Simultaneous removal of NOx and SO2 using two-stage O3 oxidation combined with Ca(OH)2 absorption

Performance and mechanism of CO2 absorption during the simultaneous removal of SO2 and NOx by wet scrubbing process

The co-removal of CO2 while removing SO2 and NOx from industrial flue gas has great potential of carbon emission reduction but related research is lacking. In this study, a wet scrubbing process with various urea solutions for desulfurization and denitrification was explored for the possibility of CO2 absorption. The results showed that the urea-additive solutions were efficient for NOx and SO2 abatement, but delivered < 10% CO2 absorption efficiency. The addition of Ca(OH)2 dramatically enhanced the CO2 absorption, remained the desulfurization efficiency, unfortunately restricted the denitrification efficiency. Among various operating parameters, pH of solution played a determining role during the absorption. The contradictory pH demands of CO2 absorption and denitrification were observed and discussed in detail. A higher pH of solution than 10 was favorable for CO2 absorption, while the oxidizing of NO to NO2, NO2- or NO3- by NaClO2 was inhibited in this condition. When 7 < pH < 10, it was favorable for the conversion and absorption of NO and NOx. However, the conversion of HCO3- to CO32- was significantly inhibited, hence preventing the absorption of CO2. Large part of Ca(OH)2 became CaCO3 with a finer particle size, which covered the unreacted Ca(OH)2 surface after the reaction. Kinetic analysis showed that the CO2 absorption in urea-NaClO2-Ca(OH)2 absorbent was controlled by chemical reaction in early stage, then by ash layer diffusion in later stage.

Advancements and sustainable strategies for the treatment and management of wastewaters from metallurgical industries: an overview

Metallurgy is pivotal for societal progress, yet it yields wastewater laden with hazardous compounds. Adhering to stringent environmental mandates, the scientific and industrial sectors are actively researching resilient treatment and disposal solutions for metallurgical effluents. The primary origins of organic pollutants within the metallurgical sector include processes such as coke quenching, steel rolling, solvent extraction, and electroplating. This article provides a detailed analysis of strategies for treating steel industry waste in wastewater treatment. Recent advancements in membrane technologies, adsorption, and various other processes for removing hazardous pollutants from steel industrial wastewater are comprehensively reviewed. The literature review reveals that advanced oxidation processes (AOPs) demonstrate superior effectiveness in eliminating persistent contaminants. However, the major challenges to their industrial-scale implementation are their cost and scalability. Additionally, it was discovered that employing a series of biological reactors instead of single-step biological processes enhances command over microbial communities and operating variables, thus boosting the efficacy of the treatment mechanism (e.g., achieving a chemical oxygen demand (COD) elimination rate of over 90%). This review seeks to conduct an in-depth examination of the current state of treating metallurgical wastewater, with a particular emphasis on strategies for pollutant removal. These pollutants exhibit distinct features influenced by the technologies and workflows unique to their respective processes, including factors such as their composition, physicochemical properties, and concentrations. Therefore, it is of utmost importance for customized treatment and disposal approaches, which are the central focus of this review. In this context, we will explore these methods, highlighting their advantages and characteristics.

Advances in air pollution control for key industries in China during the 13th five-year plan

Industrial development is an essential foundation of the national economy, but the industry is also the largest source of air pollution, of which power plants, iron and steel, building materials, and other industries emit large amounts of pollutants. Therefore, the Chinese government has promulgated a series of stringent emission regulations, and it is against this backdrop that research into air pollution control technologies for key industrial sectors is in full swing. In particular, during the 13th Five-Year Plan, breakthroughs have been made in pollution control technology for key industrial sectors. A multi-pollutant treatment technology system of desulfurization, denitrification, and dust collection, which applies to key industries such as power plants, steel, and building materials, has been developed. High-performance materials for the treatment of different pollutants, such as denitrification catalysts and desulfurization absorbers, were developed. At the same time, multi-pollutant synergistic removal technologies for flue gas in various industries have also become a hot research topic, with important breakthroughs in the synergistic removal of NO_x, SO_x, and Hg. Due to the increasingly stringent emission standards and regulations in China, there is still a need to work on the development of multi-pollutant synergistic technologies and further research and development of synergistic abatement technologies for CO₂ to meet the requirements of ultra-low emissions in industrial sectors.

Multi-process and multi-pollutant control technology for ultra-low emissions in the iron and steel industry

The iron and steel industry is not only an important foundation of the national economy, but also the largest source of industrial air pollution. Due to the current status of emissions in the iron and steel industry, ultra-low pollutant emission control technology has been researched and developed. Liquid-phase proportion control technology has been developed for magnesian fluxed pellets, and a blast furnace smelting demonstration project has been established to use a high proportion of fluxed pellets (80%) for the first time in China to realize source emission reduction of SO₂ and NO_x. Based on the characteristics of high NO_x concentrations and the coexistence of multiple pollutants in coke oven flue gas, low-NO_x combustion coupled with multi-pollutant cooperative control technology with activated carbon was developed to achieve efficient removal of multiple pollutants and resource utilization of sulfur. Based on the characteristics of co-existing multiple pollutants in pellet flue gas, selective non-catalytic reduction (SNCR) coupled with ozone oxidation and spray drying adsorption (SDA) was developed, which significantly reduces the operating cost of the system. In the light of the high humidity and high alkalinity in flue gas, filter materials with high humidity resistance and corrosion resistance were manufactured, and an integrated pre-charged bag dust collector device was developed, which realized ultra-low emission of fine particles and reduced filtration resistance and energy consumption in the system. Through source emission reduction, process control and end-treatment technologies, five demonstration projects were built, providing a full set of technical solutions for ultra-low emissions of dust, SO₂, NO_x, SO₃, mercury and other pollutants, and offering technical support for the green development of the iron and steel industry.

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.

Simultaneous removal of NOx and SO2 from simulated marine ship flue gas in a novel wet scrubbing system based on divided diaphragm seawater electrolysis technology: efficiency optimization and economic assessment

This work constructed a divided diaphragm seawater electrolysis system with two tandem packed towers for the synergistic removal of NO_x and SO₂. The first tower was mainly used to oxidize NO and SO₂ by AC (active chlorine), and the second tower was used to further absorb NO_x. The factors affecting on NO removal, including ACC (active chlorine concentration), pH value, initial NO concentration and temperature in the oxidation tower were investigated. Moreover, the effect of different inlet gas concentrations and current values were explored. The results showed that with the increase of ACC, the NO and NO_x removal efficiency increased rapidly, but when the ACC was higher than 500 mg/L [Cl₂], the removal efficiency did not increase further in the oxidation tower. Low pH values in the oxidation tower were favorable for NO removal. NO removal efficiency reached a maximum at 40 °C. Higher NO and SO₂ concentrations were favorable for NO removal. The decline of pH in the anode cell was not conducive to the storage of AC in the continuous electrolysis removal process. NO_x and SO₂ were almost completely removed after being scrubbed in the oxidation and absorption towers. The relationship between current and removal efficiency of NO and SO₂ in the oxidation tower was also analyzed. Finally, the removal mechanism and the application prospects were discussed.