An oxygen storage and heat storage type flue gas residual fuel post-oxidation system and process

Abstract

The present application belongs to the field of fuel combustion, and particularly relates to a kind of residual fuel post-oxidation system and process of oxygen storage and heat storage type flue gas, the purpose is to burn as much as possible through the low concentration residual gas fuel in flue gas by passing a small amount of pure oxygen, to improve the utilization efficiency of fuel chemical energy, while reducing the impurity gas in flue gas except CO2, H2O, reduce the energy consumption of flue gas CO2 compression purification process.The oxygen carrier in the post-oxidation chamber promotes the conversion of residual fuel in flue gas, provides lattice oxygen buffer for fuel conversion, and the heat generated in the process of fuel conversion is also accumulated in the oxygen carrier bed, which is beneficial to stabilize the temperature fluctuation of flue gas and realize the energy flow integration of the system.In addition, the post-oxidation system adjusts the oxygen supply and the amount of desuperheating water by sampling the composition, temperature and other state parameters of flue gas at the inlet and outlet of the system, to real-time control the residual fuel amount and flue gas temperature at the outlet of the post-oxidation chamber, further to meet the operation requirements.

Description

Technical Field

[0001] This invention belongs to the field of fuel combustion, specifically relating to an oxygen-storage and heat-storage flue gas residual fuel post-oxidation system and process. Background Technology

[0002] Against the backdrop of peak carbon emissions and carbon neutrality, the low-carbon transition of fossil fuels has become an urgent need to ensure the security and economy of the overall energy structure. Low-cost carbon capture, utilization, and storage (CCUS) technologies are key to this. Among these, chemical looping combustion (CLC), as a carbon capture technology with great potential in fuel combustion, has received increasing attention in recent years. Unlike the traditional one-step combustion process, CLC technology breaks it down into two independent sub-processes: oxidation and reduction, which are isolated by atmosphere. A metal oxide oxygen carrier circulates and transfers lattice oxygen and heat between the two sub-processes. The fuel is oxidized by the oxygen carrier at a temperature lower than that of conventional combustion, producing mainly CO2 and H2O as byproducts. Therefore, CO2 is easily separated and captured. Thus, chemical looping combustion technology has the advantages of in-situ CO2 separation, energy cascade utilization, and low NOx emissions.

[0003] To date, research in the field of chemical looping combustion has primarily focused on the development of high-performance oxygen carriers (OC), reactor design and operation, and the integration of energy and material flows in the system. Among these, the performance of the CLC reactor is the main bottleneck limiting the utilization rate of fuel chemical energy and CO2 capture costs in the CLC process, thus attracting significant attention. Based on the different mechanisms by which the oxygen carrier participates in oxidation and reduction reactions, chemical looping combustion reactors can be classified into dual fluidized bed reactors and co-located fixed bed reactors, with the former being more commonly used. A dual fluidized bed reactor consists of two fluidized bed reactors connected in series, with oxygen carrier particles circulating between them. A dual fluidized bed chemical looping combustion reactor includes an air reactor, a fuel reactor, and auxiliary components such as a cyclone separator, flow sealing valve, and connecting pipes. The fuel reactor can be used to introduce gaseous fuels or solid fuels (produced through in-situ pyrolysis and gasification). Generally, air reactors and fuel reactors often employ one of the following fluidized bed types: bubbling bed, turbulent bed, or fast bed, to meet the requirement of rapid oxygen carrier circulation. However, because the gas in the oxygen carrier particles accumulates and forms bubbles in the bed during fluidization, these bubbles rise and penetrate the bed, inevitably preventing some of the gaseous fuel in the bubbles from contacting and reacting with the oxygen carrier. In other words, a portion of the gaseous fuel in the fuel reactor will always remain unconverted, which is unavoidable (Lyngfelt A, Leckner BA 1000MWth boiler for chemical-looping combustion of solid fuels-Discussion of design and costs. Applied Energy, 2015, 157:475-487.). Furthermore, the reactivity of the oxygen carrier also affects the degree of gaseous fuel conversion, and deactivation phenomena such as oxygen carrier sintering during operation can also adversely affect fuel conversion. Generally, unconverted gaseous fuel can account for 5-30% of the total fuel (Lyngfelt A, Brink A, ...). et al. 11,000h of chemical-looping combustion operation—Where we and where do we want to go? International Journal of Greenhouse GasControl, 2019, 88:38-56.). Various solutions have been proposed to alleviate this problem, such as using higher-performance oxygen carriers and optimizing reactor parameters, but these also mean higher energy consumption, higher costs, or more limited operating ranges. Therefore, a more popular approach is to arrange a post-oxidation chamber (POC) downstream of the fuel reactor and introduce high-purity oxygen to further burn the residual fuel in the flue gas until it is completely burned (Berguerand N, Lyngfelt A. Design and operation of a 10kWth chemical-looping combustor for solid fuels-Testing with South African coal. Fuel, 2008, 87(12):2713-2726.). This process can also be called oxygen polishing. In this process, high-purity oxygen can be obtained from a technologically mature cryogenic air separation device, and the oxygen supply can be flexibly adjusted to match the post-oxidation process with different operating conditions. This process can make the carbon capture efficiency of the entire chemical looping combustion system close to 100%, while the system complexity remains within an acceptable range. In addition, the cost increase due to the production of pure oxygen is also within a reasonable range. Due to the low oxygen demand, when the fuel conversion rate in the fuel reactor is 90%, the additional energy consumption of the system will only increase by 0.6% (Lyngfelt A. Chemical-looping combustion of solid fuels-Status of development. Applied Energy, 2014, 113: 1869-1873.).

[0004] Although the technical route of the post-oxidation chamber is relatively clear, few researchers at home and abroad have studied this technology. Only the 100kWth reactor at Chalmers University of Technology in Sweden (Mei D, Linderholm C, Lyngfelt A. Performance of an oxy-polishing step in the 100kWth chemical looping combustion prototype. Chemical Engineering Journal, 2021, 409, 128-202) and the 1MWth reactor at the Technical University of Darmstadt in Germany have adopted the post-oxidation system. J, Orth M, Epple B. Design and operation of a 1MWth chemical looping plant. Applied Energy, 2014, 113: 1490-1495. Both systems introduce fuel reactor flue gas and pure oxygen into a single space. The former uses an enlarged section design for its post-oxidation chamber, while the latter uses a straight-pipe design. Both operate with an empty tower, meaning the post-combustion chamber is vacant. With the assistance of the post-oxidation system, both chemical looping combustion devices achieve high fuel conversion efficiency and carbon capture efficiency.

[0005] However, the aftercombustion chamber control redundancy in empty tower operation is poor, and its adaptability to changes in operating conditions, especially extreme conditions, is weak. This puts greater pressure on the air separation oxygen supply system and increases the difficulty of system control and operating costs. Furthermore, for pilot-scale and larger-scale chemical looping combustion devices, while fuel conversion is crucial, the system's self-heating operation is also a core factor limiting its operational effectiveness. Currently, existing devices of various scales, both domestically and internationally, have not achieved self-heating operation and rely on electric heating or fuel supplementary combustion to maintain system operation. Energy integration is a problem that must be solved for pilot-scale and larger-scale chemical looping combustion devices and is an essential path to achieving self-heating operation. Therefore, how to ensure that the combustion system has a certain degree of redundancy in energy control and increase the resistance to thermal integration and the ability to smooth fluctuations are urgent problems to be solved. Summary of the Invention

[0006] The purpose of this invention is to improve the energy utilization efficiency of chemical looping combustion systems and reduce the difficulty of energy integration. The proposed post-oxidation system in this invention burns low-concentration residual gaseous fuel in the flue gas as completely as possible by introducing a small amount of pure oxygen into the post-combustion chamber, thereby improving the utilization efficiency of fuel chemical energy. Simultaneously, it reduces impurity gases in the flue gas other than CO2 and H2O, lowering the energy consumption of the CO2 compression and purification process. At this time, the presence of an oxygen carrier in the post-oxidation chamber promotes the conversion of residual fuel in the flue gas, providing a lattice oxygen buffer for fuel conversion. Furthermore, the heat generated during fuel conversion is also accumulated in the oxygen carrier bed, providing a thermal buffer for the chemical looping combustion system, stabilizing the flue gas temperature, and facilitating the energy flow integration of the system.

[0007] According to a first aspect of the present invention, the present invention first proposes an oxygen-storage and heat-storage flue gas residual fuel post-oxidation system, the post-oxidation system comprising a combustion flue gas separation unit, a first sampling unit, a post-oxidation chamber, an oxygen supply unit, and a second sampling unit, wherein a first circular pipe and a second circular pipe are respectively provided at the inlet and outlet of the post-oxidation chamber, and a first gas detection point and a second gas detection point connected to the first sampling unit and the second sampling unit are respectively provided in the first circular pipe and the second circular pipe.

[0008] The first circular tube has a double-layer structure with an inner tube and an outer tube. The combustion flue gas separation unit is connected to the post-oxidation chamber through the outer tube, and the oxygen supply unit is connected to the post-oxidation chamber through the inner tube. The post-oxidation chamber is filled with an oxygen carrier.

[0009] According to one embodiment of the present invention, the post-oxidation chamber is a cylindrical hollow structure, and the diameters of the first circular tube and the second circular tube are both smaller than those of the post-oxidation chamber.

[0010] According to one embodiment of the present invention, the oxygen carrier contains an active component, which is one or more of Fe2O3, CuO, and NiO. The particle size of the oxygen carrier is 10-20 mm. The oxygen carrier is packed in a dense phase or by first packing the oxygen carrier into multiple layered modules and then stacking the multiple layered modules in the post-oxidation chamber.

[0011] According to one embodiment of the present invention, the first gas detection point and the second gas detection point are used to simultaneously detect the composition and temperature of residual fuel in the flue gas.

[0012] According to one embodiment of the present invention, the combustion flue gas separation unit includes a cyclone separator, the cyclone separator including an air inlet located on the side of the cyclone separator, an air outlet located at the top of the cyclone separator, and a riser located at the bottom of the cyclone separator.

[0013] According to one embodiment of the present invention, the cyclone separator is a two-stage cyclone separator.

[0014] According to one embodiment of the present invention, the second circular tube has a water spray cooling device on its exterior.

[0015] According to one embodiment of the present invention, the post-oxidation system further includes a PID control unit, which controls the oxygen supply amount of the oxygen supply unit and the water spraying amount of the water spraying and desuperheating device based on the sampling results of the first sampling unit and the second sampling unit.

[0016] According to another aspect of the present invention, the present invention also provides a post-oxidation process for residual fuel in flue gas using the above-described system, comprising the following steps:

[0017] S1: First, the residual fuel flue gas enters the cyclone separator through the air inlet. The gas and solid components in the residual fuel flue gas are separated by the action of the cyclone separator to form a flue gas stream and a solid stream. The flue gas stream flows out from the top outlet of the cyclone separator, while the solid stream falls into the riser from the bottom of the cyclone separator. The volume ratio of gaseous fuel in the flue gas stream is 5-30%, and the temperature of the flue gas stream is 900-950℃.

[0018] S2: The first sampling unit is used to sample the flue gas stream flowing out of the top outlet of the cyclone separator to detect its composition and temperature;

[0019] S3: After the flue gas stream and the pure oxygen stream pass through the first circular tube, they enter the post-oxidation chamber in a non-premixed form for combustion;

[0020] S4: After the flue gas stream from combustion exits the oxidation chamber, the second sampling unit is activated to sample the flue gas stream exiting the oxidation chamber; the PID control unit adjusts the oxygen supply of the oxygen supply unit and the water spray volume of the water spray desuperheating device according to the sampling results of the first and second sampling units, so as to further stabilize the composition and temperature of the flue gas stream exiting the oxidation chamber.

[0021] According to one embodiment of the present invention, in step S2, before the first sampling unit samples the flue gas stream, the flue gas stream is subjected to heat exchange through a heat exchanger at a temperature of 500-550°C.

[0022] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0023] (1) Since the post-oxidation chamber of the present invention is loaded with an oxygen carrier, the residual fuel in the flue gas stream can be fully converted in the post-combustion chamber, which is beneficial to improving the energy utilization efficiency of the combustion system.

[0024] (2) The preferred oxygen carrier of the present invention can not only play the role of assisting combustion, but also has a higher degree of fuel conversion and heat storage, and can be used as an oxygen / heat storage pool to provide a buffer for subsequent PID system regulation.

[0025] (3) The present invention sets up flue gas sampling units before and after the post-oxidation chamber and feeds back the detection results of both to the PID control unit, thereby reducing the difficulty of dynamic control of the energy integration process in real time. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the residual fuel post-oxidation process in a regenerative oxygen fuel reactor according to an embodiment of the present invention.

[0027] Figure 2 This diagram illustrates the particle loading method in the post-oxidation chamber and the flue gas / oxygen entry method. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] This invention proposes an oxygen-storage and heat-storage flue gas residual fuel post-oxidation system. The post-oxidation system includes a combustion flue gas separation unit, a first sampling unit, a post-oxidation chamber, an oxygen supply unit, and a second sampling unit. The inlet and outlet of the post-oxidation chamber are respectively provided with a first circular pipe and a second circular pipe. The first circular pipe and the second circular pipe are respectively provided with a first gas detection point and a second gas detection point connected to the first sampling unit and the second sampling unit.

[0030] The first circular tube has a double-layer structure with an inner tube and an outer tube. The combustion flue gas separation unit is connected to the post-oxidation chamber through the outer tube, and the oxygen supply unit is connected to the post-oxidation chamber through the inner tube. The post-oxidation chamber is filled with an oxygen carrier.

[0031] In some embodiments, the post-oxidation chamber is a cylindrical hollow structure, and the diameters of the first and second circular tubes are smaller than those of the post-oxidation chamber.

[0032] In some embodiments, the oxygen carrier contains an active component, which may be one or more of Fe2O3, CuO, and NiO. The particle size of the oxygen carrier is 10-20 mm. The oxygen carrier is packed in a dense-phase manner or by first packing the oxygen carrier into multiple layered modules and then stacking the multiple layered modules in the post-oxidation chamber.

[0033] In some embodiments, the first gas detection point and the second gas detection point are used to simultaneously detect the composition and temperature of residual fuel in the flue gas.

[0034] In some embodiments, the combustion flue gas separation unit includes a cyclone separator, which includes an air inlet located on the side of the cyclone separator, an air outlet located at the top of the cyclone separator, and a riser located at the bottom of the cyclone separator.

[0035] In some embodiments, due to the large flow rate of the flue gas stream, a two-stage cyclone separator is preferred to ensure the separation effect.

[0036] In some embodiments, the second circular tube has a water spray cooling device on its exterior.

[0037] In some embodiments, the post-oxidation system further includes a PID control unit, which controls the oxygen supply of the oxygen supply unit and the water spray volume of the water spraying and cooling device based on the sampling results of the first sampling unit and the second sampling unit.

[0038] The following are specific examples:

[0039] Example 1

[0040] Figure 1 This is a schematic diagram of the residual fuel post-oxidation process in a regenerative thermal oxygen fuel reactor, which specifically includes the following steps:

[0041] S1: First, the residual fuel flue gas enters the cyclone separator through the air inlet. The gas and solid components in the residual fuel flue gas are separated by the action of the cyclone separator to form a flue gas stream and a solid stream. The flue gas stream flows out from the top outlet of the cyclone separator, while the solid stream falls into the riser from the bottom of the cyclone separator. The volume ratio of gaseous fuel in the flue gas stream is 10%, and the temperature of the flue gas stream is 950°C.

[0042] S2: The first sampling unit is used to sample the flue gas stream to detect its composition and temperature; before detection, the flue gas stream is heated by a heat exchanger at a temperature of 550°C to prevent residual fuel from failing to ignite in the afterburner.

[0043] S3: After passing through the first circular tube, the flue gas stream and the pure oxygen stream enter the post-oxidation chamber in a non-premixed form for combustion, such as... Figure 2As shown, this embodiment employs a concentric sleeve air intake to prevent residual fuel from igniting and being blown out, while simultaneously enhancing the mixing degree of fuel and oxygen. Oxygen flows through the inner tube of the first circular tube, while the outer tube carries the flue gas stream. The oxygen carrier particles have a size of 10 mm, and the active components are Fe2O3 and CuO. The presence of the oxygen carrier enhances the turbulence and mixing effect of the airflow, and since it can also participate in the reaction, the contact degree between the residual gaseous fuel and oxygen and the oxygen carrier is significantly strengthened, thus improving the conversion degree of the gaseous fuel. Furthermore, the lattice oxygen in the oxygen carrier provides considerable oxygen storage redundancy for the post-oxidation chamber. When the residual fuel in the flue gas suddenly increases significantly due to factors such as changing operating conditions and fluidization fluctuations, the PID control system cannot adjust the oxygen supply in time due to the system's time lag. At this time, the oxygen carrier becomes the main force for fuel conversion, preventing fuel slippage. Simultaneously, in the post-oxidation chamber, because the combustion process of the gaseous fuel is relatively fast, the reaction area (which can be called the reaction front) will remain basically near the inlet. However, the heat generated by the reaction will move downstream with the airflow. The area where the heat fluctuates (which can be called the thermal front) will also move downstream slowly at a speed much lower than the gas flow rate. The time for heat fluctuations to be transferred from the inlet to the outlet of the post-oxidation chamber is usually on the order of minutes to hours, i.e., heat lag. However, since the post-oxidation chamber has made heat storage redundancy (oxygen carrier loading) to cope with this heat lag in advance, when the flue gas temperature suddenly changes significantly due to factors such as changing operating conditions, thermal integration control, and operational fluctuations, the flue gas temperature at the outlet of the post-oxidation chamber always fluctuates more gently due to the existence of this redundancy. This makes the control of subsequent water spray desuperheating, thermal integration control and other control processes more precise, which is conducive to the self-heating operation of the post-oxidation system.

[0044] S4: After the flue gas stream flows out of the oxidation chamber, the second sampling unit is activated to sample the flue gas; the PID control unit adjusts the oxygen supply of the oxygen supply unit and the water spray volume of the water spray de-cooling device according to the sampling results of the first and second sampling units, so as to further stabilize the composition and temperature of the flue gas stream.

[0045] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A post-oxidation process for residual fuel in flue gas, characterized in that, The oxygen-storage and heat-storage flue gas residual fuel post-oxidation system includes: a combustion flue gas separation unit, a first sampling unit, a post-oxidation chamber, an oxygen supply unit, and a second sampling unit. The inlet and outlet of the post-oxidation chamber are respectively provided with a first circular pipe and a second circular pipe. The first circular pipe and the second circular pipe are respectively provided with a first gas detection point and a second gas detection point connected to the first sampling unit and the second sampling unit. The first circular tube has a double-layer structure with an inner tube and an outer tube. The combustion flue gas separation unit is connected to the post-oxidation chamber through the outer tube, and the oxygen supply unit is connected to the post-oxidation chamber through the inner tube. The post-oxidation chamber is filled with an oxygen carrier. The oxygen carrier contains an active component, which is one or more of Fe2O3, CuO, and NiO. The particle size of the oxygen carrier is 10-20 mm. The oxygen carrier is packed in a dense-phase manner or by first packing the oxygen carrier into multiple layered modules and then stacking the multiple layered modules in the post-oxidation chamber. The combustion flue gas separation unit includes a cyclone separator, which includes an air inlet located on the side of the cyclone separator, an air outlet located on the top of the cyclone separator, and a vertical pipe located at the bottom of the cyclone separator; the second circular pipe has a water spray cooling device on its exterior. The post-oxidation system also includes a PID control unit, which controls the oxygen supply of the oxygen supply unit and the water spray volume of the water spraying and desuperheating device based on the sampling results of the first sampling unit and the second sampling unit. Includes the following steps: S1: First, the residual fuel flue gas enters the cyclone separator through the air inlet. The gas and solid components in the residual fuel flue gas are separated by the action of the cyclone separator to form a flue gas stream and a solid stream. The flue gas stream flows out from the top outlet of the cyclone separator, while the solid stream falls into the riser from the bottom of the cyclone separator. The volume ratio of gaseous fuel in the flue gas stream is 5-30%, and the temperature of the flue gas stream is 900-950℃. S2: The first sampling unit is used to sample the flue gas stream flowing out of the top outlet of the cyclone separator to detect its composition and temperature; S3: After the flue gas stream and the pure oxygen stream pass through the first circular tube, they enter the post-oxidation chamber in a non-premixed form for combustion; S4: After the flue gas stream from combustion exits the oxidation chamber, the second sampling unit is activated to sample the flue gas stream exiting the oxidation chamber; the PID control unit adjusts the oxygen supply of the oxygen supply unit and the water spray volume of the water spray desuperheating device according to the sampling results of the first and second sampling units, so as to further stabilize the composition and temperature of the flue gas stream exiting the oxidation chamber.

2. The flue gas residual fuel post-oxidation process according to claim 1, characterized in that, In step S2, before the first sampling unit samples the flue gas stream, the flue gas stream is subjected to heat exchange through a heat exchanger at a temperature of 500-550°C.

3. The flue gas residual fuel post-oxidation process according to claim 1, characterized in that, The post-oxidation chamber is a cylindrical hollow structure, and the diameters of the first and second circular tubes are both smaller than those of the post-oxidation chamber.

4. The flue gas residual fuel post-oxidation process according to claim 1, characterized in that, The cyclone separator is a two-stage cyclone separator.

Images