Coal Combustion Flue Gas Research Articles

Salts-activated synthesis of Cu/Co co-doped biochar for efficient immobilization of elemental mercury from coal combustion flue gas

Mercury immobilization from coal combustion flue gas remains challenging due to the shortage of cost-effective sorbents. In this study, Cu/Co co-doped biochar (CuxCoyBCT) was synthesized through one-step pyrolysis of wood loaded with Cu and Co salts, which was applied to remove elemental mercury (Hg0) from the simulated flue gas. The BET surface area and pore volume of CuxCoyBC650 were vastly higher compared with CuBC650 because of the catalytic effect of cobalt. The synergistic effects between Cu and Co facilitated the transformation of Cu2O into CuO during pyrolysis. The doping of Co resulted in a more uniform dispersion of CuOx and highly dispersed CoOx were also observed in CuxCoyBCT. For this reason, the Hg0 removal performance of CuxCoyBCT was obviously improved after Co doping. The optimal Cu/Co molar ratio and pyrolysis temperature were 1:1 and 650 °C, respectively. The sample of Cu1Co1BC650 showed satisfactory Hg0 removal efficiency (>88 %) over a broad temperature range (100 °C–180 °C). It was remarkable that SO2 facilitated Hg0 removal and H2O had negligible effect on Hg0 removal over CuxCoyBCT. The presence of O2 and NO was conductive to Hg0 removal. The mechanism of Hg0 removal over CuxCoyBCT was further revealed. The results indicated that the heterogeneous adsorption and catalytic oxidation of Hg0 occurred simultaneously, where chemisorbed oxygen, CuO, and Co3O4 served as active components.

Enhancing Concrete with Ultrafine Fly Ash: Mechanical Strength and Frost Resistance

Fly ash, a byproduct collected from the flue gas of coal combustion, serves as an effective additive in concrete. It offers environmental benefits by converting waste into a valuable resource, thus promoting energy conservation, emission reduction, and waste utilization. Additionally, fly ash enhances the mechanical properties and frost durability of concrete. Commonly used as a partial substitute for cement, it helps conserve resources. However, its use may compromise early strength and durability, which limits its applications. The transformation of raw fly ash into ultrafine fly ash through mechanical grinding increases its fineness and specific surface area, thereby boosting its reactivity and micro-aggregate effects. This process produces denser C-S-H gel and optimizes the concrete microstructure. Research shows that although ultrafine fly ash may slightly reduce early concrete strength, it significantly enhances long-term strength, with a 10% substitution improving early compressive strength by 20.2% and later strength by 13.7%. However, excessive fly ash content can reduce frost resistance, with an optimal substitution level at 25% significantly enhancing this property compared to standard concrete. Blending ultrafine fly ash with other mineral admixtures further boosts mechanical properties and frost durability. Challenges include increased processing costs and early strength deficiencies, along with the necessity to control heavy metal content for environmental and health safety. Future research should aim to optimize fly ash particle distribution and reactivity, develop cost-effective production methods, and blend fly ash with other minerals to improve concrete’s mechanical and frost resistance properties, thus expanding its potential applications.

Simulation and experimental study of gas-phase diffusion coefficient of selenium dioxide

Improving the removal effect of selenium in wet flue gas desulfurization system is a key way to reduce the emission of selenium pollutants from coal-fired power plants. In order to clarify the removal mechanism of selenium pollutants in the desulfurization tower, it is necessary to obtain accurate selenium gas-phase diffusion coefficient. In this paper, molecular dynamics simulations were used to carry out theoretical calculations of gas-phase diffusion coefficients of SeO2 (the main form of selenium in coal combustion flue gas). The gas-phase diffusion coefficients of SeO2 in the range of 393 K–433 K were measured by a self-developed heavy metal gas diffusion coefficient testing device to verify the accuracy of the molecular dynamics calculations. Furthermore, the calculated gas-phase diffusion coefficients of SeO2 under typical binary and ternary components were obtained by correcting on the basis of Fuller's formula. Finally, a single-droplet absorption model for SeO2 was constructed and experiments were carried out to compare the effect of the gas-phase diffusion coefficient on the accuracy of the model calculations. The error of the model calculations was reduced from 8.09 % to 1.96 % after the correction. In this study, the gas-phase diffusion coefficient of SeO2 in the low-temperature range of coal-fired flue gas was obtained. This study can provide basic data for the development of selenium migration mechanism and control technology.

Optimizing removal of elemental mercury from flue gas using halide‐impregnated red mud

AbstractMercury (Hg0) emission from coal‐fired industrial plants poses severe threats to ecosystem sustainability and human health, urging the development of novel and cost‐effective adsorbents to treat industrial flue gas. Herein, the modification of industrial residual red mud (RM) through the impregnation of hydrogen halides (HH) and its adsorption characteristics for removing elemental mercury from combustion flue gas was reported. Experimental investigation of HH‐modified RM reveals that the hydrogen iodide (HI)‐modified RM with a concentration of 1.5 M had a maximum Hg0 removal efficiency of 98%, whereas hydrogen bromide (HBr) 1.5 M modified RM had a maximum Hg0 removal efficiency of 90%. The effect of various parameters, such as reaction temperature and halide concentrations, were also found to be influential for the adsorption efficiency of the modified RM. Moreover, it is important to highlight the chemisorption characteristics of HI‐modified RM, which significantly enhances the efficiency of the removal process. The Hg0 removal efficiency increases with the increase in HI concentration (1.5 M @ 93%) with an optimal reaction temperature of 140°C. Furthermore, the maximum Hg0 removal attained with a change in NO concentration was 98% at 200 ppm. However, increasing the SO2 concentration reduces the efficiency of RM for removing Hg0 in simulated coal combustion flue gas. The pseudo‐second‐order model (R2 = 0.98) accurately describes the adsorption of in kinetic investigations, indicating a chemisorption mechanism. This analysis of the chemisorption mechanism highlights the efficiency of halide‐modified industrial solid waste, which has the potential to be used in the design of economical and innovative adsorbents for reducing environmental pollution. The present study employed specific reaction parameters such as reaction temperature, halide loading contents, and different flue gas compositions, which had not been extensively explored.

Facile fabrication of regenerable spherical La0.8Ce0.2MnO3 pellet via wet-chemistry molding strategy for elemental mercury removal

Perovskite-based sorbents have received extensive attention in the field of mercury abatement. However, the excellent Hg0 adsorption performance on the lab scale hardly transforms into industrial-scale utilization because of the elutriation and microcrystalline nature of powdery perovskite sorbent. Hence, the granulation of perovskite into pellets is a strongly solicited and urgent demand. In this work, a universal granulation strategy is exploited for fabricating perovskite sorbent pellets for Hg0 capture from coal combustion flue gas (CCFG) based on a facile wet-chemistry method. This route takes advantages of the unique thermal sensitivity and thermal decomposition characteristics of agar powder and surface tension of medium to simultaneously trade off the molding, pore creation, and mechanical property of perovskite-based sorbent pellets. Besides, silica sol was also added to further enhance the physical strengths of sorbent pellets. The obtained perovskite sorbent pellet (i.e., LCMO-A-Z-2) with a favorable BET surface area of 113.16 m2 g−1 and pore diameter of 8.81 nm, largely facilitating Hg0 diffusion and capture over sorbent pellets. LCMO-A-Z-2 was further employed to Hg0 adsorption experiment under simulated CCFG, which exhibited satisfactory Hg0 adsorption capacity of 2.07 mg g−1 and nearly identical Hg0 adsorption performance after 5 cycles. The weight loss was approximately 13 % after 1000 rotations in the anti-attrition ability experiment suggesting its outstanding mechanical strength. It is reasonable to deduce this granulation method can be readily extended to other powdery sorbents. This work makes first step towards the application of sorbent pellets under application-relevant conditions and support the ultimate implementation of traditional sorbents in various large-scale industrial scenarios.

In situ activation synthesis of tire-derived sorbents for efficient immobilization of elemental mercury from flue gas

Mercury removal from coal combustion flue gas remains a daunting challenge because of the lack of cost-effective sorbents. In this study, the in situ activation synthesis of tire chars was realized through SO2 induction and the tire-derived sorbents were used for elemental mercury (Hg0) removal from the simulated flue gas. Therein the sulfur species in tire chars are regulated. The results indicated that the specific surface area of tire chars was slightly decreased whereas more micropores were generated after SO2 activation. Compared with raw tire char, the sulfur content of tire-derived sorbents was obviously increased. The tire-derived sorbents also contained more sulfur- and oxygen-containing functional groups. For this reason, the Hg0 removal performance of tire-derived sorbents was dramatically increased after SO2 activation. The optimum pyrolysis temperature for the synthesis of tire-derived sorbents was 600 °C. The SO2 concentration in activation atmosphere had little effect on the Hg0 removal performance of tire-derived sorbents. The presence of SO2, NO and O2 was beneficial for Hg0 removal·H2O had little effect on Hg0 removal. The Hg0 adsorption capacity of tire-derived sorbents was further compared with the previously reported sorbents through adsorption dynamic simulations. Furthermore, the mechanism of Hg0 removal over tire-derived sorbents was revealed through XPS analysis and mercury temperature programmed desorption. It was found that the Hg0 removal process was mainly dominated by chemisorption, where organic sulfur species, CO group and COOH/C(O)–O–C group served as active sites for Hg0 capture.

Copper selenide anchored on Ti3C2 MXene via Lewis acidic etching route for efficient removal of gaseous elemental mercury

A fundamental obstacle that restricts the use of metal selenides for gaseous elemental mercury (Hg0) immobilization is the failure to take both the optimization of intrinsic structure favorable for Hg0 diffusion and adequate exposure of metal selenide towards Hg0 into consideration. In this work, a Ti3C2 MXene/Cu2Se sorbent for Hg0 sequestration was synthesized via a Lewis acid etching route combined with room-temperature selenization pathway. During this strategy, copper chloride plays a dual role, i.e., an etching agent for the Ti3C2 MXene synthesis and a precursor for Cu0 decoration. Cu2Se precursors (Cu0) were dispersedly and firmly pre-anchored on the substrate, effectively avoiding the agglomeration and warranting excellent dispersion of Cu2Se. Compared with pristine Cu2Se, Ti3C2 MXene/Cu2Se exhibits advantageous structural characteristics fully boosting Hg0 diffusion kinetics. Meanwhile, the enhanced dispersion of Cu2Se from the prefixation of Cu0 largely enhances the exposure and utilization of selenide. Consequently, Ti3C2 MXene/Cu2Se shows a Hg0 adsorption capacity of 147.64 mg g−1, which is much higher than those of Cu2Se and most other metal selenides. Impressively, its uptake rate of 688.99 μg g−1 min−1 is the highest record rate in metal selenides. Moreover, Ti3C2 MXene/Cu2Se still maintained outstanding Hg0 adsorption performance under relatively high reaction temperature with the shelter of Ti3C2 MXene. Typical fuel gas situations including coal combustion flue gas, smelting flue gas, natural gas have negligible influences on its Hg0 adsorption performance, indicating its extensive applicability and flexibility for actual industrial situations. This work also provides valuable hints for the trade-off of structural properties and ligands exposure to design Hg0 sorbents with satisfactory Hg0 sequestration performances.

Mercury removal from coal combustion flue gas by mechanochemically sulfur modified straw coke and its mercury stability

This work uses widely sourced rice straw as raw material, sulfur containing substances as modifiers, and mechanochemistry as modification methods to prepare the mechanochemical sulfur modified rice straw char mercury removal adsorbent (S-SC). The influence of modifiers, flue gas components, and the environmental stability of mercury removal products were systematically studied. The mechanochemical sulfur modification (elemental sulfur (ES), Na2S, NaHS) can improve the mercury removal performance of raw rice straw char (R-SC). It enhances mercury adsorption and capture. The ES is the best sulfur specie whose mercury removal rate firstly increases and then decreases as the amount of sulfur added increases. Sulfur modification promotes mercury forms convert to HgS (red) or even HgSO4 with higher thermal stability. The thiophene/elemental sulfur are the main sulfur species for promoting mercury removal. SO2 and NO inhibit mercury removal by ES-SC, while HCl has a promoting effect. As their concentration in the flue gas increases, the proportion of mercury removed by adsorption increases, and the adsorbed mercury transforms into a more thermally stable mercury form. The mercury forms of the spent ES-SC are mainly oxidized and residual form with TCLP leaching rate of zero, which has good environmental leaching stability.

Mechanochemical activation of natural metal sulfide minerals for Vapor-Phase mercury immobilization

Man-made metal sulfides (MSs) have been proven to be effective traps for permanent elemental mercury (Hg0) immobilization from anthropogenic sources. However, the fabrication of MSs generally involves complex steps and adopts hazardous precursors, hence compromising its cost-effectiveness and environmental-friendliness. The earth-abundant natural MS minerals might be optimal alternatives to the synthetic MSs, while most of them suffer from limited Hg0 adsorption capacity. Herein, a mild mechanochemical approach under a solid state with the aid of cupric chloride (CuCl2) was developed to modify pyrrhotite (Fe7S8) from calcination of natural pyrite for Hg0 capture from flue gas. After the CuCl2 aided mechanical milling, the Hg0 adsorption capacity and uptake rate of the CuCl2 modified pyrrhotite (CuCl2@Fe7S8) reached as high as 283.3 mg g−1 and 188.75 μg g−1min−1, approximately 400 folds higher than that of raw pyrrhotite. The characterization and density functional theory calculation results reveal that the superior performance of CuCl2@Fe7S8 was primarily attributed to the mechanochemical approach which not only introduced hetero-ligands (i.e., Cl) to the adsorbent to combine with Hg0 but also generated extremely active copper sulfide for binding Hg0. The excellent resistance to temperature fluctuation and flue gas interference and its magnetic separation recyclability warrant the application of CuCl2@Fe7S8 in real-world conditions. Integrated Hg0 removal technologies based on the performance-enhanced recyclable CuCl2@Fe7S8 were also proposed for potential applications in different industrial scenarios including coal combustion flue gas.

Thiol-grafted MnOx/TiO2 as a dual-site adsorbent for removal of Hg0 from simulated coal-fired flue gas

Emissions of elemental mercury (Hg0) from coal-fired power plant have become a great threaten to the ecosystems. Adsorption is a practical strategy for abating Hg0, but limited Hg0-targeted sites is a stumbling block to developing high-efficiency adsorbents. This work aims to design an efficient adsorbent for Hg0 purification at high gas hourly space velocities (GHSV) is achieved by co-implanting porous TiO2 with inorganic–organic dual functional sites (SH and MnOx). The 2SH-MnOx/TiO2 prepared at SH: MnOx ratios of 2:6 is demonstrated a Hg0 removal efficiency of 90 % at 175 °C under a GHSV of 120,000 h−1. Based on Hg-Temperature Program Desorption (Hg-TPD) analysis, the adsorbed Hg0 converted to HgS and HgO at the SH and MnOx sites of the adsorbents, respectively. The existence of MnOx was revealed to facilitate the generation of HgS. Theoretical calculations suggested that the co-existence of SH and MnOx promotes Hg0 adsorption and boost electrons transfer from Hg0 to adsorbent surface. This study provides a new prospect in developing an advanced alternative adsorbent to increase the efficiency of Hg0 removal from coal-combustion flue gas.

Low temperature oxidation of o-xylene by Mn-based catalysts prepared by hydrothermal calcination: Influence mechanism of complicated flue gas components and intermediate product

Catalytic oxidation technology has proven to be an effective method for purifying flue gas of CFPPs. However, conventional catalysts face limitations such as limited activity and vulnerability to contamination from SO2 and H2O. This study aims to assess the efficiency of a newly synthesized Mn-based catalyst, prepared via a hydrothermal-calcination technique, in removing VOCs from simulated coal combustion flue gas. The results demonstrate that the catalyst produced through hydrothermal synthesis, followed by calcination at 400 °C, exhibits a catalytic oxidation efficiency of 96.2% for VOCs at 350 ℃. Furthermore, the catalyst demonstrates anti-poisoning properties. To gain a deeper understanding, we utilized DRIFTS to investigate the mechanism of o-xylene adsorption on the catalyst surface, reaction conversion intermediates, and the influence of complex flue gas components (NH3, NO, and SO2) on the catalytic reaction process. Our investigation provides insight in the improvement of Mn-based catalysts for the removal of VOCs from coal flue gas.

Experimental study on the photocatalytic oxidation of mercury in flue gas with a nano-flowered photocatalyst

To solve the scientific problem of efficient removal of singlet mercury from coal combustion flue gas, we propose to combine it with photocatalytic technology. We have successfully synthesized a novel photocatalytic material by growing iron oxide nanoparticles in situ on the surface of bismuth tungstate material and analyzed the physicochemical properties, chemical composition, morphological structure, and optical properties of the material by XRD, SEM, TEM, EPR, and UV characterization methods. Heterojunctions and oxygen vacancies were constructed to achieve efficient photocatalytic oxidative removal of singlet mercury. The mechanism of action of the enhanced photocatalytic performance is described to provide a feasible solution for the future preparation of photocatalytic materials with high catalytic activity.

Mercury removal over Ce-doped LaCoO3 supported on CeO2 at low temperatures from coal combustion flue gas

Mercury has a significant impact on environment and is mainly derived from coal-fired power plant. Herein, we report a potential route for efficient removal of Hg0 via oxidation reactions using Ce-doped LaCoO3 supported on CeO2 catalyst. Catalyst characterization results proved that Ce can successfully substitute a desired part of Co into the LaCoO3 crystal lattice via a sol–gel method. The Hg0 removal experiments suggest that Hg0 removal efficiency decreased in the order of La0.875Ce0.125CoO3/CeO2 > La0.875Ce0.125CoO3 > LaCoO3. The presence of O2 provided more active oxygen and resulted in approaching 100% Hg0 removal efficiency. Introducing H2O and sole SO2 would significantly reduce the Hg0 removal efficiency as a result of competitive adsorption on the actives sites of the catalyst. On the other hand, SO2 could reacted with Hg0 in the presence of O2 and thereby recover the high Hg0 removal efficiency and the La0.875Ce0.125CoO3/CeO2 catalyst presented a good performance towards sulfur resistance. Furthermore, the catalyst still exhibited a high Hg0 removal efficiency performance after five times consecutive recycles.

First-Principles Study of Hg0 Immobilization on a Defective Pyrite Surface

The formation of defects over a crystal surface could significantly improve the elemental mercury (Hg0) removal performance of pyrite (FeS2). Herein, the role of surface defects in Hg0 immobilization over FeS2(100) was investigated by adopting quantum chemistry. The contribution of surface defects to mercury immobilization over pyrite was mainly manifested in facilitating Hg0 adsorption. Compared with a perfect pyrite surface, a defective pyrite surface exhibited a higher affinity to Hg0, whose adsorption energy was up to −53.03 kJ/mol. In addition, surface defects could induce the dissociation of HCl, a common component in coal combustion flue gas, which provided active chlorine (Cl*) for subsequent Hg0 oxidation. The Langmuir–Hinshelwood mechanism is responsible for Hg0 oxidation over the defective FeS2(100) surface. First, Hg0 and HCl were simultaneously adsorbed over the defective surface, and the presence of defects could promote Hg0 adsorption and HCl dissociation. Subsequently, adsorbed Hg0 would combine with the adjacent active Cl* site, whose energy barrier was 92.60 kJ/mol. Eventually, HgCl could spontaneously react with another Cl* site to form a HgCl2 molecule. Thus, the formation of a HgCl intermediate was the rate-determining step for Hg0 oxidation over a defective pyrite surface. This work reveals the role of defects in Hg0 immobilization over a pyrite surface, which provides a scientific basis for the design and modification of natural mineral sulfide sorbents.

Granulation of Mn-based perovskite adsorbent for cyclic Hg0 capture from coal combustion flue gas

Circulating adsorbents in a fluidized bed integrating elemental mercury (Hg0) adsorption and oxidized mercury decomposition/desorption processes could simultaneously achieve adsorbents recycling and mercury recovery during the flue gas mercury removal. The granulation of adsorbent powder is essential to reduce elutriation the looping system. Herein, powdery La0.8Ce0.2MnO3 perovskite adsorbent, which has been demonstrated to be highly efficient for Hg0 removal, was moulded into 0.8–1 mm pellets by an extrusion-spheronization method. Meanwhile, microcrystalline cellulose (MC) was used as pore-creating template to constructing porous pellets. The results show that the La0.8Ce0.2MnO3 pellets with 20 % MC added during the pelleting process (LCMO-MC) exhibited 90 % Hg0 removal efficiency under a gaseous hourly space velocity (GHSV) of 380,000 h−1, which was comparable to that over the corresponding powdery adsorbent. The LCMO-MC performed well in Hg0 removal at a wide temperature window from 50 to 200 °C. SO2 and H2O displayed slight interference in Hg0 removal, while O2 and NO enhanced Hg0 removal over LCMO-MC. During six adsorption-decomposition/desorption cycles, the LCMO-MC presented outstanding cyclic durability and about 97 % Hg0 removal efficiency was achieved with a GHSV of 50,000 h−1. The excellent Hg0 removal capacity of LCMO-MC was ascribed to the existence of abundant pore channels for Hg0 diffusion, which in-situ retained during the burning of pore-creating templates at high temperature and newly formed accompanying with the burning gas release. These results demonstrate that the template (i.e., MC) assisted extrusion-spheronization approach is promising to mould adsorbent pellets for Hg0 removal in a fluidized-bed system, which could simultaneously realize adsorbent recycling and mercury recovery.

Removal of elemental mercury from flue gas over a low-cost and magnetic sorbent derived from FeSO4-flocculated sludge and rice straw

Capture of elemental mercury (Hg0) from coal combustion flue gas by sorbent injection is still associated with challenges, such as high-cost starting materials, difficulty in separation/reuse of sorbent and SO2 poisoning, in its large-scale application. This work highlighted a facile method to prepare a cost-effective and magnetically responsive mercury sorbent by pyrolysis of FeSO4-flocculated sludge and rice straw. Fe3O4, Fe2O3 and short-chain polysulfide in the sorbent were proven to be the main active sites for Hg0 adsorption/oxidation. Appropriate addition of rice straw into sludge boosted the development of porous structure of the sorbent, which facilitated the migration of Hg0 onto the absorption sites. With straw/sludge mixing ratio of 1:1 and pyrolysis temperature of 700 °C, the obtained SR1T7 exhibited good Hg0 capture ability under harsh gas conditions (1000 ppm SO2 and 3% H2O). At 125 °C, the Hg0 adsorption capacity and average adsorption rate were estimated to be 9.63 mg/g and 1.96 × 10−3 mg/(g⋅min), respectively. To extend its service life, the spent SR1T7 could be collected by magnetic separation, followed by thermal regeneration. SR1T7 might be a prospective alternative to traditional carbon-based mercury sorbent, due to its excellent Hg0 capture ability, good recyclability, decent SO2 resistance and low cost.

Mechanochemical preparation of well-structured copper sulfide for elemental mercury sequestration from coal combustion flue gas

Among various metal sulfides, copper sulfide (CuS) was found to be the most efficient one for the abatement of elemental mercury (Hg0) pollution in coal combustion flue gas because of the enrichment of under-coordinated sulfur along the 〈001〉 direction. Unlike saturated sulfur, the under-coordinated sulfur exhibits a dual role in oxidizing and immobilizing Hg0, but how to effectively synthesize (001) surface exposed CuS through a facile method has long been challenging in the Hg0 controlling community. In this work, a feasible synthesis strategy based on mechanical ball-milling procedure was proposed to synthesize (001) surface exposed CuS under mild conditions. Owing to the controllable nucleus formation and favorable crystalline growth manner under mechanochemical condition, the as-obtained CuS-based sorbent via ball-milling was primarily consisted of well-structured nanosheet containing abundant under-coordinated sulfur ligands, ensuring the adequate exposure of active sites. Consequently, the CuS as obtained exhibited the Hg0 adsorption capacity and uptake rate as high as 86.22 mg g−1 and 112.04 μg g−1 min−1, far surpassing those benchmark metal sulfides as reported in previous studies. Notably, the Hg0 uptake rate of the CuS nanosheet surpasses that of CuS nanoparticle with irregular agglomeration by approximate ten folds. The under-coordinated sulfur, especially polysulfide (Sx2-), was demonstrated to be the primary ligand accounting for the oxidation and sequestration of Hg0 over the surface of CuS nanosheet. This facile synthesis logic with scale-up potential may also be applicable in the preparation of other metal sulfides in addition to CuS, marking an effective attempt stepping towards the industrial application of metal sulfides for Hg0 immobilization from coal combustion flue gas.

A study on the applicability of pulverized coal combustion flue gas desulfurization of alkali metal-based pretreatment desulfurization agent

An experiment was conducted to reduce sulfur oxides by burning low-calorie, low-sulfur sub-bituminous coal treated with an alkali metal-based coal pretreatment desulfurization agent. As a result of pre-combustion treatment with 0.3% desulfurization agent, it was possible to reduce sulfur dioxide by 96.83ppm from 97.10ppm to 0.27ppm on average compared to raw coal at 6% reference oxygen concentration, and the maximum reduction rate was found to be 99.70% on average. Additional research is needed on whether such a reduction rate is possible even in the case of high-sulfur coal treatment, but by using an alkali metal-based pre-combustion desulfurization agent, the emission of sulfur dioxide could be dramatically reduced for low-sulfur sub-bituminous coal. In the future, it will be possible to minimize the emission of sulfur dioxide to the atmosphere by operating in combination with FGD, which is a post-treatment facility.

Investigations into NOx Formation Characteristics during Pulverized Coal Combustion Catalyzed by Iron Ore in the Sintering Process

Sintering accounts for about 50% of the total NOx emissions of the iron and steel industry. NOx emissions from the sintering process can be simulated using the emissions from coke combustion. However, the generation and emission law for NOx burning in the sintering process of pulverized coal is still not clear. The formation characteristics of NOx during coal combustion catalyzed by iron ore fines and several iron-containing pure minerals were studied in this paper. The results showed that iron ore fines can improve the NOx emission rate and increase the total NOx emissions during coal combustion. The type and composition of the iron ore fines have an important impact on the generation and emission of NOx in the process of coal combustion. The peak concentration and emissions of NOx in coal combustion flue gas with limonite, hematite or specularite added increased significantly. The peak value for the NOx concentration in the coal combustion flue gas with magnetite or siderite added increased, but the emissions decreased. Therefore, the generation of NOx in the sintering process can to a certain extent be controlled by adjusting the type of iron-containing raw materials and the distribution of the iron-containing raw materials and coal.

Ultra-high adsorption of Hg0 using impregnated activated carbon by selenium.

Activated carbon was one of the main adsorptions utilized in elemental mercury (Hg0) removal from coal combustion flue gas. However, the high cost and low physical adsorption efficiency of activated carbon injection (ACI) limited its application. In this study, an ultra-high efficiency (nearly 100%) catalyst sorbent-Sex/Activated carbon (Sex/AC) was synthesized and applied to remove Hg0 in the simulated flue gas, which exhibited 120 times outstanding adsorption performance versus the conventional activated carbon. The Sex/AC reached 17.98 mg/g Hg0 adsorption capacity at 160 °C under the pure nitrogen atmosphere. Moreover, it maintained an excellent mercury adsorption tolerance, reaching the efficiency of Hg0 removal above 85% at the NO and SO2 conditions in a bench-scale fixed-bed reactor. Characterized by the multiple methods, including BET, XRD, XPS, kinetic and thermodynamic analysis, and the DFT calculation, we demonstrated that the ultrahigh mercury removal performance originated from the activated Se species in Sex/AC. Chemical adsorption plays a dominant role in Hg0 removal: Selenium anchored on the surface of AC would capture Hg0 in the flue gas to form an extremely stable substance-HgSe, avoiding subsequent Hg0 released. Additionally, the oxygen-containing functional groups in AC and the higher BET areas promote the conversion of Hg0 to HgO. This work provided a novel and highly efficient carbon-based sorbent -Sex/AC to capture the mercury in coal combustion flue gas. Graphical abstract Selenium-modified porous activated carbon and the interface functional group promotes the synergistic effect of physical adsorption and chemical adsorption to promote the adsorption capacity of Hg0.