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

Comparative Study of Sorbents for Spray Dry Scrubbing of SO2 from Flue Gases

This study presents the findings of an investigation involving the absorption of SO₂ from flue gases, using three different sorbents, in a spray dryer. Experimentation involved the evaluation of three sorbents, i.e., hydrated lime (Ca[OH]₂), limestone (CaCO₃), and trona (Na₂CO₃·NaHCO₃·2H₂O), and their relevant properties, for flue gas desulfurization by spray dry scrubbing. Experiments were conducted to explore the effects of spray characteristics in the spray drying scrubber on SO₂ removal efficiency using the selected sorbents. The ranges of various operating parameters were considered, including the stoichiometric molar ratio of (1.0-2.5), the inlet gas phase temperature of (120-180 °C), and an inlet SO₂ concentration of 1000 ppm. The use of trona gave better SO₂ removal characteristics; a high SO₂ removal efficiency of 94% was recorded at an inlet gas phase temperature of 120 °C and a stoichiometric molar ratio of 1.5. Under the same operating conditions, Ca[OH]₂ and CaCO₃ gave 82 and 76% SO₂ removal efficiency, respectively. Analysis of the desulfurization products by X-ray fluorescence (XRF) and Fourier transform infrared (FTIR) spectroscopy revealed the presence of CaSO₃/Na₂SO₃, a product of the semidry desulfurization reaction. A significant proportion of unreacted sorbent was observed when Ca[OH]₂ and CaCO₃ sorbents were used at a stoichiometric ratio of 2.0. Trona also gave the highest degree of conversion (96%) at a stoichiometric molar ratio of 1.0. Ca[OH]₂ and CaCO₃ gave 63 and 59%, respectively, under the same operating conditions.

Application of Ca-based adsorbents in fixed-bed dry flue gas desulfurization (FGD): a critical review

Sulfur dioxide, which comes from the flue gas emitted by the steel and coal power industries, is extremely harmful to humans and the natural environment. Due to its high efficiency and economy, dry fixed-bed desulfurization technology and Ca-based adsorbents have attracted wide attention. In this paper, a detailed outline of the process of the fixed-bed reactor, performance indexes, economic value, recent research, and industrial applications of the dry fixed-bed desulfurization process was summarized. The classification and properties, preparation method, desulfurization mechanism, and influencing factors of Ca-based adsorbents were discussed. This review indicated the challenges in the commercialization of dry Ca-based fixed-bed desulfurization and demonstrated the possible solutions. It is beneficial to promote industrial application by improving the utilization efficiency of Ca-based adsorbent, reducing the amount of adsorbent and operation cost, and developing ideal regeneration methods.

Resource utilization of high-concentration SO2 for sulfur production over La-Ce-Ox composite oxide catalyst

Sulfur dioxide is one of the main causes of air pollution such as acid rain and photochemical smog, and its pollution control and resource utilization have become important research directions. La₂O₃ was incorporated into CeO₂ to enhance the surface basicity of La-Ce-O_x catalyst and increase the concentration of chemisorbed oxygen, thereby promoting the improvement of catalytic performance of SO₂ reduction by CO. Results have showed that the incorporation of La₂O₃ would not only increase the concentration of chemisorbed oxygen and hydroxyl on the catalyst surface, but also increase the basicity of the catalyst, thereby facilitating the adsorption of SO₂ on the catalyst surface. The 12%La-Ce-O_x was the optimal catalyst, and its SO₂ conversion at 350-400 ℃ reached close to 100%, and the sulfur yield at this temperature range was higher than 93%. Finally, according to the in situ infrared diffuse reflectance spectrum, it was found that the main reaction intermediates of 12%La-Ce-O_x in the catalytic reduction of SO₂ were weakly adsorbed sulfate, SO₃^2-, non-coordinating CO₃^2-, monodentate carbonate, and CO, so the catalytic reaction followed the L-H and E-R mechanisms simultaneously.

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.

Effect of CO2 on the Desulfurization of Sintering Flue Gas with Hydrated Lime

The effect of carbon dioxide (CO₂) on the desulfurization of sintering flue gas with hydrate (Ca(OH)₂) as an absorbent was investigated, and the formation of calcium carbonate (CaCO₃) and its effect on the desulfurization was discussed. The competitive relationship between carbon dioxide (CO₂) and sulfur dioxide (SO₂) with the deacidification agent in sintering flue gas is discussed thermodynamically, showing that sulfates are more likely to be generated under high oxygen potential conditions and that SO₂ reacts more preferentially than CO₂ under a thermodynamic standard state. The amount of produced CaCO₃ increases under the condition that the CO₂ concentration is absolutely dominant to SO₂ in the sintering flue gas atmosphere. The effect of temperature, humidity and CO₂ concentration on the desulfurization of Ca(OH)₂ are discussed experimentally. The increasing temperature is not conducive to desulfurization, and the humidity can promote desulfurization, while excessive humidity could inhibit desulfurization. The suitable relative humidity is 20%. In situ generated calcium carbonate has a certain desulfurization effect, but the desulfurization effect is not as good as Ca(OH)₂. However, a large proportion of CaCO₃ was produced in the desulfurization ash under the condition that CO₂ concentration was absolutely dominant to SO₂ in the sintering flue gas atmosphere.

Influence of H2O and SO3 on fine particles coagulation for sintering flue gas after desulfurization in an alternating electric field

Electric coagulation of fine particles has been studied in the simulated sintering flue gas after semi-dry desulfurization to quantify the influence of H₂O and SO₃. The electric coagulation platform has a DC charging zone and an AC coagulation zone. Fine particles were divided into different diameter intervals to deeply explore the impact of H₂O and SO₃, including less than 0.15 μm (PM_0.15), 0.15-0.5 μm (PM_0.15-0.5) and 0.5-1 μm (PM_0.5-1). The particle charge, mass fractions of fine particles, and the mean diameter are measured and compared under water and SO₃ atmosphere. The experiments showed that the increasing AC voltage helps particles larger than 0.5 μm to coagulate but has little effect on the rest particles without H₂O or SO₃. Both H₂O and SO₃ enhance the PM_1.0 AC coagulation. When flue gas relative humidity went up from 20 to 80%, the charge per particle maximally increased by 120%, as well as the mass fraction of PM_0.5-1, PM_0.15-0.5, and PM_0.15 decreased by 83.2%, 64.5%, and 66.6%, respectively. When the SO₃ concentration rose up from 0 ppm to 12.3 ppm, the charge per particle maximally increased by 100%, as well as the mass fractions of PM_0.5-1, PM_0.15-0.5, and PM_0.15 decreased by 54.5%, 28.6%, and 33.3%, respectively. The impact of water and sulfuric mist on the particle intervals was sequenced as: PM_0.5-1 > PM_0.15 > PM_0.15-0.5. The influence on PM_1.0 AC coagulation was sequenced as H₂O > sulfuric mist > AC voltage. Through data regression, H₂O had approximate linear correlation with the particle mass fractions while the impact of sulfuric mist was non-linear. The interparticle forces were calculated to analyze the dominant force of particle AC coagulation with water: liquid bridge force > Coulomb force >  > van der Waals force. The liquid bridge force indicated that liquid film was form on the surface of fine particles when water or sulfuric mist was added into the system which was the main reason enhancing the AC coagulation.