Simultaneous Removal of SO2 and NOx by Calcium Hydroxide at Low Temperature: Effect of SO2 Absorption on NO2 Removal

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.

O3 oxidation combined with semi-dry method for simultaneous desulfurization and denitrification of sintering/pelletizing flue gas

With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies, the emission of pollutants such as SO₂ and NO_x has received unprecedented attention. Considering the increase of the proportion of semi-dry desulfurization technology in the desulfurization process, several semi-dry desulphurization technologies such as flue gas circulating fluidized bed (CFB), dense flow absorber (DFA) and spray drying absorption (SDA) are briefly summarized. Moreover, a method for simultaneous treatment of SO₂ and NO_x in sintering/pelletizing flue gas by O₃ oxidation combined with semi-dry method is introduced. Meantime, the effects of key parameters such as O₃/NO molar ratio, CaSO₃, SO₂, reaction temperature, Ca/(S+2N) molar ratio, droplet size and approach to adiabatic saturation temperature (AAST) on denitrification and desulfurization are analyzed. Furthermore, the reaction mechanism of denitrification and desulfurization is further elucidated. Finally, the advantages and development prospects of the new technology are proposed.

SO2 Absorption by Multiple Biomass Ash Types

As the severity of environmental pollution continues to increase and ultralow emission standards are proposed, biomass power plants must implement additional processes to control SO₂ emission. Biomass ash can be utilized as a sorbent for flue gas desulfurization because of its strong alkalinity. In this study, the characteristics of SO₂ absorption in simulated flue gas using four types of typical biomass ashes were studied in fixed bed experiments. The results showed that the addition of water, the increase in water vapor, and the lower temperature were beneficial for SO₂ absorption. The main components of wheat straw ash are KCl and SiO₂, cotton stalk ash is rich in K₂O and calcium compounds, poplar bark ash has a considerable content of calcium compounds, and corncob ash contains large amounts of KCl and K₂O. Alkali substances, such as oxides or carbonates of potassium and calcium, play a crucial role in SO₂ absorption. The SO₂ removal effect of corncob ash was the best owing to the abundance of potassium oxides. Meanwhile, wheat straw ash performed worst in SO₂ removal due to the small amount of K₂O and Ca. The desulfurization products were mainly potassium and calcium sulfate.

Simultaneous wet desulfurization and denitration by an oxidant absorbent of NaClO2/CaO2

The simultaneous wet removal performance of NO and SO₂ was studied using the oxidant absorbent NaClO₂/CaO₂. The factors were studied including NaClO₂ and CaO₂ concentrations, reaction temperature, and gaseous components, such as SO₂, NO, O₂, and CO₂. The products in liquid and solid phases were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and ion chromatography to determine the mechanism of simultaneous desulfurization and denitration by NaClO₂/CaO₂. The results indicated that the removal efficiency of SO₂ was in the range of 98-99.9%, and the removal efficiencies of NO and NO_x were 99.4% and 95.0%, respectively. The removal efficiencies of NO and NO_x increased with the increase of NaClO₂ and CaO₂ concentration and reaction temperature. The gaseous components had a stronger effect on NO_x removal efficiency, followed by NO removal efficiency, and SO₂ removal efficiency. As SO₂ concentration increased, the generation of sulfite species promoted the removal of NO and NO_x. Competition for NO₂ and SO₂ absorption by absorbent inhibited the removal efficiencies of SO₂ and NO_x. The presence of O₂ was beneficial for removing SO₂, NO, and NO_x, while the presence of CO₂ was not. The main products in the liquid and solid phases were NO₃^-, NO₂^-, SO₄^2-, and CaSO₄. The reaction mechanism for simultaneous wet removal of SO₂ and NO by NaClO₂/CaO₂ is proposed and discussed.

Estimating source strengths of HCl and SO2 emissions in the flue gas from waste incineration

HCl and SO₂ emission is one of the major concerns related to municipal solid waste incinerator (MSWI). In this study, a material flow analysis model was developed to estimate the HCl and SO₂ concentrations in the MSWI flue gases (FGs), and their concentrations in the full-scale MSWI were monitored. The calculated concentrations of HCl and SO₂ in the FG were 770-1300 mg/Nm³ and 150-640 mg/Nm³, respectively, in close agreement with the monitored values. More than 99% of Cl and 92% of S from the FG were captured into solid residues by the air pollution control (APC) systems. Moreover, since only 48.4%-67.5% of Cl and 21.3%-53.4% of S were transferred to the FG from the municipal solid waste (MSW), it was more reliable to estimate the source strengths and release amounts of HCl and SO₂ in the FG based on the amounts of Cl and S in the APC residues (AR) and exhaust gas rather than in the MSW. This simple method is easily applicable and the estimated results could provide scientific basis for the appropriate design and operation of the APC systems as well as corrosion control of heat recovery systems.

Synthesis of MnNi–SAPO-34 by a one-pot hydrothermal method and its excellent performance for the selective catalytic reduction of NO by NH3

MnNi–SAPO-34 with Mn and Ni incorporated in the framework of SAPO-34 prepared by a one-pot hydrothermal synthesis method exhibits excellent NH₃-SCR activity, which is attributed to the strong interaction between the Mn and Ni species.