A method and a system for producing and transferring heat, and a thermal mixing unit

Abstract

A method for producing and transferring heat The method comprises producing heat in a first thermal device (910) and heating particulate material in the first thermal device (910) and conveying a part (MIH) of the particulate material, the part (MIH) having a first temperature (T1), from the first thermal device (910) to a mixing unit (100). The method comprises conveying a part (MIC) of particulate material, the part (MIC) having a second temperature (T2), from a second thermal device (920) to the mixing unit (100) and mixing the part (MIH) of the particulate material coming from the first thermal device (910) with the part (MIC) of the particulate material coming from the second thermal device (920) in the mixing unit (100) to form particulate material having a third temperature (T3). The method comprises conveying at least a part (MOH) of the particulate material having the third temperature (T3) from the mixing unit (100) to the second thermal device (920). A system for the same. A mixing unit suitable for the method.

Description

[0001] A method and a system for producing and transferring heat, and a thermal mixing unit

[0002] Technical field

[0003] The invention relates to a method for producing heat and transferring heat. The invention relates to temperature and heat transfer control by direct contact mixing of particulate materials from multiple sources and temperatures. The invention relates to a system for performing the method. The invention relates to controlling the composition of the material in question by separating material fractions therefrom. The invention relates to a thermal mixing unit for transferring heat from a first material circulation to a second material circulation by direct contact of particulate materials of the material circulations.

[0004] Background

[0005] Fast pyrolysis is a thermal process, in which hot particulate material is contacted with carbon-containing material to pyrolyze the material. A heat source for the process may be e.g. a fluidized bed combustor. Such a system is known in the field of pyrolysis e.g. from the publication WO 2016 / 166413.

[0006] A prior art system, wherein hot particulate material is produced in the fluidized bed boiler (or more generally, in a first thermal device 910) and used in the pyrolysis reactor (or more generally, in a second thermal device 920), is shown schematically in Fig. 1 a.

[0007] A problem in such a system is that the particulate material receivable from the first thermal device 910 (e.g. the fluidized bed boiler) may be extremely hot, even hotter than practically can be used in the second thermal device 920 (e.g. the pyrolysis reactor). Reasons for the material being too hot depend on the application. E.g. in torrefaction, too hot particulate material may promote reactions or volatilization of such compounds that should not be reacted / volatilized. Equipment may have been made of materials that can not withstand such a high temperature. Pyrolysis products may thermally dissociate, if contacted with too hot particulate material. In all such cases, the bed material receivable from the first thermal device 910 as such would be too hot for use. For these reasons, there is a need to cool down the particulate material before feeding it to the second thermal device 920.

[0008] As a first solution to the problem, the inventors considered a cooler for cooling the particulate material, as shown in Fig. 1 b. However, it was soon realized that particularly in such an application where a lot of cooling is required, the cooling produces a lot a heat, which possibly is not utilizable. Therefore, such a solution in many cases results in significant energy losses. Energy loss, such as heat loss, may have to be compensated by using more fuel to produce the same amount of heat or other type of energy. Thus, the solution of Fig. 1 b was found not to be optimal in terms of efficiency for all applications.

[0009] The present invention is aimed at a solution for cooling the particulate material without the need for removing heat therefrom.

[0010] As a solution to the problem, the inventors found that instead of a cooler for cooling the particulate material, a thermal mixing unit 100 (see e.g. Figs. 2a to 2d) can be used to mix hot particulate material coming from the first thermal device 910 (e.g. fluidized bed combustor) with cooler particulate material coming from the second thermal device 920 (e.g. pyrolysis reactor). Upon mixing, the temperature of the mixture of the particulate materials will be less than the temperature of the particulate material coming from the first thermal device 910. A part of the mixture may then be fed to the second thermal device 920 to be used therein according to the needs. Another part of the mixture and / or a part of the material receivable from the second thermal device 920 may be fed to the first thermal device 910 to be re-heated. The inventors consider that this concept is widely applicable also in the context of other heat producing devices (i.e. other types of first thermal devices 910) and / or in the context of other heat consuming devices (i.e. other types of second thermal devices 920). Hereinafter the term mixing unit is used for the thermal mixing unit. A system and a method according to the invention is disclosed in more specific terms in claims 12 and 1 , respectively. In addition, the inventors consider that an embodiment of the mixing unit as such can be utilized also in some other fields. A mixing unit according to the invention is presented in claim 19 in isolation from the system. However, the mixing unit may be part of the system.

[0011] Brief description of the drawings

[0012] Fig. 1 a illustrates a prior art system comprising a fluidized bed boiler (an example of a first thermal device), pyrolysis reactor (an example of a second thermal device), and channels for exchanging particulate material in between,

[0013] Fig. 1 b illustrates a comparative example system comprising in addition to the devices of Fig. 1 a a cooler in between the thermal devices for cooling the particulate material,

[0014] Figs. 2a-2d illustrate embodiments of a system comprising a first thermal device, a second thermal device, and a mixing unit,

[0015] Fig. 3 illustrates an embodiment of a mixing unit comprising a mixer and a concentrator,

[0016] Fig. 4 illustrates a mixing unit consisting of a mixer,

[0017] Fig. 5 illustrates a mixing unit consisting of a mixer,

[0018] Fig. 6 illustrates an embodiment of a mixing unit functioning as a mixer and / or a concentrator,

[0019] Fig. 7 illustrates an embodiment of a mixing unit consisting of concentrator,

[0020] Fig. 8 illustrates an embodiment of a system comprising a first thermal device, a second thermal device, a mixing unit comprising a mixer and a concentrator, and channels for guiding particulate material on one hand between the first thermal device and the mixer, and on the other hand between the second thermal device and the mixer, and

[0021] Fig. 9 illustrates an embodiment of a system comprising a mixing unit 100 and a secondary mixing unit 100b consisting of a concentrator for separating a light material fraction from particulate material.

[0022] In the figures, Sz denotes an upward vertical direction. Detailed description

[0023] Figures 2a to 2d illustrate embodiments of a system that comprises a first thermal device 910, a second thermal device 920, and a mixing unit 100. The first thermal device 910 is for producing heat and for heating particulate material. The second thermal device 920 is configured to utilize, store, or utilize and store the heat produced in the first thermal device 910. A corresponding method comprises producing heat in the first thermal device 910 and heating particulate material in the first thermal device 910. Some of this heat is transferred to the second thermal device 920 through a mixing unit 100 as detailed below.

[0024] The mixing unit 100 is used for mixing particulate material MIH receivable from the first thermal device 910 with particulate material Mic receivable from the second thermal device 920 for the purpose of producing cooler particulate material by the mixing. To elaborate, by mixing the particulate material MIH receivable from the first thermal device 910 with the particulate material Mic receivable from the second thermal device 920 a mixture will be produced. In line with this, the method comprises conveying a part MIH of the particulate material from the first thermal device 910 to the mixing unit 100. Within this description, a first temperature T 1 is defined such that this part MIH has the first temperature Ti. The method further comprises conveying the part Mic of the particulate material from the second thermal device 920 to the mixing unit 100. Within this description, a second temperature T2 is defined such that this part Mic has the second temperature T2. Reference is made to Figs. 2a to 2d. The second temperature T2 is less than the first temperature T1 (i.e. T2<TI).

[0025] Furthermore, the method comprises mixing the part MIH of the particulate material coming from the first thermal device 910 with the part Mic of the particulate material coming from the second thermal device 920 in the mixing unit 100 to form particulate material having a third temperature T3. The particulate material having the third temperature T3 is the mixture as discussed above. In other words, the particulate material having the third temperature T3, which is conveyed to the second thermal device 920 as detailed below, is the mixture of particulate material MIH receivable from the first thermal device 910 and the particulate material Mic receivable from the second thermal device 920. Because of the mixing, the third temperature T3 is between the first and second temperatures (i.e. T2<TS<TI).

[0026] Correspondingly, the system comprises a mixing unit 100 for mixing particulate material MIH receivable from the first thermal device 910 with particulate material Mic receivable from the second thermal device 920.

[0027] As detailed above, at least a part of the mixture will be stored or utilized in the second thermal device 920. Therefore, in the system the mixing unit 100 is for the purpose of conveying at least a part of the mixture MOH of the particulate materials to the second thermal device 920. Likewise, the method comprises conveying at least a part MOH of the particulate material having the third temperature T3 from the mixing unit 100 to the second thermal device 920 for storing the heat to the particulate material arranged in the second thermal device 920 or for utilizing the heat of the particulate material in second thermal device 920. By conveying the particulate material having the third temperature T3 from the mixing unit 100 to the second thermal device 920 heat is transferred to the second thermal device 920.

[0028] Moreover, to re-heat the particulate material in the first thermal device 910, some particulate material is transferred from the second thermal device 920 to the first thermal device 910. Referring to Figs. 2a and 2b, the particulate material may be transferred through the mixing unit 100. Referring to Fig. 2c, the particulate material may be transferred directly from the second thermal device 920 to the first thermal device 910 such that the material entering the first thermal device 910 bypasses the mixing unit 100. Referring to Fig. 2d, a part of the particulate material may be transferred directly from the second thermal device 920 to the first thermal device 910 and another part may be transferred through the mixing unit 100.

[0029] Figs. 2a and 2b show a preferable embodiment. According to these figures, the method comprises conveying particulate material Moc from the mixing unit 100 to the first thermal device 910. Within this description, a fourth temperature T4 is defined such that this particulate material Moc has the fourth temperature In this way, in the method and in use of the system according to the embodiments of Figs. 2a, 2b, and 2d, two particulate material circulations are formed. In a first circulation, hot particulate material MIH having the first temperature Ti runs from the first thermal device 910 to the mixing unit 100 and cooler particulate material Moc having the fourth temperature T4 runs from the mixing unit 100 back to the first thermal device 910. Because this first material circulation hands over heat to a second circulation, the first temperature T1 is greater than the fourth temperature T4 (i.e. TI>T4). In the second circulation, less hot particulate material MOH having the third temperature T3 runs from the mixing unit 100 to the second thermal device 920 and coolest particulate material Mic having the second temperature T2 runs from the second thermal device 920 to the mixing unit 100. Because this second material circulation hands over heat to a process within the second thermal device 920, the third temperature T3 is greater than the second temperature T2 (i.e. Ts>T2). Moreover, because the mixing of the particulate material within the mixing unit 100 equalizes temperature differences between the material that are mixed, the first temperature T1 is greater than the third temperature T3 (i.e. Ti>Ts). This also solves the problem indicated in the background.

[0030] Depending on the structural details of the mixing unit 100, the fourth temperature T4 may equal the second temperature T2 (i.e. T4=T2), the fourth temperature T4 may equal the third temperature T3 (i.e. T4=Ts), or the fourth temperature T4 may be between the second temperature T2 and the third temperature Ts (i.e. T2<T4<Ts). Reference is made to Figs. 2a, 2b, and 8.

[0031] However, in certain applications, heat-treated particulate material may be withdrawn from the mixing unit 100 for other purposes than serving as a heat transfer medium. For example, torrefied material may be withdrawn from the mixing unit and stored as fuel. The reference 930 in Fig. 2c refers to any other equipment 930 receiving material from the mixing unit 100, other than the first or the second thermal device 910, 920. The equipment 930 may be e.g. a storage for heat-treated material. To enable circulation of hot particulate material in such a case, the material to be heated may bypass the mixing unit 100 as detailed above and shown in Fig. 2c. In Fig. 2c, the material MIC2 bypasses the mixing unit 100 through a bypass 316. Referring to Figs. 2a to 2d and 8, correspondingly, the system comprises a first channel 311 for conveying particulate material from the first thermal device 910 to the mixing unit 100, a second channel 312 for conveying particulate material from the second thermal device 920 to the mixing unit 100, and a third channel 313 for conveying particulate material from the mixing unit 100 to the second thermal device 920. The embodiments shown in Figs. 2a, 2b, 2d, and 8 also comprise a fourth channel 314 for conveying particulate material from the mixing unit 100 to first thermal device 910. The embodiments shown in Figs. 2c and 2d comprise a bypass 316 for conveying particulate material directly from the second thermal device 920 to first thermal device 910.

[0032] In the embodiment of Figure 2a, the part MOH going to the second thermal device 920 from the mixing unit 100 and the part Moc going to the first thermal device 910 from the mixing unit 100 leave the mixing unit 100 through separate to channels 313, 314. Thus, the fourth temperature T4 may be different from the third temperature T3. In an embodiment, the fourth temperature T4 is less than the third temperature T3. Further details will be given below.

[0033] In the embodiment of Figure 2b, the part MOH going to the second thermal device 920 from the mixing unit 100 and the part Moc going to the first thermal device 910 from the mixing unit 100 initially leave the mixing unit 100 from the same outlet, which is then divided into two separate channels 313, 314. The division of parts (MOH, MOC) to determine the amount entering each channel 313, 314 and eventually the respective thermal devices 920, 910 (respectively) can be done according to the process and system needs. In the embodiment of Fig. 2b, the fourth temperature T4 equals the third temperature T3.

[0034] As detailed above, in the method, mixture of particulate material MIH receivable from the first thermal device 910 and particulate material Mic receivable from the second thermal device 920 is conveyed to the second thermal device from the mixing unit 100. Correspondingly, the third channel 313 is for conveying a mixture of particulate material MIH receivable from the first thermal device 910 and particulate material Mic receivable from the second thermal device 920 from the mixing unit 100 to the second thermal device 920. Effectively, the part MIH having the first temperature Ti is used to heat the part Mic having the second temperature T2 to form particulate material having the third temperature T3. A part MOH of the particulate material having the third temperature T3 is then conveyed to the second thermal device 920. Another part having this temperature may be conveyed to the first thermal device 910 (see Fig. 2b), or a part Moc having a fourth temperature T4 may conveyed to the first thermal device 910 (see fig. 2a), or material MIC2 from the second thermal device 920 is only conveyed to the first thermal device 910 through the bypass 316 (see Fig. 2c). Material MIC2 may be conveyed from the second thermal device 920 to the first thermal device 910 through the bypass 316 and material (Mic, Moc) may be conveyed from the second thermal device 920 to the first thermal device 910 through the mixing unit 100 (see Fig. 2d).

[0035] The mixing unit 100 in the configurations of Figures 2a to 2d differs from the cooler illustrated in the comparative example of Figure 1 b in that the cooling is enabled by mixing the particulate materials receivable from the two thermal devices 910, 920 as discussed above. The heat of the part MIH having the first temperature T1 is effectively transferred to the incoming ‘Warm material’ flow of Figure 1 b and retained within the process, instead of being transferred outside of the process and lost as is done with the cooler in Figure 1 b. Another function of the mixing unit 100 may be the separation of different material fractions from the particulate material flow between the first thermal device 910 and the second thermal device 920, thereby concentrating valuable materials.

[0036] In an embodiment, the temperature of the particulate material is reduced in the mixing unit 100 by an amount that is sufficient for the process. Moreover, considering that using the mixing unit 100 involves some investments, a temperature difference should not be negligible. In an embodiment, the first temperature T1 is at least 50 °C higher than the third temperature T3. In a preferred embodiment, the first temperature T1 is at least 100 °C, at least 150 °C, or at least 200 °C higher than the third temperature T3. For example, the first temperature T1 may be 50 °C to 500 °C, 150 °C to 500 °C, or 200 °C to 500 °C higher than the third temperature T3.

[0037] An absolute value of the first temperature T1 depends on the type of the first thermal device 910. In a preferable embodiment, the first thermal device 910 comprises a combustor, such as a fluidized bed combustor. In such an embodiment, the first temperature T 1 is, for example, at least 700 °C, or 700 °C to 1100 °C, preferably at least 750° C, and more preferably 750° C to 1100° C.

[0038] In a preferable embodiment, the second thermal device 920 is configured to thermally treat carbon-containing material within the second thermal device 920. In such an embodiment, the third temperature Ts is preferably at most 650 °C, or 300 °C to 650 °C, preferably at most 500 °C, more preferably 300 °C to 500 °C.

[0039] These temperature levels may vary and are dependent on the system configuration, the thermal devices 910, 920 used, and configuration of the mixing unit 100. In an embodiment, the first thermal device 910 comprises a fluidized bed combustor. Preferably, the first thermal device 910 comprises a fluidized bed boiler, such as a circulating fluidized bed boiler. In this case, the first thermal device 910 is used for burning solid fuel to heat particulate material, such as sand. As an alternative to a fluidized bed combustor, first thermal device 910 may comprise of a variety of other means for producing heat, such as an electric heater.

[0040] The second thermal device is 920 is configured to utilize, store, or utilize and store heat produced in the first thermal device 910. The second thermal device 920 can comprise a pyrolysis reactor, a gasification reactor, a torrefaction reactor, or a storage for hot particulate material. Preferably the second thermal device 920 comprises a pyrolysis reactor, a gasification reactor, or a torrefaction reactor, for thermally treating carbon-containing material.

[0041] Such a second thermal device 920, if present, is also used for this purpose. Accordingly, an embodiment of the method comprises conveying the particulate material that is conveyed to the second thermal device 920 into the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, and treating thermally carbon-containing material in the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively, by using heat of the particulate material that is conveyed from the mixing unit 100 to the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively. Such an embodiment further comprises feeding carbon- containing material to the second thermal device 920. With reference to Figs. 8 and 9, the carbon-containing material may be fed directly to the second thermal device 920 or the carbon-containing material may be to the fed to the third channel 313, through which the carbon-containing material would then enter the second thermal device 920.

[0042] Hereinabove, carbon-containing material refers to a material that comprises carbon. In an embodiment, the carbon-containing material refers to a material that comprises at least 25 w% (percentage by weight) carbon in terms of dry mass, and preferably the material comprises at least 40 w% carbon in terms of dry mass. Carbon-containing material may comprise or consist of biomass. Carbon-containing material may comprise polymer materials, e.g. plastics. Carbon-containing material may comprise or consist of residue-derived material, such as refuse-derived fuel (RDF) and / or solid recovered fuel (SRF). In general, SRF is a special type of RDF, and SRF has a standardized quality.

[0043] Carbon-containing material may comprise polymer materials, e.g. plastics. Carbon-containing material may comprise or consist of residue-derived material, such as refuse-derived fuel (RDF) and / or solid recovered fuel (SRF). In general, SRF is a special type of RDF, and SRF has a standardized quality. The carbon-containing material may comprise or consist of biomass. Biomass may comprise materials of animal origin and / or material of plant origin. In general, material of plant origin comprises lignocellulosic material.

[0044] Each one of pyrolysis, gasification, and torrefaction is somewhat sensitive to the temperature of the material that is used for heating carbon-containing material especially when the carbon containing material is biomass. E.g. in pyrolysis and gasification of biomass, the product may thermally dissociate or degrade, if contacted with too hot material. Likewise, in torrefaction contact of biomass with too hot material might result in pyrolysis instead of torrefaction . Thus, guiding too hot particulate material into the second thermal device 920 may result in undesirable product distribution. In this way, in all these processes there is a need for using, as a heat source, particulate material having a temperature that is lower than a temperature in a furnace. In such a case, in particular biomass and materials receivable from the biomass by gasification, pyrolysis or torrefaction are sensitive to temperature. Therefore, a particularly appealing application of the invention is one in which biomass is treated in the second thermal device 920 by pyrolysis, gasification, or torrefaction, whereby the second thermal device is a pyrolysis reactor, a gasification reactor, or torrefaction reactor, respectively, and biomass is fed to the second thermal device 920. Herein biomass refers to carbon-containing material that is a renewable organic material that comes from plants or animals.

[0045] A pressure in the first thermal device 910 may be, e.g., substantially atmospheric or slightly less than atmospheric, particularly when heating the particulate material in the first thermal device 910 involves combustion. A pressure in the second thermal device 920 may be, e.g., higher than atmospheric. This has beneficial effect in such embodiments that involve thermal treatment of carbon-containing material. For these reasons, in an embodiment, a pressure in the first thermal device 910 is less than a pressure in the second thermal device 920. Preferably, a pressure in the first thermal device 910 is at least 5 kPa less than a pressure in the second thermal device 920. More preferably, a pressure in the first thermal device 910 is 5 kPa to 90 kPa, such as 10 kPa to 90 kPa, less than a pressure in the second thermal device 920. As an example, a pressure in the first thermal device 910 is, in an embodiment, 0.5 to 1 .05 bar(a) and a pressure in the second thermal device 920 is 1 .1 to 10 bar(a). Herein the unit bar(a) stands for bar and is used for the absolute pressure (i.e. not an overpressure relative to atmospheric).

[0046] Figure 3 illustrates a preferable embodiment of the mixing unit 100. In the embodiment of Fig. 3, the mixing unit 100 comprises a first chamber 210 and first nozzles 212 arranged at a bottom of the first chamber 210. The mixing unit 100 further comprises a second chamber 220 and second nozzles 222 arranged at a bottom of the second chamber 220. When the mixing unit 100 is used, the part MIH of the particulate material coming from the first thermal device 910 is guided to the first chamber 210 through a first inlet 111 and the part Mic of the particulate material coming from the second thermal device 920 is guided to the second chamber 220 through a second inlet 112. Moreover, a part of the particulate material coming from the second thermal device 920 is guided through a first internal channel 321 to the first chamber 210 from the second chamber 220. In use, a first bed B1 of particulate material is arranged in the first chamber 210 and a second bed B2 of particulate material is arranged in the second chamber 220. The particulate material within the first chamber 210 is fluidized by feeding fluidizing gas (Gi, G11) through the first nozzles 212 to mix the particulate materials in the first chamber 210 to form the particulate material MOH having the third temperature Ts, i.e. the mixture of the particulate material received from the first and second thermal devices (910, 920). In this way, a function of the first chamber 210 is to mix the particulate materials. Thus, the first chamber 210 can be seen as a mixer of the mixing unit 100. In addition to mixing the particulate material, the fluidizing gas has the effect of enhancing material flow. Therefore, the mixing unit 100 does not need mechanical conveyors for conveying the particulate material. Having the particulate material in a fluidized state alone may be sufficient for arranging proper material circulations, at least when the inlets and outlets of the first and second thermal devices are arranged on proper heights, as clear to a skilled person. The fluidizing gas is guided from an upper part of the first chamber 210 to an upper part of the second chamber 320 through a second internal channel 322.

[0047] The particulate material within the with second chamber 220, which is received only from the second thermal device 920, is fluidized by feeding fluidizing gas G12 through the second nozzles 222 to separate an upper material fraction MLand a lower material fraction MH from the particulate material received in the second chamber 220. In this way, a function of the second chamber 220 is to concentrate the materials of the upper material fraction ML. In this way, the second chamber 220 can be seen as a concentrator of the mixing unit 100. Referring to Fig. 3, the lower material fraction MH is guided to the first internal channel 321 to the first chamber 210, and through the first chamber 210 after mixing with the particulate material coming from the first thermal device 910 to the second thermal device 920. Referring to Figs. 3 and 8, in an embodiment, the upper material fraction ML is guided to the first thermal device 910 as the particulate material Moc having the fourth temperature T4. In addition to the upper material fraction ML, excess fluidizing gas G01 can be guided to the first thermal device 910. Referring to Figs. 3 and 2c, in an embodiment, the upper material fraction ML is guided to another equipment 930, e.g., for storing.

[0048] Thus, the part MOH of the particulate material that is guided from the mixer 100 to the second thermal device 920 comprises at least a part of the lower material fraction MH. Moreover, in an embodiment, the particulate material Moc that is guided from the mixing unit 100 to the first thermal device 910 comprises the upper material fraction ML. In an embodiment, the upper material fraction ML comprises solid particulate material and the lower material fraction MH comprises solid particulate material. However, in between the mixing unit 100 and the first thermal device 910 a further concentrator may be used upon needs. Thus, in an embodiment, the particulate material Moc that is guided from the mixing unit 100 to the first thermal device 910 comprises a part of the upper material fraction ML.

[0049] As detailed above, a function of the first chamber 210 is to mix the particulate materials with each other, whereby the first chamber 210 constitutes a mixer. However, a function of the second chamber 220 is to separate the upper material fraction MLand a lower material fraction MH from the particulate material, whereby the second chamber 220 constitutes a concentrator. However, also the concentrator may be used to mix the materials. Therefore, the mixing unit 100 comprises at least one of a mixer and a concentrator. That is, the mixing unit 100 comprises at least one of the first chamber 210 and the second chamber 220 in the meaning discussed above.

[0050] In general, mixing of the material improves by using a high rate of fluidizing gas. Conversely, separation of material requires only a mild fluidizing velocity. Therefore, in an embodiment, a velocity of the fluidizing gas G11 used to fluidize material in the first chamber 210 is higher than a velocity of the fluidizing gas G12 used to fluidize material in the second chamber 220. Typically, when the second thermal device 920 is used to thermally treat carbon-containing material, the upper material fraction MLwill contain a lot of residuals of the carbon containing material and the lower material fraction MH will contain mainly solid particulate material other than such residuals, e.g. sand. In an embodiment a content of residuals of the carbon-containing material of the upper material fraction ML is higher than a content of residuals of the carbon- containing material of the lower material fraction MH.

[0051] The embodiment of Fig. 3 is also beneficial because therein the fourth temperature T4 is less than the third temperature T3. This is due to the separation of materials (ML, MH) in the second chamber 220 and mixing the materials (MH, MIH) in the first chamber 210 subsequently. It is the mixing that transfers heat between the particulate materials. Therefore, the temperature of the material coming from the second thermal device 920 is only increased in the first chamber 210 by mixing with the material coming from the first thermal device 910; however, the upper material fraction ML is separated already in the second camber 220 before the mixing. This is beneficial in terms of energy balance in the process. Thus, in a preferable embodiment, the fourth temperature T4 is less than the third temperature T3. The fourth temperature T4 may be, e.g., at least 20 °C or at least 50 °C less than the third temperature T3.

[0052] However, the mixing unit 100 does not need to comprise a chamber for separating the upper and lower material fractions. Instead, the materials may only be mixed. Moreover, the material may be mixed also, e.g., in a channel for feeding the material to a concentrator (see Fig. 7).

[0053] Figure 4 illustrates another embodiment of the mixing unit 100. In this embodiment the mixing unit 100 comprises a chamber 210, 220 and nozzles 212, 222 arranged at a bottom of the chamber 210, 220. The chamber can be referred to as first chamber 210 or as a second chamber 220. However, if the mixing unit 100 only comprises one chamber, it might be logical to refer to the chamber as a first chamber. Moreover, if a primary technical function of the chamber 210, 220 is to mix material, it has the same function as the first chamber 210 of the embodiment of Fig. 3. In Fig. 4, particulate material from the first thermal device 910 enters the chamber 210, 220 at the first temperature T1 through a first inlet 111 and particulate material Mic from the second thermal device 920 enters the chamber 210, 220 at a second temperature T2 through the second inlet 112. Obviously, these particulate materials could enter the chamber 210, 220 through only one inlet. In Fig. 4, fluidizing gas Gi is fed through the nozzles 212, 222 to fluidize and mix the parts (Mic, MIH) of particulate material for heat to be transferred and recovered between the parts (Mic, MIH) of particulate material. Gases Go are guided out of the mixing unit 100 near the particulate material inlets. A part MOH of particulate material at a third temperature T3 and a part Moc of particulate material at a fourth temperature T4 leave the mixing unit 100 through an outlet 121. In this embodiment, the third temperature T3 is equal to the fourth temperature T4.

[0054] Figures 5, 6, and 7 illustrate other embodiments of the mixing unit 100, the mixing unit 100 comprising a chamber 210, 220 be it called the first chamber 210 or the second chamber 220. What has been said about numbering the chamber in the context of the embodiment of Fig. 4 applies to the embodiment of Fig. 5, 6, or 7.

[0055] As for the inlet or inlets, in the embodiment of Figure 5 or 6, the part MIH of the particulate material heated in the first thermal device 910 enters the first chamber 210 at the first temperature Ti through the first inlet 111 and the part Mic of the particulate material used or stored in the second thermal device 920 enters the first chamber 210 at the second temperature T2 through the second inlet 112. In the embodiment of Figure 7, both the part MIH of the particulate material at the first temperature T1 and the part Mic of the particulate material at the second temperature T2 enter the chamber 210 through the first inlet 111. Therefore, in the embodiment of Fig. 7, some mixing of the parts of the particulate material take place already by guiding the parts of the material to the chamber 220. The embodiments of Figs. 3 to 7 comprise a first inlet 111 for receiving particulate material MIH from the first thermal device 910. In addition, the embodiments of Figs. 3, 4, 5, and 6 comprise a second inlet 112 for receiving particulate material MIH from the second thermal device 920. However, the second inlet 112 is not needed (see Fig. 7 and / or the discussion related to Fig. 4).

[0056] As for the outlets, in the embodiment of Figure 5, the part MOH of the particulate material at the third temperature T3 and the part Moc of particulate material at the fourth temperature T4 leave the mixing unit 100 through a first outlet 121 , i.e. through the same first outlet 121. In the embodiments of Figures 6 and 7, the part MOH of particulate material at the third temperature T3 leaves the mixing unit through a first outlet 121 and the part Moc of particulate material at the fourth temperature T4 leaves the mixing unit 100 through a second outlet 122. In the embodiments of Figs. 4 and 5, the third and fourth temperatures are equal, because the particulate material is taken through only one outlet 121. Moreover, in the embodiments of Figs. 6 and 7 the third and fourth temperatures are at least substantially equal, because the particulate materials mix before guiding the parts through the first and second outlets 121 , 122.

[0057] Concerning the fluidizing gas, the embodiments of Figs. 5, 6, and 7 further comprise an outlet for letting out (used) fluidizing gas Go. To fluidize the materials within the beds (B1 , B2), (fresh) fluidizing gas Gi is fed through the nozzle arrangements (212, 222). Reference is made to Figs. 5, 6, and 7. In line with what has been said above, in the embodiments of Figs. 6 and 7, the (used) fluidizing gas Go could be led out through second outlet 122 (as an alternative or in addition to the outlet shown in Figs. 6 and 7).

[0058] As readable from the above, the mixing unit 100 of the embodiment of Fig. 5 serves mainly the purpose of mixing materials and in this way functions substantially in a similar manner as the first chamber 210, i.e. the mixer, of the embodiment of Fig. 3. However, the mixing unit 100 of the embodiment of Fig. 7 serves mainly the purpose of separating materials and in this way function substantially in a similar manner as the second chamber 220, i.e. the concentrator, of the embodiment of Fig. 3.

[0059] Naturally such mixers and / or concentrators and / or mixing units comprising both a mixer and a concentrator may be arranged in cascade e.g. in the second material circulation, as depicted in Fig. 9. Therein a secondary mixing unit 100b according to Fig. 7 serves for the purpose of separating a light material fraction ML and the mixing unit 100, which is arranged after the secondary mixing unit 100b and is according to the embodiment of Fig. 5, mixes the particulate materials coming from the first thermal device 910 and from the secondary mixing unit 100b. In this way, the secondary mixing unit 100b act mainly as a concentrator and the mixing unit 100 acts as a mixer. However, compared to the embodiment of Fig. 3, cascading the two mixing units as in Fig. 9, has the result that the third temperature Ts equals the fourth temperature T4, which is energetically not as favorable as the embodiment of Fig. 3, in which the fourth temperature T4 is less than the third temperature T3.

[0060] Even if the embodiment of Fig. 7 of the mixing unit serves mainly the purpose of separating materials, it also further mixes the materials therein. Thus, when particulate material from the first thermal device 910 is guided to the mixing unit 100 and particulate material from the second thermal device 920 is guided to the mixing unit 100, these materials are mixed with each other. Then part of the mixture of the materials may be used in the second thermal device 920 and another part may be guided to the first thermal device 910 for re-heating, in line with Fig. 2b, or taken for other use in line with Figs. 2c and 2d. When the mixing unit 100 does not comprise a first chamber 210 in the meaning of a mixer as discussed above and comprises the second chamber 220 in the meaning of a concentrator as discussed above, the method comprises guiding particulate material from the first thermal device 910 to the second chamber 220. Moreover, particulate material may be guided directly from the second chamber 220 to the second thermal device 920. However, as depicted in Fig. 3, when two chambers 210, 220 are used, particulate material from the first thermal device 910 may be guided directly to the first chamber 210.

[0061] As detailed above, in the method and / or in a use of the mixing unit, there may be a pressure difference between the first thermal device 910 and the second thermal device 920 so that a pressure in the second thermal device is higher than in the first thermal device 910. To control the flow of the particulate material in the two material circulations discussed above, in such an embodiment, preferably, a pressure lock is generated in the mixing unit 100 by arranging the particulate materials to enter and exit the mixing unit 100 to / from suitable levels so that a fluidized bed B1 , B2 arranged in the mixing unit generates hydrostatic pressure that serves as the pressure lock for the pressure difference between the first and second thermal device 910, 920.

[0062] More specifically, and with reference to Figs. 3, 5, 6, and 7 in an embodiment, the particulate material that comes from the second thermal device 920 to the mixing unit 100 is configured to enter a chamber 220, 210 of the mixing unit 100 at a first location Loci and the particulate material that is let out from the mixing unit 100 to be guided to the first thermal device 910 (or the equipment 930) is configured to exit the chamber 220, 210 of the mixing unit 100 at a second location Loc2, wherein the second location Loc2 is arranged higher than the first location Loci . Figs. 3, 5, 6, and 7 indicate a height difference AH between the first location Loci and the second location Loc2 so that the second location Loc2 is at a higher level than the first location Loci and AH is positive. In an embodiment, the height difference AH is at least 500 mm. Moreover, when there is a fluidized bed B1 , B2 arranged between the locations Loci and Loc2, a hydrostatic pressure is generated by the fluidized bed B1 , B2 in such a way that the mixing unit 100 forms a pressure lock. Thus, in the method, a fluidized bed B1 , B2 of particulate material is arranged in the chamber 210, 220 of the mixing unit 100, and a surface Surf of the fluidized bed B1 , B2 is arranged at a same level as the second location Loc2 or at a higher level than the second location Loc2 to form a pressure lock between the second thermal device 920 and the first thermal device 910. The arrow Sz in Figs. 3 to 7 indicates an upward vertical direction in the method and / or a use of the system or the mixing unit.

[0063] Concerning the first location Loci , the mixing unit 100 may comprise a first pipe 411 so that an opening of the first pipe 411 is arranged at the first location Loci . Reference is made to Figs. 3 and 7. In this way, when the particulate material from the second thermal device 920 is guided to the mixing unit 100 through the first pipe 411 , the particulate material enters the mixing unit (e.g. the second chamber 220 thereof) at the first location Loci . Reference is made to Figs. 3 and 7. Also, even if not shown by a separate reference number, in Figs. 5 and 6 the first location Loci is arranged at an opening of a pipe (i.e. an opening of the second channel 312 guiding the part Mic of the particulate material, see also Fig. 2a).

[0064] Concerning the second location Loc2, the mixing unit 100 may comprise a second pipe 421 (see Fig. 5) so that an opening of the second pipe 421 is arranged at the second location Loc2. In this way, when the particulate material exits the mixing unit 100 through the second pipe 421 , it must enter the second pipe 421 at the second location Loc2. Also, even if not shown by a separate reference number, in Figs. 3, 6, and 7 the second location Loc2 is arranged at an opening of a pipe (i.e. an opening of the fourth channel 314 guiding the part Moc of the particulate material, see also Fig. 2a). Preferably, at least a part of the first internal channel 321 is arranged below the first location Loci . This improves the separation of the material within the second chamber 220, when the second chamber is used as a concentrator (see Fig. 3).

[0065] Figure 8 illustrates an embodiment of a system having the thermal devices 910, 920 and a mixing unit 100 as discussed above. The system comprises the first thermal device 910, here a circulating fluidized bed boiler, and the second thermal device 920, here a pyrolysis reactor, and a mixing unit 100. Starting from the first thermal device 910, the arrows within the circulating fluidized bed boiler indicate the circulation of particulate matter inside the circulating fluidized bed boiler. A part MIH of the particulate matter at the first temperature Ti is taken from the circulation through the first channel 311 to enter the mixing unit 100 through the first inlet 111 of the mixing unit. The operation of the mixing unit 100 has been described before. A part MOH the particulate matter in the third temperature T3 is directed to the second thermal device 920 using the first outlet 121 through the third channel 313. As this particulate matter travels through the second thermal device 920, the temperature of the material decreases to a second temperature T2 due to heat transfer within the second thermal device 920.

[0066] The part Mic of the particulate matter in this second temperature T2 is guided through the second channel 312 and enters the mixing unit 100 through the second inlet 112. A part Moc of particulate matter leaves the mixing unit 100 at the fourth temperature T4 and returns to the particulate matter circulation within the first thermal device 910 through the fourth channel 314. This is a simplified characterization of the particulate matter circulations within the process. Such a process is also shown in Fig. 2a. However, as readable from Figs. 2c and 2d, the material that is conveyed from the second thermal device 920 to the first thermal device 910 does not need to flow through the mixing unit 100. Thus, the channel 314 is not necessary (see Fig. 2c).

[0067] As detailed above, Figure 8 shows the system and illustrates the channels 311 , 312, 313, and 314 between the devices. In the embodiment of Fig. 8, the first thermal device comprises 910 a fluidized bed boiler. In general, a fluidized bed boiler comprises a heat exchanger 912 configured to receive heat transfer medium HMi and to let out heated heat transfer medium HMo. In the boiler, the heat transfer medium HMi comprises water and / or steam. It is heated by recovering heat from flue gases or from the bed material, depending on the location of the heat exchanger 912. In Fig. 8, the heat exchanger 912 is configured to recover heat from flue gases.

[0068] In the embodiment of Fig. 8, the second thermal device 920 comprises a pyrolysis reactor, which produces product gas. In a reasonably similar manner, a gasification reactor could be comprised by the second thermal device 920 and would be configured to produce product gas; however, with a different chemical composition. Moreover, in a reasonably similar manner, a torrefaction reactor could be comprised by the second thermal device 920.

[0069] Common to all these is that the particulate material let out from the second thermal device 920 comprises thermally treated carbon-containing material. As detailed above, such material may be separated as the upper material fraction ML and guided to the first thermal device 910, e.g. for burning therein. However, in some applications, like in torrefaction, is might be useful to collect the thermally treated carbon-containing material and use it elsewhere than in the first thermal device 910. Reference is made to Figs. 9, 2c, and 2d showing collection of heat-treated material (reference ML in Fig. 9 and Moc in Figs. 2c and 2d) without guiding that material to the first thermal device 910. Instead, the material may be stored in the equipment 930.

[0070] As detailed in connection with the embodiment of Fig. 3, a technical function of the second chamber 220 of the mixing unit of Fig. 3 is to separate materials, in particular the upper material fraction ML that typically has a high content of residuals of the carbon containing material. Moreover, as evident, the mixing unit of Fig. 7 substantially corresponds to the second chamber 220 of the mixing unit of Fig. 3. Therefore, the mixing unit of Fig. 7 can be used to separate an upper material fraction ML and a lower material MH fraction from the material(s) entering the mixing unit of Fig. 7.

[0071] Therefore, the mixing unit 100 of the embodiment illustrated in Figure 7 may also be used primarily for separating at least an upper material fraction ML from a particulate material flow. This may be done, for example, in a system where a part of the upper material fraction ML is to be collected and separated from the system. For example, if torrefied material is to be collected from the system. When used to separate material, the material from which different fractions are to be separates are guided through the inlet 111 to the second chamber 220. Notable, in such a case only one material may be guided through the inlet 111 , as detailed below.

[0072] In particular, the mixing unit of the embodiment illustrated in Figure 7 may be used in connection with the second channel 312 of the embodiment of Fig. 8 so that only the particulate material coming from the second thermal device 920 enters the chamber 220 of the mixing unit of Fig. 7 through the first inlet 111 , and the material to be guided to the mixing unit 100 exits the first outlet 121 (see Fig. 7). This embodiment is also illustrated in Fig. 9. In this way, the thermally treated carbon-containing material (i.e. the light material fraction ML shown in Fig. 9) may be collected from the second outlet 122 and utilized according to needs. In addition, or alternatively, the mixing unit of the embodiment illustrated in Figure 7 may be used in connection with the fourth channel 314 of the embodiment of Fig. 8 so that the particulate material coming only from the mixing unit 100 enters the chamber 220 through the first inlet 111 , and the material to be guided to the first thermal device 910 exits the first outlet 121 (see Fig. 7). In this case, the temperature of the material guided through the first inlet would be the fourth temperature T4 (now shown in Fig. 7). In this way, the thermally treated carbon-containing material may be collected from the second outlet 122 and utilized according to needs. In such a case, the particulate material Moc that is guided from the mixing unit 100 to the first thermal device 910 only comprises a part of the material leaving the mixing unit towards the first thermal device 910 (since a part of the material may be separated therefrom by a concentrator).

[0073] The upper material fraction ML receivable from the second outlet 122 of the mixing unit of Fig. 7 and depicted in Fig. 9 in these cases case could be, for example, treated and refined carbon-containing material. Such a scenario may include a torrefaction reactor as the second thermal device 920, wherein a torrefaction reactor is used to produce a recoverable upper material fraction ML, which is recovered through a second outlet 122 and at least a part of the lower material fraction MH leaves through the first outlet 121 and is returned back to the system, for example to a first thermal device 910 or another mixing unit 100 within the system (e.g. the mixing unit shown in Fig. 8). In another scenario, the second thermal device 920 may comprise a pyrolysis reactor and at least a part of the upper material fraction ML is collected instead of being utilized in a first thermal device 910, for example a combustor.

[0074] The separation of residual of the carbon-containing material has also further technical benefits at least when the second thermal device 920 is a pyrolysis reactor or a gasification reactor, and the process in the second thermal device 920 is a pyrolysis process or a gasification process, respectively. At least in these processes, the quality of the product gas can be deteriorated by the presence of undesired products and impurities, such as char. As bed material is repeatedly circulated between the mixing unit 100 and the second thermal device 920, the impurity concentration within a second thermal device 920 could rise without the material separation and affect both the operation of the second thermal device 920 and the purity level of a desired product. How much the impurity concentration could rise without material separation depends on the process details. In any case, as depicted in Fig. 9, the secondary mixing unit 100b separates the light material fraction ML from the second material circulation and in this way helps to keep the impurity level low within the second material circulation. Notably, the secondary chamber 220 of the mixing unit of Fig. 3 performs the same technical function. Thus, in the embodiment of Fig. 8, the secondary chamber 220 of the mixing unit 100 way helps to keep the impurity level low within the second material circulation.

[0075] It is also noted that the combination of the secondary mixing unit 100b and the mixing unit 100 of Fig. 9 may be called a mixing unit, or a combined mixing unit. This combined mixing unit comprises a first chamber for mixing the materials, the first chamber being arranged in the mixing unit 100. This first chamber serves thus for the same purpose as the first chamber 210 of the embodiment of Fig. 3 of the mixing unit. This combined mixing unit further comprises a second chamber for separating an upper fraction and a lower fraction of materials from a material entering the second chamber. This second chamber serves thus for the same purpose as the second chamber 220 of the embodiment of Fig. 3 of the mixing unit. Moreover, that part of the second channel 312 that is configured to convey material from the secondary mixing unit 100b to the mixing unit 100 forms an internal channel of the combined mixing unit. This channel serves thus for the same purpose as the first internal channel 321 of the embodiment of Fig. 3 of the mixing unit. However, the combined mixing unit of Fig. 9 lacks the second internal channel 322 of the embodiment of Fig. 3, because the fluidizing gases may be handled in a different manner.

[0076] The mixing unit of the Figure 3, 6, or 7 may be used as the mixing unit 100 of e.g. the system of Fig. 2a. The mixing unit of the Figure 4 or 5 may be used as the mixing unit 100 of e.g. the system of Fig. 2b. However, the inventors consider that the mixing unit of Fig. 3 may find also relevant use in some other fields of technology involving material separation and mixing.

[0077] As indicated above, the mixing unit of Fig. 3 may be used as part of a system comprising the thermal devices 910 and 920. However, the inventors consider that the mixing unit of Fig. 3 may find use also in isolation from the system. In this way an embodiment of the mixing unit, be it in isolation from the system or a part of the system, comprises a first inlet 111 and a second inlet 121. As readable from the above, when used as part of the system, the first inlet is for receiving particulate material MIH from the first thermal device 910 and the second inlet 112 is for receiving particulate material Mic from the second thermal device 920.

[0078] The mixing unit 100 further comprises a first outlet 121 for letting out mixture MOH of the particulate materials from the mixing unit 100, and a second outlet 122 for letting out particulate material Moc from the mixing unit. Optionally, the second outlet 122 is also for letting out gas G01 from the mixing unit 100.

[0079] The mixing unit 100 further comprises a first chamber 210, a second chamber 220, and a first internal channel 321 configured to guide particulate material from the second chamber 220 to the first chamber 210. In the mixing unit 100, the first inlet 111 is configured to let in particulate material to the first chamber 210, the second inlet 112 is configured to let in particulate material to the second chamber 220, the first outlet 121 is configured to let out at least particulate material from the first chamber 210, and the second outlet 122 is configured to let out at least particulate material from the second chamber 220. In the embodiment of Fig. 3, the mixing unit 100 further comprises a second internal channel 322 configured to guide gases G02 from the first chamber 210 to the second chamber 220. The second internal channel 322 is arranged above the first internal channel 321. However, referring to Fig. 9 and discussions elsewhere in the description related to a combined mixing unit, a mixing unit that comprises a first chamber, a second chamber, and a first internal channel does not need to comprise also the second internal channel.

[0080] In addition, the mixing unit 100 comprises first nozzles 212 arranged at a bottom of the first chamber 210 and second nozzles 222 arranged at a bottom of the second chamber 220. The first nozzles 212 are configured to fluidize the particulate material within the first chamber 210 by feeding fluidizing gas G11 through the first nozzles 212, and the second nozzles 222 are configured to fluidize the particulate material within the second chamber 220 by feeding fluidizing gas G12 through the second nozzles 222. What has been said about the locations Loci and Loc2 applies. In an embodiment, the mixing unit 100 comprises the first pipe 411 so that an opening of the first pipe 411 is arranged at the first location Loci . This applies irrespective of the whether the mixing unit 100 is part of the system or manufactured in isolation of the system.

[0081] The following Examples elucidate aspects of the disclosure:

[0082] 1 . A method for producing and transferring heat, the method comprising

[0083] - producing heat in a first thermal device (910) and heating particulate material in the first thermal device (910),

[0084] - conveying a part (MIH) of the particulate material, the part (MIH) having a first temperature (Ti), from the first thermal device (910) to a mixing unit (100),

[0085] - conveying a part (Mic) of particulate material, the part (Mic) having a second temperature (T2), from a second thermal device (920) to the mixing unit (100),

[0086] - mixing the part (MIH) of the particulate material coming from the first thermal device (910) with the part (Mic) of the particulate material coming from the second thermal device (920) in the mixing unit (100) to form particulate material having a third temperature (T3),

[0087] - conveying at least a part (MOH) of the particulate material having the third temperature (Ts) from the mixing unit (100) to the second thermal device (920) thereby transferring heat to the second thermal device (920), and

[0088] - conveying particulate material (Moc, M0C2) to the first thermal device (910) from the second thermal device (920) and / or from the mixing unit (100), wherein

[0089] - the first temperature (T1) is greater than the third temperature (T3; Ti>Ts), and

[0090] - the third temperature (T3) is greater than the second temperature (T2; Ts>T2).

[0091] 2. The method of Example 1 , comprising

[0092] - conveying particulate material (Moc) having a fourth temperature (T4) from the mixing unit (100) to the first thermal device (910), wherein

[0093] - the first temperature (T1) is greater than the fourth temperature (T4).

[0094] 3. The method of Example 1 or 2 or the system of any of the Examples 12 to 17, wherein

[0095] - the first thermal device (910) comprises a fluidized bed combustor; preferably,

[0096] - the first thermal device (910) comprises a fluidized bed boiler, such as a circulating fluidized bed boiler.

[0097] 4. The method of any of the Examples 1 to 3 or the system of any of the Examples 12 to 17, wherein

[0098] - the second thermal device (920) comprises a pyrolysis reactor, a gasification reactor, a torrefaction reactor, or a storage for hot particulate material; preferably,

[0099] - the second thermal device (920) comprises a pyrolysis reactor, a gasification reactor, or a torrefaction reactor, and the method comprises

[0100] - conveying the particulate material that is conveyed to the second thermal device into the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, and

[0101] - treating thermally carbon-containing material, such as biomass, in the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively, by using heat of the particulate material that is conveyed from the mixing unit (100) to the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively.

[0102] 5. The method of any of the Examples 1 to 4, wherein

[0103] - the first temperature (Ti) is at least 50 °C higher than the third temperature (T3); preferably,

[0104] - the first temperature (Ti) is at least 100 °C, at least 150 °C, or at least 200 °C higher than the third temperature (Ts); for example,

[0105] - the first temperature (Ti) is 50 °C to 500 °C, 150 °C to 500 °C, or 200 °C to 500 °C higher than the third temperature (Ts); for example,

[0106] - the first temperature (Ti) is at least 700 °C, preferably at least 750° C, more preferably 750° C to 1100° C, and

[0107] - the third temperature (Ts) is at most 650 °C, preferably at most 500° C, more preferably 300° C to 500° C.

[0108] 6. The method of any of the Examples 1 to 5, wherein - a pressure in the first thermal device (910) is less than a pressure in the second thermal device (920); preferably,

[0109] - a pressure in the first thermal device (910) is at least 5 kPa less than a pressure in the second thermal device (920); preferably,

[0110] - a pressure in the first thermal device (910) is 5 kPa to 90 kPa, such as 10 kPa to 90 kPa, less than a pressure in the second thermal device (920); preferably,

[0111] - a pressure in the first thermal device (910) is 0.5 to 1 .05 bar(a) and

[0112] - a pressure in the second thermal device (920) is 1 .1 to 10 bar(a).

[0113] 7. The method of any of the Examples 1 to 6, wherein

[0114] - the mixing unit (100) comprises a first chamber (210) and first nozzles (212) arranged at a bottom of the first chamber (210), and the method comprises

[0115] - guiding the part (MIH) of the particulate material coming from the first thermal device (910) to the first chamber (210),

[0116] - guiding at least a part (MH) of the particulate material coming from the second thermal device (920) to the first chamber (210), and

[0117] - fluidizing the particulate material within the first chamber (210) by feeding fluidizing gas (Gi, G11) through the first nozzles (212) to mix the particulate material in the first chamber (210) to form the particulate material (MOH) having the third temperature (Ts).

[0118] 8. The method of any of the Examples 1 to 7, wherein

[0119] - the mixing unit (100) comprises a second chamber (220) and second nozzles (222) arranged at a bottom of the second chamber (220), optionally without comprising the first chamber (210) and the first nozzles (212) of Example 7, and the method comprises

[0120] - guiding the particulate material coming from the second thermal device (920) to the second chamber (220), and

[0121] - fluidizing the particulate material within the second chamber (220) by feeding fluidizing gas (Gi, G12) through the second nozzles (222) to separate an upper material fraction (ML) and a lower material fraction (MH) from the particulate material, wherein - the part (MOH) of the particulate material that is guided from the mixing unit (100) to the second thermal device (920) comprises at least a part of the lower material fraction (MH); preferably,

[0122] - the upper material fraction (ML) comprises solid particulate material and

[0123] - the lower material fraction (MH) comprises solid particulate material; more preferably

[0124] - particulate material (Moc) is guided from the mixing unit (100) to the first thermal device (910) and

[0125] - the particulate material (Moc) that is guided from the mixing unit (100) to the first thermal device (910) comprises the upper material fraction (ML) or a part of the upper material fraction (ML).

[0126] 9. The method of any of the Examples 1 to 8, wherein

[0127] - the particulate material that comes from the second thermal device (920) to the mixing unit (100) is configured to enter a chamber (220, 210) of the mixing unit (100) at a first location (Loci ) and

[0128] - the particulate material that is let out from the mixing unit (100) to be guided to the first thermal device (910) or to other equipment (930) is configured to exit the chamber (220, 210) of the mixing unit (100) at a second location (Loc2), wherein

[0129] - the second location (Loc2) is arranged at least 500 mm higher than the first location (Loci ),

[0130] - a fluidized bed (B1 , B2) of particulate material is arranged in the chamber (210, 220) of the mixing unit (100), and

[0131] - a surface (Surf) of the fluidized bed (B1 , B2) is arranged at a same level as the second location (Loc2) or at a higher level than the second location (Loc2) to form a pressure lock between the second thermal device (920) and the first thermal device (910).

[0132] 10. The method of any of the Examples 1 to 6, wherein

[0133] - the mixing unit (100) comprises a first chamber (210), first nozzles (212) arranged at a bottom of the first chamber (210), a second chamber (220), and second nozzles (222) arranged at a bottom of the second chamber (220); and the method comprises

[0134] - guiding the particulate material coming from the first thermal device (910) to the first chamber (210), - guiding the particulate material coming from the second thermal device (920) to the second chamber (220),

[0135] - fluidizing the particulate material within the with second chamber (220) by feeding fluidizing gas (G12) through the second nozzles (222) to separate from the particulate material within the with second chamber (220) an upper material fraction (ML) and a lower material fraction (MH),

[0136] - guiding the lower material fraction (MH) from the second chamber (220) to the first chamber (210),

[0137] - fluidizing the particulate material within the first chamber (210) by feeding fluidizing gas (G11) through the first nozzles (212) to mix the particulate material in the first chamber (210) to form particulate material having the third temperature (T3), and

[0138] - guiding particulate material (Moc) from the mixing unit (100) to the first thermal device (910) or to other equipment (930), wherein

[0139] - the particulate material (Moc) that is guided from the mixing unit (100) to the first thermal device (910) or to the other equipment (930) comprises the upper material fraction (ML) or a part of the upper material fraction (ML); preferably

[0140] - a velocity of the fluidizing gas (G11) used to fluidize material in the first chamber (210) is higher than a velocity of the fluidizing gas (G12) used to fluidize material in the second chamber (220).

[0141] 11 . The method of Example 10, wherein

[0142] - a pressure in the first thermal device (910) is less than a pressure in the second thermal device (920),

[0143] - the particulate material that comes from the second thermal device (920) to the mixing unit (100) is configured to enter the second chamber (220) of the mixing unit (100) at a first location (Loci ) and

[0144] - the particulate material that is let out from the mixing unit (100) to be guided to the first thermal device (910) or to the other equipment (930) is configured to exit the second chamber (220) of the mixing unit (100) at a second location (Loc2), wherein

[0145] - the second location (Loc2) is arranged at least 500 mm higher than the first location (Loci ),

[0146] - a fluidized bed (B2) of particulate material is arranged in the second chamber (220) of the mixing unit (100), and - a surface (Surf) of the fluidized bed (B2) is arranged at a same level as the second location (Loc2) or at a higher level then the second location (Loc2) to form a pressure lock between the second thermal device (920) and the first thermal device (910) or the other equipment (930).

[0147] 12. A system for producing and transferring heat, the system comprising

[0148] - a first thermal device (910) for heating particulate material,

[0149] - a second thermal device (920) configured to utilize and / or store heat produced in the first thermal device (910), and

[0150] - a mixing unit (100) for mixing particulate material (MIH) receivable from the first thermal device (910) with particulate material (Mic) receivable from the second thermal device (920) for the purpose of conveying at least a part of the mixture (MOH) of the particulate materials to the second thermal device (920),

[0151] - a first channel (311 ) for conveying particulate material from the first thermal device (910) to the mixing unit (100),

[0152] - a second channel (312) for conveying particulate material from the second thermal device (920) to the mixing unit (100),

[0153] - a third channel (313) for conveying particulate material from the mixing unit (100) to the second thermal device (920), and

[0154] - a fourth channel (314) for conveying particulate material from the mixing unit (100) to first thermal device (910) and / or a bypass (316) for conveying particulate material from the second thermal device (920) to the first thermal device (910).

[0155] 13. The system of Example 12, wherein

[0156] - the mixing unit (100) comprises

[0157] • a first inlet (111 ) for receiving particulate material (MIH) from the first thermal device (910),

[0158] • an outlet (121 ) for letting out mixture (MOH) of the particulate materials from the mixing unit (100),

[0159] • a first chamber (210), and

[0160] • first nozzles (212) arranged at a bottom of the first chamber (210), and

[0161] - the system comprises means for guiding at least a part of the particulate material receivable from the second thermal device (920) to the first chamber (210) of the mixing unit (100), wherein

[0162] - the first inlet (111 ) is configured to let in particulate material to the first chamber (210), and - the first nozzles (212) are configured to fluidize the particulate material within the first chamber (210) by feeding fluidizing gas (Gi, Gn) through the first nozzles (212).

[0163] 14. The system of Example 12 or 13, wherein

[0164] - the mixing unit (100) comprises

[0165] • an / the outlet (121 ,122) for letting out mixture of the particulate materials from the mixing unit (100),

[0166] • a second inlet (112) for receiving particulate material from the second thermal device (920), the mixing unit (100) optionally not comprising the first inlet (111 ) of Example 13,

[0167] • a second chamber (220), the mixing unit (100) optionally not comprising the first chamber (210) of Example 13, and

[0168] • second nozzles (222) arranged at a bottom of the second chamber (220), wherein

[0169] - the second inlet (112) is configured to let in particulate material to the second chamber (220),

[0170] - the outlet (121 ,122) is arranged at upper part of the second chamber (220), and

[0171] - the second nozzles (222) are configured to fluidize the particulate material within the second chamber (220) by feeding fluidizing gas (Gi, G12) through the second nozzles (222).

[0172] 15. A mixing unit (100) in isolation from the system of Example 12 or the system of any of the Example 12 to 14, wherein the mixing unit (100) comprises

[0173] - a first inlet (111 ) for receiving particulate material (MIH), e.g., from a / the first thermal device (910),

[0174] - a second inlet (112) for receiving particulate material (Mic), e.g., from a / the second thermal device (920),

[0175] - a first outlet (121 ) for letting out mixture (MOH) of the particulate materials from the mixing unit (100),

[0176] - a second outlet (122) for letting out particulate material (Moc) and, optionally, also for letting out gas (G01) from the mixing unit (100),

[0177] - a first chamber (210),

[0178] - a second chamber (220), - a first internal channel (321 ) configured to guide particulate material from the second chamber (220) to the first chamber (210),

[0179] - first nozzles (212) arranged at a bottom of the first chamber (210), and

[0180] - second nozzles (222) arranged at a bottom of the second chamber (220), wherein

[0181] - the first inlet (111 ) is configured to let in particulate material to the first chamber (210),

[0182] - the second inlet (112) is configured to let in particulate material to the second chamber (220),

[0183] - the first outlet (121 ) is configured to let out material from the first chamber (210),

[0184] - the second outlet (122) is configured to let out material from the second chamber (220),

[0185] - the first nozzles (212) are configured to fluidize the particulate material within the first chamber (210) by feeding fluidizing gas (Gn) through the first nozzles (212), and

[0186] - the second nozzles (222) are configured to fluidize the particulate material within the second chamber (220) by feeding fluidizing gas (G12) through the second nozzles (222).

[0187] 16. The mixing unit (100) or the system of Example 15, configured such that

[0188] - particulate material that is guided through the second inlet (112) into the mixing unit (100) is configured to enter the second chamber (220) of the mixing unit (100) at first location (Loci ) and

[0189] - particulate material that is guided through the second outlet (122) out of the mixing unit (100) is configured to exit the second chamber (220) of the mixing unit (100) at a second location (Loc2), wherein

[0190] - the second location (Loc2) is arranged at least 500 mm higher than the first location (Loci ).

[0191] 17. The mixing unit (100) or the system of Example 15 or 16, comprising

[0192] - a second internal channel (322) configured to guide gases (G02) from the first chamber (210) to the second chamber (220), wherein

[0193] - the second internal channel (322) is arranged above the first internal channel (321 ).

Claims

Claims:1 . A method for producing and transferring heat, the method comprising- producing heat in a first thermal device (910) and heating particulate material in the first thermal device (910),- conveying a part (MIH) of the particulate material, the part (MIH) having a first temperature (Ti), from the first thermal device (910) to a mixing unit (100) comprising a second chamber (220) and second nozzles (222) arranged at a bottom of the second chamber (220), the mixing unit (100) optionally not comprising a first chamber (210),- conveying a part (Mic) of particulate material, the part (Mic) having a second temperature (T2), from a second thermal device (920) to the mixing unit (100) and guiding the particulate material coming from the second thermal device (920) to the second chamber (220),- fluidizing the particulate material within the second chamber (220) by feeding fluidizing gas (Gi, G12) through the second nozzles (222) to separate an upper material fraction (ML) and a lower material fraction (MH) from the particulate material,- mixing the part (MIH) of the particulate material coming from the first thermal device (910) with the part (Mic) of the particulate material coming from the second thermal device (920) in the mixing unit (100) to form particulate material having a third temperature (T3),- conveying at least a part (MOH) of the particulate material having the third temperature (Ts) from the mixing unit (100) to the second thermal device (920) thereby transferring heat to the second thermal device (920), and- conveying particulate material (Moc, M0C2) to the first thermal device (910) from the second thermal device (920) and / or from the mixing unit (100), wherein- the first temperature (T1) is greater than the third temperature (T3; Ti>Ts),- the third temperature (T3) is greater than the second temperature (T2; Ts>T2),- the particulate material having the third temperature (T3) and conveyed from the mixing unit (100) to the second thermal device (920) comprises a mixture of particulate material (MIH) receivable from the first thermal device (910) and particulate material (Mic) receivable from the second thermal device (920), and- the part (MOH) of the particulate material that is guided from the mixing unit (100) to the second thermal device (920) comprises at least a part of the lower material fraction (MH).

2. The method of claim 1 , comprising- conveying particulate material (Moc) having a fourth temperature (T4) from the mixing unit (100) to the first thermal device (910), wherein- the first temperature (T1) is greater than the fourth temperature (T4).

3. The method of claim 1 or 2, comprising- treating thermally carbon-containing material, such as biomass, in the second thermal device (920) by using heat of the particulate material that is conveyed from the mixing unit (100) to the second thermal device (920), wherein- a content of residuals of the carbon-containing material of the upper material fraction (ML) is higher than a content of residuals of the carbon-containing material of the lower material fraction (MH).

4. The method of any of the claims 1 to 3, wherein- the first thermal device (910) comprises a fluidized bed combustor; preferably,- the first thermal device (910) comprises a fluidized bed boiler, such as a circulating fluidized bed boiler.

5. The method of any of the claims 1 to 4, wherein- the second thermal device (920) comprises a pyrolysis reactor, a gasification reactor, a torrefaction reactor, or a storage for hot particulate material; preferably,- the second thermal device (920) comprises a pyrolysis reactor, a gasification reactor, or a torrefaction reactor, and the method comprises- conveying the particulate material that is conveyed to the second thermal device into the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, and- treating thermally carbon-containing material, such as biomass, in the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively, by using heat of the particulate material that is conveyed from the mixing unit (100) to the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively.

6. The method of any of the claims 1 to 5, wherein- the first temperature (Ti) is at least 50 °C higher than the third temperature (T3); preferably,- the first temperature (Ti) is at least 100 °C, at least 150 °C, or at least 200 °C higher than the third temperature (Ts); for example,- the first temperature (Ti) is 50 °C to 500 °C, 150 °C to 500 °C, or 200 °C to 500 °C higher than the third temperature (Ts); for example,- the first temperature (Ti) is at least 700 °C, preferably at least 750° C, more preferably 750° C to 1100° C, and- the third temperature (Ts) is at most 650 °C, preferably at most 500° C, more preferably 300° C to 500° C.

7. The method of any of the claims 1 to 6, wherein- a pressure in the first thermal device (910) is less than a pressure in the second thermal device (920); preferably,- a pressure in the first thermal device (910) is at least 5 kPa less than a pressure in the second thermal device (920); preferably,- a pressure in the first thermal device (910) is 5 kPa to 90 kPa, such as 10 kPa to 90 kPa, less than a pressure in the second thermal device (920); preferably,- a pressure in the first thermal device (910) is 0.5 to 1 .05 bar(a) and- a pressure in the second thermal device (920) is 1 .1 to 10 bar(a).

8. The method of any of the claims 1 to 7, wherein- the mixing unit (100) comprises a first chamber (210) and first nozzles (212) arranged at a bottom of the first chamber (210), and the method comprises- guiding the part (MIH) of the particulate material coming from the first thermal device (910) to the first chamber (210),- guiding at least a part (MH) of the particulate material coming from the second thermal device (920) to the first chamber (210), and- fluidizing the particulate material within the first chamber (210) by feeding fluidizing gas (Gi, G11) through the first nozzles (212) to mix the particulate material in the first chamber (210) to form the particulate material (MOH) having the third temperature (Ts); preferably, the method comprises- guiding the lower material fraction (MH) to the first chamber (210).

9. The method of the claim 8, wherein- a velocity of the fluidizing gas (Gn) used to fluidize material in the first chamber (210) is higher than a velocity of the fluidizing gas (G12) used to fluidize material in the second chamber (220).

10. The method of any of the claims 1 to 9, wherein- the upper material fraction (ML) comprises solid particulate material and- the lower material fraction (MH) comprises solid particulate material; preferably- particulate material (Moc) is guided from the mixing unit (100) to the first thermal device (910) and- the particulate material (Moc) that is guided from the mixing unit (100) to the first thermal device (910) comprises the upper material fraction (ML) or a part of the upper material fraction (ML).11 . The method of any of the claims 1 to 10, wherein- the particulate material that comes from the second thermal device (920) to the mixing unit (100) is configured to enter the second chamber (220) of the mixing unit (100) at a first location (Loci ) and- the particulate material that is let out from the mixing unit (100) to be guided to the first thermal device (910) or to other equipment (930) is configured to exit the second chamber (220) of the mixing unit (100) at a second location (Loc2), wherein- the second location (Loc2) is arranged at least 500 mm higher than the first location (Loci ),- a fluidized bed (B2) of particulate material is arranged in the second chamber (210) of the mixing unit (100), and- a surface (Surf) of the fluidized bed (B2) is arranged at a same level as the second location (Loc2) or at a higher level than the second location (Loc2) toform a pressure lock between the second thermal device (920) and the first thermal device (910); preferably,- a pressure in the first thermal device (910) is less than a pressure in the second thermal device (920).

12. A system for producing and transferring heat, the system comprising- a first thermal device (910) for heating particulate material,- a second thermal device (920) configured to utilize and / or store heat produced in the first thermal device (910), and- a mixing unit (100) for mixing particulate material (MIH) receivable from the first thermal device (910) with particulate material (Mic) receivable from the second thermal device (920) for the purpose of conveying at least a part of the mixture (MOH) of the particulate materials to the second thermal device (920),- a first channel (311 ) for conveying particulate material from the first thermal device (910) to the mixing unit (100),- a second channel (312) for conveying particulate material from the second thermal device (920) to the mixing unit (100),- a third channel (313) for conveying mixture of particulate material (MIH) receivable from the first thermal device (910) and particulate material (Mic) receivable from the second thermal device (920) from the mixing unit (100) to the second thermal device (920), and- a fourth channel (314) for conveying particulate material from the mixing unit (100) to first thermal device (910) and / or a bypass (316) for conveying particulate material from the second thermal device (920) to the first thermal device (910), wherein- the mixing unit (100) comprises• a first outlet (121 ) for letting out the mixture (MOH) of the particulate materials from the mixing unit (100),• a second outlet (122) for letting out particulate material (Moc) from the mixing unit (100),• an inlet (111 , 112) for receiving particulate material from the second thermal device (920),• a second chamber (220), the mixing unit (100) optionally not comprising a first chamber (210), and• second nozzles (222) arranged at a bottom of the second chamber (220), wherein- the inlet (111 , 112) is configured to let in particulate material to the second chamber (220),- the second outlet (122) is arranged at upper part of the second chamber (220), and- the second nozzles (222) are configured to fluidize the particulate material within the second chamber (220) by feeding fluidizing gas (Gi, G12) through the second nozzles (222).

13. The system of claim 12, wherein- the first thermal device (910) comprises a fluidized bed combustor; preferably,- the first thermal device (910) comprises a fluidized bed boiler, such as a circulating fluidized bed boiler.

14. The system of claim 12 or 13, wherein- the second thermal device (920) comprises a pyrolysis reactor, a gasification reactor, a torrefaction reactor, or a storage for hot particulate material; preferably,- the second thermal device (920) comprises a pyrolysis reactor, a gasification reactor, or a torrefaction reactor, and the method comprises- conveying the particulate material that is conveyed to the second thermal device into the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, and- treating thermally carbon-containing material, such as biomass, in the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively, by using heat of the particulate material that is conveyed from the mixing unit (100) to the pyrolysis reactor, the gasification reactor, or the torrefaction reactor, respectively.

15. The system of any of the claims 12 to 14, configured such that- particulate material that is guided through the inlet (111 , 112) into the mixing unit (100) is configured to enter the second chamber (220) of the mixing unit (100) at first location (Loci ) and- particulate material that is guided through the second outlet (122) out of the mixing unit (100) is configured to exit the second chamber (220) of the mixing unit (100) at a second location (Loc2), wherein- the second location (Loc2) is arranged at least 500 mm higher than the first location (Loci ).

16. The system of any of the claims 12 to 15, wherein- the inlet (111 , 112) for receiving particulate material from the second thermal device (920) forms a second inlet (112) of the mixing unit,- the mixing unit (100) comprises• a first inlet (111 ) for receiving particulate material (MIH) from the first thermal device (910),• a first chamber (210), and• first nozzles (212) arranged at a bottom of the first chamber (210),- the system comprises means for guiding at least a part of the particulate material receivable from the second thermal device (920) to the first chamber (210) of the mixing unit (100),- the first inlet (111 ) is configured to let in particulate material to the first chamber (210), and- the first nozzles (212) are configured to fluidize the particulate material within the first chamber (210) by feeding fluidizing gas (Gi, G11) through the first nozzles (212).

17. The system of claim 16, wherein- the mixing unit (100) comprises a first internal channel (321 ) configured to guide particulate material from the second chamber (220) to the first chamber (210),- particulate material that is guided through the second inlet (112) into the mixing unit (100) is configured to enter the second chamber (220) of the mixing unit (100) at first location (Loci ), and- at least a part of the first internal channel (321 ) is arranged below the first location (Loci ).

18. The system of claim 17, wherein- the mixing unit (100) comprises a second internal channel (322) configured to guide gases (G02) from the first chamber (210) to the second chamber (220), wherein- the second internal channel (322) is arranged above the first internal channel (321 ).

19. A mixing unit (100) comprising- a first inlet (111 ) for receiving particulate material (MIH), e.g., from a / the first thermal device (910),- a second inlet (112) for receiving particulate material (Mic), e.g., from a / the second thermal device (920),- a first outlet (121 ) for letting out mixture (MOH) of the particulate materials from the mixing unit (100),- a second outlet (122) for letting out particulate material (Moc) and, optionally, also for letting out gas (G01) from the mixing unit (100),- a first chamber (210),- a second chamber (220),- a first internal channel (321 ) configured to guide particulate material from the second chamber (220) to the first chamber (210),- first nozzles (212) arranged at a bottom of the first chamber (210), and- second nozzles (222) arranged at a bottom of the second chamber (220), wherein- the first inlet (111 ) is configured to let in particulate material to the first chamber (210),- the second inlet (112) is configured to let in particulate material to the second chamber (220),- the first outlet (121 ) is configured to let out material from the first chamber (210),- the second outlet (122) is configured to let out material from the second chamber (220),- the first nozzles (212) are configured to fluidize the particulate material within the first chamber (210) by feeding fluidizing gas (Gn) through the first nozzles (212), and- the second nozzles (222) are configured to fluidize the particulate material within the second chamber (220) by feeding fluidizing gas (G12) through the second nozzles (222).

20. The mixing unit (100) of claim 19, configured such that- particulate material that is guided through the second inlet (112) into the mixing unit (100) is configured to enter the second chamber (220) of the mixing unit (100) at first location (Loci ) and- particulate material that is guided through the second outlet (122) out of the mixing unit (100) is configured to exit the second chamber (220) of the mixing unit (100) at a second location (Loc2), wherein- the second location (Loc2) is arranged at least 500 mm higher than the first location (Loci ).21 . The mixing unit (100) of claim 19 or 20, comprising- a second internal channel (322) configured to guide gases (G02) from the first chamber (210) to the second chamber (220), wherein - the second internal channel (322) is arranged above the first internal channel(321 ).

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