A honeycomb packed bed for carbon capture

Abstract

This invention discloses a honeycomb packed bed for carbon capture, relating to the field of flue gas adsorption in porous media environments. This invention is a novel fixed-bed concept reactor that uses porous silicon carbide ceramic monomers as the honeycomb frame and utilizes a layered flow channel network to reduce the pressure drop of the fixed bed, applying a honeycomb micro-packed adsorption bed to the adsorption and decarbonization process. The micro-packed bed has a cylindrical outer shell and two parallel layers of adsorbent inside, with honeycomb ceramic as the frame and a central cylindrical channel as a free channel. The internal pressure drop of the packed bed is extremely low, the fluid distribution is uniform, and the adsorption load is uniform throughout the packed layer. Simulation of introducing raw flue gas from a power plant demonstrates that the flow-type micro-packed bed has a good adsorption effect on CO2, showing promising application prospects for industrial flue gas treatment.

Description

Technical Field

[0001] This invention belongs to the field of flue gas adsorption in porous media environments, and in particular relates to a honeycomb packed bed for carbon capture. Background Technology

[0002] CO2 capture is CCUS The first step in this technology is also the most difficult and costly. Based on the different coupling points of the combustion process, CO2 capture methods are divided into three main categories: pre-combustion capture, post-combustion capture, and oxygen-enriched combustion. Fixed-bed reactors are an important post-combustion capture method for CO2 absorption. There are three basic types of fixed-bed reactors: ① Axial adiabatic fixed-bed reactor: Fluid flows axially from top to bottom through the bed, with no heat exchange between the bed and the outside environment. ② Radial adiabatic fixed-bed reactor: Fluid flows radially through the bed, using either centrifugal or centripetal flow, with no heat exchange between the bed and the outside environment. Compared to axial reactors, radial reactors have shorter fluid flow distances, larger flow channel cross-sectional areas, and smaller pressure drops. However, the structure of radial reactors is more complex than that of axial reactors. Both of these types are adiabatic reactors, suitable for situations where the reaction heat effect is small, or where the reaction system can withstand temperature changes caused by the reaction heat effect under adiabatic conditions. ③ Tubular fixed-bed reactor: Consists of multiple reaction tubes connected in parallel. The catalyst is placed inside or between the tubes, and the heat carrier flows through the tubes for heating or cooling. The tube diameter is usually between 25 and 50 mm, and the number of tubes can be as high as tens of thousands.

[0003] The main problem with fixed beds is the large pressure drop, which requires the use of larger adsorbent particles. However, as the size of the adsorbent particles increases, the diffusion resistance within the particles increases, leading to a decrease in adsorbent utilization efficiency. How to reduce bed pressure drop while improving adsorption efficiency is an important research topic in the field of adsorption. The commonly used methods to reduce the pressure drop of adsorption beds are mainly the following two: (1) Using a radial bed, the fluid passes through the adsorbent bed radially. Since the radial distance is smaller than the axial distance, the bed resistance is reduced. The main disadvantage of a radial bed is that the adsorbent load is uneven. The fluid velocity is faster at the axis of the radial bed, and the adsorbent load is large; the fluid velocity is slower at the circumference and the load is lower. The uneven load makes it impossible for the adsorbent to be fully utilized. (2) Using a monolithic adsorbent, the advantages are a large specific surface area, many pores, and extremely low pressure drop. Foreign scholars have proposed using honeycomb-type monolithic adsorbents directly formed from activated carbon powder to remove volatile organic compounds (VOCs) from the air; preparing Pt / SnO2-loaded foam ceramics can achieve pressure drop and mass transfer performance between granular and honeycomb ceramics; and using activated carbon fibers with higher packing density to press and mold for removing methyl ethyl ketone (MEK) from the air, with an adsorption mass exceeding 99.9%. Overall, the main disadvantage of monolithic adsorbents is the relatively low loading of the effective component. Summary of the Invention

[0004] This invention draws on the structural characteristics of radial beds and monolithic adsorbents to propose a novel adsorption bed geometry—the honeycomb packed bed. A cylindrical, closed porous honeycomb structure is fabricated using porous ceramics. Modified molecular sieves are used as solid adsorbents and filled into the honeycomb structure according to a specific arrangement. Fluid flows radially within the adsorption bed. The packed bed structure is optimized using COMSOL Multiphysics software to reduce flow pressure drop and eliminate internal diffusion resistance.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A honeycomb-filled ceramic bed for carbon capture includes a shell, four inlets, a filler zone, a honeycomb ceramic frame, a free channel, and a conical outlet;

[0007] The outer shell is cylindrical, made of polypropylene, suitable for high-temperature operation, and possesses excellent thermal and mechanical properties with no gas permeability. Four inlets are symmetrically distributed on the upper surface of the cylinder.

[0008] The packing section is made of modified molecular sieves, which are used to purify flue gas and have adsorption properties for CO2 and N2.

[0009] The honeycomb ceramic frame enclosing the filler area is cylindrical, with no less than two layers, and the honeycomb ceramic frame uses porous silicon carbide ceramic monomers.

[0010] The honeycomb-type filling bed has a free channel in the center, which divides the honeycomb ceramic frame into several cylindrical grids of the same size, with gaps between the grids.

[0011] There is a flow guiding device in the middle of the first layer of honeycomb ceramic frame. There is a gap between the flow guiding device and the outer shell, which guides part of the gas to descend through the free channel part of the packed bed.

[0012] The bottom of the honeycomb packed bed has a conical outlet for fluid collection and discharge.

[0013] The free channel of the two-layer honeycomb ceramic frame is cross-shaped when viewed from the front cross-section of the filling bed. The two-layer honeycomb ceramic frame in the front cross-section is divided into four rectangular grids of the same size by the free channel.

[0014] The bottom center of the lowest layer of the honeycomb ceramic frame is sealed with filler; fluid passing through the filler and fluid passing through the free channel flow back and forth in the free channel, selectively entering from the side or top of the honeycomb ceramic frame.

[0015] This honeycomb packed bed needs to be vertically suspended in the air, and the entire device performs fluid adsorption at room temperature. CO2, N2, and O2 gas cylinders are prepared, and the three fluids are mainly powered by a blower. The fluids enter simultaneously from four inlets, ensuring both uniform fluid entry into the packed bed and sufficient time for the fluid to pass through the packing material. First, the packed bed is heated, and only N2 gas is introduced. Under these conditions, the modified molecular sieve has virtually no adsorption capacity for the fluid, effectively removing various fluid impurities from the packed bed. The packed bed is then cooled to room temperature, and all three fluids are introduced simultaneously. Most of the fluid is directly adsorbed by the molecular sieve through the first permeable wall. A flow guiding device is located directly above the center of the first honeycomb ceramic permeable wall to guide the flow. Some gas passes through the central cylindrical free channel of the packed bed, which significantly reduces the pressure drop of the packed bed. The honeycomb ceramic frame surrounding the packing is cylindrical and hollowed out. There are gaps between the two frames, which are not tightly connected, reducing the diffusion resistance of the fluid. The fluid that has just passed through the first layer of packing and the fluid that has passed through the central cylindrical free channel of the packed bed flow back and forth in the cross-shaped free channels on the side. Some fluid enters the packing from above the second layer of honeycomb ceramic permeable wall, and some fluid enters the packing through the side permeable walls, ensuring the uniformity and completeness of fluid adsorption. All fluid passes through the bottom honeycomb ceramic permeable wall and flows to the conical free channel, and returns to the inlet through the outlet pipe for cyclic adsorption.

[0016] This invention uses COMSOL Multiphysics to model a honeycomb packed bed. Flow in the free channel is described by the steady, incompressible Navier-Stokes equations, while flow in the porous medium is described by the Forchheimer-modified Brinkman equations. The adsorption of flue gas by the packed bed is described by the "dilute mass transport in porous media," and the adsorption isotherm follows the Langmuir equations. Transient studies are added to calculate the average pressure surface value at the inlet of the packed bed and the concentrated mass adsorbed on the bed. A multiphysics model is established, ensuring accurate coupling. The absorption of CO2 by the adsorbent and the overall pressure drop of the packed bed under the condition of power plant flue gas are studied, analyzed, and simulated, providing a reference for the analysis and calculation of flue gas absorption by honeycomb packed beds. Attached Figure Description

[0017] Figure 1 A schematic diagram of the frontal cross-sectional structure of a typical packed bed;

[0018] Figure 2 This is a cross-sectional view of the present invention;

[0019] Figure 3 This is a schematic diagram of the overall structure of the present invention;

[0020] Figure 4 This is a flowchart of the present invention;

[0021] Figure 5 This is a comparison chart of CO2 adsorption capacity between the honeycomb-type packed bed of the present invention and a conventional packed bed.

[0022] In the diagram: 1. Packed bed inlet; 2. Flow guiding device; 3. Honeycomb ceramic permeable wall; 4. Packing zone;

[0023] 5. Sealing device; 6. Housing; 7. Filled bed outlet. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be further described in detail below with reference to the examples and accompanying drawings.

[0025] Example 1: Based on the three basic components of a honeycomb-type packed bed, a geometric model of the packed bed is established; such as... Figure 2 , Figure 3 As shown, the components of the honeycomb packed bed of the present invention include an external inlet 1, a flow guiding device 2, a honeycomb ceramic frame 3, a filling zone 4, a sealing device 5, a shell 6, and an outlet 7; the shell 6 is 70mm high, 25mm in radius, and 3mm thick; the inlet is 10mm high and 5mm in radius; the distance between the top of the honeycomb ceramic frame 3 and the shell 6 is 4mm; the flow guiding device 2 is 3.5mm high, leaving a 0.5mm gap for some fluid; the honeycomb ceramic frame 3 is 15mm high and 2.5mm thick, leaving sufficient filling space, and the two layers of honeycomb ceramic frames are parallel to each other; the free channel in the middle of the packed bed has a radius of 3mm, the two layers of honeycomb ceramic frames are spaced 2mm apart, the overall free channel has a cross shape on the side, and a cylindrical shape when viewed from above; the bottom of the packed bed is a conical free channel with a height of 10mm, a top radius of 25mm, and a bottom radius of 5mm.

[0026] This invention relates to a honeycomb packed bed that needs to be vertically suspended in the air. The entire apparatus is used for fluid adsorption experiments at room temperature. CO2, N2, and O2 gas cylinders are prepared, and the three fluids are powered primarily by a blower with a maximum pressure of 10 kPa. The fluids enter simultaneously through four inlets, with CO2, N2, and O2 comprising 13.40%, 80.45%, and 6.13% respectively. This ensures both uniform fluid entry into the packed bed and sufficient time for the fluids to pass through the packing material. First, the packed bed is heated to 120°C, and only N2 gas is introduced until the bed mass no longer changes. Under these conditions, the modified molecular sieve exhibits virtually no adsorption capacity for the fluids, effectively removing various fluid impurities from the packed bed. The packed bed is then cooled to room temperature, and the three fluids are introduced simultaneously in proportion. Most of the fluid passes through the first permeable wall. The gas is directly adsorbed by molecular sieves. A flow guiding device is located directly above the center of the first layer of honeycomb ceramic permeable wall, guiding some of the gas through the cylindrical free channel in the center of the packed bed, which can significantly reduce the pressure drop of the packed bed. The honeycomb ceramic frame surrounding the packing is cylindrical and hollow inside. There are gaps between the two frames, which are not tightly connected, reducing the diffusion resistance of the fluid. The bottom center of the second layer of honeycomb ceramic frame is sealed by the packing material. The fluid that has just passed through the first layer of packing and the fluid that has passed through the cylindrical free channel in the center of the packed bed flow back and forth in the cross-shaped free channel on the side, selectively entering from the side or top of the permeable wall, greatly reducing the pressure drop. The modified molecular sieve can more comprehensively adsorb CO2. All the fluid passes through the bottom honeycomb ceramic permeable wall and flows to the conical free channel, and returns to the inlet through the outlet pipe for cyclic adsorption.

[0027] The outer shell of the packed bed is made of polypropylene, which performs reliably at high temperatures, has good thermal and mechanical properties, and is gas-permeable. The packing material 4 is a modified molecular sieve in powder form, typically with a high porosity, generally between 40% and 50%, exhibiting strong adsorption capacity for CO2 and N2. The permeable wall 3 is composed of honeycomb ceramics, with a porosity typically between 30% and 90%. The adsorbent is encapsulated, separated, and bound by the framework of the honeycomb ceramics. To fill the powdered molecular sieve, the porosity of the honeycomb ceramics usually needs to reach a high level so that the molecular sieve powder can be fully filled and provide a good adsorption surface area. Generally, the porosity of the honeycomb ceramics should be above 80% to effectively fill the molecular sieve powder, ensuring sufficient contact of the molecular sieve powder and providing sufficient surface area and channels during adsorption to achieve efficient CO2 adsorption. The bottom of the packed bed is conical, which facilitates gas collection to the outlet. Figure 1This is a cross-sectional view of a typical packed bed, including two inlets, two free channels, three ceramic permeable walls, two packed bed layers, and one outlet. The inlets are located at the top of the packed bed, where molecular sieve powder is filled and sealed between two layers of cylindrical honeycomb ceramic permeable walls to form an adsorbent bed. The bottom free channel is conical, and fluid flows out from the circular channel opening.

[0028] This invention uses COMSOL Multiphysics software to model a honeycomb packed bed. The flow in the free channel is described by the steady and incompressible Navier-Stokes equation, the flow in the porous medium is described by the Forchheimer modified Brinkman equation, the adsorption of flue gas in the packed bed is described by the "dilute mass transfer in porous media", and the adsorption isotherm obeys the Langmuir equation.

[0029] Based on the inlet radius of the packed bed and the gas cylinder flow rate, the gas inlet velocity can be calculated to be 2 m / s; the outlet pressure is static pressure, set to 0, and the overall pressure drop of the packed bed is obtained as the average inlet pressure. The average pressure surface value at the inlet is then calculated. Figure 5 As shown, when power plant flue gas is introduced into both honeycomb packed beds and ordinary packed beds under the same parameters, the average inlet pressure of the honeycomb packed bed is about 96 Pa, while that of the ordinary packed bed is about 338 Pa. It can be seen that the pressure drop of the honeycomb packed bed is much lower than that of the ordinary packed bed, and the free channels in the packed bed have a good effect on reducing the pressure drop.

[0030] With the Langmuir constant and maximum adsorption capacity parameters remaining constant, a transient study was added, with the output time step set to 200 h and data recorded every 0.5 h; Figure 5 As shown, the adsorption effect of the first layer adsorbent of the honeycomb packed bed and the ordinary packed bed on CO2 is not much different. The second layer adsorbent of the former has a significantly improved effect compared to the latter, and has been in the leading position for 200 hours. It can be seen that the honeycomb packed bed has a certain improvement in flue gas adsorption effect compared with the ordinary packed bed under the condition of extremely low pressure drop.

Claims

1. A honeycomb packed bed for carbon capture, characterized in that, It includes an outer shell, four inlets, a filling zone, a honeycomb ceramic frame, a free channel, and a conical outlet; The outer shell is a cylindrical structure made of polypropylene; four inlets are symmetrically distributed on the upper surface of the cylinder. The packing section is made of modified molecular sieves, which are used to purify flue gas and have adsorption properties for CO2 and N2. The honeycomb ceramic frame surrounding the filler area is cylindrical, and there are no fewer than two layers of the honeycomb ceramic frame. The honeycomb filling bed has a free channel in the center, which divides the honeycomb ceramic frame into several cylindrical grids of the same size, with gaps between the grids; There is a flow guiding device in the middle of the first layer of honeycomb ceramic frame. There is a gap between the flow guiding device and the outer shell, which guides part of the gas through the free channel part of the packed bed. The bottom of the honeycomb packed bed has a conical outlet for fluid collection and discharge; The honeycomb ceramic frame has two layers, and the free channels are cross-shaped when viewed from the front cross-section of the filling bed. The two layers of the honeycomb ceramic frame in the front cross-section are divided into four rectangular grids of the same size by the free channels. The bottom center of the lowest layer of the honeycomb ceramic frame is sealed with filler.

2. The honeycomb packed bed for carbon capture according to claim 1, characterized in that, The honeycomb ceramic frame uses porous silicon carbide ceramic monomers.

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