Simultaneous Removal of SO2 and NO from Flue Gas Using Multicomposite Active Absorbent

Modeling based on machine learning to investigate flue gas desulfurization performance by calcium silicate absorbent in a sand bed reactor

Flue gas desulfurization (FGD) is a critical process for reducing sulfur dioxide (SO2) emissions from industrial sources, particularly power plants. This research uses calcium silicate absorbent in combination with machine learning (ML) to predict SO2 concentration within an FGD process. The collected dataset encompasses four input parameters, specifically relative humidity, absorbent weight, temperature, and time, and incorporates one output parameter, which pertains to the concentration of SO2. Six ML models were developed to estimate the output parameters. Statistical metrics such as the coefficient of determination (R2) and mean squared error (MSE) were employed to identify the most suitable model and assess its fitting effectiveness. The random forest (RF) model emerged as the top-performing model, boasting an R2 of 0.9902 and an MSE of 0.0008. The model's predictions aligned closely with experimental results, confirming its high accuracy. The most suitable hyperparameter values for RF model were found to be 74 for n_estimators, 41 for max_depth, false for bootstrap, sqrt for max_features, 1 for min_samples_leaf, absolute_error for criterion, and 3 for min_samples_split. Three-dimensional surface plots were generated to explore the impact of input variables on SO2 concentration. Global sensitivity analysis (GSA) revealed absorbent weight and time significantly influence SO2 concentration. The integration of ML into FGD modeling offers a novel approach to optimizing the efficiency and effectiveness of this environmentally crucial process.

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 SO_x and NO_x 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 NO_x 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.

Effect of Absorbents on NOx Removal through Polyvinylidene Fluoride (PVDF) Hollow Fiber Membrane Modules

NOx (NO and NO2) are air toxins that endanger life and represent a hazard to the environment, such as photochemical smog, global warming, acid rain, ozone depletion, and the occurrence of respiratory infections. Some technological strategies to diminish NOx emissions to meet regulations depend on two techniques: the dry process and the wet process. This study applies polyvinylidene fluoride (PVDF) hollow fiber membrane modules as a medium to remove NOx from solutions containing several absorbents such as hydrogen peroxide and nitric acid (H2O2-HNO3) solutions, sodium chlorite and sodium hydroxide (NaClO2-NaOH) solutions, and sodium chlorate and sodium hydroxide (NaClO3-NaOH) solutions. The experimental results showed that the oxidant’s strength influences NOx removal efficiency, where the absorbent solutions containing hydrogen peroxide had the highest removal efficiency as hydrogen peroxide is the most potent oxidant, followed by sodium chlorite and sodium chlorate. The three pairs of absorbents also gave a high NOx removal efficiency (above 90%), which means that all the absorbents used in the study are very potential to be used to diminish NOx via the wet process. NOx removal efficiency at the same feed gas flow rate increased as the number of fiber and absorbent concentrations is increased. However, NOx removal efficiency is reduced as the feed gas flow rate is increased at the same membrane module and absorbent concentration.

Enhanced oxidative removal of NO by UV/in situ Fenton: Factors, kinetics and simulation

A series of experiments on the oxidative removal of NO from flue gas using a novel in situ Fenton (IF) system was performed in the presence of ultraviolet light (UV). The comparison tests revealed that the in situ Fenton system facilitated by UV (UV/IF) has a better oxidation ability of NO than that of the IF system due to the photochemical effect on the generation of oxidative species like (OH). Both of the aforementioned oxidation efficiencies were higher than that of the conventional Fenton system (CF) depending on the premix of Fe²⁺ and H₂O₂ solutions, which attribute to the improvement of (OH) yield and valid utilization with continuous addition of fresh reagents and UV radiation. In follow-up experiments, the effects of UV power, gas flow rate, reagent temperature, Fe²⁺/H₂O₂ molar ratio, initial pH, initial concentration of NO and SO₂ and volume fraction O₂ and CO₂ on the oxidative removal of NO by UV/IF method were investigated respectively. Moreover, the results of kinetic analysis indicated that NO oxidation was confirmed to have a pseudo-first-order kinetics pattern. The rate constants decreased slightly with increasing liquid temperature, and then the apparent activation energy of NO oxidation reactions in the UV/IF system was calculated as -5.62 kJ/mol by the Arrhenius equation. Furthermore, the reaction mechanism and application prospects concerning NO oxidative removal by using the UV/IF system was speculated in brief. Finally, the computational fluid dynamics (CFD) simulations revealed that the improvement of axial and radial gas hold-up would enhance the gas-liquid contact and accelerate the oxidation reactions on the interface. In addition to reasonable control of process parameters, the optimization of reactor interior structure needs to be carried out via CFD simulation and experimental validation in future research, both are favourable to promote the NO oxidation efficiency and large-scale development of this technology.

Valorization of Raw and Calcined Chicken Eggshell for Sulfur Dioxide and Hydrogen Sulfide Removal at Low Temperature

Chicken eggshell (ES) is a waste from the food industry with a high calcium content produced in substantial quantity with very limited recycling. In this study, eco-friendly sorbents from raw ES and calcined ES were tested for sulfur dioxide (SO2) and hydrogen sulfide (H2S) removal. The raw ES was tested for SO2 and H2S adsorption at different particle size, with and without the ES membrane layer. Raw ES was then subjected to calcination at different temperatures (800 °C to 1100 °C) to produce calcium oxide. The effect of relative humidity and reaction temperature of the gases was also tested for raw and calcined ES. Characterization of the raw, calcinated and spent sorbents confirmed that calcined eggshell CES (900 °C) showed the best adsorption capacity for both SO2 (3.53 mg/g) and H2S (2.62 mg/g) gas. Moreover, in the presence of 40% of relative humidity in the inlet gas, the adsorption capacity of SO2 and H2S gases improved greatly to about 11.68 mg/g and 7.96 mg/g respectively. Characterization of the raw and spent sorbents confirmed that chemisorption plays an important role in the adsorption process for both pollutants. The results indicated that CES can be used as an alternative sorbent for SO2 and H2S removal.

The study on continuous denitrification, desulfurization of pyrolusite/activated coke hybrid catalyst

The SO₂ removal and regeneration of ACP improved its NO removal activity, while the denitrification had almost no effect on the desulfurization. The metal sulfate of ACP-Rn showed catalytic activity for NO reduction although there is also a reverse effect.

Simultaneous removal of SO₂, NO and Hg⁰ through an integrative process utilizing a cost-effective complex oxidant

A novel process of pre-oxidation combining with post-absorption to simultaneously remove SO2, NO and Hg(0) from flue gas was proposed. A vaporized complex oxidant (CO) consisted of cost-effective H2O2 and NaClO2 was prepared to oxidize Hg(0) and NO, then the oxidation products were absorbed by the Ca(OH)2 solution that was followed. For the establishment of the optimal reaction conditions, the influences of various reaction factors on the simultaneous removal of SO2, NO and Hg(0) were investigated, i.e., the molar ratio of H2O2 to NaClO2 in CO, the adding rate of CO, the pH of CO, the reaction temperature, the flue gas residence time and the coexistence gases. The experimental results indicated that the desulfurization was constant in all tests, whereas the removal of NO and Hg(0) was primarily affected by the NaClO2 addition, the adding rate of CO, the pH of CO, and the reaction temperature. Meanwhile, NO and SO2 were characterized as the promoters for the Hg(0) removal. Under the optimal reaction conditions, the best simultaneous removal efficiencies were 100% for SO2, 87% for NO and 92% for Hg(0). According to the characterizations of removal products by UV-vis, EDX, XRD, AFS and XPS, the reaction mechanism was speculated.

Abatement of SO2-NOx binary gas mixtures using a ferruginous active absorbent: Part I. Synergistic effects and mechanism

A novel ferruginous active absorbent, prepared by fly ash, industrial lime and the additive Fe(VI), was introduced for synchronous abatement of binary mixtures of SO2-NOx from simulated coal-fired flue gas. The synergistic action of various factors on the absorption of SO2 and NOx was investigated. The results show that a strong synergistic effect exists between Fe(VI) dose and reaction temperature for the desulfurization. It was observed that in the denitration process, the synergy of Fe(VI) dose and Ca/(S+N) had the most significant impact on the removal of NO, followed by the synergy of Fe(VI) and reaction temperature, and then the synergy of reaction temperature and flue gas humidity. A scanning electron microscope (SEM) and an accessory X-ray energy spectrometer (EDS) were used to observe the surface characteristics of the raw and spent absorbent as well as fly ash. A reaction mechanism was proposed based on chemical analysis of sulfur and nitrogen species concentrations in the spent absorbent. The Gibbs free energy, equilibrium constants and partial pressures of the SO2-NOx binary system were determined by thermodynamics.

A novel pre-oxidation method for elemental mercury removal utilizing a complex vaporized absorbent

A novel semi-dry integrative method for elemental mercury (Hg(0)) removal has been proposed in this paper, in which Hg(0) was initially pre-oxidized by a vaporized liquid-phase complex absorbent (LCA) composed of a Fenton reagent, peracetic acid (CH3COOOH) and sodium chloride (NaCl), after which Hg(2+) was absorbed by the resultant Ca(OH)2. The experimental results indicated that CH3COOOH and NaCl were the best additives for Hg(0) oxidation. Among the influencing factors, the pH of the LCA and the adding rate of the LCA significantly affected the Hg(0) removal. The coexisting gases, SO2 and NO, were characterized as either increasing or inhibiting in the removal process, depending on their concentrations. Under optimal reaction conditions, the efficiency for the single removal of Hg(0) was 91%. Under identical conditions, the efficiencies of the simultaneous removal of SO2, NO and Hg(0) were 100%, 79.5% and 80.4%, respectively. Finally, the reaction mechanism for the simultaneous removal of SO2, NO and Hg(0) was proposed based on the characteristics of the removal products as determined by X-ray diffraction (XRD), atomic fluorescence spectrometry (AFS), the analysis of the electrode potentials, and through data from related research references.