat exchanger 3 and, if no heat is generated in the process, for example, if no reaction product is produced in the batch process, no heat transfer fluid should be directed through the heat exchanger 3 from the second container 13 to the first container 7. Conversely, if the flow rate of reaction product increases and thus the temperature of the heat transfer fluid rises, the mass flow rate must be increased. To adjust the mass flow rate of the heat transfer fluid passing through the heat exchanger 3, a third valve 51 can be provided in the first line 5, as shown here.Since the third temperature controller 49 measures the temperature of the heat transfer fluid and is therefore not detected when a new batch process starts and heat is again released from the process, it is necessary to initiate a standard start sequence when heat is generated again in the process and reaction product to be cooled is supplied to the heat exchanger 3. For this purpose, it is possible, for example, to provide a recirculation flow through the heat exchanger 3 via a bypass, so that any temperature change in the heat transfer fluid is detected and, as soon as this occurs, regular operation is restarted. Alternatively, it would also be possible, for example, to send a signal to the pump 17 to restart the flow of the heat transfer fluid through the heat exchanger 3 when reaction medium flows into the heat exchanger 3 again through the first valve 41.

[0109] The fill level in the first tank 7 determines the amount of energy available for steam generation. A rising fill level in the first tank 7 means that more heat has been stored and therefore more steam can be generated. A second level controller 40 sets a setpoint for a load controller 53, whereby the setpoint can vary based on the minimum and maximum steam quantities that can be processed by the compressor 19. The current load value is calculated from the current steam flow to the compressor 19. If the currently calculated load is below the setpoint received from the level controller 39, the load controller 53 increases the setpoint for a second flow controller 55, which controls the flow from the first tank 7 to the second tank 13 via the valve 11.Increasing the flow rate from the first tank 7 to the second tank 13 transfers more energy from the first tank to the second tank, thus affecting the pressure in the second tank 13. To maintain a constant pressure in the second tank 13, the steam flow 15 is manipulated. If the pressure rises above a setpoint, a pressure regulator 63 increases the setpoint for a third flow regulator 65, which controls the steam flow to the compressor 19 via a fourth valve 67. A fourth flow regulator 69 for fresh water supplied via the supply line 20 receives the same setpoint from the pressure regulator 63 to compensate for the amount of water withdrawn via the steam line 15. For this purpose, the fourth flow regulator 69 controls a fifth valve 71.

[0110] Should the amount of steam generated in the second container 13 be less than the minimum amount required by the compressor 19, a bypass 73 can be provided for continuous operation of the compressor 19, through which more compressed steam is returned to the 240384W001

[0111] 16

[0112] Steam line 15 is routed to the suction side of compressor 19 to increase the total amount of steam compressed in compressor 19. For this purpose, an expansion device, such as a throttle, is incorporated in bypass 73 to expand the recirculated steam. The steam mass flow rate taken downstream of the branch of bypass 73 on the pressure side of compressor 19 corresponds to the steam mass flow rate taken from the second tank 13. The pressure of the steam supplied to compressor 19 can also be regulated via bypass 73. This is achieved by controlling the expansion device in bypass 73 via pressure regulator 63. The mixing of the steam recirculated via the bypass and the steam taken from the second tank 13 results in the required pressure for supply to compressor 19.Furthermore, to avoid excessively frequent shutdowns of compressor 19, it is also possible to return all compressed steam via the bypass if no steam can be generated in the second vessel 13. In this case, however, particularly if it is foreseeable that no steam can be generated for an extended period, for example, during a longer break between two batches, it is preferable to switch off compressor 19 if possible. In order to operate the compressor for as long as possible even when no heat is generated in the process, the first vessel 7 and the second vessel 13 are preferably dimensioned such that sufficient heat transfer fluid is available even during a typical break between two batches to enable continuous steam generation.

[0113] To monitor the process, it is further advantageous if, as shown here, the temperature in the first container 7 is recorded with a first temperature sensor 59 and the temperature in the second container 13 is recorded with a second temperature sensor 61.

[0114] In addition to the direct compression of the steam taken from the second container 13, as shown in Figures 1 and 2, it is also possible to omit a compressor 19, so that the steam is drawn from the second container 13 at the pressure at which it is taken and supplied for its intended use. If the temperature of the drawn steam is sufficiently high for the intended use, compression can be omitted. Alternatively, it is also possible to compress the steam directly in the process in which it is to be used. If the steam taken from the second container 13 is not compressed, it is still necessary to regulate the pressure in the second container 13 to maintain a constant temperature. In this case, pressure regulation is preferably achieved via a valve in the steam extraction line.

Claims

240384W001 17 Patentansprüche 1. Device for utilizing waste heat comprising at least one heat exchanger (3) for transferring heat from a process to a heat transfer medium which is heated in the heat exchanger (3) but does not evaporate, a first container (7) for storing the heat transfer medium at a first temperature and a second container (13) for storing the heat transfer medium at a second temperature, wherein the first temperature is higher than the second temperature, wherein the heat exchanger is accommodated in a first line (5) connecting the second container to the first container and an expansion device (11) is accommodated in a second line (9) connecting the first container (7) to the second container (13), wherein a pump (17) is further accommodated in the first line (5) with which the fluid can be compressed and conveyed from the second container (13) to the first container (7).and the second container (13) includes a steam line (15) for steam extraction.

2. Device according to claim 1, characterized in that at least one compressor (19) is included in the steam line (15).

3. Device according to claim 1 or 2, characterized in that the second container (13) is a flash container and the expansion element (11) is arranged at the inlet to the flash container.

4. Device according to one of claims 1 to 3, characterized in that more than one heat exchanger (3) is incorporated in the first line (5), wherein heat can be transferred from a process to the heat transfer medium in each of the heat exchangers (3).

5. Device according to claim 4, characterized in that the heat exchangers (3) are connected in such a way that the heat transfer medium flows through at least two heat exchangers (3) in series.

6. Device according to claim 4 or 5, characterized in that the heat exchangers (3) are connected in such a way that the heat transfer medium flows through at least two heat exchangers (3) in parallel.

7. Method for utilizing waste heat with a device according to any one of claims 1 to 6, comprising: (a) Transferring heat from the process to the heat transfer medium in the heat exchanger (3), whereby the heat transfer medium is heated but not evaporated; (b) Feeding the heated heat transfer medium into the first container (7); 240384W001 18 (c) Extraction of heat transfer fluid from the first container (7) and expansion of the heat transfer fluid extracted from the first container (7) so that the heat transfer fluid is partially evaporated and a liquid phase and a gaseous phase are obtained, wherein the heat transfer fluid is expanded in an expansion device (11) in the second line (9) or upon entry into the second container (13); (d) Separating the liquid phase and the gaseous phase in the second container (13); (e) Extraction of the gaseous phase as steam via the steam line (15).

8. Method according to claim 7, characterized in that the steam taken from the second container (13) is compressed in at least one compressor (19).

9. Method according to claim 7 or 8, characterized in that the second container (13) is a flash apparatus and the heat transfer medium expands upon entering the second container (13) and is partially evaporated.

10. Method according to one of claims 7 to 9, characterized in that the liquid phase from the second container (13) is returned to the first container (7) through the heat exchanger (3), wherein the return of the heat transfer medium from the second container (13) to the first container (7) is preferably interrupted when the process does not release any heat.

11. Method according to one of claims 7 to 10, characterized in that the process comprises a cooling circuit (1) in which a coolant flows which absorbs heat from the process and the coolant subsequently releases the heat to the heat transfer medium in the heat exchanger (3).

12. Method according to one of claims 7 to 10, characterized in that a cooling circuit (1) is included through which a coolant flows which absorbs heat from several processes and then releases this heat to the heat transfer medium in the heat exchanger (3).

13. Method according to one of claims 7 to 12, characterized in that the heat transfer medium is water.

14. A method according to any one of claims 7 to 13, characterized in that the process comprises a chemical reaction, cooling of a material stream or cooling of an apparatus.

15. Method according to one of claims 7 to 14, characterized in that the quantity of heat transfer medium that flows from the second container (13) through the heat exchanger (3) into the 240384W001 19 first container (7) is regulated so that the temperature of the heat transfer fluid downstream of the heat exchanger (3) has a temperature within a predetermined setpoint range and that the quantity of heat transfer fluid flowing from the first container (7) through the second line (9) into the second container (13) and the pressure in the second container (13) are regulated so that the fill level in the first container (7) remains within a predetermined setpoint range and, upon entering the second container (13), so much heat transfer fluid evaporates that the quantity of vapor produced, which is taken from the second container (13) and supplied to the compressor (19), is within the operating limits of the compressor (19).

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