湍球塔床层液相含率预测的数学模拟

利用搭建的湍球塔实验装置,考察了操作气速、静床高度、喷淋液量、支承网开孔率和湍球直径等参数对湍球塔床层压降和液相含率的影响特性;运用因次分析π定理和偏最小二乘法,得到了液相含率的回归模型。引入前人Gel和V-Noakovic模型,并基于文献实验数据对各模型预测效果作了对比分析。结果表明,偏最小二乘法处理小容量液相含率样本和自变量强相关问题行之有效,用液相含率新模型预测两组文献实验数据的均方百分比误差分别为2.5%和3.1%,预测的精确度优于Gel和V-Noakovic模型,且新模型适用范围更大。偏最小二乘法用于湍球塔床层液相含率预测建模切实可行。     

Analysis on a Hydrophobic Hollow-Fiber Membrane Absorber and Experimental Observations of CO2 Removal by Enhanced Absorption

Abstract

In this paper an extended analysis on a hollow-fiber membrane absorber is conducted for CO₂ removal from flue gases. A rigorous model of gas–liquid mass transfer is developed on both narrow channels in and around the hollow fibers, including the gas absorption occurring from the reaction between CO₂ and aqueous K₂CO₃ absorbent. CO₂ concentration profiles can be obtained regardless of the placement of the flowing absorbent. Experimental observations of the CO₂ concentration in both the reject and permeate outlets compared with theoretical prediction allow us to understand the influence of flow rates of feed gas as well as absorbent on CO₂ absorption. For the flowing K₂CO₃ absorbent a kinetic constant can be chosen which will provide the best possible agreement between experiment and reactive model prediction. This fact emphasizes that the pseudofirst-order kinetic can be employed to describe the facilitation effect. The overall mass transfer coefficients were determined from the experimentally observed concentration changes. The CO₂ permeation flux was found to be enhanced as the K₂CO₃ concentration was increased, suggesting that CO₂ removal is entirely controlled by the reaction. The enhanced selectivity factor for CO₂/N₂, which decreases with increasing absorbent flow rate, reached as high as 1200 with 15 wt% K₂CO₃ absorbent.     

Molecular Simulation Study for CO2 Clathrate Hydrate

The present work has concentrated on the structure of CO₂ hydrate in the NPT ensemble using SPC (simple point charge) intermolecular potential model of water by the Monte Carlo (MC) molecular simulation. A mixture of water and CO₂ placed arbitrarily in a cubic cell has been used as a model system to simulate the CO₂ clathrate hydrate at temperatures ranging from 150–280 K and pressure up to 10 MPa. The result shows that the obtained MC simulation agrees well with the results obtained by molecular dynamic (MD) simulation. The present work is also directed to the study of structure with TIP4P potential model of water.     

Modeling and Simulation of a Bubbling SO2 Absorber with Granular Limestone Slurry and an Organic Acid Additive

The absorption of SO₂ into limestone slurry containing suspended reactive particles was performed in a bubble reactor with continuous feeding of both gas and liquid phases at a constant pH and high temperature (50 °C). An absorption model with a reaction plane based on the film model was developed. The effect of limestone particle size, concentration, acetic acid additives, and inlet SO₂ concentration on the concentration distribution of chemical species in the liquid film and SO₂ absorption rate were simulated. Increasing the concentration of limestone slurry, adding acetic acid additives into the system or decreasing the limestone particle size or inlet SO₂ concentration caused the reaction plane in the liquid film to shift towards the gas‐liquid interface. Model and experimental results were compared, and it was shown that the model fits the experimental data well.     

Solubility of CO2 in Aqueous Piperazine and its Modeling using the Kent‐Eisenberg Approach

A systematic investigation of the equilibrium solubility of CO₂ in aqueous piperazine solutions was conducted in a double‐jacketed stirred cell reactor. The solubilities of CO₂ in the solution were measured at 20, 30, 40, and 50 °C with CO₂ partial pressures ranging from 0.4–95 kPa. Generally the aqueous piperazine solution exhibits the same characteristics as conventional alkanolamines. Increasing the CO₂ partial pressure increases the gas loading, however increasing the temperature or concentration decreases the CO₂ loading. The values of the CO₂ loading obtained confirm that the piperazine forms stable carbamates. The equilibrium solubility data were analyzed using a Kent‐Eisenberg approach. Representation of the model is generally in good agreement with that of the experimental data, especially at high temperature.     

Modeling and Experimental Study of CO2 Removal by Alkanolamines in a Packed Bed

Absorption of CO₂ by monoethanolamine, diethanolamine, and triethanolamine solutions in a lab–scale packed bed tower was investigated. A model for analyzing the heat and mass transfer mechanism in the presence of reaction was developed and validated using the measured data for MEA and TEA solutions and the results were compared with the others' experimental data. The well-known correlations for determining Henry's constant, as a critical parameter in the presented model, were evaluated and it was shown that the available correlations are often limited to a narrow range of operating conditions which could limit the applicability of the available models.     

CO2 Absorption into Aqueous Solutions of Monoethanolamine,Methyldiethanolamine, Piperazine and their Blends

The removal of carbon dioxide from industrial gases, e.g. in thermal power stations to meet the discharge limits for CO₂ in flue gases, is usually achieved with a reactive absorption technique using aqueous solutions of alkanolamines. From the absorption performance point of view, primary and secondary amines are preferred. However, in case the costs of the solvent regeneration are also taken into account, tertiary amines are much more attractive. In order to combine the specific advantages of tertiary and primary/secondary alkanolamines, both types of solvents are mixed. In this paper, mixtures of monoethanolamine and methyldiethanolamine with piperazine as absorption activator are experimentally compared with respect to CO₂ removal performances at 25 °C. The absorption process in a special packed column has also been simulated with the use of published data on reaction kinetics, physicochemical properties (densities, viscosities, diffusivities, Henry coefficients) of the CO₂‐amines systems, including experimentally determined hydrodynamic and mass transfer characteristics of the CO₂ scrubber.     

CO2 Absorption into Aqueous Solutions of a Polyamine (PZEA), a Sterically Hindered Amine (AMP), and their Blends

Among numerous techniques existing for reducing CO₂ emissions, CO₂ capture by absorption in aqueous alkanolamine solutions was specifically studied in this work. For the choice of the adequate amine solution, two major criteria must be taken into account: absorption performances (higher with primary and secondary amines) and energy costs for solvent regeneration (more interesting with tertiary and sterically hindered amines). The different types of amines can also be mixed in order to combine the specific advantages of each type of amines, an activation phenomenon being observed. Aqueous solutions of (piperazinyl‐1)‐2‐ethylamine (PZEA, a polyamine known as absorption activator) and 1‐amino‐2‐propanol (AMP, a sterically hindered amine), pure or mixed with other amines, are experimentally compared with respect to CO₂ removal performances by means of absorption test runs achieved in a special gas‐liquid contactor at 25 °C. The positive impact of addition of PZEA to monoethanolamine (MEA), N‐methyldiethanolamine (MDEA), and AMP solutions was clearly highlighted. The absorption performances have also been satisfactorily simulated with coherent physicochemical data.     

Performance of CO2 absorption in a diameter-varying spray tower

The application of spray towers for CO₂ capture is a development trend in recent years. However, most of the previous jobs were conducted in a cylindrical tower by using a single spray nozzle, whose configuration and performance is not good enough for industrial application. To solve this problem, the present work proposed a diameter-varying spray tower and a new spray mode of dual-nozzle opposed impinging spray to enhance the heat and mass transfer of CO₂ absorption process. Experiments were performed to investigate the mass transfer performance (in terms of the CO₂ removal rate (η) and the overall mass transfer coefficient (K_Ga_e2 are major factors, which affect the absorption performance and the maximums of η and K_Ga_e that are 94.0% and 0.574 kmol·m^-3·h^-1·kPa^-1, respectively, under the experimental conditions. Furthermore, new correlations to predict the mass transfer coefficient of the proposed spray tower are developed in various CO₂ concentrations with a Pearson Correlation Coefficient over 90%.     

现代二氧化碳吸收工艺研究

综述了现代二氧化碳吸收工艺研究进展,介绍了目前国内外现有的二氧化碳吸收方法,包括物理吸收法、膜吸收法、化学吸收法、离子液体法、电化学法和O2/CO2燃烧法,简要介绍了各种吸收方法的特点及所做研究,重点讨论了工业应用较广的化学吸收法,分析了离子液体法与其他有机溶剂比较的优缺点,并对新工艺方法进行了展望.     

湍球塔气流入口方式的CFD模拟

对湍球塔不同入口方式进行了流场的数值模拟,通过比较不同入口方式的塔内流场不均匀度,得出最佳的气流入口方案。将模拟结论应用于实际工程,测量结果与模拟结果比较吻合。     

Nonstationary Simulation Model of Absorber with Falling Film of Suspension

A nonstationary model of SO₂ absorption from a gas phase to a countercurrent falling film of absorbing slurry was developed. Laminar, wavy and turbulent film structures were considered based on published information. Resistances to the mass transfer on the gas and the liquid sides of the interphase were considered, together with chemical reactions in the liquid phase. Relevant chemical equilibria in the liquid phase were modeled. Original experimental data on the neutralization reagent dissolution rate presented as a polydispersed two‐phase system of solids and on the rate of dissolved sulfite oxidation were used. The model was verified with experimental data from a laboratory‐scale falling‐film absorber using a single vertical tube under various geometrical and operating conditions, and a very good agreement was found with the experiment. Parametric sensitivity analysis showed the critical parts of the model.     

Simulation of Post‐Combustion CO2 Capture,a Comparison among Absorption,Adsorption and Membranes

Post‐combustion CO₂ capture was studied in the favorable context where the captured CO₂ can be reused in a neighboring industrial process. Three technologies for CO₂ capture, absorption by amines, adsorption on activated carbon, and separation using polymer membranes, were considered, modeled and compared. The three capture processes were designed for achieving the same performances. The models were integrated in a commercial flowsheeting software. The results show that, for a targeted CO₂ purity of 95 %, the membrane process appears to be the least energy consuming. A next step will be to quantify the environmental benefits using life cycle assessment.     

Rapid Prediction of CO2 Solubility in Aqueous Solutions of DEA and MDEA

In the present work, a simple‐to‐use correlation is developed to predict the solubility of CO₂ in aqueous solutions of DEA and MDEA as a function of the reduced partial pressure and temperature. Using the interaction parameters generated, the model is applied to correlate the CO₂ loading in different amine solutions. The results from the proposed correlation have been compared with the reported experimental data and it was found that there is a good agreement between the observed data and the model predictions over a wide range of operating conditions in aqueous solutions of both diethanolamine (DEA) and methyldiethanolamine (MDEA).     

Experimental validation of a rate-based model for CO2 capture using an AMP solution

Detailed experimental data, including temperature profiles over the absorber, for a carbon dioxide (CO₂) absorber with structured packing in an integrated laboratory pilot plant using an aqueous 2-amino-2-methyl-1-propanol (AMP) solution are presented. The experimental gas-liquid material balance was within an average of 3.5% for the experimental conditions presented. A predictive rate-based steady-state model for CO₂ absorption into an AMP solution, using an implicit expression for the enhancement factor, has been validated against the presented pilot plant data. Furthermore, a parameter sensitivity analysis for the proposed model has been carried out.     

Mass transfer performance of structured packings in a CO2 absorption tower

This paper studies the mass transfer performance of structured packings in the absorption of CO2 from air with aqueous NaOH solution. The Eight structured packings tested are sheet metal ones with corrugations of different geometry parameters. Effective mass transfer area and overall gas phase mass transfer coefficient have been measured in an absorption column of 200 mm diameter under the conditions of gas F-factor in 0.38–1.52 Pa0.5 and aqueous NaOH solution concentration of 0.10–0.15 kmol·m?3. The effects of gas/liquid phase flow rates and packing geometry parameters are also investigated. The results show that the effective mass transfer area changes not only with packing geometry parameters and liquid load, but also with gas F-factor. A new effective mass transfer area correlation on the gas F-factor and the liquid load was proposed, which is found to fit experiment data very well.     

CO2 Absorption and Regeneration Using Amines with Different Degrees of Steric Hindrance

The influence of steric hindrance in amines upon different characteristics in carbon dioxide chemical absorption, namely, absorption rate, carbon dioxide loading, and regeneration degree, has been analyzed. Aqueous solutions of monoethanolamine, 1‐amino‐2‐propanol, and 2‐amino‐2‐methyl‐1‐propanol were used to compare their behavior during carbon dioxide absorption. The presence of one or two methyl groups on the carbon next to the amino group produced changes in the analyzed parameters. In addition, the influences of the gas‐flow rate and amine concentration on the chemical solvent behavior were studied to improve the mass transfer under different experimental conditions.     

Numerical Investigation of the Effect of Using CO2 as the Refrigerant in a Heat Pump Tumble Dryer System

CO₂ appears to be a suitable refrigerant for dryer operation conditions due to its thermophysical and environmentally friendly properties. In this study, a heat pump tumble dryer system using CO₂ as the refrigerant was theoretically investigated, and a computer model was developed using MATLAB software. The changes in the energy consumption and drying time, depending on the inlet CO₂ pressure into the gas cooler, inlet CO₂ temperature into the evaporator, air mass flow rate, and dryer efficiency, are presented. The results show that the optimum operating parameters are extremely effective in reducing the drying time and energy consumed.     

Feasibility analysis and process simulation of CO2 dehydration using triethylene glycol for CO2 pipeline transportation

The operation of dehydration is very important in the process of gas transportation. This study aims to evaluate the application feasibility of CO₂ dehydration using triethylene glycol, which is also called TEG for short. Aspen Plus software was used to simulate the dehydration process system of CO₂ gas transportation using TEG dehydration. Parameter analysis and process improvement were carried out for the simulation of dehydration process. At first, a sensitivity analysis was conducted to analyze and optimize operating conditions of conventional CO₂-TEG dehydration process system. Subsequently, a recycle unit was introduced into the conventional CO₂-TEG dehydration process system, it can be found that the improved process system with the recycle unit has a higher CO₂ recovery rate which was about 9.8% than the conventional one. Moreover, the improved process system showed excellent operation stability through the comparison of simulation results of several processes with various water contents in their feed gases. Although the energy consumption is increased by about 2%, the improved process was economically and technically feasible for the long-term availability of CO₂ pipeline transportation. The simulated results showed that the improved CO₂-TEG process system has promising application prospects in CO₂ dehydration of CO₂ gas transportation with high stability.