Method for predicting the mass transfer rate control steps of organic amine solution absorbing CO2 in packed towers

Abstract

The present application relates to a method for predicting the mass transfer rate control step of CO2 absorption by an organic amine solution in a packed column, obtaining the gas phase mass transfer coefficient and the liquid phase mass transfer coefficient under different G and C conditions, and determining the mass transfer rate control step; establishing a database of the corresponding relationship between the feed flow rate, the concentration of the organic amine, and the mass transfer rate control step; obtaining the feed flow rate and the concentration of the organic amine under the to-be-predicted working condition, and comparing with the database to obtain the mass transfer rate control step of CO2 absorption by the organic amine solution under the to-be-predicted working condition. The present application can intuitively determine the mass transfer rate control step by establishing a database of the corresponding relationship between the feed flow rate of the mixed gas, the concentration of the organic amine, and the mass transfer rate control step, and can provide guidance for the industrial application of the organic amine absorption of CO2.

Description

Technical Field

[0001] This invention relates to a method for controlling the mass transfer rate of CO2 absorption by organic amine solution in a packed tower, belonging to the field of carbon dioxide capture and separation technology. Background Technology

[0002] In recent years, the massive emissions of greenhouse gas CO2 have caused global warming, and environmental problems such as ozone layer depletion and acid rain have become increasingly serious, attracting widespread attention. Currently, carbon capture and storage (CCS) is recognized as an effective solution for CO2 emission reduction. Among these methods, organic amine compound absorption has become one of the main methods for industrial gas purification due to its advantages such as fast absorption rate, large absorption capacity, and low economic cost. Many reactors are used for CO2 absorption by organic amine compounds, such as packed towers, bubble columns, and wet-wall towers. Packed towers, as important gas-liquid separation equipment in current chemical industrial production, are valued for their high mass transfer efficiency, large processing capacity, and good operational stability. The mass transfer performance of CO2 absorption by amines in packed towers has been extensively studied because it directly determines the CO2 separation efficiency and optimal operating conditions. The selection of operating conditions determines the CO2 throughput and directly determines the economic cost of capture; therefore, it is necessary to understand the mass transfer rate control steps to achieve efficient and low-cost CO2 absorption.

[0003] For CO2 absorption, the most representative mass transfer models include the two-film model, the solute permeation model, and the surface renewal model. While the solute permeation and surface renewal models better explain the actual transfer process mechanistically, they currently cannot perform complex calculations of key mass transfer parameters. Therefore, at present, calculations related to mass transfer are still based on the two-film model. This theory is based on molecular diffusion through two stagnant films: a liquid film and a gas film. According to the two-film theory, the CO2 absorption process is determined by three steps: mass transfer in the gas phase (CO2 reaches the interface from the bulk gas phase via convection and diffusion), dissolution at the interface, and mass transfer in the liquid phase (CO2 enters the bulk liquid phase from the interface via diffusion and convection). The resistance of CO2 across the interface is minimal and can be ignored. Therefore, during CO2 absorption, under different operating conditions, the mass transfer rate is controlled by either the gas film or the liquid film. By calculating the mass transfer resistance of the gas and liquid films, we can theoretically guide the setting of experimental operating conditions and analyze the rate control steps from the perspective of different operating conditions.

[0004] In actual production processes, applying this method to determine the mass transfer rate control steps is quite complex, requiring extensive research to obtain relevant data, which is time-consuming and labor-intensive. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for predicting the mass transfer rate control step of CO2 absorption by organic amine solution in a packed tower, thereby simplifying the prediction process of the mass transfer rate control step.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A method for predicting the mass transfer rate control step of CO2 absorption by an organic amine solution in a packed tower, comprising the following steps:

[0008] S1, Get G1, C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0009] Get G2, C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0010] Get G3, C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0011] ...;

[0012] Get G n-1 C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0013] Get G n C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0014] Get G H C M Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0015] Get G H C M+1 Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0016] ...;

[0017] Get G H C m-1 Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0018] Get G H C m Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps.

[0019] ...;

[0020] Establish a database of the correspondence between feed flow rate, organic amine concentration, and mass transfer rate control steps;

[0021] Where n is a positive integer not less than 3, N, H, M, and m are positive integers, 1 ≤ H ≤ n, 1 ≤ N ≤ m, and 1 ≤ M ≤ m; G n C is the feed flow rate of the mixed gas; m G1, G2, ..., G6 represent the concentrations of organic amines in the organic amine solution. n-1 G n Increasing sequentially, C M C M+1 ... C m-1 C m The values ​​increase sequentially; optionally, n is 3-8 and m is 2-6; further optionally, n is 4-6 and m is 3-6.

[0022] S2. Obtain the feed flow rate and organic amine concentration under the predicted operating condition, compare them with the database, and obtain the mass transfer rate control step for the organic amine solution absorbing CO2 under the predicted operating condition.

[0023] Furthermore, the gas-phase mass transfer coefficient (kmol / (m)) was obtained through calculation. 2 ·s·kPa), gas phase mass transfer coefficient k G The calculation formula is:

[0024]

[0025] The liquid phase mass transfer coefficient (kmol / (m)) was obtained by calculation. 2 ·s·kPa), liquid phase mass transfer coefficient k L The calculation formula is:

[0026] Where G is the feed velocity of the mixed gas, and D G The diffusion coefficient (m) of the gas mixture in the gas film 2 / s), A T The total specific surface area of ​​the packing (m²) 2 / m 3 ), μ G The viscosity of the gas mixture (kg / (m·h)) is p. G The density of the gas mixture (kg / m³) 3 ), d p R is the nominal diameter of the packing (m), and R is the gas constant (kPa·m). 3 / kmol·K), where T is the feed temperature (K) of the organic amine solution. The diffusion coefficient (m) in CO2 organic amine solution 2 / s), k2 is the dynamic constant (m 2 / s), C sol bulk This represents the concentration of the organic amine solution in the liquid phase. Henry's coefficient (kPa·m) 3 / kmol).

[0027] The above calculation formula is derived from: Onda, K., Takeuchi, H., and Okumoto, Y., "Mass Transfer Coefficients Between Gas and Liquid Phases in Packed Columns", Journal of Chemical Engineering of Japan, 1, 56-62 (1968);

[0028] Liu F, Rochelle GT, Wang T, et al.CO2 absorption rate in biphasicsolvent of aminoethylethanolamine and diethylethanolamine[J].ChemicalEngineering Journa1, 2021, 404:126503;

[0029] Liu Fei. Study on the mechanism of carbon dioxide capture by amine two-phase absorbent [D]; Zhejiang University, 2020.

[0030] Furthermore, the mass transfer rate control step is determined by comparing the gas phase mass transfer coefficient and the liquid phase mass transfer coefficient. Specifically, when the gas phase mass transfer coefficient is greater than the liquid phase mass transfer coefficient, the mass transfer rate control step is liquid film control; when the gas phase mass transfer coefficient is less than the liquid phase mass transfer coefficient, the mass transfer rate control step is gas film control.

[0031] Furthermore, the organic amine solution is an aqueous solution of one or more of LDEEA, LHMDA, and MEA.

[0032] For different organic amine solutions, the feed rate of the mixed gas has a significant impact on the gas-phase mass transfer coefficient, and the gas-phase mass transfer coefficient also varies considerably for different packing systems. By adjusting the gas flow rate and the type of packing, corresponding databases can be obtained, enabling direct determination of the mass transfer rate control steps under different operating conditions and / or organic amine systems.

[0033] This invention establishes a database of the correspondence between the feed flow rate of the mixed gas, the concentration of organic amines, and the mass transfer rate control steps. This allows for a simple and intuitive determination of the mass transfer rate control steps, providing guidance for the industrial application of organic amines in CO2 absorption. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a mass transfer and absorption simulation experimental setup. Detailed Implementation

[0035] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0036] Example 1

[0037] This embodiment uses an aqueous MEA system (total organic amine concentration of C). m The process of CO2 absorption by organic amine solution was simulated and predicted (the simulation device is as follows). Figure 1 As shown in the figure, the mass transfer rate control steps of the absorption process were studied. The main operating parameters of the absorption process include: G, lean liquid load α(0), and T(303.15K). Lean liquid load α refers to the CO2 content in the organic amine solution entering the absorption tower. The mixed gas consists of nitrogen and CO2.

[0038] The packed tower is a DX-1000 structured packing tower with a diameter of 0.026m and a packing height of 0.97m.

[0039] A method for predicting the mass transfer rate control step of CO2 absorption by an organic amine solution in a packed tower, comprising the following steps:

[0040] S1. Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G1 and C1, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0041] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G2 and C1, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0042] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G3 and C1, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0043] ...;

[0044] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G5 and C1, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0045] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G6 and C1, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0046] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G3 and C1, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0047] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G3 and C2, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0048] ...;

[0049] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G3 and C4, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0050] Obtain the gas phase mass transfer coefficient and liquid phase mass transfer coefficient under conditions G3 and C5, compare the magnitudes of the gas phase mass transfer coefficient and liquid phase mass transfer coefficient, and determine the mass transfer rate control step.

[0051] ...;

[0052] Establish a database of the correspondence between feed flow rate, organic amine concentration and mass transfer rate control steps, as detailed in Table 1;

[0053] Where n is a positive integer not less than 3, and m is a positive integer; G n C is the feed flow rate of the mixed gas; m G1, G2, ..., G6 represent the concentrations of organic amines in the organic amine solution. n-1 G n Increasing sequentially, C1, C2, ..., C m-1 C m Increase sequentially.

[0054] Specifically, the gas-phase mass transfer coefficient k is obtained through calculation. G The calculation formula is:

[0055]

[0056] The liquid phase mass transfer coefficient, k, is obtained through calculation. g The formula for calculating ' is: Where G is the feed velocity of the mixed gas, and D G Let A be the diffusion coefficient of the gas mixture in the gas film. T The total specific surface area of ​​the packing material is μ. G The viscosity of the gas mixture is 0.0625 kg / (m·h), ρG The density of the gas mixture is 1.358 kg / m³. 3 ), d p R is the nominal diameter of the packing (0.026 m), and R is the gas constant (8.314 kPa·m). 3 / kmol·K), where T is the feed temperature of the organic amine solution (303.15K). K is the liquid-phase diffusion coefficient of CO2, and k2 is the kinetic constant (13600m). 3 / s kmol), C sol bulk This represents the concentration of the organic amine solution in the liquid phase. is the Henry coefficient.

[0057] Table 1. Database of correspondences between feed flow rate, organic amine concentration, and mass transfer rate control steps.

[0058]

[0059]

[0060] S2. The feed velocity of the mixed gas under the predicted operating condition is 23000 kg / m³. 2 The concentration of the organic amine is 5 mol / L. Comparing this to the database in Table 1, it can be directly predicted that the mass transfer rate control step for CO2 absorption by the organic amine solution under this predicted operating condition is liquid film control. In this case, during production, the feed rate of the mixed gas can be further increased to enhance the mass transfer process.

[0061] Example 2

[0062] Repeat Example 1, except that the solution used is an organic amine solution, which is an LDEEA / LHMDA solution.

[0063] The database of the correspondence between the feed flow rate, the concentration of organic amines and the mass transfer rate control steps is shown in Table 2.

[0064] Table 2 LDEEA / LHMDA Feed Rate and Mass Transfer Rate Control Procedures Database

[0065]

[0066] The feed velocity of the mixed gas under the predicted operating condition is 23000 kg / m³. 2 The organic amine concentration was 3 mol / L. Comparing this to the database in Table 2, it can be directly predicted that the mass transfer rate control step for CO2 absorption by the organic amine solution under this predicted operating condition is gas film control. Therefore, in production, the concentration of the organic amine can be further increased to enhance the mass transfer process.

[0067] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for predicting the mass transfer rate control step of CO2 absorption by an organic amine solution in a packed tower, characterized in that, Includes the following steps: S1, Get G1, C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. Get G2, C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. Get G3, C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. ……； Get G n-1 C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. Get G n C N Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. Get G H C M Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. Get G H C M+1 Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. ……； Get G H C m-1 Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. Get G H C m Under the given conditions, determine the gas-phase mass transfer coefficient and liquid-phase mass transfer coefficient, and then use these factors to determine the mass transfer rate control steps. ……； Establish a database of the correspondence between feed flow rate, organic amine concentration, and mass transfer rate control steps; Where n is a positive integer not less than 3, N, H, M, and m are positive integers, 1 ≤ H ≤ n, 1 ≤ N ≤ m, and 1 ≤ M ≤ m; G n C is the feed flow rate of the mixed gas; m G1, G2, ..., G6 represent the concentrations of organic amines in the organic amine solution. n-1 G n Increasing sequentially, C M C M+1 ... C m-1 C m Increase sequentially; S2. Obtain the feed flow rate and organic amine concentration under the predicted operating condition, compare them with the database, and obtain the mass transfer rate control step for the organic amine solution absorbing CO2 under the predicted operating condition. In S1, the gas phase mass transfer coefficient k is obtained through calculation. G The calculation formula is: The liquid phase mass transfer coefficient, k, is obtained through calculation. L The calculation formula is: Where G is the feed velocity of the mixed gas, and D G Let A be the diffusion coefficient of the gas mixture in the gas film. T The total specific surface area of ​​the packing material is μ. G ρ is the viscosity of the gas mixture. G Let d be the density of the gas mixture. p Where is the nominal diameter of the packing material, R is the gas constant, and T is the feed temperature of the organic amine solution. K is the liquid-phase diffusion coefficient of CO2, and k2 is the kinetic constant. The concentration of the liquid solution. The Henry coefficient; In S1, when the gas phase mass transfer coefficient is greater than the liquid phase mass transfer coefficient, the mass transfer rate control step is liquid film control; when the gas phase mass transfer coefficient is less than the liquid phase mass transfer coefficient, the mass transfer rate control step is gas film control. The organic amine solution is an aqueous solution of one or more of LDEEA, LHMDA, and MEA.

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