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Mercury, a toxic heavy metal, poses significant risks to human health. Coal-fired power plants are the largest anthropogenic sources of mercury emissions, making mercury removal from flue gas imperative. Among various mercury adsorbents, metal selenides show promising potential in mercury capture. Here, we reported the synthesis of a novel three-dimensional hierarchical flower-like material, SnSe2, and its debut application in flue gas mercury capture. Under the influence of low-coordinated selenium, the introduction of abundant selenium vacancy defects led to the exposure of additional active sites in the adsorbent. Additionally, the presence of Sn enhanced gas selectivity and promoted electron transfer processes, thereby augmenting Hg0adsorption and oxidation performance. Benefiting from these advantages, SnSe2exhibited superior mercury removal performance over a wide temperature range (30–180 °C), with a saturated mercury adsorption capacity of 2027.23 μg/g, surpassing that of commercial activated carbon. Furthermore, the presence of NO in flue gas improved mercury adsorption performance, while high concentrations of SO2do not affect mercury removal efficiency, as elucidated by adsorption kinetics models. Moreover, the mercury adsorption mechanism was demonstrated through mercury temperature-programmed desorption (Hg-TPD) and density functional theory (DFT) calculations. Finally, toxicity characteristic leaching procedure (TCLP) experiments confirmed SnSe2as an efficient and permanent adsorbent for mercury, offering insights into the application of novel mercury removal materials.

Carbon-based materials (e.g., activated carbon and biomass carbons) are widely used porous materials for adsorbing gaseous Hg0as a result of the developed porous structure. However, scarcity of active sites on the carbon-based material surface impedes its application. Existing mainstream modification methods (acid/alkaline substances, halides, sulfides, metal oxides, etc.) have deficiencies relating to high energy consumption, extreme working conditions, and/or secondary pollution. In this work, hydroxyl radicals (•OH) produced by the photochemical advanced oxidation process (UV/H2O2AOP) are used to modify three kinds of carbon-based materials (activated carbon, wheat straw biochar, and corn straw biochar) to form more oxygen-containing functional groups on carbon surfaces, and then these modified carbon-based materials are used to adsorb gaseous Hg0. The interaction between free radicals and the carbon surface, modification mechanism, and adsorption principle of Hg0are preliminarily explored. The UV/H2O2AOP can significantly raise the quantity of oxygen-containing functional groups on carbon surfaces, further resulting in the improvement of the Hg0removal performance. The average Hg0removal efficiencies of the three modified samples (WSW–UV/H2O2AOP, MSW–UV/H2O2AOP, and AC–UV/H2O2AOP) are up to 90.59, 87.55, and 91.46%, respectively, which are significantly higher than those samples modified by UV or H2O2alone (a new synergistic effect for modification is discovered). Chemically adsorbed oxygen (O*) and a C–O functional group are proven to play a vital important function in the adsorbing removal process of Hg0over the tested modified samples.

In this paper, PtCu alloys with varying Pt/Cu ratios were deposited onto TiO2nanocrystals to selectively photoreduce CO2into CH4. The experimental results show that the appropriate Pt/Cu deposition ratio significantly improves CH4production with 100% selectivity. The PtCu alloy not only effectively promotes the separation/transfer of photogenerated charges, but is also beneficial for the adsorption of CO2and the formation and activation of intermediates (CO2−, *COOH, *CO, and *CHO). Furthermore, two paths for *CO formation are observed on the surface of PtCu/TiO2, providing sufficient *CO for CH4generation. Density functional theory calculations show that the synergistic effect of PtCu reduces the activation energy barriers of *CO2and *CHO and inhibits the desorption of *CO, which simultaneously optimizes the efficiency and selectivity of CO2reduction. These findings may provide new insights for exploring alloy cocatalysts for regulating the product selectivity of photocatalytic CO2reduction.

A new type of internally illuminated honeycomb photoreactor was designed. The honeycomb catalyst prepared by using Ce-doped TiO2with 1%–2% vanadium and tungsten was employed for mercury removal from simulated industrial flue gas. The adsorption kinetics in the reaction process were studied. The results showed that the internally illuminated honeycomb photoreactor had good mercury removal performance. When the temperature was 25°C and the ultraviolet (UV) light intensity reached 80 µW/cm2, the mercury removal efficiency reached 92.5%. The mercury removal efficiency increased significantly with the doping ratio of Ce. XPS analysis showed that the oxidation state of Ce changed from 4 to 3 in the mercury removal reaction and produced lattice oxygen, which acts as an oxidant. O2can promote mercury removal by honeycomb catalysts; SO2and HCl also had positive effects, while NO had an inhibitory effect on mercury removal. Kinetic research in the reaction process showed that the quasi-first-order dynamic model had good fitting results, and the correlation coefficients of the fitting results for multiple sets of experimental data were more than 0.999.

Mercury emitted from coal-fired power production industries is an enormous threat to human health and ecosystems. Sorbent injection is a promising and feasible strategy for mercury removal from the flue gas. Activated carbons (ACs) are the most explored mercury sorbents, which generally displayed high adsorption capacity. However, ACs still suffer from some disadvantages, such as impeding the utilization of fly ash in concrete production, difficulty to be regenerated for recycle, and so on. Thus, many noncarbon sorbents have been developed as supplementary options besides ACs for mercury removal. A review on the recent progress regarding noncarbon sorbents for removing mercury is provided. In this contribution, the Hg0removal capacities of natural minerals, waste-derived sorbents, metal oxides, metal sulfides, and magnetic adsorbents have been summarized. Particularly, the modification methods as well as their intrinsic roles for each types of noncarbon sorbents have been presented and discussed in depth. This work provides guidance for the design and exploration of noncarbon adsorbents, which can be applied in both coal-fired power plants and other nonpower production industries.

Oxygen carriers (OCs) are the key factor in chemical looping combustion (CLC), a promising and efficient technology for converting coal and biomass into pure carbon dioxide and high concentrations of hydrogen. However, existing CLC techniques cannot completely separate OCs and ash, which could affect the performance of the OCs through the interaction with the ash-forming mineral matter at a high temperature. In this work, the effect of solid–solid carbothermal reactions on the Fe-based OC was systematically examined via changes in the carbon content and temperature. Furthermore, the CLC of the Fe-based OC was simulated by a fixed bed reactor, with oxidizing and reducing gases switched constantly. The results indicated that the added amount of biomass carbon had a significant influence on the Fe-based OC. Under highly reducing conditions, the reduction between Fe2O3and C took precedence and inhibited the reaction between Fe2O3and minerals. Under weakly reducing conditions, the reactions between Fe2O3and minerals were promoted. In the looping experiment of the Fe-based OC and ash, a small amount of ash could promote the reduction of Fe2O3. When ash accumulated, some foreign ions (Ca2+, K+, and Na+) in the ash interacted with the aluminosilicate to form compounds with lower melting points, covering the surface of Fe2O3particles to hinder the reaction. Increasing the cycle temperature not only accelerated the reaction of Fe2O3but also promoted the formation of large particles, such as (Fe2SiO4)x·(Fe3O4)1–xand CaMgSi2O6, which aggravated sintering and decreased the oxygen-releasing performance of the OC.

Sorbent injection in coal-fired flue gas is complicated, and the performance of sorbents in a duct is much different from that in a fixed bed. For a better understanding of sorbent injection performance in the actual flow state, experiments on mercury removal by CuCl2-modified activated carbon (CuCl2-AC) were conducted in an entrained flow reactor. The effects of reaction conditions and gas flow parameters have been researched, such as initial Hg0concentration, sorbent injection concentration, residence time, and reaction temperature. Compared with raw activated carbon, CuCl2-AC exhibits superior performance in mercury removal under various conditions. Experimental results show that Hg0removal efficiencies of CuCl2-AC rise with an increase of initial Hg0concentration and residence time. In the entrained flow reactor, influences of flue gas components and reaction temperature are not remarkable on the performance of CuCl2-AC. Besides, the results of the entrained flow reactor show good agreement with the mass-transfer adsorption model for sorbents in flue gas, which indicates that CuCl2-AC has the potential for mercury capture after being injected into the duct.

As an important contributor to the atmospheric SOA formation, the oxidation of the sesquiterpenes including α-Cedrene are widely considered to play a significant role in atmospheric chemistry, especially for the HOMs formation. Comparable concentrations of the sesquiterpenes (SQTs) detected over the marine boundary layer as those of in terrestrial ecosystems in recent atmospheric campaign, which aroused extensive concern of the SQTs oxidation and its impact on SOA formation in the marine atmosphere. In this work, we comprehensively investigated the oxidation of a representative sesquiterpene (α-Cedrene) initiated by OH, Cl, ClO and BrO radicals and the resulting HOMs formation. For the initial reactions, OH/Cl/ClO/BrO addition reactions are favored over H-atom abstractions by these radicals from the thermodynamic aspect. Seven main first-generation products yielded from the sequential oxidation of the addition adducts by O2and NO/HO2radical under different atmospheric conditions, such as 2-acetyl-1,1,4-trimethyloctahydropentalene-3a-carbaldehyde. Furthermore, three pathways of the HOMs formation were proposed and compared, (1) autoxidation, (2) multiple H abstractions by OH, Cl, ClO and BrO radicals and the succeeding reactions with HO2, and (3) the sequential association reaction of peroxy radicals and OH radical to form ROOOH. For the HOMs formation from the oxidation of α-Cedrene by OH and BrO radicals, the pathway (2) and (3) are thermodynamically feasible under the atmospheric conditions. As most of the H abstractions by Cl and ClO radicals could be difficult to occur, the produced HOMs with more than four or five oxygen atoms could be restricted. To our knowledge, this is the first report for clarifying the oxidation processes of SQTs in the marine atmosphere, which would contribute to the evaluation of the impacts of biogenic volatile organic compounds on the Marine atmosphere.

High-purity hydrogen was produced by catalytic steam reforming of coke oven gas (COG) in a fluidized bed membrane reactor (FBMR), assisted by calcined dolomite and a tubular palladium membrane. This membrane-assisted and sorption-enhanced steam-COG reforming process was denoted as MA-SE-SRCOG. A novel bimetallic Ni–Fe/mayenite (Ca12Al14O33) catalyst was first tested in a fixed bed reactor and was then applied to steam reforming of COG in the pilot-scale FBMR. The Ni-0.1Fe/mayenite catalyst showed good sulfur tolerance during steam reforming of COG, and no carbon deposition was detected on the catalyst surface. Partial substitution of “free oxygens” in Ca12Al14O33by sulfur to form Ca12Al14O32S was observed by XRD characterization. With hydrogen being separated by palladium membrane and CO2being captured by calcined dolomite, a hydrogen recovery efficiency > 1.7 along with a CH4conversion of 0.93 and near-zero CO selectivity was achieved by steam reforming of COG at 560 °C, S/C = 4 in the FBMR. Initial CO and H2contents suppressed conversion of CH4during steam reforming of COG at specific operating temperature, and restrictions from initial CO were more serious than initial H2. MA-SE-SRCOG efficiently overcame the restrictions of initial CO and H2and was able to produce over 4.0-fold H2from COG. A hydrogen permeation flux of 2.14 × 10–2–3.34 × 10–2mol/m2·s having a purity of >99.9 vol % (with deletion of N2) was obtained at the permeation side. Excessive steam (S/C > 4) was observed to decrease CH4conversion, which could be ascribed to the decreased residence time of reactants and increased bypassing of reactants through large voids in the reactor at a high S/C ratio. Over high concentration of steam in the reactor side also inhibited permeation of H2. Strong attachment of filler particles on the Pd membrane surface was detected by EPMA analysis, but no metal contents from the catalyst/sorbent were found inside the Pd layer yet after 30 h serving in FBMR.

Magnetic biochar (MBC) has been proven to be an efficient sorbent for elemental mercury (Hg0) removal from coal-fired flue gas in our previous studies. However, SO3is an acidic component of flue gas, and its role in Hg0removal by MBC has not been determined. In this work, the Hg0removal behaviors and the mechanisms involved were investigated in the presence of SO3. The results showed that SO3notably impeded the Hg0adsorption process, whereas the oxidation efficiency of Hg0increased as the SO3concentration increased. The inhibitory effect of SO3on Hg0adsorption was attributed to competitive adsorption between SO3and Hg0as well as the formation of metal sulfates on the MBC surface. Moreover, the addition of SO3into the atmosphere resulted in the generation of HgSO4, especially when H2O was also present. Additionally, the deposition of HgSO4and H2SO4further hindered the removal of Hg0by MBC. Nevertheless, SO3promoted the formation of C═O groups, resulting in the higher Hg0oxidation efficiency observed. In addition, more mercury that was adsorbed on the MBC was transformed into HgO in the presence of SO3. This work illustrated the effect of SO3on Hg0removal by MBC and explained the mechanism involved, which will help with the further development of an efficient sorbent for Hg0removal.

In this study, montmorillonite (MT) was modified separately with CuO and CuCl2through impregnation and then used to remove elemental mercury from simulated coal-fired flue gas. The effects of several factors, including the Cu loading amount, reaction temperature, and partial flue gas components as well as the stability of the mercury removal properties of the sorbents, were investigated. Various techniques, including Brunauer–Emmett–Teller measurements, X-ray fluorescence analysis, X-ray diffraction analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy, were used to characterize the physicochemical properties of the sorbents. The obtained results showed that the sorbents with the optimal Cu loading rates, namely, 10.0% CuO/MT and 1.0% CuCl2/MT, exhibited high and stable performances, with their average Hg0removal efficiencies being approximately 71.0 and 92.0%, respectively, at 150 °C. Moreover, the effects of the reaction temperature on the mercury removal properties of the two sorbents were different. Both O2and NO significantly promoted the removal of elemental mercury, whereas SO2inhibited it. The mechanisms of Hg0capture are discussed based on the obtained results. Both the lattice oxygen (Oα) and the chemisorbed oxygen (Oβ) species contribute to the catalytic oxidation of Hg0in the case of 10.0% CuO/MT. On the other hand, for 1.0% CuCl2/MT, the active chlorine (Cl*) species and Cu in the oxidation state (Cu2+) aid the catalytic oxidation of Hg0. Hence, 1.0% CuCl2/MT, which exhibited excellent Hg0removal performance, can be considered a promising Hg sorbent for various applications.

Mercury emission is an important issue during in-situgasification chemical-looping combustion (iG-CLC) of coal. This work focused on experimentally “isolating” two elementary subprocesses (coal pyrolysis and char gasification) during iG-CLC of coal, identifying mercury distribution within the two subprocesses, and examining the effects of a hematite oxygen carrier (OC) on the mercury fate. The mercury measurement accuracy was carefully ensured by comparing online measurements (by a VM 3000 instrument) and benchmark measurements (by the standard Ontario Hydro Method, ASTM D6784) as well as repeated tests (10 times for each case). The mercury mass balance was 115% for the entire iG-CLC. A total of 44.7% of the mercury was released as the gas phase form within the coal pyrolysis process at a typical CLC operation temperature (950 °C), whereas 13.4% was released during the char gasification process. The release rate and amount of mercury were minimally affected by the presence of OC; however, the OC promoted the conversion of Hg0(g) to Hg2+(g). Only a small amount of mercury was absorbed by the OC and transported into the air reactor along with carbon residue, released as Hg0(g) and Hg2+(g) or remained in the OC and coal ash as particulate mercury.

Using an selective catalytic reduction (SCR) catalyst to oxidize and remove elemental mercury (Hg0) synergistically is a promising method for mercury emission control in coal combustion power plants and is currently attracting widespread interest. In this study, a developed mercury thermal desorption (Hg-TPD) approach, combined with other associated methods, was employed for the identification of mercury species in the Mn-based SCR catalysts that have been used for synergistic Hg0removal. The analysis results demonstrated that the Hg0adsorption on the catalysts was a necessary process for the Hg0removal, though the SCR catalysts removed Hg0mainly through catalytic oxidation and the amount of the adsorbed mercury contributed only a little to the Hg0removal efficiency. This essential adsorption process was mainly realized through chemisorption. HgO was the prime species that was identified to form in the catalysts, and a little amount of adsorbed HgCl2, Hg(NO3)2, and Hg-OM was detected as well in the samples spent in the simulated coal-fired flue gases. O2, HCl, NO, and high concentration of CO2in the flue gas all promoted the adsorption capacity and the generation of the related Hg compounds, so that they were conductive to Hg0removal efficiency, whereas a similar phenomenon was not observed in the presence of SO2, NH3, and H2O, and meanwhile the amount of adsorbed HgO was decreased, so that the efficiency was inhibited. The mobility testing by a sequential extraction procedure indicated that most of the retained Hg belonged to the mobile fraction, which was in accordance with the identification results of the Hg-TPD analysis. The consequences of this research would create a better understanding of the Hg0removal mechanism over the Mn-based SCR catalysts and provide additional information on the disposal of the retired catalysts in the environment.

TiO2catalyst in an internal-illuminated honeycomb photoreactor was prepared for Hg0removal from flue gas. The Hg0removal efficiency was above 95% under the optimal operation condition. With the increasing TiO2coating value, the Hg0removal efficiency significantly increased. The catalyst calcined at 400 °C presented optimal Hg0removal performance, while higher calcination temperature weakened the Hg0photocatalytic removal activity. Similar Hg0removal performances were obtained under UV irradiation when the reaction temperature was in the range 25–90 °C, and 1.5 mW/cm2of UV light irradiation was competent for Hg0photocatalytic removal. With the same quantity utilization of TiO2catalyst, the internal-illuminated honeycomb photoreactor presented better Hg0removal performance than the fixed-bed reactor. Finally, the procedure of Hg removal from flue gas over TiO2catalyst in internal-illuminated honeycomb photoreactor was proposed, and the product in the Hg0photocatalytic removal process was analyzed as well.

The LaMnO3, CeMnO3, and PrMnO3perovskite oxides were synthesized by the sol–gel method and employed as the catalyst of selective catalytic reduction (SCR) for NO removal and synergistic mercury removal from coal combustion flue gas. The experimental results indicated that CeMnO3exhibited the best NO and Hg0removal activity among the three catalysts. NO conversion over CeMnO3could reach a maximum value of 89.2% in the atmosphere of 4% O2+ 400 ppm NO + 400 ppm NH3, and the optimal reaction temperature for the NO removal was 200–250 °C, demonstrating good low-temperature catalytic activity. Hg0removal efficiency of CeMnO3decreased with the rise of the reaction temperature. The individual flue gas components of O2, HCl, NO, and CO2had promotions on the Hg0removal over CeMnO3, while SO2, NH3, and H2O displayed inhibitory actions on the efficiency. The performance of CeMnO3on simultaneous NO and Hg0removal was the best at 200–250 °C in simulated coal-fired flue gas. Specifically, the NO conversion and Hg0removal efficiency were, respectively, 73.7% and 80.9% at 200 °C, and both the efficiencies remained excellent stability during a long experimental period. A series of characterization analyses were also carried out to identify the physicochemical properties of the catalysts. The results demonstrated that the superior catalytic performance of CeMnO3mainly derived from the abundance of chemisorbed oxygen and the great activity of Mn3+besides Mn4+in the catalyst.

La1–xAxMn1–yByO3(A = Ca, Sr and Ce, B = Cu, Co and Fe, x= 0/0.2, y= 0/0.2) perovskite catalysts were employed for simultaneous NO and Hg0removal. The perovskite structure is beneficial for low temperature catalysis. The substitution of A-site cations with cerium (Ce) cations significantly improved the catalytic activity of perovskite catalyst. 90% NO conversion and 98% Hg0oxidation was attained using La0.8Ce0.2MnO3catalyst at 200 °C. Hg0oxidation posed negligible effect on NO reduction. Compared to the N2plus 4% O2atmosphere, Hg0oxidation was significantly facilitated by selective catalytic reduction atmosphere. The enhancement in Hg0oxidation was probably attributed to NO2originated from NO. Furthermore, a possible reaction mechanism was proposed, in which surface oxygen, Mn4+and Ce4+contributed to NO and Hg0removal. Such knowledge provides useful information for the development of effective and economical NO and Hg0removal technology for coal-fired power plants.

•A novel twin reactor was developed to achieve high CO2hydrogenation.•The reactor enables the control of CO2hydrogenation and water splitting independently.•H2produced from H2O splitting can effectively enhance the CO2hydrogenation in gas phase.•Location of H2- and CO2-photocatalyst in different phases significantly promoted CO2reduction.

Efficient and economical technologies are essential to the control of SO2, the emission of which poses serious health concerns and environmental risks. Photocatalysis is an attractive method for reducing SO2emissions. To reduce energy consumption for excess moisture evaporation, a dry photocatalytic oxidation (DPCO) system was used instead of a traditional gas–liquid process in this study. Considering that TiO2is a widely applied photocatalyst for the purification of gaseous pollutants, this study investigated the photocatalytic removal of SO2over different TiO2-based nanofibers. Results show that the reduction of SO2was mainly due to oxidation. Under ultraviolet irradiation, the removal of SO2was enhanced by the presence of NO2, which was formed by the oxidation of NO. More interestingly, the SO2removal efficiency remains 100% over cerium-based titania nanofibers with an increase in gas humidity, indicating that this sample has excellent resistance to H2O. This is very beneficial for application in an actual flue gas atmosphere, where H2O is inevitable. In contrast, H2O played a bifacial effect in the photocatalytic removal of SO2over copper-based titania nanofibers. Under low levels of H2O (<4%), competitive adsorption for active sites leads to the deactivation of photocatalytic activity, while addition of 8% H2O resulted in more SO2dissolution. Nevertheless, the promoting effect was limited; competitive adsorption was the major factor. Accordingly, the main reaction products are H2SO4and H2SO3. These indicate that combining photocatalysis technology with TiO2-based nanofibers is a promising strategy for oxidizing SO2during a DPCO process.

Enhanced CO2photocatalytic reduction over ZnO/CeO2nanocomposites.

To make an accurate assessment on transformation behaviors of arsenic in coal at a high temperature, a typical high-arsenic coal collected from southwest China has been chosen in the study and a series of high-temperature experiments in different atmospheres have been conducted with the help of a lab-scale drop-tube furnace. Fine particulate matter were collected by a low-pressure impactor, for obtaining their mass size distributions and further quantifying for arsenic distributions and speciation in fine particles of different sizes. The results indicated that the bleeding ratios of arsenic in air combustion, CO2gasification, and N2pyrolysis were 85, 65, and 45%, respectively, at 1300 °C. The ratio was found to remain relatively constant when the temperature increased from 1200 to 1400 °C. Organically associated arsenic would be more inclined to vaporize in N2pyrolysis, while both organic and inorganic associated arsenic would vaporize in CO2gasification and air combustion. Pyrite-associated arsenic would vaporize together with sulfur in pyrite inclusions. The decomposition of pyrite followed the principle of an unreacted core model and was mostly controlled by the surface sulfur vapor pressure. Mass size distributions of fine particulate matter generated from coal gasification presented a bimodal distribution, and two major peaks appeared at 0.4 and 5 μm. Particles in the size range of 5 μm were presented as a round shape with pores and cracks on the surface, while particles in the size range of 0.4 μm were confirmed to be soot. Arsenic was obviously enriched in fine particles with a size of around 0.1–0.2 μm in both combustion and gasification. The major speciation of arsenic identified in fine particles generated from coal combustion was As2O5and Ca3(AsO4)2, while that in fine particles generated from coal gasification was As2O5, As, AsO, and Ca3(AsO4)2.

Economic sustainability is one of the main factors restricting development of mercury pollution control technology in the flue gas. Renewable magnetospheres separated from fly ash can be used as adsorbent for mercury removal from coal-fired flue gas. Based on the actual working condition of the 1000 WM coal-fired unit, this paper analyzes the impact of magnetosphere and mercury recovery technology on the economic benefits of this technology. The results show that the recovery of magnetospheres and mercury can obtain higher economic returns. This not only can realize the deduction of operating costs, but also has certain economic investment potential. When the magnetic separation rate is greater than 6% and the selling price of the magnetosphere is greater than 720 CNY/t, the revenue of the magnetosphere recovery system can offset the operating cost of whole system. The internal rate of return of the system can reach 50% at most. When the selling price of mercury selenide is lower than 450 CNY/g, the single mercury recovery income is insufficient to offset the mercury removal cost. Within the selling price range of 450–500 CNY/g mercury selenide, the system can generate revenue, and the product qualification rate directly affects the profit and loss of the system. The coupling of magnetospheres and mercury recovery systems can make economic and technical parameters more moderate. When the selling price of magnetospheres is higher than 600 CNY/t, the magnetic separation rate is higher than 6%, and the selling price of mercury selenide is higher than 350 CNY/g, the internal return of the system will fluctuate within 13%∼120%, and the static investment recovery period will remain within 6 years. Overall, this study can provide economic guidance for mercury removal technology with renewable magnetospheres and provide data support for further commercialization of technology.

Oxyfuel combustion with carbon capture and sequestration (CCS) is a carbon-reduction technology for use in large-scale coal-fired power plants. Significant progress has been achieved in the research and development of this technology during its scaling up from 0.4 MWthto 3 MWthand 35 MWthby the combined efforts of universities and industries in China. A prefeasibility study on a 200 MWelarge-scale demonstration has progressed well, and is ready for implementation. The overall research development and demonstration (RD&D) roadmap for oxyfuel combustion in China has become a critical component of the global RD&D roadmap for oxyfuel combustion. An air combustion/oxyfuel combustion compatible design philosophy was developed during the RD&D process. In this paper, we briefly address fundamental research and technology innovation efforts regarding several technical challenges, including combustion stability, heat transfer, system operation, mineral impurities, and corrosion. To further reduce the cost of carbon capture, in addition to the large-scale deployment of oxyfuel technology, increasing interest is anticipated in the novel and next-generation oxyfuel combustion technologies that are briefly introduced here, including a new oxygen-production concept and flameless oxyfuel combustion.

Emission of carbon dioxide is considered to be the main cause of the greenhouse effect. Mineral carbonation, an important part of the CCS technology, is an attractive option for long-term CO2sequestration. In this study, wollastonite was chosen as the feedstock and the feasibility of direct aqueous mineral carbonation in the simulated flue gas was investigated via a series of experimental studies carried in a stirred reactor. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), ion chromatography (IC) and thermal decomposition were used to determine the carbonation conversion. The influences of various factors, including reaction temperature, reaction pressure, solution composition, heat-treatment and particle size, were discussed. Concurrently, the effects of SO2and NO presented in simulated flue gas were also investigated and a possible mechanism was used to explain the results. Experimental results show that reaction temperature, reaction pressure and particle size can effectively improve the carbonation reaction. Addition of 0.6 M NaHCO3was also proved to be beneficial to the reaction and heat-treatment is not needed for wollastonite to get a higher carbonation conversion. Compared with carbonation in purified CO2gas, CO2sequestration directly from simulated flue gas by mineral carbonation is suggested to have a certain degree of economic feasibility in the conditions of medium and low-pressure. A highest carbonation conversion of 35.9% is gained on the condition of T=150°C, P=40 bar and PS<30 μm in distilled water for 1 h.

Abstract: An exergy life cycle assessment (ELCA) model based on life cycle assessment (LCA) and exergy methodology was developed to assess a 2×300 MW coal-fired power plant, and the results indicated that the exergy input in operation phase of power plant accounts for 99.89% of the total input and only 0.11% in construction and decommission phases. Direct and indirect exergy inputs account for 93.03% and 6.97%, respectively. Compared with coal-fired power generation system before carbon emission reduction, exergy input-output ratio of life cycle “CO2 zero-emission” energy system and exergy efficiency are about 5.563 and 17.97%, respectively, which increases by 62.47% and declines by 11.21% approximately. The model quantifies the energy, resource consumption and pollutant emissions of system life cycle using exergy as the basic physical parameter, which will make the assessment more objective and reasonable.

Abstract: A two-dimensional transient model has been developed to describe the catalytic methane reforming (MSR) coupled with simultaneous CO2 removal by different absorbents under non-isothermal, non-isobaric and non-adiabatic operating conditions. The influences of temperature, pressure and steam/carbon (S/C) on enhancement were taken into account. The results showed that the hydrogen mole fraction (dry basis) higher than 94% could be achieved using Li4SiO4, CaO, and HTC as CO2 acceptors at the operating conditions of 550°C and 0.1 MPa. When the reaction temperature varied from 500°C to 600°C, the initial CO2 capture rates were HTC>CaO>Li4SiO4>Li2ZrO3, and the saturation rates HTC>CaO>Li4SiO4>Li2ZrO3. Increasing the reaction temperature would improve the CO2 capture rate and available CO2 capacity. For Li4SiO4, although the adsorbing rate increased as the operating temperature increased, the capacity almost did not change. At 550°C, increasing the working pressure could promote the enhancing factors of Li4SiO4,Li2ZrO3 and HTC. There was an optimal steam/carbon ratio between 2–4.5 such that all CaO, Li4SiO4, HTC and Li2ZrO3 would obtain the biggest enhancement for H2 production at the pre-breakthrough stage.

Abstract: In this study, a detailed technical-economic analysis on a O2/CO2 recycle combustion power plant (Oxy-combustion plant) retrofitted from the existing coal-fired plant (with a capacity of 2×300 MW) in China was carried out by using life cycle assessment (LCA) and life cycle cost (LCC) method. The CO2 emissions, investment cost, cost of electricity and CO2 avoidance cost within the life cycle were calculated respectively. The results showed that the CO2 emission avoidance rate of retrofitted Oxy-combustion plant in the life cycle was about 77.09% without taking account of the CO2 compression; the annual cost increased by 5.9% approximately, the net power decreased by 21.33%, the cost of electricity increased by 34.77%, and the CO2 avoidance cost was about 28.93 USD/t. Considering the compression process of CO2, the avoidance rate of CO2 emission was about 73.35% or so; the annual cost increased by 9.35% approximately, the net power decreased by about 26.70%, the cost of electricity increased by 49.13%, and the CO2 avoidance cost was about 45.46 USD/t. The carbon tax (the CO2 tax) should be more than about 24 USD/t and 34 USD/t under the condition of considering CO2 compression or not, respectively, which is beneficial to promote transformation of existing coal-fired plant for reducing the CO2 emissions.

Abstract: Systematic experiments were conducted on a fixed-bed reactor to investigate the interaction between fly ash and mercury, the results implied that fly ash can capture mercury effectively. Among different fly ashes, the unburned carbon in the FA2 and FA3 fly ashes has the highest mercury capture capacity, up to 10.3 and 9.36 μg/g, respectively, which is close to that of commercial activated carbon. There is no obvious relationship between mercury content and carbon content or BET surface area of fly ash. Petrography classification standard was applied to distinguish fly ash carbon particles. Carbon content is not the only variable that controls mercury capture on fly ash, there are likely significant differences in the mercury capture capacities of the various carbon forms. Mercury capture capacity mainly depends on the content of anisotropy carbon particles with porous network structure.