Double Film Theory Research Articles

Numerical analysis of SO2 removal characteristics in industrial flue gas desulfurization reactor by spray drying adsorption

The flue gas desulfurization reactor by spray drying adsorption plays a crucial role in the process of gas purification. This study employed the multi-phase particle-in-cell method to accurately model the three-dimensional motion of particles of different sizes in the flue gas desulfurization reactor. The double-film theory was utilized to simulate the heat and mass transfer processes of desulfurization slurry droplets. Additionally, this study conducted a comprehensive analysis of various factors affecting gas-solid flow and mass transfer processes, including flue gas inlet velocity and temperature, Ca/S molar ratio, slurry particle size, and slurry temperature. The results demonstrate that the simulated and experimental results are in good agreement, validating the reliability of the developed model. The axial mass fluxes of gas and particles exhibit contrasting distributions in the central part and near the wall, with the turbulent viscosity being particularly pronounced in the top nozzle region. The inlet velocity of flue gas has a limited effect on the axial mass flux of particles, whereas the Ca/S molar ratio exerts a more significant influence. Furthermore, the Ca/S molar ratio has a substantial impact on the spatial distribution of flue gas temperature. The inlet velocity of flue gas and slurry particle size are negatively and positively correlated with particle residence time, respectively. Based on the mass transfer characteristics, the reactor interior can be divided into three zones: a high-efficiency desulfurization zone, a low-efficiency desulfurization zone, and a partial desulfurization zone. For the investigated operating conditions, the desulfurization efficiency is most strongly influenced by the slurry particle size, followed by the flue gas inlet velocity, Ca/S molar ratio, flue gas inlet temperature, and slurry temperature.

Design on CO2 capture based on adsorption-absorption integration and energy storage for energy supply buildings with fixed carbon emission

ABSTRACT A novel design for the energy storage by adsorption-absorption for the partial CO2 capture of the energy supply buildings with fixed CO2 emission is proposed. The new design successfully utilizes the attainment of the low energy consumption and implements energy storage through adsorption part, overcoming the deficiencies of poor selectivity through absorption part. Numerical approaches have been developed for modeling the adsorption-absorption procedure, while attaining satisfactory agreement with experimental data. The adsorption process is modeled based on the finite volume method, and the absorption process is simulated based on the double-film theory and the rate-based model. The issue of operating parameters upon system assessments has received considerable critical attention by numerical implementations. The results show that the mass fraction of CO2 in the flue gas has been increased to 39.0%. The comprehensive enhancement effects are instrumental at a height of 20 m in the absorption tower. As the CO2 concentration of the flue gas increases from 5.0% to 20.0%, the absorbent flow, absorber diameter, and reboiler specific load decrease by 13.0%, 42.1%, and 16.6%, in respective. The present analysis and design will provide guidance and gain fresh prominence with advantages in the CO2 capture and purification.

Thermofluidic characteristics for a novel complementary adsorption-absorption post-combustion partial CO2 capture system

A novel complementary adsorption-absorption post-combustion partial CO2 capture strategy was proposed to decrease the energy penalty by integrating the rotary adsorption wheel with traditional chemical absorption process. The finite volume method is used for modeling the adsorption process, and the absorption process is simulated based on the rate-based model and the double-film theory. The techno-economic analyses of the novel complementary system were performed. In the adsorption part, the CO2 concentration of the flue gas can be effectively improved from 5.0%, 10.0% and 15.0% as much as to 17.3%, 27.0% and 33.7%, respectively. By adjusting the flue gas ducts of the adsorption wheel, the flue gas can be concentrated to a CO2 concentration making the absorption process work economically. The performance of the rotary adsorption wheel influenced by different geometrical and operational parameters were investigated. The energy penalty of the chemical absorption part can be significantly decreased. The major equipment cost was dramatically decreased by 48.6%, and the levelized cost of CO2 capture was decreased by 32.3%, when the CO2 concentration in the flue gas was increased from 5% to 20%. In addition, the acceptable investment of the rotary adsorption wheel has been estimated. The smallest acceptable capital cost of rotary adsorption wheel for coal-fired boiler corresponding to one payback year is 3.72 M$.

Role of 1-methylimidazole in regulating the CO2 capture performance of triethylenetetramine-based biphasic solvents

Biphasic solvents are promising candidates for CO2 capture for low regeneration energy consumption. In this study, a novel phase splitter 1-methylimidazole (1-MI) was proposed for triethylenetetramine (TETA) aqueous solvent. 1-MI was proved to act as a phase splitter to induce the phase separation and as an absorption promoter to enhance the absorption rate. By tuning the concentrations of TETA and 1-MI, good phase separation performance was obtained in TETA-1-MI biphasic solvent, achieving a CO2-rich phase loading of 5.41 mol/L. 13C NMR revealed that the upper layer was the CO2-lean phase, containing 1-MI and a small amount of water, while the lower layer was the CO2-rich phase and mainly comprised of TETAH+ and TETA-carbamate. The kinetics results based on the double-film theory indicated that the CO2 absorption rate was mainly controlled by the gas film mass transfer resistance at lower CO2 loading and then by liquid film mass transfer resistance when CO2 loading was higher than 1 mol/L. Owing to the good phase separation behavior triggered by 1-MI, the regeneration heat of TETA-1-MI was 2.26 GJ/t CO2, which was comparable to that of the second-generation solvents, and 43.5 % lower than that of 5 M monoethanolamine (MEA). The present findings indicated that TETA-1-MI had a large loading capacity, high absorption rate, and low energy consumption, which can serve as a novel candidate for CO2 capture.

Efficient Synthesis of α-FeOOH from Pickling Wastewater in Falling Film Tower and Its Kinetics.

An efficient way to synthesize α-FeOOH from pickling wastewater in a falling film tower was proposed for the first time. This method overcomes the shortcomings of the traditional air oxidation method, and its production efficiency is increased by 16 times. The purity of α-FeOOH synthesized from pickling wastewater can reach 96.3%, and the iron recovery rate is greater than 90%. At the same time, we have systematically studied its kinetics in the falling film tower. The reaction rate constant k at different temperatures was also determined with the activation energy Ea = 32.2497 kJ/mol and the pre-exponential A = 47.4132 s–1. In addition, based on the double-film theory, a corresponding macrokinetic model was established. Also, the Hatta number in the reaction system was obtained, which proved the excellent gas–liquid mass transfer performance in the falling film tower. This work provides a promising method for the efficient production of α-FeOOH and the recycling of pickling wastewater.

Analysis of Henry’s law and a unified lattice Boltzmann equation for conjugate mass transfer problem

The most challenging problem for simulating conjugate mass transfer problem is the variable concentration jump described by the double film theory at the phase interface. In the present paper, the physical mechanism of Henry’s law is analyzed, and it is found that Henry’s law can be expressed as a relation between two constant weight coefficients in lattice Boltzmann method (LBM). As a consequence, a unified multi-relaxation-time (MRT) lattice Boltzmann equation (LBE) for conjugate mass transfer is proposed. The asymptotic analysis proves that the interface conditions, including the concentration jump determined by the double film theory and mass flux continuity, can be ensured with second-order accuracy. Five test cases containing both transient and steady conjugate mass transfer problems with straight or curved interfaces are calculated to validate the present method. The results show that the proposed MRT LBE has both simplicity and good accuracy. It is capable of simulating conjugate mass transfer at both steady and transient periods, with a stationary or moving interface. Especially, it has a good numerical stability at large distribution coefficient and diffusivity coefficient ratio.

Development of Kinetic Model for Reactions Between Cu-Containing Multicomponent Slag and Liquid Sulfide Using Coupled Reaction Model

Copper smelting slag contains less than 2 mass pct of Cu oxide and 30–50 mass pct of FexO. Each year, the grade of copper ore decreases, while the amount of slag generated in the copper smelting process increases. In this study, a coupled reaction model to simulate the reaction between multicomponent slag and FeS-based matte was developed using reported thermodynamic data and double-film theory for the recycling of copper smelting slag. The activity coefficients of oxides in the multicomponent slag were calculated using a regular solution. The activity coefficients of Cu2O in the slag and those of FeS, Cu2S, and CaS in the FeS-based matte used previously reported data. The behaviors of Cu in slag and matte were confirmed by comparing the simulated results and the reported solubility of Cu in the slag in the temperatures ranging from 1473 K to 1573 K. In addition, the effect of the input amount of FeS on the copper content of the slag was verified by comparing the results of reaction model to experimental results. Using the reaction model, the influences of the initial ratio of FeO/SiO2 of the slag, temperature, and matte composition on the behaviors of Cu in the slag and matte were investigated.

Building and Verifying a Model for Mass Transfer and Reaction Kinetics of the Bunsen Reaction in the Iodine–Sulfur Process

The iodine–sulfur (IS) process is one of the most promising thermochemical water-splitting processes for nuclear hydrogen production. The Bunsen reaction, which produces sulfuric and hydriodic acids for two decomposition reactions, plays a crucial role in the IS process. Insufficient kinetics data and models of the Bunsen reaction have caused difficulties for designing a Bunsen reactor and optimizing and improving the efficiency of the process. The mass transfer and kinetics mechanism of the Bunsen reaction, which is a complicated gas–liquid slurry process, were first analyzed and proposed on the basis of double-film theory and thermodynamics calculation, and intrinsic reaction rate equation models were deduced with different hypothesized reaction mechanisms. Then, the models were further improved, and the experimental kinetics data were used to verify the models. Finally, a set of reaction rate equations was developed, thereby confirming its reliability for calculating the reaction kinetics data. The bui...

Mass transfer in ammonia-based CO2 absorption in bubbling reactor under static magnetic field

Using double film theory, the mass transfer in the absorption process in ammonia-based CO2 capture under a static magnetic field was investigated in a bubbling reactor. The effect of the gas flow rate, CO2 inlet concentration, ammonia concentration, and reaction temperature on the interfacial area and mass transfer coefficients were investigated. Under a static magnetic field, the volumetric mass transfer coefficient of CO2 absorption for an ammonia concentration of 10 wt% reached 18.7 × 105 mol/(m3 s Pa), which was 15.3% higher than that achieved without the magnetic field. By introducing the magnetic field, the estimated interfacial area per unit volume increased from 177.44 to 199.2 m2/m3 and the CO2 absorption process was promoted. In addition, the overall volumetric mass transfer coefficient and estimated interfacial area per unit volume were improved.

Experimental research of ammonia escape in CO2 absorption using ammonia solution in wetted-wall column

Ammonia solution has many advantages to be used for CO2 capture, while ammonia escape is a serious problem of this technology. Ammonia escape leads to absorbent loss and secondary pollution. At present, there were few relevant researches on ammonia escape coefficient. The mass transfer coefficient of ammonia escape in absorption was studied theoretically based on double film theory. The relationship between mass transfer coefficient and other variables in the absorption process is analyzed through experiments, mass transfer coefficient of ammonia escape was strongly influenced by temperature, CO2 partial pressure, gas flow rate, and L/G. Compared with previous researches, mass transfer coefficients under different conditions were obtained in this study. In the experiments, max value of mass transfer coefficient reached 0.00071mol/(kPa×m2×s). This research result has a certain reference value for solving the problem of ammonia escape in CO2 capture using ammonia solution, as well as the development of this technology.

A Kinetic Model to Simulate the Reaction Between Slag and Matte for the Production of Ferromanganese Alloy from Steelmaking Slag

Manganese is used as a key alloying element in various advanced steel products to improve their mechanical properties. The authors have proposed an innovative process to recycle Mn from steelmaking slag. In this process, steelmaking slag is first sulfurized to separate P and Mn, and then the matte is oxidized to increase the Mn/Fe ratio. The equilibrium distribution ratio of Mn, Fe, and Ca between slag and matte has been already clarified. To design an industrial process, a kinetic model to simulate the various reactions that occur simultaneously between the matte and slag was developed by applying the coupled reaction model. In this kinetic model, the mass transfer was calculated by the double film theory by assuming the equilibrium at the interface. The calculation results agreed well with the concentration changes of each element in the matte and slag obtained by experiments. The optimum conditions for the treatment were discussed using this model, and multi-step sulfurization and oxidation processes were proposed.

Effect of Concentration of CO<sub>3</sub><sup>2–</sup> on Nucleation of CaCO<sub>3</sub> in the Reaction System which Industrial Solid Waste Phosphogypsum Mineralize Flue Gas

In the system of CaSO₄·2H₂O-NH₃-CO₂-H₂O which flue gas CO₂ is mineralized by solid waste phosphogypsum, the formation of CaCO₃ through heterogeneous nucleation would decrease the reaction speed by raping around the surface of phosphogypsum. One improvement is to keep the homogeneous nucleation of CaCO₃ in liquid phase by controlling the concentration of CO₃^2–. In this study, initial specific molar concentration of <italic>C</italic>r(the concentration of CO₃^2– versus the solubility of CaSO₄·2H₂O) was designed as characteristic variable to study the nucleation of CaCO₃ under fixed adding of CaSO₄·2H₂O whiskers and excessive amount of CO₃^2–. The results showed that: when <italic>C</italic>_r<italic>&lt;</italic>8, formation of CaCO₃ were mainly through homogenous nucleation; while <italic>C</italic>_r&gt;20, formation of CaCO₃ were mainly through heterogeneous nucleation. The nucleation could be theoretically explained by the reaction plane model based on the double film theory, in which the CaCO₃ particles were supposed only precipitated at a reaction plane in the diffusion layer. The relative distance between the reaction plane and the surface of CaSO₄·2H₂O was defined as <italic>φ</italic>, decreased as the increase of <italic>C</italic>_r and have a critical distance (<italic>φ</italic>₀). When <italic>C</italic>_r&lt;8,then <italic>φ</italic>&gt;<italic>φ</italic>₀, formation of CaCO₃ is homogenous nucleation in liquid phase; while <italic>C</italic>_r&gt;20, then <italic>φ</italic>&lt;<italic>φ</italic>₀, CaCO₃ particles formed on the surface of CaSO₄·2H₂O through heterogeneous nucleation. The results of this work contributed to the design of mineralization of CO₂ with phosphogypsum.

Recovery of silica from sodium silicate solution of calcined boron mud

The effect of several parameters on the recovery of silicon dioxide from calcined boron mud (CBM) such as stirring speed, temperature, sodium silicate concentration, and carbonation time was studied. The recovery of silicon dioxide is 88 % when the stirring speed is 450 r·min−1, temperature is 60 °C, sodium silicate concentration is 1 mol·L−1, and the carbonation time is 6 h. The effect of carbonation time on the recovery of silicon dioxide is divided into three kinetic regimes, and the carbonation process of sodium silicate solution follows a second-order reaction based on the double-film theory model. The apparent rate constant of the three kinetic regimes is 0.064, 3.178, and 1.130 L·h·mol−1, respectively. The amorphous SiO2 products obtained by carbonating the purified solution have 99.6 % purity and are spherical with diameters of about 100 nm.

Mass transfer of ammonia escape and CO2 absorption in CO2 capture using ammonia solution in bubbling reactor

The mass transfer of CO2 capture using ammonia solution in the bubbling reactor was studied; according to double film theory, the mass transfer coefficient models and interface area model were built. Through our experiments, the overall volumetric mass transfer coefficients were obtained, while the interface areas in unit volume were estimated. The volumetric mass transfer coefficients of ammonia escaping during the experiment were 1.39×10−5–4.34×10−5mol/(m3sPa), and the volumetric mass transfer coefficients of CO2 absorption were 2.86×10−5–17.9×10−5mol/(m3sPa). The estimated interface area of unit volume in the bubbling reactor ranged from 75.19 to 256.41m2/m3, making the bubbling reactor a viable choice to obtain higher mass transfer performance than the packed tower or spraying tower.

A Study on Gas–Liquid Film Thicknesses and Heat Transfer Characteristics of Vapor–Gas Condensation Outside a Horizontal Tube

Noncondensable gases deteriorate heat transfer in the condensation process. It is therefore necessary to study vapor–gas condensation heat transfer process and analyze main factors influencing the process. Based on the double-film theory and the Prandtl boundary layer theory, this investigation developed a mathematical model of gas–liquid film thicknesses and local heat transfer coefficient for studying laminar film condensation in the presence of noncondensable gas over a horizontal tube. Induced velocity in the gas film, gas–liquid interfacial shear stress, and pressure gradient were considered in the study. Importantly, gas–liquid film separations were analyzed in depth in this paper. It obtained the distributions of gas–liquid film thicknesses, local heat transfer coefficient, condensate mass flux, and gas–liquid interfacial temperature along the tube surface, and analyzed the influences of bulk velocity, total pressure, bulk mass concentration of noncondensable gas and wall temperature on them, providing a theoretical guidance for understanding and enhancing vapor–gas condensation heat transfer. Gas film thickness and gas–liquid film separations have certain effects on vapor–gas condensation heat transfer. The average dimensionless heat transfer coefficients are in agreement with the data from related literatures.

Studies on magnesium-based wet flue gas desulfurization process with oxidation inhibition of the byproduct

This paper presents a novel magnesium-based wet flue gas desulfurization (FGD) process in which sodium thiosulfate is used to inhibit the oxidation of desulfurization byproduct. Effects of different operating variables in FGD process were experimentally researched in a spray scrubber. The results showed that the magnesium-based wet FGD process was more suitable for low SO2 concentration flue gas and indicated that the adding of Na2S2O3 could slightly enhance the desulfurization process and the MgSO3 content in the byproduct could be maintained above 95% when the thiosulfate-sulfite ratio was controlled above 1:6. A desulfurization process model was established by the double-film theory of mass transfer. The calculated mass transfer coefficients were in reasonable agreement with the experimental values and the absorption process was found to be controlled by gas-film diffusion.

Modeling of ammonia-based wet flue gas desulfurization in the spray scrubber

A mathematical model of ammonia-based wet flue gas desulfurization process was developed based on the double film theory. The calculated results of the desulfurization system for two 220 t·h−1 boilers per unit by this model were compared to that of corresponding measured data. It was found that the calculated results agree well with the measured data for the operating conditions of pH, liquid/gas ratio and SO2 concentration. This model can provide predictions of the absorption performance of an ammonia-based wet flue gas desulfurization process and appears to be helpful for designing scrubbers for SO2 absorption with ammonia absorbent.

A Nonequilibrium Stage Model To Simulate the Chemical Absorption of SO2

A nonequilibrium stage model was developed to simulate chemical absorption of SO2 in flue gas by sodium phosphate solution and ethylenediamine/phosphoric acid solution. The predicted values fit well with the experimental results. Using this model and the double-film theory, the accurate phase equilibrium constant in the nonequilibrium stage model was obtained. The absorption process of SO2 in the simulating of flue gas was predicted for different ratios of liquid flux to vapor flux (L/V) and absorber concentrations in a laboratory packed tower (0.03 m in diameter, and 0.6 m in packed section height,) using sodium phosphate buffer solution and ethylenediamine/phosphoric buffer solution. The relative error of SO2 concentration in exhaust gas between predicted and experimental results is <30%. When the SO2 concentration axial profile in liquid phase was predicted using the above nonequilibrium model, the relative error was <15%. The model can be used for the process design, optimization, and popularization.

Modeling the Absorption of Acidic Gases by Alkanolamine Solutions Incorporating Several Reactions

A general model, based on double film theory, is developed to study absorption with chemical reactions. In the liquid film region, the model is a set of differential equations that describe the mass transfer accompanying several chemical reactions; the resolution of the system is achieved by the finite difference method using an implicit scheme combined with Newton's method. Continuity equations and equilibrium coefficients are exploited in the treatment of the bulk region, which is based on the Newton-Raphson method; the results are used directly as boundary conditions in the liquid film equations. Maxwell-Stefan equations have been used as a rigorous approach in this model.

Numerical simulation of air-cooling tower

A mathematic model for packed air-cooling tower thermodynamic calculation is set up in this paper on the basis of fundamental heat and mass transfer equations. Based on the Double Film theory, direct equation-solving method is used to simulate air-cooling tower, and variation of parameters is taken to analyze the data and results of the program.