SELECTIVE GAS ABSORPTION UNDER PRESSURE

For selective removal of H2S from much larger quantities of CO₂ under pressure, an industrial prototype spray column has been constructed. Sodium hydroxide solution was atomized by a pressure nozzle of special design and entered the scrubber as fine spray to contact the sour gases.

Several operating variables were examined in order to indicate optimal operating conditions for maximum selectivity of H₂S over CO₂. Fine mist and short contact time favor this selective absorption process. An optimum inlet reactant concentration was found dependent upon the H₂S content relative to CO₂ in the inlet sour gas mixture. A special nozzle/shield configuration to avoid contact of sour gas with highly turbulent liquid during droplet formation significantly improved the selectivity.     

ABSORPTION OF CARBON DIOXIDE WITH A FREELY FALLING AQUEOUS SODIUM HYDROXIDE SOLUTION DROP

Measurements for the rates of absorption of carbon dioxide from carbon dioxide-air mixtures with a water and an aqueous sodium hydroxide solution drop falling freely were made for Fourier number Fo = 1.53 · 10^-5 — 9.83 × 10^-5, initial concentration of aqueous sodium hydroxide solution C_BO — 0.05 — 0,4 mol/1 and feed gas concentration of carbon dioxide y = 0.05 — 1.0. Observed dimensionless rates of absorption were compared with the theoretical values by the present model and gave a good agreement with theory. The effect of drop diameter on the enhancement factor, which is a measure of the effect of chemical reaction on the rates of absorption of carbon dioxide with a freely falling alkaline solution drop, were also discussed by using numerical simulation     

SIMULTANEOUS ABSORPTION OF H2S AND CO2 INTO A SOLUTION OF SODIUM CARBONATE

The simultaneous absorption of H₂S and CO₂ has been studied both experimentally and theoretically. A model has been developed which predicts the absorption rates of H₂S and CO₂ into a sodium carbonate solution. The absorption rates are calculated according to the two-film theory. In the liquid film, the finite rate of the CO₂ reaction was considered. Otherwise, in the liquid film as well as in the liquid bulk, equilibrium conditions for all reactions were assumed. Absorption experiments were performed on a packed column using a counter-flow strategy. In the experiments the influence of the initial carbonate concentration, the gas flow rate and the temperature on the removal efficiencies of H₂S and CO₂ and the selectivity of H₂S were investigated. It is desirable to absorb the H₂S but not the CO₂. The agreement between the absorption model and the experimental results from the absorber tower was satisfactory. The mass transfer coefficients were determined by fitting the experimental data to the model with respect to the H₂S and CO₂ content in the outgoing gas. The H₂S content was used to determine the gas side mass transfer coefficient and the CO₂ content was used to determine the liquid side mass transfer coefficient, The effective contact area of mass transfer was taken from published data. With a constant packing height, both the experiments and the model indicated that high carbonate concentration benefits the removal efficiency of H₂S. Higher gas flow rate also benefits the selectivity for H₂S. However, the removal efficiency will decrease. At higher temperatures the selectivity and the removal efficiency of H₂S decreased. Under the conditions investigated, the absorption of H₂S was essentially controlled by gas-side mass transfer and the absorption of CO₂ was controlled by liquid-side mass transfer     

PERTURBATION ANALYSIS OF GAS ABSORPTION WITH CHEMICAL REACTION: A NONVOLATILE LIQUID REACTANT

Enhancement factors for gas absorption in a liquid containing a nonvolatile reactant are calculated using a regular perturbation technique. The perturbation solutions are found to be quite accurate in the slow reaction regime but lead to erroneous results for moderate and large reaction rates. To extend these solutions to the intermediate and fast reaction regimes, we have used the method of Padé approximants and Shanks transformations. The results obtained by these acceleration techniques are shown to be in excellent agreement with the direct numerical solutions for the enhancement factors in the intermediate and fast reaction regimes.     

GAS ABSORPTION INTO WAVY AND TURBULENT NON-NEWTONIAN FALLING LIQUID FILMS IN A WETTED-WALL COLUMN

Average Him thickness and liquid-side mass transfer coefficient for the absorption of oxygen in wavy and turbulent power-law model falling liquid films are measured. Considerable reduction in (he film thickness with resulting increase in the mass transfer coefficient are obtained as compared to that predicted by the theoretical laminar flow equation assuming no slip at the wall.     

硫化氢吸收塔主吸收段压差高原因分析及解决措施

分析低温甲醇洗装置硫化氢吸收塔主吸收段压差高的原因,采取了无氧条件下清洗塔盘、工艺调优等处理措施,较好的解决了问题,保证了该塔在高负荷下的安全稳定运行。     

ABSORPTION OF H2S INTO AQUEOUS METHYLDIETHANOLAMINE

The absorption of H₂S into aqueous methyldiethanolamine (MDEA) was studied experimentally over the temperature range 15 to 35°C and for MDEA concentrations from 10 to 25 wt% using a laminar liquid jet device and a stirred-cell absorber. The contact times ranged from 2 × 10^-3 to 1 × 10^-2 seconds for the jet absorber and from 6 to 38 seconds for the stirred-cell absorber. It was found that the absorption rate data for both devices could be modelled assuming an instantaneous reaction regime for the reaction between H₂S and MDEA. The experimental results were interpreted to give an estimate for the diffusion coefficient of MDEA in water. Diffusion coefficient results are consistent for the two apparatuses. A lower bound for the second-order rate constant for the reaction between H₂S and MDEA is estimated from the experimental data to be 1.4 × 10¹⁰cm³/g mole s at 25°C     

碳酸钠溶液吸收H2S气体的传质性能及数学模型分析

采用Na2CO3溶液在填料塔中分别吸收高、低浓度H2S气体,通过测定总体积传质系数(KGa),采用基于Box-Behnken设计的响应面分析方法研究吸收液流量、浓度和气体流量对KGa的影响,建立了Na2CO3溶液吸收高、低浓度H2S的二次响应曲面模型. 结果表明,在高、低H2S吸收体系中,各因素对KGa的影响规律基本一致,在低浓度H2S吸收体系中对KGa的影响更大. KGa与3个因素之间不是简单的单调函数关系,吸收液流量和浓度具有较强的相互增效作用. 处理H2S浓度为2.16%(j)、气体流量为720 L/h的体系时,当吸收液浓度为0.082 mol/L、其流量为11.28 L/h时,KGa最大;处理H2S浓度为20.1%(j)、气体流量为720 L/h的体系时,吸收液浓度为0.764 mol/L、其流量为11.28 L/h时,KGa最大.     

SIMULTANEOUS ABSORPTION OF CARBON DIOXIDE AND HYDROGEN SULFIDE IN HOT CARBONATE SOLUTIONS IN A PACKED ABSORBER-STRIPPER UNIT

An experimental investigation for the simultaneous absorption of CO₂ and H₂S in 20 wt% hot K₂CO₃ solution have been conducted in a pilot scale packed absorber-stripper. The effects of liquid circulation rate, gas flow rate, inlet gas composition, steam pressure at bottom of stripper, and DEA promoter concentration, on the individual gas removal % and stripping efficiency were studied. The results showed that the performance of the absorber and stripper influenced one another and so must be considered together.     

基于NaOH溶液CO2膜吸收系统的膜结构及传质性能

碳捕集与利用技术是实现减碳目标的有效方案。膜系统气体吸收技术能够实现CO₂以\mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{-}、\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{2}-}形式存储在无机碱性吸收剂中,并还原成甲醇、乙醇等清洁燃料。本文采用膜单侧浸泡实验法和传质实验,分别考察了疏水性微孔滤膜聚四氟乙烯（PTFE）膜、聚偏氟乙烯（PVDF）膜、聚丙烯（PP）膜在NaOH碱性溶液中的结构和CO₂传质特性的变化。结果表明,PTFE膜和PP膜在NaOH碱性溶液中溶胀率上升,孔径减小,孔隙率下降,疏水性下降,传质系数下降;PVDF膜在NaOH溶液中会发生反应,结构被破坏,传质系数接近无膜吸收,但无法起到相界面的作用,不能直接用于以NaOH为吸收剂的膜吸收系统。     

Numerical simulation of the mass transfer process of CO2 absorption by different solutions in a microchannel

The flow and mass transfer characteristics of CO₂ absorption in different liquid phases in a microchannel were studied by numerical simulation. The mixture gas phase contained 5 vol% CO₂ and 95 vol% N₂ , and the different liquid phases were water, ethanol solution, 0.2 M monoethanolamine solution, and 0.2 M NaOH solution, respectively. Based on the permeation theory, the distribution of velocity and concentration in the slug flow was obtained by local simulation of flow and mass transfer coupling and was described in depth. The influence of contact time and bubble velocity on the mass transfer of the whole bubble was highlighted. The volumetric mass transfer coefficient on the bubble cap and liquid film, CO₂ absorption rate, and enhancement factor were calculated and analyzed. The results showed that the volumetric mass transfer coefficients of chemical absorption were ~3 to 10 times that of physical absorption and the CO₂ was absorbed more completely in chemical absorption. The new empirical correlations for predicting the mass transfer coefficient of the liquid phase were proposed respectively in physical absorption and chemical absorption, which were compared with the empirical formulas in the literature. The volumetric mass transfer coefficients obtained by predictive correlations are in good agreement with those obtained by simulation in this paper. This work made a basic prediction for CO₂ absorption in microchannel and provides a foundation for later experimental research.     

Hydrophobic protic ionic liquids tethered with tertiary amine group for highly efficient and selective absorption of H2S from CO2

Developing absorbents with both high absorption capacity of H₂S and large selectivity of H₂S/CO₂ is very important for natural gas sweetening process. To this end, a class of novel hydrophobic protic ionic liquids (ILs) containing free tertiary amine group as functional site for the absorption of H₂S were designed in this work. They were facilely synthesized through a simple neutralization‐metathesis methodology by utilizing diamine compounds and bis(trifluoromethylsulfonyl)imide as the building blocks for cation and anion, respectively. Impressively, the solubility of H₂S can reach 0.546 mol mol^?1 (1 bar) and 0.225 mol mol^?1 (0.1 bar), and the selectivity of H₂S/CO₂ can reach 37.2 (H₂S solubility at 1 bar vs. CO₂ solubility at 1 bar) and 15.4 (H₂S solubility at 0.1 bar vs. CO₂ solubility at 1 bar) in the hydrophobic protic ILs at 298.2 K. Comparing the hydrophobic protic ILs with other absorbents justifies their superior performance in the selective absorption of H₂S from CO₂. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4480–4490, 2016     

微通道内二乙醇胺/乙醇溶液吸收CO2的传质性能

利用高速摄像仪实验研究了微通道内二乙醇胺（DEA）/乙醇溶液吸收CO₂的传质过程。采用图像法得到微通道内气泡的体积变化,根据微通道进出口压力,计算得到了气液两相从开始接触到平衡时的平均传质系数k。分别考察了气液相流量和DEA浓度对传质系数的影响。结果表明：传质系数随着液相流量和溶液中DEA浓度增大而增大。对于给定的液相流量和DEA浓度,k随着气相流量增大而增大并逐渐趋于一个恒定值。提出了一个传质系数预测式,预测值和实验结果吻合良好。     

基于微吸收器的CO2吸收过程研究进展

微化工技术在流体流动、过程强化、传质与反应过程等领域备受关注,本文归纳整理了3种不同类型的微吸收器（微降膜吸收器、微通道吸收器和微网格吸收器）捕集CO₂过程中的水力学性质和传质过程及其机理研究进展,并对3种微吸收器吸收CO₂过程中存在的问题进行分析总结,同时对微吸收器能快速工业化提出展望。其中重点介绍了微通道泰勒流吸收器的水力学流动特性,包括泰勒流气泡的生成机制、气泡和液弹的长度、气泡的输运和运动速度、气泡截面形状及液膜厚度和气液两相流压降;归纳了微通道泰勒流吸收过程的传质过程机理和传质系数的模型以及不同影响因素（通道截面尺寸,通道长度,主通道结构及入口形状,气、液相组成及其流速,吸收剂和系统压力）作用下CO₂吸收效率和传质系数的研究进展。     

CO2吸收增强气化制备氨合成原料气的可行性

以煤和低浓度煤层气共气化制备氨合成原料气,煤层气提供合成所需的氮组分,从而取消常规制气的补氮过程或替代空气气化;采用CO2吸收增强制气,在造气工段制得φ(H2)/φ(N2)=3,φ(CO2+CO)≤0.30%,φ(H2)≥70%的粗煤气,可直接进入醇烷化或醇烃化精制岗位.为论证系统的可行性和适宜操作条件,采用热力学平衡模型分析煤气组分随制气反应条件变化的规律,提出可一步制得φ(H2)/φ(N2)=3,φ(CO2+CO)≤0.30%,φ(H2)≥70%的制气反应条件和煤层气流量;根据煤层气温度、压力与爆炸极限的关系,确定催化转化/脱氧反应器的操作参数.结果表明,以合成原料气组分衡量,基于CO2吸收增强气化的煤和低浓度煤层气制气方法可行,且有利于简化调比和气体净化过程.     

Absorption and desorption of carbon dioxide in several water types

This study investigated the effect of water type on the rate of CO₂ transfer from/to an aqueous phase with varying degree of water salinity. The absorption and desorption experiments were conducted on reverse osmosis product, brackish well, and brackish water reverse osmosis reject waters as well as seawater in a mechanically agitated tank. Results show that the direction of mass transfer has a major impact on the value of the volumetric mass transfer coefficient, k_La, with the absorption experiments always rendering higher values. Furthermore, k_La values always decreased with salinity in both absorption and desorption experiments until a certain critical salinity value was reached, beyond which mass transfer increased again. However, k_La values were found to decrease continuously with an increase in the water alkalinity in absorption experiments, while no clear conclusion could be drawn for the alkalinity effect in the case of desorption experiments. These observations suggest that the effect of alkalinity should be further investigated to elucidate its impact along with the salinity on the volumetric mass transfer rate.     

动力波洗涤器中碱液吸收低浓CO_2的传质特性

为研究动力波洗涤器内的气液传质特性,在动力波洗涤器中,进行NaOH溶液吸收混合气体中微量CO2气体的吸收实验。参考填料塔中钠碱溶液吸收低浓气体的传质模型,测定了动力波洗涤器中NaOH溶液吸收低浓CO2的气相体积总传质系数KGa及吸收效率η。研究了气相速度、NaOH溶液质量分数及液气比对KGa的影响,结果表明:KGa随着气相速度及NaOH溶液质量分数的增加而增大,但NaOH溶液质量分数小于气相速度对KGa的影响;随着液气比的提高,KGa逐渐减小,η开始随着液气比的提高而增加,但到一定数值后,效果不明显;回归了KGa的准数关联式,并依据液气比对KGa及η的综合评价,提出洗涤管直径为100 mm,NaOH溶液质量分数为10%,液气比操作范围在0.005—0.025时,动力波洗涤器具有较高的综合传质性能,为工业应用提供参考。     

磷石膏强化氨法CO2捕集机理与模型

基于化学活性颗粒强化气液吸收机理,建立了磷石膏悬浮液强化氨法烟气CO₂捕集模型。以液膜内量纲一传质距离λ^*为特征参数,增强因子E=1/λ^*+qβλ^*/2。用恒温反应器在不同搅拌转速及磷石膏颗粒固含量下实验测定CO₂吸收增强因子对模型进行检验,结果表明:随颗粒固含量由5%增加到30%(质量分数),增强因子由1.69增加到2.10;而随搅拌转速从150 r·min^-1增加到300 r·min^-1,增强因子仅由1.75略增到1.80,表明磷石膏颗粒固含量及溶解速率是影响增强因子的控制性因素。实验结果与模型预测值吻合良好, 偏差小于10%。     

Kinetics of the absorption of carbon dioxide into aqueous ammonia solutions

Experiments were performed in a customized double stirred tank reactor to study the kinetics of CO₂ absorption into NH₃ solutions at concentrations ranging from 0.42 to 7.67 kmol·m^?3 and temperatures between 273.15 and 293.15 K. The results show that the reactive absorption was first order with respect to CO₂ but fractional order (1.6–1.8) with respect to ammonia. Experimental data can be satisfactorily interpreted by a termolecular mechanism using and . © 2016 American Institute of Chemical Engineers AIChE J, 62: 3673–3684, 2016     

Spatial Scale Effects on Rayleigh Convection and Interfacial Mass Transfer Characteristics in CO2 Absorption

Concentration gradient‐induced Rayleigh convections in the CO₂ absorption process were investigated by the hybrid Lattice‐Boltzmann/finite‐difference method (LBM‐FDM). The spatial scale effects on Rayleigh convection were studied by simulating Rayleigh convections with different liquid layers. The scale of convection increased with the liquid layer height but the average mass transfer coefficient showed the adverse tendency. The Rayleigh convection had a pronounced effect on the surface renewal. For better assessment of the renewal intensity, two statistical quantities were proposed. The transient variations of these quantities provided a good following feature with the mass transfer coefficient which confirms their accuracy and precision in characterizing the mass transfer process.