System for waste heat recovery from a gaseous stream

Abstract

The invention pertains to a system for waste heat recovery from a gaseous stream, wherein the system comprises: a waste heat valorisation tower having a first inlet for entering said gaseous stream; a second inlet for entering a stream of a first liquid loop; a means for contacting said gaseous stream with said first liquid loop stream such that heat passes from said gaseous stream to said first liquid loop stream; a first outlet for carrying out said gaseous stream; and a second outlet for carrying out said stream of said first liquid loop; at least one heat pump, the low-temperature heat exchanging side of which is connected to said tower via at least said first liquid loop; and at least one first heat exchanger, which is connected to the high-temperature heat exchanging side of said at least one heat pump, via at least a second liquid loop.

Description

[0001] SYSTEM FOR WASTE HEAT RECOVERY FROM A GASEOUS STREAM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of recovery of waste heat, more in particular recovery of waste heat from a gaseous stream. The present invention further relates to a method for use in same and to the use of a waste heat valorisation tower for said waste heat recovery.

[0004] BACKGROUND OF THE INVENTION

[0005] Drying processes on an industrial scale are known to require massive amounts of heat. In fact, drying is known to be one of the most energy-consuming operations in industrial plants.

[0006] Processes containing drying steps are part of many chemical or industrial processes and comprise more in particular the preparation or fabrication of food products, grains, biomass, pharmaceuticals, wood and textile. In particular with regard to food products, drying is used to inhibit microbial growth.

[0007] Drying processes typically require a source of heat and an agent to remove the vapor produced during the process. In direct or convective drying, a gaseous stream such as air is applied by convection to a solid substance and carries away moisture from said solid substance in the form of humidity. Heating solid matter by air has been found to reduce the air humidity around the solid and to accelerate drying. As the solid matter heats up, the higher temperatures speed up diffusion of water from the interior of the solid to its surface. Typically, the gaseous stream, e.g. air, has an increased moisture level and an increased temperature when exiting a drying oven as compared to entry of said oven. The heat carried away by the gaseous stream has a lot of condensation energy which is typically dissipated in the environment, possibly after passage in a heat exchanger, while the gaseous stream may be returned at least partly to an inlet of the drying oven via a loop circuit. Such configurations typically result in a significant loss of waste heat. With energy prices skyrocketing at the time of the invention and in view of the continuous effort to reduce the carbon footprint of industrial processes, there is a need for recovering a maximum attainable level of waste heat. One particular industry in which drying processes play a critical role is in the malting of grains, such as barley. Typically, malting of grains comprise the steps of steeping, germinating and drying grain to convert it into malt. It is known that the main carbon emissions in a malting plant are caused by the drying process, or kilning process, in which the green malt is dried from a state of having a high initial moisture content, typically 40-44%, to a dried state of having a lower moisture content of about 4.5 % humidity. This is generally done by spreading the grain kernels over a surface, typically in trays in a kiln or heat chamber, where it is ventilated by large quantities of heated air. Such air is typically heated by use of fossil fuels.

[0008] Based on the above, there therefore is a need for a system to recover waste heat from an industrial process comprising a gaseous stream containing waste energy, e.g. in the form of condensation energy, wherein said gaseous stream may be a product stream from a drying process, wherein a maximum of waste heat can be recovered or recuperated, and wherein said system uses a minimum of energy to obtain such waste heat recovery.

[0009] SUMMARY OF THE INVENTION

[0010] The inventors have surprisingly found that the system and method according to the present invention fulfills the above mentioned needs and overcomes the above mentioned disadvantages.

[0011] In an aspect of the present invention, there is provided a system for waste heat recovery from a gaseous stream, the system comprising:

[0012] A waste heat valorisation tower having a first inlet for entering said gaseous stream; a second inlet for entering a stream of a first liquid loop; a means for contacting said gaseous stream with said stream of said first liquid loop such that heat passes from said gaseous stream to said stream of said first liquid loop; a first outlet for carrying out said gaseous stream; and a second outlet for carrying out said stream of said first liquid loop;

[0013] At least one heat pump, the low-temperature heat exchanging side of which is operably connected to said waste heat valorisation tower via at least said first liquid loop; At least one first heat exchanger, which is each operably connected to the high-temperature heat exchanging side of one or more heat pump of said at least one heat pump, via at least a second liquid loop.

[0014] It is an advantage of the system according to the invention that waste heat originating from an industrial process, such as a drying process, such as a kilning process, can be recovered to a maximal extent, wherein only a minimum amount of energy has to be procured. The energy that has to be provided for operating the system as described herein would mainly consist of electricity for running circulating pumps and the heat pumps.

[0015] It has been surprisingly found that a vertical tower of the cooling tower type, can advantageously be used in such a system for an optimal waste recovery, thereby transferring said waste heat from a gaseous stream to a liquid stream.

[0016] It has further been found that such a vertical tower can be combined with a series of heat pumps, wherein the heated liquid stream can transfer its energy to a series of heat pumps.

[0017] Furthermore, it has been advantageously found that a well-considered optimal and independent arrangement of the heat pumps, both on the low-temperature heat exchanging side as on the high-temperature heat exchanging side, allows for the necessary heating, thereby requiring a minimal amount of heat pumps. It has advantageously been found that a heat exchanger on the high-temperature side of the heat pumps can return said waste heat to said industrial process or any other industrial process requiring heat. It is thus an advantage of the system as described herein that waste heat with a low value can be converted into a high-temperature stream with a high economic value that can be used or re-used in an industrial process.

[0018] It has been found that waste heat can be recovered by using the system as described herein to such an extent, that the need for external carriers or sources of energy, such as fossil fuels and / or electricity, for said industrial process, more in particular for heating a gaseous stream for use in a drying process, can be cut by at least 60%, even at least 70% and even at least 80%. As such, only at most 40%, even only at most 30% and even only at most 20% of the heat demand for the industrial process has to be met by an external energy source or carrier, which includes electricity for powering heat pumps and fossil fuels for operating burners for further heating a gaseous stream to a required temperature. The rest of the energy or heat demand can be met by the recovery of waste heat by the system as described herein. It will be appreciated that the share of the heat demand which is met by said external energy sources or carriers, can fluctuate in time. Likewise, the share of each external energy source or carrier may also fluctuate with respect to each other, e.g. the amount of electricity for powering said heat pumps may vary with respect to the amount of fossil fuels used for operating any additional burners, the ratio of which may be dictated by economic considerations. In one such a scenario, heat pumps may be used to such an extent that burners become superfluous, thereby avoiding the need for any fossil fuels.

[0019] In an aspect of the invention, there is provided a method for recovering waste heat in a gaseous stream, the method comprising: providing said gaseous stream to a waste heat valorisation tower; contacting said gaseous stream with a stream of a first liquid loop, thereby allowing heat to transfer from said gaseous stream to said stream of said first liquid loop; directing said stream of said first liquid loop out of said waste heat valorisation tower; transferring heat from said first liquid loop to the low temperature heat exchanging side of at least one heat pump; transferring heat from the high temperature heat exchanging side of said at least one heat pump to a second liquid loop; directing said second liquid loop into at least one first heat exchanger; and transferring heat, in said at least one first heat exchanger, from said second liquid loop to a fluid stream. In an aspect of the invention, there is provided a use of a waste heat valorisation tower for waste heat recovery of a gaseous stream, preferably an air stream, said waste heat valorisation tower comprising:

[0020] A first inlet, preferably at or near a lower end of the tower, for entering said gaseous stream;

[0021] A second inlet, preferably at or near an upper end of the tower, for entering a stream of a first liquid loop;

[0022] A means for contacting said stream of a first liquid loop with said gaseous stream such that heat passes from said gaseous stream to said stream of said first liquid loop; a first outlet for carrying out said gaseous stream; and a second outlet for carrying out said stream of said first liquid loop.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Exemplary embodiments will now be described in more detail with respect to the drawings in which:

[0025] Figure 1 shows a system for kilning malted or germinated grain as known in the state of the art;

[0026] Figures 2a-2c show configurations according to the invention wherein at least one heat pump is operably connected with a waste heat valorisation tower;

[0027] Figures 3a-3b show configurations according to the invention wherein at least one second heat exchanger is operably connected with a waste heat valorisation tower via a first liquid loop, and with at least one heat pump via a corresponding fluid loop;

[0028] Figures 4a-4b show configurations according to the invention wherein at least one first heat exchanger is operably connected with at least one heat pump via a second liquid loop;

[0029] Figure 5 shows a system according to the invention;

[0030] Figure 6 shows a system according to the invention, which is integrated in an industrial process, being a kilning process. DETAILED DESCRIPTION

[0031] In the context of the present invention, the term "comprising" should not be interpreted as excluding features or elements other than those explicitly mentioned. It should be construed as specifying the presence of the features or elements indicated, but does not exclude the presence or addition of one or more other features or elements. Thus, the scope of the expression "a method comprising steps A and B" should not be limited to methods consisting only of steps A and B. Accordingly, the terms "comprising" and "including" encompass the terms more restrictive "consisting essentially of" and "consisting of".

[0032] In the context of the present invention, if an element or component is said to be selected from a list of recited elements or components, it should be understood that the element or component can also be any one of the individual recited elements or components in said list, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components.

[0033] An aspect of the invention relates to a system for the recovery of waste heat, preferably waste heat from an industrial process. Said waste heat may relate to waste heat in a gaseous stream or in a gaseous form, produced by or originating from an industrial process. Said waste heat may be originating directly from an industrial process, e.g. in the form of a product stream. Alternatively, said waste heat may be recovered from an industrial process through the intervention of a heat exchanger. Said waste heat may relate at least partly to waste heat in the form of condensation energy. The term "condensation energy" relates herein to the latent heat of condensation, being the energy released when water vapor condenses to form liquid droplets.

[0034] Preferably, said waste heat may be provided by a drying process and said gaseous stream is originating from said drying process.

[0035] For the purpose of the invention, the term "drying" or "drying process" relates herein to a mass transfer process, wherein water or another solvent is removed by evaporation from a solid substance. As a result of a drying process, a gaseous stream will be formed, having an elevated temperature, due to passage in a drying oven or chamber. Said gaseous stream may be containing a high amount of energy, which may be at least partly in the form of condensation energy.

[0036] A particular industry in which such gaseous streams are being formed during the process, is the industry of producing malted grains, e.g. malted barley, wheat, rye, corn, oats, and rice.

[0037] One of the process steps for producing malted grains involves kilning or drying. The aim of kilning is to stop the previous germination process step and to reduce the grain moisture content. Kilning is typically performed batchwise and contains several steps. In a first optional step, typically called the "free drying stage", the temperature of the kilning oven and of the air stream flowing through the oven may be kept at low or ambient temperature to dry the grain without causing the enzymes to denature. In a second step, the incoming air temperature may be raised for forcing the drying of the grain. The relative humidity of the air coming from the bed gradually drops during the forced drying process step. In a last process step, typically called the "curing stage", the air temperature entering the kilning oven may be raised above 80°C, provoking chemical reactions in the malt, such as the Maillard reaction, and providing the malt with its colour. In a last step, the kilned malt is cooled and the kilning oven is emptied. As mentioned herein, kilning allows to reduce the water content of the grain from around 40-45% to less than 5% by weight.

[0038] Although throughout the text, reference will repeatedly be made to the kilning of grains, e.g. for defining process parameters which prevail in the context of grain kilning, it will be appreciated by the person skilled in the art that the principles and components of the system and method as described herein apply to a variety of drying processes and that consequently said process parameters can be adjusted accordingly.

[0039] Referring now to Figure 1, a system 10 for kilning malted or germinated grain, e.g. kilning germinated barley, as known in the state of the art, is shown.

[0040] The system 10 as shown in Figure 1, contains two kilns 20a, 20b or kilning ovens, for the purpose of drying grain, such as barley. Both kilns 20a, 20b are typically thermally insulated to reduce temperature losses. Both kilns are provided with kiln floors 21a, 21b, or malt beds, which are typically meshed to allow air to pass through and which carry the malt or grain to be malted. Air 25a, 25b is heated in one of the gas burners 30a, 30b, 30c, and enters the kiln 20a, 20b typically from below. Referring to Figure 1, kiln 20a, is provided with heated air 25a by a single gas burner 30a, whereas kiln 20b is provided with heated air 25b by gas burners 30b and 30c, placed in parallel. It will be appreciated that many configurations have been developed or can easily be built, the designs or which are the result of several factors, such as size of the installation and space restrictions.

[0041] The heated air 25a, 25b passes through the kilns 20a, 20b, taking excess moisture with it. The heated air 25a, 25b leaves the kilns 20a, 20b and is guided to a heat exchanger 40, which may be a glass tube heat exchanger (GTHE). As can be seen in Figure 1, after leaving their respective kilns 20a, 20b, the heated air 25a and 25b are merged to form one air stream. Most of the time during the process, the heated air 25a, 25b may be leaving the kilns 20a, 20b at a temperature of around 22-40°C and at a relative saturation of 60- 100%, wherein such parameters may depend on the stage of the kilning process as well as on outdoor conditions, such as the temperature and relative humidity of ambient air. Preferably, the heated air 25a, 25b leaving the kilns 20a, 20b may have a temperature of 26-30°C and be 100% or near 100% saturated. In the heat exchanger 40, the heated air 25a, 25b passes heat to a fresh air stream 26, which relates to ambient air and is taken from the surroundings and has most of the time a lower temperature in comparison with the heated air 25a, 25b. As a result of passage in the heat exchanger 40, the heated air 25a, 25b, will be condensed and the latent condensation heat will heat up the fresh air stream 26. It has been found that such a fresh air stream 26 can be preheated from 5°C to a temperature of 24°C by a heat exchanger or highly efficient GTHE system 40. However, it will be appreciated that in warm climates, the fresh air stream 26 entering the heat exchanger 40 may have a higher temperature.

[0042] The fresh air stream 26 is thus preheated by a highly efficient heat exchanger 40, providing internal recuperation of energy. The fresh air stream 26 is subsequently guided to the gas fired burners 30a, 30b, 30c, wherein the air is further heated to a certain temperature, in accordance with the kilning process steps as described here above. Typically, setpoints may range from 50°c to 85°C. The fresh air stream 26 is thus heated by the gas burners 30a, 30b, 30c and forms heated air 25a, 25b. The heated air 25a, 25b is then directed to the kilns 20a, 20b as described here above. On the other hand, the heated air 25a, 25b, originating from the kilns 20a, 20b respectively, and passing through the heat exchanger 40 typically leaves said heat exchanger 40 at a temperature which is between 15°C and 35°C, the temperature being usually 22°C to 28°C, and at a saturation of 60-100%, usually 100% or near 100%. The waste heat in said heated air 25a, 25b is typically dissipated in the surrounding environment.

[0043] It will be appreciated that air flow rates are very dependent on the size of the system, but can easily be more one million m3per hour.

[0044] In an aspect of the invention, there is provided a system 100 for waste heat recovery from a gaseous stream 101, the system 100 comprising:

[0045] A waste heat valorisation tower 110 having a first inlet 111 for entering said gaseous stream 101; a second inlet 112 for entering a stream of a first liquid loop 102; a means 115 for contacting said gaseous stream 101 with said stream of said first liquid loop 102 such that heat passes from said gaseous stream 101 to said stream of said first liquid loop 102; a first outlet 113 for carrying out said gaseous stream 101; and a second outlet 114 for carrying out said stream of said first liquid loop 102;

[0046] At least one heat pump 120, the low temperature heat exchanging side of which is operably connected to said waste heat valorisation tower 110 via at least said first liquid loop 102;

[0047] At least one first heat exchanger 130, which is each operably connected to the high-temperature heat exchanging side of one or more heat pump of said at least one heat pump 120, via at least a second liquid loop 103.

[0048] According to the invention, the system 100 comprises a waste heat valorisation tower 110, wherein said waste heat valorisation tower 110 has a first inlet 111 for entering a gaseous stream 101; a second inlet 112 for entering a stream of a first liquid loop 102; a means 115 for contacting said gaseous stream 101 with said stream of said first liquid loop 102 such that heat passes from said gaseous stream 101 to said stream of said first liquid loop 102; a first outlet 113 for carrying out said gaseous stream 101; and a second outlet 114 for carrying out said stream of said first liquid loop 102.

[0049] In embodiments according to the invention, said waste heat valorisation tower 110 has the shape or form of a tower, chimney or chamber, preferably having an opening at or near the top, said opening facing preferably upwards or substantially upwards. Said opening may be said first outlet 113 for carrying out said gaseous stream 101 or may comprise said first outlet 113. In other words, the gaseous stream 101 entering the waste heat valorisation tower 110 via or through said first inlet 111 may exit the tower 110 via or through said opening at or near the top of the tower 110, preferably to be dissipated in the environment. Hence, said waste heat valorisation tower 110 relates to an open vertical tower.

[0050] In embodiments according to the invention, said waste heat valorisation tower 110 has the design and / or components of a "cooling tower", or has the design and / or components similar to a cooling tower.

[0051] A cooling tower, as it is known in the industry, typically relates to a device that cools or condenses a coolant stream, usually a water stream, to a lower temperature, by interaction with a gaseous stream, such as air, which gaseous stream flows out of the tower to the environment, thereby injecting waste heat into the atmosphere with the outflowing gaseous stream. Typically, such a coolant stream has the purpose of cooling a reactor or a heat-generating device, and enters the cooling tower at an elevated temperature and leaves the cooling tower at a lower temperature due to heat exchange with the gaseous stream.

[0052] Herein, the way said waste heat valorisation tower 110 works or functions, differs from the cooling tower in its traditional use in that said stream of a first liquid loop 102, being a liquid stream, does not relate to a liquid stream that is cooled in the tower by heat exchange with air or a gaseous stream 101. Indeed, heat transfer occurs from said gaseous stream 101 towards said stream of a first liquid loop 102, or, in other words, said stream of a first liquid loop 102 is heated by heat present in the gaseous stream 101, which gaseous stream may be air, and which heat may have been recovered as waste heat, e.g. from condensation energy, in a drying process. The spontaneous heat transfer is the result of a temperature difference between the stream of a first liquid loop 102 and the gaseous stream 101.

[0053] The insight and understanding that a cooling tower qualifies to transfer heat from a gaseous stream containing waste heat to a liquid - thereby reversing the traditional way of use of a cooling tower - is one of the central and crucial concepts of the invention.

[0054] Said gaseous stream 101 enters said waste heat valorisation tower 110 by use of said first inlet 111. As mentioned herein, said gaseous stream 101 can originate from or can be connected to an industrial process, such as a drying process or drying oven, in a direct manner or possibly after passing through a heat exchanger 240, upstream from said first inlet 111, which heat exchanger 240 may have for purpose to recover already a part of the waste heat of said industrial process, such as a drying process, or any other industrial or chemical process producing heat.

[0055] In embodiments according to the invention, said gaseous stream 101 may be air or may relate to an air stream, which air stream may have been drawn from the surroundings. Alternatively, said gaseous stream 101 may relate to gases comprising at least one of nitrogen, carbon dioxide and oxygen.

[0056] In preferred embodiments, said gaseous stream 101 is ambient air which contains waste heat recovered from an industrial process, preferably a drying process. Using air has the advantage that no caustic or flammable elements enter the waste heat valorisation tower 110.

[0057] In embodiments according to the invention, said gaseous stream 101 has a temperature Ti at said first inlet 111, wherein said temperature Ti is at least 10°C, preferably at least 12°C, more preferably at least 14°C, even more preferably at least 16°C, more preferably at least 18°C, even more preferably at least 20°C, and most preferably at least 22°C. It will be understood that temperature Ti is at most 90°C, preferably at most 80°C, more preferably at most 70°C, even more preferably at most 60°C, more preferably at most 50°C and most preferably at most 40°C. In the context of a malting process as described herein, the gaseous stream 101 forthcoming from a heat exchanger 240 recovering heat from a kilning process will have a temperature of between 15°C and 35°C, preferably between 18°C and 32°C, and typically a temperature between 22°C and 28°C, and typically be around 24°C.

[0058] In embodiments according to the invention, said gaseous stream 101 has a relative humidity of at least 40%, preferably at least 50%, more preferably at least 60%, even more preferably at least 70%, more preferably at least 80%, even more preferably at least 90%, more preferably at least 95%, even more preferably at least 97% and most preferably at least 99%. In preferred embodiments, said gaseous stream 101 has a relative humidity of 100% or around 100%. In the context of a malting process as described herein, the gaseous stream 101, forthcoming from a heat exchanger 240 recovering heat from a kilning process, will typically have a relative humidity of more than 80%, be 100% or around 100%. The term "relative humidity" relates herein to the ratio of the partial pressure of water vapor in a mixture to the equilibrium vapor pressure or saturation vapor pressure of water at a given temperature.

[0059] In embodiments according to the invention, said gaseous stream 101 enters said waste heat valorisation tower 110 at a controlled temperature and relative humidity. By having controlled values for temperature and relative humidity, it is understood that said values are determined by an industrial process and are the consequence thereof, and are therefore not entirely determined by environmental conditions. Within the context of waste heat recovery from a drying process in a kiln, it may thus be expected that these parameters for the gaseous stream 101 will follow the operation cycle of the kiln, wherein during said curing stage, said gaseous stream 101 may have a temperature exceeding 80°C, as well as have a relative humidity that goes temporarily below 40%. As such, it may be considered acceptable if the values measured for temperature and relative humidity, especially for said gaseous stream 101, temporarily fall outside the ranges as expressed herein, if these values are a consequence of the process steps of said industrial process, and if such exceptions do not take more than 40% of the total process cycle time.

[0060] In embodiments according to the invention, said first inlet 111 is at or near a lower end of said waste heat valorisation tower 110. In embodiments according to the invention, said second inlet 112 for entering a stream of a first liquid loop 102 is at or near an upper end of said waste heat valorisation tower 110.

[0061] In embodiments according to the invention, said second outlet 114 for carrying out or for exiting said stream of said first liquid loop 102 is at or near a lower end of said waste heat valorisation tower 110.

[0062] Said first inlet 111, second inlet 112, first outlet 113 and second outlet 114 preferably relate to four distinct channels or means for channelling matter in or out said tower 110.

[0063] The waste heat valorisation tower 110 further has a means 115 for contacting said gaseous stream 101 with said stream of said first liquid loop 102 such that heat passes from said gaseous stream 101 to said stream of said first liquid loop 102. Said means 115 for contacting may include a heat exchanger; a radiator; wherein said stream of said first liquid loop 102 forms a closed circuit; and a packing, said packing being preferably chemically inert and preferably comprising at least one plastic, ceramic or metal material; wherein said stream of said first liquid loop 102 and said gaseous stream 101 are physically contacted and mixed.

[0064] In embodiments according to the invention, said waste heat valorisation tower 110 relates to an open vertical tower of the "dry cooling tower" type, or "closed-circuit cooling tower", or has the components and design of, or similar to, a dry cooling tower, or closed-circuit cooling tower. Waste heat valorisation towers 110 of this type conduct said stream of a first liquid loop 102 in a closed circuit through the tower, thus physically separating the stream of a first liquid loop 102 from said gaseous stream 101. Said closed circuit for said stream can comprise a multi-tubular closed circuit, forming a heat exchanger, and / or a radiator. Heat exchange is typically performed through a heat exchanger on the basis of convective heat transfer. Water can be sprayed on said closed circuit and said gaseous stream 101 may be made to contact the external surface of said closed circuit through a fan-induced draft. The advantage of this design is that the stream of the first liquid loop 102 and the gaseous stream 101 are not mixed and the liquid stream 102 is not exposed to contamination and external conditions.

[0065] In preferred embodiments according to the invention, said waste heat valorisation tower 110 relates to an open vertical tower of the "wet cooling tower" type, or "open-circuit cooling tower", or has the components and design of, or similar to, a wet cooling tower, or open-circuit cooling tower. Waste heat valorisation towers 110 of this type provide for an opportunity in an appropriate space for having physical contact between said gaseous stream 101 and said stream of the first liquid loop 102, thereby exposing the latter to external conditions and contamination.

[0066] Typically, such a tower comprises a packing, wherein such contact can take place. Preferably, said second inlet 112 for entering a stream of a first liquid loop 102 is situated at or near an upper end of said waste heat valorisation tower 110, wherein said stream is sprayed on top of said packing by use of spray heads or nozzles. The stream of a first liquid loop 102 will then trickle down, through the packing, due to gravity. Below the packing, such a tower typically contains a container or reservoir for collecting said stream, which reservoir or container is operably connected to said second outlet 114.

[0067] Preferably, said first inlet 111 is at or near a lower end of said waste heat valorisation tower 110, wherein said gaseous stream 101 is drawn upwards, towards said first outlet 113 for carrying out said gaseous stream 101, which is preferably at or near the top or which relates to an opening at or near the top, as described herein.

[0068] It will be appreciated by the person skilled in the art, that heat exchange will mainly occur in the packing, where the seeping liquid and / or water, and the gaseous stream 101, drawn towards the first outlet 113, will contact.

[0069] In embodiments according to the invention, said packing may relate to a chemically inert material, and may comprise at least one of a plastic material, a ceramic material and / or a metal material. Said packing may relate to a random packing, having a random distribution of comparably small pieces of packing material stacked into a packing volume, as known in the art. Alternatively, said packing may be a structured packing, having a comparably large structure with a well-defined shape.

[0070] In embodiments according to the invention, said waste heat valorisation tower 110 is provided with a drain. Preferably, said drain is provided near a lower end or at the bottom of the tower 110. Indeed, it will be appreciated that, since said gaseous stream 101 typically has a high relative humidity and a temperature higher than the stream of said first liquid loop 102, water may condense from said gaseous stream 101 and become part of said stream of a first liquid loop 102, which would increase the total amount of liquid in the first liquid loop. Hence, a drain may need to be provided to keep the total amount of liquid or water in the first liquid loop 102 near a constant value.

[0071] In embodiments according to the invention, said waste heat valorisation tower 110 is a mechanical draft tower. For the purpose of the invention, the term "mechanical draft tower" implies that said tower contains a mechanical way of moving or transporting the gaseous stream 101, or of inducing movement in said gaseous stream 101. Preferably, said waste heat valorisation tower 110 is an induced draft tower, provided with a fan (not shown on the figures) at or near the first outlet 113 of the tower. Preferably, said fan at or near the first outlet 113 of the tower 110 draws said gaseous stream 101 towards the fan and out of the tower 110 via said first outlet 113. Alternatively, said waste heat valorisation tower 110 is a forced draft tower, having a blower preferably at or near the first inlet 111 of the tower 110, forcing said gaseous stream 101 into and through the tower.

[0072] In alternative embodiments according to the invention, said waste heat valorisation tower 110, or any other part of the system 100, is not provided with a fan or blower and said gaseous stream 101 is transported through the tower by a pressure that is caused or provided by a fan or blower that is part of the industrial process and / or drying process, e.g. upstream of the gaseous stream 101. More in particular, in the context of waste heat recovery from a drying process in a kiln, said kiln may be provided with at least one fan or blower, having enough capacity to transport said heated air 25 or gaseous stream 101 through the tower 110 and out of the tower via said first outlet 113.

[0073] In embodiments according to the invention, said waste heat valorisation tower 110 has a crossflow design, wherein, upon making contact, the general direction of flow of said gaseous stream 101 is substantially perpendicular to the general direction of flow of said stream of a first liquid loop 102. The term "substantially perpendicular" relates herein to an angle of 90° + / - 10°. In preferred embodiments according to the invention, said waste heat valorisation tower 110 has a counterflow design, wherein, upon making contact, the general direction of flow of said gaseous stream 101 is substantially opposite to the general direction of flow of said stream of a first liquid loop 102. The term "substantially opposite" relates herein to an angle of 180° + / - 10°.

[0074] According to the invention, the system comprises at least one heat pump 120.

[0075] Heat pumps are devices which are used for the purpose of transferring heat, typically for the purpose of heating confined spaces, using the refrigeration cycle or reverse Carnot cycle.

[0076] In embodiments according to the invention, said at least one heat pump 120 relates to a so called water-to-water heat pump. It will be appreciated that said at least one heat pump 120 shares the same technical features or is similar to a commercial water-to-water heat pump which is typically used for recovering heat from ground water or surface water for the purpose of heating confined spaces.

[0077] In embodiments according to the invention, heat is absorbed from a liquid loop, at the low-temperature side of each of said at least one heat pump 120, said heat directly or indirectly originating from said waste heat valorisation tower 110 and said first liquid loop 102, and wherein, at the high-temperature side of the pump, heat is transferred to a second liquid loop 103.

[0078] Each of said at least one heat pump 120 as used herein comprises at least a low- temperature heat exchanger, a high-temperature heat exchanger, and a medium for transporting heat from the low-temperature heat exchanging side of the heat pump to the high-temperature heat exchanging side of the heat pump, wherein said medium is forming a closed loop containing said low-temperature heat exchanger and said high- temperature heat exchanger. Said low-temperature heat exchanger is thereby situated at the low-temperature heat exchanging side of the heat pump, whereas said high- temperature heat exchanger is situated at the high-temperature heat exchanging side of the heat pump.

[0079] In embodiments according to the invention, each of said at least one heat pump

[0080] 120 comprises individually the following four components: an evaporator 121, a compressor 122, a condenser 123 and an expansion valve 124, which four elements are typically connected in that order, via a heat transfer medium, being typically a refrigerant.

[0081] Typically, the evaporator 121 relates to said low-temperature heat exchanger which is entered by said refrigerant as a low-temperature liquid, which refrigerant subsequently absorbs heat from a heat source by evaporation at a low pressure and leaves said evaporator 121 as a low-temperature vapour.

[0082] The refrigerant in the form of a low-temperature vapour then enters the compressor 122, which raises the low pressure of the low-temperature refrigerant to a pressure that is sufficiently high to match the desired condensing temperature in the condenser 123. During compression, not only the pressure but also the temperature of the refrigerant increases.

[0083] The refrigerant then enters the condenser 123 as a high-temperature vapour. The condenser 123 relates to said high-temperature heat exchanger, wherein heat is rejected or transferred to a heat sink by condensation at a high pressure, such that the refrigerant leaves as a high-temperature liquid.

[0084] The refrigerant then returns from the condenser 123 to the evaporator 121 and is transformed from a high-temperature, high-pressure liquid to a low-temperature, low- pressure liquid before entering the evaporator 121. This is typically achieved by use of an expansion valve 124. When the refrigerant in the form of a hot liquid passes through such a valve 124, both the pressure and temperature will drop. Indeed, as the pressure drops, the refrigerant will start to evaporate in the valve 124 and the heat of evaporation is taken from the refrigerant itself which causes its temperature to drop and the result is a low- temperature, low-pressure mix of liquid and vapour.

[0085] In embodiments according to the invention, said refrigerant may be selected from the following: water; glycol; a water / glycol mixture; NH3 (R717); butane; a chlorofluorocarbon (CFC) and / or hydrochlorofluorocarbon (HCFC), such as HCFC-22, Freon-12 and Freon-21; a hydrofluorocarbon (HFC) and its mixtures, such as R134a, R125, R32 (HFC-32) and R410-a; a hydrofluoroolefin (HFO), such as HFO-1234ze, HFO-1234yf and HFO-1336mzz; and mixtures thereof. According to the invention, the low-temperature heat exchanging side of said at least one heat pump 120, relating to the low-temperature heat exchanger or evaporator 121, is operably connected to said waste heat valorisation tower 110 via at least said first liquid loop 102. It will be understood that the wording "via at least said first liquid loop" implies that said connection can be direct or indirect.

[0086] Typically, said first liquid loop 102 consists of two parts, a first part going from said second inlet 112 to said second outlet 114, leading all the way through the inside of the vertical tower 110. As described hereabove, said first part can conduct said stream of a first liquid loop 102 in a closed circuit through the tower 110, as in a dry cooling tower, or conduct it through the vertical tower, permitting physical contact with said gaseous stream 101, as in a wet cooling tower. A second part, which is situated outside of said waste heat valorisation tower 110, starts at the second outlet 114 and goes to said second inlet 112.

[0087] In embodiments according to the invention, such as in the context of waste heat recovery from a drying process in a kiln, a stream of said first liquid loop 102 has a temperature at said second outlet 114, which is at least 4°C, preferably at least 7°C, more preferably at least 10°C, and most preferably at least 15°C. It will further be understood that a stream of said first liquid loop 102 has a temperature at said second outlet 114, which is at most 34°C, more preferably at most 30°C and most preferably at most 25°C. It will be appreciated that a stream having a comparably high temperature at said second outlet 114 will result in a better overall efficiency for the system 100 than a stream having a comparably lower temperature at said second outlet 114.

[0088] In preferred embodiments according to the invention, said first liquid loop 102 has a temperature T2 at said second outlet 114, wherein T2 is equal or higher than (Ti- 5) °C, preferably equal or higher than (Ti-4) °C., more preferably equal or higher than (Ti- 3) °C, and most preferably equal or higher than (Ti- 2) °C.

[0089] In embodiments according to the invention, e.g. in the context of waste heat recovery from a drying process in a kiln, a stream of said first liquid loop 102 has a temperature at said second inlet 112, which is at least 1°C, preferably at least 4°C, more preferably at least 7°C, and most preferably at least 10°C. It will further be understood that a stream of said first liquid loop 102 has a temperature at said second inlet 112, which is at most 31°C, preferably at most 27°C and most preferably at most 24°C.

[0090] In embodiments according to the invention, said first liquid loop 102 contains at least one filter for filtering particles that somehow got introduced in the flow. Preferably, said at least one filter is placed at the second outlet 114 and / or upstream of, but near, a low-temperature heat exchanger of a heat pump or a second heat exchanger.

[0091] In embodiments according to the invention, said first liquid loop 102 comprises or consists of water.

[0092] In embodiments according to the invention, said low-temperature heat exchanging side of each of said at least one heat pump 120 is operably connected with said waste heat valorisation tower 110 via said first liquid loop 102, so that a stream of said first liquid loop 102 leaving said waste heat valorisation tower 110 via said second outlet 114 passes through each of said low-temperature heat exchanging side of said at least one heat pump 120 before returning to said second inlet 112. As such, said low- temperature heat exchanging side of said at least one heat pump 120 is directly connected to said first liquid loop 102. In such embodiments, said first liquid loop 102, or a stream thereof, will typically contain or pass through the following elements: second inlet 112, means 115 for contacting said gaseous stream 101 with said stream of said first liquid loop 102, second outlet 114, and each of said low-temperature heat exchanger of said at least one heat pump 120.

[0093] Said at least one heat pump 120 may herein relate to a plurality of heat pumps, which heat pumps may have been arranged in series and / or in a parallel configuration, or in combinations thereof.

[0094] In preferred embodiments, the total number of said at least one heat pump 120 is an even number.

[0095] In preferred embodiments, no more than two low-temperature heat exchangers, or evaporators 121, are placed in series. Hence, in such embodiments, no more than two heat pumps of said at least one heat pump 120 are placed in series. Referring now to Figures 2a-2c, configurations according to the invention are shown wherein said at least one heat pump 120 is operably connected with said waste heat valorisation tower 110.

[0096] Figure 2a illustrates a waste heat valorisation tower 110, which is directly operably connected by use of a first liquid loop 102 with the low-temperature heat exchangers of two heat pumps. The two heat pumps are placed in series.

[0097] Figure 2b illustrates a waste heat valorisation tower 110, which is directly operably connected by use of a first liquid loop 102 with the low-temperature heat exchangers of four heat pumps. One pair of said four heat pumps is arranged in a parallel configuration with regard to the other pair. Each pair of heat pumps is arranged in series.

[0098] Figure 2c illustrates a waste heat valorisation tower 110, which is directly operably connected by use of a first liquid loop 102 with the low-temperature heat exchangers of six heat pumps. All six heat pumps are placed in a parallel configuration.

[0099] It will however be appreciated by the person skilled in the art that the final number, configuration and arrangement of said at least one heat pump 120 will depend on several factors and limitations, including the size of the installation, e.g. the flow rate of the gaseous stream, space restrictions for arranging said system, and the like.

[0100] In preferred embodiments according to the invention, at least one second heat exchanger 140 is operably connected with said waste heat valorisation tower 110 via said first liquid loop 102 so that a stream of said first liquid loop 102 leaving said waste heat valorisation tower 110 via said second outlet 114 passes through said at least one second heat exchanger 140 before returning to said second inlet 112. As a consequence, each of said at least one second heat exchanger 140 is directly connected to said first liquid loop 102. In such embodiments, said first liquid loop 102, or a stream thereof, will typically contain or pass through the following elements: second inlet 112, means 115 for contacting said gaseous stream 101 with said stream of said first liquid loop 102, second outlet 114, and said at least one second heat exchanger 140.

[0101] In embodiments according to the invention, said at least one second heat exchanger 140 relates to two or more second heat exchangers which may be arranged in series and / or in a parallel configuration, or in combinations thereof, with respect to said first liquid loop 102 or with regards to the first liquid loop side of said two or more second heat exchangers.

[0102] Advantageously, by using at least one second heat exchanger 140, the first liquid loop 102 can be separated from said at least one heat pump 120, so that any contaminations that may be present in the stream of said first liquid loop 102, do not enter said at least one heat pump 120, more in particular its low-temperature heat exchanger, and damage or corrode any equipment.

[0103] In embodiments according to the invention, said at least one second heat exchanger 140 is configured to transfer heat from a stream of said first liquid loop 102 to an own corresponding fluid loop 141. Each of said at least one second heat exchanger 140 is for this purpose provided with an own corresponding fluid loop 141, which is operably connected in its turn with a heat pump of said at least one heat pump 120.

[0104] A corresponding fluid loop 141 therefore connects a side from one of said at least one second heat exchanger 140 with the low-temperature heat exchanging sides of one or more heat pumps, transferring heat from the former to the latter.

[0105] In an embodiment according to the invention, said at least one second heat exchanger 140 relates to one second heat exchanger, which is operably connected by use of said corresponding fluid loop 141 with one heat pump.

[0106] In embodiments according to the invention, said at least one second heat exchanger 140 relates to one second heat exchanger, which is operably connected by use of said corresponding fluid loop 141 with two or more heat pumps, which may be organised in a parallel or series configuration, or combinations thereof. Preferably, said one second heat exchanger is operably connected with two heat pumps. Preferably, said two heat pumps are placed in series.

[0107] In embodiments according to the invention, said at least one heat pump 120 relates to one or more first subsets 125 of heat pumps, wherein each first subset 125 may contain one or more heat pump of said at least one heat pump 120. A first subset 125 having two or more heat pumps may have the heat pumps arranged in a parallel or series configuration, or combinations thereof. It will be understood that a grouping of heat pumps in first subsets 125 pertains to the low-temperature exchanging side of the heat pumps. In embodiments according to the invention, said at least one second heat exchanger 140 relates to two or more second heat exchangers, wherein each of said two or more second heat exchangers is operably connected, by use of its corresponding fluid loop 141, with one of said first subsets 125 of heat pumps, and as a consequence to the low-temperature heat exchanging side of each of the heat pumps belonging to that particular first subset 125. Hence, each low-temperature heat exchanging side of said one or more heat pump belonging to one such first subset 125 is operably connected with one particular corresponding second heat exchanger of said at least one second heat exchanger 140.

[0108] It will hence be understood that each of said at least one second heat exchanger 140 transfers heat from said first liquid loop 102 to its own corresponding fluid loop 141, and therefrom to each of the low-temperature heat exchanging sides of a first subset 125 of heat pumps, which first subset is part of or integrated in such a corresponding fluid loop 141.

[0109] In other words, each low-temperature heat exchanging side of a heat pump belonging to one such first subset 125 is operably connected with one particular second heat exchanger via its corresponding fluid loop 141.

[0110] Heat pumps which are part of a first subset 125 of heat pumps may have been arranged in series and / or in a parallel configuration, or in combinations thereof.

[0111] In preferred embodiments, the number of heat pumps in a first subset 125 is an even number.

[0112] In preferred embodiments, no more than two low-temperature heat exchangers, or evaporators 121, in a first subset 125 are placed in series. Hence, in such embodiments, no more than two heat pumps in a first subset 125 of heat pumps are placed in series.

[0113] In alternative embodiments, said at least one second heat exchanger 140 and said first subset 125 do not have to form a one-on-one combination or link, as, according to alternative embodiments, two or more single second heat exchangers 140 may e.g. be arranged in parallel or series with regard to a single first subset 125.

[0114] In embodiments according to the invention, said corresponding fluid loop 141 comprises water, and / or a refrigerant selected from the following: glycol, NH3 (R717); butane; a chlorofluorocarbon (CFC) and / or hydrochlorofluorocarbon (HCFC), such as HCFC-22, Freon-12 and Freon-21; a hydrofluorocarbon (HFC) and its mixtures, such as R134a, R125, R32 (HFC-32) and R410-a; a hydrofluoroolefin (HFO), such as HFO-1234ze, HFO-1234yf and HFO-1336mzz; and mixtures thereof. Preferably, said corresponding fluid loop 141 comprises water or a mixture of water and glycol.

[0115] In embodiments according to the invention, such as in the context of waste heat recovery from a drying process in a kiln, the corresponding fluid loop 141 can have a temperature upon leaving said second heat exchanger 140, which is at least 0.0°C, preferably at least 2.5°C, more preferably at least 5.0°C, even more preferably at least 7.5°C and most preferably at least 10.0°C. It will further be understood that the corresponding fluid loop 141 can have a temperature upon leaving said second heat exchanger 140, which is at most 33.0°C, preferably at most 30.0°C more preferably at most 27.5.0°C, even more preferably at most 25.0°C and most preferably at most 23.0°C.

[0116] In embodiments according to the invention, such as in the context of waste heat recovery from a drying process in a kiln, the corresponding fluid loop 141 can have a temperature upon entering said second heat exchanger 140, which is at least -2.0°C, preferably at least 0.5°C, more preferably at least 3.0°C, even more preferably at least 5.5°C and most preferably at least 8.0°C. It will further be understood that the corresponding fluid loop 141 can have a temperature upon entering said second heat exchanger 140, which is at most 30.0°C, preferably at most 27.5°C more preferably at most 25.0°C, even more preferably at most 22.5°C and most preferably at most 20.0°C.

[0117] Referring now to Figures 3a-3b, configurations according to the invention are shown wherein at least one second heat exchanger 140 is operably connected with said waste heat valorisation tower 110 via said first liquid loop 102, and with said at least one heat pump 120 via said corresponding fluid loop 141.

[0118] Figure 3a illustrates two second heat exchangers 140a, 140b, which are connected in a parallel configuration to a waste heat valorisation tower 110 via a first liquid loop 102, and each to a first subset 125a, 125b of two heat pumps via a corresponding fluid loop 141a, 141b. Each first subset 125a, 125b contains two heat pumps which are arranged in series.

[0119] Figure 3b illustrates a single second heat exchanger 140, which is connected to a waste heat valorisation tower 110 via a first liquid loop 102, and to a first subset 125, having four heat pumps, via a corresponding fluid loop 141. One pair of said four heat pumps is arranged in a parallel configuration with regard to the other pair. Each pair of heat pumps is arranged in series.

[0120] It will however be appreciated by the person skilled in the art that the final number, configuration and arrangement of said at least one second heat exchanger 140, its corresponding fluid loops 141 and first subsets 125 of heat pumps, will depend on several factors and limitations, including the size of the installation, e.g. the flow rate of the gaseous stream, space restrictions for arranging said system, and the like.

[0121] According to the invention, the system comprises at least one first heat exchanger 130. Each of said at least one first heat exchanger 130 is operably connected to a high- temperature heat exchanging side of one or more heat pump of said at least one heat pump 120, via at least a second liquid loop 103.

[0122] In embodiments according to the invention, said at least one first heat exchanger 130 relates to two or more first heat exchangers which may be arranged in series and / or in a parallel configuration, or in combinations thereof, with respect to said at last one second liquid loop 103, meaning with regards to the second liquid loop side of said two or more first heat exchangers.

[0123] In embodiments according to the invention, said at least one first heat exchanger 130 is configured to transfer heat from said second liquid loop 103 to a fluid stream 104 , wherein said at least one first heat exchanger 130 has a third inlet 131 and third outlet 132 for said fluid stream 104, and a fourth inlet 133 and a fourth outlet 134 for said second liquid loop 103.

[0124] In preferred embodiments, said at least one first heat exchanger 130 has a counterflow design, wherein the general direction of flow of said second liquid loop 103 is substantially opposite to the general direction of flow of said fluid stream 104.

[0125] In embodiments according to the invention, each of said at least one first heat exchanger 130 is further operably connected with said at least one heat pump 120, via said second liquid loop 103, so that a stream of said second liquid loop 103 leaving said at least one first heat exchanger 130 via said fourth outlet 134 passes through each of said high temperature heat exchanging side of said at least one heat pump 120 before returning to said fourth inlet 133 of each of said at least one first heat exchanger 130.

[0126] In embodiments according to the invention, said at least one heat pump 120 may relate to a plurality of heat pumps, which heat pumps may have been arranged in series and / or in a parallel configuration, or in combinations thereof. In such embodiments, the high-temperature heat exchanging sides of each of said at least one heat pump 120, may have been arranged in series and / or in a parallel configuration, or in combinations thereof.

[0127] In embodiments according to the invention, said at least one first heat exchanger 130 is integrated in an industrial process that requires heat, said process being preferably the industrial process from which said waste heat is recovered by the invention. Preferably, said industrial process is a drying process, such as a drying process in a kilning oven.

[0128] In embodiments according to the invention, said at least one first heat exchanger 130 transfers heat from said second liquid loop 103 to a fluid stream 104, which fluid stream 104 may be a liquid stream or a gaseous stream.

[0129] According to the invention, the high-temperature heat exchanging side of each of said at least one heat pump 120, relating to the high-temperature heat exchanger or condenser 123, is operably connected to one of said at least one first heat exchanger 130 via at least a second liquid loop 103.

[0130] In an embodiment according to the invention, said at least one first heat exchanger 130 relates to one first heat exchanger, which is operably connected by use of said second liquid loop 103 with one heat pump.

[0131] In embodiments according to the invention, said at least one first heat exchanger 130 relates to one first heat exchanger, which is operably connected by use of said second liquid loop 103 with two or more heat pumps, which may be organised in a parallel or series configuration, or combinations thereof. Preferably, said two or more heat pumps are organised in a series configuration. According to said embodiment, said one first heat exchanger is operably connected in series with two or more heat pumps. In embodiments according to the invention, said at least one heat pump 120 relates to one or more second subsets 126 of heat pumps, wherein each second subset 126 may contain one or more heat pump of said at least one heat pump 120. A second subset 126 having two or more heat pumps may have the heat pumps arranged in a parallel or series configuration, or combinations thereof. It will be understood that a grouping of heat pumps in second subsets 126 pertains to the high-temperature exchanging side of the heat pumps. In embodiments, said first 125 and second 126 subsets may relate to or contain the same heat pumps. Preferably, said first 125 and second 126 subsets will contain different heat pumps of said at least one heat pump 120.

[0132] In embodiments according to the invention, each second subset 126 may contain one or more heat pump of said at least one heat pump 120, wherein each high- temperature heat exchanging side of said one or more heat pump belonging to one such second subset 126 is operably connected with one particular corresponding first heat exchanger of said at least one first heat exchanger 130, via a second liquid loop 103.

[0133] In embodiments according to the invention, said at least one first heat exchanger 130 relates to two or more first heat exchangers, wherein each of said two or more first heat exchangers is operably connected, by use of a second liquid loop 103, with one of said second subsets 126 of heat pumps, and as a consequence to the high-temperature heat exchanging side of each of the heat pumps belonging to that particular second subset 126. Hence, each high-temperature heat exchanging side of said one or more heat pump belonging to one such second subset 126 is operably connected with one particular corresponding first heat exchanger of said at least one first heat exchanger 130.

[0134] It will hence be understood that each high-temperature heat exchanging sides of a second subset 126 of heat pumps, is configured to transfer heat to one particular corresponding first heat exchanger of said at least one first heat exchanger 130, by use of said second liquid loop 103.

[0135] Heat pumps which are part of a second subset 126 of heat pumps may have been arranged in series and / or in a parallel configuration, or in combinations thereof.

[0136] In embodiments, the number of second subsets 126 is one.

[0137] In preferred embodiments, the number of second subsets 126 is two, three or more. In preferred embodiments, each heat pump in a second subset 126 is arranged in a series configuration.

[0138] Alternatively, said at least one first heat exchanger 130 and second subset 126 do not have to form a one-on-one combination or link, as, according to alternative embodiments, two or more single first heat exchangers 130 may be arranged in parallel or series with regard to a single second subset 126.

[0139] In embodiments according to the invention, said second liquid loop 103 comprises water, and / or a refrigerant selected from the following: glycol, a water / glycol mixture, NH3 (R717); butane; a chlorofluorocarbon (CFC) and / or hydrochlorofluorocarbon (HCFC), such as HCFC-22, Freon-12 and Freon-21; a hydrofluorocarbon (HFC) and its mixtures, such as R134a, R125, R32 (HFC-32) and R410-a; a hydrofluoroolefin (HFO), such as HFO-1234ze, HFO-1234yf and HFO-1336mzz; and mixtures thereof. Preferably, said second liquid loop 103 comprises water or a mixture of water and glycol.

[0140] In embodiments according to the invention, said system 100 further comprises a buffer tank 150, which buffer tank is configured to temporarily store heat. Preferably, said buffer tank 150 is operably connected to said second liquid loop 103, for storing heat provided by said second liquid loop 103. Advantageously, an excess of heat can provisionally be stored, wherein the stored heat can be used to ensure a continuous supply of heat, which further increases the self-reliance of the system 100. It is a further advantage of a buffer tank 150 that heat can be temporarily stored at a chosen time, e.g. when electricity prices are low, which lowers the overall cost for operating the system. It will be furthermore be appreciated that providing a buffer tank 150, may reduce the number and / or capacity of heat pumps in the system and / or alter the configuration of heat pumps, which may further reduce the cost of investment, due to the lower price of buffer capacity.

[0141] Although a variety of arrangements for heat pumps is therefore possible, it is preferred, in embodiments according to the invention, that no more than two heat pumps are placed in series on the low-temperature heat exchanging side of the heat pumps. In contrast, up to five, even up to ten, even up to fifteen and even up to twenty heat pumps can be arranged in series on the high-temperature heat exchanging side of the heat pumps. It has surprisingly been found that the configuration of the system as described herein, combining, at the low-temperature side of the heat pumps, an arrangement of low-temperature heat exchangers placed in series of two, with, at the high-temperature side the heat pumps, an arrangement of all high-temperature heat exchangers placed in series, allows for a maximum recovery of waste heat, wherein a minimum of energy is used by the system to obtain such waste heat recovery.

[0142] More in particular, it has been found that such configurations of the system allow for a coefficient of performance which is at least 2.0, preferably at least 3.0, more preferably at least 3.5, even more preferably at least 4.0, more preferably at least 4.5., even more preferably 5.0, more preferably at least 5.5, even more preferably at least 6.0, more preferably at least 6.5, even more preferably at least 7.0, more preferably at least 7.5 and most preferably at least 8.0.

[0143] In the context of recovering waste heat from a kilning process, wherein a gaseous stream entering the waste heat valorisation tower typically has a temperature Ti of around 24°C, it has been found that a stream from said second liquid loop 103 exiting the last high-temperature heat exchanger of said heat pumps placed in series can have a temperature of at least 30.0°C, preferably at least 35.0°C, more preferably at least 40.0°C, even more preferably at least 45.0°C, preferably at least 50.0°C, more preferably at least 55.0°C, even more preferably at least 60.0°C, preferably at least 65.0°C, more preferably at least 70.0°C, even more preferably at least 75.0°C, preferably at least 80.0°C, more preferably at least 85.0°C, even more preferably at least 90.0°C, and most preferably at least 95.0°C.

[0144] In embodiments according to the invention, such as in the context of waste heat recovery from a drying process in a kiln, the second liquid loop 103 can have a temperature at the fourth outlet 134 which is at least 20.0°C, preferably at least 25.0°C and more preferably at least 30.0°C. It will further be understood that the second liquid loop 103 can have a temperature at the fourth outlet 134 which is at most 50.0°C, preferably at most 45.0°C and most preferably at most 40.0°C.

[0145] In embodiments according to the invention, such as in the context of waste heat recovery from a drying process in a kiln, the fluid stream 104 can have a temperature at the third outlet 132 which is at least 40.0°C, preferably at least 45.0°C, more preferably at least 50.0°C and most preferably at least 55.0°C. It will further be understood that the fluid stream 104 can have a temperature at the third outlet 132 which is at most 90.0°C, preferably at most 85.0°C more preferably at most 80.0°C, and most preferably at most 75.0°C.

[0146] Referring now to Figures 4a-4b, configurations according to the invention are shown wherein at least one first heat exchanger 130 is operably connected with heat pumps of said at least one heat pump 120, via said second liquid loop 103.

[0147] Figure 4a illustrates a single first heat exchanger 130, which is connected to a second subset 126 of heat pumps via a second liquid loop 103. The second subset 126 contains four heat pumps which are arranged in series. The first heat exchanger 130 transfers heat to the fluid stream 104, which is in concurrent flow with second liquid loop 103.

[0148] Figure 4b illustrates two first heat exchangers 130a, 130b, which are arranged in parallel and which are connected to a single second subset 126 of heat pumps via a second liquid loop 103. The second subset 126 contains four heat pumps which are arranged in series. The first heat exchanger 130a, 130b transfers heat to the fluid streams 104a, 104b, respectively, which are in counterflow with said second liquid loop 103.

[0149] Referring now to Figure 5, a system 100 according to the invention is illustrated. Waste heat valorisation tower is connected with two second heat exchangers 140a, 140b, arranged in parallel, via said first liquid loop 102. Each second heat exchanger 140a, 140b is connected to a first subset 125a, 125b containing two heat pumps, via said corresponding fluid loop 141a, 141b. The heat pumps in each first subset 125a, 125b are arranged in series. Two first heat exchangers 130a, 130b each receive heat via second loops 103a and 103b respectively, from second subsets 126a and 126b, respectively. The heat pumps in subsets 126a, 126b are all arranged in series. Said first heat exchangers 130a, 130b transfer heat to fluid streams 104a, 104b respectively, which streams are arranged in counterflow configuration.

[0150] Referring now to Figure 6, a system 100 according the invention is illustrated, which system is integrated with an industrial process, being a drying process, the drying process being a kilning process, as explained herein. Waste heat valorisation tower 110 is connected with two second heat exchangers 140a, 140b, arranged in parallel, via said first liquid loop 102. Each second heat exchanger 140a, 140b is connected to a first subset 125a, 125b containing two heat pumps, via said corresponding fluid loop 141a, 141b. The heat pumps in each first subset 125a, 125b are arranged in series. One first heat exchanger 130 is integrated in an industrial process and receives heat, via said second liquid loop 103, from a single second subset 126. The heat pumps in said single second subset 126 are all arranged in series. Said first heat exchanger 130 transfers heat to said fluid stream 104 in a concurrent flow which relates herein to fresh air stream 26. The stream 26 is heated by passage through said first heat exchanger 130 and enters gas burner 30, where it is further heated. Air stream 26 forms now heated air stream 25 and passes through the kiln 20 and through the heat exchanger 240, where part of the heat is transferred to said fresh air stream 26. The stream 25 is then guided towards the waste heat valorisation tower 110, where it enters in the form of gaseous stream 101 via the first inlet 111.

[0151] Based on the above, it will thus be understood that on the low-temperature side of said the at least one heat pump 120, typically a plurality of heat pumps, a first liquid loop 102 is thus used for connecting said at least one heat pump 120 to said waste heat valorisation tower 110. On the high-temperature side of said at least one heat pump 120, typically a plurality of heat pumps, a second liquid loop 103 is thus used for connecting said first heat exchanger 130 to said at least one heat pump 120.

[0152] In other words, the low-temperature side of every heat pump in the system 100 is connected to said waste heat valorisation tower 110, directly or indirectly, via said first liquid loop 102, and the high-temperature side of every heat pump in the system 100 is connected to said at least one first heat exchanger 130, directly or indirectly, via said second liquid loop 103.

[0153] It is understood that all definitions, preferences, embodiments and preferred embodiments hereinabove, also apply for all further aspects and embodiments, as described below.

[0154] In an aspect of the invention, there is provided a method for recovering waste heat in a gaseous stream 101, the method comprising: providing said gaseous stream 101 to a waste heat valorisation tower 110; contacting said gaseous stream 101 with a stream of a first liquid loop 102, thereby allowing heat to transfer from said gaseous stream 101 to said stream of said first liquid loop 102; directing said stream of said first liquid loop 102 out of said waste heat valorisation tower 110; transferring heat from said first liquid loop 102 to the low temperature heat exchanging side of at least one heat pump 120; transferring heat from the high temperature heat exchanging side of said at least one heat pump 120 to a second liquid loop 103; directing said second liquid loop 103 into at least one first heat exchanger 130; and transferring heat, in said at least one first heat exchanger 130, from said second liquid loop 103 to a fluid stream 104.

[0155] In an aspect of the invention, there is provided a use of a waste heat valorisation tower 110 for waste heat recovery of a gaseous stream 101, preferably an air stream, said waste heat valorisation tower 110 comprising:

[0156] A first inlet 111, preferably at or near a lower end of the tower, for entering said gaseous stream 102;

[0157] A second inlet 112, preferably at or near an upper end of the tower, for entering a stream of a first liquid loop 102; and

[0158] A means 115 for contacting said stream of a first liquid loop 102 with said gaseous stream 101 such that heat passes from said gaseous stream 101 to said stream of said first liquid loop 102; a first outlet 113 for carrying out said gaseous stream 101; and a second outlet 114 for carrying out said stream of said first liquid loop 102.

[0159] In preferred embodiments, said waste heat valorisation tower 110 further comprises: A container at the lower part of the tower for receiving said stream of said first liquid loop 102, which container is connected to a second outlet 114 for carrying out said stream of said first liquid loop 102.

[0160] In preferred embodiments, said waste heat valorisation tower 110 further comprises:

[0161] A blower or fan, situated near or at the top of the waste heat valorisation tower 110, for drawing said gaseous stream 101 into the tower 110 and for exiting said gaseous stream 101 via a first outlet 113.

Claims

CLAIMS1. A system (100) for waste heat recovery from a gaseous stream (101), wherein said gaseous stream (101) is a product stream from a drying process, the system (100) comprising:A waste heat valorisation tower (110) having a first inlet (111) for entering said gaseous stream (101); a second inlet (112) for entering a stream of a first liquid loop (102); a means (115) for contacting said gaseous stream (101) with said stream of said first liquid loop (102) such that heat passes from said gaseous stream (101) to said stream of said first liquid loop (102) ; a first outlet (113) for carrying out said gaseous stream (101); and a second outlet (114) for carrying out said stream of said first liquid loop (102); wherein said means (115) for contacting said gaseous stream (101) with said stream of said first liquid loop (102) comprise a packing, wherein said stream of said first liquid loop (102) and said gaseous stream (101) are physically contacted and mixed;At least one heat pump (120), the low-temperature heat exchanging side of which is operably connected to said waste heat valorisation tower (110) via at least said first liquid loop (102);At least one first heat exchanger (130), which is each operably connected to the high-temperature heat exchanging side of one or more heat pump of said at least one heat pump (120), via at least a second liquid loop (103), wherein said at least one first heat exchanger (130) is configured to transfer heat from said second liquid loop (103) to a fluid stream (104), which then forms a heated air stream (25), which is then passing through a drying oven of said drying process.

2. The system (100) according to claim 1, wherein said low-temperature heat exchanging side of each of said at least one heat pump (140) is operably connected with said waste heat valorisation tower (110) via said first liquidloop (102), so that a stream of said first liquid loop (102) leaving said waste heat valorisation tower (110) via said second outlet (114) passes through each of said low-temperature heat exchanging side of said at least one heat pump (120) before returning to said second inlet (112).

3. The system (100) according to claim 1, wherein at least one second heat exchanger (140) is operably connected with said waste heat valorisation tower (110) via said first liquid loop (102) so that a stream of said first liquid loop (102) leaving said waste heat valorisation tower (110) via said second outlet (114) passes through each of said at least one second heat exchanger(140) before returning to said second inlet (112), wherein each of said at least one second heat exchanger (140) is configured to transfer heat from said first liquid loop (102) to its own corresponding fluid loop (141), wherein said at least one heat pump (120) relates to one or more first subsets (125) of heat pumps, wherein each first subset (125) contains one or more heat pump, wherein each low-temperature heat exchanging side of said one or more heat pump belonging to one such first subset (125) is operably connected with one particular corresponding second heat exchanger of said at least one second heat exchanger (140) via said corresponding fluid loop(141).

4. The system (100) according to any one of claims 1-3, wherein said first inlet (111) is at or near a lower end of said waste heat valorisation tower (110), and wherein said second inlet (112) is at or near an upper end of said waste heat valorisation tower (110).

5. The system (100) according to any one of claims 1-4, wherein said gaseous stream (101) relates to an air stream.

6. The system (100) according to any one of claims 1-5, wherein said first liquid loop (102) comprises water.

7. The system (100) according to any one of claims 3-6, wherein each one of said at least one second heat exchanger (140) is operably connected via its corresponding fluid loop (141) with at least two heat pumps, preferably with two heat pumps.

8. The system (100) according to any one of claims 3-7, wherein no more than two heat pumps in a first subset (125) of heat pumps are placed in series.

9. The system (100) according to any one of claims 1-8, wherein said at least one first heat exchanger (130) is configured to transfer heat from said second liquid loop (103) to a fluid stream (104), wherein said at least one first heat exchanger (130) has a third inlet (131) and third outlet (132) for said fluid stream (104), and a fourth inlet (133) and a fourth outlet (134) for said second liquid loop (103).

10. The system (100) according to any one of claims 1-9, wherein said at least one first heat exchanger (130) is further operably connected with said at least one heat pump (120), via said second liquid loop (103), so that a stream of said second liquid loop (103) leaving said at least one first heat exchanger (130) via said fourth outlet (134) passes through each of said high temperature heat exchanging side of said at least one heat pump (120) before returning to said fourth inlet (133) of said at least one first heat exchanger (130).

11. The system (100) according to any one of claims 1-9, wherein said at least one heat pump (120) relates to one or more second subsets (126) of heat pumps, wherein each second subset (126) may contain one or more heat pump of said at least one heat pump (120), wherein each high-temperature heat exchanging side of said one or more heat pump (120) belonging to one such second subset (126) is operably connected with one particular corresponding first heat exchanger of said at least one first heat exchanger (130), via a second liquid loop (103).

12. The system (100) according to any one of claims 1-11, wherein at least one of said second liquid loop (103), said corresponding fluid loop (141) and / or at least one heat pump (120) contains a refrigerant which is selected from the following: water; glycol; a water / glycol mixture; NH3 (R717); butane; a chlorofluorocarbon (CFC) and / or hydrochlorofluorocarbon (HCFC), such as HCFC-22, Freon-12 and Freon-21; a hydrofluorocarbon (HFC) and its mixtures, such as R134a, R125, R32 (HFC-32) and R410-a; a hydrofluoroolefin (HFO), such as HFO-1234ze, HFO-1234yf and HFO-1336mzz; and mixtures thereof.

13. Method for recovering waste heat in a gaseous stream (101), wherein said gaseous stream (101) is a product stream from a drying process, the method comprising: providing said gaseous stream (101) to a waste heat valorisation tower (110); contacting said gaseous stream (101) with a stream of a first liquid loop (102), thereby allowing heat to transfer from said gaseous stream (101) to said stream of said first liquid loop (102); directing said stream of said first liquid loop (102) out of said waste heat valorisation tower (110); transferring heat from said first liquid loop (102) to the low temperature heat exchanging side of at least one heat pump (120);transferring heat from the high temperature heat exchanging side of said at least one heat pump (120) to a second liquid loop (103); directing said second liquid loop (103) into at least one first heat exchanger (130); and transferring heat, in said at least one first heat exchanger (130), from said second liquid loop (103) to a fluid stream (104), which then forms a heated air stream (25), which is then passing through a drying oven of said drying process.

14. Use of a waste heat valorisation tower (110) for waste heat recovery of a gaseous stream (101), wherein said gaseous stream (101) is a product stream from a drying process, preferably an air stream, said waste heat valorisation tower (110) comprising:A first inlet (111), preferably at or near a lower end of the tower, for entering said gaseous stream (102);A second inlet (112), preferably at or near an upper end of the tower, for entering a stream of a first liquid loop (102);A means (115) for contacting said stream of a first liquid loop (102) with said gaseous stream (101) such that heat passes from said gaseous stream (101) to said stream of said first liquid loop (102), wherein said means (115) for contacting said gaseous stream (101) with said stream of said first liquid loop (102) comprise a packing, wherein said stream of said first liquid loop (102) and said gaseous stream (101) are physically contacted and mixed; a first outlet (113) for carrying out said gaseous stream (101); and a second outlet (114) for carrying out said stream of said first liquid loop (102), wherein said at least one first heat exchanger (130) is configured to transfer heat from said second liquid loop (103) to a fluid stream (104), which then forms a heated air stream (25), which is then passing through a drying oven of said drying process.

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