HEAT RECOVERY TREATMENT SYSTEM AND METHOD FOR OPERATING SAID SYSTEM

Abstract

The invention relates to a processing system comprising a processing unit (1, 60, 100) that can be operated between an upper (To) and a lower (Tu) temperature. A first heat accumulator (3, 61) and a second heat accumulator (4, 62) are operationally interconnected by means of a line arrangement (L) for a heat-transporting medium, said processing unit (1, 60, 100) being arranged in a first section (I) of said line arrangement (L) between the first (3, 61) and the second heat accumulator (4, 62).

Description

Process system for heat recovery and methods for its operation The present invention relates to a process system with a process unit operable between an upper and a lower temperature according to the preamble of claim 1 and a method for cyclically heating and cooling a process unit operable between an upper and a lower temperature according to the preamble of claim 13. Processes that occur at different temperature levels are widespread in engineering. In these processes, one step takes place at a higher temperature and another at a lower temperature, or a process step occurs during a temperature change. Many applications involve chemical reactions using a catalyst. It is often advantageous to heat a process unit to a higher temperature range and then cool it to a lower temperature range, repeating this temperature change cyclically for continuous production. One of the numerous applications lies in the production of solar fuels, whose starting materials, H₂ (hydrogen) and CO (carbon monoxide), are formed from H₂O (water) and CO₂ (carbon dioxide) with the input of energy—namely heat at high temperatures. A gas mixture containing mainly H₂ and CO—along with other gases—is called synthesis gas or simply syngas. This syngas is used to produce liquid or gaseous hydrocarbon fuels. In an ETH dissertation No. 21864 "SOLAR THERMOCHEMICAL CO2 AND H20 SPLITTING VIA CERIA REDOX REACTIONS" by Philipp Furier, an experimental solar cerium reactor is described with which synthesis gas can be produced under irradiation with concentrated sunlight (2865 suns, i.e. a thermal radiation of up to 2865 kW / m2). Sunlight at the aforementioned concentration can be generated on an industrial scale, for example, using a dish concentrator developed by the applicant in accordance with WO 2011 / 072410, thus making the commercial production of synthesis gas using renewable energy a realistic possibility. According to the aforementioned ETH dissertation, in a first, endothermic process step, cerium is reduced to an upper temperature of 1800 K, forming oxygen; subsequently, after the reduction is complete, the cerium is cooled to a lower temperature of 1100 K, and in a subsequent process step, the synthesis gas is produced by exothermic re-oxidation; in this process, the heat required endothermically is much greater than the heat generated exothermically.This process can be repeated cyclically for continuous synthesis gas production; consequently, the cerium must be periodically heated to 1800 K and cooled to 1100 K. A double-ring cerium support structure is proposed for the recovery of heat extracted during cooling. Two counter-rotating, adjacent cerium rings with a common axis of rotation are positioned between the warm zone (1800 K) and the cold zone (1100 K) such that one section of each ring is located in the warm zone at a 12 o'clock position and the opposite section is located in the cold zone at a 6 o'clock position.Due to the counter-rotation of immediately adjacent cerium rings, the cold section of a first cerium ring moves clockwise towards the warm zone, and the warm section moves towards the cold zone. Similarly, in a second cerium ring rotating counter-clockwise, the cold section moves towards the warm zone and the warm section towards the cold zone, with both cerium rings passing each other and thus continuously exchanging thermal energy. Accordingly, warm sections are cooled and cold sections are heated, enabling heat recuperation. However, the efficiency of this recuperation is inherently low, at approximately 25%. The demands on the design and stability of counter-rotating, adjacent cerium rings—heat transfer, heat radiation, and mechanical complexity—are considerable. Similar problems to those described above arise in other areas of the prior art when a process unit is to be operated at different temperatures and the heat extracted during cooling is to be recovered. The invention therefore aims to further develop a process system with a process unit that can be operated between an upper and a lower temperature range, such that heat recovery can be improved. The process system should also be usable for temperatures above 1000 K, so that the process unit can, for example, be designed as a reactor for synthesis gas. The problem underlying the invention for the process system is solved by the features of claim 1. By providing two heat storage units between which the process unit is located, one heat storage unit can be discharged to heat the process unit, and heat not absorbed by the process unit can be used to charge the second heat storage unit – analogously for cooling the process unit. This allows losses to be reduced and thus the efficiency to be increased. The problem underlying the invention is also solved by the method according to claim 13. By cyclically changing the flow direction between the heat storage units, and thus through the process unit, the heat present in the system can be alternately moved back and forth through the process unit, alternately heating and cooling it, which, in addition to improved efficiency, also allows for a simplified design of the process system. The problem underlying the invention for the method is solved by the features of claim 13. Because the flow direction between the heat storage elements, and thus through the process unit, changes cyclically, the heat present in the system can be alternately moved back and forth through the process unit, alternately heating and cooling it. This allows for improved efficiency and a simplified design. Preferred embodiments of the present invention have the features of dependent claims 14 to 16. The invention is explained below by way of example with reference to figures. Identical objects in the figures are generally designated by the same reference numerals. It shows: Fig. 1 shows a schematic representation of the process system according to the invention with a series connection of a heat storage device, a process unit and a further heat storage device, Fig. 2 shows a temperature profile of the process unit, Fig. 3 shows a preferred embodiment of a layered heat storage system with diagrams of the temperature distribution prevailing in it during operation. Fig. 4 shows a preferred embodiment of a process system according to the invention with layered heat storage units and diagrams showing the temperature distribution prevailing in the process system during operation. Fig. 5 shows the embodiment of the process system from Figure 4 with diagrams showing the temperature distribution prevailing in the process system in an alternative operating mode. Fig. 6 shows a schematic representation of a further embodiment of the process system according to the invention with a third heat storage device for external heat, Figures 7a to 7d show the process system of Figure 6 in four different switching states, and Figure 8 shows a view of the hot side of an implemented process system according to Figure 6. Figure 1 shows a process system 1 according to the invention, with a process unit 2 that can be operated between an upper and a lower temperature, wherein a first 3 and a second heat storage unit 4 are operatively connected to each other by a pipe arrangement L for a heat-transporting medium, and wherein the process unit 2 is arranged in a first section I of the pipe arrangement between the first 3 and the second heat storage unit 4. Thus, each of the heat storage units 3, 4 has an end 3a, 4a facing the process unit 2 and an end 3b, 4b facing away from it, and the first section I of the pipe arrangement has the pipe sections 5a, 5b, which connect the heat storage units 3, 4 to the process unit 2. In the embodiment of the invention shown, the process unit 2 is designed as a cerium reactor suitable for the reactions described in ETH Dissertation No. 21864. For this purpose, it is connected on the inlet side via a line 16a and a valve 11 to a CO2 tank 8 and via a valve 12 to an H2O tank 9, and on the outlet side via a line 16b, a valve 13, and a pump 14 to a syngas tank 10, in which a gas mixture consisting mainly of CO and H2 as end products is collected. Furthermore, it is evident that the first 3 and the second heat storage unit 4 are connected on their respective sides 3b, 4b, facing away from the process unit 2, by means of a second section II of the pipe arrangement L via its pipe 6. The two sections I and II of the pipe arrangement L create a circuit of the heat-transporting medium flowing within it, which can be, for example, argon, a medium suitable for heat transport even at high temperatures. A pump arrangement 15 allows the flow direction of the heat-transporting medium to be maintained in both directions of the circuit and reversed if necessary. For the sake of simplicity, the pump arrangement 15 is shown here with two pumps 15a and 15b, which can be connected to or disconnected from the circuit via valves 15c and 15c. Of course, in a specific case, a person skilled in the art can design the pump arrangement 15 according to their needs. It should be noted that in another embodiment, not shown, the conduit section II can also be omitted. For example, the heat storage units 3, 4 are then open on their sides 3b, 4b facing away from the process unit 2, i.e., connected to the environment, so that the heat-transporting medium can be ambient air, which flows through the heat storage units 3, 4, the process unit 2, and thus through conduit section I. Here, too, the person skilled in the art will choose either the illustrated closed circuit or an open arrangement, depending on the specific case (design of the process unit for any industrial process with the corresponding upper and lower temperatures). Finally, it is possible to provide tanks for the heat-transporting medium on the sides of the process unit 2 facing away from it, instead of conduit section II, so that a medium other than ambient air can then be used.As mentioned above, in the embodiment shown in the figure, process unit 2 is designed as a cerium reactor, which is operated cyclically with a lower temperature in the range of, for example, 1300 °K and an upper temperature in the range of, for example, 1800 °K (here too, the person skilled in the art can easily determine all parameters according to the selected process). Accordingly, the reactor must be continuously heated and then cooled again. According to the invention, during the cooling of the reactor, the heat removed from it is stored in a predetermined manner in one of the heat storage units 3, 4 and used for subsequent (re)heating, thus being recuperated.An efficiency of 100% is not possible, with the consequence that heat must be supplied to the reactor from the outside when heating it in an upper temperature range up to the upper temperature (here 1800 °K), for example by the sun 7, which illuminates the process unit 2 (here the cerium reactor), or indirectly via another heat storage unit, not shown here to reduce the load on the figure, which in turn is charged by solar energy (or by heat obtained from other sources) (see Figure 6 below). Thus, in the embodiment shown, the process unit 2 is designed as a solar reactor illuminated by the sun 7 and filled with cerium oxide (CeO2). Figure 2 qualitatively shows a diagram with a temperature profile in the process unit 2 (Figure 1), which is designed as a cerium reactor and whose operating temperature alternates between the lower temperature Tu (here 1300 °K) and the upper temperature T0 (here 1800 °K). At time tu, apart from a start-up process, the reactor, which is at the lower temperature Ty, begins to heat up through recuperated heat from the heat storage units 3 and 4 (Figure 1). This raises the reactor temperature to TR (the temperature achievable through recuperation), which is reached at time tR. Further heating to T0 (reached at time t0) requires additional heat, which must be supplied externally, for example, by illuminating the reactor with sunlight, as mentioned above. The temperature curve thus passes through the points Py, PR, and P0, where the efficiency of the recuperation is given by the ratio of the areas under the curve segments Pu to PR and PR to P0. During the heating of the reactor from Ty to T0, the cerium is reduced, and O2 is released freely and continuously through a line (not shown in Figure 1) to relieve pressure. After reaching T0, only traces of O2 remain in the reactor, which cools slightly to temperature TK, the start of reactor cooling, during the short residence time in the upper temperature range due to heat losses. The heat extracted from the reactor until the end of cooling to temperature TKE at time tKE is stored in the heat storage tanks 3 and 4. As soon as the reactor reaches temperature TKE, O2 and H2O (preferably in vapor form) are fed into the reactor through line 16 (Figure 1). Synthesis gas is formed through the re-oxidation of the cerium and is fed into the syngas tank via line 16b (Figure 1). During re-oxidation, the reactor continues to cool slightly to the temperature Tu, which is reached at time tUE.The cycle can then begin anew. For the thermal storage units 3 and 4, their operating temperature TB, i.e., the maximum temperature of the heat stored within them, lies between TK and TR, since a certain temperature difference between the heat-exchanging medium and the reactor or the thermal storage units is unavoidable. According to Figure 1, the reactor is cooled by drawing a colder heat-transporting medium, for example, from the first thermal storage unit 3, through pipe section 5a into the reactor (process unit 2), where it is heated and then conveyed via pipe section 5b into the second thermal storage unit 4. This heat is thereby charged, and with the flow reversed, the second thermal storage unit 4 can release heat to warm the reactor. This cycle can be repeated continuously. A particularly favorable efficiency of the recuperation can be achieved if, according to a preferred embodiment of the invention, the first 3 and the second heat storage 4 are designed as stratified heat storage units, i.e., heat storage units that can be operated with a defined temperature distribution in order to achieve a particularly high efficiency and a simple, also cost-effective design in a simple manner according to the invention. Figure 3 schematically shows a preferred embodiment of a stratified heat storage device 30, i.e., a heat storage device that can form a temperature stratification with a predetermined temperature profile during operation, as described below. The heat storage device 30 shown here essentially comprises an elongated, insulating casing 31 and a heat-storing filling 32 made of bulk material such as gravel or, for example, finer or coarser rock (or other suitable materials). Lines 30a and 30b for a heat-transporting medium, here a gas such as ambient air or, for example, argon in the case of high operating temperatures, open at its ends. The gas or argon flows lengthwise through the heat storage device 30 via the spaces present in the bulk material, thus transferring heat to or absorbing heat from the bulk material, depending on whether the heat storage device 30 is to be charged or discharged with heat.Figure 3 further shows diagrams 34, 40, 45, and 50 with different temperature distributions along the length of the heat storage unit 30, depending on the current operating state. The temperature range extends from an ambient temperature TUG to an operating temperature TB. The diagrams depict the operating states with different gas or argon flow directions: first from line 30a to line 30b (i.e., to the right), and then conversely from line 30b to line 30a (i.e., to the left), corresponding to the direction of the arrows shown in the diagrams. Diagram 34 shows the temperature distribution of the heat storage unit 30, which is initially at ambient temperature TUG, during the charging with heat, for which it is flowed through by a gas with an operating temperature TB to the right, in the direction of the arrow. Four temperature distribution curves 35 to 38 are visible, corresponding to the progressive loading times ti to t4. At the beginning of the loading process, the bulk material 32 located at the inlet of the heat storage unit 30 heats up, causing the gas to lose temperature. Consequently, subsequent batches of bulk material 32 are heated less, and later batches are heated even less due to the continuous temperature loss of the gas. At time tx, a step-like temperature distribution decreases in the direction of flow, as shown by curve 35. As the loading process continues, the step-like temperature distribution shown by curve 36 (time t2) develops. This means that the step increases in height with the rising temperature of the bulk material 32 at the inlet of the heat storage unit 30, although the step itself shifts only slightly in the direction of flow.Finally, at time t3, the bulk material reaches the operating temperature TB of the gas at the inlet side, so that with further loading, the temperature stage runs through the bulk material 32 in the direction of flow, see curve 37 at time t4. In other words, a temperature stage or ramp is created in the storage tank during loading, which builds up at the beginning of loading (curves 35 and 36) and then shifts in the direction of flow during further loading (curve 37) until it reaches the other end of the heat storage tank 30 and has, in a sense, passed through it, so that the heat storage tank 30, which is fully loaded at time t4, has a temperature distribution according to curve 38 at the level of the operating temperature TB. It should be noted that the gas flowing in at operating temperature TB leaves the heat storage unit at the lower ambient temperature TUG until the stage reaches its outlet (here at line 30b).Figure 3 shows in diagram 40 the temperature distribution when charging is stopped at time t3 and the heat storage tank 30 is subsequently discharged by passing a gas at ambient temperature TUG through the heat storage tank 30 from line 30b in the reverse flow direction. As mentioned, charging is stopped at time t3, and the heat distribution thus corresponds to curve 37. At time t4, the temperature stage has shifted to the left, and the heat distribution corresponds to curve 41. It should be noted that the gas flowing in at ambient temperature TUG leaves the heat storage tank at operating temperature TB until the stage reaches its outlet (here at line 30a). Figure 3 shows in diagram 45 the temperature distribution in the heat storage tank 30 when charging is only partially complete (but still flowing to the right, i.e., from line 30a to line 30b, see Figure 3).(the direction of the arrow) the temperature of the inflowing gas from TB drops, for example to TUG, here at time t2 of diagram 34, i.e. after a temperature distribution according to curve 37 of diagram 40 is present. The inlet bulk material thus heats the gas flowing in at TUG to the operating temperature TB and cools down slightly in the process. The gas, now heated to TB, continues to flow to the right and heats the immediately downstream area of ​​the bulk material 32 to TB, losing heat in the process. As a result, an even further downstream area of ​​the bulk material 32 is still heated, but to a lower temperature, and so on. At time t3, this results in a temperature distribution according to curve 46. The gas still flowing in at temperature TUG continues to cool the inlet bulk material 32, but absorbs its heat and transports it further in the flow direction. At time t4, the temperature distribution according to curve 47 is formed, and with the gas continuing to flow in at temperature TUG, the temperature distribution according to curve 48 is formed at time t5.In other words, the temperature distribution no longer forms as a step, but as a wave that propagates through the heat storage unit 30 in the direction of flow. It should be noted that in this operating condition, the gas flowing in and out at the lower temperature TUG continues to form and propagate through the heat storage unit 30 in the direction of flow until the wave reaches the outlet at line 30b. Only then does a discharge of the heat storage unit 30 begin, lasting until the wave has completely passed through line 30b. It should be emphasized that waves of various shapes can form, depending, for example, on how the temperature flowing into the heat storage unit is changed. Hereafter, the term "wave" will simply be used for all these possible wave shapes.Figure 3 shows in diagram 50 the temperature distribution in the heat storage tank 30 when, at the moment of the temperature distribution according to curve 48 (diagram 40), the flow direction is reversed at time t5*, so that the gas then (still at the lower temperature TUG) now flows from line 30b to line 30a to the left, see the direction of the arrow. As mentioned, the initial situation at the moment of the reversal of the flow direction is the temperature distribution according to curve 48 at time t5*, but now the wave of the reversed flow direction moves accordingly to the left, towards line 30a. A time interval after the reversal of the flow direction is followed by the temperature distribution according to curve 51 at time t6* and then by that according to curve 52 at time t7*.It should be noted that during the discharge of the heat storage unit 30 shown in diagram 50, the gas flows in at ambient temperature TUG and initially also flows out at ambient temperature TUG until the preceding temperature edge of the wave has reached the line 30a, whereby the temperature then rises to the operating temperature TB in accordance with the rising edge of the wave and then falls again in accordance with the following, descending edge, until the heat storage unit 30 is completely discharged. In suitable operation, i.e., operation with only partial loading even with continuous flow of the heat-transporting gas, the heat storage unit 30 has a warm side and a cold side, see diagrams 34 and 40 of Figure 3, whereby the cold side essentially remains at the ambient temperature TUG, although the warm side reaches the operating temperature TB. This also applies to operation with a wave according to diagrams 45 and 50, if the wave is only shifted into the heat storage unit 30 to such an extent that the warm side of the heat storage unit has not yet fallen to the lower temperature (for example, up to the heat distribution according to curve 47 in diagram 45). Figure 4 shows a process system 60 according to the invention in a preferred embodiment with two layered heat storage units 61, 62 which are designed according to Figure 3 and contain a heat-storing bulk material 66. A process unit, indicated here only by dashed lines as a cerium reactor 63, is arranged between the first heat storage unit 61 and the second heat storage unit 62, with the line sections 64a and 64b of a first section I of the line arrangement L (Figure 1) visible, which connects the cerium reactor 63 to the heat storage units 61, 62 in an operational manner.Further shown are the outlets 65a and 65b of the line 6 of the second section II of the line arrangement L (Figure 1), which is not shown to relieve the figure and which enable the circulation of the heat-transporting medium (here again argon) in both flow directions, namely to the right from the outlet 65a to the outlet 65b and vice versa to the left from the outlet 65b to the outlet 65a. By operating the process system 60, the cerium reactor 63, as shown in Figure 2, is cyclically switched between an upper temperature T0 and a lower temperature Ty. Diagrams 70 to 74 illustrate the heat exchange between the first 61 and second heat storage units 62 and the reactor 63. However, to clarify the interaction between the heat storage units, the diagrams initially show the interaction without the external (solar) heat input between the recuperation temperature TR and the upper temperature T0 (see Diagram 20, Figure 2), but rather starting from the TR between T0 and the operating temperature TB of the heat storage units 61 and 62. Regarding the external heat input, see below, with reference to Figures 6 and 7a to 7d. Diagrams 70 to 74 show temperature distribution curves 76 to 80 of different operating states of the arrangement consisting of the cerium reactor 63 with the first 61 and the second heat storage unit 62, where sections A, B and C each represent the range orindicate the length in the flow direction of the heat transporting medium of the first heat storage unit 61, the cerium reactor 63 and the second heat storage unit 62. Diagram 70 shows the temperature distribution curve 76 after the first part of a start-up process of the process system 60 at time tQ. The first heat storage tank 61 is charged with heat such that a temperature wave W with a peak temperature TB is present, with the edges of the wave W dropping to the ambient temperature TUG, here for example 300 °K. The cerium reactor 63 and the second heat storage tank 62 are still at the ambient temperature TUG. For the second part of the start-up process, argon at ambient temperature TUG flows from the outlet 65a to the right through the first heat storage tank 61, the cerium reactor 63, and the heat storage tank 62 into the outlet 65b, see the direction of the arrow in Diagram 70, with the result that the wave W moves to the right in the direction of flow, as described in Diagram 45, Figure 3. Diagram 71 shows the temperature distribution curve 77 at time_tig, where the temperature wave W has shifted so far to the right in the flow direction that its leading edge abuts the cerium reactor 63 and partially passes through it. This means that the argon has flowed through the cerium reactor 63 with an increasing edge temperature TF, lying between TUG and TB, and has heated it accordingly. Because the temperature wave W enters the cerium reactor 63 from TUG with an increasing edge temperature TF, it continuously heats it, so that the temperature difference between TF and that of the reactor 63 always remains small. Naturally, the argon loses some heat as a result; see the temperature drop in the temperature distribution curve 71 in section B, after which the argon exits the cerium reactor 63 at a temperature below TF.The second heat storage tank 62 is finally heated by the incoming argon, so that the temperature distribution curve 77 exhibits a slope in section C; see the description of Figure 3, in particular Diagram 34, Curve 35. It follows that the heat stored in the heat storage tank 61 is used to heat the reactor 63, but also serves to charge the heat storage tank 62. It further follows that the wave W passing through the cerium reactor 63 does not, in a sense, "see" it (with the exception of the temperature drop due to the heat exchange of the argon with the reactor 63), but is of course torn apart by the length of the reactor 63 (section B), as shown by the temperature distribution curve 77. In summary, the start-up process is complete as soon as the temperature distribution corresponds to temperature distribution curve 77: reactor 63 is at Tu, with the first heat storage unit 61 being charged with a wave W such that reactor 63 can be brought to TB by this wave and subsequently cooled back down to Ty. In other words, reactor 63 is located at point Py of diagram 20 in Figure 2. Diagram 72 shows the temperature distribution curve 78 later, at time tn, where wave W has penetrated far enough into the cerium reactor 63 that it is being supplied with argon at the upper temperature TB. The cerium reactor has thus been brought to a temperature TR (Figure 2) close to the upper temperature T0 and is located at point PR of Diagram 20, Figure 2. According to the description for Figures 1 and 2, the cerium reactor 63 is then preferentially brought to T0 (i.e., to point P0 in Diagram 20) by the heat from solar radiation; see the description below for Figures 6 and 7. Diagram 73 shows the temperature distribution curve 79 at time ti2, where the wave W has continued to migrate through the cerium reactor 63 between time tn and ti2, so that its subsequent falling edge now passes through it and the crest of the wave W has entered the second heat storage unit 62. As long as the subsequent edge of the wave W passes through it, the cerium reactor 63 continuously releases heat to the argon, since the argon, due to the falling edge, is always cooler than the cerium reactor, which loses heat with a delay, despite the ongoing heat loss from the reactor 63. Again, the difference between the current temperature of the argon and the reactor 63 is small. At the moment tu, reactor 63 is located at point PKE of diagram 20, figure 2. For the re-oxidation of the cerium, and the associated cooling of reactor 63 to Ty (point Py in diagram 20, figure 2), the flow of argon can be stopped.The flow direction then switches to the left in the direction of the lower arrow, i.e., from line 65b to line 65a. Wave W then moves to the left, heating reactor 63 as it passes through the preceding rising flank and subsequently cooling it through the following falling flank. Diagram 74 shows the temperature distribution curve 80 at time t14, where wave W has passed through cerium reactor 63 to such an extent that, after heating to TR (and to T0 by external heat, see Diagram 20, Figure 2), it has cooled back down to TKE, and the corresponding heat is stored in the heat storage unit 61.In summary, after a start-up process according to Diagram 70, the process system 60 exhibits a temperature distribution according to Diagram 71. The wave W is then sent through the reactor 63 in one flow direction (here: to the right), resulting in the temperature distribution according to Diagram 73. From there, the wave W is sent back through the cerium reactor 63 in the other flow direction (here: to the left) until the temperature distribution according to Diagram 74 is reached. This forms the starting point for a new cycle, i.e., again in one flow direction to the state according to Diagram 73 and then back in the other flow direction to the state according to Diagram 74, and so on, for as long as the process is to run. Starting from the center of the reactor 73, the wave W moves to symmetrically located end positions in the heat storage units 61 and 62.After the start-up process, the wave W extends over the length LSYM from the cerium reactor 63 into the two heat storage units 61 and 62, or sections A and C, respectively, as shown in Diagram 74 in conjunction with Diagram 73. This means that during operation, the two heat storage units remain at ambient temperature TUG and thus cold at their outer sections located at the openings 65a and 65b, while inside the process system, a cyclic heat exchange takes place between the reactor 63 and the heat storage units 61 and 62 by the wave W, which oscillates continuously back and forth according to Diagrams 73 and 74. Figure 5 shows a further embodiment of the invention in which the process is not symmetrical (Figure 4) but asymmetrical, in that the wave W, which passes through the reactor 63 to the right, is stopped at the temperature distribution shown in Diagram 72 (Figure 4).To illustrate this, Figure 5 shows such a sequence with diagrams 85 to 87, which correspond to diagrams 71, 72, and 74 of Figure 4. That is, their temperature distribution curves 88 to 90 (at times jjo to j«) are the same as temperature distribution curves 77, 78, and 80. However, as mentioned, the point at which the flow direction is switched is different. This switch occurs when, according to diagram 86, the temperature distribution follows curve 89. Thus, the heating of reactor 63 proceeds from the state shown in diagram 85 to that shown in diagram 86, and the cooling after the flow switch proceeds from the state shown in diagram 86 to that shown in diagram 87, whereupon the cycle begins anew. Accordingly, the oscillating wave W penetrates less deeply into the second heat storage unit 62 than into the first heat storage unit 61, meaning that its end positions are no longer symmetrical but asymmetrical.The corresponding lengths LASYM are shown in Diagram 87 in conjunction with Diagram 86. It follows that the second heat storage element 62 can advantageously be made shorter than in the embodiment according to Figure 4, while of course the two outer ends of the heat storage elements 61, 62 at the openings 65a and 65b also always remain at the ambient temperature TUG and thus cold. The heat losses in the heat exchange described with reference to Figures 4 and 5 are low, and the efficiency of the heat recuperation achieved in this way is high. Furthermore, in conjunction with the description of Figure 2, a person skilled in the art can readily determine the switching times of the flow for the specific case with regard to any process with cyclically changing temperature. In particular, by the steepness of the flanks of the wave W and its velocity through the reactor 63, a person skilled in the art can determine the temperature difference to which the reactor is exposed during heating or cooling, which conversely also makes it possible to design it only for predetermined small temperature differences. In the embodiment of the process system 60 described in Figures 4 and 5, the first 61 and the second heat storage units 62 together have a heat-storing filling of bulk material 66, wherein the heat-transporting medium is preferably a gas, particularly preferably argon. Furthermore, the heat storage units 61 and 62 on their side facing away from the reactor 63 (at the outlets 65a and 65b) always operate at ambient temperature TUG, while their sides facing the reactor 63 at the pipe sections 64a and 64b (after the start-up process) always operate at elevated temperatures between Ty and TB, the peak temperature of the (reciprocating) shaft W. Accordingly, the first heat storage unit (61) and the second heat storage unit (62) each have a cold side during operation, preferably with a second section (II) of the pipe arrangement (L) connecting these cold sides. Even without the second section II, the cold sides can be connected to the environment or to other systems, as is the case in an embodiment described with reference to Figure 1. It should be noted that in actual operation, the cold sides can warm up slightly over time. If necessary, a person skilled in the art can then provide a cooling unit for the heat-transporting medium in the second section II of the pipe arrangement L, or design the process system so that it can cool down during the interruptions that occur during solar operation (at night).Figures 4 and 5 further show that the heat storage units 61 and 62 are connected to each other via the lines 64a and 64b (section I of the line assembly L), while, according to Figure 1, all necessary switching elements for the operation of the process system, such as the pump assembly 15, can be provided in the second section II of the line assembly L – with the advantage that the switching elements are arranged on the cold side, thus free from high temperatures, and can therefore be designed with a correspondingly simple construction. On the hot side, which, depending on the application, can be at temperatures above 1300 °K or 2300 °K or more, simple pipe connections such as ceramic tubes are sufficient. It follows that, preferably, switching elements for the operation of the first and second sections of the line assembly are arranged in the second section of the line assembly.The first line section is particularly preferred as it is free of switching elements for the operation of the process system. The heat storage units 60, 61 must be designed with a minimum length so that their cold side does not exceed the ambient temperature TUG during operation. Graphically, this minimum length is represented in Figures 4 and 5 by an associated length LSYM or LASYM for each heat storage unit 60, 61 – these are the distances in sections A and C that the shaft W needs to travel back and forth. The lengths LSYM and LASYM of the heat storage unit 61 in the embodiments according to Figures 4 and 5 are equal, while the length LASYM of the heat storage unit 62 in Figure 5 is shorter than LSYM of the heat storage unit 62 in Figure 4 due to the shaft W penetrating less deeply into the heat storage unit 62. It follows that the person skilled in the art can dimension the length of the heat storage units in the embodiment according to Figure 4 to a minimum LSYM, and in an embodiment according to Figure 5 the length of one heat storage unit (here the second heat storage unit 62) can be shortened once again to LASYM, which allows for more economical manufacturing. It should be emphasized here that the cold side of the heat storage unit is at ambient temperature TUG for most applications. However, depending on the specific case, it may be advisable for the cold sides, i.e., the sides of the heat storage unit facing away from the process unit, to operate at a higher temperature, for example, up to 400 K or even higher – if, for instance, the heat-transporting fluid is also circulating in other systems connected to the process system or is itself in heat exchange with such other systems. In this context, however, the term "cold side" is always used to distinguish it from the hot side of the heat storage unit. A person skilled in the art can provide a specifically designed start-up procedure for operation with a cold side that is above ambient temperature TUG – this does not change the operating principle according to the invention as described in Figures 3 to 5.From the preceding description relating to Figures 1 to 5 and also according to the embodiments described in Figures 6 to 8, a further method for the cyclic heating and cooling of a process unit 2, which can be operated between an upper and a lower temperature, is derived, characterized in that the process unit is operationally connected between a first 3 and a second heat storage unit 4. - wherein the first 3 and the second 4 heat storage units release heat in the upper temperature range when charged, and the temperature tends towards the lower temperature during discharge, wherein the first 3 and the second 4 heat storage units can be charged first with heat in the lower temperature range and then in the upper temperature range during a charging process, and wherein by a cyclic change in the flow direction of a heat-transporting medium flowing through the first 3 and the second heat storage 3 - and thus through the process unit 2 - this process unit 2 is alternately moved back and forth between the upper temperature and the lower temperature. Preferably, a flow direction is maintained before the cyclic reversal until the process unit 2 is heated from the lower temperature to a recovery temperature and subsequently cooled back down to the lower temperature (see the embodiment according to Figure 4). Preferably, the heat storage units are operated with a wave-like temperature stratification, forming a wave W. Particularly preferably, the change in flow direction is synchronized such that, in continuous, symmetrical operation, the wave oscillates back and forth equally far into and out of both heat storage units. Alternatively, the change in flow direction can also be synchronized such that, in asymmetrical operation, the wave oscillates back and forth less far into one heat storage unit than the other, preferably only up to its temperature peak, and then out again.The advantages achievable through the invention with a cold (and warm) side of the heat storage unit are realized in particular when, preferably during operation, the shaft W only partially reaches the sides of the heat storage unit facing the process unit, such that these sides remain below a predetermined temperature, but preferably not reach them at all, such that these sides remain cold. Finally, the expert can also adjust the flow to the process unit in such a way that the current temperature difference between the heat-transporting medium flowing through it and the process unit does not exceed a predetermined value. In all the embodiments shown, the process unit can be designed as a directly or indirectly illuminated solar reactor. Figure 6 shows a scheme of a process system 100 in which the external heat, here solar energy, is introduced indirectly, i.e. without direct illumination of the process unit 2 (Figure 1) by the sun, between the points Pß and P2 in diagram 20 of Figure 2. The figure shows a process unit, again configured as a cerium reactor 63, into which the lines required for transporting the heat-carrying medium and all reactants are operationally connected. Visible are lines 101a and 101b of a first section I of a line arrangement L, as well as a second section II of the line arrangement L with a pump arrangement 103 comprising pumps 103a and 103b, each equipped with a check valve, and a tank 104 for the heat-carrying medium, in this case again argon. Also visible are the CO2 tank 8, the H2O tank 9, and the syngas tank 10 (see the description of Figure 1). A first heat storage tank 61 and a second heat storage tank 62 are configured according to the embodiment shown in Figure 4. As far as, and apart from the direct illumination of reactor 63 by the sun 7 (Figure 1), the process system 100 corresponds to that of Figure 1.In addition, a third heat storage unit 110 and a solar receiver 111 for sunlight (purple) are added, both of which can be connected to the circuit for the heat-transporting medium. The receiver 111 and the heat storage unit 110 are designed to generate and store heat with at least the upper temperature T2, respectively. Preferably, the third heat storage unit 110 is designed as a stratified heat storage unit according to Figure 3 and is charged and discharged according to Diagram 40 of Figure 3. Furthermore, in the second section of the pipe arrangement L, it is connected via pipes 115a and 115b (there via pump 103c) to the argon tank 104 and via pipe 115c to an inlet designed as pipe 116 to the reactor 63.The solar receiver 111 is connected to the argon tank 104 via line 117a (via pump 103d) and, via line 117b, can be selectively connected to either line 116 or line 115c, so that the heat-carrying medium (here: argon) heated by the receiver can be pumped either directly into the reactor 63 or into the third heat storage tank 110, driven by pump 103d in line 117a. Valves 118a to 118c, together with lines 101c to 101f and the check valves assigned to pumps 103a to 103d, determine the flow and path of the heat-carrying medium in the process system 100. It should be emphasized that the dashed line shown in the figure forms the boundary in process system 100 between its hot side, which includes reactor 63, and its cold side, in which all switching elements such as valves and the pump assembly 103 are located. This again clearly illustrates the advantageous arrangement according to the invention, which allows all switching elements to be arranged simply and cost-effectively in the cold area (preferably at ambient temperature TUG), while in the hot area, at temperatures between TR and T0, which can exceed 1300 °K or 2300 °K, only piping for the heat-transporting medium and substances reacting or generated in the reactor is required, which can also be made of materials such as ceramics, simply and cost-effectively. Line 117b forms a third section III and line 115c a fourth section IV of the line arrangement L. This results in the following: according to the embodiment shown, in the first section I of the pipe arrangement L, in the flow direction upstream of the process unit, an inlet 116 for the heat-transporting medium is arranged in the region of the upper temperature; further preferably, a solar receiver is provided for heating the heat-transporting medium, wherein a third section of the pipe arrangement connects the solar receiver to the inlet; and finally, particularly preferably, a third heat storage unit is provided, which a fourth section of the pipe arrangement connects to the inlet, wherein heat from the solar receiver can be stored in this third heat storage unit. The embodiment according to Figure 6 shows that for any solar-powered process system, the receiver can be arranged remotely from the process unit (for example, a reactor for chemical reactions or another unit for heat utilization), either in direct connection to a process unit of the process system or indirectly via a heat storage device associated with the receiver. Figures 7a to 7d show how the process system 100 can be switched (and also operated for the process steps described above) for the various operating phases of the reactor 63 shown in Figure 2, with the heat storage devices 61 and 62 preferably being operated according to Figures 4 and 5. Figure 7a shows a switching state of the process system 100 in the period t0 to tK or in the period tKE to tuE (see Figure 2, Diagram 20, with the points P0 to PK and PKE to PUE), in which the reduction of the cerium is complete orRe-oxidation takes place, and therefore there is no flow of the heat-transporting medium through reactor 63. During these time periods tR to t0 and tKE to tUE, respectively, heat from the solar receiver 111 can be stored in the third heat storage tank 110 by means of the heat-transporting medium (here: argon). For this purpose, pump 103d drives argon from tank 104 through receiver 111, where it absorbs heat, then through lines 117b and 115c into heat storage tank 110, which is thereby heated, and finally, cooled to ambient temperature tUG, back into tank 104. The lines thus active are highlighted in bold in the figure. Fig. 7b shows a switching state of the process system 100 for a flow running to the right in the embodiments of Figures 4 and 5, i.e., for example, in the period tu to tR or between points Py to PR (see Fig. 2), in which the reactor 63 is heated by recuperated heat, i.e., heat stored in the first heat storage tank 61. Initially, the temperature distribution in the heat storage tanks 61, 62 corresponds to Diagram 71 of Figure 4 or Diagram 85 of Figure 5, depending on the embodiment according to which the process system is operated. For this purpose, pump 103b drives argon from tank 104 through the receiver through the first heat storage unit 61, where it is charged with heat, then through line 101b into reactor 63 and from there through line 101a into the second heat storage unit 62, which is thereby charged with heat, and finally, cooled to ambient temperature tUG, back into tank 104.The active lines are highlighted in bold in the figure. This switching state also occurs when, during the period tK to tKE or between points PK to PKE (see Fig. 2), heat is extracted from the reactor 63 to be cooled and stored in the heat storage tank 62 for recuperation, as shown in diagram 73 of Figure 4. Then, argon, whose temperature is decreasing, flows from the heat storage tank 61 through the reactor 63, where it absorbs the reactor's heat and stores it in the heat storage tank 62. Fig. 7c shows a switching state of the process system 100 during the period tR to t0, or between points PR and P0 (see Fig. 2), in which the reactor 63 is heated to the upper temperature T0 by the external heat stored in the third heat storage unit 110 (here from the receiver 111). As mentioned above, the heat storage unit 110 can also be charged by energy sources other than solar energy – and an energy source other than the sun could supply heat to the process system 100 instead of the receiver 111. For this purpose, pump 103c drives argon from tank 104 through the thermal storage tank 110, where it absorbs heat, then through lines 115c and 116 into reactor 63, and from there through line 101a into thermal storage tank 62, which is thereby heated to a temperature above TR, and finally, cooled to ambient temperature tUG, back into tank 104. The lines active in this way are highlighted in bold in the figure. Alternatively, pump 103d can also be activated, so that heat-carrying fluid heated by receiver 111 and the third thermal storage tank 110 simultaneously flows through line 116 into the reactor. Likewise, only pump 103d can be activated, but not pump 103c, so that the switching state of the process system 100 corresponds to that of Figure 1 with direct solar illumination of the reactor. It should be emphasized that in Diagram 73 of Figure 4 and Diagram 86 of Figure 5, the peak temperature of the shaft W is shown above TR without this heat input, since these diagrams discuss the displacement of the shaft W as a result of the setup of the process system 60 shown therein. However, in a switching state according to Figure 7c of a process system according to the invention, the efficiency increases again due to the external heat thus recuperated. It should also be noted that this avoids the slight, continuous decrease in the peak temperature of the moving shaft in Diagrams 45 and 50 of Figure 3, so that the temperatures TR and T0 can actually remain constant over an arbitrarily long operating period. In this specific case, the person skilled in the art can easily design the process system 100 accordingly. Fig. 7d shows a switching state of the process system 100 for a counterclockwise flow in the embodiments of Figures 4 and 5, i.e., for example, for a reverse wave W according to diagram 73 of Figure 4 in the period tu to tR or between points Pu to PR (see Fig. 2), in which the reactor 63 is heated by recuperated heat, i.e., unlike in Fig. 7b, heat stored not in the first heat storage tank 61, but in the second heat storage tank 62. The reverse wave W also causes the cooling of the reactor 73 in the period tK to tKE or between points PK to PKE (see Fig. 2), whereby heat is extracted from the reactor 63 to be cooled and stored in the heat storage tank 61 for recuperation. For this purpose, pump 103a drives argon from tank 104 through the heat storage tank 62, then through line 101a into reactor 63 and from there through line 101b into heat storage tank 61, and finally, cooled to ambient temperature tUG, back into tank 104. The lines active in this way are highlighted in bold in the figure. Figure 8a shows a view of the hot side of a realized process system 100 according to the scheme of Figure 6. Shown is a shell 120 for the hot side components, as well as a connection flange 121 for attaching the shell 120 to the installation site of the reactor 63. The figure omits the second section II of the piping arrangement L, as well as tanks 8 to 10 for CO2, H2O, and the syngas tank 10, in which the gas mixture consisting mainly of CO and H2 as end products is collected. All these components can be easily designed and positioned by a person skilled in the art in this specific case, since they only need to be designed for the ambient temperature range TUG (or, depending on the specific case, another comparatively low temperature), and, as mentioned, comparatively expensive high-temperature switching devices or high-temperature pumps in the hot section of the piping arrangement L can be avoided. Visible in shell 2 are the first to third thermal storage units 61, 62, and 110, the reactor 63, and the receiver 111, which is located behind a section 122 in shell 120 that is transparent to sunlight. Also visible are the line 117a leading to the receiver 111 for transporting cold heat, the lines 117b and 116 leading from the receiver 111 to the reactor 63, and the lines 101a and 101b of the first section I of the line arrangement L. Somewhat obscured behind thermal storage unit 110 is the line 119 from the reactor 63 to the syngas tank 10 (not shown here) (Figure 6).

Claims

Patent claims A process system with a process unit (1, 60, 100) operable between an upper (T0) and a lower (Tu) temperature, characterized in that a first heat storage unit (3, 61) and a second heat storage unit (4, 62) are operatively connected to each other by a conduit arrangement (L) for a heat-transporting medium, wherein the process unit (1, 60, 100) is arranged in a first section (I) of the conduit arrangement (L) between the first (3, 61) and the second heat storage unit (4, 62). A process system according to claim 1, characterized in that the first heat storage unit (61) and the second heat storage unit (62) are connected on their respective sides facing away from the process unit (60, 100) by means of a second section (II) of the conduit arrangement L. A process system according to claim 1 or 2, characterized in that the first heat storage unit (61) and the second heat storage unit (62) are designed as stratified heat storage units.A process system according to any one of claims 1 to 3, characterized in that the first heat storage unit (61) and the second heat storage unit (62) have a heat-storing filling of bulk material (66) and preferably the heat-transporting medium is a gas, particularly preferably argon. A process system according to any one of claims 1 to 4, characterized in that the first heat storage unit (61) and the second heat storage unit (62) each have a cold side during operation and that preferably a second section (II) of the pipe arrangement (L) is provided, connecting these cold sides. A process system according to any one of claims 2 to 5, characterized in that a cooling unit for the heat-transporting medium is arranged in the second section (II) of the pipe arrangement (L).A process system according to any one of claims 2 to 6, characterized in that switching elements for the operation of the first (I) and the second section (II) of the piping arrangement (L), preferably for the entire process unit (1, 60, 100), are arranged in the second section (II) of the piping arrangement (L). A process system according to any one of claims 1 to 7, characterized in that the first piping section (I) is free of switching elements for the operation of the process system. A process system according to any one of claims 1 to 8, characterized in that the process unit (2) is designed as a solar reactor illuminated by the sun. A process system according to any one of claims 1 to 9, characterized in that an inlet for the heat-transporting medium in the region of the upper temperature (T0) is arranged in the first section I of the piping arrangement (L) upstream of the process unit (60, 100) in the flow direction.Process system according to claim 10, characterized in that a solar receiver (111) is provided for heating the heat-transporting medium, wherein a third section (III) of the piping arrangement (L) connects the solar receiver (111) to the inflow. Process system according to claim 11, characterized in that a third heat storage unit (110) is provided, which a fourth section (IV) of the piping arrangement (L) connects to the inflow, such that heat from the solar receiver (111) can be stored in this third heat storage unit (110). Method for cyclically heating and cooling a process unit (2, 63) that can be operated between an upper and a lower temperature, characterized in that the process unit (2, 63) is operably connected between a first (3) and a second heat storage unit (4). wherein the first heat storage device (3) and the second heat storage device (4) release heat in the upper temperature range when loaded and the temperature tends towards the lower temperature during a discharge, wherein the first heat storage device (3) and the second heat storage device (4) can be charged first with heat in the lower temperature range and then in the upper temperature range during a charging process, and wherein a heat-transporting medium flowing through the first heat storage unit (3) and the second heat storage unit (4) – and thus through the process unit (2) – alternately moves the process unit (2) between the upper and lower temperatures. Method according to claim 13, wherein a flow direction is maintained before the cyclic reversal until the process unit (2) is heated from the lower temperature to an efflux temperature and subsequently cooled back down to the lower temperature. Method according to claim 13, wherein the heat storage units (3, 61, 4, 62) are operated with a wave-like temperature stratification forming a wave W.A method according to claim 15, wherein the change in flow direction is timed such that the wave continuously oscillates back and forth in symmetrical operation, entering and exiting both heat storage units (3, 61, 4, 62) to the same extent. A method according to claim 15, wherein the change in flow direction is timed such that the wave continuously oscillates back and forth in asymmetrical operation, entering and exiting one heat storage unit to a lesser extent than the other, preferably to its temperature peak. A method according to any one of claims 15 to 17, wherein, during operation, the wave W does not reach the sides of the heat storage units facing away from the process unit, such that these sides remain cold. Method according to claim 14, wherein the flow is adjusted to the process unit such that the current temperature difference between the heat-transporting medium flowing through it and the process unit does not exceed a predetermined value. Method according to one of claims 13 to 15, characterized in that the process unit is designed as a directly illuminated solar reactor.