Thermochemical reactor system for a temperature swing cyclic process with integrated heat recovery and a method for operating the same

Abstract

Disclosed is a thermochemical reactor system and method for a temperature swing cyclic process with integrated heat recovery having at least two modules, wherein each module includes at least one chemical reaction zone and at least one thermal energy storage unit. The at least two modules are operationally connected for at least one heat transfer fluid for transporting heat between the two modules. Each chemical reaction zone includes at least one reacting material that undergoes in a reversible manner an endothermic reaction at temperature T.sub.endo and an exothermic reaction at temperature T.sub.exo, wherein T.sub.endo and T.sub.exo differ from each other. The at least one reacting material is provided in at least one encapsulation within each of the chemical reaction zones such that a contact of the reacting material and the at least one heat transfer fluid is avoided.

Claims

1. A thermochemical reactor system for a temperature swing cyclic process with integrated heat recovery comprising: at least two modules, wherein each module comprises at least one chemical reaction zone (CRZ) and at least one thermal energy storage unit (TES); wherein the at least two modules are operationally connected for at least one heat transfer fluid (HTF) for transporting heat between the two modules; wherein each chemical reaction zone (CRZ) comprises at least one reacting material that undergoes in a reversible manner an endothermic reaction at temperature T.sub.endo and an exothermic reaction at temperature T.sub.exo, wherein T.sub.endo and T.sub.exo differ from each other; wherein the at least one reacting material is provided in at least one encapsulation within each of the chemical reaction zones (CRZ) such that a contact of the reacting material and the at least one heat transfer fluid is avoided.

2. The reactor system according to claim 1, wherein the at least one reacting material in each chemical reaction zone is at least one metal oxide undergoing reduction at reduction temperature T.sub.red and oxidation at oxidation temperature T.sub.ox, wherein T.sub.red and T.sub.ox differ from each other.

3. The reactor system according to claim 1, wherein the at least one reacting material in each chemical reaction zone is at least one material undergoing adsorption at adsorption temperature T.sub.adsorp and desorption at desorption temperature T.sub.desorb of at least one compound.

4. The reactor system according to claim 1, wherein the at least one reacting material in each chemical reaction zone is at least one material undergoing carbonation by reacting with CO2 at carbonation temperature T.sub.carb and de-carbonation by releasing CO.sub.2 at de-carbonation temperature T.sub.decarb of at least one compound, wherein T.sub.carb and T.sub.decarb differ from each other.

5. The reactor system according to claim 1, wherein each chemical reaction zone is arranged adjacent to the corresponding thermal energy storage unit (TES).

6. The reactor system according to claim 1, wherein the at least one encapsulation containing the reacting material is arranged perpendicular, parallel or in any other angle to the flow direction of the HTF through the at least one chemical reaction zone.

7. The reactor system according to claim 1, wherein the at least one encapsulation is provided in form of at least one tube, a tube bundle or a chamber.

8. The reactor system according to claim 1, wherein the reacting material is provided in at least two encapsulations.

9. The reactor system according to claim 8, wherein the encapsulations are arranged parallel and/or perpendicular to each other.

10. The reactor system according to claim 1, wherein the encapsulation is made of a material with a good thermal conductivity.

11. The reactor system according to claim 1, wherein at least two reacting materials with different reduction/oxidation temperatures or different adsorption/desorption temperatures or different carbonation/decarbonation temperatures are used, wherein the different reacting materials are arranged in series along the flow direction of the HTF.

12. The reactor system according to claim 11, wherein each of the different reacting material is arranged in a tube or stack such that a temperature gradient is created between the different reacting materials.

13. The reactor system according to claim 1, wherein the thermal energy storage units store thermal energy in the form of sensible heat (SHS) and/or latent heat (LHS), and/or heat of reaction of reversible thermochemical reactions (TCS).

14. The reactor system according to claim 1, wherein the thermal energy storage units comprise a heat storage material comprising a porous structure made of a ceramic material in the form of bricks, channels, pellets, or spheres made of zirconia, silica, or alumina.

15. The reactor system according to claim 1, wherein the reactor system is coupled to at least one external source of thermal energy (ESE) for heating the HTF.

16. The reactor system according to claim 15, wherein the external source of thermal energy obtains process heat from a solar receiver and/or electrical heating elements and/or plasma torches and/or combustion of fuels.

17. The reactor system according to claim 1, wherein the heat transfer fluid (HTF) is air, carbon dioxide, helium, steam, molten salt, molten metals, molten glass, nitrogen, argon, synthetic oils.

18. A method for operating the reactor system according to claim 1, wherein one of the two chemical reaction zones is operated at the temperature T.sub.endo of the endothermic reaction and the other chemical reaction zone is operated at the temperature T.sub.exo of the exothermic reaction of the reacting material, wherein the heat required for the chemical reaction zones is provided by a heat transfer fluid.

19. The method according to claim 18, wherein one of the two chemical reaction zones is operated at the reduction temperature T.sub.red and the other chemical reaction zone is operated at the oxidation temperature T0x of a metal oxide used as reacting material.

20. The method according to claim 19, wherein the metal oxide as reacting material is used for converting water and carbon dioxide to syngas comprising hydrogen and carbon monoxide or for converting methane, water, and carbon dioxide to syngas comprising hydrogen and carbon monoxide.

21. The method according to claim 19, wherein the metal oxide as reacting material is used for converting water and carbon dioxide to hydrocarbons.

22. The method according to claim 19, wherein the metal oxide as reacting material is used for the separation of oxygen from air or from any other gas mixtures.

23. The method according to claim 18, wherein one of the two chemical reaction zones is operated at the adsorption temperature T.sub.adsorp and the other chemical reaction zone is operated at the desorption temperature T.sub.desorb of the reacting material.

24. The method according to claim 23, wherein the adsorbing/desorbing reacting material is used for the separation of carbon dioxide and/or water from air or from any other gas mixtures containing any of these compounds.

25. The method according to claim 18, wherein one of the two chemical reaction zones is operated at the carbonation temperature T.sub.carb and the other chemical reaction zone is operated at the decarbonation temperature T.sub.decarb of the reacting material.

26. The method according to claim 25, wherein the carbonation/decarbonation reacting material is used for the separation of carbon dioxide from gas mixtures containing any of these compounds.

27. The method according to claim 18, wherein the heat transfer fluid is heated by the external source of thermal energy.

28. The method according to claim 18, wherein the temperature and temperature profile (thermocline) of the chemical reaction zones is additionally controlled and maintained by extracting, heating and injecting the heated heat transfer fluid at different positions along the chemical reaction zones and/or the thermal energy storage units.

29. The method according to claim 18, wherein the temperature and temperature profile of the chemical reaction zones is additionally controlled and maintained by extracting HTF from any position of the TES unit to transport the stored heat into the respective chemical reaction zone.

30. The method according to claim 18, wherein the temperature profile is controlled by having multiple ports along the modules for extraction and injection of HTF.

31. The method according to claim 18, wherein the temperature profile inside at least one module is steepened by injecting HTF at an intermediate position of the temperature profile cutting off a certain portion of the temperature profile.

32. The method according to claim 31, wherein the criteria for switching the HTF injection port is determined based on comparing the actual stored energy between two ports and a target/reference energy.

33. The method according to claim 18, wherein the temperature profile is controlled by extracting HTF at one port of a module and injecting it back at another port of a module.

34. The reactor system according to claim 3, wherein that at least one material is at least one gas.

35. The reactor system according to claim 3, wherein the at least one gas is CO.sub.2.

36. The reactor system according to claim 8, wherein the reacting material is provided in three or more encapsulations.

37. The reactor system according to claim 10, wherein the material is at least one of aluminum, silicon carbide, or high-temperature alloys.

38. The method according to claim 21, wherein the hydrocarbons comprise CH.sub.4.

Description

(1) The invention is now explained in more detail with reference to the figures by means of an example. It shows:

(2) FIG. 1 a scheme of a first embodiment of the present thermochemical reactor system;

(3) FIG. 2a a scheme of a variant of an encapsulation of the reacting material perpendicular to the HTF flow direction;

(4) FIG. 2b a scheme of further variants of an encapsulation of the reacting material;

(5) FIG. 2c a scheme of yet further variants of an encapsulation of the reacting material;

(6) FIG. 2d a scheme of a first variant of an encapsulation of the reacting material parallel to the HTF flow direction;

(7) FIG. 2e a scheme of an encapsulation variant for redox material in syngas process;

(8) FIG. 3a a scheme of a first cascaded encapsulation variant;

(9) FIG. 3b a scheme of a second cascaded encapsulation variant;

(10) FIG. 3c a scheme of a cascaded encapsulation variant for redox material in syngas process;

(11) FIG. 4a an ideal temperature profile in a reactor system according to FIG. 1;

(12) FIG. 4b a degraded temperature profile in a reactor system according to FIG. 1;

(13) FIG. 5a Movement of temperature profile to bring the left tank to reduction temperatures;

(14) FIG. 5b further moving of temperature profile without upgrading the compressed air in the CSP receiver;

(15) FIG. 5c Thermocline control to obtain a uniform oxidation temperature plateau in the right redox zone;

(16) FIG. 5d pushing back thermocline without upgrading;

(17) FIG. 6a Temperature profile during charging process; and

(18) FIG. 6b Temperature profile during discharging process.

(19) In FIG. 1 a first embodiment of the present reactor system in the form of a dual-storage reactor system is shown. The dual-storage reactor system consists of two vertically oriented thermal energy storage units (thermocline TES) such as packed beds of inert material. A chemical reaction zone (CRZ) comprising encapsulated redox material is placed on top of the thermocline TES, respectively. The packed beds serve as thermal energy storage (TES) units in which axial temperature gradients (thermoclines) are established.

(20) The two combined CRZ/TES are operationally linked to each other by a heat transfer fluid (HTF) transporting heat through the system between both CRZ/TES units. A heating section for heating the HTF is provided between the two CRZ/TES such that the HTF heated in said heating section may flow into the CRT/TES, respectively.

(21) By pumping HTF back and forth between the two CRZ/TES, the thermoclines in the CRZ/TES are shifted along the axial direction, and therefore the redox materials are alternately exposed to T.sub.red and T.sub.ox. The sensible heat is thereby recuperated between the reduction and oxidation steps.

(22) The flow direction of the HTF transporting the heat for the heating section to the chemical reaction zones and the thermal storage units is switched if the redox material in the one of the two chemical reaction zones operated at the reduction temperature T.sub.red of the redox material is reduced to a certain extent and/or if the redox material in the other chemical reaction zone operated at the oxidation temperature T.sub.ox of the redox material is oxidized back to a certain extent.

(23) Process heat obtained by concentrated solar radiation is added to the HTF between the reaction zones to provide the reduction enthalpy and to compensate for thermal losses and thermocline degradation.

(24) FIGS. 2a-2e illustrate certain variants of the encapsulation of the reacting material.

(25) In FIG. 2a the reacting material is encapsulated in tubes which are arranged perpendicular to the flow direction of the heat transfer fluid within the chemical reaction zone. Thereby a variety of different arrangements of the encapsulations are possible. FIG. 2b illustrates some examples of possible arrangements; (a) parallel tube layers (bundles) with parallel stacking of the layers, (b) parallel tube layers with perpendicular stacking of the layers, (c) parallel tube layers with stacking of the layers in a certain angle (0-90 degree).

(26) The reactive material can also be encapsulated in stacks similar to fuel-cell stacks. Thereby, the heat transfer fluid flows through dedicated channels while the reactive material is contained in separated chambers. Such arrangements are shown in FIG. 2c. The reactive material (e.g. CeO.sub.2) is arranged in grooves or deepening within a block of inert encapsulation material (e.g. Al.sub.2O.sub.3). The HTF flows through channels in the inert encapsulation material, whereby grooves containing the reactive material and the HTF channels are arranged perpendicular to each other.

(27) There may be more than one block or stack of inert encapsulation material, for example two or three blocks. In this case the blocks or stacks may be arranged parallel or perpendicular to each other.

(28) The reacting material may also be encapsulated in tubes or stacks which are arranged parallel to the HTF flow direction (see FIG. 2d). Here, the encapsulation extends through the whole length of the TES but only contains the reacting material within the reactive zone. The remaining part of the tube or stack can be empty or filled with inert material. Again tube bundles or stacks could be used.

(29) In FIG. 2e an encapsulation variant for redox material in syngas process is shown. Here the redox material is encapsulated in Al.sub.2O.sub.3 tubes. In each chemical reactor zone three tubes filled with the redox material are arranged parallel to each other. The tubes are placed within each chemical reaction zone perpendicular to the flow direction of HTF.

(30) In this manner, direct contact between the HTF and redox material is avoided allowing the use of any suitable HTF. Furthermore, TES and CRZ can be operated at different pressures and gas atmospheres. For example, the TES units can be operated at p>P.sub.ambient (overpressure) to decrease the pumping work, while the CRZ can be operated at p<p.sub.ambient (vacuum) during thermal reduction and/or p>p.sub.ambient during oxidation to enhance the chemical reaction.

(31) Each tube has a gas inlet and a gas outlet at the opposite ends allowing a gas flow through the tube and sufficient contact time of the reactants (such as CO.sub.2, H.sub.2O) with the redox material.

(32) As depicted in FIG. 2e the left chemical reaction zone is operated at the reduction temperature T.sub.red of the redox material. In the course of the (endothermic) reduction of the redox material oxygen is released that is flushed out by feeding an inert gas into the encapsulation or extracted by applying a vacuum at the outlet.

(33) The right chemical reaction zone is operated at the oxidation temperature T.sub.ox of the redox material. CO.sub.2/H.sub.2O is fed into the redox material having T.sub.ox and is converted to CO/H.sub.2 that is subsequently continuously discharged from the redox material in the tube. At the same time the reduced redox material is oxidized to its original state or a defined oxidation state in the course of the (exothermic) oxidation.

(34) FIGS. 3a-c illustrate variants of a cascaded arrangement of the reacting material. Here instead of using a single reacting material multiple reacting materials that reduce and oxidize at different temperatures to create a cascaded dual-storage reactor are used.

(35) In FIG. 3a the reacting materials are encapsulated in tubes or stacks to prevent direct contact of the heat transfer fluid and the reacting materials. Here, the different reacting materials are arranged along the height of the reactive zone, such that the different thermodynamic and kinetic properties of the individual materials, e.g. reduction and oxidation behavior, fit best the temperature distribution inside the chemical reaction zone. For example, in the top part of the chemical reaction zone where the highest temperatures are reached, a material with suitable thermodynamic and kinetic properties for these temperatures is selected, e.g., CeO.sub.2. In lower levels of the reaction zone, where the temperatures are lower than in the top part, reacting materials with different thermodynamic and kinetic properties than in the top part are selected which operate favorably at these lower temperatures, e.g., doped CeO.sub.2 or perovskites.

(36) FIG. 3a shows schematically the arrangement of three different reacting materials for the case of parallel tube bundles arranged perpendicular to the flow direction of the heat transfer fluid. Similar arrangements can be achieved by stacks.

(37) If the encapsulation is parallel to the flow direction of the heat transfer fluid, the different reacting materials can be layered within the same encapsulation such that again the material with the most appropriate thermodynamic and kinetic properties at the highest temperature is positioned in the hottest region while the one with the most appropriate thermodynamic and kinetic properties at lower temperatures is positioned in the region of the reactive zone where the lowest temperatures are obtained. FIG. 3b shows schematically the arrangement of three different reacting materials.

(38) FIG. 3c shows such a cascaded arrangement suitable for syngas production. Here Redox Material 1 has the most appropriate thermodynamic and kinetic properties at the highest temperatures compared to the other redox materials such that; T.sub.red/ox_Material 1>T.sub.red/ox Material 2>T.sub.red/ox Material 3. Materials and corresponding optimal operation temperatures for this arrangement could be besides many possibilities.

(39) In the embodiment of FIG. 3 a first layer comprises pure CeO.sub.2; T.sub.red=1500° C., T.sub.ox=900° C. (material 1), the lower second layer comprises 5 mol % Zr4+ doped ceria; T.sub.red=1400° C., T.sub.ox=700° C. (material 2) and the lowest third layer comprises Lanthanum-strontium-manganese perovskite La.sub.1-xSr.sub.xMnO with x=0.3; T.sub.red=1300° C., T.sub.ox=500° C. (material 3).

(40) FIGS. 4a, b illustrate the ideal and actual temperature profiles in a dual storage reactor, respectively.

(41) The production of syngas with the dual-storage reactor is maximized if the redox material is always exposed to either the reduction or the oxidation temperature. This implies that near the reaction zone the temperature profile should ideally be a discontinuity separating two plateaus at the reduction and oxidation temperatures. Furthermore, a third plateau at a low temperature is desired because this reduces the cost of the pump that moves the HTF back and forth. To minimize the height and therefore the material cost of the packed beds, this third plateau should ideally be separated from the plateau at the oxidation temperature by a second discontinuity. Therefore, the complete ideal temperature profile—the so-called thermocline—in the dual-storage reactor is as shown in FIG. 4a.

(42) However, the ideal temperature profile cannot be realized in practice because several physical mechanisms cause the discontinuities to become degraded, i.e., smeared (see FIG. 4b). These mechanisms include: limited heat-transfer rates between the HTF and the storage material, axial heat conduction and radiation along the storage, heat exchange with the storage container and insulation, mixing of the HTF at different temperatures due to vertical flows at the inlet and outlet and bypass flows at the container wall.

(43) As the thermocline becomes more and more degraded, the production of syngas will decrease and there is a danger that the maximum operating temperature of the pump will be exceeded, requiring that the dual-storage reactor be shut down.

(44) Actions taken to prevent degradation of the thermocline are usually referred to as “thermocline control”. In the dual-storage reactor, thermocline control is partly achieved by the heating section because the heated HTF flows into a packed bed at a constant temperature equal to the reduction temperature.

(45) To maintain a plateau at the oxidation temperature, however, thermocline control is necessary. This can be done in several ways: flushing the TES to push thermocline out of the storage, combination of different geometries/materials, e.g., combined sensible/latent-heat storage, extracting, upgrading, and returning the HTF at certain positions of the thermocline, siphoning HTF out of the TES at the location of the thermocline, and sliding flow (inlet and outlet moving with thermocline position).

Example 1

(46) Description of the Dual-Storage Reactor Setup

(47) The dual-storage reactor consists of two connected tanks each containing a section or module with a thermocline TES and a zone with redox material (as shown in FIG. 1).

(48) In the reaction zones, alumina tube bundles are stacked, containing inside ceria as the reacting material (FIG. 2). The thermocline TES consist of packed beds of alumina spheres. The HTF is compressed air (e.g., at 20 bar). Pumping of the HTF is usually performed at the cold side. Concentrated solar radiation/energy is used to heat the HTF in a receiver (heating section).

(49) To support the reduction of ceria, the tubes are flushed with inert gas while also a vacuum is pulled (left side of FIG. 2).

(50) ${\mathrm{CeO}}_2->{\mathrm{CeO}}_{2\text{-}\delta }+\frac{\delta }{2}{O}_2$

(51) During oxidation of ceria, CO.sub.2 and H.sub.2O are injected into the tubes to produce syngas (right side of FIG. 2).
CeO.sub.2-δ+δH.sub.2O.fwdarw.CeO.sub.2+δH.sub.2
CeO.sub.2-δ+δCO.sub.2.fwdarw.CeO.sub.2+δCO
Operation Steps

(52) In the following the individual steps of the operation are discussed separately. Since the two tanks are identical, for brevity only a half cycle is discussed. The second half of the cycle will then be identical to the first half, only that all operation actions are flipped between the left and the right tank.

(53) At the beginning, the ceria of the left tank is in the oxidized state and the ceria of the right tank is in the reduced state. The following steps are performed in order to bring the ceria of the left tank in the reduced state and the ceria of the right tank in the oxidized state (and producing syngas).

(54) First Step (FIG. 5a, FIG. 2e Left Side)

(55) Compressed air is pumped from the bottom of the right tank through the right tank, and is then upgraded by a concentrated solar radiation receiver to the desired reduction temperature (T.sub.red=1500° C.). The HTF mass flow rate may be adjusted to obtain the desired reduction temperature, depending on the momentary direct normal irradiation (DNI) and the inlet temperature into the receiver. The upgraded compressed air enters then the left tank and leaves it at the bottom as cold compressed air (FIG. 5a). In this way, the high temperature plateau of the right tank is moved from the right tank to the left tank.

(56) Simultaneous (perpendicular) flow inside tubes containing ceria: Inside the tubes of the right tank, there is no flow. In the tubes of the left tank, a small flow of inert gas is injected and the total pressure is reduced (e.g. to 10 Pa) by pulling a vacuum, see FIG. 2e, left side.

(57) Second Step (FIG. 5b)

(58) Once the ceria of the left tank is reduced, the redox material of the right tank is usually not yet at oxidation temperatures but at somewhat higher temperatures due to limited thermocline steepness (see FIG. 5a). To further cool down and to prevent spreading of the high temperature plateau (at ˜T.sub.red), the hot compressed air leaving the right tank can be directed to the left tank without upgrading it with solar energy, resulting in the temperature profiles shown schematically in FIG. 5b. In this way, heat is still recuperated but no spreading of the thermocline occurs.

(59) Inside the right tubes there is again no flow while in the left tank vacuum is still pulled to increase the reduction extent (FIG. 2e, left side).

(60) Third Step (FIG. 5c)

(61) Due to thermocline degradation, the temperature plateaus degrade over time. To reestablish the plateaus, thermocline control is needed. In order to obtain a uniform oxidation temperature in the redox zone of the right tank, compressed air is extracted at the top and at the bottom of the right reaction zone and its mixture is injected in the middle of the right reaction zone (FIG. 5c).

(62) Fourth Step (FIG. 2e, Right Side)

(63) CO.sub.2 and H.sub.2O are injected into the tubes of the right redox section to oxidize the ceria and produce syngas (FIG. 2e, right side).

(64) Fifth Step (FIG. 5d)

(65) After oxidation of the right redox zone, compressed air is pumped from the bottom of the left tank through the right tank, and then without upgrading it with solar energy, it enters the right tank and leaves it at the bottom as cold compressed air (FIG. 5d). In this way, heat is still recuperated but no spreading of the thermocline occurs.

(66) At the end of the fifth step, the temperature distribution is the same as at the beginning of step one, just with the distributions flipped between the left and the right tank. Hence the next half of the cycle will be the same procedure, just with all actions flipped between the two tanks.

Example 2: Temperature Profile (Thermocline Control)

(67) According to an embodiment of the present method HTF is injected ahead of thermocline. Several additional ports are placed inside the TES. The thermocline is then steepened by injecting fluid ahead of the thermocline front based on certain criteria. An example of this method applied during the charging phase can be seen in FIG. 6a. Here the inlet port is switched before the whole thermocline region has passed the respective port. This leads to a cut-off of the thermocline, entrapping a portion of the thermocline within the storage tank while the charging continues between the new inlet port and the outlet port with a steeper thermocline. During the following discharging, the entrapped portion of the thermocline is flattened out due to dispersion effects (axial conduction, limited convective heat transfer) and gets then pushed out of the tank (FIG. 6b). The analogous injection strategy can be performed during charging.

(68) It is also possible, that more TC control strategies may be used for this example, such as: Pushing out of the thermocline at medium-high temperatures: Due to the heat of oxidation which is produced during oxidation, excess heat might be present at ˜T.sub.ox. This heat needs to be extracted in order to prevent a continuous temperature increase in the two tanks, making re-oxidation more and more difficult. This can be done, for example, by extracting part of the thermocline at the end of the second step by injecting compressed air at the bottom of the left tank and extracting compressed air at the top of it at around T.sub.ox. This heat could be used e.g. to run a turbine for electricity production. Instead of performing step two, one could extract fluid from (approximately) the middle of the right tank and insert it into the left tank to bring the left tank to oxidation temperatures. This would avoid moving of the whole temperature profile. After oxidation of the left tank, the same amount of fluid would then be returned from the left tank top to the middle of the right tank. Instead of mixing fluids in the reaction zone (step three), the mixing to obtain a plateau at T.sub.ox could be performed in the thermocline TES (e.g. at the beginning of step one). This would have the advantage, that the flow distributors inside the tanks would not have to be made out of ceramic but could be made out of steel. Different mixing/extracting/injecting possibilities exist to increase the steepness of the temperature gradients, such as siphoning.