Porous foam reactor with radiation secondary uniform distribution and optimization method thereof

Abstract

The invention discloses a porous foam reactor with radiation secondary uniform distribution and an optimization method thereof.The porous foam reactor comprises porous foam of a cylindrical structure, a cylindrical cavity is formed in the end face of the porous foam, a secondary reflector matched with the cylindrical cavity is arranged in the cylindrical cavity, the secondary reflector is provided with a conical surface, and the conical surface is provided with a cylindrical surface. Uneven Gaussian distribution radiation can be secondarily distributed in the porous foam; according to the optimization method, an optical-CFD coupling model is established by utilizing TracePro and Fluent for simulation, and optimal reactor structure parameters are determined. Radiation and temperature distribution in the reactor can be homogenized by using the secondary reflector, so that the stability and efficiency of the reactor are improved.

Description

Technical Field

[0001] The invention relates to a porous foam reactor and an optimization method thereof, in particular to a porous foam reactor with secondary uniform radiation distribution and an optimization method thereof. Background Art

[0002] Solar-driven CRM (CH4-CO2 reforming) reactions utilize clean solar energy to convert CH4 and CO2 into H2 and CO, achieving the simultaneous elimination of both greenhouse gases and producing high-value-added synthesis gas. As a result, they are gaining increasing attention. Porous foam reactors, with their excellent thermal conductivity, superior mechanical strength at high temperatures, and high surface area, are ideal reactor configurations for CRM reactions. However, due to the single-sided light reception and Gaussian radiation distribution characteristics of solar concentrating systems, radiation often only reaches the surface of the foam. Local overheating caused by uneven temperatures accelerates catalyst deactivation, while excessively low temperatures at the rear end of the foam inhibit the reaction. Incompletely reacted hydrocarbons deposit within the foam pores, forming carbon deposits. Summary of the Invention

[0003] Objects of the invention: The first object of the present invention is to provide a porous foam reactor with good radiation and temperature uniformity; the second object of the present invention is to provide an optimization method for the porous foam reactor.

[0004] Technical solution: The present invention provides a porous foam reactor with secondary uniform distribution of radiation, comprising a porous foam of cylindrical configuration, wherein the end face of the porous foam is provided with a cylindrical cavity, wherein a corresponding secondary reflector is arranged in the cylindrical cavity, wherein the secondary reflector has a conical surface and can secondary distribute the non-uniform Gaussian distribution radiation inside the porous foam.

[0005] Furthermore, the diameter d of the cylindrical cavity is 14 mm, the depth h is 11 mm, and the mirror bevel angle θ is 45°.

[0006] Furthermore, the porous foam is made of nickel-chromium alloy and manufactured through 3D printing; the secondary reflector is made of haynes 230 as a raw material and manufactured through turning and polishing processes.

[0007] Furthermore, the surface of the secondary reflector is coated to insulate heat and isolate gas.

[0008] The method for optimizing the porous foam reactor of the present invention comprises:

[0009] (1) Obtain the radiant energy flux distribution of the light source through experiments and fit it to a Gaussian distribution expression;

[0010] (2) The Gaussian distribution expression and the porous foam reactor model were imported into the TracePro optical simulation software. The transmission, reflection, and absorption of radiation in the porous foam reactor were predicted using the Monte Carlo ray tracing method. The radiation energy flux distribution in the porous foam reactor was solved and fitted into a polynomial.

[0011] (3) Using Fluent simulation software to establish a multi-physics model that couples chemical reactions, porous media flow, fluid-solid heat transfer, radiation transmission and absorption to simulate the reaction process in the porous foam reactor; using a user-defined function (UDF) to import the polynomial obtained in step (2) as the foam radiation heat flow boundary condition into Fluent software to achieve data coupling between the optical simulation software and the CFD solver;

[0012] (4) Changing the reactor structural parameters, repeating steps (2) to (3) for multiple calculations, taking the highest solar-to-fuel conversion efficiency as the optimization goal, and determining the optimal reactor structural parameters; the reactor structural parameters include the diameter d and depth h of the cylindrical cavity and the mirror bevel θ.

[0013] Furthermore, in step (1), a xenon lamp is used as the light source, and the radiation energy flux distribution is tested using a heat flux testing instrument.

[0014] Furthermore, in step (1), the fitted Gaussian distribution expression is: q = Aexp(-x 2 / B)+q0, where q represents the radiation energy flux density, W / m 2 ; x represents the distance from the focus, mm.

[0015] Furthermore, in step (2), the porous foam reactor model is imported into TracePro software, the physical properties of each material of the reactor are set, and the experimentally measured Gaussian radiation distribution is used as the light source for calculation to simulate the radiation energy flow distribution in the porous foam reactor.

[0016] Furthermore, in step (3), the control equations are discretized using the finite volume method, and the SIMPLE format solution method is selected; the DO radiation model is adopted; the laminar viscosity model is selected for the porous foam fluid domain; and the second-order upwind difference format is used to discretize the parameters;

[0017] By setting up a porous fluid domain that is completely consistent with the solid domain mesh, a one-to-one mapping strategy is then used between the fluid unit and the solid unit center to achieve data exchange and coupled calculation, thereby realizing convective heat transfer between the solid domain and the fluid domain.

[0018] Furthermore, in step (4), the diameter d of the cylindrical cavity ranges from 6 to 18 mm, the depth h ranges from 7 to 23 mm, and the mirror bevel angle θ ranges from 1° to 45°.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0020] (1) The present invention utilizes a secondary reflector to redistribute the radiation that was originally absorbed on the surface into the porous foam, thereby enhancing the radiation and temperature uniformity of the reactor, improving the stability of the reactor, and effectively suppressing the agglomeration and sintering of the catalyst caused by high temperature.

[0021] (2) The secondary distributed radiation in the present invention can continuously provide energy for the CRM reaction, realize the spatiotemporal matching of energy transfer and reaction requirements, and maintain temperature conditions conducive to efficient CRM reaction everywhere in the foam domain, thereby improving the solar energy-to-fuel conversion efficiency of the reactor to a certain extent.

[0022] (3) The present invention established an optical-CFD coupling model through TracePro and Fluent, and used it for reactor parameter optimization. It has been verified that the optical-CFD coupling model has high accuracy.

[0023] The present invention provides support for the application and promotion of efficient CO2 conversion and utilization and solar-driven clean fuel synthesis technology. At the same time, the porous foam reactor with secondary uniform distribution of radiation designed by the present invention also provides a unique idea for the design of other light or photothermal catalytic reactors or volumetric solar thermal absorbers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 2 is a schematic structural diagram of a porous foam reactor according to an embodiment of the present invention;

[0025] Figure 2 This is a flowchart of a method for optimizing a porous foam reactor according to an embodiment of the present invention;

[0026] Figure 3 is the verification result of the optical-CFD coupling model in the embodiment of the present invention, wherein Figure 3 (a) is the comparison and verification of components and efficiency, Figure 3 (b) is the temperature field comparison verification;

[0027] Figure 4 is the optimization result of the structural parameters of the porous foam reactor in the embodiment of the present invention;

[0028] Figure 5 This is the gas-solid temperature cloud diagram of the simulation results in the embodiment of the present invention (left: fluid domain, right: solid domain), where Figure 5 (a) is the traditional cylindrical configuration, Figure 5 (b) is the optimized configuration;

[0029] Figure 6The temperature comparison between the optimized configuration and the traditional cylindrical configuration in the experimental test of the embodiment of the present invention is shown;

[0030] Figure 7 The results of thermogravimetric testing of the optimized configuration after reaction and the traditional cylindrical configuration in the embodiment of the present invention are shown;

[0031] Figure 8 This is a picture of the optimized configuration after the reaction in the embodiment of the present invention;

[0032] Figure 9 (a) is a comparison of the conversion rates of the optimized configuration and the traditional cylindrical configuration in the embodiment of the present invention, Figure 9 (b) is a comparison of the light-fuel efficiency of the optimized configuration in the embodiment of the present invention and the traditional cylindrical configuration. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings.

[0034] This embodiment of the present invention provides a porous foam reactor with uniform secondary radiation distribution. The reactor comprises a cylindrical porous foam with a cylindrical cavity defined at the end. A secondary reflector, with a conical surface, is positioned within the cavity to distribute uneven Gaussian radiation within the porous foam. The porous foam is manufactured using a nickel-chromium alloy via 3D printing. The secondary reflector is manufactured using Haynes 230 through turning and polishing.

[0035] like Figure 2 As shown, an embodiment of the present invention further provides a method for optimizing a porous foam reactor, comprising the following steps:

[0036] (1) The radiation energy flux distribution of the light source is obtained through experiments and fitted into a Gaussian distribution expression.

[0037] The light source is a xenon lamp, and the radiation energy flux distribution is tested using a heat flux testing instrument.

[0038] The Gaussian distribution expression of the fitting is: q = Aexp(-x 2 / B)+q0, where q represents the radiation energy flux density, W / m 2 ; x represents the distance from the focus, mm.

[0039] (2) The Gaussian distribution expression and the porous foam reactor model were imported into the TracePro optical simulation software. The Monte Carlo ray tracing method was used to predict the transmission, reflection and absorption of radiation in the porous foam reactor. The radiation energy flow distribution in the porous foam reactor was solved and fitted into a polynomial.

[0040] Specifically, the porous foam reactor model was imported into TracePro software, the physical properties of each material in the reactor were set, and the experimentally measured Gaussian radiation distribution was used as the light source for calculation to simulate the radiation energy flow distribution in the porous foam reactor.

[0041] (3) Fluent simulation software is used to establish a multi-physics field model that couples chemical reactions, porous media flow, fluid-solid heat transfer, radiation transmission and absorption to simulate the reaction process in the porous foam reactor.

[0042] The polynomial obtained in step (2) is imported into the Fluent software as the foam radiation heat flow boundary condition using a user-defined function (UDF) to achieve data coupling between the optical simulation software and the CFD (computational fluid dynamics) solver.

[0043] The governing equations were discretized using the finite volume method (FVM), and the SIMPLE solution was chosen. The DO radiation model was employed. A laminar viscosity model was chosen for the porous foam fluid domain. To ensure computational accuracy, a second-order upwind difference scheme was used to discretize the parameters. To accelerate convergence, the relaxation factor for each parameter was set to 0.7, and the momentum and energy residual convergence criteria were set to 10. -6 .

[0044] UDF can simulate the coupled chemistry, flow, heat transfer, and radiation multiphysics fields in porous foam domains, a feat normally impossible with Fluent, to address the non-equilibrium thermal effects of porous media. Specifically, this is achieved through a dual-element model: a porous fluid domain is set up with a mesh identical to the solid domain. A one-to-one mapping strategy is then used between the fluid and solid cell centers to exchange data and perform coupled calculations, enabling convective heat transfer between the solid and fluid domains.

[0045] To verify the accuracy of the model, the optical-CFD coupled model was used to simulate the performance of traditional cylindrical porous foam in a reactor and compared with the experimental results (the dimensional parameters such as diameter and length and the experimental conditions were the same as those of the optimized configuration). Figure 3 As shown, the model results are in good agreement with the experiments, and the product component ratio, solar-to-fuel conversion efficiency and temperature field distribution are similar to the experimental results.

[0046] (4) Changing the reactor structural parameters, repeating steps (2) to (3) for multiple calculations, taking the highest solar-to-fuel conversion efficiency as the optimization goal, and determining the optimal reactor structural parameters; the reactor structural parameters include the diameter d and depth h of the cylindrical cavity and the mirror bevel θ.

[0047] To ensure the processability of the reactor structure, the diameter d of the cylindrical cavity ranges from 6 to 18 mm, and the depth h ranges from 7 to 23 mm; to ensure that the secondary reflector has a high reflectivity, the mirror bevel angle θ ranges from 1° to 45°.

[0048] The test porous foam reactor constructed by the present invention is as follows Figure 1 As shown, it is a 100-watt self-regenerating CRM foam reactor, which uses a xenon lamp to simulate focused solar energy, and the radiation energy flux intensity on the reactor surface is Gaussian distributed.

[0049] Comparative Example

[0050] The preparation and testing method of a conventional uniform-pore cylindrical porous foam reactor comprises the following steps:

[0051] (a) Nickel-chromium alloy porous foam was manufactured using 3D printing. Its shape is a cylinder with a diameter of 30 mm and a height of 30 mm, a pore diameter of 1 mm, and a porosity of 0.8.

[0052] (b) Preparation of Ni / MgAlO x -LDH catalyst and load it on porous foam;

[0053] (c) Before the test, the total optical power and energy flux distribution were measured. The total optical power of the xenon lamp was measured to be 153.1W using an optical power meter.

[0054] The measured radiation energy flux distribution is fitted into the Gaussian distribution expression: q = 677040exp(-x 2 / 38.111)+84930, where q represents the radiation energy flux density, W / m 2 ; x represents the distance from the focus, mm;

[0055] (d) placing the catalyst-loaded porous foam in the center of the reactor crucible and using quartz wool to support the foam so that it is flush with the highest point of the crucible;

[0056] (e) placing thermocouples at the center of the front surface of the foam, the edge of the front surface of the foam, the fluid outlet, and the fluid inlet;

[0057] (f) introducing a mixed gas of CH4, CO2, and N2 into the reactor as a purge gas at a flow rate of 1000 mL / min, wherein the flow rate ratio of CH4, CO2, and N2 is 4:4:2, and the flow rate is precisely controlled by a mass flow meter;

[0058] (g) After three hours of scrubbing, turn on the xenon lamp and adjust the reactor position to ensure that the center of the light spot is located in the center of the foam;

[0059] (h) The catalyst loaded on the porous foam surface absorbs light energy and converts it into heat energy, photothermally catalyzing the CRM reaction to produce CO and H2;

[0060] (i) During the test, the gas was continuously and stably introduced into the reactor, and the outlet gas composition and concentration were measured using a gas chromatograph.

[0061] After 30 hours of testing, the results showed that the conventional cylindrical porous foam reactor achieved a maximum solar-to-fuel conversion efficiency of 32.46%. After the reaction stabilized, the average solar-to-fuel conversion efficiency reached 29.92%. The average conversion rates of CH4 and CO2 after the reaction stabilized were 59.76% and 71.53%, respectively. The average yields of H2 and CO were 98.47 and 121.31 mmol / (min·g), respectively. The foam front surface temperature at the time of stabilization was 1260 K. Excessive surface stability can lead to catalyst agglomeration and sintering, resulting in radiation loss and impaired heat transfer.

[0062] Test Case

[0063] like Figure 4 As shown in the figure, the optical-CFD coupling model optimization shows that when the diameter d of the cylindrical cavity is 14 mm and the depth h is 11 mm, the solar-fuel conversion efficiency of the reactor is the highest, which is 39.60%. Compared with the simulation results of the traditional cylindrical configuration (η chem =33.83%), achieving a 17.06% relative efficiency improvement. When the mirror bevel angle is too small, most of the incident light cannot be reflected back onto the foam, resulting in radiation loss. Considering that the incident light is unpolarized, the reflectivity of the mirror surface decreases significantly when the incident angle of unpolarized light exceeds 45°, so the mirror bevel angle θ is set to 45°.

[0064] Numerical simulation results show that compared with the traditional cylindrical foam, the optimized configuration radiation peak is increased from 761.97kW / m 2 Reduced to 230.19kW / m 2 .

[0065] like Figure 5The figure shows the gas-solid temperature cloud diagram of the traditional cylindrical configuration and the optimized configuration. Due to the significant reduction in the radiation peak, the maximum temperature of the solid domain of the optimized configuration is significantly reduced (from 1209.67K to 1042.20K). The spatial homogenization effect of the radiation field and the temperature field reduces the peak temperature and thus suppresses the surface radiation heat dissipation, while promoting the increase of the temperature inside the porous foam. Because the front surface of the traditional cylindrical foam absorbs most of the radiation at a shallow point, and the radiation is Gaussian distributed, a local high temperature zone of 1209.67K is formed in the center of the solid domain surface, and its temperature drops sharply along the axial direction, resulting in a lower temperature of the solid domain inside the foam. In contrast, the temperature of the solid domain inside the foam of the optimized configuration increases and presents a more uniform temperature field distribution, proving that the optimized configuration effectively enhances heat conduction in the axial solid domain. Thanks to this feature, the optimized configuration has a better fluid-solid heat transfer effect: the average temperature of the fluid domain of the traditional cylindrical configuration and the optimized configuration is 850.24K and 955.06K, respectively, an increase of 12.33%. Unlike the trend of the fluid domain temperature of the traditional cylindrical configuration first increasing and then decreasing along the axis, the temperature distribution of the optimized fluid domain is more uniform and there is almost no temperature drop along the axial direction.

[0066] The reaction gas flows into the foam, where it undergoes a fluid-solid heat exchange process to raise its temperature before undergoing the CRM reaction. Because CRM is a highly endothermic reaction, its conversion efficiency is significantly correlated with thermodynamic conditions. Thermodynamic analysis shows that the reaction must proceed above 873K to achieve high conversion rates. Excessively low temperatures can reduce CRM conversion and promote the RWGS side reaction. Figure 5 The temperature cloud map of the mid-flow region shows the fluid domains with temperatures above 873K for the two configurations. This shows that when the reaction gas flows through the traditional cylindrical foam, it only reaches a high temperature for a short period of time. After the gas heats up sharply at the front end of the foam, it undergoes the CRM reaction and continuously absorbs heat. However, when the gas flows through the lower-temperature rear half of the foam, the CRM reaction performance deteriorates due to the low temperature. In contrast, the gas maintains a high temperature for the vast majority of the time in the optimized foam, which helps maintain a high conversion rate for the CRM reaction within the foam domain, suppresses side reactions, and improves the reaction selectivity. This indicates that secondary distributed radiation can continuously provide energy for the CRM reaction, achieving a spatiotemporal match between energy transfer and reaction requirements, and maintaining temperature conditions conducive to efficient CRM reactions throughout the foam domain.

[0067] The porous foam was produced according to the obtained porous foam reactor structural parameters. The other parameters of the porous foam were consistent with those of the traditional cylindrical foam.

[0068] The treatments such as catalyst loading before testing of the porous foam reactor with secondary radiation and uniform distribution are consistent with those of the comparative example; the testing method of the porous foam reactor with secondary radiation and uniform distribution is consistent with that of the comparative example.

[0069] After 30 hours of long-term testing, the results showed that the highest solar-to-fuel conversion efficiency of the optimized configuration was 33.94%, the average solar-to-fuel conversion efficiency after the reaction stabilized was 32.23%, the average conversion rates of CH4 and CO2 after the reaction stabilized were 64.50% and 72.55%, respectively, the average yields of H2 and CO were 102.68 and 126.64 mmol / (min·g), respectively, and the foam front surface temperature was 1126K when stable.

[0070] Depend on Figure 6 As shown in the figure, the maximum temperature of the front surface of the foam of the optimized configuration was measured by the thermocouple in the experiment. It was 1126K, which was 134K lower than that of the traditional cylindrical configuration; the outlet temperature was 871K, which was 25K higher. This further shows that the unique structure of the optimized configuration significantly improves the temperature uniformity and fluid-solid heat exchange capacity of the reactor, resulting in a more uniform catalytic bed temperature and enhanced reaction performance, and suppresses the problem of catalyst durability degradation caused by catalyst agglomeration and sintering due to local high temperature.

[0071] Thanks to the better temperature uniformity, the solar-to-fuel conversion efficiency of the present invention did not show a significant decrease after a 30-hour long-term test. Thermogravimetric analysis (TGA) was used to perform programmed temperature oxidation tests on the optimized configuration and the traditional cylindrical configuration after the reaction to determine the amount of carbon deposits. The results are as follows: Figure 7 As shown in the figure, the carbon deposits of the optimized configuration and the traditional cylindrical configuration account for 7.91% and 10.25% of the total mass respectively, and the carbon deposit ratio is reduced by 22.83%, which further proves the enhanced reaction stability of the optimized configuration.

[0072] The picture of the optimized configuration after 30h test is as follows Figure 8 As shown in the figure, it can be seen that after the reaction is completed, the secondary reflector can still maintain a good reflectivity, but due to the reaction between the gas and the secondary reflector, it becomes blue-green, which affects the secondary distribution of radiation to a certain extent. Figure 9As shown, although the excellent uniformity and fluid-solid heat exchange capacity can improve the reaction performance of the reactor, due to the adverse effects of high temperature conditions and reaction environment on the secondary reflector, the reactor efficiency has only been slightly improved, which is lower than the best result in the optical-CFD coupling calculation. After the optimized reactor is stabilized, the average efficiency (32.23%) and the maximum efficiency (33.94%) of the reactor are increased by 7.74% and 4.56% respectively compared with the traditional cylindrical configuration. After stabilization, the average conversion rates of CH4 and CO2 (64.50% and 72.55%) are increased by 7.93% and 1.42% respectively. In order to fully utilize the excellent performance of the present invention, the surface coating of the secondary reflector can be optimized (such as a silicon dioxide film layer) to insulate heat and isolate gases. The present invention can also be applied to light or photothermal catalytic porous foam reactors or volumetric solar thermal absorbers with lower reaction temperatures to achieve their radiation and temperature homogenization functions.

Claims

1. A porous foam reactor with secondary uniform distribution of radiation, characterized in that: The invention comprises a porous foam with a cylindrical configuration, wherein the end surface of the porous foam is provided with a cylindrical cavity, wherein a corresponding secondary reflector is arranged in the cylindrical cavity, and the secondary reflector has a conical surface and can redistribute the non-uniform Gaussian distribution radiation inside the porous foam.

2. The porous foam reactor according to claim 1, characterized in that The diameter d of the cylindrical cavity is 14 mm, the depth h is 11 mm, and the mirror bevel angle θ is 45°.

3. The porous foam reactor according to claim 1, characterized in that The porous foam is made of nickel-chromium alloy and manufactured through 3D printing; the secondary reflector is made of haynes 230 as raw material and manufactured through turning and polishing processes.

4. The porous foam reactor according to claim 1, characterized in that The surface of the secondary reflector is coated to insulate heat and isolate gas.

5. A method for optimizing a porous foam reactor according to claim 1, characterized in that: include: (1) Obtain the radiant energy flux distribution of the light source through experiments and fit it to a Gaussian distribution expression; (2) The Gaussian distribution expression and the porous foam reactor model were imported into the TracePro optical simulation software. The transmission, reflection, and absorption of radiation in the porous foam reactor were predicted using the Monte Carlo ray tracing method. The radiation energy flux distribution in the porous foam reactor was solved and fitted into a polynomial. (3) Using Fluent simulation software to establish a multi-physics model that couples chemical reactions, porous media flow, fluid-solid heat transfer, radiation transmission and absorption to simulate the reaction process in the porous foam reactor; using a user-defined function (UDF) to import the polynomial obtained in step (2) as the foam radiation heat flow boundary condition into Fluent software to achieve data coupling between the optical simulation software and the CFD solver; (4) Changing the reactor structural parameters, repeating steps (2) to (3) for multiple calculations, taking the highest solar-to-fuel conversion efficiency as the optimization goal, and determining the optimal reactor structural parameters; the reactor structural parameters include the diameter d and depth h of the cylindrical cavity and the mirror bevel θ.

6. The optimization method according to claim 5, characterized in that: In step (1), a xenon lamp is used as the light source, and the radiation energy flux distribution is tested using a heat flux testing instrument.

7. The optimization method according to claim 5, characterized in that: In step (1), the fitted Gaussian distribution expression is: q = Aexp(-x 2 / B)+q0, where q represents the radiation energy flux density, W / m 2 ; x represents the distance from the focus, mm.

8. The optimization method according to claim 5, characterized in that: In step (2), the porous foam reactor model is imported into TracePro software, the physical properties of each material in the reactor are set, and the experimentally measured Gaussian radiation distribution is used as the light source for calculation to simulate the radiation energy flow distribution in the porous foam reactor.

9. The optimization method according to claim 5, characterized in that: In step (3), the control equations are discretized using the finite volume method and the SIMPLE format solution method is selected; the DO radiation model is adopted; the laminar viscosity model is selected for the porous foam fluid domain; the second-order upwind difference format is used to discretize the parameters; By setting up a porous fluid domain that is completely consistent with the solid domain mesh, a one-to-one mapping strategy is then used between the fluid unit and the solid unit center to achieve data exchange and coupled calculation, thereby realizing convective heat transfer between the solid domain and the fluid domain.

10. The optimization method according to claim 5, characterized in that: In step (4), the diameter d of the cylindrical cavity ranges from 6 to 18 mm, the depth h ranges from 7 to 23 mm, and the mirror bevel θ ranges from 1° to 45°.

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