SO2 Absorption Research Articles

CFD MODEL TO ANALYZE SO2 ABSORPTION IN A SEAWATER DROPLET

In the recent years, seawater scrubbers have become an interesting option to reduce SO2 emissions in marine engines. In this regard, this paper proposes a numerical model to analyze SO2 absorption in seawater. A single seawater droplet was analyzed, and the developed model was used to predict the influence of several parameters on the desulphurization efficiency, such as the droplet diameter, SO2 concentration, alkalinity and temperature. It was found that a droplet of 200 μm initial diameter can absorb up to 1.77∙10-14 mol of S for the parameters analyzed, and this reduction improves when the alkalinity and SO2 concentration are increased and diameter, seawater temperature and gas temperature are reduced. Differences up to of 21.5%, 19.8%, 2.2% and 16.3% in the S reduction were obtaining varying the SO2 initial concentration, alkaline initial concentration, initial liquid temperature and initial gas temperature respectively.

Simulation investigation on marine exhaust gas SO2 absorption by seawater scrubbing

Ships have become an important source of SO2 emission in coastal areas with the rapid development of maritime transport. It’s of great significance to develop marine scrubber for reducing SO2 emission of ships. In this study, numerical simulation of a full-scale marine spray scrubber is conducted to investigate two-phase flow pattern and SO2 absorption process in the scrubber. A desulfurization model based on seawater absorbent is couple into the simulation, which considers the mass transfer between phases and seawater aqueous phase chemistry simultaneously. Distribution ring is introduced in the scrubber to enhance the desulfurization performance of the scrubber. The result of simulation shows that the distribution ring can optimize effectively the distribution of gas-liquid phases and enhance the SO2 absorption. Under vertical condition, the desulfurization efficiency could be promoted approximate 6% after installing distribution ring. The inclined condition resulting from the ship swinging could lead to the uneven distribution of droplets and an obvious decrease (8.7%) of desulfurization efficiency, whereas the desulfurization performance of scrubber could be ensured with distribution ring installed even under inclined condition. Finally, a spray scrubber design scheme has been developed and successfully applied in EGCS of a container ship. Test result shows the outlet average value of SO2/CO2 can be reduced to 3.55. Meanwhile, the consistency of test data and calculation result indicates the applicability of the numerical model established for the simulation and optimization of the scrubber in industrial applications also. Exhaust gas cleaning system (EGCS) is an effective method to reduce SO2 emission of marine industry. However, different from land desulfurization tower, the application of spray scrubber in EGCS faces more problems due to the different application scenarios and complex sea conditions (inclined condition resulting from ships swinging and so on) during sailing. In this work, a numerical model capable of investigating physical and chemical phenomena in the scrubber simultaneously is established, which can produce great amount of data for the operation instruction of EGCS and the design and optimization of marine spray scrubber. The distribution ring is introduced in the marine spray scrubber to intensify the SO2 absorption and enhance the desulfurization performance of scrubber under different working conditions.

Finding Optimized Process Conditions to Minimize Precipitations in an SO2 Absorption Process Using Thermodynamic Process Simulation

A process model to describe SO2 absorption from exhaust gas using an absorptive magnesium-based slurry was developed in Aspen Plus® V10. The model includes the thermodynamic description of the electrolyte system MgO-CaO-SO2-H2O-O2-CO2, including precipitation reactions in the system. The property method electrolyte-NRTL with an asymmetric reference state was chosen as the thermodynamic method. The model was evaluated using plant data for pH value, HSO3- and SO3-- content of the liquid phase from an industrial SO2 absorption venturi system of the pulp and paper industry. The model shows good accuracy in describing the pH value and the combined HSO3- and SO3-- content. Sensitivity analyses were performed to identify key parameters that influence unwanted precipitation reactions in the system and to support the optimization of the SO2 absorption process. Temperature and the Mg(OH)2/SO2 ratio in the system were identified as key parameters influencing the formation and precipitation of sulfites. The pH value was identified as a key parameter affecting the precipitation of magnesium hydroxide. The model predicts the precipitation of Mg(OH)2 at a pH value of higher than 8 and the precipitation of MgSO3 trihydrate at a temperature higher than 78 °C or a slurry/SO2 ratio higher than around 4. The performed analyses can support optimized process design decisions for SO2 absorption processes to avoid limiting precipitation issues.

Research on Control Method of Wet Desulfurization System for Coal-fired Boiler

In wet flue gas desulfurization technology, the key factor affecting flue gas SO2 absorption is the control of slurry pH value in the absorption tower. However, most of the commonly used pH value control methods have some defects and cannot fully meet the system control requirements. On the basis of the analysis for the problems in the control process, this paper discussed a control strategy based on internal model control algorithm. The system simulation test showed that this control method had good dynamic performance, robustness and anti-interference, which could realize the relatively accurate control of pH value for wet flue gas desulfurization system, and achieve the control goal.

Mechanistic insight into absorption performance assessment for SO2 by mixed ionic liquids

In this work, the thermodynamic feasibility, absorption results and molecular mechanism of capturing SO2 with mixed ionic liquids (MILs) for 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) and 1-ethyl-3-methylimidazolium chlorine ([EMIM][Cl]) were investigated for the first time. The analysis of excess enthalpy of SO2 and IL systems shows the thermodynamic feasibility of SO2 capture process by the ionic liquids (ILs). The results of free volume (Vf) and fractional free volume (FFV) of the MILs system indicating that adding [EMIM][Cl] to [EMIM][SCN] could increase the SO2 absorption capacity. Then the weak interaction between molecules was analyzed microscopically, indicating that the van der Waals force played a leading role in the process of SO2 absorption. Moreover, molecular dynamics (MD) simulations were carried out for the process of MILs absorption of SO2, and the interaction between molecules and the distribution state were further analyzed in terms of interaction energy, radial distribution functions (RDFs) and spatial distribution functions (SDFs). Overall, the study on MILs desulfurization mechanism could provide new perspective for the design of green and efficient flue gas desulfurization solvents.

Simultaneous Removal of SO2 and NO x Using Steel Slag Slurry Combined with Ozone Oxidation.

In this work, steel slag slurry was used in combination with O3 oxidation for the simultaneous removal of SO2 and NOx in a laboratory-scale wet flue gas desulfurization process. The effects of the oxidation temperature, steel slag concentration, initial SO2 concentration, and pH value on the desulfurization and denitrification efficiencies were studied. The results showed that the highest NOx removal efficiency occurred at an oxidation temperature of 90 °C. With an increase of the oxidation temperature above 90 °C, the denitrification efficiency decreased due to the decomposition of N2O5. The effect of the SO2 concentration on denitrification was complicated. When the concentration of SO2 was 500 ppm, generation of SO32– promoted the absorption of NO2. However, higher SO2 concentrations strengthened the competitive absorption of SO2 and NOx. In the pH range of 8.5–4.5, the denitrification efficiency was maintained at about 96%. The component analyses of the aqueous solution and the solid residue were conducted to investigate the compositions of the absorption products. The results showed that NO3– and SO42– were the major anions in the aqueous solution. The nitrogen balance was analyzed to be 95.8%, clearly illustrating the migration and transformation path of nitrogen. In the solid residue, most alkaline substances were consumed, and the final products were mainly CaSO4 and FeO. Accordingly, the reaction mechanism of simultaneous desulfurization and denitrification using steel slag combined with ozone oxidation was proposed.

A comparative study of the catalytic and non-catalytic ozone based processes for simultaneous of SO2 and NOX removal

Ozonation process alone is not sufficient to remove both the SO2 and NOX gases, when treated simultaneously. Therefore in this work, a suitable technique to remove SO2 and NOX simultaneously has been evaluated using combination of O3, H2O2 and a solid catalyst. OMS-2, a manganese based catalyst have been incorporated with O3 and H2O2 for enhanced radical generation. This preferably enhances the oxidation of SO2 and NOx species in aqueous medium simultaneously. The role of some important process parameters have been tested on the performance of SO2 and NOX absorption. To get the maximum removal of SO2 and NOX, the neutral pH, temperature close to 300–320 K, and H2O2 at 0.2 mol L−1 concentrations was found to be the optimum condition. The use of catalyst (approximately 2 g L−1) + O3 + H2O2 shows promising results on the removal of SO2 and NOX. In addition to that, the kinetics of the catalytic ozonation and peroxone removal of SO2 and NO2 has been evaluated. The cost estimation study for the ozone and peroxone based catalytic processes has been presented with comparison of the respective flue gas %removal.

Density functional theory studies on ortho-position adsorption of SO3 at step sites of a CaO surface with SO2 and CO2

With the application of high-sulfur coal and oxy-fuel combustion in power plants, the formation of SO3 in flue gas has strongly enhanced. Hence, the removal of SO3 has received growing attention. Within this context, SO3 sorption using calcium-based sorbents is an interesting approach. In this study, we analyzed the steps on a CaO surface and examined their influence on the adsorption of SO3 molecules using density function theory calculations. The results indicate that steps with O and Ca atoms at the edges are the most stable terminations and also the best terminations for SO3 adsorption. SO3 molecules bind to OCaO sites by SSO3 atoms and weak bonds between Ca and OSO3 are formed. At edge sites, the adsorption energy of SO3, SO2 and CO2 shows a remarkable increase compared to that on a flat surface, whereas it decreases at the top site nearby the edge. The adsorption energy of SO3 is also affected by the OCaO that interacts with SSO3 and the Ca near the OCaO. Interestingly, the SO3 adsorption energy can increase if an SO3, SO2 or CO2 molecule previously adsorbed at a neighboring site. SO3 adsorption is more stable than SO2 and CO2 absorption on step surface and has an advantage in competitive adsorption with SO2 or CO2. The calculation results thus indicate that the formation of a step surface could be an effective method to enhance SO3 sorption on calcium-based sorbents.

Sulfur dioxide absorption characteristics of aqueous amino acid solutions

The SO2 absorption/desorption performances of 14 aqueous amino acid solutions were evaluated to identify efficient absorbents to remove SO2 from coal-powered plant emissions. SO2 absorption/desorption experiments were conducted at 298.15 and 373.15 K, respectively, using 600 ppmv SO2 (N2 balance) and N2 purging. Thereafter, the absorption/desorption loadings and rates of the solutions, as well as their net cyclic capacities, were compared. The SO2 absorption mechanisms were explored via 13C NMR, 1H NMR, and UV–Vis analyses, and the relationship between the pKa values and absorption performances of the 14 aqueous amino acid solutions was investigated. Furthermore, the effects of absorption temperature, absorbent concentration, and inlet SO2 concentration on the SO2 absorption performances of the solutions were explored. 5-Aminovaleric acid, 4-aminobutyric acid, β-alanine, and histidine were identified as suitable SO2 absorbents based on their absorption/desorption performances and their net cyclic capacities. Furthermore, the net cyclic capacities of these four absorbents were similar or superior to those of previously reported deep eutectic solvents and ionic liquids. The results of this study provide a strategy for preparing eco-friendly SO2 absorbents.

Efficient absorption of low partial pressure SO2 by deep eutectic solvents based on pyridine derivatives

Efficient and reversible absorption of SO2 by deep eutectic solvents (DESs) has drawn much attention in recent years. In this work, a new type of deep eutectic solvents (DESs) were synthesized via pyridine derivatives, nicotinamide, aminopyridines and hydroxypyridines, as the hydrogen bond donors (HBDs) with common quaternary ammonium salt ionic liquids (ILs) as hydrogen bond acceptors (HBAs). The studied DESs exhibited an attractive absorption behavior for SO2, especially for low concentration SO2. The 1-allyl-3-methylimidazolium chloride (AmimCl)/2-aminopyridine (2-NH2Py) (2:1) and 1-butyl-3-methylimidazolium chloride (BmimCl)/3-aminopyridine (3-NH2Py) (2:1) could capture 0.273 and 0.223 g SO2/g DES at 293 K and 1.0 kPa, respectively, surpassing that of most DESs and ILs in the present literature. The influence of DES composition, temperature and pressure on SO2 absorption performance was systematically investigated. Moreover, the absorption mechanism studied by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopies indicated that the efficient absorption of SO2 was ascribed to the chemical interaction between the pyridine nitrogen atom and SO2.

SO2 capture by tricyanomethanide ionic liquids: Unraveling anion-gas interactions by resonance Raman spectroscopy

Interactions concerning the high SO2 absorption capacity in 1-butyl-3-methyilimidazolium tricyanomethanide (BMITCM) were analyzed through Raman spectroscopy. The SO2 symmetric stretching band, νs(SO2), remained equal in shape and wavenumber regardless the SO2 molar fraction, suggesting no specific interaction between TCM and SO2. However, by increasing the Raman excitation energy from 568 to 405 nm, a pre-resonance condition was reached, where a shifting and broadening of νs(SO2) is noticed. Such results evidence solvation states where charge transfer interactions between TCM and SO2 prevail, corroborating the high absorption capacity of TCM based ionic liquids.

NH2-MIL-125 filled mixed matrix membrane contactor with SO2 enrichment for flue gas desulphurization

Membrane absorption is a convenient and efficient flue SO2 capture technology. In this study, NH2-MIL-125 filled mixed matrix membrane contactor (MMMC) is constructed by Non-solvent Induced Phase Separation (NIPS) method. The functional groups and metal active sites on the surface of NH2-MIL-125(Ti) exhibit high affinity for SO2. The microporous structure of NH2-MIL-125(Ti) provides storage for adsorbed SO2, which is conducive to the formation of SO2 enrichment zone in the membrane. The membrane morphology, wetting resistance, and light responsiveness et al of MMMC have been tested. The combination of NH2-MIL-125(Ti) adsorption and membrane absorption process effectively promotes the transfer of gas molecules in the membrane pores. The SO2 absorption flux of MMMC filled by NH2-MIL-125(Ti) has a significant increment, reaching 8.81 × 10−4 mol·m−2·s−1 and 9.77 × 10−4 mol·m−2·s−1 under non-light and visible light conditions respectively, which is comparability with results in literature. The membrane phase mass transfer coefficient calculated by Wilson model is 149.6 s·m−1, which shows the low resistance in membrane. The SO2 absorption flux keep stable after 4 cycles of tests. The membrane contactor coupled with function fillers enhances the SO2 capture ability and further promotes the enrichment of SO2, which has favorable development foreground.

Comparison of various chemical compounds for the removal of SO2 and NOx with wet scrubbing for marine diesel engines

Seawater, NaOH, NaClO, NaClO2, H2O2, and KMnO4 were used as scrubbing liquids to react with SOx and NOx separately in a customized wet scrubber. The absorption of SO2 in the aqueous phase was influenced by three factors: pH, ionic concentration, and oxidation potential. For NOx removal, the effectiveness of various chemical compounds can be ranked from least to most effective as follows: seawater, NaOH, H2O2 < NaClO < KMnO4 < NaClO2. This effectiveness was influenced by the chemical compound’s ability to oxidize NO to NO2, absorb the NO2 that was formed, and retaining the nitrogen in the aqueous phase. High oxidation potential promoted the oxidation of NO to NO2 but hindered the absorption of NO2. NaClO2 was superior compared to NaClO in all three categories of oxidizing, absorption and retention. NaClO could not retain a significant amount of NO2 which it absorbed in the aqueous phase. The pH around 8 provided a good balance between oxidation versus absorption/retention and reactant utilization for the chlorine-based oxidants. KMnO4 had the lowest reactant consumption rate; only half a mole was consumed for every mole of NO removed, compared to around 2–3 mol of chlorite or 3–5 mol of hypochlorite.

Highly efficient and reversible low-concentration SO2 absorption in flue gas using novel phosphonium-based deep eutectic solvents with different substituents

Four hydrogen bond acceptors (HBAs) with different carbon chain length substituents, including methyl-triphenyl phosphonium bromide (MTPB), ethyl-triphenyl phosphonium bromide (ETPB), propyl-triphenyl phosphonium bromide (PTPB), and butyl-triphenyl phosphonium bromide (BTPB), combined with ethylene glycol (EG) were developed to synthesize four low-viscosity deep eutectic solvents (DESs). In this study, the effect of different substituents in DESs on low-concentration SO2 absorption was systematically studied at 30–70 °C. Experimental results show that the EG-MTPB DES has a higher SO2 absorption capacity and a lower viscosity than other DESs. The reason for the higher SO2 absorption capacity of EG-MTPB DES was described by viscosity experiments and quantum chemical calculations. It was shown that the strong polarization ability of the CH3 group promotes the absorption of SO2 by DESs. 1H NMR and FTIR results indicated that chemical interactions primarily exist between the S of SO2 and Br, and the O of SO2 and the H atom of EG form hydrogen bonds. The density functional theory (DFT) results also confirm that the charge of the Br atom migrated to the S atom. Also, thermostability and regeneration experiments showed that the EG-MTPB DES exhibits good stability and can thus be used for industrial flue gas desulfurization.

Towards estimating absorption of major air pollutant gasses in ionic liquids using soft computing methods

Capture of air pollutant gases using novel and green solvents is obtaining widespread attention. Accurate estimation of this process is complex. We have estimated the absorption of CO2, CH4, H2S, N2O, SO2 and CO gases in ionic liquids (ILs). We have applied Multilayer Perceptron-Artificial Neural Networks (MLP-ANN), Hybrid-Adaptive Neuro Fuzzy Inference System (Hybrid-ANFIS), Particle Swarm Optimization-Adaptive Neuro Fuzzy Inference System (PSO-ANFIS) and Coupled Simulated Annealing-Least Squares Support Vector Machine (CSA-LSSVM). We have gathered 3060 data of 72 IL-Gas mixtures for 40 types of ILs. The inputs of these models are: Temperature (T), pressure (P), IL molecular weight (MwIL), IL critical temperature (Tc, IL), IL critical pressure (Pc, IL), IL acentric factor (ωIL), gas molecular weight (Mwgas), gas critical temperature (Tc, gas), gas critical pressure (Pc, gas), gas kinetic diameter (d) and the acentric factor (ωgas). The CSA-LSSVM model produces best estimation with an Average Absolute Relative Deviation (AARD) of 8.7%. The results suggest the solubilities of the gases in ILs are correlated with structural factors of ILs. Estimation of the equilibrium behaviors in ionic liquids is of importance in simulation and design of solvent-based pollutant gas capture processes.

Effect of Gas-Liquid Contact Intensification on Heat and Mass Transfer in Deflector and Rod Bank Desulfurization Spray Tower

The deflector and the rod bank are commonly used to optimize flue gas distribution in the original spray tower (OST) of a wet flue gas desulfurization system (WFGD). In this paper, the internal optimization mechanism of the deflector desulfurization spray tower (DST) and the rod bank desulfurization spray tower (RBST) are studied. Based on the Euler–Lagrange method, the standard k-ε turbulence model, an SO2 absorption model and a porous media model, the numerical simulation of the desulfurization spray tower is carried out with the verification of the model rationality. The results show that there are gas-liquid contact intensification effects in DST and RBST. Compared with OST, gas-liquid contact intensification enhances the heat and mass transfer effects of DST and RBST. The temperature difference between inlet and outlet of flue gas increased by 3.3 K and the desulfurization efficiency of DST increased by 1.8%; the pressure drop decreased by 37 Pa. In RBST, the temperature difference between the flue gas inlet and outlet increased by 5.3 K and the desulfurization efficiency increased by 3.6%; the pressure drop increased by 33 Pa.

Capture of Acidic Gases from Flue Gas by Deep Eutectic Solvents

Up to now, many kinds of deep eutectic solvents (DESs) were investigated for the capture of acidic gases from flue gases. In this review, non-functionalized and functionalized DESs, including binary and ternary DESs, for SO2, CO2 and NO capture, are summarized based on the mechanism of absorption, physical interaction or chemical reaction. New strategies for improving the absorption capacity are introduced in this review. For example, a third component can be introduced to form a ternary DES to suppress the increase in viscosity and improve the CO2 absorption capacity. DESs, synthesized with halogen salt hydrogen bond acceptors (HBAs) and functionalized hydrogen bond donors (HBDs), can be used for the absorption of SO2 and NO with high absorption capacities and low viscosities after absorption, due to physicochemical interaction between gases and DESs. Emphasis is given to introducing the absorption capacities of acidic gases in these DESs, the mechanism of the absorption, and the ways to enhance the absorption capacity.

Enhanced SO2 Absorption Capacity of Sodium Citrate Using Sodium Humate

A novel method of improving the SO2 absorption performance of sodium citrate (Ci-Na) using sodium humate (HA–Na) as an additive was put forward. The influence of different Ci-Na concentration, inlet SO2 concentration and gas flow rate on desulfurization performance were studied. The synergistic mechanism of SO2 absorption by HA–Na and Ci-Na was also analyzed. The consequence shows that the efficiency of SO2 absorption by Ci-Na is above 90% and the desulfurization time added with the Ci-Na concentration rising from 0.01 to 0.1 mol/L. Both the desulfurization efficiency and time may increase with the adding of HA–Na quality in Ci-Na solution. Due to adding HA–Na, the desulfurization efficiency of Ci-Na increased from 90% to 99% and the desulfurization time increased from 40 to 55 min. Under the optimum conditions, the desulfurization time of Ci-Na can exceed 70 min because of adding HA–Na, which is nearly doubled. The growth of inlet SO2 concentration has little effect on the desulfurization efficiency. The SO2 adsorption efficiency decreases with the increase of inlet flow gas. The presence of O2 improves the SO2 removal efficiency and prolongs the desulfurization time. Therefore, HA–Na plays a key role during SO2 absorption and can dramatically enhance the SO2 adsorption performance of Ci-Na solution.

Understanding Gas Solubility of Pure Component and Binary Mixtures within Multivalent Ionic Liquids from Molecular Simulations.

Understanding the molecular-level solubility of CO2 and its mixtures is essential to the progress of gas-treating technologies. Herein, we use grand canonical Monte Carlo simulations to study the single-component gas absorption of SO2, N2, CH4, and H2 and binary mixtures of CO2/SO2, CO2/N2, CO2/CH4, and CO2/H2 of varying mole fractions within multivalent ionic liquids (ILs). Our results highlight the importance of the free volume effect and the anion effect when interpreting the absorption behavior of these mixtures, similar to the behavior of CO2 found in our previous study (Phys. Chem. Chem. Phys. 2020, 22, 20618-20633). The deviation of gas solubility between the pure component absorption versus the binary absorption, as well as the solubility selectivity, highlights the importance of the relative affinity of gas species within a mixture to the different anions. The absorption selectivity within a specific IL system can be predicted based on the relative gas affinity to the anion.

Tuning the structure of pyridinolate-based functional ionic liquids for highly efficient SO2 absorption

A series of pyridinolate anion-functional ionic liquids (ILs) containing different kinds of cations were designed and prepared, including tri-n-hexyltetradecylphosphonium [P66614], tri-n-butylethylphosphonium [P4442], and 1,1,3,3-tetramethylguandinium [TMG] cations and pyridinolate [PyO] anions with different N positions. Densities and viscosities at different temperatures were measured because of their importance for the absorption of SO2. Effect of different structures on the absorption of SO2 was studied, including the type and the alkyl chain length of cations, and the N positions of [PyO] anions (2-, 3-, and 4-). Additionally, effects of SO2 concentration and temperature for absorption were investigated. Especially, up to 6.00 and 2.53 mol SO2 per mole IL could be obtained by [P66614][4-PyO] at 1 bar and 0.1 bar of SO2, respectively, when absorptions performed at 20 °C. The results indicate that (1) the aprotic cations weakened the cation⋯anion interaction and resulted in the released active sites on the anions, and (2) N position has an influence on charge distribution of [PyO] anions and resulted in the tunable absorption of SO2. Reversible SO2 absorption and [P66614][4-PyO] regeneration could be performed several times without losing efficiency. Furthermore, the mechanism of absorption was studied through FT-IR and NMR methods and the results showed that the absorption of SO2 by [P66614][4-PyO] includes physisorption and chemisorption.