Semi-dry Flue Gas Desulfurization Research Articles

Resource utilization of semi-dry flue gas desulfurization ash by thermal treatment on sintering machine

Semi-dry flue gas desulfurization ash (SFGDA) is an abandoned Ca and S resource that is currently stacked without appropriate disposal methods. A technology with industrialization potential, SFGDA, and iron ore thermal processing is an effective approach to obtaining calcium ferrite and industrial sulfuric acid. This study investigated the thermochemical reaction mechanism of SFGDA during high-efficiency pyrolysis employing Fe2O3 and coke powder for self-heating. The results showed that the addition of coke powder enhanced the thermal efficiency and reduced the decomposition temperature, while the reaction is accelerated by the lightning-fast combination of Fe2O3 with the CaO produced during pyrolysis to generate calcium ferrite products. The optimal conditions were determined to be a coke powder dosage of 10% and Fe2O3 dosage of 50%. In semi-industrial experiments, the SFGDA achieved a desulfurization rate of 99% and a calcium ferrite content of 85%. The calcined product CaO from CaSO4 and CaSO3 in the form of calcium ferrite products, with a minimal amount of CaSO4. In addition, during the high-temperature calcination process performed by the sintering machine, the majority of the sulfur within the raw materials migrates as SO2 and is subsequently emitted into the flue gas. Following, this SO2 is captured and utilized for the production of commercially valuable sulfuric acid. When the yield of enabled to calcined product corresponds to 1 ton, it could potentially dispose of 882 kg of SFGDA, culminating in a high-value, harmless, and large-scale SFGDA treatment in steel industry.

Research on the characteristics of flue gas purification reaction in spouted bed

Semi-dry flue gas desulfurization and purification technology is a promising flue gas treatment technique. This study numerically investigated the influence of factors such as nozzle expansion angle, and fluidized particles diameter on the purification of SO2 and HF in the spouted bed. The study showed that in nozzle expansion angles of 5-25°, the 10° expansion angle is optimal for SO2 and HF purification efficiency. The fluidized particles' diameter affects purification efficiency. Desulfurization and defluorination efficiency are optimal when the ratio of fluidized particle diameter to slurry droplet diameter is 15. When Ca(OH)2 accounts for 0.005–0.01 of the slurry, desulfurization and defluorination efficiency are most cost-effective. According to the principle of chemical equilibrium, a higher Ca/S ratio facilitates a complete reaction with SO2 and HF, ensuring effective purification of the flue gas. The optimal Ca/S ratio is 2.5, with a desulfurization efficiency of 93.55% and a defluorination efficiency of 99.79%.

CFD analysis of the spray droplet parameters effect on gas-droplet flow and evaporation characteristics in circulating fluidized bed desulfurization tower

The circulating fluidized bed flue gas desulfurization (CFB-FGD) process is a promising semi-dry flue gas desulfurization technology. The gas-droplet flow characteristics and droplets evaporation characteristics are critical to improving the desulfurization efficiency of the FGD tower. The effects of droplet parameters, including spray droplet diameter, spray droplet velocity, spray droplet mass flow rate and spray angle are investigated. Two evaluation indices, the coefficient of variation of droplet concentration (CV) and droplet mass-weighted life, are adopted to evaluate mixing degree of gas-droplet and droplet evaporation time, respectively. Results show that as the spray droplet diameter increases from 40 µm to 80 µm, the amount of water droplets trapped by tower wall increases from 3% to 21%. Increasing the spray droplet velocity and spray droplet mass flow rate could effectively increase the turbulent kinetic energy, which could improve the turbulent mixing ability. Moreover, droplet with smaller diameter and high velocity are beneficial to improving the temperature distribution uniformity. When the spray droplet mass flow rate exceeds 2.7 kg/s, the temperature in the tower would be lower than the dew point temperature, resulting in corrosion of the tower wall. Furthermore, the evaporation rate of droplets decreases with the increase of droplet diameter, spray droplet velocity and spray mass flow rate, while increases with the increase in the spray angle. This study would provide a better reference for the optimum operating scheme in practical applications.

Leaching and Oxidization of Semi-Dry Flue Gas Desulfurization Ash of Copper Recycling Industry

Leaching and Oxidization of Semi-Dry Flue Gas Desulfurization Ash of Copper Recycling Industry

Multiple field synergy mechanism of the desulfurization process in the intensified spouted beds

The semi-dry flue gas desulfurization process in the conventional spouted bed (CSB), integral multi-jet spouted bed (IMJSFB), spouted bed with longitudinal vortex generator (SB with LVG) and swirl blade nozzle (SB with SBN) was simulated using the multi fluid model. Meanwhile, the multiphase reaction system of intensified spouted beds was explored based on the field synergy theory. The analysis of the synergy angle among three fields of the gas phase velocity, temperature, and pressure in the spouted bed shows that adding intensification structures can effectively enhance the gas heat transfer and reduce the gas drag and pressure drop. The intensified spouted beds also had better synergy among the multiphase field of velocity, velocity gradient, and temperature gradient. The desulfurization efficiencies in the CSB, SB with LVG, IMJSFB, and SB with SBN were 77.75 %, 80.85 %, 87.97 %, and 88.81 %, respectively, and the promotion effects in descending order of SBN > multi-jets > LVG.

CFD-DEM simulations of a gas-solid-liquid fluidization system: Effects on the flow field and particle behavior of semi-dry desulfurization fluidized bed

Gas-solid-liquid multiphase flow systems have been widely applied in energy engineering, petrochemical industries, biochemical industries and food industries, etc., which usually involve multi-physical processes and multi-reaction stages. As a typical gas-solid-liquid multiphase flow system, the semi-dry flue gas desulfurization fluidized bed has been widely applied by small and medium-scale thermal power plants for its advantages of excellent mixing effect, relatively high efficiency and low cost. This study focused on the fluid hydrodynamics, wet particle motions and the transfer efficiency (SO2 removal efficiency) in a fluidized bed via two-way coupled CFD-DEM numerical simulations with the implementation of different semi-dry desulfurization stages (“constant-rate” absorption stage, “falling-rate” absorption stage and solid absorption stage) as well as the liquid bridge force. To avoid the fast evaporation of small droplets, simulations based on larger particles (Geldart group D) were also conducted to clarify the influence of varying liquid volume contents. Results revealed that the existence of liquid layers would partly enhance the desulfurization efficiency, while in this case the bed exhibits poor fluidization characteristics. Adding humification water in the solid absorption stage would transform the reaction stage from solid absorption stage to “constant-rate” absorption stage, which improves the desulfurization efficiency significantly. It could also be summarized that the increase of Ca/S molar ratio would enhance the desulfurization efficiency partly, but the improvement would not be obvious when the Ca/S molar ratio is greater than a certain range.

A multi-criteria group decision making framework for sustainability evaluation of sintering flue gas treatment technologies in the iron and steel industry

The iron and steel industry (ISI) is at a critical stage of upgrading to ultra-low emission technologies in China. It is imperative to construct a life cycle sustainability evaluation framework as a guide for the selection of ultra-low emission technologies for the ISI. This research developed a novel multi-criteria group decision making framework. Four mature treatment technologies for sintering flue gas (SFG) were selected for analysis from an environmental, economic, and technological multi-dimensional perspective. The results of the life cycle assessment and life cycle costing are incorporated into the evaluation framework. The sustainability of ultra-low emission technologies was evaluated by combining Bayesian and hesitant fuzzy set theories for the first time. The results revealed that of the four alternatives considered, the most sustainable technology consists of semi-dry flue gas desulfurization, bag filter, and selective catalytic reduction denitrification. Triple sensitivity analysis and comparative analysis verified the consistency, robustness, and superiority of the proposed methodology. The interrelationship among criteria showed that technical maturity is key to enhancing the sustainability of ultra-low emission technologies, as it has a significant impact on costs and improves the environmental impact of the system. The conclusions provide optimization suggestions for further improving the sustainability of ultra-low emission technologies for SFG of ISI.

Effect of swirling spouting intensification structure on semi-dry desulfurization process in 3D spouted beds

The swirling blade nozzle structure was introduced at the inlet of flue gas in the spouted bed to enhance interphase mixing and improve the desulfurization efficiency. The computational fluid dynamics (CFD) and experimental methods were used to study the gas–solid two-phase flow, water vaporization and semi-dry flue gas desulfurization processes in a spouted bed with an integral swirling blade nozzle (SB with an ISBN). It is found that the introduction of the swirling blade can significantly intensify heat and mass transfer process in spouted beds, the gas–liquid-solid temperature in the SB with an ISBN is higher than that of the conventional SB. During the desulfurization process, the desulfurization efficiency of spouted bed with an ISBN is about 85.42 %, while that of conventional SB is 76.14 %, and the desulfurization efficiency is increased by 12.2 %.

Sources apportionment of water-soluble inorganic salts in CPM from coal-fired power plants with different emission control technologies

Different control technologies to reduce emissions of sulfur oxides and nitrogen oxides from coal-fired boilers have been adopted globally, leading to significant reductions in these gas emissions, especially over the past several years in China. Comparatively, little attention has been paid to the potential effects of these control technologies on particulate matter (PM) emissions, especially condensable particulate matter (CPM), which is harmful to the atmosphere and human health. In this study, we measured filterable and condensable PM emissions in five coal-fired commercial-scale boilers installed with SNCR or SCR for NOx control and wet, semidry, or dry flue gas desulfurization (FGD) for SO2 emission controls. Water-soluble ionic components in PM were analyzed. The experimental results show that the CPM accounts for 55.9% to 95.1% of total particulate matter (TPM) and is composed primarily of water-soluble SO42- and NH4+, with (NH4)2SO4 being the dominant CPM aerosols. Experimental results also reveal that the flue gas emission control technology significantly affects CPM emission from coal-fired boilers. Since the production of (NH4)2SO4-rich CPM results from the use of ammonia solution for NOx reduction, boilers emit more CPM with SNCR than with SCR because the former operates with a higher ammonia/NOx ratio than the latter. Additionally, the CPM emission is related to the FGD technology installed. Boilers installed with wet FGD emit the lowest CPM, followed by semidry and dry FGDs, because of their decreased capabilities of dissolving and absorbing water-soluble components.

Characteristics of the particulate matter and its toxic substances from different stationary coal-fired sources

Condensable particulate matter (CPM) and uncaptured fine filterable particulate matter (FPM) from various stationary coal-fired sources cause haze weather to harm human health. In this study, we measured the emissions of FPM, CPM, and polycyclic aromatic hydrocarbons (PAHs) from household stoves, small-capacity boilers, and industrial-scale circulating fluidized bed (CFB) boilers. CFB systems installed with dry and semidry flue gas desulfurization (FGD) systems and ammonia-based NOx control systems (SCR/SNCR) emit lesser filterable PM but substantially higher CPM than household stoves and small-capacity boilers. The results indicate that these air emission control technologies have side effects on promoting the generation and emission of CPM, which is rich in (NH4)2SO4 and NH4HSO4. CFB boilers with wet FGD technology exhibit lower CPM emission, suggesting the positive effects of dissolving and absorbing of gypsum slurry on CPM emission. Various small coal-fired stoves burning different types of coal do not significantly affect CPM but the PAHs emissions. Based on the data of this investigation, we estimated the emission inventory of CPM from various stationary coal-fired sources, aiming to provide valuable insights into setting priorities for improving the atmospheric environment in China.

Effects of NOX and O2 on the Reaction of Ca(OH)2 with CO2 at Low Temperatures

The effects of NOX and O2 on the reaction of Ca(OH)2 with CO2 were studied under low-temperature and humid conditions prevailing in dry or semidry flue gas desulfurization processes. Without the simultaneous presence of NOX and O2, the extent of the carbonation of Ca(OH)2 was low and not affected by the concentration of CO2, NOX, or O2. With the simultaneous presence of NOX and O2, the carbonation of Ca(OH)2 was greatly enhanced, and the CO2 capture increased by more than 2 times at a relative humidity higher than 40%; in addition, the relative humidity and NOX concentration had positive effects, the temperature and O2 concentration had negligible effects, but the CO2 concentration had a negative effect. The simultaneous presence of NOX and O2 enhanced the formation of nitric and nitrous acids and salts of calcium nitrate and nitrite. The deliquescence of these salts collected a great quantity of water and thus enhanced the reactions of Ca(OH)2 with the reactive gases. Ca(OH)2 could be completely converted when reacted with the mixture of CO2, NOX, and O2 at a relative humidity ≥ 50% and a NOX concentration ≥ 300 ppm; CaCO3 formed would further react with NOX and O2 to form Ca(NO3)2 when Ca(OH)2 was depleted. The highest CO2 capture obtained was 0.49 g of CO2/g of sorbent (reacted at 60 °C, 70% relative humidity (RH), 12.6% CO2, 2400 ppm NOX, and 5% O2 for 1 h). The major products for the reactions of NO2 with Ca(OH)2 and CaCO3 were calcium nitrite and nitrate, respectively. The capture of CO2 in practice is preferably carried out before removing NOX and after removing SO2 from the flue gas. This work is useful to the development of technologies for CO2 capture using solid wastes containing CaO/Ca(OH)2.

Numerical simulation and optimization of semi-dry flue gas desulfurization in a CFB based on the two-film theory using response surface methodology

Semi-dry circulating fluidized bed flue gas desulfurization(CFB-FGD) is a major industrial FGD technology. Assuming that only one desulfurizer particle is wrapped in each droplet for mass transfer and dissolution, this study proposed a two-film theory-based simplified desulfurization model, with which CFB desulfurization was performed. After model verification, this study simulated the hydrodynamics and desulfurization reaction characteristics and explored the effects of inlet SO2 concentration(A), gas velocity(B), circulating particle mass flux(C), and jet water volumetric flux(D) on the desulfurization efficiency. Simulation results coupling with response surface methodology (RSM) analysis could not only quantitatively reflect the effect degree of a single variable but also apply to the interaction between parameters, thus determining the optimal parameters. RSM results showed that D and CD were the independent and interaction parameters, respectively, that most significantly affected desulfurization efficiency. The simulation under the optimal operating parameters showed that the desulfurization efficiency was greatly improved, reaching 99.69%.

Numerical simulation of gas-droplets mixing and spray evaporation in rotary spray desulfurization tower

Motion and evaporation of droplets significantly affect the semidry flue gas desulfurization efficiency and long-term operation. Both the flow field distribution and the heat and mass transfer in the spray towers are studied by numerical simulation, and the process of droplet motion and evaporation is analyzed in detail. Then, two indices, mixing variance and droplet mass-weighted life, are provided to quantify gas droplet mixing and the droplet group evaporation time. The simulation results show that the radial penetration distance of the droplets is longer with the diameter increase, and the appropriate swirl number improves the mixing between the flue gas and droplets. With the increase of droplet diameter and velocity, the droplet distribution in the tower is more widely, obtaining the optimum mixing variance. The droplet mass-weighted life is promoted linearly with the increase of average droplet diameter and the decrease of flue gas temperature. With flue gas temperature increase from 458 k to 488 K, the droplet mass-weighted life decreases linearly by 31%. In comparison, the initial droplet velocity and spray angle have a slight effect on the droplet mass-weighted life.

Sulfite removal from flue-gas desulfurization residues of coal-fired power plants: Oxidation experiments and kinetic parameters estimation

Semi-dry flue-gas desulfurization (FGD) processes abate 99% of atmospheric emissions of sulfur dioxide from coal-fired power plants at the expense of producing daily tones of solid FGD residues containing sulfites, sulfates, carbonates and hydroxides of calcium and magnesium, besides fly-ashes. In this work, a fluidized-bed reactor pilot plant was used for experiments of dry-oxidation of FGD residues aiming at converting sulfites into sulfates in order to upgrade such residues for utilization as raw material to the cement industry. A two-dimensional design of experiments on the plane of feed air temperature and reactor time-on-stream was conducted in the pilot plant generating sulfite conversion data and transient reactor temperature profiles. These data were used for estimating the first-order kinetic parameters of sulfite conversion via non-linear regression following the Maximum Likelihood Principle. The optimized Arrhenius factor and Arrhenius activation energy obtained via the Nelder–Mead Flexible Simplex method were, respectively, 0.001 mol/kg.s.bar and 14146.5 J/mol. This kinetic model allows designing large-scale plants for treatment of semi-dry FGD residues in order to beneficiate it for utilization in the cement industry, avoiding the disposal and environmental costs of landfilling such residues.

Environmental and economic impact assessment of three sintering flue gas treatment technologies in the iron and steel industry

Increasingly stringent pollutant emission standards pose a new challenge to the control of air pollutants in China's iron and steel industry (ISI). This study quantified and compared the environmental and economic effects of three typical sintering flue gas ultra-low emission treatment technologies in China's ISI, namely, semi-dry flue gas desulfurization + semi-dry flue gas denitration with O3 + bag filter (SSOB), wet flue gas desulfurization + wet electrostatic precipitator + selective catalytic reduction denitration (WWS), and semi-dry flue gas desulfurization + bag filter + selective catalytic reduction denitration (SBS) by conducting a life cycle assessment coupled with life cycle costing method. Using 1 ton of sinter as the functional unit and “cradle to gate” as the system boundary, the environmental impact of the three treatment technologies is 0.1822, 0.1298, and 0.117, respectively and the total economic cost is 11.622, 10.353, and 10.435 RMB, respectively. The ozone oxidation, semi-dry flue gas desulfurization (FGD), and semi-dry flue gas denitration processes are the key processes of SSOB with electricity, liquid oxygen, and sodium sulfite as key substances. Wet flue gas desulfurization process and selective catalytic reduction (SCR) denitration process are the key processes in WWS while electricity is the key substance. Semi-dry FGD and SCR denitration are the key processes in SBS, with electricity and lime as the key substances. SBS has optimal environmental performance, while WWS has lowest economic costs. Optimization suggestions for each technology are presented based on the influence degree of key processes. The research findings will be valuable for the selection and optimization of ultra-low emission technologies of ISI.

Application of Semi-dry Flue Gas Desulfurization Technology in Circulating Fluidized Bed Boilers

The application of semi dry desulphurization technology in a circulating fluidized bed boiler is introduced in the paper. The principle and technical characteristics of semi dry desulphurization process are described in detail. The semi dry desulfurization process has certain reference value in the application of circulating fluidized bed boilers.

Characteristics of water-soluble ions in condensable particulate matter emitted from stationary sources in Wuhan

This study investigated the concentration and characterization of condensable particulate matter (CPM) and filterable particulate matter (FPM) emitted from different stationary sources in Wuhan. The concentrations of FPM and CPM were measured based on USEPA Method 202 and the water-soluble ions in particulate matter were analyzed using ion chromatography. The micro-morphological characteristics of the CPM were detected with scanning electron microscopy (SEM) techniques. The CPM concentrations for coal-fired plant A (Stack#1), coal-fired plant B (Stack#2), sintering plant (Stack#3), incineration plant (Stack#4), cement plant (Stack#5), glass plant (Stack#6) and biomass combustion plant (Stack#7) were 20.30 ± 1.51, 26.00 ± 1.53, 28.68 ± 1.15, 6.82 ± 0.55, 5.41 ± 1.59, 8.49 ± 0.76 and 25.50 ± 1.50 mg/Nm3, which were much higher than the corresponding FPM values except for Stack#3. These results indicate that different types of stationary sources in Wuhan do emit some CPMs. The CPMs collected from wet flue gas desulfurization (WFGD) plants were much higher than semi-dry flue gas desulfurization (SDFGD) plants. Moreover, SO42−, Cl−, NH4+ and NO3− were the major water-soluble ions in the CPM, which accounted for more than 90% of the total ions. These major ions could be mainly transformed from their gaseous precursors of SOX, HCl, NH3 and NOX, respectively. Na+ was more likely to form solid particles and was collected in the CPM filter, while SO42− was more likely to be collected in the impringer in the form of dissolved particulate matter.

Numerical investigation on the water vaporization during semi dry flue gas desulfurization in a three-dimensional spouted bed

Gas–solid two-phase flow and water vaporization processes tend to have a significant impact on the efficiency of flue gas desulfurization with a powder-particle spouted bed. According to the numerical results obtained in this study, the 2D spouted bed developed a classic three-area flow, and the 3D spouted bed entered into a bubbling-like state. The gas and particles flowed in the opposite direction at the junction of the cone and cylinder. The water vaporization rate was higher at the junction of the spout area and the annulus area, lower at the center of the spout area, and the lowest in the annulus area of the 3D spouted bed. Furthermore, it was found that a larger gas velocity, a higher liquid temperature, and a lower gas humidity leads to a higher water vaporization process.

Performance evaluation of semi-dry flue gas desulfurization and denitration from flue gas of a glass melt using nonthermal plasma combined process

Performance evaluation of semi-dry flue gas desulfurization and denitration from flue gas of a glass melt using nonthermal plasma combined process

Calcium sulfate whisker one-step preparation using semi-dry flue gas desulfurization ash and directional growth control

Abstract Calcium sulfate whiskers were prepared under hydrothermal conditions by a one-step method using semi-dry flue gas desulfurization ash with iron ore sintering as the raw material. The effects of temperature, time, speed, and other factors on the calcium sulfate whiskers morphology and growth rule were systematically studied in a high-pressure hydrothermal reaction system. The results demonstrate that the presence of calcium carbonate inhibits high-efficiency desulfurization ash oxidation at low temperatures and affects calcium sulfate whiskers growth. The calcium sulfite content in flue gas desulfurization ash increased to 81.17% when glacial acetic acid was used as the raw material for pickling. In the supersaturated hydrothermal system, the one-step preparation of calcium sulfate whiskers from flue gas desulfurization ash was successful at a reaction temperature of 140 °C, time of 30 min, initial pressure of 2 MPa, initial solid–liquid ratio of 1:30, and rotation speed of 300 r/min. A medium solution purification link was added to create calcium sulfate whiskers products in the hydrothermal reaction system. Calcium sulfate whiskers products with an average diameter of less than 0.8 μm and average aspect ratio of over 140 were obtained at a purification temperature of 60 °C, purification agent concentration of 0.6 mmol/g, temperature of 140 °C, time of 30 min, and speed of 100 r/min.