Method for predicting decarbonization efficiency of alcohol amine absorption liquid in packed tower

Abstract

The invention discloses a method for predicting the decarbonization efficiency of an alcohol amine absorption liquid in a packed tower, which comprises the following steps: firstly, calculating the concentration of a CO2 outlet at the top of the packed tower through an established prediction model, and then further obtaining the decarbonization efficiency of the alcohol amine solution according to the concentration of a CO2 inlet at the bottom of the packed tower. The scientific and effective prediction model is established for the decarburization efficiency of the alcohol amine absorption liquid in the packed tower, and the decarburization efficiency of the alcohol amine absorption liquid can be accurately predicted only by determining the empirical parameters corresponding to the alcohol amine solution through limited experimental data based on the model. Therefore, process parameters are optimized, so that the performance of the absorbent is optimal, and reliable technical support is provided for theoretical perfection and industrial development of the alcohol amine absorption liquid.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon dioxide capture, and in particular relates to a method for predicting the decarbonization efficiency of an alcohol amine absorption liquid in a packed tower. Background Art

[0002] The large-scale combustion of fossil fuels will lead to the release of a large amount of carbon dioxide, and the greenhouse effect is becoming increasingly severe. Therefore, how to efficiently capture carbon dioxide has become the most hotly debated issue at present. Among the methods of capturing carbon dioxide, the chemical absorption method using chemical solutions as absorbents is currently the most advantageous method. Chemical solutions have outstanding advantages such as fast absorption rate, large absorption capacity, and low economic cost, and have therefore attracted extensive research. Chemical absorbents are the core of the entire capture process, and their decarbonization efficiency plays a vital role in improving the carbon dioxide capture rate and reducing the operating process costs.

[0003] The mass transfer performance of carbon dioxide absorption by chemical solvents is the most important parameter for examining absorbents, and the removal rate of carbon dioxide in the packed tower is the most direct indicator for measuring mass transfer performance. It directly determines whether the decarbonization task meets the requirements and is the most important parameter for designing process parameters such as the tower height and diameter of the packed tower. Therefore, establishing a prediction model for the removal rate of carbon dioxide in a packed tower is conducive to optimizing design investment and reducing operating costs, which has important practical significance for industrial applications. Summary of the invention

[0004] Purpose of the invention: In view of the lack of research on the mass transfer performance of chemical solutions in packed towers, the present invention provides a method for predicting the decarbonization efficiency of alcohol amine absorption liquid in a packed tower, which is conducive to the optimization of packed tower process design and carbon dioxide capture process flow, and provides reliable technical support for the theoretical improvement and industrial development of alcohol amine absorption liquid.

[0005] Invention content: To achieve the above-mentioned purpose, the present invention provides a method for predicting the decarbonization efficiency of an alcohol amine absorption liquid in a packed tower. In the packed tower, an alcohol amine solution is used to absorb CO2, wherein the alcohol amine solution flows from the top of the tower to the bottom of the tower, and the CO2-containing gas flows from the bottom of the tower to the top of the tower. The CO2 outlet concentration at the top of the packed tower is calculated by the following formula:

[0006]

[0007] Among them, y out represents the CO2 outlet concentration at the top of the packed tower, y in represents the CO2 inlet concentration at the bottom of the packed tower, P represents the total pressure, Vr represents the volume of the packed tower, G represents the gas flow rate, L represents the flow rate of the alcoholamine solution in the packed tower, and P CO2 Indicates the partial pressure of CO2, α eqand α represent the equilibrium solubility and CO2 load of the alcoholamine solution under the CO2 partial pressure, respectively, C represents the concentration of the alcoholamine solution, T is the feed temperature of the alcoholamine solution, and a, b, m, and n are empirical constants corresponding to the alcoholamine solution;

[0008] The decarbonization efficiency of the alcohol amine solution is then obtained as follows:

[0009]

[0010] Specifically, the alcohol amine solution is DMEA / MAE / TGME / H2O, and its corresponding empirical constants include: a=0.6, b=185.9, m=-1260, n=2.45.

[0011] Beneficial effect: The present invention establishes a scientific and effective prediction model for the decarbonization efficiency of the alcoholamine absorption liquid in the packed tower. Based on the model, only limited experimental data are needed to determine the empirical parameters corresponding to the predicted alcoholamine solution, so that the decarbonization efficiency of the alcoholamine absorption liquid can be accurately predicted, thereby optimizing the process parameters to optimize the absorbent performance, providing reliable technical support for the theoretical improvement and industrial development of the alcoholamine absorption liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of absorption and mass transfer experiment in an embodiment of the present invention;

[0013] Figure 2 Graph showing the relationship between the CO2 outlet concentration and the total mass transfer coefficient of the packed tower in an embodiment of the present invention;

[0014] Figure 3 : is a graph showing the relationship between the feed temperature of the alcohol amine solution and the decarbonization efficiency in an embodiment of the present invention;

[0015] Figure 4 This is a graph showing the relationship between CO2 load and decarbonization efficiency in an embodiment of the present invention;

[0016] Figure 5 This is a comparison chart of the experimental value and the predicted value of the decarburization efficiency in the embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0018] The present invention provides a method for predicting the decarbonization efficiency of an alcohol amine absorption liquid in a packed tower. In the packed tower, an alcohol amine solution is used to absorb CO2, wherein the alcohol amine solution flows from the top of the tower to the bottom of the tower, and the CO2-containing gas flows from the bottom of the tower to the top of the tower. The absorption rate of the alcohol amine solution can be calculated according to the following formula:

[0019]

[0020] in, represents the absorption rate of the alcohol amine solution, G represents the gas flow rate, Ω represents the tower cross-sectional area, P represents the total gas pressure in the tower, and y out represents the CO2 outlet concentration at the top of the packed tower, y in represents the CO2 inlet concentration at the bottom of the packed tower, Vr represents the volume of the packed tower, is the total mass transfer coefficient of CO2 absorbed by alcohol amine solution, P CO2 Indicates the partial pressure of CO2 in the tower, and P CO2 It can be calculated as follows:

[0021]

[0022] in, represents the CO2 partial pressure at the inlet of the packed tower, represents the CO2 partial pressure at the outlet of the packed tower, which can be derived from formula (2):

[0023]

[0024] From formula (1) and (3), we can get:

[0025]

[0026] Furthermore, the absorption of carbon dioxide by alcohol amine solution is a liquid film controlled process, and the overall mass transfer coefficient (K G a v ) and enhancement factor (E), liquid phase mass transfer coefficient (K L ) has a positive correlation, among which the liquid phase mass transfer coefficient (K L ) and the power of the liquid flow rate (L a ), while the enhancement factor (E) is proportional to the effective alcohol amine solution concentration (α eq -α)C, partial pressure of carbon dioxide (P CO2 ), feed temperature (T) has the following relationship:

[0027]

[0028] That is, with (α eq -α)C and exp mT is positively correlated with P CO2The relationship between the total mass transfer coefficient and each variable can be further obtained:

[0029]

[0030] Through certain experimental analysis, the expression of the total mass transfer coefficient can be obtained:

[0031]

[0032] Among them, a, b, m, and n are all empirical constants corresponding to the alcohol amine solution, which can be obtained from formulas (4) and (7):

[0033]

[0034] The decarbonization efficiency of the alcohol amine absorption liquid in the packed tower is obtained as follows:

[0035]

[0036] For example, 2 mol N,N-dimethylethanolamine (DMEA) / 1.25 mol 2-methylaminoethanol (MAE) / triethylene glycol monobutyl ether (TGME) / H2O (mass ratio: TGME:H2O=9:9) is used as the absorption liquid. The decarbonization efficiency of the alcohol amine absorption liquid is tested under different solution feed temperatures, CO2 loads and other conditions. Then, according to the experimental data, the formula (8) is optimized and solved to obtain a=0.6, b=185.9, m=-1260, n=2.45. Therefore, the CO2 outlet concentration at the top of the packed tower is calculated by the following formula:

[0037]

[0038] The decarbonization efficiency of the absorption liquid is further obtained as follows:

[0039]

[0040] Wherein, η represents the decarburization efficiency, with the unit being 1;

[0041] y in It represents the CO2 inlet concentration at the bottom of the packed tower, with the unit of 1;

[0042] y out It indicates the CO2 outlet concentration at the top of the packed tower, with the unit of 1;

[0043] P represents the total gas pressure, in kPa;

[0044] Vr represents the volume of the packed tower, in m 3 ;

[0045] G represents the gas flow rate, the unit is kmol / (m2 h);

[0046] L represents the flow rate of the amine solution in the packed tower, in m 3 / (m 2 h);

[0047] P CO2 Indicates the partial pressure of CO2 in kPa;

[0048] α eq and α represent the equilibrium solubility and CO2 load of the solution at this CO2 partial pressure, respectively, and both have a unit of 1;

[0049] C represents the concentration of the alcoholamine solution, in mol / L;

[0050] T represents the feed temperature of the alcoholamine solution, in K.

[0051] Specifically, in this embodiment, the concentration of the alcohol amine solution is not higher than 6 mol / L, the feed temperature is not higher than 343.15K, and the flow rate is not higher than 11.7m 3 / (m 2 ·h), CO2 load does not exceed 0.7mol / mol, gas flow does not exceed 50kmol / (m 2 h).

[0052] The prediction results of the above embodiment are verified through a series of experiments.

[0053] Experiment 1: Mass transfer experiment operation steps;

[0054] Schematic diagram of absorption mass transfer experiment Figure 1 As shown, the air compressed by the air compressor flows through the air flow meter, and CO2 flows through the carbon dioxide flow meter through the carbon dioxide pressure reducing valve. The two air flows are mixed in the mixer at a predetermined flow rate to form a mixed gas with a certain carbon dioxide partial pressure. After sufficient mixing, it flows into the bottom of the tower; the alcohol amine solution is controlled by a constant flow pump at a certain flow rate, flows through a constant temperature water bath and is heated to a specified temperature before entering the top of the tower. The gas-liquid two-phase countercurrent contact is fully absorbed. After the test runs for 25 minutes, the temperature at various locations in the tower is stable, indicating that the absorption experiment has reached equilibrium. The carbon dioxide concentration and the corresponding temperature at different tower heights are recorded using a carbon dioxide analyzer. The above mass transfer experiment can obtain experimental data under different conditions, and various empirical constants can be obtained by fitting.

[0055] Experiment 2: CO2 outlet concentration of packed tower (Lny out ) and the total mass transfer coefficient (K G a v )

[0056] Using the method described in Experiment 1, the relationship between the outlet concentration of CO2 in the packed tower and the total mass transfer coefficient is as follows: Figure 2 shown. Figure 2 It shows that the CO2 outlet concentration of the packed tower is linearly related to the total mass transfer coefficient. The experimental results verify the correctness of equation (4).

[0057] Experiment 3: Effect of solution feed temperature (T) on decarburization efficiency (η);

[0058] Using the method described in Experiment 1, under the conditions of 0.1MPa total pressure, 0.2mol / mol CO2 load and 15kPa CO2 partial pressure, the feed temperature of the amine solution was changed to study the effect of the solution feed temperature (T) on the decarbonization efficiency. The experimental results are shown in Figure 3 As shown in the figure, with the increase of solution feed temperature, the CO2 outlet concentration decreases and the decarbonization efficiency increases, which indicates that the decarbonization efficiency is positively correlated with the solution feed temperature (T).

[0059] Experiment 4: Effect of CO2 loading (α) on decarbonization efficiency (η);

[0060] Using the method described in Experiment 1, under the conditions of 0.1MPa total pressure, 313.15K solution feed temperature and 15kPa CO2 partial pressure, the CO2 load of the solution was changed to study the effect of CO2 load in the solution on the decarbonization efficiency. The experimental results are shown in Figure 4 As shown in the figure, as the CO2 load increases, the decarbonization efficiency decreases, which indicates that the decarbonization efficiency is negatively correlated with the CO2 load.

[0061] Experiment 5: Comparison of experimental and predicted values ​​of decarburization efficiency (η);

[0062] The relationship between the CO2 outlet concentration simulated by the method described in Experiment 1 and the CO2 outlet concentration predicted by the above model is as follows: Figure 5 This indicates that the two are in good agreement.

[0063] In summary, different working conditions are designed, i.e., different solution feed temperatures, different CO2 loads, different solution flow rates, and different solution concentrations, etc., and the decarbonization efficiency under different conditions is tested. It is found that the experimental results are exactly as predicted by the model, thereby verifying the accuracy of the model prediction. Of course, the method provided by the present invention can be used not only to predict the decarbonization efficiency of the alcohol amine absorption liquid in the packed tower, but also to predict the decarbonization efficiency of other similar acidic gases.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting the decarbonization efficiency of an alcohol amine absorption liquid in a packed tower, characterized in that: In a packed tower, an amine solution is used to absorb CO2, wherein the amine solution flows from the top to the bottom of the tower and the CO2-containing gas flows from the bottom to the top of the tower. The CO2 outlet concentration at the top of the packed tower is calculated by the following formula: Among them, y out represents the CO2 outlet concentration at the top of the packed tower, y in represents the CO2 inlet concentration at the bottom of the packed tower, P represents the total pressure, Vr represents the volume of the packed tower, G represents the gas flow rate, L represents the flow rate of the alcoholamine solution in the packed tower, and P CO2 Indicates the partial pressure of CO2, α eq and α represent the equilibrium solubility of the alcoholamine solution and the CO2 load at the CO2 partial pressure, respectively, C represents the concentration of the alcoholamine solution, T is the feed temperature of the alcoholamine solution, and a, b, m, and n are empirical constants; The decarbonization efficiency of the alcohol amine solution is then obtained as follows:

2. The prediction method according to claim 1, characterized in that: The alcohol amine solution is DMEA / MAE / TGME / H2O, and its corresponding empirical constants include: a=0.6, b=185.9, m=-1260, and n=2.45.

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