Method for using waste heat from industrial processes

Abstract

The invention relates to a method for using waste heat from industrial processes, comprising: (a) transferring heat from at least two processes to a temperature-control medium; (b) supplying the temperature-control medium to a heat pump or to a heat-pump park comprising at least two heat pumps; (c) transferring heat from the temperature-control medium to a working medium in a heat exchanger of at least one heat pump and / or using the heat from the temperature-control medium for the desorption of refrigerant in an absorption heat pump.

Description

[0001] Methods for utilizing waste heat from industrial processes

[0002] Description

[0003] The invention relates to a method for utilizing waste heat from industrial processes.

[0004] In many industrial processes, heat must be dissipated for cooling. This is typically achieved using heat exchangers, in which heat from the process is transferred to a coolant. Depending on the type of process and the amount of heat to be dissipated, cooling water, for example, is used.

[0005] Currently, the coolant used, especially cooling water, is cooled after passing through the heat exchanger, for example in a coolant cooling system, an air cooling system, or a cooling tower. This process removes the heat transferred to the coolant, which is not utilized. In many cases, the temperature of a single process is not high enough for efficient and effective use of the waste heat, or insufficient heat is removed from the process to allow for efficient and effective utilization.

[0006] To utilize heat from material flows with comparatively low temperatures, it is known to use heat pumps.

[0007] For heating or cooling large structures, it is known from WO-A 2023 / 149878 to connect a stratified storage tank to a heat pump in order to supply heat to the stratified storage tank. This heat is extracted from the water contained in the stratified storage tank for heating the structure. The heat required for operating the heat pump can be extracted, for example, from the ambient air or a body of water, or it can also originate from waste heat.

[0008] An energy circuit for heating and / or cooling buildings in a city district is described in US Patent 2012 / 0279681. For this purpose, the buildings are connected to the energy circuit to extract heat for heating or to supply heat for cooling. To maintain thermal equilibrium in the energy circuit, it is connected to at least one source from which heat can be supplied or removed. This source could be, for example, a heat pump or multiple heat pumps utilizing geothermal energy.

[0009] A network with two heat stations, each supplying heat to consumers, is known from US Patent 2013 / 0299126. The first heat station provides heat for residential or commercial buildings, and the second heat station supplies heat for industrial use. If heat is released, for example during cooling, it is fed back into the respective heat station. Both heat stations are connected to a heat source. The heat stations provide a base load, and heat can also be transferred between them. To provide this base load, each heat station includes a heat pump and a heat storage unit.

[0010] German patent DE-U 296 06 696 describes a thermal storage tank for a heating system. The thermal storage tank is heated by external heat sources, for example solar energy, process waste heat or heat pumps.

[0011] However, none of the known processes are suitable for utilizing waste heat from industrial processes where only small amounts of heat are released or where the cooling medium that absorbs the released heat has only a low temperature.

[0012] Especially when the heat is to be used for steam generation, which is to be used as an energy carrier in industrial processes, for example for heating, the use of heat from low-temperature material flows or from processes in which only small amounts of heat are released is not very effective and efficient.

[0013] The object of the present invention was therefore to provide a method in which the waste heat from industrial processes, in particular from processes in which only a little waste heat is generated or in which the coolant used for cooling is only heated to a small degree, can be used effectively and efficiently.

[0014] This problem is solved by a process for utilizing waste heat from industrial processes, comprising:

[0015] (a) Transferring heat from at least two processes to a temperature control medium;

[0016] (b) Supply of the temperature control medium to a heat pump or a heat pump park with at least two heat pumps;

[0017] (c) Transferring heat from the temperature control medium to a working fluid in a heat exchanger of at least one heat pump and / or using the heat from the temperature control medium for the desorption of refrigerant in an absorption heat pump.

[0018] Unlike known industrial processes where the waste heat from a process stage is used for heat integration within the same process, or where the heat from a process stage is used directly in a heat pump, transferring heat from at least two processes to a temperature control medium allows for the utilization of waste heat from processes that generate only small amounts of heat or where the coolant used for heat dissipation is only heated to a temperature too low for conventional heat integration. Industrial processes within the scope of the present invention are all processes involved in the mass production of goods using standardized production methods. In particular, processes that include thermal processes or that generate heat due to high speeds require cooling to operate stably.Thermal processes include thermal separation processes such as distillation, rectification, evaporation, condensation, absorption, adsorption, extraction, crystallization, and chemical reactions, particularly oxidations. Even in processes that require heat input, it is necessary to cool at least some of the material streams. These processes typically comprise several stages, with heat being added or removed depending on the individual stage. Distillation, rectification, and evaporation processes, in particular, require both the input of heat to carry out the process and the removal of heat for cooling and condensation of the vaporized material stream.

[0019] The inventive method is particularly suitable for utilizing waste heat from industrial processes in which the temperature of the coolant increases by a maximum of 40 K, more preferably by 5 to 35 K, and particularly by 15 to 25 K. If water is used as the coolant, this means that no more than 170 MJ per m³ of coolant is required to cool the process stage or process. 3 Coolant, preferably 20 to 150 MJ per m³ 3 Coolant and in particular 63 to 105 MJ per m³ 3 Coolant is absorbed. Furthermore, the process is particularly suitable when only a small coolant flow is required for cooling. A small coolant flow is defined as one so small that the heat cannot be efficiently used for heat generation in a heat pump or heat pump system. Typically, such a coolant flow is no greater than 340 m³. 3 / h, preferably in the range of 20 to 250 m 3 / h and especially 50 to 150 m 3 / h.

[0020] By transferring heat from at least two processes to a temperature control medium, it is possible to utilize the heat generated in processes or process stages that produce little waste heat and which is currently being discharged unused.

[0021] To transfer the heat generated in a process to the temperature control medium, the medium can be used as a coolant in a heat exchanger within the process. If at least one material stream is cooled in the process, the temperature control medium can be used directly to cool that stream. In this case, the material stream releases heat to the temperature control medium in the heat exchanger. Alternatively, the temperature control medium can flow through the equipment being cooled within the process, absorbing heat from it. Examples of such equipment include reactors, motors, control units that emit heat, or other directly cooled devices or apparatus.

[0022] Regardless of whether a material flow or an apparatus is being cooled in the process, it is alternatively possible to use a separate temperature control medium for cooling the material flow or the apparatus. In this case, the separate temperature control medium used for cooling is preferably circulated in a loop, so that the absorbed heat must also be dissipated to enable a continuous process. It is preferred in this case that the temperature control medium absorbs heat from the separate temperature control medium in a heat exchanger, with the separate temperature control medium being used as a coolant in a heat exchanger within the process.

[0023] Any temperature control medium known to those skilled in the art is suitable as a heat transfer medium to which heat from at least two processes is transferred. Preferably, a heat transfer medium is used that remains liquid when absorbing heat from the at least two processes. Suitable heat transfer media include, for example, water, mixtures of water with an alcohol, such as water-glycol mixtures. Water is particularly preferred as a heat transfer medium to which heat from at least two processes is transferred.

[0024] If an additional cooling medium is used in a process stage to cool the material stream or equipment, and this medium acts as a coolant, any coolant suitable for cooling a material stream or equipment can be used. Suitable options include coolants that do not change their phase and coolants that evaporate upon absorbing heat from the material stream or equipment being cooled. Suitable gaseous coolants include, for example, air, nitrogen, or carbon dioxide, with carbon dioxide preferably being used in its supercritical state.Suitable liquid coolants include, for example, water, water-glycogen mixtures or heat transfer oils, and suitable coolants that evaporate by absorbing heat include, for example, cyclopropane, cyclobutene, ethane, propane, isobutane, n-butane, neopentane, propadiene, cis-butene, trans-butene, isobutene, 1,3-butadiene, propyne, 1-butyne, dimethyl ether, ammonia, R151A, R1224yd(Z), R40, R1233zd(E), R1234ze(Z), R245cb2, R152a, R134A and mixtures of at least two of these coolants.

[0025] Any heat exchanger suitable for indirect heat transfer—that is, heat transfer from one fluid stream to another across a wall separating the fluid streams—can be used to transfer heat to the temperature control medium. Examples of suitable heat exchangers include shell and tube heat exchangers, plate heat exchangers, and spiral heat exchangers.

[0026] To absorb heat from more than one process, the temperature control medium can flow through several heat exchangers in series, each transferring heat from a specific process or process stage to the temperature control medium. When the heat exchangers are connected in series, it is important to ensure that the sequence is chosen so that the temperature difference between the incoming temperature control medium and the material stream to be cooled is sufficiently large to allow the material stream to be cooled to the required temperature.

[0027] To ensure that the temperature control medium can absorb sufficient heat from the individual processes or process stages, particularly when the processes or process stages are operated at similar temperatures and thus the material streams to be cooled have a similar temperature, preferably differing by no more than 15 K, more preferably by no more than 8 K, and especially by no more than 3 K, it is advantageous if the heat exchangers in which the heat is transferred to the temperature control medium are connected in parallel. Depending on the inlet temperature to the individual heat exchangers and the outlet temperature of the temperature control medium from the individual heat exchangers, it is of course also possible for the heat exchangers to be connected in series with the temperature control medium flowing through them, even if the material streams to be cooled have a similar temperature.

[0028] If the heat exchangers, in which heat is transferred to the temperature control medium, are connected in parallel, it is further preferred if cold temperature control medium flows from a distribution line into the heat exchangers and heated temperature control medium flows from the heat exchangers into a collecting line and the heated temperature control medium is supplied to the heat pump or the heat pump system.

[0029] Regardless of whether the heat exchangers are connected in parallel or in series, it is still preferred if the temperature control medium flows through a ring main, so that the temperature control medium first absorbs heat from the processes, then transfers it to the heat pump or heat pumps in the heat pump park and then absorbs heat from the processes again.

[0030] If the heat exchangers are connected in parallel, it is further preferred if the distribution line and the collection line form the ring line, wherein the distribution line is connected to the collection line downstream of a supply line branching off into a last heat exchanger from the distribution line and upstream of a line from the last heat exchanger that leads into the collection line.

[0031] In addition to connecting heat exchangers in parallel or in series, it is of course also possible to connect some of the heat exchangers in series and others in parallel. If some of the heat exchangers are connected in series and others in parallel, the parallel heat exchangers can be connected to the series-connected ones, or vice versa. Alternatively, it is also possible to arrange at least one group of parallel-connected heat exchangers between heat exchangers connected in series. If heat exchangers connected in series are located upstream of heat exchangers connected in parallel, the series-connected heat exchangers are located in the distribution line before a supply line branches off to the first of the parallel-connected heat exchangers.Heat exchangers connected in series and arranged downstream of heat exchangers connected in parallel can either be located in the ring main before the first outlet pipe of one of the parallel heat exchangers enters the manifold, or the heat exchangers connected in series can either be located between outlet pipes of parallel heat exchangers in the manifold, or the heat exchangers connected in series are located downstream of the last outlet pipe of the parallel heat exchangers that enters the manifold.Furthermore, it is also possible that at least one heat exchanger is arranged in the distribution line between two supply lines branching off from the distribution line to parallel connected heat exchangers and / or at least one heat exchanger is arranged in the collecting line between two outlet lines of parallel connected heat exchangers that open into the collecting line.

[0032] If the temperature control medium is supplied to a heat pump park with at least two heat pumps, it is possible that all heat pumps in the heat pump park are used for one purpose, or that at least two heat pumps in the heat pump park are used for different purposes.

[0033] One possible application for which the heat pumps of the heat pump park or even the individual heat pump can be used is the production of steam, which can be used, for example, as an energy carrier for heating processes, whereby the steam can be low-pressure steam, medium-pressure steam or high-pressure steam.

[0034] 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.

[0035] 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, preferably in the range of 147 to 210°C and particularly in the range of 151 to 200°C.

[0036] High-pressure steam within the scope of the present invention is steam with a pressure in the range of 8 bar(abs) 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.

[0037] A compressor or a compressor cascade can be used to generate medium-pressure or high-pressure steam, with a compressor cascade having at least two compressors in which the steam is compressed in stages being preferred. The compressor cascade makes it particularly possible to first compress the steam to the pressure of medium-pressure steam, extract the portion to be used as medium-pressure steam, and then further compress the remaining steam to high-pressure steam.

[0038] To regulate the steam temperature, which is typically increased so significantly due to the energy input during compression that the steam becomes highly superheated and therefore usually too hot for feeding into a steam network or for further compression in a subsequent compressor stage, and to increase the steam volume, it is preferred to add additional water to the compressed steam. Injecting the additional water lowers the steam temperature to the desired temperature while simultaneously increasing the steam volume. When using multiple compressors, additional water can be added downstream of one or more compressors. It is particularly preferred that the additional water is added downstream of each compressor with the longest possible inlet section. The water is preferably sprayed into the compressed steam to accelerate its evaporation and prevent droplet streaks.

[0039] In addition to generating steam, or as an alternative to generating steam, it is also possible and preferred that at least one heat pump is used to heat and / or evaporate, in particular heat, water for a district heating network. Buildings, such as residential or office buildings, can be efficiently heated via the district heating network. Furthermore, the district heating network can also supply the necessary heat for hot water preparation in residential and office buildings.

[0040] Heat pumps used for steam generation or water heating can be closed-loop or open-loop heat pumps.

[0041] Closed-loop heat pumps comprise a closed circuit for a working fluid that is evaporated in a first heat exchanger by heat transfer from the temperature control fluid. The evaporated working fluid is then compressed in a compressor and, in a second heat exchanger, releases heat to water, primarily through condensation. The water is thus heated or at least partially evaporated. After heat transfer, the working fluid expands again and is then returned to the first heat exchanger. Particularly when steam is to be generated, it is preferred that the water evaporates completely in the second heat exchanger.

[0042] In an open-vented heat pump, water is used as the working medium. The water is heated directly in a heat exchanger by heat transfer from the temperature control fluid, then fed to a flash unit where it partially evaporates. Alternatively, it is at least partially evaporated in the heat exchanger by heat transfer from the temperature control fluid. If only partially evaporated, the water is then separated into liquid water and steam in a phase separator. In either case, the steam can then be further compressed in at least one compressor as described above.

[0043] When using a closed-loop heat pump, it is alternatively possible to heat the water for steam generation in the second heat exchanger and then expand it in a flash steam generator. In this process, the water must be expanded to a pressure at which some of it evaporates. The steam can then be extracted from the flash steam generator and compressed to the desired pressure in at least one compressor. The unevaporated water is preferably returned to the second heat exchanger for heating. If some of the water evaporates in the second heat exchanger, the partially evaporated water can be fed to a phase separator, where the steam is separated from the liquid, unevaporated water. The steam can then be compressed to the desired pressure in at least one compressor as described above, and the unevaporated water is preferably returned to the second heat exchanger.

[0044] Besides generating steam or heating water, it is also possible to heat or evaporate any other heating medium in the heat pump. The heating medium can be selected depending on the intended application, i.e., the process to be heated. Suitable heating media besides water include, for example, water-alcohol mixtures, especially water-glycogen mixtures, or heat transfer oils. Processes that are heated with the heating medium or, alternatively, with the steam generated in the heat pump, include distillations, rectifications, desorptions, regeneration steps of adsorptions, stripping processes, and / or the thermal dissolution of solids / crystals.

[0045] If at least one heat pump is used to heat water, the water can be used, for example, to heat at least one building and / or at least one pipe. The pipe can be any pipe carrying a medium that flows through it at a minimum temperature. Alternatively, the heated water can also be used to heat a water pipe, for example, to prevent the water in the pipe from freezing.

[0046] In addition to heat pumps that are used to heat or evaporate water or a heating medium, it is also possible that at least one heat pump is an absorption heat pump for generating cold.

[0047] Conventional absorption heat pumps operate, for example, on the basis of a water-lithium bromide process or a water-ammonia process. With the water-lithium bromide process, absorption heat pumps can achieve a cooling temperature of +5 °C, making this technology particularly suitable for building cooling. Using water-ammonia technology, absorption chillers can reach -10 °C; in a cascade installation, temperatures as low as -30 °C can be achieved if the waste heat is at a level above 90 °C. This allows them to enter the application range of compression chillers, which, depending on the refrigerant, can operate well into the double-digit sub-zero range (°C).

[0048] In the context of the present invention, a heat pump system is understood to be an area on which at least two heat pumps are arranged. These heat pumps obtain the heat required for their operation from the temperature control medium to which heat has been transferred from at least two processes. For this purpose, the heat pumps can be arranged such that the first heat exchangers of each heat pump, in which the temperature control medium releases heat, are connected in series or in parallel. A combination of heat exchangers connected in series and in parallel is also possible, in which case the heat exchangers of the process stages in which heat is transferred to the temperature control medium can be connected as described above. A series connection of the heat pump heat exchangers is particularly advantageous when the heat pumps are used for different applications at different temperatures.This means, for example, that steam at different temperatures is generated in the heat pumps, or that, for example, one heat pump is used for steam generation and another for heating water. However, it is preferable to connect the heat exchangers of the heat pumps, in which the temperature control fluid transfers heat to the working fluid, in parallel, whereby the flow rate of the temperature control fluid supplied to the respective heat exchanger can be adjusted for different heat requirements in different heat pumps.

[0049] In addition to the use of heat pumps with a single heat exchanger, as described above, in which heat is transferred from the temperature control medium to the working fluid, it is also possible to use heat pumps that include more than one, preferably two, evaporators. In this case, the entire working fluid is heated to a first temperature in a first evaporator and at least partially evaporated. After evaporation, the working fluid is split into a liquid and a gaseous stream, and the gaseous stream is compressed in a compressor, thereby being heated further. The liquid stream is fed to a second evaporator and at least partially evaporated there as well.If more than two evaporators are included, after each evaporator except the last, the working medium is split into a liquid and a gaseous partial stream. The gaseous partial stream is compressed and further heated by the compression, while the liquid partial stream is fed to a subsequent evaporator. In the last evaporator in the series, the supplied liquid partial stream is completely evaporated, and the working medium exiting the last evaporator is completely compressed and further heated in the process. The use of two evaporators is particularly preferred. When using two evaporators, it is further preferred that the liquid partial stream exiting the first evaporator is evaporated and superheated at a higher temperature in the second evaporator, thus generating higher-pressure vapor. In this way, compression energy can be saved in the compressor for compressing the vapor exiting the second evaporator.

[0050] Preferably, the size of each partial flow is selected such that the working fluid of each partial flow has the same pressure and substantially the same temperature after compression. After compression, the individual partial flows are recombined and then fed into a heat exchanger, where heat is transferred from the working fluid to a water flow. The working fluid typically condenses at least partially during this process. The working fluid exiting the heat exchanger is then expanded and fed back to the first evaporator. In such a series connection of several evaporators of a heat pump for the working fluid, it is possible for the evaporators for the temperature control fluid to be connected in parallel or in series. In a series connection of the evaporators for the temperature control fluid, it is particularly preferred if the temperature control fluid and the working fluid flow counter-currently through the heat exchangers.The efficiency of the heat pump can be increased by such a multi-stage, particularly two-stage, evaporation of the working fluid. The at least two industrial processes whose waste heat is utilized can be carried out at different locations or at the same location. For economic reasons and to keep pipelines as short as possible, it is preferable for the industrial processes to be carried out at the same location.

[0051] The term "at different locations" is understood to mean that the locations are separated from each other by a non-industrially used area, for example, by agricultural or forestry land, towns, a river, or nature reserves. Industrial processes that are carried out at separate and demarcated locations, where the locations are separated from each other only by a road, for example, are understood within the scope of the present invention to be "carried out at the same location".

[0052] The term "at the same location" specifically includes integrated sites where several industrial processes of one company or even of different companies are carried out, but are located on a contiguous site. Such integrated sites are particularly common among companies in the chemical industry, known as chemical integrated sites.

[0053] In this context, an "industrial site" is understood to be a contiguous area where one or more industrial processes are carried out, for example, a combined production site, particularly a chemical production site. In contrast to an industrial site, a commercial site or industrial park is an area where businesses are located that do not manufacture goods on an industrial scale. Examples include craft businesses, office buildings, shopping centers, and other service providers.

[0054] In order to minimize pipe lengths, especially for conveying the temperature control medium from the industrial processes to the heat pump or heat pump park, and thus reduce line losses, it is preferred if the at least two processes are carried out at one industrial site.

[0055] If the temperature control medium is used as a heat transfer medium for only one heat pump, it is preferable if the heat pump is located at the same industrial site where the processes are carried out whose heat is transferred to the temperature control medium.

[0056] When the temperature control medium is supplied to a heat pump system, the heat pump system may be located either outside the industrial site or within the industrial site. If the heat pump system is located within the industrial site, it is particularly preferable that it forms a self-contained unit. In particular, if the heat pumps of the heat pump system provide steam for operating processes at the site, it is preferable for the heat pump system to be located either at the same industrial site or in the immediate vicinity of the industrial site where the processes are carried out.

[0057] If the heat pump or heat pump system is located outside the industrial site, it is preferable for the heat pump or heat pump system to be connected to the industrial site only via a first line for transporting the cold temperature control medium and a second line for transporting the heated temperature control medium, provided that no steam or heated water generated by the heat pumps is required at the industrial site. Connection to the industrial site via only the first and second lines is therefore particularly suitable if the heat pump system generates water or steam for district heating, for example, for commercial or residential areas.The coupling via the first and second lines has the advantage that simple connection is possible in this way and that, in particular, it is possible to install additional heat pumps or to decommission already installed heat pumps if necessary, for example if the purposes of use change, such as if more or less steam is needed to heat processes or if the area heated by district heating changes, for example by supplying additional buildings with district heating.

Claims

Patent claims 1. Methods for utilizing waste heat from industrial processes, comprising: (a) Transferring heat from at least two processes to a temperature control medium; (b) Supply of the temperature control medium to a heat pump or a heat pump park with at least two heat pumps; (c) Transferring heat from the temperature control medium to a working fluid in a heat exchanger of at least one heat pump and / or using the heat from the temperature control medium for the desorption of refrigerant in an absorption heat pump.

2. Method according to claim 1, characterized in that at least two heat pumps of the heat pump park are used for different purposes.

3. Method according to claim 1 or 2, characterized in that at least one heat pump is used for heating and / or evaporating water for a district heating network.

4. Method according to one of claims 1 to 3, characterized in that at least one heat pump is an absorption heat pump for generating cold.

5. Method according to one of claims 1 to 4, characterized in that at least one heat pump is used to heat water with which at least one building is heated and / or at least one pipe is heated.

6. Method according to one of claims 1 to 5, characterized in that the temperature control medium is used as a coolant in a heat exchanger of a process.

7. Method according to one of claims 1 to 6, characterized in that the temperature control medium in a heat exchanger absorbs heat from a further temperature control medium, wherein the further temperature control medium is used as a coolant in a heat exchanger of the process.

8. Method according to one of claims 1 to 7, characterized in that the heat exchangers in which heat is transferred to the temperature control medium are connected in parallel, wherein cold temperature control medium flows from a distribution line into the heat exchangers and heated temperature control medium from the heat exchangers into a collecting pipe and the heated temperature control medium is fed to the heat pump or heat pump park.

9. Method according to claim 8, characterized in that the distribution line and the collection line form a ring line, wherein the distribution line is connected to the collection line downstream of a supply line branching off from the distribution line into a last heat exchanger and upstream of a line from the last heat exchanger opening into the collection line.

10. Method according to one of claims 1 to 9, characterized in that the temperature control medium is water.

11. Method according to one of claims 1 to 10, characterized in that the at least two processes are carried out at an industrial site.

12. Method according to claim 11, characterized in that the heat pump or heat pump park is coupled to the industrial site only via a first line for transporting the cold temperature control medium and a second line for transporting the heated temperature control medium.

13. Method according to claim 11 or 12, characterized in that the heat pump park is located outside the industrial site.

14. Method according to claim 11 or 12, characterized in that the heat pump park is arranged as a self-contained unit within the industrial site.