Coal-fired Flue Gas Research Articles

Effect of CO2 on the heterogeneous condensation of water vapor on insoluble fine particles

Heterogeneous condensation preconditioning technology has generated broad interest in removing fine particles from coal-fired flue gas due to its economic and environmental advantages. Here, a flow cloud chamber was used to study the effect of 0%–90% CO2 concentrations on the growth performance of insoluble fine particles with different operational conditions. The results suggest that a higher CO2 concentration in the particle growth environment is detrimental to the fine particles growth. The higher the CO2 concentration, the worse the growth performance. The adverse effect of CO2 on the growth performance decreases with the increase of growth time and the increase of supersaturation caused by temperature, and does not change significantly with the increasing particle concentration.

Hierarchical Fe/ZSM-5 zeolites for efficient Hg0 removal from coal-fired flue gas

Coal-fired induced mercury pollution is an increasing threat to both human health and ecological environment. Herein, to boost Hg0 removal from coal-fired flue gas, we report hierarchically porous Fe/ZSM-5 zeolites through facile chemical treatment (NaOH and HNO3 etching) and FeCl3 post-impregnation. Despite being impregnated with extremely low Fe dosage (0.4 w.t.%), Fe/ZSM-5 by acid-etching shows desirable demercuration (DeHg) ability (>90% under N2 + O2), which largely surpasses the parent ZSM-5 as well as state-of-the-art zeolite-based and carbon-based materials with significantly higher FeCl3 impregnation dosage. Besides, acid-etched Fe/ZSM-5 exhibits good SO2 resistance and long-term DeHg stability under 1200 ppm SO2 and 10% H2O flue gas condition. Comprehensive characterizations and density functional theory (DFT) calculations are further employed to interpret DeHg mechanism. Hierarchical Fe/ZSM-5 produced by acid etching highlights two essential merits: (1) hierarchical porosity significantly facilitates the dispersion of Fe sites and their accessibility to Hg0; (2) reactivity of Fe sites is largely modulated by Bronsted acid, leading to a shielding effect to SO2 as well as the enhanced Hg0 bonding and oxidation performance. The promise of hierarchical zeolites demonstrated in this work would advance the development of low-cost and carbon-free materials for the DeHg application in real-world flue gas.

Study on the treatment of spraying wastewater from coal-fired flue gas by using discharge free radicals

Study on the treatment of spraying wastewater from coal-fired flue gas by using discharge free radicals

Experimental Study on the Removal of NO from Coal-Fired Flue Gas by the Na2SiO3/Fenton System

Experimental Study on the Removal of NO from Coal-Fired Flue Gas by the Na₂SiO₃/Fenton System

Simultaneous Adsorption of Gaseous Hg0 and Hg(II) by Regenerable Monolithic FeMoSx/TiO2: Mechanism and its Application in the Centralized Control of Hg Pollution in Coal-Fired Flue Gas

FeMoSx/TiO2 was investigated as a regenerable sorbent to simultaneously adsorb Hg0 and Hg(II) from coal-fired flue gas for the centralized control of Hg pollution discharged from coal-fired power plants. The performance of FeMoSx/TiO2 for Hg(II) and/or Hg0 adsorption was evaluated on a fixed-bed reactor at 80 oC, and the mutual interference between Hg0 adsorption and Hg(II) adsorption was analyzed using individual adsorption, simultaneous adsorption, and two-stage adsorption. FeMoSx/TiO2 displayed an excellent capacity for individual Hg0 adsorption (41.8 mg g-1) and a moderate capacity for individual Hg(II) adsorption (0.48 mg g-1). Two types of adsorption sites were present on FeMoSx/TiO2 for gaseous Hg adsorption (S0 and FeS2/MoS3 sites). X-ray photoelectron spectroscope and kinetic analyses demonstrated that Hg0 and Hg(II) could adsorb onto S0 sites, whereas only Hg0 was adsorbed onto FeS2/MoS3 sites. As Hg0 competed with Hg(II) for the S0 sites, the amount of Hg(II) adsorbed slightly decreased by 16% in the presence of Hg0. However, Hg0 adsorption onto the FeS2/MoS3 sites predominated over the Hg0 adsorption onto FeMoSx/TiO2 and it was not inhibited in the presence of Hg(II). Therefore, the amount of Hg0 adsorbed on FeMoSx/TiO2 was only decreased by 2% in the presence of Hg(II).

As2O3 removal from coal-fired flue gas by the carbon-based adsorbent: Effects of adsorption temperature and flue gas components

Gaseous As2O3 emitted from the coal-fired power plant is one of the most carcinogenic and harmful pollutants. In this work, the commercial activated carbon (AC), wood chip-based biomass coke (BC), and KOH activated high-sulfur petroleum coke (PC) were selected, and the effects of adsorption temperature and flue gas components on gaseous As2O3 removal of the carbon-based adsorbents were investigated. The results show that under the basic adsorption conditions, the As2O3 removal ability satisfies BC > PC > AC with the best arsenic removal ability of BC at 150 ℃. Increasing the adsorption temperature benefits the oxidation of As3+ to As5+ on the surface of the three carbon-based adsorbents. Oxygen-containing functional groups (C–O and O–C=O), Al2O3, K2S, and K2SO4 are the main active sites for As2O3 chemisorption. Overall, increasing adsorption temperature leads to the first increase and then decrease in arsenic removal ability of carbon-based adsorbents. Physical adsorption is the main reason for the change in their arsenic removal ability. The weakening degree of physical adsorption is higher than the promotion of chemisorption with increasing adsorption temperature. NO has inhibitory effects on the As2O3 removal by BC. Low concentration (<4000 ppm) SO2 can promote the As2O3 removal by BC due to the formation of SO42- and the increased content of oxygen-containing functional groups.

Simultaneous removal of NO and elemental mercury from coal-fired flue gas using natural ferruginous manganese ore at low temperature

Natural ferruginous manganese ore (FMO) was developed as a cost-effective NH3-SCR catalyst for the simultaneous removal of NO and elemental mercury (Hg0) from coal-fired flue gas. The chemical composition, pore structure, crystal structure and surface chemistry of FMO were characterized by different methods. The results showed that FMO was constructed with sheet-like structures. There were massive slit-shaped pores in the FMO. Manganese and iron oxides existed in an amorphous form. After calcination, the NO removal performance of FMO was obviously decreased due to the decomposition of MnO2. A high NH3/NO ratio was conductive to NO removal but excessive NH3 was unnecessary for NO removal. NO could promote Hg0 removal whereas Hg0 had little effect on NO removal. The effects of different SCR atmosphere (inlet, middle layer, and outlet), reaction temperature (100 °C–400 °C), and flue gas composition (O2 and SO2) on NO/Hg0 removal was also studied. At the optimal temperature (200 °C), the NO removal efficiency was greater than 80% and the Hg0 removal efficiency was close to 100%. To some extent, FMO presented preferable SO2 poisoning resistance probably because of the presence of iron oxide. The mechanism of NO/Hg0 removal over FMO was further described. Both fast SCR and conventional SCR reactions happened over FMO during NO removal. Mn4+, Fe3+, and lattice oxygen were first consumed and then replenished by gaseous O2. FMO served as a catalyst for Hg0 oxidation during a long period of denitration process.

Cu-VWT Catalysts for Synergistic Elimination of NOx and Volatile Organic Compounds from Coal-Fired Flue Gas.

A dual-function catalyst, designated as Cu5-VWT, has been constructed for the synergistic removal of NOx and volatile organic compounds under complex coal-fired flue gas conditions. The removal of toluene, propylene, dichloromethane, and naphthalene all exceeded 99% (350 °C), and the catalyst could effectively block the generation of polycyclic aromatic hydrocarbons. Mechanistic studies have shown that Cu sites on the Cu5-VWT catalyst facilitate catalytic oxidation, while V sites facilitate NOx reduction. Thus, toluene oxidation and NOx reduction can proceed simultaneously. The removal of total hydrocarbons and nonmethane total hydrocarbons from 1200 m3·h-1 real coal-fired flue gas by a monolithic catalyst were determined as 92 and 96%, respectively, much higher than those of 54 and 72% over a commercial VWT catalyst, indicating great promise for industrial application.

Experimental study and modified modeling on effect of SO2 on CO2 absorption using amine solution

Understanding the competitive mechanism in absorption process between SO2 and CO2 is essential for simultaneous absorption of SO2 and CO2. In this study, the effect of SO2 on CO2 absorption using amine solution was studied experimentally and theoretically. The CO2 absorption rates in MEA/MMEA/MDEA solutions were determined using wetted wall column. Results showed that the reduction of flue gas temperature was beneficial for CO2 absorption at the typical coal-fired flue gas CO2 concentration. On this basis, the effect of SO2 on CO2 absorption performance was studied. Firstly, the overall CO2 mass transfer coefficient decreased under exposure to SO2. Secondly, in the presence of SO2, pH variation of amine solution increased. In addition, the saturated CO2 capacity largely decreased when SO2 was continuously bubbled into the solution. Furthermore, the quantum chemical calculation showed that CO2 had little effect on the absorption performance of SO2 whereas SO2 greatly weakened the interaction between CO2 and amines. The overall CO2 mass transfer coefficient was modified considering the effect of SO2. The competitive absorption factor, χ, was introduced to modify the CO2 liquid phase diffusion coefficients. The average deviation of overall CO2 mass transfer coefficient narrowed to 1.76 % (0.5 mol/L MEA), 1.13 % (1.0 mol/L MEA), 1.88 % (1.0 mol/L MMEA) and 1.43 % (1.0 mol/L MDEA) respectively, which agreed well with the experimental results.

Study on Comprehensive Purification Technology of Coal-fired Flue Gas

Study on Comprehensive Purification Technology of Coal-fired Flue Gas

The Effects of Physical-Chemical Evolution of High-Sulfur Petroleum Coke on Hg0 Removal from Coal-Fired Flue Gas and Exploration of Its Micro-Scale Mechanism.

As the solid waste by-product from the delayed coking process, high-sulfur petroleum coke (HSPC), which is hardly used for green utilization, becomes a promising raw material for Hg0 removal from coal-fired flue gas. The effects of the physical–chemical evolution of HSPC on Hg0 removal are discussed. The improved micropores created by pyrolysis and KOH activation could lead to over 50% of Hg0 removal efficiency with the loss of inherent sulfur. Additional S-containing and Br-containing additives are usually introduced to enhance active surface functional groups for Hg0 oxidation, where the main product are HgS, HgBr, and HgBr2. The chemical–mechanical activation method can make additives well loaded on the surface for Hg0 removal. The DFT method is used to sufficiently explain the micro-scale reaction mechanism of Hg0 oxidation on the surface of revised-HSPC. ReaxFF is usually employed for the simulation of the pyrolysis of HSPC. However, the developed mesoporous structure would be a better choice for Hg0 removal in that the coupled influence of pore structure and functional groups plays a comprehensive role in both adsorption and oxidation of Hg0. Thus, the optimal porous structure should be further explored. On the other hand, both internal and surface sulfur in HSPC should be enhanced to be exposed to saving sulfur additives or obtaining higher Hg0 removal capacity. For it, controllable pyrolysis with different pyrolysis parameters and the chemical–mechanical activation method is recommended to both improve pore structure and increase functional groups for Hg0 removal. For simulation methods, ReaxFF and DFT theory are expected to explain the micro-scale mechanisms of controllable pyrolysis, the chemical–mechanical activation of HSPC, and further Hg0 removal. This review work aims to provide both experimental and simulational guidance to promote the development of industrial application of Hg0 adsorbent based on HSPC.

Recycle of waste activated coke as an efficient sorbent for Hg0 removal from coal-fired flue gas

The desulfurized activated coke was recycled through thermal regeneration to recover Hg0 from coal-fired flue gas. And the thermal treated activated coke was also prepared for comparison. BET, acid-base titration, XPS and O2-TPD characterizations were performed to identify the structural and chemical properties. Although possessing decreased BET surface area and enlarged pore diameter after thermal treatment, AC-400 exhibited the enhanced Hg0 removal performance due to the generation of oxygen functional groups, while the treatment at 900 °C resulted in the decomposition of surface active oxygen species. Besides, not only the strengthened promotion on the formation of carbonyl and ester groups, but also the deposition of SO42− during regeneration should be responsible for the superior activity of regenerated desulfurized activated coke (RAC) for Hg0 removal. Besides, O2 addition could weaken the competition between NO/SO2 and Hg0, and facilitate the formation of Hg(NO3)2/HgSO4. In combination with Hg-TPD, the specific surface area was in closely correlation with the physisorption of Hg0 on activated coke, and the chemisorption, as the predominant mechanism, of Hg0 mainly depended on the surface active oxygen species. Moreover, when reacted at 60 °C, the Hg0 adsorption priority on RAC was as follows: ester ≥ carbonyl ≥ SO42− ≥ physisorption, and the carbonyl was the leading active sites for mercury adsorption.

Highly efficient removal of toluene over Cu-V oxides modified γ-Al2O3 in the presence of SO2

Developing efficient catalysts with good resistance to complex flue gas is essential for VOCs removal in coal-fired flue gas. In this study, by exploring the effect of transition metal oxide additive, metal loading and bimetallic synergy on toluene oxidation in coal-fired flue gas, 10Cu-3V/γ-Al2O3 is identified as the optimal catalyst. It achieves 90% of CO2 generation at 350 ℃, which is decreased by ca. 46 ℃ compared with 13Cu/γ-Al2O3. And it also exhibits good resistance to H2O and good stability. ICP-OES, N2 adsorption-desorption isotherms, XRD, TEM, XPS, EPR and H2-TPR analyses were applied to characterize the catalyst composition and physicochemical properties. Doping V into 13Cu/γ-Al2O3 not only leads to better dispersity of CuO and homogeneous elements distribution that benefits to produce more active centers, but also constitutes the redox cycle of V5+ + Cu+ ↔ V4+ + Cu2+ which induces more surface chemical oxygen (Osur). Moreover, since SO2 is the main inhibiting factor in toluene oxidation, the SO2 poisoning mechanism was illustrated by XPS, TG and in situ DRIFT analyses in depth.

Influence of SO3 on the MnOx/TiO2 SCR catalyst for elemental mercury removal and the function of Fe modification

Elemental mercury (Hg0) is a highly hazardous pollutant of coal combustion. The low-temperature SCR catalyst of MnOx/TiO2 can efficiently remove Hg0 in coal-burning flue gas. Considering its sulfur sensitivity, the effect of SO3 on the catalytic efficiency of MnOx/TiO2 and Fe modified MnOx/TiO2 for Hg0 removal was investigated comprehensively for the first time. Characterizations of Hg-TPD and XPS were conducted to explore the catalytic mechanisms of Hg0 removal processes under different conditions. Hg0 removal efficiency of MnOx/TiO2 was inhibited irreversibly from 92% to approximately 60% with the addition of 50 ppm SO3 at 150 ℃, which resulted from the transformation of Mn4+ and chemisorbed oxygen to MnSO4. The existence of H2O would intensify the inhibitory effect. The inhibition almost disappeared and even converted to promotion as the temperature increased to 250 ℃ and above. Fe modification on MnOx/TiO2 improved the Hg0 removal performance in the presence of SO3. The addition of SO3 caused only a slight inhibition of 1.9% on Hg0 removal efficiency of Fe modified MnOx/TiO2 in simulated coal-fired flue gas, and the efficiency maintained good stability during a 12 h experimental period. This work would be conducive to the future application of MnOx/TiO2 for synergistic Hg0 removal.

Facile synthesis of phosphorus-doped porous biochars for efficient removal of elemental mercury from coal combustion flue gas

• An efficient sorbent was synthesized for Hg 0 removal through heteroatom doping. • More pore networks and functional groups were formed on the biochar after P doping. • The Hg 0 adsorption capacity of biochar was increased by 411 times after P doping. • The C-P = O, C = O, and O-C = O groups served as active sites for Hg 0 removal. Heteroatom doping is an effective method to modify carbonaceous sorbents and improve their chemical reactivity. In this study, P-doped biochars (PBCs) derived from one-step pyrolysis of H 3 PO 4 -laden biomass were developed for elemental mercury (Hg 0 ) removal from coal-fired flue gas. Sample characterization showed that there were massive micropores and slit-shaped mesoporous in the PBCs. The specific surface area and pore volume of PBCs was obviously enhanced after P doping. In addition, more organic functional groups were generated on the PBCs surface, particularly the C-P=O and C=O groups. The PBCs presented far higher mercury removal efficiency compared with raw biochars (BCs). The influences of pyrolysis temperature (700 °C-1000 °C), adsorption temperature (25 °C-180 °C), and various flue gas components (NO, SO 2 , O 2 , HCl, and H 2 O) on mercury removal performance were also analyzed. At the optimum temperature (100 °C), the Hg 0 adsorption capacity of PBC 900 was increased by more than 400 times compared with BC 900 , which was also higher than that of a commercial brominated activated carbon. The mechanism responsible for Hg 0 removal was further revealed. The results suggested that chemisorption dominated the Hg 0 removal process, where the C-P=O, C=O, and O-C=O groups could serve as electron acceptors, accelerating the electron migration process for Hg 0 oxidization.

Effect of Fouling Layer (Acid–Ash Reaction) on Low-Temperature Corrosion Covering Heating Surface in Coal-Fired Flue Gas

Improving the efficiency of coal-fired boiler is beneficial for greenhouse gas control, mainly for carbon dioxide (CO2). The low-temperature corrosion covering heating surfaces is a frequent threat for coal-fired thermal equipment. The corrosion is induced by a fouling layer, where the ash deposition and condensed acid in coal-fired flue gas react mutually. The corrosion experiments were designed to investigate the reactions of representative acid solution between basic oxides, non-basic oxides, and fly ash particles covering metal surfaces. Scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), X-ray fluorescence (XRF) and X-ray diffraction (XRD) were used to analyze the reaction particles and metal samples collected from experiments. The corrosion rates of 316L steel, 20# steel, Corten steel and ND (09CrCuSb) steel by the sulfuric solution of different concentrations with and without particles were obtained. The results showed that corrosion rate could be reduced by reacted particles, followed as: basic oxides particles &gt; fly ash particles &gt; non-basic oxides particles. Meanwhile, the deposited ash particles with smaller sizes contribute to a deeper acid–ash reactions due to more alkaline oxides accumulated. Thus, the metal surfaces will be covered by denser attachments, playing a function of corrosion resistance. The effect of fouling layer on low-temperature corrosion was obtained, guiding a safe and efficient operation of heat equipment in coal-fired flue gas.

Coordinative sulfur site over flower-structured MoS2 for efficient elemental mercury uptake from coal-fired flue gas

Metal sulfides have recently been considered as promising options for mercury removal owing to their large number of active sulfur sites, environmental friendliness, morphological diversity, resistance to high concentrations of sulfur dioxide, high activity and low cost. Herein, due to the strong affinity between Hg and S, MoS2 was selected to adsorb Hg0 from coal-fired flue gas in power plants. The mercury removal experiments indicate that compared with ZnS, CuS and SnS, MoS2 has the strongest ability to remove elemental mercury. The effects of different adsorption temperatures and different gas components (O2, NO, SO2) and other reaction conditions on the removal performance of Hg0 were further discussed. It was found that the presence of O2, NO or SO2 had no significant effect on the removal of Hg0 by MoS2. Thanks to the abundant edge unsaturated sulfur sites, the flower-like MoS2 not only exhibits good sulfur resistance, but also has excellent long-term stable properties. The equilibrium adsorption capacity of MoS2 is 54.308 mg g−1, and the initial adsorption rate is 66.79 μg g−1 min−1. It is better than most metal sulfide adsorbents, in which the equilibrium adsorption capacity is 24 times that of sulfur modified activated carbon (S-AC), and the initial adsorption rate is 133 times that of S-AC. Moreover, density functional theory (DFT) calculations proved that elemental mercury was chemically adsorbed on surface of MoS2 nanosheets, forming stable HgS. This work can promote the proper design and innovation of adsorbent materials and achieve fruitful treatment of environmental pollutants.

Construction of Cu-BTC by carboxylic acid organic ligand and its application in low temperature SCR denitration

The removal of NO has always been a hot issue in the treatment of coal-fired flue gas. In this paper, a hydrothermal synthesis method was used to prepare porous denitration catalysts with polycarboxyl organic isomers (trimellitic acid, phthalic acid, and benzoic acid). And then developed as the NO removing catalysts for low temperature selective catalytic reduction (SCR) with NH3. XRD, BET, SEM, FTIR, XPS, Raman, H2-TPR, NH3-TPD and TG were used to analyze the crystallinity, microscopic morphology, surface functional groups and metal content. The results showed that: (1) From the crystal structure analysis, the catalyst prepared with 1,3,5 and 1,2,4-benzenetricarboxylic acid as ligands (1,3,5-A and 1,2,4-B) was Cu-BTC. (2) 1,3,5-A catalyst had a huge specific surface area, up to 1421.32 m2/g, and a pore volume up to 0.5798 cm3/g. (3) The prepared catalysts were applied to NH3-SCR denitration, and the catalyst with Cu-BTC structure had relatively high catalytic performance, and the overall catalytic capacity showed an increasing trend with the temperature. (4) 1,3,5-A catalyst had stability and catalytic activity. When the temperature was 270 °C, the denitration efficiency reached 83.87%. And within 8 h, the denitration efficiency was stable up to 82%.

Retention of trace elements in coal-fired flue gas by a novel heterogeneous agglomeration technology

Heterogeneous agglomeration (HA) is a very potential technology for coal-fired flue gas treatment. In this paper, the distribution and migration mechanisms of trace elements (TEs) such as Se, As and Pb in CFPPs were studied on a 30,000 m3/hr pilot-scale experimental platform. The influences of HA on the removal efficiency of gaseous and particulate TEs were well analyzed. The results showed that Se, As and Pb were enriched in fly ash, and their sensitivity to particle size is quite different. The content of Se was the highest in PM1, reaching 193.04 mg/kg at the electrostatic precipitator (ESP) outlet. The average particle size of the total dust before ESP increased significantly from 21.686 to 62.612 µm after injecting the heterogeneous agglomeration adsorbent, conducive to its further removal by ESP. In addition, the concentrations of gaseous Se, As and Pb in the flue gas decreased after adsorbent spray, and accordingly, their contents in the hierarchical particles increased, indicating that the adsorbent could effectively promote the adsorption of gaseous trace elements in fly ash and reduce the possibility of their escape to the atmosphere. Total concentrations of Se, As and Pb emitted by wet flue gas desulfurization (WFGD) are 0.223, 0.668 and 0.076 µg/m3, which decreased by 59.98%, 47.69% and 90.71%, respectively. Finally, a possible HA mechanism model was proposed, where chemical adsorption, physical condensation and collision agglomeration of gaseous TEs and fine particles with adsorbent droplets occurred to form larger agglomerates.

Techno-economic evaluation of a novel membrane-cryogenic hybrid process for carbon capture

• Sub-ambient membrane-cryogenic process was designed for carbon capture. • Effect of selectivity-enhanced membrane were explored. • Parasite load of CFG and BFG decreased 7.11% and 15.55% respectively. • Hybrid process was competitive for scenarios with high CO 2 -content flue gas. Gas separation properties of membranes are the significant parameters in CO 2 capture process. It has been reported that membranes with high permeance and moderate CO 2 /N 2 selectivity are suitable for CO 2 capture from coal-fired flue gas. However, with emerging high selectivity membrane and novel processes, it is essential to evaluate the influence of membrane selectivity on carbon capture performance, especially the significance of sub-ambient membrane operation. In this work, a sub-ambient membrane-cryogenic hybrid process was designed for CO 2 capture from coal fired and blast furnace flue gas. It was found that energy consumption of vacuum can be saved when membranes with high selectivity were operated at sub-ambient condition. The cost and energy consumption of the optimal cases for coal fired flue gas were 36.14 $/tCO 2 and 1.87 GJ/tCO 2 according to the economic evaluation. The parasite load decreased 7.11% over the base case of 168 MW. In addition, the capture cost and energy consumption of optimal case for blast furnace flue gas were 28.81 $/tCO 2 and 1.55 GJ/tCO 2 , respectively. The parasite load decreased 15.55% over the base case of 17.81 MW. The designed hybrid processes presented competitive potential when applied in high CO 2 -content scenarios. In summary, the hybrid process based on membranes and cryogenic has been proven to have economic advantages under simulated conditions, indicating that it has the potential to be amplified by industrialization.