A low temperature chemical looping combustion method of a low temperature chemical looping combustion system

Abstract

The application discloses a low-temperature chemical chain combustion method of a low-temperature chemical chain combustion system, wherein the chemical chain combustion system comprises an air reactor, a fuel reactor, a cyclone separator, a return feeder, an isolator and related connecting components. In the temperature range of 300-500 DEG C, the gas-phase fuel is converted into CO2 and H2O through a chemical chain combustion chain reaction process by relying on a single-atom-dispersed supported oxygen carrier with a catalytic active component. The single-atom-dispersed supported oxygen carrier provides the lattice oxygen required for fuel conversion by using a transition metal oxide, and uses an isolated dispersed noble metal single atom as the catalytic active component, so that the low dosage of the noble metal of the oxygen carrier and the high catalytic efficiency are both achieved, the reaction path and the kinetic mechanism of the original gas-solid reaction are changed, the reaction temperature of the chemical chain combustion is reduced, the sintering and agglomeration of the oxygen carrier are avoided, and the operation cost of the reaction system is reduced.

Description

Technical Field

[0001] This invention discloses the field of chemical looping combustion technology, specifically relating to a low-temperature chemical looping combustion method for a low-temperature chemical looping combustion system. Background Technology

[0002] Chemical looping combustion is a novel flameless combustion technology with internal CO2 separation characteristics. It can not only achieve efficient and low-cost CO2 capture during combustion, but also effectively reduce fuel-borne NO. x Generating and significantly reducing the energy consumption of the reaction system, chemical looping combustion is widely regarded as one of the energy conversion technologies for large-scale industrial decarbonization in the future. Utilizing an alternating redox oxygen carrier circulating between the air reactor and the fuel reactor, chemical looping combustion converts the abundant gaseous oxygen molecules in the air into lattice oxygen of metal oxides, realizing the transfer of oxygen via a physically circulating oxygen carrier. The stepwise reaction mechanism of chemical looping combustion breaks down the one-step process of traditional combustion into two steps, avoiding direct contact between fuel and air, and preventing the dilution effect of air nitrogen on the gaseous product CO2, thus achieving a high concentration of CO2 enrichment at the fuel reactor outlet.

[0003] The self-heating balance of the reactor and its high operating costs are key issues hindering the further industrialization of chemical looping combustion. To achieve high fuel conversion efficiency, chemical looping combustion devices typically operate at high temperatures of 900–1000°C, requiring a high oxygen carrier particle circulation rate to transfer the exothermic oxidation heat in the air reactor to the endothermic reduction heat in the fuel reactor. However, high-temperature operation not only significantly increases the heat transfer requirements between reactors but also substantially increases the heat dissipation of the reaction device, making it difficult for pilot-scale fuel reactors to maintain the required operating temperature and significantly increasing the additional operating costs due to heat dissipation losses. Furthermore, oxygen carriers are prone to surface sintering and particle agglomeration at high temperatures, causing a sharp decline in particle reactivity and flow properties, forcing the particle circulation of the chemical looping reaction system to stagnate. Therefore, avoiding large-scale sintering and agglomeration of oxygen carrier particles is a necessary prerequisite for the long-term, stable operation of chemical looping combustion systems. During the fluidization process of the oxygen carrier particles circulating between reactors, they constantly undergo fluidization collisions with the reactor walls and other particles, and are subjected to chemical stress and thermal stress due to temperature differences. This makes them highly susceptible to breakage into fine particles, which are then carried out of the reactor system by the high-speed fluidizing gas flow, resulting in a decrease in the amount of oxygen carrier bed material. Higher reaction temperatures will exacerbate the structural damage to the oxygen carrier particles, increasing wear and tear on the particles and the operating costs of the chemical looping combustion system.

[0004] Copper-based oxygen carriers possess many advantages that other oxygen carriers struggle to match. They exhibit oxygen decoupling properties, excellent reactivity and chemical thermodynamic potential, and both redox processes are slightly exothermic, reducing the temperature difference between the air reactor and the fuel reactor and simplifying the self-heating equilibrium operation of chemical looping combustion reactors. However, copper's low melting point makes it prone to large-scale particle agglomeration at high temperatures, which can clog reactor pipelines, terminate particle circulation and the chain reaction of chemical looping combustion, thus limiting the further application of copper-based oxygen carriers in chemical looping combustion processes.

[0005] In traditional industrial catalysis, some complex chemical reactions require high Gibbs free energies, typically necessitating high temperatures and the addition of noble metal catalysts to overcome the chemical reaction energy barrier and achieve reactant conversion. This consumes significant amounts of fossil fuels and expensive noble metals, limiting the further commercial application of industrial chemical products. Single-atom catalysts, with their noble metal components supported on a carrier in the form of dispersed single atoms, maximize the number of atomic active sites on the catalyst surface, increasing the specific surface area and surface free energy of each atom, achieving near 100% atomic utilization. This reduces catalyst manufacturing costs while enhancing catalytic performance. Furthermore, unlike the bonding between supported nanoparticles and the substrate, the strong interactions or surface lattice reconstruction between noble metal atoms and the carrier allow the noble metal single atoms in the catalyst to be fixed to the carrier through chemical bonds, resulting in higher thermal stability and extended catalyst lifespan compared to traditional catalysts.

[0006] In chemical looping combustion processes, oxygen carriers undergo sintering and agglomeration under high-temperature conditions, affecting the system's reaction stability and particle flow properties. Furthermore, excessively high reaction temperatures increase heat loss in the reactor, exacerbating particle wear on the oxygen carrier and leading to a sharp increase in system operating costs. Ensuring stable and efficient operation of the reaction system at lower reaction temperatures is a problem that needs to be solved. Simultaneously, the economic aspects of the oxygen carrier should be considered; reducing the amount of oxygen carrier used and its production costs without compromising its reactivity and system combustion efficiency is crucial to achieving good economic benefits. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a low-temperature chemical looping combustion method for a low-temperature chemical looping combustion system. The system has a simple structure, reduces power loss during the fluidization process of the oxygen carrier, achieves highly active conversion of gaseous fuel molecules under mild conditions, avoids sintering of the oxygen carrier, reduces heat loss in the reaction system and wear of the oxygen carrier, and has lower operating costs than conventional chemical looping combustion systems. This invention is significant for the industrial application of chemical looping combustion technology.

[0008] To address the problems in the existing technology, the technical solution adopted by this invention is as follows: A low-temperature chemical looping combustion method for a low-temperature chemical looping combustion system includes the following steps: Step 1: Construct a low-temperature chemical looping combustion system; Step 2: Oxidized single-atom supported oxygen carrier particles react with the syngas introduced at the bottom of the fuel reactor under the catalysis of Pt atom active centers to transform into reduced single-atom supported oxygen carrier particles, water vapor and CO2. Step 3: Each product is transported to the fuel cyclone separator through the riser for gas-solid separation. The reduced oxygen-carrying particles fall along the inner wall of the fuel cyclone separator in a spiral path to the isolator. The fluidizing gas introduced into the isolator is water vapor or CO2. At the same time, CO2 and water vapor can be simply condensed after being discharged through the exhaust pipe to obtain high-concentration CO2. Step 4: The reduced single-atom supported oxygen carrier particles in the isolator enter the air reactor through the pipeline. They react with the oxygen in the air introduced at the bottom and are transformed into oxidized single-atom supported oxygen carrier particles. They are then transported to the air cyclone separator. During this reaction, oxygen molecules in the air are transformed into lattice oxygen in the oxygen carrier particles. The gas supplied at the bottom of the air reactor is air. Step 5: After the oxidized single-atom supported oxygen carrier particles and the oxygen-deficient air are separated by gas and solid in the air cyclone separator, the oxidized oxygen carrier particles enter the return feeder along the downcomer, the oxygen-deficient air is discharged from the exhaust pipe, and the fluidizing gas introduced into the return feeder is N2. Step 6: The oxidized single-atom supported oxygen carrier is returned to the fuel reactor via the return feeder and the next cycle begins.

[0009] As an improvement, the low-temperature chemical loop combustion system sequentially includes a fuel reactor, a fuel cyclone separator, an isolator, an air reactor, an air cyclone separator, and a return feeder connected by pipes. The outlet of the fuel reactor is connected to the inlet of the fuel cyclone separator via a riser pipe, and the bottom of the fuel reactor has a gaseous fuel inlet. The top of the fuel cyclone separator has a flue gas outlet, and the bottom is connected to a downcomer and connected to the inlet of the isolator. The bottom of the isolator has a fluidizing gas inlet, and the position of the isolator near the bottom is connected to the lower part of the air reactor via a pipe. The bottom of the air reactor has an air inlet, and the outlet of the air reactor is connected to the inlet of the air cyclone separator via a riser pipe. The top of the air cyclone separator has an oxygen-deficient air inlet, and the downcomer connected to the bottom is connected to the inlet of the return feeder. The bottom of the return feeder has a fluidizing gas inlet, and the position near the bottom is connected to the lower part of the fuel reactor 1 via a pipe.

[0010] As an improvement, the fuel reactor is a bubbling fluidized bed.

[0011] As an improvement, the air reactor is a rapid fluidized bed.

[0012] As an improvement, the fuel reactor, air reactor, and return feeder are stocked with a single-atom supported oxygen carrier bed, which comprises a single-atom noble metal catalytic component platinum, an active material copper, and an inert support. Specifically, it could be Pt1 / Cu. x O oxygen carrier.

[0013] As an improvement, the reaction temperature of the fuel reactor is 300~500℃.

[0014] As an improvement, the reaction temperature range of the air reactor is 350~550℃.

[0015] The single-atom supported Pt1 / Cu used in the aforementioned low-temperature chemical looping combustion system cycle x O-carrier, prepared by the following methods: Coprecipitation method: Under stirring conditions and in an alkaline environment, copper nitrate aqueous solution and chloroplatinic acid aqueous solution are titrated into sodium carbonate solution in an appropriate ratio. The resulting precipitate is filtered, washed, and then calcined to obtain Pt1 / Cu. x O oxygen carrier.

[0016] Impregnation method: Cu x The O carrier is immersed in a chloroplatinic acid aqueous solution with continuous stirring, and platinum particles are gradually adsorbed onto the Cu. x O support, then the remaining liquid is evaporated to dryness, and finally the obtained solid particles are dried and calcined to obtain Pt1 / Cu. x O oxygen carrier.

[0017] The single-atom supported oxygen carrier prepared by the above method has platinum atom noble metal components that replace copper-based metal oxide surface atoms or oxygen vacancies and are stably fixed on the oxygen carrier surface. When reacting with gaseous fuels, the syngas reacts with the Pt-supported oxygen carrier, which acts as a catalytic active center to provide catalytic activity to promote the reduction of the oxygen carrier particles, generating a large number of oxygen vacancies on its surface, thus achieving efficient syngas combustion conversion under low-temperature conditions. The effective active component copper in the oxygen carrier particles provides lattice oxygen, ensuring the oxygen content required for the oxidation of combustible gases.

[0018] Beneficial effects: Compared with the prior art, the low-temperature chemical looping combustion method of the low-temperature chemical looping combustion system of the present invention relies on the excellent reactivity of the single-atom supported oxygen carrier to achieve a stable and efficient chemical looping combustion process of gaseous fuels in a low temperature range of 300~500℃.

[0019] The specific advantages are as follows: (1) The low-temperature chemical looping combustion system based on single-atom catalysis of the present invention has a simple structure and reduces the power loss during the fluidized operation of the oxygen carrier.

[0020] (2) The oxygen carrier bed material used in this invention reduces the loading size of precious metal platinum particles to the single-atom level, which greatly improves the utilization efficiency of platinum metal. At the same time, by means of oxygen atom coordination and defect capture, the metal atoms are stabilized, so that the catalyst can maintain structural stability under long-term reaction conditions, thus extending the service life of the oxygen carrier.

[0021] (3) This invention innovatively applies a single-atom catalyst to the chemical looping combustion process. By utilizing the synergistic effect of different metal components and sites of the catalytic oxygen carrier, the relevant reaction kinetic steps and gas-solid reaction mechanism in the original chemical looping combustion process are changed. This achieves high-activity catalysis of gas phase fuel molecules under mild conditions, avoids the sintering of copper-based oxygen carriers, reduces heat loss of the reaction system and wear of copper-based oxygen carriers, and the system operating cost is lower than that of conventional chemical looping combustion systems. This is of certain significance for the industrial application of chemical looping combustion technology. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a low-temperature chemical looping combustion system based on single-atom catalysis according to the present invention, wherein 1-fuel reactor, 2-fuel cyclone separator, 3-isolation device, 4-air reactor, 5-air cyclone separator, and 6-return feeder. Detailed Implementation

[0023] The following embodiments are provided to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0024] Example 1

[0025] A low-temperature chemical looping combustion system based on single-atom catalysis includes, in sequence, a fuel reactor 1, a fuel cyclone separator 2, an isolator 3, an air reactor 4, an air cyclone separator 5, and a return feeder 6 connected by pipes. The outlet of the fuel reactor 1 is connected to the inlet of the fuel cyclone separator 2 via a riser pipe, and the bottom of the fuel reactor 1 is provided with a gaseous fuel inlet. The top of the fuel cyclone separator 2 is provided with a flue gas outlet, and the bottom is connected to a downcomer pipe and connected to the inlet of the isolator 3. The bottom of the isolator 3 is provided with a fluidizing gas inlet, and the position of the isolator 3 near the bottom is connected to the lower part of the air reactor 4 via a pipe. The bottom of the air reactor 4 is provided with an air inlet, and the outlet of the air reactor 4 is connected to the inlet of the air cyclone separator 5 via a riser pipe. The top of the air cyclone separator 5 is provided with an oxygen-deficient air inlet, and the downcomer pipe connected to the bottom is connected to the inlet of the return feeder 6. The bottom of the return feeder 6 is provided with a fluidizing gas inlet, and the position near the bottom is connected to the lower part of the fuel reactor 1 via a pipe.

[0026] Specifically, the fuel reactor 1 is a bubbling fluidized bed, and the air reactor 4 is a fast fluidized bed.

[0027] The single-atom supported oxygen carrier bed material used in this invention was prepared using the previously reported co-precipitation method of supported Pt and Cu catalysts. The specific preparation method is as follows: Aqueous solutions of chloroplatinic acid and copper nitrate were slowly added dropwise to a continuously stirred sodium carbonate solution, with the pH of the final mixed solution controlled at approximately 8.5. After stirring continuously for 3 hours and allowing complete precipitation at room temperature, the solution was aged in a 25°C incubator for 4 hours to achieve the desired particle size distribution. The resulting precipitate was then filtered, washed repeatedly with distilled water, and subsequently dried and baked at 60–80°C for 4 hours. The resulting black particles were Pt1 / Cu. x O oxygen carrier.

[0028] The oxygen carrier prepared by the above method was identified as an atomically monodisperse oxygen carrier after HAADF-STEM characterization.

[0029] More specifically, the single-atom supported oxygen carrier bed material used in this invention can be a single-atom Pt1 / FeO. X catalyst( Nature Chem 3, 634–641 (2011)).

[0030] More specifically, the unit-supported oxygen carrier bed material used in this invention can be a unit-based Pt1 / CeO2 catalyst ( Nat Commun 13, 7070 (2022)).

[0031] Example 2

[0032] The above-mentioned method of using a low-temperature chemical looping combustion system based on single-atom catalysis includes the following steps: Step 1: Oxidized oxygen carrier particles react with the gaseous fuel introduced at the bottom of fuel reactor 1 under the catalytic action of Pt atomic active centers to transform into reduced oxygen carrier particles, water vapor, and CO2. During the reaction, the valence state of the oxygen carrier particles decreases, the coordination structure of the Pt single-atom active sites changes, metal-metal coordination increases, and metal-oxygen coordination decreases. The reaction temperature of fuel reactor 1 is 300~500℃. The synthesis gas supplied at the bottom of fuel reactor 1 includes CO, CH4, and H2.

[0033] When the gaseous fuel is H2, Pt / Cu x When O is the oxygen carrier, H2 has good reactivity and can carry high-valence states... The copper metal oxide is reduced to elemental copper, so the above-mentioned oxidized oxygen carrier is Pt / CuO, and the reduced oxygen carrier is Pt / CuO. The bulk consists of Pt / Cu and Pt / Cu2O.

[0034] The chemical reaction that occurs in fuel reactor 1 is as follows: Pt / CuO+H2→Pt / Cu2O +H2O (Formula 1) Pt / Cu2O+H2→Pt / Cu +H2O (Formula 2) The chemical reaction that occurs in air reactor 4 is as follows: Pt / Cu2O +O2→CuO / Pt (Equation 3) Pt / Cu + O2 → Pt / CuO (Equation 4) When the gaseous fuel is CO, Pt / Cu x When O is the oxygen carrier, the above-mentioned oxidized oxygen carrier is Pt / CuO, and the reduced oxygen carrier is Pt / Cu2O.

[0035] The chemical reaction that occurs in fuel reactor 1 is as follows: Pt / CuO + CO → Pt / Cu2O + CO2 (Equation 5) The chemical reaction that occurs in air reactor 4 is the same as that in formula (3).

[0036] When the gaseous fuel is CH4, Pt / Cu x When O is the oxygen carrier, the above-mentioned oxidized oxygen carrier is Pt / CuO, and the reduced oxygen carrier is Pt / Cu2O.

[0037] The chemical reaction that occurs in fuel reactor 1 is as follows: Pt / CuO+CH4→Pt / Cu2O+CO2+H2O (Formula 6) The chemical reaction that occurs in air reactor 4 is the same as that in formula (3).

[0038] In step 2, each product is transported to the fuel cyclone separator 2 through the riser for gas-solid separation. The reduced oxygen carrier particles fall along the inner wall of the fuel cyclone separator 2 in a spiral path to the isolator 3. The fluidizing gas introduced into the isolator 3 is water vapor or CO2. At the same time, CO2 and water vapor can be simply condensed after being discharged through the exhaust pipe to obtain high-concentration CO2.

[0039] Step 3: The reduced oxygen carrier particles in the isolator 3 enter the air reactor 4 through the pipeline. They react with the oxygen in the air introduced at the bottom and are transformed into oxidized oxygen carrier particles. They are then transported to the air cyclone separator 5. During this reaction, oxygen molecules in the air are transformed into lattice oxygen in the oxygen carrier particles. The reaction temperature range of the air reactor 4 is 350~550℃, and the gas supplied at the bottom of the air reactor 4 is air. Step 4: After the oxidized oxygen carrier particles and the oxygen-deficient air undergo gas-solid separation in the air cyclone separator 5, the oxidized oxygen carrier particles enter the return feeder 6 along the downcomer, and the oxygen-deficient air is discharged from the exhaust pipe. The fluidizing gas introduced into the return feeder 6 is N2.

[0040] Step 5: The oxidized oxygen carrier is returned to fuel reactor 1 via return feeder 6 to begin the next cycle. The single-atom catalytic oxygen carrier particles continuously circulate between the two reactors to transfer energy and lattice oxygen, avoiding localized high-temperature phenomena and improving the fuel combustion efficiency of gaseous fuels.

[0041] Example 3

[0042] A cold-state experiment was conducted at room temperature using quartz sand instead of the aforementioned single-atom catalytic oxygen carrier. The bed material quantity was 2.2 kg, and the particle size was 0.15-0.35 mm. All gases were replaced with air. The average gas flow rate introduced into the bottom of air reactor 4 and fuel reactor 2 was 30 L / min, and the gas flow rate introduced into the bottom of return feeder 6 and isolator 3 was 4 L / min. The circulation of solid particles in air reactor 4 and fuel reactor 2 basically reached dynamic equilibrium. No throttling phenomenon was found during the circulation process of the entire system. The gas-solid distribution was uniform, and the fluidization state was good.

Claims

1. A low-temperature chemical looping combustion method for a low-temperature chemical looping combustion system, characterized in that: Includes the following steps: Step 1: Construct a low-temperature chemical looping combustion system. The low-temperature chemical loop combustion system comprises, in sequence, a fuel reactor (1), a fuel cyclone separator (2), an isolator (3), an air reactor (4), an air cyclone separator (5), and a return feeder (6) connected by pipes. The outlet of the fuel reactor (1) is connected to the inlet of the fuel cyclone separator (2) via a riser pipe. The bottom of the fuel reactor (1) is provided with a gas fuel inlet. The top of the fuel cyclone separator (2) is provided with a flue gas outlet, and the bottom is connected with a downcomer pipe that connects to the inlet of the isolator (3). The bottom of the isolator (3) is provided with a... The fluidizing gas inlet is connected to the bottom of the air reactor (4) via a pipe near the bottom. The bottom of the air reactor (4) is provided with an air inlet, and the outlet of the air reactor (4) is connected to the inlet of the air cyclone separator (5) via a riser pipe. The top of the air cyclone separator (5) is provided with an oxygen-deficient air outlet, and the bottom downpipe is connected to the feed inlet of the return feeder (6). The bottom of the return feeder (6) is provided with a fluidizing gas inlet, and the bottom of the return feeder (6) is connected to the bottom of the fuel reactor (1) via a pipe near the bottom. Step 2: The oxidized oxygen carrier particles react with the gaseous fuel introduced at the bottom of the fuel reactor (1) under the catalytic action of the Pt single-atom active center to transform into reduced oxygen carrier particles, water vapor and CO2. Step 3: Each product is transported to the fuel cyclone separator (2) through the riser pipe for gas-solid separation. The reduced oxygen carrier particles fall along the inner wall of the fuel cyclone separator (2) in a spiral path to the isolator (3). The fluidizing gas introduced into the isolator (3) is water vapor or CO2. At the same time, CO2 and water vapor can be obtained by simple condensation after being discharged through the exhaust pipe. Step 4: The reduced oxygen carrier particles in the isolator (3) enter the air reactor (4) through the pipeline. They react with the oxygen in the air introduced at the bottom and are transformed into oxidized oxygen carrier particles. They are then transported to the air cyclone separator (5). During this reaction, the oxygen molecules in the air are transformed into lattice oxygen in the oxygen carrier particles. The gas transported at the bottom of the air reactor (4) is air. Step 5: After the oxidized oxygen carrier particles and the oxygen-deficient air are separated by gas and solid in the air cyclone separator (5), the oxidized oxygen carrier particles enter the return feeder (6) along the downcomer, and the oxygen-deficient air is discharged from the exhaust pipe. The fluidizing gas introduced into the return feeder (6) is N2. Step 6: The oxidized oxygen carrier particles are returned to the fuel reactor (1) via the return feeder (6) to begin the next cycle. The oxygen carrier is a single-atom supported Pt1 / Cu type. x O; The reaction temperature of the fuel reactor (1) is 300~500℃; The reaction temperature range of the air reactor (4) is 350~550℃.

2. The low-temperature chemical looping combustion method of the low-temperature chemical looping combustion system according to claim 1, characterized in that, The fuel reactor (1) is a bubbling fluidized bed.

3. The low-temperature chemical looping combustion method of the low-temperature chemical looping combustion system according to claim 1, characterized in that, The air reactor (4) is a rapid fluidized bed.

4. The low-temperature chemical looping combustion method of a low-temperature chemical looping combustion system according to claim 1, characterized in that, The fuel reactor (1), air reactor (4), and return feeder (6) contain a bed of monoatomic loaded oxygen carrier material.

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